I thought I knew what prop RPM was for but at this point I'm at a loss as to when I should increase it, when I should decrease it (with respect to speed, altitude, power, situations). If someone could clarify, I would appreciate it.Thank you,Jas

Well, as a start, you could run the various checklists which will tell you what RPM to set.Hook

I am not that knowledgeable on the "proper" use of propeller rpm in an airplane, I am sure someone will come along and explain it in much better detail.What I have found by trial and error, when I fly with power, I adjust the prop rpm to where it just " sounds right" to me. Full power and I want to go as fast as I can, I crank in full rpm.When low power and descending, I reduce rpm to help reduce speed - watch what happens with your speed as at lower power when you reduce rpm, it will help slow the aircraft down.And when landing, on final I will reduce it a little more to again, help slow the aircraft more - if I get a little too slow, I will crank a little more rpm in, rather than nudging up the throttle.As I cross the runway threshold, pull to idle, and start my flare, I turn down to min rpm on the prop. Seems to help the plane settle in for a smooth touchdown.Again, this may be way wrong compared to appropriate procedures for the prop rpm, just what I have found myself doing now that I have it mapped to a rotary on my throttle and have been playing around with it.Hope something in there helps,

Thank you for the replies. I'm aware of the checklists and I have run through them but my point was that adjusting RPM doesn't seem to do much other than change the pitch of the blades chopping the air. No real noticeable change in speed.

Thank you for the replies. I'm aware of the checklists and I have run through them but my point was that adjusting RPM doesn't seem to do much other than change the pitch of the blades chopping the air. No real noticeable change in speed.

Play with it some more I think you will see it actually does change the speed.Get straight and level at a cruise speed, go to full rpm for a few moments, then start cranking it down whilst watching your speed.I also really see it as mentioned when I am slow and landing.Also of course, you need to be in a plane that has a variable rpm propeller.I am thinking the Icon does not.

The general idea behind the prop control is tourque control like the gears in your car. You take off and climb with full prop for maximum tourque. Then lower the prop for the cruise phase of the flight to minimize fuel flow and engine wear. Approach and Final use full prop for as much tourque as possible in case of an emergency when the need for maximum power may be required such as a botched final where a go around would be needed.Try this, takeoff with full prop. Then, try it again with 25% or 50% prop. You should notice a difference, it's like pulling away in 4th gear in a car.Ian.

What I'd usually do in the RV (the real one). Takeoff with prop knob full forward. Engine revs to 2700 rpm, as set by the prop governor. If there is a lot of houses underneath, I can pull it back a 100 rpm...........as the RV has plenty of power. My C/S prop has a prop restriction of 2000-2250 rpm. For cruise, I'd usually pull it back between 2300-2350. It's quieter that way. And then I just leave it, unless I want to climb. To climb, I pull back on the stick, while pushing the prop lever forward for a higher rpm, and then add more throttle, if it isn't at full already. As for coming into the pattern, I can just leave the prop at 2350 rpms. It still slows the aircraft easily, as if it's an air brake. You don't push full forward, until the throttle has been pulled back, and you're on final. If you push the prop to high rpms too early, it's like down shifting to too low a gear on a car or motorcycle. The engine really revs up, and you get thrown forward against the seat belt. The engine doesn't like it! If you forget to push the prop forward on the landing..............you'll notice that it's lacking some power if doing a touch and go. I've done that, and probably just about everyone with a C/S has. Just push the knob forward, and it's back to normal.edit: a couple of notes: The constant speed prop is real valuable when flying in higher altitude mountain country. They allow the engine to rev to full horsepower. They also act as a wonderful speed brake. A fixed pitch prop is always a compromise. It can either be pitched for takeoff power, or a fast cruise...............but is usually pitched somewhere between. The C/S is also usually quieter, as you can pull back the rpms.One more note: Unlike a car, to go the fastest.....................the prop knob will be full forward, or just a bit back, My RV does it's best at around 2625 rpm.L.Adamson

Like others have mentioned the variable speed prop is more for fuel efficiency and engine wear and tear which is virtually useless in a sim, and totally useless in Flight. In the better pay wares for FSX (J41 or Turbine Duke and others) it does make a difference, but in Flight there's no real reason not to leave it at full forward all the time.

Hi All,As Stated above, Constant speed propellers and correlated RPM handle are to be considered as a car shift gear.The general principle is the following:

• High RPM gives you max respons from the engine like in 1st gear. When increasing/decreasing throttle, speed will increase / decrease more rapidely.You can also compare it to a screw with a small pitch, when you turn it into wood for one round it will not go very deep into the wood, a high pitch screw will go much deeper into wood in one turn.
• Low RPM gives you slower respons from the engine like in 5th gear.

Mean reason for this is when at high TAS (in cruise) you need your popeller to rotate at a lower rate otherwise, the addition of propeller rotation speed and TAS of the aircraft can lead to reach speed of sound at propeller blade tip which leads to heavy shockwaves on propeller blades and engine crank shaft.

Rule of thumb to use a constant speed propeller on a normally aspirated engine (no Turbo):

• take off : High RPM full throttle (MAP)
• After take off (+/- 400 ft AGL if no obstacle to clear) reduce to climb power which is MAP 25' and 2500 RPM ajuste speed for best climb rate or best climb angle.
• When reaching level flight: upon the speed you want to fly, select a power setting: 85%, 75%, 65% are usually used. These power settings can be achieved by selecting a couple MAP/RPMUsually Normal aspirated engines feel better between 6000-8000 ft for cruise depending on temperature.
  • 85% stay at MAP25' and RPM 2500 (setting called 25/25) gives you highest airspeed in cruise but also highest fuel consumption. This power setting is also known as high speed cruise.
  • 75% reduce to MAP 24' and RPM 2400 (setting called 24/24) gives you a fair airspeed and normal fuel consumption. This power setting is also known as normal cruise.
  • 65% reduce to MAP 23' and RPM 2300 (setting called 23/23) gives you a low airspeed but will save your fuel. This power setting is also known as long range cruise.

  [*]Don't forget to lean your engine when climbing as air becomes thiner with altitude, you need to decrease the amount of fuel in the mixture fuel /air in the carburator. To control the correct setting of your mixture control, use a EGT gauge (Exhaust gas Temperature) lean up to peak EGT then enrich a bit one graduation or use the MAP indicator lean your mixture util MAP decrease then re-enrich mixture for about one inch in mouvement of the mixture lever.[*]Don't forget to ALWAYS move your levers in the following order:

  • Increasing power: Mixture, Propeller, Throttle
  • Decreasing power: Throttle, Propeller, Mixture

  [*]Descent: when starting descent try to throttle back very easy to avoid thermal shocks to the engine. Same for the mixture, do not re-enrich to fast to avoid thermal shocks. When descending TAS will increase and MAP will too, search for a setting close to what you had in cruise.[*]Approach: Put Mixture full rich. Keep you propeller to your cruise setting adjust speed with throttle and aircraft pitch.[*]Final approach and landing: Put slowly propeller to high RMP verify Mixture full rich, adjust speed with aircraft pitch and descent with thottle. Be prepared for go-around.

Note: This a very brief summary on how to handle a constant speed propeller, don't shoot at me if it is not exactly what should be done in a RW aircraft.

hope this will help

Amedee

Like others have mentioned the variable speed prop is more for fuel efficiency and engine wear and tear which is virtually useless in a sim, and totally useless in Flight.In the better pay wares for FSX (J41 or Turbine Duke and others) it does make a difference, but in Flight there's no real reason not to leave it at full forward all the time.

Well unless you want to maximize the range you can get out of your fuel load of course.

Like others have mentioned the variable speed prop is more for fuel efficiency and engine wear and tear which is virtually useless in a sim, and totally useless in Flight.In the better pay wares for FSX (J41 or Turbine Duke and others) it does make a difference, but in Flight there's no real reason not to leave it at full forward all the time.

As mentioned earlier I probably am not doing it correctly per se, however I do find it helps on landing during final, and flaring for touchdown by reducing rpm, sometimes I will pull it all the way back.Someone mentioned leaving it on full, for instance if a touch and go is needed - I agree one would need full rpm in that instance, the rotary I have it mapped to on my throttle is very easy for me to move with my thumb, and have done touch and gos in that manner.Perhaps eventually I will get to where I just leave it on full once again as I used to, who knows... enjoying playing around with it though - sound effects from it are really good as well.

In a previous thread you mentioned you use prop RPM for approach and landing to control your speed, When i did my CPL, that was a big issue, You should have it in full when landing in case of a GO-around is needed, And as you said your thumb is close to the lever so its not a problem, But IRL it is super easy to forget something as small as throwing th prop to full if a go-around is needed, how do I know......I've done it while float flying in college, and let me tell you, i landed on the water for a touch and go, put full throttle, the craft didnt respond how it was suppose to, it was actually kind of a scary thig, till i figured out my prop rpm wasnt in full.Again, I know this is a sim and you wont bite the big one doing it your way, but IRL your instructor would be all over you for doing it the way you are.P.S also, little story on going from the standad throttle and mixture, to adding a prop rpm lever, In my college days doing my floats, i was coming in to dock, when you get close to the dock we would pulll the mixture the engine would die, and coast it to the dock, well, my first solo coming in, i pulled the prop rpm lever instead of the mixture, waiting for the engine to quit(which never did), let me tell you, i hit the dock at a good clip, didnt damage anything other then the tire that was hanging on the side of the dock for a cushion, but just shows you how something as small as adding a third lever can play with your mind. So moral of that story, if you put your Prop RPM to full on final as the checklist says, you will always have power for your go around shoudl another aircraft get in your way. muahahahahaha

Like others have mentioned the variable speed prop is more for fuel efficiency and engine wear and tear which is virtually useless in a sim, and totally useless in Flight.

That is not a true statement at all.I reduce my RV-6A's prop rpm to slow down on descents, until I'm slow enough to lower my flaps (this was recommended to me by a real RV pilot).After I have slowed down and have my flaps lowered, I crank the prop rpms back up.

Yes arwen, I actually do that too, I just mean nothing is going to break or wear out, nor do you HAVE to reduce the prop speed to slow down, :)Amedee- best post I've ever seen on the variable speed prop!

Don't forget to ALWAYS move your levers in the following order:Increasing power: Mixture, Propeller, ThrottleDecreasing power: Throttle, Propeller, MixtureDescent: when starting descent try to throttle back very easy to avoid thermal shocks to the engine. Same for the mixture, do not re-enrich to fast to avoid thermal shocks. When descending TAS will increase and MAP will too, search for a setting close to what you had in cruise.Approach: Put Mixture full rich. Keep you propeller to your cruise setting adjust speed with throttle and aircraft pitch.Final approach and landing: Put slowly propeller to high RMP verify Mixture full rich, adjust speed with aircraft pitch and descent with thottle. Be prepared for go-around.

A few clarifications. Depending on the situation, many pilots will leave throttle at full, and just decrease RPMs. At high altitude airports, unless your airplane is turbocharged, you won't go to full rich for takeoffs or landings. You can usually find this in the manufacturers POH, but not always on a checklist, especially if the airport is at a low altitude. The only time I'm full rich at my 4607' airport, is for engine start. I lean right after start, and readjust for takeoff. Running rich, fouls the sparkplugs and decreases performance. 3000' msl + density altitude, is the time to really start thinking about the leaning process. And for a different discussion, there is running ROP & LOP.