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RVs Crash Worthiness
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/Re...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 |
vertical vs. horizontal forces
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/14b...8a671a0a35.pdf Quoting one of the greats: Quote:
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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.
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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... |
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let's learn and act from their painful lesson......
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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.) |
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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. |
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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.
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![]() ![]() 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." :( |
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. Quote:
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9A Accident
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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.
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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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Old trick - loiter in lift, skedaddle in sink.
Well flown. Dave |
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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. ![]() |
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
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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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