Bill Daniels wrote:
Actually, John, I've done better than that. I have several cable tension
traces from a Skylaunch made with a tensiometer load cell at the glider.
The data shows horrific tension surges as the transmission shifts up and
down during the launch. These surges were violent enough to break weak
links and the cable. Surges such as these would be unacceptable in a $200
junkyard winch. Given the price of the Skylaunch, we should expect MUCH
better.

I stand by exactly what I wrote. It's extremely foolish to allow a winch
transmission to shift - particularly when it's easy to prevent it. Just
because big American V8's and automatic transmissions are dirt cheap is no
reason to use them without the needed modifications.

BTW, I do like the Skylaunch paint job.

Bill Daniels


"John Galloway" wrote in message
...

Bill,

If you were to stand beside a Skylaunch winch (which
has a big American petrol/LPG V8 and a fully functioning
3 speed auto box) you would notice that the box is
in 3rd gear by the time that the glider is leaving
the ground and the rest of the launch is normally carried
out in 3rd gear.

John Galloway


At 17:36 30 March 2007, Bill Daniels wrote:

'toad' wrote in message
egroups.com...

Ok, thanks. That's the physics as I understood it.

With a modern winch, I won't have to worry about reverse
control. But
with an old technology ground launch, I do.

Todd


Actually, it's neither difficult nor expensive to eliminate
the worst
problems with an automatic transmission.

Replacing the stock valve body in the transmission
with a 'manual valve
body' allows the winch driver to lock out 1st and 2nd
gears. (Google 'manual
valve body'). These gadgets replace the stock 'PRND2L'
shift pattern with
'RN321' which can be further restricted to 'N3' with
a simple shift gate.
This results in the transmission starting in 3rd and
remaining there
throughout the launch.

For a bit more money and little more effort, the stock
1800 RPM stall torque
converter can be replaced with a 'high stall' TC that
lets the transmission
slip up to say 2800 RPM during power up for a softer
but still energetic
launch. It also prevents a heavy glider in strong
wind conditions from
bogging down the winch engine. Don't do this without
adding an effective
transmission cooler.

It won't be perfect, but it's FAR better than the stock
setup.

Bill Daniels







Hi Bill

I don't understand the mechanics well enough, but this is what we have.

Our little red monster - which looks scrappy but has served well for nearly 30
years consists of:

1x Ford 352 V8 Windsor in stock condition - (Removed from a galaxie I believe.)
1x Standard manual transmission
1x Ford Ranchero one ton truck axle with the differential and one axle locked.

The Single drum is driven from the other hub.

I presume we have the 1,800 RPM stall torque converter as I have not seen any
modifications, and the transmission acts locked from around 2000RPM.

Shifter is 'RN321' manual override.
We launch in 2nd gear - to prevent the engine bogging down. Typically RPM is in
the 3,500 - 3,800 range with a 55-65kt launch in the glider. We only shift to
third manually when needed to retrieve the cable fast. First is locked out.

Am I right in assuming the locked differential and axle are changing the gearing
on the axle. (I think it is a nominal 3.59:1 ratio)

By the way - this setup is nearing the end of it's life at around 50,000 launches.
There is now runout on axle bearings, and oil weeping from the transmission, the
guide rollers are worn beyond machining and the drum rim is deformed. The winch
driver thus gets exposed to quite a lot of vibration, although the cable appears
to absorb most of the vibrations as they are not noticeable in the glider. The
engine is still running well, although it goes through fuel pumps with
distressing frequency (about every 4,000 launches.)

The "capital" cost per launch is tiny.
Fuel is around one litre per launch - less than 1US$.
Maintenance cost is negligible. Filters and batteries mainly.

Now we have to build a replacement - and I wonder where we will find components
as robust.