RV structural integrity

[Andy Lamborn]

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/glas...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

[Geico266]

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!

[bfilarsky]

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

http://www.ntsb.gov/ntsb/GenPDF.asp?...98FA171&rpt=fi

[Kyle Boatright]

Originally Posted by Andy Lamborn

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/glas...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

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.

[pierre smith]

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,

[Ramendala]

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

[SvingenB]

Originally Posted by Andy Lamborn

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."

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.

[Kevin Horton]

Originally Posted by SvingenB

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?

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).

[Bill Wightman]

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...

[rvbuilder2002]

Originally Posted by Ramendala

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

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.