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-   -   Engine quit on stall pratice (https://vansairforce.net/community/showthread.php?t=133887)

sblack 01-25-2016 08:53 AM

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.

Guy Prevost 01-25-2016 10:24 AM

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

TS Flightlines 01-25-2016 10:29 AM

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

Guilhermepilot 01-25-2016 10:58 AM

Alex

That's what I am pressuming as well

Guilhermepilot 01-25-2016 11:00 AM

Tom

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

beav 01-25-2016 11:18 AM

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.

BillL 01-25-2016 06:10 PM

Quote:

Originally Posted by sblack (Post 1048468)
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.

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?

sblack 01-26-2016 07:30 AM

Quote:

Originally Posted by BillL (Post 1048584)
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?

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.

bobmarkert 01-26-2016 08:58 AM

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


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