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RPM loss on takeoff roll

W

William

Well Known Member
A little background. I own a RV6A with a carbureted o320 and fixed pitch sensenich metal prop. Everything has 70 hours on it since overhaul. I've noticed on initial takeoff roll my rpm are around 2250 and by 60 knots my rpms drop to 2210. Plane still climbs over 1000 feet/minute. The plane has done this from day one. I've already done a static fuel flow test and get acceptable results. Measuring both at the gaskolator and at the carb inlet. Is this typical for a fixed pitch prop?

Thanks
Bill
 
William said:
A little background. I own a RV6A with a carbureted o320 and fixed pitch sensenich metal prop. Everything has 70 hours on it since overhaul. I've noticed on initial takeoff roll my rpm are around 2250 and by 60 knots my rpms drop to 2210. Plane still climbs over 1000 feet/minute. The plane has done this from day one. I've already done a static fuel flow test and get acceptable results. Measuring both at the gaskolator and at the carb inlet. Is this typical for a fixed pitch prop?

Thanks
Bill
Click to expand...

Just speculating, but if a portion of your prop blade was stalled and cavitating at the beginning of the takeoff roll, then unstalled as speed built, you *might* see this.
 
William said:
I've noticed on initial takeoff roll my rpm are around 2250 and by 60 knots my rpms drop to 2210.
Click to expand...

How are you measuring and on what are you displaying your RPM?
What is the accuracy of the sensor and the display?
 
Prop stall

Mine does that also. I've always assumed that part of the prop is stalled at low airspeed and that the RPM sags as the prop "bites " better further into the takeoff. I have a totally different engine and prop from your though.

-Andy
 
I have the same engine and prop and mine has always done this. When I spoke with Sensenich about it (many years ago) they indicated that they have seen this behavior with some models but seemed surprised that the 70CM7S9 was doing that. They did say that it must be slightly stalled at first and that the RPM drops once the prop unstalls.
 
Thanks everyone for the responses. Prop stall is something I never thought of though it does make sense. The rpm is coming from my Mgl Avionics Odyssey and efis.

Thanks
Bill
 
Sorry man, your engine is no good. Neither is your prop. They are worthless. I can help you dispose of them. Anything for a bro. :p
 
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