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What constitutes an engine overspeed

Allan / Cummins Spinners

Allan / Cummins Spinners

Active Member
Hi Guys,

I just wanted to ask what RPM beyond Redline (which is 2700 for me) constitutes an overspeed condition.

The reason I ask is that I see may people here on the forums talking about having props pitched for best cruise at a specific RPM and being able to achieve xxx Knots at say 2740 RPM.

So my question is how far beyond the RPM redline is considered OK and still safe for the engine?

Cheers
 
Allan / Cummins Spinners said:
Hi Guys,

I just wanted to ask what RPM beyond Redline (which is 2700 for me) constitutes an overspeed condition.

The reason I ask is that I see may people here on the forums talking about having props pitched for best cruise at a specific RPM and being able to achieve xxx Knots at say 2740 RPM.

So my question is how far beyond the RPM redline is considered OK and still safe for the engine?

Cheers
Click to expand...

Here's Lycoming's take on the subject:

http://www.lycoming.com/Portals/0/t...8-2012)/Engine Inspection after Overspeed.pdf
 
Wow based on the Lycoming recommendations there must be a lot of people carrying out lots of inspections and making lots of log book entries :D

Cheers
 
Have been told by long time experienced folks that RPMs are not the problem. Manifold pressure is the problem. Will be interesting to hear from the racers and engine guys here.
 
It's not so much an engine problem, more so a propeller problem. I test flew an RV-10 that went over 3,000 RPM and Hartzell said that it needed teardown and inspection if it exceeded 10% or 2970, since the CS prop's redline is 2700.

FWIW, the Formula 1 guys run over 4,000 RPM's with their conti's during a race. I used to ferry my Cassutt at 3100 RPM.



Best,
 
The acro guys see higher RPMs consistently. With the newer light weight composite and wood props, not as big a deal.
I've got a 3 blade Performance Propeller on my Skybolt. I see 3000 RPM when I'm doing acro. (when I'm looking!)
 
Overspeed

The hartzell constant speed two blade as originally used on the Pitts S1T is not tolerant of overspeed.

The Sensenich fixed pitch metal used on the Pitts S1S is very tolerant of overspeed. Cherokee 180 prop, I don't recall the number. I ran my Pitts 300 hours at up to 3500 r/m and 700 additional hours with increased pitch at 3300 r/m. This was for acro which was the majority of the time. Cross country at 26-2700 r/m.
The prop used on the Pitts cannot be repitched into a pitch that would be useable on RV's. The special Sensenich metal prop for the RV's has its own limitations.
Manifold pressure has nothing to do with overspeed. I ran full throttle at near sea level altitudes much of the time in the Pitts.
In 20 plus years of involvement in IAC competition I never heard a Pitts that was not operating in the 33-3500 r/m range. You can tell by the sound. Never heard of an engine failure on a Pitts resulting from overspeed. TBO was generally considered 1200 hours although some went considerably more.
 
As i seem to recall, Lycoming engines don't like overspeeds due to valve train damage, particularly cam issues. Having overhauled low time engines that have been oversped, can say cams are sometimes found damaged.

Btw, prop stresses aren't just due to centrifugal loads, they can be related to blade resonances that cause large spikes in vibratory loads. Those loads can reduce blade and hub fatigue life to very low times that aren't addressed by the manufacturer.
 
Overspeed Too

Jim,
I'm with you on this. I have owned three Pitts S1's, S1C, factory S1S, and a pumped up S1S for about 15 years (contests) and 730 hrs. A flight was maybe, 20 minutes, a few longer if cross country. The engine was at 3000RPM or above diving into the box, never below. Always noted how smooth it ran at 3000 and a little laboring at 3200, but 3500 it was working. At OSH talked with Lycoming over the years and when asked " don't worry until you get to 4000 RPM" was the answer, depending on whether there was an attorney behind them. And yes, 1200hrs then overhaul was probably the limit on a O360, solid crank, Sensenich type doing acro. I did mine at 1000hrs.. Yes, a parachute was involved at all times, and NO, would probably not ride it down unless over an airport. Point it away from people and get out. Never did, and really can't think of too many people it has happened to. Lyc's are stronger than you think after the way I treated them, and not hard acro either , but simple stuff(For a Pitts). Yes, LYC has it's rules. Obey them for long life and health. Just got 2460 hrs. out of a O360A4M. Tore it down, 1 part out of spec. It could have gone another 200 hrs easy. There is a guy on my field who put 5050hrs on a O320!!!!! (he flys almost every day though)

BTW...When you hear a Pitts (O360, w/Sensenich) and its very loud, the prop tips are supersonic and just above 2920RPM. If its noisy the whole flight, then...

Just some data points!!
 
Overspeed

I contacted a friend who was involved in aerobatic competition a couple years before I started. He never heard of a four cylinder Lycoming that failed because of overspeeding for acro. In 1000 hours the only problems I had with my 0 360A4A were accessory problems. A minor problem with the PS5 carb and a mag failure.
The cam problems occur regardless of how the engine is treated. A bit of rust on a lifter and it starts wearing the cam quite rapidly.
The cross country racers that are getting good results are running the four cylinder Lycomings in the 3000 r/m range.
Another bit of information about metal props. In the late 60's early 70's Sensenich built custom metal props for the 0 200 powered Formula One racers. These props had three vibration ranges. The two lower r/m ranges were transitioned on every acceleration and deceleration. The higher range was right where the faster airplanes flew for a race. After several prop failures Sensenich stopped making the racing props.
A few years later Sensenich was making special metal props for the Wittman Tailwind, for both the four cylinder Continental and the four cylinder Lycoming. I believe the Lycoming props were only for the 0 290's. These props were discontinued also.
The RV metal props as far as I know are the first special metal props Sensenich has made since that time.
 
overspeed

hgerhardt said:
Something to read which may or may not be relevant: http://aviation-safety.net/wikibase/wiki.php?id=40857 The previous holder of my N-number, this Pitts crashed due to a propeller blade separating mid-span due to fatigue allegedly caused by prop overspeed.

Heinrich
Click to expand...

I am quite familiar with the accident airplane. All I can say is the airplane was a LONG ways from meeting my personal standards. The broken propeller blade failure started with a leading edge defect. The crankshaft flange was outside the specified tolerance. This was an angle valve engine with a metal fixed pitch prop of unknown history.
This is not applicable to the majority of four cylinder powered Pitts S1 aircraft which typically run parallel valve engines.
Read the report, there is a lot more there than in the abbreviated report and a lot that never made it to the NTSB report.
The vast majority of failures of metal props originate from damaged leading edges.
 
Every time this issue comes up I feel obligated to state that I had a complete engine failure running at 2900 rpm. This was straight and level, not while doing aerobatics.
There will always be differences in results when running past the manufacturers recommendations. Most have no issues, I did.
 
Tom Martin please elaborate

More details please on engine failure at 2900 rpm s. How was failure related to overspeed?
 
Overspeed

Some of the four cylinder Lycoming helicopter engines are rated for 3200 r/m.
Thousands of hours of Pits S1 and similar aircraft operating at r/m up to 3500 with no problem.
A failure at 2900 r/m is not related to overspeed. Either a flawed part that would have failed any way below 2700 or an error in the engine build.
 
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