riddle me this: my ground looping eindecker...

THAT involves FLYING! My absolute FAVORITE kind of testing!

On Aug 10, 5:10 pm, Robert Roland wrote:

Hold on a minute. You must never have driven an old forklift with the steering a bit worn, and probably never any forklift at higher speed. They are nasty beasts. The CG is behind the non-steering wheels and they don't want to go straight for anything. I nearly rolled forklifts a few times. The forklifts you see cruising on the streets have extremely rigid, hydraulically-boosted non-feedback steering, and some are articulated for highway travel to control the nastiness. People who want to see taildragger instability should fool with a grocery cart: push it forward and see it roll straight, then push it backward and watch it swap ends. Don't knock over the mayonnaise display:-)

Yes you will. Seldom, but possible. A too-fast touchdown, especially with flaps applied, will cause such a low deck angle that the nosewheel alone will be on the ground; now we have a really bad taildragger configuration with the CG a LONG way aft of the only wheel on the ground. It's called wheelbarrowing and it's a result of very poor flying skills. It has broken many perfectly good full-scale airplanes and hurt a few people. Many pilots forget that angle of attack is related to airspeed, and that AOA decreases with airspeed and increases as airspeed falls, in a 1-G condition. The too-fast touchdown can only be done if the AOA, and therefore the pitch angle in this situation, is very low. Dropping flaps changes the angle of incidence of the wing and makes it worse. The same scenario can result in porpoising, another airplane-buster. Back to the toe-in/toe-out debate: The toe-out works on full- scale airplanes, while many modelers find that toe-in works for them. Many model landing gears are simple wire affairs or thin leaf springs that have little torsional resistance, and the wheels' rolling drag tends to torque the wheel's axle to a toe-out condition. In applying toe-in, I think they are unconsciously correcting for gear leg twist; toe-out for them would just give them further toeing-out when rolling that would just make the airplane nasty. The full-scale gear is pretty rigid and the wheels are so big that surface drag is much smaller, in proportion, than that experienced on models. They don't twist much at all. The manufacturers of taildraggers usually call for zero (straight-ahead) to maybe a degree of toe-out. I have been flying real taildraggers for a long time and have encountered some with toe-in; they're no fun at all. One had one wheel straight and the other toed-in; if I didn't touch down in a slight crab so that the airplane's rolling track bisected the wheels' tracks, it would jump to one side away from the toed-in wheel, and do it quite violently. I took the grass whenever I could.

Dan

"Six_O'Clock_High> wrote

Right Arm.. .I mean, right on!

I fly exclusively off of grass, and I settled for toe out, after some testing like this, some time ago.

It might be noticed that most of my planes are home brew ugly stick and fun fly types, of different sizes.

Throw in a lazy bee with taller than normal gear of my own design. Of course, it has a straight axle, on it, so no toe in/out. It does fine, also.

Scale ships may be totally different. Perhaps I'll have to build one and do some testing for it!

And any model airplane pilot knows how important it is to locate the CG correcly. It is exactly the same mechanics at work: We are placing the CG slightly in front of the center of lift to achieve stability.

| I looked at full sized airplane info,

Good idea.

| because anything with models is likely to just be opinion, and | proves nothing.

Bad assumption.

There's a lot of wisdom among modelers, and a lot of bunk among full scale pilots. And vice versa.

And what works in a big plane often doesn't work in a small plane, and vice versa.

| * ALL IN ALL ... My take on it. Take the time to adjust from an | extreme setting of perhaps 4 degrees toe in, then repeat it with 4 | degrees toes out, and stood several landings each way. Then try 0 | degrees, and compare your notes. You should be able to get a good | opinion on it all, after all of the experimentation!

Seems reasonable, though I'd suggest more moderate amounts of toe-in and toe-out first -- four degrees is a lot, so what if it leaves you with a plane that you can't even control on the ground?

Also note that full scale pilots are in general much less willing to do this sort of testing -- because if it goes wrong, they've probably just done thousands of dollars of damage to their plane, where we might have scuffed a wingtip or broken a prop.