Wheel Pant Alignment

OK, I am almost afraid to ask this, becasue I bet there are going to be a whole lot of different ideas...but here goes!

I am installing my wheel pants (-8), and using the method in the Orndorf videas. Basically, this has the airplane on its gear, with the tail on a stand to level the longerons, a centerline established underneath, and the pants aligned to the centerline (laterally), and level fore and aft based on the height of the tail and the nose (of the pant). I did this, and eveything is parallel and level to a 16th of an inch.

According to Van's instructions, you do this with the aircraft on jacks, with the wheels just touching the floor. Same idea to level fore and aft, and make them parallel. They also tell you to align the pants with the center tread line on the tire. Makes sense.

When I aligned my gear legs, the axles were parallel to as close as I can measure - unloaded of course (sticking straight up in the air). Of course, with the weight on the gear, they sweep up, and as a result, are toed in.

Because the Orndorf method has the gear legs compressed, this means that the wheels are not parallel, and if the pants are, then they don't align with the wheel tread!

So.....do I want to jack things up (per Van's instructions) and get the pants parallel to each other as well as the wheels? Have the Orndorf's taken a shortcut that doesn't work (please, no flame intended, I'm learning!)? Any suggestions?

Now I see why so many people leave the pants off at first....another jigsaw puzzle...

Paul Dye

When I aligned my gear legs, the axles were parallel to as close as I can measure - unloaded of course (sticking straight up in the air). Of course, with the weight on the gear, they sweep up, and as a result, are toed in.

Click to expand...

Something doesn't sound right here. The -8 gear legs are different from the other RVs. The toe-in/out shouldn't be affected by whether the weight is on the gear.

With the weight off the gear, the bottom of the wheel will be closer to the centerline than the top (camber), but the distance of the front and back of the wheel from the centerline (toe) should stay the same. This is why it shouldn't really matter whether the weight is on the gear or not for an -8.

All the other RVs are different though...

James Freeman

Thanks for the reply James.

I agree that it doesn't seem to make a lot of sense, but maybe rotating from tail on the ground to level flight contributes to an illusion. Camber rotates into another plain or something....it is not a major effect, but seems noticeable.


After writing my first post, I went back to work, and jacked the plane up to take the load off. I checked the axle alignment, and they are right on. Reassembling, the gear and pants came closer into alignment. After takigng them all apart once more, then reassembling with the noses back on, I got the pants nice and parallel (same distance now to nose and tail to tail). Didn't get a chance to measure relative to the fuselage - the mosquitoes chased me out of the garage, and I'll have to do that tomorrow.

The bottomline is that after thinking about it, I want the pants parallel, in alignemnt with the aircraft centerline, and level with the longerons - with the gear in "flight" alignment (unloaded) - right? That will be minimum drag in flight...


Paul Dye

Jacking the plane up and taking the weight off of the gear has more to do with installing the gear leg fairings, than it does with installing the wheel pants. The wheel pants can be installed with the plane leveled or not and actually my opinion is that you should at least check the wheel pants with the tail on the ground to make sure you have adequate ground clearance, since that is the atitude you will be at on the ground. Of course the wheel pants need to be parallel to the line of flight, and in line with the tire itself, but as you said earlier, on the -8, this isn't a problem with the weight on the gear.
In building two RVs, I have learned to try not to make somthing more difficult than it really is. Good luck!

FInished with alignment!

Thanks for the response ...

I finished up the alignment and mounting tonight, and you're right - if you keep it simple, it isn't really hard. I elected to make sure they lined up with the airstream in flight, and were parallel to each other - and also checked the tail clearance in three-point attitude as you mentioned (I'd seen that on someone else's website as well...)

Now it's time for more pinhole filling, sanding, and priming - what fun!

Paul

Wheel Alignment

OK, I searrched and found this link referencing wheel alignment, but didn't go quite far enough for my own little dilema...so here goes

Paul, I am getting ready to install my pants two weeks ago. In checking the tire alignment, I found a good source for gouge on the Grove gear site when trying to figure exactly how much toe you might have, and the required shims to accomplish the correction. After applying this procedure, I found that I have 1 degree toe out on each tire (weight off wheels), but with the aircraft in a three point, the toe is perfect.

This was referenced, but I never saw a fix. Will shims help? Or should I choose one over the other. Any ideas would be nice, Thanks

Flies, Lands, and Taxis Geat!

Boy, this is an old thread! After 170 hours of flying, and several hundred landings, all I can report is that doing things the way I did, the airplane has no bad handling characteristics (that I can tell), and the speeds are right up to what Van says they should be. That tells me that both the wheel alignment and the pant alignment worked out - at least for me!

Paul

repeat

Paul, In reading your earlier thread, it sounded like you had the same problem that I have encountered. The toe seems to be changing with the transition from three point to weight off wheels. Did you have the same problem and how did you fix???

Thanks

It doesn't sound like you even have a problem, to me. As long as your gear is aligned on the ground, you should be good to go since proper toe in or out is a setting you need to reduce tire wear. In flight this isn't a problem, as long as the wheel pants are in line with the air stream. (Everything with in reason, of course.) If you get wear on the tires, you can shim the axles later, but based on what you have said, if they really are aligned on the ground there should be no need for this. Make sure you roll the plane around on the ground before all of your measurements so the gear legs get to their normal position when the plane is at rest. If you just let the plane down off of the jacks, or a hoist, the legs will not be at their normal ground position until the plane is moved around some.

Hwood said:

Paul, In reading your earlier thread, it sounded like you had the same problem that I have encountered. The toe seems to be changing with the transition from three point to weight off wheels. Did you have the same problem and how did you fix???

Thanks

Click to expand...

Basically, my gear is all aligned per Van's instrucitons. Everything is parallel with the weight off the wheels, including the pants. I started down the path of trying to figure out camber and caster and toe-in, and it made my head hurt, so I kept it really simple and built it per plans - worked great!

Paul

Hwood said:

Paul, In reading your earlier thread, it sounded like you had the same problem that I have encountered. The toe seems to be changing with the transition from three point to weight off wheels. Did you have the same problem and how did you fix???

Click to expand...

Hwood,

I agree that this issue of toe in/out on the -8 isn't discussed much. I was puzzled when I first set mine because the plans say to set it to 0 with the fuse level but while double-checking it, I found, as you have, that it changes significantly towards a toe-in setting when transitioning to three-point attitude. This is because of the significant camber of the gear (which incidentally might be worse with the stiffer Grove gear).

I was worried about this because I had heard that toe-in was an unstable arrangement and I didn't know how the airplane would behave with my gear set per the plans. As it turned out, I wasn't happy with how my plane handled on the ground in the three-point attitude at landing speeds. It wasn't a huge issue because I quickly realized, as most others have, that the the -8 likes to be wheel landed and you usually hold the tail off until the speed is bled off significantly. However, it still bothered me, so at my first condition inspection, I shimmed my axles out half a degree each. It might be my imagination, or the benefit of a year's experience, but it seems to handle somewhat better with the new arrangement. There are lots of other variables in this ground handling equation, like what type of tailwheel steering mechanism one is using, so don't take this as gospel, but I think it makes sense to have the gear set slightly toe-out in the level attitude so that it will be neutral, or close to it, in the three-point attitude.