Takeoff distances

[Kilo Charlie]

Has anyone done calculations for takeoff distances for various density
altitudes, weights and winds for their sailplane-towplane combination?
Every powered plane POH has a table but there are none in the glider books
for obvious reasons (HP of towplane for one).

The Arizona Soaring Assn flies out of some high (6600') and short (3900')
runways (not concurrently) and in our typical conditions would like to fly
with ballast but are revisting the idea that we should limit weights after
some long takeoff rolls and/or slow climbs. We usually do not have good
bail out options at most of our fields for rope breaks as an added issue.

Casey Lenox
Phoenix
KC

[[email protected]]

On Apr 7, 6:55 am, "Kilo Charlie" > wrote:
> Has anyone done calculations for takeoff distances for various density
> altitudes, weights and winds for their sailplane-towplane combination?
> Every powered plane POH has a table but there are none in the glider books
> for obvious reasons (HP of towplane for one).
>
> The Arizona Soaring Assn flies out of some high (6600') and short (3900')
> runways (not concurrently) and in our typical conditions would like to fly
> with ballast but are revisting the idea that we should limit weights after
> some long takeoff rolls and/or slow climbs. We usually do not have good
> bail out options at most of our fields for rope breaks as an added issue.
>
> Casey Lenox
> Phoenix
> KC

I don't have any data, but you might consider collecting your own data
using GPS data loggers. I am sure other clubs would be interested in
the data. A ballasted single is going to weight about what a 2-place
does, so if you can tow a 2-place you can (probably) tow a single,
especially considering the (usually) better aerodynamics of the
single.

It would be interesting in comparing actual data to extrapolated
estimates using POH data.

Tom

[Kilo Charlie]

> wrote in message
oups.com...
> On Apr 7, 6:55 am, "Kilo Charlie" > wrote:
> I don't have any data, but you might consider collecting your own data
> using GPS data loggers. I am sure other clubs would be interested in
> the data. A ballasted single is going to weight about what a 2-place
> does, so if you can tow a 2-place you can (probably) tow a single,
> especially considering the (usually) better aerodynamics of the
> single.
>
> It would be interesting in comparing actual data to extrapolated
> estimates using POH data.
>
> Tom

Thanks Tom. I also wondered if I could go back and look at logs from
various sites and try to recreate what the density altitude was and then
somehow determine what my actual liftoff point was from the log. I would
think that at least the climb rate could be determined.

I am a bit surprised at the lack of opinions re this so far. It is data
that we should be able to generate and definitely would be helpful to those
of us flying out of hot high airports.

Casey

[Andy[_1_]]

On Apr 11, 5:38 pm, "Kilo Charlie" > wrote:
> I am a bit surprised at the lack of opinions re this so far. It is data
> that we should be able to generate and definitely would be helpful to those
> of us flying out of hot high airports.

If you had data you would need to careful in its interpretation.
Glider launches usually take place when thermal activity has started.
Wind shear and thermal downdrafts can be expected and, singly or in
combination, and they can easily reduce climb rate to zero or make it
negative.

Let's say the data show you only need 1000 foot of the 5000ft runway
and the predicted climb rate is 200fpm for the first 500ft, and the
predicted thermal strength is 6kts, and the wind is gusty. Would you
launch? I suspect the answer would be yes. We do it all the time and
usually it works out ok.

Since I know what prompted the question I'll comment that Williams has
similar conditions to Flagstaff. That airport has a poor record for
summer takeoff accidents and that's for airplanes without a glider in
tow. Usually it works out ok though.

Andy

[Kilo Charlie]

"Andy" > wrote in message
oups.com...
> On Apr 11, 5:38 pm, "Kilo Charlie" > wrote:
>
> If you had data you would need to careful in its interpretation.
> Glider launches usually take place when thermal activity has started.
> Wind shear and thermal downdrafts can be expected and, singly or in
> combination, and they can easily reduce climb rate to zero or make it
> negative.
>
> Let's say the data show you only need 1000 foot of the 5000ft runway
> and the predicted climb rate is 200fpm for the first 500ft, and the
> predicted thermal strength is 6kts, and the wind is gusty. Would you
> launch? I suspect the answer would be yes. We do it all the time and
> usually it works out ok.
>
> Since I know what prompted the question I'll comment that Williams has
> similar conditions to Flagstaff. That airport has a poor record for
> summer takeoff accidents and that's for airplanes without a glider in
> tow. Usually it works out ok though.
>
> Andy

So your response seems to be similar to some other local pilots Andy.....the
data is not reliable. Would you then surmise that those Flagstaff accidents
were by pilots that looked in their POH and found that it was incorrect? I
think not. My opinion is that they felt that the data was bogus as well and
went by the "feels right to me" approach ending in disaster.

Casey

[toad]

In reading those types of accident reports, it seems that most of the
pilots didn't think about there takeoff performance charts at all.
They did not do a take off calculation. They just thought, "I've
allways made it before." Nor did they think, "Hey, I'm halfway down
the runway. I should be flying by now, better abort."

For a glider takeoff. It would be interesting to have good data on
expected takeoff rolls and climb rates. Each set of data would be
specific to towplane-glider pairs. Takeoff surface and winds would
have to be carefully recorded in addition to a GPS log with location
and airspeeds.

Any calculations would be suspect until experimentally verified. So
skip the calculations and start recording data. Get a flight log of
every takeoff. Try and quantify surface types, towplane ID and
winds. Then plot the data and make your conclusions.

And then use the data with a grain of salt.

Todd Smith
3S

[Gary Nuttall]

And keep a note of how much fuel the tug has on board.
How heavy the glider pilot is. How clean the glider
wings are. What time of day it was. Outside Air Temperature,
pressure and moisture content. Local CAPE and Lifted
Index. Length of rope (and its elasticity). Power
setting of tug. What mood each of the pilots were
in. Stick position on ground run. Local thermal and
wave activity. All can have an effect on take-off
distance and climb rate.

There's so many variables that I'd be dubious of any
metrics developed beyond the fact that high altitude,
high temperature and heavy gliders do not make a good
combination.

Anybody who comes up with a set of explicit numbers
and sticks to them is likely to discover how often
theory doesn't work in practice!

Happy soaring
Gary Nuttall




At 14:24 12 April 2007, Toad wrote:
>
>In reading those types of accident reports, it seems
>that most of the
>pilots didn't think about there takeoff performance
>charts at all.
>They did not do a take off calculation. They just
>thought, 'I've
>allways made it before.' Nor did they think, 'Hey,
>I'm halfway down
>the runway. I should be flying by now, better abort.'
>
>For a glider takeoff. It would be interesting to have
>good data on
>expected takeoff rolls and climb rates. Each set of
>data would be
>specific to towplane-glider pairs. Takeoff surface
>and winds would
>have to be carefully recorded in addition to a GPS
>log with location
>and airspeeds.
>
>Any calculations would be suspect until experimentally
>verified. So
>skip the calculations and start recording data. Get
>a flight log of
>every takeoff. Try and quantify surface types, towplane
>ID and
>winds. Then plot the data and make your conclusions.
>
>And then use the data with a grain of salt.
>
>Todd Smith
>3S
>
>

[toad]

Ok, maybe a big block of salt :-)

In practice, my takeoff performance check is: If I'm not flying by X
distance down the runway, pull the release and land straight ahead.

Toad

On Apr 13, 8:56 am, Gary Nuttall
> wrote:
> And keep a note of how much fuel the tug has on board.
> How heavy the glider pilot is. How clean the glider
> wings are. What time of day it was. Outside Air Temperature,
> pressure and moisture content. Local CAPE and Lifted
> Index. Length of rope (and its elasticity). Power
> setting of tug. What mood each of the pilots were
> in. Stick position on ground run. Local thermal and
> wave activity. All can have an effect on take-off
> distance and climb rate.
>
> There's so many variables that I'd be dubious of any
> metrics developed beyond the fact that high altitude,
> high temperature and heavy gliders do not make a good
> combination.
>
> Anybody who comes up with a set of explicit numbers
> and sticks to them is likely to discover how often
> theory doesn't work in practice!
>
> Happy soaring
> Gary Nuttall
>

[Kilo Charlie]

"Gary Nuttall" > wrote in message
...
> And keep a note of how much fuel the tug has on board.
> How heavy the glider pilot is. How clean the glider
> wings are. What time of day it was. Outside Air Temperature,
> pressure and moisture content. Local CAPE and Lifted
> Index. Length of rope (and its elasticity). Power
> setting of tug. What mood each of the pilots were
> in. Stick position on ground run. Local thermal and
> wave activity. All can have an effect on take-off
> distance and climb rate.
>
> There's so many variables that I'd be dubious of any
> metrics developed beyond the fact that high altitude,
> high temperature and heavy gliders do not make a good
> combination.
>
> Anybody who comes up with a set of explicit numbers
> and sticks to them is likely to discover how often
> theory doesn't work in practice!
>
> Happy soaring
> Gary Nuttall


Continues to amaze me at how much disdain glider pilots have for
quantitation. I suppose that may be what draws some of them into the
soaring in the first place. I also enjoy that aspect but think that
attitude has gotten many powered pilots into bad situations. To think that
we are immune to it because we don't have engines is naive.

Casey

[Tuno]

I for one would try to use numbers derived from sound data. My
glider's VNE was derived from something, and it's a number I heed
religiously.

2NO

[Cats]

On Apr 13, 2:03 pm, "toad" > wrote:
> Ok, maybe a big block of salt :-)
>
> In practice, my takeoff performance check is: If I'm not flying by X
> distance down the runway, pull the release and land straight ahead.

If you are not flying how come you need to land? :)

[Bill Daniels]

"Kilo Charlie" > wrote in message
...
>
> "Gary Nuttall" > wrote in message
> ...
>> And keep a note of how much fuel the tug has on board.
>> How heavy the glider pilot is. How clean the glider
>> wings are. What time of day it was. Outside Air Temperature,
>> pressure and moisture content. Local CAPE and Lifted
>> Index. Length of rope (and its elasticity). Power
>> setting of tug. What mood each of the pilots were
>> in. Stick position on ground run. Local thermal and
>> wave activity. All can have an effect on take-off
>> distance and climb rate.
>>
>> There's so many variables that I'd be dubious of any
>> metrics developed beyond the fact that high altitude,
>> high temperature and heavy gliders do not make a good
>> combination.
>>
>> Anybody who comes up with a set of explicit numbers
>> and sticks to them is likely to discover how often
>> theory doesn't work in practice!
>>
>> Happy soaring
>> Gary Nuttall
>
>
> Continues to amaze me at how much disdain glider pilots have for
> quantitation. I suppose that may be what draws some of them into the
> soaring in the first place. I also enjoy that aspect but think that
> attitude has gotten many powered pilots into bad situations. To think
> that we are immune to it because we don't have engines is naive.
>
> Casey

I agree, Casy

It would be a big safety factor if we had takeoff performance charts
available. I've been involved in some extremely hazardous high density
altitude takeoffs where the tug was unable to provide adequate climb
performance.

Having enough information to decline the tow might save a few lives. It
seems like a major safety oversight that we don't have hard information on
this. If the STC for a tow hook doesn't require new performance charts, it
should. The glider tow chart should add glider gross weight and L/D to the
tugs TO performance chart and make 300FPM the minimum acceptable climb rate.

I have flown light airplanes in the high and hot western US all my life and
ALWAYS looked at the performance chart before takeoff. Many who didn't left
crumpled aluminum on mountainsides. I think charts would have to be
developed empirically from tests on a specific tug but once there were a few
data points, interpolation should be possible.

I also agree with the poster who selects a go-no-go point on the runway for
release if not airborne. Keep in mind that gliders have a high L/D in
ground effect and usually poor wheel brakes so leave a generous safety
margin for getting stopped after an aborted TO.

Bill Daniels

[FreeFlight107]

Also remember that density altitude will affect your height for a 180
back to runway.

i.e. two large men in a Grob, field elevation 3,700 ft msl, air temp
107F, rope break at 220 ft above field.

It was not enough altitude for at least one such senario. They plowed
into trees short of the runway.

Wayne Walker

[toad]

On Apr 13, 11:00 am, "Bill Daniels" <bildan@comcast-dot-net> wrote:

<snip>

> If the STC for a tow hook doesn't require new performance charts,
> it should.

I don't believe that there would ever be another tow hook approved in
the US, if this was required by the FAA. The amount of testing and
analysis that would be required would break any club's budget.

> I think charts would have to be
> developed empirically from tests on a specific tug but once there were a few
> data points, interpolation should be possible.

Interpolation (between data points ) or extrapolation (beyond the data
set ) ?

Interpolation to a different tug ? or to a different glider ?

You might be able to extrapolate to different gliders, but different
tugs could be vastly different, even if they were similar in major
specifications ( ie same horsepower, weight and wing loading). A
different prop size or having a constant speed prop would make a great
difference, for example.

If I had a specific tug in mind, I might come up with different tables
for single seat glass (with and without water), 2 seat glass and 2
seat trainer.

But I think it would take many-many flights to gather the data.

Todd Smith
3S

[toad]

On Apr 13, 10:32 am, "Kilo Charlie" > wrote:
> Continues to amaze me at how much disdain glider pilots have for
> quantitation. I suppose that may be what draws some of them into the
> soaring in the first place.

Well, there's not much in glider flying that CAN be quantified with
any confidence. For example, you can quantify your still air L/D, but
on final glide, you have to estimate the lift/sink potential and that
is qualitative estimation (inspired guesswork).

Todd Smith
3S

[Bill Daniels]

All airplanes already have performance charts in the POH. These charts
aren't custom developed for each serial number but for the test airplane and
copys provided for all identical production airplanes. If the airplane is
subsequently modified with a different engine or prop, modified performance
charts are always required as part of the STC. Tugs are no different.

For a tug, all that's needed is additional inputs for glider weight and L/D
(Both highly quantifiable). With these data, the tow combinations takeoff
distance and rate of climb can be accurately predicted.

It's a bit of work to develop these performance charts but the payoff is
saved lives and tugs. I can't see a rational reason not to do it. It's a
responsible thing to do.

I've developed expanded charts for airplanes I've owned. Piper, for
example, seems to think nobody flies their singles above 6000 feet since no
data are provided above that altitude. I extended my ROC charts to 18,000
feet by noting the performance over a dozen flight or so. I also noted the
takeoff distances on each takeoff and added that to the charts.

For a tug, all you have to do is keep notes on each tows performance and
plot the date later. Soon you have the needed chart.

Bill Daniels


"toad" > wrote in message
oups.com...
> On Apr 13, 11:00 am, "Bill Daniels" <bildan@comcast-dot-net> wrote:
>
> <snip>
>
>> If the STC for a tow hook doesn't require new performance charts,
>> it should.
>
> I don't believe that there would ever be another tow hook approved in
> the US, if this was required by the FAA. The amount of testing and
> analysis that would be required would break any club's budget.
>
>> I think charts would have to be
>> developed empirically from tests on a specific tug but once there were a
>> few
>> data points, interpolation should be possible.
>
> Interpolation (between data points ) or extrapolation (beyond the data
> set ) ?
>
> Interpolation to a different tug ? or to a different glider ?
>
> You might be able to extrapolate to different gliders, but different
> tugs could be vastly different, even if they were similar in major
> specifications ( ie same horsepower, weight and wing loading). A
> different prop size or having a constant speed prop would make a great
> difference, for example.
>
> If I had a specific tug in mind, I might come up with different tables
> for single seat glass (with and without water), 2 seat glass and 2
> seat trainer.
>
> But I think it would take many-many flights to gather the data.
>
> Todd Smith
> 3S
>

[toad]

Oh, I have no problem with a club collecting the data and making the
charts, but your post seems to state that those actions should be
required before the FAA approves the tug installation. The FAA
requirement if what I would object to.

And no, it wouldn't require data for each serial number, but for each
type of tug.

Todd

[Jack]

FreeFlight107 wrote:
> Also remember that density altitude will affect your height for a 180
> back to runway.
>
> i.e. two large men in a Grob, field elevation 3,700 ft msl, air temp
> 107F, rope break at 220 ft above field.
>
> It was not enough altitude for at least one such senario. They plowed
> into trees short of the runway...

....having executed the 180 degree turn immediately, with optimum
bank, g-load, and airspeed control -- as always?

Do you have enough information to make that claim, that it was
simply a matter of density altitude? If you do, then perhaps we, or
at least you, already have all the metrics that are needed. Perhaps
you can share them with us, for future use?


Jack

[Gary Nuttall]

Not as much as it disturbs me that there might be people
out there who will stake their lives against a set
of numbers in a book. The margins of safety are so
much tighter in a glider/sailplane than a powered aircraft
and a minor change in any one part of the equation
could have dramatic results.

Let's be clear here.....Some numbers you can be confident
in becuase they've been measured in a certain, calibrated
and controlled environment and as such I 'trust' them
- e.g. VNE/VDF are tested in still air with a new airframe.
Even then, I'm not going to fly right up to the limits!

The problem I have with calculating a takeoff run is
that there are just so many variables involved that
you cannot consistently and safely rely on the results.
As Todd's post suggests, work out a go/no go point
and if you're not airborne, release.

As a glider pilot I act within both my and the glider's
limits. I trust my instincts that if something doesn't
feel right, I abandon the launch while it's still safe
to do so. Maybe it's a US vs UK thing but here in
the UK we take personal responsibility for our actions.
If you're not sure that you have sufficient distance
to take-off then why would you trust a set of numbers
that say otherwise ? I think the concept of calculating
takeoff runs is actually quite interesting but the
sheer number of variables involved make it an impracticable
exercise.

Gary


At 14:36 13 April 2007, Kilo Charlie wrote:
>
>'Gary Nuttall' wrote in message
...
>> And keep a note of how much fuel the tug has on board.
>> How heavy the glider pilot is. How clean the glider
>> wings are. What time of day it was. Outside Air
>>Temperature,
>> pressure and moisture content. Local CAPE and Lifted
>> Index. Length of rope (and its elasticity). Power
>> setting of tug. What mood each of the pilots were
>> in. Stick position on ground run. Local thermal
>>and
>> wave activity. All can have an effect on take-off
>> distance and climb rate.
>>
>> There's so many variables that I'd be dubious of any
>> metrics developed beyond the fact that high altitude,
>> high temperature and heavy gliders do not make a good
>> combination.
>>
>> Anybody who comes up with a set of explicit numbers
>> and sticks to them is likely to discover how often
>> theory doesn't work in practice!
>>
>> Happy soaring
>> Gary Nuttall
>
>
>Continues to amaze me at how much disdain glider pilots
>have for
>quantitation. I suppose that may be what draws some
>of them into the
>soaring in the first place. I also enjoy that aspect
>but think that
>attitude has gotten many powered pilots into bad situations.
> To think that
>we are immune to it because we don't have engines is
>naive.
>
>Casey
>
>
>

[[email protected]]

On Apr 13, 2:09 pm, Gary Nuttall
> wrote:
> Not as much as it disturbs me that there might be people
> out there who will stake their lives against a set
> of numbers in a book. The margins of safety are so
> much tighter in a glider/sailplane than a powered aircraft
> and a minor change in any one part of the equation
> could have dramatic results.
>
> Let's be clear here.....Some numbers you can be confident
> in becuase they've been measured in a certain, calibrated
> and controlled environment and as such I 'trust' them
> - e.g. VNE/VDF are tested in still air with a new airframe.
> Even then, I'm not going to fly right up to the limits!
>
> The problem I have with calculating a takeoff run is
> that there are just so many variables involved that
> you cannot consistently and safely rely on the results.
> As Todd's post suggests, work out a go/no go point
> and if you're not airborne, release.
>
> As a glider pilot I act within both my and the glider's
> limits. I trust my instincts that if something doesn't
> feel right, I abandon the launch while it's still safe
> to do so. Maybe it's a US vs UK thing but here in
> the UK we take personal responsibility for our actions.
> If you're not sure that you have sufficient distance
> to take-off then why would you trust a set of numbers
> that say otherwise ? I think the concept of calculating
> takeoff runs is actually quite interesting but the
> sheer number of variables involved make it an impracticable
> exercise.
>
> Gary
>
> At 14:36 13 April 2007, Kilo Charlie wrote:
>
>
>
>
>
> >'Gary Nuttall' wrote in message
> ...
> >> And keep a note of how much fuel the tug has on board.
> >> How heavy the glider pilot is. How clean the glider
> >> wings are. What time of day it was. Outside Air
> >>Temperature,
> >> pressure and moisture content. Local CAPE and Lifted
> >> Index. Length of rope (and its elasticity). Power
> >> setting of tug. What mood each of the pilots were
> >> in. Stick position on ground run. Local thermal
> >>and
> >> wave activity. All can have an effect on take-off
> >> distance and climb rate.
>
> >> There's so many variables that I'd be dubious of any
> >> metrics developed beyond the fact that high altitude,
> >> high temperature and heavy gliders do not make a good
> >> combination.
>
> >> Anybody who comes up with a set of explicit numbers
> >> and sticks to them is likely to discover how often
> >> theory doesn't work in practice!
>
> >> Happy soaring
> >> Gary Nuttall
>
> >Continues to amaze me at how much disdain glider pilots
> >have for
> >quantitation. I suppose that may be what draws some
> >of them into the
> >soaring in the first place. I also enjoy that aspect
> >but think that
> >attitude has gotten many powered pilots into bad situations.
> > To think that
> >we are immune to it because we don't have engines is
> >naive.
>
> >Casey- Hide quoted text -
>
> - Show quoted text -

The process of acquiring and analyzing the data will establish if it
is reliable or not. If it is not reliable there will be a large
scatter for the same set of conditions. The fundamental set of
parameters include, but are not limited to:
1. Tow plane POH take-off distance (this takes into account density
altitude and type of runway)
2. Glider total weight
3. Glider L/D
4. Wind
All of the other things mentioned are very minor compared to the above
factors, and will be represented as a scatter in the predicted take-
off distance. This can be accounted for with a safety margin, which
MUST be added to any POH calculation anyway. Exactly what are you
proposing as an alternative, launching without regard to available
data? This task is not on the level of a molecular chemical reaction
dynamics calculation. Personally, I would feel much more comfortable
having the data if I were the one being towed. If someone will collect
the data I would be happy to help them analyze it, something I do for
a living.

Tom

[Kilo Charlie]

"Gary Nuttall" > wrote in message
...
> Not as much as it disturbs me that there might be people
> out there who will stake their lives against a set
> of numbers in a book. The margins of safety are so
> much tighter in a glider/sailplane than a powered aircraft
> and a minor change in any one part of the equation
> could have dramatic results.
>
> Let's be clear here.....Some numbers you can be confident
> in becuase they've been measured in a certain, calibrated
> and controlled environment and as such I 'trust' them
> - e.g. VNE/VDF are tested in still air with a new airframe.
> Even then, I'm not going to fly right up to the limits!
>
> The problem I have with calculating a takeoff run is
> that there are just so many variables involved that
> you cannot consistently and safely rely on the results.
> As Todd's post suggests, work out a go/no go point
> and if you're not airborne, release.
>
> As a glider pilot I act within both my and the glider's
> limits. I trust my instincts that if something doesn't
> feel right, I abandon the launch while it's still safe
> to do so. Maybe it's a US vs UK thing but here in
> the UK we take personal responsibility for our actions.
> If you're not sure that you have sufficient distance
> to take-off then why would you trust a set of numbers
> that say otherwise ? I think the concept of calculating
> takeoff runs is actually quite interesting but the
> sheer number of variables involved make it an impracticable
> exercise.
>
> Gary

Wow....I certainly didn't think that this question would degenerate into a
US bashing exercise but ya just never know on ras!

You clearly have a bug up your patoot re quantitation Gary. I think that
Bill, Tuno and I are on the same page though. I would challenge Gary's
remark that "The margins of safety are so much tighter in a glider/sailplane
than a powered aircraft". In fact I think that the opposite is true but
then that is for another discussion. I'll only say that the glider on tow
is always in better shape than the towplane if the engine quits.

Nowhere did I say that this is a matter of inches and would choose to "push
to the limits" based upon an equation without the usual margin of safety
added to it. Currently we have no place to begin the discussion based upon
facts so that is what I'd like to see happen. And also who said anything
about the FAA getting involved???

Whether any of you like to admit it or not you are all using data on each
glider flight....esp if you go XC. If L/D is worthless then why not try to
make that field far off in the distance in your 1-26?

So I would surmise that some of you would choose to head up to a high
altitude site on a hot day, take a tow then while rolling make a decision as
to whether you feel safe continuing. That would seem like a big waste of
time to me.

And Gary.....I love you guys in the UK......great sense of humor, great
beers and some awesome racing pilots......but lets face it......you ain't
got no high altitude soaring sites....at least not in Great Britain. ;-)

Cheers,
Casey Lenox
KC
Phoenix

[[email protected]]

Hmmmm,

I don't see consulting charts as the solution...rather just another
data point. I choose to fly where most days the density altitude at
launch is somewhere between 10k'-12k'(Salida, Buena Vista, Leadville,
Telluride). I have never considered constructing a graph....not that
it might not help. I try to launch by 11am, downhill if possible, no
water if behind a Cub, plenty of water if behind a 260Pawnee, no mid
afternoon launches into strong thermal conditions. I like at least
7500' of runway. Pawnees are not great climbers at 70 knots, and I
have done my share of fence inspection tours grinding around low. I
accept the risk/reward by refusing to fly with water if I have any
doubts...and just a couple of degrees of temperature can make a huge
difference IMVHO.

Having flown in these conditions for the last 9 years, piloting and
fuel load affect the safety of the launch as much as POH climb
prediction. Ever towed behind a pilot who had not set the fuel
mixture correctly? Or did not stay down in ground effect to
accelerate? Or with a big guy at the stick who just topped off the
tanks?

I would be curious what the predicted climb rate for the Cessna
150/180 based at Telluride would be on a hot day...not sure I really
would want to know :)

[Bill Daniels]

Stu has a lot of experience flying in the colorado high country so I respect
his views. However. I'd like to make a few comments below.
> wrote in message
ups.com...
> Hmmmm,
>
> I don't see consulting charts as the solution...rather just another
> data point. I choose to fly where most days the density altitude at
> launch is somewhere between 10k'-12k'(Salida, Buena Vista, Leadville,
> Telluride). I have never considered constructing a graph....not that
> it might not help. I try to launch by 11am, downhill if possible, no
> water if behind a Cub, plenty of water if behind a 260Pawnee, no mid
> afternoon launches into strong thermal conditions. I like at least
> 7500' of runway. Pawnees are not great climbers at 70 knots, and I
> have done my share of fence inspection tours grinding around low. I
> accept the risk/reward by refusing to fly with water if I have any
> doubts...and just a couple of degrees of temperature can make a huge
> difference IMVHO.

All reasonable precautions.
>
> Having flown in these conditions for the last 9 years, piloting and
> fuel load affect the safety of the launch as much as POH climb
> prediction. Ever towed behind a pilot who had not set the fuel
> mixture correctly? Or did not stay down in ground effect to
> accelerate? Or with a big guy at the stick who just topped off the
> tanks?

Unfortunately, I have seen all this happen - it is the mark of a very poor
pilot. I try not to get to know them since I don't want to be invited to
their funeral.

ANY properly trained airplane pilot knows how to use takeoff charts which
includes knowing the takeoff weight including fuel and pilot weights as well
as density altitude and wind. Adding glider weight and L/D doesn't add that
much work. Properly done, the results will be very accurate. I've never
seen actual takeoff performance differ from the POH by more than 5% - most
often it's dead on.

Pilots of airplanes with fixed pitch propellers can set the mixture simply
by adjusting for max RPM. This is, by definition, max power which is about
100 degrees rich of peak EGT. You can't hurt an engine at high density
altitudes doing this so set it for max power for every takeoff. If you can
hold constant airspeed, this works while climbing too so max power can be
maintained througout the climb.
>
> I would be curious what the predicted climb rate for the Cessna
> 150/180 based at Telluride would be on a hot day...not sure I really
> would want to know :)
>
Actually, I would want to know so I can exercise my PIC and perhaps decline
the tow if I deem the performance too low.

Bill Daniels

[Eric Greenwell]

Gary Nuttall wrote:

> As a glider pilot I act within both my and the glider's
> limits. I trust my instincts that if something doesn't
> feel right, I abandon the launch while it's still safe
> to do so. Maybe it's a US vs UK thing

Very likely - how often does a pilot in the UK have to decide if an
airport at a 10,000 foot density altitude that has never seen a towplane
is safe to use? Here in the USA, I"ll bet we have this problem much more
frequently.

> but here in
> the UK we take personal responsibility for our actions.

I think it's the same here, too. After all, the tow can go bad for
several reasons besides a high density altitude tow at an airport that's
never been used for towing! And, of course, it's not dependent only on
the glider pilot: the towpilot should notice HE'S not off the ground
early enough, and let the glider go so the towplane pilot can deal with
the towplane's problem. In fact, the combination can still be in trouble
even if the glider has taken off "in time", because the critical element
is the towplane taking off in time. It's hard for the glider pilot to
assess this.

What I think Kilo Charlie and the others are trying to determine is if
it's even worth taking a towplane to this potential site. Without
experience at a similar site, looking for pertinent numbers seems like a
better idea than just showing up and trying it.

> If you're not sure that you have sufficient distance
> to take-off then why would you trust a set of numbers
> that say otherwise?

Perhaps because you've verified the table or equation in other
situations, and added a margin for safety, and because you are using a
towplane, towplane pilot, and glider pilot you trust to handle the
situation, even if things go wrong.

> I think the concept of calculating
> takeoff runs is actually quite interesting but the
> sheer number of variables involved make it an impracticable
> exercise.

Nonsense. You aren't trying to precisely determine takeoff runs, but
decide if the situation is "safe enough". They know how the towplane
operates compared to it's POH values, and the addition of the glider can
be calculated (it's just drag and weight, not a huge number of
variables), so a sensible estimate can be determined.

--
Eric Greenwell - Washington State, USA
* Change "netto" to "net" to email me directly
* "Transponders in Sailplanes" http://tinyurl.com/y739x4
* "A Guide to Self-launching Sailplane Operation" at www.motorglider.org

[Gary Nuttall]

My concern was based on the principle that somebody
was developing an 'absolute' model which was based
on a limited number of parameters without considering
the wide range of factors that influencing launch distances
and climb rates.

If you're simply trying to establish a guideline of
height vs density vs temperature vs wind strength/direction
vs glider performance vs tug power to develop a minimum
runway length required, then fair enough - andI agree
that high temp and high altitiude is something that
we don't have an issue with in the UK. Nonetheless
we do have situations where runway length, tug power
and weight of glider are sometimes at a limit that
needs to be considered by the tug and glider pilot.
This comes down to a simple calculation.....if in
doubt, don't!

Gary

At 02:06 14 April 2007, Eric Greenwell wrote:
>Gary Nuttall wrote:
>
>> As a glider pilot I act within both my and the glider's
>> limits. I trust my instincts that if something doesn't
>> feel right, I abandon the launch while it's still
>>safe
>> to do so. Maybe it's a US vs UK thing
>
>Very likely - how often does a pilot in the UK have
>to decide if an
>airport at a 10,000 foot density altitude that has
>never seen a towplane
>is safe to use? Here in the USA, I'll bet we have this
>problem much more
>frequently.
>
>> but here in
>> the UK we take personal responsibility for our actions.
>
>I think it's the same here, too. After all, the tow
>can go bad for
>several reasons besides a high density altitude tow
>at an airport that's
>never been used for towing! And, of course, it's not
>dependent only on
>the glider pilot: the towpilot should notice HE'S not
>off the ground
>early enough, and let the glider go so the towplane
>pilot can deal with
>the towplane's problem. In fact, the combination can
>still be in trouble
>even if the glider has taken off 'in time', because
>the critical element
>is the towplane taking off in time. It's hard for the
>glider pilot to
>assess this.
>
>What I think Kilo Charlie and the others are trying
>to determine is if
>it's even worth taking a towplane to this potential
>site. Without
>experience at a similar site, looking for pertinent
>numbers seems like a
>better idea than just showing up and trying it.
>
>> If you're not sure that you have sufficient distance
>> to take-off then why would you trust a set of numbers
>> that say otherwise?
>
>Perhaps because you've verified the table or equation
>in other
>situations, and added a margin for safety, and because
>you are using a
>towplane, towplane pilot, and glider pilot you trust
>to handle the
>situation, even if things go wrong.
>
>> I think the concept of calculating
>> takeoff runs is actually quite interesting but the
>> sheer number of variables involved make it an impracticable
>> exercise.
>
>Nonsense. You aren't trying to precisely determine
>takeoff runs, but
>decide if the situation is 'safe enough'. They know
>how the towplane
>operates compared to it's POH values, and the addition
>of the glider can
>be calculated (it's just drag and weight, not a huge
>number of
>variables), so a sensible estimate can be determined.
>
>--
>Eric Greenwell - Washington State, USA
>* Change 'netto' to 'net' to email me directly
>* 'Transponders in Sailplanes' http://tinyurl.com/y739x4
>* 'A Guide to Self-launching Sailplane Operation' at
>www.motorglider.org
>

[[email protected]]

And don't forget to pump up those tires on the tug and glider.....

[Andy[_1_]]

On Apr 13, 7:04 pm, Eric Greenwell > wrote:
What I think Kilo Charlie and the others are trying to determine is
if
it's even worth taking a towplane to this potential site. Without
experience at a similar site, looking for pertinent numbers seems like
a
better idea than just showing up and trying it.



No, ASA has flown at the site (Clark Memorial, Williams, AZ ) before
but for our next contest there the organizers have decided that water
ballast will not be allowed. Some members have questioned that rule
on the basis that some pilots used water ballast last time they were
there and thought the risk was acceptable.

I think limiting the discussion to takeoff distance misses the point.
I like to know if I can expect a climb rate that will allow me to
return to the airport, or other known safe landing area, from any
point in the tow.


Andy

[Jack]

Andy wrote:

> I think limiting the discussion to takeoff distance misses the point.
> I like to know if I can expect a climb rate that will allow me to
> return to the airport, or other known safe landing area, from any
> point in the tow.

This sounds to me like an absolutely essential point for a safe
operation anywhere, anytime.


Jack

[Bert Willing]

Then you probably don't want to fly out of quite a number of places in
Europe :-(

"Jack" > wrote in message
et...
> Andy wrote:
>
>> I think limiting the discussion to takeoff distance misses the point.
>> I like to know if I can expect a climb rate that will allow me to
>> return to the airport, or other known safe landing area, from any
>> point in the tow.
>
> This sounds to me like an absolutely essential point for a safe operation
> anywhere, anytime.
>
>
> Jack

[Jack]

Bert Willing wrote:
> Then you probably don't want to fly out of quite a number of places in
> Europe :-(
>
> "Jack" > wrote in message
> et...

>> Andy wrote:
>>
>>> I think limiting the discussion to takeoff distance misses the point.
>>> I like to know if I can expect a climb rate that will allow me to
>>> return to the airport, or other known safe landing area, from any
>>> point in the tow.

>> This sounds to me like an absolutely essential point for a safe operation
>> anywhere, anytime.


That is true. I am fortunate enough to soar over the relatively flat
fields of N. Illinois -- and that's the way I like it. It's a lot
more fun when the risk is minimized for those of us who have been
lucky enough to have lived to maturity in spite of the risks.



Jack

[Kilo Charlie]

"Andy" > wrote in message
oups.com...
> On Apr 13, 7:04 pm, Eric Greenwell > wrote:
> What I think Kilo Charlie and the others are trying to determine is
> if
> it's even worth taking a towplane to this potential site. Without
> experience at a similar site, looking for pertinent numbers seems like
> a
> better idea than just showing up and trying it.
>
>
>
> No, ASA has flown at the site (Clark Memorial, Williams, AZ ) before
> but for our next contest there the organizers have decided that water
> ballast will not be allowed. Some members have questioned that rule
> on the basis that some pilots used water ballast last time they were
> there and thought the risk was acceptable.
>
> I think limiting the discussion to takeoff distance misses the point.
> I like to know if I can expect a climb rate that will allow me to
> return to the airport, or other known safe landing area, from any
> point in the tow.
>
>
> Andy

Eric has hit it on the head. Andy is a very knowlegable pilot but at least
last year did not fly out of Williams in his glider (he came to visit in his
airplane with a broken arm) just as a matter of full disclosure which seems
to be where he was attempting to head.

I honestly don't care which parameter you choose.....takeoff distance, climb
rate, etc. I would think that it all will have a decent correlation wrt
density altitude.....but then I'm just a stupid doctor and not an engineer
like Andy.

We have NO airports with safe bailout fields anymore....not that we ever did
but Turf had a potential spot at least. So its a totally moot point re
that. I have towed at gross weight out of Ely (6200'), Parowan (5900') and
Moriarty (6200') and yes the takeoff rolls were long and the climb rates
were low but by the end of the runway or just beyond was at 200 feet and the
experienced tow pilots did a slow low bank turn back over the airport until
we were at a high enough altitude to look for lift elsewhere. I never felt
that my life was in more danger there than on a 110 degree day at 2000'
towing uphill with no wind at El Tiro which we do all of the time. The ASA
is also now towing out of a 3900' length runway uphill on the lee side of
some hills. So where do we draw the line?

So I do think that Eric is correct in that I do wish to have the best
numbers we can generate wrt takeoff distances (or climb rate!) so that we
have a starting point to evaluate a go, no-go situation whether it be
heading to a high site on a very hot AZ weekend or whether or how much water
we may put in.

The data would be helpful....period. If the naysayers wish to ignore that
its their choice. I for one believe my POH and along with some common sense
will be following it for my Columbia on hot days and would like to be able
to use it for my LS-8/Pawnee combo too.

Casey

[Mike the Strike]

Casey started this thread in response to the decision of the ASA
Contest Committee to disallow the use of water ballast at the field
discussed above for competitors in a club contest. I am one of the
three ASA Contest Committee members who reached this unanimous vote.

Our decision was based mostly on safety issues (a towplane will
produce only about half the thrust at a density altitude of 10,000
feet compared to standard sea level) and at last year's event there
were several tows that pilots there described as "scary". Although
the majority of our experienced pilots could probably launch safely,
we do have a number of newcomers racing with us. We will also only
have one towplane, so the turn-around time will also be shortened by
restricting take-off mass. Water is also not available on airport, so
will have to be brought in by contestants.

Based on these factors, the decision seemed a no-brainer to me, but a
couple of pilots accused us of being over-protective and demanded the
right to determine the risk for themselves.

It is indisputable that take-off runs will be longer and rates of
climb slower at this site, but the controversy seems to have been
whether or not the Committee was too conservative in introducing this
rule (accusations of "nannying" were flying on the ASA web site!).

In mediation, I have suggested that we ask the tow pilot in question
(an excellent and very experienced one) for his take on the problem,
but I doubt that we will change our opinion.

Mike

[CindyB]

> Our decision was based mostly on safety issues (a towplane will
> produce only about half the thrust at a density altitude of 10,000
> feet compared to standard sea level) and at last year's event there
> were several tows that pilots there described as "scary". Although
> the majority of our experienced pilots could probably launch safely,
> we do have a number of newcomers racing with us. We will also only
> have one towplane, so the turn-around time will also be shortened by
> restricting take-off mass. Water is also not available on airport, so
> will have to be brought in by contestants.
>
> Based on these factors, the decision seemed a no-brainer to me, but a
> couple of pilots accused us of being over-protective and demanded the
> right to determine the risk for themselves.
>

It seems only right that the organizers took the prudent course.
With a single tug to protect, and an experienced tow pilot to make the
unilateral final decision, there won't be any meaningful argument.

Truly, I find that most glider pilots won't bother to actually "figure
things out",
unless the soaring weather is garbage and they want entertainment
while swilling
beverages. So, since our weather was chilly and vile today, I figured
I would
toss ras the only published reference of which I am aware on the
topic.

http://www.eaa1000.av.org/technicl/takeoff/topaper.htm

It's been on the web for awhile. Don't know why it wasn't found by
the many
contributors to this thread. Despite all the pretty equations, they
ended up by saying
they didn't have enough consistent data, and that changes in weight
and wind made a
pot load of difference. Duh.

Any time it feels hinky .... fly dry, or find a longer, lower runway.
Racing be stuffed. I'd rather have my friends around for another
season.

Cindy B

[Kilo Charlie]

"CindyB" > wrote in message
ups.com...
> contributors to this thread. Despite all the pretty equations, they
> ended up by saying
> they didn't have enough consistent data, and that changes in weight
> and wind made a
> pot load of difference. Duh.
>
> Any time it feels hinky .... fly dry, or find a longer, lower runway.
> Racing be stuffed. I'd rather have my friends around for another
> season.
>
> Cindy B

Thanks for this link Cindy.....it does appear to be the only study available
to try to answer this question. Your conclusions are, as we say in the
scientific field, not supported by the data however. I didn't see this on a
google search prior to posting this question but maybe you're a more
experienced "googler" than I.

First of all re the weight....this is a quote from the study:
"The lines in Figure 11 seem to imply that the takeoff ground roll data were
not a function of weight, which is an absurd conclusion. This conclusion
further points to the danger of quick conclusions from data with lots of
scatter." So this would mean that the data are suspect to begin
with.....large amount of scatter and not enough points to be able to make
firm conclusions.

Re the wind this is another quote from the study:
"These lines should not be given a lot of weight, given the poor correlation
shown in Table 2." Again not a reliable set of data.

Having said this I may just have to agree with the post that said that there
are too many variables to be able to make firm conclusions other than to
rely upon experience. Too bad but thanks again for the article!

So how about some of those high density altitude pilots out there....any
"scary" tows? Do folks that routinely fly out of high DA fields always tow
dry? What kind of towplanes are being used?

Casey