Drift Due to Engine Torque

H. Glauert

doi:10.1108/eb029566

Glauert, H.

1932-07-01 00:00:00

176 AIRCRAFT ENGINEERING July, 1932 Some Reasons for Reconsideration of the Conclusions Arrived at by Wing Commander Wackett By H. Glauert, F.R.S., F.R.Ae.S.* I N a n article on this subject, published in t o balance the torque Q, rudder angle ξ is then balance th e torque, an d will no t modify the resulting th e February issue of AIRCRAFT EN applied to balance the yawing moment due to angle of sideslip appreciably. GINEERIN G this year, Wing Commander L. J. th e application of the ailerons, and finally, a A point of greater importance is tha t in a tractor Wacket t suggests that an aeroplane must fly at velocity v of sideslip is acquired to balance the aeroplane the torque is largely taken up directly a n appreciable angle of yaw in order to counteract sideforce due to the application of the rudder. b y the wings owing to the difference of incidence th e torque of the engine and airscrew. He gives Thi s sideslip in turn introduces rolling and yawing on opposite sides of the fuselage duo t o the rotation a n approximate formula for calculating this angle moment s which necessitate further adjustments of of the slipstream. Instead of pulling down an of yaw, and describes a scries of experiments which th e aileron and rudder angles, but a closer ex aileron or twisting the wing to a larger incidence, appea r to confirm his calculation. Since the aminatio n of the problem and the fact that the which always involves an increased drag, the angle of yaw suggested by this investigation is sideslip is extremel y small show tha t these secondary necessary extra lift is obtained by the air striking surprisingly large and would have serious effects adjustment s arc negligibly small. This con th e wing a t a larger angle of incidence. The lift on navigation and gunnery, I have made a closer ception leads to the set of equations:— force is then inclined forwards and reduces the examinatio n of the problem. This analysis has ξL =Q increase of drag which would otherwise occur, and led me to doubt the validity of Wing Commander a n analogous effect occurs on the opposite side ζN =ξN Wackett' s conclusions, since the calculated angle ζ ζ of the fuselage. Thus the yawing moment is in of yaw is negligibly small if th e torque is balanced vY = Y v ζ ζ fact less than has been assumed in deriving the b y use of the ailerons and if the aeroplane is wher e L is th e rolling moment due to unit aileron ζ formula (2), and the angle of yaw will be even maintaine d on a level keel. angle and the other stability derivatives have smaller than calculated above. The residual Th e torque of the engine and airscrew is trans similar definitions. Now to a close approximation rotatio n of the slipstream behind the wings, which mitte d to the air as the rotation of the slipstream. where l is the distance of the rudder from the is generally only a small fraction of the initial I n general this rotation is largely checked as the centr e of gravity of the aeroplane an d the rotation , will modify the flow over the rudder. slipstream passes the wings of the aeroplane, but negative sign arises from the convention that a I t will be necessary to set the rudder to a different th e residual effects of the rotation exert an appre lateral force to starboard and a yawing moment angle, but no additional side force arises on this ciable influence on the tail unit, which becomes tendin g to yaw the nose of the aeroplane to star account. apparen t mainly as a turning tendency when the board are regarded as positive. The system of This analysis and discussion suggest that Wing engine is switched off. For simplicity, however, equation s then gives Commande r Wackett's estimate of an angle of i t will be assumed in the first place tha t the slip ya w of th e order of 4 deg. is a serious over-estimate, strea m passes backwards without any reaction on duo to his assumption that the necessary rolling an y part of the aeroplane. It is then necessary an d by comparison with the original formula (1) momen t is obtained by sideslip and not by use of for the wings to provide a rolling moment to we obtain th e ailerons, and that the actual angle of yaw is balance the torque. Wing Commander Wackett less than 0∙1 deg. There remains, however, the assumes tha t this rolling moment will be obtained difficulty of explaining his experimental results, b y sideslip, and his calculation of the velocity v Numerical values have been inserted in these which appear t o confirm the larger estimate. These of sideslip is the n simply formulæ for a Bristol Fighter aeroplane for which experiment s arc clearly difficult to make accurately, v L Q .(1) o v a full set of stability derivatives is available. bu t Wing Commander Wackett appears to have where Q is the torque of the airscrew and L is Assuming a torque of 1,000 lb./ft., the following mad e careful preparations and to have obtained th e rolling moment due t o unit velocity of sideslip. values of the angle of yaw β were derived from the reasonably consistent results. There is, however, I t will also bo necessary to use th e rudde r to balance formulæ (1) and (2) respectively :— thi s one point of uncertainty. He states that he th e yawing moment due to this sideslip and to V (m.p.h.) β β maintaine d his speed correctly to 1 m.p.h . and his allow the aeroplane to acquire a small lateral tilt 0 6 3 5∙2 deg. 0∙09 deg. course to 0∙5 deg., but he makes no reference to t o balance th e side force due to the sideslip and th e lateral tilt of the aeroplane. If, in fact, he 77 4∙2 deg. 0∙09 deg. t o the use of the rudder. Wing Commander concentrate d on th e correct adjustment of elevators 110 2∙3 deg. 0∙05 deg. Wackett' s calculation, therefore, assumes implicitly an d rudder without operating the ailerons, he Th e values of βo confirm Wing Commander tha t the aeroplane flies with one wing down, and would be acting in accordance with the assumption Wackett' s estimate of 4 deg. for a D.H. 9A aero 1 have estimated this angle of lateral tilt to be on which his formula (1) is based, and might be plan e when the torque is balanced by sideslip approximatel y 3 deg. for his aeroplane. expecte d to obtain that larger angle of yaw, but withou t use of the ailerons, but the values of I n this simple calculation it is assumed that th e aeroplane would fly with lateral tilt. In the β show that the sideslip is negligibly small when no use is made of the ailerons, but the more usual absence of definite information on this point, it th e aeroplane is flown on a level keel and the flying practice would be to maintain the aeroplane is suggested that a plausible explanation of the torqu e is balanced by use of the ailerons. on a level keel or, in other words, to balance the experimenta l results is tha t the ailerons were not I n practice, an aeroplane, rigged symmetrically, torqu e by use of th e ailerons rathe r tha n b y allowing used to correct the lateral tilt. If the aeroplane which was subjected t o a powerful torque reaction, th e aeroplane to sideslip. The motion can then were correctly flown without lateral tilt, th e present would tend to fly one wing down, and this tendency be described as follows. Aileron angle ξ is applied analysis suggests that the resulting angle of yaw- would be corrected by rigging the port and star- would be negligibly small, and hence that Wing * Mr. Glauert is a Principal Scientific Officer in the Aerodynamics board wings at different angles or by imparting Department at the Royal Aircraft Establishment. He is indebted Commande r Wackett's concluding comments and a twist to the wings. Any such action is virtually to the Air Ministry for permission to publish this note, but it, recommendation s are not valid. equivalen t to the application of the ailerons to of course, represents only his own views on the subject. device was still in the experimental stage, and he thought it therefore desirable not to refer to it.— Aircraf t Performance Testing EDITOR. ] To the Editor of AIRCRAFT ENGINEERING COWLIN G OF AIR-COOLED ENGINES. I t is regretted that in a footnote to the article wit h the above title on page 123 of the May issue SIR,—I n the article by S. Scott-Hall on "Aero use at ground level in order to obtain a predeter it was stated that the experiments referred to plan e Performance Testing," in the May issue mined definite increase on the normal boost, with were carried out at the N.PL , whereas they were th e statement is made that the automatic boost a substantial increase in the power available for actuall y mad e in th e No. 1 7-ft. tunnel a t th e R.A.E. control developed by th e Bristol Company has the tak e off. disadvantag e tha t normal boost cannot be exceeded I n a leading article in the June issue reference Your s faithfully, a t any stage from ground level up . This statement wa s inadvertently made to the work of Mr. Irving TH E BRISTOL AEROPLANE COMPANY LTD., is not correct, as on all supercharged Bristol Mercury in developing the ring-type cowling. This was, of A. H. R. FEDDEN, an d Pegasus engines a t present in production, the course, a slip of the pen for Mr. Irving's colleague Chief Engineer. automati c boost control fitted incorporates an a t the N.P.L, Mr. Townend—which would, we [The reason for Mr. Scoll-Hall's apparent mis over-riding device which the pilot can bring into think , be clear from the context. statement is thai at the time the article was written the

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$176 AIRCRAFT ENGINEERING July, 1932 Some Reasons for Reconsideration of the Conclusions Arrived at by Wing Commander Wackett By H. Glauert, F.R.S., F.R.Ae.S.* I N a n article on this subject, published in t o balance the torque Q, rudder angle ξ is then balance th e torque, an d will no t modify the resulting th e February issue of AIRCRAFT EN applied to balance the yawing moment due to angle of sideslip appreciably. GINEERIN G this year, Wing Commander L. J. th e application of the ailerons, and finally, a A point of greater importance is tha t in a tractor Wacket t suggests that an aeroplane must fly at velocity v of sideslip is acquired to balance the aeroplane the torque is largely taken up directly a n appreciable angle of yaw in order to counteract sideforce due to the application of the rudder. b y the wings owing to the difference of incidence th e torque of the engine and airscrew. He gives Thi s sideslip in turn introduces rolling and yawing on opposite sides of the fuselage duo t o the rotation a n approximate formula for calculating this angle moment s which necessitate further adjustments of of the slipstream. Instead of pulling down an of yaw, and describes a scries of experiments which th e aileron and rudder angles, but a closer ex aileron or twisting the wing to a larger incidence, appea r to confirm his calculation. Since the aminatio n of the problem and the fact that the which always involves an increased drag, the angle of yaw suggested by this investigation is sideslip is extremel y small show tha t these secondary necessary extra lift is obtained by the air striking surprisingly large and would have serious effects adjustment s arc negligibly small. This con th e wing a t a larger angle of incidence. The lift on navigation and gunnery, I have made a closer ception leads to the set of equations:— force is then inclined forwards and reduces the examinatio n of the problem. This analysis has ξL =Q increase of drag which would otherwise occur, and led me to doubt the validity of Wing Commander a n analogous effect occurs on the opposite side ζN =ξN Wackett' s conclusions, since the calculated angle ζ ζ of the fuselage. Thus the yawing moment is in of yaw is negligibly small if th e torque is balanced vY = Y v ζ ζ fact less than has been assumed in deriving the b y use of the ailerons and if the aeroplane is wher e L is th e rolling moment due to unit aileron ζ formula (2), and the angle of yaw will be even maintaine d on a level keel. angle and the other stability derivatives have smaller than calculated above. The residual Th e torque of the engine and airscrew is trans similar definitions. Now to a close approximation rotatio n of the slipstream behind the wings, which mitte d to the air as the rotation of the slipstream. where l is the distance of the rudder from the is generally only a small fraction of the initial I n general this rotation is largely checked as the centr e of gravity of the aeroplane an d the rotation , will modify the flow over the rudder. slipstream passes the wings of the aeroplane, but negative sign arises from the convention that a I t will be necessary to set the rudder to a different th e residual effects of the rotation exert an appre lateral force to starboard and a yawing moment angle, but no additional side force arises on this ciable influence on the tail unit, which becomes tendin g to yaw the nose of the aeroplane to star account. apparen t mainly as a turning tendency when the board are regarded as positive. The system of This analysis and discussion suggest that Wing engine is switched off. For simplicity, however, equation s then gives Commande r Wackett's estimate of an angle of i t will be assumed in the first place tha t the slip ya w of th e order of 4 deg. is a serious over-estimate, strea m passes backwards without any reaction on duo to his assumption that the necessary rolling an y part of the aeroplane. It is then necessary an d by comparison with the original formula (1) momen t is obtained by sideslip and not by use of for the wings to provide a rolling moment to we obtain th e ailerons, and that the actual angle of yaw is balance the torque. Wing Commander Wackett less than 0∙1 deg. There remains, however, the assumes tha t this rolling moment will be obtained difficulty of explaining his experimental results, b y sideslip, and his calculation of the velocity v Numerical values have been inserted in these which appear t o confirm the larger estimate. These of sideslip is the n simply formulæ for a Bristol Fighter aeroplane for which experiment s arc clearly difficult to make accurately, v L Q .(1) o v a full set of stability derivatives is available. bu t Wing Commander Wackett appears to have where Q is the torque of the airscrew and L is Assuming a torque of 1,000 lb./ft., the following mad e careful preparations and to have obtained th e rolling moment due t o unit velocity of sideslip. values of the angle of yaw β were derived from the reasonably consistent results. There is, however, I t will also bo necessary to use th e rudde r to balance formulæ (1) and (2) respectively :— thi s one point of uncertainty. He states that he th e yawing moment due to this sideslip and to V (m.p.h.) β β maintaine d his speed correctly to 1 m.p.h . and his allow the aeroplane to acquire a small lateral tilt 0 6 3 5∙2 deg. 0∙09 deg. course to 0∙5 deg., but he makes no reference to t o balance th e side force due to the sideslip and th e lateral tilt of the aeroplane. If, in fact, he 77 4∙2 deg. 0∙09 deg. t o the use of the rudder. Wing Commander concentrate d on th e correct adjustment of elevators 110 2∙3 deg. 0∙05 deg. Wackett' s calculation, therefore, assumes implicitly an d rudder without operating the ailerons, he Th e values of βo confirm Wing Commander tha t the aeroplane flies with one wing down, and would be acting in accordance with the assumption Wackett' s estimate of 4 deg. for a D.H. 9A aero 1 have estimated this angle of lateral tilt to be on which his formula (1) is based, and might be plan e when the torque is balanced by sideslip approximatel y 3 deg. for his aeroplane. expecte d to obtain that larger angle of yaw, but withou t use of the ailerons, but the values of I n this simple calculation it is assumed that th e aeroplane would fly with lateral tilt. In the β show that the sideslip is negligibly small when no use is made of the ailerons, but the more usual absence of definite information on this point, it th e aeroplane is flown on a level keel and the flying practice would be to maintain the aeroplane is suggested that a plausible explanation of the torqu e is balanced by use of the ailerons. on a level keel or, in other words, to balance the experimenta l results is tha t the ailerons were not I n practice, an aeroplane, rigged symmetrically, torqu e by use of th e ailerons rathe r tha n b y allowing used to correct the lateral tilt. If the aeroplane which was subjected t o a powerful torque reaction, th e aeroplane to sideslip. The motion can then were correctly flown without lateral tilt, th e present would tend to fly one wing down, and this tendency be described as follows. Aileron angle ξ is applied analysis suggests that the resulting angle of yaw- would be corrected by rigging the port and star- would be negligibly small, and hence that Wing * Mr. Glauert is a Principal Scientific Officer in the Aerodynamics board wings at different angles or by imparting Department at the Royal Aircraft Establishment. He is indebted Commande r Wackett's concluding comments and a twist to the wings. Any such action is virtually to the Air Ministry for permission to publish this note, but it, recommendation s are not valid. equivalen t to the application of the ailerons to of course, represents only his own views on the subject. device was still in the experimental stage, and he thought it therefore desirable not to refer to it.— Aircraf t Performance Testing EDITOR. ] To the Editor of AIRCRAFT ENGINEERING COWLIN G OF AIR-COOLED ENGINES. I t is regretted that in a footnote to the article wit h the above title on page 123 of the May issue SIR,—I n the article by S. Scott-Hall on "Aero use at ground level in order to obtain a predeter it was stated that the experiments referred to plan e Performance Testing," in the May issue mined definite increase on the normal boost, with were carried out at the N.PL , whereas they were th e statement is made that the automatic boost a substantial increase in the power available for actuall y mad e in th e No. 1 7-ft. tunnel a t th e R.A.E. control developed by th e Bristol Company has the tak e off. disadvantag e tha t normal boost cannot be exceeded I n a leading article in the June issue reference Your s faithfully, a t any stage from ground level up . This statement wa s inadvertently made to the work of Mr. Irving TH E BRISTOL AEROPLANE COMPANY LTD., is not correct, as on all supercharged Bristol Mercury in developing the ring-type cowling. This was, of A. H. R. FEDDEN, an d Pegasus engines a t present in production, the course, a slip of the pen for Mr. Irving's colleague Chief Engineer. automati c boost control fitted incorporates an a t the N.P.L, Mr. Townend—which would, we [The reason for Mr. Scoll-Hall's apparent mis over-riding device which the pilot can bring into think , be clear from the context. statement is thai at the time the article was written the$

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Drift Due to Engine Torque

Drift Due to Engine Torque

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Drift Due to Engine Torque

Drift Due to Engine Torque

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