RV-7/7A In-Flight Breakup Accident Information

[Mark Burns]

Mike,
It's P/N VS-809

It was $31.50 in 2012

Mark

Originally Posted by alcladrv

Could someone share the correct part number for the appropriate vertical stab fibreglas tip to install on an RV7 to match the RV8 rudder?

Picture downloaded from Mark Burns' post above:

Attachment 29796

Thanks,

Mike

[swift12]

Originally Posted by BillL

Thanks, I followed this accident as I had talked to Dean several times before the accident. My son self-toured NZ and Dean was kind to give him a north end tour. My son was impressed with his methodical approach to safety. Noted the 244kts, too much for what ever reason.

I am certainly interested in learning, including that we may speculate after a report is out.(thanks DanH!) A new arena!! Although my intended learning is all in the technical arena. Numbers numbers numbers.

The 9 (7tall) rudder compared to the 8 (7short) is 11% heavier, CG is 27% farther from the spar, and area is 30% greater with a .016 skin vs .020. Both have the same counterweight, giving the 8 a better balance percent. It really should not surprise anyone that the it would improve flutter margin. We get reminded every 12-18 months of this.

Fly safe.

All good Bill….as I say to my colleagues it’s not who’s right it’s what’s right….and can we learn anything from it. Interesting about the numbers on the rudders. Reading a lot of this stuff makes me keen on investigating it further throughout my build and perhaps looking at an 8 rudder instead. I won’t be doing any low level aeros and don’t enjoy spinning. it seems to me the 8’s haven’t had these failures….mmmm

[Snowflake]

Originally Posted by skylor

Really? What about the ailerons? They have counterbalances but are not 100% balanced.

Yes, but they are also used differently... The aileron is designed to carry an aerodynamic load during flight... The rudder is essentially intended to float in trail most of the time until it's needed.

Of course, that said, the elevators are intended to carry a load full time as well, and they are balanced... So... Hmm.

Good call! Additional counterbalance weight at the rudder tip could quite possibly have negative consequences on the resonant frequency of the entire rudder/vertical stabilizer system. What "seems" like a good thing could really be a bad thing!

This is very true as well, and I wouldn't suggest changing what Van's recommends. I haven't read that part of the build manual, it just seemed to me that if the control was going to be balanced, that it would make sense that it be balanced, not "partly balanced." I admit it's been a while since I studied control surface design, I may be forgetting something fundamental.

Does the build manual say to build the rudder first, or the elevators? Could it be that the manual goes into detail on the elevators, and then later when building the rudder it assumes you know all about balancing from doing the elevators and don't need a refresher?

[DanH]

Re balancing, Glenn earlier posted a link to an excellent paper well worth reading. I repeat the link here:

https://raptor-scientific.com/conten...l_Surfaces.pdf

[RV8JD]

"BillL" brought to my attention another in-flight breakup of an RV-7 (N731RV; Arlington, AZ; 6/27/2017). I added it to the spreadsheet in Post #1 of this thread. Links to the NTSB report and the docket can be found there.

From the NTSB Final report:

"Probable Cause and Findings

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

The inflight overstress separation of the vertical stabilizer and rudder during flight which resulted in the pilot's inability to maintain airplane control. Contributing to the accident was an inflight collision with a bird."

[Tandem46]

Originally Posted by RV8JD

… in-flight breakup of an RV-7 (N731RV; Arlington, AZ; 6/27/2017)…Contributing to the accident was an inflight collision with a bird."[/indent][/i]

Yeah, this accident has been discussed on here before. I agree with others that it’s doubtful a “rock pigeon” brought down this RV. The NTSB does mention: “It is possible that the pilot made an evasive maneuver before or during impact with the bird, that in combination, resulted in an overstress structural failure of the, vertical stabilizer and rudder”.
I agree.

[Z-EDD]

Originally Posted by Snowflake

Yes, but they are also used differently... The aileron is designed to carry an aerodynamic load during flight... The rudder is essentially intended to float in trail most of the time until it's needed.

Of course, that said, the elevators are intended to carry a load full time as well, and they are balanced... So... Hmm.


This is very true as well, and I wouldn't suggest changing what Van's recommends. I haven't read that part of the build manual, it just seemed to me that if the control was going to be balanced, that it would make sense that it be balanced, not "partly balanced." I admit it's been a while since I studied control surface design, I may be forgetting something fundamental.

Does the build manual say to build the rudder first, or the elevators? Could it be that the manual goes into detail on the elevators, and then later when building the rudder it assumes you know all about balancing from doing the elevators and don't need a refresher?

I have just re-read the instructions for the RV-7 empennage. Note these instructions were updated at the time of the HS service bulletin in 2014 and are in the newer “check box” format and rather more detailed than the old instructions, which I don’t have access to right now. Construction of the rudder is detailed before the elevators and contains no reference to balancing. Elevator construction is last in the sequence and has 2 references to balancing. In the pre- amble it is mentioned that the elevators are balanced control surfaces. Under “finishing the elevators” it is stated to conduct final balancing after the elevators are finished and painted, and the preferred method is to leave the counterweights slightly heavy and then balance by drilling small holes on the inner face of the counterweight.

So no mention of balancing the rudder, followed by considerable detail on balancing the elevators. For whatever reason the designer never intended the rudder to be fully balanced.

[rv8ch]

Originally Posted by Z-EDD

... For whatever reason the designer never intended the rudder to be fully balanced.

Which is completely reasonable. The paper that has been referenced a couple of times in this thread talks about this - it's not always desirable to have the CG on the hinge line.

[Snowflake]

Originally Posted by Z-EDD

For whatever reason the designer never intended the rudder to be fully balanced.

Until someone from Van's weighs (sorry) in on this I don't think we can conclude what the designer's intent was. We can only conclude that instructions for balancing were not included in the manual... And I think most of us would agree that not everything is in the manual.

Originally Posted by rv8ch

The paper that has been referenced a couple of times in this thread talks about this - it's not always desirable to have the CG on the hinge line.

This is true. Different aircraft with different configurations will have different margins for flutter and different control harmonization and feel. But I would have expected that two control surfaces that are so similar in configuration (Elevator and Rudder on an RV) and used in the same performance envelope would have similar requirements for balancing.

But, there are differences, elevator is pushrod controlled and is usually under load, rudder is cable controlled and usually floating, etc. etc. It would be great if someone from Van's could comment on this but given the litigious society we live in I can understand why they don't.

At the end of the day I don't think it's been shown that an RV-7/7A operated within the published design/performance envelope is at any risk.

[rv6ejguy]

Originally Posted by Snowflake

At the end of the day I don't think it's been shown that an RV-7/7A operated within the published design/performance envelope is at any risk.

Agree. If there was a systemic fault here, dozens or hundreds of 7s would have crashed by now, given the thousands flying.