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SB 14-01-31; RV-6, 7, 8

This is one of those times when I wish Van's tech support had an active presence on VAF.

Bob and All.

Although as he states, the opinions expressed on this forum are strictly his, HE WROTE THE SB. The "he" is VAF screen name "RVBuilder2002", Scott McDaniels who builds the prototypes for Van's (amongst other duties). Please go back and read what Scott wrote. It's very informative and helps separate the wheat from the chaff.

I will check my very early built HS (1993) , yet recently completed -6 (2011) on Monday.
 
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Having spent an hour reviewing all this now, here is my 2c worth.

We built a 7 - not inspected yet :rolleyes:

On the print for the horizontal stabiliser, it clearly refers to notching the spar with appropriate dimensions.

Now we are on with the 8 - Dwg 3 for the 8 does not have any reference to the same notches and there is just a blank area on the print.

Neither do the instructions refer to notching the spar.

I cannot see any logic to this and can only surmise that for the 8, this is a serious omission by Vans, or, between the 7 and 8 designs being finalised, it was not considered necessary. That doesn't stack up though when you closely examine the iso view of the stab as mentioned by Andy earlier as the notches are there.

If the stab is cracked, I think it will be quicker and more importantly - safer - to re-manufacture a stabiliser rather than try and drill out many important rivets and attempt to re rivet them with precious little access.

I think Vans should offer this as an alternative to the mods and be pretty sharp about it.

How about you confirm your builder number, send in an order and they supply a stabiliser kit up to the new spec for cost plus a suitable margin so they are not out of pocket ?

We are inspecting on Tuesday and I will report back. Come the Spring, my intention is to build a new stab and have done with it - it will make resale easier and I will be happier knowing that all the rivets have gone in once :D
 
Bob and All.

Although as he states, the opinions expressed on this forum are strictly his, HE WROTE THE SB. The "he" is VAF screen name "RVBuilder2002", Scott McDaniels who builds the prototypes for Van's (amongst other duties). Please go back and read what Scott wrote. It's very informative and helps separate the wheat from the chaff.

I will check my very early built HS (1993) , yet recently completed -6 (2011) on Monday.

Yes, I understand that and have read. By active I mean regularly answering in official capacity. Like, Mel only with a paycheck. :*)
 
Question:
What is the best way, when I just began to build my first RV7 Empennage ? Wait for better components from VAN'S ? Include the extra sheets ? Continue building ... ? :confused:
Thanks, Achim

Highly suggest you put in the fix now.
 
Having spent an hour reviewing all this now, here is my 2c worth.

We built a 7 - not inspected yet :rolleyes:

On the print for the horizontal stabiliser, it clearly refers to notching the spar with appropriate dimensions.

Now we are on with the 8 - Dwg 3 for the 8 does not have any reference to the same notches and there is just a blank area on the print.

Neither do the instructions refer to notching the spar.

I cannot see any logic to this and can only surmise that for the 8, this is a serious omission by Vans, or, between the 7 and 8 designs being finalised, it was not considered necessary. :D

Remember that the -7 was released a long time after the -8, so the implication that Vans forgot the notches between the -7 and -8 is mistaken.
 
Point taken.

So.... why wasn't a rev done on the 8 prints ?

Our 8 kit is 6 years newer than our 7.

Either way - I think drilling out 160 rivets and replacing them isn't a sensible way forward.

The lower splice angle is a significant load path item. Even removing and re riveting that with such limited access doesn't thrill me.
 
If the stab is cracked, I think it will be quicker and more importantly - safer - to re-manufacture a stabiliser rather than try and drill out many important rivets and attempt to re rivet them with precious little access.

I think Vans should offer this as an alternative to the mods and be pretty sharp about it.

How about you confirm your builder number, send in an order and they supply a stabiliser kit up to the new spec for cost plus a suitable margin so they are not out of pocket ?

We are inspecting on Tuesday and I will report back. Come the Spring, my intention is to build a new stab and have done with it - it will make resale easier and I will be happier knowing that all the rivets have gone in once :D

I pretty much agree with the above, no matter how careful you are drilling out rivets, the holes tend to oversize in thin material due to the rivet expanding when driven.

The part I don't like about building a new horiz is then you will have to back drill the front attach points accurately without oversizing the longeron holes, that won't be easy.

No doubt building a new stab will be quite a bit more work than accomplishing the repair, so I'm still on the fence on this.

SN# 70214
 
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Yes, especially since Van's has acknowledged in the past the existence of edge distance issues at that attach point. Oh, dear, what to do? I count 66 rivets to be drilled out in addition to redrilling rivets holes where, in some cases, ideal deburring of each part may not be attainable. This is really quite a conundrum.

As Darwin said to me on Facebook, Van's will market a spaceship kit before I have enough hours on the airframe to be a problem, but what about the next guy who owns it? It's as much an ethical dilemma as a technical one.

Oh by the way, I'm builder 70240. So the original DWG 3 (Feb. 2001, no revision) with prepunched skins but no prepunched parts existed at least up to the first 240 kits.
 
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It appears from those who have inspected their aircraft that most higher time airframes are cracked. This could mean that thousands of RV's will be grounded. For those of us without the tools and skills to make this repair what options are available? Would it be acceptable as a example to ferry the aircraft to someone to complete the repair? I suspect there will be some individuals setting up what amounts to a mod line doing these repairs but you have to get the aircraft there.

George
 
Informal survey after discussions

Are the airplanes affected operated off tarmac or grass ?

We are discussing the differences between the high frequency stresses imposed on the stabiliser when taxiing on uneven ground compared to the gradual but large load imposed during aeros.

This was noted with engine mount cracks some time ago.

Not drifting the thread but may be a factor.
 
RV-6A
O-360 A1A
Hartzel constant speed
Tail built 1994-5
No notch
No acro
Some grass/dirt operation
No notch on plan
Total time 650 hours
No cracks
 
From a legal aspect.....

It appears from those who have inspected their aircraft that most higher time airframes are cracked. This could mean that thousands of RV's will be grounded. For those of us without the tools and skills to make this repair what options are available? Would it be acceptable as a example to ferry the aircraft to someone to complete the repair? I suspect there will be some individuals setting up what amounts to a mod line doing these repairs but you have to get the aircraft there.
George

Since service bulletins are not mandatory, as far as the FAA is concerned, this would be your decision. Ferrying the aircraft would be legal.
Whether or not it is prudent would be your decision.
 
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No Cracks

No cracks found.

RV-8
IO-360
CS composite Prop

Over 1700 hours of severe use to include spins, hammerheads, loops and snap rolls. Up to 5.5 positive and 2 negative G's on a regular basis.
 
I pretty much agree with the above, no matter how careful you are drilling out rivets, the holes tend to oversize in thin material due to the rivet expanding when driven.

The part I don't like about building a new horiz is then you will have to back drill the front attach points accurately without oversizing the longeron holes, that won't be easy.

No doubt building a new stab will be quite a bit more work than accomplishing the repair, so I'm still on the fence on this.

SN# 70214

Walt,

I was looking at the shear load carrying capability of a -4 AD rivet in MIL-HDBK-5J - table 8.1.2(b) and it (without lowering factors) is 389 lbs in single shear. The cherry max table gives 664 lbs and Hi-Lok gives 95ksi shear strength compared to an AD rivet of 30ksi. The Hi Lok smallest available is -5 size so that would also be a larger safety factor.

I have tested a squeezed -4 and a Cherry Max for pull strength and tightness in the hole. There is no doubt that the squeezed rivet is tighter, a good thing for + cyclical loads, but the hi-lok seems could be very tight and is held in tension, so it could be better than the CherryMax.

Are these valid structural options for either the rivets hard to reach, or one wishing to use the -5 hi-lok with an enlarged hole reamed to the proper diameter? I know the prices escalate rapidly, but this is just a structural question.

Thanks,
 
Walt it might be that Vans included the relief notch detail for the first time when they reissued the RV7A HS drawing on 7/20/01.

What strikes me as strange however is that Mark Strahler (post #74) has obvious relief notches on his RV6.

The -6 plans did not call for any sort of relief notch.

The text just says that the cutoff flange end should be "filed and polished smooth"
 
Having just reviewed the thread from the start - all who have posted photos, with cracks show the crack propagating from the relief notch !!!!!!
 
No cracks noted

Completed the inspection this AM. No cracks noted. It seems the stress relief notches have been "eased" appropriately with a file.

Light acro
Grass strip
 
No cracks in mine.

2006 RV7A, 1000hrs
IO 360
Hartzell blended airfoil CS
Some light acro
Minimal grass strip ops

I have a smooth notch at the bend area, do not remember if was punched or if I made it as this was the 5th RV I built.

Martin Sutter
Building and flying RV's since 1988
EAA Technical Counselor
 
FYI - a very slight thread drift....

For those considering a rebuild of the HS.

Last week I ordered a new front spar assembly, and root ribs (HS 404&405) when I drilled out a rivet connecting the HS405 to HS702 to HS710 and enlarged a hole into a figure eight (I smashed the machined head of the 470 badly before the shop head was set- made centering very difficult). Anyway, this is the note I got from VANS shipping:

I'm sorry we we are temporarily out of the HS-405, and HS-404
We should have more in by 2/28/14

Note the one month delay. This may be a factor for some folks in their decision. As I am redoing this section anyway I think I will build the HS in accordance with the SB - although I read that as optional for those not yet flying.

Cheers
Rick
 
2004 RV8
190hrs
Light acro
Grass and paved strips
180hp. CS prop
No cracks
Have notches, one is even a double

35i9o9i.jpg

10hqdk8.jpg
 
One crack found

Of the 4 locations of concern, I found one crack. All 4 have the stress relief. The particulars are as follows:

Late quick build RV-6 kit (has early RV-7/RV-8 tail)
Bought flying with 113 hours
O-360, Hartzell C/S
Now 560 hours TT
Only acro has been a handfull of barrell rolls since I've owned it
Number of grass strips can be counted on one hand
I push/pull with a towbar attached to the tailwheel




Two things are of particular concern - per the SB, if a crack is found, Vans advises grounding until the horiz stab is modified. No "no acro" or any reduced speeds, or any other operational change until complied with, just ground it.

Second, without the guidance in this SB, I never would have seen this crack in a hundred condition inspections, and I consider myself (or used to!) a conscientious, careful, owner/mechanic.

My confidence is shaken. I always considered the RV airframe to be quite stout with adequate margins built in, given proper construction and operation. Maybe I'm overreacting...
 
RV6, 575 hours, no cracks. Lot's of acro, but nothing like Ron and his team.
I put "relief" notches here even though, evidently, they where not called for in the plans. From my prior sheet metal experience I must have known to do it. it is common practice to do this at the corner of any bend. They are smaller, looks like a #30 drill size, and poorly finished, at least to my standards today. This was my first build and that is the first thing you build.
Regardless, no cracks.
In regard to the repair, AC-43.13 1b gives guidance to acceptable repairs. The only acceptable method for a spar repair is one engineered by the manufacturer. Of course, when it comes to experimental aircraft, AC-43 is just a good guide, you can do whatever you want, and if you are the builder, you are the manufacturer. The repair from Van's is certainly a "boots and suspenders" repair, very involved, and well beyond what I would do if I had discovered a crack prior to the SB. However, they need to engineer the best solution long term and have to be very conservative. I respect that.
I absolutely would not make this repair unless I had a crack.
 
HS cracks

It will be interesting to see if any trend will become apparent due to engine HP or other factors. I know that on start up, I get a pretty hard shake that has to put some stress on the area we are talking about. I am running the 200HP engine. I have no clue on the start up forces relative to the inflight or taxi forces.

Even with acro, I would think that the forces would at least build up a lot slower than a starting shake.

Maybe some of our engineering friends could chime in and shed some light on this.

Even if that were the case, I don't know what we could do different on existing aircraft other than the repetitive inspections.

Scott, Is there talk of beefing this up or incorporating the SB doublers on new aircraft?

I have not had the chance to check mine yet.
 
My confidence is shaken. I always considered the RV airframe to be quite stout with adequate margins built in, given proper construction and operation. Maybe I'm overreacting...

I think that the initial reaction is understandable, but when you sit down and take the emotion out of it, you realize that the airplanes don't know that the SB has been issued. If you weren't on the internet on Friday, and took off on a long trip in your RV6,7,or 8, you'd have done so with confidence, and the odds that anything bad would have happened are extremely remote. The fact is, there are LOTS of these airplanes flying around with cracks (we know that by the number of high-time flyers posting about their cracks - they didn't just happen yesterday) and airplanes aren't falling out of the sky.

The fact is, the area is pretty robust, and there is some structural redundancy there. Once I found a crack, I certainly would be fixing to restore the redundancy, but I wouldn't be completely distraught by it. Remember the 737 skin cracks a year or so back? I didn't lose faith in the 737 - they engineered a fix and we all go flying on them regularly.

There is no such thing as risk-free flight. There is always the chance of a hidden defect in your airplane. The RV's have proven to be pretty rugged and reliable over many decades and thousands of airplanes. So we have found the first "life limited component" - OK, we'll fix them and move on.

As co-owner of one of the oldest and most experienced RV-6's on the planet, I will not be surprised if we find a crack when we inspect it (neither Louise or myself are currently in the same town as the airplane) - but I wouldn't have been quaking in my boots if I had flown it yesterday and found a crack today.

We'll get through this.
 
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I agree with Paul here. Scott was pretty clear that this was not the result of an accident but rather the result of an inspection. And inspection on a high-time airframe. And guess what? All indications so far are that we will continue to see them on high-time ariframes. The "why" is yet to be understood, and may not ever be understood with so many variables in the field. CLearly they are all built differently, equipped differently, engined differently, etc. That means as metal airplanes go they all have different harmonics. I noticed this impact quite clearly in the apparent lack of baffling cracking when using composite propellers, most likely due to the change in harmonics.

The reality is that RV's aren't falling out of the sky due to this crack, and most likely they won't start falling out of the skies tomorrow or the next day or next week. I have found Van's to be of very highest integrity, and IF this was that serious they would have taken a very hard stance and recommended grounding until compliance.

Sure, it's not fun to do, and no doubt a lot of people will help. There may even be some follow-on easier solutions that come forth. We certainly seem to have a lot of very intelligent and creative people who have been successful at many after-market items for the RV's. I wouldn't be surprised if we see that here, too. :)

I assure you that even if I found a crack in mine today, I would still fly it until I can get the parts from Van's and install them.

Vic
 
RV6
Small tail
No notches
200 hp 10 to 1 pistons
Moderate acro
Limited grass
710 hours
Composite CS prop
No cracks!
Phew!

George
 
Inspected my -8 today which was an early quick build kit. No cracks found. Relief notches present.

Aircraft has 552 TTAF, O-360-A1A, Whirlwind 200RV propellor (although for the first half of its life it had a Hartzell CS), and has done limited acro. Aircraft is always moved in/out of the hangar with a tailwheel tow bar.
 
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cracks

Paul,
you have a way of thinking that has put my emotions on a much lower
plane. I am looking at the temp. -4F, and wondering about my 6A in an
unheated hangar in Minn. What to do? I know every one of us with a
6,7,8, are thinking about the cracks. Like you said, we will get thru this.
Dale
 
Agree with Paul

I've read all of this and agree with everything Paul has said. There are many here that are in the aviation business and as a result, see SB's, AD's etc a lot more than others. Certainly there are those with far greater experience than me in this area.

As an example, the helicopter I fly at work has several reoccurring SB's. This involves inspections and nothing more unless something is discovered. If there is something that could immediately affect the safety of flight, there are AD's. Then, there are Emergency AD's. These could take on several forms but usually involve Grounding until action is taken.

Regarding the Van's SB, it is a SERVICE BULLETIN!!! Don't read into it, just follow it. If you don't have cracks, then continue to inspect. If this was a matter of extreme safety, I'm confident Van's engineers would have issued an Emergency Service Bulletin. The planes are not falling out of the sky. These wonderful planes are engineered with safety as the first priority.

The area of concern is a tough area. I think I would probably do more damage trying to fix it. I would follow the bulletin but possibly amp up the inspection cycle to include inspection every oil change as an example. Then after the initial rush of new stab purchases for those who damaged there stabs trying to fix something that wasn't broken, I'd consider building a new one:eek:

Building a new stab can be accomplished in time. For now, just follow the Service Bulletin as written.
 
It would be awfully nice if Vans himself would put a paragraph about all of this. Might help with all the anxiety. I was a buyer, not a builder, so an RV 8 builder mechanic looked at mine. Thank goodness, no cracks, but the plane is still young at 291 hours.
 
No cracks RV6a 2007

no relief notches, 3 of spots have nasty V or square invitations for cracks to start, but otherwise well built. Thank you Jerry for building a sturdy plane. Light acro, more details below. Plan to file & polish rounded relief notches in near future on the top, can't get access to lower spots.
 
Inspected 2 today

My RV 8.
first flown 2010.
serial # 2816
no relief notches (none on plans, rev1 of page 3)
no cracks
grass strip
220 hours
light acro.

A friends RV 6
unknown hours
no relief notches
no cracks
 
Scott - it appears you may be the only one who has actually done the repair? If so, and to others that may be doing this, in the few pictures presented here, the cracks appear to form in the location of the bend or relief and start heading toward the rivet hole on the rib flange or in Walt's case, toward the rivet in the angle, but his is barely formed. What did you find on your ships?
Is it possible the crack will stop there and form a natural stop drill? You can't see under the rib flange to know unless you take it apart.
Perhaps it is too early to tell if it would stop there and not propagate.
Just a curious observation.
I appreciate all you do to keep the fleet safe.
 
...As an example, the helicopter I fly at work has several reoccurring SB's....

Its a helicopter! Of course it does!

The Hueys I used to work and fly on had several areas in the tail-boom and "****-hole" (main gearbox mount) areas that were prone to cracks. We inspected and only installed the approved "repairs" when we found cracks. Its just all part of maintaining an airframe.
 
No cracks on my Super Six

1998 RV-S6
1250 TT
IO-540
80" Hartzell D-Twist first 900 hrs
80" Hartzell BA past 350 hrs
Moderate Acro, Racing, mostly paved runways
No Notches
No Cracks

I inspect the tail at least quarterly due to the racing, and appreciate the info in this SB...it adds even more detail to the inspection! Mirror, magnifying glass and cell phone camera worked well! The crick in the neck should be gone soon too! ;)

Cheers,
Bob
 
1998 RV-S6
1250 TT
IO-540
80" Hartzell D-Twist first 900 hrs
80" Hartzell BA past 350 hrs
Moderate Acro, Racing, mostly paved runways
No Notches
No Cracks

I inspect the tail at least quarterly due to the racing, and appreciate the info in this SB...it adds even more detail to the inspection! Mirror, magnifying glass and cell phone camera worked well! The crick in the neck should be gone soon too! ;)

Cheers,
Bob
Well, that settles it. If anybody was cracked it would be Nasty. Oh wait, we're talking about the airplane...never mind... ;)
 
Mine is OK

I checked my vintage 1998 horizontal stabilizer today and it is fine. No cracks. No notch, but it seems when I built mine, it had a narrower web, so no notch really required. IO-360, Catto 3 blade, operate mostly off grass, mild aerobatics, 210 hours
1h858k.jpg
 
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Thanks Paul

I think that the initial reaction is understandable, but when you sit down and take the emotion out of it, you realize that the airplanes don't know that the SB has been issued. If you weren't on the internet on Friday, and took off on a long trip in your RV6,7,or 8, you'd have done so with confidence, and the odds that anything bad would have happened are extremely remote. The fact is, there are LOTS of these airplanes flying around with cracks (we know that by the number of high-time flyers posting about their cracks - they didn't just happen yesterday) and airplanes aren't falling out of the sky.

The fact is, the area is pretty robust, and there is some structural redundancy there. Once I found a crack, I certainly would be fixing to restore the redundancy, but I wouldn't be completely distraught by it. Remember the 737 skin cracks a year or so back? I didn't lose faith in the 737 - they engineered a fix and we all go flying on them regularly.

There is no such thing as risk-free flight. There is always the chance of a hidden defect in your airplane. The RV's have proven to be pretty rugged and reliable over many decades and thousands of airplanes. So we have found the first "life limited component" - OK, we'll fix them and move on.

As co-owner of one of the oldest and most experienced RV-6's on the planet, I will not be surprised if we find a crack when we inspect it (neither Louise or myself are currently in the same town as the airplane) - but I wouldn't have been quaking in my boots if I had flown it yesterday and found a crack today.

We'll get through this.

Thanks Paul for your cool headed response. I inspected the Doll yesterday and found one crack. I put the fairing back on and went flying. I will order the repair kit and do the repair during the conditional inspection due in March. In the mean time I will avoid high G aerobatics. Like you said this is a very robust area. The heavy .125 810 and 814 angles holding the left and right front spars together, overlaps the crack in the thin spar web. I'm not afraid that the tail is about to fall off. I imagine that I've been flying with this crack for quite sometime now. Maybe years..... I had a hard time seeing the crack, even when I knew just where to look as a result of the bulletin.

I will attempt to repair the HS as per Bulletin, but if I can't drill out the #4 rivets without damaging the holes, then I will have to decide if I want to drill off the skins, do the repair to the frame, and then replace the skins, or build an new HS. The repair has been done as per bulletin at the factory, so I'm pretty sure I can do it as well. If I drill off the skins, or build and new HS, I hope I can get a good paint match with the fourteen year old metallic silver paint.

Walt made a very good point about the need to back drill a new HS to the longerons. That will require very careful work.

I have always felt that I could do a better job building the HS then I did. I learned how to build in metal on that part! The riveting is not as nice as the rest of the airplane.
 
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Not on crack

RV-7A
2005 vintage tail and plans (with notch)
IO-360-M1B 180 HP Mags
CS Blended Hartzell
Flying 20 months
200 hours
Very smooth relief notches.
No cracks

I have been passing the word because a number of RVs in my area are 2nd owner. One 160 Hp fixed pitch no notch RV6A was checked OK today.
 
Inspected mine yesterday and found no cracks.

300 hrs
Nicely rounded notches per plans
Plans from 2008
IO,360 200hp, hartzell cs
Mostly pavement some grass
Push/pull via tailwheel bar

Will continue yearly inspection.
 
RV-8A
O-360 180 HP
Constant speed prop
Flying since 2003
420 hours (110 in last six months)
Gentlemen's aerobatics. Mostly rolls.
Seldom on grass strips
Relief notches
No cracks.
 
You're bold Paul

Even though it was about 25 degrees this morning, I grabbed the drill driver and pulled the empennage fairing off our RV-8 this morning – took about three minutes. A quick look with the inspection mirror and camera shows that the Valkyrie doesn’t have the relief notches ….and no cracks either! I had the pictures in the camera and the fairing back on before Click and Clack got to the answer to last week’s puzzler – total time, about ten minutes.

Right Side:
P1000831.JPG


Left Side (That vertical line is a hair scar in the paint – not a crack):
P1000832.JPG


Of course, I had the fairing off last week when I signed off the Condition Inspection – but did I really look at that spot with a mirror? Would I have noticed it? Better safe than sorry.

1702.5 hours TT
Lots of Acro!
Paul


Removing that fairing in 25 degree temperature, you are bold! I'd be afarid of it breaking in that cold temp at least the way mine wraps around the horizontal and vertical. I have to flex and distort mine to get it off.

Glad yours didn't have cracks. Yours being one of the higher time in service 8's that some what comforting.
 
Thanks Paul for you cool headed response. I inspected the Doll yesterday and found one crack. I put the fairing back and went flying. I will order the repair kit and do the repair during the conditional inspection due in March. In the mean time I will avoid high G aerobatics. Like you said this is a very robust area. The heavy .125 810 and 814 angles holding left and right front spars together, overlaps the crack in the thin spar web. I'm not afraid that the tail is about to fall off. I imagine that I've been flying with this crack for quite sometime now. Maybe years..... I had a hard time seeing the crack, even when I knew just where to look as a result of the bulletin.

I will attempt to repair the HS as per Bulletin, but if I can't drill out the #4 rivets without damaging the holes, then I will have to decide if I want to drill off the skins, do the repair to the frame, and then replace the skins, or build an new HS. The repair has been done as per bulletin at the factory, so I'm pretty sure I can do it as well. If I drill off the skins, or build and new HS, I hope I can get a good paint match with the fourteen year old metallic silver paint.

Walt made a very good point about the need to back drill a new HS to the longerons. That will require very careful work.

I always felt that I could do a better job building the HS then I did, as I learned how to build in metal on that part! The riveting was not as nice as the rest of the airplane.

I concur with both Danny and Paul, I'll continue to fly mine without concern until parts become available (which won't be long I assume). Right now I am leaning more torwards just building a new stab. I'm working on a tool list to do the job and have located drill bushings and double margin treaded drills bits that should enable me to do the back drilling with a high degree of accuracy.

Now I just need to find a skinny midget helper to crawl in the tail.

I'm also planning on being ready for some repair work should the need arise.
 
Free of cracks

RV-6
0-320 with Sensenich metal prop
Mild aerobatics
Flying since 1997
Approximately 650 Total Time
No relief notches
NO cracks.

Fernando
 
http://i58.tinypic.com/1h858k.jpg

Is this is not a more desirable configuration for transferring load from the horizontal plane to the vertical plane? Seems like a relief like the one in the SB only serves to concentrate the load at that location.
 
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.........I'm working on a tool list to do the job and have located drill bushings and double margin treaded drills bits that should enable me to do the back drilling with a high degree of accuracy. ......

What is a double margin threaded drill bit? :confused: Not familiar. Thanks.
 
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