Auto Tow Information

"Marc Ramsey" wrote in message
news

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.

Larry Pardue 2I

How long is your runway and what altitude do you achieve on launch?

Mike Schumann

"Larry Pardue" wrote in message
...

"Marc Ramsey" wrote in message
news

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.

Larry Pardue 2I

"Mike Schumann" wrote in message
k.net...
How long is your runway and what altitude do you achieve on launch?

Mike Schumann


As I said, long. From about 7,000 to 8,800. Typical altitudes on launch
are around 1,500 to 2,000+ feet AGL.

Larry Pardue 2I

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

The usual...The land was sold and is now a housing development.

The club in question had to move to a local airport.

Bob

On 19 Aug 2005 22:33:40 -0700, "Frank Whiteley"
wrote:

Any idea why it isn't done today?

Frank Whiteley

In article .com,
Frank Whiteley writes
Single drum turn around time is similar to autotow. If you retrieve
your rope at 15mph, it will take 5+minutes to get the rope back to the
launch point on a 6000ft run and another minute to get the tow car back
to the other end. Then the launch take up and launch you are talking
10 minute cycles or 6 launches per hour. If you're flying one Blanik,
or 5-6 gliders in a small club, this is fine. With parafil, we ran 4-6
minute cycle times.

Frank, have you ever been to the Midland GC site at the Long Mynd?

The scheme they use is to have a single drum winch, which launches the
glider and a much smaller one which retrieve the cable.

The two cables attach to 2 corners of a triangular piece of iron,
another cable with the launching rings and parachute goes to the
remaining corner. This system has been in use for at least 45 years, and
is the most efficient way I've seen of getting launched. But it wouldn't
work too well on an aerodrome site.




I've not timed it, but it was VERY quick, much quicker than


--
Mike Lindsay

Yes, but we were bungee launching the day we brought the SHK there, so
I didn't get to see the winch in action. Great for a ridgetop site. I
suspect it could be adapted for a longer run also. Have also heard of
HG sites with dual winches allowing those gliders to make 180 turns at
each end.

Frank Whiteley

The Mynd "triangle" is made of light alloy now, and there have been a series
of detail small improvements to the gear generally. No parachute is used
when the retrieve winch is in use.

The Mynd winchmaster (Colin Knox) has now built a new retrieve winch, so
there are now two in use at the Mynd (not at the same time!). He has used
an entirely different principle to engage drive when the retrieve starts.

Of much more general interest, Skylaunch have built their second retrieve
winch (the first is of course at the Mynd). They have demonstrated it at
Lasham, and their Chief Flying Instructor has sent the following message to
their Yahoo One List:

"Following a successful midweek retrieve winch trial at Lasham a month
ago we are planning to have a weekend trial and evaluation of the new
system. The planned date for the trial is 10/11th September."

I had always supposed that such a system could not work at an airfield such
as Lasham, obviously I was completely wrong.

W.J. (Bill) Dean (U.K.).
Remove "ic" to reply.


"Mike Lindsay" wrote in message
...


In article .com,
Frank Whiteley writes

Single drum turn around time is similar to autotow. If you retrieve
your rope at 15mph, it will take 5+minutes to get the rope back to the
launch point on a 6000ft run and another minute to get the tow car back
to the other end. Then the launch take up and launch you are talking
10 minute cycles or 6 launches per hour. If you're flying one Blanik,
or 5-6 gliders in a small club, this is fine. With parafil, we ran 4-6
minute cycle times.


Frank, have you ever been to the Midland GC site at the Long Mynd?

The scheme they use is to have a single drum winch, which launches the
glider and a much smaller one which retrieve the cable.

The two cables attach to 2 corners of a triangular piece of iron,
another cable with the launching rings and parachute goes to the
remaining corner. This system has been in use for at least 45 years, and
is the most efficient way I've seen of getting launched. But it wouldn't
work too well on an aerodrome site.

I've not timed it, but it was VERY quick, much quicker than

Mike Lindsay

When I was at Halton 1993 and 1994 they used a retrieve winch at times
with a multi-drum winch (two drum). I don't recall exactly how they were
working the two drums, but I do recall (from having driven it a few
times) that operating the retrieve winch took some care in regard to
timing when to engage it for the retrieve (which I seem to recall was
done just after the glider released and before the cable reached the
ground - therefore it used a parachute). It was quite easy to break the
retrieve cable as I recall.

Maybe someone who was there at Halton and more expert in its
construction and use could pass on some details?

Rgds,

Derrick Steed