REFLECTOR: Fw: No management fuel systems

Mon Jan 16 09:34:53 CST 2012

From: Duane Swing 
Sent: Monday, January 16, 2012 8:58 AM
To: 'Lou Stedman' 
Cc: 'John Abraham' ; 'Scott Swing' 
Subject: RE: REFLECTOR: No management fuel systems

Hi Lou,

Since your e-mail ended up on my desk, I will answer it from my prospective. It really doesn’t matter much that the Velocity uses a sump system. If a fuel cap is not installed properly, or for other reasons, fuel imbalance will certainly be the result. I have heard of at least one case where the engine quit with NO fuel in the sump, NO fuel in one main tank and almost FULL fuel in the other main tanks. In this case, as I recall, the vent system came out of the main tanks and went down-hill before then angling up to the manifold at the top of the firewall. With his fuel tanks full, the excess fuel filled the vent lines and blocked any venting that would have eliminated this problem. A good rule of thumb here is fuel should always flow DOWN and the vent lines should always angle UP. On our first TXL, with full fuel, the vent lines would fill with fuel during acceleration and rotation and push the fuel all the way to the manifold valve at the top of the firewall and then push on out the bottom vent line into the slip stream. In other cases, even with a slight air leak at the fuel cap, a low pressure will slow the fuel drain from the tank with the leak. Usually once the pressure drop from one side to the other is great enough, the fuel will again drain to the sump but one tank will always show more fuel than the other. Certainly a fuel selector valve (Right – Off – Left) without the sump tank would stop this imbalance but require fuel management by the pilot. Our first SUV and at least one of our XL’s we built here was set up this way. As you know, Danny preferred simplicity and is why he selected the sump system. 

As a side note, I have owned two Aerostars and they were plagued with a similar problem. Unlike most other twin engine fuel systems, Ted Smith wanted a simple fuel management system and they used three tanks. Two mains and one sump. Left wing tank fed the left engine and the right wing tank fed the right engine. The sump tank fed both engines when the mains were near empty. No selectors needed to fly to empty if all works as advertised.  Several years into the production the airplanes were falling out of the sky due to one engine starving for fuel even though one of the main tanks were still nearly full. Here is what was happening: Low air pressure over a leaking fuel cap on one wing tank slowed or stopped the fuel flow to that engine. By design, the fuel then diverted to the sump tank until it was empty and then the engine would quit. The only way to prevent the problem was to cross feed if the pilot was aware of what was happening. The final AD note required replacement of the O rings on the main fuel tank caps every annual.

If it ain’t broke, don’t fix it, seems to be the feeling by most. Don’t be casual with your fuel system. What might work fine for years might not work the next time you fly so stay alert to fuel imbalance possibilities and land if not sure.

Duane Swing

From: Lou Stedman [mailto:stedmanlou at roadrunner.com] 
Sent: Saturday, January 14, 2012 5:09 PM
To: info at velocityaircraft.com
Subject: Fw: REFLECTOR: No management fuel systems

Not sure if you read the Reflector but If not could you comment on the weather we should be concerned about this. I know that Burt always had a running battle with Dan so I don’t know how much of this to believe. Thanks

From: vance atkinson 

Sent: Saturday, January 14, 2012 8:50 AM

To: Velocity Aircraft Owners and Builders list 

Subject: Re: REFLECTOR: No management fuel systems

I an in contact with Terry Schubert now ( actually last night) and we agree that the key here is the left fuel line and right fuel line are T'eed together.  This is not the same as the sump system the Velocitys have, and I also have, in my Cozy for 20 trouble free years now.  I have written to Burt asking for a more detailed explanation of his letter.  
When he replies I will post it on the Reflector.

Vance Atkinson
EAA Tech and Flt Advisor
COZY N43CZ
VEZ  N3LV

On 1/13/2012 5:13 PM, Lou Stedman wrote: 

I am a member of CSA and received this notice today. Is this something that we Velocity drivers should be concerned with? Does the sump tank take away this problem?

CSA Article Correction

Terry Schubert CSA Newsletter Editor

CSA # 105 January 2012, page 23, No Management Fuel System article correction.

Subsequent to January 2012 CSA issue mailing, I received e-mails from both Burt Rutan and Mike Melvill. They both felt the No Management Fuel System was potentially dangerous. The common sump fuel system fed by both tanks simultaneously could only be safely used on a gravity system without a fuel pump.

I had no idea that this fuel system was viewed as being so dangerous. I stand corrected. The No Management Fuel System author is an IA and has built two Long-EZs and flown a couple thousand hours in them. Another highly experienced Cozy builder I checked with has about the same time in his Cozy with a similar system.

Communication from Burt and Mike follow and explain the reason for concern.

***************

Email from Burt Rutan

Terry and Mike,

I do read the CSA newsletters to stay in touch a bit, even in retirement.

What I saw in #105 may represent a serious safety issue. A builder is recommending a "No Management Fuel system" by teeing together both fuel tanks. While this may work ok for a while, it would be dangerous if a fuel cap is lost or is not installed after fueling OR if there is a leak in a fuel cap seal. What happens is that all the fuel is transferred in flight to one side and dumps out the cap that is missing or is leaking. This can cause engine failure.

For reference, the VariEze had the "both" fuel system, with a tee at the bottom of the fuselage. It works ok on a Cessna 150 where the tee is a full 4 ft below the tanks. However, if the tee is only several inches below the tanks, a small difference in tank vent pressure can put air to the tee and fail the engine. There were several Varieze engine failures due to loss of fuel cap, or leak of a fuel cap. For the LongEz I designed a much safer fuel system, with sumps that assured a low amount of unusable fuel and made sure the fuel could not swap sides or vent overboard.

Burt

***********

Email from Mike Melvill

Terry, 

Burt is not kidding about this. In a Long-EZ/Cozy the fuel tanks MUST be switched separately, and must separately feed the engine. Teeing them together is dangerous as hell! This teeing idea only works on gravity fed systems with no fuel pump, can you say Cessna 15, C172 etc. Look around---all GA planes with two or more fuel tanks plus an engine driven fuel pump have a fuel tank selector valve just as the RAF plans call out. Do not ever change this or you will eventually find yourself out of gas with one tank full, and no way to get to that fuel. It has happened before to several EZ folk! Why is it that we never learn from lessons learned? Please put a stop to this stupidity!

The big point really is this; Aside from high wing, gravity fed planes like the Cessna 150, there are NO certified aircraft with two fuel tanks or more PLUS a fuel pump, that don’t use a fuel tank selector valve! None! The reason the FAA insists on a fuel selector valve in such a plane is this: if a fuel cap is accidentally left off or has a leaky ‘O’ ring seal, or for some reason comes off in flight, the result is always the same. You will run out of fuel with one tank full!! 

This is due to the fact that the fuel caps are generally on top of a wing where there is low pressure in flight due to the airfoil providing lift. When a fuel cap is missing the fuel is sucked out of this fuel tank. With no fuel valve, the fuel in the tank with a cap, is drawn across the ‘T’ at the low point (where the fuel selector used to be) into the tank without a cap. The engine continues to run until the tank still equipped with a fuel cap is empty. Then you are out of gas and the engine quits in spite of the fact that you have an essentially full tank of fuel in the tank with NO cap!! The fuel pump starts sucking air from the now empty tank with the cap, and the low pressure above the tank with NO cap won’t allow the fuel pump to deliver the remaining fuel (usually a full tank) to the engine. Having a fuel tank selector valve in a Long-EZ (as well as in all Cherokees, all Cessnas bigger than C150’s & on and on) prevents this problem from happening. The bottom line is this: If you have more than one fuel tank AND you have a mechanical engine driven fuel pump, you must have a fuel tank selector valve!

This exact scenario happens to Cessna 150’s as well as to Variezes if they loose one fuel cap! In a gravity fed fuel system such as C150 & Varieze with no fuel selector, this problem can’t be fixed. That is why it is so important to remember to replace the fuel caps on gravity fed planes!) Wes and Milly Gardner had this happen to them and I believe we talked about this back then in the CP. 

Mike

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Lou Stedman
Velocity SEFG
N7044Q
Olean, NY

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