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