![]() |
If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
Thread Tools | Display Modes |
|
#1
|
|||
|
|||
![]()
On Aug 3, 7:30*am, Peter Higgs wrote:
Hi All, I have flown from the Long Myndd, which at 1600ft asl is the highest gliding club in UK, situated on a 4 mile long N/S ridge. So as long as there is more than a 15 knot Westerly wind it does not really matter how high you get on the winch... * you WILL GO UP ! They are the only club still able to use Bungee Launching, to catapult a glider the 50 or so yards from the ridge top, into the rising ridge lift. As for the recent Winch Launching debate, we did find that the woven Dynema cable used on a SkyLaunch winch did break quite often. * This was thought to be because it was used in muddy conditions, or on an abrasive tarmac runway. *It was replaced by some sort of normal 3 strand plastic rope (8 and 10 mm.) which was easier to splice, and gave better results. These nylon ropes do stretch a bit first on 'All Out' and can give a very quick initial acceleration, only limited by the weak link I guess. A good winch driver is the best 'constant tension' device, he can judge the tension from the cab, by looking at the bow in the cable. *If its too much he winds it in a bit faster, and if it is as tight as a bow string, he just backs off the power a little. Pete Pete, Dyneema/Spectra is so light that it doesn't' bow enough for the winch driver to get much tension information from it. There has to be an automatic method of limiting or controlling rope tension. Anyway, tension recordings show it changes way too fast for a human to react. I spent today walking and inspecting the Spectra (Plasma rope) on the Hydrowinch prototype and found it to be in very good shape. It was still soft and pliable - almost like new. I'd predict at least 3000 launches on this rope and maybe 5000. That's in line with other good winch designs. The airfield is a mix of about 2500 feet of old rough asphalt (tarmac) plus 6000 feet of rough weeds, wild grass and cactus patches. Most people wear protective footwear. Spectra/Dyneema provides considerable warning of airfield surface wear - it gets very fuzzy long before the strength deteriorates to where it would need to be replaced. This is caused by individual micro fibers snagging on the rough surface. I don't know of anyone who has replaced Dyneema for this reason Damage due to poor winch design is also easy to see. The rope gets hard, stiff, squared off and shiny due to local overheating on cylindrical rollers or poorly designed sheaves. There will be cut strands visible where the rope gets nicked on sharp metal edges. Rope breaks will be experienced at about 100 launches. This will limit the useful live to only a few hundred launches which makes it uneconomic to use with old steel wire winch designs. The winch itself is by far the worst source of rope damage. Airfields, even very bad ones, do little damage. |
#2
|
|||
|
|||
![]()
Strange therefore how our winch drivers at Lasham, including the amateur
volunteers, managed to cope perfectly well with a synthetic cable when we tried it out on a purely manual driven Tost winch without ANY automatic gizmos! You still have the climb rate, glider appearance, and any signals from the pilot to go on. UHMWPE cable does bow a bit, but less than steel. It also drifts a long way sideways in a crosswind after release. We got just over 2500 launches from it, with most of the wear being caused by ground abrasion where it was pulled across our rough concrete cross runways. Derek Copeland At 23:20 14 August 2009, bildan wrote: Dyneema/Spectra is so light that it doesn't' bow enough for the winch driver to get much tension information from it. There has to be an automatic method of limiting or controlling rope tension. Anyway, tension recordings show it changes way too fast for a human to react. I spent today walking and inspecting the Spectra (Plasma rope) on the Hydrowinch prototype and found it to be in very good shape. It was still soft and pliable - almost like new. I'd predict at least 3000 launches on this rope and maybe 5000. That's in line with other good winch designs. The airfield is a mix of about 2500 feet of old rough asphalt (tarmac) plus 6000 feet of rough weeds, wild grass and cactus patches. Most people wear protective footwear. Spectra/Dyneema provides considerable warning of airfield surface wear - it gets very fuzzy long before the strength deteriorates to where it would need to be replaced. This is caused by individual micro fibers snagging on the rough surface. I don't know of anyone who has replaced Dyneema for this reason Damage due to poor winch design is also easy to see. The rope gets hard, stiff, squared off and shiny due to local overheating on cylindrical rollers or poorly designed sheaves. There will be cut strands visible where the rope gets nicked on sharp metal edges. Rope breaks will be experienced at about 100 launches. This will limit the useful live to only a few hundred launches which makes it uneconomic to use with old steel wire winch designs. The winch itself is by far the worst source of rope damage. Airfields, even very bad ones, do little damage. |
Thread Tools | |
Display Modes | |
|
|
![]() |
||||
Thread | Thread Starter | Forum | Replies | Last Post |
Saturday 072807 in Oshkosh Pt 2 - the C17 [08/14] - "08 C17 hope they used the really thick bungee cords on the cargo.JPG" yEnc (1/1) | Just Plane Noise[_2_] | Aviation Photos | 0 | July 30th 07 10:48 PM |
AOPA Expo, meeting JayB, getting stuck in Lancaster on the way home,fulfilling the commercial certificate long solo x-c...long | Jack Allison | Piloting | 6 | November 19th 06 02:31 AM |
nose bungee replacement concern | Dick | Owning | 1 | November 1st 06 03:58 PM |
Puchacz shock cord (bungee) failure | [email protected] | Soaring | 4 | July 1st 06 09:18 PM |
Another Long Cross Country: HPN to PAO in 6 Days (long) | Journeyman | Piloting | 19 | June 15th 06 11:47 PM |