FR2492338A1 - METHOD FOR REDUCING THE TOTAL RESISTANCE OF AIRCRAFT - Google Patents

Abstract

PROCESS FOR REDUCING THE TOTAL RESISTANCE OF AIRCRAFT ACCORDING TO THE PRINCIPLE OF ACTIVE INCREASE IN THE THICKNESS OF THE BOUNDARY LAYER. WIND TURBINES 14 ARE PLACED IN FRONT OF THE LEADING EDGE 11A OF THE WINGS AND AT THE POINT 10A OF THE FUSELAGE, TURBINES IN THE WAKE OF WHICH ARE THE SURFACES OF THE AIRCRAFT EXPOSED TO THE FLOW. THE POWER ON THE WIND TURBINES SHAFT IS TRANSMITTED, BY LINK SHAFTS 14A ARRANGED IN THE WING 11 AND IN THE FUSELAGE 10, TO BE CONVERTED INTO A PROPULSION FORCE, TO PROPELLERS 15 PLACED IN THE AREA OF THE EDGE OF THE LEAK 11B OF THE WINGS AND IN THE TAIL 10B OF THE FUSELAGE.

Description

"Method of reducing the total resistance of airplanes."

  The present invention relates to a method for reducing the

  total resistance of aircraft according to the principle of

  active layer thickness.

  We know that the turbulent boundary layer has the following characteristics:

  that the increase in its thickness is accompanied by a

  reduction of the resistance or drag of friction, in pre-

  the presence of a hydraulically smooth wall. We could therefore

  drag the drag of an airplane by inserting the

  face exposed to flow in a thickened boundary layer

  near the leading edge. However, when the increase

  the thickness of the boundary layer is obtained by passive means, the resistance or drag of pressure or shape due to these means exceeds by several times the reduction

  obtained on the drag of friction. Aerodynamic resistance

  of a vehicle, which consists of the

  pressure and friction drag, can not

  not be reduced by the passive increase in

boundary layer.

  German Patent Application 24 28 683 relates to non-sharpened or sharp-edged vehicles, for which the reduction of the resistance must be obtained by an aerodynamic fairing of the untapered bodywork. This document

  does not aim at the frictional drag nor is it aimed at

reduce reduction.

  From German Patent 603,034, a wind turbine is known to allow to obtain an increase of the lift by the fact that compressed air is directed to

  through nozzles on the upper face of the wing. This-

  during, the turbo-fan shown can not cause a reduction in the total resistance - and is not provided for this purpose - because the thrust turbine is exposed to the full dynamic pressure of the free intake. It is therefore not possible to obtain an improvement in the thrust, because the propulsion rotor is not disposed in the wake of the wind turbine. It is only in the case proposed by the present invention that the impulse on admission and, therefore, the

  resistance to the thrust generator intake are sensi-

  lower than the iV 0 tracer force from

  impulse at admission in case of undisturbed admission.

  The current state of the art, to which the German Patent 542,471, the German Patent Application 25,06,974 and the US Pat. No. 4,149,688, still have not indicated any possibility. to get

  a significant reduction in drag.

  The object of the present invention is to obtain a reduction

  the resistance or drag of an airplane, by actively increasing the thickness of the boundary layer, and converting the power

the tree thus generated.

  The present invention achieves this objective by the fact that wind turbines are placed in front of

  the leading edge of the wings and at the end of the fuselage, tur-

  in the wake of which the surfaces of the aircraft exposed to the flow and whose power on the shaft is transmitted, by connecting shafts arranged in the wing and in the fuselage, and to be converted into a propulsion force, to propellers placed in the area

  the trailing edge of the wings or tail of the fuselage.

  According to another characteristic of the process proposed by

  the present invention, and to obtain a yield of

  As high as possible, the propellers operate entirely in the trough of the wake, at full pressure, of the aircraft, the surface of the propellers being reduced, in the zone of the tips of the blades, with respect to the surface located in the

  the blade feet area, and a uniform distribution of

  as much as possible of the speed being thereby obtained in

downstream of the plane.

  According to another characteristic of the process proposed by

  the present invention, the aircraft is propelled by means of group

  turbo-propulsion pumps through drive shafts

  a transmission mechanism, a linkage shaft

and a tail propeller.

  According to another characteristic of the method proposed by the present invention, the ratios of the surfaces to the turbines

  wind turbines is chosen in such a way that H / ry iv 7.

  The present invention will be better understood by means of the

  detailed description of a mode of implementation of this

  method, taken as a non-limiting example and illustrated by the accompanying drawing, in which: - Figure 1 is a plan view of an aircraft designed according to the present invention; FIG. 2 is a sketch illustrating the principle of the active increase in the thickness of the boundary layer, using a rotor made in the form of a wind turbine; FIG. 3 is a diagram giving a comparison of the velocity profiles downstream of the wind turbine with the profile of the boundary layer having the same thickness of quantity of the movements; FIG. 4 is a diagram indicating the influence of the ratio of the surfaces to the wind turbines on the ratio of the driving powers, in the case where there is identity between the thrust and the drag or resistance; FIG. 5 is a diagram which shows the relationship between the ratio of the driving powers and the parameter "increase of the thickness of the boundary layer"; FIG. 6 is a diagram which indicates the influence of the three yields XT 't P and, TW on the ratio of the powers in the case where there is identity between the thrust and the drag, and FIG. 7 is a diagram. indicating the ratio of

  values of drag or resistance, for the case of an identification

  between the power of the turbine and the power of the

  lice, and the report of the Powers for the case where there is

  between thrust and drag.

  The general concept of the present invention provides for

  to hold, with active means, in the form of a wind turbine, an increase in the thickness of the boundary layer, the excess power of these wind turbines, placed in the area of the leading edge of the wings of an airplane , being transmitted, via connecting shafts, to propellers placed in the trailing edge area, and used

for propulsion.

  Figure 1 shows an exemplary embodiment. An aircraft, powered by two turbo-boosters 13, comprises, at its nose 10a, a wind turbine 14, whose rotor is connected, via a connecting shaft 14a, to a propeller 15, placed at the tail lOb of the plane. The power on the tree of

  two turbo-propulsion units are transmitted, via

  of transverse trees 14b, a transmission mechanism

  16, and the connecting shaft 14a, to the propulsion propeller.

sion 15.

  Devices with similar rotors are arranged

  two sides of the fuselage of the aircraft on the wings 11, to

  see on the leading edge lia wings the wind turbines-

  14, and on the trailing edge llb wings propellers 15, each turbine and each helix being respectively connected by a connecting shaft 14a. In this case, however, no additional training power is provided to the

pairs of rotors.

  Starting from the fact that the turbulent boundary layer has

  characteristic that the increase of its thickness

  In the presence of a hydraulically smooth wall, the following conditions can be applied to the flat plate> 5 g W (1v = 0.012 yv 2 (V) 1 4 (1) or with J (X) = 0.036 x 0.8 (V / Vo) 0'2 (2)

J W (>) = 0.0288c V-2 () 0.2 (3)

  In these equations, r W denotes the boost voltage

  at the wall, the thickness of the momentum of the

  limit, etY9 =, ulp the kinematic viscosity of the air.

  Equation (3) shows that the friction at the wall, at the trailing edge of the plate, is only 87% of the corresponding value for x = 0.5 L and 63% of the pushing pressure at the wall for x = 0.1 L. It follows that the drag of an aircraft is considerably reduced when, according to the proposal according to the present invention, the surface exposed to the flow is inserted in a boundary layer. thickened in the leading edge area. If, however, this increase in the thickness of the boundary layer is obtained using passive means, the pressure or shape drag due to these means then exceeds by several times the gain or economy that one realizes on friction drag. By the following proposed measures

  the present invention, friction drag is found in

  in the case of aircraft, from 35 to 50% with a supplement

of relatively minimal weight.

  An analysis, which is the subject of a

  in Figure 2, makes it possible to explain more clearly the

  present invention. The study focuses on the incomprehensible flow

  sible and uniform around a thin plate, without incidence, length L, on the leading edge of which is

  a wind turbine 14, not faired, of height 2H, the pres-

  total pressure being lowered in the wind turbine 14,

of value 1/2 P & V2 - (V.0 -

  In the rotor plane of the turbine, the speed of

  is equal to: V = V00 - Au / 2. The mass of air yields, per unit of time, a determined amount of energy,

  so that for the power PT on the shaft the following equation

  is applicable: PT = pH Au (V00 - Cu / 2) .T (4)

  IT designating the efficiency of the turbine. From the theorem

  In the case of the conservation of the momentum, the rotor resistance WT = ihT Su = fH LSu (V -Cu / 2) (5) downstream of the wind turbine, the flow velocity drops to the value V00 -b u. At this point, the wake of the wind turbine has a height of

H. (VOO - Du / 2) / (Voo - u).

  The trough of the wake has a momentum thickness of: VK = .2V1_ u) H. If we neglect the transition from the profile of the boundary layer of the rectangular shape directly downstream of the wind turbine (Figure 2) to the known form of the fully constituted turbulent boundary layer, u (y) ç y) 1/7

V - -O (6)

Vo o

  it may be assumed, for the subsequent calculation of the

  that it behaves between the leading edge and the trailing edge, as if its origin was at the point x = -L = - (2 "VK <) 5/4 Vo 001/4

O 0.036 3

  0 At the trailing edge of the plate, the thickness of the mold

then is: -

  K = 0. 036 (L + L) '(/ Voo) 0.2 (7)

HK = 006 L0

  From this value, the friction drag was calculated.

  WR: WR = 2 v (HK-vK) (8) The velocity profile of the boundary layer according to equation (6) is given by:

SHK 7 HK

  and from equations (6) and (9), the velocity distribution can be calculated directly before the tail propeller, 15. The single helix is designed in such a way that the air which flows into the "current tube" takes a speed of V far downstream of the plane. The increase of the speed is obtained by an increase of the total pressure in the rotor,

elevation which is equal to: -

  1p E 2V u2 (y) 2P oo uHK (Y) ^ From this is calculated the energy increase of

  air per unit of time and the rise in the amount of

  air pressure, and then the thrust Sp can be calculated

  the power Pp absorbed by the helix. From the resistance

  of the WT turbine, the amount of flow

  3-VK, friction drag WR, prop thrust Sp and power Pp absorbed by the propeller, the resulting propulsive force SRES for PT = P or the driving power can be determined. Pp PT for Sp = WT + WR. i

249Z338

  For the driving power of the conventional reference aircraft, the following equation is applicable: P = A. Voo / o TW (10) equation in which WR denotes the resistance of the flat plate without increasing the thickness of the boundary layer,

  P the corresponding drive power, and X TW returns it

  propulsion drive. The ratio of the driving powers, with and without increasing the thickness of the boundary layer, is thus, in unaccelerated horizontal flight, equal to: Pavec 0.9 H / K 1P 4T9 <(1- A u / 2Voo ) (11) without 0.036 L '(9 / Voo) / 9 TW This shows that the ratio of the powers depends on the dimensional parametersr VK / L, T' t P 'TW'

H /, VK and ReL.

  It is necessary to underline the fundamental difference which exists between the yields' 9 T and 'p, on the one hand, and 2 TW' on the other hand. While VTW drive performance does take

  not only account for the power losses due to rubbing

  In the wake of shock waves and spin in the wake, but also jet loss, this loss is not included in the rotors T and P yields. The efficiency I TW of the thrusters will therefore generally be substantially lower than X T and p. When calculating the resulting resistance or drag force WREs, for the case where the power absorbed by the propeller is equal to the output power of the turbine, the determining equation for the surface of the turbine must be established.

the Hp propeller.

  FIG. 3 gives a comparison of the velocity profiles downstream of the wind turbine, for several values of the ratio of the H / 3VK surfaces, with the boundary layer profile of the same momentum thickness, profile in which

  transforms the rectangular profile after a certain time

  flow. To take into account a yield of tur-

  High external jet "jet = 1 - SUc / 2Voo, H / - VK should be chosen as large as possible." See also Figure 4. In addition, the transition to the favorable boundary layer profile from the point of view drag requires a length

  the larger the outer edge of the silencer

  the distance away from the wall. A quick transition to the boundary layer profile is assured, for example, by a

surface port of H /, $ VK = 7.

  Figure 5 shows the relationship between the ratio of

  and the parameter for increasing the thickness of the boundary layer 19VK / L for two combinations of the yields' IQ T '' J p and ITW It is found that even without increasing

  the thickness of the boundary layer, a gain in

  this is therefore achieved, since the helix, disposed in the "wake trough" of the cell, has, due to the low rate of admission, a yield of

very high propulsion.

  As the thickness of the boundary layer increases, an additional power gain is recorded, which reaches a maximum value for a given ratio.

  thicknesses. When the increase in thickness is

  However, the drive power starts to increase again, since then the power losses in both rotors are felt to a still greater extent. In general, it should be said that the ratio of the most favorable thicknesses, from the point of view power (5 VK / L) opt. is even greater than the losses in the

rotors are weaker.

  Figure 6 shows the decisive influence of the efficiency of the turbine q Tl of the efficiency of the propeller p. and performance of

  TW thrusters on the power gain, which can be

  with the measures proposed by the present invention and

  according to the applied principle. Curves in solid lines

  for each case, give the maximum power gain, while the curves in broken lines apply to the limit case 4 VK = 0, that is to say without wind turbine. As can be seen, one can count on a gain of power for all conceivable yields. The present principle becomes particularly interesting in the range 'QT' lpt 0, 9 and <TW <pP For a rotor efficiency of 0.92, which corresponds to the state of the art of propellers about 40 years ago, and for a thruster efficiency of 0.75 (modern transport aircraft with dual-circuit propulsion in cruising flight), the saving on drag or drag is

  36%. Of this percentage, 11% is attributable to the increase

  active thickness of the boundary layer, 10%

  favorable propeller propulsion equipment operating in

  the wake and 15% of the low propulsive propulsion

comparable reaction.

  The efficiency of the rotors should be able, with modern profiles, to be increased to 0.96. It would be possible in this case, using the method proposed by the present invention, to reduce by 47% the power consumption necessary to overcome the friction of the boundary layer. As shown in Figure 5, we would get the power saving

  maximum in the case of a ratio of increase of the thickness

  boundary layer of m VK / L = 0.0035. With H = 7 4VK 'this corresponds to a wind turbine height of

H / L = 0.0245.

  Figure 7 gives a comparison of the ratios of

  their resistance or drag for PT = Pp and the power ratio for SRES = 0, each time for the optimum ratio of increasing the thickness of the boundary layer 25.3 VK / L. It can be seen that the relative decrease in drag is generally slightly lower than the relative power gain. This is due to the fact that propulsion efficiency

  of the propeller, which is significantly more favorable than the

  conventional jet propulsion system, is not fully

  used in the case of free rotors.

  Thanks to the proposal made by the present invention

  to artificially increase the thickness of the

  limit layer of the flow, using wind turbines

  In front of the leading edge of the wings and the fuselage tip, it has been possible to reduce the friction drag of the aircraft quite considerably. The power on the shaft of each of the rotors of the wind turbines is transmitted, by the fuselage and the wings, to a propeller arranged

  in the area of the trailing edge of the wing or at the tail of the

  selage, and is converted into a propulsive force. It goes without saying that the reduction of 35 to 50% obtained on the friction drag can result, either by an increase in the radius of action, or by a corresponding increase in the

payload.

Claims (4)

  1.- Method for reducing the total resistance of   planes according to the principle of actively increasing the thickness   boundary layer, characterized in that wind turbines (14) are placed in front of the leading edge (1a) of the   wings and the tip (10a) of the fuselage, turbines in the sil-   where the exposed aircraft surfaces are   flow, and whose power on the tree is trans-   by connecting shafts (14a) arranged in the wings (11) and in the fuselage (10) to be converted into a propulsive force, to propellers (15) placed in the trailing edge area (11b). ) wings and in the tail (lob) of the fuselage. 2. A process according to claim 1, characterized in that, to obtain a propulsive efficiency as high as possible, the propellers (15) operate entirely in the trough of the wake, at total pressure, of the aircraft, the surface of the in the area of the tip of the blades, with respect to the surface in the area of the blade roots, and a distribution as uniform as possible   speed being thereby obtained downstream of the aircraft.   3. A process according to any one of claims 1   and 2, characterized in that the aircraft is propelled by turbo-propulsion units (13) via drive shafts (14b), a transmission mechanism (16),   a connecting shaft (14a) and a tail propeller (15).   4.- Method according to claim 1 or 2, characterized in that the ratio of the surfaces to the wind turbines is   chosen from such, that H / $ VK TO- 7.