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General Forums => Aces High General Discussion => Topic started by: Zanth on June 14, 2003, 02:27:37 AM

Title: Saying goodbye to warbirds
Post by: Zanth on June 14, 2003, 02:27:37 AM
They were nice enough to give me a free month at warbirds.  I had not much chance to use it, but was nice to revisit.  

It reminded me of the one thing Aces High fails at badly.  When your airplane goes faster it should soumd like it is going faster.  Every single one of ya know what i talking about, and it is an odd failing for a game that does rest of game sound so cool.
Title: Re: Saying goodbye to warbirds
Post by: beet1e on June 14, 2003, 02:38:34 AM
Quote
Originally posted by Zanth
It reminded me of the one thing Aces High fails at badly.  When your airplane goes faster it should soumd like it is going faster.  Every single one of ya know what i talking about, and it is an odd failing for a game that does rest of game sound so cool.
Zanth, you are absolutely WRONG. The way AH has it modelled is correct. And that's because most of the WW2 planes had constant speed, variable pitch propellers. I have had to explain this so many times that I saved the explanation, and reproduce it below in blue text, extracted from an old BBS post.

Many of these planes had constant speed variable pitch propellers. As power is increased, the pitch of the propeller blades increases. The load on the prop also increases so the set speed is maintained. In a climb, the prop would tend to slow down. The prop governor detects this and adjusts the blades to a finer pitch - again, to maintain the set speed. In a dive, loading on the prop is reduced, the pitch increases. I believe that early Spitfires did not have the VP prop, and the pilot would have to throttle back in a dive to avoid over-speeding the engine. The VP prop is able to soak up that power by adjusting the pitch, and no need to throttle back.  If throttling back, the only time the engine RPM would decrease is when the pitch of the blades reaches minimum and the throttle is closed still further.

If you’ve ever flown a real plane with fixed prop, and then move onto something with a CSVP prop, believe me, you would never want to go back! It makes engine management so much easier. You just have to remember to increase throttle to maintain manifold pressure as the plane gains altitude. But you’d have to do that anyway even with a fixed prop, as power/RPM decreases with altitude.

For me, the way Aces High models CSVP props is one of its good points. I wish WB would too.

Over to funked to explain how CSVP governors work - something to do with lead weights sliding along the prop shaft in response to centrifugal force?  Geez, I’m lost already.

Two of my former Dutch squaddies (Lapwin & Zepher) took a ride in a real P51 - I have the film they made. And when Lapwin landed he made the comment that the engine note remains unchanged in dives/pullups. I don't think he had believed it until that day, and as he walked towards the camera he said "Scrmbl was right". :D Of course I was right!

Now, if we could only get them to calibrate the magnetic compass the right way round instead of backwards, we would be in good shape. The compass is calibrated backwards in both AH and WB, but is correct in IL2.
Title: Saying goodbye to warbirds
Post by: Staga on June 14, 2003, 04:45:35 AM
http://www.stagas.net/bf109/08.%20In-Cockpit_flight.mp3

Bf109G-2 "Black 6" inflight recording from cockpit. ~12mb.

In beginning of the record you'll hear inertia-starter whining before engine (DB605) starts up, taxi'ing to the runway, take off, flying the plane (wind noise is all that changes, engine rpm stays same) and throttling back when beginning to land the plane (here the RPM goes down few times), landing and rolling back to the pit.
Taken from CD "Checkflight Gustav" and record can be ordered from Here (http://www.spitcrazy.com/sounds_of_aviation.htm) or from Here (http://www.ghosts.com/records.html) (for example, check your local shops first).
Title: Re: Saying goodbye to warbirds
Post by: _Schadenfreude_ on June 14, 2003, 06:36:43 AM
Quote
Originally posted by Zanth
They were nice enough to give me a free month at warbirds.  I had not much chance to use it, but was nice to revisit.  

It reminded me of the one thing Aces High fails at badly.  When your airplane goes faster it should soumd like it is going faster.  Every single one of ya know what i talking about, and it is an odd failing for a game that does rest of game sound so cool.


I tried it too before settling in here - still only 15 people online in there?
Title: Saying goodbye to warbirds
Post by: Janov on June 14, 2003, 07:40:24 AM
Great explanation, Beet1e!

In addition, the constant speed prop not only makes engine management easier, it also allows the prop to operate closer to its optimum angle of attack, for most of the airplanes speed.

In Aces High you will want to leave your propeller (and thereby engine) RPM at highest RPM most of the time. This will yield the highest power, since engine power is a function of RPM. It can be adjusted with the + and - keys in the numpad. You may want to reduce your RPM a bit during cruise, to save fuel and reduce noise (for the sake of the sheep :) ).
You will definately want to reduce your RPM to minimum while in a poweless glide (after engine has quit due to whatever reason). This will put the propblades into a low angle of attack (relative to onrushing headwind), thereby decreasing your overall drag, and allowing you to glide MUCH further.
BTW, a short push on the WEP-Button will snap your RPM back to high-RPM, so maximum power is available again.

Litjan, CO 1. Hessische Freibierstaffel
Title: Saying goodbye to warbirds
Post by: Kweassa on June 14, 2003, 08:35:46 AM
Even if they were governed to a point, shouldn't abrupt or harsh sequence of events put pressure on things? Like suddenly engaging into a power dive, or going to high speeds that go over 700, 800 and 900km/h?

 Currently, the only thing that keeps pilots from just WEPping down full throttle in a 60~70 degrees dive, is fear of overspeed. For some planes that manage some bit of elevator authority even over 450mph, they just soar down anythime in any configuration.

 The only instances I tinker with the RPM control during combat, is when using speed sensitive planes like the Ta152s or compression freaks like the 109/P-38, in order to 'contain' the dive speed to a certain point with low RPM, trims and rudder use - so that the plane maintains sufficient speed for chase, but doesn't overspeed.

 ...

 However, if constant speed props and governers can so adequately manage the engine RPM in any given situation, what's the deal with the fear of over-revving in real life? Were only the earliest planes without automatic devices susceptible to such problems?

 In IL-2:FB, even though some aspects of engine management is fubared(like, the Hurricane which runs over 3000 RPM at 110% throttle and doesn't overheat at all..), it still gives out some interesting results for comparison.

 For instance, if you dive at extreme speeds with full throttle - even if you are at high speeds with radiators fully open - , though the RPM is still contained to certain limits the plane's engine really go under the pressure. If you do too many of those high speed dives the engine quickly overheats, or functions erratically after a long run.. or in extreme cases, it can just quit if you ignore the danger signs for too long. Most German planes are depicted in this manner in IL-2:FB.

 Another interesting point, is the Soviet planes in other hand, feel much more like AH planes, and almost never have to tinker with any type of RPM management - naturally, 109 and 190 fans of IL2:FB, are very suspicious and displeased with such different results.

 ....

 So all in all, which can be considered right?

 Did pilots really not worry about over-revving, if they had reliable RPM governers? Were RPM manually controlled only for the sake of fuel conservation??

 I don't think they were anything like the digital, electronically operated things we have in nowadays fighters. There must have been some limits to high speeds, were there not?

 I wonder if someone can clarify that for me.
Title: Re: Saying goodbye to warbirds
Post by: Ledg on June 14, 2003, 01:55:55 PM
Quote
Originally posted by Zanth
 When your airplane goes faster it should soumd like it is going faster.  


One thing sims don't seem to model is increased wind noise in a side-slip. Why is that? It would add to the ability to maintain coordinated flight.
Title: Saying goodbye to warbirds
Post by: 327thBS on June 14, 2003, 02:43:11 PM
while were on the subject of sound would'nt be cool if when u broke the sound barreir in a me-163 or something of that nature that u here the LOUD boom that comes after u broken the sound barrier ???:confused:
Title: Saying goodbye to warbirds
Post by: Glasses on June 14, 2003, 04:46:54 PM
The loud boom you would hear would be from you body hitting the gorund at 750mph while a  second later the pieces of the me163 would follow earthward.

Simply the 163 didn't have the structural integrity to sustain transonic flight, the Me262 however  was said that it broke the sound barrier while on dives regularly,in what condition I don't know. :D
Title: Saying goodbye to warbirds
Post by: JB73 on June 14, 2003, 06:27:35 PM
Quote
Originally posted by 327thBS
while were on the subject of sound would'nt be cool if when u broke the sound barreir in a me-163 or something of that nature that u here the LOUD boom that comes after u broken the sound barrier ???:confused:
i have yet to be at 750 (close to sound barrier) in ANY plane in AH yet.

the closest i have gotten is 640 in a 163 @ 35,000 feet. the plane was fully compressed and the slightest touch of the stick sent me to the tower from too many g's.
Title: Saying goodbye to warbirds
Post by: beet1e on June 15, 2003, 04:39:48 AM
Kweassa - we're talking about a few different things here. The pilot's operating handbook (POH) of any aeroplane will contain a list of "V-Speeds". These are the speeds at which actions are required, or must not be exceeded for some reason. For example, airliners taking off reach first V1 (the point at which the option to abort the take off has expired) and then V2 - rotate, ie it's ready to fly. There's another V-Speed - VNE. Velocity - Never Exceed! On modern aircraft that speed is denoted by a red line on the air speed indicator. It is this speed that a diving plane would be apt to exceed, resulting in airframe damage, control flutter, or breakup of the airframe. Even gliders/sailplanes have a VNE.

Interesting to see you talk about the "RPM Control". A plane with a constant speed prop will have a throttle AND an RPM control. The throttle controls the amount of fuel/air delivered to the engine of course, and the RPM control, usually known as the prop governor control, is used to set the engine speed. On some aircraft (eg motor gliders) the prop pitch can be varied between three fixed positions - fine, coarse, and feather. But a constant speed prop of the type we have in AH is different. The speed is set, and the governing mechanism varies the prop blade pitch to maintain the set speed. So when you mentioned "RPM Control", I was unsure of what you meant, as we have only one engine control in AH.

The nice thing about CSVP props is that the airspeed of the plane can be increased - as in a dive - and the engine speed will stay the same (up to a point) because the prop adjusts to soak up the power from the engine - a bit like changing to a higher gear in a car. By the same token, in a gentle climb the prop pitch will be reduced as the governor detects the increased engine load - like changing down a gear on a hill.

The method of operation is quite different. Because the engine speed stays the same across a range of throttle settings, an additional instrument is required to show how much power is being delivered by the engine. This instrument is the manifold pressure gauge. Take off would be with the prop set to max speed (fully fine pitch). After take off, power would be reduced by decreasing throttle to a particular manifold pressure setting, and then the prop speed would be reduced to climb speed, then eventually to cruise speed.

I have a couple of observations on how AH models the CSVP prop. One is that an audible engine note change occurs immediately the throttle setting is decreased. What would actually happen is that the throttle could be reduced quite a way before that happened - the governor would detect the reduced power output from the engine, and would decrease prop pitch to compensate. Only when fully fine pitch had been reached would further throttle reduction cause a reduction in engine speed. The other thing I notice about AH is that with the engine stopped, manifold pressure drops to zero. This is incorrect. With the engine stopped, the manifold pressure gauge would indicate the ambient barometric pressure.

Still, HTC have done a good job of modelling everything, considering we fly from keyboards. I don't think I'd want to see prop governors and mixture control settings introduced. Well not yet.
Title: Saying goodbye to warbirds
Post by: Pei on June 15, 2003, 04:58:31 AM
Quote
Originally posted by Staga
http://www.stagas.net/bf109/08.%20In-Cockpit_flight.mp3

Bf109G-2 "Black 6" inflight recording from cockpit. ~12mb.

In beginning of the record you'll hear inertia-starter whining before engine (DB605) starts up, taxi'ing to the runway, take off, flying the plane (wind noise is all that changes, engine rpm stays same) and throttling back when beginning to land the plane (here the RPM goes down few times), landing and rolling back to the pit.
Taken from CD "Checkflight Gustav" and record can be ordered from Here (http://www.spitcrazy.com/sounds_of_aviation.htm) or from Here (http://www.ghosts.com/records.html) (for example, check your local shops first).


Thanks for that staga!
Title: Saying goodbye to warbirds
Post by: Bluedog on June 15, 2003, 05:39:22 AM
Just for those of you who feel that you need some kind of sound cue that lets you know when you are speeding up or slowing down, just crank the 'wind volume' slider right up....the faster you go, the more wind you can hear.

When I first came to AH from WB years ago, I found this to be one thing that took a lot of getting used to, and the wind volume thing worked fine for me.
Title: Saying goodbye to warbirds
Post by: Batz on June 15, 2003, 06:18:53 AM
Quote
So when you mentioned "RPM Control", I was unsure of what you meant, as we have only one engine control in AH.


Ah does have "rpm control". But it works like this

When you reduce rpm in ah instead of a "coaser" pitch its actually reverse. So say if you are in a 109 and your eng hit, reduce rpm to min this will give you "fine pitch" and you will glide a lot further then a high rpm setting.

Fine pitch should = high rpm

coarse pitch should = low rpm

With "coarse pitch"  drag should increase and so glide should be shorter.

I guess ah planes have some sort of hybrid "feathering".  Atleast in my experience since I never mess with rpm except when my eng is damaged. In the the hub theres a spring  that drives the prop towards "coarse pitch" ("low RPM"), while governor oil pressure opposes this. This means that a governor failure — or loss of oil pressure — the prop moved towards low RPM (high pitch), and right on into feather, which is nothing more than extremely high pitch. Full feathering is something you see in twin eng planes.

So ah atleast when eng is damaged

fine pitch = low rpm

coarse pitch = high rpm

I am unsure if its this way when adjusting rpm with the eng functioning in ah.

Complex eng management (rpm pitch fuel mixture ect) arent that difficult from the players end (i dunno about the programming side). Its a few extra button clicks or a rotary adjustments.

The problem comes (as with IL2 fb) with the lack of documentation. In real life the pilot knew what powerband  to keep his aircraft in for a given situation. The manual told him so.

In fb one has to fumble around (because specs dont match real life manuals) until you figure out whats the best power settings.

If ah went with a cem then I would hope there would be documentation for showing the correct power settings.

But my point is kweassa is correct that ah has "rpm" setting. Its just confusing in how it works in ah.
Title: Re: Saying goodbye to warbirds
Post by: Grendel on June 15, 2003, 06:28:39 AM
Quote
Originally posted by Zanth

It reminded me of the one thing Aces High fails at badly.  When your airplane goes faster it should soumd like it is going faster.  Every single one of ya know what i talking about, and it is an odd failing for a game that does rest of game sound so cool.


That's more about the "feeling" the plane. The sound cue help you on knowing what the plane is actually doing. You don't feel it on your pants, the player isn't feeling anything, but by clever use of sound the player has some "feeling" on how the plane is behaving, what it is doing, and has a better grasp on the situation.

That's one of the things WB has always done extremerely well.
Title: Saying goodbye to warbirds
Post by: hitech on June 15, 2003, 10:56:25 AM
You are mistaken batz, best glide on a plane with an eng out is course pitch.

In fact my RV8 has a areobatic prop that will go to course pitch on loss of oil pressure to lower drag in a glide.

HiTech
Title: Saying goodbye to warbirds
Post by: Tumor on June 15, 2003, 06:57:18 PM
Quote
Originally posted by hitech
.
In fact my RV8 ....

HiTech



Oh, well aren't WE just special! :)
Title: Saying goodbye to warbirds
Post by: rshubert on June 15, 2003, 11:37:19 PM
Quote
Originally posted by hitech
You are mistaken batz, best glide on a plane with an eng out is course pitch.

In fact my RV8 has a areobatic prop that will go to course pitch on loss of oil pressure to lower drag in a glide.

HiTech


Did you build it, or buy it?  Tail wheel or tricycle?
Title: Saying goodbye to warbirds
Post by: mwjayd on June 16, 2003, 12:03:42 AM
glasses wrote ......The loud boom you would hear would be from you body hitting the gorund at 750mph while a second later the pieces of the me163 would follow earthward.

Simply the 163 didn't have the structural integrity to sustain transonic flight, the Me262 however was said that it broke the sound barrier while on dives regularly,in what condition I don't know......................... ............................. ............................. ............

 I broke the sound barrier before.....no wait that was wind ...sorry bout that..:D
Title: Saying goodbye to warbirds
Post by: flakbait on June 16, 2003, 12:48:57 AM
Yup, coarse-pitch (low-rpm) is the best for gliding. Because the prop angle is closer to 90º (inline with the flight path) there's hardly any drag. Fine pitch (high-rpm) means the prop is somewhere around 30º, creating a mess of drag if the engine goes out. In fact, with the prop at 30º on a dead engine, you'll end up with the prop turning the engine!

Most turbo-props, twins, and some aerobatic AC these days have a large spring in the prop dome. The purpose of that spring is to regulate RPM with oil pressure. When oil press and the spring force are equal, you get whatever RPM you set. If the oil pressure suddenly drops to zilch that spring will drop the regulator down to the stop. As a result, it auto-feathers the prop. John Deakin did a nice write-up on props, with pictures, over here...

http://www.avweb.com/news/columns/182082-1.html


As for the sound of the engine increasing pitch as speed goes up, uhhh no. That doesn't happen. You may be going faster and faster, but the engine isn't. It's still turning over at 40" of manifold pressure and 2,400 RPM. Because the engine doesn't increase speed, there's no change in the engine pitch. It isn't a car with an automatic gearbox that changes gears every so often. The engine-to-prop gear-ratio is fixed, and can only be changed on the ground. Since there aren't any gears to change, and the engine speed stays the same whether you're at 120mph or 400mph, you won't hear any change in the sound. Now if you hit WEP you will hear a change, because the manifold pressure increases with WEP.



-----------------------
Flakbait [Delta6]
Delta Six's Flight School (http://www.worldaccessnet.com/~delta6)
Put the P-61B in Aces High
(http://www.worldaccessnet.com/~delta6/sig/geek.gif)
Title: Saying goodbye to warbirds
Post by: beet1e on June 16, 2003, 03:41:25 AM
Quote
Originally posted by flakbait
Yup, coarse-pitch (low-rpm) is the best for gliding. Because the prop angle is closer to 90º (inline with the flight path) there's hardly any drag. Fine pitch (high-rpm) means the prop is somewhere around 30º, creating a mess of drag if the engine goes out. In fact, with the prop at 30º on a dead engine, you'll end up with the prop turning the engine!
hehe, flakbait. That reminds me of the 109 I used to fly. No not Me109, but Gröb 109 motor glider. I would stop the engine in flight and feather the prop. The aircraft would turn a hell of a lot better with the engine stopped - no gyroscopic force resisting the turn. When I wanted to restart the engine, I'd turn on the ignition, unfeather the prop to the FINE position, and nose down to 95 knots. Just as I hit 95, the prop would start to turn and the engine would fire up.
Title: Saying goodbye to warbirds
Post by: Kweassa on June 16, 2003, 06:16:21 AM
Um...

 So then, what of those over-revving things?

 In what situations would a pilot over-rev his engine then?

 Or, did that not happen at all, if the pilot just sets his RPM to a certain amount? Is over-revving a problem only when the RPM governers are damaged or so?
Title: Saying goodbye to warbirds
Post by: ViFF on June 16, 2003, 07:32:16 AM
There are two situations I can think of where a pilot can over-revv his engine:

In fixed pitch props it would be pretty easy.. prop blades don't change angle, so as airspeed increases (like when in a dive) the airstream will windmill the prop and shoot engine rpm's above red line limits. It all depends what angle the blades are fixed at to boot. Varies with different a/c. Some are fixed to low speeds like in trainers or banner towing a/c, some for higher speeds like the Hurri Mk1a or older ww1 a/c.

Same with Variable pitch (VP) props which are not CSVP. These types have a direct linkage from the blade angle to the Prop lever in the cockpit, the pilot has to constantly monitor the RPM gauge and manage the prop angle as airspeed increases/decreases to avoid over revving or underevving.

CSVP uses an indirect linkage, they still have a prop lever next to the throttle, but it sets an RPM  as opposed to a BLADE ANGLE like in the older generation variable pitch props. CSVP has been the standard since WW2, so thats a no brainer. The biggest advantage of a CSVP over the old VP is that it reduces pilot workload. All the pilot has to do is move the prop lever to set an RPM, and the prop governor will do it best changing the blade angles to keep that RPM as he transitions through various airspeeds.

Now in both VP & CSVP the prop governor has an angle limit to how far it can change the blade of the prop to compensate for the extra speed.

Its modelled verywell in Aces High as well. Take a Mustang up to 26k, make sure your at max RPM (2,400 i think ?) and start diving with WEP. Somewhere around 550-600 IAS you'll see that the RPM actually rises beyond the MAX you usually see, and you will hear the audible increase in engine RPMS.  Thats the point where the prop governor has reached its MAX coarse pitch available (somewhere around 35-45 degrees in actual blade pitch) to compensate for the increased airspeed windmilling the prop.

The other case I can think of (and this is not moddeled in AH) is if the prop governor is damaged, and the blades are stuck at a certain angle. Overreving would then occur much like in a fixed pitch prop. This is modelled in WW2OL and IL-2.
Title: Saying goodbye to warbirds
Post by: ViFF on June 16, 2003, 07:48:34 AM
Just as a point of interest, I should note that AH does NOTmodel the interaction between manifold pressure and prop rpm. Over revving an engine is not the only thing a pilot needs to worry about, but also about over torqueing an engine.

When you increase pitch on a blade (reduce rpm's), its harder for the engine to turn the prop, cause of the higher angle of attack between the blade and the airstream its plowing through. In a real aircraft, you can set a certain MP/Boost setting (for piston engines) or N1/2 setting (for turboprops). If you horse around with the RPM lever you see how the engine responds...

Increase RPM (reduce pitch) and the engine MP will drop (less torque on the engine cause the prop causes less drag/lift due to lower angle of attack as it plows throgh the air around it).

Decrease RPM (increase pitch) and the engine MP will rise (more torque on the engine cause the prop is trying to plow through more air).
Title: Re: Re: Saying goodbye to warbirds
Post by: joeblogs on June 16, 2003, 12:20:12 PM
It is possible to overspeed a plane with a constant speed propller in a very steep dive.  

All that it takes is to push the propeller governer to the stop.  Then the remaining excess power will drive the engine faster.

That's why manuals for WWII US planes include instructions on RPM management in a dive.

Yes it would be far worse with a fixed pitch propeller.

-Blogs

Quote
Originally posted by beet1e
Zanth, you are absolutely WRONG. The way AH has it modelled is correct. And that's because most of the WW2 planes had constant speed, variable pitch propellers. I have had to explain this so many times that I saved the explanation, and reproduce it below in blue text, extracted from an old BBS post.

Many of these planes had constant speed variable pitch propellers. As power is increased, the pitch of the propeller blades increases. The load on the prop also increases so the set speed is maintained. In a climb, the prop would tend to slow down. The prop governor detects this and adjusts the blades to a finer pitch - again, to maintain the set speed. In a dive, loading on the prop is reduced, the pitch increases. I believe that early Spitfires did not have the VP prop, and the pilot would have to throttle back in a dive to avoid over-speeding the engine. The VP prop is able to soak up that power by adjusting the pitch, and no need to throttle back.  If throttling back, the only time the engine RPM would decrease is when the pitch of the blades reaches minimum and the throttle is closed still further.

If you’ve ever flown a real plane with fixed prop, and then move onto something with a CSVP prop, believe me, you would never want to go back! It makes engine management so much easier. You just have to remember to increase throttle to maintain manifold pressure as the plane gains altitude. But you’d have to do that anyway even with a fixed prop, as power/RPM decreases with altitude.

For me, the way Aces High models CSVP props is one of its good points. I wish WB would too.

Over to funked to explain how CSVP governors work - something to do with lead weights sliding along the prop shaft in response to centrifugal force?  Geez, I’m lost already.

Two of my former Dutch squaddies (Lapwin & Zepher) took a ride in a real P51 - I have the film they made. And when Lapwin landed he made the comment that the engine note remains unchanged in dives/pullups. I don't think he had believed it until that day, and as he walked towards the camera he said "Scrmbl was right". :D Of course I was right!

Now, if we could only get them to calibrate the magnetic compass the right way round instead of backwards, we would be in good shape. The compass is calibrated backwards in both AH and WB, but is correct in IL2.
Title: Saying goodbye to warbirds
Post by: Grimm on June 16, 2003, 12:31:25 PM
Quote
Originally posted by JB73
i have yet to be at 750 (close to sound barrier) in ANY plane in AH yet.

the closest i have gotten is 640 in a 163 @ 35,000 feet. the plane was fully compressed and the slightest touch of the stick sent me to the tower from too many g's.


JB73,

Here a stupid trick for offline horsing around.  

Take an AR234 with Rato pods,  Dont use the Rato.   start it in a climb and go do somethings around the house, return when you have alot of ALT.  

Put it full power in a medium to shallow dive and build speed.  Dont touch the stick go into compression and wait for the wings to break off.    

The Rato pods are still there,  Now hit the Rato and accelerate.  I think you will break 700 before you auger in....  

Its funny looking because the wings are gone, but the Pods are just hanging in midair.
Title: Saying goodbye to warbirds
Post by: flakbait on June 16, 2003, 01:46:59 PM
What ViFF said. (btw, max RPM in a P-51 is 3 grand)

For the most part it's fairly hard to over-rev the engine with a constant-speed prop. Starting your decent from cruise without adjusting power in a Cessna would probably do it, but WW2 fighters are a different story. Hamilton-Standard props had a gear/roller-cam arrangement that regulated RPM with oil pressure, while others had the spring system mentioned above. Curtiss Electric props are marvelous little doohickeys that use an electric motor to directly control prop pitch. When you set, say, 2,500 RPM there's two things happening...

For the H-S type props a governor-controlled valve opens, letting oil pressure on the outside of the dome-plate rise. When that pressure rises, the plate pushes back against the roller, rotating a sleeve via the cam on the ass-end of the prop dome. At the same time, oil is let out from behind the dome-plate. The sleeve has beveled gears on it that match up with the prop blades, and when the cam is moving backwards it sets high RPM. Oil pressure on the inside of the dome plate acts like an RPM "lock", via hydraulic force. Since you can't compress a given volume of oil into a smaller volume, pressure rises. Prop governors are driven by the engine, and as engine speed increases the governor wants to dump oil in behind the dome-plate to lower RPM. But, if that roller cam hits the stop, the blades are at full low RPM and speed is still increasing. After a certain point hydraulic "lock" takes over, and the prop is driving the engine. If RPM is already at redline, don't plan on getting away without any engine damage. With any H-S type prop you'd probably end up blowing the prop control oil line to the hub. Along with the valves and valve heads if this condition went unchecked. What about glycol lines? If pressure went unchecked, those could possibly blow too.

With spring-type props, the same thing happens. At high speed the governor starts letting oil out from behind the dome-plate while the spring is slamming that plate right down to the stop. But, unlike the H-S type, you don't have to worry about blown oil lines. You'd probably end up with some damage to the cylinder valves but beyond that not much would happen.

Curtiss Electric props give direct control over blade pitch, but had it even worse than the H-S. When it worked the Curtiss prop could set exact pitch, and RPM, however you wanted it set. It did this via an electric motor. But if the electric motor crapped out, or the wiring corroded, it would "run wild" because there wasn't any oil pressure used to control RPM. Electrically adjusted Hamilton props don't have this problem: If the motor conks out, the prop governor tries keeping the last RPM setting.

No matter which type of prop it is (even the new Hartzells and McCauleys), every one of them has the same problem. Once the mechanical limits of the prop governor, dome-plate, or pitchmotor have been reached the propellor is not a constant-speed prop anymore. It's a fixed pitch prop. Remember though, really bad things only happen when you over-rev the engine. And that takes at least 400mph or more in these aircraft. Some won't start to over-rev until nearly 500mph. Going up around 550-600mph makes all this a moot point; the prop blades probably would've shattered at that point from blade-tip speeds going super-sonic.


See the above link from AVweb for really detailed info.

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Title: Saying goodbye to warbirds
Post by: Eagler on June 16, 2003, 01:48:20 PM
set all sounds to 75-80%(max) and wind at 100%, crank up wav volume in windows
Title: Saying goodbye to warbirds
Post by: Kweassa on June 16, 2003, 06:41:08 PM
Hmm..

 Thanks for the explanation guys.

 I was really having doubts about whether a WW2 plane can just go merrily into a full throttle power dive.

 So, would it be safe to assume that while there may be different tolerance levels to certain speeds according to plane type, usually pilots would not think to use full throttle in steep dives and chases, for the sake of their engine?
Title: Saying goodbye to warbirds
Post by: brendo on June 16, 2003, 07:52:10 PM
The little aeroplance I fly has a fixed prop, so you have to be constantly managing the throttle to ensure that you do not over-rev and also still have best power out of the engine through various speeds.

My engine does sound like the Warbirds sim sounds. But the problem is nearly no WWII aircraft had a fixed prop in 1939.

Your engine shouldnt sound like it is going up and down like a car.

Gratuitous image below
(http://www.members.optusnet.com.au/poges/over.jpg):D
Title: Saying goodbye to warbirds
Post by: naziteck on June 16, 2003, 08:25:33 PM
HEY GUYS WHEN IS ACES HIGH GOING TO COME OUT ????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????????PLZ TELL ME!!!!!!!!!!!!!!!!!!!!!!!!!!??????????????????????????????????????????????????????????????????????? PLZ
Title: fixed props in '39
Post by: joeblogs on June 16, 2003, 08:56:53 PM
Uhh yes some did...

Quote
Originally posted by brendo
The little aeroplance I fly has a fixed prop, so you have to be constantly managing the throttle to ensure that you do not over-rev and also still have best power out of the engine through various speeds.

My engine does sound like the Warbirds sim sounds. But the problem is nearly no WWII aircraft had a fixed prop in 1939.

Your engine shouldnt sound like it is going up and down like a car.

Gratuitous image below
(http://www.members.optusnet.com.au/poges/over.jpg):D