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]

28152816

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

[1600vw]

If you think this way, why do a preflight, it should be ok......

[steveinindy]

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.

Even the "established" designs seem to have an unacceptably high rate of "engine out" incidents during the flight test phase. Not nitpicking but is it really that much trouble to build a wooden ramp and get the plane up on it using either a bunch of your buddies or a winch? I don't think it is. Then again, I have been planning for this from day one with regards to my design.

[WLIU]

There is a BIG difference between what in the engineering world we call "design verification" and what we call "manufacturing test".

What the last few posts are talking about falls under the heading of manufacturing test or final acceptance test and is completely valid to do on a new to you aircraft.

Design verification is the analysis and test that a perfectly constructed example functions as expected. So for a clean sheet design, you can use substantially equivalent existing aircraft to determine how much design verification you need to do.

I will suggest that for a post build quality control activity, before you put any fuel in the system, you should blow out the lines with shop air. Much less messy and will actually have a greater cleaning effect than simple fuel flow. But be careful as you can damage stuff with excess pressure. If you are bolting stuff together and waiting until just before your first flight to see what works, I suggest thinking up some more quality control checks along the way. Much less hassle to find problems early.

As for the accident rate of existing designs, I will suggest that actual mechanical problems are rare. Most unforunately originate in the pilot seat. Now we can have a separate discussion about whether airplane controls and systems are "user friendly" and provide too many opportunities for pilot error. But I have not seen a report of an actual fuel system failure, i.e., component failure, causing an accident in many many years.

Best of luck,

Wes
N78PS

[nrpetersen]

A couple of items I got into with the rebuild of my '41 Piper J4A-

The 85 hp engine came with a Bendix-Stromberg carb, but according to the engine Type Certificate, that carb requires about a 48 inch head of fuel for adequate fuel flow at full power. The Marvel Schebler equivalent only requires about a 15 inch head. Since The Cub was feeding it from a cowl tank, I had to replace the carb with a Marvel Schebler. In other words - read those FAA Type Certficates, including the notes at the end!

Although I didn't have a fuel pump of course, any tiny air leaks in the suction line can quickly compromise the max flow of any fuel pump. Depending on the nature of the suction leak, some leaks could be unidirectional (i. e. air in only) and show only under suction, and not from a pressure test.

[rleffler]

But I have not seen a report of an actual fuel system failure, i.e., component failure, causing an accident in many many years.

Best of luck,

Wes
N78PS

I personally know about two in EAB aircraft. The failures weren't a design issue, but simply an inattention to detail during assembly. In both cases, fittings either came loose or were not properly tighten when installed. Neither resulted in any injuries, but totalled both aircraft.

[WLIU]

So those are assembly errors rather than the failures of mechanical components. Which we see a distressingly large number of in the homebuilt world. The EAA encourages the use of the technical counselor program and we could all benefit from more use of that resource and perhaps we should encourage tech counselors to do more twisting and tugging on things in the airplane projects that they look at.

In the certificated aircraft world there is a non-zero number of accidents caused by maintenance errors made by FAA certificated maintenance folks. This points out that "pilot error" covers more people than just the guy who drives the airplane.

All of which adds up to our looking in the mirror when we think that there is something amiss with the airplane.

Fly safe,

Wes
N78PS

[rleffler]

Wes,

You raise an interesting point. Who's responsibility is it to validate that all nuts, fittings, etc are properly assembled and torqued to the corrct value?

With EAB, it's the builder, who sometimes can't see the forest because all the trees are in his way.

I've seen Tech Conselors test something they think looks amiss, but I've never seen one due a comprehensive review.

Some DARs do a great job, but it isn't really required. But not all DARs are safety fanatics and don't do that extra mile.

Certainly we know that FSDO inspections are all over the map and most don't even touch a wrench.

I've been thinking about this a lot recently, since I have my airworthiness inspection coming soon.

I've already invited other builders (several are Tech Counselors) and offered them a bribe for each and every issue that they bring to my attention. I may be buying quite a few lunches and some adult beverages, but in the end I hope that they will find and identify all issues that for whatever reason, I may have overlooked. We all make mistakes, we just need to come up with a consistent methodology to find and fixed them before that first flight.

[WLIU]

That is actually a pretty good approach. If your friends are like mine, they will welcome the challenge to earn the more free adult beverages. And their motivation works to your advantage.

I firmly believe that if is in each of our best interests to offer our friends that sort of challenge as I would rather be embarrassed by someone I know before I go aviate rather than suffer my embarassment in front of the EMT who pulls me from the wreck.

I have been in aviation long enough to earn an A&P. But as an engineer one reason that I have not gone down that road is that though I can do more and better math than my certificated mechanic friends, I know that they look at airplanes for problems every day and they have a valuable perspective on the airworthiness of the parts that come from my computer and through my hands. So I am not so wrapped up in the process that I am above having them check the end result of my work. If I can't explain it, if it does not look like it came from a factory, I should swallow my pride and do better. Plus I make a point of paying for their professional time in addition to socially sharing a beer which creates mutual respect, helps keep them in business so I can keep pestering them, and creates a "we're all in this together" social bond. The latter is particularly important when the FAA schedules a visit to look at something that I designed, drafted, documented. built, and put onto my aircraft.

Using your friends as more hands and eyes to check your work is very constructive. We should all do more of this.

Fly safe,

Wes
N78PS