RV structural integrity

Surfing the internet the other day I found this posting:

"I never completed the RV 4 I was building, so I can't tell you if the rudder
would have fluttered at 260 MPH. I came close to that speed doing aerobatics
in one that a friend owned, but I wouldn't recommend approaching that speed
in one. Also, because of all the structural failures in RV's I never felt
comfortable in one. Second to RV structural failures are Lancairs. I have
never heard of a structural failure in any Glasair."

Here's the link for anyone interested: http://www.matronics.com/digest/glasair-list/Digest.Glasair-List.2007-07-14.txt

This writer's comments contradict the impression I've gotten which is that RV's have a fairly enviable reputation for structural integrity, not withstanding the RV-8 and RV-3 incidents.

He was building an RV-4, though I don't think his comments were type-specific. Have there been any failures in -4's? I haven't heard of any (I've heard of somebody bending the horizontal stab doing acro over gross).

Intuitively (maybe not correctly or rationally) I'm inclined to trust metal structures more than composite ones (I hope that comment doesn't cause a rash of hate mail......), particularly over long periods of time.

I'd like to hear others' views on the structural integrity issue.

Andy

I've never heard of a structural failure in any RV.

IMHO Composites are stronger than metal, in the sort & long term, and offer better shapes for aerodynamics that metal cannot do.


I cannot believe anyone reads a Matronics forum in that old fashioned forum style. It took me 20 mins just to find the RV section.

Thank goodness for VAF!

Here's one...... granted it was the pilots fault (overstressed the airframe)

http://www.ntsb.gov/ntsb/GenPDF.asp?id=LAX98FA171&rpt=fi

Andy Lamborn said:

Surfing the internet the other day I found this posting:

"I never completed the RV 4 I was building, so I can't tell you if the rudder
would have fluttered at 260 MPH. I came close to that speed doing aerobatics
in one that a friend owned, but I wouldn't recommend approaching that speed
in one. Also, because of all the structural failures in RV's I never felt
comfortable in one. Second to RV structural failures are Lancairs. I have
never heard of a structural failure in any Glasair."

Here's the link for anyone interested: http://www.matronics.com/digest/glasair-list/Digest.Glasair-List.2007-07-14.txt

This writer's comments contradict the impression I've gotten which is that RV's have a fairly enviable reputation for structural integrity, not withstanding the RV-8 and RV-3 incidents.

He was building an RV-4, though I don't think his comments were type-specific. Have there been any failures in -4's? I haven't heard of any (I've heard of somebody bending the horizontal stab doing acro over gross).

Intuitively (maybe not correctly or rationally) I'm inclined to trust metal structures more than composite ones (I hope that comment doesn't cause a rash of hate mail......), particularly over long periods of time.

I'd like to hear others' views on the structural integrity issue.

Andy

Click to expand...

The -3's had their issues.

A -4 lost its Horizontal Stab a few years ago. Apparently the builder left out 2 of the 4 attachment bolts. Otherwise, the -4 and -6 series have been bulletproof.

The -7 and -8 series suffered the wing failure in the -8 prototype, but that is the only structural failure I know of in those aircraft.

To the best of my knowledge, the -9 and -10 have perfect records.

Other than the -3's, I'd say this is a pretty good record.

Several

The RV's do absolutely not have a bad reputation for any structural issues...the reverse is true. The RV-4 that came apart in Oz was overweight with two good sized guys, past the aft CG and doing aerobatics way over the aerobatic gross. They fell out of a maneuver, hauling a$$ way over redline when the rudder fluttered and the airplane came apart and went in nearly straight down.

The -8 in question was tested by a very respected company and the wings revealed that they endured over 9 G's......Van's ultimate design load.

Yes, that little stick between your legs can easily become a wing removal tool, as has been demonstrated.

Regards,

Andy,

Your misconception of composites is pretty common. The FAA had the same issue when Burt Rutan designed the Starship for Beech (a.k.a. Star pig). They added over 1000lbs of unnecessary weight because they did not understand composites back then either.

Key note: There has never been a structure failure of any Vari-eze, Long-ez or Cozy aircraft when built TO THE PLANS. The latest Vari-eze issues are attributed to incorrectly built wing spars and the Long ez issues from the past were caused by builders leaving off lay-ups in the winglets or one where the pilot forgot to bolt on the canard (bondo’d in place “temporarily”). There have been static load tests done of the Long ez type canard that were poorly built and deemed “unacceptable” to Rutan that failed at 10-14g’s (multiple canards). 

This is not hate mail  I just find that there is still a lot of misconceptions when it comes to composites and there is a lot of fear in the RV community over the fiberglass work. Makes me laugh when I hear people say, “finally back to Al” where I have heard the opposite in my previous life.

For your long term concerns, composite structures offer some advantages over Al. Composites will not fatigue nor corrode over time and actually dampen the vibrations in airplanes relieving some of that stress as well.

FWIW The RV-3 spar failures scared the heck out of me and turned me away from the VAF planes initially. That followed by the rudder change in the -7 AFTER kits have been sold did not sit well with me either. (now that may cause hate mail)

I am slowly coming back, maybe even build a -7 or 8 here soon.

FWIW

Ryan

Andy Lamborn said:

Surfing the internet the other day I found this posting:

"I never completed the RV 4 I was building, so I can't tell you if the rudder
would have fluttered at 260 MPH. I came close to that speed doing aerobatics
in one that a friend owned, but I wouldn't recommend approaching that speed
in one. Also, because of all the structural failures in RV's I never felt
comfortable in one. Second to RV structural failures are Lancairs. I have
never heard of a structural failure in any Glasair."

Click to expand...

I'm no aerobatic guru, I only have a few hours in a Cessna 152A some 10-15 years ago. But, how (and why) do you end up doing 260 MPH doing aerobatics? A perfectly good loop in the 152 start at 110-120 knots, and if you do it perfect you end up doing 110 at the bottom again. An RV with much more power can probably accelerate through an equal loop starting at 110 knots.

SvingenB said:

I'm no aerobatic guru, I only have a few hours in a Cessna 152A some 10-15 years ago. But, how (and why) do you end up doing 260 MPH doing aerobatics?

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RVs have much lower drag than a 152. If you fly the aerobatic manoeuvre correctly, there is no problem. But, if you screw up, and the nose ends up pointing way below the horizon, and you don't fly the airplane (i.e. level the wings, apply an appropriate amount of g, and pull power to idle), the airspeed will increase very rapidly.

There must have been more to the story in that Australian accident - e.g. something happened that restricted flight control movement, or confusion about who had control, or a medical issue, etc. We will never know the real answer.

You can kill yourself in any airplane if you try hard enough (same story for your car, skateboard, etc).

Self imposed problems

I think many of the problems we have in aviation, regarding aerobatic aircraft, are self imposed. The RV's are pretty tough, very easy to fly and can make you feel like you're the Ace of the Base when you're out there to try your first aileron roll just because you know the airplane can do it.

Like Pierre said, that "wing removal tool" is all too often the culprit in a well designed airplane coming apart. (Pierre, you crack me up sometimes )

I've taught aerobatics since 1987 (T37's) and still do. Way too many pilots out there think they can just go and do it without any help. Maybe. And maybe not. All it takes is just one split-s out of an aileron roll, or a simple lack of situational awareness and you're looking at an airspeed indicator thats way past redline, and then you're only a ham-fisted pull away from yanking the machine apart.

A few years back, one of the guys in my old EAA chapter came to me and confessed he'd been doing a-rolls in his KR2, alone. Feeling pretty good about it, he took his daughter up for a ride and split-s'ed out of a simple roll. He put so much g on the airplane, it buckled both upper wing skins. He landed in one piece, but believe me he learned that lesson. I've seen enough USAF students hamfist Tweets doing maneuvers they've practiced for weeks and overstress a 6.67g airplane. That airplane had an 18g per second onset rate, and the RV's are about the same I'd guess. That means, with sufficient airspeed, you can go to 6 g's in only 1/3 of a second. Wham!

You've probably heard it said that the RV's are "confidence inspiring" planes to fly. I think this is true. But it can lead us into doing things that are really over our heads, and that's not good. I think we're flying some of the best sport planes ever here, and if it weren't for that, the accident rate might be alot higher than it is.

Of course, this is all simply my rambling, but remember these two laws of aviation do apply no matter what:

1) Gravity never takes a day off
2) The ground never misses

Fly safe...

Ramendala said:

FWIW The RV-3 spar failures scared the heck out of me and turned me away from the VAF planes initially. That followed by the rudder change in the -7 AFTER kits have been sold did not sit well with me either.

Ryan

Click to expand...

Sometimes changes happen...
Like adding ailerons to the the wings of the original varieze because the differential elevators on the canard had almost no roll effect, or the flow fences to the L.E. of the wing on the longeze, or the Ronz airfoil canard to solve the rain induced pitch excursions, etc., etc.

If you do a little more research about the RV-7(A) rudder change you will find that it was not that big of a deal. In fact Van's Aircraft's RV-7 and RV-7A demonstrators are still flying with the original rudder.

The only reason the different rudder was offered was because the airplane was initially advertised as having the exact same same spin recovery as the RV-6(A). After more in depth testing at a later date, it was found to be a little slower in recovery than the RV-6 (but not to a dangerous extent).
Since it wasn't what Van had originally said, he gave a different rudder to anyone that wanted it (it wasn't a mandatory change). All subsequent were then delivered with the new rudder.

Ramendala said:

Andy,

....That followed by the rudder change in the -7 AFTER kits have been sold did not sit well with me either. (now that may cause hate mail)

I am slowly coming back, maybe even build a -7 or 8 here soon.

FWIW

Ryan

Click to expand...

Ryan,

The -7 rudder upgrade (which is a -9 rudder) was (is) a non event. My free kit is still up on the shelf - unbuilt. As another guy mentioned, Van's tested the tall rudder and then reinstalled the short original version.

Having built and flown a LEZ and Cozy MKIV, I concur with your statements about composit integrity. BUT overall, the canards lack "total performance". None of them are suited to fly out of anything but 3000' of hard surface. Some get by with less but it can be dicey. I flew the EZ out of 2600' with the 0235 and it was OK most days. Forget grass, I did it twice and refinished the prop twice on account of it.

The RV's are structurally sound. But like the canards, they can not be flown through rocks by dumb pilots or recovered from a vertical dive way over the red line. The flight control system of the RV's is far superior to the canards. You can actually keep the wings level on final in a gusty cross wind.

Do not let ignorant speculation about RV structural integrity be a part of the decision making process to make the switch. You will love it, the pilot who does not like flying an RV has not been born.

To my knowledge, all RV structural failures occured during bad amateur aerobatics. Contrast that to the hundreds of Beechcraft Bonanzas that lost their wings and tails in non-aerobatic flight before Beech applied a 100 dollar fix to the tail.

Aside from the early -3 wing problem, RV's are very strong. A little aerobatic instruction will go a long way toward preventing these kinds of problems.

Kevin Horton said:

There must have been more to the story in that Australian accident - e.g. something happened that restricted flight control movement, or confusion about who had control, or a medical issue, etc. We will never know the real answer.

Click to expand...

The owner/pilot of the RV that you refer to did not build the plane (I am assuming we're talking here about the RV4 that lost its empennage). He purchased it a couple of months before he crashed it. Some-one I know inspected the plane when it was up for sale and described it as "a VERY poor example of workmanship". So Kevin is right.....we will never know the real answer as to why it lost its tail in this case because the ATSB in Australia is not interested in allocating limited human resources to extensively investigate Experimental crashes.

As soon as the ATSB calculated that the plane was over aerobatic gross (and with a very aft CG) they drew a conclusion from that.

And all the RV builders who felt comfortable with a finding of pilot error were happy with the conclusion.

RV builders are always saying that there is a huge amount of structural redundancy in an RV (you know the usual blurb.....10% of all rivets can be left out etc etc). And that is probably true for the type of flying that most pilots do whereby they probably never get past 3 G.

But it's at the upper limits of specified structural endurance (and beyond those limits in the case of a crash) where good workmanship becomes truly important.

Captain Avgas said:

The owner/pilot of the RV that you refer to did not build the plane (I am assuming we're talking here about the RV4 that lost its empennage). .

Click to expand...

I was told that the final report has been published. I am offering this as very third hand information (I have not seen the report)... What I was told is that the airplane did not lose any of its empenage. It was found that a ballast weight had been bolted into the aft tail below the elevator control horns to compensate for an IO-360 200HP engine. After the owner (at time of crash) purchased the the airplane, the engine was changed (to a lighter engine) but the ballast weight was not removed (probably didn't know it was there) and apparently no reweigh/weight and balance was done. The airplane was calculated to be severely aft C.G. at the time of the accident flight, and apparently was executing aerobatic maneuvers.

I can not personally confirm any of this since I have not read the report so some or all could be in error, but this is what I was told was in the report.

rvbuilder2002 said:

It was found that a ballast weight had been bolted into the aft tail below the elevator control horns to compensate for an IO-360 200HP engine. After the owner (at time of crash) purchased the the airplane, the engine was changed (to a lighter engine) but the ballast weight was not removed (probably didn't know it was there) and apparently no reweigh/weight and balance was done. The airplane was calculated to be severely aft C.G. at the time of the accident flight, and apparently was executing aerobatic maneuvers.

Click to expand...

IMO, lot's of years of R/C ; and larger models where the airplane actually has to fly using it's wing, instead of just engine thrust has advantages.

You get to see actual "inflight" results of tail heavy planes, "return to the airport" un-recoverable spins, accelerated spins, and much more! Makes you think twice & three times, while building a plane you actually sit in.

Interesting about the ballast weight, though.

L.Adamson -- RV6A

rvbuilder2002 said:

I was told that the final report has been published. I am offering this as very third hand information (I have not seen the report)... What I was told is that the airplane did not lose any of its empenage. It was found that a ballast weight had been bolted into the aft tail below the elevator control horns to compensate for an IO-360 200HP engine. After the owner (at time of crash) purchased the the airplane, the engine was changed (to a lighter engine) but the ballast weight was not removed (probably didn't know it was there) and apparently no reweigh/weight and balance was done. The airplane was calculated to be severely aft C.G. at the time of the accident flight, and apparently was executing aerobatic maneuvers.

I can not personally confirm any of this since I have not read the report so some or all could be in error, but this is what I was told was in the report.

Click to expand...

Firstly let's confirm that we're talking about the same incident, namely RV4 VH-ZGH, that crashed on 23/2/07 at Clyde North, Victoria, Australia. For more specific details one can access the ATSB investigation here:
http://www.atsb.gov.au/publications/investigation_reports/2007/AAIR/aair200701033.aspx

For a fuller report a .pdf file can be downloaded from the same site. The following seems to be relevant:

1. Witnesses reported seeing parts coming off the plane as it spiralled towards the ground. The report states that: "Both right and left tailplane, the fin and rudder were recovered in trees approximately 117 metres from the main aircraft impact point", and further that: "Examination of the seperated tail structures indicated twisting and tearing of the attachment fittings".
I think that quite positively suggests that this aircraft lost its tail.

2. The centre of gravity was calculated to be within limits for the Normal Category but aft of limits for the Aerobatic Category.

3. The report claims the aircraft was 145kg over the Aerobatic gross weight. However that included fuel. My understanding is that Vans do not require that wing fuel needs to be included in this calculation. On that basis the plane was 7kg over gross in the Normal Category and 62 kg over gross in the Aerobatic Category.

4. There doesn't appear to be anything in the report about additional ballast weight in the tail of the plane.

The questions that interest me are:

a) The plane had a cg aft of that specified for aerobatics and that could have caused the plane to enter an unrecoverable spin (and witnesses in fact reported that it WAS initially in a spin). But a spin is not a manoevre that places unreasonably high stresses on the tail.

b) The plane had a gross weight over the specified aerobatic gross. But exceeding gross is likely to lead to structural failure of the wings before failure of the tail. That's the way it usually works.

The Empennage is the part of the RV that many novice builders use as "a piece to practice on" as they develop their previously non-existent fabrication skills. I'm not saying that this is relevant in this case...but it might be.

Captain Avgas said:

4. There doesn't appear to be anything in the report about additional ballast weight in the tail of the plane.



.

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The report you linked too, is the preliminary report.

The report I mentioned is the detailed report.

It wasn't mentioned to me that portions of the emp. were found that far away from the main wreckage. (Like I said, it was third hand information) I find it interesting that both the elevator counter weights were found adjacent to the main wreckage site. It seems suspicious, if the part of the airplane that the elevators attach too supposedly departed prior to ground impact.

rvbuilder2002 said:

It seems suspicious, if the part of the airplane that the elevators attach too supposedly departed prior to ground impact.

Click to expand...

Scott, firstly I don't believe for one minute that this incident had anything to do with the structural integrity of Vans empennage design. I just want to clarify that point.

In reality an RV losing a complete empennage is virtually unheard of. People spin or dive their RVs into the ground from time to time...but they always take their horizontal and vertical stabilisers with them.

When the ATSB reported that this aircraft was over Aerobatic Gross and had a cg beyond aft aerobatic limits everyone just nodded and said "yep, that's the cause of the crash alright".

But still the nagging question remains: Why did the plane lose its complete empennage.

In the RV community discussing the possibility of structurally deficient builders' workmanship is a bit like discussing the long lost family uncle with the penchant for paedophilia....no-one wants to go there.

Everyone wants to believe that every RV at Oshkosh is of equal or better build quality than a Cessna. But of course it's simply not true (nothing could be further from the truth). The real truth is that when it comes to RV build quality there's an ENORMOUS difference across the spectrum....and many planes at the lower end have sizeable skeletons rattling around in the closet.

Captain Avgas said:

But still the nagging question remains: Why did the plane lose its complete empennage..

Click to expand...

Total speculation, but it could be that with the aft C.G. condition, the resultant light elevator forces allowed the pilot to easily over G the airplane trying to recover from the low level spiral dive the witnesses observed.
There is no rule that says an airplanes wing will be the first thing to fail if the airplane is pushed to a point of failure...just speculating though.

Captain Avgas said:

In the RV community discussing the possibility of structurally deficient builders' workmanship is a bit like discussing the long lost family uncle with the penchant for paedophilia....no-one wants to go there.

Everyone wants to believe that every RV at Oshkosh is of equal or better build quality than a Cessna. But of course it's simply not true (nothing could be further from the truth). The real truth is that when it comes to RV build quality there's an ENORMOUS difference across the spectrum....and many planes at the lower end have sizeable skeletons rattling around in the closet.

Click to expand...

I mostly agree with you (and I have said so in this forum numerous times).
I tend to think that the major majority of RV's have been carefully constructed, but with over 5500 now having been flown, that still leaves room for a lot of sub par RV's (I have done prepurchase inspections on quite a few of them).

For posterity... the airworthy condition and construction quality of any RV should be suspect until it has been verified by someone that is familiar with RV's and preferably the model of RV in question.

<That statement is in no way intended to imply that construction quality or airplane condition were a factor in the accident being discussed, we'll leave that up to the investigators to determine>

Captain Avgas said:

Scott, firstly I don't believe for one minute that this incident had anything to do with the structural integrity of Vans empennage design. I just want to clarify that point.

In reality an RV losing a complete empennage is virtually unheard of. People spin or dive their RVs into the ground from time to time...but they always take their horizontal and vertical stabilisers with them.

When the ATSB reported that this aircraft was over Aerobatic Gross and had a cg beyond aft aerobatic limits everyone just nodded and said "yep, that's the cause of the crash alright".

But still the nagging question remains: Why did the plane lose its complete empennage.

In the RV community discussing the possibility of structurally deficient builders' workmanship is a bit like discussing the long lost family uncle with the penchant for paedophilia....no-one wants to go there.

Everyone wants to believe that every RV at Oshkosh is of equal or better build quality than a Cessna. But of course it's simply not true (nothing could be further from the truth). The real truth is that when it comes to RV build quality there's an ENORMOUS difference across the spectrum....and many planes at the lower end have sizeable skeletons rattling around in the closet.

Click to expand...

Bob: I hope you don't talk your self out of finishing and flying you RV. You will miss out on one of lifes true pleasures.

casper said:

Bob: I hope you don't talk your self out of finishing and flying you RV. You will miss out on one of lifes true pleasures.

Click to expand...

Dear Doyle, the only real intention of my postings on this matter is to encourage all builders to take the time, and expend the effort, to obtain the knowledge and skills necessary to build a fine aircraft to the best of their abilities.....and to discourage them from rushing their projects and cutting corners. That's the agenda.

Because beyond the personal satisfaction of a job well done, we all have a responsibility to our families, to future passengers, and to the Experimental category at large to produce a well constructed and safe aircraft.

Parachutes

Aren't parachutes worn during aerobatics in case of emergency?

Yes, but the chance of getting the opportunity to use it is pretty close to nil.

6.6flylow said:

Aren't parachutes worn during aerobatics in case of emergency?

Click to expand...

They may be, but in the US they are not required for aerobatics. This is one of those wonderful, mysterious areas of the FARs.

By the definition of aerobatics (section 91.303) for the purposes here, almost any RV flight involves aerobatics for much of the time we are not in cruise flight. You may fly aerobatics without exceeding a 20 degree angle of bank. Aerobatics are "an intentional maneuver involving an abrupt change in an aircraft's attitude, an abnormal attitude, or abnormal acceleration, NOT NECESSARY FOR NORMAL FLIGHT." That pretty much defines most of my RV flying and I'm glad no parachutes are required.

Parachute requirements are a separate deal and are in section 91.307. It is real simple. If more than one person is on aboard and you exceed a bank angle of 60 degrees or a pitch angle of 30 degrees, parachutes are required. There are exceptions, as there need to be, because very normal training maneuvers exceed those limits.

I have long thought it pretty much impossible to make a completely legal flight. The FARs are very broad and very vague and you can be violated if someone in the FAA wants to do that. It is very possible to make a very illegal and very safe flight. The parachute requirements are one of the most widely ignored FARs. I don't condone that, but I don't believe it necessarily has any impact on safety, particularly in aircraft in which it has not been demonstrated that inflight egress is even possible.

Full disclosure requires me to mention that I am retired from the FAA.

n5lp said:

Full disclosure requires me to mention that I am retired from the FAA.

Click to expand...

Is that requirement another one of those obscure little known FAR's?

rvbuilder2002 said:

Is that requirement another one of those obscure little known FAR's?

Click to expand...

Uh, I dunno Scott. I may have signed some stuff when I left though.

By the way I was just thinking about this stuff some more. One of my favorite maneuvers is a wingover. I might go to 120 degrees of bank or so and about 20 or 30 degrees of pitch. That would mean I would legally need a parachute if I had a passenger. The maximum G loading will be, maybe, 1.3. Shoot, even a roll is about 1.5 G in the pullup and less in the actual roll. No airframe stress at all. On the other hand, just a normal flight instruction steep turn is 2 Gs.

Yeh, I know things can be messed up, but regulations don't really help that.