Car

PlasticCigar said:
I keep seeing this mentioned as if it is a fact, but I’m unconvinced. Perhaps my Google skills are lacking, but I can’t find any convincing studies showing that the initial power reduction after takeoff causes an engine failure.

Has anyone come across documentation to support this? I’ve certainly seen many accident reports describing engine power loss shortly after takeoff and some of those happened after power reduction but this wouldn’t mean the power reduction caused it.

I’ve only experienced one engine failure shortly after takeoff and it would have happened around the time I normally reduce the power but I hadn’t actually touched anything yet which makes me think that the “don’t touch the power or your engine will quit” advice is a little misguided.

Thoughts?
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It is extremely unlikely for a mechanical failure to occur during power reduction. But human errors are more likely. For instance, you might pull the mixture knob instead of the throttle, or in a twin you might pull one throttle instead of both. That surprise element could lead to bad results. That is a good reason to leave everything where they are until you are at a safe altitude.
 
sarangan said:
It is extremely unlikely for a mechanical failure to occur during power reduction.
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It’s extremely unlikely for non-pilot induced mechanical failures to occur during any phase of flight, but they do happen.

Altitude is insurance, so I don’t see any reason to fiddle with the engine(s) (unless absolutely necessary) until you reach a safe altitude. If it’s running, leave it alone.
 
PlasticCigar said:
don’t touch the power or your engine will quit
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I always just assumed it was a "don't fix it if it ain't broken" kind of thing

However, in turbo airplanes I do keep my hand on both mixture and throttle monitoring fuel flow and manifold pressure on the roll and during initial climb
 
One has to be careful to assign cause and effect. Just because an engine failed when the power was first reduced does not mean that the power reduction caused the failure. More likely, this is merely a coincidence. During takeoff, engines are developing maximum power and are under maximum stress, which is very likely a cause of more frequent failures than when operating under less stressful conditions. Power reductions after takeoff occur immediately after a sustained period of high-power, high-stress operation. Of course, if an engine control failed, that would be an obvious direct cause.
 
This sort of thing isn't alone. There are plenty of OWTs in aviation. I heard the failure-on-power-reduction nearly 50 years ago when I started flying.

Two strokes can do it, though. The ultralights have had some issues with it. Those little engines generate a lot of power for their size and weight, which means there's also a lot of waste heat, and if a pilot takes off without warming the thing up properly he gets the pistons hot so fast that they can get tight in their cylinders, which haven't warmed up and expanded enough to maintain the clearances. When the throttle is reduced the engine gets less fuel, which also means it gets less oil, as the oil is mixed with the fuel (at least in the older engines) and between the tightness of the piston in the cylinder and the sudden reduction in lube, it can seize. Happened twice to a friend before someone told him about this.
 
Cold seizing in a 2-stroke is about dissimilar metals expansion rates. Aluminum pistons grow faster than the bore. It happens from improper warmup, not lubrication.
 
Ryanb said:
If it’s running, leave it alone.
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That advice works very well and I used it a number of years ago when I was doing phase one on a plane I had completed (not the one I have now). In setting up the engine and carb I had the overall mixture in the carb set too rich although it ran fine on the ground in a two minute WOT test. On climb out at about 150' the engine was running a bit rough but it was running so I decided to let it continue to climb until I could get a safe altitude. My ground crew guy was on the radio yelling about the rough engine but I ignored him telling me what I already knew. It was evident to me that it was rough from being too rich but I left it alone until I had 1000' feet on downwind and then I slowly pulled the mixture back and it cleared up.

On the ground he asked me why I didn't lean the mixture earlier. I told him it was running well enough to climb and I wasn't gonna change nothing until I had some altitude in case what I did made things worse. He agreed!
 
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I think this applies more to jet engines where bad things tend to happen on a thermal cycle. In several aircraft I flew the procedure if you had engine issues was to set a specific RPM and then don’t touch it until you had the field made. Some jets would run for extended periods of time without oil by melting their bearings but as soon as you made a power change they came unglued.
 
if there is a partial obstruction in the fuel system, the engine may empty the carb bowl and then stumble if not quit. A normal run up won't catch this. Happened to me from a partially frozen gas line - actually slush ice in the gascolator.:eek:

Beware of fuel that has been severely chilled below freezing. Dissolved water will come out of solution as ice crystals.

This was not caused by a power reduction per se.
 
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It's because of shock cooling.

:stirpot: :devil::popcorn:
 
Can someone clarify what type of aircraft/engine has issues when power is initially reduced and when this issue occurs?

Carb vs non carb? Constant speed vs fixed pitch? What altitude?

so we shouldn’t set for 25” mp and 2500 rpm after takeoff and just leave throttle wide open and prop full forward until when?

kind of a serious question. Just wondering what the parameters are for someone saying, “don’t touch the power or your engine will quit.”
 
Deelee said:
Can someone clarify what type of aircraft/engine has issues when power is initially reduced and when this issue occurs?

Carb vs non carb? Constant speed vs fixed pitch? What altitude?

so we shouldn’t set for 25” mp and 2500 rpm after takeoff and just leave throttle wide open and prop full forward until when?

kind of a serious question. Just wondering what the parameters are for someone saying, “don’t touch the power or your engine will quit.”
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been flying many years. I have never heard of that happening. My 182 I always bring the power back. Any plane I have ever flown that called for it I always did it.
 
Deelee said:
Can someone clarify what type of aircraft/engine has issues when power is initially reduced and when this issue occurs?

Carb vs non carb? Constant speed vs fixed pitch? What altitude?

so we shouldn’t set for 25” mp and 2500 rpm after takeoff and just leave throttle wide open and prop full forward until when?

kind of a serious question. Just wondering what the parameters are for someone saying, “don’t touch the power or your engine will quit.”
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Common sense would say don’t rush to do anything. I wouldn’t mess with anything below 500’. If you can wait until 1000’ AGL, great, but not much gained delaying beyond 1000’.

Personally, I’d be more concerned about turning off boost pumps, or other after takeoff items below 500’ than power reduction.
 
Deelee said:
so we shouldn’t set for 25” mp and 2500 rpm after takeoff and just leave throttle wide open and prop full forward until when?
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Unless there is a limitation on max power during climb, there is no reason to pull the power back in NA airplane until you reach your target altitude. You can pull the prop back to 2500-2600 for noise reduction, but leave the throttle full open.
 
Total B.S. I reduce power after every takeoff. Says to do so in my POH, and I've a few other reasons. Besides, if the power goes out that fast I can land on the remaining runway.
 
Reduce power why? I wind down the prop a little but throttle stays full until I’m at my cruise altitude, but I acknowledge I cruise lower than most of you. There’s no reason to reduce power until you’re comfortable with your altitude. Even if you have a 5 minute restriction, you can put a lot of distance between you and the ground in 5 minutes.
 
Stewartb said:
Reduce power why? I wind down the prop a little but throttle stays full until I’m at my cruise altitude, but I acknowledge I cruise lower than most of you. There’s no reason to reduce power until you’re comfortable with your altitude. Even if you have a 5 minute restriction, you can put a lot of distance between you and the ground in 5 minutes.
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It all depends. If I’m going high enough I never reduce the throttle. Just pull back the prop and lean with the mixture. No reason to restrict the intake...
 
The last 6 engine failures I've suffered:
1. Throttling back to descend from altitude. Tecnam P-92. Turned out to be a problem with the carbs.
2. The next 5 were all on the same day, extremely cold weather, and the 65 hp Cub with the wooden prop just didn't have enough flywheel effect to keep running when I pulled the throttle to land.
I've never heard of an engine quitting while throttling back to cruise climb or cruising speed.
Now that I've said that, I'm sure the Cub will oblige me on Thursday.
 
MauleSkinner said:
isnt winding down the prop a little reducing the power?
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Technically speaking, sure, but that's not what they're talking about. Reducing throttle reduces fuel flow. In high power conditions I want the fuel flow to cool the engine. Reducing throttle isn't doing the engine any favors. The only reason I twist the prop back is to reduce noise. Climb performance is still plenty good.
 
Stewartb said:
Technically speaking, sure, but that's not what they're talking about. Reducing throttle reduces fuel flow. In high power conditions I want the fuel flow to cool the engine. Reducing throttle isn't doing the engine any favors. The only reason I twist the prop back is to reduce noise. Climb performance is still plenty good.
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All true, but the OP’s question was about reducing power, not just MP or fuel flow. Are you indicating that the reduction of fuel flow From pulling the throttle back an inch or two could result in engine failure?
 
Not sure if OWT or saw in a report/study that most mechanical failures occur with a change in engine settings.
So, I was taught and follow, unless I have some overriding reason (usually noise factors), leave the power settings alone till 1000 AGL.

Tim
 
tspear said:
leave the power settings alone till 1000 AGL
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..that's the other part of it.. there's really no reason to mess with it until you are at at least 1K AGL..
 
Shepherd said:
extremely cold weather, and the 65 hp Cub with the wooden prop just didn't have enough flywheel effect
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interesting.. couple questions

-what does the cold weather have to do with? Thicker oil so more internal "resistance" to overcome?
-when in flight, wouldn't the props windmill effect sort of have a flywheel effect?
-how does it stay running on the ground?
 
Closing the throttle and leaving rpms alone is going to add stress to powertrain, is it not? Crank, rods, wrist pins. No?
 
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Stewartb said:
Technically speaking, sure, but that's not what they're talking about. Reducing throttle reduces fuel flow. In high power conditions I want the fuel flow to cool the engine. Reducing throttle isn't doing the engine any favors. The only reason I twist the prop back is to reduce noise. Climb performance is still plenty good.
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While technically correct, I think what you trying to say is the reducing throttle leans the mixture. Which is true for some engines. It is pretty easy to tell if an engine has an Full Power Enrichment Feature or not if you have a good EGT guage.

The only engines I have found recommend reducing power after take off are engines with constant speed props and they usually don't have a Full Power Enrichment Feature.

A lot of engines are only rated for 100% power for 5 minutes. Usually with a fixed pitch prop this isn't an issue as most can't produce much over 75% power in a climb anyway.

I have been told that a number of years ago (30+) one of the engine manufacture sent a factory rep to a large operator of 206's in Alaska that were have frequent engine failures at only 2-300hrs on the engines (Broken Cranks IIRC). They determined the issue was the operators were operating them per the manual which then stated to take off and climb with full power. The issue is when the Density Altitude is 8000 feet BELOW sea level the engines are producing something like 125% power, well above what they are rated for. This operator changed their procedure to take off and climb at reduced power and they stopped having premature engine failures.

Brian
 
I always left power untouched til I hit pattern altitude, then set to 25 squared for normal climb. No science behind that, just easy to remember and made sense. However, this thread made me check my POH, which says full power for normal climb, so I'll start doing that instead. Live and learn.
 
Tantalum said:
interesting.. couple questions

-what does the cold weather have to do with? Thicker oil so more internal "resistance" to overcome?
-when in flight, wouldn't the props windmill effect sort of have a flywheel effect?
-how does it stay running on the ground?
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FYI: We are talking temperatures on the field of -7 degrees F and colder.
1. No idea what the problem is. Neither do any of the mechanics who have been working on it for the past 4 years.
2. You would think so, but when you pull the power to idle, the engine shuts down. It's exactly like flipping the mags off.
3. On the ground you keep it above 1,000 rpm below that, silence.
It's a really weird situation. They have replaced the carbs, throttle cable, carb heat cable (carb heat works fine, no carb ice, ever) inductor, mags, fuel tank.
Once again, we are waiting for cold weather to see what happens. If it still fails, time to upgrade to 85hp.
Nothing like a little mystery to add to the drama and excitement.
 
Salty said:
Closing the throttle and leaving rpms alone is going to add stress to powertrain, is it not? Crank, rods, wrist pins. No?
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That's backwards, I believe. Reduce MP first, then RPM. Increase RPM first, then MP. Constant Speed Prop training 101, keep MP less than RPM.
 
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Ed Haywood said:
I always left power untouched til I hit pattern altitude, then set to 25 squared for normal climb. No science behind that, just easy to remember and made sense. However, this thread made me check my POH, which says full power for normal climb, so I'll start doing that instead. Live and learn.
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I do this to keep my CHTs under control. In the summer they can get way too high during climb.
 
Ed Haywood said:
That's backwards, I believe. Reduce MP first, then RPM. Increase RPM first, then MP.
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It’s what’s been described above in the thread.
 
Salty said:
Closing the throttle and leaving rpms alone is going to add stress to powertrain, is it not? Crank, rods, wrist pins, as well as more pressure in the cylinder. No?
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Cylinder pressure should actually go down due to a lack of air and fuel flow. It’s takes fuel and air to make power, which generates cylinder pressure. In Stewart’s example above, leaving a constant throttle and dialing RPM back would increase cylinder pressure, since the RPM is reduced via increased load (since throttle is constant). The RPM only goes down because pitch goes up. Same as shifting up in a manual transmission car with constant throttle.

important to note that I’m not an AP nor did I stay in a holiday inn express.

with regard to the OP, I doubt it would cause acute failure, but there are aircraft with a fuel enrichment feature at WOT. It’s possible to reduce throttle only to the point that this shuts off but power hasn’t been retarded enough to make up for the lost enrichment in terms of cooling (sort of like the red box concept of ROP/LOP operation). IOW, an attempt to preserve the engine could actually make it worse than leaving it at WOT.
 
Omalley1537 said:
Cylinder pressure should actually go down due to a lack of air and fuel flow. It’s takes fuel and air to make power, which generates cylinder pressure. In Stewart’s example above, leaving a constant throttle and dialing RPM back would increase cylinder pressure, since the RPM is reduced via increased load (since throttle is constant). The RPM only goes down because pitch goes up. Same as shifting up in a manual transmission car with constant throttle.

important to note that I’m not an AP nor did I stay in a holiday inn express.

with regard to the OP, I doubt it would cause acute failure, but there are aircraft with a fuel enrichment feature at WOT. It’s possible to reduce throttle only to the point that this shuts off but power hasn’t been retarded enough to make up for the lost enrichment in terms of cooling (sort of like the red box concept of ROP/LOP operation). IOW, an attempt to preserve the engine could actually make it worse than leaving it at WOT.
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I already edited out the cylinder pressure part. I still think the rest is true.
 
brcase said:
While technically correct, I think what you trying to say is the reducing throttle leans the mixture.
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Closing the throttle reduces air flow. Opening the throttle increases air flow. Fuel is metered by air flow so the ratio stays constant. Mixture is a separate control.
 
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