RV structural integrity

[David-aviator]

Originally Posted by Ramendala

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

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.

[Yukon]

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.

[Captain Avgas]

Originally Posted by Kevin Horton

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.

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.

[rvbuilder2002]

Originally Posted by Captain Avgas

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). .

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.

[L.Adamson]

Originally Posted by rvbuilder2002

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.

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

[Captain Avgas]

Originally Posted by rvbuilder2002

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.

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/...200701033.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.

[rvbuilder2002]

Originally Posted by Captain Avgas

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



.

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.

[Captain Avgas]

Originally Posted by rvbuilder2002

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

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.

[rvbuilder2002]

Originally Posted by Captain Avgas

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

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.

Originally Posted by Captain Avgas

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.

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>

[casper]

Originally Posted by Captain Avgas

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.

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.