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  #1  
Old 03-18-2011, 03:17 PM
DeltaRomeo DeltaRomeo is offline
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Join Date: Jan 2005
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Exclamation Fuel System Safety (NTSB stuff: RV-10)

From the factory FB page.

"We've had several RVator articles over the years about the perils of modifying the fuel system, but it may be time to revisit the subject.

We were recently contacted by the NTSB with regard to a fuselage fire in an RV-10 with an automotive engine installed. This had what was described as a 'standard RV-10 fuel system', but the picture below forwarded by the NTSB showed plumbing which left our technical staff's jaws hanging slack in disbelief. We counted 28 clamps on the rubber hoses, but may have missed some.

Obviously, we strongly discourage any deviation from the plans, but if a builder decides that changes must be made, it is best to use approved aviation practices for fuel systems as outlined in AC43.13. The AN fittings and aluminum line shown in typical RV plans are based on current certified airplane standards and are reliable. The arrangement as shown is potentially lethal, more so if used in high pressure systems (Lycoming fuel injection systems typically run around 25psi, some automotive types may be 60psi or higher!). The cause of the presumed fuel leak/fire in this case is not known, and we await the NTSB's verdict with interest, but irrespective of their conclusion, a fuel system like this is simply a Bad Idea.

Whilst we have great freedom to experiment with RVs, the fuel system is one area where proven aerospace techniques and materials are always the best course."
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Last edited by DeltaRomeo : 03-18-2011 at 03:21 PM.
  #2  
Old 03-18-2011, 03:37 PM
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Mike S Mike S is offline
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Quote:
Originally Posted by DeltaRomeo View Post
The cause of the presumed fuel leak/fire in this case is not known, and we await the NTSB's verdict with interest,
O.K., please folks, learn from this, but please keep the speculation to yourselves.
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VAF 909

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Flying as of 12/4/2010

Phase 1 done, 2/4/2011

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Last edited by Mike S : 03-19-2011 at 09:37 AM.
  #3  
Old 03-19-2011, 11:31 AM
Kyle Boatright Kyle Boatright is offline
 
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Quote:
Originally Posted by Mike S View Post
O.K., please folks, learn from this, but please keep the speculation to yourselves.
This. The guy lost his plane and suffered burns in the accident, as did his daughter. I'm sure he's suffered enough without a bunch of armchair quarterbacks rehashing things.
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Marietta, GA
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  #4  
Old 03-19-2011, 08:08 PM
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flion flion is offline
 
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Even that was more speculation than I was willing to do.
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  #5  
Old 03-19-2011, 11:07 PM
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9GT 9GT is offline
 
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Quote:
Originally Posted by Kyle Boatright View Post
This. The guy lost his plane and suffered burns in the accident, as did his daughter. I'm sure he's suffered enough without a bunch of armchair quarterbacks rehashing things.
I don't think Van's or anyone else is trying to make the builder look bad. Members on this forum who have been here a while know who the owner of this plane was and are sympathetic to his loss and are grateful he and his daughter were not killed in this tragic accident. I consider this to be nothing more than a good reminder to adhere to and follow acceptable standard aviation practices when building.
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  #6  
Old 03-20-2011, 06:26 AM
David-aviator David-aviator is offline
 
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My frontal lobe tells me I should not comment on this subject but something needs to be said about the photo and the use of high pressure fuel injection hose in an airplane.

I have been flying with it since 2003. I changed the entire hose material about 18 months ago as a precaution and found the material as good as new. None of the clamps were loose, none have ever leaked. Each had to be cut to be removed. They are not screw type clamps. (I do not use hose forward of the firewall with the Lycoming, I did with the Subaru engine.)

They key here is to use proper hose and clamps. There is fuel hose and there is high pressure fuel injection hose. The only clamps to use are OETiker. Once installed with the OETiker plier they are very difficult to remove. Many, many auto installations are done this way and last forever. You see an auto fire on the side of the road now and then, they are mostly caused by an electrical problem, not a fuel leak.

Aluminum fuel line is safe and recommended as per Van's. But the flaring tools we use are not very precise and frequently the flare is not perfect. That can lead to flare cracking and a fuel leak. I happens. None of this is totally bullet proof.

The fuel system in the photo appears to have been reconstructed. I wonder if the clamps are original?
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  #7  
Old 03-20-2011, 07:38 AM
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DanH DanH is online now
 
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Let's move away from speculation and onward to education. Hose clamps are not forbidden in aviation, but there are details to safe use.

First, the common clamps in the photo are no longer used in auto and truck applications where long term reliability is required. They have a well known problem; the clamped rubber extrudes out through the slots over time, which results in a loss of clamp pressure.



Reliable clamps have no slots. They are either solid bands pulled with a screw or worm clamps with embossed threads rather than slots.



Small diameter hoses for high pressure fuel have their own special clamp. Not suprisingly, it is known as a "fuel injection clamp" at your local auto parts store:



Slotted band clamps are fine if long-term clamp pressure isn't critical. An example might be an accessory case breather hose or any SCAT tube.

The second problem involves fit. Band clamps tend to be treated as if one size fits many diameters. Actually the range can be narrow, and the problem gets worse as the tube gets smaller and/or the clamp gets cheaper. The screw body of the clamp is often shaped with an inner radius matching the middle of the intended diameter range. Using this clamp on a tube at the far end of the possible range results in poor clamp pressure in the areas of radius mismatch:



It's not just a slotted clamp problem; you must look closely at fit when using any clamp style.
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  #8  
Old 03-20-2011, 08:46 AM
RV8R999 RV8R999 is offline
 
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Great info Dan!

Where do you get all the neat diagrams????
  #9  
Old 03-20-2011, 09:28 AM
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Mike S Mike S is offline
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Default Thank Dan!!

Quote:
Originally Posted by DanH View Post
Let's move away from speculation and onward to education.
Exactly!!

One more item, this is the non pressure side of the system, as I recall.
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Mike Starkey
VAF 909

Rv-10, N210LM.

Flying as of 12/4/2010

Phase 1 done, 2/4/2011

Sold after 240+ wonderful hours of flight.

"Flying the airplane is more important than radioing your plight to a person on the ground incapable of understanding or doing anything about it."
  #10  
Old 03-20-2011, 10:50 AM
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skylor skylor is offline
 
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Quote:
Originally Posted by Mike S View Post
Exactly!!

One more item, this is the non pressure side of the system, as I recall.
The assembly in the picture has two fuel injection pumps plumbed in parallel with each other and rubber hose with worm screw type hose clamps are clearly visible on both sides of the fuel pumps. The rubber hose and hose clamps are definitely used on the high pressure side of this particular assembly.

Skylor
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