Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: Wildcatdad on November 20, 2013, 07:53:33 PM
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Okay, so what plane do you guys think is the most survivable and for what reasons. I know some planes have lots of armor, but what do you guys feel takes a bunch of damage and returns home? Also, what do you feel soaks up the most damage? Note: Bombers not included. :salute
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P-47s and FW-190f
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What he said along with F4F/FM2 and F6F.
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Hellcat.
- oldman
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Pick a fast one... Fast planes survive by not being around to shoot at... It would bore me to death to play the game that way, but it seems to be the trendy thing to do... :bolt:
I've been enjoying getting into furballs in planes that really aren't fast enough to get away, and seeing how long I can stay alive. Way way way way more fun than cruising around at 14k in a Pony/190 etc looking to dive/shoot/extend to a safe distance... ::yawn::
edit to change a then into a than, because that kind of thing annoys me sometimes!
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The most survivable . . . hmmm . . .
I'd say the P-51, La-7, and FW 190D-9, since they are the fastest down low and have other attributes as well.
For sturdiness, the A-20 is by far the sturdiest plane that can be used as a fighter (although it might be disqualified since it's not classified as a fighter). The P-47, F6F, and F4U seem quite sturdy. Maybe the P-38, too.
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The plane that takes the most hits and keeps going? The Ki.
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Absorbing hits, F6F-5.
Most survivable in actuality at AH combat alts, Me262 followed by Tempest followed by La-7.
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I think the P47, 190A/F, and F6F all win the "absorb hits the best" game.
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From my personal experience.
Ki-43, Fm2, Ki-84 and the F6F
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109K seems to be pretty survivable. High speed at any altitude, tied for second best climb in the game, and enough acceleration you can afford to blow quite a bit of E on hard evasive maneuvers.
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I am surprised not to see Yak 9U comments. O thought they were really heavily armored? :headscratch:
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I am surprised not to see Yak 9U comments. O thought they were really heavily armored? :headscratch:
While I have not anything to stand on, I'd be willing to bet if anything the armor and structural integrity of the newer -9U and -3 are LESS than the older -7B and -9T.
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Okay, so what plane do you guys think is the most survivable and for what reasons. I know some planes have lots of armor, but what do you guys feel takes a bunch of damage and returns home? Also, what do you feel soaks up the most damage? Note: Bombers not included. :salute
:airplane: Anything that is in front of my .50 cals! Can't kill anything with them anymore. Some talk that they were toned down by the guys in the MLW arena, but I think most of mine is packet lost between me and the servers.
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Okay, so what plane do you guys think is the most survivable and for what reasons.
According to the stats page it is the P-40E. Only 52 deaths this tour, the lowest of any fighter. It also fits my personal experience since I don't remember ever shooting one down, while I blast LA7, P-51s and Spit16 left and right. These planes survive so well by doing the only logical thing - stay in the hangar where it's safe.
(http://media-cache-ak0.pinimg.com/736x/de/cf/fe/decffea38bf142387fc274660affb1e7.jpg)
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109K seems to be pretty survivable. High speed at any altitude, tied for second best climb in the game, and enough acceleration you can afford to blow quite a bit of E on hard evasive maneuvers.
Lol no.
A plane that can take a lot of hits - P-47D-40. Absolute tank.
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Lol no.
A plane that can take a lot of hits - P-47D-40. Absolute tank.
Of course its an absolute tank. It needs to be, considering it maneuvers like a freight van, has a big target profile, and is only exceptionally fast once you get above 20k. Hell, my 109K could run you down or escape your WEP'd up D40 at most altitudes on military power. With WEP my K4 is 20+MPH faster right up through 23k or so.
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The US Navy fighters in general can be damn tough to bring down. The F4F/FM-2 are just plain hard to hit solidly because they're so small, and even if you do hit them solid they can still soak up a ton of punishment before going down, while both the F6F and F4U generally need a good sustained hosing to drop (though the Corsair is more prone to losing the outer wing section). Even cannon fire may need more than a snapshot
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Of course its an absolute tank. It needs to be, considering it maneuvers like a freight van, has a big target profile, and is only exceptionally fast once you get above 20k. Hell, my 109K could run you down or escape your WEP'd up D40 at most altitudes on military power. With WEP my K4 is 20+MPH faster right up through 23k or so.
From my experiences a good burst from 6 .50 cals seem to take it down quite easily. A true flying tank in game is the IL-2. Cannon after cannon round just seem to be absorbed into the skin of the plane.
As far as that K4 "run you down" thing, no. The P47's are far heavier than the K4 and are the best divers in game.
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The P47's are far heavier than the K4 and are the best divers in game.
I don't think that is universally true.
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I don't think that is universally true.
The P47's don't compress like the 109 does at about 450 MPH.
The P47's have better stability and handling at higher speeds.
The P47's also are more resistant to parts shredding off in high speed dives.
In theory the P47 is technically better than the K4.
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The P47's don't compress like the 109 does at about 450 MPH.
The P47's have better stability and handling at higher speeds.
The P47's also are more resistant to parts shredding off in high speed dives.
In theory the P47 is technically better than the K4.
Sorry, I meant about being the best divers in the game. They do compress so dives from high altitude may be better for P-51s and Spitfires. It dives that terminate below 480mph the Mossie may gain ground on the P-47, not sure.
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F6F
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I notice FM2s and A-20s take a disproportionate amount of 50s to kill. I usually fly the 51D, and I can't count on a snapshot to kill either one of them. So it's either don't engage, or chop throttle, drop the flaps and see if I can nail them before I am out of E.
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I notice FM2s and A-20s take a disproportionate amount of 50s to kill. I usually fly the 51D, and I can't count on a snapshot to kill either one of them. So it's either don't engage, or chop throttle, drop the flaps and see if I can nail them before I am out of E.
Pretty bad proposition. You're giving up pretty much every advantage the P-51 has and playing right into the strength of the FM-2.
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If you find yourself completely compromised, i.e. at a major disadvantage in E, pursued by multiple attackers or up against an uber fighter, you might have fun in a zero. Sure, it can't take hits. What it can do is evade really well while maintaining the ability to achieve superior angles and turn to the offensive. If the pilot maintains SA, and has reasonable familiarity with the aircraft, you will find him hard to shoot down. If he can get the fight co-E, then you'll really struggle unless you're much better. In WWII, zeros were lost in droves only when the quality of the Japanese aircrew had been significantly degraded when compared to US pilots. I do not fear fighting anything in the zero one on one - even when I'm at a significant E disadvantage. If I'm in most other fighters in a 1-1, I feel that the relative E state and relative aircraft performance are much more likely to dictate the outcome. When you practice what I call the boom and turn, then the zero is at its best. This is when you have E (usually much more altitude) than an opponent. You dive on him and raise your airspeed to the point that his nominal advantage in straight line speed is nullified. If he tries to run, you will overtake him. If he tries to turn then he finds himself turn-fighting a zero. The key is superior SA. You must have it to survive in a zero. I get killed often, but mostly on slash attacks by unseen cons in 1 vs. multiple opponent situations. I know you'll laugh, but I think that if I play my game, I have the strongest chance of survival in an A6M5. You'll find it hard to hit me in your P47 one on one and I'm certainly no great pilot. Granted, your P47 or F6 can soak up damage. It's much easier to hit you, though...
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Spitfire had a higher critical mach than the P-51, which in turn had a higher critical mach than the P-47. So the P-47 should not be the best diver in the game.
So what factors effect diving capability? All planes are acted on by gravity (9.8m/s^2), so that's a constant. So wouldn't it boil down to drag and thrust? Wouldn't the plane that accelerates fastest in level flight also accelerate fastest in a dive?
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To an extent, but weight also has a bit to do with it as well. Keep in mind that the Corsair and Hellcat don't have great level acceleration, but both have very good dive acceleration.
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The P47's don't compress like the 109 does at about 450 MPH.
The P47's have better stability and handling at higher speeds.
The P47's also are more resistant to parts shredding off in high speed dives.
In theory the P47 is technically better than the K4.
I never understood this thinking... When you have (or worse don't) altitude, diving only gives you so much time to get separation. And then the guy runs you down. Now the K-4 will climb, right to 19,000ft wep up and run you until your 100+ miles behind enemy lines if he needs to. Diving IMHO is just as valuable as roll rate. Ya it's good, but it won't keep you alive.
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Actually, rate of roll is VERY valuable. The ability to change directions quickly can make a HUGE difference in a fight
Also, keep in mind diving ability has more value than an ability to get away. If I'm in a Corsair, I have confidence that aside from a handful of opponents, if someone goes nose down to try to escape they're not going to get away from me because I WILL run them down, and at high dive speeds will also be able to outmaneuver them in a high-speed dive, to boot.
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In level flight, T - D = m * a, where a is acceleration, m is mass of aircraft, T is thrust, and D is drag; or a = (T - D) / m. T = thrust of engine, D = drag = 0.5 * C_D * rho * v^2 * S, where C_D = coefficient of drag, rho = density of air, v = velocity of aircraft, S = wing area. Let me define Z as 0.5 * rho * v^2 * S. Then D = C_D * Z. Also from aerodynamics of airfoils, C_D = C_D_min + C_L^2 / (pi * e * A), where C_D_min is drag at zero lift, e is Oswald's efficiency factor, and A is aspect ratio of the wings. In level flight, L = W = weight = m * g = C_L * Z. Overall, a = T / m - C_D_min * Z / m - m * g^2 / (Z * pi * e * A).
So, in level flight, a is highly negatively impacted by m. Not only do you have the T/m term, but m * g^2 / (Z * pi * e *A) is substantial (the contribution to drag as a result of generating lift). C_D_min is much smaller than drag due to lift in level flight.
In a vertical dive pulling zero g's of lift, T + W - D = m * a. Overall, a = T / m + g - C_D_min * Z / m, as lift and thus C_L is zero. Here, T/m is negatively impacted by m, but at all speeds for WWII aircraft, and especially at speeds above near zero, T/W is much less than 1. So T/m is much less than g. C_D_min * Z / m is reduced as m gets larger, so the negative contribution from parasitic drag is lessened by larger mass.
Assuming that I haven't made any math errors (which is certainly possible), general trends from above: all else equal, a heavier plane accelerates more poorly in level flight (no surprise there) but accelerates better in a vertical dive (at least when starting at a high enough speed) compared to a lighter version.
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Assuming that I haven't made any math errors (which is certainly possible), general trends from above: all else equal, a heavier plane accelerates more poorly in level flight (no surprise there) but accelerates better in a vertical dive (at least when starting at a high enough speed) compared to a lighter version.
The math made my head hurt, but the end results are certainly borne out in game. As I noted before, the heavy Corsair and Hellcat certainly don't accelerate remarkably well in level flight (excluding the -4*), but point them at the ground and there's not a lot of opponents that can run on them or catch them in a dive.
* = There certainly seems to be an effect of the propeller that I don't see you accounting for, unless it's covered in the unintelligible (to me) stream of equations. For example: The F4U-4 is no lighter than the other Corsairs and its HP advantage over the other marks isn't really that significant, but it sure as hell accelerates and climbs a LOT better (not to mention the top level speed boost). The MAJOR difference is that four-bladed paddle prop. Or for a simpler example: The F4U-1A has improved level acceleration and climb over the F4U-1 despite the same engine output, loaded weight, and a marginal drag increase from the raised cockpit (the stall spoiler also added a small amount of drag on the starboard wing). The F4U-1 had the early toothpick prop, while our 1A is modeled with the later paddle-type.
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Anecdotal, but Gregory Boyington was shot down in a dive in his F4U by a Zero pursuing him.
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Anecdotal, but Gregory Boyington was shot down in a dive in his F4U by a Zero pursuing him.
Ya you might out dive the zero but I doubt you can out dive a bullet!
:salute
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I never understood this thinking... When you have (or worse don't) altitude, diving only gives you so much time to get separation. And then the guy runs you down. Now the K-4 will climb, right to 19,000ft wep up and run you until your 100+ miles behind enemy lines if he needs to. Diving IMHO is just as valuable as roll rate. Ya it's good, but it won't keep you alive.
I've rarely had issues diving away in a 109. Unless I've got a big horde on my 6 o'clock, and they're all just spraying, D600 is usually enough separation that I can just motor away. Few exceptions being the La-7, F4U-4, and Tempest.
Besides escaping, diving evens out energy stats pretty well. And in the case of the K4, it also puts you ahead of your opponent in terms of climb and acceleration with almost absolute certainty, and puts you right up near the head of the pack for speed.
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* = There certainly seems to be an effect of the propeller that I don't see you accounting for
I didn't give any detail on that, but T is affected a lot by the propeller. T = eta * 375 * gamma * BHP / v, where eta is propeller efficiency, gamma is how much of full power is being applied (0 = none, 1 = full BHP), BHP = horsepower of engine, and v is aircraft velocity.
And of course BHP matters a lot.
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The P47's don't compress like the 109 does at about 450 MPH.
The P47's have better stability and handling at higher speeds.
The P47's also are more resistant to parts shredding off in high speed dives.
In theory the P47 is technically better than the K4.
The FW190A8/F8 don't compress like the P47s
FW190A8/F8 has better stability at 550mph+ than the P47s
FW190A8/F8 take at least as many bullets as a P47, and is also a much smaller target.
However a 190a8/f8 does not stand a chance 1vs1 vs pretty much any plane in a knifefight, even some 4-engine buffs out-turn it at slow speed (!). :headscratch:
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* = There certainly seems to be an effect of the propeller that I don't see you accounting for, unless it's covered in the unintelligible (to me) stream of equations.
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The MAJOR difference is that four-bladed paddle prop.
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I didn't give any detail on that, but T is affected a lot by the propeller. T = eta * 375 * gamma * BHP / v, where eta is propeller efficiency, gamma is how much of full power is being applied (0 = none, 1 = full BHP), BHP = horsepower of engine, and v is aircraft velocity.
The prop makes things much more complicated in a high speed dive. Paddle blade prop were much more efficient then the toothpick ones at low speeds and (at least in the case of the P-47s) increased climb and acceleration tremendously. However, they were less efficient at high speeds which reduced the low altitude top speed by a couple mph. Altitude factors in because at high alt the IAS which is the speed relevant to lift provided by a wing (fixed or rotating) is quite low. Most P-47 pilots considered this a very good trade off.
At high enough speed the prop starts to act as a speed break and instead of pushing the air through it, the wind is trying to rotate the prop instead. The RPM of the prop is limited which means that the angle of attack much be reduced at high speeds in order not to damage the engine and prop. Pilots had to reduce the RPM when entering such dives. At a terminal speed dive the prop is a huge hindrance and for this reason jets dive so much better then prop planes and also keep their over-speed better when leveling out. I do not know enough prop theory to say what kind of a prop is better in a dive, but I suspect that a prop with minimal filling factor (not sure if this is the correct term - the fraction of disk area filled by the blades) will be less of a problem in high speed dives.
Now, if you have two planes with a similar prop, one heavier then the other, and we are at a high speed dive where the prop is a major factor in drag, then engine power is irrelevant and weight is the only factor to counter the prop drag. Perhaps this is one reason the heavy American radials were good in dives.
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I'm not sure the 190A is as sturdy as a P-47. I've read lots of accounts of P-47's absorbing a lot of damage and making it back. Of course, reading about it and a statistical analysis are two different things, but it's the best I have to go on.
190A's can be excellent in a scenario environment (against their historical adversaries and historical conditions). 190A-5's did wonderfully in "Enemy Coast Ahead" against Spit IX's, for example.
(http://electraforge.com/brooke/flightsims/scenarios/201110_enemyCoastAhead/pics/frame1/013-workTheTiffie-Image-0020.jpg)
(http://electraforge.com/brooke/flightsims/scenarios/201110_enemyCoastAhead/pics/frame2/012-chasingDrBone-Image-0024.jpg)
(http://electraforge.com/brooke/flightsims/scenarios/201110_enemyCoastAhead/pics/frame4/008-hitSpit-Image-0011.jpg)
And 190D's do fine against late-war allied aircraft there, too (such as in the scenarios "The Final Battle" and "Winter Sky"). The thing that helps them is the superb handling at speed, great roll at all speeds, and very low amount of oscillation upon control movement, making shots more precise, plus lots of firepower, lots of ammo load, and good top speed vs. their historical adversaries.
(http://electraforge.com/brooke/flightsims/scenarios/201204_winterSkyDeathGround/pics/frame1/003-kill38-SNAG-0002.jpg)
(http://electraforge.com/brooke/misc/9950/200711_zz/pics/frame2/014-hitP38-SNAG-0019.jpg)
(http://electraforge.com/brooke/misc/9950/200711_zz/pics/frame4/009-kill47-SNAG-0014.jpg)
(http://electraforge.com/brooke/misc/9950/200711_zz/pics/frame4/015-killTempest-SNAG-0023.jpg)
(http://electraforge.com/brooke/misc/9950/200711_zz/pics/frame4/024-killsSpit-SNAG-0043.jpg)
(http://electraforge.com/brooke/misc/9950/200711_zz/pics/frame3/003-snapWing-SNAG-0003.jpg)
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Thrust from prop planes drops off rapidly with velocity (like 1/v). Jet engines are more akin to constant thrust with velocity. Jets also tend to have lower C_D_min than prop planes. I think these are more the reasons that jet would accelerate faster in high-speed dives than propeller planes.
I haven't done the math on it, but my intuition tells me that props do not act like brakes at higher speeds but just that thrust goes to zero and that the reason prop planes hit a terminal velocity in a vertical dive lower than Mach 1 is that shock waves off various parts of the aircraft create an enormous amount of drag, enough to keep the plane lower than Mach 1, but not because of the prop.
I seem to recall that some dive experiments were done with some prop planes with prop removed, and they still hit compressibility and stayed there.
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I haven't done the math on it, but my intuition tells me that props do not act like brakes at higher speeds but just that thrust goes to zero and that the reason prop planes hit a terminal velocity in a vertical dive lower than Mach 1 is that shock waves off various parts of the aircraft create an enormous amount of drag, enough to keep the plane lower than Mach 1, but not because of the prop.
I seem to recall that some dive experiments were done with some prop planes with prop removed, and they still hit compressibility and stayed there.
Unless the prop is feathered it will be windmilling and that means drag and lots of it. To be effective, the rotation speed of the blade needs to be similar or faster then the air velocity through the prop disk. This is probably the reason to remove the props on the experiments that you mentioned. If I recall correctly, the dive speed record in a Spit included the prop breaking apart during the dive.
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Unless the prop is feathered it will be windmilling and that means drag and lots of it. To be effective, the rotation speed of the blade needs to be similar or faster then the air velocity through the prop disk. This is probably the reason to remove the props on the experiments that you mentioned. If I recall correctly, the dive speed record in a Spit included the prop breaking apart during the dive.
Again, I could be wrong and haven't done the math, but my intuition is that, if you look at tip speed at top level speed and full RPM, we'll find that tip speed in a 0.9 M dive and lower RPM wouldn't imply that the disk of the prop is acting as a brake.
I believe that the main effect of props at very high speeds is that the tips can go supersonic, making thrust go to near zero, but not significantly less than zero.
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Doing some quick calculations shows (if I didn't make a math mistake) that prop tips for fighters are commonly supersonic during just normal flying.
Consider a P-47 with a 13' diameter prop running at 2700/2 RPM (divided by 2 since gear ratio to prop is 0.5 for the P-47). From v = r * domega/dt = 13'/2 * 2700 rev / 2 min * 2 * pi / 1 rev * 60 min/1 hr * 1 mile / 5280 ft = 626 mph, which is the speed of the prop tip when the plane is sitting still. When the plane is moving forward, the speed of the prop tip is sqrt(v^2 + 626^2), where v is speed of the aircraft. It doesn't take much speed of the aircraft or much altitude to get prop-tip speed to mach 1.
At 15,000 ft., mach 1 is 721 mph, so once you hit 360 mph true, the prop tips are supersonic.
Prop efficiency goes to zero as speed of a prop plane nears mach 1, but I don't think that it goes negative. So I don't think that the prop is acting as a brake during a high-speed dive.
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Prop efficiency goes to zero as speed of a prop plane nears mach 1, but I don't think that it goes negative. So I don't think that the prop is acting as a brake during a high-speed dive.
Prop drag goes up dramatically as the prop approaches Mach 1. It becomes, in effect, a giant air brake....
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Prop drag goes up dramatically as the prop approaches Mach 1. It becomes, in effect, a giant air brake....
I don't think so. I think its thrust goes to zero (or near zero), not that the prop acts like an air brake at high speeds.
A windmilling prop acts like a brake (unlike a stationary, feathered prop) because energy from the air flow is being used to rotate the engine faster than it would otherwise rotate (i.e., faster than if there were no wind). For example, with a plane parked on the runway, chop throttle to zero and set prop RPM to RPM_max, and the prop for a lot of planes won't be spinning at RPM_max. It will only get to RMP_max under that throttle setting if something else ads power to the rotation.
In a full-power dive to high speeds and prop RPM set to RPMx, your engine is already spinning it at RPMx, and it will maintain RPMx in the dive. It would only act as a brake under a particular condition that I don't believe to be the case in high-speed dives, namely drag on the prop so great that the full HP of the engine can't spin the prop at that speed by itself. I doubt that's the case for 1500 to 2000 HP engines even if much of the blade length is supersonic.
I could go through calculations on that (working to figure out the drag on the blades at, say, 0.85 M, and seeing if 1500 HP can't still spin it). That seems like a lot of work, so I'll ponder if there is a simpler way to show it.
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If you look at what portion of the prop is supersonic, you find that there isn't that much extra prop length subjected to sonic or transonic drag between max level speed at 30k and some portion of a terminal-velocity vertical dive.
At 30k and 430 mph for a P-47D-40 on WEP, at a point 0.84 along the prop blade, it is travelling at Mach 1. (At 30k, speed of sound is 678 mph. So, (f * 626)^2 + (430)^2 = 678^2 happens at f = 0.84.) The prop at 30k max-speed flight is certainly not an air brake, and 1 foot of the prop being supersonic isn't enough to absorb all engine power reducing thrust to zero.
At 15k and 0.85 M, at a point 0.61 along the prop blade, it is travelling at Mach 1. (At 15k, speed of sound is 721 mph. So, (f * 626)^2 + (0.85 * 721)^2 = 721^2 happens at f = 0.61.) The point where the prop is supersonic is 0.23 * 6.5 feet more, or 1.5 feet more than the 30k case.
1.5 more feet of prop blade being subjected to transonic drag isn't likely, I don't think, to turn the prop from generating still substantial thrust into an air brake.
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I could go through calculations on that (working to figure out the drag on the blades at, say, 0.85 M, and seeing if 1500 HP can't still spin it). That seems like a lot of work, so I'll ponder if there is a simpler way to show it.
Put your pen down for a minute Brooke. I think you are confusing drag on the plane (=force pushing the plane backwards) and drag on the blade. I am not an aero-engineer, but lets try to think this over together. Lets assume that your engine has enough HP to keep the constant RPM regardless.
The usual description of lift and drag is with respect to the bulk airflow, so forces directed along the flow are drag and those perpendicular to it are lift. Now look at the flow from the point of view of the blade. It has airflow coming at it due to rotation at speed w*r (w=rotation frequency, r=radius of prop element) and another component of speed due to the travel of the plane through the air: v.
This gives an angle "b" to the total flow:
tan(b)=v/(w*r)
In order to have a positive angle of attack, the blade has to be pitched at an angle greater than "b" (pitch=0 is idle, pitch=90 is feathered). As you can see, the angle depends on "r" and this is why props have a twist to them, to keep the angle of attack constant at a certain optimized speed v! (w is constant).
Now lets look at the blade as a wing. It has lift Lb and drag Db. I use the "b" in Lb and Db to emphasize that we are looking through the point of view of the blade. Lb and Db are relative to the airflow on the blade. I'm sure you can convince yourself that this flow is tilted at an angle 90-b from the direction of travel of the plane. Therefore, only part of Lb contributes to pulling the plane forward and part makes it harder to rotate the blade. Same for Db, some of it slows the plane down and some resists the rotation of the blade.
The thrust for the planeis:
T=Lb * cos(b)
and the "anti-thrust" or "prop drag" that tries to slow down the plane is:
D = Db * sin(b)
You can already see that when the plane's speed "v" increase, "b" increase and therefore T goes down, while D goes up! The lift and drag on a wing have very similar expressions except for a different coefficient for lift and drag, which are a function of the angle of attack. If the lift coefficient is CL, the drag coefficient CD scales like CL^2. Therefore we get approximately:
D/T = CD/CL * v/(w*r) ~ CL * v/(w*r)
You can see that if "v" is getting larger than the blade rotation velocity w*r, you tend to produce more prop drag than thrust. At some point the net prop drag will be larger than the thrust. From here you can also see that increasing the the RPM (w) is generally more efficient than increasing the angle of attack (increasing CL), as long as you do not go sonic with the blade.
The complete picture is worse. We did not include form drag on the blade which will increase hugely when it goes supersonic. Since this operates in the same direction as Db (which we used as induced drag only) it will also have a component in the direction opposite of the plane travel. Also, the blade has a twist, i.e. a variable pitch angle as a function of length, which as we mention is optimized for a given RPM ("w") and plane velocity ("v"). If you increase "v" much beyond the optimized conditions, parts of the blade can get into a negative angle of attack and produce even more effective prop drag. Think of an infinite "v" (effectively v>>w*r) - the blade does not rotate and is pitched entirely into the airflow as if it was feathered. Part of the blade produce lift that tries to rotate it one way and the other part produce opposite lift, and both parts produce induced drag that slows the plane down.
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When Curtiss Wright was testing transonic propeller designs, they used a P-47D-40-RE to do the high Mach dive tests. To establish a baseline for the airframe alone, they removed the blades from the propeller on the Jug. They installed lead ballast to provide for the correct CG. The engine was functional, solely for the purpose of generating hydraulic and electrical power. The prop-less P-47 was towed to 32,000 feet by a specially rigged B-29. After getting airborne, test pilot Herb Fisher started the engine and folded the landing gear.
At altitude, at 330 mph TAS, Fisher pulled the release handle and rolled into a near vertical dive. The P-47 attained a maximum speed of Mach 0.88, before Fisher initiated the pull-out (using the dive recovery flaps). Fisher started the engine to get hydraulic power. He flew the Jug down to a picture-perfect landing, despite suffering some damage to the control surfaces.
Repaired, the same P-47 was used for more than 100 dive tests. The maximum dive speed ever attained with a propeller installed was Mach 0.83 (on three occasions). The typical dive was in the Mach 0.79 to 0.80 range.
The difference was the drag of the propeller. Being an airfoil, prop blades are subject to the same physics as any airfoil. The drag rise as the blades approach Mach 0.8 is rapid and charts almost vertically. The dynamic loading on blades can be extreme. Fisher suffered two instances where blades were distorted from the loads. It was not unusual for prop shafts to shear under the stress. Indeed, a Spitfire PR managed to just exceed Mach 0.9 AFTER the prop shaft had sheared during a dive (there was other airframe damage as well).
Fisher's P-47. This is one of the propellers that was later distorted during a dive. The blades were bend back 9" measured at the tips.
(http://www.mediafire.com/convkey/c0b7/70u88s296c8xmt7fg.jpg)
One of Herb's dive tests, plotted....
(http://www.mediafire.com/convkey/2209/ednh1l1r47iyl3tfg.jpg)
Here's useful link to a document that may help readers understand drag issues at transonic airfoil speeds...
http://www.dept.aoe.vt.edu/~mason/Mason_f/TransonicAeroPres.pdf (http://www.dept.aoe.vt.edu/~mason/Mason_f/TransonicAeroPres.pdf)
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Here's useful link to a document that may help readers understand drag issues at transonic airfoil speeds...
http://www.dept.aoe.vt.edu/~mason/Mason_f/TransonicAeroPres.pdf (http://www.dept.aoe.vt.edu/~mason/Mason_f/TransonicAeroPres.pdf)
Interesting read. Thanks.
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When Curtiss Wright was testing transonic propeller designs. . . .
Thanks, Widewing. That is a great post.
I'd say I was quite definitively wrong in my thoughts about prop effects in compressibility and stand corrected. :aok
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In aceshigh the most survivable aircraft is the P51.
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Put your pen down for a minute Brooke. I think you are confusing drag on the plane (=force pushing the plane backwards) and drag on the blade.
Good to point out, but I'm not misunderstanding that and know the directions of the various vectors in play.
I'm also aware of how drag varies with speed, including the increase in the transonic region (i.e., this sort of thing:
(http://www.aerospaceweb.org/question/aerodynamics/area-rule/transonic-drag.jpg)
My feeling was based on propeller theory (which isn't wrong) with the added estimation of how big is the effect on the prop of compressibility/wave drag in the terminal-velocity dive (where I was wrong). I have a reference with experimental data that are good up to a prop-tip speed of about Mach 1.05. But 0.85 M at 15k gives a tip speed of Mach 1.2.
From Widewing's post, extrapolation from tip speed of 1.05 M to 1.2 M isn't good enough. There are other factors that come into play beyond what the extrapolation accounts for.
Thanks, guys -- I do stand corrected. <S>
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This is not on topic exactly, but one of the things from Widewing's post that strikes me is how amazingly courageous those test pilots were in doing those dive tests.
Test pilots were brave overall, but taking planes that sometimes came apart in terminal-velocity dives and doing repeatedly as a test seems especially brave.
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In case anyone is interested in props outside of compressibility speeds.
T = eta * 375 * gamma * BHP / v,
where T is thrust in pounds, eta is propeller efficiency, gamma is a factor for how much of full power is being applied (1.0 for full power, 0.5 for half power, 0 for no power, etc.), BHP is the brake horsepower of the engine, and v is the aircraft velocity in miles/hour. eta depends on aircraft speed and properties of the particular propeller. It can be looked up for particular aircraft, or it can be estimated in a variety of ways (some better than others, of course).
For props with good ability to absorb the power of the engine, it can be approximated reasonably well by knowing the advance ratio (J) and the power coefficient (C_P):
J = 88.0 * v / (N * D),
where v is aircraft speed in mph, N is prop rotation in RPM, and D is prop diameter in feet; and
C_P = 52.5 * gamma* BHP / [(N / 1000)^3 * D^5 * rho / rho_0],
where gamma is fraction of full power being applied, BHP is engine brake horsepower, N is prop RPM, D is prop diameter in ft, rho is the air density, and rho_0 is the air density at standard sea level.
With these, you can get eta from charts like this one:
(http://electraforge.com/brooke/flightsims/aces_high/stallSpeedMath/eta.jpg)
This is all without corrections for compressibility. Here is a chart of effect on prop efficiency from compressibility based on numerous experimental tests:
(http://electraforge.com/brooke/misc/aces_high/etaAdjustment.jpg)
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I don't think so. I think its thrust goes to zero (or near zero), not that the prop acts like an air brake at high speeds.
A windmilling prop acts like a brake (unlike a stationary, feathered prop) because energy from the air flow is being used to rotate the engine faster than it would otherwise rotate (i.e., faster than if there were no wind). For example, with a plane parked on the runway, chop throttle to zero and set prop RPM to RPM_max, and the prop for a lot of planes won't be spinning at RPM_max. It will only get to RMP_max under that throttle setting if something else ads power to the rotation.
In a full-power dive to high speeds and prop RPM set to RPMx, your engine is already spinning it at RPMx, and it will maintain RPMx in the dive. It would only act as a brake under a particular condition that I don't believe to be the case in high-speed dives, namely drag on the prop so great that the full HP of the engine can't spin the prop at that speed by itself. I doubt that's the case for 1500 to 2000 HP engines even if much of the blade length is supersonic.
I could go through calculations on that (working to figure out the drag on the blades at, say, 0.85 M, and seeing if 1500 HP can't still spin it). That seems like a lot of work, so I'll ponder if there is a simpler way to show it.
I have to agree with Brooke on this. A prop axt as a giant airbrake but the is pulling which goes to figure that it would equal zero thrust. It is pulling enough to compensate for the airbrake but not enough to accerate the plane.
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P47, hellcat, and the Ki84 take the most punishment....the 51 if you fly it like it was designed for is probably the most survivable plane..(excluding the jet)..not because it can take alot because it cant....its just so damn fast.....
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P47, hellcat, and the Ki84 take the most punishment....the 51 if you fly it like it was designed for is probably the most survivable plane..(excluding the jet)..not because it can take alot because it cant....its just so damn fast.....
There are faster fighters in AH than the P-51. The P-51 is not the most survivable prop plane in AH regardless of how you fly it. Flown to maximize speed the Tempest is more survivable down low and the P-47M and N, Ta152, Bf109K-4 and Spitfire Mk XIV are more survivable up high.
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There are faster fighters in AH than the P-51. The P-51 is not the most survivable prop plane in AH regardless of how you fly it. Flown to maximize speed the Tempest is more survivable down low and the P-47M and N, Ta152, Bf109K-4 and Spitfire Mk XIV are more survivable up high.
didn't say it was the "fastest"......
and I assumed non perk rides.
K4 cant dive or get to the speeds a 51 can....
47 and 152 ill give ya :neener:
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The P47's don't compress like the 109 does at about 450 MPH.
The P47's have better stability and handling at higher speeds.
The P47's also are more resistant to parts shredding off in high speed dives.
In theory the P47 is technically better than the K4.
Better at being a brick? :rofl
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K4 cant dive or get to the speeds a 51 can....
they can go up to about 550-570 mph in a dive, not far or equal to a P51, they are much less controllable during that dive though.
One member of the few (eatg) did just that, following my A8 all to the deck, I could easy out-roll him easy during pull-up phase, but I missed my shot rolling into him, and he slowed down and could soon outmanoeuvre my plane and get one 30mm to hit.
If I had more altitude he would not have caught me though since terminal dive speed is over 600mph in the A8.
I read here in the forum the spitfire had higher dive speed than the 190a, but I have never seen anyone succeeding accomplish that i AH.
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I read here in the forum the spitfire had higher dive speed than the 190a, but I have never seen anyone succeeding accomplish that i AH.
It does, but that is past controlability for either of them. The 190 accelerates into the dive faster, but the Spitfire had a higher terminal velocity. The Fw190's dive acceleration is vastly more useful than the academic note about terminal dive speed that has no combat application.
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Without reading the entire thread. Has somebody put forth that such and such plane dives faster because it's heavier yet?
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Sorry, but I do not agree, I've been chased down to terminal speed many many times, with the two second-best divers after me (P47 and P51), I consider the p47 the most dangerous opponent in a dive.
It does, but that is past controlability for either of them. The 190 accelerates into the dive faster, but the Spitfire had a higher terminal velocity. The Fw190's dive acceleration is vastly more useful than the academic note about terminal dive speed that has no combat application.
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K4 cant dive or get to the speeds a 51 can....
they can go up to about 550-570 mph in a dive, not far or equal to a P51, they are much less controllable during that dive though.
One member of the few (eatg) did just that, following my A8 all to the deck, I could easy out-roll him easy during pull-up phase, but I missed my shot rolling into him, and he slowed down and could soon outmanoeuvre my plane and get one 30mm to hit.
If I had more altitude he would not have caught me though since terminal dive speed is over 600mph in the A8.
I read here in the forum the spitfire had higher dive speed than the 190a, but I have never seen anyone succeeding accomplish that i AH.
So basically the K4 isn't as good catching the 95% of aircraft that will have to flee from it's superior performance?
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Sorry, but I do not agree, I've been chased down to terminal speed many many times, with the two second-best divers after me (P47 and P51), I consider the p47 the most dangerous opponent in a dive.
How is that relevant to Spitfires?
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The P47's don't compress like the 109 does at about 450 MPH.
The P47's have better stability and handling at higher speeds.
The P47's also are more resistant to parts shredding off in high speed dives.
In theory the P47 is technically better than the K4.
The P-47 suffered from the same compressibility issues as the P-38 did in a high speed dive.
ack-ack
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:airplane: Anything that is in front of my .50 cals! Can't kill anything with them anymore. Some talk that they were toned down by the guys in the MLW arena, but I think most of mine is packet lost between me and the servers.
The .50 caliber machine guns have not been toned down, despite the claims of a few in the MW arena. Basically, those people have no clue as to what they're speaking of and have no data to back up their claims.
ack-ack
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More than likely they didn't know how to use them properly, either, and think just seeing hit sprites should be rewarded with giant chunks of the enemy's planes pop out.
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I tried to say I have never ever seen a spit even close to terminal speed of the 190a, but 47s, and 51s are good second with 550mph+
There used to be a FM error where the 110c could do a 540mph+ pullup from a dive, but I think HTC have fixed it.
How is that relevant to Spitfires?