Takeoff distances

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

"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