Larry Pardue wrote:
"Marc Ramsey" wrote...
Many in the group fly in the western US, where summer density altitudes
range up to 10,000 feet. Yes, the numbers I've run indicate that we need
at least a 250 HP turbo diesel (not so much for the HP as the torque) to
be able to launch something as mundane as a Grob 103 with two aboard.

I'm curious about how these calculations work. At Hobbs, NM, elevation
3,700 feet and long runways, the 90 HP winch, using heavy wire, doesn't
have any trouble at all with a Grob 103 loaded with two aboard.

Makes me wonder what we are doing wrong.

It is purely a function of ones assumptions when performing the
calculations. I'd like to launch a loaded Grob 103 at 8000 foot density
altitude, no wind, to 2000 feet from a 5000 foot runway. My basic
assumption was that to achieve optimal launch height for a given cable
length, one needs to be able to pull hard enough to break the weak link
at any point during the climb. I also assumed that there would be 20%
mechanical losses. This establishes some relatively high minimum HP and
torque levels. If I can I dig up the spreadsheet, I'll post the full
set of numbers.

None of this says that you can't launch a glider on less horsepower, it
just says that you can't get very close to optimal height for a given
length of the runway...

Marc