My RV-8 landing gear box mod

AX-O · #1 03-02-2008, 10:41 PM

I spent about 1.5 hrs designing the cover plates and about 8.5 hrs installing the mod. This is the entry from kitlog. I hope it helps someone out there.

Today was a very long day. As always building takes much longer than you expect/plan. After figuring out how I wanted to do the gearbox mod, it was time to start building. My design has twenty K1100-08 nutplates. Basically the cover plate is 3/4 of an inch wider than the opening. The center of the nutplates is approximately 9/32 inch from the edge of the hole. I wanted to go further away but could not due to the aluminum angles behind F802C (after seeing the end result, I would not go more than 11/32 from the edge). The 14 vertical nutplates are 1 and 3/32 inch away from center to center. The #40 holes (that hold the nutplates) were machine countersunk. The #19 holes were dimpled using the pneumatic squeezer. AN426AD3-3.5 rivets were used to rivet the nutplates and AN509 8R8 screws were used to secure the cover plate. I am very happy with the result. I hope the mod was worth the approximately 10 hrs of work.

Adam · #2 03-03-2008, 04:40 AM

Very nice!, if I did it again I would have done exactly what you designed.

DanH · #3 03-03-2008, 08:26 AM

Axel,
It is definitely worth the work, as you shall see in due course. Nice job!

Bubblehead · #4 03-03-2008, 10:21 AM

I like it a lot except considering all you're replacing is the little piece between the holes, I think you may have overdone it screws! Several people have just left the long slot open too without problems. I believe that the piece is in tension in a hard landing so buckling in that area is not a concern.

You could probably eliminate 1/2 the fasteners and be fine.

I did not do any stress analysis on this but am a ME with a Professional Engineers license and have 25 years of experience.

One other suggestion. When you get these mounted and the landing gear bolts in place, make sure that a socket can get onto the nuts so you can check torque on the bolts at condition inspection time. The other little screws, bolts, nuts and things in the area interfere with tools, as does the ridge that goes past the nut just inboard of the bolts. I don't have my preview plans here or I'd give you the part numbers.

Several of us have modified 3/8" drive sockets to fit, and it's easier to do that when you're building the plane than at the first condition inspection. I've also thought about replacing the stock bolts with slightly longer bolts with a hardened steel spacer under the nuts to raise the nut up so an open end wrench would fit on it.

Here's a post with some information and pictures of the socket I use. http://www.vansairforce.com/communit...t=22602&page=2 I use a piece of quare stock in the socket along with an open end wrench but someone else told me he used a 3/8" drive universal and an extension. That might even be easier.

BuckWynd · #5 03-03-2008, 10:36 AM

Quote:

Originally Posted by Bubblehead

I think you may have overdone it screws! Several people have just left the long slot open too without problems. I believe that the piece is in tension in a hard landing so buckling in that area is not a concern.

You could probably eliminate 1/2 the fasteners and be fine.

I think Axel probably read this thread from a year ago, where the consensus seemed to be that there should be approximately 20 screws in this plate, based on an admittedly "quick and dirty" engineering analysis of the tension and shear loads in the gear tower.

vansrv8 · #6 03-03-2008, 11:26 AM

I should have done it..to late now

I assume your gonna bring your brake line out of the top hole now?

AX-O · #7 03-03-2008, 12:04 PM

Quote:

Originally Posted by BuckWynd

I think Axel probably read this thread from a year ago, where the consensus seemed to be that there should be approximately 20 screws in this plate, based on an admittedly "quick and dirty" engineering analysis of the tension and shear loads in the gear tower.

I did. It was the only information that I could find. I just matched the number of rivets on the side to the number of nutplates. The other 3 nutplates above and below, I spaced for consistency.

AX-O · #8 03-03-2008, 12:09 PM

Quote:

Originally Posted by vansrv8

I should have done it..to late now

I assume your gonna bring your brake line out of the top hole now?

I will have to look into that. My Groves air foil landing gear should be home soon. I don't know how all that interfaces yet.

RV8RIVETER · #9 03-03-2008, 02:31 PM

Quote:

Originally Posted by vansrv8

I should have done it..to late now

I assume your gonna bring your brake line out of the top hole now?

May not be. I just did mine, had an unbelievably hard time getting gear bolts attached, so I took out the "ziz wheel" and cut that dividing web just as AXO. I did not put as many screws in, 4 arc'd on top and bottom plus 3 spaced down the middle of each side, but it was pretty easy to get my sqeezers in there. Instead of a backing ring I made 2 arcs out of 0.40 and and 2 long thin ones for the sides. I bought a piece of cheap plexi at Home Depot for the canopy skirt and had plenty left over to make "cover plates". Just shape, drill and cleco to box, then use it as a template to make the aluminum plate. It did not take very long, though would have been alot easier earlier.

As for the brake line I already had it configured for the middle hole, so I made a circular notch in the cover plate for it.

Bubblehead · #10 03-03-2008, 03:04 PM

I really think this many screws is overkill. We have removed a little piece of aluminum and replace it with a big piece of aluminum with a bunch of screws, and people are wondering if they have enough screws? This is not a weak spot on the airplane! See Kahuna's post on the other thread.

In reality I think we could just make a small plate the same size and shape as the removed part and screw it in place with 3 screws on each side. Even a rectangular plate across the same area as the removed portion would suffice. I can't prove it without doing the numbers and I don't have time to do that, but many things in engineering can be done through reason and common sense. Look at the size, shape, stiffness and resistance to buckling of the removed piece. Then look at the replacement.

That aside, the great thing about home builts is we can do it however we want to! I'm happy for AX-O that he did a high-quality mod and is building the plane he wants. Better to err on the side on caution! His wormanship looks great, and the important thing is he's comfortable with it! He knows he can fly with confidence in this modification. More power to him!

BTW - my -8 still has the original holes. If I ever have to do a lot of work in there maybe I'll modify the towers, but the only time I go in there is to check the torque on the landing gear bolts, and I've got that down to a 10 minute job once the front seat back is out. If I was building this now I would modify it.

John D. BSME, PE