After many flights on my SM F15, I started to have probs with the elevator clevises. While the plane was apart I went ahead and replaced the servo arm with the new JR plastic arm with the metal ring around the screw. Its a smidge thicker than the average arm.

When I tackled the clevis issue, I went with the Dubro 4-40 locking clevises on the servo end and a swivel link on the control horn end. I switched to the Hangar 9 Titanium pushrods too. I like the Dubros because they are self tapping and the pushrods come with one end reverse threaded so I cannot come loose in flight. When I put the clevis on, the servo arm was just a tad too thick and I couldnt get the locking clip to go on the pin. I tried and tried and finally gave up. I drilled a 1/16" hole through the plastic part of the clevis and safety wired it together so now it cant come apart at all.

Before I fly it like that, I would like to see if anyone sees a potential problem here.

Thanks,
Mike

Although I am far from an expert, I wouldn't trust that setup. I could never be assured that the pin has good engagement to both clevis arms which is essential for a strong setup. I would opt for the thinner servo arm in that case. If you really want that servo arm, then I would investigate a clevis that would fit properly.

I am not expert either (and your way might be fine), but I like to use double trussed arms where possible.

I like these Nelson arms. You can set the to the width you need with spacers then use a ball link.

Nelson has a new arm now, it is not double truss, but it clamps to the output spline, gets rid one one more sloppy fit.

I have same consideration.-
Personally I like to use the 4-40 metal clevise from Dubro.....and use a shrink tube to secure the clevis from openning....good luck.

The pin goes all the way through both sides... I guess Ill have to try a different servo arm.

Mike

I would not use that set up. I'm afraid you have severly weakened the clevis, and like Topgun2mo stated if the clevis pin does not engage both sides, you may have a problem.

No expert here too. You will DEFINITELY have issues if the pin does not bear well on BOTH sides in a high load situation. There will be unwanted slop or worse. The solution is simple. I would simply remove a few thousands off of the thickness of that servo arm, locally where you need it. But leave full thickness at the root (where the max moment is) and be certain that there is no abrubt thickness change in the transition (too sharp a change would be a high stress concentration).

Why can't you use ball links on both ends?

I guess I could just use ball links on both ends...that may be the solution. I just ordered a set of aluminum arms from Hangar 9. I have a set of the Dubro servo arms here. I guess I will give this some thought. Overwhelmingly though the response is not to use the safety wire. The pin does go all the way through, but I had the same concerns and I dont want to risk anything or anyones safety.

Thanks guys...Ill let you know what I do.

Mike

Just thinking...the other option may be to put the ball link on the servo side and the clevis on the control arm side.

Mike

I was cruising the Nelson Hobby Specialties web-site [link]http://www.nelsonhobby.com[/link] last week and I came across the clamping control wheel. What a cool idea!

Matt,
Did you cut down that double arm? All the double arms on the web-site seem to be more suited for giant scale and too long
for most jets. I'll just be that Jerry would make some jet-friendly arms if we ask real nice like. Jerry is a great guy to talk to.

I have been using Hayes Products HD 4-40 clevises with titanium turnbuckle rods. These clevises are quite sturdy and have an internal groove on the pin that snaps into the clevis. I don't know if the Hayes clevises would solve the think arm problem though. After moving to the desert 5 years ago, I have noticed that the hot-dry climate makes plastic parts brittle. I have had to boil the the Hayes clevises in water for 20 minutes or so just like we used to do to nylon propellers in order to keep them pliable enough to spread enough to attach to the servo arm. I have some reservations about any high loaded plastic control system parts. Especially on flying stabs that are back near the exhaust pipe in a very harsh environement.

Matt, I think that you have the best idea with the double arm and the ball clevis.

Mike, I don't think that the safety wire will provide any measure of security on the clevis. You would be better off using a piece of fuel tubing.

Tailwinds,

John

Is right, but the angle between the pin and the retiner holes is suppose to be 90 degrees....
Congratulations for asking [sm=thumbup.gif]

Hi John,

Yes those are cut down Nelson arms, or you could just have them cut yourself, my Dad makes a similar part for his buddies on a CNC mill.

Jerry does not make those anymore, but he makes those neat clamping arms that you have in that picture. I would prefer double truss that use that clamp, but he does not have those..it is not TOO bad cause those wheels are pretty thick, and my servo arms are very short. I think maybe SWB or airwild make the clamping arms as well.

Just to back up, I agree with Mark, having the balance weight out on the end, and driving from near the root is not good. If the surface is not stiff I would think you could cause more troubles than you fix, but I am not a rocket scientist like Rocketman!!

Sorry double post

I ended up swapping control arms to one of the heavy duty dubro arms. Then the clevises snapped right on. I was using one of the new JR heavy duty control arms but like I said it was too thick and no matter how you look at it...it was a plastic arm. Anyone have probs with the plastic dubro arms?

Mike