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Engine Speed (RPM) Overshoot on 50% Throttle

  • dany_amin
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10 months 2 weeks ago - 10 months 2 weeks ago #18088 by dany_amin
The engine is 914F working on a Long EZ inspired homebuilt aircraft. it has shown normal behavior while testing and taxi's but during flight, it just maintained its Revolution per minute (RPM)/Speed to 5400 at 50 % Throttle. On reduction in throttle setting, it lowered RPM's for a while and then again maintained the same value around 5400.
Even on reducing the throttle setting to 10% RPMs were around 4900.
Everything else including Airspeed, Rate of Descent is normal for the flight part. Even CHTs, EGTs and all other are normal and within limits

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Last edit: 10 months 2 weeks ago by dany_amin.

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10 months 2 weeks ago #18103 by admin
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10 months 2 weeks ago #18104 by Wang Shu
Replied by Wang Shu on topic Engine Speed (RPM) Overshoot on 50% Throttle
I think cabal for servo motor stuck /Hard /worn out during airborne operation , as the cable operator Turbo charger with increased in RpM, closing the waste gate.
irre-respectively operation may interpt the TCU command.
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10 months 2 weeks ago #18125 by dany_amin
Replied by dany_amin on topic Engine Speed (RPM) Overshoot on 50% Throttle
Thank you for your reply. it is calibrated and had flights before.

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10 months 2 weeks ago #18126 by dany_amin
Replied by dany_amin on topic Engine Speed (RPM) Overshoot on 50% Throttle

RotaxOwner Admin wrote: Which TCU do you have? Is the throttle calibrated?
( see www.rotax-owner.com/videos-topmenu/elearning-videos/481 or www.rotax-owner.com/videos-topmenu/elearning-videos/478 )


Thank you for your reply. yes throttle is calibrated and had numerous flights in past.

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10 months 2 weeks ago #18127 by dany_amin
Replied by dany_amin on topic Engine Speed (RPM) Overshoot on 50% Throttle

Wang Shu wrote: I think cabal for servo motor stuck /Hard /worn out during airborne operation , as the cable operator Turbo charger with increased in RpM, closing the waste gate.
irre-respectively operation may interpt the TCU command.


That is the first thing I checked on my landing. perfectly okay. there is no wear and tear of the cable.
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10 months 2 weeks ago #18132 by Bill Hertzel
Replied by Bill Hertzel on topic Engine Speed (RPM) Overshoot on 50% Throttle
What happens with the Manifold Pressure as the RPMs change without command?

Just to cover all bases...
Does this plane have a variable pitch prop?
Does the gearbox have the clutch option installed?

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2 months 3 days ago #20509 by Wang Shu
Replied by Wang Shu on topic Engine Speed (RPM) Overshoot on 50% Throttle
what type of maintenance due after over shooting of RPM 6400-6500 IF OBSERVED.

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2 months 2 days ago #20511 by Wang Shu
Replied by Wang Shu on topic Engine Speed (RPM) Overshoot on 50% Throttle
6200-6500 Rpm overshoot for 63 second, where as 14 second only over shoot at 6500.
Heavy maintenance book suggestest for valve guide Checking, crank shaft out of round verification etc.
All system inspection, Detailed Engine afftected inspection.
05-50-00 page 10
what is expert suggestion please

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2 months 2 days ago #20513 by kenryan
Replied by kenryan on topic Engine Speed (RPM) Overshoot on 50% Throttle
Just took my Rotax training. Instructor said in case of overspeed pushrods must be inspected.

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2 months 2 days ago #20519 by Bill Hertzel
Replied by Bill Hertzel on topic Engine Speed (RPM) Overshoot on 50% Throttle

Wang Shu wrote: 6200-6500 Rpm overshoot for 63 second, where as 14 second only over shoot at 6500.
Heavy maintenance book suggestest for valve guide Checking, crank shaft out of round verification etc.
All system inspection, Detailed Engine afftected inspection.
05-50-00 page 10
what is expert suggestion please


As you are already aware, the expert suggestion IS the Line Maintenance Manual Section 05-50-00 Page 10.

Over 6500 for ANY length of time...
Complete Internal Engine inspection and Overhaul.
Replace Crankshaft.
Inspect/Replace Pushrods, Valve/Piston Collision. Compression Check, etc.

Three options.
1. Replace Engine.
2. Overhaul Engine.
3. Make sure your life insurance is current and pretend it didn't happen and fly on. :ohmy:

You know you need to do Option #1 or #2.
You are looking for somone to tell you Option #3 is OK! It isn't!
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2 months 2 days ago #20520 by Wang Shu
Replied by Wang Shu on topic Engine Speed (RPM) Overshoot on 50% Throttle
Yes of couse, but i start the Engine at Ground level , its  found....100%.ok. IT smoothly touched 5800. then ?
whats NEXT SOLUTION......?

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2 months 2 days ago #20521 by Bill Hertzel
Replied by Bill Hertzel on topic Engine Speed (RPM) Overshoot on 50% Throttle

Wang Shu wrote: Yes of couse, but i start the Engine at Ground level , its  found....100%.ok. It smoothly touched 5800.

Then ? what's NEXT SOLUTION......?


Then, I guess you have chosen Option #3.
I wish you well.
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1 month 3 weeks ago #20599 by Wang Shu
Replied by Wang Shu on topic Engine Speed (RPM) Overshoot on 50% Throttle
please help me in finding problem if any in propeller that was MT.brand, composite type, 03 blade. Any Repair required?

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