North American NA-133 - Navalized P-51H Mustang
At NARA was a folder on the XF8B and the North American Liquid Cooled VF and my guess as to what the NAA Liquid VF was turned out to be correct. There were no eye popping brochures, but a mass of correspondence back and forth. There was even some Jet VF specifications buried in the correspondence as well (!).
It's quite clear that North American was aiming at the same market that the F8F was being aimed at; since one of the drawings (reproduced in reduced format) was one comparing the NA-133 to the F8F. The other drawing was a much clearer version of the badly degraded mimeograph copy I found at the NHHC's Aviation History Branch.
COMMENT ON MILITARY REQUIREMENTS COMMENT
1. As stated in letter, Bureau has checked none of the figures quoted by Vought, but even on basis of figures presented, the liquid cooled design is considered to possess "no outstanding advantages". If designs were checked on comparable engine ratings, the liquid cooled design would be inferior in all aspects of performance, as detailed below.
2. Regarding the spot - as pointed out in the letter, a different arrangement of equipment and wing folding was used in the two designs. The liquid cooled design has the guns in the outer panel with ammunition outboard of the 4 guns. The air cooled design shown in the tabulation has the guns in the center section with the ammunition inboard of the 6 guns. By moving the wing fold inboard, and ammunition outboard, a folded span of less than 16.5 feet is obtained without difficulty. Such an arrangement gives a spot of 205 ft. for 36 liquid cooled airplanes, and 202 ft. for 36 air cooled airplanes, or as stated in the letter, substantially identical spots result.
3. Performance and engine - The ratings used for performance and performance figures must be considered together. As shown in the tabulation, the liquid cooled engine design has slightly better speed, (7 mph max.) and better climb (475 fpm max.) through the medium altitudes. Above 23000 ft., the air cooled has a large, speed and climb advantage, giving a higher average V max. and R/C. These figures are based on a liquid cooled Allison engine rated at 2100 BHP. Army power plant personnel have informed Bureau personnel that no such engine is in sight. A comparison of Allison engine present ratings and expected future ratings are shown on the attached sheet. Correcting Vought performance figures back to Army engine ratings will make the air cooled design superior throughout the altitude range. The 2700 BHP rating used for the 2 stage R 2800E engine, is 50 HP more conservative than Bureau estimates. It is considered that the 2100 BHP Allison engine is far more problematical than the 2700 BHP R 2800 E.
4. In view of the greater interest in jet and turbine powered VF types, it was considered unnecessary to attempt a thorough evaluation of the air cooled or liquid cooled designs submitted by Vought. Mil. Req. has concurred in this general conclusion. It is suggested that further liquid cooled vs. air cooled arguments be. held in abeyance pending receipt of North American's proposal, and evaluation of P-51D with arresting hook now at NAMC, Phila.
C. L. Fike
[Written on Paper]
This was in reply to caustic Mil Req comment. the letter was deleted from files at direction of Adm.
This is essentially a P-51 and presumably incorporates improvements based on P-51 experience. While the P-51 did not have entirely adequate directional and longitudinal stability, the e.g. has been moved forward somewhat. We have no means for checking this in the time available but it would appear that the destabilizing effect of 4-blade prop and increased power may offset much of the gain due to forward shift in c.g.
Variable dihedral may turn out to be very effective. It is understood that negligible weight is involved to obtain this feature.
There should be some concern about gas tanks on the wing tips. The weight moment may be quite troublesome at low speeds. There should be some check on flutter effects.
It is not known how the stall will compare with P-51. The stall of the XP-51 was none too good. The lift coefficient developed on the P-51 was rather low.
24 July 1944
From: Military Requirements.
SUBJ: Experimental Carrier Fighter Powered by Liquid Cooled Engine, Request for Proposal.
Ref: (a) DCNO (Air) Conf. memo. Op-31-CL-MML (SC) A21-1, Ser. 053031, dated 21 March 1944.
1. Ref. (a) was routed through the Bureau of Aeronautics for answer and comment. Both ref. (a) and the answer thereto aroused comment which indicated violent disagreement on the part of those concerned. The fact remains that the Mustang outstrips all other VF of its time. The variance of opinion itself expressed by the interested parties indicates an experimental venture in the liquid cooled airplane is necessary.
2. If carriers are to remain a potent force in warfare, then their airplanes must equal or better in performance those of the enemy, regardless of their operating base, To do so, though, it may be necessary to. launch all planes by an auxiliary means in order that their performance be not inferior due to the take off handicap, provided they can land safely on return.
3. It is believed that any carrier fighter designed for use within the coming five year period should have a Vmax of 475 m.p.h. - at a critical altitude of 25,000. Vmax at SL should be at least 425. This plane, in its fighting weight, should climb to 30,000 ft. in five minutes. Its combat radius should be 300 miles in the escort version, 75 miles in the interceptor version. Either version should be able to remain in the air six hours. The present air situation in the Pacific is entirely the result of fighting a fifth rate air power. The problem of protecting a carrier in the near future will be that of meeting an enemy attack force picked up at radar range and coming in at 400 m.p.h. Their missiles will probably be of the homing variety. No longer will slow attack groups circle your task force prior to attack. To stop such an attack, you will not want a fighter that is also a dive bomber, also a ground attack plane, also a long range scout. You will need the best flying machine that can be built or carrier aviation will disappear on the first attack.
4. It is, therefore, requested that a proposal for such a fighter, powered by the appropriate liquid cooled engine, with the performance suggested in paragraph 3 above, be asked for from interested companies. It is particularly desired that North American be asked for such a proposal. The problem itself will indicate the type of take-off necessary to produce the best possible fighter. A parallel proposal using a liquid cooled engine - Jet combination seems in order.
5. The purpose of this proposal is to obtain the smallest aircraft possible for carrier use without loss of range and performance.
R. E. DIXSON
This may be the memo that started it all:
21 Mar. 1944
From: DCNO (Air)
To: Chief, BuAer
SUBJ: US Navy Aviation Experimental Program - Review of.
1. It is requested that the Aviation experimental program be subjected to a study and review.
2. It Is considered that experiences of the war and the present trend of design within the Navy may point to the necessity of reefing our sails and. departing on a new tack.
3. The weights and physical measurements of our newer airplanes are increasing rapidly with the result that we shall soon be forced into reduction of carrier complements. To obtain increased performance the natural and logical step has been an increase in power. However, the direct result of this has been larger engines presenting greater frontal areas with correspondingly larger fuselages to accomodate them.
4. Possibly we have reached the place in the development of the air-cooled engine where we should sever our many years of allegiance and look to a design of aircraft incorporating liquid cooled in line power plants.
5. The size and weights of our projected designs is ample evidence of the fact that our engineers must concentrate on smaller and more compact aircraft with which to do the job at hand. If the liquid cooled in line engine represents the step necessary to achieve the results, we should then be spending some of our time and money on development of that article.
J. S. McCain
Deputy Chief of Naval Operations
SUBJ: Model VF Airplane - North American Aviation Model 133, Liquid Cooled Proposal -Summary of.
(a) NAA Conf. Ltr. AL-874, dated 20 Oct. 1944•
(b) NAA Conf. Ltr. AL-889, dated 3 Nov. 1944-
(c) DCNO (Air) Conf. Memo. OP31-C1-MML, (SC) A21-1, Serial 053031, dated 21 March 1944.
(d) Mil. Req. Conf. Memo. Aer-R-3-LCS, dated 24 July 1944.
(e) Engr. Conf. Memo. Aer-E-211-GS, VF, dated 21 Aug. 1944.
(f) Mil. Req. Conf. Memo. Aer-R-3-JTB, dated 2 Sept. 1944.
Encls : (HW)
(A) Performance Summary and Comparison, dated 11—22 —44.
(B) VF Speed vs. altitude Comparison, dated 11 —2 2 —44.
(C) VF Climb vs. Altitude Comparison, dated
(D) VF Combat Radius vs. T.O. Dist. Comparison dated 11-24-4-4.
(E) Comparison, NA-133 vs. Mil. Req. Specification, dated 11-22-44.
(F) V-1650-11 Engine Rating Curve Sheet, dated 11-13-44.
1. By refs. (a) and (b), North American Aviation, Inc. has submitted engineering, cost and delivery data on a carrier basedVF airplane powered with a V-1650-11 liquid cooled engine, as Informally requested by the Bureau.
2. The history of this proposal dates back to ref. (c), which requested a review of the aviation experimental program to determine whether carrier based aircraft should be utilizing liquid cooled engines to obtain high performance in smaller' sizes of airplanes. Comments on ref. (c) indicated a wide diversity of opinion on the question, and ultimately resulted in ref. (d) requesting that proposals from various contractors be obtained for a carrier based VF airplane powered with a liquid cooled engine. Ref. (f) provided a clarification of requirements as requested by ref. (e). A number of contractors were requested informally to submit such designs, but North American Aviation was the only company willing to submit a complete proposal. Chance Vought made some preliminary studies in a comprehensive fighter design survey, but reached the conclusion that other types of power plants were more suitable for future fighters. The remaining contractors were unwilling to attempt liquid cooled designs at this time.
3. The North American Model 133 is similar to the P-51H Airplane being procured by the Army. The power plant is a fuel injection, Packard built, Merlin V-1650-11 engine equipped for water injection, and the installation is substantially identical to that of the P-51H. The wing has been redesigned for folding, 10 sq. ft. of area added, slotted flaps incorporated instead of split flaps, and larger ailerons with power boost have been installed. The landing gear has been modified to meet Navy strength requirements. The fuselage fuel tank of the P-51H has been eliminated, and the wing fuel cells capacity reduced to give a total of 150 gal. of protected fuel. Elimination of the fuselage fuel tank reduces the e.g. travel, permitting use of a smaller horizontal tail, while maintaining adequate longitudinal stability. Arresting and catapult provisions are basically similar to those installed on a P-51D, though somewhat improved from a drag standpoint.
4. The interested branches of the Engineering and Maintenance Divisions have examined the data available, and a number of details found which require correction if the design Is to be procured. The discrepancies are not major, and do not affect the performance of the airplane to a sufficient extent to require submission of a revised proposal. Wing tip drop tanks of 50 gal. capacity have been proposed, primarily to better the airplanes spotting characteristics by allowing the tail to pass under the center section of the wing. The nonstandard tanks seriously complicate the fuel system, introduce handling and filling complexities as well as aggravating the logistics problem. Since the spotting advantage of 39 airplanes as compared to 32 airplanes in a 200 ft. deck length exists only when bomb racks and rocket launchers are not installed, it is considered that a standard 100 gal. tank suspended from the wing bomb rack is a superior installation.
5. Performance characteristics of any airplane are proportional to the engine ratings available. In ref. (e), Engineering requested certain data to permit establishment of naval ratings for liquid cooled engines. Military Requirements, in ref. (f), indicated that power plant reliability and fuel type were to be at the contractor's discretion. North American's performance was submitted on 90 inch manifold pressure ratings, using 150 grade fuel and water injection. These ratings are not in agreement with Army, British or Packard data. Two Bureau performance estimates were made, one to check the NAA figures, and the other at the weights estimated by the Bureau, slightly higher than those of NAA, and at the engine ratings given by the Army as their anticipated future ratings. These ratings are shown on End. (F), with the V-1650-3 present rating indicated for comparative purposes only. It will be noted that the normal rating of the engine is less than the R-1820 or R-1830 at sea level, while the W.E.P. rating used by North American approaches that of the R-2800.
6. A summary of performance characteristics for the design Is shown on Encl. (A), while speed,, and climb curves comparing the airplane with the F8F-1, F8F-2 ("E" Engine) and F2G-1 are included as Encls. (B) and (C). The F8F performance shown is the Bureau estimate of the production airplanes with both the present "C" engine and the future "E" engine, while the F2G-1 is shown at the current military rating. Previous comparisons using the "E" engine have been subjected to criticism as a hypothetical engine. The V-1650-11 engine is not scheduled for production until June 1945, and the NAA-133 airplane is not promised until 9 months after date of contract, it therefore appears proper to use the "E" engine in the comparison since current estimates are that it will start in production by 1 Sept. 1945. An experimental F8F-2 should be flying during the spring of 1945. A plot showing combat radius (standard VF problem) spotted against take-off distance is included as Encl. (D).
7. Encl. (E) shows a comparison of the characteristics of the NAA-133 airplane with those specified by Mil-Req. It is obvious that the design fails to meet the desired performance by a wide margin.
8. The most serious disadvantages of the NAA-133 design for carrier use that have been mentioned are:
(a) Increased vulnerability inherent in any liquid cooled arrangement over air cooled types.
(b) Increased maintenance because of addition of radiators and aftercoolers.
(c) The airplane as presented will possess the poor ditching characteristics of the P-51 series airplanes.
(d) Introduction of liquid cooled type will increase logistic problems, and necessitate an additional training program.
9. This memorandum has been prepared to summarize the NAA-133 proposal data for use in the conference now scheduled for 1400, Monday, Nov. 27, 1944.
W. Z. FRISBIE