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Copyright 2008 by
Randy Pflanzer
Technology Professionals Consortium
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    Wheel Pants

Wheel Pants

     

At first, I had the engine mount and the gear mounted to the fuselage, per the plans.  I quickly decided that mounting the pants and fairings in this manner was NOT the optimal way of doing things.  Since my work table was not sturdy enough for the weight of the mount and gear, I fabricated a quick table and mounted it to a metal table stand from my band saw.  I used a couple of bricks to balance things out.  By adjusting the legs, I was able to level the mount front to back and side to side.

I really think this is a better way to get not only the wheel pants, but more importantly, the gear leg fairings mounted so that they are in-trail with the center line of the airplane.  This is a very important alignment.  You will have a lot of induced drag with the gear hanging out in the wind.  If you want the optimum airspeed that your engine can deliver, you HAVE TO HAVE the gear leg fairings in perfect trail.  That is very difficult to do with the approach outlined in the plans.  The wheel pants aren't too bad, but the gear leg fairings are very difficult to get right.  With the process outlined on this and the following pages, all I'll need to do is use some plumb bobs to get the mounting accurate.  Of course, this approach assumes that the firewall is square with the centerline of the airplane.

     

First step is to sand the overlap joint to get a good, straight mating surface.  Take some time to do a good job here because it will be very noticeable when the pants are painted.  Next, I drilled some attach holes to hold the two parts together.  I started at the top center of the joint and used 3 spacing around the outside.  I skipped the second hole from the bottom because this is generally where the attachment is to the axle nut.  On the inside, I just drilled one hole at the top and one at the bottom and left the rest of them off.  This is the area where the gear leg fairing will attach and I didnt want to put a hole where Id be unable to get a screwdriver.  I can add additional attach holes here later, after the fairing is added.

     

The challenge with the wheel pants is that they have to be aligned in five different planes.  The key that Ive found is to secure the pants in one plane at a time and then build on that in subsequent steps.  The first step is to get the proper forward/aft position of the wheel pants on the tire.  I taped a 1 spacer to the top of the tire.  Then holding the forward part of the pant on the tire, I marked the edges of the cut out for the gear leg. 

      

Over on the table, I set the forward edge of the cut out at 3 from the aft edge and cut out the opening for the gear leg.  I then trimmed the top and outside edge of the tire opening until 1) the outside of the wheel pant would rest against the axle mounting nut and 2) the wheel pant attach bracket fit inside the wheel pant by about to 1.  This is your key measurement to get the right fore and aft distance. 

When trimming the tire opening in the wheel pants, remember a couple of points.  One, dont trim anything off the inside edge because the wheel pant is offset to the inside by almost and youll have too much room on the inside the way it is.  Second, dont worry about doing the final cuts until you have the wheel pants bolted in their final position.  Just cut enough of the pant away to get the desired fit and leave the final cuts until later.

        

Next, I set the correct camber of the wheel pant so that it matched the tire.  To do this, I fit the aft section of the pant to the tire.  I trimmed just enough of the flange so that the aft section would mate with the forward section.  I also trimmed the outside and bottom edges of the tire opening until the outside edge of the pant rested against the axle mounting nut.  By looking down at the aft section without the forward section in place, you can see the right amount of camber, or tilt, to give the pants.  To set this, I had to bend the inside mounting brackets in, towards the tire, to give me enough clearance to get the pant on.  For me, the brackets stand out away from the tire way too much.  I put two marks on the edge of the wood spacer taped to the tire and two corresponding marks on the flange.  This allows me to align the pants in the right camber when the two halves are together.  Also, this effectively sets the proper outside/inside shifting of the wheel pant on the tire because the outside surface is resting on the axle mounting nut.  You should notice that the centerline of the wheel pant is offset towards the inside by anywhere from 5/8 to .  This should provide adequate clearance inside the pant for the brake caliper.

     

I then assembled the two halves around the tire.  I supported the wheel pants with wood spacers on the floor so that the pants would stand in the right fore/aft position without me holding them.  Next, I set the proper fore and aft tilt of the wheel pants.  I dropped a plumb off the bottom of the tire and measured back 7 .  I put marks on the floor so I could re-check this measurement during the next step.

     

The final step, and the most important, is to set the pant so that it is in-trail with the centerline of the airplane.  First, I dropped two plump lines, one alongside the wheel pant, and measured over to the centerline of the wheel pant at both the top and bottom of the pant.  I also dropped a plump line off of the tire so I could verify the tilt of the pant.  If everything lines up okay, check the location of the inside mounting flanges.  Keep bending these parts until the flanges rest against the inside of the wheel pants and make contact at the top and bottom of the flange.  This took me a half-dozen times before I got the right fit.  Take your time and get this right otherwise your mounting screws will bow the wheel pants when they are mounted, a fact that will become painfully evident when you paint your parts.  Once the fit of the bracket was perfect, I marked and drilled pilot holes for all five of the mounting screws/bolts.  I disassembled the pants, drilled the holes to their final size, and remounted the pants to recheck again.

     

With the pant mounted, I took my Dremel tool and cut the tire opening to the final size.  Since the pant is offset over the tire, the opening will not be symmetrical.  That's no big deal because it is on the bottom and the only people who will see this are the surprised RV pilots as they look up to see you zoom past them by about 20 kts, and they'll be busy cleaning out their trousers.  After fitting the lower gear fairing, I mounted the plate nuts to the fairings using aluminum strips as backing.  The wheel pants see a lot of wear and tear so I don't want the holes wallowing out.

     

I also glassed a three ply layer of cloth over the main attach holes.  This will provide some additional mounting strength. Once the cloth dries, I'll drill out the holes.  I also glassed in the rear inside panel to the pants.

Next are the gear leg stiffeners and gear leg fairings.  That work starts on the next page.

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