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#11
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I finally installed an Alko AKS 1300 (shown at the
same web site) on my Toyota 4 Runner and Cobra (DG808) after trying everything else short of relocating the axle and it worked. Expensive but much less trouble than reworking the trailer. At 04:48 15 June 2005, Ian wrote: On Mon, 13 Jun 2005 08:15:23 -0700, rolfh wrote: We're towing a DG-500M in a Cobra trailer, and it has a definite sway, fortunately it usually damps fairly well. Life was worse with a strong crosswind. We had 2 thoughts: 1. tonuge weight - are we shooting for tongue weight about 10% of the total trailer weight? 2. Hitch height - any thoughts? I used to own a half share in a Nimbus 2. My partner and I had both previously rolled a glider trailer, writing off the car, in separate incidents with different trailers. So when we discovered the home built Nimbus trailer could not be towed over 80km/hr we were determined to fix it. Our solution was: 1) We moved the trailer axle back to increase the tow ball weight. We aimed for 50kg but ended up with close to 60kg. Up from about 20kg. 50kg is near the limit of most cars, above this and you will need to tow with a truck. 2) We bought a 'Trapezium' towbar stablizer. This is a device which bolts onto the towbar. It has a mechanism which moves the tow ball from side to side as the trailer rotates around the tow ball. The effect of this is to move the pivot point well forward of the tow ball, close to the rear axle of the tow vehicle. This changes the geometry of the system and radically reduces the tendency to sway. Google found a writeup on this device on the bottom of this page. http://www.swift-owners-club.co.uk/s...abilisers.html It is a South African invention, originally developed by a glider pilot. It is VERY effective with a glider trailer due to the length of the trailer. I don't know whether they are still available, but if you find one, be sure to know they work. These two in combination resulted in a trailer which was stable at speeds over 120 km/hr. I was never brave enough to try towing any faster. Double axle trailers are also much more stable. If the mod is done carefully, adding a second axle to a trailer can often provide a permanent fix. Of course you must have an appropriate tow car. Beware, modern cars are lighter, but old glider trailers remain the same. Many pilots only discover that the car they own is not suitable for towing the glider that they fly after they have successfully completed their first outlanding. Worst still, the discovery is often made with an inexperienced friend driving the car ... Have fun. Ian |
#12
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Gary Evans wrote:
I finally installed an Alko AKS 1300 (shown at the same web site) on my Toyota 4 Runner and Cobra (DG808) after trying everything else short of relocating the axle and it worked. Expensive but much less trouble than reworking the trailer. I presume the standard ball won't work, because this device would slowly unscrew it? |
#13
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The standard ball works fine if....
Most standard balls have flat sides so they can be gripped by a wrench while the nut on the bottom is being tightened. Carefully mark where these flats lie on the hitch, and have two small bars welded onto the hitch. This will keep the ball from turning. On 6/16/05 7:57 PM, in article Nlose.222$SF5.199@fed1read07, "Greg Arnold" wrote: Gary Evans wrote: I finally installed an Alko AKS 1300 (shown at the same web site) on my Toyota 4 Runner and Cobra (DG808) after trying everything else short of relocating the axle and it worked. Expensive but much less trouble than reworking the trailer. I presume the standard ball won't work, because this device would slowly unscrew it? -- Bob bobgreenblattATmsnDOTcom --fix this before responding |
#14
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Agree with a little weight in the front of the trailer. Add a tool kit,
you may use it. Don't severely overload the trailer tongue, this takes weight off your steering axle (bad idea). Agree on using trailer tires, they take more pressure! Also: Check tow vehicle shocks, change to heavy duty. Check tow vehicle front end alignment. Check tow vehicle and trailer tire pressure. Fiberglass top trailers may need spoilers added to the vertical fin. Jim |
#15
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Dear Rolf
You are up against the basic fact that the weight distribution with such two seater trailers can be really terrible with regard to forcing excessive rear overhang. Yes the configuration with fuselage and wing roots to the front produces the best ease of rigging, but with a serious compromise in towing stability in that the axle(s) are further forward than desirable. There is nothing better that you can do than get the axle(s) well back, but too far and then of course the tongue weight goes up unacceptably. You may still be able to get some weight out of the front of the trailer and redistribute it to the rear. The more you can do this the more you can move the axle(s) back maintaining a constant drawbar weight. Just because a spare wheel seems not important at 15 to 18 kg, it is actually useful if you can relocate it from the front end to the rear end somehow, or at least to the side and rear of the trailer wheel mudguard. Can you fit a stowage tray/box, sideways pullout on rails, behind the axle and underfloor? This may get some of the miscellaneous stuff out of the front of the trailer and help get weight to the rear such that you can then relocate the axle(s) aftwards. You do not say whether your trailer is single axle or dual axle. If single axle then you can fit dual axles which, even if the centre position of the axle set is the same as for single axle, will get some rubber contact with the road at further back distance than before. I know of so much hassle with two seaters towed on a single axle, I would never go down that path. Always double axle for me. Yes the trailer quote to me for such a Cobra German trailer three years included the suggestion that the dual axle axle requirement I included was unnecessary. Rubbish I say. Getting the axles back also helps reduce side area aft of the wheels. To understand this issue better, go to the rear of your trailer when attached to your car. Push sideways against the rear end and feel how soft it is in comparison to when you go to the front end and do the same. Pushing at the rear causes sway, whereas when you push sideways against the front you feel the lateral resistance of all the tyres, car plus trailer. So the bow wave from the passing truck or cross wind through the trees can cause large trailer sway angles because of the low resistance at the rear to side force. Side area and rear overhang are tails that wag the dog. I have had good results with a Hayman Reese sway stabiliser. I have looked at the ALKO product as on the face of it potentially better. Someone has commented on this list on the sway stabiliser from Alko and noted the need to anchor the tow ball. I seem to recollect that on the ALKO website here in Australia I recently saw this device (which I have seen also in the real world) AND also shown was the additional ALKO part required to hold the ball to the tow tongue and prevent the ball being turned by the sway stabiliser. Fit tyres with stiffer sidewalls. See also article by Funston in Technical Soaring July 1989, p90-95. If you want it and can't get it closer to home send me a direct email with a real world address. Cheers Roger Druce Australia wrote in message oups.com... Howdy - I know this topic has come up before, but we're searching for the latest theories: We're towing a DG-500M in a Cobra trailer, and it has a definite sway, fortunately it usually damps fairly well. Life was worse with a strong crosswind. We had 2 thoughts: 1. tonuge weight - are we shooting for tongue weight about 10% of the total trailer weight? 2. Hitch height - any thoughts? Thanks! Rolf |
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