engine driven fuel pump flow checks

[simpleflying]

The LAA/IC-FF form for carrying out fuel flow checks for first permit to test indicates that both engine driven and electric pumps must be checked. Checking an engine driven pump with the engine at full power seems a hazardous occupation! I seem to remember hearing somewhere that this has been amended on this web site but cannot find any trace. Anyone know anything about this?

[mike newall]

The electronic version of the form explains it.

On higher power engines, it is sufficient to check the output of the electric pump without endangering your life with props and petrol

If you have a low power gravity fed system, it may be prudent to check the pump, but with RV's etc - No !

[G-AWMN]

I seem also to have read that in some cases this check can be waved but my inspector has insisted that I do a check on my plane prior to flying after a major rebuild as if the pump is faulty we might only find out at 200 feet on the first take off. I completed the test today.

My engine is a VW with an engine driven pump. My inspector agreed that a full throttle run was dangerous and suggested that we do the test at 1500 rpm.

The set up was fitting a simple T piece into the fuel pipe between the pump and carb. To the T another tube was fitted that routed upwards approx. 12" and then backwards and down into a measuring jug. The jug was strapped to a main wheel to stop it blowing away. (Luton Minor) This tube was clamped closed with a small G clamp. The 12" rise or head gives sufficient pressure to keep the engine running. The engine was started and set at 1500 rpm and standing in a position just in front of the main wheel but behind the firewall I was able to reach foward to the G clamp and open this clamp to start drawing fuel. In this position I was clear of the prop even at full reach so relatively safe. A helper had a stop watch and called when 2lt had been collected. This helper avoided me having to move from my almost safe position. The engine was then stopped and the extra pipework removed.

In my case at 1500 rpm it took 3 mins and 6 seconds to draw 2lt of fuel at 1500rpm or 38.7lt above required to keep engine running. Flat out a VW should use about 18lt an hour so I do not think I have a problem.

Only Issue I have is when I send in the paperwork will the LAA be happy with the 1500 rpm test!

Stuart Penfold

[simpleflying]

thanks Mike and Stuart. Mine is an RV6 so a bit of a beast so glad not to do it!

[rans6andrew]

funny train of thought!

if you take the pipe from the T piece upwards for 12 inches that may well create a "head" of pressure but the moment you feed it back down the head will be reduced. By the time it gets down to the level of your undercarriage leg the pipe will be sucking (syphoning) from the T piece and creating a negative head. Luckily the restriction caused by the clamp will cause a backpressure. You really ought to have a fuel pressure gauge, at the same height as the carb fuel inlet pipe, to ensure that the minimum pressure needed by the carb is maintained while the measured drain off is being taken.

Rans6....

[mikehallam]

It might be nonsense, but if e.g the pump is adequate at mid rev's, you can't be sure it/the whole fuel feed system won't cavitate or perhaps not function at double the capacity, or even meet the 1500 rpm output when running at t/off & climb rev's !!

mike.

BTW. The poor old 'plane every single take off is at WOT and at first static, as that doesn't bother the P1, I think that one ought to consider test P1 sitting in a/c, stick back, brakes full on and chocked.
[Perhaps if the plane might pull onto the nose a scew in stake and rope to the tail skid too ?]
Jug taped to something firm and give it the same rev's that you want it to work on - and provide plenty of fuel.

[paul330]

I had recently been checking this out and as I understood the requirements, only an electric pump check is required on bigger fuel injected engines. I believe you are more checking that the pipe work, filters etc are not blocked with insects/dead rats rather than the efficiency of the pumps.

[Rob Swain]

I think that one ought to consider test P1 sitting in a/c, stick back, brakes full on and chocked.

Last time I tried something like this I tied the tailwheel to the hangar with some stout rope!