How many clicks, lean mix to full rich, etc?

[Human Drone]

Esteeeeeemed fellow aviators:

I'm learning more about setting up my Saitek X-52 with all it's buttosnand slides and wheels and such, and it has occurred to me that the thumb slide on the throttle would be a great place to put the mixture (I know, just fly auto mixture!). But in the Saitek profile editor I have to split the range into bands, or something, in order to do this... Hmm wait, maybe this won't work... It'd have to be CTRL+ going rich and CTRL- going lean... dang. There should be a way to do this, but maybe I'm limited by the keyboard interface the original programmers were limited by.

I was going to ask how many CTRL+ or CTRL- does it take to go from full lean to full rich, and split the slide into that many bands, but I don't think thta will work. I guess I'll go ahead and post this and see if anyone has any better ideas. Same idea was going to be applied to prop pitch...

Anyway, thanks all, for your time.

Tom

 

[hairyspin]

I was going to ask how many CTRL+ or CTRL- does it take to go from full lean to full rich, and split the slide into that many bands, but I don't think thta will work. I guess I'll go ahead and post this and see if anyone has any better ideas. Same idea was going to be applied to prop pitch...

I'm not sure about this, I think CFS3 lets you set prop rpm, not pitch, simulating a constant-speed propellor unit. It's a pity because I fondly remember the AvHistory RealityX extensions for CFS2 where prop pitch was adjustable. It's useful for early war aircraft as well as long-range missions in Japanese carrier-launched aircraft: reduce throttle a fair bit (and so slow down), set pitch fully coarse and watch your cruising speed climb again without guzzling fuel.

 

[Human Drone]

Thanks, Harry, but the entry in the CFS3.xca file expressly says PROP_PITCH_INCR (or _DECR) for Shift+/-, respectively. I've never messed with it, but I keep trying to learn more about it. You just helped me learn about how prop pitch works!

Tom

 

[Human Drone]

I CAN put my mixture on a slider! But prop rpm?!

Here is an update and a question.

You CAN put your mixture on a slider with the X52 (or, I suppose, any joystick that had such a device). It's done once you in CFS3, from the main menu, Controls, and you scrolll down to "Mixture Axis" and then "add Assignment" and slide your slider until it's recognized. I haven't had a chance to try out that assignment yet as to how it will work out, but one part of me is thinking, "Fantastic! Better immersion!" and the other part of me is thinking, "Great... you get shot to pieces most of the time as it is, and now you're giving yourself MORE to keep an eye on...!"

So as to the prop, you CAN put your prop pitch on a slider or other continuous type of control as well in the same manner. And if I recall (rough weekend), there are prop rpm settings as well. Whether they actually work, I can't comment.

But finally my question: Variable prop pitch I can understand, but I've never heard of variable prop rpm. I always figured prop rpm was engine rpm, as shown by your tach. How would that be accomplished, some sort of hydrostatic fluid coupling like my tractor drive?

Best,

Tom

 

[hairyspin]

Constant speed propellor

If you have an engine rpm gauge in the VC, try altering throttle and watch what happens to the engine revs. Then try altering prop revs with shift-minus or shift-plus on the main keyboard and try it again.

 

[greycap.raf]

I did a short test yesterday after reading this thread, I wanted to know how the rpm decrease affects speed. The result was that when flying at, say, 70% throttle and 2750 rpm (a Spitfire XIV was used for the test) the cruising speed was X but I could reduce the rpm by quite a few hundred rpm without affecting the speed. I think I went as low as 2250 rpm and the aircraft was still cruising at the same speed but consuming slightly less fuel.

Then again it would be possible to dig into the air file and specifically the propeller tables in such a way that under a certain rpm the propeller would automatically use a certain coarse pitch setting. The problem is that I know it can be done, I just don't know how it is done but it's probably worth trying.

 

[Human Drone]

Hairyspin, I thank you for that link, and Graycap, it sounds like there must be some implementation of a constant speed prop in our air models - I have no idea about the "under the hood" workings of CFS3, but yours is consistent with what Hairyspin's link said, at least.

Hmm, maybe a good flight dynamics guy will show up to the thread and enlighten us...

Thanks to you both,

Tom

 

[greycap.raf]

I might actually be the flight dynamics guy you're looking for.

Every air file has two propeller tables - one that defines the propeller efficiency at a certain pitch and a certain speed, and one that defines which pitch setting is used at the current speed and power setting. They're total gibberish when you first look at them but trial and error is enough to decode them to an extent, I still don't know exactly why the values are like they are but at least I know how changing them affects the aircraft's performance.

And more testing. This time with a Bf 109K-4 (one of those painted by Nigel and flight modelled by me), altitude around 2500 feet, power setting 72%. Cruising at 2800 rpm the speed was 275 mph, at 2500 rpm 280 mph and at 2250 rpm 284 mph. It seems the propeller automatically switches to a noticably more coarse setting at the revs decrease - just like it should - and that change is more than enough to counter the power loss. Looking at the estimated speeds and pitch settings in AirWrench it seems the propeller goes from 30 to 40 degrees and the fuel consumption is, although very slightly but still, decreased while the speed is increased.