Which order do you adjust MP and RPM?

flhrci

flhrci

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David
I was watching a video today refreshing my knowledge of constant speed props in preparation for a 182 check out Saturday and came to a realization.

http://www.youtube.com/watch?v=GNsnXjxopJM&list=WL51DECC211199F171

This guy says to adjust MP first, then RPM for cruise. For climb, RPM first, then MP. It has been several years since I last flew a constant speed prop plane and I could swear I was taught to always adjust RPM first no matter what phase of flight. Or does it matter?

What do the masses of POA do?

David
 
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Re: Which order do you adujst MP and RPM?

flhrci said:
This guy says to adjust MP first, then RPM for cruise. For climb, RPM first, then MP.
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He has it.

Power up: Prop then MP

Power down: MP then Prop
 
Re: Which order do you adujst MP and RPM?

Bill Jennings said:
He has it.

Power up: Prop then MP

Power down: MP then Prop
Click to expand...

Thanks for confirming Bill. I guess I may have been taught wrong. The speaker does explain why to do it that way so I do understand the why.

David
 
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MP then RPM when decreasing power, opposite for increasing for me. I typically only touch the prop twice though, once to set it for cruise then again to full RPM in the pattern.
 
Re: Which order do you adujst MP and RPM?

flhrci said:
Thanks for confirming Bill. I guess I may have been taught wrong. The speaker does explain why to do it that way so I do undertsnad the why.

David
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Hard to hurt the durable engines found in 182s but if/when you graduate to real high power planes, especially with turbos, I wouldn't want to cram 40inhg down the throat of a high strung engine running 400rpm below max.


Also, expect to have to fine tune the MP after the RPM is set, it will creep up as you pull the prop back.
 
It's also worthwhile looking at the performance charts too for acceptable MP/rpm combinations. On the DA40 for instance it generally isn't necessary to pull the throttle on the initial climbout power reduction, just the prop.
 
Something else I just realized is that I had never treated the MP as the "throttle." Geeze, I was messed up. :eek:

David
 
Sac Arrow said:
It's also worthwhile looking at the performance charts too for acceptable MP/rpm combinations. On the DA40 for instance it generally isn't necessary to pull the throttle on the initial climbout power reduction, just the prop.
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Thanks Sac. Working on the POH right now as I have time.

David
 
flhrci said:
Thanks Sac. Working on the POH right now as I have time.

David
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There is a reason why the quadrant is arranged as such, so you can go "throttle prop mixture" on power down and do the reverse on power up. Just pull the levers, or knobs in your case in sequence.
 
Do nothing by rote.

MP/RPM is dependant on what you are doing. For instance, after takeoff in a Cessna 185/206 with the IO-520 engine that revs to 2850RPM on takeoff.

First power reduction is prop to 2550.
 
Yup. High RPM, low throttle, rich mixture = OK. Low RPM, high throttle, lean mixture = don't do that.

That tells you what order to do things in.
 
Skylane81E said:
MP then RPM when decreasing power, opposite for increasing for me. I typically only touch the prop twice though, once to set it for cruise then again to full RPM in the pattern.
Click to expand...

This is what I was taught and practice. And with the addition of a slight reduction of prop after takeoff once climb out is assured to reduce tip noise (bring it to just inside top of green arc, ~2600 RPM I think)
 
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kevmor99 said:
I would guess he means to keep RPMs higher than MP (2500rpm without MP being higher than 25") although some POH's have exceptions (27" and 2500 rpm, etc).
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I'd reword that to "most POHs". Think takeoff power, for one. Old legend that may have had some applicability once in some circumstance, but not anymore. Yet, it won't die.

MAKG1 said:
Yup. High RPM, low throttle, rich mixture = OK. Low RPM, high throttle, lean mixture = don't do that.
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Isn't High MP, Low RPM, Lean mixture the most efficient way to run the engine? That's what Lindbergh taught P-38 pilots in the Pacific during WWII to do to extend their range.
 
I've always thought of it as the MP moves within the envelope of the prop lever. Helps my mind sort out which moves when. (Except climb out when I pull the prop back slightly for the neighbors...)
 
RussR said:
Isn't High MP, Low RPM, Lean mixture the most efficient way to run the engine? That's what Lindbergh taught P-38 pilots in the Pacific during WWII to do to extend their range.
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Yup. Engines run most efficiently right below the detonation limit, and with as high a temperature as possible.

Efficiency is not the issue. If your engine could tolerate CHTs of thousands of degrees, the engine would run a whole lot more efficiently there. And lubrication systems work best at high RPM, regardless of MP.

Your engine would also run more efficiently with the timing advanced. But most of us would like an engine that lasts 2000 hours, rather than blowing itself up with detonation in short order.
 
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I fly in high country with a naturally aspirated engine, the throttle is the one you push in all the way on takeoff and never touch again until you land right? :goofy:
 
Unless I'm staying below 3000', I never touch the throttle until it's time to slow down for descent. I set gross power with the prop and fine power with the mixture.
 
Henning said:
Unless I'm staying below 3000', I never touch the throttle until it's time to slow down for descent. I set gross power with the prop and fine power with the mixture.
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So, say you're on a short hop, VFR at 3500, would you be at full throttle and what RPM?
 
kgruber said:
Do nothing by rote.

MP/RPM is dependant on what you are doing. For instance, after takeoff in a Cessna 185/206 with the IO-520 engine that revs to 2850RPM on takeoff.

First power reduction is prop to 2550.
Click to expand...
If you are only going to change one you only change that one. I don't know the 185 in particular but there are a lot of aircraft in which the initial change is a prop-only one. There are bunch of other engine configurations which don't involve changing both. For example from cruise until prop full forward, I don't know too many aircraft in which I do a change in prop.

Is that the case with the reduction you are talking about?

But in the situations in which you are going to change both, the general rule of "Prop forward, throttle back" works well.
 
e.pie said:
I fly in high country with a naturally aspirated engine, the throttle is the one you push in all the way on takeoff and never touch again until you land right? :goofy:
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LOL. Actually, I do change throttle in the high country during the descent with a normally-aspirated engine. My ultimate target is the MP I will want at pattern altitude so, as MP increases during the descent, I bring it back so I don't have a huge reduction at the end.

It's prop I don't usually change from cruise until ready to land.
 
Henning said:
Unless I'm staying below 3000', I never touch the throttle until it's time to slow down for descent. I set gross power with the prop and fine power with the mixture.
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Yeap... you want WOT for best volumetric efficiency.

Once I get to cruise altitude (generally around 5000 since most of my trips are <150miles) it's generally MP back to 20", RPM back to ~2000 RPM, lean out the engine to > 25d LOP, push MP all the way back up (generally hits 25") then I set my power using the mixture all the while staying under peak EGT.

http://youtu.be/g18vHgiQ3OY
 
Bill Jennings said:
So, say you're on a short hop, VFR at 3500, would you be at full throttle and what RPM?
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I'd be at 27" and ~2100rpm...LOP with power set by the mixture. I want to open throttle as much as possible while at the same time keeping RPM as low as possible to maximize efficiency.

I had some haze this day and didn't want to go too high so used it to see how far I could push things on my Aztec twin. 14gph total (7 per side), 1850rpm @25"

http://youtu.be/qwSeoKa1reQ

The POH limitations on the Lycoming IO540C4B5 are 1800rpm 25" manifold pressure and 2000rpm 27" manifold pressure.
 
VA Aviator said:
No, just a way to remember what's already been said.
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So, how does that mnemonic work?


(And yes, there is a reason I didn't go on an overs square rampage, I thought it might have been something else.)
 
Actually, the way I remember it is: reducing power left to right, increasing power right to left :)
 
Sac Arrow said:
It's also worthwhile looking at the performance charts too for acceptable MP/rpm combinations. On the DA40 for instance it generally isn't necessary to pull the throttle on the initial climbout power reduction, just the prop.
Click to expand...

Yep... the Mooney is this way.
 
onwards said:
Actually, the way I remember it is: reducing power left to right, increasing power right to left :)
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That's the "rule of thumb" I was taught.
Push from the right - pull from the left.
 
There are too many variables for a mnemonic.

You need to understand what is needed and then do it, in whatever sequence is required.

It is not rocket surgery.
 
MAKG1 said:
Yup. High RPM, low throttle, rich mixture = OK. Low RPM, high throttle, lean mixture = don't do that.

That tells you what order to do things in.
Click to expand...

Can you explain that and elaborate on the limitations? Could you also expound on why Lindbergh was wrong as well as the entire 8th Army Air Force as well as all the rest of the US aviation branches who doubled their range and TBO by doing what you say is 'Bad'?
 
onwards said:
Who knows? that's what my instructor also taught me, and it stuck.
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May want to do some learning, especially if you are, or intend to be, an owner. It'll save you a lot of money in fuel and maintenance.
 
Henning said:
Can you explain that and elaborate on the limitations? Could you also expound on why Lindbergh was wrong as well as the entire 8th Army Air Force as well as all the rest of the US aviation branches who doubled their range and TBO by doing what you say is 'Bad'?
Click to expand...

It's only about order. Don't read in more than that.

Lindbergh never said it was a good thing to lower your prop RPM before lowering the throttle, and there is no way you can double the range of your aircraft or TBO by doing something for a second or so.

The POH has actual limits in it for what to configure to. Don't go outside those unless you're trained and prepared to deal with the consequences.
 
MAKG1 said:
It's only about order. Don't read in more than that.

Lindbergh never said it was a good thing to lower your prop RPM before lowering the throttle, and there is no way you can double the range of your aircraft or TBO by doing something for a second or so.

The POH has actual limits in it for what to configure to. Don't go outside those unless you're trained and prepared to deal with the consequences.
Click to expand...

Have you read "the Lindbergh Doctrine"? Your post said "high MP, low RPM, lean mixture = bad"
 
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