75% power???
in General Tech Discussion
6 years ago
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by Eugene Klimenko » 6 years ago
So, after converting your engine to injection, guys reporting more power and big fuel savings. Almost one gallon per hour. Where is better numbers coming from? Only from altitude compensation and better fuel/air mixture ? What do they need to do for 75% power?
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by Bill Hertzel » 6 years ago
In a Carburated 912, the mixture is commonly fixed at slightly rich of peak across the range.
The Fuel injected versions continuously vary the mixture.
Above 90% power, the mixture is set Rich of Peak to keep the temperatures down.
Below 90% power, the mixture is leaned. ECO Mode!
The Burn Flame Temps go up but the total Heat is less. The cylinders do not overheat (OverTemp)
Think of it as a hotter but smaller flame.
This makes for a more efficient engine.
Do not confuse Temperature and Heat.
Heat is the total Energy. Temperature is the density of that energy.
Ex. When you compress Air, the temperature goes UP because the heat in the air now occupies a smaller space.
Higher Heat Density equal Higher temperatures. The temperature changes but the Total Heat remains the same.
Leaning the mixture raises the Heat (Energy) produced from each gallon of fuel.
The result is more power is produced from a smaller amount of fuel. Increased Efficiency!
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75% power is not the necessarily the same as 75hp it is 75% of whatever power is available.
Actual power can be determined from Displacement, RPM, and MAP with general assumptions about atmospheric components (Humidity, etc.) and fuel flow (Rich, Lean)
Otherwise, it is just commonly approximated from RPM. Close enough!
All things being equal, throttle any engine back to ≈90% Max rpm and you will be close to 75% power.
What is the great concern about 75% power?
Bill Hertzel
Rotax 912is
North Ridgeville, OH, USA
Clicking the "Thank You" is Always Appreciated by Everyone.
Thank you said by: Eugene Klimenko
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by Peter Biltz » 6 years ago
As I can see all this discusion is when having a fix pitch propeller. How should I set RPM and Manifold pressure, to get sertain % usage and best fuel-air mixture, when using a constant speed propeller eg. MTV-21....?
When using a 914 Engine there are several percentages and manifold pres in the flight manual.
Thanks.
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by Eugene Klimenko » 6 years ago
Thank you! There is no concern about 75% Power. I am only trying to educate myself and arguing with my designer in Europe.
This is what I am hearing from over there:
--------------- " Eugene : Here in Europe - for more planes we are using roughly 4000-4800 rpm for cruise flights, 5000 for fast flights - and more 5000 only for take-offs and short flights ( showing of aircraft abilities or speed records = with bigger fuel consumption)
yes, usually 3800 is used as recomended bottom limit.
all my friends are flying with another approach :
for them rpm= fuel consumption
fuel consumption by 5000 rpm = 20 liters per hour
fuel consumption by 5500 rpm = 27 liters per hour
average fuel consumption in ROTAX 912ULS in our airports is
"more 15 liters per hour" = 4300-4700 rpm"--------------------
How did that happen, that we are translating same bible from Rotax so different!!!??? Who is right and who is wrong here ???
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by Eugene Klimenko » 6 years ago
This is all I can find in my biblefullsizeoutput_15a2.jpeg (You do not have access to download this file.)
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