Pitts and Extra constant speed prop behavior

[wnt2fly2001]

First off let me say, great sim !!!! I have always dreamed of owning a Pitts Special and until I hit the lottery, this is going to be the closest I get to having one The virtual cockpit, interior and exterior textures, dynamic shadows, all make it feel like I am sitting in the real thing.

Having never flown a constant speed prop aircraft in real life though, I do have a question on the behavior of the prop rpm with various throttle settings. I hate to compare this sim to either FSX or X-Plane, but in those when the throttle is reduced to lower m.p. settings, the prop rpm shows an almost instantaneous reduction as well. What I am seeing in Aerofly though is that even pulling the throttle back to idle, it takes some time before the prop rpm decreases, almost as if the airspeed is keeping the rpm's high. Even in a vertical dive after a hammerhead, the engine noise/prop rpm increases as the airspeed does, even though I'm leaving the throttle at idle. It seems strange to be in the traffic pattern at 15 in. manifold pressure and to hear the engine sounding like it's at full throttle and see the rpm still at 2700.

Is there any way to adjust this?

Looking forward to seeing what this sim does in the future!

Darrell

[J.Schweigler]

Hi Darrell,

The behavior itself is absolutely correct. Or better the way it works. But the physics behind are not 100% right, wich makes it difficult to set up the prop as it should be. Let me explain:

Constant speed prop means that a governor tries to hold the desired prop RPM what ever you do using a variable pitch of the prop blades. If you open or close the throttle, the propeller will work it out. Normally when you're on the ground with engine idle, the prop is in its full fine position. -Minimum pitch, wich basicly allowes a very high RPM. Now when throtteling up, the prop will reach the RPM you set up. Normally you can throttle up completely on the ground standing still and the prop will reach the full RPM at full throttle. Now the plane begins to move and gains airspeed. A fixed pitch prop like the Robin has, would speed up now. Not a constant speed. So while increasing airspeed, the prop will increase blade pitch.

Now in cruise flight, you have a rather high blade pitch. If you throttle down now, the blade pitch will decrease, because the governor tries to hold the RPM. So up to a certain point, the RPM will be the same as before.
As soon as the air is not able to windmill the prop fast enough anymore, the RPM will drop.

We have a little problem in the physics here, wich causes a problem between the airspeed wich is still able to windmill the prop at full RPM and the full fine position of the prop blades to reach full RPM on the ground.
We will look over this in future.

There is another issue in there: Sound! FSX sound engine is crap, because it generates the sound via engine power. I don't know the X-Plane sound engine. But you must generate sound by RPM and power. We do it on the Extra, and it comes close to the real thing, but it is not completely right. The idle sound with high RPMs basicly sounds like the high RPM with full throttle, only less noisy, but in reall life there is another thing in there, maybe less bass or something, wich is not yet implemented, because it is hard to figure out, what it actually is! This gives also an impression of a wrong modeled propeller model, but alltogether it is not as wrong, as you think.

Basicly it is a very good simulation of a constant speed prop already. It only needs a last bit of tuning ;-)

BTW do you know the option to controll the RPM? As a tip: fly the Extra at 2500RPM @ 25ingh in aerobatics, and 2300@23 in cruise. 2700 and full throttle is only used for take off or really hard maneuvers.

Best regards, Joachim

[wnt2fly2001]

Hi Joachim, thanks for that detailed response. I understand just the "basics" of how a constant speed prop works, and as I said, I have no "real world" experience in dealing with them. Truthfully, I have not flown the Extra in Aerofly more than a couple of flights, as that takes time away from me enjoying the Pitts but I will try it out and listen for what you are talking about and use the power settings you suggested. Usually in the Pitts I'm at 2700/25, or sometimes 2500/25 for acro and try to fly the traffic patterns around 2500/15.

Thanks again!
Darrell

[J.Schweigler]

2700 is too high for the pitts as well. Try the same settings as for the Extra. It should be a good start.

[wnt2fly2001]

2700 is too high for the pitts as well. Try the same settings as for the Extra. It should be a good start.

Tried 2500/25 in the Pitts, MUCH better !!!

Are there any plans in future versions to introduce the capability to shut the engine down and open the canopy? I like to "get out" of my plane after a nice flight and admire it with the engine shut off !

Darrell