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7A elevator spar crack

So Walt, may I come by your hangar this week, Thurs early before I go to work and take some pictures of what I should be looking for exactly. My plane is in Tucson and I'd like to look at it closely when I get back home Friday.

I would sure appreciate you showing me on another RV.

Absolutely, love to have you.

I would also be happy to inpect any RV that wants to drop in for a quick tail inspection.
 
Wow! Good catch, I can see if the hing eye bolts are not in alignment, every control surface deflection would cause the center eye bolt hinge to load in and out, causing a work harden crack?
 
Looks like we have a similar issue

elevator%20crach
RV7a, 2005 model about 900 hours.
 
Yes, Bill, I would say that you guys do have a similar and significant issue. Good catch! Plenty of good resources on the field if you need assistance besides your A&P partner.
 
Another elevator crack found

elevator%20crach
RV7a, 2005 model about 900 hours.

I was hoping I was the only one with a crack.
The 900 hours is the same as mine (908).

Bill,
What engine and prop do you have?

My plans to get the elevator spar out without affecting the glassed up tip were flawed:(
It can't be done. At least not any way that I can see. So, I'll be in the fiberglass business again in a day or two:eek:

Mark
 
Just read the last few days of this post

and a couple comments came to mind:

First, well informed Mooney drivers are taught to wiggle the left and right elevators against each other (one up, one down) to check the total clearance in the rather complicated structure connecting the two elevators together. I've carried that pre-flight procedure over the RV by wiggling the left trim tab with one hand against the right elevator with the other hand. That way I catch any looseness in both the elevator and trim tab mechanisms simultaneously. If I find any movement, I investigate before committing aviation.

Second, I have never liked control stick or rudder pedal gust locks because they can result in repeated alternating loads on the whole control system. Especially if the airplane is parked tail into the prevailing wind. "At the control surface locks" are more of a pain to install, and arguably easier to miss on pre-flight, but seem to provide better protection of the "system" than stick/yoke/pedal devices.

Third, I balanced my elevators independently for the reasons suggested earlier. Vne + 10% A OK.

Fourth, doing the annual condition now and will be adding that second bolt between the left and right elevators. Thanks.

Doing my annual now and thanks to this thread took a careful look at the subject area. Sleeping better now...;)
 
I have noticed on a couple of RVs that if the elevator is moved trailing edge down, it does not "float" back up on it's own. Did the elevators on either of the RVs where cracks were found in the spar behave similarly?
 
I have noticed on a couple of RVs that if the elevator is moved trailing edge down, it does not "float" back up on it's own. Did the elevators on either of the RVs where cracks were found in the spar behave similarly?

This can be caused by friction at any one of (or a multiple of)12 different pivot locations in the pitch control system (14 points in an RV-4 or 8). It is one of the things that is a variable when comparing the handling qualities of one RV to another depending on the amount of friction, but most significantly it can effect dynamic pitch stability.

If you want the best flying RV possible... make sure your elevators move as freely as possible.
 
If you want the best flying RV possible... make sure your elevators move as freely as possible.

This is exactly why my tech counselor told me - it was tedious getting everything lined up but it's like butter now and drifts to a trailing edge-up attitude on it's own.

I was wondering if excessive friction might result in extra stress on the attach points but in thinking about it further it seems such friction loads would be minuscule compared to flight-induced loads.
 
I have noticed on a couple of RVs that if the elevator is moved trailing edge down, it does not "float" back up on it's own.

If you want the best flying RV possible... make sure your elevators move as freely as possible.

If you have manual trim the very stiff trim cable is going to prevent the elevator from traveling or balancing freely. Mine pretty much balanced out without the trim cable attached but not so much once the stiff cable is attached.

FWIW, when I asked Van's about this, Ken Scott told me to balance first and then hook up the trim cable. In addition, he added "The balance is always a bit approximate...there's no need to go chasing grams here."
 
Elevator Balance

Ref Dan H (post 29) and Terry Frazier (post 57).
I wonder how many people actually take the time to check the balance on their elevators after paint. I am sure that their is a margin for error but it is something that should be done. When I was doing the elevators on my rocket I came across an interesting idea on Vern Little's Rocket web site. He installed a quarter inch nutplate just behind the counterbalance weight under the elevator tip. This allows you to install washers on the inboard side for fine tuning after paint. Worked like a charm for me. I balanced mine slightly heavy to start with for paint weight compensation but still had to add 3 washers on each elevator. I explained to my painter how to balance the elevators but after paint when I went to pick up the airplane I asked if it was done and I got the deer in the headlights look. The rocket moves along at pretty good speed so I wanted it correct (now) Needless to say I took care of it my self. I went over everything carefully prior to flying the airplane.
Point is Dont take for granted that the painter did the ballance on your elevators. If you dont know for sure its probably worth the time to check them. Their is certainly nothing to lose.
Ryan
 
Paul,
This is why I install an extra AN3 bolt and spacer between the two elevator horns securing the two elevators together in addition to the rod end bolt.
Ryan

Ryan, can you give us an idea how you did that, would you show us a photo?

Thanks Pit
 
Sorry Pit I see now it was the extra bolt you were talking about. I will pull the cover and get some pictures tomorrow afternoon and see if I can remember how to post a couple pic's.
Ryan
 
Crack

We have the Matituck TMXO360 180hp with hartzell blended airfoil prop.

Is there any other repair you have considered that does NOT include taking the elevator apart?

I was hoping I was the only one with a crack.
The 900 hours is the same as mine (908).

Bill,
What engine and prop do you have?

My plans to get the elevator spar out without affecting the glassed up tip were flawed:(
It can't be done. At least not any way that I can see. So, I'll be in the fiberglass business again in a day or two:eek:

Mark
 
I have noticed on a couple of RVs that if the elevator is moved trailing edge down, it does not "float" back up on it's own. Did the elevators on either of the RVs where cracks were found in the spar behave similarly?

I have the same "issue" with my elevators, but it is caused by the resistance created by the mechanical cable to the trim tab.
 
I have the same "issue" with my elevators, but it is caused by the resistance created by the mechanical cable to the trim tab.

I think it is probably caused by a different issue.
Since the manual cable is stiff, it actually wants to straighten out, helping the elevators return to the neutral position.
You probably have some system friction.
 
No other options really

We have the Matituck TMXO360 180hp with hartzell blended airfoil prop.

Is there any other repair you have considered that does NOT include taking the elevator apart?

Bill,
To repair (patch) the spar you would still have to take the elevator apart.
The spar is $18. So repairing it would be silly at that point.
I wish the spar was made of a bit thicker material.

I did email Vans customer service with a link to this thread on Saturday.
I did not request any engineering help from them in that email.
I just wanted them to be aware that I found a crack and that my plan was to replace the spar.

Mark
 
I have the same "issue" with my elevators, but it is caused by the resistance created by the mechanical cable to the trim tab.

Are you testing this and expecting to return to neutral position with the push/pull rod connected?
 
Ref Dan H (post 29) and Terry Frazier (post 57).
I wonder how many people actually take the time to check the balance on their elevators after paint. I am sure that their is a margin for error but it is something that should be done. When I was doing the elevators on my rocket I came across an interesting idea on Vern Little's Rocket web site. He installed a quarter inch nutplate just behind the counterbalance weight under the elevator tip. This allows you to install washers on the inboard side for fine tuning after paint. Worked like a charm for me. I balanced mine slightly heavy to start with for paint weight compensation but still had to add 3 washers on each elevator. I explained to my painter how to balance the elevators but after paint when I went to pick up the airplane I asked if it was done and I got the deer in the headlights look. The rocket moves along at pretty good speed so I wanted it correct (now) Needless to say I took care of it my self. I went over everything carefully prior to flying the airplane.
Point is Dont take for granted that the painter did the ballance on your elevators. If you dont know for sure its probably worth the time to check them. Their is certainly nothing to lose.
Ryan

Good idea as far as making sure it was done properly. I like your method of having an easy option to maintain flight control balance after paint, mods, repairs, etc (through the life of the aircraft). On all Boeing aircraft, it's always interesting to see them in the factory before final paint. The rudders are all installed painted while the fin is still bare so that the control surface can be custom balanced depending on the paint scheme. Each color represents a different weight due to the required coats and pigment densities, and then among different paint jobs there are complexities that add or take away from finished paint weight.
 
An Observation

I was hoping I was the only one with a crack.
The 900 hours is the same as mine (908).

Bill,
What engine and prop do you have?

My plans to get the elevator spar out without affecting the glassed up tip were flawed:(
It can't be done. At least not any way that I can see. So, I'll be in the fiberglass business again in a day or two:eek:

Mark

I find the following items very curious:

1. Both elevator spar cracks discovered and discussed in this thread occurred on RV-7A's at approximately 900 Hrs

2. Both of the incidents involving apparent in flight stabilizer departures that led to this thread have also occurred on -7A's

Could this possibly be indicative of an airframe harmonic frequency issue unique to the -7A? Not speculating, just questioning...

Skylor
 
I find the following items very curious:
Could this possibly be indicative of an airframe harmonic frequency issue unique to the -7A? Not speculating, just questioning...

With a sample size of TWO, it may or may not be a 7A issue period. We do not know if all 7s have been checked.

Is the tail section the same on a 8A as a 7A?

What about wind issues on the ground? Was that a common factor?
 
...I just wanted them to be aware that I found a crack and that my plan was to replace the spar...

Mark, I trust you don't need the pneumatic rivet squeezer I bought from you to complete this repair. I have grown rather fond of it. If you were closer, however, and really needed it, I would gladly let you use it. ;)

Don
 
With a sample size of TWO, it may or may not be a 7A issue period. We do not know if all 7s have been checked.

Is the tail section the same on a 8A as a 7A?

What about wind issues on the ground? Was that a common factor?

The horizontal stabilizer is different on 7's and 8's. The 7 stabilizer has to accommodate a wider fuselage.

Also, if harmonic resonance has any part in this, the 7 and 8 fuselages are very different and should have different natural frequencies.
 
Mark, I trust you don't need the pneumatic rivet squeezer I bought from you to complete this repair. I have grown rather fond of it. If you were closer, however, and really needed it, I would gladly let you use it. ;)

Don

Hey Don,
I'm glad to hear the squeezer is doing well:)
I hated to sell it but toward the end of the build money was tight!

Thanks for your offer, but I'll be able to use my hand squeezer and buck the rest.

Mark
 
Second bolt install

Ryan, can you give us an idea how you did that, would you show us a photo?

Thanks Pit

29bd154.jpg

This is the second bolt with the spacer it is important that the spacer where ever you choose to put your bolt does not interfear with the rod end throughout full travel. It is also important that you have a snug fit with the spacer so as not to squeeze the horns together when the bolt is torqued. Let me say this makes sense to me but I am not an engineer so take it for what its worth.
It may not look like it but I do have the threads comming through the nuts here.

16h9jyr.jpg
[/IMG]

This is a wrench I put together to make securing the bolts easier.
 
Dan just putting the control surfaces on again after painting and I too will check every thing to made sure no binding and secure.
I like others do not want problems down the road.
Jack
 
Adding the second bolt in the elevator horns was pretty common back in the '90's when my RV-6 was built. Here are a couple of photos showing the extra access hole on the right side of the fuse that makes it much easier to torque down the bolts:

finsh215.jpg


Just stick a socket on an extension in the hole to catch the nuts on the bolts.

Here is the little window to seal the hole:

finsh214.jpg


The handle riveted to the window makes it easy to work it in around the pushrod to get it in place for attachment inside the fuse.
 
I got the spar out

I removed the doubler from the rod end attach point of the spar tonight.
I was shocked at what I saw!

Look at the crease line caused by the edge of the doubler on right side of photo. It's really worse than the photo shows. Sighting down the spar, it's still very straight.

20130925_211431.jpg


20130925_212006.jpg


For this to happen the elevator tip had to move to the rear.
Was this maybe a result of the storm at Oshkosh in 2012?

Here's both sides of the crack.

20130925_213126.jpg


20130925_213114.jpg


I'd forgotten how heavy the counterweight is! That's a lot of weight hanging out there.

My tail did hit the ground once when a large passenger got on his step too soon. It was a slow motion ride on the way down but stopped with a thud.
If the counterweight was "up", (elevator nose down) this could have made this crease I suppose.

The rod end jam nut was tight. So tight in fact that the dye didn't even get under it!

20130925_204703.jpg


I'm seriously considering adding a longer doubler. Longer to the outboard side.

Thoughts?

Mark
 
It's interesting that the crack did not touch the rivet hole.

The rivet head and tail held the doubler so tight to the spar that the stress was just outside of the rivet area.
 
the second bolt

This is the second bolt with the spacer it is important that the spacer where ever you choose to put your bolt does not interfear with the rod end throughout full travel. It is also important that you have a snug fit with the spacer so as not to squeeze the horns together when the bolt is torqued. Let me say this makes sense to me but I am not an engineer so take it for what its worth.
It may not look like it but I do have the threads comming through the nuts here.

Ryan, now I got the idea. Was it recommended by Van's?

Thanks Pit
 
Mark, Bill,

Best to confirm facts before moving further. Could you each address a few basic items about your installations?

(1) The five hinge points on the stabilizer are in perfect alignment?

(2) The three hinge points on this elevator were in perfect alignment before dis-assembly?

(3) Elevator balance was neutral, under-balanced, or over-balanced?

(4) Elevators balanced separately or together?

(5) Bill, which elevator, right or left?
 
Last edited:
Update

We took the elevator off last night and our crack is very similar to the above pictures.

Dan, we did not build it so:

1&2 (uncertain at this point)

3 Balance on effected elevator seems very good (right side)

4 (uncertain)

5 Right side elevator, outboard attach point.

Best to confirm facts before moving further. Could you each address a few basic items about your installations?

(1) The five hinge points on the stabilizer are in perfect alignment?

(2) The three hinge points on this elevator were in perfect alignment before dis-assembly?

(3) Elevator balance was neutral, under-balanced, or over-balanced?

(4) Elevators balanced separately or together?

(5) Bill, which elevator, right or left?[/QUOTE]
 
Ryan, now I got the idea. Was it recommended by Van's?

Thanks Pit

I would say that this was not a recommendation from Vans. If it were it would be in the plans. I will say I believe Vans design in this area is sound and has proven its self over hundreds of thousands of hours. I have done many condition inspections on RV's and found the elevators with a slight amount of play at the trailing edges requiring A re torque of the pushrod bolt. This was just my way of taking care of the possibility of play.
Ryan
 
Mark,

The vertical crease could have been formed if the the AN4 rivets were set with excessive pressure on the rivets.

It is difficult to image sufficient side load force on the elevator to cause that bending crease without damage to the elevator skin, trailing edge of the HS itself.
 
Some answers for Dan

Mark, Bill,

Best to confirm facts before moving further. Could you each address a few basic items about your installations?


Dan, see by answers below
(1) The five hinge points on the stabilizer are in perfect alignment?
It's been almost five years since the build. I'll remove the left elevator and re-check.
(2) The three hinge points on this elevator were in perfect alignment before dis-assembly? I can say that the bolts just slid right out with little effort. And just the other day I did look down through the rod ends and saw the hole in the horn in what looked like perfect alignment.
(3) Elevator balance was neutral, under-balanced, or over-balanced?
Again, it's been to long to remember.
(4) Elevators balanced separately or together?
Don't remember. At the airport last night, left elevator very free and slighty tail heavy.
(5) Bill, which elevator, right or left?

I do plan to replace left elevator spar also. If it was caused by wind or tail impact the left side was there too;)

One thing I just thought of, the left elevator counterweight is trimmed to offset the weight of the electric trim if I remember correctly.
So there would be a slight difference in force applied during a storm or tail impact.

Mark
 
Mark,
Do you by chance use gust locks on the tips of the elevators?

Walt,
Never used any gust locks on the elevators. I just used the seat belt around the stick to hold them back.

I was thinking that a gust lock on the tips would be better. But now you have me thinking otherwise.

Mark
 
Mark,

The vertical crease could have been formed if the the AN4 rivets were set with excessive pressure on the rivets.

It is difficult to image sufficient side load force on the elevator to cause that bending crease without damage to the elevator skin, trailing edge of the HS itself.

No, I could see it happening if the side load was applied directly along the line of the spar. The other hinge points would assist in this happening.

It would be interesting to see a detailed view of the other hinge points.
 
Perhaps this would be a good time for folks to review Van's article on VNE as well.

http://www.vansaircraft.com/pdf/hp_limts.pdf

Good advice, but we also have to keep in mind that there are plenty of Rockets flying with completely stock RV-8 tails. Normal cruise speed for many of these Rockets is at or in excess of the published VNE for the RV-8.

Based upon this fact and the lack of other RV-s falling out of the sky, I think it is more likely that we have an issue with basic craftsmanship or external damage than a basic design flaw.

I think it is prudent to do a careful inspection, but I'm hearing lots of "beef up" talk in this thread. let's make sure we are addressing the real problem before we try "fix" a design issue that might not exist.
 
I think it is prudent to do a careful inspection, but I'm hearing lots of "beef up" talk in this thread. let's make sure we are addressing the real problem before we try "fix" a design issue that might not exist.

Yes, exactly correct.
 
Vans input

I have spoken with the factory twice on this so they are aware and following the thread. I have not suggested any design flaws, just wanted their advice and input. I appears the parts in the 7a elevator (spar, doubler and nutplate) are that same that were used in the RV6 tails.



Good advice, but we also have to keep in mind that there are plenty of Rockets flying with completely stock RV-8 tails. Normal cruise speed for many of these Rockets is at or in excess of the published VNE for the RV-8.

Based upon this fact and the lack of other RV-s falling out of the sky, I think it is more likely that we have an issue with basic craftsmanship or external damage than a basic design flaw.

I think it is prudent to do a careful inspection, but I'm hearing lots of "beef up" talk in this thread. let's make sure we are addressing the real problem before we try "fix" a design issue that might not exist.
 
I have spoken with the factory twice on this so they are aware and following the thread. I have not suggested any design flaws, just wanted their advice and input. I appears the parts in the 7a elevator (spar, doubler and nutplate) are that same that were used in the RV6 tails.


How can that be when the -6 tail is shorter than the -7's?
 
...I think it is prudent to do a careful inspection, but I'm hearing lots of "beef up" talk in this thread. let's make sure we are addressing the real problem before we try "fix" a design issue that might not exist.

Good point.

Many times, when a part is "beefed up", it simply shifts the load to a different part of the structure which can can cause cracks / failures in other areas.

I would suggest you wait until Van's has a chance to evaluate the problem and engineer a solution before "beefing" anything up.

As for those who have cracks that need to be addressed, follow Van's advice. You will be good for another 900 hours and can address it then, if the cracks reappear.

Just my $.02 worth and remember, you got what you paid for.
 
This is very interesting from a design standpoint. The crack appears to have formed on the thinner piece, but still at the sharp edge presented by the plate nut. Additionally, the crack appears to be within the area covered by the doubler. This means that 1. the doubler could also be cracked, 2. the stiffness of the flat doubler appears to be less than the spar when the rod eye is loaded vertically and 3. the edge of the doubler did not cause a stress concentration that led to the fracture. I hope Vans will be doing an FEA of this area. A simple channel shape of the doubler would spread that load better laterally, but the designer would have to evaluate that option as well.

This may address why it happened there, through no apparent failure of the builder or maintenance, but not what developed a loading condition sufficient to fatigue this area. Warm days on the gulf coastal areas do present a lot of bumps in the warm months (many of them) at relatively low altitudes, but what other reasons could this bird be seeing more loading cycles than another? And, is it only on the lower edge and not showing much loading on the upper edge because this is the typical load direction for keeping the nose up and it is not precipitated by some overwhelming aerodynamic cyclic load?

I hope some answers will come from Vans. Meanwhile, the good news is that it can be inspected, it can be found, and seems to be a pretty robust design, this crack notwithstanding.
 
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