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Aviation History
1926
1926 - 0355.PDF
May 27, 1926 Supplement to FLIGHT LENGINEERINGSECTION Edited by C. M. POULSEN May 27, 1926 CONTENTS PAGE A Suggested Method for Attaining Stability in the Original Lay-Out of an Aeroplane Design. By F. S. Barnwell " ... 49 Aircraft Performance. By J. D. North, F.R.Ae.Soc 53 Duralumin. By Leslie Aitchison, D.Met., B.Sc, F.I.C., M.I.A.E. ... 55 OUR CONTRIBUTORS Captain F. S. Barnwell, the first instalment of whose article was published last month, concludes in the present issue his exposition of a suggested method for attaining stability in the original lay-out of an aeroplane design. As pointed out in the April 29 issue of THE AIRCRAFT ENGINEER, Captain Barn well's article is a somewhat lengthy one, so that it was found impossible to publish it in one issue. Con- sequently, some of the illustrations were given last month, the remaining ones being published in the present issue. In the text published last month, reference was made to some of the illustrations now given, and similarly this month reference is made to the illustrations published in the first instalment. It will be found, we think, that the empirical method sug- gested by Captain Barnwell, if used with discretion and commonsense, is capable of giving good results, although in certain respects it may not be entirely beyond criticism. We should appreciate, as would also tho author of the article, the views of readers on the different points raised, and shall be pleased to devote any reasonable space in the Correspond- ence columns of FLIGHT to a discussion of the method. Mr. J. D. North, whose series of articles on aircraft per- formance has aroused very great interest, continues in the present issue with a discussion of scale effect, and points out that the phenomenon which we commonly call interference, i.e., the change in air flow around a body caused by the presence of other bodies near it, is likely to be subject to con- siderable scale effect. Mr. North makes the interesting observation that the failure of modern machines to give the performance, and particularly the climb, which their lower- power loading would indicate, may be due to the larger bodies of modern machines as compared with earlier aeroplanes. Dr. Leslie Aitchison, whose articles on the subject of Duralumin have contributed greatly to a wider knowledge of the peculiarities and treatment of this interesting material, deals in the present issue with methods of heating Duralumin, notably the salt bath, and calls attention to the necessity for allowing ample time for the metal to reach the desired tem- perature . A SUGGESTED METHOD FOR ATTAINING STABILITY IN THE ORIGINAL LAY-OUT OF AN AEROPLANE DESIGN By F. S. BARNWELL (Conclw'ed from page 40) Lateral Stability. Consider the case of an aeroplane, flying steadily along a rectilinear flight-path, being given (by a momentary use of the controlling surfaces, or by a veering in the direction of the wind) a certain degree of yaw to its flight-path, say, of tail-to- port attitude :—assuming that the fin surface be sufficient to give " stability in yaw," the tail of the aeroplane will com- mence to swing to starboard and this rotation in yaw will (by causing the speed of the starboard wing tip to become greater than that of the port wing tip) cause the aeroplane to commence rotating in roll (or " banking ") in the port wing tip down direction ; assuming, to simplify the argument (it is also approximately true) that the oscillations in yaw and in roll be " dead beat," it follows that the aeroplane tends to " finish up " with a certain amount of port wing tip down " bank " ; but such attitude entails side slip to port (equivalent, of course, to yaw in tail-to-port attitude, again) ; hence the procedure will continue, the rate of yawing and the angle of bank " building up." In the foregoing it has been aBsumed, of course, that there is no rolling moment duo to an attitude of yaw. To attain lateral stability it is necessary that the aeroplane possess, in addition to a certain degree of " stability in yaw," a certain degree of " stability in roll " (" stability in roll " being taken as of the sense previously defined for coefficients of rolling moment). In the particular case being considered, should the aeroplane possess some degree of " stability in roll," it will commence to " bank " port wing tip up in addition to commencing to yaw tail to starboard ; and, should the relative values of " stability in roll " and " stability in yaw " be correct, the aeroplane will " finish up " on an " even keel," meaning that it possesses lateral stability in the sense originally defined. SL Put in another form, if for any aeroplane the value ^rT o^ be correctly adjusted, the aeroplane will be laterally stable. If the value of «^r be too small, the machine tends to a condition of increasing rate of yawing and increasing bank,XL " spiral instability " ; whilst, if the value of ^be too large, 308a
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