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Crack in VS attach plate

dougweil

Well Known Member
Hi all:

Our local FBO was doing an inspection on an RV-9A and found this crack in the vertical stab attach plate (F-781 on my RV-7... could be F-981 on the 9A). I know nothing else about it and I am not familiar with this aircraft. Just thought I would share the photo. It might be a wise inspection item to include in a condition inspection.

img6015m.jpg


Note sure about the elongated holes either.

img6016l.jpg


img6018pq.jpg
 
??

Larry, why would you assume this? Something I'm
missing? This is now the second post of a similar
crack discovery in the same general area. Something Vans
should be looking into?
 
Just started my Condition Inspection

Good post Doug. This looks like someone designed their own version of a very important piece using the wrong metal. If that happened I ask WHY do people do this? Larry
I'm going to take a close look in this area as I recently had to leave 3TP tied down thru some pretty heavy storms passing thru Killeen, Tx. Wind was strong enough to break my rudder gust lock and slam the rudder into the elevator. From the picture, how can you tell this is the wrong metal?
Terry
 
Good post Doug. This looks like someone designed their own version of a very important piece using the wrong metal. If that happened I ask WHY do people do this? Larry

I would look at it and say that the bend is a little too high and the back of the part - the radius of the bend - was resting on the sharp edge of the vertical stab spar...:rolleyes:
 
Good post Doug. This looks like someone designed their own version of a very important piece using the wrong metal. If that happened I ask WHY do people do this? Larry

Here is a link to one other report of cracking in this part:

http://www.vansairforce.com/community/showthread.php?t=87124

Note that in that case the crack was through one of the bolt holes. Like the case discussed in this thread, the crack originated at the perimeter of the part at the apex of a concave angle.

So far as I know, in neither of the reported cases was there any indication that the part was other than as supplied by Vans.

Thanks, Bob K.
 
Was all that paint chipped away as part of the inspection, or was it all chipped away already prior to being inspected? If the latter, then wouldn't that indicate some seriously abnormal vibration has been going on?
 
I made an incorrect statement earlier thinking of the 4/6/7/8 models sorry for assumption and wasted words. Larry
 
Doug,
When did the airplane go into service and how many hours are on it now?
Thanks for the information.
Best regards,
Chuck
 
Both this and the one in the other thread have the attach plate on the forward side of the VS front spar, when it should be riveted to the back side.
 
Check Dwg 27

The dwg shows the F-981 Vert Stab Attach plate (ISO View) positioned in front of the spar. Am I mising something?
 
The dwg shows the F-981 Vert Stab Attach plate (ISO View) positioned in front of the spar. Am I mising something?

Unless the drawing has changed, the 981 plate sites aft of the VS front spar (broken lines).

VS702_981.jpg


Not saying this is absolutely correct for all installations. The written instructions indicate such. I think it would depend upon the trimming of the VS forward spar. Like Gil mentioned earlier, the plate in question is wrapped around the sharp end of the forward spar. Having the plate on the back side is more forgiving of spar length.
 
As posted, we're seeing contributing factors like bad bends, galling stress, etc. But the bottom line is that it gives me the neck-hair thing. The 2 threads on this have different cracks, but in the same place. Snap rolls anyone? Hangar horsin' on the vertical? Coincidence?
 
Unless the drawing has changed, the 981 plate sites aft of the VS front spar (broken lines).

<snip>

Not saying this is absolutely correct for all installations. The written instructions indicate such. I think it would depend upon the trimming of the VS forward spar. Like Gil mentioned earlier, the plate in question is wrapped around the sharp end of the forward spar. Having the plate on the back side is more forgiving of spar length.

If I read the drawing correctly the factory punched holes are in the attach plate.

This would mean that match drilling needs to be done from the more restricted aft side.

I could easily see how a builder could incorrectly place the plate on the front surface for easier drilling.

Am I correct in saying that only the attach plate, and not the spar, is pre-punched?
 
As posted, we're seeing contributing factors like bad bends, galling stress, etc. But the bottom line is that it gives me the neck-hair thing. The 2 threads on this have different cracks, but in the same place. Snap rolls anyone? Hangar horsin' on the vertical? Coincidence?

More likely Nate's comment...

Both this and the one in the other thread have the attach plate on the forward side of the VS front spar, when it should be riveted to the back side.
 
If I read the drawing correctly the factory punched holes are in the attach plate.

Am I correct in saying that only the attach plate, and not the spar, is pre-punched?

Yes, the 981 plate is pre-punched. I used and angle drill while the VS was held in position for a few holes. Then removed the VS and match drilled the rest.
 
Someone sent me a PM asking me why I have a strong opinion about the placement of 981. Here's my reply:

I don't think it's an absolute requirement, but I am a plans kind of guy, and the plans clearly show the plate behind the spar.

The key I think is to be sure the 981 plate is flat against the fuselage aft deck and the HS forward spar when determining position relative to the VS and drilling to the VS forward spar. If the 981 plate will not lay flat against all three surfaces (aft deck, HS spar, and VS spar) when the VS is in position (aft spar nice and plum), then a position change (move to the front of VS spar, or back), or shims may be necessary.


I'll also add that if you determined that the 981 plate NEEDS to be on the front of the VS forward spar, then be sure that the spar is trimmed as to not extend into the bend radius of the 981 plate, and that the spar has sufficient edge distance for the required rivets.
 
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Someone sent me a PM asking me why I have a strong opinion about the placement of 981. Here's my reply:

I don't think it's an absolute requirement, but I am a plans kind of guy, and the plans clearly show the plate behind the spar.


I think the plate being on the forward side is critical in this case.

See that the crack is at the very edge of the forward VS spar. Bending the plate over this edge has concentrated the bend stress at the very point that the crack has occurred.

If it had been riveted on the aft side in accordance with the plans the stress would have been distributed over the full bend, substantially reducing the likelihood of cracking.
 
Good timing....

I think the plate being on the forward side is critical in this case.

See that the crack is at the very edge of the forward VS spar. Bending the plate over this edge has concentrated the bend stress at the very point that the crack has occurred.

If it had been riveted on the aft side in accordance with the plans the stress would have been distributed over the full bend, substantially reducing the likelihood of cracking.

Edit: I just checked my RV-7 vert stab and the F-781 plate is installed on the front side of the forward spar, like in the pictures above. I rechecked my plans, and, sure enough, my copy of RV-7 drawing 27A (in two views) clearly shows it installed on the front of the vert stab forward spar. So it looks like the plans for the RV-7 and RV-9 are different.

When I assembled my vert stab to the fuselage, everything lined up and the front vert stab spar, front horiz stab spar, F-781 plate, and vert stab rear spar were perfectly aligned with no shims required. By the way on my F-781 the pre-drilled holes were NOT elongated.

I will ensure that the forward spar is trimmed sufficiently so that it does not intrude on the F-781 plate bend radius.
 
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How difficult will it be to inspect it for cracks in the future if it is in the back? I haven't assembled mine yet, but it looks pretty tight back there to see. Maybe this is a place to double up? That possibly could just move the stress to the edge of the bracket, so maybe not a fix. There are quite a few 6, 7, and 9s flying without cracks, so as long as it can be inspected and there is an easy fix, thats good news. I would be interested if any with F-981 mounted as shown on the plans - in the back have had any cracks? Maybe a SB to inspect at annual would be a good idea.

And thanks Nate for the info you have provided - as well as the discussion by others. It could save someone from a real bad day.
 
Good thread. It made me wonder and I dig my 5 years old log. The plate is indeed at the back.



VSbackplate.jpg




It's very easy to check during condition inspection especially unprimed unpainted . :)
 
Edit: I just checked my RV-7 vert stab and the F-781 plate is installed on the front side of the forward spar, like in the pictures above. I rechecked my plans, and, sure enough, my copy of RV-7 drawing 27A (in two views) clearly shows it installed on the front of the vert stab forward spar. So it looks like the plans for the RV-7 and RV-9 are different.

When I assembled my vert stab to the fuselage, everything lined up and the front vert stab spar, front horiz stab spar, F-781 plate, and vert stab rear spar were perfectly aligned with no shims required. By the way on my F-781 the pre-drilled holes were NOT elongated.

I will ensure that the forward spar is trimmed sufficiently so that it does not intrude on the F-781 plate bend radius.

I went back and looked at my 7 build pics and mine is also on the front of the spar. The plans are in the hangar so I can't check em but I am pretty sure I would have followed the plans.

I am not really sure but from looking at my pics vs these pics posted here it kinda looks like the 9 has more of a bend in that plate than the 7 does due to the angle of the spar. Can anyone confirm this?

This one kind has my attention...

How many hours and what type of flying does this airplane see?
 
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I went back and looked at my 7 build pics and mine is also on the front of the spar. The plans are in the hangar so I can't check em but I am pretty sure I would have followed the plans.

I am not really sure but from looking at my pics vs these pics posted here it kinda looks like the 9 has more of a bend in that plate than the 7 does due to the angle of the spar. Can anyone confirm this?

This one kind has my attention...

How many hours and what type of flying does this airplane see?

There seems to be a big difference on the -7.

The attach plate is not pre-punched for the bolts into the horiz. stab spar, and is not attached to the "base" across the longerons. A shim is also specifically allowed on the plans.

This gives a lot more tolerance in positioning so the radius of the bend is not forced against the bottom of the vert. stab spar.
 
There are quite a few 6, 7, and 9s flying without cracks, so as long as it can be inspected and there is an easy fix, thats good news.
I suspect a more accurate statement is that there are quite a few flying that have not been inspected for cracks in this area. I plan to check mine next time i'm at the airport.
 
I suspect a more accurate statement is that there are quite a few flying that have not been inspected for cracks in this area. I plan to check mine next time i'm at the airport.

With more than that plate to inspect under that faring, why wouldn't it be inspected during your annual?.................:eek:
 
There seems to be a big difference on the -7.

The attach plate is not pre-punched for the bolts into the horiz. stab spar, and is not attached to the "base" across the longerons. A shim is also specifically allowed on the plans.

This gives a lot more tolerance in positioning so the radius of the bend is not forced against the bottom of the vert. stab spar.

Yes, the RV9 and RV7 plans are completely different in this area. It looks like the RV9 horiz stab front spars carry straight through in this area and the RV7 has a spar carry-through assembly (due to the angled horiz stab front spars). This changes how the vert stab front spar attaches to the horiz stab front spar. On the RV9 the F-981 plate attaches to the rear of the vert stab front spar and to the front of the horiz stab front spar and has a bottom flange, and on the RV7 the F-781 plate attaches to the front of the vert stab front spar and to the rear of the horiz stab carry-through assembly.

Apples and oranges...
 
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With more than that plate to inspect under that faring, why wouldn't it be inspected during your annual?.................:eek:
In fact, it's been part of my annual since the crash of the -7A a couple of years ago when the vertical stab separated in flight. But while I know I looked at mine after that, I can't remember whether my spar is ahead or behind the mounting plate and I want to check next time i'm out there.
 
Good Catch

Nate,

Yep, you are correct, after you blew up the drawing it is clearly to be mounted on the aft side. Very timely, I hadn't riveted mine yet.
 
The F-981 can be mounted on either side of the spar

According to my directions (page 8-17 of the 12/13/04 Rev), paragraph 6 under Fitting the Vertical Stabilizer says:

"If the rear spar bends aft at the top when the front spar is clamped, the vertical spar may be mounted on the rear of the F-981 plate."

So, unless there is a newer rev out there that I'm not aware of, we have the option and mine is on the front of the spar. I'm just short of 40 hours on the airframe but I will still inspect for a crack the next time I'm out at the hangar.

This is scary stuff!!
 
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955 Hrs - No cracks

Inspected this last night and found no issues at 955 hrs. Added a special inspection to the annual checklist, too. Only takes 5 min to pull the emp fairing and give it a good once over.

Added hardwiring for the GDL39 as well - that was a bit more fun.....but worth it!
 
According to my directions (page 8-17 of the 12/13/04 Rev), paragraph 6 under Fitting the Vertical Stabilizer says:

"If the rear spar bends aft at the top when the front spar is clamped, the vertical spar may be mounted on the rear of the F-981 plate."

My F-981 plate is installed forward of the VS spar as well on my RV-9A. If I remember correctly, it just seemed to fit better that way. I can see putting a doubler on there, perhaps including the two upper bolts and several of the VS spar to F-981 plate rivets. I predict a service bulletin in the near future.
 
I checked with the mechanic working on this airplane and it appears that this crack may have been there quite a while. The airplane is TruTraks "old" RV-9A that has 1200 total time on it. They have installed a new bracket and it will soon be back flying again.
 
Agree with Mike. I'll definitely add reinforcement to this area on my 9A, and on my 8 under construction. Seems like good insurance, and easy and light.

I think this attach bracket can see significant bending stress in turbulence or hard aerobatics. Another possibility is cyclical stress from the propeller slipstream.

Roger Bloomfield
Colorado
 
Grain of the metal

Looking at the photo it looks as if the crack is following the grain of the metal, if it is, the bracket should have been folded with the grain going the other direction for better strength. Just my thoughts..
 
I am surprised at all the speculation. Other than Kelly Johnson.
I just finished this part last week and it is the factory part and is installed properly.
The directions clearly state on the RV-9(A) that the plate can be installed to the front or rear of the VS-702. Which ever gives you a better rudder hinge alignment.
However the multiple cracks we have seen are troublesome.
 
Big thanks ...

..... to Kelly and Mark W. for checking the exact wording in the 9/9A plans. As I was reading this thread, I remembered being given the option of putting the attach plate on the front or rear of the VS spar ... then I quickly thought my memory must be wacko. As I was getting increasingly concerned - about both my VS attach and my memory - Kelly and Mark clarified it WAS in the plans after all. Whew! Feeling reprieved ....:eek:
 
Mine is fine

After 1154 hrs and two twisted rudder locks (first a 1/8" ss rod, later two 3/16" ss rod) due to strong gusts my F-981 showed no cracks.
F-981 installed at the rear of spar.
 
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..... to Kelly and Mark W. for checking the exact wording in the 9/9A plans. As I was reading this thread, I remembered being given the option of putting the attach plate on the front or rear of the VS spar ... then I quickly thought my memory must be wacko. As I was getting increasingly concerned - about both my VS attach and my memory - Kelly and Mark clarified it WAS in the plans after all. Whew! Feeling reprieved ....:eek:

The fact that Vans usually accurate parts can fit either way says something about the tolerances in the area.

A careful inspection for all those who mounted it on the front of the fin spar to see that no part of the radius of the connector plate touches the bottom of the fin spar would be in order.

Then feel reprieved...:)

The two examples shown would appear to fit into this category.
 
Gil, thanks for your insight on this. Im with Vlad - this is a good thread. Full of info and real concern for getting this right. The thread on the -12 window is the same way - not full of opinions, but everyone trying to find a solution to a problem. People are stepping up to test and to provide material for the test. It is appreciated by us first time builders.
 
Rv7

There seems to be a big difference on the -7.

The attach plate is not pre-punched for the bolts into the horiz. stab spar, and is not attached to the "base" across the longerons. A shim is also specifically allowed on the plans.

This gives a lot more tolerance in positioning so the radius of the bend is not forced against the bottom of the vert. stab spar.
I checked mine finished in 2004 today. On my RV7 the forward VS spar continued down with the attach plate to the two top bolts in the horizontal spar. Those bolts go through the attach plate and the VS spar. The tongue of the spar that continues with the attach plate bends with it! There is no stress riser like the 9 in the original photos on my 7.
 
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"Assembly stress?"

Let me preface this comment by saying that I'm not a builder, only a purchaser/repairer..........

It looks like there could be a possibility of having added stress during assembly. If the attaching bracket was not fitted so that it was very closely and correctly lined up with the front spar, (in other words if the bracket had a small gap between it and the front spar,) then when the bolts were tightened down, they would pull the bracket down tight. That would add a permanent "assembly stress" which would exacerbate any vibration or prop-pulse cyclical loads.

More likely it is what Mel said, the radius of the bend is in the wrong place.

Just my $2 worth. (I'm raising the floor of marginal advice to reflect the value of the modern dollar.) :rolleyes:
 
So let's assume, for argument's sake, that the plane is assembled and flying, the VS shows no cracks, and is assembled according to plans.

What would be the options for additional attachments to create a "belt-and-suspenders" "fix" to the issue, both with and without removing the entire VS and with and without de-riveting and re-riveting parts into place?

E.g., what about a "clip" made of angle aluminum on each side, bolted to the flanges on the VS spar and the HS spar? What about straps? Etc., etc....

Just thinking out loud about what might be good solutions to prevent catastrophic failure should a crack appear...
 
Before We "Fix" It, We Need To Identify The Problem

Like Ted Change in a previous post, my plane was tied down during a storm violent enough to destroy the gust lock and slam the rudder into the elevator. I've since made a new lock out of heat treated tool steel. Just finished my condition inspection and a close look at the attach plate showed no deformation or cracking.
I've seen builders put parts on without deburring. Also seen overtorquing significant enough to break bolts. I've even seen bread bag ties used as safety wire. Before assuming a design problem, we may want to also consider a build problem or an overstress flight problem. Like Pete Howell, I'm going to continue to look closely at this area, but eight years and nearly 800 hours tells me this may not be an issue. The great value in a forum is being able to continually share this type of info with a wide sample of builders.
Terry, CFI
RV9A N323TP
 
I inspected mine today and found my F-981 was installed on the FWD side of the V.S. spar. Though it is not cracked, it does appear to be under some stress there.

I seem to recall that the plate, when installed on the AFT side, caused a pre-load on the rear spar. So that's why I went with the installation I chose.

Anyway, I do find the current installation unacceptable and ordered a new F-981 and am planning to use it as a "doubler" for the existing plate.

This thread alone was worth my $25 annual dues to the VAF!
 
ordered a new F-981 and am planning to use it as a "doubler" for the existing plate.

This thread alone was worth my $25 annual dues to the VAF!

Now that is a great idea. Using a new one as a doubler - perfect. Thanks for the idea. I think I will order a second one and when I get to that part, I will start with both.
 
I inspected mine today and found my F-981 was installed on the FWD side of the V.S. spar. Though it is not cracked, it does appear to be under some stress there.

I seem to recall that the plate, when installed on the AFT side, caused a pre-load on the rear spar. So that's why I went with the installation I chose.

Anyway, I do find the current installation unacceptable and ordered a new F-981 and am planning to use it as a "doubler" for the existing plate.

This thread alone was worth my $25 annual dues to the VAF!

The easier solution may be to just un-rivet it from the fin spar and make an appropriate shim that will remove the "stress" you mention.

Doubling up the part without removing the built-in stress may not be a good idea.
 
The easier solution may be to just un-rivet it from the fin spar and make an appropriate shim that will remove the "stress" you mention.

Doubling up the part without removing the built-in stress may not be a good idea.

Good points. I don't think that it is "pre-loaded", just "riding the radius". I will make sure however that a shim is not necessary. Trimmiming about a 1/4" off the lower end of the VS FWD spar should clear up the radius issue. Doubling it will ease my mind.
 
Cracking Issue!

...I inspected mine the other day as well and observed no crack but I am very nervous about this part. I loosened all the bolts to see if it was happy in it's current location (on the front of the spar) or was stressed and it wasn't. I slip my plane very hard at times, landing on extremely short strips in the mountains. This action puts considerable stress on the VS, namely this part that is in question. I am concerned enough about it that I am making a new part for my plane out of 4130 Chrome Moly and will replace it. I think adding 3 or 4 ozs. is well worth the security and peace of mind, knowing the tail will stay put. If it were to leave it definitely would ruin your day. If anyone has thoughts on this, or would like one please post or let us know. Thanks, Allan...
 
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