Van's Air Force
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What is this Bump on tail of my RV-7?
- Thread starter dilamipo
- Start date
Looks like a hard landing to me. The crease goes through the inspection plate so it can't be a manufacturing error. It could possibly have changed the incidence of the stabilizer slightly to negative thus requiring a little foreward trim in level flight.
High_Flyer
Well Known Member
Common on taildraggers
Hi,
This is quite common on RV-tailwheel using bumpy grass runways...
The cure is to rivet an angle just below the inspection plate.
Here are 3 pictures I received from another builder in the U.K.
I've done it on my RV-7 (not flying yet), very easy to do. I used some surplus angle received with my kit.
Alain.
Hi,
This is quite common on RV-tailwheel using bumpy grass runways...
The cure is to rivet an angle just below the inspection plate.
Here are 3 pictures I received from another builder in the U.K.
I've done it on my RV-7 (not flying yet), very easy to do. I used some surplus angle received with my kit.
Alain.
Robert Anglin
Well Known Member
Agree!
The smoking rivets behind the rudder cable would seem to indicate something more than just the common hump at this site has happened here.
Most every thing has a fix, it just takes time and some sheet metal work.
Yours, R.E.A. III #80888
The smoking rivets behind the rudder cable would seem to indicate something more than just the common hump at this site has happened here.
Most every thing has a fix, it just takes time and some sheet metal work.
Yours, R.E.A. III #80888
brad walton
Well Known Member
Good eye Robert. Looks like there was some excessive tail wheel loads beyond the design capabilities
Dimitri,
I agree with the other posters that it looks like your tail area took some kind of a hit. I notice that the leading edge to the tailwheel fork at the bottom shows a lot a wear, possibly may even have taken a blow of some kind--like falling into a pothole or something.
If it were me, I would pull everything apart, remove your tailwheel spring, remove the horizontal stab/vertical stab and rudder because you are going to need access to assess the damage and do the repair.
One other recommendation: looks like you could really use one of the after-market tailwheel forks like those sold by JD Air or Vince Frazier. This might prevent the kind of damage that apparently happened here.
I agree with the other posters that it looks like your tail area took some kind of a hit. I notice that the leading edge to the tailwheel fork at the bottom shows a lot a wear, possibly may even have taken a blow of some kind--like falling into a pothole or something.
If it were me, I would pull everything apart, remove your tailwheel spring, remove the horizontal stab/vertical stab and rudder because you are going to need access to assess the damage and do the repair.
One other recommendation: looks like you could really use one of the after-market tailwheel forks like those sold by JD Air or Vince Frazier. This might prevent the kind of damage that apparently happened here.
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Side Load
To me it looks like a classic case of side-loading the tailwheel - it falls off the pavement and gets caught on an edge, or the two bolts that hold the socket to teh spring shear as the tail is being swung around and it falls off an edge. Either way, the tailwheel itself comes to a sudden stop while the fuselage is still trying to swing, and you put a slight kink in the fuselage structure. I've seen it on a couple airplane's, and both have had a sudden tailwheel stop event.
Just one possibility.
Paul
To me it looks like a classic case of side-loading the tailwheel - it falls off the pavement and gets caught on an edge, or the two bolts that hold the socket to teh spring shear as the tail is being swung around and it falls off an edge. Either way, the tailwheel itself comes to a sudden stop while the fuselage is still trying to swing, and you put a slight kink in the fuselage structure. I've seen it on a couple airplane's, and both have had a sudden tailwheel stop event.
Just one possibility.
Paul
I disagree that this is common. I've inspected a lot of RVs over the last 35 or so years and I find this rare. Yes, I've seen it, but not often.
Bob Martin
Well Known Member
OK, Here's my "guess"!
On the -4 & -6, the center "J" stiffener continues all the way to the tail at the bottom of the inspection panel.
The -7 was designed after the -9. The -9 was not designed with a tailwheel version in mind.
Perhaps the designer didn't think that last bit of stiffener was needed on a tricycle. When the -7 came out, this was simply overlooked
My $.02!
Mel,
Doesn't the six have another longeron in this area and access on only one side, plus a smaller access panel as well?
Perhaps this is why the -6 is superior to the -7 ???
On the -4 & -6, the center "J" stiffener continues all the way to the tail at the bottom of the inspection panel.
The -7 was designed after the -9. The -9 was not designed with a tailwheel version in mind.
Perhaps the designer didn't think that last bit of stiffener was needed on a tricycle. When the -7 came out, this was simply overlooked
My $.02!
az_gila
Well Known Member
Mel,
Doesn't the six have another longeron in this area and access on only one side, plus a smaller access panel as well?
Perhaps this is why the -6 is superior to the -7 ???
Yes, it looks like the downside to the larger -7 access panel is the loss of the middle J-stringer in the aft most fuselage bay compared to the -6 models.
Look at the bottom of the rudder fairing. If there is not indication of contact damage from the tail wheel, then the scenario Paul described above is likely the cause.
N477RV (the RV-7 owned by Van's and used by Mike Seager for transition training) has spent its entire life based on a grass runway airport. It is just a few hrs shy of 4800 hrs T.T. and has had nothing like this occur (not to mention all of the plopped in landings it has endured during training).
The inertia of the induced by the tail swinging can induce huge twisting loads on the tail spring mount if the tail wheel comes to a stop suddenly.
David Paule
Well Known Member
High_Flyer
Well Known Member
Sorry...
OK, looking at all the posts since this morning it seems that I gave incorrect informations.
I apologize if what I wrote was not good.
However it makes sense to me to put a reinforcing angle at that location, with all the precautions that others have stated.
Alain.
OK, looking at all the posts since this morning it seems that I gave incorrect informations.
I apologize if what I wrote was not good.
However it makes sense to me to put a reinforcing angle at that location, with all the precautions that others have stated.
Alain.
Ralph Inkster
Well Known Member
I agree with Paul's theory that the tail wheel was abruptly side loaded. Looking at that skin, I'd check further for possible internal damage.
The things I would check is; bolt holes in F711 & F712 bulkheads are not stretched, WD409 tail spring weldment wasn't cracked, F711 & F712 bulkhead rivet flanges were not stretched out, lower J strip not buckled.
The ripple in the skin has taken a lot of rigidity away from that section of the fuselage, stiffeners (more than one) might restore most but not all to that area.
First off- I'd be phoning the mothership for their suggested course of action.
The things I would check is; bolt holes in F711 & F712 bulkheads are not stretched, WD409 tail spring weldment wasn't cracked, F711 & F712 bulkhead rivet flanges were not stretched out, lower J strip not buckled.
The ripple in the skin has taken a lot of rigidity away from that section of the fuselage, stiffeners (more than one) might restore most but not all to that area.
First off- I'd be phoning the mothership for their suggested course of action.
cajunwings
Well Known Member
cdmiller
Well Known Member
Tailwheel side load
I have seen this exact deformation in the same location in an RV-8 that was ground looped. As the plane veered off the runway, the Tailwheel got caught in muddy grass while the fuselage continued to swing around. The rear part of the fuselage was buckled slightly where the Tailwheel spring attaches to the two rear fuselage bulkheads. Repair involved replacing both rear bulkheads (they both are double bulkheads), and the bottom rear fuselage skin. The top flat fuselage plate, under the horizontal stabilizer, may also be deformed and need to be replaced. It will still be difficult to remove the bump on the side fuselage skin. The bump can be minimized with an aluminum angle on the inside as suggested by others.
Dan Miller
I have seen this exact deformation in the same location in an RV-8 that was ground looped. As the plane veered off the runway, the Tailwheel got caught in muddy grass while the fuselage continued to swing around. The rear part of the fuselage was buckled slightly where the Tailwheel spring attaches to the two rear fuselage bulkheads. Repair involved replacing both rear bulkheads (they both are double bulkheads), and the bottom rear fuselage skin. The top flat fuselage plate, under the horizontal stabilizer, may also be deformed and need to be replaced. It will still be difficult to remove the bump on the side fuselage skin. The bump can be minimized with an aluminum angle on the inside as suggested by others.
Dan Miller
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az_gila
Well Known Member
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Infidel
Well Known Member
Same thought here and suspect an anomaly that pronounced, would likely extend to the vertical and possibly horizontal stabs.
Side load is what came to my mind when I saw the photo. Reading the thread I still think that may be the case and I am not the only one thinking the same way.
Boyd Birchler
Well Known Member
I have looked at a lot of RV7 and all I have seen so far have a bulge just below the access panel on each side. I think the answer is to put a angle as described just below the opening. The 7 was designed with access holes on each side that are larger than the single hole on the RV6.
The center part of the side skin just below the access opening is in compression from the weight of the plane on the tail spring transferred to the tail cone, that's what causes the bulge. If you pick up the tail by the horizontal and the bulge goes away it is likely harmless: however I think the angle stiffener added just below the opening is a superb modification that would prevent a hard landing from producing permanent deformation.
Another way to obtain the same objective would be to increase the thickness of the access cover and add several more nut plates around the opening so that the plate would become structural and carry some of the compression loads. Four screws is simply not enough to transfer the loads be across the cover panels.
The center part of the side skin just below the access opening is in compression from the weight of the plane on the tail spring transferred to the tail cone, that's what causes the bulge. If you pick up the tail by the horizontal and the bulge goes away it is likely harmless: however I think the angle stiffener added just below the opening is a superb modification that would prevent a hard landing from producing permanent deformation.
Another way to obtain the same objective would be to increase the thickness of the access cover and add several more nut plates around the opening so that the plate would become structural and carry some of the compression loads. Four screws is simply not enough to transfer the loads be across the cover panels.
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It may not amount to anything without the addition of a stiffener as discussed, and I'm not at the hangar to check my aircraft, but aren't there *6* screws holding that plate on (two that go through the plate into the longeron which is tapped for those screws? (Might even be more, I dunno).
If so, they appear to be missing from the photo. Also, it looks to me like the flange on the aft spar of the VS is bent, too.
Isn't a structural cover plate a contradiction in terms?
Good luck with the inspection and repairs, Dimitri.
Thank everybody spent some time to reply me.
To be true the first photo is the tail of one RV9 that one friend of mine is looking to buy. This RV9 is in spain and we have fly it last week end.
Seem everything ok except that problem on the tail, so we consider to buy that airplane and then when it will be in italy to made the fix.
About my RV7 it has also these bumps on the tail even if the problem is very light.
Indeed every RV7 that I have seen in Italy have that problem, less or more.
I attach the pics of the tail of mine
To be true the first photo is the tail of one RV9 that one friend of mine is looking to buy. This RV9 is in spain and we have fly it last week end.
Seem everything ok except that problem on the tail, so we consider to buy that airplane and then when it will be in italy to made the fix.
About my RV7 it has also these bumps on the tail even if the problem is very light.
Indeed every RV7 that I have seen in Italy have that problem, less or more.
I attach the pics of the tail of mine
Smilin' Jack
Well Known Member
Bulge
Went to the airport and inspected my RV7. I too have this problem. Hardly noticeably there but it is.. mine is slightly less than Dimitri. So I walked over to a friends hanger and looked at his 6. He too has a ever so slight bulge but putting your hand on it you can feel it... So off to look at another 7. Same as mine...
I took photo's outside and inside of mine sent them to Van's
We'll see what they say, I also included the 6 photos. On mine there is no distortions on the inside, in fact you can not even notice any bulge on the inside.
There are no working rivets nor bulkhead distortions.
I will continue to look at other RV7's. Perhaps we do need a continuation of a small channel across the lower section of the inspection plate which attaches to the two bulkheads.
I am waiting for a response from Van's
Went to the airport and inspected my RV7. I too have this problem. Hardly noticeably there but it is.. mine is slightly less than Dimitri. So I walked over to a friends hanger and looked at his 6. He too has a ever so slight bulge but putting your hand on it you can feel it... So off to look at another 7. Same as mine...
I took photo's outside and inside of mine sent them to Van's
We'll see what they say, I also included the 6 photos. On mine there is no distortions on the inside, in fact you can not even notice any bulge on the inside.
There are no working rivets nor bulkhead distortions.
I will continue to look at other RV7's. Perhaps we do need a continuation of a small channel across the lower section of the inspection plate which attaches to the two bulkheads.
I am waiting for a response from Van's
maniago
Well Known Member
Us too!
FWIW weve had this issue on the Mustang2 for many years as well (not sure about the midget) and the factory change is to make a full skin doubler that fits inside the tail cone between the last two buklheads - a double skin wall if you will - the inside doubler is .032 and the original skin .025. I also added an additional bulkhead at the factory suggestion as I plan on a lot of grasswork, and have therefore leaf springs and 7" TW. The additional BH is rivetted to the back of second to last BH so I have BH flanges facing forward and facing aft and obviously a double line of rivets there picking up the skin. We have a longitudinal skin flange extending all the way back to the vert spar, but no additional longerons extending back there like you guys do.
Of additional note, a post build fix in our case is to add the full skin doubler outside the skin - same idea. Not sure how youd do that with your inspection cover. We have our inspection hole in the previous bay.
FWIW weve had this issue on the Mustang2 for many years as well (not sure about the midget) and the factory change is to make a full skin doubler that fits inside the tail cone between the last two buklheads - a double skin wall if you will - the inside doubler is .032 and the original skin .025. I also added an additional bulkhead at the factory suggestion as I plan on a lot of grasswork, and have therefore leaf springs and 7" TW. The additional BH is rivetted to the back of second to last BH so I have BH flanges facing forward and facing aft and obviously a double line of rivets there picking up the skin. We have a longitudinal skin flange extending all the way back to the vert spar, but no additional longerons extending back there like you guys do.
Of additional note, a post build fix in our case is to add the full skin doubler outside the skin - same idea. Not sure how youd do that with your inspection cover. We have our inspection hole in the previous bay.
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Smilin' Jack
Well Known Member
I have installed a beef up to the area described after talking to Scott McDaniels,
It is not a item recommended by Van's or Scott at this time.
Since the 7 fuselage is a RV9A the mid horizontal J angle was not carried through to the aft bulkhead as in the RV6, RV 8 or the RV14. I talked to Scott and he said he had seen it but not in sufficient quantity.
It took two days, did not have to remove the tail as all work was done through the aft inspection panels.
I did this as I had a extremely slight bulge and after looking at several other RV7" decided it was a nice improvement to the area. The nice part is the bulge was eliminated.
It is about 5 pages long and if you would like me to email you a copy please send me an email.
Thanks
Jack Hunt
[email protected]
It is not a item recommended by Van's or Scott at this time.
Since the 7 fuselage is a RV9A the mid horizontal J angle was not carried through to the aft bulkhead as in the RV6, RV 8 or the RV14. I talked to Scott and he said he had seen it but not in sufficient quantity.
It took two days, did not have to remove the tail as all work was done through the aft inspection panels.
I did this as I had a extremely slight bulge and after looking at several other RV7" decided it was a nice improvement to the area. The nice part is the bulge was eliminated.
It is about 5 pages long and if you would like me to email you a copy please send me an email.
Thanks
Jack Hunt
[email protected]
BillL
Well Known Member
Email sent Jack. My non-flying 7 has the pucker in that last station. I thought it was just due to the second bulkhead pulling it in. The pucker will allow it to buckle at a much lower load in compression.
Thanks,
