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APPENDIX III

A HIGH SPEED INVESTIGATION OF THE BURNELLI XB-AB-3

MODEL IN THE N.A.C.A.

8-FOOT HIGH-SPEED WIND TUNNEL

BY EDMUND V. LAITONE.

SUMMARY.

The high speed possibilities of a 0.16 scale model of the Burnelli Aircraft Corporation XB-AB-3 design were investigated in the N. A. C. A. 8-foot high speed wind tunnel at Mach numbers from 0.18 to 0.65 with corresponding Reynolds numbers of 2,500,000 to 7,000,000.

Drag measurements were made with fixed transition in order to provide a better basis for the estimation of the full-scale drag coefficient increments. Static pressure measurements were made in order to estimate the critical speed. The rate of air flow and internal head loss in the cooling ducts were also measured.

At 20,000 feet altitude and at 0-degree angle of attack the model would have a critical speed of approximately 376 miles per hour. However, if the hatch and fuselage lower surface were redesigned the critical speed under the same conditions could probably be increased to approximately 440 miles per hour. The external drag of the duct appeared too high indicating that a more suitable design locating the exit farther aft would be beneficial.

INTRODUCTION.

The Materiel Division of the United States Army Air Corps requested the N. A. C. A. to investigate the high-speed possibilities of the Burnelli Aircraft Corporation XB-AB-3 design. A model of this airplane suitable for testing in the N. A. C. A. 8-foot high-speed wind tunnel was provided by the Burnelli Aircraft Corporation.

The test programme was arranged by representatives of the Material Division, the Burnelli Aircraft Corporation, and the N. A. C. A. to provide data to aid in the performance estimates and to study the compressibility effects as outlined in reference 1. The Mach number range for most of the tests extended from 0.18 to 0.65 giving a corresponding Reynolds Number range of 2,500,000 to 7,000,000 based on the mean aerodynamic chord, 24.34 inches, of the complete model.

Static pressure measurements were taken at the critical locations on the model in order to determine the effects of compressibility and to estimate the critical speed. The drag measurements were made with transition fixed at the probable full-scale location whenever necessary in order to provide a better basis for estimation of the full-scale drag coefficient increments. The rate of air flow and internal head loss in the cooling ducts were also measured.

The tests were conducted with the assistance of Messrs. Berkok and Applegate, representatives of the Burnelli Aircraft Corporation, and Mr. J. A. Roche of the Materiel Division Liaison Office.

 

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1939 Burnelli X-BAB-3

 

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UNITED STATES ARMY AIR CORPS TEST RESULTS

BURNELLI FIGHTER BOMBER X-BAB-3

SEPTEMBER 19 - 1939

 

From studies of the research made by the Burnelli Co., the NACA and the Air Corps, the Military adaptability of the basic design has the following advantages over the orthodox streamlined dead-weight fuselage.

  1. The coefficient of drag is the lowest known for any useful airplane today.

  2. The coefficient of lift is greater .

  3. The lifting fuselage has distinct advantages for the installation of power plants, bombs, armament and all other accessories over the streamlined fuselage.

  4. From wind tunnel tests already conducted by the NACA and NYU the performance is exceptionally good in every phase.

  5. The design embodied extremely good factors of safety -- considerably higher than the streamlined fuselage type.

  6. The design is simple of construction and in the opinion of the Air Corps lends itself to high speed production better than any design and therefore the valuable time element involved in all production contracts can be taken advantage of to its fullest extent.

  7. It is apparently a cheaper airplane to build because of the time element referred to in 6 above.

[emphasis added].

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