AX-O

AX-O

Well Known Member
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.

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Axel,
It is definitely worth the work, as you shall see in due course. Nice job!
 
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/community/showthread.php?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.
 
Bubblehead said:
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.
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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.
 
Looks good..

I should have done it..to late now:) I assume your gonna bring your brake line out of the top hole now?
 
BuckWynd said:
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.
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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.
 
vansrv8 said:
I should have done it..to late now:) I assume your gonna bring your brake line out of the top hole now?
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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.
 
vansrv8 said:
I should have done it..to late now:) I assume your gonna bring your brake line out of the top hole now?
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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.
 
This ain't rocket surgery!

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
 
Perfect!

Axel,
Your timing is perfect! I'm right behind you with my RV8 with the -1 fuselage kit. Thanks for the great writeup and details. Also, your craftsmanship looks excellent!

Cheers
 
Thanks for all the compliments guys. BTW, I have the template that I used to make the cover plates. It is on a regular sheet of paper. If anyone is interested I can mail you a copy.
 
Is anyone doing calculations to return the metal part back to it's true strenth
or are all the mods just winging it hoping for the best.. Let's see the data if anyone has done it.:

Thanks
 
RV505 said:
I see you cut a hole in your gear tower for scat hose ..Did you modify it to return it back to it's original strenth on the insde with a doubler?
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No. I definatley did not do that. There was no need to return it to its original strength. That box is huge overkill for the loads is transferring.

BTW, That scat tube is for the rear heat.
If your nervous about that, you dont want to see the method for getting it through the spar.
http://mstewart.net/super8/rearheat/index.htm

Best
 
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Kahuna said:
No. I definatley did not do that. There was no need to return it to its original strength. That box is huge overkill for the loads is transferring.

BTW, That scat tube is for the rear heat.
If your nervous about that, you dont want to see the method for getting it through the spar.
http://mstewart.net/super8/rearheat/index.htm

Best
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Are you saying the only engiering you did was "experimental and flight testing will determine if the wings will rip off or not."?
 
RV505 said:
Are you saying the only engiering you did was "experimental and flight testing will determine if the wings will rip off or not."?
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No, what im saying is I looked at it, cut the hole, went flying.

I have many holes in my plane that were implemented in this fashion.
 
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That's what you said. You Cut a hole and went flying with no enginering involved but it's ok because the wings didn't fall off.. Thanks for the info! I'll copy this for my notes Thanks
 
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RV505 said:
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That's what is said. You Cut a hole and went flying with no enginering involved but it's ok because the wings didn't fall off.. Thanks for the info! I'll copy this for my notes Thanks
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Geez, Kahuna. Better not tell him what you hung on the firewall!
 
RV505 said:
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That's what you said. You Cut a hole and went flying with no enginering involved but it's ok because the wings didn't fall off.. Thanks for the info! I'll copy this for my notes Thanks
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RV505,
I don't want this to get out of hands. I posted my work in case someone else that wanted to use the information/mod could evaluate it for their own project/use. Also to archive the info. Ultimately the person(s) building the aircraft have to be happy with the work that has been completed. If you don't feel comfortable doing some of the mods posted on this forum, you have the choice of not using them. But please don't make judgment on what people did in that manner. In advance thank you for respecting my post and keeping the information pertinent to the gear mod topic.
 
Sorry if you took it that way.. I think the spirit modification is good and I would consider modification of my own gear tower However I think it is reasonable to request if anyone did any enginering calculations to ensure the metal was brought back to it's original strenth. If not, did vans have any input to the gear tower modifcation? It would be nice to compare notes and calculations. I belive it is responsible to obtain all pertinet information to make a educated decsion before a modification would go forward. Kahuna told me and showed me how he did it.. I wasn't passing judgement, just asking.
 
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As Paul Simon once said "...But I'll repeat myself, at the risk of being crude..."

Let's just use a little common sense. If you take out a little piece and very completely attach a bigger piece, you are probably all right. If not, your device was marginal to begin with!

If you take a big piece out and replace it with a small piece, you should be more cautious and thorough. If you take the small part out all together you should be very cautious. From reading about Kahuna's landing technique on the other thread I would say it all worked out fine. He may not have done the analysis, but he sure has tested it!

Since Kahuna's removal of the little piece has not brought trouble, I would say AX-O's modification is more than sufficient.

By the way, people are talking about "strength" in this post. Designs are not always designed just for strength. Sometimes it could be buckling, or deflection, or fatigue limits...

In my "day job," strength is rarely the issue because we deal with big loads and lots of cycles so fatigue (and wear) considerations usually rule the day. A few of our other products need stiffness because of customer perceptions of quality = stiffness. In a previous life in an aluminum structure environment fatigue and deflection were the important criteria.

Hopefully I got this enough off topic to put this one to rest!
 
Let's just use a little common sense. If you take out a little piece and very completely attach a bigger piece, you are probably all right. If not, your device was marginal to begin with!



If you take a big piece out and replace it with a small piece, you should be more cautious and thorough. If you take the small part out all together you should be very cautious. From reading about Kahuna's landing technique on the other thread I would say it all worked out fine. He may not have done the analysis, but he sure has tested it!

Since Kahuna's removal of the little piece has not brought trouble, I would say AX-O's modification is more than sufficient.

By the way, people are talking about "strength" in this post. Designs are not always designed just for strength. Sometimes it could be buckling, or deflection, or fatigue limits...

In my "day job," strength is rarely the issue because we deal with big loads and lots of cycles so fatigue (and wear) considerations usually rule the day. A few of our other products need stiffness because of customer perceptions of quality = stiffness. In a previous life in an aluminum structure environment fatigue and deflection were the important criteria.

Hopefully I got this enough off topic to put this one to rest![/QUOTE]

Ok, I'm also an BSME /A&P. While I'll agree with your analogy in regards to most secodary structures. I don't agree with your good enough justification on the gear tower assy. However, let's agree to not agree. I found the answer I was seeking. Thanks. I'm done
 
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RV505 said:
Let's just use a little common sense. If you take out a little piece and very completely attach a bigger piece, you are probably all right. If not, your device was marginal to begin with!



If you take a big piece out and replace it with a small piece, you should be more cautious and thorough. If you take the small part out all together you should be very cautious. From reading about Kahuna's landing technique on the other thread I would say it all worked out fine. He may not have done the analysis, but he sure has tested it!

Since Kahuna's removal of the little piece has not brought trouble, I would say AX-O's modification is more than sufficient.

By the way, people are talking about "strength" in this post. Designs are not always designed just for strength. Sometimes it could be buckling, or deflection, or fatigue limits...

In my "day job," strength is rarely the issue because we deal with big loads and lots of cycles so fatigue (and wear) considerations usually rule the day. A few of our other products need stiffness because of customer perceptions of quality = stiffness. In a previous life in an aluminum structure environment fatigue and deflection were the important criteria.

Hopefully I got this enough off topic to put this one to rest!

Ok, I'm also an BSME /A&P. While I'll agree with your analogy in regards to most secodary structures. I don't agree with your good enough justification on the gear tower assy. However, let's agree to not agree. I found the answer I was seeking. Thanks. I'm done
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A ME would be able to show us the calculations, not ask for them.
 
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