Why still no dive acceleration difference?

[JtD]

"the balance of propeller power"

Which is already modelled including Mach effects. Like I said, some aspects are there. This is one.

[Crumpp]

When speed building up, what happens to P47/P51/Tempest? There airscrew tips reach/break sonic barrier??? howabout 109/190's airscrew?

IIRC, the FW-190 tested is a G series by WerkNummer.

The maximum helical tip velocity is extremely important to any propeller design. At about mach .85 most propellers will begin to dramatically decrease efficiency as the normal shock formation disrupts flow. Yes, they break the sound barrier.

You can see the effect in any fast aircraft equipped with a CSP and the ability to over speed the propeller. Climb to about 12,500 feet, preferably on a hot summer day and set the aircraft for 75% cruise. If you increase to maximum rpm and manifold pressure, you will see a drop in your airspeed.

Maybe one could simulate the effect just by decreasing propeller efficiency sharply at Mach .85.

As you stated, propellers are extremely complicated and there are lots of trade-offs in design. For example, adding blades does increase the co-efficient of power but adding blades decreases propeller efficiency. The materials one chooses also has a large effect on propeller design. Metal blades have good power absorption but are fatigue limited. The primary reason for a metal propeller is cheap production and erosion resistance. Metal propellers have excellent erosion resistance so they be flown in the rain. Wooden blades have even better power absorption and unlimited fatigue life. Wooden blades can delaminate in the rain and require some sort of protection in order not to erode. The German wooden propellers were wrapped in metal mesh, fabric covered, and covered with a thick resin.

In the event of a prop strike, metal transferred more force to the engine resulting in more damage. Wooden propellers tend to act like a circuit breaker and disintegrate transferring less force to the engine. It is cheaper to replace a propeller than an engine.

[BlackBerry]

Let's discuss this record.

(C)

(1) 10000 fett to 3000 feet, starting at 250 m.p.h., diving at angle of 65 degree with constant throttle setting. The FW-190 pulled away rapidly at the beginning but the P-47 passed it at 3000 ft with a much greater speed and had a decidedly better angle of pull out.

Jtd's explanation:

The differences in initial acceleration between individual planes is there, if you fly them properly. Some of the acceleration differences you see as simple statements "this one is better" has a lot to do with engine management. If say an Fw 190 and a P-47 cruise side by side and then go into a full power dive, the guy in the 190 slams the throttle forward and off he goes, while the guy in the P-47 adjusts mixture, then rpm and then the throttle and then starts to accelerate. Gives the 190 a two second head start. But even without considering this, if you compare a 190A-4FR with a P-47D-22 at medium altitude in 4.11, you'll be getting something similar to the test you quoted.

It sound reasonable, in a real world combat, the engine management can't be neglected, but this is a "test" to determine dive accelaration so P47 should prepare for diving: at first setting rich-mixture, rpm/pitch to 3000rpm, throttle to 40% so that actual engine rpm is 2000 or so(although pitch is fine), criusing side by side with fw190 @250mph IAS. Next step for P47 is just slam the throttle forward and dive.

BTW, I am doubt fw190A4 could PULL AWAY RAPIDLY from P47d at initial dive in 4.11m.

My GUESS about that historical test:

When diving from 250mph to 380 mph or so, the speed of tip of P47's airscrew firstly reached 0.8 Mach than fw190's due to its greater rotating speed. When P47's reached 0.8 Mach and suffered from obvious airscrew efficience drop while 190's remained at BELOW 0.8 Mach, 190 had more thrust and outdove P47 rapidly.

But 380mph IAS(just my estimate) is the turning point, where P47's tip breaks sound barrier, and the drag coefficient of airscrew tip DECREASES, P47's efficiency INCREASES as we known that the majority of airscrew thrust is from tip section of propeller. From 380mph to 450mph, it was 190's turn to suffer from efficiency drop due to it's 0.8-1.0 Mach tip speed, P47 began to catch up with 190, and the P47's hugh weight advantage boosted its taking over because the higher speed, the more important role of weight. Therefore P47's diving accelarartion became astonishing-------quickly catched up fw190 200yard ahead, and passed 190 with MUCH GREATER SPEED like "thunderbolt".

[MadBlaster]

It's good thinking. I'll take a shot.

I think if the props on both planes are nearing 450 TAS and running inefficiently, you must fall back to the drags of the planes themselves. We know that the wing loading on p47-22 is greater than fw 190A. We also know that fw190A out turns a p47-22 based on the fan plots. So, I think we can conclude that the p47 is simple more aerodynamically streamlined for diving (less draggy) and this is why it eventually catches up and surpasses the 190A in a dive. I don't think the p47 prop all of a sudden gets more efficient when it breaks the sound barrier, but I could be wrong about that. Anyway, it is not the weight of the p47, but more so that the 190 wing simply generates more lift and that creates a drag. Yes, there is a weight difference. But if both planes were shaped as same sized spheres and one is twice as heavy as the other, I think you won't get that much separation.

Also ot, don't ever dive after a p51 in 109. Climb, pursue and hope he turns. If he is diving away from his home base, you have him. Simply cut off the angle.

[BlackBerry]

Originally Posted by MadBlaster

It's good thinking. I'll take a shot.

I think if the props on both planes are nearing 450 TAS and running inefficiently, you must fall back to the drags of the planes themselves. We know that the wing loading on p47-22 is greater than fw 190A. We also know that fw190A out turns a p47-22 based on the fan plots. So, I think we can conclude that the p47 is simple more aerodynamically streamlined for diving (less draggy) and this is why it eventually catches up and surpasses the 190A in a dive. I don't think the p47 prop all of a sudden gets more efficient when it breaks the sound barrier, but I could be wrong about that. Anyway, it is not the weight of the p47, but more so that the 190 wing simply generates more lift and that creates a drag. Yes, there is a weight difference. But if both planes were shaped as same sized spheres and one is twice as heavy as the other, I think you won't get that much separation.

Also ot, don't ever dive after a p51 in 109. Climb, pursue and hope he turns. If he is diving away from his home base, you have him. Simply cut off the angle.

The "no-lift" drag coefficeint for P47D-37 is "0.0256",it's a constant below 0.8 Mach. The test 0f 1943 December between fw190G and P47D was definitely below 0.8 Mach. You can see that P47 has a big wing of 25.87 square meters:

P-47D-27 = 0.0256 * 25.87 = 0.662272

0.662272 is also a constant, if you want to get drag force of the wind, multiple speed^2:

0.662272X(250mph)^2

I have no fw190G's data, fw190G-1 based on A4; G-2 based on A5, they are both 1.42ata( 42").

let's put aside propeller's thrust at first, only gravity and wind drag(there are some induced force but I just calculate roughly).


gXweightXcos(60)-dragcoefficentX(speed)^2= (dive-accelaration)Xweight

that is

dive-accelaration=gXcos(60)-dragcoefficentX(speed)^2/weight

P47's weight is almost twice of fw190A4, so at 250mph speed it's almost impossible for fw190 to outdive P47 in il2 4.11m. But in real world, fw190 pulled away rapidly!

The only factor we didn't include is the detailed airscrew efficeiency curve espicielly when tip reachs 0.8-1.0 Mach and above.
Spitfire.LF.IXC
[Mass]
Empty 2650.0
TakeOff 3300.0

[Squares]
Wing 19.0
Aileron 1.32
Flap 2.125
Stabilizer 1.90
Elevator 1.20
Keel 0.85
Rudder 1.10

[Polares]
lineCyCoeff 0.092
AOAMinCx_Shift 0.0
Cy0_0 0.1
AOACritH_0 16.0
AOACritL_0 -17.0
CyCritH_0 1.4
CyCritL_0 -0.7
CxMin_0 0.0232
parabCxCoeff_0 5.4E-4




P-47D-27
[Mass]
Empty 4630.0
TakeOff 6583.0

[Squares]
Wing 25.87
Aileron 1.45
Flap 2.76
Stabilizer 3.50
Elevator 2.05
Keel 1.30
Rudder 1.10

[Polares]
lineCyCoeff 0.092
AOAMinCx_Shift 0.9
Cy0_0 0.17
AOACritH_0 16.0
AOACritL_0 -15.0
CyCritH_0 1.25
CyCritL_0 -0.8
CxMin_0 0.0256
parabCxCoeff_0 4.8E-4


Bf-109G-2 = 0.027 * 16.16 = 0.43632
Spitfire.LF.IXC = 0.0232 * 19.0 = 0.4408
P-47D-27 = 0.0256 * 25.87 = 0.662272



Someone says

On the R-2800 engines the Reduction Gear ratio was about 50%, the crankshaft would produce about 50% more power strokes per revolution than a direct drive engine. On the dash 21 (P-47 Thunderbolt) engine it was 16:8 ratio. On most other R-2800 engines the ratio is 16:9, 16 revolutions of the engine give 9 revolutions of the prop. The numbers have no common multiple, it's a vibration control function.

The R-1830 of the C-47, and R-2800, and that R-4360 are geared engines, notice how large the nose case is - where the "crankshaft" and the prop meet.

R-2800 engine, 2700rpm, 50% reduction for airscrew=1350rpm, 4m diametre. On the ground when engine at full rpm, the propeller's tip's rotating speed is:

3.14X4X1350/60=282m/s=282/340=0.83 Mach

Wow, it's seems that P47's designer just want to make the tip speed approach sonic as soon as posssible. Why? The supersonic state for airscrew's tip? We all know P47 was intently designed for high altitude escort where the sonic speed is samller than 340m/s on the ground, and P47 often dives at hight speed at high aititude, therefore P47's airscrew tip must often beyond 1 Mach.

airscrew=the twisted and rotating "wing" above 1 Mach, what does this mean in il2?

Again we analysis 1943's test.

(C)

(1) 10000 feet to 3000 feet, starting at 250 m.p.h., diving at angle of 65 degree with constant throttle setting. The FW-190 pulled away rapidly at the beginning but the P-47 passed it at 3000 ft with a much greater speed and had a decidedly better angle of pull out.

When p47 flew on 10000 feet@250 mph IAS,what's the speed of propeller's tip?

At 5,000' TAS = IAS + 9%
At 10,000' TAS = IAS + 16%
At 15,000' TAS = IAS + 25%
At 20,000' TAS = IAS + 36%
At 25,000' TAS = IAS + 49%
At 30,000' TAS = IAS + 64%

250 mph IAS=290mph TAS=130m/s, rotating speed is 282m/s, combination speed is 310m/s, Mach number=310/328=0.945Mach

When slam throttle full forwards and dives 60 degree, P47's airscrew will probably be the first one to suffer from sonic barrier.0.95-1.0 Mach. This is probably the reason why P47 was outdived by fw190G from 250 mph(initial diving stage). As speed building up to 650km/h or so (3000ft altitude), mach number=1.

(Probably)Fw190's airscrew tip entered 0.9-1.0 Mach later than P47, that's why 190 outdove P47 at the begining, but when both of them were all suffering from low airscrew efficiency at high speed, P47 will gain on 190, the formula I'v posted above demonstrates this clearly.


When P47 dives to 7500 altitude @800 km/h TAS, and tip mach number is 1.16. Hamilton standard airscrew is NACA-16 series which is laminar flow airfoil.

<<Static characteristics of Hamilton Standard propellers having Clark Y and NACA 16 series blade sections>>
http://digital.library.unt.edu/ark:/...etadc62146/m1/

[MadBlaster]

hmm, before I read further, I think we need zero lift drag coefficient for 190 to say that weight is the deciding factor. wiki says 27.87 m² for p47 wing area and 18.30 m² for 190A. Agree with you that denominator (i.e., weight) is almost twice as large for p47 verses 190, but numerator? To keep simple math, assume zero drag coeff=1 for both planes, 190 weighs "1" and p47 weighs "2" (weight on relative basis to each other). Then drag coefficient portion of numerator

-dragcoefficentX(speed)^2/weight

where you did this -> P-47D-27 = 0.0256 * 25.87 = 0.662272 (i assume your using 25.87 for wing area)

(i.e., use 1 instead of .0256 and 1 for speed since same for both planes and 2 for weight p47 and 1 for weight of 190)

27.87/2 (p47) or 18.3/1 (190) is bigger??? The latter is bigger, and since it is a subtraction from this gXcos(60), wing area and/or differences in zero drag coeff may be the deciding factor in the calculation of dive acceleration, not the weight. And if this is the case, dive acceleration is less for 190 than p47. Sorry,if this is confusing. It's late here.

[BlackBerry]

Originally Posted by MadBlaster

hmm, before I read further, I think we need zero lift drag coefficient for 190 to say that weight is the deciding factor. wiki says 27.87 m² for p47 wing area and 18.30 m² for 190A. Agree with you that denominator (i.e., weight) is almost twice as large for p47 verses 190, but numerator? To keep simple math, assume zero drag coeff=1 for both planes, 190 weighs "1" and p47 weighs "2" (weight on relative basis to each other). Then drag coefficient portion of numerator

-dragcoefficentX(speed)^2/weight

where you did this -> P-47D-27 = 0.0256 * 25.87 = 0.662272 (i assume your using 25.87 for wing area)

(i.e., use 1 instead of .0256 and 1 for speed since same for both planes and 2 for weight p47 and 1 for weight of 190)

27.87/2 (p47) or 18.3/1 (190) is bigger??? The latter is bigger, and since it is a subtraction from this gXcos(60), wing area and/or differences in zero drag coeff may be the deciding factor in the calculation of dive acceleration, not the weight. And if this is the case, dive acceleration is less for 190 than p47. Sorry,if this is confusing. It's late here.

27.87/2=13.93 much smaller than 18.3, so P47 has smaller subtraction from this g*cos(60).


BTW, this link says VDM 3m diametre has a 0.54 prop reduction gearing. Fw190A8 :VDM 9-12176A10 ft, 11 ¾ in. diameter 390 lbs

BMW-801D 2700rpm

FockeWulf190BMW 801D radialVDM prop mechanism was built into the nose case of the engine itself, along with 1.72 to 1 cooling fan drive, 0.54 prop reduction gearing, magneto, oil pump, and front camshaft drive.

http://www.enginehistory.org/Convent...20Electric.pdf

So in 1943's test, @10000ft ,250mph IAS, fw190A4's propeller tip speed=(254^2+130^2)^0.5=286m/s=0.87Mach, less than 0.95 Mach of P47's.

Some P47's has 16:9 reduction which provides higher Mach number (1.05Mach ).

In conclusion, My opinion is that when p47 and fw190a4 at full engine 2700rpm dive from @10000ft ,250mph IAS, fw190's tip speed is about 0.87mach while p47's is around 0.945-1.05 Mach. Probably at that time P47's propeller's efficiency is quite lower than fw190, so p47 was outdove rapidly at initial diving stage.
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