Corsair Turning Ability in AH

[Knegel]

Just another reason why a plane with full flaps dont take that much advantage out of the higher lift:

The plane with full flaps conditions will turn with a much smaler speed than the one without flaps and although the max CL is a bit higher, the resulting lift is smaler, cause the different speeds. Since both planes need to waste the same lift to overcome the same -1G to keep a level turn, the slower flying plane need to waste more % of its lift  to stay in a level flight. With other words, as slower the plane fly, as less it can bank. (if i remeber right, speed influence the lift in square).

So although the full flap condition result in a better max CL, the "excess lift" stand in a less good relation.

Further more the full flap condition while a sustained turn and climb result in a not to smal "nose down" position. So the thrust line have a much worse direction(in relation to the no flap thrust line).

Further more, without flaps the planes have a higher max AoA of around 2°, this provide a even better thrust line(the thrustline point more toward the center of the turn and more upward while climbing).

Further more the planes have a basic trim setup for higher speeds, so while flying at very slow speed more trim or rudder variation is needed(more drag, more yaw/shift moments, less lift).

While a full banked flight at slower speeds, the upward lift by the fuselage is much smaler, as result the plane have even less max lift and cant be banked that much again.



Isnt it like this?
At the same turn rate the g-forces are the same, this is comperable with a steady climb. Both planes must create the same lift and same ammount of drag and so same ammount of exess thrust.  
So if a plane in AH turn sustained at different speeds with max AoA  with same G-force,  they should also climb with max AoA same good (same excess thrust).

So my question remain:
Why the F4U-4 lose around 30% climb ratio (max AoA), while a very similar turn ratio(5% difference) at max AoA indicate a very similar g-force and so lift and drag and so excess thrust?

Greetings,

Knegel

[F4UDOA]

Krusty,

Where did this quote come from?

every one I know that has major time in tem is do not get low and slow and try to maneuver. The stall below 200 kts and 6k AGL is unrecoverable as the wing drops and a spin results which is unrecoverable given the altitude. Given altitide the F4u is still a monster in the spin, and the few pilots I know that have intentionally spun the Corsair say they will never try it again."

I have read countless accounts of F4U handling and I have never read that. In fact the P-51D has far worse high speed stalls than the F4U.

In the 1989 Flight test performed by the SoETP (Socioty of Experamental Test Pilots) they documented the stalls of the P-47D , F6F-5, P-51D and FG-1D.

The 3G accelerated Stall results power on (METO Power) are as follows with high loss listed (All speeds IAS) No flaps.

P-47D
Stall Warn=126Knots
Stall Speed = 109Knots
High loss= 100FT

P-51D
Stall Warn=122Knots
Stall Speed= 122Knots <== No Warning at all
Hight Loss= 500FT

F6F-5
Stall Warn=100Knots
Stall Speed= 95Knots
Hight Loss= 150FT

FG-1D
Stall Warn=103Knots
Stall Speed= 100Knots
Hight Loss= 150FT<=Same as the F6F

A couple of other notes about the test,

1. The F6F was 400lBS lighter than the F4U when tested and it should be 200LBS heavier. So you can imagine the results would be different with the extra weight.
2. The F6F IAS/CAS problem was apparent during this test so it's air speed was more than likely higher than indicated.

I will try to scan the rest of the report so you can see it. In the final conclusion the pilots make note of the "Gentle Stall" of the F4U and call it the "Weapon of Choice" for air to air combat among those tested.

[Saxman]

From what I understand, the Mustang's departure behavior was absolutely wicked, especially where there was gas in the fuselage tank. The P-51 just had the benefit of not trying to land on a carrier deck.

[dtango]

Isnt it like this?
At the same turn rate the g-forces are the same, this is comperable with a steady climb. Both planes must create the same lift and same ammount of drag and so same ammount of exess thrust.

Knegel:

(1) same turn rate does not mean the same g-forces.

(2) one of the fundamental issues is that a steady climb is not the same as a sustained turn.  More specifically the variables that effect power required are non-linear so you can't equate power-required in a steady climb to   power-required in a sustained turn.

(3) the NACA F2A-3 report demonstrates the above.

No time to post anything else on this topic at the moment .

Let me be clear.  I'm not suggesting there isn't anything wrong with the AH flap model.  

However you can't make the conclusion that the AH flap model is wrong based on the assessment thus far because the physics in the argument is inaccurate.

Tango, XO
412th FS Braunco Mustangs

[Brooke]

I have redone the calculations of turn rate and turn radius based on a much-more appropriate modeling of thrust vs. velocity (as suggested by Badboy).

The results are here.  Again, if anyone sees any problems with the math, please let me know:

http://www.electraforge.com/brooke/flightsims/aces_high/stallSpeedMath/turningMath.html

[Brooke]

I added a little more detail to the P-51D and F4U-1 models (calculating C_L_max for each based on stall speeds listed in the pilots' manuals).

The models still show turn rate for F4U-1 with full flaps slightly less than without flaps, but it is a very close thing.  The F4U-1 truly has an amazing wing, with excellent C_L_max, expecially amazing flaps, with even more excellent C_L_max (at least compared to a plane like the P-51D).  All it takes to get turn rate with full flaps to be about the same as turn rate without flaps is a little better e or C_D_min (or both) with flaps than what I'm assuming.

[dtango]

Originally posted by Brooke
All it takes to get turn rate with full flaps to be about the same as turn rate without flaps is a little better e or C_D_min (or both) with flaps than what I'm assuming.

Yep, that's the secret .  At higher angles of attack the drag polar ceases to be parabolic because lift dependent drag is strongly influenced by viscous separation.  Gripen and I pointed this out earlier.  What that means is e is no longer constant at higher aoa's but varies with aoa.  For the type of flaps in question (non-fowlers) Clmax occurs at a lower aoa with flaps down vs. with flaps up.  So if e varies with aoa then "voila!", e is better (higher) with flaps down vs. with flaps up.

Tango, XO
412th FS Braunco Mustangs

[Krusty]

F4UDOA: The quote is directly from Bodhi, who works on corsairs for a living and probably talks to their pilots frequently. You can ask him specifically for more detail, I was merely quoting something he said not too long ago in another thread.

[F4UDOA]

Brooke,

I was looking at your math most of which frankly sailed over my head but I did notice one thing. Your Clmax numbers seem high on both the P-51D and F4U-1.

I recalculated the Clmax number (power off) for the F4U in clean and landing condition and came up with this.

(391*11,300) / (97MPH^2 * 314) Clean no power
4418300 / 2954426
1.49Clmax

(391*11,300) / (86MPH^2 * 314) Landing condition no power
4418300 / 2322344
1.9 This is the listed Clmax in the Vought documentation as well.

Question:

If two aircraft fly circles around the same center point but one flys a greater radius than the other they may both be flying at the same rate even if one is flying much slower than the other. IE the aircraft flying closer to the Axis may be flying at 120MPH and the one flying further away from the axis can be flying at 160MPH and they can both have the same turn rate.

I believe this explains why Knegal doesn't understand why the flaps do not cause the F4U-1 to lose turn rate despite flying much slower however I cannot prove this mathmatically. Do you agree?

Thanks

[F4UDOA]

Krusty,

I did not know that about Bodhi, I will have to ask him.

One thing that I find in reading about modern Corsair pilots/owners that is common is the ease of flying the F4U. From the SETP to Jeff Ethell and multiple other articals etc it is a common theme. Even the 1944 JFC echoes the same findings in stability and control.

The general theme with the F4U is stay within the flight envelope and you are safe. When exceeding it the stalls can be dramatic but are recoverable. This is common to most warbirds except the F6F. The P-51 stall behaivior far exceeds the F4U but it was land based so it did not have the same criteria for success.

The findings of the SEPT test were that the F4U was for the experianced pilot and the F6F was almost like flying a trainer and was better for less experianced pilots (Ensigns). The F4U did give ample stall warning and had higher G-Limits than the F6F without entering buffet in max performance turning.

The Strength of AH (IMHO) is that it reley's on fact not annecdote. I think many in this community expect the F4U to spin and crash everytime you pull the stick. This airframe stayed in service for 30 years without change, I don't think it was quite that lethal.

[Saxman]

IIRC the biggest problem with the Corsair's departure wasn't just the port wing drop during the stall at low speeds in of itself, but inexperienced pilots over reacting and trying to power on too hard to compensate. That much torque that suddenly contributed to a significant number of the fatal spins at low altitude.

You can see this to lesser degrees in AH (yes, I DO think it's milder than it should be). Put the F4U in landing configuration at reduced power near stall speed, trimmed for level flight or slow descent. As the plane stalls and the left wing dips jump right to power on full. The F4U makes a noticeable attempt to roll left.

[dtango]

Originally posted by F4UDOA
If two aircraft fly circles around the same center point but one flys a greater radius than the other they may both be flying at the same rate even if one is flying much slower than the other. IE the aircraft flying closer to the Axis may be flying at 120MPH and the one flying further away from the axis can be flying at 160MPH and they can both have the same turn rate.

I believe this explains why Knegal doesn't understand why the flaps do not cause the F4U-1 to lose turn rate despite flying much slower however I cannot prove this mathmatically. Do you agree?

F4UDOA: Yes that is correct.

turn-rate = gravity * sqrt ( gload^2 - 1) / V

For instance two planes at different airspeeds and turning at different g's:

mph g rate
170 2.90 20.1
110 2.02 20.1

Different airspeeds, different g-load's, but same turn rate.

Actually I think the main source of Knegel's issue is that he's misapplying

Ps = (T - D) * V / W

between a steady climb and a sustained turn.

Tango, XO
412th FS Braunco Mustangs

[Charge]

"I think many in this community expect the F4U to spin and crash everytime you pull the stick."

Yes I'm sure Knegel was trying to point that out...

"Actually I think the main source of Knegel's issue is that he's misapplying
Ps = (T - D) * V / W
between a steady climb and a sustained turn."

And you claim that a loop and a sustained turn are the same?

Do you assume the speed to decay to the extent that the acceleration upward against the G gradient stays at 1 G? Do you assume that when the plane goes down the G gradient once again stays the same OR that the average between the rise and fall stay the same? If so, then why cannot WW2 fighters fly constant loops without losing altitude even if they can fly constant turn at some G without losing altitude?  

-C+

[dtango]

It is if you remove gravity as Knegel was suggesting.  You should read before you reply .

Tango, XO
412th FS Braunco Mustangs

[Brooke]

Originally posted by F4UDOA
Brooke,

I was looking at your math most of which frankly sailed over my head but I did notice one thing. Your Clmax numbers seem high on both the P-51D and F4U-1.

I recalculated the Clmax number (power off) for the F4U in clean and landing condition and came up with this.

(391*11,300) / (97MPH^2 * 314) Clean no power
4418300 / 2954426
1.49Clmax

(391*11,300) / (86MPH^2 * 314) Landing condition no power
4418300 / 2322344
1.9 This is the listed Clmax in the Vought documentation as well.

Question:

If two aircraft fly circles around the same center point but one flys a greater radius than the other they may both be flying at the same rate even if one is flying much slower than the other. IE the aircraft flying closer to the Axis may be flying at 120MPH and the one flying further away from the axis can be flying at 160MPH and they can both have the same turn rate.

I believe this explains why Knegal doesn't understand why the flaps do not cause the F4U-1 to lose turn rate despite flying much slower however I cannot prove this mathmatically. Do you agree?

Thanks

I was using stall speed for the F4U with power on.  I think that is more accurate, as power is on during stallfight turns.  For C_L_max with power off, though, here is how it would turn out (with v_stall = 97 mph calibrated airspeed, clean, power off).  97 mph = 97 * 1.467 ft/sec = 142 ft/sec, W = 11300 lbs, rho = 0.0748 lbs/ft^3 / 32 ft/s^2, S = 314 ft^2:

C_L_max = 11300 / (0.5 * 0.0748/32 * 142^2 * 314) = 1.53

So, that is a bit less than the C_L_max you get when v_stall (with power on) = 94 mph.

With flaps down, power off (86 mph = 126 ft/sec):

C_L_max = 11300 / (0.5 * 0.0748/32 * 126^2 * 314) = 1.94

For the question, yep, a plane with a smaller turning radius could have a smaller turning rate than a plane with a larger turning radius.  This is often what happens with full flaps.  The plane without flaps has a larger turning radius but also a larger turn rate.

Knegel, I think, believes that the fact that the F4U has a higher turn rate with full flaps (unlike most planes) points to a problem in its flight model in Aces High.  I talk about that in the document.  It's unusual, but I'm not sure it's a problem.  It depends on what things like e and C_D_min are for F4U's with full flaps.