Letter resulting from SECNAV’s Request
March 3, 1935
To: Dr. W. F. Durand, Stanford University
Stanford University, California
My Dear Dr. Durand:
At the request of the Secretary of the Navy, as expressed in the enclosed copy of his letter, the Science Advisory Board desires to appoint you chairman of the following committee:
– William F. Durand, chairman, Professor Emeritus of Mechanical Engineering, Stanford University
– Theodor von Karman, Professor of Aeronautics and Director of the Daniel Guggenheim Laboratory, California Institute of Technology
– William Hovgaard, Professor of Naval Design, Massachusetts Institute of Technology
– Stephen Timoshenko, Professor of Engineering Mechanics, University of Michigan
– Alfred V. de Forest, Associate Professor of Mechanical Engineering, Massachusetts Institute of Technology
– R. A. Millikan, Director of the Norman Bridge Laboratory of Physics, and Chairman of the Executive Council, California Institute of Technology
– Frank B. Jewett, President Bell Telephone Laboratories
– Charles F. Kettering, President, General Motors Research Corporation
I hope very much that you may find it possible to undertake this assignment.
It will be left to the judgment of this committee to determine its best course of procedure. It will, of course, be free to call in for consultation such men as Dr. Lewis of the National Advisory Committee for Aeronautics, Dr. Tuckerman of the Bureau of Standards, and Dr. Hunsaker of M.I.T. I am sure also that the members of the Navy Department and of the Goodyear-Zeppelin organization may be counted upon for co-operation. I understand also that there are at least some aspects of the problem which are pretty well agreed upon as forming a starting point for the investigation.
It has been the practice of our Board and of its committees to serve without compensation except for reimbursement of expenses incident to the work. I believe that the Navy Department will provide funds to take care of such expenses and also to provide such technical assistance as may be desirable.
I should be pleased to receive your acceptance to this appointment if this is possible, at your early convenience.
Very sincerely yours,
(s) KARL T. COMPTON, Chairman
Report No.1: JANUARY 16, 1936
GENERAL REVIEW OF CONDITIONS AFFECTING AIRSHIP DESIGN AND CONSTRUCTION WITH RECOMMENDATIONS AS TO FUTURE POLICY
Honorable C. A. Swanson, SECNAV, Washington, DC
My Dear Mr. Secretary:
The Committee appointed at your request by the Science Advisory Board is intended to review and analyze the past and present situation as to the design and construction of airships and to make recommendations as to their future design and construction.”
We have understood the first phase in the specification of our field of investigation as indicating a study, historical and analytical in character, and logically essential in order to proceed with the second specification relating to the future of such construction.
At the present time we desire to make a report of progress relating in particular to the basic question of the practicability of the design, construction, and operation of airships with a reasonable assurance of their safety and reliability, and with such technical characteristics as to offer good promise of potential usefulness for either commercial or military (naval) use.
While, in accordance with our instructions, we make no attempt to discuss the technical phases of the uses of airships, either military (naval) or commercial, we cannot present our conclusions regarding the practicability and potential usefulness of such structures independent of some recognition of the general fields in which they seem to offer effective service.
Thus referring to the Annual Report of the Secretary of the Navy for 1935 and in particular to the report of Rear Admiral King to the Secretary, uses of the following character seem to be indicated:
- Coastal-patrol service, especially detection of submarines and mines.
- Guidance of troop convoys and naval vessels through mine fields.
- It is also common knowledge that the large airship is looked to especially for services of the character of strategic reconnaissance and as an airplane carrier.
For the first-mentioned services, nonrigids (blimps) and rigid airships of small or moderate size are indicated; while for the last-named service, ships of the largest size will be required.
In the commercial field, we recognize the possibility of effective service for ships of various sizes, small, medium, or large, according to the various traffic requirements. Demonstration of such service in recent years is given by the “Graf Zeppelin” of the Luftschiffbau-Zeppelin, and is further indicated by the continuing policy of this Company as evidenced not only by their construction of the L.Z.129, now approaching her test trials, but also their announced intention of building additional ships.
We now consider, therefore, the basic question: Can a reasonably safe and useful airship be designed, constructed, and operated, and, if so, under what broad conditions?
Design And Construction Of A Safe And Useful Airship
The answer to this question turns immediately on the meaning attached to the two words “safe” and “useful.”
First, regarding safety in the various means of transport. Nothing is entirely safe. Railway travel has its accidents and casualties, surface ships are wrecked, airplanes crash, and the automobile, including errors of operation, is perhaps the most unsafe of all modern agencies of transport. Yet in the face of these all too familiar occurrences, we do not contemplate giving up any of these means of transport.
The reason is partly or perhaps largely psychological. These means of transport have established themselves as a part of our modern civilization. They are performing a service which, in the mass estimate of our people, justifies their retention and development in the general scheme of the transport of persons and things, despite the numerous continuing accidents and casualties.
Obviously it is impossible to fix any definite percentage or measure of performance as constituting a safe surface ship, a safe airplane, or a safe airship. We may perhaps, however, define a safe airship as one, the performance of which, in the mass estimate of those interested in this mode of transport and with some competence of judgment, is such as to justify its present retention in the general scheme of transport and its development at least to the point of demonstrating whether or not it is or will be capable of attaining and retaining an assured and useful place among other competitive means. The point here is that, quite aside from the question of safety, the airship, especially the airship of the largest size, must be considered as not yet having acquired a wholly assured place as an agency of transport, and in order to make practicable a satisfactory determination of this latter question the structure itself must be given a measure of safety which, in the mass estimate of those with some competence of judgment, will justify its further development and use to the point of definite demonstration.
In connection with the general question of airship safety and the future of the airship as an agency of transport, we have given special attention to the record of the principal casualties which have marked the development of this type of structure. Regarding these casualties, both in the United States and in Europe, we note especially two points:
All development of a new form of transport and more broadly all new developments are subject to possible hazards. This has been true in marked degree with the airplane, the heavier-than-air form of air transport. We have, however, accepted these hazards and casualties as a part of the price which must be paid for all such steps forward.
Our study of the record of these casualties leads us to the belief that, with the lessons which have been drawn from them, and with the general advance in our understanding of the technical problems of airship design, construction, and operation, the probability of a repetition of such casualties under like conditions should, for future construction, be reduced to a point which if not vanishing entirely, may be considered as ‘acceptable’ in comparison with the promise of useful service.
Regarding the question of a useful airship, we have already referred, in broad terms, to the apparent fields of potential service for structures of this character and we do not consider that further discussion of this phase of our problem is essential at this point.
Regarding the safety of such types of construction, we consider the entire record of the service of small nonrigids and of rigid airships of moderate size, in convoy and patrol services, during the Great War and elsewhere, as warranting the assertion that safe and useful ships of these types and sizes can be designed, constructed, and operated.
As regards airships of the largest size, such as the “Akron” type and upward, it becomes necessary to define more carefully the conditions under which a reasonable and proper margin of safety can be secured.
With reference to this type, your Committee is prepared to give likewise an answer in the affirmative, as to the practicability of a safe and useful airship, but under general conditions as follows:
- Design in the light of the most careful and thorough analysis of world experience with airships up to the present time and including in particular all failures and casualties, regarding the causes of which reasonably adequate information is available.
2. Design in the light of the most recent studies and advances in the mechanics of typical airship structures.
3. Specification of aerodynamic loads, whether due to maneuvers or to storm conditions (gusts, etc.), in the light of the most recent and careful studies based on:
- a) Approved aerodynamic theory, including the most recent advances.
- b) Results of wind-tunnel research and of experience with actual ships.
- c) Recent advances in meteorological science with special reference to the structure of gusts, polar fronts, line squalls, etc.
4. Construction under conditions as to supervision and inspection which will insure the practicable approach in the completed structure to the qualities and characteristics contemplated in the design.
5. On the completion of the structure itself, opportunity for operation, under some co-operative arrangement between builder and owner, over a period of time sufficient to permit the taking of strain gauge readings at all critical points of the structure and other technical observations under progressively more and more exacting conditions (maneuvers and weather) up to and including conditions approaching the most severe to be anticipated. Such period of test should not be curtailed or hurried. It is of vital and fundamental importance. It will furthermore give opportunity for the development and correction of many matters, important or otherwise, which may always be expected when a new design first takes the air.
6. When delivered for service, operation by personnel thoroughly trained and experienced in the handling of airships and in the light of the most complete meteorological information available, analyzed for the guidance of the command by an experienced aerologist trained in the more recent advances in meteorological science.
Of these various conditions, it seems proper to note at this point that for the designs of the “Akron” and the “Macon,” Nos. 1, 2, 3, and 4 seem to have been met within the measure of the information available at the time when these designs were developed. While there have been differences among experts in airship design regarding the relative value of certain general types of structure, especially as to certain features of what may be called English design and German Zeppelin design, the adoption of the general type of Zeppelin structure seems to have been justified on the ground of successful experience. And with the adoption of this general type of design, the requirements of conditions Nos. 1-4, as based on the information available at that time, and the methods of design then current, seem to have been consistently undertaken.
The history of the trial runs, however, shows that condition No. 5 was not adequately met.
Regarding operation as referred to in condition No. 6, we express no present opinion, especially in the sense of indicating responsibility for the loss of either the “Shenandoah,” the “Akron,” or the “Macon.” Furthermore, in the cases of these ships, the question of operation as a factor involving personal responsibility for their loss has already been passed on by official Naval Boards of Inquiry, and a review of the findings of these various Boards is no part of the specified duty of this Committee.
Improvements In Conditions For Airship Design Since 1928
Regarding airship design and construction at the present time or in the immediate future, as compared with the situation in 1928 when the designs of the “Akron” and the “Macon” were developed, improvement in these various conditions may be noted as follows:
Condition No.1: There is a large amount of actual experience available at the present time which was not available at the earlier period. This includes:
a) Actual flying experience with the “Akron” and the “Macon” for 3257 hours of time and over 160,000 miles of distance, together with the special studies relating to the conditions surrounding the loss of these two ships.
b) The experience of the “Graf Zeppelin” in demonstration flights around the world and in commercial flights during the past six years aggregating some 11,868 hours of flying and covering some 736,289 miles of distance. Through the kindness of Captain Eckener and his Governing Board in permitting both officers of the Navy and American engineers in civil life to participate in the trips of this ship in regular flights between Europe and South America, the salient features of this long and successful period of airship operation are at the disposal of American designers in connection with the development of new designs.
Condition No.2: In recent years there have been developed certain advances and refinements in the theoretical treatment of the mechanics of structures such as airships, all of which will aid in obtaining enlarged assurance of the desired and contemplated relation between the loads assumed and the strength of the structure provided to carry such loads.
Condition No.3: The importance of aerodynamic loads and of due allowance for their effect on the structure has received continued and careful study over the period since the preparation of the “Akron”-“Macon” design and there has been a continued accumulation of information which, we believe, will serve as a more adequate basis for the estimate of such loads than was possible in 1928. In addition this Committee has now under investigation certain phases of this general problem, especially as regards the aerodynamic load on fins and its distribution, together with studies on the structure of gusts and their influence on airship structures as a whole or locally. We have also in mind recommendations for further studies on this particular subject, all of which should aid in making practicable a more adequate estimate of the loads to be provided for, due to various combinations of aerodynamic conditions.
Likewise in meteorology, since the period of the design of the “Akron” and the “Macon,” there have been great, even revolutionary, changes in the technique of accurate forecasting. It may be assumed that there will always be a possible hazard for airships, or for any aircraft, in extreme weather conditions; but with these more recent advances in the science of meteorology and with the enlarged information now available from more numerous sources and points of observation, it would seem that there should be no serious difficulty in avoiding such extreme hazards. Here again, the six-year experience of the “Graf Zeppelin” seems to furnish proper ground for this general conclusion.
On the whole, therefore, and with special reference to airships of the larger sizes, we believe that it is practicable to design, construct, and operate such airships with a reasonable assurance of safety and with a presumptive life which should serve to permit of a demonstration of their capacity for useful service, whether commercial or military (naval).
Recommendations As To Future Construction
It has been already pointed out that the experience with large airships in the United States has not as yet been sufficient to give ground for a wholly settled opinion as to the character and extent of their potential usefulness, either commercial or naval.
In view, therefore, of our expressed opinion as to the practicability of the design, construction and operation of such airships with a reasonable margin of safety and with the presumption of capacity for useful service, it is the unanimous opinion of this committee that the best interests of the services in which airships give promise of useful and effective service both commercial and naval, require a continuing program of construction and use.
And in pursuance of this opinion it is our recommendation that the Navy Department should continue with a positive, carefully considered program of airship construction, including nonrigids and rigid ships of small or moderate size as service requirements might indicate, and extending to a ship or ships of large size, to the point, at least for the latter, of furnishing ground for definite conclusions regarding the capacity for useful naval service of constructions of this character.
We further recommend most strongly that the first large airship built under such a program should, at least for a time, be considered not an adjunct to the Fleet but rather a flying laboratory or flying training ship, not only for extensive technical observations of the structure under operating conditions, but also for enlarging our knowledge regarding the best conditions of service for such vessels, and, as well, for giving opportunity for the training of officers and crew in the technique of handling airships under all conditions of weather and service.
In a subsequent report or reports we shall, with suitable recommendations and supporting documents, present in some detail material more fully and directly responsive to the technical phases of your letter of instructions.
V. DE FOREST
FRANK B. JEWETT
CHARLES F. KETTERING
F. DURAND, Chairman, SPECIAL COMMITTEE ON AIRSHIPS
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