Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: Chalenge on May 10, 2016, 02:56:31 PM
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The AHWiki has this information on some airplanes, but it is conspicuously missing from all 109 pages.
Has anyone worked out CV for the Bf109 lineage?
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I have always felt comfortable between around 250 - 275 mph. But that is a big gap.
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Yeah, especially since Spatula seems to have thought it was 225 for the P-51.
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clean stall speed multiplied by 2.44/2.45 which ever is easiest!
This should give a very close estimate to CV give a 6 G limit.
YMMV.
:salute
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Yeah, especially since Spatula seems to have thought it was 225 for the P-51.
225 is more like the 109F. Varying with weight and altitude.
clean stall speed multiplied by 2.44/2.45 which ever is easiest!
This should give a very close estimate to CV give a 6 G limit.
YMMV.
:salute
:aok
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CV is the minimum speed a plane can turn 6gs?
boo
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More or less. It is the minimum speed in which the aircraft can pull its maximum rated Gs. So if that's 6 Gs . . .
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6G is blackout limit in AH. Structural limit for the 109 should be around 8G.
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With the new move able HUD in the beta for speed\alt, you can move that onto your gunsight reflector plate and turn off the reticle. Then perform clean stalls while watching the HUD. I don't know if it shows up when filming, but a third party film capture should get it.
Always wondered if Hitech has a session file he can generate for each aircraft that gives you data like corner velocity. Wasn't Widewing working on those graphs at one time which gave CV relative to alt? Having that pop out with the speed and climb graphs would probably be overkill for the vast majority of piu, piu, piuers in our game.
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Corner velocity is only good to know! It cant be maintained in level flight so I consider it as something that's good to know but of little use in actual combat.
Something I find useful is the amount of G you can pull when below CV! Like in the case of the 190's at 225mph you can only pull 2.5 G before you will stall a wing! At that speed a spit can pull 5 G and a zero can pull to blackout.
Then there's weight and alt as both have effects on CV. So while it may be useful to know,it's not as useful as many think.
:salute
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Well, I would like to know if someone has an easy method of finding CV for each airplane, especially if that can be discovered "on the fly" as it were.
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Well, I would like to know if someone has an easy method of finding CV for each airplane, especially if that can be discovered "on the fly" as it were.
Just turn hard in a shallow descending helix until your speed reduces and you can't pull to black, then increase descent angle a bit more until you can. Continue to bracket the speed down to a reasonably accurate value.
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The easy way to find accelerated stall speed is a shallow climbing spiral while holding a given g load. Divide the result by the square root of your load factor then multiply by the square root of 6. For example a 3g climbing spiral that stalls at 200 is divided by 1.73 and the result multiplied by 2.44.
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6G is blackout limit in AH. Structural limit for the 109 should be around 8G.
I have often wondered about several aspects of the Bf 109 structural load limits - for example, was the German design philosophy to design to limit stress based on yield and ultimate on a 1.5 factor? Was the design limit load 8G? Was 8G for the original design combat weight? Did it evolve to include additional structural design features as the combat Gross Weight increased from model to model?
For example - the P-51 structural build up was 8G at 8000 pounds for limit load. By the time the P-51D was operational, at combat weight of 10,200 pounds (sans external fuel) the limit load decreased to ~ 6.3 Limit, 9.5 Ultimate.
What was the design Limit and Ultimate G Load for the Bf 109G?
Second question - what was the constant altitude sustained turn G load for the Bf 109 and at what CL. All aircraft form drag increases nearly linearly (but at different rates) as AoA increases to region of stall. Additionally, prop/engine efficiency to convert HP to thrust gets 'iffy' in the 180-225 mph range to analytics for Thrust produced is equally iffy when modeling Thrust and Drag in curvilinear flight. Total Profile Drag for a P-51 for example, increases nearly 50% in climb and the contribution for the wing component of a 109 has to be a lot more than a 51.
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Drgondog,
I seem to recalla 12 G max load on the 109 wing,with an 8 G limit that GScholz state that would be a 1.5 load factor. I also recall the brits used a 2.0 factor but I could be mistaken as it's been awhile since I've checked such things..... :old:
As for your 2nd question..... That is slightly over my head,or as I like to say above my pay grade...... :devil
I do enjoy your contributions,I always learn something when you post so plz continue to post!
:salute
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Limit load and failure load are more the result of the construction material used than design. An aluminum structure typically will fail at 1.5 times the load where it starts deforming. So if a structure starts deforming at 8G it will typically fail at or near 12G.
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Technically correct re: material based structural analysis. That said, very few fighter aircraft departed from 2024/24 S, 14S etc, etc for which mil spec values for tensile strength were documented (in US). So, the engineer didn't have to look at Stress vs Deformation charts and 'guess' the elastic Yield point.
The stress analysis was performed on each component, panel and joint to check for safety factor >+ .01 for the applied loads driving the calculated maximum stress.
For US the max load was usually the max design AoA related (dive pullout), but failure occurred on empennage when the actual applied loads exceeded the design targets. For US, for example, the lateral applied load factor was 2G until the P-51H. IIRC the Brits were 1G lateral
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6G is blackout limit in AH. Structural limit for the 109 should be around 8G.
A 1989 test of the F6F/FG-1/P-51/P-47D with modern instrumentation showed "The minimum 6G "Corner Speed" on all these aircraft is very close to maximum METO level Speed, so around 320-350 MPH at 10 000 ft..
This would be roughly the same on the Me-109G... But remember this is for level turns...
At this level of power (basically maximum continuous), the minimum speed for 6G LEVEL TURNS is quite high. This does not mean you cannot pull these Gs at lower speeds on dive pull-outs.
However, at very reduced power settings, the Me-109G will turn its best rate of level turn at around 160-180 mph, according to Fin ace Karhila.
Most WWII fighters similarly turned at their best rate with much reduced power outputs, particularly the P-51 Mustang and FW-190A (Red Fleet 1943: "The FW-190A will inevitably offer turning combat at minimum speed"). The trick on the Mustang involved 3 steps: Shallow flap settings, Prop put on full coarse pitch, and throttle reduced, the more reduction the tighter the turning ability.
The assumptions these things worked like jets is nonsense: 6G in level turns meant such a rapid loss of speed it was entirely useless when you had to steadily pepper targets for hundreds of rounds before your 2% hit rate had any effect at all (this is why boom and zoom was always a marginal practice, and required high velocity or centralized guns, plus a very vulnerable target)...
This is also why the concept of "Corner Speed" is entirely a post-war construct.
Gaston
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Couple of things here:
1: ww2 fighters cannot sustain their corner since they do not have enough power. It takes excessive down nosing in a ww2 fighter to get corner. Also 6G is not a magic corner G.
2: Reducing throttle does not make you turn better. Best turn rate, even in ww2 birds, is ALWAYS at full power for a sustained turn. Reducing throttle in a sustained turn is only good for getting a better radius, not rate. And Radius us is primarily necessary for one-circle geometry.
HOWEVER. Corner speed is not a post war construct. It always existed, even on ww2 birds. It simply cannot be sustained on ww2 birds due to power limitations.
Additionally, there is no such thing as a single corner speed. Corner speed for any airplane is subject to altitude and weight. It changes based on these conditions. So if you are heavier, the corner speed generally goes up. Same for altitude. IF your lighter, it goes down. The differences can be significant.
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Gaston, corner speed is simply the lowest speed you can pull max g. Your 160-180 best rate remark refers to best sustained turn which is entirely different from corner speed and as was pointed out the actual speed in either case depends on weight and altitude.
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Couple of things here:
1: ww2 fighters cannot sustain their corner since they do not have enough power. It takes excessive down nosing in a ww2 fighter to get corner. Also 6G is not a magic corner G.
2: Reducing throttle does not make you turn better. Best turn rate, even in ww2 birds, is ALWAYS at full power for a sustained turn. Reducing throttle in a sustained turn is only good for getting a better radius, not rate. And Radius us is primarily necessary for one-circle geometry.
HOWEVER. Corner speed is not a post war construct. It always existed, even on ww2 birds. It simply cannot be sustained on ww2 birds due to power limitations.
Additionally, there is no such thing as a single corner speed. Corner speed for any airplane is subject to altitude and weight. It changes based on these conditions. So if you are heavier, the corner speed generally goes up. Same for altitude. IF your lighter, it goes down. The differences can be significant.
Just one (very long-winded) correction: reducing speed below corner velocity will not reduce the minimum turn radius (i.e. pulling max G limited by airspeed) in a level turn - it will increase it.
Max G is proportional to the square of velocity, as is the lateral acceleration required to maintain a given turn radius. The actual G available to make the turn, however, is not all of the G that you are pulling. The Geometry involved is A^2 +B^2 = C^2, where C is the total G produced, A is the G used to turn, and B is 1 (for a level turn).
If you are pulling 2 G in a level turn, your wings are producing 1 G to remain level, and are producing 1.73 G (square root of 3) of lateral acceleration to keep you on that radius. If you were to increase speed by 10%, you can pull 1.21 * 2 = 2.42 G, of which 2.2 G is used for lateral acceleration. The acceleration needed to maintain the same radius would only be 2.09 G (1.73 * 1.21), so you are therefore traveling along a shorter radius. The extreme end of this example is that if you are flying *exactly* at your stall speed to maintain 1 G, you cannot turn at all without stalling, and your turn radius is therefore theoretically infinite.
For a sustained turn, yes, slowing down can get you a shorter turn radius. Performance-wise, however, pulling throttle is not the way to do it unless for some reason you started out above your corner speed - you would simply pull more G, maximizing your turn rate and minimizing your radius while allowing the increased drag to slow you toward your sustained turn speed.
Mike
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Just one (very long-winded) correction: reducing speed below corner velocity will not reduce the minimum turn radius (i.e. pulling max G limited by airspeed) in a level turn - it will increase it.
Max G is proportional to the square of velocity, as is the lateral acceleration required to maintain a given turn radius. The actual G available to make the turn, however, is not all of the G that you are pulling. The Geometry involved is A^2 +B^2 = C^2, where C is the total G produced, A is the G used to turn, and B is 1 (for a level turn).
If you are pulling 2 G in a level turn, your wings are producing 1 G to remain level, and are producing 1.73 G (square root of 3) of lateral acceleration to keep you on that radius. If you were to increase speed by 10%, you can pull 1.21 * 2 = 2.42 G, of which 2.2 G is used for lateral acceleration. The acceleration needed to maintain the same radius would only be 2.09 G (1.73 * 1.21), so you are therefore traveling along a shorter radius. The extreme end of this example is that if you are flying *exactly* at your stall speed to maintain 1 G, you cannot turn at all without stalling, and your turn radius is therefore theoretically infinite.
For a sustained turn, yes, slowing down can get you a shorter turn radius. Performance-wise, however, pulling throttle is not the way to do it unless for some reason you started out above your corner speed - you would simply pull more G, maximizing your turn rate and minimizing your radius while allowing the increased drag to slow you toward your sustained turn speed.
Mike
I think maybe you are either misunderstanding what I meant or you are perhaps leaving some important factors out. Either way, take one look at a EM diagram for any modern fighter and you will see what I mean. Less speed = smaller radius, but worse turn rate for sustained turns. Less speed also means a shorter reletive radius to someone who is flying faster, sustained or no.
Take for example a scissors, which is a textbook example of a 1-circle geometry fight. In a one Circle Geometry, Radius is paramount, not rate. This is why people who are in nose to nose fights dump flaps and an chop throttle. Getting slower means a smaller radius, and this is why the person with the larger radius will end up out front: and lose.
If you are nose to tail, rate is king, and so long as you are not above corner speed you should be a max power.
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Shift8, Mike is agreeing with you. Note his last paragraph. For a sustained turn, yes, slowing down can get you a shorter turn radius.
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Yes it appears we are talking past each other lol
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The Corner velocity:
Vc = SQRT[ (2Nmax*W)/(rho*CLmax*S)]
For a P-51D, 2N= (2*6.3) at GW=10,200 pound full internal combat load. The factor "6.3" for maximum G load is derived from the Limit load envelope, and of course far less than the 8G design Limit Load for the fully loaded Mustang I/P-51-1 at 8,000 pounds. Allowable "G" for the P-51D then is extracted from 8*8000/10200= 6.27
The P-51H was designed for 7.3G Limit load at fully loaded internal combat gross weight of 9500 pounds.
No WWII came close to achieving level Corner Velocity . Among the factors were a.) CLmax derived for two dimensional airfoil section and experimental data gathered in level flight stalls. in a high G turn CLmax is degraded by virtue of asymmetric lift distribution between 'high' and low wing. b.) The Free body forces on a turning fighter are difficult to calculate with precision as the balance between Thrust and Drag as well as true thrust of a max power engine/prop system in that medium airspeed envelope. Additional Drag calculation requires introducing trim drag due to rudder and aileron deflections.
When you look at data from turning tests - say from VVS testing of Allied and Axis fighters - and back out the CLmax based on turn rates and time to complete 360 degrees of 'level' turns, you should find about 10-20% lower CLmax than Stall CLmax.
I've been wrong before, but I don't get too excited when folks get lathered up about Corner Velocity and Calculated Turn performance for the above reasons.
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We use 6g as the practical limit for corner speed because that's when the pilot blacks out in Aces High.
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Just in case anyone is curious, I spend alot of time measuring this sustained level turn times of AH planes at sea level with equivalent fuel loads a max power. The fuel loads are as close to equal as possible in terms of time available to fly at MIL, not percent or weight. The planes are in order of best to worse. Where the time in seconds is the same, the former plane has a slight advantage somewhere between seconds. The P-38 and Corsair times are with Full flaps deployed. The reason for this is that they are the only two planes on the list that get sustained turn rate improvements in level flight with any degree of Flap. All other planes on this list ultimately have worse turn rates with any degree of flap if the turn is sustained and level. Turn radius improves on all planes with flaps in level turns. These figures are accurate, as each test as painstakingly done over and over again to assure accuracy.
Zero: 13 seconds
P-38L: 16 seconds.
Spit 16: 16 seconds
Corsair-1A: 17 seconds
Yak-3: 17 seconds
La-7: 18 seconds
Bf109G-14: 18 seconds
P-51D: 19 seconds
FW190A5: 20 seconds
FW190D-9: 20 seconds
P-47D25: 21 seconds
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You might want to test the Corsair with 2 notches flaps. I believe that gives the Corsair it's fastest sustained turn.
Were you riding the stall buffet for the tests?
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You might want to test the Corsair with 2 notches flaps. I believe that gives the Corsair it's fastest sustained turn.
Were you riding the stall buffet for the tests?
Yes I was right on the edge of the envelope. That is why I did at least 10 runs for each. Also now that you mention it the corsair was at 3 notches, more than that and it fell to 18 seconds.
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Testing is a pain. Good job. :aok Equivalent fuel is different. We usually use 25%. If you look at the climb and speed charts in the hanger they show weights that often don't match any loadout. I assume they use weights to match published charts from the actual aircraft.
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Yes, they do use the combat weights of the plane so far as the ones ive checked. I used equal fuel in terms of time because I see it as the most fair. IE: a mustang shouldnt be penalized vs a 109 simply because its 25% fuel is alot more gas than a 109s 25%. IIRC, a mustang has as must time as a 109 at 25% fuel as a 109 with 50%. Its one of the reasons I think ww2 turn testing, although rare in the first place, is all over the place in terms of results. I doubt anyone was comparing like that.
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Also speaking of the Aces High charts, I would like to mention that despite its age AH probabaly has the best flight models of ANY ww2 sim when it comes to historical accuracy and relative ship performance. The newer sims have FM's are a smidge better in terms of being less quirky, but they suck when it comes to getting the number right. :)
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Yes, they do use the combat weights of the plane so far as the ones ive checked. I used equal fuel in terms of time because I see it as the most fair. IE: a mustang shouldnt be penalized vs a 109 simply because its 25% fuel is alot more gas than a 109s 25%. IIRC, a mustang has as must time as a 109 at 25% fuel as a 109 with 50%. Its one of the reasons I think ww2 turn testing, although rare in the first place, is all over the place in terms of results. I doubt anyone was comparing like that.
I don't see it as a penalty. We use 25% at sea level as a standard for consistent results but it could just as easily be full fuel at 10,000 ft altitude. When you fight you don't know how much fuel the bandit has unless it's specified for dueling. A P-51 on fumes vs a 109 with full fuel still has to assess relative performance and guess if a slow turn is a new pilot or a tricky one dangling bait.
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I don't see it as a penalty. We use 25% at sea level as a standard for consistent results but it could just as easily be full fuel at 10,000 ft altitude. When you fight you don't know how much fuel the bandit has unless it's specified for dueling. A P-51 on fumes vs a 109 with full fuel still has to assess relative performance and guess if a slow turn is a new pilot or a tricky one dangling bait.
True, in actual combat I cannot know what my or the enemies fuel state will be. But I think a comparison must by definition be done at the most equivalent loads. Testing a fully fueled pony vs a fully fueled 109 for example would just be penalizing the mustang for having a capability margin the 109 doesnt even have. Fueling all the planes equal in percent doesn't always give a valid comparison since many planes have different max fuels, making the percent value quite relative. Speaking duels though, when its private I usually do insist on equal loads in terms of time as close as the game will allow for. I do agree with your general point on the fumes pony vs a heavy 109. It is true enough that in a real engagement you will have to assess agility on the fly. I think however its good to have a good baseline measurement from a "all things the same" standpoint that can be extrapolated from. For example, if you test both a 109 and 51 at 25%, it tends to lead to the impression that the two planes are significantly different in turn rate, when in fact the difference is small enough that pilot usually is the determining factor.
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The way I see it the heavier P-51 is paying a weight penalty because of it's range advantage and the 109 is paying a range penalty for it's weight advantage. Even if you are simply comparing best WW2 turn performance the weight of the aircraft includes the fuel load or it's just a glider. I'm not saying you're wrong to adjust fuel it just seems overly complicated without a practical benefit. You can't have all things the same with different aircraft. Adjusting one difference to change one measurement while making another measurement worse is not equivalence in my opinion.
Your method is an interesting different way of comparison but I think it's an artificial equivalence. :salute
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The way I see it the heavier P-51 is paying a weight penalty because of it's range advantage and the 109 is paying a range penalty for it's weight advantage. Even if you are simply comparing best WW2 turn performance the weight of the aircraft includes the fuel load or it's just a glider. I'm not saying you're wrong to adjust fuel it just seems overly complicated without a practical benefit. You can't have all things the same with different aircraft. Adjusting one difference to change one measurement while making another measurement worse is not equivalence in my opinion.
Your method is an interesting different way of comparison but I think it's an artificial equivalence. :salute
The benefit imo is that is provides a baseline with the planes in a state of equal time in the air. The P-51's base airframe weight is not due to it being long ranged. Its overall weight due to fuel is. Comparing without fuel doesnt seem to have a point either since neither plane can fly in that state. It is not fair imo to compare two planes at equal fuel percent when for one plane that might be 500lbs more fuel (exaggerated etc) IIRC, a P-51D and 109G-14 each have about 25min of fuel with the 109 at 50% and the Mustang at 25%. The percent is arbitrary however, because it does not have anything at all to do with doing a equal comparison of aircraft capability. Essentially what time comparison is doing is: "lets compare the planes with whatever amount of fuel gives each plane a equal time in the air." But I digress.
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They all fly without fuel. They just can't take off. :D
I understand your point, however since you can only load fuel in 25% increments it makes sense to me to test them that way.
Capability is a general term for aircraft performance which includes range. You might want to be more specific since you are only comparing some aspects of performance.