Tractor Gyro Mains placement

[SamL]

If you notice all the early tractor gyros used tail dragger configurations.
The mains were always placed as far forward as possible near the engine.
My theory is to get as much drag behind them as possible, ie: RTV, CofG, and as much tail area dragging behind them, which all aids in directional ground handling stability.
My question is more so aimed at the exact positioning of the mains, comparing eg. Little Wing, and Cierva's C-30.
Do we place them anywere, or was there a reason for Cierva's forward placement.
Is my theory right or wrong ??????????????

Regards Sam L.

[chuter]

One thing I didn't know when building mine: if the CG is too far behind the mains it makes it more likely to ground loop.

I had the mains as far forward as I could get them, but ended up moving them back about a foot to make taxiing easier.

[PW_Plack]

Sam,

Control surfaces behind CG don't make much difference in ground handling. In fact, moving the CG further aft of the main gear makes a taildragger's ground handling worse.

If I had to guess, I'd imagine main gear location on these early gyros had more to do with attaching them at the strongest possible point. These things were built to take "drop-in", or near-vertical landings.

The reason taildraggers oversteer and ground-loop more easily is because their CG is aft of the main gear. (If it wasn't, they'd fall forward on their props.) The tricycle gear aircraft can have the CG forward of the mains for more ground stability.

I remember seeing this idea demonstrated years ago, building Boy Scout Pinewood Derby cars with my son. Pinewood Derby cars are gravity-powered, carved from pine wood, and use lead weights to make all finished cars weigh the same. They run in tracks made with grooves and little "curbs" to hold the cars on course.

My son and I reasoned that if the weights were as far aft as possible, the car would start the race with more potential energy, which might provide a slight edge. Instead, the car kept wanting to fishtail in the track, chattering its way down the course, and finishing behind smoother-tracking cars with the weights in the front.

[Ga6riel]

since the relationship between the CG and the disc is always more or less the same
the balance is to have the mains forward of the CG
and as far aft as not to nose over under hard brakes
if the mains are too far forward a ground loop is guaranteed as Bob will attest.
usual route for FW taildraggers (is there a better source?) is the wheel centre situated on a line at 13 to 17 degrees forward and down from the CG in the level flight position, the level flight attitude being some 10 to 15 degrees nose down from the ground position static attitude.
the mains also need to toe out, this is an often overlooked cause of ground loops so essential to factor in

cars have a forward CG by and large, unlike cars like VW Beetles which did not, the CG was at the jacking point about 8" in front of the rear wheels
hence a VW was more stable dynamicly when going backwards, as it would try to do if you lost it in a turn
when it did it was difficult to recover from its most stable attitude and would be almost certain to roll if that equilibrium was upset during 'recovery'

[WHY]

SamL

PW Black's second paragraph probably has one of the greatest reasons that the gear was so far foward, also those radials were very heavy, When Ron mounted his radial on his Little Wing he had to relocate his main gear to get the desired balance. If you can get hold of a 1991 May issue of Rotorcraft ( PRA) there is an article in it by Jim Eich on a tractor he build that he nicked named the Squirrel because of the way it handled on the ground with him trying to fly it.

He and his friend Norm Regnier had built it figuring the balance with Norm's weight and Jim was "considerable" heavier than Norm and Jim told me the He figured it was trying to still keep the tail wheel on the ground after the mains were trying to lift off and the made a commpletely un-managable machine but later when Norm tried to fly it everything worked great, so there are literally two balance points that are necessary to get correct, one is the proper tail weight when on the ground and the other is the c-g balance in the air.

Also it seems that most tractor gyros take off in the three point position, ullike FW that raise the tail on take off.

Tony

[SamL]

Also it seems that most tractor gyros take off in the three point position, ullike FW that raise the tail on take off.
Tony

Good points Tony, FW raise there tail to increase there airspeed by reducing there drag.
In a gyro we do the same by lowering the disc angle.

Also you are right, I see Ron did slightly sweep the struts forward on his radial powerd LW.

See link below for more info on this subject.
http://www.asra.org.au/forum/index.php?topic=1866.from1151411877;topicseen#msg1 7082

Sam.

[WHY]

Sam

I am looking at the very same question as you have posted, since I am building a tractor using a fixed wing tail dragger fuselage ( single place) and modifying it to a gyro configuration.

my theory is that there is some percentage of the total weight (loaded) that should be on the tail wheel for a good ground handling capability, at this point in time I have not been able to determine what that percentage is and how much range plus or minus is acceptable because it will obviously vary with pilot weight and fuel usage. Also the three point ground angle is something I have not determined yet but am working on it.

Would be interesting to have some of the experienced pros comment on this

Tony