Fuel System Testing

[Dave Prizio]

Thanks to those of you who attended our webinar last night on fuel system testing. One of the questions posed was if I could make the formulas for determining required fuel flow available to everyone. I would like to do that here.

The formulas from last night are:

Gravity systems: Horsepower x BSFC x 1.5 x .36 = Ounces/minute

Pressure systems: Horsepower x BSFC x 1.25 x .36 = Ounces/minute

BSFC is brake specific fuel consumption in pounds per horsepower-hour

For those of you who did not listen in, these formulas calculate the amount of fuel that needs to flow through your fuel system when you perform your tests to be sure your system is delivering adequate flow prior to first flight. For more information a recording of the webinar is available online at http://bcove.me/eqeh02yu

[1600vw]

Its missed the webinar. I moved and my e-mail changed, I have lost contact with a lot of stuff like the webinars. Anyway I thought it was funny you posted this today as I was working on my fuel system today.

My tank has to go into the machine shop to have this new finger strainer installed. I was robbed and my tools where stolen so now its tough to work on anything. I miss my Taps and dies.


This is what I had for a fuel finger strainer. The one on the left is the old one. This is a very bad design in a fuel strainer. The new one on the right is the right way to do this.

Fly Smart

[steveinindy]

For those of you who did not listen in, these formulas calculate the amount of fuel that needs to flow through your fuel system when you perform your tests to be sure your system is delivering adequate flow prior to first flight.

Is anyone else doing "tilt tests" on their builds to make sure they have sufficient fuel flow in a climb attitude before trying to actually take off? I brought this up to a few folks whom I know from around Indy locally during lunch and received looks and comments that gave me the impression that they felt it was overkill to do this.

[Cobrajock24]

When I get to that point in my build on my Kitfox IV, I will CERTAINLY be doing so, in both the climb and descent attitudes to be DARN sure mine works properly. At a bare minimum this is simply one less thing to REALLY wonder about during my first flight climbout!

[1600vw]

Is anyone else doing "tilt tests" on their builds to make sure they have sufficient fuel flow in a climb attitude before trying to actually take off? I brought this up to a few folks whom I know from around Indy locally during lunch and received looks and comments that gave me the impression that they felt it was overkill to do this.

I mentioned this to a couple people in my hangar and I received the same looks and comments as others. Everyone believes this is not needed, over kill is what they say.

Myself I never thought about nose down. I just reinstalled my tank and will do this test. Since I have a 40hp engine I will add my 20lbs of fuel and go from there. My tank shows empty with 20lbs of fuel added to it.

I will add one gallon at a time and do each of these test. I put my plane on scales and take weight reading as each gallon is added, I then do a W/B with each gallon added to make sure I stay with in the CG from empty to full. I post these numbers in my plane. This makes my A&P happy, so I do it. He asked me to do this and I smiled and said sure not a problem.

I am really excited to redo these test and compare them to last years tests. After replacing not only that finger strainer but removing a couple 90 degree fittings I bet I see a big improvement in not only flow but pressure, since flow = pressure.

I used the Push-Loc system, no more clamps and no special tools needed to assemble. A little expensive but well worth it and its all "AN" fittings.

Fly Smart

[1600vw]

Look at those pics I posted of those strainers.

Look at the one on the left, that is not dirt you see plugging that screen but soilder, or whatever the builder used to afix that screen to that fitting.

You see very little openings in that screen. I tried to get pics of both sides. That strainer should have never been used, if you are using something like this..STOP. The one on the right is what you are looking for. Wicks and Aircraft Spruce sell this same strainer you see in the pic. They are under 10 bucks.

I would put this Finder Strainer on my list of things that need to be serviced or cleaned every year or so many hours. Maybe 100 hrs. Since we fly this type of planes maybe at most 100hrs a year do this yearly at the end of the year or on your condition inspection.

Fly Smart

[WLIU]

I will suggest that if you are building an established design, fuel flow testing is likely overkill. If currently flying examples of an aircraft have enough fuel flow, yours should be OK.

If you have a clean sheet design, one thing you can look at is existing flying aircraft with similar fuel systems. If you are building something that looks like a Rutan canard design, look at the fuel system in those airplanes and check your design for similarity. If your system has the same relationship between the tanks and the engine in height, uses the same types of pumps, etc., you can expect the same operating performance and reasonably waive a flow test. Look at the facts and do what a reasoned analysis says makes sense.

Best of luck,

Wes

[Dave Prizio]

The tests do seem like overkill and are without a doubt a lot of work. However, fuel system failures are a significant cause of fatal accidents in new experimental amateur-built airplanes,accounting for almost 1/3 of all in-flight engine failuresin experimental amateur-built aircraft.Sticking with a well-proven design for your fuel system is a very good idea. Most creative fuel system designs that I have seen are less safe than the simple, proven designs used by most kit makers.

The Homebuilt Aircraft Council is asking kit manufacturers to do this testing and make it available to builders, so they can eliminate the tilt tests if they stick to the kit manufacturer's fuel system design. However, if you have designed the plane yourself or have designed your own fuel system, all of these tests need to be done to be sure your fuel system will work in all normal flight conditions. And even if the manufacturer has completed the most extensive testing regimen, you still need to do the basic level fuel flow test on your own plane and should verify fuel flow in all attitudes during your Phase I flight testing.

[rleffler]

I will suggest that if you are building an established design, fuel flow testing is likely overkill. If currently flying examples of an aircraft have enough fuel flow, yours should be OK.

I don't agree. If you have an established design, I would agree that you don't need to validate that the design can deliver the appropriate fuel flow. However, I would still conduct at least the basic flow tests to ensure that there is no construction debris in the line. I know of one case that was caught during the initial fuel flow test (loose proseal in a tank) and another case caught during Phase I (debris in the fuel distribution spider) that caused a problem with a single cylinder. We don't want to discover a blockage inflight.

[1600vw]

I will suggest that if you are building an established design, fuel flow testing is likely overkill. If currently flying examples of an aircraft have enough fuel flow, yours should be OK.

Wes

You "should" be ok....scary. Why not check and be sure your ok.

How about the man buying the used airplane. He is thinking the same if he just flies it saying. It "should" be ok..... are you going to put your life on "should be ok"

Fly Smart