Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: Minotaur on December 09, 2000, 12:02:00 PM
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I have dragged this topic over from another thread, but I feel that it is worth some clarification. The reason is that most commonly, any effect encountented by prop effects is slang labled as "torque" by the average player. This is much the same way as the term "compression" is often misused.
By HiTech:
<snip>
Just so everyone knows the effects from the prop. They are 5
1. Vortex / slipstream
2. Gyroscopic
3. Torque.
4. PFactor.
5. Thrust
<snip>
Thrust is the easy one to understand. No problems here.
Torque comes into play only when a change in prop/engine RPM occurs. Basically this change in RPM, attempts to cause the rest of the A/C to rotate in the opposite direction. For a CW rotational prop, torque causes CCW rotation on throttle up. IE: The A/C must provide counter torque by means of pilot control to remain wings level.
Gyroscopic forces are in effect at all times with the engine running. These forces are resisting the change of motion for the plane of motion perpendicular to the axis of rotion of any rotating component. The major rotating components are the engine and the prop. Any force applied to change this plane of motion is transferred to a point 90 degrees in the direction of rotation. IE: You apply force to the left front side of props plane of motion and this force is applied (translated) to the top front of the props plane of motion. This is for CW prop rotation.
Vortex / slipstream I am not completely sure about this one. I do know that thrust air flow is not laminar. This thrust air is created by a rotating propellor and also rotates in the same proportional speed and direction. This vortex of thrust air flowing over the A/C has a significant effect . In cases where the difference between A/C speed to thrust air speed is the greatest. IE: High thrust air speed and low A/C speed.
PFactor again I am also not completely sure about this one. However; I think that it has something do with prop rotation. This "something" being that the propellor blades rotate upward on one side of the A/C and downward on the other side. This somehow this causes thrust air to strike one side of the A/C with a greater amount of force than what strikes the oposite side of the A/C. Particularly the vertical part of the epinage. As is in the case of vortex air, this has greater effect at high thrust air flow rate with low A/C speed.
At one time there was a very good write up about these "Prop Effects" posted up on the HTC webpage, but I am unable to locate it now.
Keep in mind that I am not 100% on any of these prop effects and I am simply giving this thread a starting point. Those more knowledgable please chime in and help me out! (http://bbs.hitechcreations.com/smf/Smileys/default/smile.gif)
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Mino
The Wrecking Crew
"Best is the trash talk. Severly and viciously going after your enemies, their mothers, and their shabby sheep."
StSanta
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Slipstream: Causes Yaw due to one side of the prop slipstream hitting tail surfaces before the other side does.
Mot sure where the PF came from however "P" factor is: Your prop is like many different wings attached to your crankshaft each blade of the prop making its own thrust, so when your in high angles of attack the downward blade produce more thrust than those moving upwards and this also causes the aircraft to yaw.
So basically thorque is yaw which is a total of reactive forces, slipstream, gyroscopic precession and "P" factor.
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And what's perplexingly weird, there is very very torque on some planes, but a significant yawing effect (Typhoon) and on others there is alot of torque (109G10) with little yawing effect.
Some planes still feel right (P-51 has proportional torque and yaw) while some feel like they have neither (F4U) Without combat trim, auto takeoff, etc you can firewall several planes you only need to trim the nose up a bit, and apply slight rudder pressure till the tail comes up and the plane will fly it's self down the runway.
- Jig
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As an aside, I checked the Typhoon and Yak again, with all the autos off and neutral trim.
These two have the right torque but it is extremely week in both yaw and torque
These, and all of the planes have no immediate reaction to going from stall and idle to full throttle other then a nose pitch up (due to the force need to keep the nose up at that speed) None roll on their own axis, but all that I've looked yaw sligtly left, pitch up, and roll slightly left in what looks like a low speed high yoyo.
I'll post a film when I get home this evening.
- Jig
[This message has been edited by Jigster (edited 12-09-2000).]
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When looking at a plane with counter rotating propellers, will all 5 forces still be present?
Thrust will of course, but how is it for the others. Do they reduce ,enlarge or simply dissappear?
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jets are so much easier to model, stupid propeller
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Torque from accelerating the propeller mass is non-existent in every sim I've ever flown. It's always only an 'aerodynamic' torque, that being resistence to rotation of the blades, which for any constant rpm can be figured by
Torque = Horsepower * 5252 / RPM
The slipstream effects that I believe are being modelled are an increase in angle of attack on the left wing with a corresonding decrease on the right wing, which causes a *right* roll, that counters the torque effect mentioned above. Depending on how much wing area is involved and the slipstream velocity, it appears that this effect is overpowering the torque effect in some planes.
Given that the ailerons on say, an F4u at 100 mph can make some 20000 ft-lbs of torque, the aerodynamic torque of 3900 ft-lbs, which comes from 2000 hp at 2700 RPM is not very large and is easily countered with ailerons.
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The gyroscopic forces can be very spectacular. The aerobatic maneuver "Lomcevak" uses the gyroscopic force of the propeller to cartwheel in the air. It starts off as a roll with the tail describing a cone (much like these spinning toys when they start wobbling). here is an avi videa showing an Extra 300 doing a Lomcevak:
http://www.tote.com/tumble1.avi (http://www.tote.com/tumble1.avi)
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Thanks for moving this topic from my thread Mino. I wanted to discuss it a little more, but I was afraid A) My thread was too long, and B) My thread was degenerating into a flamefest. (http://bbs.hitechcreations.com/smf/Smileys/default/frown.gif)
I guess I'm looking for an expert opinion here: Is the torque in AH 1.04 at more realistic levels as compared to 1.03. 1.03 was pretty harsh on takeoff and landing for planes like the f4u, typhoon, and even the spit. Based on what I've read, this is realistic. In 1.04 the torque is still there, but it is no longer a factor to be worried about. I know that in 1.03 if I was flying a hog (offline of course (http://bbs.hitechcreations.com/smf/Smileys/default/wink.gif) ) and immediately after starting the engine I went immediately to wep the plane would be uncontrolable. Just about everything I read about *any* WWII fighter will say something about sudden increases in throttle during takeoff and landing. In 1.04 I punch wep immediately after the engine starts and I start to roll. There isn't a single plane that doesn't straighten out perfectly once the tail comes off the ground. To me this doesn't seem right. Why would the tail coming off the ground reduce torque effects so much? Is this realistic?
I think part of the fun (for me at least) was getting some of the bigger planes off the ground when heavily loaded with bombs. In 1.04 once the tail comes off the ground you have nothing to worry about.
(http://bbs.hitechcreations.com/smf/Smileys/default/smile.gif)
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bloom25
THUNDERBIRDS
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Well, maybe you need to split these up into two different groups.
Three of those YAW the airplane to the left (P-factor, Slipstream, and Gyroscopic)
Torque ROLLs the plane to the left (when you throttle up).
Slipstream is caused by the propellor blade vortex. They corkscrew around the fuselage and add preasure to the left side of the vertical tail fin. If there is an equal sized fin under the tail, this will cancel out the yaw motion, but adds more preasure to roll the plane, plus it is usually impractical and gets scraped on the ground in bad landings.
P-factor is when the airplane is pitched up at low speed, but moving horizontally. There is an angle for the propellor to work with. The decending blades on the right side of the prop arc are at high angles of attack, make more thrust than the ascending blades on the left. Yet more power to YAW the plane left.
Gyroscopic comes into play when you pitch up to get off the runway. You've just tilted a spinning disc, and it will react in a 90 degree angle, yawing you to the left. When you dive it yaws you to the right.
Torque is a whole different animal. You gun the engine and get that prop applying more force to the air, it will resist you and try to roll you the other way. Props usually "roll" to the right, so you will roll to the left when you make a drastic throttle increase.
Hans.
[This message has been edited by Hans (edited 12-10-2000).]
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Just a supposition....
What if all the forces are modelled correctly for a given throttle setting when flying, but with no modelling of the forces resulting from throttle changes? Wouldn't that produce the exact effects we see in the game now? The planes seem to have all the right forces acting on them when in flight at full throttle, but they don't show the reactions we are expecting when violently moving the throttle.
Also, how does propeller RPM fit into this? Regardless of how the engine SOUNDS, due to simplified engine management are we really changing the RPM of the engine or just increasing manifold pressure? Maybe we don't see the results because "firewalling the throttle" in the game is not the same thing as doing it in real life? It could be that all the forces are modelled including engine speed changes, but the simplified engine management doesn't let us really change the RPM of the engine to get the effects we are looking for.
Thoughts?
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Lephturn - Chief Trainer
A member of The Flying Pigs http://www.flyingpigs.com (http://www.flyingpigs.com)
"A pig is a jolly companion, Boar, sow, barrow, or gilt --
A pig is a pal, who'll boost your morale, Though mountains may topple and tilt.
When they've blackballed, bamboozled, and burned you, When they've turned on you, Tory and Whig,
Though you may be thrown over by Tabby and Rover, You'll never go wrong with a pig, a pig,
You'll never go wrong with a pig!" -- Thomas Pynchon, "Gravity's Rainbow"
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I was under the impression that gyroscopic effect was most apparent on WWI fighters with rotary engines. With a rotary, the prop is attached to the propeller and the whole spiel spins around the crankshaft. The mass of moving metal caused the aircraft to nose down in right turns and nose up in left turns.
I don't know how this relates to radial engines. I didn't think gyroscopic effect was really that big of a deal on WW2 fighers. Does the radial work the same way as the rotary, or are they essentially the same kind of engine with different names?
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Meine schwester hat keine kartoffel salat? Du bist eine lustige bube!!
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"but they don't show the reactions we are expecting when violently moving the throttle."
Huh? Get in a Spit 9 with no throttle damping and do some violent throttle motions on the runway. The plane jerks to the left pretty suddenly. Not sure what more you guys want. I don't fly the other planes much so maybe the Spit is the only one that does it?
[This message has been edited by funked (edited 12-10-2000).]
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PS Hans, I think you have the gyro yaw directions reversed. Remember angular momentum is conserved and the net angular momentum vector of the engine/gearbox/prop system points forward.
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I didn't think gyroscopic effect was really that big of a deal on WW2 fighers
It is mainly during start and stop (low speed) and when the plane is stalled that the gyroscopic forces are noticable since they are relatively weak compared with the aerodynamic forces under normal flight.
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(see Bod's post way above)
FYI the lomcevak (correct spelling?) has many varieties. It is basically a spin around different axes of the plane. It is a departure from controlled flight that is only in part due to gyroscopic effects, the maneuver is mostly due to aerodynamic effects...
[This message has been edited by washedup (edited 12-10-2000).]
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Originally posted by funked:
"but they don't show the reactions we are expecting when violently moving the throttle."
Huh? Get in a Spit 9 with no throttle damping and do some violent throttle motions on the runway. The plane jerks to the left pretty suddenly. Not sure what more you guys want. I don't fly the other planes much so maybe the Spit is the only one that does it?
[This message has been edited by funked (edited 12-10-2000).]
Right, such as the Typhoon which has an enormous prop and alot of horsepower. It only ever so slightly rolls to the right when going from right above stall speed to full throttle.
On other planes though, it's very evident...the G10, La5, P-51, (among others) have a strong jerk tendency when you punch it.
I doubt it is across the board but some planes seem to have very little reaction to throttle inputs.
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The lomcevak is a transition between an upright snap roll and an inverted snap roll. The elevator control is reversed 1/2 way through the maneuver when the plane still has lots of energy, before the upright snap is completed. The momemtum of the rotation combined with the opposite control input makes for a nose over tail kindof tumble before the plane settles into an inverted spin.
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Wells, what you are describing is definitely not a lomcevak. A lomcevak is a controlled maneuver (controlled by throttle. ie gyro effect). I found a good description on the net. I got the book they refer to, and it really is excellent reading (practiced a bit in a C-152 Aerobat, not the lomcevak though (http://bbs.hitechcreations.com/smf/Smileys/default/wink.gif). Another maneuver that needs gyroscopic forces to be done right and *controlled* is the flat spin by the way.
from http://www.charlesriverrc.org/articles/flying/donstackhouse_whatisalomcovak.htm (http://www.charlesriverrc.org/articles/flying/donstackhouse_whatisalomcovak.htm)
>Can anyone describe what a Lomchevak is. I have heard it several times and don't know what it is? <
That's easy! It's simply one of the most misunderstood families of maneuvers in the history of aerobatics. As solid evidence of this, I offer ALL of the previous posts to this thread!
If you REALLY want to understand Lomcovaks, find a copy of the book "Aerobatics" by the British champion aerobatics pilot Neil Williams, pub. by Airlife Publications, ISBN # 0 9504543 0 3 . Turn to page 189, the beginning of Chapter 22, "What is a lomcovak?" and begin reading. After you finish, go back to the beginning and read the entire book, you'll be glad you did. This is simply the best book on the general subject of aerobatics I've ever read!
A Lomcovak is NOT an inverted spin. It is NOT a non-precision maneuver. The pilot is NOT "just along for the ride". Recovery does NOT just occur at random without any control by the pilot. It is NOT a single maneuver, but rather an entire family of maneuvers, all of which are very precise and controlled from beginning to end IF they are properly done.
The key element in a Lomcovak is that the airplane's attitude and motion is controlled by four primary flight controls rather than the usual three. The fourth attitude control in this case is gyroscopic precession from the prop, controlled via the throttle. This is why it's extremely difficult (that's spelled i-m-p-o-s-s-i-b-l-e) to do a true Lomcovak with a model; in most cases our props simply aren't heavy enough to provide sufficent precession forces.
There are five main types of Lomcovaks. There are also variations within each type. All are performed under negative "G".
The one most folks are familiar with is the "Main" Lomcovak. This begins from an inverted climb. As airspeed decays to near zero, the pilot initiates something initially resembling an inverted snap roll, so that the aircraft has a rotation rate about the pitch, yaw and roll axes as it reaches zero speed. The aircraft performs three foward tumbles, each one at 45 degrees to the plane of the previous tumble. At the end of the third tumble, the aircraft recovers into a vertical dive.
The "Cap" Lomcovak begins like a hammerhead, but as the airplane rotates to the halfway point, with the fuselage horizontal and the wing vertical, a combination of gyroscopic precession (caused by the yawing rotation from the vertical entry) and down elevator cuases the airplane to perform a single forward tumble, with the plane of the tumble horizontal. As the plane returns to its initial position, throttle is closed and the aircraft yaws the rest of the way to a vertical downline for recovery. I haven't done a complete true Lomcovak myself, but I once did part of a positive "G" variation of this by accident in a DeHavilland Chipmunk, which is how I discovered that Chipmunks do not like to do hammerheads to the left! It's a really weird feeling the first time.
The "Positive Conic" and "Negative Conic" Lomcovaks describe a cone shape in the sky, with the airplane pointed upwards as it sweeps out the cone shape with its underside. The point of the cone is at the prop for the positive conic, and at the tail for the negative conic.
Finally, there is a version resembling the "Main" Lomcovak, but entered from knife edge rather than inverted flight. This one is particularly violent.
The pilot is near the center of rotation for most Lomcovaks. These maneuvers are very disorienting, but not generally too stressful in terms of "G" forces on the pilot. However, since Lomcovaks use the precession forces from the prop as one of the flight controls, as you might imagine, the forces on the prop, crankshaft, engine mounts and engine are extremely severe. The centrifugal forces on things like wing panels can also be surprisingly high, and usually totally different from what the engineers were thinking when the airframe was designed. It is prohibited in a number of aircraft, and results in severe life limits on the rotating components in a number of other aircraft.
Shortly after the maneuvers were invented by the Czechs, some of the top Russian pilots started trying them in their Yak 18's. Shortly after that, there were a series of prop, crankshaft and engine fractures on Yak 18's, including one where the entire engine was yanked off of the firewall by its roots! Right after that, the word went out from "upstairs" to the members of the Russian aerobatic team that anyone caught doing Lomcovaks in a Yak could expect his address to be changed to a gulag in Siberia IMMEDIATELY.
There are a number of other manuevers that also impose severe stress on props and engines. Snap rolls and flat spins are some of the worst. However, nothing can break a crankshaft quite so well as a good Lomcovak. One project I was involved in during my previous career (before I quit to go into the R/C model business full-time) was assisting development of a Kevlar-bladed prop for aerobatic aircraft that would have the strength to tolerate this sort of abuse, and low enough inertia to protect the engine as well. It was well received by the aerobatics enthusiasts, a number of whom had already been through the harrowing experience of landing an already sensitive and tailheavy aerobatic aircraft deadstick, with a few score pounds of aluminum missing from the nose.
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Interesting stuff.
Nobody has responded to my post about engine controls in AH.
When we "firewall the throttle" in Aces High, aren't we just changing the manifold pressure? If so, why would there be any extra torque? I wouldn't expect much of a reaction unless we quickly changed the RPM of the engine itself. I don't think we do this when we advance the throttle in AH. Somebody please correct me if I'm wrong. Also does this vary from plane to plane? I don't know.
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Lephturn - Chief Trainer
A member of The Flying Pigs http://www.flyingpigs.com (http://www.flyingpigs.com)
"A pig is a jolly companion, Boar, sow, barrow, or gilt --
A pig is a pal, who'll boost your morale, Though mountains may topple and tilt.
When they've blackballed, bamboozled, and burned you, When they've turned on you, Tory and Whig,
Though you may be thrown over by Tabby and Rover, You'll never go wrong with a pig, a pig,
You'll never go wrong with a pig!" -- Thomas Pynchon, "Gravity's Rainbow"
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From a logical stand point:
You can not fix engine RPMs and vary prop RPMs with a large change in speed. EG: the aircraft idles at 900 engine RPMs and stays there. If you could do this, you'd have aircraft that burned 5 GPH and ran over everything at speeds near 400mph. So, in order to increase speed you MUST increase engine RPM. Manifold pressure is one indication of changing engine speed.
Leph, every aircraft type will be different. Each engine can only pull so many inches of MAP, and props rotate at an individual speed. This means each aircraft will have it's own vices. Stomping the throttle in a 109 should flip you over. Do the same thing in a Jug and you'll probably do a good wing wobble. Weight, design, construction materials, engine speed, prop speed; each is different in every type of aircraft.
I don't know how or what HTC did to FUBAR prop RPMs. Dialing a Hog back to 35" MAP and 2,150 prop RPM should drastically increase range. It doesn't. Funked has proved fuel flow is too high at cruise settings in another post. Prop RPM is like an old Star Trek set joke; GNDN. Meaning it Goes Nowhere, Does Nothing. Torque from the engine, vortex effects etc... should literally give you whiplash if you stomp the gas in anything near stall. It doesn't.
Regardless what HT, Pyro, and GOD HIMSELF says, these effects have either: A) been SNAFUed or B) has a glitch that needs fixing. Either way, it's not correct right now. F4U takeoffs are a sinch, the 109 doesn't bite your bellybutton when you floor it, and the N1K2 simply screams down the runway like a jet. There is a problem, and it will get fixed.
Only question is, how long it'll take.
If I seem a bit peeved, it's because I miss the 1.03 effects. Something nice about watch some wanna-be hot rod slam into the tower on takeoff.
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Flakbait
Delta 6's Flight School (http://www.worldaccessnet.com/~delta6)
"For yay did the sky darken, and split open and spew forth fire, and
through the smoke rode the Four Wurgers of the Apocalypse.
And on their canopies was tattooed the number of the Beast, and the
number was 190." Jedi, Verse Five, Capter Two, The Book of Dweeb
(http://www.worldaccessnet.com/~delta6/htbin/custom1.jpg)
[This message has been edited by flakbait (edited 12-11-2000).]
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Hehehe, I understand your motivation flakbait. (http://bbs.hitechcreations.com/smf/Smileys/default/smile.gif)
All I am pointing out is that we have very simplified engine controls. When you talk about "stomping the throttle" in real life, this likely meant revving the RPM's up quickly. In AH, I don't think it works that way. I'll have to check tonight at home, but it seems to me our throttle pretty much only works the MAP, not RPM. All I'm saying is that you basically can't "slam the throttle" in AH in the same way, so we can't compare the two.
The thing is, do we ask Pyro to look at the forces themselves, or at how the engine controls are modelled? They are two very different things. I'll do some checking tonight at home and see what I find, but I suspect the control has something to do with it.
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Lephturn - Chief Trainer
A member of The Flying Pigs http://www.flyingpigs.com (http://www.flyingpigs.com)
"A pig is a jolly companion, Boar, sow, barrow, or gilt --
A pig is a pal, who'll boost your morale, Though mountains may topple and tilt.
When they've blackballed, bamboozled, and burned you, When they've turned on you, Tory and Whig,
Though you may be thrown over by Tabby and Rover, You'll never go wrong with a pig, a pig,
You'll never go wrong with a pig!" -- Thomas Pynchon, "Gravity's Rainbow"
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When we "firewall the throttle" in Aces High, aren't we just changing the manifold pressure? If so, why would there be any extra torque?
All the AH planes have constant speed propellers. This means that an automatic controller in the hub (in most cases) adjust the aoa, or pitch of the blades so that the RPM are constant regardless of engine power. If you increase throttle, the RPM wants to encrease as well, but when the controller feels this initial increase the pitch is adjusted so that the propeller grabs more air - the aoa on each blade is increased. With increased aoa the drag (torque) and lift (thrust) on each blade is increased so that the RPM is helt constant. When decreasing the throttle the controller will automatically decrease pitch. Very much like an automatic transmission in a car, but with infinitely many shifts.
Basicly this means that with the pitch lever, the pilot sets the RPM that the controller shall maintain, and with the throttle he sets the HP (thrust and torque). With a set RPM any change in throttle will change the torque.
With a set throttle a decrease in RPM will increase torque, but also decrease HP, so the net effect is slightly more torque and less thrust. Increae in RPM will do the opposite.
IMO the engine management is modelled correctly, with exceptions of the late war LW planes who all had Kommandogerät (everything is fully automatic with only one main lever to adjust, i think). The gyroscopic forces seems to be way too low IMO, but then i have never flown a real warbird.
[This message has been edited by bod (edited 12-11-2000).]
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Governors can only compensate so fast (about 2-3 degrees/sec or about 200 rpm/sec) If you cob the throttle faster than the prop can compensate, you should see an increase in rpms as well, before they settle back down.
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Not only can you hear this in a constant speed airplane (re: Wells' comment above), you can feel it with a noticable acceleration or deceleration.
The one thing that AH constant speed prop systems definatly does not do is increase manifold pressure when RPM's are reduced. You must reduce throttle before reducing RPM's with a real constant speed prop driven aircraft. Conversely, RPM's are increased before increasing the throttle setting. Reducing RPM's while keeping the throttle full forward can reduce engine life to a matter of seconds as internal engine pressures exceed the metal's ability to contain them. (I saw the results when this happened to a P-51 in 1991. Blew two holes through the engine casting when the connecting rods let loose. The pilot landed dead stick as he was over the runway when it happened.)
MiG
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As stated before, it's much like a transmission...say you start out in low gear with an automatic...
What will happen when you punch it? If it's got enough power the wheels are going to squal because there is more torque then is needed to set the car in motion. The transmission can't respond to engine speed changes instantly, and it does have limits on how much load it can put on the engine.
If it could instantly respond to engine RPM it would shift into second or third to supply enough load on the engine to keep the RPM's down and remove the excess torque, but that doesn't happen because of mechanical linkage. In contstant speed props the either the oil pressure or the electrical type hubs create a noticable delay between input of power untill the actual pitch change occurs (because the prop has to change speed first)
thus the delay in compensation, if I remember right. One has to change before the other.
[This message has been edited by Jigster (edited 12-11-2000).]
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MSCFS has a very good engine-model with seemingly correct RPM-manifold pressure-thrust relations which also take into account the dynamic behavior wells mentioned. Even the Komandogerät in the 190 is modelled.