How capable was the Ki-44?

[Irregualr23]

Then about calibration charts: As you point out what you find in flight manuals (PEC's) usually stops far short of the stall speed, which I think is for the simple reason that these are for navigational purposes only, and when it comes to stall, the only thing the pilot needs to know is what he reads off his airspeed indictor. However, extrapolating from the PEC curve, this on the Spitfire looks to be about 15-20 mph lower than if it was calibrated. In addition, and as I see you have already pointed out, calibration in this regime is not linear, to which I think we could add maybe afflicted by large fluctuations, so I would be very vary of any Clmax values derived from calibration of an aircraft's airspeed IAS as for the Hellcat, especially if we have no idea about how the calibration was done.

Due to the nature of deck-landing aircrafts, both the Hellcat and the Corsair have relatively more stall tests than the AAF planes. As I've quoted multiple sources, including three independent testing institutions( NAS Pax, NACA and ARC), especially that the ARC report had give the calibration data at the stall speed, I would believe the Hellcat's power-off CLmax = 1.5 a high confidence, only very few ww2 aircrafts have rich testing data on stalling characteristic than the F4U and F6F.

Also Buno.58310 test by NAS Pax. had provided the non-linear region of calibration in stall region.

 

[Holtzauge]

Due to the nature of deck-landing aircrafts, both the Hellcat and the Corsair have relatively more stall tests than the AAF planes. As I've quoted multiple sources, including three independent testing institutions( NAS Pax, NACA and ARC), especially that the ARC report had give the calibration data at the stall speed, I would believe the Hellcat's power-off CLmax = 1.5 a high confidence, only very few ww2 aircrafts have rich testing data on stalling characteristic than the F4U and F6F.

Yes, you have quoted three independent testing institutions but one of those (NACA) seem to place Clmax at 1.36 to 1.39? So based on the evidence presented so far I can't see why 1.5 should be the number we should go with? Especially seeing we have no idea about how they made the calibration (as in how did they arrive at the PEC chart you posted above)? And before anyone says, well NAS Pax are reputable and know what they are doing, well then I think many would say the same about NACA? And yet they seem to come to different conclusions, one says 1.36 to 1.39, and the other 1.5? In addition, if the F6F really did have a Clmax of 1.5 that would put it in a class of its own, since I know of no other WW2 fighter aircraft that has a power off, no flaps Clmax as high as that.

 

[Irregualr23]

Yes, you have quoted three independent testing institutions but one of those (NACA) seem to place Clmax at 1.36 to 1.39? So based on the evidence presented so far I can't see why 1.5 should be the number we should go with? Especially seeing we have no idea about how they made the calibration (as in how did they arrive at the PEC chart you posted above)? And before anyone says, well NAS Pax are reputable and know what they are doing, well then I think many would say the same about NACA? And yet they seem to come to different conclusions, one says 1.36 to 1.39, and the other 1.5? In addition, if the F6F really did have a Clmax of 1.5 that would put it in a class of its own, since I know of no other WW2 fighter aircraft that has a power off, no flaps Clmax as high as that.

The NACA test showed a steady state CLmax = 1.5 for 1.5 seconds before roll-off. Perhaps you misread the value?

If you are refering to this report then keep in mind these are buffet boundaries, and NACA had pointed several scatter points to be "CLmax 2deg above initial separation". One should distinguish between buffet boundary and stall boundary:

This curve is been cited in the report JFC and been specifically quoted as buffet-boundary.

Even for the NACA report 1044, the F6F-3 was the one been tested to have the highest lift-coefficient curve, higher than another test planes. Given that it has the largest MAC and largest effective Reynold's number, this isn't surprising. Keep in mind the buffet-boundary of the F6F was cutted off at Mach 0.35, and the conventional airfoil plane should obtain maximum CLmax around Mach 0.2 like the P-39.

If you compare it:

P-39 CLmax = 0.95 @ Mach 0.45, F6F-3 CLmax = 1.1 @ Mach 0.45
P-39 CLmax = 1.1 @ Mach 0.35, F6F-3 CLmax = 1.35 @ Mach 0.35 --- Cut off for F6F-3.
Mach effect slope for P-39: -0.15 per Mach 0.1 F6F-3: -0.25 per Mach 0.1

At Mach 0.2:
P-39 CLmax = 1.35 - 1.4 (test value, non-linear increasing near M0.2), assume linear increasing for F6F-3 we should have a power-off CLmax = 1.6 @ Mach 0.2, since the test was made for power-off condition on all 5 propeller driven aircrafts, except for the P-80 which was set to be power-on.

And yet they seem to come to different conclusions, one says 1.36 to 1.39, and the other 1.5? In addition, if the F6F really did have a Clmax of 1.5 that would put it in a class of its own, since I know of no other WW2 fighter aircraft that has a power off, no flaps Clmax as high as that.

If F6F has CLmax 1.36 to 1.39 which would mean the F4U would be less than 1.25 according to the NACA value and basic wing planform theorem, which wouldn't be possible. In addition many WW2 fighter has great CLmax, as I have quoted the P-38 is also at the class of power-off clean CLmax = 1.5. Also, be very careful for using power-off CLmax at stall speed to extrapolate CLmax at optimal flight speed, certain planes with small MAC may get Re effect at critical and rise the CLmax from 1.35 to 1.45 at certain speed/altitude range, as been tested by the NACA, and I believe it is also a reason for the success of FW-190 and P-51:

The astonishing MAC = 8.12ft gives F6F very good Re numbers even at very low airspeed and that's why it has very good CLmax and lift-boundary across speed-range, with a non-twisted, clean NACA 230 tapered wing with lambda = 0.5 I am not surprised to see this figure of CLmax = 1.5.

If you want to prove it wrong then you have to cite your source. As I have already did more than 5+ cases from 3 independent institution for the CLmax of F6F. Now it's your turn.

 

[Holtzauge]

The NACA test showed a steady state CLmax = 1.5 for 1.5 seconds before roll-off. Perhaps you misread the value?
View attachment 853908

If you are refering to this report then keep in mind these are buffet boundaries, and NACA had pointed several scatter points to be "CLmax 2deg above initial separation". One should distinguish between buffet boundary and stall boundary:
View attachment 853902
This curve is been cited in the report JFC and been specifically quoted as buffet-boundary.
View attachment 853903

Even for the NACA report 1044, the F6F-3 was the one been tested to have the highest lift-coefficient curve, higher than another test planes. Given that it has the largest MAC and largest effective Reynold's number, this isn't surprising. Keep in mind the buffet-boundary of the F6F was cutted off at Mach 0.35, and the conventional airfoil plane should obtain maximum CLmax around Mach 0.2 like the P-39.
View attachment 853907
If you compare it:

P-39 CLmax = 0.95 @ Mach 0.45, F6F-3 CLmax = 1.1 @ Mach 0.45
P-39 CLmax = 1.1 @ Mach 0.35, F6F-3 CLmax = 1.35 @ Mach 0.35 --- Cut off for F6F-3.
Mach effect slope for P-39: -0.15 per Mach 0.1 F6F-3: -0.25 per Mach 0.1

At Mach 0.2:
P-39 CLmax = 1.35 - 1.4 (test value, non-linear increasing near M0.2), assume linear increasing for F6F-3 we should have a power-off CLmax = 1.6 @ Mach 0.2, since the test was made for power-off condition on all 5 propeller driven aircrafts, except for the P-80 which was set to be power-on.


If F6F has CLmax 1.36 to 1.39 which would mean the F4U would be less than 1.25 according to the NACA value and basic wing planform theorem, which wouldn't be possible. In addition many WW2 fighter has great CLmax, as I have quoted the P-38 is also at the class of power-off clean CLmax = 1.5. Also, be very careful for using power-off CLmax at stall speed to extrapolate CLmax at optimal flight speed, certain planes with small MAC may get Re effect at critical and rise the CLmax from 1.35 to 1.45 at certain speed/altitude range, as been tested by the NACA, and I believe it is also a reason for the success of FW-190 and P-51:
View attachment 853904
The astonishing MAC = 8.12ft gives F6F very good Re numbers even at very low airspeed and that's why it has very good CLmax and lift-boundary across speed-range, with a non-twisted, clean NACA 230 tapered wing with lambda = 0.5 I am not surprised to see this figure of CLmax = 1.5.

If you want to prove it wrong then you have to cite your source. As I have already did more than 5+ cases from 3 independent institution for the CLmax of F6F. Now it's your turn.

No, I have not misread any values. The 1.5 figure you have chosen to highlight within the red rectangle is a transient. If you read what written about that test is that it says that the pilot continued to control the aircraft through the stall, and if you go back in that histogram to about 3 s in, you can see that the stall begins about there when the saw-tooth values appear. In addition there is a side-slip when the "bump" to 1.5 occurs about 9 s in. In addition, I suggest you look up hysteresis in conjunction to stalls, and you will find that transient values can be significantly higher than the steady state Clmax, just like the "bump" shows.

This whole discussion started with you claiming (which we now have concluded was a baseless claim) that NAS Pax had done a good job in calibration and better than NACA, and now at the end of this discussion we can conclude that we don't actually know how they (NAS Pax) did it.

Finally, I think we are going round in circles now and we will just have to agree to disagree. I have come to understand that you have the firm conviction that the F6F is in a class of its own with a Clmax of 1.5, while I think it is much more plausible that it has a Clmax in the order of what many other aircraft with NACA 230-series airfoils and wing planforms like the F6F had, and which would be in the order of 1.35 to 1.4, just as the attached figure from NACA WR L 717 shows for the F6F.

So with that my participation in this discussion is at an end. And why don't you start another thread if you want to continue to discuss the F6F Clmax? After all, the title of this thread is "How capable was the KI-44?".

 

[Irregualr23]

No, I have not misread any values. The 1.5 figure you have chosen to highlight within the red rectangle is a transient. If you read what written about that test is that it says that the pilot continued to control the aircraft through the stall, and if you go back in that histogram to about 3 s in, you can see that the stall begins about there when the saw-tooth values appear. In addition there is a side-slip when the "bump" to 1.5 occurs about 9 s in. In addition, I suggest you look up hysteresis in conjunction to stalls, and you will find that transient values can be significantly higher than the steady state Clmax, just like the "bump" shows.

If you look at the figure 4 you will find this is the condition where the pilot hold the control fix during the flow separation. The aircraft will bounce out of the steady-state due to the buffet, separation and rolling-moment if no control input. In other word, Figure 14 only showed the behaviour of initial separation on the F6F aircraft (where CL goes non-linear), instead of showing the CLmax value which was obtained with control input as in Figure 5 that I've quoted.

The saw-tooth value of transverse G value only means a buffet is onset, but not a stall, the test used filtered normal force to derive the time-varying CL so don't worry for roll-off happens < 1G. We are talking about CLmax stall boundary, not a buffet boundary. F6F-3 does have an annoying wide buffet boundary problem which been solved in -5, which I have quoted the buffet boundary from the JFC.

If you do unsteady CFD calculation with time-step 0.0025s, a 1.5 seconds time window would mean a 600 time-step result and can be taken as a steady-state for sure. The NACA tests include the boundary plot above were all done with steady turn, with no fast pitching, so your "instantaneous vortex" theory may work for the P-47 overclaiming case, but not all cases.

If you are comparing F6F with other planes that uses NACA 230 (FW-190, for example), then you've to count the effect for varying MAC ( F6F has 30% larger MAC than FW-190), geometric twist ( the wing of the Hellcat has no twist, while FW-190 has a specific twist optimized for aileron operation). Just looking at the wing profile won't help much.

FW-190 wing twist:

A wing twist will reduce the lift and also CLmax, and also a reason for planes using 0 geometric wash-out (P-38, P-40, F6F) to have relatively large CLmax.

This whole discussion started with you claiming (which we now have concluded was a baseless claim) that NAS Pax had done a good job in calibration and better than NACA, and now at the end of this discussion we can conclude that we don't actually know how they (NAS Pax) did it.

At least NACA did sometimes forget to correct the installation error.

 

[Irregualr23]

No, I have not misread any values. The 1.5 figure you have chosen to highlight within the red rectangle is a transient. If you read what written about that test is that it says that the pilot continued to control the aircraft through the stall, and if you go back in that histogram to about 3 s in, you can see that the stall begins about there when the saw-tooth values appear. In addition there is a side-slip when the "bump" to 1.5 occurs about 9 s in. In addition, I suggest you look up hysteresis in conjunction to stalls, and you will find that transient values can be significantly higher than the steady state Clmax, just like the "bump" shows.

This whole discussion started with you claiming (which we now have concluded was a baseless claim) that NAS Pax had done a good job in calibration and better than NACA, and now at the end of this discussion we can conclude that we don't actually know how they (NAS Pax) did it.

Finally, I think we are going round in circles now and we will just have to agree to disagree. I have come to understand that you have the firm conviction that the F6F is in a class of its own with a Clmax of 1.5, while I think it is much more plausible that it has a Clmax in the order of what many other aircraft with NACA 230-series airfoils and wing planforms like the F6F had, and which would be in the order of 1.35 to 1.4, just as the attached figure from NACA WR L 717 shows for the F6F.

So with that my participation in this discussion is at an end. And why don't you start another thread if you want to continue to discuss the F6F Clmax? After all, the title of this thread is "How capable was the KI-44?".

View attachment 853930

Take the example fof the P-47D-30 test, the test didn't record CL so I calculated using weight they provided during stall test around 12,400lbs:
A rudder-fixed stall would only produce a clean power-off CLmax ~= 1.21 for the P-47, which is obviously too low for a plane with such a large MAC:

The CLmax ~= 1.35 is obtained using control input to obtain the actual stall after the initial roll-off, looks better:

Using rudder to correct and approach actual stall is the conventional measure in the stall test, as been quoted still in both reports, the stall in Figure 5/34Conc. was cited as "final stall"/"actual stall".

One should note the difference between the initial stall and the final/actual stall, because the stall margin is also an important characteristic to be considered and designed.

 

[andrewgeorge]

Instant turn rate, I 100% believe that. If the fight was prolonged, the Hellcat is a heavy girl and I don't think it has the power to sustain that for very long at all. Apart from maybe the Ha-45 -equipped planes that were likely detuned and it's harder to figure out exactly what they performed like, a sustained fight would have been extremely dangerous. A Ki-44 has a lot of power for its small frame.

Wasn't there a J2M ace who would constantly enter dogfights in it whenever possible?

Makes sense. In a sustained rate fight the Hellcat would be in trouble against a lighter opponent.

I've read (from Henry Sakaida) about Lt. Akamatsu piloting a J2M and successfully engaging P-51s in a dogfight in April, 1945. Supposedly a lot of IJNAF pilots at the time were skeptical that it could go toe to toe with American fighters in a dogfight the way an A6M could. Not too many other accounts of J2M pilots.

 

[Steamed_Banana]

Ki-44 had a lot of power but very small (and weirdly shaped) wings with a high wing loading between 37 -41 lbs per sq ft. It was not known to be a good turning aircraft.

 

[Steamed_Banana]

(although because of this well known fact it was fitted with some hard core maneuver flap settings, I think 20 - 35 degrees something in that ball park. So maybe that made up for it...)

 

[GregP]

I think NAS Patuxent River did very well on calibrating airspeed when testing the Hellcat and the Corsair. If you calculate CLmax according to the stall speed based on IAS listed on the manual, you would get over-stated CLmax since that IAS included pitot installation error (the one particularly affecting F6F showing lower IAS), and the stall may be counted when the wing starts to drop instead of the plane starts to lose altitude (1G stall).

Given values F6F-5 BUNO.58310
mass_kg = 5633*1 # kg
g = 9.81 # m/s^2
rho = 1.225 # kg/m^3
V_kph = 157.78 # km/h
V_f_kph = 136 # km/h
S = 31 # m^2
# Convert velocity to m/s
V = V_kph * (1000 / 3600) # m/s
V_f = V_f_kph * (1000 / 3600) # m/s
# Calculate weight (W = mass * g)
W = mass_kg * g # N
# Calculate lift coefficient (C_L)
C_L0 = (2 * W) / (rho * V**2 * S)
C_L1 = (2 * W) / (rho * V_f**2 * S)

CLmax of F6F-5 Buno 58310 (starboard pylon) power off clean: 1.515, power off landing: 2.039

Given values F6F-3 BUNO.25892
mass_kg = 5154*1 # kg
g = 9.81 # m/s^2
rho = 1.225 # kg/m^3
V_kph = 150.53 # km/h
V_f_kph = 80*1.61 # km/h
CLmax of F6F-3 Buno 25892 power off clean: 1.523, power off landing: 2.080

Hellcats in reduced condition:
F6F-3 BUNO.40164 with 2x20mm cannons: CLmax power off clean: 1.478, power off landing: 1.962 (cannon barrels reduce aerodynamic performance)
F6F-5 BUNO.72731(Full pylons, Rocket racks, airplane not very good condition as 5mph slower than Buno.78467 in same loading configuration):
power off clean: 1.443, power off landing: 1.941 ( reduced aerodynamic performance due to pylons, and reduced airframe&finish)

As for the Corsair:
F3A-1 Buno.04691
mass_kg = 5415*1 # kg
g = 9.81 # m/s^2
rho = 1.225 # kg/m^3
V_kph = 104.5*1.61 # km/h
V_f_kph = 86.5*1.61 # km/h
S = 29.17 # m^2
CLmax of F3A-1 Buno 04691 power off clean: 1.361 power off landing: 1.986

F4U-1 Buno.02155
mass_kg = 5077*1 # kg
g = 9.81 # m/s^2
rho = 1.225 # kg/m^3
V_kph = 101.5*1.61 # km/h
V_f_kph = 83.5*1.61 # km/h
S = 29.17 # m^2
CLmax of F4U-1 Buno.02155 power off clean: 1.353 power off landing: 1.999

F4U-4 Buno.80765 CLmax power off clean 1.471 power off landing 1.948 (The power-off clean here was tested when plane starts to roll so could be over-stated)

NACA values for F4U-4 still shows 1.37 for power off clean (they called Glide condition), though I think NACA does not doing as accurate as NAS Pax. on calibrating airspeed and measuring these values during test flights:
View attachment 851583

It is still possible that F4U-4 had imporved aerodynamic performance of the wing and thus giving it higher CLmax than the F4U-1, and possbily a reason it was listed to turn tighter than the F4U-1D even though the wing-loading is heavier:
View attachment 851584

Note the tests still involve a lot of uncertainties and errors, an 1-2mph error might incur some significant difference in calculated CLmax, thus I am listing various cases to compare. All stall speeds were calibrated to sea-level.

Nobody dogfights in a ppwer-off condition, so that is not really a consideration for any combat or normal flight.

Power-on, clean, it says 1.62. Decent. I'd ballpark it somewhere near 1.55 or so and realize it could get slightly better or worse.

 

[Irregualr23]

Nobody dogfights in a ppwer-off condition, so that is not really a consideration for any combat or normal flight.

Power-on, clean, it says 1.62. Decent. I'd ballpark it somewhere near 1.55 or so and realize it could get slightly better or worse.

Most people (and also most of flight simulators) tend to use power-off CLmax as the basis, because the power-on CLmax benefited heavily from high volume propeller slipstream and engine thrusts, which the effect diminishes in higher speed and high G turns. At higher speed, the increased dynamic pressure from propeller decreases as the advanced ratio J =V/nD increases with free-stream air velocity V increases, also as the lift becomes so large in a 6G turn, the thrust/lift value becomes very little, the CLmax will eventually approach the power-off value.

Of course, in calculation, it would still remain larger as in the graph, however, the following mach effect and aeroelastic effect that take place in a higher speed high G turn would then reduce the CLmax, thus the eventually back to the level of power-off CLmax near stall speed, and even worse than that.

 

[SaparotRob]

Nobody dogfights in a ppwer-off condition, so that is not really a consideration for any combat or normal …

Your aviation education is obviously comic book deficient.

 

[special ed]

Didn't Robin Olds shoot down a 109 with both engines in his P-38 stopped?

 

[SaparotRob]

Didn't Robin Olds shoot down a 109 with both engines in his P-38 stopped?

In his case, I wouldn't doubt it.

 

[SaparotRob]

Nobody dogfights in a ppwer-off condition, so that is not really a consideration for any combat or normal flight.

Power-on, clean, it says 1.62. Decent. I'd ballpark it somewhere near 1.55 or so and realize it could get slightly better or worse.

Slight threadjack:
GregP, does the Planes of Fame Museum's A6M52 still have the same livery as in this picture?

 

[GregP]

Your aviation education is obviously comic book deficient.

Well, perhaps. I DID used to read Steve Canyon ... and Blackhawks.

 

[GregP]

Slight threadjack:
GregP, does the Planes of Fame Museum's A6M52 still have the same livery as in this picture?

View attachment 875868

Yes. Still looks great. Hasn't flown in over a year because we found a bottom cylinder with very leaky valves, causing investigation which uncovered 2 more leaky valves in two other cylinders. So ... the cylinders and valves are being worked on slowly. Plans-built cylinders and valves for a Nakajima Sakae 31are not 3D printed items ....

But, it WILL fly again, and not too far in the future.

 

[SaparotRob]

Yes. Still looks great. Hasn't flown in over a year because we found a bottom cylinder with very leaky valves, causing investigation which uncovered 2 more leaky valves in two other cylinders. So ... the cylinders and valves are being worked on slowly. Plans-built cylinders and valves for a Nakajima Sakae 31are not 3D printed items ....

But, it WILL fly again, and not too far in the future.

As long as I have you, when I visited The Planes of Fame Museum in September or October of 1986 there was a B-17 parked outside. It was awaiting funding for restoration. What happened to it?

 

[GregP]

Still outside. Being restored, but the corrosion is likley faster than the restoration just now. Not always that way. Depends on what is being worked on and how long it takes. It looks pretty good. We need to make a new bomb bay door (right) and the left wing has some rear spar issues. Still, it is likely to be ferried to Santa Maria in the near future, within a few years, with 4 different engines and props anyway. If so, restoration will continue. If not, then other arrangements will be made, and restoration will still continue.

There is a whole volunteer crew working on it and the interior, other than the cockpit just now, looks pretty good. The cockpit needs attention that it WILL get. The question is "when?"

We DO have a VERY freshly-restored F8F Bearcat. Actually, it really isn't an F8F, it isa G-58. The fuselage and at least one wing are from Alford Williams' old Gulfhawk aircraft, one of only two G-58's ever built. The G-58 was a civilian Bearcat with no armor and no guns, so it's lighter than an F8F-1 or F8F-2.


View: https://youtu.be/BQ0yErrjexk

Cheers!

 

[GregP]

Here is a video of the first post-restoration test flight, before it was painted, with Steve Hinton narrating.


View: https://youtu.be/mtewKHbYTNU