Takeoff distances

"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

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

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

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

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

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

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

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

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

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