Fuselage self-propulsion by static-pressure thrust - CAFE Foundation

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FUSELAGE SELF-PROPULSION BY STATIC-PRESSURE THRUST: WIND-TUNNEL VERIFICATION Fabio R. Goldschmied' Monroeville, PA 15146 d' Abstract CAP = (QxAB25/qoUoV0~66) Fan air power .-.J - * The novel concept of body self -propulsion by static-pressure thrust has been introduced and verified in the wind-tunnel by direct integration of radial pressure distributions for self-propelled &symmetric bodies with slot suction BLC and stern jet discharge. This concept also means that power can be supplied only to BLC, since the jet discharge is achieved at jet total-head equal to free-stream's; the skin-friction drag is offset entirely by the pressure thrust. It is the most efficient form of body self-propulsion. It also has been shown that 50% power reduction has been achieved as compared to the test body/wake-propeller NASA configuration, with only 1% of its mass flow. A total aircraft power reduction of 40% to 60% is feasible as compared to current General Aviation aircraft at 200 !E" cruise speed. CDF = (F/qoYo'") c~~ = 'DW C~~ Cos = (QxAE20/~oUoV 0 'Il' = 'DW + 'DS Nomenclature Airfoil chord Airfoil wake-drag coeff. Body wake drag coeff. Reference body wakedrag coeff . Body friction-drag coeff. Body pressure-drag coeff . 66) Body equivalent suction drag coeff . Body total drag coeff. C - - CD = T- (T/%Vo.") Body thrust coeff. c = (P-Po/so) Static pressure coeff. P Cpt = (E-PO/%) Total pressure coeff. Cg = (AHz5/qo) Total-pressure rise coeff. CQ = (Q/UoV 0.66) BLC suction flow coeff Cm = (m/pouoV BLC suction mass flow coeff. Gms = AIAA 87-2935 coef f . (01 Fan shaft power coeff. [O] Jet diameter or propeller dia. [ftl Max. body diameter [ftl F Skin-friction drag [Ibl 5 Body suction-slot width [it] E Fluid total-head [lb/ft2] bE Total-head rise [lh/ft2] Jet thrust of airfoil m = PQ jet-flap [Ibl Body length [ftl BLC suction mass flow [lb x secjft] Propeller speed [l/secl P 2 q = 1/2 pu Q Static pressure Dynamic head BLC suction flow [lb/f t2] [l b/ft2] [ft3/sec] R Body radius [ftl RL = (LU0/4 Length Reynolds Number [O] Rv = (U0V0'33/~ Volume Reynolds Number [O] T Thrust Pbl V Body volume [ft31 U Fluid velocity [f t/sec] x Axial coordinate [ftl x Propeller shaft torque [ft-lb] w Wake-drag (measured by Subscripts 0 Free-stream Consulting Engineer; Associate Fellow,AIAA j Jet Copyright 1987 by Fabio R.Goldschmied P.E. R Reference body wake traverse) [Ibl Boundary-layer displacement thickness [ft] Fan efficiency 101 Boundary-layer momentum thickness [ftl 2 Kinematic viscosity [ft /set] 2 4 Mass density [lb-sec /ft ] Skin-friction [lb/f t2] Jet angle of jet-flap [deg] 1 Edge of boundary-layer 2 Suction-slot inlet (Sta. 2, Fig. 4, Ref. 22) 5 Jet discharge (Sta. 5, Fig. 4, Ref. 22)
I. Introduction This paper attempts to focus the attention of aeronautical engineers on the great potential of aerodynamic static-pressure thrust AKA form thrust AKA negative pressure drag AKA negative form drag for fuselage self-propulsion. Over thirty years have elapsed since the initial aerodynamic research phase in the 1950's; younger engineers today seem to be totally unaware of this early work after HW 11. It is still relevant to quote J. B. Edwards 1 (1961) : "Our aeroplanes still follow the old concept of the powered glider, although thcy have become more refined as time has passed. It is truc, of course, that the acceptance of this concept results in a great simplification of the aircraft design procedure. One set of problems and considerations is divorced from the other and all is well, provided that consistent definitions of drag and thrust are accepted by the people working on these two separated sets of problems. The airirame group measures its achievement by the lift/drag ratio .... The engine group measures its cruising achievement in terms of specific fuel consumption ..." It would appear downright iconoclastic to even suggest that power can be usefully and efficiently applied to the airframe itself to increase lift and to eliminate drag, even to the point of creating "pressure thrust"; this is why some authors have employed the curious semantic appellative of "negative drag" for pressure thrust. Pressure thrust has been documented experimentally in several known cases. Perhaps the best-known case is that of the shrouded Dropeller: .I. E. Fanucci, et a1 (1974)' carried out an excellent experimental investigation at West Virginia University. Figure 1 presents the test set-up and Figure 2 presents the measured thrust vs. power, with the three categories of propeller thrust, shroud thrust and total thrust. At max. power it can be seen that the shroud pressure thrust is 60% of the total, while the propeller reaction thrust is 40%. Another well- known case is that of the airfoil with jet-flap. I. M. Davidson (1961)3 discusses the jet-flap airfoil and states: "Naturally the jet reaction J itself has a thrust component of only J cos $ but the difference J(1-cos #) is recovered in the guise of an aerodynamic pressure thrust distributed over the surface of the airfoil'. -2- Fig. 1 ~ Wind-Tunnel Layout of Experimental Shrouded Propeller (From Ref. 2) c-----I 0.25 0.5 0.75 1.0 POWER HP Fig. 2 - Experimental Shrouded Propeller Performance: Thrust YS Power (From Ref. 21 N A. Dimmock (1957) 4 presents experimental wind-tunnel results of a 12.5% thick airfoil with jet-flap at 0 = 58" from the chord line, as presented in Figure 3. The measured total thrust was 76.5% of the jet thrust, while the axial component of the jet thrust was only 52.5%. Thus 31% of the total measured thrust was pressure thrust and 69% was reaction thrust. B. S . Stratford (1956)5 was very aware of the potential for reducing or reversing the pressure drag of an airfoil with jet flap. The following is quoted from his Ref. 5 (pp. 181 and 182): "The form drag (which is that part of the two-dimensional drag transmitted by the normal pressure forces and not by skin friction) may be associated with the boundary layer displacing the main flow from the true profile of the aerofoil and thereby preventing the full -
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Fuselage self-propulsion by static-pressure thrust - CAFE Foundation

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