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XyZspineZyX
09-25-2003, 07:17 PM
Two separate issues which I've found during the course of playing FB and preparing an aticle on CEM.

1. From Hurri 2 manual max boost at sea-level was +16 psi in S ratio (2nd s/charger gear) and +14 psi in M ratio (1st s/charger gear). These levels were achieved by operating the 'boost control cut-out' (WEP in game terms). The boost control normally limited boost to +12 psi for normal operation, but cutting it out allowed the full boost being developed by the supercharger to be delivered to the engine. FB 1.0 achieved both these boost levels. In 1.11 M ratio is correct, but in S ratio boost remains at +12 psi. The only indication on the gauges is a kick on the MAP needle when WEP is deselected. It seems WEP in 2nd gear is disabled. Otherwise FB engine specs are remarkable like figs from the manual.

2. With throttle closed (so next to no fuel passing through engine) and 'low pitch' or high rpm demanded on prop speed control, deceleration should be marked, because the CSU must fine the blade angle so that the airflow drives the prop (like a windmill) in order to maintain the high rpm. This creates more drag than running the prop at a lower rpm. However, in FB deceleration is hardly noticeable and you have to reduce prop rpm to get any real deceleration. Yet reducing rpm ought to give less drag! Anyway, it's not just my theory, this prop braking thing; here's a couple of quotes:

"...you could close the throttle and you'd feel yourself sliding through the air. If you wanted to slow up, you had to put the propeller in fine pitch, which acted sort of like a brake." From an American Spitfire pilot. (this was originally posted by someone around here in another context and I copied it at the time)

"For landing, fine pitch or high RPM is desired as it adds drag and shortens the landing run. It also ensures that full power is available by increasing the throttle, should it be needed as in the case of a go-around." This is from the Target Rabaul engine management notes. Interestingly their sim shows the same fault as FB! In my one and only test flight, I could not slow the Zeke enough to land at hi rpm and zero throttle, but had to drop the rpm too before I could slow down.

[I notice that MAP does not drop at all when the throttle is closed at moderate speed, which may be why the airflow is not needed to drive the prop. What is happening here?]

Apologies if these have been noted before, but I've not seen them. A little surprised no one has noted the second point before. Or is this the big reason why 'CEM is all porked dude?' As always, I'd welcome any correction to my ideas from anyone more technically competent /i/smilies/16x16_smiley-wink.gif

Point 1 is pretty small in the grand scheme of things, although it does mean the Hurri has slightly less power available at max combat settings.

Point 2 seems pretty fundamental to the whole engine management game.

Kernow
249 IAP

XyZspineZyX
09-25-2003, 07:17 PM
Two separate issues which I've found during the course of playing FB and preparing an aticle on CEM.

1. From Hurri 2 manual max boost at sea-level was +16 psi in S ratio (2nd s/charger gear) and +14 psi in M ratio (1st s/charger gear). These levels were achieved by operating the 'boost control cut-out' (WEP in game terms). The boost control normally limited boost to +12 psi for normal operation, but cutting it out allowed the full boost being developed by the supercharger to be delivered to the engine. FB 1.0 achieved both these boost levels. In 1.11 M ratio is correct, but in S ratio boost remains at +12 psi. The only indication on the gauges is a kick on the MAP needle when WEP is deselected. It seems WEP in 2nd gear is disabled. Otherwise FB engine specs are remarkable like figs from the manual.

2. With throttle closed (so next to no fuel passing through engine) and 'low pitch' or high rpm demanded on prop speed control, deceleration should be marked, because the CSU must fine the blade angle so that the airflow drives the prop (like a windmill) in order to maintain the high rpm. This creates more drag than running the prop at a lower rpm. However, in FB deceleration is hardly noticeable and you have to reduce prop rpm to get any real deceleration. Yet reducing rpm ought to give less drag! Anyway, it's not just my theory, this prop braking thing; here's a couple of quotes:

"...you could close the throttle and you'd feel yourself sliding through the air. If you wanted to slow up, you had to put the propeller in fine pitch, which acted sort of like a brake." From an American Spitfire pilot. (this was originally posted by someone around here in another context and I copied it at the time)

"For landing, fine pitch or high RPM is desired as it adds drag and shortens the landing run. It also ensures that full power is available by increasing the throttle, should it be needed as in the case of a go-around." This is from the Target Rabaul engine management notes. Interestingly their sim shows the same fault as FB! In my one and only test flight, I could not slow the Zeke enough to land at hi rpm and zero throttle, but had to drop the rpm too before I could slow down.

[I notice that MAP does not drop at all when the throttle is closed at moderate speed, which may be why the airflow is not needed to drive the prop. What is happening here?]

Apologies if these have been noted before, but I've not seen them. A little surprised no one has noted the second point before. Or is this the big reason why 'CEM is all porked dude?' As always, I'd welcome any correction to my ideas from anyone more technically competent /i/smilies/16x16_smiley-wink.gif

Point 1 is pretty small in the grand scheme of things, although it does mean the Hurri has slightly less power available at max combat settings.

Point 2 seems pretty fundamental to the whole engine management game.

Kernow
249 IAP

XyZspineZyX
09-25-2003, 09:24 PM
Well, I'll bite, though I am most probably not more technically minded, hopefully someone can explain this to everyone's satisfaction. But regarding Prop Pitch, I do not disagree that 'Full Fine' pitch should give some 'braking' effect (the amount is arguable by anyone of course, how to determine?), and this is evident (IMHO) on all model Bf109's on manual pitch, and 'fining' the prop pitch (higher percentage of FB HUD, 100% for example). So surely you'll agree that it works on non-CSP variable pitch props (Bf109 series).

Now, regarding constant speed props (which I believe you are refering to), in which the prop pitch is not directly adjustable (at least in FB, and most CSP systems of the era, though some may have had 'manual' control) when the pilot cuts throttle (MAP) at a reasonably high rate of speed (300kph+) the Constant Speed Governor does Not get a call for higher RPM's due to the aircraft momentum still pushing it through the air, and thus windmilling the prop (RPMs). So the CSP Governor remains in a less than full fine state, resulting in less drag and less 'braking' effect felt by pilot. I believe the effect can be seen (I have noted it in my normal ride, the FW190, which is a CSP With a prop pitch guage), when the aircraft begins to slow down (300 and below), the prop pitch Does begin to 'fine' in order to maintain a given RPM, but it is unable; at this time the 'braking' effect can be noticed.

Don't get me wrong, I'm not an expert, this is just how I explain it to myself in the game, and I'm sure the FB also cannot model Every subtlety (what simulation could?), though its interesting Targetware has similar results.

I have a very poor grasp of the complexities of Manifold Pressure and how it relates to aircraft engines. I believe a gentleman named FlightVector once gave some great information on this very subject, but obviously it didn't sink in because I'm still using my same arguement (correct or not, I'm not sure).

XyZspineZyX
09-25-2003, 11:12 PM
Thanks for the reply Lignite. Yes, the 109s are different and you certainly get the rapid revving to destruction if you have too fine a pitch for the TAS. I can't say I've noticed more deceleration in those cases, (too worried about other things!) but it would seem probable.

...............V
...............V
...............V
...............V
...............V
>>>>>>>>

Imagine the 'triangle of velocities' at a point on the prop blade. The Vs are represent the oncoming airflow (TAS) for a prop moving up the page. The >s are the rotation of the prop, to the right. So the airflow relative to the prop comes from the top V to the left > ie about 45 degrees top right to bottom left. To provide any thrust in this condition the blade angle must be >45 degs - ~55 degs maybe. Lets say the throttle and prop speed are set fairly high. Everything is in equilibrium with power from engine driving the prop at a positive angle of attack.

We leave prop speed alone, but cut the power. Now there is not enough energy from the engine to overcome the load on the prop. That would slow it down, but the CSU fines the angle so that it is negative (to relative airflow) - ~35 degrees. Now the airflow drives the prop to maintain the rpm. As you say it windmills. However, this windmilling is the very drag that ought to slow us down. Setting a lower rpm would reguire less work out of the windmilling prop, so would produce less drag. Yet in game you slow quicker if you reduce rpm.

You are correct that it will not fully fine the angle, as you could do with a variable pitch prop, so the braking will be less, but the CSU prevents over-revving, which would otherwise be a risk. Note, in our simple example the blade is still at a fairly big 35 degrees or so.

In normal operation increasing prop speed or throttle = more power. I suspect that modelling what happens when throttle is set to ~zero, when prop speed is more related to drag than power is the problem.

Kernow
249 IAP


Message Edited on 09/26/03 03:19PM by Kernow

Message Edited on 09/26/0303:20PM by Kernow

adlabs6
09-26-2003, 12:18 AM
Point 2 above, the increase of deceleration while increasing prop angle has bothered me often. I too figured that less deceleration should occur when the prop is providing less drag. I did a test in the QMB, using an He-111, which allow prop feathering. I wanted to see if a prop past maximum pitch, or feathered would provide even more deceleration. I could not see this happening, though I do believe that the multi engined planes have a differenct behavior to engine control than single engine planes. Correct me if I'm wrong on that.

Still, when the throttle is lowered, should not the plane slow down? I have flown the P-39 in tests, and when I am flying level and close the throttle (0%), I see little deceleration, only minor RPM decrease, and the manifold pressure decreases only slightly also.

My usual technique for decending an aircraft is to close the throttle, allow the nose to fall, and I control the airspeed during decent with nose pitch.

This technique doesn't work well, at least on the P-39 in FB. It is difficult to decend at less than 200 MPH IAS even when keeping the nose only +/- 5? below the horizon. Only by increasing the nose angle to 5? or greater above the horizon can I decend at near 160 MPH IAS, such as on approach for landing. This is with the throttle fully closed and the pitch at 0%.

Surely I am no expert, and certainly not a pilot. I just have noticed that my old techniques don't seem to apply sometimes in FB.

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XyZspineZyX
09-26-2003, 03:45 AM
I always land with prop set too 100% usually throttle at about 10% to 20% and it definately slows you down I mainly fly the 109's

JG4_Tiger

adlabs6
09-26-2003, 07:38 AM
Something else I was thinking on this subject. Would not closing the throttle and having the prop windmill to near 3000RPM on the P-39 (or any plane) cause damage to the drive train from backlash?

This is of course not simulated, but still, damage would seem likely.

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XyZspineZyX
09-26-2003, 12:00 PM
Point 2, I think, would have to rely a lot more on the relative performance, compared to the planes that directly influence the RPM via pilot control.


Essentially what you have theorized is right: very small amount of fuel and air are entering the engine, but the RPM remains constant for some time - something's producing the power and it isn't the fuel. Thus, yes, throttle idle while RPM at max, will act as a brake in a sense.

But the question is, just how fast can they act up?

Obviously during the first few moments when the throttle is pulled back to idle, the CSP will adjust itself as flat as possible, to automatically retain the set RPM as long as it can. And when it can retain that rate no more, the RPM will begin to drop. But all along during that drop, the props will stay flat - because, the RPM set by the pilot is still at 100%, indicating that the system will always try to maintain as high RPM level as possible.

Yes, there will be decceleration due to the 'braking effect' of the props meeting the air, but it may not be as efficient as one thinks. Overall, "how fast the engine/prop turns", effects speed more than "at what angle the prop meets the air." If the RPM is still set to 100%, the engine will drop revolutions at a slow rate. Mandatory procedure for quick decceleration would be first pulling the throttle back gently, and then reducing the RPM also.

Compared to that, the linked system of German planes closes down the manifold at the same time, pulling the RPM to lower levels. Logically, this seems way more efficient and faster to react, when talking about decceleration.

However, it obviously takes a hit the other way around - a good example is some people's complaints on how VVS planes 'jumpstart' immediately towards the runway even at low throttle, while German planes take a looong time to taxi.

This is not because there is something wrong with the acceleration, but due to how the system works just the opposite way in this situation than presented above.

When VVS planes start their engines, their RPM rate is already set for 100% efficiency. When they push forward on the throttle 30%, it means their engine will be turning at 100% RPM possible with 30% throttle - whereas, when German planes push throttle forward, their engine will be turning 30% RPM possible at 30% throttle. German planes would have to swith to manual control, and set their RPM levels to as high as possible at 30% throttle, to achieve the same effect. (but since the CSP also becomes dead when its switched to manual, unlike VVS planes, German planes have a danger of overreving the engine)

...

So, I don't think there's anything particularly wrong with it. Maybe the decceleration rate is indeed a bit too low.. but relatively, it will always be lower than engine systems which influences both RPM and maifold control at the same time.

A good option to request for, will be the mechanical lock system for the planes that had them - like the P-47, where the RPM lever and the throttle lever was side by side, and by linking it mechanically, it sort of duplicated the effect of German systems.. although not internally, but the end effect being pretty simular - RPM and throttle control both at the same time.



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XyZspineZyX
09-26-2003, 12:21 PM
"Something else I was thinking on this subject. Would not closing the throttle and having the prop windmill to near 3000RPM on the P-39 (or any plane) cause damage to the drive train from backlash?"

Yes, that seems very likely.

I tried a quick test with the P-39s, and the windmill just stops dead at 3200~3300RPM. It increases as expected up to 3200, but then it refuses to go further than that. Maybe that's the 'breaking point', but no damages received from that.

Well, in truth, the structural failure occurs shortly after 3200 - windmilling the props up to that level itself takes a really high dive speed... so it's either the effect is modelled but we don't have a chance to see it, or it's not modelled since nobody in their sane minds would do it.

However, to my knowledge, variety of things can happen when automatic props systems are under high pressure, and it might be nice to see them modelled..(but then again, it might also be frustrating)






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XyZspineZyX
09-26-2003, 01:47 PM
adlabs6 wrote:
- Point 2 above, the increase of deceleration while
- increasing prop angle has bothered me often. I too
- figured that less deceleration should occur when the
- prop is providing less drag. I did a test in the
- QMB, using an He-111, which allow prop feathering. I
- wanted to see if a prop past maximum pitch, or
- feathered would provide even more deceleration. I
- could not see this happening, though I do believe
- that the multi engined planes have a differenct
- behavior to engine control than single engine
- planes. Correct me if I'm wrong on that.
-

I thought they were essentially the same, although only multi-engined ac can feather props (after all, they're the only ones which are still going anywhere after an engine failure /i/smilies/16x16_smiley-wink.gif ). A feathered prop is just the extreme example of coarse pitch and we all know it's used to reduce drag. I think it probably does that in game, IIRC the tests I did quite a while ago on the He-111. It follows that fine pitch should create more drag, but it doesn't seem to. (doesn't create more drag than coarse pitch I mean, not more than feathered, which it does)

Tiger & Kweassa, you're probably right that the 109 variable pitch system slows more rapidly. I also think you're probably correct, Kweassa, in thinking that as far as the game is concerned rpm & throttle determine power and the blade angle isn't considered. Indeed that would seem to explain exactly what you observe in the game.

Some other good points too. It may not be a good idea to let the airflow drive the prop excessively. Some more modern props have 'negative torque systems' to prevent the prop from being windmilled too hard, but I'm not sure what they had, if anything, in WW2. There's a red light which comes on in the P-39 if you cut the throttle at speed; I'd always wondered if this was some sort of negative torque warning light?

Kernow
249 IAP

XyZspineZyX
09-26-2003, 03:24 PM
Hi all,
regarding point 2 of the original message, I am quite sure that, in the game, the Hurries have manual pitch control, i.e. they've not constant speed (i.e., you control directly the pitch, not rpm). You can check this by varying throttle at a selected pitch, and you'll see various rpm. Don't know anyway if this can affect the reasoning.
Maybe more important, some time ago in this forum appeared links to a web site with articles concerning engine management, etc. on civil planes (can't remember the URL) by an expert pilot and in one of them he explained that (me too was surprised), due to aerodynamical reasons, biggest drag in a descent is obtained not at very fine prop angles but at intermediate angles.
Hope this can be useful to the discussion.

XyZspineZyX
09-26-2003, 04:37 PM
rosaenrico wrote:
- Hi all,
- regarding point 2 of the original message, I am
- quite sure that, in the game, the Hurries have
- manual pitch control, i.e. they've not constant
- speed (i.e., you control directly the pitch, not
- rpm). You can check this by varying throttle at a
- selected pitch, and you'll see various rpm. Don't
- know anyway if this can affect the reasoning.

Should be a CSU and I think that rpm stabilizes after momentary fluctuation when throttle is moved. If they did have manual pitch control I would probably have wrecked the engine, since I put it to 100% 'prop pitch' in combat /i/smilies/16x16_smiley-wink.gif

- ...due to aerodynamical reasons, biggest
- drag in a descent is obtained not at very fine prop
- angles but at intermediate angles.
- Hope this can be useful to the discussion.
-
-

Thanks for that Rosaenrico. That sounds correct. I didn't say that you needed a fine angle in an absolute sense; just a finer angle for max rpm. If you look at the simple diagram I used as an example the approx blade angle needed to drive the prop was still 35 degs (AOA of -10). (Starting at 55 degs (AOA of +10), as in the example, for cruising is not untypical). To take an extreme example, if the blades were flat-on to the airflow (0 deg) you would get a lot of drag, although the flow would not rotate the prop either way. By selecting an angle which gives a slight negative angle relative to the airflow (eg 35 degs relative to air coming from 45 degs) energy is extracted from the airflow to drive the prop (ie drag is created). More energy can be extracted by allowing the air to drive the prop than can be dissipated in turbulence around the flat-on prop blades. Hence, as you say, 'biggest drag in a descent is obtained not at very fine prop angles but at intermediate angles'


Kernow
249 IAP

XyZspineZyX
09-26-2003, 08:26 PM
Hi Kernow,
very clarifying reply from you http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif
I've never realised till now (done a flight to check it up just now) that Hurries actually have CSP in the game!

Well, at least from what you can see in a normal cruise;

but if i set up 100% rpm and then start diving (even at moderate rate), propeller doesn't seem able to control rpm even at the very beginning, leading very rapidly to overravving; so this not-CSP like behaviour is due to the delayed (too slow) response of the mechanism?

Thank you

XyZspineZyX
09-26-2003, 10:43 PM
Seems backwards to me. If I had prop pitch at 100% (higher rpm setting) and I wanted to slow down fast only adjusting prop or engine I would just leave the pitch at 100% and cut the throttle.

The way it is now you take it to 0% pitch and the plane almost comes to a screeching halt. Isn't 0% like feathering the prop? You'd think that would help you glide better not slow you down even faster.

adlabs6
09-26-2003, 11:30 PM
CrackFerret wrote:
- Seems backwards to me. If I had prop pitch at 100%
- (higher rpm setting) and I wanted to slow down fast
- only adjusting prop or engine I would just leave the
- pitch at 100% and cut the throttle.

That's how my previous flight sim experiences have been. It seems just to be an oddity in the CEM of some planes I guess. I don't distinctly remember this effect in FB v1.0.


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XyZspineZyX
09-26-2003, 11:31 PM
CrackFerret wrote:
- Seems backwards to me. If I had prop pitch at 100%
- (higher rpm setting) and I wanted to slow down fast
- only adjusting prop or engine I would just leave the
- pitch at 100% and cut the throttle.
-
- The way it is now you take it to 0% pitch and the
- plane almost comes to a screeching halt. Isn't 0%
- like feathering the prop? You'd think that would
- help you glide better not slow you down even faster.

Precisely CrackFerret. When you take all the technical stuff away, that's exactly what I'm saying. I felt I had to add the detailed explanation to avoid all the 'no man I think it might work differently,' or 'try turning V-synch off, blah' replies /i/smilies/16x16_smiley-wink.gif Fortunately it seems to have worked /i/smilies/16x16_smiley-happy.gif

Please could anyone 'in the know' either:

- confirm this is a known 'bug,' or

- explain how I've got it all wrong.

Having looked at other aircraft now, I'm sure it's something to do with MAP remaining virtually unchanged when the throttle is closed. This means the engine is still driving the prop despite the pilot's best efforts to take the power away.

Kernow
249 IAP

adlabs6
09-27-2003, 03:24 AM
Kernow wrote:
- Having looked at other aircraft now, I'm sure it's
- something to do with MAP remaining virtually
- unchanged when the throttle is closed. This means
- the engine is still driving the prop despite the
- pilot's best efforts to take the power away.

Indeed. My testing the P-39 showed that level cruise at 100% prop/110% power and the manifold pressure was 41 inches. Reducing the power to 0% resulted in an initial decrease in manifold pressure to 39 to 40 inches, but seconds later it had climbed back to near 41 inches. The rate of decent during this ocurrence was less than 100 feet per minute, and the airspeed did not noticably drop.

Not quite right, at least according to my information.

Another interesting bit I saw... If the prop pitch is set at 100% and the power at 0%, the manifold pressure would appear to rise as the propeller windmilled to higher RPM's. I'll have to play with this more when I have time later tonight.

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XyZspineZyX
09-27-2003, 03:33 AM
"The way it is now you take it to 0% pitch and the plane almost comes to a screeching halt. Isn't 0% like feathering the prop? You'd think that would help you glide better not slow you down even faster."

That applies only when the propellers have stopped rotating. If the props are rotating, then it is still creating thrust, thus, the rate the engine revolves is much more influential factor in managing speed, than what angle the propeller is at.

Note that the percentage numbers between 0~100% does not necessarily mean it literally - 0% 'prop pitch' does not mean that it is set to 0 RPM. It merely means the lowest possible RPM setting at the given condition. As long as the the props are still turning, it will never be 'feathered' at 0 RPM.




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adlabs6
09-27-2003, 06:32 AM
This subject got me wanting to see how several of the popular planes in FB behave. So I did some *simple* tests to see what happens when I go from 100% pitch and power and chop the throttle. Then from there what happens when you set pitch to 0%. Of course my tests aren't in any way "scientific" and they were not meant to be so. Here is a short paper I compiled this evening.

NOTICE: I AM NOT AN EXPERT ON THIS SUBJECT. I AM NOT PROPOSING THAT THESE NUMBERS ARE EITHER REALISTIC OR NOT. I AM SORRY I SHOULD NEED THIS NOTICE IN THE FIRST PLACE. /i/smilies/16x16_smiley-indifferent.gif

Anyway...

=========================
Power/RMP/Manifold pressure test by adlabs6 9/26/03

Testing process:
QMB, 2000 meters altitude, Level autopilot enabled. Each aircraft was allowed to reach speed at the beginning of each flight. This speed is the starting speed of the test, shown as 100%pitch and 100%power. A "?" means I didn't find that data. For example, I couldn't read the Russian dials to be sure which was the manifold pressure guage, if it was even present. Sorry!

Each column below shows the following information:
Aircraft name
KMH / RPM / Manifold Pressure (All airspeeds are read from the speedbar.)

Each test consists of three stages, shown in rows from top to bottom:
100% Prop Pitch & 100% Power
100% Prop Pitch & 0% Power
0% Prop Pitch & 0% Power

For each testing stage, a 15 second period was allowed for engine stabilization, at which point the sim was paused and data recorded. Timing began when the power and pitch controls reached 0%.

1)Hurricane MkIIb
370/3000/? (100% Pitch / 100% Power)
300/2900/? (100% Pitch / 0% Power; measured 15 seconds after throttle change)
260/1800/? (0% Pitch / 0% Power; measured 15 seconds after pitch change)

2)I-153P
300/2200/?
210/1500/?
190/600/?

3)I-16 Type24
370/2200/?
270/2200/?
240/900/?

4)IL2 3M '43
350/2160/?
290/1820/?
250/1400/?

5)Lagg-3 '43
420/2700/?
350/2640/?
320/1080?

6)La5FN
430/2400/?
360/2340/?
320/1080/?

7)La7 3B20
480/2400?/?
400/2340?/?
350/1200?/?
(La7 Tach is hidden behind stick, my moving the stick could have fouled readings)

8)Mig3U
450/2160/?
380/2100/?
340?940/?

9)P-39 Q10
420/3000/41
350/2900/41
310/1800/29

10)P-40M
400/3000/41
320/2900/40
290/1800/28

11)P-47 D27
430/2600/51
370/2600/51
350/1000/34

12)Yak3
490/2700/?
390/2640/?
350/1020/?

13)B-239
350/2000?/79
280/2000?/76
250/1000/55

14)Bf-109K4

Manual Pitch
260/600/0.8 (Engine dead within seconds @ 100% / 100%)
270/2500/1.4 (Spiked here...) (100% / 0%)
250/2500/1.4 (Stabilized here) (100% / 0%)
270/600/0.9 (0% / 0%)

Auto Pitch
420/2450/1.35 (100% Power)
350/800/0.9 (0% Power)

15)Fw-190 A9
420/2800/1.6
380/1100/0.85
340/900/0.85

16)Fw-190 D9
450/3000/1.4
400/1000/0.85
380/700/0.85
============================

Of all the planes I tested that I could find the manifold pressure on, only the Fw190 series behaved as I would have expected an airplane to when lowering the throttle. They seemed to reduce engine power, and RPM in each case when I lowered the throttles, and only the RPM was affected by the pitch controller. Later when I have time to retest, and identify the manifold guages, I'll see about finding if any Russian planes respond the same way.

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Message Edited on 09/27/0305:39AM by adlabs6

XyZspineZyX
09-27-2003, 09:56 AM
kweassa wrote:
- "The way it is now you take it to 0% pitch and
- the plane almost comes to a screeching halt. Isn't
- 0% like feathering the prop? You'd think that would
- help you glide better not slow you down even
- faster."
-
- That applies only when the propellers have stopped
- rotating. If the props are rotating, then it is
- still creating thrust, thus, the rate the engine
- revolves is much more influential factor in managing
- speed, than what angle the propeller is at.
-

Yes, <u>if</u> the prop is creating thrust, but the blade angle determines whether it is creating thrust or drag. The props do not necessarily create thrust just because they are rotating at a positive blade angle; they must also have a positive angle of attack relative to the oncoming airflow.

- Note that the percentage numbers between 0~100%
- does not necessarily mean it literally

Yep, for the Hurricane the propeller speed control was calibrated to 1800 rpm (min) and 3000 rpm (max)


'but if i set up 100% rpm and then start diving (even at moderate rate), propeller doesn't seem able to control rpm even at the very beginning, leading very rapidly to overravving; so this not-CSP like behaviour is due to the delayed (too slow) response of the mechanism Rosaenrico.

Yes, I've seen that too. It could be due, as you say, to sluggish CSU response. Ultimately, there are limits on the blade travel (high and low pitch 'stops') and eventually the blade can coarsen no more, at which point rpm will rise if speed increases further. Hmmm this raises another question: At this point there is no point in selecting a lower rpm (or coarser pitch) because the blade has reached the limit of its travel. But what happens in the game?? Will have to check, but I suspect rpm will respond instantly.

Kernow
249 IAP

Yes - at least for the Hurricane - I was right. Went up in QMB, got settled down at full throtle & 100% prop; put nose down and saw rpm rise; waited for it to control, but it continued to rise slowly; this appears to simulate the CSU being unable to coarsen the blade any more; however on selecting 10% pitch (ie demanding an even coarser pitch than the CSU/prop could provide) the rpm immediately dropped back drastically.

I think 'prop pitch' pretty much does what throttle used to do in IL-2, ie directly controls power output, rather than actually controls the prop. It's probably a bit more complicated because throttle also plays a part. At least for CSU equipped ac, I think FB 'prop pitch' directly controls rpm and doesn't do it via the propeller blade angle.

Message Edited on 09/27/0309:18AM by Kernow

adlabs6
09-27-2003, 03:32 PM
Kernow wrote:

- I think 'prop pitch' pretty much does what throttle
- used to do in IL-2, ie directly controls power
- output, rather than actually controls the prop.
- It's probably a bit more complicated because
- throttle also plays a part. At least for CSU
- equipped ac, I think FB 'prop pitch' directly
- controls rpm and doesn't do it via the propeller
- blade angle.

I think this is probably correct. In a P-39Q1 I tried doing a climb using recomended engine settings of 2500RPM @ 35HG. My attemps to set the HG with the throttle, then adjust the RPM were constantly thwarted! Setting 35HG with the throttle, and then winding down the RPM resulted in the plane barely being able to maintain level flight, since the engine HG was being reduce by the RPM control itself. The only way I could achieve *near* these numbers was to get the throttle on up to 70 or 80%, then adjust RPM to achieve the 2500RPM... as well as the 35HG!

Engine power was being directly controlled by the prop pitch controls.

Clearly something is wrong. It should be possible to select the desired engine power using ONLY the throttle. Small changes made to propeller RPM should certainly not effect the manifold presure. And from my experience with CEM on other sims, changing the engine power setting with throttle is fully possible while maintaining the constant propeller RPM.

Is the CEM simply nonsence? I don't understand how this could happen. It seems as though we are simply sliding the autopitch system up and down it's programmed scale manually using the pitch control, rather than individually controlling the engine and RPM. This could be correct, if the autopitch is programmed with preset RMP/power information, and we then are allowed to slide that program up and down the scale using the pitch controller. Could this explain the link between the controls?

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XyZspineZyX
09-27-2003, 06:28 PM
Dont forget about the 0 prop pitch instant engine cool exploit http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif leaving radiators closed at all times. less drag And as far as the 0 prop pitch mid air slow down people turning off thier engine in flight has the same effect then restart it right away,

but you cant slow down much by throttling back dont make much sense at all.


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XyZspineZyX
09-27-2003, 06:57 PM
You didn't read any of what we were discussing above, did you?



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XyZspineZyX
09-27-2003, 07:07 PM
Adlabs, the FW190 uses an an auto system that reduces RPM for you as you reduce 'throttle' (MAP), unless you switch it to auto (which I don't believe you did) when it acts as all the other Constant Speed Props (P47, Hurri, La5). It is actually operating as all of the other aircraft, right or wrong I don't know. It looks like they are all very consistant (which they should be, again, right or wrong I don't know).

I tend to agree there is something incorrect with the Manifold Pressure and how it is currently featured, which in turn may be effecting aircraft/prop drag amongst other things. I also think I read somewhere that the 1.2'alpha' leak has (or is intended to) change the Manifold Pressure behavior.

XyZspineZyX
09-27-2003, 07:18 PM
"Yes - at least for the Hurricane - I was right. Went up in QMB, got settled down at full throtle & 100% prop; put nose down and saw rpm rise; waited for it to control, but it continued to rise slowly; this appears to simulate the CSU being unable to coarsen the blade any more; however on selecting 10% pitch (ie demanding an even coarser pitch than the CSU/prop could provide) the rpm immediately dropped back drastically."

Frankly, I think the info we have on how FB deals with the system, or what kind of system the real planes had, is too little.

Theoretically, what you said in the quoted comment is a true oddity, but only when we assume only the prop angles control the rate of engine revolution. The 'Prop Pitch' command in FB may actually mean more than just setting the prop angle - ie. some sort of direct reduction in engine revolution may be happening through some process we are not aware of. Direct engine braking? Different gear ratios? Who knows. Were the real warplanes like that, too? That also, I have know idea of.

....

"I think 'prop pitch' pretty much does what throttle used to do in IL-2, ie directly controls power output, rather than actually controls the prop. It's probably a bit more complicated because throttle also plays a part. At least for CSU equipped ac, I think FB 'prop pitch' directly controls rpm and doesn't do it via the propeller blade angle."

I agree. That's why I started out with the comment that misconceptions are derived from the game terminology. I think the term "prop pitch" in the game is inadequate.

It should be "Prop/Engine RPM" or something, I think.


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XyZspineZyX
09-27-2003, 09:25 PM
kweassa wrote:
- "I think 'prop pitch' pretty much does what
- throttle used to do in IL-2, ie directly controls
- power output, rather than actually controls the
- prop. It's probably a bit more complicated because
- throttle also plays a part. At least for CSU
- equipped ac, I think FB 'prop pitch' directly
- controls rpm and doesn't do it via the propeller
- blade angle."
-
- I agree. That's why I started out with the comment
- that misconceptions are derived from the game
- terminology. I think the term "prop pitch" in the
- game is inadequate.
-
-
- It should be "Prop/Engine RPM" or something, I
- think.

Some have said to increase dive speed to coarsen the prop a bit. That is, they have said to do it because they seemded to think it worked for them in practice.

Also, I have found that on a shallow dive at landing, coarsening the prop actually speeds me up a bit (at 0% throttle).

The above is about the P-47 though. Not sure if it works out the same on all planes.

adlabs6
09-27-2003, 09:27 PM
ZG77_Lignite wrote:
- Adlabs, the FW190 uses an an auto system that
- reduces RPM for you as you reduce 'throttle' (MAP),
- unless you switch it to auto (which I don't believe
- you did) when it acts as all the other Constant
- Speed Props (P47, Hurri, La5). It is actually
- operating as all of the other aircraft, right or
- wrong I don't know. It looks like they are all very
- consistant (which they should be, again, right or
- wrong I don't know).


Hello,

Very sorry there, I forgot to note in my tests above that the Fw-190's were tested with the auto system disabled. This is shown clearly in stage three of the test, when I reduced the pitch setting to 0%, and the RPM decreased. In auto mode there would have been no effect from a manual pitch change.

That's why I found the very clear decrease in RPM and MAP interesting in the Fw-190's (manual mode). No other plane I tested showed that same kind of response on throttle down.

In fact, the only reason I did a test of the K4 auto system was because the manual tests were fouled by immediate engine failure. Notice there is no third test test stage on the auto tests, since pitch is not user adjustable in auto mode.

Lastly, I must have missed the 1.2 information about CEM. Hopefully there will be some positive changes, on many fronts this next time around.

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XyZspineZyX
09-27-2003, 10:34 PM
My mistake Adlabs, it appears you are correct. The FW190A (and D I guess) series does seem to model Manifold Pressure differently than the other CSP's in the game, much more like the old Il-2 through FB1.0 days (you'd think I'd have noticed this being a dedicated FW190 driver, Doh! I fly with Kommandergerat I guess).

Though I don't know exactly what it means, it is some usefull information; maybe other aircraft will be upgraded to a similar 'engine model'?

XyZspineZyX
09-27-2003, 10:44 PM
kweassa wrote:
-
-
- Frankly, I think the info we have on how FB deals
- with the system, or what kind of system the real
- planes had, is too little.
-
-
- Theoretically, what you said in the quoted comment
- is a true oddity, but only when we assume only the
- prop angles control the rate of engine revolution.
- The 'Prop Pitch' command in FB may actually mean
- more than just setting the prop angle - ie. some
- sort of direct reduction in engine revolution may be
- happening through some process we are not aware of.
- Direct engine braking? Different gear ratios? Who
- knows. Were the real warplanes like that, too? That
- also, I have know idea of.

I believe that rpm was controlled by pitch angle alone. More modern props do have other features to adjust things for unusual situations, but I'm not aware of such things in WW2. However, it would be nice if the game told us how the system works. The lack of information only reinforces the impression there's been some sort of 'fudge.'


- I agree. That's why I started out with the comment
- that misconceptions are derived from the game
- terminology. I think the term "prop pitch" in the
- game is inadequate.
-
-
- It should be "Prop/Engine RPM" or something, I
- think.

Or even 'propeller speed control' like it was called in RAF documents at least. And which is exactly what it did. Of course the German system would need a different name.

I've seen a reference to CEM/manifold pressure issues being addressed in 1.2 also. So maybe all these issues are connected to the lack of any noticeable throttle-MAP linkage in the game.

Kernow
249 IAP

XyZspineZyX
10-01-2003, 10:51 AM
Maximum propeller drag is at min throttle and max RPM. At that setting, the engine is basically acting as a large air pump, drawing power from the engine.

And no, the drive trains will not be damages as they are designed to handle it.

The Hurri indeed has a CSP. On all aircraft, the RPM will fluctuate a bit when changing power. That's how a CSP works. On some aircraft, the fluctuations might not be enough for you to notice them though.

On the ground (no forward airspeed) the prop will likely be resting on the min pitch stops throughout much of the power range (until you hit the RPM set in the CSP). Thus, power will control RPM directly. That's what enables you to do a mag check. In the air, the prop is unlikely to hit the min pitch stops even in a idle power/max RPM configuration. It would only happen in the slow end of the speed range if it does.

A CSP in a dive at full throttle will often eventually hit the maximum pitch stops of the propeller. From then on, it is effectively a fixed pitch prop, the prop governor is unable to reduce RPM and the only way to reduce RPM is to reduce power.

In Il-2:FB pre-patch, reducing the prop RPM setting reduced the RPM even in this situation. If that is still the case (have not tested), it is an error in the modelling.

How the engines and propellers of these aircraft worked is no mystery, at least not to some of us. No "direct braking" (or prop brakes, as they're called), and no different gear ratios in the prop gear box.

Three things determine RPM (in a given atmosphere): Pitch angle, shaft power and airspeed.

Cheers,
Fred


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XyZspineZyX
10-01-2003, 11:06 AM
"A CSP in a dive at full throttle will often eventually hit the maximum pitch stops of the propeller. From then on, it is effectively a fixed pitch prop, the prop governor is unable to reduce RPM and the only way to reduce RPM is to reduce power.

In Il-2:FB pre-patch, reducing the prop RPM setting
reduced the RPM even in this situation. If that is still the case (have not tested), it is an error in the modelling."


It's still the case, unfortunately.

It's also impossible to overrev any CSP prop in the game with full throttle, no matter how fast or steep the dive -- also a major error, from what I understand.

XyZspineZyX
10-01-2003, 11:10 AM
The very big effect you seem to miss is the fact that if the prop is windmilling it's not pulling!

If you fly with half the throttle you'd probably have lower rpm than let's say 2800 rpm, if you had no prop at all. This means that if you set your CSP to run 2800 rpm the prop is windmilling... Now instead of pulling the aircraft with half of the thrust it's braking a bit. The difference is huge!

This is exactly one of the most important issues with CEM it totally eliminates the essential advantages of automatic systems of FW and Bf.

The second point is going in a dive with a prop that's already windmilling...essentially it means that you face a risk of overrevving.

There are no penalty cases for crossing the controls. High MP coarse pitch or low MP fine pitch.

As for the instruments they live their own life and are not a reliable insight to the true power output. Bf MP, for example follows rpm not throttle...

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XyZspineZyX
10-01-2003, 01:04 PM
To some degree, I can buy the relationship between MP and throttle as the charging will increase with increasing RPM.

But something is still porked in the powerplant model, no doubt about it.

Cheers,
Fred

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XyZspineZyX
10-02-2003, 11:31 PM
effte wrote:
- Maximum propeller drag is at min throttle and max
- RPM. At that setting, the engine is basically acting
- as a large air pump, drawing power from the engine.

- A CSP in a dive at full throttle will often
- eventually hit the maximum pitch stops of the
- propeller. From then on, it is effectively a fixed
- pitch prop, the prop governor is unable to reduce
- RPM and the only way to reduce RPM is to reduce
- power.
-
- In Il-2:FB pre-patch, reducing the prop RPM setting
- reduced the RPM even in this situation. If that is
- still the case (have not tested), it is an error in
- the modelling.
-
-
- Cheers,
- Fred
-

Thanks for all that Fred, it confirms what I thought. I was pretty sure I understood the basic mechanics, but the bizarre in-game effects were giving me doubts!

Hope that 1.2 sorts it out; it sounds like they're working on MAP at least. Real engine management is (or will be)one of the best things about FB. /i/smilies/16x16_smiley-happy.gif

Kernow
249 IAP