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RVs Crash Worthiness

dlomheim

Well Known Member
I met a Federal accident investigator a number of years ago, and since I am building a "9A", he related to me a story of an RV accident he had worked on in California. The final "official" report is located here:

https://app.ntsb.gov/pdfgenerator/R...ID=20050415X00465&AKey=1&RType=Final&IType=LA

The most interesting thing about this accident that he related is what happened to the RV airframe after it went "beak to beak" with a large dump truck. He said as the pilot glided into a California DOT parking lot, it just cleared a hook and ladder fire truck, bounced once or twice and then had a head on collision with a parked dump truck. The deceleration loads were transmitted through the pilot's shoulder straps and to the aft longerons where they attach. That loading pulled the tail into itself until it couldn't crush together anymore; and since there was still energy to be shed the double row of rivets that secure the tail section to the front (at the back of the baggage area) were all sheared off! This then allowed the tail section to slide forward, and the pilot's head struck the instrument panel and was lacerated, but thankfully he survived. Hearing that story again affirmed for me, how crucial it is (in a forced landing), to ensure we maintain enough airspeed at touchdown to kill the descent, and then take our chances w/any ground objects we might encounter.

Doug Lomheim
RV-9A Mazda 13B/FWF
RV-3A sold
 
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I remember watching an EAA webinar talking about off-airport landings. Speed has a dramatic affect on whether or not you survive (no surprise). Even as much as 5-10 knots can mean the difference between life and death. Also, finding a spot that can absorb (cushion) all the energy (field of crops, young trees, etc.) helps too.
 
Also... Stopping the aircraft using any part of the aircraft that you're not in will help reduce your chance of injury as well. The more energy you can remove from the system the less is available to go into you as the plane comes to a stop.

ie. Put the fuselage between two trees so the wings fold and slow you down, drag a wingtip or ground-loop at the last minute and turn some of the linear momentum into angular momentum (converting forms consumes energy), hit an object obliquely rather than head on, etc. etc.
 
Some key points from the accident data base

I have read through all the RV accidents reports for all RV's except I have not completed the RV-4 list, need to finish the RV-4s. It has been many months since I have done this, but I made some key observations about the RV fleet.

First, if you can make it to an airport or large flat area and control the closure rate with the ground (vertical velocity), you are going to survive. You may crunch the plane, injure your pride, but you are going to see your family. If you forget to fly the plane and stall, you are going to die. Die is a very blunt statement, but that is what the data shows. I was stunned at how many stalls there were in the database, many from very experienced pilots with many hours in the accident plane, many in the traffic pattern.

I would say that once you descend below an altitude at which you cannot recover from a stall, you only actions should be to ensure that your vertical velocity at touchdown is the same as a normal landing. Stop fiddling with knobs, restarting engine, or what ever the emergency is and fly the plane.

In this specific case, the air frame did what it was designed to do, absorb the energy, each rivet that popped absorbed energy. I would have thought that the air-frame would have deflected/crushed before breaking the rivets so there might be something to look at there, but that should be determinable analysis as to whether the joint is stronger than a single layer of the parent material. At the point the air frame deflected and started popping rivets, it was giving up its life to save the occupants.

Consider that energy 1/2*Mass*Velocity^2. Velocity dissected into vectors of horizontal and vertical components defines the forces. If the vertical component of velocity is 5, the energy component is (5*5) 25. If it is 10, the energy is (10*10) 100, four times higher. If it is 20, energy is 16 times higher. Vertical speed into the heavenly body call earth is deadly.
 
This topic is one which we would all like to shovel under the carpet and bury forever. I'm very, very glad to see it being discussed here in such open and frank terms. It's this kind of discussion that takes away all the nice fluff and replaces it with cold, hard facts that we need to make life-saving decisions.

One of the reasons we chose our current project airplane is because of the survivability of its design. It has a strong track record of protecting its occupants. I've had discussions with potential builders about how we chose our particular aircraft type, and I've seen them cringe when I list survivability as one of the key factors. If you're not looking at survivability when you choose your next airplane then you are overlooking a life-critical design element.
 
Design for survivability?

Given that the basic structure of a Vans Aircraft appears similar to other small aluminum airplanes, what is it specifically about a Vans Aircraft that was designed with survivability in mind?

Michael-

Don't get me wrong, I love my RV-9A!
 
Hard Surface vs Soft Surface

I have read analysis that, other factors being kept equal (low approach speed and modest (gliding) approach angle) that trying to put down on a hard surface is preferable over a soft one.

The reason is deceleration rates (G's) between the two surfaces can be dramatically different.

Hard surfaces impacted at a low angle resist sudden stops and usually result in a long slide. The G-loading of the stop is therefore more modest on its peak, onset and duration.

Soft surface accident sites, on the other hand, many times bear witness to "digging in" and a sudden stop over a few yards, or maybe even feet. "G" onset is immediate and can exceed survivability levels very quickly.

The takeaway for me was try to find a hard surface to put down on and then manage the approach to touch at min speed and low angle. Seemed counterintuitive to a field landing to me at the time, but the evidence presented was pretty compelling...
 
--- snip ---

Consider that energy 1/2*Mass*Velocity^2. Velocity dissected into vectors of horizontal and vertical components defines the forces. If the vertical component of velocity is 5, the energy component is (5*5) 25. If it is 10, the energy is (10*10) 100, four times higher. If it is 20, energy is 16 times higher. Vertical speed into the heavenly body call earth is deadly.

Given that the basic structure of a Vans Aircraft appears similar to other small aluminum airplanes, what is it specifically about a Vans Aircraft that was designed with survivability in mind?

Michael-

Don't get me wrong, I love my RV-9A!

The stall speed is what helps make the RV survivability. See Ben Nabors post above. As I was taught as a Student Pilot, fly the airplane. IF you are in control at the lowest possible speed, fly the aircraft into the softest least expensive object, there is a much better chance of surviving than in an uncontrolled crash.
 
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Given that the basic structure of a Vans Aircraft appears similar to other small aluminum airplanes, what is it specifically about a Vans Aircraft that was designed with survivability in mind?

Michael-

Don't get me wrong, I love my RV-9A!

Just to name one: stall speed. There are some fast EAB airplanes that have a stall speed well over 61 kias. They tend to do poorly in forced landings.
 
let's learn and act from their painful lesson......

......... the pilot's head struck the instrument panel and was lacerated, but thankfully he survived. .........

One of my pet peeves is the razor sharp edge of the glareshield. Look at a 30-year old car,....the dash is much more friendly to impact than our cabin.
especially with the long belt attach run in the RV, you ARE going to hit things with your head...especially if your impact has side or other loads, which is the norm.
even helmets lack much face protection. Think long and hard about all the **** you are suspending in front of your face, I know I have a big portable GPS and some other elements that will cause me grief. Most of us have iPads and things that will fly around on impact.
There is much to be learned from a crashworthiness audit of our cabin and restraint system.
(A previous post referred to the Glastar/sportman, whose steel cage is credited with an extremely low fatal crash rate.)
 
This seems to be correct. If we stall and pancake in, our chances of survival are lower. Here's an interesting paper that talks about this, mainly related to helicopters.

https://pdfs.semanticscholar.org/14b0/b412c17aa8bbe4f8dc5955c3d68a671a0a35.pdf

Quoting one of the greats:

Years ago I went to a talk by an NTSB investigator who talked about this (and had some pretty gnarly photos to go with it). He said that in many cases (most?) where the plane is stalled and thus falls to earth, rather than a controlled crash "landing", what happens to the human body is that the sudden stoppage causes all the internal organs to basically continue on their way downward, tearing away from the rest of the internal structure. The lungs and airway tear away, and if the occupant is still miraculously alive at that time, they suffocate because there's no longer a viable airway. Gruesome.

Bottom line...never, ever, ever stall the plane during an emergency landing...fly it all the way through the crash and you will probably live. Stall it in...game over, man.
 
The most interesting thing about this accident that he related is what happened to the RV airframe after it went "beak to beak" with a large dump truck. He said as the pilot glided into a California DOT parking lot, it just cleared a hook and ladder fire truck, bounced once or twice and then had a head on collision with a parked dump truck. The deceleration loads were transmitted through the pilot's shoulder straps and to the aft longerons where they attach. That loading pulled the tail into itself until it couldn't crush together anymore; and since there was still energy to be shed the double row of rivets that secure the tail section to the front (at the back of the baggage area) were all sheared off! This then allowed the tail section to slide forward, and the pilot's head struck the instrument panel and was lacerated, but thankfully he survived. Hearing that story again affirmed for me, how crucial it is (in a forced landing), to ensure we maintain enough airspeed at touchdown to kill the descent, and then take our chances w/any ground objects we might encounter.

Here is where a properly designed brace between the two harness attach points at the longerons could absorb some of the energy and reduce the chance of the head to contact the panel.
 
In an off-field landing, the goal IS NOT to land at the slowest forward speed, it is to land at ZERO vertical speed. Keep that in mind and you have a chance.
 
In an off-field landing, the goal IS NOT to land at the slowest forward speed, it is to land at ZERO vertical speed. Keep that in mind and you have a chance.
Yeah, belts are designed to take the loads of a frontal collision. So glad that our planes are designed for 5-point harnesses. Make sure the lap portion is positioned low so your pelvis takes the load, not your abdomen.
 
First, if you can make it to an airport or large flat area and control the closure rate with the ground (vertical velocity), you are going to survive. You may crunch the plane, injure your pride, but you are going to see your family. If you forget to fly the plane and stall, you are going to die.
Having survived an RV9A crash that completely destroyed the aircraft with my passenger and I receiving only minor injuries I can state this is so very true. I will never forget December 26, 2012, 5:45pm at KSSI.

20121226_181939.jpg

20121226_183951.jpg


The famous Bob Hoover, who survived several crashes, once said (paraphrased) "Never stop flying the airplane. If you have to, fly it all the way through the crash."

:(
 
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Crash

Galin,
Not sure if you have shared the details already, but if not, I would be interested in hearing about your -9a incident and fire. The pics look scary.


Having survived an RV9A crash that completely destroyed the aircraft with my passenger and I receiving only minor injuries I can state this is so very true. I will never forget December 26, 2012, 5:45pm at KSSI.

20121226_181939.jpg

20121226_183951.jpg


The famous Bob Hoover, who survived several crashes, once said (paraphrased) "Never stop flying the airplane. If you have to, fly it all the way through the crash."

:(
 
Galin,
Not sure if you have shared the details already, but if not, I would be interested in hearing about your -9a incident and fire. The pics look scary.
In 2013 I did a short write up of the incident for our website in the ADVENTURES section under the 2012 "Almost 3rd Annual Florida to Caribbean" trip. After the crash, I swore never to fly again but several pilot friends helped me overcome my fears and am eternally grateful for that. Since then I have talked to other pilots that have had similar incidents to help them possibly get back into flying.
:cool:
 
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9A Accident

In 2013 I did a short write up of the incident for our website. After the crash, I swore never to fly again but several pilot friends helped me overcome my fears and am eternally grateful for that. Since then I have talked to other pilots that have had similar incidents to help them possibly get back into flying.
:cool:

Galin: Thanks for sharing your story, and I'm glad it all ended with only the loss of the a/c! No doubt there are freak and unpredictable weather anomalies out there that can exceed the performance of even an RV...

Doug
 
weird weather

I've seen things that make me never want to underestimate weather. Saw a rogue gust of wind from the right rear lift a wing on a landing T6 (if I recall correctly) and put him off the runway. I can't imagine that there was anything he could have done to predict or prevent this. Thankfully no injuries.
 
I was a passenger in an RV-6A, on final, about 5 feet above the runway, when a sudden wind gust picked up our left wing so violently that the right wing tip scraped the runway. How the pilot regained control I'll never know. We were returning from a long cross country and could see pre-frontal activity about ten miles away. In retrospect a straight-in long final would have gotten us on the ground quicker than the standard pattern we flew. The pilot/builder repaired the damage. We considered ourselves lucky.
P.S. Although it wasn't a "crash" I afterward wondered how a non-RV would have withstood our event.
 
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Galin: Thanks for sharing your story, and I'm glad it all ended with only the loss of the a/c! No doubt there are freak and unpredictable weather anomalies out there that can exceed the performance of even an RV...

Doug

Yes, there are. I was flying a B-767-200 from EZE to IAH. Over the Gulf of Mexico at 38,000 feet, we had to penetrate a frontal line than ran from horizon to horizon. While in the clouds, and at full throttle, the big Boeing was losing airspeed rapidly. The downdraft was so intense that we could not maintain altitude. Only one thing to do...do down. We punched through the other side in a minute or so, but my knuckles were white from pushing the thrust levers through the instrument panel!
 
In an off-field landing, the goal IS NOT to land at the slowest forward speed, it is to land at ZERO vertical speed. Keep that in mind and you have a chance.

Some of the best advice I ever got: Fly the aircraft all the way to the accident!
G
 
SAAA Airsport Magazine Article

Hi All,

There was an article covering buckling similar (but not identical) to that described at the start of this thread in a recent SAAA Airsport magazine. A screenshot of the article may be seen below. It came along a little late for my build, however it may be of benefit to others.

Regards,

Tom.

2rrrwxh.jpg
 
Thanks, Tom!

I am very interested in obtaining the plans that are "available on request". How might I go about that?

Happy New Year!

Merrill
 
Me too!

Although I'll probably try to figure out a lighter version.

DR and Tom, that one posting justified my VAF donations this year. Thanks!

Dave
RV-3B, now on the fuselage, and not too far along to add this.
 
I agree with David. This is great info and would love the plans. I went to the site and they only have to Spring 2016 online. I hope the summer 2016 is uploaded soon so we can download it.

On another note, SAAA Airsport has a great magazine. Very well done. Now I have a whole new series of issues to read!

http://www.saaa.com/Home/AirsportPublic.aspx
 
Hi Guys,

I've written to the author of the article requesting further information, so let's see what comes of it.

Cheers,

Tom.
 
RV Crash Worthiness

Here is where a properly designed brace between the two harness attach points at the longerons could absorb some of the energy and reduce the chance of the head to contact the panel.

Does anyone have any pictures of the longerons pulled in towards each other from a crash? I may have missed it, but I didn't see any reference to this in the OP link to the crash report.

Yes, it would be an easy (and cheap) to make a brace between the two harness attach points, but before doing so, I'd like to be sure I'm not just creating a solution looking for a problem.
 
Often in a crash, the deformation is momentary and the only sign, besides injuries, is some residual local yielding. Most of the deformation is actually elastic and rebounds.

Dave
 
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