Speculation

I was involved with responding to an experimental crash not many years ago.

Some Fed came down and at the crash site I helped establish control continuity.

After the plane was moved to a hangar another pilot and I examined the tubular spar and noticed something that could have been a key to the accident. A proper analysis may have required that the spar area be sent to some testing facility.

To my knowledge, it never was and the plane may have been scrapped before such analysis was done.

I have no input into what happens with the RV aircraft but I hope that it is not scrapped before someone can objectively and properly examine the parts to try to establish the real cause...no matter what it was.

As a new builder with limited mechanical knowledge, I do not have the insight of most of the posters on this forum. Differing opinions are common on VAF, so I research this forum thoroughly as well as other sources for information that will help me build and eventually fly safely.

I learn from speculative posts, because they remind me to consider many things, more than what might be included in an official accident report. Besides, investigators must certainly begin their efforts with some speculation, deliberately or perhaps intuitively, as to likely or possible causes after ruling out non-contributing factors.

Despite its benefit, speculation is a problem in this forum because it is public. And since many of us have a degree of connection to each other, such comments are bound to have an effect personally. No matter how the good heart of the poster, the first speculative post always seems to be annoying. Furthermore, a speculative post inserted into a thread intended to convey sympathy to friends and family is never appreciated nor appropriate.

This group is very knowledgeable and I appreciate those who take the time to relate to impart their experiences and their wisdom in order that we might all be safer. And I also appreciate the compassion and respect seen on VAF, especially apparent in this latest tragedy.

Possible Cause of failure

I ferried the subject aircraft when purchased with Tony, from Independence, OR to Phoenix. He was a great cockpit companion, and a careful and safe pilot, and seemed uninterested in "yanking and banking", was content with controlled maneuvers.

I have issued a lot of Certificates of Airworthiness to RV's, and have found on some aircraft critical items in stress that could lead to failure under the right circumstances. I am in no way suggesting that there was any defect in the subject aircraft, but in light of the failure, perhaps we can all take a look at our aircraft to make sure our inspections include a look at critical areas.

Suppose the forward vertical fin to horizontal attach bracket is attached in such a manner as to place stress on the bracket. Vans plans call for adding a shim if the bracket and spar do not line up exactly.

Then add another non related action, such as the rudder flapping in a wind storm, causing sufficient stress on the attach bracket to begin to propagate a crack. suppose the crack continued to propagate across the attach bracket to a point of failure.

Continued loads from the rudder to the vertical fin could then cause weakening of the lower vertical spar attach area, especially the upper left bolt where the AN960 washer should have been installed as a spacer.

When a point of ultimate failure would be reached in flight, the rudder would have been retained by the rudder cables and the rudder cable horn, perhaps separating from the vertical fin nanoseconds into the event.

It will be a year before the NTSB makes a ruling of probable cause, which may result in a service instruction. In the meantime, our RV's when built according to plans and flown within the envelope, are amazingly strong, safe machines.

We can keep them safe by being diligent on our inspections, and repairing or replacing anything that is out of tolerance.

I just performed a dye penetrant inspection of my RV-7 bracket and spar, all is well.

My condolences to the family. He loved to fly!

Gary.

DanH said:

Except that the track is always presented as a straight line between the reporting points. That's not necessarily the actual aircraft track. As Sam says, "smart beaconing" is an automatic clue suggesting rapid heading changes, not straight lines.

You can prove it to yourself here with a little calculation. Measure the distance between reporting points. Record the number of seconds for each of those legs, based on the times in the beacon reports. Now divide the distances by the seconds to get feet per second, convert to MPH, then compare to the reported velocities. You'll find the values will be lower than reported, indicating the vehicle was taking an indirect, longer, path between points.

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Just a couple more comments on the APRS tracker;

Velocities reported are of course GPS-derived ground speed and direction, so wind can be a considerable factor.

It has been my experience that if the ground track of the aircraft varies more than just a few degrees within a few seconds, Smart Beaconing kicks in and sends a beacon. This resolution depends on the particular configuration of the tracker, but these little devices are usually quite predictable when installed properly.

The APRS tracker painted a pretty clear picture of what most likely happened in the Georgia accident. It remains to be seen whether or not it will be useful in the investigation of this tragedy.

I have had a couple of recent discussions on bird strikes in a RV. I know birds generally dive when they see a aircraft close by. I have had many bird strikes over the course of my flying career including one where the aircraft never flew again. That was however at 360KIAS. I have pondered how the HS stab would fair in a collision with even a large duck at 180 knots. Generally I would expect the wing to serve as a sort of blocker but given the tendency for birds to fold their wings and dive I wonder if it is possible to take a direct hit on the stab. Has anyone seen a RV series aircraft where that has happened?

George

Bird Strike

I know of a bird strike, believed to be a turkey buzzard, on the tip of the horizontal stabilizer in a Sukhoi SU29. It was the pilots habit to operate at or near Vne while descending in the area where the strike occurred. The Sukhoi stabilizer is a unique construction/material. The skins are a composite material, believed to be a Kevlar style fabric with epoxy resin. The ribs are a relatively soft sheet metal and the skin is bonded as well as blind riveted to the sheet metal. On the subject aircraft the bird strike pulled the skin loose from the outboard ribs but the skin then popped back into place with little apparent damage to the skin.
The stabilizer was replaced with a temporary stabilizer from another aircraft. There was no damage to attach fittings. Vne on the SU29 is approximately 270 statute.
The relationship of wing to horizontal tail on the Sukhois is very similar to RV's. In both cases the stabilizer is far enough above the wing so that is unlikely that the wing provides any bird strike protection for the stabilizer.
There has been a recent case where a bird strike brought down a Cessna Citation, I don't know what model. Another case many years ago where a United Airlines Vickers Viscount lost the entire tail from a bird strike.
I believe striking a large bird at high speed is capable of removing the entire horizontal tail from an RV.

jrs14855 said:

.....
I believe striking a large bird at high speed is capable of removing the entire horizontal tail from an RV.

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If that's the case, the impact point should be easy to determine if all of the tail parts are found.

A question to the group here

I started my RV-7 in 2002. Soon after I completed the empennage Van sent out the service bulletin and the parts to build the "new rudder" for better spin recovery. The thing that I remember is the new rudder was "borrowed" from the RV-9. My original rudder is made from .025 aluminum and the new one was .016 if I remember correctly. Does anyone else recall that? The new rudder has something like 30% more surface area but thinner materials I believe.
The other thing I wonder about is the "round blob in a countersink" when you rivet the rudder wedge. Is it better to place every other rivet the opposite direction or all of them one way? I just wonder if the changes to the rudder design are involved in these terrible failures. I certainly notice that after the SB and new rudder fuss that Van continues to operate the original RV-7 with the old "small" rudder.

Thanks for listening, Kev

jchang10 said:

http://www.backcountrypilot.org/community/forum/latest/witnessed-a-fatal-rv-7-crash-13501#p180249

This is an interesting first-hand account of the NTSB investigation for the recent rv-7 crash in Jackson Hole, i believe. According to him, the investigator exceeded his expectations, and he changed his tune on the NTSB after this experience. This is just a 1 person account of course and is based on a single investigator.

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I am that person /witness.....

I have full faith the NTSB investigator in charge of the crash of N820RV will do the absolute best she can to determine the cause...

More dialog can be read here about my involvement.

http://www.pilotsofamerica.com/forum/showthread.php?t=63468

http://www.pilotsofamerica.com/forum/showthread.php?t=63537