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Opinions on structural failures

Kaldragon

Member
Good afternoon all, I've been thinking about buying an RV-4 or -6 for a while now (really a year or two...), and now that Im starting to get to the phase of asking for people to do pre-buys, I'm starting to question the safety aspect.

So far, I've been under the assumption that if I have an experienced RV mechanic do a pre-buy, as well as look over the aircraft with a mechanic friend of mine, that we dont find anything structurally wrong, the build looks good/decent, and I do some transition training, that I'll have something that is roughly equivalent in safety to a certified aircraft.

Now, I do understand that the accident rate of experimental aircraft versus certified is higher, but that many of those accidents are due to mechanical failure within the first few hours of flight testing, or from lack of transition training after purchasing a used experimental aircraft.

Now, thats not what Im overly concerned about due to the above, what I'm wondering is if I could safely do "gentleman aerobatics" in an old RV.

When I brought up the topic of doing aerobatics in an RV (after I had bought it of course), both a mechanic I had asked to do a prebuy, as well as a seller had seemed hesitant to say they were comfortable doing them in old RVs. I've also seen posts about others not feeling comfortable doing aerobatics in something "I haven't built", and I've heard what I've heard many times (and myself have said) in certified aircraft, "it's an old airframe, are you sure you want to test it?".

Reading through the statistics, I understand that more often than not, its not structural failure, but loss of control that leads to accidents in experimental aircraft. I dont know if thats from there being no old bold pilots, or if the structure itself is inherently safe. I understand that test RVs have been loaded to upwards of 9 Gs, so at least a properly assembled, new RV should be perfectly safe within the set limitations. So assuming I get aerobatic training, am I just as safe doing say a loop, spin, inverted flight etc, in an RV with inverted oil, as I would be in something like a Citabria? What do you guys think?

Sorry for the text wall!
 
The designs are well proven. An older airframe doesn't concern me as much as the workmanship does. That said, I think aluminum construction in general, and the Vans designs in particular have a lot of safety margin for less than idea workmanship. The biggest question mark of any used airplane is the quality and condition of the wing and tail attach holes in the structure. These holes need to be of the correct size and roundness for the bolts to fit correctly. If the builder failed to generate a round hole, or ended up with too large of a hole, the stresses will be concentrated on surrounding fasteners, as that fastener is no longer carrying its share. This condition really isn't inspect-able without going through great effort. So you have to gauge the integrity of the builder by the attributes of the visible workmanship.
Personally, I think I have less concern about this topic than you do.
Cheers,
Rick
 
Of course, if you haven't already had proper aerobatic training, you probably should get that before doing it in your own airplane.

Dave
 
RV-6A Warning

I bought an RV-6A about 11 months ago. I had a local expert accompany me for a pre-buy. We did not do a detailed inspection - removing tail and wing fairings for instance. The plane looked gorgeous, the hangar immaculate and the same owner for 18 years with consistent, logged maintenance. I bought the plane and now have 100 hours personal time, with plane at ~700 hours.

A few weeks ago I had a conditional inspection from a local mechanic that races RVs, has built a few, and has been working on them for years. During the CI we found that rear wing spar bolt was too large on left side, and the rudder attach was short, with two bolt connections not connected. There was no sign of structural cracks so obviously these are holding up, but needless to say they need to be fixed. This will require some pretty major surgery.

Bottom line, do a thorough pre-buy inspection. You never know what you will find on experimental aircraft.
 
I did a lot of research on the RV6 and could not find a single incident of inflight failure. The RV7 has had some issues but generally they occurred well outside its operating range. I did not look as hard at the RV4 but don’t recall seeing inflight failures On RV4’s.
 
So far, I've been under the assumption that if I have an experienced RV mechanic do a pre-buy, as well as look over the aircraft with a mechanic friend of mine, that we dont find anything structurally wrong, the build looks good/decent, and I do some transition training, that I'll have something that is roughly equivalent in safety to a certified aircraft.

Well.... no.

In my experience, about half the homebuilts out there need to be rewired. There are also stories of fuel system errors, incorrect hardware, non-aircraft fittings, all kinds of things. Lots of those won't show up on an inspection.

When you buy a homebuilt, you're not merely buying a piece of machinery. You're also buying the knowledge, skills and attitudes of the builder, and those are hard to quantify. Pick up on all the cues and clues as to how well the plane was built.

Even so... my RV-9A had avionics that were installed by a "professional" avionics shop. They did a terrible job (word choice substantially cleaned up).

Even after a careful inspection, count on finding one major problem after purchase.

Then again, these days there are lots of spam cans that have questionable maintenance histories, so your comment about equivalence may be valid -- it's just that they may be equivalent at a lower than desirable level.
 
In Texas you have a great tailwheel & RV training / instructor - Bruce Bohannon.

A search of this forum will reveal several great testimonials.
 
My Airworthiness Certificate contains the approved aerobatics for my aircraft and there is a log entry stating that those maneuvers were performed during Phase I. If the aircraft you are considering has similar, then you would not be the test pilot for those aerobatics - assuming that nothing else in the logs shows damage that might compromise the structure. The older RVs were designed extremely stout (the main wing spar attachment, for instance) and even the newer ones are no sissies. I'd say that if there are no construction red flags noted in the pre-buy and it has been tested in Phase I, you should be able to do the aerobatics without undue concern.
 
I bought an RV-6A about 11 months ago. I had a local expert accompany me for a pre-buy. We did not do a detailed inspection - removing tail and wing fairings for instance. The plane looked gorgeous, the hangar immaculate and the same owner for 18 years with consistent, logged maintenance. I bought the plane and now have 100 hours personal time, with plane at ~700 hours.

A few weeks ago I had a conditional inspection from a local mechanic that races RVs, has built a few, and has been working on them for years. During the CI we found that rear wing spar bolt was too large on left side, and the rudder attach was short, with two bolt connections not connected. There was no sign of structural cracks so obviously these are holding up, but needless to say they need to be fixed. This will require some pretty major surgery.

Bottom line, do a thorough pre-buy inspection. You never know what you will find on experimental aircraft.

As you learned, cleanliness and meticulous record keeping are not synonymous with competence and skill. One should not be swayed by "a gorgeous looking airplane" that appears to be well cared for. Many times the extent of the owners skill ends with cleaning and polishing and that level of care can't be applied to the structural or mechanical elements. What is underneath and not seen is what counts when discussing safety and reliability.

Larry
 
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There is no relationship between what some random person is “comfortable” with and what is safe. Comfortable means nothing. If you want to feel safe by a nice shiny airplane like that other poster did, thinking he had a robust airframe. If you want to be SAFE, which is different, open up the airplane and thoroughly inspect the wing and tail attachments, all the control surface hinges and balance weights, and the entire flight control system to ensure everything is tight, all cotter pins are there etc. If there are a couple of clinched rivets here and there it is not such a big deal. Edge distances on the bolts that hold major bits on, that's a bigger deal.

The basic designs are sound.

The other issue is that control forces, particularly at aft cg are lighter than many other airplanes. So it could be easier to over stress the airplane than it might be for other aircraft. That is not necessarily a bad thing at all, provided you understand it and are either sufficiently experienced to adapt or you can get training. Im not sure if you can get dual for aeros in an rv 4 without exceeding the aerobatic weight. And you would be at a pretty aft cg. But if you have a good back ground, and a g meter, you could check yourself out. Lots of people do aerobatics in the 4.
 
RV-4 and aerobatics

Can only speak for my RV-4, which I bought just after it received the airworthiness certificate in 2004. I primarily use it for aerobatics and in aerobatic competition. It now has over 1900 hours. When I’m practicing aerobatic sequences, the G meter typically reads plus 5+, and negative 3 (-) Gs. You can see examples of the different sequences from primary to intermediate on a YouTube search of “willyeyeball”. The RV-4 is a tough and perfect platform for aerobatics up to the intermediate level. Thanks Van for this magnificent machine. Just stay within the operating limits after good training:).
 
Comparing to certified is apples and oranges -- I owned a 1968 Citabria and with that old wooden spar, I could never quite bring myself to do aero in it.

Yes with EAB there is plenty of potential for gotchas FWF and under the panel, but as for the structure, it's not difficult to get in and see everything that matters. RV-4s are solid, and age won't have much to do with it unless there's corrosion, shoddy workmanship or visible evidence of overstress. DO get an inspection by someone who knows RVs well.
 
G’s beat up airplanes...

G’s beat up airplanes. Period. Even the super high speed jets get thrown away after 6000-8000 hours of use. The F/A-18 had problems with vertical stabilizer cracks due to loads under G. F-16’s have reinforcements at the wing roots. The USN F-16N’s got trashed because they did nothing but high G BFM.

Bottom line, if you’re going to fly any airplane to the edge of its performance envelope, you owe yourself a detailed and rigorous inspection schedule of the airframe beyond a standard condition inspection. You may find cracks, or damage. Found early, most can probably be repaired. But I wouldn’t expect the airframe to last to its 12,000 hour fatigue life Van’s puts out if every flight is a +6/-3 roller coaster.

If your flying is more recreational, without pegging the G meter every flight, you’re probably fine with the standard inspection schedule.

Just my $0.02
 
But I wouldn’t expect the airframe to last to its 12,000 hour fatigue life Van’s puts out if every flight is a +6/-3 roller coaster.

Maybe depends on the model. The RVator had an article that touched on this and the cycle limit was assuming the profile of a military trainer. Based on that, I’m not sure I’d agree with your perspective.

I absolutely agree with you on inspections, however. Anyone who has seen an S-N diagram for aluminum knows why, and I think too often condition inspections are not given the respect they deserve.
 
I taught aerobatics for years in Citabrias, Decathlons and Stearmans. I really don't know a lot about how the RV's were tested but I think it's fair to say that their track record is pretty decent.
Personally I've viewed RV's as very capable performers in the Sportman class but reading this thread I see someone is using theirs in Intermediate class which is certainly a big step above Sportsman class.
Anytime you are using an aircraft for aerobatics you want to ensure yourself that it's in tip top condition and of course you want do very comprehensive walk arounds.
That said the most important aspect of aerobatics is your training and ultimately your skill levels. You can do gentlemen aerobatics and never pull more than 3 G's, your loops won't be perfectly round and you won't be drawing good lines as expected in competition but you'll have wonderful experiences and your skill levels will be many factors higher than 95% of pilots out there these days.
You'll learn new visual :)reference points and you'll be completely at home in any attitude once you've received real good training. Any pilot that loses control of the aircraft during normal inside maneuvers has never been properly trained and is certainly not skilled.
The average person needs around 10 hours dual to really feel comfortable doing inside maneuvers and that training would, with some practice allow you to complete in Sportsman class.
Personally I think it might be wise to consider learning in something like a Citabria or Decathlon as they will make you a better pilot....they have to be flown through the maneuver s coordinating rudder and aileron....the RV tends to make you look a lot better than you are.
To sum up, learning aerobatics is a wonderful way to improve your basic skills, makes you a more confident and more capable pilot and adds a big fun factor on those beautiful days when you just have time for a trip out to the practice area and back.
 
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