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Karbonkid

Member
ok, not sure why I am second guessing myself on this but figure there are many with answers here.

When you fly at 2400 RPM full rich will you fly slower than you will at 2400 leaned for max power?

some reason I feel there is more to this than 2400 puts x ammt of power to the air which makes y speed.... but I may be off
 
Leaning

Fuel injection will definitely gain a couple knots at best power. Carb depends on the individual setup. A pressure carb has no significant change at low altitude. Float carb depends on the individual setup. Most POH's call for leaning for takeoff above 4-5000', again this may not hold true for some unique installations.
 
Karbonkid said:
ok, not sure why I am second guessing myself on this but figure there are many with answers here.

When you fly at 2400 RPM full rich will you fly slower than you will at 2400 leaned for max power?

some reason I feel there is more to this than 2400 puts x ammt of power to the air which makes y speed.... but I may be off
Click to expand...

It's not called "Best Power" for no reason :)
 
2,400 RPM...fixed pitch prop...same speed no matter what the mixture (all else being equal).

2,400 RPM...constant speed prop...more power=more speed. If leaning gets you more power, speed will increase because the propeller pitch will increase. (all else being equal).
 
At 2,300 RPM, I can see 10 KIAS, 10 Kts Ground Speed change with only a mixture change. The mixture change cost me 1.5 GPH fuel flow for the extra fuel burn to get 10 Knots.

Best Power mixture or Best Economy mixture is what I typically run.

Full Rich and Max Power can be the same thing at standard sea level but at altitude, Full Rich may be less power than Max Power mixture setting. The answer to your question depends on altitude.
 
If you lean towards best power in the climb, you can see the climb rate go up. Watch CHT of course.
 
With a FP prop, starting at 2400 RPM, the RPM's will increase as the plane accelerates with leaning because you are producing more power.

Full rich is too rich, thus you are not optimizing your fuel to air ratio for maximum power. Leaning it to the proper stoichiometric mixture ratio produces the best power. However, depending on your CHT's you might want to run it a little rich to keep your temps down.
 
Study this graph, the answers are all there including many to questions you have not asked.

Landmarksgraph_zpsbfb07cbb.gif
(Courtesy Advanced Pilot Seminars)

At around 75dF ROP is where the "peak power" is found, and while you can fly there for periods of time at high power settings, without destroying or causing significant harm that is not what the maker intended. And hence you have a mixture knob.

If you want to get the most out of your engine while maintaining stress levels on the engine (induced from Internal Cylinder Pressure ICP) then use the appropriate amount either LOP or ROP as your mission requires.

Take a look here at this interactive. http://www.advancedpilot.com/redbox.html
 
rjbob said:
2,400 RPM...fixed pitch prop...same speed no matter what the mixture (all else being equal).

2,400 RPM...constant speed prop...more power=more speed. If leaning gets you more power, speed will increase because the propeller pitch will increase. (all else being equal).
Click to expand...

Agree totally.
 
Because the rpm changed. Mike was agreeing with the post that said, for a fixed pitch prop at a single fixed rpm, the mixture setting has no effect on airspeed. Yes, by leaning for max power you can get a higher rpm, and thus a higher airspeed, but that was not the point.
 
Sorry, missed that detail. Not interested in a fixed vs. CS prop discussion.
I like to think Klaus had something to say about that, on similar HP at Reno this year. But I may be mistaken. Wouldn't be the first time....
 
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N941WR said:
With a FP prop, starting at 2400 RPM, the RPM's will increase as the plane accelerates with leaning because you are producing more power.

Full rich is too rich, thus you are not optimizing your fuel to air ratio for maximum power. Leaning it to the proper stoichiometric mixture ratio produces the best power. However, depending on your CHT's you might want to run it a little rich to keep your temps down.
Click to expand...

As a learning point, stochiometric mixture is representative of best economy and is fixed at 14.7:1 air to fuel mixture. Best power is in the 12.5 - 13:1 range. It is really an automotive term that I rarely see in aviation. It requires a sensor in the exhaust to measure. While I have one in all my hot rods, I have never seen one in an airplane. EGT is a similar method, more directly related to mixture efficiency. Auto's don't typically use it, as fuel air ratio is a better measurement eventhough it is indirectly related to efficiency. This is mostly to help deal with detonation margins and is based upon standard assumptions of how fuel air ratios relates to mixture efficiency.

Larry
 
flyingriki said:
Sorry, missed that detail. Not interested in a fixed vs. CS prop discussion.
I like to think Klaus had something to say about that, on similar HP at Reno this year. But I may be mistaken. Wouldn't be the first time....
Click to expand...

Mike's got it (of course…shmart engine/powerplant feller, he is!)…in a FP, it seems leaning for best RPM = leaning for best power, or sump'n close to it. It's those up and downdrafts during leaning that drive me batty, thus a CS is my pref (and I'm kiddin' around…not starting a debate!).

Klaus showed his prowess at HP pro-duction &drag re-duction...and prop selection and RPM were factors. He's good at it too! I qualled right behind him, and watched him cut a pylon on Lap 1 of our first heat. It was the closest to him I got all week. He was penalized 12 seconds on the cut, but after the cut, he also managed to build a 13 second lead on me…which kept me behind him, and him pulling away all week…all doggone week! ;)

If you nail the FP prop just right, it can be mighty fast…or a mighty good climber! It's nailing it that is the science…and art!

lr172 said:
As a learning point, stochiometric mixture is representative of best economy and is fixed at 14.7:1 air to fuel mixture. Best power is in the 12.5 - 13:1 range. It is really an automotive term that I rarely see in aviation. It requires a sensor in the exhaust to measure. While I have one in all my hot rods, I have never seen one in an airplane. EGT is a similar method, more directly related to mixture efficiency. Auto's don't typically use it, as fuel air ratio is a better measurement eventhough it is indirectly related to efficiency. This is mostly to help deal with detonation margins and is based upon standard assumptions of how fuel air ratios relates to mixture efficiency.

Larry
Click to expand...

There are guys using O2 sensors in various race and non-race aircraft. They have to change the sensors often due to the lead, but its a system that looks promising for truly finding best power, or best economy.

David's chart is a good one too. Playing with the red knob up high on X-C's really shows the relationship of CHTs, EGTs and FF…and speed. Looks a lot like that graph!

Cheers,
Bob
 
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Most guys running alt (automotive) engines use O2 sensors, and don't have to replace them as often because they also run mogas. (win-win-win)

:)
 
flyingriki said:
Sorry, missed that detail. Not interested in a fixed vs. CS prop discussion.
I like to think Klaus had something to say about that, on similar HP at Reno this year. But I may be mistaken. Wouldn't be the first time....
Click to expand...

I wasn't starting an FP/CS discussion. I was merely pointing out that your original question has a different answer depending on whether you have a fixed pitch or a constant speed prop.

Bottom line...if one makes a fixed pitch prop spin faster, the speed will increase.

If the RPM remains constant, regardless of any mixture control change, the speed will remain the same.
 
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