Mini-Winch for FES

On Friday, June 5, 2020 at 1:26:21 PM UTC-4, wrote:
Good and cheap are mutually exclusive. A good, safe machine won't be cheap.

Right, but I thought the idea of the original question was to see if sacrificing some good (higher than 300 foot tow?) might make cheap and safe possible.

Seems like a small corner case until there are lots more FES, but still fun to think about.

Agreed! It's a fun thought experiment for a growing sector of the sport.

For me, the issue is that if I have a setup which can get me to 300', it can get me a lot higher for minimal extra effort. 300' would mean about 600' of linear space, which is unlikely to fit in the area before a runway. So once I'm using any part of the runway, I might was well use the entire length.

From a mechanical perspective, the only substantial difference between 300' and 3000' is the length of rope and the total energy required. The angles, forces, and power stays the same.

Some crucial distinctions of a 100' long catapult-style launch are that there's no hardware on the runway so it can plausibly be completely autonomous; the angles are purely horizontal so the spooling system is simplified and the hook cannot drift down onto the runway; a 3 second launch means that motor cooling is not an issue due to the thermal mass of the motor; and a launch failure is very graceful, with a worst case result of rolling down the runway at a leisurely 30-40kts.

On Fri, 05 Jun 2020 11:00:11 -0700, sebesta wrote:

On Friday, June 5, 2020 at 1:26:21 PM UTC-4, wrote:
Good and cheap are mutually exclusive. A good, safe machine won't be
cheap.

Right, but I thought the idea of the original question was to see if
sacrificing some good (higher than 300 foot tow?) might make cheap and
safe possible.

Seems like a small corner case until there are lots more FES, but still
fun to think about.

Agreed! It's a fun thought experiment for a growing sector of the sport.

For me, the issue is that if I have a setup which can get me to 300', it
can get me a lot higher for minimal extra effort. 300' would mean about
600' of linear space, which is unlikely to fit in the area before a
runway. So once I'm using any part of the runway, I might was well use
the entire length.

The rule of thumb over here is that you get to 1/3 of the cable length,
not 1/2, but it depends on wind too. Our Skylaunch (around 400 hp from V8
on LPG and 1000m (3270 ft) of cable gets me to 1200ft on a light breeze
and 1400 ft plus in more normal summer weather with a reasonable wind
gradient (Std Libelle, not pulling hard, so around 1/2.5 of line length
on average.

A low power winch won't do nearly as well.



--
Martin | martin at
Gregorie | gregorie dot org