posted 03-28- 02:30 AM               

While it works really well for fixed pitch props (simulated by minPitch and maxPitch set the same), variable pitch props don't sound quite right, well to me anyway.

As what often happens with these "simple" changes, it uncovers a lot of other things that need some improvement. Assuming my assumptions below are correct, it is fairly simple change, once I know the details... This is where the vast pool of expertise we call the FSIC comes in...

I assume that you can categoprise props into three categories:

1) Fixed Pitch
2) Manually variable pitch
3) Automatic variable pitch (Constant Speed Prop?)

Fixed pitch is an easy one of course, but the other two while simple on the surface need some expert help...

So, for 2), was this simple a lever or something that allows the pilot to adjust the prop pitch from min to max? Is this even real

For 3, I guess there are three factors from my reconning. a) the prop RPM, b) the prop pitch and c) the engine manifold pressure.

I have no idea about this but my thought is that the pilot controls RPM via the throttle and the prop pitch changes to stablise to a set manifold pressure. Currently in SDOE the implementation of "Constant Speed" is that the pitch works to stablise to a set RPM.

In any case, if someone knows all the details for a this prop pitch issue it would be great if you could describe it for me.

Bryan

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Wings with Wires

posted 03-28- 06:27 AM               

While I'm no expert on this, I think most of the German prop fighters had a lever or switch mounted on the throttle lever that allowed the pilot to adjust the prop pitch manually. There was even a little gauge to show what pitch was selected. This would fall into category 2 above imo.

Here's a pic showing the prop pitch indicator and the switch below:

While I have no actual photos of this, this is how the German fighters in B17II are

Also, I think most WWII prop aircraft had manual prop pitch control, though I'm not too sure of this, someone correct me if I'm wrong.

Glad someones' working on a patch, keep it up

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Visit FS:SDOE Online

posted 03-28- 06:30 AM               

One example of 3) is the Mustang in Mig Alley, where two propeller speeds can be selected, one for cruising and another for performance. My guees is that the constant RPM setting is used simply because of the characteristic of a typical engine in that it gives its peak power at a given RPM, so it's best to keep it running there by altering the prop pitch.

posted 03-28- 08:29 AM               

For a constant speed operation you would typically have two levers, a throttle and one, for want of a better term, that sets desired RPM.

Throttle works as normal, providing more engine power. the "RPM" lever sets up a governer which adjusts pitch to try and maintain the set RPM.

So, what is missing currently from the SDOE constant speed implementation is a RPM setting lever, and a manifold pressure guage (maybe that is there) to show power. The guage will probably be important since the pilot will no longer be able to determine engine power from RPM or engine noise.

Currently SDOE uses a fixed desired RPM

Does this sound like I have it understood?

Implementation wise, the following are probably needed:

inpPropPitchAnalog, inpPropPitchUpDigital, inpPropPitchDownDigital
Controls pitch directly when the prop is var pitch, and desired RPM when set to constant speed

inpToggleAutoPitch
Toggles var pitch props to constant speed to make it easier for the non-hardcore

propFixedPitch, propManualPitch, propConstantSpeed, propMinRPM, propMaxRPM
Some new properties for the CPropeller object to set the prop type and also the range of adjustable desired RPM.

Am I missing something?

BTW, sorry to the forum moderator, I should probably have started this in "Patch" or "Tech Forum" or something.

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Wings with Wires

Go here for info about the Unofficial Patch

posted 03-28- 01:30 PM               

Engine sounds that change with the RPM would really be nice, and the pitch thing too sounds like an added bonus!

BIG SMILIE TIME!!!!

posted 03-28- 01:45 PM               

The current P-51 does have a manifold pressure gauge in the cockpit and it works but i'm not sure what it's looking to go get it's readings.

On how to add the RPM control, I know Aces high did have it setup where + and - moved the throttle and shift + and shift - moved the RPMS (or blade pitch as they had it in an old version)

With this RPM stuff does this mean WEP will soon be a reality?

posted 03-28- 01:54 PM               

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1. Take-off

a) Taxi out with flaps

With the central engine at 1200 rpm and flaps at 15 degrees drive away.
Taxi out while visually observing the indicator instruments on the pilots instrumentboard (Illustration 17) .

b) Take-off with propellerautomatics

At arrival to starting point shall the plane be turned into the wind.
The fuel mixture lever shall be pushed to full forward (full load) and with the sideways movement into the brake be locked. Thereafter turn on the three switches operating the propellerautomatics also situated on the throttle quadrant. The revs should automaticly be held at a constant 2800 rpm [when throttle is adjusted]. After the liftoff automatics will deactivate when the setting 11:15 - 11:30 h is reached.

c) Take-off with manually controlled propeller pitch

If for some reason the automatics doesn't work or doesn't keep a constant 2800 rpm, then the automatics should be deactivated and the revs should be regulated by hand (with levers at the throttle quadrant). N e v e r control this by moving the mixture handles!
Under no conditions shall the revolutions exceed 2800 rpm. (Rpm instrument illustrated 17/4)

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So the conclusion is there mostly were one lever for controlling fuel-air mixture, one for the total amount of 'fuel power stuff' ie throttle, and one for prop-pitch. The last one is kinda like the gearbox (either you have good accelaration or high top speed). All three controls are used to make sure the engine runs at optimimum and that the RPM doesn't exceed the limit (in the plane discussed above the max engine rpm was 2800). As controlling all those levers in take-off or combat can be rather much work many planes had automatic systems for this while in those events (when you know you always wanted maximum effective acceleration and not for example fuel economy).

posted 03-28- 02:26 PM               

Variable pitch: the pilot sets a specific prop pitch ("coarse" means the prop is set to high AOA and will take a large bite of air--analagous to "low gear" in a car; "fine" means the prop is set to "flat" pitch and will turn at high RPM--the usual setting for takeoff and combat). The Bf-109 was, I believe, equipped with a variable-pitch prop. The pilot would probably have certain specific blade-angle settings for various phases of flight: takeoff, climb, cruise, combat, approach.

Constant-speed, controllable-pitch: the pitch on this prop can be adjusted by the pilot, (in the form of adjusting the RPM on the tach) but the prop contains a "regulator" which will then maintain the RPM set. Increasing the RPM will set the prop to a "flat" blade angle and the regulator will then hold that RPM by varying the blade angle. This was the most common form of "automatic" prop, I believe. Spits, Mustangs, Corsairs, Jugs, Hellcats all had some form of this.

"Constant-speed:" this prop is totally self-governing, and is tied into the engine mixture/fuel control system so that the "optimum" RPM and blade angle is maintained. The pilot simply controls the amount of fuel sent to the engine, and the prop sets itself. I think only the FW-190s (and maybe later 109s and things like the Ta-152) were equipped with this system.

Prop controls: the most common would be to have an RPM control and manifold pressure control. The throttle would control the manifold pressure (boost) and the prop control would set the RPM. There is typically a "max" boost associated with any given RPM setting, i.e. you normally increase RPM before increasing boost, and decrease boost before decreasing RPM, so that you don't "overboost" the engine by making it try to turn the prop faster than the prop is set to go (although some forms of WEP are in reality just overboosting).

A third power control you could add would be mixture, but this is usually set "full rich" for most of the things we do (takeoff, landing, fighting) and in a sim would be most useful only if the map is big enough to require range-maximizing measures.

If you really want to "get physical," you could set up the prop so that each blade is an airfoil like the wing, and have the blades controlled by DOFs like the ailerons. Then the prop control would actually change the blade angle, and vary the thrust of the prop, just like the flaps and ailerons vary the lift on the wings.

As for cockpit guages, the RPM guage actually works properly already, as near as I can tell. A way to check is to set the propMinPitch to a fairly high number, and then slow the plane way down. You'll get to a point where the prop can't regulate to 100% RPM (because it can't decrease its blade angle any further) and the RPM will begin to decay. We don't see that now, because all the props in the sim are set to propMinPitch = 0. Manifold pressure is really "fuel flow," so if that's monitored in the sim anywhere, great. Otherwise, manifold pressure is really "throttle position" any time the engine is running. The Corsair and (I think) the Jug are set up this way, but the rest of the planes appear to have manifold pressure as just an "on/off" indicator for the engine...

posted 03-28- 02:48 PM               

Something else i'd like to see added to this is a lowRPG fast prop. CFS2 has this and really looks great when the planes are crnaking up.

the fast prop has the same number of blades has the plane but the lowRPM fast prop has more blades to give you the effect of low RPM spin before is jumps to the normal prop. We can get the same effect now without it but you have to turn the RPMs up on the engine to anything above 3000 or more to get the effect.

But it's an effect with the normalprop model and not the smoothed model of an alpha layer.

posted 03-28- 06:07 PM               

What are the parameters for the fully automatic system? In other words, what is the constant speed prop system trying to stablise by adjusting pitch. I assume by fuel control system you mean throttle.

The code models the prop baldes as airfoils that change pitch. Not physically, I assume that there is some effeciency gained, since the majority airfoil path is around the props axis of rotation.

For a visual effect it would probably not be difficult to have a dial query of the pitch position, since there may also be a requirement for a gauge.

So anyway, what I might do is leave it as I have it, with fixed pitch, var pitch and RPM controlled constant speed. I will look into the fully automatic system a bit later.

I suspect the reason that engine sound was tied to Throttle in the first place was that the novice simmer might be a little disorientated by a generally constant engine sound. That's why I have left the engine sound as optional. Personally I like it the new way, but others might like to see some audio feedback from the engine when they change throttle setting.

Thanks for everyones feedback!

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Wings with Wires

Go here for info about the Unofficial Patch

posted 03-28- 06:38 PM               

What I remember of the sound is an increase in volume tied to the application of power, especially the low end. This is on modern aircraft, like a Cessna 152 and a coupla commercial turboprops. I know Michael implemented volume changes in R/C Sim. You might look at that code and see if it's easy to port over.

posted 03-28- 08:38 PM               

There is plenty of things that can be done to engine sound, like adding different sounds into the mix for power adjustment etc and also maybe some extra steps from idle to full power that can be interoperlated as the RPM increases, and the different enviroment sounds, but yes, wish list material at the moment

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Wings with Wires

posted 03-29- 08:52 AM               

quote:

---

Originally posted by Bryan Russell:
I assume that you can categoprise props into three categories:

1) Fixed Pitch
2) Manually variable pitch
3) Automatic variable pitch (Constant Speed Prop?)

---

Yes.

quote:

---

So, for 2), was this simple a lever or something that allows the pilot to adjust the prop pitch from min to max? Is this even real

---

Yes and yes. It's actually a Canadian invention, the first prop is sitting in the museum in Ottawa. The control was completely manual and a fairly typically meant the prop shook itself off the plane. Since everything tended to fail back then, they weren't used all that much. Planes were slow then anyway so it wasn't a huge problem.

quote:

---

For 3, I guess there are three factors from my reconning. a) the prop RPM, b) the prop pitch and c) the engine manifold pressure.

---

Yes.

quote:

---

I have no idea about this but my thought is that the pilot controls RPM via the throttle and the prop pitch changes to stablise to a set manifold pressure. Currently in SDOE the implementation of "Constant Speed" is that the pitch works to stablise to a set RPM.

---

From the pilots persepective all you do is set the manifold pressure, and set the prop to the proper pitch. In operation it's even simpler, after cleaning up you set the prop pitch so you're getting a cruise RPM (where the prop is at it's best) and then forget about it.

The advantage here is twofold, one is that reduced workload is good (thus the completely automatic system in the Fw 190), and another is that when these systems fail the prop goes to full fine, which is the landing setting.

The mechanics of the system is pretty simple. The centrifugal force of a weight on the prop is attempting to turn the prop to full fine, and oil pressure is pushing it the other way. The oil pressure is built up from the RPM of the prop, so if the prop increases in speed there's more pressure, that forces the prop to a courser pitch, and slows it back down. Control is via a valve that bleeds off some of the oil, the rate of which controls the set RPM.

Now as to the sound issue, you should remember that the sound of the engine is the sound of the exhaust manifold. That means that if the prop is 2400 RPM (rather typical) then for a V12 four-cycle you'll get three bangs prer RPM (did I do that right?) and that's a 7200Hz pitch.

Also these systems all reacted slowly to changes in power, over the space of a second. When you hit the throttle there's a brief time when the RPM does increase and this leads to a "whaaa...." sound for a second or so.

I have complete diagrams in my flight manuals, if you're interested I can scan them for you.

posted 03-29- 09:08 AM               

quote:

---

Originally posted by Bryan Russell:
inpPropPitchAnalog, inpPropPitchUpDigital, inpPropPitchDownDigital
Controls pitch directly when the prop is var pitch, and desired RPM when set to constant speed

---

One of my pet peeves about OP is that the controls are typically either "up a bit" OR "up all the way", and I always want the one they don't give me (perhaps this is something you can address?).

In this case we could also use a...

inpPropPitchFullCoarse
inpPropPitchFullFine
inpPropPitchToggle

The first two should be obvious, the last goes from one extreme to the other (if you're half way, go up).

quote:

---

Am I missing something?

---

propConstantSpeedRPMTime
propConstantSpeedRPMRate

These control how fast the system responds to changes in the RPM of the engine. The first is a constant, say 1 second, the later is a rate based on RPM, say 1 second per 1000 RPM. I don't know if the later is required.

propFailsCoarse
propFailsFine

Defines the behaviour when the constant-speed system fails. Examples of both are common. We don't really use this now, but it would be nice to have it in there so we could tie it out to the damage.

quote:

---

I will look into the fully automatic system a bit later.

---

This is easy to do, but would require some pretty odd code changes - you'd basically need a curve describing the "proper" RPM for the engine given various power loads - and it does change.

Before we do that, let's get in a altitude-power curve, this one can be handled AFTER.

posted 03-29- 09:14 AM               

I'm pretty sure SDOE has done constant speed right all along, I've just added extra inputs to control the desired RPM.

Yes, you do get the brief rise in RPM, and associatted engine noise when you push the throttle wide open.

He is were I use the standard programmers cop out with regards to the engine pitch; The code modifys the supplied engine sounds pitch by a constant amount, base on the RPM of the engine, its up to the plane builder to make sure the wav file has the right sound to match their aircraft

BTW, this stuff is now availiable in the 1.5.2.6 patch so you can check it out for yourselves...

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Wings with Wires

posted 03-29- 05:49 PM               

I would submit that the current modeling is probably pretty close to what was on the 190.

For the other two systems, you need to model a system where the pilot can adjust RPM, and then the sim will maintain that RPM by varying blade angle, and a system where the pilot can set pitch (or RPM) and the sim will NOT maintain the RPM, but leaves the prop "fixed" at that blade angle until the pilot changes it (in which case the RPM will vary with airspeed).

As for "noise," I hear guys say all the time that a constant speed prop maintains a constant noise level as speed changes. This is not necessarily true in all cases. If you dive the aircraft, the prop will attempt to speed up, but the regulator will then increase the blade angle to maintain the set RPM. This blade angle change MAY indeed produce a sound change. Similarly, adding power via the throttle will increase engine noise, and diving will increase wind noise (which often "blends" with the prop/engine noise).

In my experience, from the cockpit, the noises you actually are aware of are the engine noise, which you control with the throttle, and the wind, which depends on the speed. Also, every plane I've flown has a very distinct wind noise produced by lowering the gear. No sim has ever added this. I don't think I've EVER heard a "gear machinery" noise from inside the plane. What you CAN hear is a fairly loud wind noise (sounds kinda like jet exhaust, but quieter).

Unless it's a Stuka I guess, in which case there's another noise that takes over