F6F, FG-1, P-51, P-47 comparison

[Anaxogoras]

A few years ago, the Society of Experimental Test Pilots ran a flight test
comparison of the F6F-5, FG-1D (Goodyear F4U), P-47D-40 and P-51D. Chief
test pilot was John Ellis of Kal-Aero. Other pilots also participated.

The three radial jobs had versions of the R-2800 that produced appx. 2,000
hp, so differences in performance can be reasonably attributed to the
airframe (and prop). The P-51 had a V-1650-9 Merlin rated at appx. 1,500
hp.

The P-47 had a Curtiss Electric constant-speed four-blade prop.
The FG-1 and F6F both had Hamilton Standard three-bladed constant speed
props (so only the airframe made the difference between these two).
The P-51 had a Hamilton Standard Hydromatic four-bladed constant speed
prop.

Because of the age of the aircraft, structural loads were kept to 6g max.
Engines were fueled with 100LL, which limited MP by four inches on the
radials. Power was limited to maximum continuous settings (except for
take-off & climb to 10,000 ft., when military power was used),
superchargers were limited to low range. Altitude did not exceed 10,000
ft (so bomber escort altitudes were not reached).

Some of the findings:

CLIMB brake release to 10,000 ft.
Hellcat quickest at 4min 15 seconds, followed by the FG-1 at 4min 44 sec.
However, the F6F required 100 lbs of continuous right rudder making it
very tiring to operate. The P-47 trailed the FG-1 by a few seconds. The
P-51 came in last.

LEVEL ACCELERATION at 10,000 ft. using METO to max attainable speed
P-51 accelerated from 110 KIAS to 242 KIAS in 133 seconds.
P-47 accelerated from 105 KIAS to 223 KIAS in 130 seconds.
F6F accelerated from 100 KIAS to 220 KIAS in 115 seconds.
FG-1 accelerated from 100 KIAS to 230 KIAS in 162 seconds.

STALL normal (straight and level decelerating at 1 kt/sec.) and
accelerated (constant 3g turn decelerating at 1 kt/sec.)
Aerodynamic warning:
Best--P-47, with buffet 5 kt above stall.
Worst--P-51, no buffet or other warning.
FG-1 and F6F buffeted 2 kts above stall.
Decreasing aileron effectiveness and increasing longitudinal stick forces
were noticeable in all except the FG-1.
Height loss, accelerated stall:
Best--P-47, 100 ft.
Worst--P-51, 500 ft.
FG-1 and F6F both 150 ft.

Behavior during accelrated stall:
Most predictable and controllable: P-47 and F6F. Both could be flown at
will into the pre-stall buffet, which at no time was heavy enough to
present problems with tracking, and held at maximum usable lift
coefficient with ease. Sideslip became noticeable as wing heaviness
correctible with rudder. There was little tendency to depart controlled
flight.
The FG-1 suffered severe airframe buffet shortly before the stall, but at
the stall there was a strong g-break and rapid right wing drop--no matter
which direction the turn. Careful left rudder could prevent wing drop,
but then at the stall the aircraft became very unpredictable, bucking and
porpoising, with a tendency to a sudden departure.
The P-51 gave no warning whatsoever of an accelerated stall. At the
stall, the aircraft departed with complete loss of control, achieving
270-degree of roll before recovery. Departure was accompanied by violent
aileron snatch strong enough to rip the control stick from the hand.
In short, the P-51 suffered from a Part I deficiency.

SUSTAINED TURN PERFORMANCE at METO at 10,000 ft.
The F6F out-turned the other three by a conclusive margin (1g). The other
three were all about the same.
Corner speeds of all were very close to the maximum level flight speed,
implying very rapid energy loss when turning at the structural limit.
The F6F was in light airframe buffet at 6g at Vmax; the P-47 experienced
light buffet at 4.8g. The FG-1 and P-51 were buffet-free up to 6g.

MANEUVERING STABILITY stick forces/g at Vmax
FG-1--5 lbs/g (too light)
P-47--7.5 lbs/g (ideal)
F6F--12.5 lbs/g (barely acceptable)
P-51--over 20 lbs/g (excessive)

STATIC LATERAL DIRECTION STABILITY steady heading sideslips
All aircraft except the P-47 exhibited moderate or greater adverse aileron
yaw. Worst was the F6F, followed by the FG-1 and the P-51.

ROLL PERFORMANCE
1g 360-degree right (left slower--F6F worst, P-51 best)
FG-1--81 deg./sec.
F6F--78 deg./sec.
P-51--75 deg./sec.
P-47--74 deg./sec.
3g 180 degree right (left slower--P-51 and F6F best, FG-1 worst)
P-47--66 deg./sec.
FG-1--58 deg./sec.
P-51--55 deg./sec.
F6F--48 deg./sec.

DIVING ACCELERATION 30 deg. dive from 10,000 ft., 5,000 ft. begin pull-up,
level off at 4,000 ft.
Aircraft P-51 P-47 FG-1 F6F

Start Speed 110 kts 100 kts 100 kts 120 kts
Max Speed 350 kts 348 kts 315 kts 350 kts
Time 23 secs 32 secs 28 secs 25 secs
All aircraft except the P-47 needed retrimming during the dive.

AGILITY
g capture of 3g target, held for 5 seconds.
G capture and hold was easiest in the P-47, predictable and accurate. F6F
overshot the target by 0.2g. P-51 and FG-1 both overshot by 0.5g

Heading Change Time (180 deg at METO, 220 KIAS at 10,000 ft.)
FG-1--8.5 sec P-47--9.7 sec F6F--9.9 sec P-51--10.0 sec

AIR-TO-AIR TRACKING 210 KIAS at 10,000 ft. (straight & level into a 3g
turn to the left building to 4g followed by a hard reversal into a 4g
right turn.)
FG-1 best, followed by P-47, F6F and, trailing badly, the P-51. Lateral
corrections in the P-51 were difficult thanks to the very high stick
forces. During one run-thru, an effort at a longitudinal tracking
correction that put 4.5g on the plane led to a sudden departure and spin.
Poor forward visibility in all aircraft (P-47 wost, FG-1 best) made
air-to-air tracking difficult. Depressed sight-line aiming difficult to
impossible.

AIR-TO-GROUND TRACKING (90-degree roll into a 30-degree dive from 200 KIAS
at 5,000 ft. into a 3.5g right rolling pullout to a 90-degree heading
change initiated at 2,500 ft.)
The P-47 was far and away the best, accelerating 125 kts in the dive, no
retrimming required, with crisp control response. Accurate target
tracking very easy. FG-1 next best. 100 kt. acceleration. Agressive
lateral corrections required. P-51 similar to FG-1 in acceleration and
control response, but with heavier stick forces. F6F also accelerated 100
kts., but stick forces increased 20 lbs and rudder forces became so high
they interfered with accurate target tracking.

THROTTLE & PROPELLER RESPONSE
MP response instantaneous. Hamilton Standard propeller response quick and
positive. Curtiss electric prop (on P-47) sluggish in response, delaying
RPM change by 3 seconds in a change from 2,000 rpm (cruise) and 2,550 rpm
(METO).
Radial engines required pilot to manage cowl and cooler flap settings.
Merlin engine had automatic control of oil and coolant radiator flaps.

[Stoney]

Where'd you find this?  Pretty good read...

[AWwrgwy]

Now, someone interpret it for me.

Interesting (I think)


wrongway

[Murdr]

I believe one of our friends here has a copy of the actual report http://bbs.hitechcreations.com/smf/index.php/topic,26001.msg268287.html#msg268287

That's a repost of a repost of a repost, lol.  That text, or effectively the same was posted quite awhile ago somewhere on a forum or newsgroup, but I bet Gav snagged it from a recent repost over at ubi.

[BnZs]

The only things I find surprising:

The P-51's climb as compared to the Jug and Hog. However, apparently there were power limitations (1500 vs. 1795) and it was kind of an odd test to boot...release of brake and time to 10K as compared to finding ROC for a given alt.

The P-51 sustained turn being "about the same" as the Hog's. I'm going to assume the Hog was not using its maneuvering flaps setting.

Well, another interesting thing: Laminar flow airfoils are known for stalling all at once, so the P-51 stall does not surprise me. However, I've had people who have actual P-51 stick time tell me the onset of the stall is quite apparent. Curious.

[Stoney]

However, I've had people who have actual P-51 stick time tell me the onset of the stall is quite apparent. Curious.

Ahh, you have to love the wonderfully subjective world of test flight reports... 

[Anaxogoras]

Yup, murdr, repost of a repost.  Just thought I'd share because I knew someone would enjoy it.

[Krusty]

The 2000hp and 1500 hp ratings were max ratings. That means WEP.

However WEP was never used. Max continuous was used except for climb, where military was used. So basically the tests are done on cruise settings. Not exactly competitive stats at those reduced settings. Wartime testing pushed the planes more because thousands were available. Newer tests don't dare risk the multi-million-dollar assets that are almost irreplacable in this day and age.

Interesting, but not as valuable as WW2 era tests.

[BnZs]

The V-1650-7 in the P-51D was rated for 1,720 horsepower at WEP.

IIRC, R-2800-59 was used in the P-47D-40. It was rated at 2,500 horsepower at WEP.

The 2000hp and 1500 hp ratings were max ratings. That means WEP.

However WEP was never used. Max continuous was used except for climb, where military was used. So basically the tests are done on cruise settings. Not exactly competitive stats at those reduced settings. Wartime testing pushed the planes more because thousands were available. Newer tests don't dare risk the multi-million-dollar assets that are almost irreplacable in this day and age.

Interesting, but not as valuable as WW2 era tests.

[Krusty]

That makes a bit more sense, but still not exactly up to WW2 testing levels.

[Bodhi]

Newer tests don't dare risk the multi-million-dollar assets that are almost irreplacable in this day and age.

Don't be naive.  Anytime you start testing stalls in these WW2 aircraft below 10k you risk the airframe.  That's a fact. 

The Corsair is one of the worst for departure into a spin which can be all but unrecoverable. 

[Krusty]

A government military with tens of thousands of suplus planes and thousands of surplus pilots is more likely to risk it in the name of science than a private individual with a single plane and a single pilot.


I'd personally like to see an AH flight model that refelects the unstable aspects of the f4u (and p51 and other planes) stalls/spins, but I don't know if that'll happen any time soon.

[BnZs]

A government military with tens of thousands of suplus planes and thousands of surplus pilots is more likely to risk it in the name of science than a private individual with a single plane and a single pilot.

Indeed, they DO tend to use limited power settings with the old engines. Huge expense to maintain and repair. The dearth of high-octane avgas has something to do with it as well.

I'd personally like to see an AH flight model that refelects the unstable aspects of the f4u (and p51 and other planes) stalls/spins, but I don't know if that'll happen any time soon.

Well, according to the report, if you pull an accelerated stall in the P-51D, you get a snap-roll.

In Il2, if you honk back the stick in the P-51, you get a snap-roll.

In AHII, if you honk back the stick in the P-51, you get a snap-roll.

So things seem okay to me. It does seem pretty darn hard to get a rotation/flat spin in AHII. But the departure traits in AHII are bad enough to make stalling a no-no, so you can still rope people and etc., just fine.

[Krusty]

snap stalls aren't the only issue.

Used to be a definite stability boost in the 51B over the 51D in tight turns, the D would spin inward much more easily. Then since AH2 that's gone. No benefit to having a razorback anymore (a hole/flaw in the game IMO).

Several planes have these issues I'd like to see remedied, and it's not simply snap-stalling.

[Stoney]

No benefit to having a razorback anymore...

The difference in directional stability of the P-51B and D is extremely noticeable--I can discern a huge difference.  Try flying with combat trim off and note how differently they behave.