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Evidence of Suppression and Official denial is overwhelming
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Report on the
Structural Superiority of Lifting-Body Aircraft
By Lt. Col. Richard T. Cella, U.S.A.F. Reserve
1952

(Colonel) Cella is President of the R.T. Cella Corporation and of the Princeton Engineering Company. He holds bachelor and Master of Science degrees in aeronautical engineering from the Massachusetts Institute of Technology. He has been an aerodynamicist and flight test engineer with Consolidated and Grumman Aircraft Corporations. During World War II, he flew 200 missions and nine campaigns as a squadron commander in the U.S. Air Force. A former assistant to the Deputy Chief of Staff of the Air force for Research and Development, his reserve assignment is in the ballistics missiles division, Air Research and Development Command.

[Pictures not part of original report - All emphasis added]

In any problem concerning the improvement of the performance of aircraft, the engineer is faced with two primary considerations. The first is aerodynamics. The second is structure.

Experience has revealed that not much improvement along aerodynamic lines can be expected, except in the field of circulation control.

The subsonic region of aerodynamics has been so thoroughly explored, in fact, that little variation is open to the engineer. Armed with a few design parameters, he may determine with ease the entire performance capability of a new design once the power has been selected. The asymmetric power criterion limits the gross weight, which, in turn, limits the other performance and design considerations. In other words, little may be done about cruising speeds and rate of climb for a given power and gross weight.

Graphic comparison of the Lifting Body with Conventional fuselage aircraft The one vital area in which performance can be improved is payload capability. This improvement must depend principally upon structural economy. The empty weight of the average modern conventional plane is approximately 70 per cent of its gross weight.

In the medium weight category, fixed weight items average 20 per cent of gross weight, which means the pure airframe weight is 50 per cent. This is the region in which economies can be made and improvement found.

The greatest degree of improvement, it would appear, can be expected only through configuration change, and not through the development of new techniques and material.

This brings up the long-discussed subject of the "lifting body" airplane design, and the structural weight savings which can be effected through its use.

The aerodynamic capabilities of lifting body aircraft are competitive with those of conventional designs, but weight savings are manifested as payload increases.

The following weight comparisons for conventional and Burnelli lifting-body types of aircraft are illustrative of this:

ITEM CONVENTIONAL BURNELLI
IMPROVEMENT
Gross Weight 100 per cent 100 per cent
------
Empty Weight 70 per cent 50 per cent
35 per cent lighter
Airframe Weight 50 per cent 32 per cent
55 per cent lighter
Disposable Weight 30 per cent 48 per cent
60 per cent lighter
Operational Weight 12 per cent 12 per cent
-------
Payload Weight 18 per cent 36 per cent
100 PER CENT GREATER

An examination of all the facts concerned show conclusively that the Burnelli lifting-body design is superior in both load carrying capability and safety to conventional types. In addition, this capability is accomplished without sacrifice of speed and range and while still maintaining single-engine performance required by the Federal Aviation Agency.

These advantages of the Burnelli Loadmaster series are made possible through structural economy of design. In the medium weight category, Burnelli capabilities constitute an approximate 100 per cent improvement over conventional aircraft.

It is highly unfortunate that some who have tested lifting-body design did so only from the standpoint of aerodynamic competitiveness. Such a view leaves the impression that the Loadmaster is merely equal in capability to conventional aircraft.

Any consideration of the greater economy in structural weight with the aerodynamic equality factor reveals that the Burnelli design provides a plane with a far superior load-carrying capability.

It is highly unfortunate that some who have tested lifting-body design did so only from the standpoint of aerodynamic competitiveness. Such a view leaves the impression that the Loadmaster is merely equal in capability to conventional aircraft.

Any consideration of the greater economy in structural weight with the aerodynamic equality factor reveals that the Burnelli design provides a plane with a far superior load-carrying capability.

At the conclusion of World War II, the N.A.C.A. conducted drag tests for the purpose of comparing conventional aircraft designs with those employing the lifting body principle.

The tests were made at the request of the Air Technical Service Command and the results appeared in memorandum form in Report No. MR-L5E09a, which was published in June 1945.

In the studies involving conventional craft, the Douglas C-74, one of the best planes of conventional type, was used.

The tests showed the lifting-body design to be competitive with the best conventional types, as revealed in the following quotation from page 13 of the report:

"...Comparison of the power curves of the proposed design with those of a conventional airplane of the same size indicate no great difference in potentional performance."

The drag polars of the two airplanes were almost identical.

"On the basis of the comparisons made, any advantages which the lifting-body design of cargo airplane may have over the more conventional types are probably chiefly dependent on non-aerodynamic factors, which were not considered in this report."

In short, the Air Force examination of the plane did not include a structural study. This, as is obvious, resulted in a clouding of the overall subject of efficiency.

The lifting-body design used in the comparison was submitted by Col. C.F. Green, liaison officer between N.A.C.A. and the Air Technical Service Command. It included what undoubtedly was the worst combination of factors which could be employed in a lifting-body type. The fuselage was excessively thick at 25 per cent, when 18 per cent would have met requirements. Engines were mounted on the wings, in absolute contradiction of results achieved in earlier tests, which showed a drag reduction with engines faired into the forward corners of the body. This fact was verified by tunnel tests at both the Massachusetts Institute of Technology and at New York University.

The fuselage trailing edge had an excessive angle of closure which resulted in flow separation at the 60 per cent chord point, even at negative angles of attack.

Despite these many flaws in the design tested, the lifting-body aircraft proved aerodynamically competitive with conventional types.

An examination of the structural economy and simplicity of the Burnelli design, however, reveals several additional facts.

In the medium class, for instance, the Burnelli Loadmaster has an empty weight 30 per cent lower than that of conventional aircraft of the same gross load capabilities. When such fixed-weight items as engines, propellers, etc., are removed, the lifting-body airframe weight is from 50 per cent to 60 per cent lighter than that of conventional types. The following comparison of the martin 404 and the Burnelli CBY-3 bears this out:

MARTIN 404 BURNELLI CBY-3
Empty Weight 29,330 lbs. 22,000 lbs.
Fixed Weight (min) 7,500 lbs. 7,500 lbs.
Airframe Weight 21,830 lbs. 14,500 lbs.

continued ...

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