What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Wheel pants - fiberglass repair question

MacCool

Well Known Member
I'm fixing up my wheel pants (as addressed in this thread). I have some stress cracks at the mounting screw holes, which I'm reinforcing with carbon fiber on the inside and a couple layers of fiberglass on the outside.

My question is about the rear main gear fairing on both sides. The rear-most part that fits over the gear leg fairings is cracked, apparently for years. Likely due to too tight a fit with resultant jostling and vibration. My plan is not to close the two cracks...rather to just leave the cracks as they are, being afraid that they're too tight and maybe just leave them relieved.

How should I do that? The options I've been considering include just filling the whole crack with some epoxy/flox (or some JB Weld), or sanding down the gelcoat around the crack, filling the crack, and then reinforcing with a fiberglass overlay. TIA for advice.

.
 

Attachments

  • IMG_0131.jpg
    IMG_0131.jpg
    159.6 KB · Views: 299
  • IMG_0132.jpg
    IMG_0132.jpg
    140.8 KB · Views: 274
It looks like this area did not have enough surface between the two parts to bond to each other well and due to flexing it separated.

Does it fit well over the gear leg fairing or is it rather tight? It is recommended to put a few layer of tape (7-8 wraps) on the gear leg and fit it into the intersection fairing which then it creates the desired space between the gear leg and intersection fairing. Then bond them together with flox or more fiberglass. The result should have enough space that you may put one layer of UHMW tape on the gear leg fairing so it can move rather easily and not break the intersection fairing.

good luck.
 
These fairings move a disturbing amount when touching down, taxiing with any shimmy, turf runways, etc. Lots of clearance needed. Perhaps put them back on, but put some duct tape or similar over the crack, but leave 1/2" or so extra behind the crack (stick something on the sticky side here so that the flap doesn't simply adhere to itself). See if it tears - one might learn how much movement there routinely is, then leave some margin (if you choose to do anything at all, which isn't a bad plan).
 
These fairings move a disturbing amount when touching down, taxiing with any shimmy, turf runways, etc. Lots of clearance needed. Perhaps put them back on, but put some duct tape or similar over the crack, but leave 1/2" or so extra behind the crack (stick something on the sticky side here so that the flap doesn't simply adhere to itself). See if it tears - one might learn how much movement there routinely is, then leave some margin (if you choose to do anything at all, which isn't a bad plan).

Well...that's a fair point. They aren't structural...don't play a role in supporting the wheel pants.
 
I see three areas that could be fixed if you want to eliminate these cracks from re-appearing after you have fixed them - two of which you mentioned.
Putting carbon fiber in an area that is already cracked without addressing the reason for the crack will only move the stress failure to another place, possibly, because carbon fiber is stronger than fiberglass. The largest crack, at the trailing edge of both lower aft intersection fairings is because the initial installation was so tight it didn’t allow for any for/aft movement of the landing gear and the attached leg fairing. There should be enough wiggle room at the aft edge of the leg fairing to allow some flex without putting a load on the closed, immovable intersection fairing. Your intersection fairings look a little longer than most I have seen or built, which gives the leg fairing more ‘purchase’ on the lower intersection fairing and therefore more leverage to impart a force to cause a crack. To fix this you’ll need to sand out the uneven trailing edge areas of the cracks both inside and outside to clean it up and make ready for a fiberglass layup that will correct all this. You could also shorten the length of the intersection fairing if you want to and your leg fairing is long enough, but keep in mind, you may also need to repaint that leg fairing also if this is done. Of course, you will need to repaint the wheel pants when you are done with all of this, and the other two fixes. How do you do this? Make yourself an in place mold that will give you an increased gap at the aft edge of the intersection fairing after you have sanded the cracked areas aggressively and opened up he area to be re-glassed. Next put layers of epoxy wetted fiberglass over the gear leg fairing/mold, and epoxy it to the inside of the cracked intersection fairing. Here’s how I would do it: cut a couple pieces of thin aluminum to go over the gear leg fairing at the bottom, simulating where the intersection should lie in formation with it. This thin aluminum should be covered with heavy duty 3M packing tape - taped to the leg fairing, and then coated with carnoba car wax to prevent the epoxy soaked cloth from adhering to it. The wax is overkill, but ensures an easily removable mold. Make the aluminum mold wide enough at the aft edge to allow gear leg fairing aft edge fore and aft movement without impinging a load on the fixed lower intersection fairing. This little gap that you’ve created can (and should) be very thin, because the aft edge of the leg fairing is thin, and it will be barley noticeable, even to the trained eye. Then lay 3 or 4 layers of epoxy soaked fiberglass cloth over the waxed aluminum mold and attach the sanded, cleaned and now opened up wheel pant/intersection fairing on top of this wetted fiberglass leg leg firing. The wetted fiberglass will stick to the intersection fairing and not the gear leg fairing. You could also lay a layer or two to the outside of this intersection to give it a little more ‘meat’ and to close up any gap that may be visible from the original crack. If it ends up too thick, just get out your sander/grinder/sandpaper, and sand down on the outside to make it look like what you want. Writing all this down took me longer than it it would take to actually do this, and if you don’t like what you see, grind it back down and try again. Fiberglass, that none of us like to work with, is the most versatile and forgiving material that we work with on our riveted metal airplanes.

As far as the other two issues I mentioned before - the stress craters around the attach hole screws, and if you are working on this anyway, the stress cracks that appear to be coming from, possibly, your brake caliper impinging on the wheel pant surfaces because of zero clearance on the inside. You were right about adding a reinforcement layer or two to the inside of this screw attach area. Doesn’t need to be carbon fiber to work, but use what you want. The only thing you need to do to the outside of these areas is sand them down on the outside and fill the cracks with an epoxy based filler before doing the aforementioned painting of the wheel pant. Why only reinforce the area on the inside? Because you are trying to take out any preload on the area around the fastener. Get a bright light and place it so that the light from it hits the area around the wheel pant fasteners at a sharp angle. Then tighten down the fastener. If the reflected light shows any kind of deflection around the screw/fastener hole while tightening, you are putting a pre-load on that piece right at that point and will eventually crack, or show stress cracks, whether fiberglass, epoxy filler, polyester fillers (for sure), or plexiglass. Build up these areas from th back side to prevent this pre-load, and you eliminate future cracks.

As far as the stress like craters in your pictures on the lower part of the wheel pant - again, the wheel pant is hugging the landing gear assembly a little to tight, and possibly the brake caliper is causing that stress crack area - looks like it is.
Cut out the area in a small circle in the cracked area that coincides with the corner of your brake caliper. Make a rounded bubble out of that easily sandible green foam you get at a flower shop. Tape in place on the offending wheel pant-hole area, and lay 2 layers of 9oz clothe over this bubble. After cure - dig out the foam from the inside, clean it up with sand paper, etc, and lay another layer or two on the inside.

That’s what I would do anyway if it was mine. Doesn’t take that long, or cost much either, and the fixes should be permanent.
 
Stress cracks

The stress cracks around the two attach holes are likely caused by the wheel pant not contacting the bracket evenly. Place some packaging tape or plastic tape over the bracket for a mold release. Mix a bit of resin and cotton flox to a "peanut butter" consistency. Apply the mix in a small area around the holes. install the screws but do not overtighten. As soon as the resin remaining in the cup starts to harden remove the screws. After the resin completely cures grind the edges of the filler you have created so it transitions evenly to the inside of the wheel pant. One layer of cloth over the inside is optional.
 
The stress cracks around the two attach holes are likely caused by the wheel pant not contacting the bracket evenly. Place some packaging tape or plastic tape over the bracket for a mold release. Mix a bit of resin and cotton flox to a "peanut butter" consistency. Apply the mix in a small area around the holes. install the screws but do not overtighten. As soon as the resin remaining in the cup starts to harden remove the screws. After the resin completely cures grind the edges of the filler you have created so it transitions evenly to the inside of the wheel pant. One layer of cloth over the inside is optional.

Great idea, thanks.
 
These fairings move a disturbing amount when touching down, taxiing with any shimmy, turf runways, etc. Lots of clearance needed. Perhaps put them back on, but put some duct tape or similar over the crack, but leave 1/2" or so extra behind the crack (stick something on the sticky side here so that the flap doesn't simply adhere to itself). See if it tears - one might learn how much movement there routinely is, then leave some margin (if you choose to do anything at all, which isn't a bad plan).

Alex...I blame the pancake breakfast at Henning last year for running roughshod on these wheel pants.:)
 
Yes - what Jim said above for the stress cracks. That’s what I meant needs to be done in my long diatribe, but reading it confuses even me. It was 1 am and I kept nodding off.
 
I would use only glass on the inside of the pants as it will be clamped to aluminium and carbon will set up an electrolytic cell - carbon won't increase the strength to any degree. For the fairing, cloth will stop it splitting and also trimming the length down so there is not such a moment splitting it open. Wrap the gear leg in packing tape - as a release film. Scuff up the pant heavily where it is split and apply several layers of cloth. It may require a couple of pieces of wood clamped to the outside (covered in packing tape) to hold it all together. Sand the wood to an appropriate profile if required.
 
Tinnerman's

On my second 7 I used Skybolt fasteners on the wheel pants so no issues there. What I recommend is burying Tinnerman washers into the glass and then glassing over them. This way the fastener is being fastened into metal with a much wider area.

I did this on the tail fairing and the top row of fasteners for my plenum. The tail fairing only has 6 screws per side so doing the mod was easy.

You can easily do this on the wheel pants too. Regarding the crack, looks like fit was probably a little tight. To do it right you'll have to put another couple of layers around the piiece that is cracked to build up the whole piece.After that is done, you'll have to relieve the inside to provide some room for the fit.

Unfortunately, you'll have to resign yourself to the likely fact that the pants will have to be redone.

Let me know if you'd like specific info on how to bury the tinnermans.
 
Thanks for the tip. I ordered some of this style of Tinnerman washers to try as an alternative. Any experience with them? They seem to have been pretty well-received based on old posts I've seen around here.

https://www.aircraftspruce.com/catalog/hapages/g8washers.php



Yeah, they'll be redone. After I'm done re-glassing the areas I've sanded down, I'll fill everything with some microballoon/epoxy and then take them into the body shop for re-paint with Imron. The guy guessed $400 - $600 depending on how much prep work I leave him with. I hate fiberglass work...so every day that goes by, it looks like he'll be doing more and more prep work.
.
 

Attachments

  • Screen Shot 2022-05-30 at 12.49.33 PM.png
    Screen Shot 2022-05-30 at 12.49.33 PM.png
    1.3 MB · Views: 79
Last edited:
Unfortunately, you'll have to resign yourself to the likely fact that the pants will have to be redone.

Yeah, I planned from the beginning that I'd have to refinish them. After I'm done re-glassing the areas I've sanded down, I'll fill everything with some microballoon/epoxy and then take them into the body shop for re-paint with Imron. The guy guessed $400 - $600 depending on how much prep work I left him with. I hate fiberglass work...so every day that goes by, it looks like he'll be doing more and more of the paint prep work.
 
Thanks for the tip. I ordered some of this style of Tinnerman washers to try as an alternative. Any experience with them? They seem to have been pretty well-received based on old posts I've seen around here.

https://www.aircraftspruce.com/catalog/hapages/g8washers.php



Yeah, they'll be redone. After I'm done re-glassing the areas I've sanded down, I'll fill everything with some microballoon/epoxy and then take them into the body shop for re-paint with Imron. The guy guessed $400 - $600 depending on how much prep work I leave him with. I hate fiberglass work...so every day that goes by, it looks like he'll be doing more and more prep work.
.

Call if you have any questions. 480-204-0662.
 
On my -4 (similar)

I don't have a -9, but the scenario may be similar as my RV-4. I found on my -4 that when I built it, I had trimmed the gear leg fairing at the fuselage end to what seemed reasonably good clearance from the fuselage skin. The geometry of the leg fairing is such that it floats freely in the wheel pant fairing (yours appear fairly long) and the upper part of the leg fairing is secured by tabs that have a band clap around them preventing them from slipping downward. The upper fuselage intersection fairing is removable, and the leg fairing can float in at also. However, FOR/AFT movement of the tapered gear rods on grass and "hard " landings, so as the gear leg fairings were contacting the fuselage skin forcing the faring downward into the wheel pant fairing, thus casing the cracks. I trimmed my upper ends of the leg fairings so they are just barely covered by the intersection fairings, especially on the AFT side. Now they stay put, and all is good. This may be what is causing your cracks to form.
 
Back
Top