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  #1  
Old 12-24-2016, 01:16 AM
dlomheim dlomheim is offline
 
Join Date: Sep 2006
Location: (2OK2) OK City, OK
Posts: 381
Default 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

Last edited by dlomheim : 12-24-2016 at 01:24 AM.
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  #2  
Old 12-24-2016, 01:57 AM
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rv8ch rv8ch is online now
 
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Location: LSGY
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Default 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:
Originally Posted by Bob Hoover
If you're faced with a forced landing, fly the thing as far into the crash as possible.
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  #3  
Old 12-24-2016, 06:41 AM
RV74ME RV74ME is offline
 
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Location: Auburn, AL
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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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  #4  
Old 12-24-2016, 10:18 AM
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Snowflake Snowflake is offline
 
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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.
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  #5  
Old 12-24-2016, 10:18 AM
BenNabors BenNabors is offline
 
Join Date: Mar 2014
Location: Alabama
Posts: 127
Default 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.
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  #6  
Old 12-24-2016, 11:03 AM
Canadian_JOY Canadian_JOY is offline
 
Join Date: Aug 2007
Location: Ontario, Canada
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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.
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  #7  
Old 12-24-2016, 11:19 AM
Michael Burbidge Michael Burbidge is offline
 
Join Date: May 2006
Location: Sammamish, WA
Posts: 654
Default 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!
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  #8  
Old 12-24-2016, 11:40 AM
Aggie78 Aggie78 is offline
 
Join Date: May 2014
Location: Fort Worth, Texas
Posts: 436
Default 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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  #9  
Old 12-24-2016, 11:57 AM
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RV6_flyer RV6_flyer is offline
 
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Location: NC25
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Quote:
Originally Posted by BenNabors View Post
--- 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.
Quote:
Originally Posted by Michael Burbidge View Post
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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NC25 RV-6
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Building RV-8 S/N: 80012

To most people, the sky is the limit.
To those who love aviation, the sky is home.

Last edited by RV6_flyer : 12-24-2016 at 11:58 AM. Reason: spelling & grammar
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  #10  
Old 12-24-2016, 11:59 AM
BobTurner BobTurner is offline
 
Join Date: Dec 2011
Location: Livermore, CA
Posts: 6,797
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Quote:
Originally Posted by Michael Burbidge View Post
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.
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