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Aux fuel pump in 701.Aux fuel pump in 701.

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Larry Bohannon

Joined: 10 Jan 2006
Posts: 1
Location: Winder, Georgia

Posted: Sat Feb 25, 2006 10:42 am Post subject: Aux fuel pump in 701.Aux fuel pump in 701.

I was planning on installing the fuel system in my 701 as per plans. Now, with all the talk of pumps,filters,ram air tubes in the stock vented gas caps, and uneven flow from one tank or the other, I'm wondering what to do.

The plans have only the stock vented gas cap,a finger screen fitting at the exit of the tank,the two hoses joining at the stock gascolator which is mounted to the left of centerline at the low point of the fuselage and a single hose running under the pilots seat to a single shutoff valve at the pilots feet and then on to the engine. Has anyone flown with this per plans setup for any length of time?? When I saw Roger's 701  I noticed there appeared to be some clear filters in the lines where they entered the baggage compartment and he had ram air tubes in the gas caps on top of the wings. I don't know how the rest of Roger's  system is set up but even Zenith's own plane is not per their own plans!! What gives?? If we were to build it from the plans would this be unsafe?  The reason I bought the supposedly "complete" kit and plans was that someone with the know how ( Chris H. and Zenith) had already figured all this stuff out, but I saw in the Zenith newsletter about a year or so ago, where Chris was giving info and a drawing of how to put the ram air tube in the gas caps but there is nothing in the actual plans. How are we to know what to do and what is safe if Zenith doesn't even follow their own plans? Also, is anybody using the black rubber hose that came with the kit? I seem to recall reading somwhere the rubber hose breaks down inside and the pieces clog the carbs?

     I'm almost finished with my 701 airframe and I will be installing the engine and fuel system as soon as I receive the FWF kit I ordered from Skyshop. i read where the biggest cause of accidents in homebuilts is the fuel system. I only have a high school education but I can build according to plans, if the plans are correct and safe, but can anybody tell me if the plans are correct and safe or not?  Should I follow the plans exactly, even if Zenith doesn't, or should I modify? Any help/advice from the list would be greatly appreciated.

Larry Bohannon

Winder, Georgia

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jeffrey_davidson(at)earth
Guest

Posted: Sat Feb 25, 2006 11:56 am Post subject: Aux fuel pump in 701.Aux fuel pump in 701.

Larry,



On the question about "Also, is anybody using the black rubber hose that

came with the kit?":



I am going to use it on my 601 HD with leading edge tanks only.  I modeled

my fuel system after the XL system on 6K2 available on the ZAC web site.

Yesterday, I took a good look at Jim Pellien's 601XL, which is certified as

an LSA.  It uses the rubber hose too.  With the dual stick option, the hose

runs right in front of the spar through the dual stick bracket to the Andair

selector value in the console.



FWIW, I have found that the builders have a lot of input from various

sources, but that ZAC does not provide an exact fuel system design.  Several

for the 601 can be found on the ZAC web site.  This is an experimental

aircraft, so you have a lot of freedom/responsibility.  For complete

assurance, I suggest that you draw a diagram of your proposed system and

send it to ZAC for comment and validation by Nick, Sebastian, Roger, Chris,

or whoever else may answer.  In my opinion, that is how you can get the

confidence that comes with the designer's suggestions and approval on your

particular system.



Jeff Davidson

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bryanmmartin

Joined: 10 Jan 2006
Posts: 1018

Posted: Sat Feb 25, 2006 3:03 pm Post subject: Aux fuel pump in 701.Aux fuel pump in 701.

If the two wing tanks have separate vents, there could be a difference in

the pressure venting the tanks. All else being equal, this difference in

pressure is what will cause the two tanks to feed fuel at different rates.

To get some idea of how large this difference in pressure might be, you can

calculate a couple of pressure differences that the airplane will normally

encounter in flight.



One of these pressure differences is the lift generated by the wing. The

CH701 has a gross weight of 1100 pounds and a wing area of 122 square feet.

So the lift generated in level flight is 1100lb/122sqft=9lb/sqft or about

.063 psi. If we assume the pressure under the wing is the same as static

pressure then the pressure on top is .063 psi less than static.



Another pressure difference encountered in flight is the difference between

the ambient pressure and the ram air pressure, or the dynamic pressure. From

an airspeed calibration table I have, dynamic pressure at 90 mph is about

.14 psi. These are both pretty small numbers.



In the worst case, where one fuel tank cap has a ram air tube and the other

one just has a vent hole, the maximum pressure difference between the two

tanks should be about .14 psi + .063 psi = .203 psi. The fuel pressure at

the bottom end of the fuel line from the tank is the sum of the head

pressure of the fuel and the air pressure pushing down on the surface of the

fuel. If one tank is draining faster than the other, is there some point

where the difference in head pressure in the two tanks will balance out the

difference in air pressure and cause the fuel to feed evenly?



Gasoline weighs six pounds per gallon, there are about seven and a half

gallons in a cubic foot which gives 45 pounds per cubic foot or .026 pounds

per cubic inch. So the head pressure one inch below the surface of a tank of

gasoline is about .026 psi. Dividing the worst case air pressure difference

of .203 psi by .026 psi gives 7.8 inches of gasoline. So, when the level of

fuel in the "high pressure" tank is about 8 inches lower than the other,

both tanks should be feeding evenly. In reality, the air pressure difference

between the two tanks should be a lot less than this example.



Will the engine be sucking air from one tank before the other tank is empty?

The bottom of the gas tank on the 701 is about three and a half feet above

the floor of the cabin. You may empty one tank before the other but both

tanks will be empty before you start sucking air. There may be 8 inches more

fuel on one side than the other when you start sucking air but all of that

fuel will be in the fuel line. How much fuel does 8 inches of fuel line

hold? This is why most high wing Cessnas can operate with the fuel selector

in the both position with no danger of draining one tank before the other.

And, in my experience, even they don't drain fuel evenly from both tanks. On

the other hand, it is possible for a low wing airplane to drain one tank dry

and leave a significant quantity of fuel in the other, which is why you

usually draw fuel out of only one tank at a time on most low wing aircraft.



So to answer your question. Is the fuel system in the plans safe? I would

say yes. The fuel system in the plans is probably about the simplest you can

get. Can it be improved upon? Sure. The ram air tubes on the caps will

prevent small amounts of fuel from dribbling out the vent holes in flight

and staining the top of the wing, and they can improve the fuel flow

slightly. The biggest disadvantage to the system you described in your post

is that if you fill both tanks and then park the plane on a slope so that

one wing is lower than the other, fuel can flow from the high side to the

low side and overflow the low tank and cause fuel to flow out the vent.

Eliminating the vented caps and installing an interconnecting fuel vent

system can stop this from happening even though it may not completely cure

the problem of uneven feeding of fuel. Even the Cessna 150/152s I've flown

don't always feed fuel evenly from each tank.



-- 

Bryan Martin

N61BM, CH 601 XL, Stratus Subaru.



on 2/25/06 1:41 PM, Larry Bohannon at larryb54(at)alltel.net wrote:



 	  Quote: 	
		   

 

 I was planning on installing the fuel system in my 701 as per plans. Now, with

 all the talk of pumps,filters,ram air tubes in the stock vented gas caps, and

 uneven flow from one tank or the other, I'm wondering what to do.

 The plans have only the stock vented gas cap,a finger screen fitting at the

 exit of the tank,the two hoses joining at the stock gascolator which is

 mounted to the left of centerline at the low point of the fuselage and a

 single hose running under the pilots seat to a single shutoff valve at the

 pilots feet and then on to the engine. Has anyone flown with this per plans

 setup for any length of time?? When I saw Roger's 701  I noticed there

 appeared to be some clear filters in the lines where they entered the baggage

 compartment and he had ram air tubes in the gas caps on top of the wings. I

 don't know how the rest of Roger's  system is set up but even Zenith's own

 plane is not per their own plans!! What gives?? If we were to build it from

 the plans would this be unsafe?  The reason I bought the supposedly "complete"

 kit and plans was that someone with the know how ( Chris H. and Zenith) had

 already figured all this stuff out, but I saw in the Zenith newsletter about a

 year or!

 so ago, where Chris was giving info and a drawing of how to put the ram air

 tube in the gas caps but there is nothing in the actual plans. How are we to

 know what to do and what is safe if Zenith doesn't even follow their own

 plans? Also, is anybody using the black rubber hose that came with the kit? I

 seem to recall reading somwhere the rubber hose breaks down inside and the

 pieces clog the carbs?

    I'm almost finished with my 701 airframe and I will be installing the

 engine and fuel system as soon as I receive the FWF kit I ordered from

 Skyshop. i read where the biggest cause of accidents in homebuilts is the fuel

 system. I only have a high school education but I can build according to

 plans, if the plans are correct and safe, but can anybody tell me if the plans

 are correct and safe or not?  Should I follow the plans exactly, even if

 Zenith doesn't, or should I modify? Any help/advice from the list would be

 greatly appreciated.

 Larry Bohannon

 Winder, Georgia

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_________________
--
Bryan Martin
N61BM, CH 601 XL, Stratus Subaru.
do not archive.

ruruny(at)aol.com
Guest

Posted: Sat Feb 25, 2006 8:16 pm Post subject: Aux fuel pump in 701.Aux fuel pump in 701.

I am using the 701 stock fuel system also, except I have 10 gal aux tanks in each wing

outboard of the standard tanks. I'm running the rubber fuel hose per plans. Actually

the plans are very vague on much of the installation of this stock system. One of the problems 

I'm facing is locating the (2)stock gascolaters in the proper place  behind the pilots seat.

It seems the plans setup will not work as the fittings/hose will intefere with the flap handle.

Each of these have a drain which limits you on installation options. The aux tanks both meet

at one of these gascolaters,and the main tanks meet at the the other. Rubber fuel line exits 

the gascolaters and go up to a selector on the floor,just in front of the seat under my left leg.

It will be labeled inboard, outboard, off. 1 hose exits the selector(same size hose) and travels along

the left side fuselage to the right side of the firewall where I have installed an ACS gascolater.

If I'm on the main tanks and they drain unevenly in flight, I guess I could select the aux tanks for 

awhile so the mains could balance out. One question that I have is which tanks should I use first , the inboard or outboard thanks? Would it be wiser to drain the outboard tanks down first? Also, what 

about eliminating the 2 gascolaters behind the seat and use a TEE to connect them together, then

continue on to the selector. This would help in fitting everything in behind the seat without 

inteference and still leave drains in each wing and the ACS gascolater? My only other option is using 

aluminum fuel line and AN fittings, which I have no experience or idea or tools or how to do or get started.This would be a great Homebuilthelp video topic.I'm at a point with this project where there are more questions than answers with fuel and electrical. I'm tackling the electrical slowly in the cold garage this winter, but the fuel system is causing overload,so I've been avoiding the topic and work on

it. If anyone has pics of their install behind the 701 seat it would be much appreciated. 

And thanks for all the help, I like when the discussion of 701 fuel system options gets going. I feel I

know quite alot about the 601 system from the many discussions of it on the list, thanks for looking at

the 701 also and helping out.

Brian 

Long Island

N701BU   912

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steveadams

Joined: 10 Jan 2006
Posts: 191

Posted: Wed Mar 01, 2006 1:56 pm Post subject: Re: Aux fuel pump in 701.Aux fuel pump in 701.

Regarding the rubber fuel lines. They are used in the 601XL factory built LSA as well as the certified Alarus. I think they are safe, but have a 5 year life, so you will have to change them every 5 years.

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Larry Martin

Joined: 10 Jan 2006
Posts: 31
Location: Cabot, Arkansas

Posted: Wed Mar 01, 2006 8:02 pm Post subject: Aux fuel pump in 701.Aux fuel pump in 701.

If you use good fuel infection lines, the life is a lot more than five 

years.   I've seen regular fuel lines in 30 year old cars that were still in 

tack and they were subjected to a lot more abuse than they would ever have 

in an airplane.  My2centsWorth.

Larry, N1345L, www.skyhawg.com



PS, do not use poly lines, you will be sorry.

---

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_________________
701 with a Harley, www.skyhawg.com

steveadams

Joined: 10 Jan 2006
Posts: 191

Posted: Fri Mar 03, 2006 4:21 am Post subject: Re: Aux fuel pump in 701.Aux fuel pump in 701.

---

 	  Quote: 	
		  If you use good fuel infection lines, the life is a lot more than five 

years. I've seen regular fuel lines in 30 year old cars that were still in 

tack and they were subjected to a lot more abuse than they would ever have 

in an airplane. My2centsWorth. 

Larry, N1345L, www.skyhawg.com 



PS, do not use poly lines, you will be sorry. 

---



	




That is true. However, I was talking about the type of rubber hoses that come in the fuel system kit.

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Larry Martin

Joined: 10 Jan 2006
Posts: 31
Location: Cabot, Arkansas

Posted: Fri Mar 03, 2006 5:23 pm Post subject: Aux fuel pump in 701.Aux fuel pump in 701.

I think it is just regular low pressure fuel line, which is fine and will 

last a long time.  All I am saying is that Fuel Injection line is much 

better, higher quality and higher pressure, but higher price.  This type of 

fuel line, especially since it will not be exposed to the elements will last 

longer than either you or I will be flying.  So as long as it doesn't get 

cut, you don't need to ever change it out.  On the other hand poly line 

doesn't handle radiuses well, cuts easy, also gets hard and brittle with 

age.  The only down side I know of with "rubber" fuel line is that it weighs 

a little more, but the trade off in safety is well worth it.

Larry, N1345L, www.skyhawg.com

---

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_________________
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