Reduced Power takeoffs

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Mtns2Skies

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Mtns2Skies
I was going through my POH with a fine-toothed comb the other day and noticed instructions for what I interpreted to mean a reduced power takeoff. I know from taking off at high altitude airports I have no real problems taking off at 18-19" of manifold pressure given a decently long runway, so would it REALLY be the end of the world to takeoff with less than full manifold pressure now that I'm at sealevel? Is there any real merit to doing this?, or am I misinterpreting this?
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I suppose the thought is that you are more likely to have an engine failure goosing it at full power to get off a 5,000 foot runway than if you ran cruise power to get off the ground.

Interesting I guess.
 
I have used 25 squared (climb power) for take offs in C-206/7 at times. Usually in very cold weather.
 
Takeoff at full available power always. Never know what could happen. Once airborne I often run down the power to 25 square for the ascent. My POH says to do so, though it is of sufficient age to be less than trustworthy. I've read anecdotal evidence that the ship burns less oil if one does this though.
 
Full power, but I do reduce RPMs from 2700 to 2600, for noise reduction. Shouldn’t the engine already be warmed up anyway?


Tom
 
It is talking about reducing power after takeoff, not for takeoff. The previous and subsequent paragraphs both state normal takeoffs are with full throttle.
 
MooneyDriver78 said:
...Shouldn’t the engine already be warmed up anyway?

Tom
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There’s the answer: just make sure the engine is properly warmed up.

I’ve done a number of cold weather takeoffs where I’ve first had to ask Ground to give me somewhere to continue engine warmup before I get to the run up area.
 
My mech asked me to do a reduced-power takeoff yesterday. I've got two fresh cyls, and he wanted 45mins of nice and easy flying.

7,000-foot runway, 25"mp wasn't a problem.
 
In my 172 I was always doing full power take offs. In my RV-10 not so much. I can comfortably take off at reduced power and climb out without worrying about high CHTs.
 
Rgbeard said:
My mech asked me to do a reduced-power takeoff yesterday. I've got two fresh cyls, and he wanted 45mins of nice and easy flying.

7,000-foot runway, 25"mp wasn't a problem.
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Odd. My mechanic told me to run my new cylinders hard, just don't let them get hot. He told me NOT to take it easy on them. Breaks in the rings to the cylinders and reduces oil consumption long term.
 
I was also told to flog the engine (within reason) to death for break in.
 
Salty said:
No. But I don't see how that changes the ring break-in factor.
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What's your full power MP? I was told to be at 25", and stay "out of the turbo", by the engine shop, my lead A&P, and the A&P that did the work.

For many 25" is full power, AFAIK.

The asked me to do that, avoid touch and goes, and keep it cool running for the first 45mins.
 
I always use full throttle, thought there was something about it being better for the engine, but I’m not 100%

Now one thing conditions allowing, pull the prop back and fingers width to cut down on the noise.
 
Rgbeard said:
What's your full power MP? I was told to be at 25", and stay "out of the turbo", by the engine shop, my lead A&P, and the A&P that did the work.

For many 25" is full power, AFAIK.

The asked me to do that, avoid touch and goes, and keep it cool running for the first 45mins.
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LOL I did touch and goes because you can practice landings without the engine getting so hot.
 
dmspilot said:
It is talking about reducing power after takeoff, not for takeoff. The previous and subsequent paragraphs both state normal takeoffs are with full throttle.
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That's not the way I read it... Climb power settings for takeoff unless more is needed for safety (load, DA, etc.).
 
as to break in, doesn't matter if its turbo or not, run it at 65% to 75% power and watch temps. the only thing is a turbo will let you do 65% to 75% at a higher altitude which might help to keep it cool.

as to the original question, some carbs have an enrichment circuit to add fuel at wide open to help with cooling. doing a reduced power takeoff with those carbs will have a leaner mixture on TO and higher chts. that really defeats the purpose of reduce power. wide open to a safe altitude as the POH calls for.
 
CharlieD3 said:
That's not the way I read it... Climb power settings for takeoff unless more is needed for safety (load, DA, etc.).
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Normal takeoffs are with full throttle, it says. How could you read it any differently?
 
A.) GA piston engines absolutely suck

B.) Someone came and gave a talk at CAP once who allegedly knew a thing or two about engines and was a big advocate of full power takeoffs, not just for safety reasons (get up and gain altitude quick) but also had something to do with engine life.. I forget what exactly they said but the logic was that it's good for the engine to get up to max power every so often, breath, and get a full workout
 
Mtns2Skies said:
... a reduced power takeoff ... Is there any real merit to doing this?]
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I don't think so. I believe that the premise is flawed, and that the POH language reflects an understanding of engine operation that was prevalent back in the day, but is now outdated. Modern laboratory instrumentation has allowed much better understanding of what's actually going on inside of operating engines.

High power and high RPM isn't what wears or damages engine components -- it is, instead, high internal pressures and elevated temperatures. Modern engine operating techniques allow pilots to produce high power, while at the same time limiting those pressures and temps that impose wear.

Power is a good thing -- not something to be avoided. Part-power departures are like intersection takeoffs and flying with minimum fuel quantities: they're OK until something else goes wrong -- but then they've reduced our margins and survivability.
 
I don't believe the POH is advocating for reduced power take offs, but instead advocating for reducing power as soon as practical.

On the subject of reduced power take offs: Most turbine operators such as transports routinely do reduced power take offs. It's rare to see full thrust TO in day to day operations.

The Hughes/Schwiezer 269 series helicopters had an option for a "dual operating range" tach that would allow reduced RPM's for lightly loaded operations.
 
Squirrelfury said:
Power is a good thing -- not something to be avoided. Part-power departures are like intersection takeoffs and flying with minimum fuel quantities: they're OK until something else goes wrong -- but then they've reduced our margins and survivability.
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On a typical SE airplane, if someone is reducing power by 10% for takeoff, using a lightly loaded airplane, low density altitude and 200%+ runway required for take off, how is that unsafe over a full power take off?

What could go wrong that simply pushing the throttle forward wouldn't solve? The power reduction doesn't mean it's no longer there if needed.
 
On your 180 do you also have the micro switches that trigger at WOT?
 
Doc Holliday said:
On a typical SE airplane, if someone is reducing power by 10% for takeoff, using a lightly loaded airplane, low density altitude and 200%+ runway required for take off, how is that unsafe over a full power take off?
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"Unsafe"? Oh, I don't know if it's unsafe. I do know that it's less so -- that safety margins and options are reduced.

Look, just for example, at the POH performance predictions for a C-172. They suggest that a 10% reduction in power at SL will increase takeoff distances by about 9%, and reduce rate-of-climb by about 7%. If anything necessitates a takeoff abort, then that reduced-power pilot will have less room (and less time) in which to put the plane back on the runway or its overrun, before instead having to "put it into the trees" or "land it downtown".

Is it "unsafe" to perform an intersection takeoff in that same C-172 from a mid-field intersection on a 4000' runway? No! The remaining 2000' of runway still provides the proposed "200%+ of runway required". Until ... something goes wrong, and he needs that runway behind him (or, needs that runway that would have been remaining, had he instead performed his takeoff at full power).


Doc Holliday said:
What could go wrong that simply pushing the throttle forward wouldn't solve? The power reduction doesn't mean it's no longer there if needed.
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Engine roughness or catastrophic failure, an abnormal engine parameter (lost oil pressure, CHT runaway, low manifold pressure, prop overspeed), an improperly-secured engine cowl pops open, smoke in the cockpit or oil spray on the windshield, a controllability problem (aft CG, or mechanical failure of a control linkage), airspeed indication failure, attitude indication failure on an instrument departure. Probably others.
 
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Full throttle provides full fuel flow. Reducing power for takeoff makes no sense. Some of us worked hard to get the fuel flows up where they need to be. No way I'm pulling back on the throttle. I will twist the prop a little slower in cold weather.
 
Squirrelfury said:
"Unsafe"? Oh, I don't know if it's unsafe. I do know that it's less so -- that safety margins and options are reduced.

Look, just for example, at the POH performance predictions for a C-172. They suggest that a 10% reduction in power at SL will reduce takeoff distances by about 9%, and rate-of-climb by about 7%. If anything necessitates a takeoff abort, then that reduced-power pilot will have less room (and less time) in which to put the plane back on the runway or its overrun, before instead having to "put it into the trees" or "land it downtown".

Is it "unsafe" to perform an intersection takeoff in that same C-172 from a mid-field intersection on a 4000' runway? No! The remaining 2000' of runway still provides the proposed "200%+ of runway required". Until ... something goes wrong, and he needs that runway behind him (or, needs that runway that would have been remaining, had he instead performed his takeoff at full power).

Engine roughness or catastrophic failure, an abnormal engine parameter (lost oil pressure, CHT runaway, low manifold pressure, prop overspeed), an improperly-secured engine cowl pops open, smoke in the cockpit or oil spray on the windshield, a controllability problem (aft CG, or mechanical failure of a control linkage), airspeed indication failure, attitude indication failure on an instrument departure. Probably others.
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But those could happen at full power as well.

In flying transport equipment, reduce thrust was routine, but it did have perimeters. Same could be applied to SE piston aircraft as well, given runway length, wind, DA, obstacles, etc.

Back when I flew twin cessnas (402/404/421/414) and Piper Navajos when lightly loaded we would reduce TO MP slightly. Again, common sense prevailed, we wouldn't do it on short runways heavy with obstacle clearance issues.
 
Squirrelfury said:
I don't think so. I believe that the premise is flawed, and that the POH language reflects an understanding of engine operation that was prevalent back in the day, but is now outdated. Modern laboratory instrumentation has allowed much better understanding of what's actually going on inside of operating engines.

High power and high RPM isn't what wears or damages engine components -- it is, instead, high internal pressures and elevated temperatures. Modern engine operating techniques allow pilots to produce high power, while at the same time limiting those pressures and temps that impose wear.

Power is a good thing -- not something to be avoided. Part-power departures are like intersection takeoffs and flying with minimum fuel quantities: they're OK until something else goes wrong -- but then they've reduced our margins and survivability.
Click to expand...

This 100%.. it is actually better for the engine to let it turn at 2700 rpm in the climb vs 2500.. the guys at GAMI have the most technologically advanced test cell for recip engines and have found that internal cylinder pressures and heat are what puts the most wear on the jugs. Lots of old POHs have tables for cruise at 50 ROP. They have since found that at most altitudes 50 ROP is almost the absolute worst place to run your engine in terms of ICPs. Most people think they are babying and saving their engines by reducing to 25'/2500 once they get to 500-1000AGL. This is false.

Full power all the way to cruise altitude then, LOP if you have GAMI's and a good understanding of LOP ops or 100ROP min. CHTs below 380 at all times. 50ROP or peak is only really safe in NA airplanes at high altitude where the engine is not making anywhere near sea level power.
 
AnthonyS1 said:
This 100%.. it is actually better for the engine to let it turn at 2700 rpm in the climb vs 2500.. the guys at GAMI have the most technologically advanced test cell for recip engines and have found that internal cylinder pressures and heat are what puts the most wear on the jugs. Lots of old POHs have tables for cruise at 50 ROP. They have since found that at most altitudes 50 ROP is almost the absolute worst place to run your engine in terms of ICPs. Most people think they are babying and saving their engines by reducing to 25'/2500 once they get to 500-1000AGL. This is false.

Full power all the way to cruise altitude then, LOP if you have GAMI's and a good understanding of LOP ops or 100ROP min. CHTs below 380 at all times. 50ROP or peak is only really safe in NA airplanes at high altitude where the engine is not making anywhere near sea level power.
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What is 100ROP?
 
Rgbeard said:
My mech asked me to do a reduced-power takeoff yesterday. I've got two fresh cyls, and he wanted 45mins of nice and easy flying.

7,000-foot runway, 25"mp wasn't a problem.
Click to expand...

That is very bad advice from your mechanic. Breaking in the engine in at reduced power will result in cylinder glazing and high oil consumption. It also goes against the manufactures recommendations.
 
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25/2500 is a myth. Unless it’s a specific limitation, I leave my throttle wide open until I’m ready to land

I broke in an IO-360 and IO-550. Run it hard!
 
CharlieD3 said:
That's not the way I read it... Climb power settings for takeoff unless more is needed for safety (load, DA, etc.).
Click to expand...

You will not be getting fuel flow enrichment resulting in higher CHT’s and you are increasing your chances for detonation if it’s really hot or you get a bad batch of fuel. Most engines are set up to provide extra fuel flow above the power increase at full throttle to minimize possible detonation and provide max cooling.
Those discussing jet engines need to understand there is no correlation with piston engines. Your comparing two 100% different animals.
 
dmspilot said:
Normal takeoffs are with full throttle, it says. How could you read it any differently?
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Yes, normal takeoffs are with full power...

However, in order to reduce engine wear, use less, but only as little as determined by safety factors (not just limited to a cold engine, but especially if the engine has not completely warmed up).

So, I read it as: 'Normally, you would use full power on takeoff, but if you're not limited by runway length, density altitude, or any other safety concern; and wish to pamper your engine (in their opinion), use less than full power.'
 
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