Takeoff distances

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

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

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

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

"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

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

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

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

"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 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