jditton

Gents, a few thoughts on the toe in/out situation. I used to fly (and own) a taildragger, and when I first bought it it was a real bear on the ground and chewed the tyres real quick! A quick check showed the wheels had lots of toe in. After a wheel alignment to give slight toe out I then had a ***** cat and long life tyres, an unbelievable transformation in ground handling. Models behave the same as real aircraft, we just don't have the immediate feed back of the seat of the pants! As a long time aircraft engineer, my thoughts would be to look at the wheel to ground contact point in relation to the gear leg, and allow for the drag loads applied. That is, if the wheel is on the outside of the leg you could accept a little toe in to counter the drag of the wheel on the ground trying to twist the leg, the end result would be the wheels having zero toe during operation if you catch my drift. A little toe out doesn't hurt, toe in catches your attention..... in my experience.

As to cars having toe in, that depends on the drive wheels. Front wheel drive usually have toe out to allow for the geometry to flexing a little, like wise rear wheel drive carry a little toe in. The designers aim for 0 during normal ops.

Either way, suck it and see which your particular model likes!

Cheers
JD

carlbecker

My Feedback: (3)

It really depends on the model. Toe in has nothing to do about turns. Its meant to help keep a wheeled vechicle traveling straight releaving some twitchyness. Castor will also make a difference at it keeping straight. If you make a turn in a car then the Ackerman geometry takes affect keeping the inside and outside wheels at 90 degrees to the center of the circle. Toe out may very well work better for a specfic plane and I would keep adjustments to a very low degree from 0 straight ahead. Grass or pavement may have more impact then toe. Good throttle management may be more important than anything else. I use either straight or toe in usually. IMHO its best to test what works on THE airplane. Your Mileage Will Vary.

For a nose over I would look at CG, wheel location relative to the CG or binding wheels.

Hogrider

My Feedback: (392)

Hi Everyone,
I think there needs to be a clarification on the reason for the toe-in/toe-out for cars here in the states.
The reason for the toe-in for cars is because here in the states, our roads and highways have a crown down the center to help shed water. If our front-end wheels had zero toe-in/toe-out and we let go of the steering wheel our car would drift to the right, following the off camber of the road surface. Also, you would feel a force in the steering wheel which you would need to counter in order to keep the car going straight. Thus the reason for the toe-in on the right front wheel and a toe-out on the left front wheel.

jditton

I hate to disagree but...... roads worldwide are built with a crown to aid water run off, it does rain in other countries after all (except here - we're in a drought). If you adjust one wheel to give toe in or out, you'll find the steering wheel will be off centre as the wheels will naturally split the difference so to speak. ie if with the steering wheel straight ahead we adjust the toe to have the left wheel at 0, and the fight at 2 toe out, once the car is moving they will self centre to 1 degree toe out each, BUT the steering wheel will now be offset from centre. The self centring of the steering wheel (and the effort require to turn it) is mainly controlled by caster, and this will effect the tendency to drift down the camber of the road. If the camber is different on each wheel, the car will "pull" one way. Manufacturers go to great lengths to make a good compromise between all these forces, and the do remember their cars are often sold workd wide, I've yet to see differeing specs for cars sold to separate markets.

Anyway, whay are we arguing cars - I thought this was an aeroplane thread.............

Carlbecker, you're dead right, grass or pavement makes a huge difference. Given the choice I'd land on grass or gravel every time, get it right and the touchdown can be soooo smooth. Tarmac - there's always that sqeak and jolt as the tyres grip the pavement.
Cheers
JD

da Rock

Well, we're actually discussing how alignment works for planes. And most people's experience is with cars. So that's pertinent.

Matter of fact, modern cars might have toe in to make up for compliance in the suspension components. The bushings and fittings are usually "soft" so the ride feels softer. And "soft" gives. So at speed, the bushings and such give and the suspensions "open up" a bit. Toe in helps reduce the effect of that opening up.

Truth is, our models really don't usually see situations where the alignment is finely critical. Get them straight enough they aren't obviously skewed, and if you're flying off grass, no problems at all. Fly off (and with luck, back on) pavement and you'll experience some problems if the tires have treads and have some traction. Most of our tires aren't what you'd call grippy.

All the effects of alignment for our tires on our gear designs on our tail draggers really don't sum up to the effect we get from placing the footprints adequately ahead of the CG.

We've got two major things to deal with. Placing the footprints and placing the CG. Get the CG right for flight AND with consideration of the footprints' location and any decently close alignment will work for sure off grass, and give pretty much no trouble off pavement. That is, if you've also been able to place the footprints at or forward the original location.

Two things matter most. CG and footprint location. (And that're really just one thing. Footprint relative to the CG.)