Mike Williams
Senior Airman
- 572
- Oct 19, 2006
Hello Bill:
It would be natural and understandable to have misgivings about trials where the Navy compared an Army aircraft against their own or vice versa. After reexamining the Evaluation and Comparison Trials of the P-51B and F4U-1 I don't believe the findings were too terribly politicized if one assumes that the Navy was interested in comparing the P-51 against the best performance possible from standard production operational F4U's as well as F4U's that might be coming into service in the not too distant future.
Allow me to explain why I feel that this particular comparison is at least a reasonable interpretation of how the P-51 and F4U compared. The Navy utilized three aircraft in the trials, namely P-51B No. 37050, F4U-1 02390 and F4U-1A No. 17930.
Firstly, let's check the performance of the P-51 obtained by the Navy and compare it against other sources.
Level Speeds:
P-51B 37050 (Navy, Patuxent River): 358 mph at SL and 450 mph at 29,200' using 67" Hg, 3000 RPM.
P-51B No. 43-6883 (Army, Wright Field): 370 mph at SL and 442 mph at 29,400'.
P-51B FX953 (UK, Boscombe Down): 360 mph at SL and 450 mph at 28,000 ft.
See also P-51 Tactical Planning Characteristics Performance Chart and Aircraft Data Sheet for Mustang III (P-51B)
Thus it can be seen that in this respect at least, the Navy's findings are in good agreement with other flight trials and data sheets.
Climb:
P-51B 37050 (Navy, Patuxent River) 9,423/9,100 lbs.: F4U's are 750 – 1,000 ft/min superior with the P-51B loaded to 9,423 lbs and "superior in climb to 20,000 feet, and the P-51B superior above that altitude" with the P-51B loaded to 9,100 lbs..
P-51B No. 43-6883 (Army, Wright Field) 9,205 lbs.: 3,450 ft/min at 13,800 feet
P-51B FX953 (UK, Boscombe Down) 9,200 lbs.: 3,610 ft/min at 10,600 feet
Unfortunately the Navy didn't provide actual rate of climb figures for the P-51B, rather just the comparative figures as stated above.
The Navy tested two F4U's during the comparison trials. F4U-1A No. 17930 is described as "a standard production raised cabin airplane, with a surface finish in rather poor condition, but with the tail hook removed. It is considered to have been in a drag condition representative of production airplanes after moderate service." The report also notes that "F4U-1A No. 17930 was flown at the standard war emergency rating of 60" at 2700 RPM, with water injection." The level speed results obtained, along with those of another F4U-1 tested by the Navy at the same power settings for comparison, are as follows:
Level speeds:
F4U-1 No. 17930: 365 mph at SL, 431 mph at 20,300 feet. 60" MAP, 2700 RPM. 31.5" carburetor impact pressure setting. (without tailhook opening faired.)
F4U-1 No. 50070: 364 mph at SL, 421 mph at 19,850 feet. 60" MAP, 2700 RPM 31.5" carburetor impact pressure setting. (with tailhook)
In contrast the Bureau of Aeronautics-Navy Dept. Airplane Characteristics Performance data sheet lists the level speeds of the F4U-1 as 359 mph at SL and 417 mph at 19,900 feet using water injection.
It can thus be concluded that F4U-1 17930's condition while not exactly standard, is close to standard and its performance a bit stronger than would be typical of production models.
The other F4U-1 tested is certainly not typical of those F4U's entering service at the time of the trials. It's important to note that the Navy doesn't try to pass it off as standard either. "F4U No. 02390 was a standard low-cabin production airplane, in a drag condition representative of that to be expected in the F4U-4 airplane as a Marine land-based fighter. … The principle changes included sealing and fairing the wing fold hinge line, removal of the tail hook, carefully fitted cowling, and a faired and smoothed, but not polished, skin. The total speed gain, as a result of drag reduction alone, in this airplane is estimated to be 8 mph at the airplane upper critical altitude." "F4U-1 No. 02390 was flown at a special war emergency power rating of 65" manifold pressure and 2700 RPM, with water injection at an increased water flow rate." One of the conclusions of the report on F4U-1 No 50030, dated August 2, 1945 was "A combat power rating in excess of 60" manifold pressure is considered to be impractical for general use when atmospheric temperatures are in excess of NACA standard."
Climb:
F4U-1A No. 17930 max climb = 3210 ft/min at SL (12,162 lbs.)
F4U-1 No. 50070 max climb = 3460 ft/min at SL (12,162 lbs.)
F4U-1 No. 02390 unknown but stated as superior to the P-51B at various loadings except above 25,000'.
In contrast the F4U-1's climb rate as shown on the Airplane Characteristics Performance sheet is 2890 ft/min at SL at 12039 lbs and using water injection. It appears that the Navy is on less solid ground with their conclusions regarding climb comparisons of the F4U and P-51B.
Was the Navy trying to mislead their intended readership based on what we know so far? With respect to level speed performance, I don't think so, but including F4U No. 02390 in the trial does muddy things up for us in this day and age if we are just reading their conclusions, looking at the charts and not examining the details. It does appear to me, however, they were stretching the truth a bit with respect to their conclusions regarding climb. Sure, the report is probably somewhat biased but in the end I believe the F4U served the Navy well and was probably a better choice for them just as the P-51 was the better choice for the Army Air Force.
Frankly the report only touches on maneuverability and response and apparently is little more than pilot's impressions. It falls far short of "turn and acceleration comparisons at various speeds and altitudes" (well, to be fair, no one was doing that at the time) or full fledged tactical comparison trials such as those conducted by Eglin or AFDU in the UK. I'd agree with you that the report's conclusions in this respect were a bit of a stretch. A USAAF report comparing an F4U and an Allison engined P-51 provides an interesting counterpoint.
There must be a good reason why most test centers of the period used comparative, head to head testing, for performance variables such as turn, acceleration, roll, etc. Interestingly the Navy did occasionally test and quantify roll rates such as that found in this report on the F4U and this report on the F6F. Quibbles with the report analyzed here aside, on the whole I find the Navy performance testing, especially that carried out at Patuxent River, to be very thorough, professional and the equal to Wright Field or A&AEE in the UK.
I suppose this ramble is not terribly on topic to the overall thrust of this thread but it is intended as a reply to Bill's post and it's what is interesting to me at this time and hopefully some of you too. What material I've found on WWII fighter turning comparisons can be found at the link in my signature, some reports and diagrams of which have already been linked to in this thread.
