Van's Air Force
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tailwheel bolt failure
- Thread starter armondo
- Start date
If we're talking about the spring-to-socket attachment, why use only one bolt? The spring already had two holes. A single bolt in the more forward position has several drawbacks, not the least of which is drilling a new hole in the spring in a highly stressed position.
Fit is important. This drill jig was clamped to the spring undrilled, then drilled using the spring itself as the drill guide. Then the tailwheel was added and drilled the opposite direction using the drill jig as a guide. Nice tight holes.
Fit is important. This drill jig was clamped to the spring undrilled, then drilled using the spring itself as the drill guide. Then the tailwheel was added and drilled the opposite direction using the drill jig as a guide. Nice tight holes.
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vfrazier
Well Known Member
Here's related info for the other end of the tailwheel spring:
I want to pass on a little tidbit here about the bolt that holds the tailwheel spring to the tailwheel weldment. I drilled mine per Mark's instructions and found that the bolt went in too easily--this should be an interference fit (once again, my savior the "big-***" hammer should be used to put the bolt in). I wrapped a piece of scrap aluminum around the tailwheel spring and could twist it with a pair of vise-grips. Not good! If there's any play here, the bolt can eventually fail or the hole will become elongated. I have heard of failures in these bolts on RV's . Rather than taking my chances with a larger bolt and it too not being correct, I decided to fix it with a taper pin which worked out very well. Here's the recipe:
AN386-2-9A taper pin (aircraft spruce)
AN975-3 taper pin washer (aircraft spruce)
B&S #2 taper pin reamer (http://www.mscdirect.com/MSCCatLookup2.process?MSCProdID=02054021) (1/2 the price of AC$)
12" long tap handle (http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=45206)
The taper pin has the advantage that if the pin ever loosens up, you can just tighten up the nut and things should be snug again. The taper pin is an odd-sized Browne & Sharpe #2 taper, so don't confuse it with other -2 tapers.
I highly advise that the final hole size should be reamed with a hand-reamer .001-.002 under-size even if you don't use a taper-pin. There are too many variables with drilling to final size with a hand drill. Bob Japundza
From my old website, www.vincesrocket.com
I want to pass on a little tidbit here about the bolt that holds the tailwheel spring to the tailwheel weldment. I drilled mine per Mark's instructions and found that the bolt went in too easily--this should be an interference fit (once again, my savior the "big-***" hammer should be used to put the bolt in). I wrapped a piece of scrap aluminum around the tailwheel spring and could twist it with a pair of vise-grips. Not good! If there's any play here, the bolt can eventually fail or the hole will become elongated. I have heard of failures in these bolts on RV's . Rather than taking my chances with a larger bolt and it too not being correct, I decided to fix it with a taper pin which worked out very well. Here's the recipe:
AN386-2-9A taper pin (aircraft spruce)
AN975-3 taper pin washer (aircraft spruce)
B&S #2 taper pin reamer (http://www.mscdirect.com/MSCCatLookup2.process?MSCProdID=02054021) (1/2 the price of AC$)
12" long tap handle (http://www.harborfreight.com/cpi/ctaf/Displayitem.taf?itemnumber=45206)
The taper pin has the advantage that if the pin ever loosens up, you can just tighten up the nut and things should be snug again. The taper pin is an odd-sized Browne & Sharpe #2 taper, so don't confuse it with other -2 tapers.
I highly advise that the final hole size should be reamed with a hand-reamer .001-.002 under-size even if you don't use a taper-pin. There are too many variables with drilling to final size with a hand drill. Bob Japundza
From my old website, www.vincesrocket.com
JonJay
Well Known Member
Ordered the parts...
Thanks for the "recipe" Vince.
My thoughts are to remove the spring, taper-ream the hole in the spring just shy of what is needed, re-insert into the tail and finish up in assembly. It is a bit tight trying to do it all in assembly, certainly could not get a 12" tap handle on it.
Thanks for the "recipe" Vince.
My thoughts are to remove the spring, taper-ream the hole in the spring just shy of what is needed, re-insert into the tail and finish up in assembly. It is a bit tight trying to do it all in assembly, certainly could not get a 12" tap handle on it.
scsmith
Well Known Member
use a drill motor
I used an electric drill motor to turn the tapered reamer very slow, with lots of oil. Do one, put the pin in tight, then do the other. Worked great.
Also, with 2 taper pins, use the AN386-1-9, no need for pins as bit as the -2 when you have two of them. And use the B&S #1 reamer.
I used an electric drill motor to turn the tapered reamer very slow, with lots of oil. Do one, put the pin in tight, then do the other. Worked great.
Also, with 2 taper pins, use the AN386-1-9, no need for pins as bit as the -2 when you have two of them. And use the B&S #1 reamer.
Here is a picture of the taper pins installed on my RV-6. Highly recommended. I used the hand reamer as described in Vince Frazier's post above. Also, you will need a good set of leather gloves and plenty of cutting fluid. It takes a little time and a couple of blisters. I staggered mine, not sure this was necessary, but my AN3 bolts were kind of close together, so I thought this was the best way.
I think the shear force on AN3 bolts is greatest when doing a hard 90 degree turn while taxiing, and this is what causes the problem. Add a bump while doing this and you're asking for trouble.
Interestingly, there is NO shear force when the tail wheel is in trail. The taper pins are a good preventative measure!
[I just wanted to add that the initial drill size before beginning the taper operation is a size "G". I worked up to it using several intermediate sizes. This allows you to get the taper started in the hole.]
I think the shear force on AN3 bolts is greatest when doing a hard 90 degree turn while taxiing, and this is what causes the problem. Add a bump while doing this and you're asking for trouble.
Interestingly, there is NO shear force when the tail wheel is in trail. The taper pins are a good preventative measure![I just wanted to add that the initial drill size before beginning the taper operation is a size "G". I worked up to it using several intermediate sizes. This allows you to get the taper started in the hole.]
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Loose bolts
The standard AN3 bolts that come with the kits are slightly undersized for this application. There is a lot of flex at this joint and any looseness will auger out the hole with time. If you already broken bolts then the taper pin repair is a good fix. For those of use still working on new stuff, put in a close tolerance NAS bolt there before you go flying. My RV-6 (first one) has over 500hrs on it with no issues.
The standard AN3 bolts that come with the kits are slightly undersized for this application. There is a lot of flex at this joint and any looseness will auger out the hole with time. If you already broken bolts then the taper pin repair is a good fix. For those of use still working on new stuff, put in a close tolerance NAS bolt there before you go flying. My RV-6 (first one) has over 500hrs on it with no issues.
JonJay
Well Known Member
