Engine quit on stall pratice

Today, I performed some acro, and a stall. After reducing to idle speed and have my speed drained at about 53 kt engine quit, a few seconds later a restared with no issues, so on ground idle is about 700RPM pump on and off does not affect idle. Very weird.

Have you done any high AOA fuel flow testing on the ground. If not, get the aircraft to a nose high attitude, disconnect the fuel line at the fuel servo, and using your electric fuel pump measure your flow rate. You should be getting at least 150% of the takeoff fuel flow. If not, you may have a restriction in your fuel system at a high AOA. Good luck!

Did you have the fuel pump on during your acro and stall series? Carb heat out?

Low idle could make fuel pressure drop if certain engine parts are excessively worn.

Carb heat can make you lose 50-75 rpms.

When I finish my runups, the last thing I do is put the carb heat on, and pull the throttle back abruptly and make sure it continues to idle.

Where was the fuel level? Were you on the low wing (fuel)? If so, did that wing drop after the stall?

Hope you figure it out soon! That's where I'd start.

X

I am not implying a recommendation here, but was the boost pump on? (I am assuming it was not) And, have you checked the idle condition on the ground to see if the mixture is proper?

Thoughts for above - is the mechanical pump dropping pressure (and thus flow) at high suction conditions (pitch angle/AOA)? And if the pressure dropped a little, but not enough to set off your alarm, the idle fuel rate could have dropped and leaned the mixture. In the latter case, a mixture adjustment would help.

Just some thoughts.

I had a similar issue and eventually traced it down to a section of aluminum fuel line that went between my gascolator and the fuel flow meter. Once I insulated the fuel line, the problem went away.

Lightweight props also play a role. Mine idles at 480-500 but I have electronic ignition and associated timing changes, engine runs fine during stalls but quits during hammerheads.

This may seem oversimplified but are you sure you had applied carb heat?
I had a plane years ago that would freeze over incredibly fast without carb heat under the right conditions after idling down in a glide.

Guys, mine is FI and boost pump was on, i will consider all advises to solve the problem, as a matter o fact my sterba prop is very lightweight. many thanks

Guilhermepilot said:

Guys, mine is FI and boost pump was on, i will consider all advises to solve the problem, as a matter o fact my sterba prop is very lightweight. many thanks

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Try it without the boost pump. I personally don't use boost during flight unless I have a loss of fuel pressure.

Otherwise, just remember, when you notice the prop *not* spinning, put the nose down. You must be stalled!

What was outside temperature? If warm, it is probably just fuel boiling in the injector lines (or anywhere downstream of the servo), causing some intermittency in fuel delivery. With the low fuel flow rates for idle, low cooling air rate, combined with a lightweight prop, it is not too surprising it quit.

Just to be clear, it is pitch angle, not AOA, that is a factor in fuel flow. Pitch is related to the earth, so it is AC orientation relative to the gravity vector. AOA is related to the airstream. An aircraft can have a stall AOA at 0 deg pitch. AOA has no direct impact on the fuel system.

I had that happen once during testing, because I forgot to push the mixture forward from its previous very lean position for high altitude cruising and LOP testing.

Guy

Whatever the issue--Guilherme my friend be safe!!!!
Maybe we need to put a Williams FJ44 on your RV so you'll feel more comfortable!



Kidding
Tom

Alex

That's what I am pressuming as well

Tom

Those jet engines aren't funny������like our lycosauros

This happened to me as well during Phase 1 flight testing. The issue turned out to be an overly rich idle mixture. Make sure you're getting the recommended 50rpm rise on shutdown to ensure your idle mixture is set correctly.

sblack said:

Just to be clear, it is pitch angle, not AOA, that is a factor in fuel flow. Pitch is related to the earth, so it is AC orientation relative to the gravity vector. AOA is related to the airstream. An aircraft can have a stall AOA at 0 deg pitch. AOA has no direct impact on the fuel system.

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So what does the fuel see from tank level to mechanical pump when the plane is at 4 G's vertical into a loop? Where is the vector? Wouldn't AOA be more applicable here, or should we just do the vector calculations and get the relative "height" of the fuel column? Is it pitch?

BillL said:

So what does the fuel see from tank level to mechanical pump when the plane is at 4 G's vertical into a loop? Where is the vector? Wouldn't AOA be more applicable here, or should we just do the vector calculations and get the relative "height" of the fuel column? Is it pitch?

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Hmm I might have engaged keyboard before brain there. The true longitudinal angle that the fuel sees is the angle between whatever your pitch reference is, say the top longeron, and the resultant acceleration vector which is the vector sum of the vertical and longitudinal accelerations and gravity, or as we call it in engineering nomenclature Nx, Ny and g. But this is over-complicating it. In a 4g loop it would be the vector sum of the acceleration of the airplane in pitch about the center of the loop (Vsquared/r), the longitudinal acceleration which would probably be -ve on the way up and the gravity vector so it would depend where you were in the loop and yes, angle of attack would figure into that because it is the difference between your pitch datum and the flight path. But this is all academic. When you do your fuel flow test in preparation for first flight you generally use your max climb pitch attitude.

Interestingly, if you look at the fuel angle in the tank on the runway during the takeoff roll, when the airplane is accelerating, and the same angle in the tank on climb at constant speed, they are the same. I've done this simulation for large airplanes.

Engine quit during spin

A few weeks ago I had the same problem during a 6 turn spin. I fly out of KBJC outside Denver so the terrain is very high. I was at 10,000' msl / 4,000' agl. Here is the bottom line for me; I have a light weight prop and high compression engine and I was too rich for the altitude I was at when I did my spins. Here in Denver we lean for a normal takeoff. At 10,000, leaning aggressively fixed my problem. What altitude were you at when you did your stalls? This may or may not be a component of your issue.

Video of prop stopping

https://www.youtube.com/watch?v=W4BH2tp_e2Q

Bob