(castor comments removed)
A friend of mine is nearing the end of a multi-year ground-up rebuild of a Piper PA22-20 Pacer. he wants to make sure the wheel alignment is spot-on before flying but isn't sure what's best: toe-in, toe-out, or neutral. Anyone?

hotrod180 wrote:Not castor oil-- I'm talking wheel castor aka toe-in & toe-out.
A friend of mine is nearing the end of a multi-year ground-up rebuild of a Piper PA22-20 Pacer. he wants to make sure the wheel alignment is spot-on before flying but isn't sure what's best: toe-in, toe-out, or neutral. Anyone?

I don't know anything about a Pacer's alignment, but when my IA aligned the mains on my Cessna with spring steel gear a couple of weeks ago, it was to make it dead neutral. I suppose it would depend a lot on how much backward flex could be expected when touching down, which would tend to cause some toe-out. Hopefully, most of the flex would be vertical and not horizontal fore to aft. All that FWIW.

Cary

Careful, because toe is definitely not the same as caster.

On the mains, you should only have to worry about caster and camber. Caster is typically only as issue on steerable wheels.

Cannon wrote:Careful, because toe is definitely not the same as caster.

On the mains, you should only have to worry about caster and camber. Caster is typically only as issue on steerable wheels.

My IA used the term "toe-in", which is a lot easier for me to understand than caster or camber or whatever. I suppose camber must be the tilt of the wheels as the airplane sits there, right?

Cary

If you change the name of this thread I would expect Brian at Steve's Aircraft to chime in pretty quick with a response. Two other sources are the SWP drawings and ShortWingPipers.org. I worked on this a little bit back in the day with my Clipper down at Steves Aircraft.

CW

Hotrod
Caster, Camber, and toe are three different angles. What he is looking for in a pacer is the toe. The short wing site has a bunch of posts on it as does Supercub.Org. I would check both sites as someone always seems to come up with a easy way to make it work.
DENNY

If I'm not mistaken, it is best if the wheels are set to neutral during the build process. On the PA-11 this was done by putting the fuselage in a jig and welding the gear fittings part way, then putting new gear on and putting a straight piece of tubing through the axles. Then finish welding the gear fittings. At least that's how I remember it.

it is not necessarily adjustable like any cessna.
1. If you have a bent gear you can buy a new one, used one or cut yours and weld it straight.
2. Put a big ass pipe on the axle and give it a little bend. Not a fan of that method but it is done...

I usually just buy a new gear leg If it is too crooked. The only time I ever hear about it is when the tips of someone's skis are almost touching

Biggest question is what conversion gear is he using..? I would assume Univair since they are the most common..

You CAN NOT adjust toe-in / camber angles at the axle like you can on a Cessna... They are welded truss gear legs... Getting the correct toe-in is dependent on where the front main gear fittings are welded to the fuselage... If these are way off the only way to fix correctly is to cut off the fittings and re-weld in the right position...

On another note, if they are off a just a little, there has been some moderate success in bending the end of the gear by sliding a 4 to 6 foot long heavy tube over the axle stub and using brute force.... You have to be careful though because if you go too far you risk bending the streamline tube or putting stress elsewhere on the leg and therefore weakening the structure...

Brian

Rosebud tip on the torch will help with the bending.
DENNY

DENNY wrote:.. Caster, Camber, and toe are three different angles. ..........

I thought caster & toe-in/out are the same thing. If not, then just what is caster?

Caster only exists on steerable wheels. It is the angle the wheel pivots about in relation to the vertical plane. To easier visualize this imagine the front triple trees of a typical road bike (almost vertical) vs those on easy riders chopper

When it was popular to lower the front of VW's, they would tend to get squirrelly... the cure was to put shims between the bottom tubes of the front beam, and the bulkhead they bolted to, to rotate that angle back to where it was.

Take care, Rob

A guy who hit a hand line in his field flew his PA12 in to get worked on while my plane was getting annualed. The gear leg was taken off, and the mechanic clamped a couple of flanges right to his welding table. He taped a laser pointer to the axle, and we bent the leg back to where he had measured it to need to be. The guy only had about 3 hours or so billed.

Maybe this will help folks visualize the difference.

My Maule was done at 0.25* toe in...for what that's worth...

hotrod
The other guys explained caster better than I could. Old guys called it the kingpin angle because all the old straight axles had kingpins. It is basically what makes you front wheels want to return to center as you come out of a turn. You can use caster angle when you align your car to keep it from pulling to the left due to road crown, or correct for the 350lb driver. Your tailwheel being steerable has a caster angle that if not correct will cause shimmy. Gilbert Pierce of Pierce Aero did a great article on it. I am not good at linking threads just do a search with tailwheel shimmy and it will show up.
DENNY

I would say set it at zero, since this is more or less guaranteed to not impart any other forces or bending loads on anything.

Toe-IN will tend to add some stability to an otherwise unstable (taildragger) configuration. But toe-in can also try to pull the landing gear in and fold it inward under the airplane when side-loaded or when you have a wingtip try to come up. This of course would worsen a groundloop.

Toe-OUT creates more instability, immediately trying to over-steer the airplane. However, toe-out also can delay that "pulling inward and folding the gear under the airplane" when side loaded or when a wingtip tries to come up. So I've been told Toe-out can save a groundloop from happening in some circumstances.

The more educated people I've spoken to say zero or a very SMALL amount of toe-OUT.

I would be conservative, since the Pacer is noted for being a little bit quirrely, and say that zero is the safest and most common-sense bet.

I assume Maule gear is adjusted the same way as a Pacer; a big cheater bar?

whee wrote:I assume Maule gear is adjusted the same way as a Pacer; a big cheater bar?

Pretty much...

On a pacer, you NEVER want to set it with toe-out.... Always with at least 3/16 toe-in...

We have covered 25 pacers over the years and have always set the gear with toe-in before welding on the front gear fittings.... The rear gear fitting is what was the front gear fitting for the tri-cycle gear..

Brian

He bought the airplane with the t/w conversion already done. The gear legs were goofy, he sent them off to someone who claimed to have a jig and could "overhaul" them-- when they came back, they wouldn't even bolt onto the airplane. He ended up buying new Univair legs which bolted on just fine, but now he has a bunch of toe-in. He's closing in on completion and wants to correct that before flying it.