When do engines fail on takeoff?

[Cyril Gibb]

7 hours ago, Tommy said:

So it's better to reduce RPM than reducing Manifold?

That would be one of the worst things to do.

On takeoff, you want to move the peak cylinder pressure to later in the downstroke to keep cylinder pressures and temperatures low.

The 2 ways we have control to do that are (1) keeping the rpm high to have the burning mixture peak further in the downstroke and (2) running overly rich, which slows the combustion speed to have the same effect.

[Marauder]

Yeah, reduce to 25 square was the accepted wisdom in 1969 when I started flying a Mooney. And I know that many older pilots, including a friend who's a CFII, ATP, long time Mooney owner, still pull back the throttle and then the prop shortly after raising gear. But SOPs change. We also leaned to 25 ROP for cruise, and never, ever let the MP/RPM be over square.  

That was the way I learned as well. After reading that these engines are designed to run at full throttle/RPM to TBO, I started leaving everything forward until I reached altitude.


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[kmyfm20s]

2 hours ago, teejayevans said:

A. If they are not made of glass, then they can handle the pressure. Cylinder pressure is not an issue if it’s correctly timed. See other thread about STC using 10:1 helicopter pistons.
B. As I mentioned I do it to be quieter, most of my takeoffs are at dawn. We have enough problems with community’s wanting to close airports.

I don’t think the prop on your J is long enough to make significant noise reduction with rpm. If you want to hear noisy go listen to some C185 with long props take off.  I think the ones with the I0-520 have a 2900 rpm redline and puts the prop tips at the sound barrier. A rpm reduction on those make a huge difference.

[ArtVandelay]

After reading that these engines are designed to run at full throttle/RPM to TBO, I started leaving everything forward until I reached altitude.

Where did you read that?

[EricJ]

I've had three engine failures and none were related to a power setting change.    Two were at takeoff;   one was water ingestion, which may have gotten picked up due to rotation pitch up and quit just as the gear stowed and the light went out, one was a partial failure with an injector that clogged just as the end of the runway was disappearing under the nose. The other one was during a gradual descent when my fuel servo decided it had had enough after living an apparently rough life.   

I don't know if there are detailed statistics on this stuff anywhere, and they might only be significant for like engines, anyway, so who knows.

[ArtVandelay]

That would be one of the worst things to do.
On takeoff, you want to move the peak cylinder pressure to later in the downstroke to keep cylinder pressures and temperatures low.

Maybe for those with 25° timing, for those with 20° we don’t worry, peak pressure delay is baked in.

[jlunseth]

Well, remember that mixture has essentially the same effect as changing the timing.  It is not the same thing of course, but on the rich side, making the mixture richer slows the flame spread and therefore moves the peak of the pressure curve away from TDC, and also changes the shape of the curve.  The total pressure during the combustion cycle might stay the same, but the curve would be longer and more drawn out, and the peak shorter.  Rich is good on takeoff, unless you are NA and taking off from a higher altitude, and even then rich is good, it is just relative.  Less air, so less fuel is needed to maintain a rich mixture.

I was taught 25 square, but you have to quickly get over that idea with a turbo.

[cliffy]

IIRC, if you look up engine certification requirements our little 4 bangers are certified to TBO at full power rating.

Engine failure at first power reduction is a hold over from the days of radial engines. Not many today have any radial engine experience let alone any knowledge of their operation. It was also said that if it made 100 hrs it would go to TBO (on large radial engines) as many failed in the first 100 hrs. 

[ArtVandelay]

That would be one of the worst things to do.
On takeoff, you want to move the peak cylinder pressure to later in the downstroke to keep cylinder pressures and temperatures low.
The 2 ways we have control to do that are (1) keeping the rpm high to have the burning mixture peak further in the downstroke and (2) running overly rich, which slows the combustion speed to have the same effect.

Seems RPMs changes have little effect unless we’re talking drastic changes, the cylinder pressure goes down at lower RPMs.

[cliffy]

In the above graph I would agree IF you are talking an RPM GOVERNED by throttle position (there by a lower manifold pressure).

With RPM governed by LOAD (propeller control, no reduction on MP) I would disagree. 

The above chart shows no distinction.   We need more data on the chart above.

[Marauder]

Where did you read that?

I read it years ago. Not sure if it was a Busch article or something from Lycoming but I do know it changed my approach to reducing power on climbout. Like Bob, I was taught and did reduce power to 25/2500.


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[ArtVandelay]

In the above graph I would agree IF you are talking an RPM GOVERNED by throttle position (there by a lower manifold pressure).
With RPM governed by LOAD (propeller control, no reduction on MP) I would disagree. 
The above chart shows no distinction.   We need more data on the chart above.

Obviously research of piston aircraft engines is hard to find, this was from a research paper comparing gasoline vs natural gas and was done on a dynamometer. If you image google “engine cylinder pressure analysis rpm gasoline natural gas” it’s the first image to come up.

[Cyril Gibb]

Automobile engines aren’t a good match to the long stroke, slow rpm horizontally opposed aircraft engines with manual control of the mixture.  Peak pressure vs rpm is also affected by the combustion speed (anything richer or leaner than stochiometric will be slower burning.

There’s lots of articles from as far back as the 1930s.  Here’s a reasonably concise overview:

https://www.savvyanalysis.com/articles/controlling-the-combustion-event

On the other hand, I’ve also heard that anytime somebody runs oversquare, a puppy dies.

 

 

[jaylw314]

14 hours ago, JohnB said:

 A CFI told me that takeoff is correct, but more correctly he said engine failures are most likely to occur during on takeoff at the first reduction in power after takeoff. 

I believe this is patently untrue.  IIRC, fuel system failures (empty tank, contamination, bad selector, etc) are more common than any other engine loss of power scenario, and those will become apparent whether you reduce power or not.

I expect ad hoc reasoning is the problem.  After an engine failure, people will retrospectively say, gee, I reduced power right around that time, so it must have been the culprit.  The problem is, the vast majority of takeoffs and landings are done remaining in the pattern, where you were already PLANNING on reducing the power shortly after takeoff anyway.

[jaylw314]

6 hours ago, Hyett6420 said:

i was taught 25/2500 at 500, flaps at 3.... primarily due to noise its only on reading on this forum that i learnt you should keep all wide open till climb out.  I suppose London is like Santa Monica, full of Nimby peeps.

Sound intensity decreases with the square of distance, so getting away from the ground faster gives you better noise abatement than a small increase in RPM!

[cliffy]

1 hour ago, jaylw314 said:

Sound intensity decreases with the square of distance, so getting away from the ground faster gives you better noise abatement than a small increase in RPM!

I agree UNLESS you do take into effect the prop blades breaking the sound barrier. On large engines with large diameter props they do break the sound barrier and a reduction of 50 to 100 RPMs reduces the overall noise level dramatically. 

I live in a "quiet" area and the change from 2700-2900 RPM to lower (when the pilot so chooses) is very noticeable.

When leaving KLGB in the LAX area at night they have a very stringent noise monitoring system. Even in a 182, one can easily break the limit if one does not reduce the RPM before the end of the runway (going west bound, how do I know that?). 

[ArtVandelay]

Sound intensity decreases with the square of distance, so getting away from the ground faster gives you better noise abatement than a small increase in RPM!

Pretty sure they don’t care about average noise levels, peak noise levels will be more at max RPM.

[jetdriven]

Peak noise level is also higher when lower.  Your lower 2650 RPM will make it fly lower at all points downrange of brake release.  Prop slightly quieter but a lower flying, slightly less loud airplane. This airplane is not loud, its not even comparable to a bonanza.

[wrench]

I don't know about any stats or studies on it but my race car engine spontaneously disassembled after I let up on the power in quarter mile run. Also a sign on the door to the flight line at McKinley Aviation in the 80's stated "Most engine failures occur when powering back from takeoff...be ready if it happens" I don't know if the A&P there put that one up or not but it always stuck with me.

[cliffy]

OWT as it pertains to our flat four engines!   

[Bolter]

42 minutes ago, wrench said:

I don't know about any stats or studies on it but my race car engine spontaneously disassembled after I let up on the power in quarter mile run. Also a sign on the door to the flight line at McKinley Aviation in the 80's stated "Most engine failures occur when powering back from takeoff...be ready if it happens" I don't know if the A&P there put that one up or not but it always stuck with me.

I think that situation is different from a power reduction in climb.  Letting up the power at the end of a fast quarter mile would reverse the loading as well, transitioning from power out to engine braking.  Or engine breaking, in your case!  Glad your inadvertent disassembly event did not end your racing career.  

[RobertGary1]

Maybe the better question is if engine failures are more likely to happen after a change in power. Of my engine failures most have happened after a power reduction, although only the servo failure was a strong correlation to the power change. I teach my students to not touch power below TPA unless otherwise specified by the manufactures (i.e. the larger Cessnas, etc) simply because if the engine is making power don't threaten it for no reason. 

Also, the airline guys will tell you that distance from the ground is life and reducing power is contrary to that. They refer to this as stage 1 climb, get distance from the ground so if something does go wrong you have altitude to work problems out.

-Robert

[Piloto]

Mine failed on take off at KFLL, luckily I  had enough runway left to put it down. The cause was water in the tank even though I drained the tanks prior to flight. The problem was due to drain plate drain holes plugged at tank reseal. This cause the drain valve to drain from the top of the valve instead from the bottom drain hole, leaving water below un-drained. Even though this water level will not impair the engine from starting or taxing as the plane accelerates and rotates this water shift toward the back where the fuel pick up is located causing the engine to stall. I replaced the F391-53S drain valve with the F391-72 drain valve, same one used in the long range tanks. The F391-72 has the drain holes just above the thread drain plate directly exposed to the fuel in the tank so they are not impaired by sealant or debris.

José

[RobertGary1]

2 minutes ago, Piloto said:

Mine failed on take off at KFLL, luckily I  had enough runway left to put it down. The cause was water in the tank even though I drained the tanks prior to flight. The problem was due to drain plate drain holes plugged at tank reseal. This cause the drain valve to drain from the top of the valve instead from the bottom drain hole, leaving water below un-drained. Even though this water level will not impair the engine from starting or taxing as the plane accelerates and rotates this water shift toward the back where the fuel pick up is located causing the engine to stall. I replaced the F391-53S drain valve with the F391-72 drain valve, same one used in the long range tanks. The F391-72 has the drain holes just above the thread drain plate directly exposed to the fuel in the tank so they are not impaired by sealant or debris.

José

Didn't Mooney guru Don Maxwell just post a caution to not use F391-72 because the holes are too high? The -53S should have a slot for the fuel to flow at the base. I'd expect you'd notice if you drained the tank and nothing came out because it was plugged with debris.

-Robert

Edited April 10, 2018 by RobertGary1

[Jerry 5TJ]

So if failure occurs after the first power reduction, how about taking off at 90% and INCREASING power in the climb to reduce failure probability?