Takeoff distances

"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

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

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