Manifold Pressure Values?????

by geoffrey klestadt in 912iS Technical Questions 8 years ago

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Re: Manifold Pressure Values?????

by geoffrey klestadt » 8 years ago

geoffrey klestadt

27 94 94

Any progress in getting either a fuel flow vs. power chart for the 912 iS Sport or perhaps manifold pressure vs. power chart? We need to comply with SL-912 - 016.

I note that the power chart for the 912 iS sport shows a peak torque at WOT of about 130 Nm in the rpm range 4800 - 5000 which is way over the limit for maximum continuous power, Consequently it is possible to damage the engine by applying too much throttle at too low rpm. Manifold pressure or fuel flow limits vs. rpm to generate continuous, 75%, 65% and 50% power are required to be specified to avoid this situation.

I can guess from the graph on page 5-5 (Ansaugdruck = manifold pressure) that fuel flow at max continuous is about18 l/h but that is all i can guess.

Building my own aircraft with constant speed propeller, i don't have an airframe manufacturer to do this for me.

Furthermore, the Rotax data needs to be according to "indicated" fuel flow or MAP according to the rotax sensors. My Red cube flow meters are not calibrated and may sh.ho different numbers.

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Re: Manifold Pressure Values?????

by Gilles Thesee » 7 years ago

Gilles Thesee

2 9 0

Any progress in getting either a fuel flow vs. power chart for the 912 iS Sport or perhaps manifold pressure vs. power chart?

Hi all,

Any update on the subject ?
I'm new to the 912iS, but have been flying behind Rotax engines for more than 20 years, and our Rotax 914/ CS prop four seater is now 12 yrears old.
Clear power settings for the 912iS are really lacking.

Considering the different tables in the OM, clearly Rotax have done their homework with the flight tests, but their manuals leave a lot to be desired.

BTW, since Rotax only gives fuel flow vs power settings, how can one judge fuel economy compared to a plain old 912 S, for instance ?

Has someone compiled the data in the OM tables, to try an deduce ballpark manifold pressure settings ?
Thanks in advance,

Best regards,
Gilles

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Re: Manifold Pressure Values?????

by Roger Lee » 7 years ago

Roger Lee

125 5.12k 4.53k

Usually staying down at =<5200 rpm keeps you in the better fuel economy settings. Getting up to 5300-5500 does use more fuel. Flying higher will net you better fuel economy over the 912ULS too because it can adjust fuel flow better than the carbs as you climb in altitude.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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Re: Manifold Pressure Values?????

by Glenn Martin » 7 years ago

Glenn Martin

3 281 798

Ball park MAP vs Power settings...

MAP vs Power
inches hp %

29 97 100
26 72 75
25 63 65
23 53 55

Although I do not understand why you would need these, what are you trying to achieve ?

Secondly if you know fuel flow, you can calculate power from 3.72 L/hr/hp with a standard deviation of 4.8%, but again do not know why.

Assuming you have a constant speed prop and If you want to run at the most efficient point then set 5000 rpm (Engine peak torque) then open the throttle to get the desired speed/climb you want.

If you want the most "fuel efficient" settings then it will be 5000 rpm and best glide speed, at the lowest resistance, ie the highest altitude. For instance my aircraft I normally cruise at 100 kt, but at 9500 ft, 70 kts 5000 rpm I can double the range.... but most Pilots, including me, find this way too slow

Power or fuel flow is not really want Pilots want, they want the most MPG or quickest climb, or the longest duration, so you need to say what you are trying to achieve.

The performance you want depends not only on the engine but the airframe so "one size does not fit all".

In Eco mode the ECU is far better at power and fuel management than any Human. So just fly as Rotax says...

5800 rpm max for no more then 5 min
5500 rpm max sustainable power
5000 rpm most efficient engine rpm

Then think of the throttle as your wallet control, more throttle is more dollars spent per hour. The ECU and Rotax cannot tell you how much money you are comfortable with spending per hour vs the value of your time...that is your decision when you hold the throttle.

Hope this helps

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Re: Manifold Pressure Values?????

by Roger Lee » 7 years ago

Roger Lee

125 5.12k 4.53k

Part of our understanding for each 912iS use is some owners around the world get to use an in flight adjustable prop, but many have to use only a ground adjustable prop. In the US we have to use a ground adjustable.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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Manifold Pressure Values?????

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