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  #111  
Old 03-18-2015, 03:10 PM
PaulR PaulR is offline
 
Join Date: Oct 2005
Location: Geneva, AL
Posts: 491
Default 25" MP

I'm flying with a fixed pitch prop (Catto) and a Dynon EMS 120. Is it an "absolute" that anytime you are below 25" MP you are below 75% power?

I think the Dynon uses some calculation using MP and RPM, and I assume fuel flow to give a % power reading. My Catto will turn more than 2600 at 5000 DA and I think that messes up my power readings. Therefore I've used the rule of 48's I think it is.

It would be simpler to know that if I'm below 25" of MP then I can lean as I wish.
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  #112  
Old 03-18-2015, 03:43 PM
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RVbySDI RVbySDI is offline
 
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Location: Tuttle, Oklahoma
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Default

Quote:
Originally Posted by PaulR View Post
I'm flying with a fixed pitch prop (Catto) and a Dynon EMS 120. Is it an "absolute" that anytime you are below 25" MP you are below 75% power?

I think the Dynon uses some calculation using MP and RPM, and I assume fuel flow to give a % power reading. My Catto will turn more than 2600 at 5000 DA and I think that messes up my power readings. Therefore I've used the rule of 48's I think it is.

It would be simpler to know that if I'm below 25" of MP then I can lean as I wish.
Not quite sure what you are referring to concerning "rule of 48's". Whatever that is about, I think using % HP is a WAG regardless of which EFIS manufacturer being used in reference to how the % HP read out is calculated. If you are adamant about using a 75% number then be aware that even the best of calculations are an estimate. Which is still OK. Your engine will not instantly blow up if it actually is 76% or something. However, I think it perhaps may be wiser to take what Mike Busch discusses and think more in terms of CHT rather than % HP to determine when or if one runs LOP. We are concerned with detonation and pre-ignition and all that stuff anyway, are we not? Those are functions of heat after all, so, why not utilize information that deals with heat? Keeping the CHT for each cylinder south of 400 deg F will do better than trying to rely on some theoretical calculation of % HP that may or may not be correct. As long as the CHT is not above 400 deg F there is little chance of "blowing up" something regardless of what engine setting you are running, what altitude you are flying, the temp outside, the phase of the moon, or whether your engine slept in a Holiday Inn last night.
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  #113  
Old 03-18-2015, 04:42 PM
Daveontheroad11 Daveontheroad11 is offline
 
Join Date: Apr 2013
Location: WA
Posts: 22
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Quote:
Originally Posted by PaulR View Post
I'm flying with a fixed pitch prop (Catto) and a Dynon EMS 120. Is it an "absolute" that anytime you are below 25" MP you are below 75% power?
I think the answer is NO. I looked at the Lycoming I/O 360 Operator's Manual and I believe 75% is ~ 24" 2400 RPM. That gives 150 HP for IO-360 and something comparable for O-360 (something like 135 or 140 HP). Many climb at 25/25, and it is definitely >75%. Interestingly, the Extra 200 POH says to TO WOT (of course) and then pull RPM to 2500 as soon as practicable, which is very subjective (800 AGL?). They recommend WOT in the climb. I believe Mike Busch does this too, and recommends it in his EAA video on leaning.

http://bcove.me/xcda4t0b

Watched it, again, last night. Very informative. Most info is for Turbocharged airplanes. Leaning for I/O-360s is very simple. First 10 minutes of the video covers normally aspirated.
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  #114  
Old 07-29-2021, 03:58 AM
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RV10inOz RV10inOz is offline
 
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Default John Deakin - Gone West at 81

It is with enormous sadness I bring the news of one of natures greatest gentlemen has departed the living, and may he rest in peace.

Just over a year ago I lost a great mate, Walter. This year, another year of all this Covid madness, means once more I have not been able to be with and visit some of the most important people in my life.

Leisa and I were blessed to Face Time with JD a few days ago. He struggled through a few minutes, came out of the blocks hard and smiled like never before when I suggested his local Waypoint Cafe malted chocolate milkshake would fix him up.

I am so blessed to have had John Deakin in my life. I will be bold enough to say everyone on BT will no doubt share the same feelings.

To Tamiko and the boys, our condolences. JD, we love you to bits mate.

You were and forever will be ..... a legend.
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