View Full Version : CEM on p51

02-04-2004, 12:06 PM
Any hints or tips ? Is the prop pitch the only CEM?

02-04-2004, 12:06 PM
Any hints or tips ? Is the prop pitch the only CEM?

02-04-2004, 12:18 PM
Everything on the pony is automatic. All you need to do is control the throttle, flaps, stick, etc. as usual.


02-04-2004, 12:41 PM
actually the prop pitch on the mustang is manual, i use it all the time...
i find that for economy cruising and gaining speed in level flight or up to 10 degree climbs it seems efficient to have throttle and prop pitch both as low as possible in equal proportions while floating at the base of the rpm powerband. this means that if i set my prop pitch to 75 or 80 percent, then i also bring my throttle down to 75 or 80 percent.
in combat i keep throttle at WEP unless the engine is overheating and simply use prop pitch for any maneuvering..

02-04-2004, 12:52 PM
Um xenomage2000.

There is no manual prop pitch for the P-51.

Hint, if you want to no how to use manuel then youl need to take a BF109 that has manuel prop pitch, but youl need to change from auto to manual.

Historlical the P-51 did no have manuel prop pitch. Its a CPS plane.

02-04-2004, 12:59 PM
hmm, maybe you'll want to go test the p-51 just to confirm that, because i did before posting and it worked for me....

02-04-2004, 01:20 PM
well, theres no doubt that i can use manual prop pitch on the p-51... is my game broken or something then? because i remember hearing that only bf109 had manual prop pitch but i use it on just about every other plane as well!

02-04-2004, 01:38 PM
First of all in FB you can switch between auto and manuel prop pitch for the BF109.

there is no option for manuel or auto prop pitch for most alied planes. For a good reason. Most alied planes where CPS. Constant Speed Proppeler.

To try and explain how the prop pitch works for the P-51 is alot more complex then explaining manuel prop pitch.

First, its a very good idea to lern manuel prop pitch before trying to understand a CPS plane.

So take a BF109G10.

before you start the engine make shure you swich from auto to manuel. It will tell you if you have switched it to manuel prop pitch. It will say "Manuel". You may need to map the option of switching from auto to manuel though.

Try not to get too fustrated if you keep blowing the engine, it takes alot of practice.

02-04-2004, 01:44 PM
Hi xenom2k,

It seems you're yet another victim of generic labeling. The HUD shows you a control called "Prop pitch". It will say things like "Prop pitch: 70%". In fact this is simply written this way for all of the aircraft, regardless of their prop management system. The prop control system on almost every Allied aircraft is a constant-speed prop, so named because the governor mechanism regulates the prop pitch automatically in order to keep engine speed constant. When you select 70%, it corresponds to moving the prop-control lever (you could call it the rpm-control lever) to tell the governor to hold the rpm at the rpm that corresponds to a 70% setting.

Nothing wrong with your FB, just need to adjust your understanding. The 109s and some 190s can be switched into true manual mode, in which you directly set the actual prop pitch (angle of the blades). In this case it is up to YOU to maintain rpms.

Read about it here:

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02-04-2004, 01:55 PM
thank you michapma. I now have a marginally better understanding of how prop pitch works in this game. despite the community recommended faqs i read about cem i still very far from grasping its full benifits, as im sure most people are. i found that the games manuals and community faqs still dont explain enough (or maybe its just that i learn better by example and no one has ever actually said 'set that like this to get the most power/best turning ect..' they all explain the principals on which these systems operate but then leave it to you to figure out how it comes together...

02-04-2004, 01:55 PM
If this is so then why do I slow down when I lower prop pitch on the P-51 and why does the engine rev up or down? Is that just an illusion? If so then it takes away something from the sim IMO. It SEEMS to work.... If what you say is true (I know they removed mix control) I personally wish they had left it like it was.... or at least gave us the option. I just got finished reading An Ace ith the 8th by Bud Fortier and he said quite often in that book how he had to fiddle with pitch and trim and mix on his P-51... of course it was a B.
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02-04-2004, 01:59 PM
if i am understanding correctly, its because your overriding the csp govorner to simulate manual prop pitch.

02-04-2004, 02:03 PM
prop pitch control on CPS planes (almost all FB planes) actually control engine RPM. move the prop pitch and watch the RPM gauge. furthermore, the rpm stays the same regardless you are climbing or diving. clearly on CPS planes you are simply controlling rpm and not actually prop pitch. if you were controlling prop pitch, the rpm would change when diving and climbing.

02-04-2004, 02:04 PM
oh.... I think I get it.

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02-04-2004, 02:35 PM
Just because most alied planes are CPS does not mean you cant change the RPM setting.

default setting is 100%= 3200 comabt RPM. This setting will keep your RPM at 3200.

From take off and until you reach your desired altitude the RPM will stay at 3200 combat rpm. The prop pitch is Constantly changing all by its self to stay within 3200rpm.

This my friend is CPS. Its very nice to have. Real live you did not fly around at combat RPM. 2700RPM i beleave is cruze for the P-51. Once you have the RPM set to 2700 it will stay at that RPM untill you change it.

Now if you took the BF109, set it to Manual, left it at 100% prop pitch, and went full throttle you would blow the engine.

Try it, take the BF109, change it to manuel prop pitch, go full throttel and youl see that there is no governer to prevent you from over reving your engine. You can even blow the engine during take off.

CPS or auto = less fiddling with the RPM.

Manuel = constanly changing the prop pitch.


You have to realize that 3200RPM is combat for the P-51. 3200RPM = 100%.

When you said that "you lowered your prop pitch" this statement does not make sence when talking about a CPS plane with no manuel prop pitch.

All you did was lower your RPM. You actualy set the RPM lower. It will stay where you have set it until you change it.

Only time your going to go faster by lower the prop pitch is if you take a BF109 with manuel prop pitch.

It seems you are confused and are un shure of the differance between Manuel and Auto or CPS.

Think of the prop pitch in the P-51 as auto and not manuel. Its kind of like having cruse control, only your setting the RPM and not speed.

02-04-2004, 05:37 PM
Ever driven a car with a manual transmission?

Think of the "Prop Pitch" setting as the gear shift lever and the gas pedal as the "Throttle".

Also, An important factor about the P-51 ( and alot of other aircraft too..) is that the 0%-100% pich setting is realitive. The prop only changed pitch within the min and max pitch stops placed on the prop pitch control mechanics. Confusing? OK, the prop pitch on the P-51 was allowed to move 37 degrees within a 90 degree sweep (at 0 degrees the prop is edge on to the aircraft centerline and 90 degrees the prop is flatside to the aircraft centerline), so a prop pitch of 0% to 100% covers only 37 degrees of the 90 degree total sweep area.

There are the operating parameters for the P-51D

Manifold Pressure RPM Mixture Control
Take-off 40" Hg 3000 RPM Auto Rich
Climb 35" Hg 2600 RPM Auto Rich
Cruise 26"-28" Hg 2300-2400 RPM Auto Rich

They work - trust me. I have tested these settings in-game.

You really need to read these two CEM Guides again and stop between each section and test it yourself.

Eastern Skies CEM Guide (http://people.ee.ethz.ch/~chapman/il2guide/cemguide/intro.htm)

CEM by Jeff "Vulgar" Gerhardt (http://mywebpages.comcast.net/Tailspin/documents/CEM_IL2FB.htm#Introduction)

You will be suitably impressed. I often fly to and from the engagement area on 50-60% throttle and 75-80% prop pitch and average between 450 and 530kph - properly trimed of course.


02-04-2004, 06:30 PM
Um Oscar,

Most alied planes are CPS or auto prop pitch. It says this in one of your links. There is no manuel prop pitch for the P-51.

Qote from the link by Jeff about CPS(wich is most alied planes by the way).

"Some planes have an automated system called constant speed propeller or aeromechanical screw that does not need prop pitch setting input from the pilot to stay in the power band".

another qote by Jeff.

"Applying full throttle at 100% pitch setting with some aircraft may cause over revving and damage the engine. Some aircraft you will need to change prop pitch rarely, others you will need to change prop pitch frequently while conducting normal operation and or combat". maneuvers.

Power band or Combat RPM for the P-51 is 3200. This will give you max perforamnce.

Unfortanatly he does not explain CPS planes as well as he does planes like the BF109's that can use manuel prop pitch.

Unless you can prove to me that P-51 does not have CPS and that it use's manuel prop pitch, then ill continue to beleave that it is a CPS plane and that it does not have manue prop pitch.

02-05-2004, 02:13 AM
The P-51 undoubtedly uses a constant-speed propeller (CSP) control system. When you change "prop pitch" do not think of changing prop pitch, but rather rpm. The prop control system on almost every USA, Soviet and UK aircraft does NOT directly control prop pitch, but rather RPM.

Oh how unfortunate that terminology http://ubbxforums.ubi.com/infopop/emoticons/icon_rolleyes.gif. The HUD, which is the text in the mid-right section of your screen (unless you've turned it off), tells you "prop pitch" for every aircraft. (Except the TB-3, which has fixed-pitch prop, so you don't get any text for it.) However, in the P-51, P-39, P-40, Hurricane, La-7, IL-2, Yak, etc., etc. you should realize that with that control you are setting the rpm and not prop pitch.

The CSP governor works basically as follows, and I quote my own site: "A typical design uses a gear driven by the engine crankshaft to spin flyweights. Attached to these flyweights are valves that allow or block oil flow to a hydraulic mechanism in the propeller hub. As the engine rpm changes, the spinning flyweights move out or in and cause the the valves to open (or close) more, allowing oil to flow into the hydraulics in the prop hub. The change in oil pressure causes the hydraulic system to rotate the blades in the appropriate direction (i.e., change the prop pitch) in order to load or unload the engine so that the rpm is quickly brought back to the desired rpm. If the rpm is too low, the mechanism flattens the blade angles, unloading the engine and allowing the rpm to increase. If the rpm is too high, it will coarsen the blade angles, loading the engine and reducing rpm. The process does take some time though, and since the oil used for the system comes from the main engine oil system, in real airplanes this prop control does not work very well until the engine is warm. It is also real-life practice to "cycle the prop" while on the ground, that is, move the rpm control back and forth to get the old oil out and get new, warm oil in so that the system works when it is needed."

Just keep in mind that the governor has its limits in the sense that the blade angle can only change so much. The rpm tends to increase in a dive and decrease in a climb. If you watch the tachometer the rpm will also move and settle back into its value as the governor has to adjust the prop to maintain the rpm. This is modeled wonderfully in FB!

This thread prompted me to make a couple of small modifications in this text at my site, which are included in the quote above.

For even more detail, see John Deakin's Pelican's Perch article (http://www.avweb.com/news/columns/182082-1.html).

Please keep asking questions!

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02-05-2004, 02:28 AM
Good one Mike, you saved me digging out the link http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif


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02-05-2004, 02:42 AM
Deakin's series of articles is awesome. Easy and fun to read, and quite a lot of experience behind them. Unfortunately, I think they are more than the average gamer/simmer is willing to invest. http://ubbxforums.ubi.com/images/smiley/16x16_smiley-sad.gif

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02-05-2004, 07:19 AM
Super thread....I jsut learned something. I always knew and understood prop pitch and CSP but didn't know or understand the rpm limiter using prop pitch in game. I have a much better understanding now and how to apply it. thanks guys.

02-05-2004, 10:54 AM
Nothing against Oscar, or the 'guides' that he has given (my apologies as I have not read the Eastern Skies guide), but I believe he is incorrect in the operation (both historic and in FB) of the engine managment systems we have in the game. This is an unbelievably common misconception that has been 'learned' by a significantly large part of the community and is turning out to be extremely dificult to 'fix'.

Engine Management in an airplane with a Constant Speed Prop is almost NOTHING like a car's manual transmission. The term 'prop pitch' in FB is NOT relative, it is a direct relation to engine RPM (and horsepower) when in context with Constant Speed props ONLY (all American and most Soviet aircraft, also the FW190 and He-111). German Bf109's use a different system and require different operation.

Michapma has it correct in his tutorial. It really is not a dificult concept, or hard to control. The hard part seems to be overcoming the 'car transmission' analogy.

02-05-2004, 11:00 AM
I stay as far away as I can from the car analogy. No offense to anyone, but it is extremely limited and does much more harm than good.

Btw, my tutorial is the Eastern Skies tutorial. Stop by and have a look. http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif

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02-05-2004, 11:14 AM
I agree 100% with that.

these manuals or guids that some have read do not fully explain CPS managemant, let alone the differance between CPS and manuel or auto prop pitch systems.

I have gone to mudmovers and other sights and they explain manual prop pitch but only vagely explain CPS.

Some times by reading about it its no wonder some people dont realy know the differance.

Like for example Jeffs sight. He did a good job of explaining manuel prop pitch. But he only breifly talked about CPS or auto prop pitch systems. Actuely i think there where only 2 small paragraphs that said anything about CPS lol. Also these two paragraphs where mixed into his manuel prop pitch guid.

Only desent CPS management guid that i have read so far was written by Michapma. I actualy should read it a second time because even my understanding is limitted.

02-05-2004, 11:24 AM
I have a question for Michapma.

What is the best way to operate a CPS managed system in FB?

Like when in a coop and need to climb to a desired altitude ect.

02-05-2004, 12:59 PM
Maple_Tiger, if you'd really like more insight, have a look at the Deakin articles cited there. A lot of real-world discussion, but that's what inspires the sim, and it gives a lot more insight.

I should qualify my comments that I gained my whole knowledge by reading and comparing a few sims. I have an engineering background and can understand technical stuff where necessary, but I try to keep that as light as possible when explaining. So actually I shouldn't be recognized as some kind of expert, but I have read with attention and am particularly interested in CEM.

There is a paragraph or two on climbing in the section "power settings". As requested, I'll talk only about CSP systems. The "best way" is kind of vague, there can be different criteria. There is a full-emergency power climb, and then there is normal climbing to cruise altitude. For a full-power, scramble type of climb, you want to use full power: "100%" throttle and "100%" rpm. You want radiator flaps closed to minimize drag, or if your plane will overheat at the power setting you might crack it open to help out. (I don't know the trade-offs for power gained versus drag penalty for various aircraft, haven't tested.) Of course you may have to adjust mixture and supercharger with altitude as required; this varies greatly between aircraft types. If you are behaving as a pilot and climbing at normal powers, you will set the MP and rpm to their rated climb values. The rpm value is not necessarily given for your aircraft, but you should basically reduce to around the values I recommended in the guide, maybe 80-90%. Look at the values in the tables for the American aircraft and 109 engines for examples, and compare them to the full-power values.

Just as important as CEM in climbing is controlling angle of attack (AoA). In concrete terms, you should use the stick and trim to get a constant climb speed. There is a specific value of airspeed for your given aircraft (this is dependent on payload) dictated by what is called the power curve (http://www.av8n.com/how/htm/energy.html#sec-power-curve-intro). Without extensive testing, I believe that this value varies between about 220-330kph for aircraft in FB. The principle is that you can fly with the minimum amount of drag and thus corresponds to a best-rate-of-climb speed. Conveniently enough, this is usually also a good maneuvering speed, so if you are attacked while climbing you can maneuver immediately.

For simplicity in the guide I've given percentages, but I kind of see this as an immersion killer. 100% throttle means full allowed manifold pressure, although that can depend on the mixture, supercharger and even airspeed unless there is a MP regulator system To find full manifold pressure, look in a reference if possible for fun or just find out what the manifold pressure corresponds to a 100% throttle setting at redline rpm. 100% rpm means red-line rpm, which I don't guess I have to explain. As you know, reducing "prop pitch" is really setting an rpm setting for the governor. In real aircraft (how many times have I typed that in the last two years?), you have to be careful about not letting rpm be too low while manifold pressure is too high, this leads to detonation and really ruins your day. I'd love to see this modeled.

It only makes sense to climb at reduced power settings, to avoid wearing and overheating your engine. You'd be amazed how much longer you can fly at full power in a fight if you haven't already brought your engine to its limits during climb and cruising. I call this keeping a heat reserve. I suppose the engine manufacturers and the air army experts dictated those power settings for a reason.


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02-05-2004, 04:08 PM
Thanks Michapma for clearing up my misinterpretation of Prop Pitch versus RPM Control. I understand the process - I just misused the terms a wee bit.


02-06-2004, 01:27 AM
Yeah I could tell you were on the same page. I still think mentioning anything about a car analogy only hinders, I avoid it and as you can see actually try to combat it when it comes up.

Your hint about cruisng at reduced settings is a good one. You can keep a large heat reserve and conserve a lot of fuel without having to sacrifice much speed. As you go faster and faster, the drag increases disproportionally, and much more power is required to overcome it. A small sacrifice for a big gain. http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif

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02-06-2004, 10:32 AM
Mike you mentioned turning off the hud..is this in the config file? And Maple...like i said a few posts back..... I get it now...http://ubbxforums.ubi.com/infopop/emoticons/icon_wink.gif but tanx anyway...http://ubbxforums.ubi.com/infopop/emoticons/icon_wink.gif

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02-06-2004, 12:21 PM
Yes, conf.ini... set NoHudLog=1


Try it out! http://ubbxforums.ubi.com/images/smiley/16x16_smiley-happy.gif

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02-28-2004, 07:54 PM
Michapma: Please keep asking questions!

Ok thanks just a small one then? http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif

It seems to me Michapma that in some Allied aircraft when attempting to land and closing down the throttle, the engine will continue to stay at high revs

I know that it's very complex and I'm sorry that I can't say exactly which aircraft but this started with the CEM patch - I would sail over the runway hardly bleeding off any airspeed, like a BoB Spitfire http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif and I found that coarsening prop pitch towards zero helped a lot by bringing the engine revs under control quickly and the aircraft would slow up very much more quickly than being in 100% prop pitch. This is while going around if still too fst for a safe landing when approaching the runway

Changing quickly back to 100% for the landing of course when within landing speed

While this appears to work for me, some comrades are puzzled at this strange behaviour and in their experience changing to coarser pitch to slow down doesn't work even though we are all on FB version 1.22

Can you explain please how coarsening prop pitch to make the aircraft slow up - for slowing up to land if too fast with flaps already extended - works for some people and not for others?

Thanks for any info, very interesting discussion

And I promise to look at the gauges a lot more when we get our Spitfires http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif


02-28-2004, 09:17 PM
Actually im fairly certain you can have some control over prop-pitch in a CSP aircraft *indirectly*. And in some cases it might be advantagaous to manipulate the governor to do so.

Basically, from what i understand, prop pitch is automatically adjusted to try to match your RPM settings. Well, what happens when your RPM settings and airspeed are in contraposition? When they are basically conflicting? Say for example your at the top of a hammerhead- your RPM will still be trying to turn the airscrew at say 3000rpm but the prop blades will only be moving enough air to pull the plane at say 100kph. What happens (i believe) is something like cavitation. The prop pitch becomes so coarse [edit: make that fine] that it becomes grossly inefficient. It also damages the engine. Many Russian planes will never overheat at 100/100 if in a DIVE, but in a CIMB, they overheat almost immediately. This is due to how the prop pitch *setting*, indirectly set by RPM, is going beyond the range of the CSP propellor and so causing undue stress on the engine.

Im probably not saying this right, or intelligibly. When i set prop pitch to my throttle axis on my joystick, and reduce it slightly in a climb and increase it in a dive, i never overheat. Ever. Of course i don't play FB with any kind of obsession so i could be wrong.

[This message was edited by CaptEasychord on Sat February 28 2004 at 09:06 PM.]

02-28-2004, 10:03 PM
Oh and as to prop pitch/RPM during landing;

I haven't played much since 1.11. But it used to be that if you set the throttle to 0 but the pitch/rpm to 100 you would drop like a rock. I think what would happen is that the pitch would become so fine to keep the set RPM that it would no longer provide any thrust and move any air. For ex; you could glide at 20/20 but plummet to the earth at 20/100.

02-28-2004, 11:18 PM
Ming, no doubt Michapma will get in here and give you the real scoop, but I'll put my .02 in just to confuse you.

In my opinion, there are two reasons you are seeing this 'different' performance when you and your squaddies are coming in for a landing.

1: Lowering your 'prop pitch' (terrible term pasted on your screen in blue) is lowering your engine RPM, thus decreasing your available power. As soon as you level out (see #2 and short response to Captain EasyChord) you will notice you are slowing down faster because of this reduced power.

2: When coming in for a landing, everyone comes in at different angles (vsi) and speeds. This is the major cause for your mates getting differing results. Consider it this way, your in a machine that weighs many thousands of pounds, and it is Descending (read, falling), and on top of that, there is a machine attached to your motor that is trying to keep that motor running at maximum output (your CSP governor, or '100%prop pitch' in FB). So in this type of situation (what you would see in the 'hurry up' type landings many people try in FB) it is Very dificult to slow down, and there is no way your CSP type prop could appreciably help you here.

To test this, get lined up Way out (I mean 5+km) and come in at very low altitude, with throttle cut. You won't make it, you will have to add power. I alwayse try to land my a CSP plane at '100% prop pitch' (thats full RPM) and a reasonably high (such as 30-40%) throttle. To do this you just have to get further out, and wait for that speed to drop (bleed) naturally.

No doubt it is arguable (and is argued endlessly) at what speed these WWII era aircraft should 'bleed speed' with a closed throttle, but what we have now is a fairly reasonable simulation (no doubt it could be improved), imho. In previous patches, it has been notably Incorrect. Both in speed bleed and the modeling of the various prop systems. The current system is the best to date to model all of these complex problems (again, some argue Oleg has gone 'too far' in the 'floating' direction, who knows for sure?)

For CaptEasyChord: You have a point there, the prop pitch (actual prop pitch) must coarsen to lower engine RPM, so you are indirectly adjusting pitch (don't let this confuse anyone, you cannot directly control prop pitch as in Bf109's). And no doubt there are engine overspeed issues (which would also include overheating) in real life, but this is not modeled fully in FB. The largest reason you are seeing less overheating while using a lower RPM setting is the decreased power output, and in a dive the increased airspeed (and possibly prop load, not sure if that is modeled) increases cooling. To be technically correct, your doing this just backwards, in a dive you need to reduce your RPM, while in a climb (emergency type climb) you need to increase your RPM. But again, just as you know, its alwayse a good idea to reduce RPM to avoid ruining your engine.

02-29-2004, 12:39 AM
You might well be right, but i was just relating some observations from experience. I'd have to make a more thorough testing regime to repeat what ive noticed over time. But im fairly certain in planes like the I-16 you overheat much faster in a climb than in level flight with the same power settings. It might well be related to cooling and not prop-pitch related effects.

02-29-2004, 02:23 AM
RL pilot here http://ubbxforums.ubi.com/images/smiley/16x16_smiley-happy.gif (therefore an unqualified expert! http://ubbxforums.ubi.com/images/smiley/16x16_smiley-very-happy.gif)

http://ubbxforums.ubi.com/images/smiley/16x16_smiley-indifferent.gif Constant speed governors usually give up RPM authority at about 50% RPM, meaning, at idle throttle (approach) the prop should be stuck on fine pitch stop regardless of what you do with "prop" lever. That's why prop gov checks are done at runup.

A thought http://ubbxforums.ubi.com/images/smiley/16x16_smiley-indifferent.gif - If prop is on fine pitch at idle and aircraft is zipping along at 450 klicks then obviously prop is not keeping up with airstream and prop is windmilling (relative wind trying to turn it) and it is basically functioning as a brake (reverse thrust). This wouldn't be as bad as an engine out (as on B-17, say), but still . . . http://ubbxforums.ubi.com/images/smiley/16x16_smiley-indifferent.gif


"I race full real exclusively in IL2:The Forgotten Battles." - Mark Donohue

02-29-2004, 08:42 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Oscar_352nd:
Ever driven a car with a manual transmission?

Think of the "Prop Pitch" setting as the gear shift lever and the gas pedal as the "Throttle".


Good analogy. I am not diagreeing with you. I would just like to mention, as an FYI, that the gas pedal in a car is not "like" the throttle, it is the throttle http://ubbxforums.ubi.com/infopop/emoticons/icon_smile.gif

Did anyone prophesize these people? Only Travis. Come in Travis! ~ Clash