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Elevators safety and trim tab function

lucaperazzolli

lucaperazzolli

Well Known Member
I was thinking about the safety of the elevator and trim function.

My idea : in the rare case that the nut&bolt go off from the elevator horns linkage, the airplane will have two elevators free into the wind :eek:

It's ok, the pilot will need to control the pitch with engine and trim...BUT we have the trim tab only in the left elevator :eek:

Probably it's supposed (by design) that the pilot will have less pitch control with only one elevator and the other one will stay 'neutral' with no catastrofic event ...

Maybe a simple hole/bolt/spacer/nut between the horns will solve this case.

What's your thought about ?




ps: the nut in the image is a temporary one ! ;)

51.jpg
 
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You should have purchased the RV-10 as each elevator has a trim tab!!! Just joking. I don't have enough experience to have a serious opinion.
 
It's happened before.

One of our airshow pilots, Sean Tucker, had the rod-end bearing housing break during a snap roll, losing elevator control a few years ago. It was a high-powered Pitts and he decided that he couldn't land it, so he went up to near 10,000' and jumped out over open land.

That airplane had elevator trim as well.

I'd just keep a close eye on all control systems at each annual/condition inspection, Luke.

Best,
 
Solution = Drilled bolt + castle nut + cotter pin

Luca,

It seems to me the best solution to protect against the scenario you describe is simply to make sure the nut can never back out inadvertently. And that's easy to do. Instead of the lock nut shown in Van's drawings, use a drilled bolt + castle nut + cotter pin. Personally, I do this on all the critical flight control linkages.

-Roee
 
pierre smith said:
One of our airshow pilots, Sean Tucker, had the rod-end bearing housing break during a snap roll, losing elevator control a few years ago. It was a high-powered Pitts and he decided that he couldn't land it, so he went up to near 10,000' and jumped out over open land.

That airplane had elevator trim as well.

I'd just keep a close eye on all control systems at each annual/condition inspection, Luke.

Best,
Click to expand...

Thanks Pierre. I remember the Sean T. story and I spoke with him about in Oshkosh 2006, probably we need ten flying lives to stress our rv just an half that he does in his Pitts routine ;)

I have a plexy window for my horns bolt so I take a look on it at every pre-flight (and a good check on annual too).

I like to have an opinion from the community because I had an extensive DAR talk yesterday helping a friend into the certification process of his F1 Rocket Evo (that has the same RV horns & trim system); he pointed his attention on this problem. I like share it with you.

horn_window.jpg
 
roee said:
Luca,

It seems to me the best solution to protect against the scenario you describe is simply to make sure the nut can never back out inadvertently. And that's easy to do. Instead of the lock nut shown in Van's drawings, use a drilled bolt + castle nut + cotter pin. Personally, I do this on all the critical flight control linkages.

-Roee
Click to expand...

Yes, IMHO a pal-nut is another option. So you don't have to change the design idea. Thanks !

palnut.jpg
 
Luke, not to be sarcastic but this fits into the category of problems to solve, that don't really exist.:)

Thousands of RV's are flying and only a -10 had an elevator pushrod detach...builder error.

Best,
 
Use an MS17825 self-locking castelated nut with a drilled bolt and a cotter pin for additional assurance that it'll stay connected.

Dave
 
Elevator and trim safety

When I built my Tailwind in1972, Steve Wittman gave out a service letter about the elevator horns separating because the bolt had backed out or broke.:( The fix was to add another bolt aft of the control rod attach bolt locking both the horns together. That way you could fly the aircraft with the elevator trim tap.;) I did the same thing on my RV4 in 1990.:D
 
Horn interlocking spacer above the pushrod connection

Our RV-6A has a horn interlocking spacer above the pushrod connection. Due to a manufacturing error (in the horn weldments as I recall) the final space in between the horns was too large. In discussion with the factory about a fix that involved washers to fill the gaps Ken Scott suggested adding a spacer filled connection between the horns. I did that and any force that moves one elevator moves both in our airplane. 921 operating hours later at some very high speeds no downside of this attachment have been revealed.

Bob Axsom
 
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