Gear legs bolts

[Carlos Trigo]

I read some comments about the main gear legs bolts, and also the tail spring bolts.
- In the case of the main gear legs, the comments were that instead of the AN bolts indicated in the plans, at the top of the engine mount, the recommendation was to use close tolerance (NAS) bolts.
What do the majority of the taildraggers builders and flyers are using?

- In the case of the bolts which hold the tail spring to the fuselage, and which hold the tail wheel, instead of one AN4 in each end, the recommendation was to replace it for 2 AN3’s in either side.
Can someone please comment?

Thanks
Carlos

[racaldwell]

Hi Carlos,

I used taper pins on both ends of the tailspring rod. Many people use two bolts, but why go for the heavy solution? I think in terms of grams added to my build on everything. Of course, the drawback is the time it takes to go lighter. Like, it only took me six months to make my wingtips. But I saved over 15 lbs vs. the stock tips. But I like building so I am in no hurry; already have a plane to fly.

I used the AN bolts called out for in the plans for the main gear legs. The plans say to not tighten the nuts very much which I don't understand the reasoning for. Guess it is just a secure pin. The bolt in my RV gear leg is tightened to normal spec torque. I don't see why Sonex would leave it looser. Anybody know the reasoning?

Rick Caldwell
Xenos 0057

[DCASonex]

The bit with the bolts goes back a few years to when the original spec was for Stainless Steel bolts. The idea being that the cadmium plating was bad for the titanium. Then after some broken bolts, Sonex found that the cadmium vs titanium warning really only applied at elevated temperatures and the changed the spec to the stronger standard AN steel bolts. The bolts are mostly in shear, and high tension on bolts in shear reduce=s their shear Strength. A search of revisions should bring up the full record on this.

As to standard or close tolerance, might depend on what you have available in the way of letter sized drills and reamers to get a nice close fit. Personally, I have 5/16" bolts top and bottom and do tighten them. Drilling for 5/16" bolts at top is tricky and risks major damage to engine mount if done wrong.

About 400 hours and probably about 800 landings, (not counting bounces) and many far from perfect smooth landings on the gear so far and no problems

Used to be and may still be that tail springs needed to be wrapped in thin shim materiel or epoxied into the tail spring bracket once any ridges of paint have been cleaned out. Think I also used some thin shims around man gear as well.

David A.

[sonex1374]

Carlos,

Sticking with the bolts called out in the plans is probably the best plan. The upper gear leg bolts (that pass through the engine mount) have been known to break, but the factors leading to the breaks are still not well understood. It seems each case is a little different (burs on the inside of the gear leg, imbalanced tires, loose fitting leg in the engine mount socket, worn/wobbly axles on the bottom of the gear leg, and possibly over-tightening of the nuts securing the upper bolt). As these factors came to light, the factory revised the bolt specs in the plans (first changing to an AN bolt for higher strength, then changing to a castle nut so as to not overtighten the nut). While these bolt changes are a good idea, a bolt alone won't make up for an underlying problem such as a wobbly axle or out of balanced tires. My advice is to be precise with your alignment process, drill the gear leg using only a NEW cobalt drill bit using frequent applications of drill lube, and balance your entire wheel assemblies before installing them. If you find that anything is wobbly after doing all this, you'll need to correct that first. If you still can't get a good fit on your upper bolts, then maybe consider trying to source a close tolerance bolt or up-sizing to an AN5 bolt.

As for the tail spring, I don't think there has ever been any problems with the bolts holding the tail rod at either the fuselage socket or the tailwheel caster. The plans bolts work fine and don't need anything. If the rod fits loosely inside the socket you might consider something to improve the fit (thin shims, structural adhesive, etc), but this won't affect the bolts. However, even a loose fit of the rod isn't really a problem....the rod's not going anywhere.

Jeff

[Carlos Trigo]

Thank you all

For your answers and recommendations.

For the main gear legs, I will order both AN4 and AN5 bolts.
Does anybody know, or remember, the dash number of the AN4 and the AN5 bolts which will suit this application(not too long nor too short)?

Carlos

[Carlos Trigo]

I used the AN bolts called out for in the plans for the main gear legs. The plans say to not tighten the nuts very much which I don't understand the reasoning for. Guess it is just a secure pin. The bolt in my RV gear leg is tightened to normal spec torque. I don't see why Sonex would leave it looser. Anybody know the reasoning?

Rick Caldwell
Xenos 0057

Rick

I asked that question to the Sonex Tech and they answered that they feel over-tightening the nut was a contributing factor to the bolt failures, at least in 2 cases

Carlos

[racaldwell]

I suspect Sonex does this because it is a -4 bolt. Just seems small if used to tighten the steel mount to the gear leg so the tight joint friction would keep the components from shearing the bolt. I suspect David's method of using a -5 bolt tightened to clamp the joint so no slip is possible makes a stronger joint in shear than the -4 bolt used as a pin only.

Rick Caldwell
Xenos 0057