FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1920
1920 - 0260.PDF
MARCH 4, 1920 LOAD FACTORS FOR HEAVIER-THAN-AIR CRAFT THE following Technical Memo. No. 12 of the Advisory- Committee for Aeronautics, dated January 6, 1920, has been issued by the Air Ministry :— Introduction ; -.*;.•• - When the employment of aircraft for civil purposes became practicable, owing to the termination of hostilities, repre- sentatives of the aircraft industry pointed out the necessity for arriving at an agreement as to the load factors to be worked to in designing commercial aircraft. Although knowledge on this subject had increased very largely during the War the bases and methods upon which designers worked . varied considerably, and it was obvious that the matter was one requiring careful technical investigation. The Air Council therefore requested the Advisory Com- mittee for Aeronautics to appoint a Sub-Committee—upon .which the various interested bodies should be represented— to consider and report as to the definite rules which should be adopted to govern the load factors required for all classes of civil aircraft, and upon which Certificates- of Airworthiness may be based. Accordingly the Sub-Committee was con- stituted as follows :— The Chairman of the Advisory Committee for Aeronautics (ex officio). Air Council: Lieut.-Col. W. D. Beatty, R.A.F., Sqdn. Leader F. H. Bramwell, R.A.F. Royal Aeronautical Society : Lieut.-Col. O'Gorman, C.B., Mr. L. Bairstow, C.B.E., F.R.S. Society of British Aircraft Constructors : Mr. F. Handley Page, Capt. F. S. Barnwell, Mr. H. Smith, Mr. H. 0. Short. Advisory Committee'for Aeronautics : Prof. J. E. Petavel, F.R.S., Mr. F. W. Lanchester, M.Inst.C.E., Mr. R. V. South- well, M.A., Dr. T. E. Stanton, F.R.S. Sir Richard Glazebrook was appointed by the Sub-Com- mittee as its chairman. Mr. F. Handley Page was re- presented on certain occasions by Mr. H. O. Boswell or Lieut.-Col. E. T. Stedman. Mr. H. O. Short was repre- sented by Maj. Gnosspelius. At one meeting Mr. A. J. Sutton Pippard attended as a representative of the Royal Aeronautical Society in place of Lieut.-Col. O'Gorman, and Mr. Douglas, of the Royal Aircraft Establishment, also attended one meeting by invitation. The unanimous report of this Sub-Committee, which has now been approved, is given below. Its provisions will be made applicable to designs submitted to the Director of Research after March 15, 1920. This memorandum will appear in due course as Report No. T.1425 of the Advisory Committee for Aeronautics. Schedule of Load Factors for Heavier-than- Air Craft Heavier-than-air craft are now used for a variety of pur- poses, including on the one hand purely commercial work, and on the other stunt flying. The strength necessary for safety is different in the two classes : for the former class the specification need not be so exacting as for the latter in order to ensure adequate safety ; further, a lower factor is com- mercially desirable since an increase of load factor involves a decrease in the range and load-carrying capacity. Heavier- than-air craft have, therefore, been divided into two classes having regard to the different qualities of airworthiness required. This separation will necessitate the granting of two distinct types of certificates : it has been suggested that these should be readily distinguishable by the use of different colours or other means. The aircraft in the " General " Class, including all those not in the " Com- mercial " Class, should be sufficiently strong to allow of stunt flying of all descriptions. The other class, " Commercial," will include craft used for strictly commercial work involving only straight flying ; stunting of any kind will be prohibited. The schedule below is given in tabular form under these two heads. In preparing this schedule the Load Factor Sub-Committee of the Advisory-Committee for Aeronautics considered only future designs ; it is not intended that the schedule should be made applicable to machines already approved or designs submitted prior to some future date to be fixed by the Air Ministry. Further revision of the present schedule from time to time will doubtless be necessary in order that it may remain in accordance with the demands arising from improve- ments in the constructional methods and design. Method of Specifying Strength.—The first specification (a) determines the load factor when the centre of press ure is in its most forward position : this gives in each case a definite load for every part of the machine, including the tail plane and the fuselage. The second specification (b) gives the load factor when the centre of pressure is in the position corresponding to maximum horizontal speed at ground level. This also gives a definite loading. The next specification (c) gives the factor of safety in a terminal nose dive, a condition which is again quite definite for each aircraft, the air screws being assumed to be removed. The above are considered sufficient to determine the strength of the wings and of the tail plane ; also for certain loadings of the fuselage when in flight. For the strength of the fin and rudder, specification (d) gives the value of an assumed lift coefficient, which, when the maximum speed of the craft is known, determines uniquely the strength required in these parts, and also in so far as the lateral loadings are concerned in the fuselage / the values assumed for the lift coefficient are considered sufficient to cover adequately the maximum forces which can be imposed on the rudder and fin by the pilot when exerting his full force so as to obtain as rapid a turn as possible. Strength of undercarriages, specification (e), is dealt with under the conditions of both static and dynamic loads, neither case being considered sufficient by itself to meet all requirements. For the use of the tables it should be noted that the two terms, factor of safety and load factor, are defined in the accepted engineering sense, i.e., Failing strength of a member of the structure. Factor of safety - Worst possible load occurring under any condition of flight. .-'"_._• :•.-,'• • - Failing strength of a member of the structure. oaa ac or — Loa(j jn member under horizontal steady flight conditions. In addition to the figures given in the tables, on this and the following page, it is essential (/) that, in the case of any one flying wire, or duplicate pair of wires, being removed from the aircraft, the strength of the remaining portion should be such that at least one-half of the scheduled load factors and factors of safety shall be obtained under each of the foregoing conditions. For this particular case incidence or other normally redundant bracing is naturally assumed operative where necessary. COMMERCIAL CLASS. -•-•-•• [a) Load factor with C.P. in itsmost forward position 'b) Load factor withC.P. in the position cor- responding to maximumhorizontal speed at ground level .. (c) Factor of safety in terminalnose dive (d) Specified lift co- efficient forfins and rud- ders. (Under this loading the factor ofsafety of the fuselage should be unity)(«) Static load fac- tor on under- carriages («2) Specified ver-tical velocity (ft./sec.) for determin-ing travel of undercarriages Total weight of aircraft. Up to 5,000lbs. 6t 4"5t i-75t 0-5 6 10 5,000 to 10,000 lbs. 6t - 5*t 4-5t-3-75*t i-75t O'5 6-5* 1 - .: - •" ; "; .... •. . ~- *' . • '*. 10 10,000 to 30,000 lbs. 5t -~4» ,- -.; 3-75t- 3* 1-75* 0-5 -4* ...^; _. 10 Above 30,000lbs. 4 3 . X-75f 4 IO • The decrease in load factor from the larger value is directly proportiona to the increase in the weight of the craft. t In the case of aircraft which are longitudinally stable over the whole flying range, these figures may be reduced by o-5. 26O
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
