Aces High Bulletin Board
General Forums => Aces High General Discussion => Topic started by: Bullethead on September 28, 1999, 06:24:00 PM
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Gruppen-
Never had a sim with constant speed props before so I'm a bit in the dark about how to use them. Help would be appreciated here.
I understand the basic concepts, I _think_. In AH, you have an RPM control that sets the constant speed the prop maintains. You also have throttle, which changes the manifold pressure, aka how much macho is going to the prop. So as you wiggle the throttle, the prop automatically changes pitch to maintain the pre-set RPM. Is this right?
Now, seems to me that the various situations of takeoff/climb, cruise, combat, and landing would each require some optimum RPM setting. IOW, in each type of situation, you set the RPM and leave it alone while you wiggle the throttle. Is this true? If so, can somebody give me some pointers on what amount of RPM is best for each type of situation?
Or is RPM like a trim tab for the motor, something we'll have to constantly tweak in flight?
Thanks in advance.
-Bullethead <CAF>
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WOW, this game has constant speed props. Thats gonna blow some people away. Bullethead, your basic concept is correct. Each plane should have its own sets of numbers best suited to it. The supercharged engines really packed some horse-power in some planes. One thing to watch for is over boosting at a given or set RPM. You can't just cobb on the power if you have a lower RPM setting without hurting something.
Could be lots of black smoke up here for a bit. hehehee
Cool feature
Mt-Dew
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OK, first off, AH isn't exactly modelling a CS prop totally correctly...but it's better than Brand W.
And, you fly AH the same way as a real one.
It seems to have been missed in the FAQ for some reason, so I'll repost my MAP explanation here...
blk
PS-this is the same explanation I posted int he Alpha forum a few weeks back, so this may sound familiar if it did indeed end up in the FAQ...
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How come the engine's rpm doesn't change when I move the throttle?
Basically, with a fixed pitch propeller, we can measure engine power with the tachometer (rpms). But, with a constant speed (CS) prop, the tachometer should remain constant. Therefor, we've got to measure engine power some other way.
So, we have this thing called Manifold Absolute Pressure (MAP). What this is, is we measure the air pressure inside the intake manifold (the pipes that carry air into the engine). First off, standard atmosphere is 29.92 InHg (you'll see where this is going).
First, I'll explain about normally aspirated (not supercharged) engines. So, with the engine off, the MAP gage will read the ambient air pressure (29.92 InHg). We now decide to start the engine. But at idle power, the throttle plate is closed, and is restricting the flow of air (and sometimes fuel) to the cylinders. So, at idle, the engine will be at a low MAP setting (around 12 InHg MAP or so). It would try to be zero, but if there were NO air/fuel making it to the engine, it wouldn't run, so it'll be around 12 InHg MAP or so. So then, we push the throttle forward to the stop. This moves the throttle plate so that it's restricting the intake air as little as possible (if you don't know how a throttle plate works, most encyclopedias have a decent diagram). So, the engine is going to be as close to 29.92 InHg MAP as it possibly can be (since there's not supposed to be any restrictions). But the air can't be COMPLETELY unrestricted (there are turns in the induction system, the throttle plate still adds a little drag to the intake airstream and so on), so we can usually get around 29 InHg or so. So, you with me so far? As throttle setting increases, MAP increases up to 29 InHg. So, that's how we measure the engine's power with a constant rpm (high MAP equates to high power settings).
Now, remember how I said standard atmosphere was 29.92 InHg? Well, that's at Sea Level (and a "standard" day). As we climb, we lose a lot of that air density (approximately 1 InHg per 1000'). So, the maximum MAP the engine can possibly attain at altitude will decrease (because the atmospheric pressure decreases), and we get a corresponding loss of engine power at high altitude.
So, someone got smart, and decided that if we could somehow get more than ambient air pressure at altitude, the engine (and thus the aircraft) would perform better. So, basically, they compress air going into the intake manifold back to that sea level pressure (29.92 InHg). So, the engine can develop its sea level Horsepower at altitude. This is called "Normalizing." When we compress the air with a compressor driven by an exhaust driven turbine, we've got a "Turbo-Normalizer," or what's generally referred to as a "Turbocharger." but then, someone else got even smarter, and decided that if we could boost MAP back up to sea level pressure at altitude, we could increase it even more. Thus, at sea level we could get MAP in excess of 29.92 InHg. So, we're actually increasing the Horsepower of the engine to an artificially high level. This is called "Supercharging." When an exhaust driven turbine drives the Supercharger, it's called a "Turbo-Supercharger." So, how do we operate such an engine?
Well, on the P-51D in AH, the normal full throttle, on the runway MAP is 60 InHg (which corresponds pretty well to the 61 InHg redline in real life). So, 60 InHg is full throttle. And, that idle MAP setting is about 20-30 InHg because the turbo-supercharger is compressing the air just a bit there too (and that engine will draw at least 20 InHg MAP in order to keep all 12 of those high compression cylinders working...).
WEP is just giving you a boost to 65 InHg. In RL, you've got to be careful not to overboost the engine (create more HP than the engine can absorb, and the heat associated with such high power settings does a lot of damage as well). But since this is AH, you can push the engine hard, just watch how long you fly with WEP engaged.
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Bullethead: There seems to be no prop control in HA - RPM is constant.
Blk: P-51D has two-stage two-speed mechanical supercharger system - no turbo.
[This message has been edited by funked (edited 09-28-1999).]
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-blk-- said:
>>>>>>>>> PS-this is the same explanation I posted int he Alpha forum a few weeks back, so this may sound familiar if it did indeed end up in the FAQ... <<<<<<<<<<<
Thanks, but your post got cut off while still in theory before it got to practical application (http://bbs.hitechcreations.com/smf/Smileys/default/smile.gif).
So, back to the basic question. How do I know what RPM setting to use in a given situation? I assume there are curves somewhere of HP vs. RPM, fuel consumption vs. RPM, max level speed vs. RPM, etc, each for various alts. Where can I find this info? I figure it'll make quite a difference in combat, especially vs. folks who don't know how to get the most HP out of their motor (http://bbs.hitechcreations.com/smf/Smileys/default/wink.gif).
-Bullethead <CAF>
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funked said:
>>>>>>>>>> Bullethead: There seems to be no prop control in HA - RPM is constant. <<<<<<<<<<
I beg to differ. KP- and KP+ are the default RPM change keys and they do indeed work in the beta. You can use these keys to set the RPM over a wide range of values, which it then holds constant while you wiggle the throttle and change manifold pressure. This is why I want to know what the optimum RPM settings are (http://bbs.hitechcreations.com/smf/Smileys/default/wink.gif).
-Bullethead <CAF>
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For now, you're best to keep your RPM maxed out. There's more to be implemented in this area, but it's pretty much roughed in now. Once we get the fuel consumptions curves all done, this will be more of a factor.
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Doug "Pyro" Balmos
HiTech Creations
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Pyro said:
>>>>>>>>>>>>>>> For now, you're best to keep your RPM maxed out. There's more to be implemented in this area, but it's pretty much roughed in now. Once we get the fuel consumptions curves all done, this will be more of a factor. <<<<<<<<<<<<<<<<<
Thanks for the info. I look forward to seeing more added to this feature. I foresee it being a great separator of the quick from the dead. "Why does his 51 go faster than mine?" <EG>
BTW, ain't had a chance to say so yet, so thanks for the work here and good luck with this venture.
-Bullethead <CAF>
AW: 3841-
WB: blt-hd
AH: BH3841
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Don't look for performance boosts out of it. The real benefit in AH will come in the form of fuel conservation at lower throttle settings. We do want to stress the importance of fuel more, and that's why we're running faster fuel consumption rates and have drop tanks available.
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Doug "Pyro" Balmos
HiTech Creations
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Just for fun set the prop to full coarse and try to takeoff.
So,we gonna get mixture controls or are you gonna stop here?
Nuther question will changing prop pitch reduce dive speed, decceleration acceleration in the future ,also overspeed? <-havent checked it out where's Wells?
Sound files for pitch change?
Really like the Gustav on takeoff. Even managed to keep a few on the runway (http://bbs.hitechcreations.com/smf/Smileys/default/wink.gif)
Makes the 51 look like a popsiclecat
Looks pretty good after cusory inspection. no problems yet but I promise to break somthing.
<S> HTC!
PS nag.. nag.. nag (http://bbs.hitechcreations.com/smf/Smileys/default/wink.gif)
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The rule of thumb is, match rpm to the speed (if flying 2/3 top speed, use 2/3 rpm) and then use MP to maintain that speed. Fuel consumption will vary (almost directly) with both rpms and MP. For example, best range in a P-51, the settings are 1800 RPM and 185 mph IAS.
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-blk-- you need to make a correction you stated that pressure and density are the same or atleast led to air density is about 14.75psi at sea level and drops at 5000ft intervals. Not going to get techno here. But you are refering to density in above post. And another unless we have a prop tach in these fighters the rpm gauge should and will change with engine speed, we would need a prop lever to run the prop from beta range to full feather where beta is flat as in wing tip to wing tip and full feather is flat front to rear MAP does not measure the power of the prop it only mesures the pressure inside the manifold. the only indication unless a prop tach or torgue meter is installed is the seat of the pants type of feeling. A constant speed prop is attached to a gear box (planetary type) and not a shaft straight from the engine, this type of prop spins at a constant speed of about 3200 rpm's depending on type and all, the rpms of the engine are used to increase torque to the prop. The rpm's speeding up and spinning the supercharger are what increases the MAP which again does not show prop output.
Turbo supercharging is a result of the exhaust driven supersgarger?
No turbo supercharging is a crank drivne supercharger with turbochargers driven by the exhaust of the engine.
Compund tubocharging is a turbocharger that drives a shaft that is connect to the crankshaft they give about 50 more hp to they engine and are used I believe on R3350 compond turbo engines.
Almost everything you said has nothing to do with constant speed props. MAP is a good indication you are going to blow a head off or somehting not what the prop is doing.
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Tommy (INDIAN) Toon
http://www.geocities.com/~tltoon (http://www.geocities.com/~tltoon)
[This message has been edited by indian (edited 09-29-1999).]
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A constant speed prop does not need to be attached to a gear box (an normally isn't for modern airplanes), since the speed is changed by changing the pitch of the blades.
The reason for gearbox is to reduce the speed of the prop so that it wont go supersonic or to reduce noise level.
Bod
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Disclaimer: I'm not really going to debate the minute details of my explanation. I wrote that because there were people in the Alpha test who wanted to understand it as it relates to AH.
AH, is basically a CS prop with one setting (full forward). As of now, if you decrease the rpm (yes, you can, just mine you have to map the keys yourself) you just decrease torque. This is not a finished engine model. For now, just leave it at full RPM (a tad over 3,000) Then, use the MAP as a general indication of the horsepower being produced by the engine. This is how it relates to AH. Full throttle in the P-51 is 60 InHg. Climb power I use is 55, even though there's not a real reason to in AH yet, other than fuel consumption. Cruise around 45-50 InHg. Descents around 30 InHg.
blk
PS-indian, I fail to see the difference in your explanation of a turbo-supercharger. You described an exhaust driven compressor which increases the air density to a point hich corresponds to an altitude below sea level... Now I'm just curious, am I missing something?
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If you really want to understand Props and Manifold pressure, and learn about all the myth's still being passed on, then I suggest checking out this website. Every week you get an email update about what's going on in Aviation, plus they have experts who write very good articles, ranging from maintence to flight ops. You won't be dissapointed. The following link will take you to the article, but first you must join them, free by the way, to be able to view it.
http://www.avweb.com/articles/pelperch/pelp0016.html (http://www.avweb.com/articles/pelperch/pelp0016.html)
The title of the article is: "Those Marvelous Props"
There is also another related article: "Manifold Pressure Sucks!"
Check out the rest of the website and the other articles, lot's of good reading.
tshred
[This message has been edited by tshred (edited 09-29-1999).]
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Thanks for the scoop about the prop pitch! I had no idea!
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-blk-- Was trying to state that a turbo supercgarger are two different type of boost agents on the same engine. a turbo is exhaust drven where a supercharger is crank driven either directly or geared. Thought you were talking about constant speed props and how they would really work not in AH.
And to the guy who says a constant speed prop does not need a gear box prop pitch will not maintain the speed you can still run it up with engine rpms. Prop pitch helps keep from over torqueing the prop. In an airplane with a power lever and a throttle lever the rpms would be set to max 100% and the prop (or power lever) would be used to run up the torque to get take off speed. Those plane without a power lever the prop pitch does not change and the rpms ( and this is where I will agree with -blk--)and the map guage to control torque.
My apologies to -blk-- for not reading his explanation as a simple one for AH only. I have 20 years in the aviation field nd my first reaction was this is all wrong. I see now what he was aiming at.
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Tommy (INDIAN) Toon
http://www.geocities.com/~tltoon
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Hehe, isn't that wierd indian...
Just because I fly 20 hours a week and work on 'em the rest of the time doesn't mean this tuff isn't difficult for others to understand... I forget that a LOT.
blk
PS-Indian, what do you do? Repair Station, A&P? Pilot?
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-blk-- I wokr at a very large repair station for a major airline. I hold an A&P. I also just realised that I was think turbo prop so my mistake, I read that late at night and thought it sounded wrong.
See what I mean about the Trubo charger and supercharger not being the same though. it is possible to have both and did see I didnt make it very clear. So sorry again.
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Tommy (INDIAN) Toon
http://www.geocities.com/~tltoon
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the other thing indian is that your refering to turbine engines not recipricating engines. so indeed your explination is a little off.
shdo
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Indian and blk, remember WWII planes had piston engines, not turbines. At least not those with props.
Bod
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Unless I missed something, there is no pitch control associated with the throttle position, correct?
Couple of observations, after I first startup, with throttle pulled all the back to idle RPM indicator says 2500, throttle position and engine sound would have me believe 600 rpm. Work in progress or bug?
Second,if I'm at 10,000 ft AGL at 100% throttle at max cruise (say 300+), if I go into a dive, should not the engine pitch sound/rpm increase?
Third if Im at 3/4 throttle *position* and RPM indicator is at 2500, when I push the throttle forward, assumming the RPMs read the same and a constant speed prop, why does the sound pitch increase with MAP? Aren't you just increasing the load on the engine and not the RPM?
To me it looks like your not modeling CSPs, just monitoring MAP and keeping the RPM indicator at MAX rpm regardless of the situation.
ignorant and slightly confused...
Lugnut
[This message has been edited by Lugnut (edited 09-29-1999).]
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yow! It's not the propeller that's spinning, it's my decidedly insufficiently scientific head!!!!
Math! Math! Run away! Run away!
(http://bbs.hitechcreations.com/smf/Smileys/default/smile.gif)
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vv indian, them turbines can get a mite confusing, especially since any type of turbocharger has an exhaust driven turbine (http://bbs.hitechcreations.com/smf/Smileys/default/smile.gif).
Now to answer the throttle/pitch relation question:
Throttle basically has no direct impact upon RPM with a constant speed prop. However, when we increase the throttle setting (MAP), the engine produces more HP, which makes the engine want to speed up. In order to keep the RPM the same, a propellor governor regulates oil pressure to the propellor to INCREASE the blade angle. This in turn, loads the blades and the engine does not perceptibly gain speed. The opposite is also true. If I reduce the throttle setting, the load on the prop will be the same. This will cause the RPMs to decrease (we humans shouldn't be able to percieve it), but the governor senses the decrase in RPM, and lowers the blade pitch. The lowered blade pitch unloads the engine, thus the RPM remains relatively constant. See, this is why they are called Constant Speed Props.
To answer your question about diving at max throttle: with a CS prop, basically, the airspeed would uload the prop and thus it would want to speed up. However, the governor would increase the blade pitch and the RPM would remain constant. Although at some point (very extreme point usually--never happened to me in RL) you would hit the limit of the blade travel and they could go no further. The RPM would at that point increase, but I don't think you can hit it. Especially military aircraft tend to have props with a very large pitch range, so it's possible, but not probable.
As to the sound question: an engine model and a sound model are completely different. That's a nearly direct quote from HT a few nights ago BTW.
blk
PS-I really simplified that, but the prop class I took was a full semester and some people still didn't get all that...
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Gotcha on the sound issue, sounds like they aren't synched up yet.
I still maintain that you aren't going to spool up a Merlin at 2500 rpm right at start up...
Lug
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So if i read all these stuff and my head is swirling because i have to translate all these technical stuff in german in my head lol.
But now the question. Did all WWII Prop Planes have constant spinning Props ? And what was then the advantage of the engine managment of the FW 190 i read so many times about.
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Uedel not the best, but better then rest :)
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Uedel said:
>>>>>>>> But now the question. Did all WWII Prop Planes have constant spinning Props ? And what was then the advantage of the engine managment of the FW 190 i read so many times about. <<<<<<<<<<<
As I understand it, the FW had 1 handle to control everything related to the motor: throttle, prop RPM, and maybe mixture. Other planes had 3 handles, 1 for each control. Somehow the FW's was all integrated and balanced by 1940 vintage automatic control systems. I don't know if this gave any advantages other than reducing pilot workload and the amount of training needed.
-Bullethead <CAF>
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Lug, lemme ask around. I think I can have a definite answer by Monday or Tuesday (as to whether a Merlin could turn 2,500 static)
blk
PS-most of the WW2 fighters has CS props. Some early Hurricanes and I think spits has fixed pitch or two pitch props, but those were VERY early war (as in outdated by august '39), or before the war. Other than that, yes they did, with the exception of the Fw thing. Which, as a pilot, I don't like the idea. But then, I'm a control freak and don't like the idea that there's a set ratio of engine output to MAP/RPM combinations (which the FW lever essentially did assume)
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blk said:
"Which, as a pilot, I don't like the idea. But then, I'm a control freak and don't like the idea that there's a set ratio of engine output to MAP/RPM combinations (which the FW lever essentially did assume)
"
Unless I read your post wrong, here goes..
Ah, but there is, and it's published by the engine manufacturer, to get the best performance and long life out of your engine. And as a pilot, you should be following their guidelines! Them FW engineers were kind to their pilots by removing their workload! Just as an example, how many of you run your cruise setting 'square'? How many of you have actually looked at the cruise charts in your Engine Manual or POH? I own, fly and maintain a 172 with a 220hp Franklin engine. It's manuall(engine manual) recommends MP as high as 26hg with RPM's as low as 22 for optimal cruise at lowest recommended power percentage. It has handy charts for each power setting, ie 65%, 75% etc...and yet people out their say never run over square! LOL, just goes to show you how much misinformation is really out there!
All you pilots and mechanics out there should read the articles "Go Ahead, Abuse Your Engine!" found at http://www.avweb.com/articles/pelperch/pelp0008.html (http://www.avweb.com/articles/pelperch/pelp0008.html) , and "The Ten Biggest Lies
About Piston Aircraft Engines" found at http://www.avweb.com/articles/englies.html (http://www.avweb.com/articles/englies.html) in addition to the two mentioned in my post above. Again, you have to be a member, but it's free and painless! (http://bbs.hitechcreations.com/smf/Smileys/default/smile.gif). If you want to learn about all the "Old wives tales" still being taught and passed around, read these articles. There has been a lot of stuff posted in this thread, but no one has explained it correctly or better than the 4 articles I have referenced, IMHO.
ts
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blk
To me it isn't a question of could it, what I've seen and read, whether its a Merlin, P&W, Allison, BMW, DB, or whatever, when you start the plane, your going to run it at 600-800 through warm up and mag checks and get the oil temp up to normal before you do a run up it otherwise you risk wrecking the engine. 2500 is max engine RPM you don't start an engine at that setting.
Imagine starting your car up cold on a winter morning and keeping your foot in it after it catches and holding it at 5000-6000 rpm while the engine is trying to pump cold oil through it, then shortly thereafter, do a full throttle acceleration for a couple of minutes. Not likely.
Lug
PS (Stop me if you heard this) After Beechcraft made the Starship they got a call from a guy building a 3/4 scale FW replica who inquired about the Starshhips single lever engine management system that contolled throttle, pitch and mixture that he was trying to duplicate for his 190 replica (as the original had a similiar system). Beech engineers originally thought they had been innovators of a revolutionary concept in engine management, and were quite surprised to find out Focke Wulf had beaten them to the punch 40+ years prior.
PPS From what I have heard the system in the original 190s was a bit quirky in that in cruise it continually "hunted around" and made small adjustments to either the pitch, throttle or mixture, thus making it difficult for pilots to fly a constant speed, and thus fly tight formations.
[This message has been edited by Lugnut (edited 09-30-1999).]
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Lug: OHHHHH! I get what you're saying now. I agree you wouldn't do that in real life, nor would you be allowed to do it (the mechanic would choke you far sooner).
As to the single control lever... I still don't like it. If I want an expedited descent, I'm gonna be at a high RPM, and low MAP. That's not particularly harmful for the engine, unless it gets extreme, and then I can also have the added benefit of notifying everyone in town of my arrival. (http://bbs.hitechcreations.com/smf/Smileys/default/smile.gif)
Yeah, having a computer do it is supposed to make formation difficult since it's always going to be changing a number of different things. See, that's why I wouldn't like it (and we all know how much formation flying I do (http://bbs.hitechcreations.com/smf/Smileys/default/smile.gif) ). I guess my big gripe with single lever power management is...I like lots of levers, knobs, dials, switches, and Circuit Breakers. I enjoy flying complex aircraft and doing complex things with them (no gyro NDB comes to mind), but that's me and my more-levers-is-better philosophy. (http://bbs.hitechcreations.com/smf/Smileys/default/smile.gif)
blk
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You probably have heard about the new Morane-Renault diesel engines, running on JET A1 fuel. (The same manufactorer who produced the highly successful Formula 1 engines a couple of years ago).
These engines have a computer based single lever control, but with a mechanical backup system.
Right now they are waiting for the general european and US certification. The problem is of cource that that under both regulations an engine is supposed to have 2 spark plugs for each cylinder. A diesel engine has no spark plugs, and therefore new rules has to be made.
Bod
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cool info Bod.
These going to be for light plane applications or heavies?
Chisel <- diesel mech.
Those A&P mechs might have to get dirty tho. (http://bbs.hitechcreations.com/smf/Smileys/default/wink.gif)
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They are made for light planes. 200, 250 and 300 hp, i think. I got all the info at home, and can check when i am finished here.
The advantage with them is that they maintain power at altitude, 70% at 25k (This is MUCH more than normally turbocharged engines), and the fuel economy, and of cource that they run on A1 fuel, and the cimplicity and reliability of the diesel engine.
These engines are a totally new design, and have very little resemblance with the black-smoking and noisy diesel engines in trucks.
Bod
[This message has been edited by bod (edited 10-01-1999).]
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OK, I gotta come clean, I win the doofus of the week prize. Until I got my hands on the "help" file indian put together, I didnt realize that "-" and "+" actually controlled the *prop* rpm. Doh! I thought it was just the manual keys for changing the engine RPM. My previous posts in this thread assumed that the RPM gauge was displaying the engine RPM, not the prop. That makes more sense and explains why the engine pitch sound increases when throttle is advanced, I saw the MAP increase, heard the engine note rise and wondered why "rpm" didn't increase. Because its the prop rpm and not the engine rpm (moron). I guess the old planes didn't monitor engine rpm, or did we simply run out of dash space?
Lugnut
PS HTC, please don't carry on the tradition started at ICI of providing half assed help files. Put out a good readme.txt in the distribution file that explains this sh*t (http://bbs.hitechcreations.com/smf/Smileys/default/smile.gif)
(really digging the CSP now)
[This message has been edited by Lugnut (edited 10-01-1999).]
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Propeller RPM is directly proportional to engine RPM. directly geared.
I always thought they monitored crank rpm? 3000+ rpm is pretty fast for a big engine.
Think of the prop as a transmission is your car. In first gear (like fine pitch )at 1500 rpm the engine is putting out ,say, 20 HP but in 5th gear (coarse pitch) at 1500 rpm its putting out 70hp.
Now, in first gear the throttle will just be cracked open to maintain that 20hp. (low MAP= little power)
In 5th gear youll have it wide open to maintain that 70hp (high MAP= lotta power)
Sombody said only the torque is modelled so far .Lots of work still to be done but the basics are there (http://bbs.hitechcreations.com/smf/Smileys/default/smile.gif)
"These engines are a totally new design, and have very little resemblance with the black-smoking and noisy diesel engines in trucks."
HEHE, they smoke cause there worn out or out of calibration, old or new.
Take one apart and there all black inside :0
Really like to see a pic of one of them. Off to search the web!
Found 2 pics cool!
Also found another diesel aero engine under development if your interested.
http://193.26.97.194/index.html (http://193.26.97.194/index.html)
[This message has been edited by chisel (edited 10-01-1999).]
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From what I gather the way the engine should operate like this....
At idle the engine is purring queitly as a kitten. Increasing MAP/Throttle should make the engine louder.
Increasing the RPM setting should make it sound faster.
Right?
By the way...in real life what does fiddling with the RPM setting get you anyways? When do you want low RPMs and high RPMs?
Hans
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Hey, Frans....Yo tink dees guys are gut enouff to shooot us down? Ya! Dats right. Vie aw 'ere to shoot....you down!
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From : August 1942 document from the Air Tactics Dept of the Air Ministry
How to make full use of the performance of the spitfire V,VI,IX
(merlin 45 and 46)
Snip:
(iv) If you want to live on the other side,you must move fast;but equally, if you want to come back again you must save petrol. you will find your engine happier at, say +4lbs boost and 1700 rpm than at +11lbs and 2650 rpm.
Both these adjusments give the same ASI [indicated airspeed] but if you fly at +4 and 1700 you will save seven gallons of petrol an hour. It is possible to get +4lbs above 10,000 feet by reducing the revs until the boost falls to +4. Use full throttle and minimum revs above full throttle height for any desired ASI. this gives the best combination of fast cruising and minimum consumption.
(v) When you are travelling at full throttle, and full power is suddenly wanted, it is only nessesary to push the constant speed lever fully forward to get full revs and boost. To return to high speed cruising at best economical conditions, reduce your revs and not your boost.
Snip:
Excuse the typos
And no way am I typing the whole thing! (http://bbs.hitechcreations.com/smf/Smileys/default/wink.gif)
After rereading this wouldnt it be better to map the propeller control to "our" throttle than the MAP? I need more Jstick ports!!
I know, there is more to it than this.
PS German MAP gauge scaled in ATA. Spitter got it in PSI!
I sense an RAF conspiracy.
[This message has been edited by chisel (edited 10-01-1999).]
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OK, back home.
One prototype MR200 is fitted on a Socata Trinidad TB 20 for flight testing. A MR300 was currently fitted on a prototype Epsilon II Trainer at the Paris Air Show.
The main reason it is so clean is that it uses Jet A fuel, which basicly is pure kerosene, while dieses fuel has a lot of heavy components. Also the efficiency of the cumbustion is of main importance with regard to clean emmission, and they say they have done a lot of work in that area.
New Trinidad TB 20 for sale are planned to be fittet with the engine in the second halfe of year 2000. The dimensions allow it to be retrofitted in place of the Continental IO-470/520 and the Lycoming IO-360.
I also must add that custom made parts from Bosch for fuel pump and injectors, a Garret turbocharger and a completely new propeller from Hartzell are part of the package. The propeller is no new that it does not have a code yet (Constant speed of cource (http://bbs.hitechcreations.com/smf/Smileys/default/smile.gif) ).
Bod
[This message has been edited by bod (edited 10-02-1999).]
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Let me try and help out here regarding prop pitch for those who have got a bit confused with turbochargers etc, etc. - and probably end up just adding to the confusion.
Think of prop pitch as the gears in a automobile. In the early days, props just had two pitch settings: fine and coarse - like an automobile with just two gears. Fine pitch equals first gear, coarse pitch equals second gear. An just like in an auto, to accelerate (i.e take-off) you needed low gear. But if you never shifted out of low (fine) you coudn't go very fast before your engine rpm maxed out. There you were, pottering along with your engine screaming fit to bust. So once you were airborne and going a decent speed you shifted into coarse pitch (second gear). The engine and prop rpm dropped,just the way the do on the road, but if you kept your foot down (throttle forward) you went faster, till either you reached the maximum speed the thing would go or the engine rpm maxed out.
Think automobile again: on the level in top gear you can only pull just so many rpm and go just so fast, but downhill you could go right up to max engine rpm - and beyond - when you get a big bang and the engine blows up. Same in a plane, except that downhill equals diving.
The next step from props with just fine and coarse pitch was to have props with infinitely variable pitch. This was equivalent to some funny little European cars with infinitely variable transmission, done with a rubber band running on cones. So instead of being in one of two gears, you could always be in exactly the right gear for the situation if you set the prop pitch right. In theory, at least!
Incidentally, with a prop with only two pitch settings, when you came into land, you put it back in fine pitch just the same way you put your car in a low gear when approaching your driveway. This also allows you to accelerate away again pronto if you miss the approach. If you forgot, and left it in coarse pitch, when you opened the throttle not much happened - just the same as if you try to accelerate you car from 30mph in fifth gear.
If anyone wouldl like me to continue, I will follow on with a personal explanation of constant speed props and the relationship of power to engine and propeller rpm. Otherwise I'll shut up.
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Tjay of the Kraits. All my enemies die laughing.
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Oz not get it. So his beanie prop is adjustable?
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TKoKFKA-OZDS-
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Go for it! I'm listening (http://bbs.hitechcreations.com/smf/Smileys/default/smile.gif)
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One invitation is enough for me; thanks Chisel. KoK, what's a beanie, please?
So... Having established that we can think of prop pitch as the gears on your automobile, what about constant speed props? Well, for a start a C/S prop DOESN'T ACTUALLY turn at a single constant speed. What it does do, is maintain speed once you have set it (in AH by using the plus and minus keys) regardless of what you do with the throttle.
The relationship between prop pitch and prop rpm is simple but can be confusing. The less pitch we have the easier it is for the engine to turn the prop; the more pitch we have, the harder it is. {Zero pitch is when the prop blades are lying across the axis of the fuselage and doing no work. However, because they are 'edge on' the engine finds it dead easy to turn the prop. Max pitch (90 degrees) is when the blades are fully lined up with the fuselage. In the latter situation they aren't doing any useful work either, and as you can imagine, the engine would have to work its guts out just to turn the prop round - without achieving any forward thrust. but in between they are catching the air and shoving it backwards.)
Let's say you have 50% throttle applied, and you hit the minus key. The revs REDUCE because this applies MOARE pitich to the blades and as we haven't applied any more power to compensate, the engine and prop can only slow down. The opposite applies: hit plus and the revs INCREASE, 'cos you have just REDUCED pitch, making it easier for the engine to turn the prop.
Now,with a constant speed prop, if you set say 2000rpm on the prop tacho (rev counter), a gadget inside the propeller hub (the constant speed mechanism) will try to keep the engine and prop rpm at that speed. If you add power it will add pitch to absorb it: if you reduce power it will fine off (flatten) the pitch to compensate.
So, if engine and prop revs stay the same regardless of what you do with the throttle lever, how do you know how much power you have applied? That's where the manifold pressure gauge comes in.
At this stage, we needn't worry about what manifold pressure actually is,or how the engine supercharger maintains it at high altitude; just think of it as a power meter. Forget inches of mercury and all that: the lowest figure you can get is idle power, the maximum figure is full power. (Jets have their power meters calibrated in percentage to make it easy.)
So what prop rpm figure do we set when? Coming back to the automobile analogy, where fine pitch (max rpm, remember) equals low gear, use that for when you are taking off, landing, or want to accelerate from a low cruising speed. In the cruise, reduce the rpm to minimum, cos that gives the most efficient fuel consumption and then set the airspeed you want with the throttle.
HOWEVER, I understand that the effects of changing from hi to lo prop rpm are not yet modelled in AH, (SOMEONE PLEASE CORRECT ME IF I'M WRONG} so just set the prop rpm to max (fine pitch) and leave it there.
Please let me know if this has been helpful. If you want a more detailed explanation, including how the constant speed mechanism works and why it can only control rpm within certain limits, read 'Those marvellous props' by John Deakin at www.avweb.com/articles/pelperch. (http://www.avweb.com/articles/pelperch.)
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A fairly simple explantion of how constant speed props work.
If any of you have ever seen an old steam eng you probably saw a fly ball governer.
what a govener on a steam eng does is by way of centrifical force it opens a valve to let more steam into the eng when the balls are lowered (do to slowing down) and closes a valve when the balls are to high to slow down the steam eng.
Basicly it tryies to maintian a steady rpm on the govener.
Now on to Constant speed props.
A constant speed prop also has a govener in the hub of the prop, some planes like the t6 you can see the weights on the hub. Any way what happens is as the prop slows down this govener simply applies less pitch on the prop to lessen the load on the eng. when this load is lessened the eng will increase its rpm do to the decreased load. Conversrsly if the prop is spinning to fast the prop's pitch is increased by the govener to put more load on the eng and there by decrease its rpm.
When you move an rpm control of a constant speed prop all you are doing is adjusting the set point of the govener to a desired RPM.
HiTech
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Ok now for the real mess
did all WWII aircraft model constant speed
props?? If im not mistaken it would be very weird for every plane to have the exact same kind of props. DC3(C-47) and B-17 both had controllable props (hamilton standards etc)
In fact I think the Corsair does also
I havent really got a clue on the rest of the fighters.
(also wasn't there some kind of Curtis
electic prop used on the p-38 and maybe the p-39? they used to have probs with runaways with these electrics if I'm not mistaken)
The only constant speed props I'm used to seeing would be on the Crop dusters with Radial engines. These props had large counter weights of some kind near the hub that controlled speed. The crankshafts of engines fitted with these props didnt have to be drilled for hydrolic (sp) control of the prop
I guess what Im trying to say is that any plane that was able to control the pitch of the prop from within the cockpit I dont consider constant speed. If the prop adjusts itself without your intervention then I'd call that a constant speed prop.
I dont claim to be any kind of expert just speaking from my past experience in aircraft which is pretty limited. Feel free to laugh away at my ignorance.
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Tonight, it ain't right
I got to have me a week.
But I'll be back for you jack and I'll let the machine speak! Thats right Thats right (Maniac Mechanic ZZTop)
[This message has been edited by Deadman (edited 10-03-1999).]
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Thanks for that Hitech. I thought I would just try and help out any peeps who were confused as to what prop pitch did and why you needed to alter it. So I deliberately avoided the mechanical details in case it all got a bit longwinded.
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Tjay of the Kraits. All my enemies die laughing.
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Sorry HT, gotta correct you just a tad <don't kill me>. The prop governor (and that's what it is, works just like the ball governor on a steam engine) isn't mounted to the prop. The weights you see on say, a T-6 are there to help drive the prop to high pitch (because oil pressure is used to drive prop to low pitch..thus when engine quits the prop automatically moves to a high pitch). The prop governor is mounted on the engine (usually to the Accessory Section), and is driven by some accessory drive shaft.
blk
PS-no all the WW2 A/C didn't use the same props, but they were all basically the same. They all use oil pressure to either drive the prop into high or low pitch (depends on ths situation), they all have prop governors... Except those Curtiss Electric props, but they all work the same way (push prop lever forward, engine speeds up, pull it back, engine slows down)...
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I know that the 109 G-10 had an electrically operated constant speed prop.
Bod
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Thanks blk never new about the added weights on the T6 is this a common feature on us aircraft?
HiTech
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what this all points to IMO is the need to include some kind of explanation ofs CSPs in the help section at some point down the road.
Lugnut
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HT, it's common on lots of aircraft. Basically, multi-engine aircraft all use them (because that way the prop starts to feather automatically when oil pressure is lost).
The reason you don't see those weights on engines of, say, DC-3, T-28, P-47... Is that those all use Hydromatic propellors. But take a look under the spinner of pretty much any twin out there (Aztec, Duchess, Titan, Seminole, Seneca...), and you'll see them. They're also pretty common on the regional turboprops (for the same reason).
blk
PS-it's a common feature on foreign aircraft as well
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Ok i think i understand a lot better now about how this works but I actually think the game needs to be revised so that the gauge doesnt show rpm but prop pitch settings
that would seem more accurate and get away from the illusion that we are seeing engine rpm here when actually we are not. If you pushed the minus key it would move the prop pitch to increased pitch and if you pushed the plus key it would move to prop to a decreased pitch setting. (now if the game would model the sound of the prop biting more air when it was set to higher pitch settings this would be awesome)
I went to the web site mentioned in above posts and now this prop mixture and manifold pressure are a lot more clearer in my mind.
Check it out for your self and see if it doesnt clear it up for you as well.
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Tonight, it ain't right
I got to have me a week.
But I'll be back for you jack and I'll let the machine speak! Thats right Thats right (Maniac Mechanic ZZTop)
[This message has been edited by Deadman (edited 10-07-1999).]
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Deadman the indication are correct straight out of the book on props. The only way these older props were constant speed was to set the rpms of the engine which is what we are doing. by running up the manifold pressure we are really increase torque, but according to the book the rpms should rise wiht increase minifold pressure. I dont want to put the hole chapter on the board but it is indicated right in the game. Some of the older planes used springs to hold the prop at a certain pitch some default to a set pitch that still can produce thrust after all something is better than nothing. The book is from my A&P class its called Aircraft propellersand Controls.
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Tommy (INDIAN) Toon
My Homepage
indians Homepage (http://www.geocities.com/~tltoon)
The Aces High Help Page on my site
AHinfo (http://www.geocities.com/~tltoon/AHINFO.html)
To down load the following 2 files hold down shift key and left click then save to disk.
Aces High Help in Word6. The following file is in .zip format and is the word6 .doc file.
AHinfo (http://www.geocities.com/~tltoon/AHINFO.zip)
Aces High key command in Text Format
ACESHIGH (http://www.geocities.com/~tltoon/ACESHIGH.txt)
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Just to throw a wrench into the works for dedmans sake the Germans used prop pitch gauges. Basically looked like a clock. They set the pitch to this gauge for takeoff, climb etc. rather than RPM. They had a tachometer as well.
Different method same result
http:// [url=http://members.aol.com/bf109gust/index.html]http://members.aol.com/bf109gust/index.html[/url][/url]
Go here for a look. Under construction details, cockpit
[This message has been edited by chisel (edited 10-07-1999).]
[This message has been edited by chisel (edited 10-07-1999).]
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Yeah tommy I understand what your saying but
the govenor can only adjust the prop to the limits of its stops and at engine idle the guage in a real airplane wouldnt be stuck on 3000 rpm.
but you could have the prop to min pitch even tho the gov wouldnt be able to produce this rpm till the throttle was moved forward. Either the guage needs to be mapped to actual eng rpm or it needs re labeled as a prop pitch setting which to my way of seeing it work is what it's actually indicating at this point.
maybe instead of seeing a guage we could have a little lever that moved back and forth with the plus and minus keys to represent the pitch control.
Hmmm I wonder if we'll get feathering capability on the twins?
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Tonight, it ain't right
I got to have me a week.
But I'll be back for you jack and I'll let the machine speak! Thats right Thats right (Maniac Mechanic ZZTop)
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I think only the dials are implemented at this stage since neither the rpm or the manifold pressure are working correct.
The manifold pressure should also change when rpm changes for a set throttle position, and clearly it does not right now.
With regard to german planes i think all of them (at least late war) had some sort of automatic engine management. I think that was one of the reasons the Black 6 crashed a couple of years ago, when the pilot smelled "burned oil" and the engine started "running rougher". It was only the automatic engine management doing its job, but the somewhat unexperienced pilot thought something was seriously wrong, and did a terrible engine-off landing.
Bod