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Elevator to HS Clearance

rockitdoc

Well Known Member
Sponsor
The plans indicate 1-5/8" minimum distance between the torque tube and the HS rear spar web. Mine is at 1-11/16" and the leading edge of the elevator is rubbing the brackets on the HS that contain the hinge bearings.

Two solutions that I can see:

1. Increase distance from torque tube to HS rear spar by moving rod end bearings in elevators out enough so elevator clears rear spar on HS.
But how much is too much?

2. Flatten the leading edge of the HS more by bending so that it clears the rear spar of the HS.

Any help appreciated, as usual.

S
 
Do you have a photo of the elevator leading edge, edge-on? It sounds like the leading edge may have been under-bent (it can be difficult to get a smooth bend all the way back to the spar). But that's only a guess. It'd be best if you got a local tech counselor or RV-builder to look and help diagnose. As for bearing engagement, I'd want to see at least full engagement in the nutplate plus an extra turn. If you need more length than that, you'll need to rework the leading edge.
 
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Do you have a photo of the elevator leading edge, edge-on? It sounds like the leading edge may have been under-bent (it can be difficult to get a smooth bend all the way back to the spar). But that's only a guess. It'd be best if you got a local tech counselor or RV-builder to look and help diagnose. As for bearing engagement, I'd want to see at least full engagement in the nutplate plus an extra turn. If you need more length than that, you'll need to rework the leading edge.

I think that's the problem. The curve in the leading edge is not as smooth as it could be. The distance between the front spar web and the apex of the leading edge is 2", uniformly all along the leading edge (at least I was consistent in my bending). It needs to be more like 1-3/4" to 1/7/8" to provide at least 1/8" clearance as the elevator moves.
 

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  • Elevator Leading Edge HS Clearance.jpg
    Elevator Leading Edge HS Clearance.jpg
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Dealing with this myself right now. With the rod end bearings at the specified 13/16" from the elevator spar, I was just shy of the minimum 1-5/8" HS rear spar to torque tube. So I took one half turn out on the rod end bearings and then took a look at the nutplates inside with my VA-400 videoscope. Couldn't get it in very good focus but I was pretty sure that I still had about two threads showing on each. However, because the bend on my elevator leading edges isn't smooth I still had a little rubbing. Worked on that a bit and took another half turn and again checked the back of the nutplates. Looked like 1-1/2 threads as I expected. I still have just a very slight rub at the upper end of travel. This is, of course, without primer or paint. So, I've still got some reshaping to do on the leading edge. Mine have a slightly tighter curve on the upper side than the lower.
 
Funny, I did my elevators about two years ago. They rubbed, I tried rolling and bending some more and finally had a hair of clearance but it didn’t look good. I thought it looked “good enough” Two years later as I near the end, and my abilities have improved the elevators have bothered me for some time. I finally paid for new skins and all the parts I will need to build them again. Shipping wasn’t cheap, the exchange rate sucks but I will feel better knowing it’s been done right. Most people may not have seen the bad work trying to rebend that leading edge, but I would have every time I was back there. Fortunately that has been my biggest mistake so far. Hopefully I never have to drill out that many rivets again as I did this week end. This building an airplane thing is incredible. Loved every minute, mistakes and all.

Kerry
 
It's hard to tell from that photo, but I'm not sure you have achieved a good bend on the leading edge. That's a difficult bend to make in assembly, especially with the spar getting in the way as you try to form the bend. 20/20 hindsight says if I do it again I will jig up a bending rig before the skins are riveted to the spar. In fact, I'd love to see Van's pre-bend these. When I did mine, it took several attempts to get a smooth bend due to springback. Each attempt brought the curve closer to where the skin met the spar. Without it, you tend to get a sharper bend near the spar and a slightly triangular (with curved sides) cross section.
 
So, I called the mother ship this morning to find out what options I have. There are 3:

1. Back the bearings out no more than two turns (0.08"), refit and see if clearance is achieved.
I did this and no joy.

2. Try reshaping the LE to conform.
Have done this a lot. No joy. In fact, no amount of reshaping is going to work. It either hits at the apex of the LE or on the skin at full 30 degrees. There is no way to have both clear.

3. Remove rivets. Re-rivet the LE in a tighter radius using new holes spaced between the OEM holes.
I did this and tightened the radius by only one diameter of the #30 holes (not much, IOW)
This worked very well. Lots of clearance now. No chance of any interference.

IMHO Van's should make the radius tighter here so this doesn't happen to future builders. When I built it as specified, the radius from the front spar of the elevator to the top of the LE was 2" all the way across the elevator. After my 'revision' the radius is now 1-3/4". This provides plenty of clearance.
 
Photos of clearances after the revision:

This is the radius after the change. It's more like 1-7/8" now, instead of 2" before.
 

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  • LE of elev after revising.jpg
    LE of elev after revising.jpg
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This is the clearance between the LE and the rear spar of the HS:
 

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  • LE elev to spar after revising.jpg
    LE elev to spar after revising.jpg
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And, here is the distance I moved the LE over to get the tighter radius. I said it was one diameter of the #30 hole, but it's more like 1/4"
 

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  • LE elev rivet revised locations.jpg
    LE elev rivet revised locations.jpg
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Would another possible solution have been to replace the plans specified rod end bearings (MD3614M for the RV14 elevator) with the longer version (MD3616M)?
 
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