FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1943
1943 - 1455.PDF
JUNE 3RD, 1943 FLIGHT 589 CORRESPONDENCE 1 he Editor does not hold himself responsible for the views expressed by correspondents. The names and addresses of the "writers, not necessarily for publication, must in all cases accompany letters. BENDING AIRSCREW BLADES Forward Velocity of the AircraftW ITH reference to the letter of Mr. D. II. Farley in theMay 20th edition of Flight concerning the bending of w airscrew blades. In my humble opinion Mr. Farley's reasoning breaks downwhen he completely overlooks the fact that the airscrew always has the same forward velocity as the aircraft itself when inflight. Therefore, when the blade tip strikes the ground the consequent momentary frictional resistance produces (amongstother complications) the simple case of an encastered beam with a single force acting at the opposite end. This force createsa bending moment, which unfortunately usually results in per- manent deviation. R. DAVENPORT. Where Mr. Farley's Reasoning Breaks Down T)ERHAPS Mr Farley's reasoning breaks down in this matter• A when he assumes that the airscrew in flight forces the air • back, whereas it forces itself forward by pressing on the air.Thus if the tip of a blade hits a solid lump of air (shall we say) the airscrew continues to force itself and the aircraftforward but tends to leave the blade tip with the lump of ". •: air as it goes by. The analogy, though perhaps not quitesound, will convey my view. Presumably in the special case of an aircraft standing onthe ground with its motor running and suffering the sudden • collapse of its undercarriage the airscrew blades would thenbend forwards. Does experience show that this is so? . J. E. LOCKE. A Question of Relativity ON reading Mr. Farley's letter in the issue for May 20th,I was tempted to suspect that he was enjoying a quiet leg- pull. In case, however, he has succeeded in persuading anvlay readers that airscrew blades should indeed (theoretically, \ at least) be bent forward on impact with the ground, I hastento assure them that this apparent affront to common sense and experience is fallacious both in fact and from reasonable'•• deduction. ; - The whole question is one of relativity, as Mr. Farley implies, although-he has his relations a trifle confused. Consider thecase of an aircraft flying at nearly zero feet; we assume that : the machine is flying in still air and at a speed of v m.p.h. - relative both to the air and to the ground. Now the section,form and pitch of the airscrew blade are so designed that in • a gaseous medium of density approximately 0.08 lb./cu. ft.•_ and at a given r.p.m. it will "screw" its way through that medium, namely, the air, in this manner propelling the aircraft(neglecting considerations of airscrew efficiency). Mr. Farley implicitly concedes that such an airscrew, striking•- the much denser material of the ground, would be unable to •'; function in this screwing manner, and by no means can it . be imagined—considering the forward motion.of the aircraft t : relative to the ground—that the blade could be bent forward. Put simply, by Mr. Farley's own definition, if the blade cannot r push the earth back it cannot move forward, and though it'tries to push the earth forward, due to its motion with the aircraft, the stress oh the blade material is too great, and inthe^pase of metal it is bent back. "HEIR O'NAUGHT." Watering Down the Resistance IN answer to Mr. Farley, whose problem on "BendingBlades" appeared in Flight of May 20th, 1943, I would ask him to consider the case of the blades hitting a water surface,as the explanation is easier to follow. If the aircraft is flying at 300 m.p.h., then, to produce thisspeed, the airscrew is revolving fast enough to remove the air from in' front of it at a fixed rate. Now, water is a muchdenser medium than air. To remove it at a rate sufficient to give the aircraft a speed of 300 m.p'.h. more power is neededthan is necessary in air. Therefore, there will be an excess of . water in front of the airscrew blades which will constitute astrong resistance. The aircraft is still trying to fly at 300 m.p.h. due to its inertia, while the water is trying to retardthe blades of the airscrew. Hence they are bent backwards. The same applies when they touch the ground instead olwater, only here the effect is increased as the ground is, ot course, more dense and more resistant than the water. I take Flight regularly and would like to take this oppor-tunity of thanking you for your splendid articles and inspiring pictures which have given me many hours of pleasure.EDWARD HACK (Cadet Sgt. in the Oxford University "Air Squadron). MEN TO REMEMBER Mistaken Impressions About War Medals WHILST everybody agrees that additional medals are notgenerally desired at this time, the present war does throw into relief the fact that the conditions ot award m respect ofthe last war do not reflect in the present struggle r-ntirely what they were intended to represent. The Territorial Force WarMedal is an example. This decoration is commonly regarded as given to Territorials who volunteered to go overseas in thelast war, who actually did so, and who are not entitled to the 1914 or 1915 Star. In practice it dees nothing ot the sort, andthere appears to be no reason why it should be restricted to these who volunteered before September 30th, 1914, or deniedto those who volunteered whilst in the Regular Army or Kitchener's Army and subsequently transferred to the Terri-torials and then served considerable periods in France or other theatres of war. • I have a combined volunteer and T.A. Reserve service of 2S|years, from 1914 onwards, including two years in France with the infantry, R.F.C and R.A.F. I have no long-service ribbon,nor do I desire to have one, but I do think it is a ciownmg insult when I am told by a Service man of to-day that you canalways distinguish a conscript of the last war because he only has two ribbons! LONG-SERVICE VOLUNTEER. AN " AERIAL COMBATS SOCIETY" ? A Suggestion from Canada DURING this war thousands of Royal Air Force officers andN.C.O.s (including R.C.A.F.) have engaged in aerialcombats and offensive operations that have raised the records and gallantry of the R.A.F. to the highest levels of military pride and public acclaim. There are many ex-Royal Air Force officers, both here and abroad, who had the proud privilege and honour of serving eithei in the original Royal Flying Corps or the R.N.A.S. (subsequently merged into R.A.F.) and who also engaged in combats of the air during the first Great War.' Aerial combats, " old " or " new," constitute a service distinction and a proud memory for all who have experienced them It is suggested that an " Aerial Combats Society " beformed with a " Fellowship " that would permit an accepted applicant or bona fide member to enjoy an " F.A.C.S."(Fellow of Aerial Combats Society ") distinction corresponding to 'Fellowship" in other well-known societies, such as theRoyal Geographic Society, whose " Fellows " may add "F.R.G.S." to their names, if they so desire! The writer, an ex-Royal Flying Corps-R.A.F. officer, doesnot wish to imply that anyone eligible for such a " Fellow- ship. " either desires or seeiis any distinction or service recorddiscrimination, but it is believed that the majority who have experienced offensive operations in the air have an inner senseof pride, and would welcome such fellowship privileges with the understanding, interest and appreciation that characteriseattachments to other societies and associations. It is felt that such a society should have its origin in GreatBritain. Is there anyone who might undertake to start such a " fellowship " movement? Air Marshal W. A. Bishop, V.C.,D.S.O., M.C., D.F.C., among others in Canada, would, I fee! sure, be glad to be associated with a society of this character,and to co-ooerate in some suitable way. R. BARCLAY SHAW.
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
