N18RA

N18RA

Active Member
i am having some trouble installing the flap push rods in the 8. the instructions tell you to add washer to move the bottom of the rod inboard, i put in 2. trying to hook up the top end i would have to take almost half of the floor mount angle off to clear the rod. Has anyone else seen this before or have any ideas?

thanks in advance


ben
 
common problem

Hi,

Yes, this is a common problem, and I've seen a few -8's do a rather poor job of it.
If you try to use the standard supplied rod ends on the flaps, (the kind with the integral post bolt), it takes several washers to space it inward enough to allow good clearance unless you cut a monstrous hole in the fuselage. If you add that many washers, you have a pretty unsatisfactory amount of bending load going into the threaded shank of the post bolt on the bearing, AND you may also have marginal thread engagement on the nut inside.

So, what I did was abandon that rod-end, and replace with a more normal rod-end bearing with an AN bolt through it. The assembly sequence is a large captive washer under the head, then the bearing, then a small washer, then a tubular spacer sleeve (could have used a stack of washers), then through the end-rib of the flap, then the nut. I made a special wrench to hold that *&%$ nut.

Anyway, now, I get three positive benefits. 1) able to make the spacer and bolt the right length to get the bearing in a good place so the pushrod doesn't rub on the fuselage, without cutting a giant hole in the fuselage
2) I have the requisite large washer keeping the bearing captive in case the bearing fails (this is a pet-peeve of my DAR, so I earned some brownie pts too.
3) A full-strength AN3 bolt with proper portion of bolt threaded, not threaded through the flap rib and inside spacer tube.

Hope this makes sense.
 
Do you Happen to remember how long of a spacer you made, so i have a good starting point?

thanks


ben
 
If I recall....

I think it was about 3/16" or so. I will try to take a picture next time I'm at the airplane, but it may not be this week,

Steve.
 
Spacer material...

Is the AT6 rigid aluminum tubing that other spacers are made of acceptable material for the spacers?

Thanks,
Michael-
 
what Steve said

I used a spacer made from delrin rod, 1/2" dia x 5/16" long. I don't remember the length of the AN bolt, but as Steve alluded to, it was a pain getting the nut on and torqued properly.

2uqcgll.jpg



J. Baker
RV8 Finishing
 
rockbottom said:
I used a spacer made from delrin rod, 1/2" dia x 5/16" long...
Click to expand...

Your workmanship looks impeccable, but the use of Delrin there gives me the willies. The strength and stiffness of Delrin is so much lower than those of steel or aluminum that it guarantees that most of the load goes through the bolt as bending. I would really recommend the use of aluminum for that spacer, and I'd also recommend that the spacer be of as great a diameter as physically fits. I think that 3/4" would go, so I'd use that. The larger the footprint of the spacer, the lower the bearing loads are where the spacer meets the drive rib.

Thanks, Bob K.
 
I did the same thing on my -9A flap actuators. I used an AN4-11A bolt, a thin capture washer (same ones used on the elevator push rods), CM-4M rod end bearing, a 1/4" spacer with washers at each end of the spacer along with the internal tooth lock washer. When this goes on for good, I'll add some locktite (as recommended on the plans).

IMG0249-M.jpg
 
bruceh said:
I did the same thing on my -9A flap actuators. I used an AN4-11A bolt, a thin capture washer (same ones used on the elevator push rods), CM-4M rod end bearing, a 1/4" spacer with washers at each end of the spacer along with the internal tooth lock washer. When this goes on for good, I'll add some locktite (as recommended on the plans).

IMG0249-M.jpg
Click to expand...

As mentioned above, increase your spacer diameter to match that of the part you are bolting it to. It will greatly reduce the twisting motion, and reduce the load on the bolt.

Replace all of those washers with a spacer the same diameter as that reinforcement part.
 
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