Manifold Air Pressure
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Joined: Jul 2011
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From: Kent
Manifold Air Pressure
Hi All,
I'm trying to understand the process for flying with a constant speed prop on a Rotax 912 ULS. There is hardly any information on this in the POH of the aircraft concerned, but I found this in the Rotax operating manual:
https://www.dropbox.com/s/g5ojged3nl...M%20Curve.tiff
https://www.dropbox.com/s/5rn30esf3f...M%20Table.tiff
From my understanding, I should choose a desired RPM for the fuel burn/speed I want, and set the manifold pressure according to the graph or the table. Am I correct to assume this? Also, I'm aware the MAP will decrease as I gain altitude, but what I am uncertain with is whether I should maintain the MAP shown on the graph (for my required RPM) regardless of my altitude, by advancing the position of the throttle as I gain altitude? I hope this makes sense and any help would be greatly appreciated.
Josh
I'm trying to understand the process for flying with a constant speed prop on a Rotax 912 ULS. There is hardly any information on this in the POH of the aircraft concerned, but I found this in the Rotax operating manual:
https://www.dropbox.com/s/g5ojged3nl...M%20Curve.tiff
https://www.dropbox.com/s/5rn30esf3f...M%20Table.tiff
From my understanding, I should choose a desired RPM for the fuel burn/speed I want, and set the manifold pressure according to the graph or the table. Am I correct to assume this? Also, I'm aware the MAP will decrease as I gain altitude, but what I am uncertain with is whether I should maintain the MAP shown on the graph (for my required RPM) regardless of my altitude, by advancing the position of the throttle as I gain altitude? I hope this makes sense and any help would be greatly appreciated.
Josh
Last edited by flyer96; 23rd March 2014 at 20:43. Reason: Fix broken image links
Joined: Aug 2000
Posts: 1,214
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From: S Warwickshire
Don't forget that you'll need a differences training sign-off for the controllable prop, so your instructor should take you through the subtleties of operation.
You will normally climb at full throttle and, when levelling off either maintain full throttle or throttle back to just below the desired cruise MP, then when you set the cruise RPM the slight gain in MP should bring you close to the desired setting.
Generally at about 8000' or above you will probably want full throttle and control power with RPM as you won't be able to achieve more than about 21-22" MP. All this assumes non-turbo.
High MP and low RPM is the most efficient and quietest, so long as you stay within the approved limits.
You will normally climb at full throttle and, when levelling off either maintain full throttle or throttle back to just below the desired cruise MP, then when you set the cruise RPM the slight gain in MP should bring you close to the desired setting.
Generally at about 8000' or above you will probably want full throttle and control power with RPM as you won't be able to achieve more than about 21-22" MP. All this assumes non-turbo.
High MP and low RPM is the most efficient and quietest, so long as you stay within the approved limits.
