Polar Analysis from flight logs?

[Mark Zivley]

We all know what the manufacturer's polars look like, but what about our
individual planes. Has anyone done any work to develop a program that
would look at some flight logs and determine what a particular glider's
actual polar is? At one point Ball was making a vario system that would
determine the aircraft's polar over time just by flying.

For someone who already had some algorithms for computing wind from
ground track drift during thermals could take this info and then be able
to back figure from GPS ground speed what the IAS was during a
particular phase of the flight. By isolating longer sections of cruise
flight at varios airspeeds it should be do-able. Question is, has it
been done.

Mark

extra "hot" in the address to delay the spammers...

[Papa3]

Mark,

How do you propose to isolate the impact of vertical air motion? For
instance, I can fly the ridge at 100Kts and maintain altitude (same for wave
or cloudstreets). I'm sure Rolladen-Schneider (ahem, DG) would love to
publish the L/D of my LS8 from the average of my flights for a season:
"LS8, with a measured L/D of 800:1..."

Cheers,
Erik


"Mark Zivley" > wrote in message
m...
> We all know what the manufacturer's polars look like, but what about our
> individual planes. Has anyone done any work to develop a program that
> would look at some flight logs and determine what a particular glider's
> actual polar is? At one point Ball was making a vario system that would
> determine the aircraft's polar over time just by flying.
>
> For someone who already had some algorithms for computing wind from
> ground track drift during thermals could take this info and then be able
> to back figure from GPS ground speed what the IAS was during a
> particular phase of the flight. By isolating longer sections of cruise
> flight at varios airspeeds it should be do-able. Question is, has it
> been done.
>
> Mark
>
> extra "hot" in the address to delay the spammers...
>

[Mark Zivley]

Obviously ridge flight would not be conducive, nor wave, but put enough
data together from cruises during thermal flights and I bet something
could be put together.

Papa3 wrote:

> Mark,
>
> How do you propose to isolate the impact of vertical air motion? For
> instance, I can fly the ridge at 100Kts and maintain altitude (same for wave
> or cloudstreets). I'm sure Rolladen-Schneider (ahem, DG) would love to
> publish the L/D of my LS8 from the average of my flights for a season:
> "LS8, with a measured L/D of 800:1..."
>
> Cheers,
> Erik
>
>
> "Mark Zivley" > wrote in message
> m...
>
>>We all know what the manufacturer's polars look like, but what about our
>>individual planes. Has anyone done any work to develop a program that
>>would look at some flight logs and determine what a particular glider's
>>actual polar is? At one point Ball was making a vario system that would
>>determine the aircraft's polar over time just by flying.
>>
>>For someone who already had some algorithms for computing wind from
>>ground track drift during thermals could take this info and then be able
>>to back figure from GPS ground speed what the IAS was during a
>>particular phase of the flight. By isolating longer sections of cruise
>>flight at varios airspeeds it should be do-able. Question is, has it
>>been done.
>>
>>Mark
>>
>>extra "hot" in the address to delay the spammers...
>>
>
>
>

[Eric Greenwell]

Mark Zivley wrote:

> We all know what the manufacturer's polars look like, but what about
> our individual planes. Has anyone done any work to develop a program
> that would look at some flight logs and determine what a particular
> glider's actual polar is? At one point Ball was making a vario
> system that would determine the aircraft's polar over time just by
> flying.
>
> For someone who already had some algorithms for computing wind from
> ground track drift during thermals could take this info and then be
> able to back figure from GPS ground speed what the IAS was during a
> particular phase of the flight. By isolating longer sections of
> cruise flight at varios airspeeds it should be do-able. Question is,
> has it been done.

I haven't heard of it being done, and I can't imagine how one would
compensate for air motion, both vertical and horizontal, just using the
GPS info. Both motions change with location, altitude, and time. Perhaps
if the flight record included the airspeed, like some varios can supply,
there would be some hope of doing it. I don't think you could count on
the vertical motion averaging to zero during the cruises, since we
typically adjust our path to include as much up air as possible.

You can get some good info using a flight recorder, but you have to do
it when the air is calm. If you are really interested, invest in a few
high tows and make the measurements. Take a look at this test done on a
DG 800:

http://groups.yahoo.com/group/ASA-NewsGroup/message/59

You don't have to be a group member to read the message.


--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

[Richard Brisbourne]

Mark Zivley wrote:

> Obviously ridge flight would not be conducive, nor wave, but put enough
> data together from cruises during thermal flights and I bet something
> could be put together.
>

No it couldn't for exactly the same reasons ridge and wave don't work. In
typical thermal conditions air is going up and down all over the place.
Skilled pilots tend to fly in the good bits and ignore the bad bits.

Even if you could measure vertical and horizontal airspeed components,
"cruising" is likely to involve frequent speed changes, accelerations and
decelerations.



> Papa3 wrote:
>
>> Mark,
>>
>> How do you propose to isolate the impact of vertical air motion? For
>> instance, I can fly the ridge at 100Kts and maintain altitude (same for
>> wave
>> or cloudstreets). I'm sure Rolladen-Schneider (ahem, DG) would love to
>> publish the L/D of my LS8 from the average of my flights for a season:
>> "LS8, with a measured L/D of 800:1..."
>>
>> Cheers,
>> Erik

[Papa3]

Mark,

My first post came across as a bit glib - apologize for that. But, I
actually put a little thought into that subject recently while writing some
batch analysis specs for GPS log files. The problem is that a good glider
pilot will not encounter random vertical motions - even in cruise flight.
He/she will stack the deck in his favor, seeking out cloud streets or
connecting the best looking individual Cu. Thus, you can't just average
out the L/D over time on specific segments (e.g. cruise flight). What you
can do is deterimine which pilot does the best job of achieving highest L/D
on a given day. Several of the popular flight analysis programs do this
already.

I'd certainly be interested in any detailed ideas you might have.

P3

"Mark Zivley" > wrote in message
m...
> Obviously ridge flight would not be conducive, nor wave, but put enough
> data together from cruises during thermal flights and I bet something
> could be put together.
>
> Papa3 wrote:
>
> > Mark,
> >
> > How do you propose to isolate the impact of vertical air motion? For
> > instance, I can fly the ridge at 100Kts and maintain altitude (same for
wave
> > or cloudstreets). I'm sure Rolladen-Schneider (ahem, DG) would love to
> > publish the L/D of my LS8 from the average of my flights for a season:
> > "LS8, with a measured L/D of 800:1..."
> >
> > Cheers,
> > Erik
> >
> >
> > "Mark Zivley" > wrote in message
> > m...
> >
> >>We all know what the manufacturer's polars look like, but what about our
> >>individual planes. Has anyone done any work to develop a program that
> >>would look at some flight logs and determine what a particular glider's
> >>actual polar is? At one point Ball was making a vario system that would
> >>determine the aircraft's polar over time just by flying.
> >>
> >>For someone who already had some algorithms for computing wind from
> >>ground track drift during thermals could take this info and then be able
> >>to back figure from GPS ground speed what the IAS was during a
> >>particular phase of the flight. By isolating longer sections of cruise
> >>flight at varios airspeeds it should be do-able. Question is, has it
> >>been done.
> >>
> >>Mark
> >>
> >>extra "hot" in the address to delay the spammers...
> >>
> >
> >
> >
>

[Bob Gibbons]

On this topic of determining L/D from interthermal cruising, Dick
Johnson did a fascinating and underappreciated study in the late
1970's of airmass behavior between thermals. Dick flew in mostly blue
conditions and simply recoded his height loss versus distance covered
between thermals. Dick's results are reported in SOARING, June 1979.

Dick found that, on the average, the airmass between thermals has an
average sink rate related to the upgoing thermal strength. The
relationship Dick found was; the airmass sink is approximately 10% of
the lift strength.

I have always felt Dick's study explains why it is so difficult to fly
cross country (in a blue conditions) with a ship having an L/D less
than about 30:1. The probability of running into the next thermal
purely by chance becomes too low as the L/D drops.

For this discussion, I think Dick's study shows the inadvisability of
trying to deduce flight performance from interthermal measurements.

Bob

On Mon, 27 Dec 2004 20:43:41 GMT, "Papa3" >
wrote:

>Mark,
>
>My first post came across as a bit glib - apologize for that. But, I
>actually put a little thought into that subject recently while writing some
>batch analysis specs for GPS log files. The problem is that a good glider
>pilot will not encounter random vertical motions - even in cruise flight.
>He/she will stack the deck in his favor, seeking out cloud streets or
>connecting the best looking individual Cu. Thus, you can't just average
>out the L/D over time on specific segments (e.g. cruise flight). What you
>can do is deterimine which pilot does the best job of achieving highest L/D
>on a given day. Several of the popular flight analysis programs do this
>already.
>
>I'd certainly be interested in any detailed ideas you might have.
>
>P3
>
>"Mark Zivley" > wrote in message
m...
>> Obviously ridge flight would not be conducive, nor wave, but put enough
>> data together from cruises during thermal flights and I bet something
>> could be put together.
>>
>> Papa3 wrote:
>>
>> > Mark,
>> >
>> > How do you propose to isolate the impact of vertical air motion? For
>> > instance, I can fly the ridge at 100Kts and maintain altitude (same for
>wave
>> > or cloudstreets). I'm sure Rolladen-Schneider (ahem, DG) would love to
>> > publish the L/D of my LS8 from the average of my flights for a season:
>> > "LS8, with a measured L/D of 800:1..."
>> >
>> > Cheers,
>> > Erik
>> >
>> >
>> > "Mark Zivley" > wrote in message
>> > m...
>> >
>> >>We all know what the manufacturer's polars look like, but what about our
>> >>individual planes. Has anyone done any work to develop a program that
>> >>would look at some flight logs and determine what a particular glider's
>> >>actual polar is? At one point Ball was making a vario system that would
>> >>determine the aircraft's polar over time just by flying.
>> >>
>> >>For someone who already had some algorithms for computing wind from
>> >>ground track drift during thermals could take this info and then be able
>> >>to back figure from GPS ground speed what the IAS was during a
>> >>particular phase of the flight. By isolating longer sections of cruise
>> >>flight at varios airspeeds it should be do-able. Question is, has it
>> >>been done.
>> >>
>> >>Mark
>> >>
>> >>extra "hot" in the address to delay the spammers...
>> >>
>> >
>> >
>> >
>>
>
>

[John Sinclair]

I asked Dick Johnson, why couldn't I fly in calm conditions
(morning) and hold a given airspeed (say 60 knots)
and a given heading (say west) for 10 minutes, then
reverse heading to east (to cancel out any wind) and
then analyze the GPS trace to determine my ships L/D
at 60 knots. We have an accurate distance covered and
fairly accurate altitude lost, so why can't we crunch
the numbers?
Dick said the GPS info wasn't accurate enough. I thought
it was a good idea, but I defer to the master.
JJ

At 03:00 28 December 2004, Bob Gibbons wrote:
>On this topic of determining L/D from interthermal
>cruising, Dick
>Johnson did a fascinating and underappreciated study
>in the late
>1970's of airmass behavior between thermals. Dick flew
>in mostly blue
>conditions and simply recoded his height loss versus
>distance covered
>between thermals. Dick's results are reported in SOARING,
>June 1979.
>
>Dick found that, on the average, the airmass between
>thermals has an
>average sink rate related to the upgoing thermal strength.
>The
>relationship Dick found was; the airmass sink is approximately
>10% of
>the lift strength.
>
>I have always felt Dick's study explains why it is
>so difficult to fly
>cross country (in a blue conditions) with a ship having
>an L/D less
>than about 30:1. The probability of running into the
>next thermal
>purely by chance becomes too low as the L/D drops.
>
>For this discussion, I think Dick's study shows the
>inadvisability of
>trying to deduce flight performance from interthermal
>measurements.
>
>Bob
>
>On Mon, 27 Dec 2004 20:43:41 GMT, 'Papa3'
>wrote:
>
>>Mark,
>>
>>My first post came across as a bit glib - apologize
>>for that. But, I
>>actually put a little thought into that subject recently
>>while writing some
>>batch analysis specs for GPS log files. The problem
>>is that a good glider
>>pilot will not encounter random vertical motions -
>>even in cruise flight.
>>He/she will stack the deck in his favor, seeking out
>>cloud streets or
>>connecting the best looking individual Cu. Thus,
>>you can't just average
>>out the L/D over time on specific segments (e.g. cruise
>>flight). What you
>>can do is deterimine which pilot does the best job
>>of achieving highest L/D
>>on a given day. Several of the popular flight analysis
>>programs do this
>>already.
>>
>>I'd certainly be interested in any detailed ideas you
>>might have.
>>
>>P3
>>
>>'Mark Zivley' wrote in message
m...
>>> Obviously ridge flight would not be conducive, nor
>>>wave, but put enough
>>> data together from cruises during thermal flights
>>>and I bet something
>>> could be put together.
>>>
>>> Papa3 wrote:
>>>
>>> > Mark,
>>> >
>>> > How do you propose to isolate the impact of vertical
>>>>air motion? For
>>> > instance, I can fly the ridge at 100Kts and maintain
>>>>altitude (same for
>>wave
>>> > or cloudstreets). I'm sure Rolladen-Schneider (ahem,
>>>>DG) would love to
>>> > publish the L/D of my LS8 from the average of my
>>>>flights for a season:
>>> > 'LS8, with a measured L/D of 800:1...'
>>> >
>>> > Cheers,
>>> > Erik
>>> >
>>> >
>>> > 'Mark Zivley' wrote in message
>>> > m...
>>> >
>>> >>We all know what the manufacturer's polars look like,
>>>>>but what about our
>>> >>individual planes. Has anyone done any work to develop
>>>>>a program that
>>> >>would look at some flight logs and determine what
>>>>>a particular glider's
>>> >>actual polar is? At one point Ball was making a vario
>>>>>system that would
>>> >>determine the aircraft's polar over time just by flying.
>>> >>
>>> >>For someone who already had some algorithms for computing
>>>>>wind from
>>> >>ground track drift during thermals could take this
>>>>>info and then be able
>>> >>to back figure from GPS ground speed what the IAS
>>>>>was during a
>>> >>particular phase of the flight. By isolating longer
>>>>>sections of cruise
>>> >>flight at varios airspeeds it should be do-able.
>>>>>Question is, has it
>>> >>been done.
>>> >>
>>> >>Mark
>>> >>
>>> >>extra 'hot' in the address to delay the spammers...
>>> >>
>>> >
>>> >
>>> >
>>>
>>
>>
>
>

[Udo Rumpf]

J.J.
That would be good enough for me.
In the end there is nothing like flying with a bunch of gliders
fairly close together after the last thermal of the day and 25-30 miles out,
to get a real sense of how your ship is doing.
Naturally you want know what the wing loading was of each glider.
In my case I would canvas the pilots of key gliders after to establish the
weights. I was fortunately to have had conditions were this worked out well.
An ideal contest was the Seniors with six glider on final glide all leaving
the last thermal at about the same time.

Regards
Udo

>I asked Dick Johnson, why couldn't I fly in calm conditions
> (morning) and hold a given airspeed (say 60 knots)
> and a given heading (say west) for 10 minutes, then
> reverse heading to east (to cancel out any wind) and
> then analyze the GPS trace to determine my ships L/D
> at 60 knots. We have an accurate distance covered and
> fairly accurate altitude lost, so why can't we crunch
> the numbers?
> Dick said the GPS info wasn't accurate enough. I thought
> it was a good idea, but I defer to the master.
> JJ
>
> At 03:00 28 December 2004, Bob Gibbons wrote:
>>On this topic of determining L/D from interthermal
>>cruising, Dick
>>Johnson did a fascinating and underappreciated study
>>in the late
>>1970's of airmass behavior between thermals. Dick flew
>>in mostly blue
>>conditions and simply recoded his height loss versus
>>distance covered
>>between thermals. Dick's results are reported in SOARING,
>>June 1979.
>>
>>Dick found that, on the average, the airmass between
>>thermals has an
>>average sink rate related to the upgoing thermal strength.
>>The
>>relationship Dick found was; the airmass sink is approximately
>>10% of
>>the lift strength.
>>
>>I have always felt Dick's study explains why it is
>>so difficult to fly
>>cross country (in a blue conditions) with a ship having
>>an L/D less
>>than about 30:1. The probability of running into the
>>next thermal
>>purely by chance becomes too low as the L/D drops.
>>
>>For this discussion, I think Dick's study shows the
>>inadvisability of
>>trying to deduce flight performance from interthermal
>>measurements.
>>
>>Bob
>>
>>On Mon, 27 Dec 2004 20:43:41 GMT, 'Papa3'
>>wrote:
>>
>>>Mark,
>>>
>>>My first post came across as a bit glib - apologize
>>>for that. But, I
>>>actually put a little thought into that subject recently
>>>while writing some
>>>batch analysis specs for GPS log files. The problem
>>>is that a good glider
>>>pilot will not encounter random vertical motions -
>>>even in cruise flight.
>>>He/she will stack the deck in his favor, seeking out
>>>cloud streets or
>>>connecting the best looking individual Cu. Thus,
>>>you can't just average
>>>out the L/D over time on specific segments (e.g. cruise
>>>flight). What you
>>>can do is deterimine which pilot does the best job
>>>of achieving highest L/D
>>>on a given day. Several of the popular flight analysis
>>>programs do this
>>>already.
>>>
>>>I'd certainly be interested in any detailed ideas you
>>>might have.
>>>
>>>P3
>>>
>>>'Mark Zivley' wrote in message
m...
>>>> Obviously ridge flight would not be conducive, nor
>>>>wave, but put enough
>>>> data together from cruises during thermal flights
>>>>and I bet something
>>>> could be put together.
>>>>
>>>> Papa3 wrote:
>>>>
>>>> > Mark,
>>>> >
>>>> > How do you propose to isolate the impact of vertical
>>>>>air motion? For
>>>> > instance, I can fly the ridge at 100Kts and maintain
>>>>>altitude (same for
>>>wave
>>>> > or cloudstreets). I'm sure Rolladen-Schneider (ahem,
>>>>>DG) would love to
>>>> > publish the L/D of my LS8 from the average of my
>>>>>flights for a season:
>>>> > 'LS8, with a measured L/D of 800:1...'
>>>> >
>>>> > Cheers,
>>>> > Erik
>>>> >
>>>> >
>>>> > 'Mark Zivley' wrote in message
>>>> > m...
>>>> >
>>>> >>We all know what the manufacturer's polars look like,
>>>>>>but what about our
>>>> >>individual planes. Has anyone done any work to develop
>>>>>>a program that
>>>> >>would look at some flight logs and determine what
>>>>>>a particular glider's
>>>> >>actual polar is? At one point Ball was making a vario
>>>>>>system that would
>>>> >>determine the aircraft's polar over time just by flying.
>>>> >>
>>>> >>For someone who already had some algorithms for computing
>>>>>>wind from
>>>> >>ground track drift during thermals could take this
>>>>>>info and then be able
>>>> >>to back figure from GPS ground speed what the IAS
>>>>>>was during a
>>>> >>particular phase of the flight. By isolating longer
>>>>>>sections of cruise
>>>> >>flight at varios airspeeds it should be do-able.
>>>>>>Question is, has it
>>>> >>been done.
>>>> >>
>>>> >>Mark
>>>> >>
>>>> >>extra 'hot' in the address to delay the spammers...
>>>> >>
>>>> >
>>>> >
>>>> >
>>>>
>>>
>>>
>>
>>
>
>
>

[Eric Greenwell]

John Sinclair wrote:
> I asked Dick Johnson, why couldn't I fly in calm conditions
> (morning) and hold a given airspeed (say 60 knots)
> and a given heading (say west) for 10 minutes, then
> reverse heading to east (to cancel out any wind) and
> then analyze the GPS trace to determine my ships L/D
> at 60 knots. We have an accurate distance covered and
> fairly accurate altitude lost, so why can't we crunch
> the numbers?
> Dick said the GPS info wasn't accurate enough. I thought
> it was a good idea, but I defer to the master.

How long ago did you ask him? GPS is much more accurate in the last few
years, especially if using the WAAS ablities. But, let's say you know
the distance to only +/- 100 feet (it's typically more like +/- 30
feet), then flying only a mile (5000 feet) would be a 2% error, or one
L/D point for a 50:1 glider. Good enough for us, I think.

If you use the GPS for the altitude instead of the pressure altitude,
you might have to fly off a 1000 feet or so of altitude, I suppose.
Maybe Dick was referring to GPS altitude?


--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

[[email protected]]

I won't speculate on the results of this type of testing, but, around here
the wind varies considerably with altitude, even with calm conditions
in the morning. When doing performance work I would try to work
crosswind. Wind shear effects are less influential. It is a great
help to take a tape recorder and record every bump and time. A lot of
data gets thrown out.

If you take twenty minutes per point, you'll be spending a lot on tow fees.

Dennis Brown

John Sinclair wrote in message >...
>I asked Dick Johnson, why couldn't I fly in calm conditions
>(morning) and hold a given airspeed (say 60 knots)
>and a given heading (say west) for 10 minutes, then
>reverse heading to east (to cancel out any wind) and
>then analyze the GPS trace to determine my ships L/D
>at 60 knots. We have an accurate distance covered and
>fairly accurate altitude lost, so why can't we crunch
>the numbers?
>Dick said the GPS info wasn't accurate enough. I thought
>it was a good idea, but I defer to the master.
>JJ
>
>At 03:00 28 December 2004, Bob Gibbons wrote:
>>On this topic of determining L/D from interthermal
>>cruising, Dick
>>Johnson did a fascinating and underappreciated study
>>in the late
>>1970's of airmass behavior between thermals. Dick flew
>>in mostly blue
>>conditions and simply recoded his height loss versus
>>distance covered
>>between thermals. Dick's results are reported in SOARING,
>>June 1979.
>>
>>Dick found that, on the average, the airmass between
>>thermals has an
>>average sink rate related to the upgoing thermal strength.
>>The
>>relationship Dick found was; the airmass sink is approximately
>>10% of
>>the lift strength.
>>
>>I have always felt Dick's study explains why it is
>>so difficult to fly
>>cross country (in a blue conditions) with a ship having
>>an L/D less
>>than about 30:1. The probability of running into the
>>next thermal
>>purely by chance becomes too low as the L/D drops.
>>
>>For this discussion, I think Dick's study shows the
>>inadvisability of
>>trying to deduce flight performance from interthermal
>>measurements.
>>
>>Bob
>>
>>On Mon, 27 Dec 2004 20:43:41 GMT, 'Papa3'
>>wrote:
>>
>>>Mark,
>>>
>>>My first post came across as a bit glib - apologize
>>>for that. But, I
>>>actually put a little thought into that subject recently
>>>while writing some
>>>batch analysis specs for GPS log files. The problem
>>>is that a good glider
>>>pilot will not encounter random vertical motions -
>>>even in cruise flight.
>>>He/she will stack the deck in his favor, seeking out
>>>cloud streets or
>>>connecting the best looking individual Cu. Thus,
>>>you can't just average
>>>out the L/D over time on specific segments (e.g. cruise
>>>flight). What you
>>>can do is deterimine which pilot does the best job
>>>of achieving highest L/D
>>>on a given day. Several of the popular flight analysis
>>>programs do this
>>>already.
>>>
>>>I'd certainly be interested in any detailed ideas you
>>>might have.
>>>
>>>P3
>>>
>>>'Mark Zivley' wrote in message
m...
>>>> Obviously ridge flight would not be conducive, nor
>>>>wave, but put enough
>>>> data together from cruises during thermal flights
>>>>and I bet something
>>>> could be put together.
>>>>
>>>> Papa3 wrote:
>>>>
>>>> > Mark,
>>>> >
>>>> > How do you propose to isolate the impact of vertical
>>>>>air motion? For
>>>> > instance, I can fly the ridge at 100Kts and maintain
>>>>>altitude (same for
>>>wave
>>>> > or cloudstreets). I'm sure Rolladen-Schneider (ahem,
>>>>>DG) would love to
>>>> > publish the L/D of my LS8 from the average of my
>>>>>flights for a season:
>>>> > 'LS8, with a measured L/D of 800:1...'
>>>> >
>>>> > Cheers,
>>>> > Erik
>>>> >
>>>> >
>>>> > 'Mark Zivley' wrote in message
>>>> > m...
>>>> >
>>>> >>We all know what the manufacturer's polars look like,
>>>>>>but what about our
>>>> >>individual planes. Has anyone done any work to develop
>>>>>>a program that
>>>> >>would look at some flight logs and determine what
>>>>>>a particular glider's
>>>> >>actual polar is? At one point Ball was making a vario
>>>>>>system that would
>>>> >>determine the aircraft's polar over time just by flying.
>>>> >>
>>>> >>For someone who already had some algorithms for computing
>>>>>>wind from
>>>> >>ground track drift during thermals could take this
>>>>>>info and then be able
>>>> >>to back figure from GPS ground speed what the IAS
>>>>>>was during a
>>>> >>particular phase of the flight. By isolating longer
>>>>>>sections of cruise
>>>> >>flight at varios airspeeds it should be do-able.
>>>>>>Question is, has it
>>>> >>been done.
>>>> >>
>>>> >>Mark
>>>> >>
>>>> >>extra 'hot' in the address to delay the spammers...
>>>> >>
>>>> >
>>>> >
>>>> >
>>>>
>>>
>>>
>>
>>
>
>
>

[BB]

Errors in measurement can be made up for with lots and lots of data, so
long as the errors are not biased one way or another. Thus, you should
be able to get an accurate polar even in thermally air, without
spending a fortune on tow fees. Turn on data recording, then fly
absolutely straight and same speed, through thermals as well as sink,
while taking data. Turn off data recording before thermaling back up to
altitude.

The key is to fly so that on average you're not biased toward flying in
lift vs. sink. You should randomize heading (if you always go
up/downwind you'll be in streets), randomize time of turning on/off the
data recording (if you turn on after leaving a thermal and off when you
find a new one, you'll be biased toward sink). If you do this for a
season, for example getting 20 minutes of data in the 1-2 hours of
prestart fooling around at contests, you might have a really good polar
at the end of it.

You could also do the opposite: A good pilot should be flying faster
through sink and slower through lift, and should spend more time in
lift than in sink. The difference between the "polar" measured in
thermal conditions and the factory polar can be a basis of a measure of
pilot skill. A good pilot should give a polar with a worse high speed
end -- because he always flies fast through sink -- a much better low
speed end -- becasue he always flies slow through lift -- and a
positive bias -- the whole polar shifted up.

In principle, all pretty easy to add to a glide computer. Of course we
all have a long list of more important features.

John Cochrane (BB)

[Peter Creswick]

BB wrote:
> Errors in measurement can be made up for with lots and lots of data, so
> long as the errors are not biased one way or another. Thus, you should
> be able to get an accurate polar even in thermally air, without
> spending a fortune on tow fees. Turn on data recording, then fly
> absolutely straight and same speed, through thermals as well as sink,
> while taking data. Turn off data recording before thermaling back up to
> altitude.
>
> The key is to fly so that on average you're not biased toward flying in
> lift vs. sink. You should randomize heading (if you always go
> up/downwind you'll be in streets), randomize time of turning on/off the
> data recording (if you turn on after leaving a thermal and off when you
> find a new one, you'll be biased toward sink). If you do this for a
> season, for example getting 20 minutes of data in the 1-2 hours of
> prestart fooling around at contests, you might have a really good polar
> at the end of it.
>
> You could also do the opposite: A good pilot should be flying faster
> through sink and slower through lift, and should spend more time in
> lift than in sink. The difference between the "polar" measured in
> thermal conditions and the factory polar can be a basis of a measure of
> pilot skill. A good pilot should give a polar with a worse high speed
> end -- because he always flies fast through sink -- a much better low
> speed end -- becasue he always flies slow through lift -- and a
> positive bias -- the whole polar shifted up.
>
> In principle, all pretty easy to add to a glide computer. Of course we
> all have a long list of more important features.
>
> John Cochrane (BB)
>
Wouldn't it be simpler and much more scientific to arrange to do a
series of test runs over a LIDAR site, and simply post process the radar
and glider data recorder data ?

[Tim.Ward]

Eric Greenwell wrote:
> John Sinclair wrote:
> > I asked Dick Johnson, why couldn't I fly in calm conditions
> > (morning) and hold a given airspeed (say 60 knots)
> > and a given heading (say west) for 10 minutes, then
> > reverse heading to east (to cancel out any wind) and
> > then analyze the GPS trace to determine my ships L/D
> > at 60 knots. We have an accurate distance covered and
> > fairly accurate altitude lost, so why can't we crunch
> > the numbers?
> > Dick said the GPS info wasn't accurate enough. I thought
> > it was a good idea, but I defer to the master.
>
> How long ago did you ask him? GPS is much more accurate in the last
few
> years, especially if using the WAAS ablities. But, let's say you know

> the distance to only +/- 100 feet (it's typically more like +/- 30
> feet), then flying only a mile (5000 feet) would be a 2% error, or
one
> L/D point for a 50:1 glider. Good enough for us, I think.

I don't think this is quite right. Consider a 50:1 glider descending
100 meters:
It will go 100 x 50 = 5000 meters
I think vertical navigation errors are typically 1.5 times the
horizontal.
If horizontal accuracy is 10 meters, then vertical will be about 15
So when we've measured this exactly 50:1 glider sinking 100 meters, the
two worst cases we would read for a measurement are:
(5000-Herror)/(100+Verror) = 4990/115 = 43.4
(5000+Herror)/(100-Verror) = 5010/85 = 58.9

With errors of 3 meters and 5 meters, it gets closer.
4997/105 = 47.6
5003/95 = 52.6

With errors of 1 and 2 meters
4999/102 = 49.0
5001/98 = 51.0

> If you use the GPS for the altitude instead of the pressure altitude,

> you might have to fly off a 1000 feet or so of altitude, I suppose.
> Maybe Dick was referring to GPS altitude?

Probably. If I understand the technique he uses correctly, he flies a
test glider at a particular airspeed, timing the descent, to get a sink
rate for that airspeed. Then he plots the sinkrates to get the polar.
I can't see why he'd be interested in horizontal position at all.
I don't know what kind of accuracy is possible from the barometric
altimeters. It could be that a skilled pilot/data recorder can get
accuracy below the typical 20 foot tick mark on the altimeter face.

OTOH, you are correct, if I'm reading the FAA docs right, WAAS should
be able to give vertical accuracy better than 2 meters 95 percent of
the time. I don't know if the COTS handhelds can actually deliver that.
On Sam Wormsley's GPS site, there's a link that suggests that a Garmin
GPS 76 maintained about 6 meter vertical accuracy 95 percent of the
time. That's very close to the 20 foot resolution on a barometric
altimeter, and that's absolute position, rather than relative position.
That is, we don't care where we started and where we ended, but rather
how far we descended. If the error offset is pretty much the same at
the beginning and end of a run, then the relative accuracy may be much
better than the absolute position.

It might be interesting to look at the GPS speed during a descent. If
the airspeed and heading is being held constant, and the airmass is
uniform, then the GPS speed should be constant. Excursions might
indicate shears that would affect the quality of the data. You might
be able to improve accuracy by throwing out segments that indicated
non-steady-state behavior.

Tim Ward

>
> --
> Change "netto" to "net" to email me directly
>
> Eric Greenwell
> Washington State
> USA

[Andy Blackburn]

At 18:30 28 December 2004, Eric Greenwell wrote:
>How long ago did you ask him? GPS is much more accurate
>in the last few
>years, especially if using the WAAS ablities. But,
>let's say you know
>the distance to only +/- 100 feet (it's typically more
>like +/- 30
>feet), then flying only a mile (5000 feet) would be
>a 2% error, or one
>L/D point for a 50:1 glider. Good enough for us, I
>think.

At 50:1 flying a one mile distance should yield an
altitude loss of 100', so I think a +/- 100' GPS error
in altitude could yield a 'measured' L/D of between
25:1 and infinity.

A single measured glide of 10 miles, assuming no other
errors from pilot inputs or net airmass movements,
would be good to only 10%, or +/- 5 L/D points, that's
a bit better, but you'd still need to average a bunch
of runs of 10+ miles to get any kind of accuracy. Best
done in dead calm air the way Dick does.

I have tried plotting speed versus glide angle over
a number of flights. You need to adjust for wind speed
and direction (estimated from thermal drift angle and/or
ground speed differences around a circle), then you
have to convert from TAS to IAS (2% per 100'). I plotted
about 30 points and realized that I had a very low
signal to noise ratio - that is the points made a big
cloud that sort of sloped in the expected direction.

I suppose with enough data points you could get a resonable
average L/D performance for any given speed, but I
did the experiment for a different reason, I was interested
in the VARIANCE in performance that I could expect
in real world conditions, including pilot technique
and long stretches of good/bad air.

If I know the difference between expected performance
and 99% worst case performance I know how much cushion
to carry on final glides - particularly as I get closer
to home, and the ground, and have fewer options to
recover. It also may help a bit to know how early you
can start a long final glide, though this is much more
subject to observable conditions like streeting and
average thermal strength and therefore less informed
by bulk statistical analysis.

9B

[Eric Greenwell]

Andy Blackburn wrote:

> At 18:30 28 December 2004, Eric Greenwell wrote:
>
>>How long ago did you ask him? GPS is much more accurate
>>in the last few
>>years, especially if using the WAAS ablities. But,
>>let's say you know
>>the distance to only +/- 100 feet (it's typically more
>>like +/- 30
>>feet), then flying only a mile (5000 feet) would be
>>a 2% error, or one
>>L/D point for a 50:1 glider. Good enough for us, I
>>think.
>
>
> At 50:1 flying a one mile distance should yield an
> altitude loss of 100', so I think a +/- 100' GPS error
> in altitude could yield a 'measured' L/D of between
> 25:1 and infinity.

My example was for GPS distance, and pressure altitude, to indicate that
a distance measurement wasn't a problem. That's why a I later referred
to flying off at least 1000 feet if GPS altitude was used.

What I don't know is how much error change one can expect in GPS
altitudes taken 5 or 10 minutes apart. The difference (GPS start height
minus GPS finish height) might have a much smaller error than the
altitude itself, which would allow shorter glides (500 foot loss if the
differential error was only 5 feet, for example).


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Eric Greenwell
Washington State
USA

[Doug Haluza]

I have tried using a $10,000 carrier phase GPS receiver with 0.1m
precision (post-processed) for glide testing. The GPS data was so
precise, you could clearly see the antenna move a few cm when the wing
was raised for takeoff. Even when flying in the calmest conditions,
with no discernable airmass movement, the vertical motions are
significant.

In analysing the data, I could not precisely fit a straight line to the
data points from 1-2 min glides at constant airspeed, even after
correcting for slight airspeed variations using total energy. Johnson
does not have this problem because he only has two data points, one at
the beginning and one at the end of each glide. When you have about a
hundred data points, one every second, you can really see the problem.
You need a lot more data points to average out the noise.

Based on this, I doubt that you could get useful data from a less
precise GPS, with a slower sampling interval, in uncontrolled
conditions. There is just too much noise to get useful results without
an impossibly huge data set.

Eric Greenwell wrote:
> Mark Zivley wrote:
>
> > We all know what the manufacturer's polars look like, but what
about
> > our individual planes. Has anyone done any work to develop a
program
> > that would look at some flight logs and determine what a particular
> > glider's actual polar is? At one point Ball was making a vario
> > system that would determine the aircraft's polar over time just by
> > flying.
> >
> > For someone who already had some algorithms for computing wind from

> > ground track drift during thermals could take this info and then be
> > able to back figure from GPS ground speed what the IAS was during a

> > particular phase of the flight. By isolating longer sections of
> > cruise flight at varios airspeeds it should be do-able. Question
is,
> > has it been done.
>
> I haven't heard of it being done, and I can't imagine how one would
> compensate for air motion, both vertical and horizontal, just using
the
> GPS info. Both motions change with location, altitude, and time.
Perhaps
> if the flight record included the airspeed, like some varios can
supply,
> there would be some hope of doing it. I don't think you could count
on
> the vertical motion averaging to zero during the cruises, since we
> typically adjust our path to include as much up air as possible.
>
> You can get some good info using a flight recorder, but you have to
do
> it when the air is calm. If you are really interested, invest in a
few
> high tows and make the measurements. Take a look at this test done on
a
> DG 800:
>
> http://groups.yahoo.com/group/ASA-NewsGroup/message/59
>
> You don't have to be a group member to read the message.
>
>
> --
> Change "netto" to "net" to email me directly
>
> Eric Greenwell
> Washington State
> USA

[Steve Bralla]

"Tim.Ward" > writes:
>
>> the distance to only +/- 100 feet (it's typically more like +/- 30
>> feet), then flying only a mile (5000 feet) would be a 2% error, or
>one
>> L/D point for a 50:1 glider. Good enough for us, I think.
>
>I don't think this is quite right. Consider a 50:1 glider descending
>100 meters:
>It will go 100 x 50 = 5000 meters
>I think vertical navigation errors are typically 1.5 times the
>horizontal.
>If horizontal accuracy is 10 meters, then vertical will be about 15
>So when we've measured this exactly 50:1 glider sinking 100 meters, the
>two worst cases we would read for a measurement are:
>(5000-Herror)/(100+Verror) = 4990/115 = 43.4
>(5000+Herror)/(100-Verror) = 5010/85 = 58.9
>
To find and eliminate the random errors just have a second GPS receiver on the
ground under the area of the flight test. Comparing of the records would show
the GPS errors. (Any motion on a stationary receiver is GPS error.) We are
able to get better than millimeter accuracy (for earth plate motion studies)
using basically this technique, as you don't care where you are absolutely only
relative to the other point/receiver. We are interested in the polar at
higher speeds than plate motion speeds so some accuracy will be lost.

Steve

[Andy Blackburn]

At 00:00 29 December 2004, Eric Greenwell wrote:
>My example was for GPS distance, and pressure altitude,
>to indicate that
>a distance measurement wasn't a problem. That's why
>a I later referred
>to flying off at least 1000 feet if GPS altitude was
>used.
>
>What I don't know is how much error change one can
>expect in GPS
>altitudes taken 5 or 10 minutes apart. The difference
>(GPS start height
>minus GPS finish height) might have a much smaller
>error than the
>altitude itself, which would allow shorter glides
>(500 foot loss if the
>differential error was only 5 feet, for example).

Clarification noted - but distance measurement is a
problem with GPS with respect to polar calculations.

Without knowing the technique Dick Johnson uses, or
the specs on a specific pressure transducer, it's hard
to know if measuring pressure altitude through a digital
transducer is more or less accurate than the traditional
method. I'd guess it's a close call, but that has nothing
to do with GPS.

The main source of error, is being able to turn GPS
ground speed (or distance) into IAS reliably by subtracting
wind speed and adjust for altitude. An even greater
source of error is trying to use fixes from a typical
soaring day with airmass movements and pilot control
inputs, airspeed changes and flightpath deviations.

The empirical evidence is that there is way too much
randomness from the above noted effects to tease out
a anything much beyond just how much randomness there
in fact is on a typical flight.

Maybe if you did fifty 10-mile runs on a dead calm
day across five different airspeeds, you'd get less
scatter - but I think that's more or less what Dick
does, except he measures IAS directly, rather than
having to figure it out from ground speed.

9B

[Eric Greenwell]

Andy Blackburn wrote:

> Without knowing the technique Dick Johnson uses, or
> the specs on a specific pressure transducer, it's hard
> to know if measuring pressure altitude through a digital
> transducer is more or less accurate than the traditional
> method. I'd guess it's a close call, but that has nothing
> to do with GPS.

I don't know the specifics of Dick's instrument, but a digitally logged
unit has got to be better, maybe a lot better, than trying to read a
mechanical altimeter with a little vibrator on the panel!

>
> The main source of error, is being able to turn GPS
> ground speed (or distance) into IAS reliably by subtracting
> wind speed and adjust for altitude.

I think the pilots trying this are not doing that, but instead rely on
their airspeed to give them IAS. This does require calibration of the
ASI for real accuracy.

An even greater
> source of error is trying to use fixes from a typical
> soaring day with airmass movements and pilot control
> inputs, airspeed changes and flightpath deviations.

I agree completely, and expect the best data to come on the same kind of
day Dick uses; that is, not a soaring day!

It's this air mass movement that drives the Akafliegs to using "sacred
cows" to measure the motion of the test glider relative to the "cow".



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Washington State
USA

[Andy Blackburn]

At 07:30 29 December 2004, Eric Greenwell wrote:

>I think the pilots trying this are not doing that,
>but instead rely on
>their airspeed to give them IAS. This does require
>calibration of the
>ASI for real accuracy.

Actually the first post in this thread (from Mark)
read:

'Has anyone done any work to develop a program that
would look at some flight logs and determine what a
particular glider's actual polar is?'

This original idea has now morphed into a suggestion
essentially to replicate the technique used by Dick
Johnson and others, with the main difference being
using the barometric altitude transducer in a flight
computer instead of the mechanical altimeter(?). This
might offer some improvement in accuracy, but is at
least as complex to execute as the flight test techniques
used for the past 40+ years.

There are two main challenges with using flight logs
only:

1) There is no good source for IAS, so you have to
try to estimate it from GPS ground speed.

2) Typical soaring flights don't involve adequately
calm vertical airmass movement and probably not constant
enough airspeed to trust even long glides of many tens
of miles.

9B

[Cliff Hilty]

The different air masses, the different instruments
ect. ect.
obviously lead to different results. Not being the
physic's expert, I was just wondering if anyone has
tried flight testing Sailplanes in a wind tunnel? Could
you 'hard point' it and measure weights or lack of
weight to get Polar info. Im sure boeing or MD has
done something like that. I suppose that you may not
get a direct glide ratio but could get a common start
point that all gliders then could be compared to. Any
comment from the mathematicians?



At 14:00 29 December 2004, Andy Blackburn wrote:

>This original idea has now morphed into a suggestion
>essentially to replicate the technique used by Dick
>Johnson and others, with the main difference being
>using the barometric altitude transducer in a flight
>computer instead of the mechanical altimeter(?). This
>might offer some improvement in accuracy, but is at
>least as complex to execute as the flight test techniques
>used for the past 40+ years.
>
>There are two main challenges with using flight logs
>only:
>
>1) There is no good source for IAS, so you have to
>try to estimate it from GPS ground speed.
>
>2) Typical soaring flights don't involve adequately
>calm vertical airmass movement and probably not constant
>enough airspeed to trust even long glides of many tens
>of miles.
>
>9B

[Eric Greenwell]

Andy Blackburn wrote:

> This original idea has now morphed into a suggestion
> essentially to replicate the technique used by Dick
> Johnson and others, with the main difference being
> using the barometric altitude transducer in a flight
> computer instead of the mechanical altimeter(?). This
> might offer some improvement in accuracy, but is at
> least as complex to execute as the flight test techniques
> used for the past 40+ years.
>
> There are two main challenges with using flight logs
> only:
>
> 1) There is no good source for IAS, so you have to
> try to estimate it from GPS ground speed.

This data is available from various instruments, like the Cambridge 302
that I use. For the 302 it's actually the TAS, which could be combined
with the air temperature and pressure altitude to compute the IAS. The
TAS and temperature are not recorded in the 302 flight log,
unfortunately, but they could be recorded by the Ipaq connected to it
and inserted in the flight log it keeps, and this log used for the analysis.

>
> 2) Typical soaring flights don't involve adequately
> calm vertical airmass movement and probably not constant
> enough airspeed to trust even long glides of many tens
> of miles.

I think this is a show-stopper, even if the IAS is available in a flight
log.
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Eric Greenwell
Washington State
USA

[Andy Blackburn]

At 20:00 29 December 2004, Cliff Hilty wrote:
>I was just wondering if anyone has
>tried flight testing Sailplanes in a wind tunnel? Could
>you 'hard point' it and measure weights or lack of
>weight to get Polar info.

Hey Cliff,

A wind tunnel would allow you to measure lift and drag
forces directly at various speeds, angles of attack
and flap settings. From this you could generate a polar
for any weight. This would be the most accurate way
to generate a polar I believe because it is under lab
conditions with highly calibrated instrumentation.
Of course you'd need a big wind tunnel like the NASA
Ames 80'x120' low-speed tunnel. You can rent it out,
but I bet it's expensive. To cover all the speeds,
flap settings and weights you'd need several dozen
test points, which would require a few hours in the
tunnel.

http://windtunnels.arc.nasa.gov

9B

[Andy Blackburn]

At 20:00 29 December 2004, Eric Greenwell wrote:
>Andy Blackburn wrote:
>>
>> 1) There is no good source for IAS, so you have to
>> try to estimate it from GPS ground speed.
>
>This data is available from various instruments, like
>the Cambridge 302
>that I use. For the 302 it's actually the TAS, which
>could be combined
>with the air temperature and pressure altitude to compute
>the IAS. The
>TAS and temperature are not recorded in the 302 flight
>log,
>unfortunately, but they could be recorded by the Ipaq
>connected to it
>and inserted in the flight log it keeps, and this log
>used for the analysis.

Neat idea - is that a configuration item on the 302
and/or WinPilot, or do you need to write software/firmware
to make it happen? Of course you'd still need to calibrate
the 302 IAS transducer for each sailplane type, but
at least then it would automate the data capture for
the kinds of performance testing Dick Johnson does.
Maybe he already has a rig to do this, but maybe not.
It would also allow collecting data from more than
a single test subject since anyone who could take a
high tow on a calm day and hold a constant airspeed
for more than 5 minutes could contribute a test point.

Of course here I'm assuming that all 302s and sailplanes
of a particular type with the same pneumatic setup
have similar airspeed errors, which may or may not
be true.

9B

[Eric Greenwell]

Andy Blackburn wrote:
The
>>TAS and temperature are not recorded in the 302 flight
>>log,
>>unfortunately, but they could be recorded by the Ipaq
>>connected to it
>>and inserted in the flight log it keeps, and this log
>>used for the analysis.
>
>
> Neat idea - is that a configuration item on the 302
> and/or WinPilot, or do you need to write software/firmware
> to make it happen?

I don't know about Winpilot, but it's not part of SeeYou Mobile. I think
it could easily be added by SeeYou and included in the Ipaq flight log
it can already keep, and I've suggested it to SeeYou. It's just another
data "sentence" that the 302 can send out.

> Of course you'd still need to calibrate
> the 302 IAS transducer

The sensor could be (probably is already) calibrated by Cambridge and
other labs when it is calibrated for flight recorder use.

> for each sailplane type,

You wouldn't have to measure your pitot/static system if you were
interested only in your glider, and not in comparing the data with data
from other gliders; for example, if you just wanted to maximize your use
of the flaps and speeds.

> but
> at least then it would automate the data capture for
> the kinds of performance testing Dick Johnson does.

I'm sure he does use an automated logger of some kind. I don't think
he's used a "vibrating panel" for quite a while!

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Eric Greenwell
Washington State
USA

[Udo Rumpf]

>> at least then it would automate the data capture for
>> the kinds of performance testing Dick Johnson does.

>"Eric Greenwell"

> I'm sure he does use an automated logger of some kind. I don't think he's
> used a "vibrating panel" for quite a while!

I the spring of 2003 Dick Johnson when he tested my glider he still used
the hard ware he has been using for a long time.
A vibrator for the Panel, he calibrates the airspeed indicator and the
altimeter. He uses his own instruments and takes notes of temperature
and as he flies trough 500ft timed intervals. He is able to do 3 to six
speeds
for each flap setting on one flight from 12000ft. In my case he made two
flight. The other aids are a stop watch, a note pad and at least two if
not
three pencils. I would be able to provide you with a copy of the numerical
data sheet.
Regards
Udo

[Eric Greenwell]

Udo Rumpf wrote:

>> I'm sure he does use an automated logger of some kind. I don't think
>> he's used a "vibrating panel" for quite a while!
>
>
> I the spring of 2003 Dick Johnson when he tested my glider he still used
> the hard ware he has been using for a long time.
> A vibrator for the Panel, he calibrates the airspeed indicator and the
> altimeter. He uses his own instruments and takes notes of temperature
> and as he flies trough 500ft timed intervals. He is able to do 3 to six
> speeds
> for each flap setting on one flight from 12000ft. In my case he made two
> flight. The other aids are a stop watch, a note pad and at least two
> if not
> three pencils. I would be able to provide you with a copy of the
> numerical data sheet.

I was sure I'd read/heard he was using an electronic logger, at least at
one time. Did he mention if he'd tried one, or if some of the pilots
assisting him used one?

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Eric Greenwell
Washington State
USA

The Zander flight computer performs a constant L/D calculations throughout a
flight. The L/D is presented numerically on the screen. All you need to do
is note the L/D, flap setting and speed at any particular time.

David
"Mark Zivley" > wrote in message
m...
> We all know what the manufacturer's polars look like, but what about our
> individual planes. Has anyone done any work to develop a program that
> would look at some flight logs and determine what a particular glider's
> actual polar is? At one point Ball was making a vario system that would
> determine the aircraft's polar over time just by flying.
>
> For someone who already had some algorithms for computing wind from ground
> track drift during thermals could take this info and then be able to back
> figure from GPS ground speed what the IAS was during a particular phase of
> the flight. By isolating longer sections of cruise flight at varios
> airspeeds it should be do-able. Question is, has it been done.
>
> Mark
>
> extra "hot" in the address to delay the spammers...
>

[Udo Rumpf]

> Udo Rumpf wrote:
>
>>> I'm sure he does use an automated logger of some kind. I don't think
>>> he's used a "vibrating panel" for quite a while!
>>
>>
>> I the spring of 2003 Dick Johnson when he tested my glider he still used
>> the hard ware he has been using for a long time.
>> A vibrator for the Panel, he calibrates the airspeed indicator and the
>> altimeter. He uses his own instruments and takes notes of temperature
>> and as he flies trough 500ft timed intervals. He is able to do 3 to six
>> speeds
>> for each flap setting on one flight from 12000ft. In my case he made
>> two
>> flight. The other aids are a stop watch, a note pad and at least two if
>> not
>> three pencils. I would be able to provide you with a copy of the
>> numerical data sheet.

Eric wrote

> I was sure I'd read/heard he was using an electronic logger, at least at
> one time. Did he mention if he'd tried one, or if some of the pilots
> assisting him used one?

I did ask him if loggers are helpful to him and he said no.
That would indicate he may have tried using it as an aid.
Udo

[Andreas Maurer]

On Thu, 30 Dec 2004 02:46:15 GMT, > wrote:

>The Zander flight computer performs a constant L/D calculations throughout a
>flight. The L/D is presented numerically on the screen. All you need to do
>is note the L/D, flap setting and speed at any particular time.

.... and the EXACT airmass rise/fall.
This is where the task becomes impossible with current technology. :)


Bye
Andreas

[Andy Blackburn]

At 15:30 30 December 2004, Andreas Maurer wrote:
>On Thu, 30 Dec 2004 02:46:15 GMT, wrote:
>
>>The Zander flight computer performs a constant L/D
>>calculations throughout a
>>flight. The L/D is presented numerically on the screen.
>>All you need to do
>>is note the L/D, flap setting and speed at any particular
>>time.
>
>.... and the EXACT airmass rise/fall.
>This is where the task becomes impossible with current
>technology. :)

Yup.

I don't believe it is possible to distinguish sailplane
vertical motion from the vertical motion of the airmass
with any of the current instruments, since both GPS
and barometric altimeters measure distance from the
earth's surface (in different ways obviously). Therefore
vertical motion measured from these instruments will
always be relative to the ground rather than relative
to the airmass.

If you had a test boom mounted AOA vane and a good
laser gyro, however....

9B

[Tim Ward]

"Andreas Maurer" > wrote in message
...
> On Thu, 30 Dec 2004 02:46:15 GMT, > wrote:
>
> >The Zander flight computer performs a constant L/D calculations
throughout a
> >flight. The L/D is presented numerically on the screen. All you need to
do
> >is note the L/D, flap setting and speed at any particular time.
>
> ... and the EXACT airmass rise/fall.
> This is where the task becomes impossible with current technology. :)
>
>
> Bye
> Andreas



I found this laser sensor on the web:
http://www.navysbir.brtrc.com/successstories/opticalair_00045_navsea_p3.html
Not many details.
Assuming it's accurate enough, one could be used to get the glider's
vertical speed through the airmass.
Now you have both horizontal and vertical velocity measurements relative to
the local airmass.
That should simplify the problem.

Also, it might give Bill Daniels his negative-lag variometer. (Thiotimoline
being in such short supply these days)

Unfortunately, the manufacturer's website is down for revamping. I haven't
emailed the contact address.

Tim Ward

[[email protected]]

"Doug Haluza" > writes:

> I have tried using a $10,000 carrier phase GPS receiver with 0.1m
> precision (post-processed) for glide testing. The GPS data was so
> precise, you could clearly see the antenna move a few cm when the
> wing was raised for takeoff. Even when flying in the calmest
> conditions, with no discernable airmass movement, the vertical
> motions are significant.

> In analysing the data, I could not precisely fit a straight line to
> the data points from 1-2 min glides at constant airspeed, even after
> correcting for slight airspeed variations using total
> energy. Johnson does not have this problem because he only has two
> data points, one at the beginning and one at the end of each
> glide. When you have about a hundred data points, one every second,
> you can really see the problem. You need a lot more data points to
> average out the noise.

> Based on this, I doubt that you could get useful data from a less
> precise GPS, with a slower sampling interval, in uncontrolled
> conditions. There is just too much noise to get useful results
> without an impossibly huge data set.

You do not have a problem with lots of data, that's just more compute.
You will probably need another unit so you can do DGPS or RTK post
processing of the data. More data, at a faster rate is in fact simpler.
You do not have to worry about boundary conditions if your sample rate
is WAY over the responce of the airframe.

What you need to do is develop a set of Kalman filter parameters, to
fit your data, then extract the polar from them.

--
Paul Repacholi 1 Crescent Rd.,
+61 (08) 9257-1001 Kalamunda.
West Australia 6076
comp.os.vms,- The Older, Grumpier Slashdot
Raw, Cooked or Well-done, it's all half baked.
EPIC, The Architecture of the future, always has been, always will be.

[[email protected]]

Andy Blackburn > writes:

> There are two main challenges with using flight logs only:

> 1) There is no good source for IAS, so you have to try to estimate
> it from GPS ground speed.

> 2) Typical soaring flights don't involve adequately calm vertical
> airmass movement and probably not constant enough airspeed to trust
> even long glides of many tens of miles.

You really need a different logger, that records raw GPS carrier phase,
plus static, pitot and temp. And Alpha vane would also be a big help.
Also you would want to run at 10 sample/sec or possible more.

If you go to this much trouble, you may as well ues 3 sets of GPS and
can then extract full position, attitude, and velocities as well.

--
Paul Repacholi 1 Crescent Rd.,
+61 (08) 9257-1001 Kalamunda.
West Australia 6076
comp.os.vms,- The Older, Grumpier Slashdot
Raw, Cooked or Well-done, it's all half baked.
EPIC, The Architecture of the future, always has been, always will be.

[Eric Greenwell]

Tim Ward wrote:

>
> I found this laser sensor on the web:
> http://www.navysbir.brtrc.com/successstories/opticalair_00045_navsea_p3.html
> Not many details.
> Assuming it's accurate enough, one could be used to get the glider's
> vertical speed through the airmass.
> Now you have both horizontal and vertical velocity measurements relative to
> the local airmass.
> That should simplify the problem.

A Google search turned up laser airspeed sensors that, in concept, could
be used to measure L/D directly from the glider. Some of them were good
for the low speeds we need to measure sink rates. So, have one pointing
forward, one pointing down, divide the forward speed by the sink rate,
and ta-da! L/D. It wouldn't matter what the airmass was doing, since the
measurements are relative to the airmass.

Unfortunately, none of the units I saw seemed to be small, cheap, or
readily available, as their audience appeared to be military types or
rather expensive aircraft.


--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

[Lars P. Hansen]

OK, here we go: Could devices like this not also be used to detect thermals?
The description in the link below about how the laser "sees" minute dust
particles in the air seems to be well suited to thermals.

Happy New Year to all,
Lars Peder


--
Lars P. Hansen


"Eric Greenwell" > wrote in message
...
> Tim Ward wrote:
>
> >
> > I found this laser sensor on the web:
> >
http://www.navysbir.brtrc.com/successstories/opticalair_00045_navsea_p3.html
> > Not many details.
> > Assuming it's accurate enough, one could be used to get the glider's
> > vertical speed through the airmass.
> > Now you have both horizontal and vertical velocity measurements relative
to
> > the local airmass.
> > That should simplify the problem.
>
> A Google search turned up laser airspeed sensors that, in concept, could
> be used to measure L/D directly from the glider. Some of them were good
> for the low speeds we need to measure sink rates. So, have one pointing
> forward, one pointing down, divide the forward speed by the sink rate,
> and ta-da! L/D. It wouldn't matter what the airmass was doing, since the
> measurements are relative to the airmass.
>
> Unfortunately, none of the units I saw seemed to be small, cheap, or
> readily available, as their audience appeared to be military types or
> rather expensive aircraft.
>
>
> --
> Change "netto" to "net" to email me directly
>
> Eric Greenwell
> Washington State
> USA

[Tim Ward]

"Lars P. Hansen" > wrote in message
k...
> OK, here we go: Could devices like this not also be used to detect
thermals?
> The description in the link below about how the laser "sees" minute dust
> particles in the air seems to be well suited to thermals.
>
> Happy New Year to all,
> Lars Peder

Probably. It also talks about the ability to show a 3-D representation of
the airmass movement around the aircraft. Since it's eye-safe, it probably
has a fairly short range.

This ties back to Bill Daniels' wish for a variometer with a negative
delay -- to be able to see what the airmass is doing a few seconds in front
of the glider.

It's unlikely that it's as inexpensive or will be as inexpensive as handheld
GPS, but if you were serious about performance measurement, it might be
able to pay for itself in a reduced number of tows to characterize a given
aircraft or configuration. So it might make sense for a university
department or a manufacturer. At least it's light enough and rugged enough
to consider mounting it on a sailplane.

Still, some of the civilian applications (shooting, sailboats) were in
more-or-less recreational areas, so perhaps they expect to be able to keep
the cost down.


Tim Ward



> Lars P. Hansen
>
>
> "Eric Greenwell" > wrote in message
> ...
> > Tim Ward wrote:
> >
> > >
> > > I found this laser sensor on the web:
> > >
>
http://www.navysbir.brtrc.com/successstories/opticalair_00045_navsea_p3.html
> > > Not many details.
> > > Assuming it's accurate enough, one could be used to get the glider's
> > > vertical speed through the airmass.
> > > Now you have both horizontal and vertical velocity measurements
relative
> to
> > > the local airmass.
> > > That should simplify the problem.
> >
> > A Google search turned up laser airspeed sensors that, in concept, could
> > be used to measure L/D directly from the glider. Some of them were good
> > for the low speeds we need to measure sink rates. So, have one pointing
> > forward, one pointing down, divide the forward speed by the sink rate,
> > and ta-da! L/D. It wouldn't matter what the airmass was doing, since the
> > measurements are relative to the airmass.
> >
> > Unfortunately, none of the units I saw seemed to be small, cheap, or
> > readily available, as their audience appeared to be military types or
> > rather expensive aircraft.
> >
> >
> > --
> > Change "netto" to "net" to email me directly
> >
> > Eric Greenwell
> > Washington State
> > USA
>
>

[Andreas Maurer]

On Thu, 30 Dec 2004 13:36:59 -0800, Eric Greenwell
> wrote:

>A Google search turned up laser airspeed sensors that, in concept, could
>be used to measure L/D directly from the glider. Some of them were good
>for the low speeds we need to measure sink rates. So, have one pointing
>forward, one pointing down, divide the forward speed by the sink rate,
>and ta-da! L/D. It wouldn't matter what the airmass was doing, since the
>measurements are relative to the airmass.

This is exactly what is accomplished by today's L/D calculators that
use GPS speed and barometrical measured height loss over a given time.






Bye
Andreas

[Jack]

Andy Blackburn wrote:

> ...since both GPS
> and barometric altimeters measure distance from the
> earth's surface (in different ways obviously). Therefore
> vertical motion measured from these instruments will
> always be relative to the ground rather than relative
> to the airmass.

The way I see it, a barometric measurement will not be relative to the
ground at all: might even be related to the airmass, if only to a
pressure level.

Relating a barometric measurement to the ground is pretty arbitrary,
though I hear some folks are willing to do it down to 200' and 1/2
mile, on dark and stormy nights.

Some things you just have to take on faith.


--
Jack
----
"It is possible to fly without motors,
but not without knowledge and skill."
-- Wilbur Wright

[Tim Ward]

"Andreas Maurer" > wrote in message
...
> On Thu, 30 Dec 2004 13:36:59 -0800, Eric Greenwell
> > wrote:
>
> >A Google search turned up laser airspeed sensors that, in concept, could
> >be used to measure L/D directly from the glider. Some of them were good
> >for the low speeds we need to measure sink rates. So, have one pointing
> >forward, one pointing down, divide the forward speed by the sink rate,
> >and ta-da! L/D. It wouldn't matter what the airmass was doing, since the
> >measurements are relative to the airmass.
>
> This is exactly what is accomplished by today's L/D calculators that
> use GPS speed and barometrical measured height loss over a given time.

No, it's not. That will give you the glide made good over the ground, but
it includes airmass movement.

It's confusing, because glider pilots tend to use glide angle and L/D
interchangeably.
I would suggest "glide angle" for the glide relative to the ground, and
"L/D" for the performance relative to the air.
To show you what I mean:
When I get into weak shear, my 1-26 may make a glide angle of 50:1. But its
L/D is more like 20:1


Tim Ward


> Bye
> Andreas

[Eric Greenwell]

Andreas Maurer wrote:
> On Thu, 30 Dec 2004 13:36:59 -0800, Eric Greenwell
> > wrote:
>
>
>>A Google search turned up laser airspeed sensors that, in concept, could
>>be used to measure L/D directly from the glider. Some of them were good
>>for the low speeds we need to measure sink rates. So, have one pointing
>>forward, one pointing down, divide the forward speed by the sink rate,
>>and ta-da! L/D. It wouldn't matter what the airmass was doing, since the
>>measurements are relative to the airmass.
>
>
> This is exactly what is accomplished by today's L/D calculators that
> use GPS speed and barometrical measured height loss over a given time.

GPS speed and pressure altitude are referenced to the earth, not the air
mass, so they would determine a different L/D than airmass referenced
instruments. In concept, a glider flying at constant speed through
rising and falling air would have a constant L/D according to the laser
airspeed sensors, but a widely varying one based on GPS speed and
pressure altitude.


--
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Eric Greenwell
Washington State
USA

[Andy Blackburn]

At 22:30 30 December 2004, Eric Greenwell wrote:

>A Google search turned up laser airspeed sensors that,
>in concept, could
>be used to measure L/D directly from the glider. Some
>of them were good
>for the low speeds we need to measure sink rates. So,
>have one pointing
>forward, one pointing down, divide the forward speed
>by the sink rate,
>and ta-da! L/D.

Would you need an inertial platform to resolve horizontal
and vertical accurately enough or would eyeballing
it be good enough?

Also, the forward looking and downward looking lasers
would be observing different air, so it's possible
that would cause problems, depending on how far out
they look.

I think it might work - though at a hefty price I bet.

9B

[Eric Greenwell]

Andy Blackburn wrote:
> At 22:30 30 December 2004, Eric Greenwell wrote:
>
>
>>A Google search turned up laser airspeed sensors that,
>>in concept, could
>>be used to measure L/D directly from the glider. Some
>>of them were good
>>for the low speeds we need to measure sink rates. So,
>>have one pointing
>>forward, one pointing down, divide the forward speed
>>by the sink rate,
>>and ta-da! L/D.
>
>
> Would you need an inertial platform to resolve horizontal
> and vertical accurately enough or would eyeballing
> it be good enough?

Since the concept is to measure speed through the airmass, I don't think
inertial systems would help any, as they are referenced to the aircraft,
not the air.

I don't know if any of the systems would actually give us the vertical
speed accuracy we'd like. A major application seemed to be for
helicopters, which can move very slowly (and even back up), so low speed
sensing is certainly feasible. Speeds over 20-30 knots seemed to be easy
to get with the units I glanced at.

>
> Also, the forward looking and downward looking lasers
> would be observing different air, so it's possible
> that would cause problems, depending on how far out
> they look.

The distances available varied from a "a few feet" to hundreds of feet,
I think. Very application dependent: helicopters couldn't use anything
that sensed closer that the outer edge of the rotor downwash, for
example. I'm guessing one for gliders could be set for, say, 100 feet to
be far enough from the glider's influence on the airmass, and this still
have both the forward and downward airmasses close enough to be the
"same" airmass.

Some of the sensors actually sensed at right angles to the sensor beam
to measure crosswinds, and maybe one of these could be also be pointed
straight down into the same airmass the vertical speed unit was looking at.

>
> I think it might work - though at a hefty price I bet.

Yes, all the units I came across seemed to be high end or developmental,
and rather large to stick into a glider. A careful search might have
better luck.

A mitigating factor for cost is gliders already have a pretty good
forward airmass speed sensor - the ASI - so perhaps only a downward
aimed laser sensor good for measuring 100 to 500 feet per minute at 2%
accuracy would be satisfactory.


--
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Eric Greenwell
Washington State
USA

[Tim Ward]

"Eric Greenwell" > wrote in message
...
<snip>

> Some of the sensors actually sensed at right angles to the sensor beam
> to measure crosswinds, and maybe one of these could be also be pointed
> straight down into the same airmass the vertical speed unit was looking
at.
>
> >
> > I think it might work - though at a hefty price I bet.
>
> Yes, all the units I came across seemed to be high end or developmental,
> and rather large to stick into a glider. A careful search might have
> better luck.

The sensor I posted a link to was small enough to be mounted on a rifle as a
sight.
http://www.navysbir.brtrc.com/successstories/opticalair_00045_navsea_p3.html

That would seem to be a feasible size, weight and ruggedness for a glider
I've sent an email with some questions I had, but haven't yet received an
answer.

Some of the applications they mention on that website -- Automotive,
Collision Avoidance,
Cruise Control, Parking Aid, would require the cost to be fairly reasonable
(though the volume would be a lot more than sailplanes would ever give
them.)
>
> A mitigating factor for cost is gliders already have a pretty good
> forward airmass speed sensor - the ASI - so perhaps only a downward
> aimed laser sensor good for measuring 100 to 500 feet per minute at 2%
> accuracy would be satisfactory.

If the laser and optics can be made to "see" through the canopy, pointing it
upward might make for an easier install. I've seen compasses mounted on top
of the panel.
OTOH, with it pointing downwards, it might give a good input to a gear
warning device. If it can detect small particles, I'll bet it can detect a
solid surface -- and that the signals are way different.

>
>
> --
> Change "netto" to "net" to email me directly
>
> Eric Greenwell
> Washington State
> USA

[Andy Blackburn]

At 23:00 31 December 2004, Eric Greenwell wrote:
>Since the concept is to measure speed through the airmass,
>I don't think
>inertial systems would help any, as they are referenced
>to the aircraft,
>not the air.

I menat an inertial platform for attitude, not velocity.
If you the sensor isn't pointing horizontally/vertically
or parallel/perpendicular to the flight path, you will
likely get confounded results.

9B

[Eric Greenwell]

Tim Ward wrote:

>>Yes, all the units I came across seemed to be high end or developmental,
>>and rather large to stick into a glider. A careful search might have
>>better luck.
>
>
> The sensor I posted a link to was small enough to be mounted on a rifle as a
> sight.
> http://www.navysbir.brtrc.com/successstories/opticalair_00045_navsea_p3.html

I thought it was something telescope sized that sat next to the
rifleman.I can see now it's about the size of a flashlite - much smaller
than the airspeed units I saw.

> That would seem to be a feasible size, weight and ruggedness for a glider
> I've sent an email with some questions I had, but haven't yet received an
> answer.

Let us know what they write.

>
> Some of the applications they mention on that website -- Automotive,
> Collision Avoidance,
> Cruise Control, Parking Aid, would require the cost to be fairly reasonable
> (though the volume would be a lot more than sailplanes would ever give
> them.)
>
>>A mitigating factor for cost is gliders already have a pretty good
>>forward airmass speed sensor - the ASI - so perhaps only a downward
>>aimed laser sensor good for measuring 100 to 500 feet per minute at 2%
>>accuracy would be satisfactory.
>
>
> If the laser and optics can be made to "see" through the canopy, pointing it
> upward might make for an easier install. I've seen compasses mounted on top
> of the panel.

Maybe a mirror adapter to peek out the side window. If the beam is small
enough, mounting it in the baggage compartment and pointing up through a
1/2" hole in the turtledeck wouldn't bother me.

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Eric Greenwell
Washington State
USA

[Eric Greenwell]

Andy Blackburn wrote:

> At 23:00 31 December 2004, Eric Greenwell wrote:
>
>>Since the concept is to measure speed through the airmass,
>>I don't think
>>inertial systems would help any, as they are referenced
>>to the aircraft,
>>not the air.
>
>
> I menat an inertial platform for attitude, not velocity.
> If you the sensor isn't pointing horizontally/vertically
> or parallel/perpendicular to the flight path, you will
> likely get confounded results.

I think the angle of attack range for an unflapped airfoil is about 10
degrees, which would suggest errors of 0 (at high speed, for example)
increasing to 1.5% at low speed (or vice versa - depends on where you
aim the sensor). This could be easily corrected using using the
airfoil's Cl vs AOA chart. For a flapped airfoil, the fuselage AOA range
is even smaller, and the errors could likely just be ignored.

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Eric Greenwell
Washington State
USA

[Andy Blackburn]

At 07:00 01 January 2005, Eric Greenwell wrote:
>I think the angle of attack range for an unflapped
>airfoil is about 10
>degrees, which would suggest errors of 0 (at high speed,
>for example)
>increasing to 1.5% at low speed (or vice versa - depends
>on where you
>aim the sensor). This could be easily corrected using
>using the
>airfoil's Cl vs AOA chart. For a flapped airfoil, the
>fuselage AOA range
>is even smaller, and the errors could likely just be
>ignored.

50:1 is an angle of a degree and a bit so if you have
your 'straight ahead' and 'straight down' sensors canted
down/aft by just a degree from true horizontal/vertical,
you'll get a pretty accurate airspeed, but the 'vertical'
speed will likely show zero, I think, since it will
be reading off dust particles that have zero velocity
towards/away from the glider.

9B

[Eric Greenwell]

Andy Blackburn wrote:
> At 07:00 01 January 2005, Eric Greenwell wrote:
>
>>I think the angle of attack range for an unflapped
>>airfoil is about 10
>>degrees, which would suggest errors of 0 (at high speed,
>>for example)
>>increasing to 1.5% at low speed (or vice versa - depends
>>on where you
>>aim the sensor). This could be easily corrected using
>>using the
>>airfoil's Cl vs AOA chart. For a flapped airfoil, the
>>fuselage AOA range
>>is even smaller, and the errors could likely just be
>>ignored.
>
>
> 50:1 is an angle of a degree and a bit so if you have
> your 'straight ahead' and 'straight down' sensors canted
> down/aft by just a degree from true horizontal/vertical,
> you'll get a pretty accurate airspeed, but the 'vertical'
> speed will likely show zero, I think, since it will
> be reading off dust particles that have zero velocity
> towards/away from the glider.

Think of the glider flying straight and steady in still air: it is
descending (vertical motion) through the air at whatever it's sink rate
is. So, at least in concept, a laser airspeed sensor pointed straight
down will be able to measure this. Even if the sensor is aimed a few
degrees one way or the other from perpendicular, the error would be very
small, equal to sine of the angle off of perpendicular.

If the airmass is moving, the measurement would be the same, of course,
since the speed measured is the air motion relative to the glider - it's
just easier to visualize what's happening with still air.


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Eric Greenwell
Washington State
USA

[Greg Arnold]

If the sensor is aiming straight down, at a glide angle of 40/1 the air
is going 40" aft for every 1" that it rises relative to the instrument.
If the sensor is aimed slightly aft (1/40, whatever that is in
degrees), the air won't be rising at all relative to the sensor. Right?

So isn't angle crucial?

Also, can the sensors measure speed when the air mostly is going
crossways in front of the sensor?

[Andreas Maurer]

On Thu, 30 Dec 2004 16:51:25 -0800, Eric Greenwell
> wrote:


>GPS speed and pressure altitude are referenced to the earth, not the air
>mass, so they would determine a different L/D than airmass referenced
>instruments. In concept, a glider flying at constant speed through
>rising and falling air would have a constant L/D according to the laser
>airspeed sensors, but a widely varying one based on GPS speed and
>pressure altitude.

You are correct - I should have read your posting more carefully! :)
Happy New Year, btw!


Bye
Andreas

[Eric Greenwell]

Greg Arnold wrote:
> If the sensor is aiming straight down, at a glide angle of 40/1 the air
> is going 40" aft for every 1" that it rises relative to the instrument.
> If the sensor is aimed slightly aft (1/40, whatever that is in
> degrees), the air won't be rising at all relative to the sensor. Right?
>
> So isn't angle crucial?

OK, I'm persuaded! It now appears the sensor would need to be aimed up
or down rather accurately, or the at least the angle off vertical
measured accurately. Dang - that's harder. Perhaps the inertial system
would be a reasonable way to achieve this, or maybe differential GPS
system with antennas on the nose and tail.

>
> Also, can the sensors measure speed when the air mostly is going
> crossways in front of the sensor?

I think it depends on the sensor: some are optimized for speed in line
with the beam, some for speed perpendicular to the beam (cross wind
measurement, like for bullets). Perhaps there are ones that can read the
vector wind? I have no idea how much crossways speed the various sensors
can tolerate.

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Eric Greenwell
Washington State
USA

[Greg Arnold]

>
> I think it depends on the sensor: some are optimized for speed in line
> with the beam, some for speed perpendicular to the beam (cross wind
> measurement, like for bullets). Perhaps there are ones that can read the
> vector wind?


If so, you would just need a single sensor facing forward. You still
would have the problem of getting it perfectly horizontal, though.


I have no idea how much crossways speed the various sensors
> can tolerate.


I am betting that these sensors can only measure speed directly toward
or away from the sensor. Sort of like a radar gun. So I am not
understanding how they could measure a glider's sink rate.

[Bob Salvo]

It seems to me that having the sensor hanging freely like a pendulum
(pointing down) would make it measure the vertical component.

"Eric Greenwell" > wrote in message
...
>
> OK, I'm persuaded! It now appears the sensor would need to be aimed up
> or down rather accurately, or the at least the angle off vertical
> measured accurately. Dang - that's harder. Perhaps the inertial system
> would be a reasonable way to achieve this, or maybe differential GPS
> system with antennas on the nose and tail.
>

[Eric Greenwell]

Bob Salvo wrote:
> It seems to me that having the sensor hanging freely like a pendulum
> (pointing down) would make it measure the vertical component.
>
> "Eric Greenwell" > wrote in message
> ...
>
>>OK, I'm persuaded! It now appears the sensor would need to be aimed up
>>or down rather accurately, or the at least the angle off vertical
>>measured accurately. Dang - that's harder. Perhaps the inertial system
>>would be a reasonable way to achieve this, or maybe differential GPS
>>system with antennas on the nose and tail.

Maybe that would be good enough - especially for flying in smooth air,
like wave flying or early morning test flights. Or, maybe these units
would measure quickly enough, all you'd need would be occasional 5-10
seconds of smooth air.


--
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Eric Greenwell
Washington State
USA

[Robert Ehrlich]

"Lars P. Hansen" wrote:
>
> OK, here we go: Could devices like this not also be used to detect thermals?
> The description in the link below about how the laser "sees" minute dust
> particles in the air seems to be well suited to thermals.
>

I don't buy the explanation they give in the cited url (http://www.navysbir.brtrc.com/successstories/opticalair_00045_navsea_p3.html)
They pretend the device measures the speed and direction of dust particles
from the shift in the frequency of reflected light, this is well known
as Doppler effect and can only give the radial component (toward or away
from the sensor) of the speed, not its value and direction. For thermals
we are interested in the speed component which is nearly perpendicular
to the measured component, so this would be of little interest. Of course
whith several such devices on the ground, all the 3 compenents of airmass
speed could be measured, maybe this in the intended use of the device as it
is advertised, but in a glider you don't have sufficient vertical distance
for putting 2 devices which could provide an accurate value for the vertical
component of the speed.

[Robert Ehrlich]

After this discussion we are far from the original question, i.e.
can we infer anything about the polar of a glider just from GPS
fligth logs of this glider?

The obvious answer several people gave was: no because the airmass
movement is unknown.

Well, as a former mathematician, I would say this is just what the
name says: an unknown. Would we be able to determine it?

The problem is this is not a single unknown, it is an infinity of them.
And despite the fact that each track log point gives 3 equations, this
would not be sufficient for determining an infinite number of unknown.
Even when considering the finite number of unknowns consisting of the
3 components of the airmass speed at each point of the log, we have
more unknowns than equation since we have also the unknown polar we
want to determine.

So is there a solution?

We can do for other unknowns just what we do with the polar data,
which are also an infinity of unknowns: reduce their number by
assuming a simple model depending of a small number of unknowns, this
is usually done for the polar by assuming a quadratic approximation
depending only on 3 parameters.

In the same way we can assume that the horizontal components of
the wind are constant on the flight area at a given altitude, and
that the evolution with altitude could be carcterized with a few
parameter, e.g. wind speed at 3 given altitudes and polynomial
interpolation between them.

For the vertical component of airmass movement, we can assume that
the pilot is following some speed-to-fly rule caracterized by
a MC setting and the 3 parameters of the glider polar that was
used for making the MC ring or programming the flight computer.
Even these values may be considered as unknowns.

So we have now a small number of unknowns and a comparatively
large number of equations from the flight log, plus the few
ones from the physics relating position to speed, airspeed and
wind to ground speed, sink to height, sink to airspeed according
to the speed to fly rule and so on. Our system is no more undetermined
but overdetermined, probably there is no exact solution, but there
are methods for determining a most likely solution, i.e. values
for the unknowns that minimize the way the equations are not
satisfied (least square method or others).

As I am only a *former* mathematician, I will not go further
in this way, maybe somebody who is a real mathematician will
complete the job, or somebody who is teaching maths will
propose that as a project for students, this is the lazy method
I would have used when I was myself teaching :-)

[Robert Ehrlich]

Eric Greenwell wrote:
> ...
> A Google search turned up laser airspeed sensors that, in concept, could
> be used to measure L/D directly from the glider. Some of them were good
> for the low speeds we need to measure sink rates. So, have one pointing
> forward, one pointing down, divide the forward speed by the sink rate,
> and ta-da! L/D. It wouldn't matter what the airmass was doing, since the
> measurements are relative to the airmass.
> ...

The real problem then is to determine where should the down pointing
device exactly point. An error just equal to the gliding angle in
the backward direction will give an infinite L/D, and this just
about 1 degree. The direction relatively to the airframe is variable
with speed and is identical with the direction of apparent weight
only during unaccelarated flight, in this case this is also the direction
of the real weight, but we have no mean to detect that the flight has
no acceleration. Although the method is very simple in theory, I doubt
there is some practical realisation which would produce accurate enough
results for being interesting, even with a lot of money.

[Tim.Ward]

Robert Ehrlich wrote:
> "Lars P. Hansen" wrote:
> >
> > OK, here we go: Could devices like this not also be used to detect
thermals?
> > The description in the link below about how the laser "sees" minute
dust
> > particles in the air seems to be well suited to thermals.
> >
>
> I don't buy the explanation they give in the cited url
(http://www.navysbir.brtrc.com/successstories/opticalair_00045_navsea_p3.html)
> They pretend the device measures the speed and direction of dust
particles
> from the shift in the frequency of reflected light, this is well
known
> as Doppler effect and can only give the radial component (toward or
away
> from the sensor) of the speed, not its value and direction. For
thermals
> we are interested in the speed component which is nearly
perpendicular
> to the measured component, so this would be of little interest. Of
course
> whith several such devices on the ground, all the 3 compenents of
airmass
> speed could be measured, maybe this in the intended use of the device
as it
> is advertised, but in a glider you don't have sufficient vertical
distance
> for putting 2 devices which could provide an accurate value for the
vertical
> component of the speed.

It does work, but they use a little different technique.
The Doppler is only measured on particles at the focal length of the
optics.
The assumption is that the airmass (at least locally) is all the same,
and that the Doppler measurement is taken far enough away so the
effects of the airplane on the airmass are negligible.
So you send out two beams -- say, one forward at 45 degrees, one aft at
45 degrees.
It turns out that if you sum the signals from the two beams, you get
the vertical component of velocity, and if you difference the two
signals, you get the horizontal component.
Since we're measuring frequency, we can get sum and difference
frequencies from a mixer, though I have no doubt it runs through a DSP
somewhere.

So you only need one sensor head (though it puts out multiple beams).

By sending out two more beams, to each side, you can also pick up
sideslip information.
The clever thing is that they're using components developed for the
communications field, which helps to keep costs down.

Tim Ward

[Tim.Ward]

Robert Ehrlich wrote:
> "Lars P. Hansen" wrote:
> >
> > OK, here we go: Could devices like this not also be used to detect
thermals?
> > The description in the link below about how the laser "sees" minute
dust
> > particles in the air seems to be well suited to thermals.
> >
>
> I don't buy the explanation they give in the cited url
(http://www.navysbir.brtrc.com/successstories/opticalair_00045_navsea_p3.html)
> They pretend the device measures the speed and direction of dust
particles
> from the shift in the frequency of reflected light, this is well
known
> as Doppler effect and can only give the radial component (toward or
away
> from the sensor) of the speed, not its value and direction. For
thermals
> we are interested in the speed component which is nearly
perpendicular
> to the measured component, so this would be of little interest. Of
course
> whith several such devices on the ground, all the 3 compenents of
airmass
> speed could be measured, maybe this in the intended use of the device
as it
> is advertised, but in a glider you don't have sufficient vertical
distance
> for putting 2 devices which could provide an accurate value for the
vertical
> component of the speed.

It does work, but they use a little different technique.
The Doppler is only measured on particles at the focal length of the
optics.
The assumption is that the airmass (at least locally) is all the same,
and that the Doppler measurement is taken far enough away so the
effects of the airplane on the airmass are negligible.
So you send out two beams -- say, one forward at 45 degrees, one aft at
45 degrees.
It turns out that if you sum the signals from the two beams, you get
the vertical component of velocity, and if you difference the two
signals, you get the horizontal component.
Since we're measuring frequency, we can get sum and difference
frequencies from a mixer, though I have no doubt it runs through a DSP
somewhere.

So you only need one sensor head (though it puts out multiple beams).

By sending out two more beams, to each side, you can also pick up
sideslip information.
The clever thing is that they're using components developed for the
communications field, which helps to keep costs down.

Tim Ward

[Richard Brisbourne]

Robert Ehrlich wrote:

> After this discussion we are far from the original question, i.e.
> can we infer anything about the polar of a glider just from GPS
> fligth logs of this glider?
>
> The obvious answer several people gave was: no because the airmass
> movement is unknown.
>
> Well, as a former mathematician, I would say this is just what the
> name says: an unknown. Would we be able to determine it?
>
> The problem is this is not a single unknown, it is an infinity of them.
> And despite the fact that each track log point gives 3 equations, this
> would not be sufficient for determining an infinite number of unknown.
> Even when considering the finite number of unknowns consisting of the
> 3 components of the airmass speed at each point of the log, we have
> more unknowns than equation since we have also the unknown polar we
> want to determine.
>
> So is there a solution?
>
> We can do for other unknowns just what we do with the polar data,
> which are also an infinity of unknowns: reduce their number by
> assuming a simple model depending of a small number of unknowns, this
> is usually done for the polar by assuming a quadratic approximation
> depending only on 3 parameters.
>
> In the same way we can assume that the horizontal components of
> the wind are constant on the flight area at a given altitude, and
> that the evolution with altitude could be carcterized with a few
> parameter, e.g. wind speed at 3 given altitudes and polynomial
> interpolation between them.
>
> For the vertical component of airmass movement, we can assume that
> the pilot is following some speed-to-fly rule caracterized by
> a MC setting and the 3 parameters of the glider polar that was
> used for making the MC ring or programming the flight computer.
> Even these values may be considered as unknowns.
>
> So we have now a small number of unknowns and a comparatively
> large number of equations from the flight log, plus the few
> ones from the physics relating position to speed, airspeed and
> wind to ground speed, sink to height, sink to airspeed according
> to the speed to fly rule and so on. Our system is no more undetermined
> but overdetermined, probably there is no exact solution, but there
> are methods for determining a most likely solution, i.e. values
> for the unknowns that minimize the way the equations are not
> satisfied (least square method or others).
>
> As I am only a *former* mathematician, I will not go further
> in this way, maybe somebody who is a real mathematician will
> complete the job, or somebody who is teaching maths will
> propose that as a project for students, this is the lazy method
> I would have used when I was myself teaching :-)

Yeah- but would you believe the answer when you got it?

Not to mention another unknown- airflow separation during pull-ups and
pushovers, and effect of varying g-forces.

[Udo Rumpf]

Why is it not possible to refine the process that is being used by
Dick Johnson by using the gadgets that are available.
That would refine the data acquisition and would make the
resolution much finer. The work load is very high during the process.
Dick invited me to a test flight from 12000ft and not much useable
data was obtained from my only attempt. It sure takes practice.

One certainly has to chew gum, use a stop watch, make notes of time,
speed and temperature and flap settings, maintain speeds, change
speed and stabilize it.

This every 500ft, At the same time Fly a big circle around the airport,
so you have a place to land when finished. I may have left things out.

What electronic aids could be used that would help in this matter?
Udo






"Richard Brisbourne" > wrote in message
...
> Robert Ehrlich wrote:
>
>> After this discussion we are far from the original question, i.e.
>> can we infer anything about the polar of a glider just from GPS
>> fligth logs of this glider?
>>
>> The obvious answer several people gave was: no because the airmass
>> movement is unknown.
>>
>> Well, as a former mathematician, I would say this is just what the
>> name says: an unknown. Would we be able to determine it?
>>
>> The problem is this is not a single unknown, it is an infinity of them.
>> And despite the fact that each track log point gives 3 equations, this
>> would not be sufficient for determining an infinite number of unknown.
>> Even when considering the finite number of unknowns consisting of the
>> 3 components of the airmass speed at each point of the log, we have
>> more unknowns than equation since we have also the unknown polar we
>> want to determine.
>>
>> So is there a solution?
>>
>> We can do for other unknowns just what we do with the polar data,
>> which are also an infinity of unknowns: reduce their number by
>> assuming a simple model depending of a small number of unknowns, this
>> is usually done for the polar by assuming a quadratic approximation
>> depending only on 3 parameters.
>>
>> In the same way we can assume that the horizontal components of
>> the wind are constant on the flight area at a given altitude, and
>> that the evolution with altitude could be carcterized with a few
>> parameter, e.g. wind speed at 3 given altitudes and polynomial
>> interpolation between them.
>>
>> For the vertical component of airmass movement, we can assume that
>> the pilot is following some speed-to-fly rule caracterized by
>> a MC setting and the 3 parameters of the glider polar that was
>> used for making the MC ring or programming the flight computer.
>> Even these values may be considered as unknowns.
>>
>> So we have now a small number of unknowns and a comparatively
>> large number of equations from the flight log, plus the few
>> ones from the physics relating position to speed, airspeed and
>> wind to ground speed, sink to height, sink to airspeed according
>> to the speed to fly rule and so on. Our system is no more undetermined
>> but overdetermined, probably there is no exact solution, but there
>> are methods for determining a most likely solution, i.e. values
>> for the unknowns that minimize the way the equations are not
>> satisfied (least square method or others).
>>
>> As I am only a *former* mathematician, I will not go further
>> in this way, maybe somebody who is a real mathematician will
>> complete the job, or somebody who is teaching maths will
>> propose that as a project for students, this is the lazy method
>> I would have used when I was myself teaching :-)
>
> Yeah- but would you believe the answer when you got it?
>
> Not to mention another unknown- airflow separation during pull-ups and
> pushovers, and effect of varying g-forces.
>
>
>

[Tim Ward]

"Udo Rumpf" > wrote in message
...
> Why is it not possible to refine the process that is being used by
> Dick Johnson by using the gadgets that are available.
> That would refine the data acquisition and would make the
> resolution much finer. The work load is very high during the process.
> Dick invited me to a test flight from 12000ft and not much useable
> data was obtained from my only attempt. It sure takes practice.
>
> One certainly has to chew gum, use a stop watch, make notes of time,
> speed and temperature and flap settings, maintain speeds, change
> speed and stabilize it.
>
> This every 500ft, At the same time Fly a big circle around the airport,
> so you have a place to land when finished. I may have left things out.
>
> What electronic aids could be used that would help in this matter?
> Udo
>

A data logger (could be a PDA) attached to a differential carrier phase GPS
It should also be able to record accurate airspeed indicator and
temperature, or a true-airspeed reading device like the laser anemometer .
The GPS data can then be post-processed to give altitude information down to
10-15 cm or so.
The airspeed data can be be used post-flight to see just how steady-state
the data collection was.
With increased accuracy in the vertical measurement, it might be possible to
get sufficiently accurate data in say, 300 feet of altitude, allowing more
data points on a single flight.

That will make the flight card a little busier, perhaps, but fewer tows
should make the testing cheaper.

With samples every second, or even every tenth of a second, the additional
data should make it possible to improve the repeatability.

The hardware isn't cheap, but it's getting cheaper, and the data reduction
post-flight isn't a trivial problem, either, but it's doable.

Tim Ward

[Eric Greenwell]

Udo Rumpf wrote:
> Why is it not possible to refine the process that is being used by
> Dick Johnson by using the gadgets that are available.
> That would refine the data acquisition and would make the
> resolution much finer. The work load is very high during the process.
> Dick invited me to a test flight from 12000ft and not much useable
> data was obtained from my only attempt. It sure takes practice.
>
> One certainly has to chew gum, use a stop watch, make notes of time,
> speed and temperature and flap settings, maintain speeds, change
> speed and stabilize it.
>
> This every 500ft, At the same time Fly a big circle around the airport,
> so you have a place to land when finished. I may have left things out.
>
> What electronic aids could be used that would help in this matter?

In the '80s, Rudy Allemann and I did some Johnson style flight tests but
recording the time, ASI, altitude, and temperature with a camera aimed
at the panel. It made the data acquisition easier, and the pilot could
spend more time on flying, and less taking notes.

Though this probably isn't the "electronic aid" Udo had in mind, using a
digital camera would make it even easier today. It could be aimed to
include the flap handle position, and it has it's own clock to
time-stamp the pictures. Many more pictures could be taken for each run
instead of being limited to the 36 a film camera has.

While this makes the data recording easy, the ASI (including the pitot
and static if you want to compare between gliders) and altimeter still
need to be carefully calibrated.


--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

[Udo Rumpf]

> Tim Ward wrote

> The hardware isn't cheap, but it's getting cheaper, and the data reduction
> post-flight isn't a trivial problem, either, but it's doable.


Tim,
My knowledge is very limited when it comes to the points you made above.
My L Nav produces the data that is now taken manualy in the test flights.
The GN II is hooked up to my LNav making some of the data available.
All this is set up to be down loaded into my PC flight software.
How much effort would it take for some one experienced in writing this type
of software to get
the remaining data out of the LNav into the flight recorder, like
temperature, altitude, airspeed?
Regards
Udo

[Udo Rumpf]

Eric wrote
> Though this probably isn't the "electronic aid" Udo had in mind, using a
> digital camera would make it even easier today. It could be aimed to
> include the flap handle position, and it has it's own clock to time-stamp
> the pictures. Many more pictures could be taken for each run instead of
> being limited to the 36 a film camera has.
>
> While this makes the data recording easy, the ASI (including the pitot and
> static if you want to compare between gliders) and altimeter still need to
> be carefully calibrated.

This is a good idea as the data is displayed digitally. I can not remember
if speed, altitude
and temperature can be displayed simultaneously on the L Nav.
I wonder if a small digital movie camera would have a good a enough
resolution to do the job.
Regards
Udo

[Tim Ward]

"Udo Rumpf" > wrote in message
...
> > Tim Ward wrote
>
> > The hardware isn't cheap, but it's getting cheaper, and the data
reduction
> > post-flight isn't a trivial problem, either, but it's doable.
>
>
> Tim,
> My knowledge is very limited when it comes to the points you made above.
> My L Nav produces the data that is now taken manualy in the test flights.
> The GN II is hooked up to my LNav making some of the data available.
> All this is set up to be down loaded into my PC flight software.
> How much effort would it take for some one experienced in writing this
type
> of software to get
> the remaining data out of the LNav into the flight recorder, like
> temperature, altitude, airspeed?
> Regards
> Udo

As I understand it (and mind you, I was only there once,blindfolded, and it
was a dark and stormy night), Johnson's method relies on the repeatable
vertical accuracy of a mechanical barometric altimeter and a stopwatch.
That gives him an average sink rate over the period of time. If he's
recording temperature, then maybe he post-processes that to get the true
sink rate and true airspeed.
I don't know what kind of vertical accuracy he gets out of that combination
of panel shaker and altimeter. I know I once had an occasion where the
altimeter indication in a 2-33 dropped about 150 feet when I tapped it with
a finger.
If the vertical accuracy on the LNAV is as accurate as he can get, or
better, then it's probably worthwhile to try to pull the other data. I
suspect that it's not, if it's just consumer-grade GPS altitude information,
or Johnson would be using it.

I haven't looked at the LNAV programming interface, so I don't know how hard
it would be to get the information logged. The developers of Soaring Pilot
seem to be pretty amiable about adding features to the program, though.

Tim Ward

[John Ferguson]

I think that a Cambridge 302 DDV has enough data in
its proprietary GPS sentence to be able to give you
the data you need. This is a cut and paste from the
manual:
----------------------
!w
The !w sentence is a proprietary format sentence that
contains air data and
instrument settings
The format is:
!W,<1>,<2>,<3>,<4>,<5>,<6>,<7>,<8>,<9>,<10>,<11>,<12>,<13>*hh<CR><LF>
<1> Vector wind direction in degrees
<2> Vector wind speed in 10ths of meters per second
<3> Vector wind age in seconds
<4> Component wind in 10ths of Meters per second + 500
>(500 = 0, 495 = 0.5 m/s
tailwind)
<5> True altitude in Meters + 1000
<6> Instrument QNH setting
<7> True airspeed in 100ths of Meters per second
<8> Variometer reading in 10ths of knots + 200
<9> Averager reading in 10ths of knots + 200
<10> Relative variometer reading in 10ths of knots +
>200
<11> Instrument MacCready setting in 10ths of knots
<12> Instrument Ballast setting
-------------------------------

Enough data here ?

John

[[email protected]]

John Ferguson wrote:
> I think that a Cambridge 302 DDV has enough data in
> its proprietary GPS sentence to be able to give you
> the data you need. This is a cut and paste from the
> manual:
-snip-

I recall from a conversation with Dave Ellis a few years ago, that the
302 can dump a lot of flight parameters at fairly high data rates over
the serial interface.

I don't know the details, but I beleive all one needs to do is connect
a terminal program, send the appropriate query, and the 302 starts
spilling its guts. A quick call to CAI might provide the answer.

I've often thought it would be cool if one could make a request of the
302 to produce a "super" IGC log with perhaps several records per
second containing airspeed, temperature and calculated windspeed. The
IGC spec allows for such data as comments or extra fields. It
certainly has the horsepower, and the results might provide some
interesting atmospheric information.

-Tom

[Marc Ramsey]

John Ferguson wrote:
> ----------------------
> !w
> The !w sentence is a proprietary format sentence that
> contains air data and
> instrument settings
> The format is:
> !W,<1>,<2>,<3>,<4>,<5>,<6>,<7>,<8>,<9>,<10>,<11>,<12>,<13>*hh<CR><LF>
> <1> Vector wind direction in degrees
> <2> Vector wind speed in 10ths of meters per second
> <3> Vector wind age in seconds
> <4> Component wind in 10ths of Meters per second + 500
> <5> True altitude in Meters + 1000
> <6> Instrument QNH setting
> <7> True airspeed in 100ths of Meters per second
> <8> Variometer reading in 10ths of knots + 200
> <9> Averager reading in 10ths of knots + 200
> <10> Relative variometer reading in 10ths of knots + 200
>
> <11> Instrument MacCready setting in 10ths of knots
> <12> Instrument Ballast setting
> -------------------------------
>
> Enough data here ?

Not quite, it's missing indicated airspeed and temperature...

Marc

[John Ferguson]

Can you get indicated airspeed from true airspeed and
add or subtract the vector or component wind.

I am presuming that the 302 is providing the data having
already been corrected for temp and alt.

Anyone from CAI have anything to add.

John

At 04:30 09 January 2005, Marc Ramsey wrote:
>John Ferguson wrote:
>> ----------------------
>> !w
>> The !w sentence is a proprietary format sentence that
>> contains air data and
>> instrument settings

>>
>> Enough data here ?
>
>Not quite, it's missing indicated airspeed and temperature...
>
>Marc
>

[Marc Ramsey]

John Ferguson wrote:
> Can you get indicated airspeed from true airspeed and
> add or subtract the vector or component wind.

No, you need temperature (which is also missing) and altitude to
calculate IAS from TAS.

> I am presuming that the 302 is providing the data having
> already been corrected for temp and alt.

The IAS and temperature data is available internal to the 302, but is
not reported by !w or any other usable sentence. The best one can do
(without additional input) is an approximation based on altitude, which
is not accurate enough for polar work.

Marc

[F.L. Whiteley]

"Tim.Ward" > wrote in message
oups.com...
> Robert Ehrlich wrote:
> > "Lars P. Hansen" wrote:
> > >
> > > OK, here we go: Could devices like this not also be used to detect
> thermals?
> > > The description in the link below about how the laser "sees" minute
> dust
> > > particles in the air seems to be well suited to thermals.
> > >
> >
> > I don't buy the explanation they give in the cited url
>
(http://www.navysbir.brtrc.com/successstories/opticalair_00045_navsea_p3.htm
l)
> > They pretend the device measures the speed and direction of dust
> particles
> > from the shift in the frequency of reflected light, this is well
> known
> > as Doppler effect and can only give the radial component (toward or
> away
> > from the sensor) of the speed, not its value and direction. For
> thermals
> > we are interested in the speed component which is nearly
> perpendicular
> > to the measured component, so this would be of little interest. Of
> course
> > whith several such devices on the ground, all the 3 compenents of
> airmass
> > speed could be measured, maybe this in the intended use of the device
> as it
> > is advertised, but in a glider you don't have sufficient vertical
> distance
> > for putting 2 devices which could provide an accurate value for the
> vertical
> > component of the speed.
>
> It does work, but they use a little different technique.
> The Doppler is only measured on particles at the focal length of the
> optics.
> The assumption is that the airmass (at least locally) is all the same,
> and that the Doppler measurement is taken far enough away so the
> effects of the airplane on the airmass are negligible.
> So you send out two beams -- say, one forward at 45 degrees, one aft at
> 45 degrees.
> It turns out that if you sum the signals from the two beams, you get
> the vertical component of velocity, and if you difference the two
> signals, you get the horizontal component.
> Since we're measuring frequency, we can get sum and difference
> frequencies from a mixer, though I have no doubt it runs through a DSP
> somewhere.
>
> So you only need one sensor head (though it puts out multiple beams).
>
> By sending out two more beams, to each side, you can also pick up
> sideslip information.
> The clever thing is that they're using components developed for the
> communications field, which helps to keep costs down.
>
> Tim Ward
>
Still illegal under the rules IIRC, unless there's been a quiet change.

Frank Whiteley

[Tim Ward]

> > > "Lars P. Hansen" wrote:
> > > >
> > > > OK, here we go: Could devices like this not also be used to detect
> > thermals?

> > Robert Ehrlich wrote:
<disbelief that the sensors could work as described>

I wrote an explanation of how they can work <snipped>

"F.L. Whiteley" > wrote in message
...
>
> Still illegal under the rules IIRC, unless there's been a quiet change.
>
> Frank Whiteley


When I first looked at this, I would have agreed with you. But as
described, it gives just gives airspeed along all three axes.
Now, if you added a forward looking pair of beams with a longer focal length
to see any differences between the extremely local airmass and the slightly
further away airmass, _that's_ probably against contest rules.

Tim Ward

[BB]

When thermal detectors come, people will discover they love flying with
them. Contest rules will change or people will stop flying contests.
Just as with GPS.

John Cochrane

[F.L. Whiteley]

"Tim Ward" > wrote in message
nk.net...
> > > > "Lars P. Hansen" wrote:
> > > > >
> > > > > OK, here we go: Could devices like this not also be used to detect
> > > thermals?
>
> > > Robert Ehrlich wrote:
> <disbelief that the sensors could work as described>
>
> I wrote an explanation of how they can work <snipped>
>
> "F.L. Whiteley" > wrote in message
> ...
> >
> > Still illegal under the rules IIRC, unless there's been a quiet change.
> >
> > Frank Whiteley
>
>
> When I first looked at this, I would have agreed with you. But as
> described, it gives just gives airspeed along all three axes.
> Now, if you added a forward looking pair of beams with a longer focal
length
> to see any differences between the extremely local airmass and the
slightly
> further away airmass, _that's_ probably against contest rules.
>
> Tim Ward
>
Yep. That could open a slightly separate can of worms, or perhaps lead to a
rules change.

Nevertheless, an interesting topic.

Frank

[Eric Greenwell]

Marc Ramsey wrote:

>
> The IAS and temperature data is available internal to the 302, but is
> not reported by !w or any other usable sentence. The best one can do
> (without additional input) is an approximation based on altitude, which
> is not accurate enough for polar work.

Hi Marc - the 302 can report the outside temperature with Log Mode 12
(page 4 in the data port manual), so IAS could be calculated.


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Washington State
USA

[Tim.Ward]

Yes, and thinking about it a little more, you sell it as a safety
device.
The reference to the local airmass gives you your current angle of
attack.
That's a pretty good safety device right there.
The longer-distance reference gives you what your AOA will be in, say,
200 meters.
(assuming the inertially-referenced attitude doesn't change)
That's a wind-shear detector.
For a light airplane making an approach at 100 kts, that's about 4
seconds of warning.
Is that something that could be sold to IFR pilots?

Tim Ward

[Robert Ehrlich]

"Tim.Ward" wrote:
>
> It does work, but they use a little different technique.
> The Doppler is only measured on particles at the focal length of the
> optics.
> The assumption is that the airmass (at least locally) is all the same,
> and that the Doppler measurement is taken far enough away so the
> effects of the airplane on the airmass are negligible.
> So you send out two beams -- say, one forward at 45 degrees, one aft at
> 45 degrees.
> It turns out that if you sum the signals from the two beams, you get
> the vertical component of velocity, and if you difference the two
> signals, you get the horizontal component.
> Since we're measuring frequency, we can get sum and difference
> frequencies from a mixer, though I have no doubt it runs through a DSP
> somewhere.
>
> So you only need one sensor head (though it puts out multiple beams).
>
> By sending out two more beams, to each side, you can also pick up
> sideslip information.
> The clever thing is that they're using components developed for the
> communications field, which helps to keep costs down.
>
> Tim Ward

With these two beams at 45 degrees, you don't get truly the vertical and
horizontal components, rather the components along the two bissectors
of both beams, you would think this is nearly the same thing as the direction
of the components are just changed by the pitch attitude of the glider,
which is a very small angle usually, but this is sufficient for changing
lift into sink or vice-versa.

[Robert Ehrlich]

Robert Ehrlich wrote:
>
> After this discussion we are far from the original question, i.e.
> can we infer anything about the polar of a glider just from GPS
> fligth logs of this glider?
> ... <solution proposed> ...

After a bit thinking about that my conclusion is that the above
solution doesn't work. Even if the system I was talking about
is overdetermined, there is always an undetermination on the couple
vertical speed of airmass/sink speed of glider relatively to airmass,
any combination of both with the same sum satisfies in the same way
the equations, so no valuable information on the polar of the glider
can be obtained unless we add some information on the airmass, either
by some other data, or by some further modelling (e.g. assuming the
total vertical movement of the airmass is zero, which is not realistic,
or that it is some given percentage of the average lift, or anything we may
think about it)

[Eric Greenwell]

Robert Ehrlich wrote:

> After a bit thinking about that my conclusion is that the above
> solution doesn't work. Even if the system I was talking about
> is overdetermined, there is always an undetermination on the couple
> vertical speed of airmass/sink speed of glider relatively to airmass,
> any combination of both with the same sum satisfies in the same way
> the equations, so no valuable information on the polar of the glider
> can be obtained unless we add some information on the airmass, either
> by some other data, or by some further modelling (e.g. assuming the
> total vertical movement of the airmass is zero, which is not realistic,
> or that it is some given percentage of the average lift, or anything we may
> think about it)

Maybe the laser airspeed devices could be applied to flight testing, but
by having them on the ground instead of in the glider. Pointing up, they
could be used to determine how much the atmosphere is moving during a
conventional, Johnson-style, flight test. The data could then be
corrected with this measurement of the actual air mass movement.

It would take units designed for long range measurements (meteorological
instruments, likely), of course, not ones really designed for airspeed
indicators.

Or, perhaps the laser unit could be used to determine when the airmass
is steady enough to make flight testing worthwhile, even it if can't
measure the vertical velocity sufficiently accurately to make
corrections useful.


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Eric Greenwell
Washington State
USA

[Robert Ehrlich]

Eric Greenwell wrote:
>
> Robert Ehrlich wrote:
>
> > After a bit thinking about that my conclusion is that the above
> > solution doesn't work. Even if the system I was talking about
> > is overdetermined, there is always an undetermination on the couple
> > vertical speed of airmass/sink speed of glider relatively to airmass,
> > any combination of both with the same sum satisfies in the same way
> > the equations, so no valuable information on the polar of the glider
> > can be obtained unless we add some information on the airmass, either
> > by some other data, or by some further modelling (e.g. assuming the
> > total vertical movement of the airmass is zero, which is not realistic,
> > or that it is some given percentage of the average lift, or anything we may
> > think about it)
>
> Maybe the laser airspeed devices could be applied to flight testing, but
> by having them on the ground instead of in the glider. Pointing up, they
> could be used to determine how much the atmosphere is moving during a
> conventional, Johnson-style, flight test. The data could then be
> corrected with this measurement of the actual air mass movement.
>
> It would take units designed for long range measurements (meteorological
> instruments, likely), of course, not ones really designed for airspeed
> indicators.
>
> Or, perhaps the laser unit could be used to determine when the airmass
> is steady enough to make flight testing worthwhile, even it if can't
> measure the vertical velocity sufficiently accurately to make
> corrections useful.
>

OK, but this is far from the original question. Making Johnson-style flight
tests is one thing, using flight logs for polar analysis in another one.
A flight log provides some information about the polar as long a we have
or can assume some information about the airmass. We have here a huge
quantity of data it would be intersting to use. We could get some information
not found in flight test, like how far various gliders of the same model
are from the tested one, how performance degrades with time, ...

[Eric Greenwell]

Robert Ehrlich wrote:

>>Or, perhaps the laser unit could be used to determine when the airmass
>>is steady enough to make flight testing worthwhile, even it if can't
>>measure the vertical velocity sufficiently accurately to make
>>corrections useful.
>>
>
>
> OK, but this is far from the original question. Making Johnson-style flight
> tests is one thing, using flight logs for polar analysis in another one.
> A flight log provides some information about the polar as long a we have
> or can assume some information about the airmass. We have here a huge
> quantity of data it would be intersting to use. We could get some information
> not found in flight test, like how far various gliders of the same model
> are from the tested one, how performance degrades with time, ...

I think the thread drifted from the original question because no one
could think of how to account for the airmass movement in any useful
way, so people began thinking of what the next best thing might be. A
new proposal on how to achieve a polar from flight logs would bring the
thread back to the original subject, I think.

Here's another way that flight logs might used: Comparison flights using
GPS logs to determine the difference between gliders would be useful,
but that requires at least two gliders to fly together at the same
airspeed; again, useful, but as you point out, not an answer to the
original question.


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Washington State
USA

[Mike I Green]

Wouldn't it be sufficient if the other glider was calibrated?
mg
Eric Greenwell wrote:
> Robert Ehrlich wrote:
>
>>> Or, perhaps the laser unit could be used to determine when the airmass
>>> is steady enough to make flight testing worthwhile, even it if can't
>>> measure the vertical velocity sufficiently accurately to make
>>> corrections useful.
>>>
>>
>>
>> OK, but this is far from the original question. Making Johnson-style
>> flight
>> tests is one thing, using flight logs for polar analysis in another one.
>> A flight log provides some information about the polar as long a we have
>> or can assume some information about the airmass. We have here a huge
>> quantity of data it would be intersting to use. We could get some
>> information
>> not found in flight test, like how far various gliders of the same model
>> are from the tested one, how performance degrades with time, ...
>
>
> I think the thread drifted from the original question because no one
> could think of how to account for the airmass movement in any useful
> way, so people began thinking of what the next best thing might be. A
> new proposal on how to achieve a polar from flight logs would bring the
> thread back to the original subject, I think.
>
> Here's another way that flight logs might used: Comparison flights using
> GPS logs to determine the difference between gliders would be useful,
> but that requires at least two gliders to fly together at the same
> airspeed; again, useful, but as you point out, not an answer to the
> original question.
>
>

[Mike I Green]

Wouldn't it be sufficient if the other glider was calibrated?
mg
Eric Greenwell wrote:
> Robert Ehrlich wrote:
>
>>> Or, perhaps the laser unit could be used to determine when the airmass
>>> is steady enough to make flight testing worthwhile, even it if can't
>>> measure the vertical velocity sufficiently accurately to make
>>> corrections useful.
>>>
>>
>>
>> OK, but this is far from the original question. Making Johnson-style
>> flight
>> tests is one thing, using flight logs for polar analysis in another one.
>> A flight log provides some information about the polar as long a we have
>> or can assume some information about the airmass. We have here a huge
>> quantity of data it would be intersting to use. We could get some
>> information
>> not found in flight test, like how far various gliders of the same model
>> are from the tested one, how performance degrades with time, ...
>
>
> I think the thread drifted from the original question because no one
> could think of how to account for the airmass movement in any useful
> way, so people began thinking of what the next best thing might be. A
> new proposal on how to achieve a polar from flight logs would bring the
> thread back to the original subject, I think.
>
> Here's another way that flight logs might used: Comparison flights using
> GPS logs to determine the difference between gliders would be useful,
> but that requires at least two gliders to fly together at the same
> airspeed; again, useful, but as you point out, not an answer to the
> original question.
>
>

[Mike I Green]

Wouldn't it be sufficient if the other glider was calibrated?
mg
Eric Greenwell wrote:
> Robert Ehrlich wrote:
>
>>> Or, perhaps the laser unit could be used to determine when the airmass
>>> is steady enough to make flight testing worthwhile, even it if can't
>>> measure the vertical velocity sufficiently accurately to make
>>> corrections useful.
>>>
>>
>>
>> OK, but this is far from the original question. Making Johnson-style
>> flight
>> tests is one thing, using flight logs for polar analysis in another one.
>> A flight log provides some information about the polar as long a we have
>> or can assume some information about the airmass. We have here a huge
>> quantity of data it would be intersting to use. We could get some
>> information
>> not found in flight test, like how far various gliders of the same model
>> are from the tested one, how performance degrades with time, ...
>
>
> I think the thread drifted from the original question because no one
> could think of how to account for the airmass movement in any useful
> way, so people began thinking of what the next best thing might be. A
> new proposal on how to achieve a polar from flight logs would bring the
> thread back to the original subject, I think.
>
> Here's another way that flight logs might used: Comparison flights using
> GPS logs to determine the difference between gliders would be useful,
> but that requires at least two gliders to fly together at the same
> airspeed; again, useful, but as you point out, not an answer to the
> original question.
>
>

[Eric Greenwell]

Mike I Green wrote:
> Wouldn't it be sufficient if the other glider was calibrated?
> mg

I'm not sure what you mean by sufficient, but in any case, using a
comparison sailplane (calibrated or not), was not what the original
poster had in mind.

The advantage of a using a calibrated sailplane for the comparison is
you could actually calculate a polar, rather than just a relative
performance curve. Perhaps that was what you meant?

> Eric Greenwell wrote:

>>
>> Here's another way that flight logs might used: Comparison flights
>> using GPS logs to determine the difference between gliders would be
>> useful, but that requires at least two gliders to fly together at the
>> same airspeed; again, useful, but as you point out, not an answer to
>> the original question.
>>
>>


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Eric Greenwell
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USA