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  #1  
Old 06-19-2018, 09:12 AM
Marabou Marabou is offline
 
Join Date: Oct 2012
Location: Moscow
Posts: 28
Default Spin. Engine quits. Why?

I tried long spin in my 7A recently. After 3 or 4 turns at idle RPM slowly drops and approximately at seventh turn engine quits. My impression that spin at idle and lost engine are different. At least delay with recovery is much longer when prop stopped. I tried 4 times with the same result. I wonder why engine quits in a first place. I keep Mogas in one tank and Avgas in other. Both filled less than half for aerobatics. First I thought Mogas is to blame. I switched to Avgas with exactly same outcome. Next idea was that centrifugal force pushes gas out of intake. Once right at the moment when the engine was just about to stop I pushed throttle a little bit forward. I did not expect any reaction but it worked like in straight and level flight. I finished my 10 turns with engine running.
Next I tried to enter spin at 1000 RPM rather than at idle. I liked it. Engine kept 1000 RPM thru entire 10 turns. Recovery is faster and more predictable that at idle. So there are two important questions: why engine quits and is there any danger to enter spin at RPM a bit higher that idle? Engine is injected 360M1B.
Thanks in advance for help.
Sorry for poor English. I am from third world. We don?t waist too much money for stupid and useless things like education))
Here is a link to stopped engine: https://www.youtube.com/watch?v=FIOWtnijlSA
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  #2  
Old 06-19-2018, 09:49 AM
jdmunzell jdmunzell is offline
 
Join Date: Jun 2005
Location: Hamilton, VA
Posts: 419
Default Zdravstvuyte Ruslan!

Your problem is obviously a fuel starvation issue and my first thought as I was reading your post, was that you had a carbureted engine. You mention towards the end of the post that the engine is fuel injected though.

One thought might be your fuel pickup tube or flop tube. Vans put out several service bulletins in the past concerning these coming loose inside the fuel tank. You might look into weather those SBs were complied with, not knowing of course how old your airplane is or if you built it or not.

Then, possibly a problem somewhere in your fuel injection system, where you're not able to maintain adequate fuel pressure through the injectors at very low rpm.
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  #3  
Old 06-19-2018, 09:54 AM
oaklandaviator oaklandaviator is offline
 
Join Date: Dec 2014
Location: Somerville, Tn and Little Rock, Ar
Posts: 143
Default Low idle

Try raising the idle speed a bit. Mine will do that if it is set on the low side.
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  #4  
Old 06-19-2018, 10:00 AM
Kyle Boatright Kyle Boatright is offline
 
Join Date: Aug 2005
Location: Atlanta, GA
Posts: 4,677
Default

A nose down attitude and the centrifugal (yeah, I know) force from the spin may be moving fuel away from the pickups. The lower the fuel level, the bigger impact these factors would have.
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  #5  
Old 06-19-2018, 12:02 PM
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dlloyd3 dlloyd3 is offline
 
Join Date: Jun 2005
Location: Locust, NC
Posts: 443
Default

Anybody else doing 7-10 turns? (!) Video pretty dramatic even without the engine stopping.
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  #6  
Old 06-19-2018, 12:06 PM
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N941WR N941WR is offline
 
Join Date: Jan 2005
Location: SC
Posts: 12,887
Default

By adding power, even 1000 RPM's, you raise the nose slightly. This may be enough to keep from unporting the fuel puckups.

Just a guess.
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  #7  
Old 06-19-2018, 01:54 PM
luddite42 luddite42 is offline
 
Join Date: Mar 2010
Location: USA
Posts: 485
Default

Quote:
Originally Posted by N941WR View Post
By adding power, even 1000 RPM's, you raise the nose slightly. This may be enough to keep from unporting the fuel puckups.

Just a guess.
Nah, adding power only raises the nose when spinning left. Spinning right, it's a nose down effect. In any case, flattening the spin reduces the roll component of the spin and increases the yaw component. The yaw component is what's driving fuel outboard away from the fuel pickups.

And regarding an earlier post, carbs are are not impacted by spins. It's all about the G load for them. Upright spins are always positive G load, so the carb will keep feeding fuel.
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  #8  
Old 06-19-2018, 03:13 PM
BruceW BruceW is offline
 
Join Date: Aug 2005
Location: Elk Grove, CA
Posts: 190
Default

I did the same thing once (ONCE) in a Citabria. (upper wings & gravity feed).
I voted for the centripetal force keeping the fuel mixture going up the Lycoming vertical induction. Added just a bit more RPM on the next one, and worked fine.

BTW, DONT dive down after going dead stick to get the prop turning. Doesnt work, and lose that valuable altitude.
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  #9  
Old 06-19-2018, 03:17 PM
jrs14855 jrs14855 is offline
 
Join Date: Apr 2008
Location: Lake Havasu City AZ
Posts: 2,644
Default Restart

Quote:
Originally Posted by BruceW View Post
I did the same thing once (ONCE) in a Citabria. (upper wings & gravity feed).
I voted for the centripetal force keeping the fuel mixture going up the Lycoming vertical induction. Added just a bit more RPM on the next one, and worked fine.

BTW, DONT dive down after going dead stick to get the prop turning. Doesnt work, and lose that valuable altitude.
Depends on the airplane compression ratio and prop. Cassutt with a wood prop restarts at around warp factor 8.
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  #10  
Old 06-19-2018, 03:47 PM
Marabou Marabou is offline
 
Join Date: Oct 2012
Location: Moscow
Posts: 28
Default Restart

Thanks to all for answers. About restart. It restarts just well at about 110 knots. Of cource if remaining altitude allows.
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