US3013744A

US3013744A - Vtol boundary layer control system

Info

Publication number: US3013744A
Application number: US14243A
Authority: US
Inventors: John F Klapproth
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1960-03-11
Filing date: 1960-03-11
Publication date: 1961-12-19
Anticipated expiration: 1978-12-19
Also published as: BE602328A; GB921300A

Description

Dec. 19, 1961 J. F. KLAPPROTH VTOL BOUNDARY LAYER CONTROL SYSTEM Filed March 11, 1960 m m M ,qrragusy- United States Patent Office Patented Dec. 19, 1961 3,013,744 VTOL BOUNDARY LAYER CONTROL SYSTEM John F. Klapproth, Cincinnati, Ohio, assignor to General Electric (Jompany, a corporation of New York Filed Mar. 11, 1960, Ser. No. 14,243 8 Claims. (Cl. 244-12) The present invention relates to a VTOL or vertical take-off and landing system and more particularly, to such a system wherein the lift per horsepower for a given fan size is considerably increased.

In VTOL systems, which are considered to be aircraft capable of taking-off and landing vertically, many variations have been proposed. One of the common systems is the use of large fans in the fuselage or wings which are designed to move large quantities of low velocity air therethrough in order to obtain upward lift on the vehicle body on which the fans are mounted. In such a system, it is apparent that limitations are encountered on the size of the fan that can be used. Thus, it is desirable to increase the effectiveness of a given wing or fuselage mounted fan by some suitable means in order to obtain the necessary lift within the confines of the structure available. In other Words, it is desirable to obtain more lift per horsepower with restriction to a given fan diameter which may be required by certain installations. As a general rule in such applications, to increase the effectiveness per horsepower, it is necessary to use a larger diameter fan, more mass flow, and a lower pressure ratio across the fan. This effectiveness per horsepower to fan diameter is normally in a one to one relationship. Where structural limitations are encountered, it is desirable to remove this one to one relationship to give some degree of flexibility and selection in the fan and still obtain a certain lift per horsepower.

It is a primary object of the present invention to disclose a VTOL system enabling more effective use of the available fan forming part of the system.

Another object is to disclose and provide such a system wherein a given diameter fan and a given horsepower may be utilized more effectively.

A further object is to provide such a system wherein flexibility is provided in the selection of the fan diameter to provide the same lift where there is no limit on the fan diameter.

Briefly stated, my invention provides a body such as a wing or fuselage having a duct for the passage of air to provide lift on the body, and having fan means disposed in the duct to force the air therethrough and provide the lift. A diffusing boundary layer control means is provided downstream of thefan to controllably spread the fan discharge along the lower surface of the body and produce a fiow area larger than the cross-sectional area of the duct.

While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter which I regard as my invention, it is believed the invention will be better understood from the following description taken in connection with the accompanying drawing in which:

FIGURE 1 is a schematic diagram showing the invention applied to a fuselage of an aircraft;

FIGURE 2 is a schematic showing of a modification of the invention applied to a body such as a wing;

FIGURE 3 is another modification similar to that shown in FIGURE 2;

FIGURE 4 is still another modification of the invention as it might be applied to a wing; and

FIGURE 5 is a modification using a combination of FIGURE 2 and FIGURE 3 and illustrating a means for controlling diffusion.

- 2 and 3 for illustration, to be described hereinafter.

Referring first to FIGURE 1, there is shown a VTOL system having a body to be lifted which may be any suitable aircraft 10. Disposed in the body 10 such as'a fuselage, there is provided a duct 11 which preferably passes from the top of the aircraft to the bottom thereof in a substantially vertical directiontherethrough. In order to move large masses of low velocity air through the duct and provide lift on the body 10, suitable fan means 12 is provided in the duct. The fan 12 may be driven by any suitable means not shown and, in all cases, may be placed relative to the duct as in FIGURE 1 or in the duct substantially at the outlet or exit plane as in FIG- URES 2, 3 and 5.

It is known in such an installation that in general the lift per horsepower available from the fan 12 increases as the pressure ratio across the fan is reduced. However, a reduced pressure ratio generally results in a reduced air flow through the fan 12, severely reducing the total lift available from a given fan diameter. As a consequence, conventional arrangements having the fan through-flow velocity essentially equal to the effective discharge velocity have a nearly unique relation between lift per horsepower and lift per square foot of fan area. Under these conditions, any attempt to increase the lift per horsepower can only be realized at the expense of reduced lift for a given fan size or an increase in fan size for a required lift. Conversely, attempts to reduce the size of the fan for a given lift can be realized only at a sacrifice in lift per horsepower or an increase in required horsepower.

By the present invention it is possible to circumvent the nearly unique relation generally existing between lift per horsepower and lift per square foot of fan area, to take advantage of reduced fan pressure ratio without the associated reduction in available lift or to increase fan effectiveness without the associated penalty in lift per horsepower.

This is accomplished first in FIGURE 1 by providing a diffuser boundary layer control means downstream of the fan 12. Effective boundary layer control permits a spreading or diffusion of the flow along the under surface of the body. Such diffusing through boundary layer control may take a number of forms as shown in FIGURES Referring again to FIGURE 1 any suitable manifold means 15 may be provided to effect the boundary layer control and diffuse the flow downstream of the fan and provide the area increase. In effect, the instant invention then widens out the discharge area of the fan from that shown at area 13 to that shown at the effective area 14. By this means, any given diameter fan may be selected to have an effective lift per horsepower equivalent to that of a much larger diameter fan and thus be utilized in more confined areas where structural limitations are imposed. To say it another way, as the velocity downstream of the fan is decreased by means of diffusing through boundary layer control, the lift per horsepower is increased. Any suitable means to obtain this result is contemplated by the invention herein disclosed.

Referring next to FIGURE 2, a specific structure is shown for illustration by which the diffusing by boundary layer control downstream of the fan may be obtained. It will be noted in this figure that the body 10 may be thought of as the wing as opposed to the fuselage in FIGURE 1 since the invention is applicable to either. The diffusion is obtained in this modification by the provision of ducts 16 connecting the upstream and the downstream portions of the fluid passage. By providing the ducts 16 leading as shown in FIGURE 2, it is possible to use the upstream portion of the fluid passage or duct through the body 10 as a low pressure sink to remove the boundary layer fluid adjacent the exit plane of the main flow duct through the bleed ducts in the direction shown by the arrows. It will be apparent that this is a form of boundary layer control to form a diffuser by means of which the downstream air flow may be induced to follow the lower surface of the wall of body 10 and thus widen out the discharge area into an area larger than that of the duct.

A further modification is shown in FIGURE 3 of a typical diffusing mechanism that may be used to controllably spread the fan discharge over the lower surface of the body into an area larger than the duct. In FIG- URE 3, the body 10 may again be illustrative of a wing having a fan 12 therein driven by any suitable means to induce air flow from the upper surface to the lower. Where the previous FIGURE 2 bled boundary layer air from the lower surface in order to induce the flow to follow the surface of body 10, the instant modification has pipes or equivalent 17 that contain high pressure fluid, such as air, to be discharged through slots 18 peripherally of the fan in a direction tangential to the body surface near the exit plane of the duct to induce the flow to follow the lower surface of body 10 as shown in FIGURE 3. Thus, this form of blowing boundary layer control also controllably spreads the fan discharge along the lower surface to produce a flow area larger than that of the duct.

Referring to FIGURE 4, a mechanical means of doing the same spreading action is illustrated. This modification employs difiuser vanes 19 that physically bend the flow of fluid downstream of the fan to controllably spread it into a larger area than the duct area as shown. Obviously, this latter modification entails some losses by providing physical structure in the passage whereas the modifications of FIGURES 2 and 3 may be controlled by suitable valve means not shown and do not impose any physical obstructions in the fluid flow since both modifications in FIGURES 2 and 3 are out of the main flow and disposed along the periphery of the fan.

In order to obtain a unique relation between net lift from the system for each operating condition, a positive means of controlling the amount of diffusion is desirable. Such control means may, in a wing installation, fix the downstream diffusion border or separation point by the usual wing flap as shown at 20 in FIGURE 5. A positive location of the stagnation streamline can be obtained on the upstream side by a controlled extendable or rotatable portion of the wing as flap 21 which may be extended as shown in FIGURE in dotted lines during lift or retracted as shown in solid lines during cruise or high speed flight and used in intermediate positions during transition. FIGURE 5 also illustrates a combination of diffusing by boundary layer control means such as ducts 16 of FIGURE 2 and pipe 17 of FIGURE 3, either or both of which may be used to obtain the desired flow pattern.

It will be apparent that in those applications where a restriction is applied on the available diameter of fan that can be used, the instant invention permits more effective lift per horsepower by providing an effective diffuser downstream of the fan by means of boundary layer control to controllably spread the fan discharge along the lower surface of the body and produce a flow area larger than the duct.

While I have hereinbefore described a preferred form of my invention, obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

I claim:

1. A VTOL system including a body having a duct therethrough, fan means disposed in the duct to direct air through the duct and create a lift force on the body, and boundary layer control diffusing means downstream of the fan to controllably spread the fan discharge along the lower surface of the body and produce a flow area larger than the duct.

2. A VTOL system including a body having a substantially vertical duct therethrough, fan means disposed in the duct to direct air through the duct and create a lift force on the body, and boundary layer control diffusing means adjacent the exit plane of the duct to controllably spread the fan discharge along the lower surface of the body and produce a flow area larger than the duct.

3. A VTOL system including a body having a substantially vertical duct therethrough, fan means disposed in the duct to direct air downward through the duct and create a lift force on the body, and boundary layer control diffusing means in the body adjacent the fan periphery to controllably spread the fan discharge along the lower surface of the body and produce a flow area larger than the duct.

4. Apparatus as described in claim 3 wherein the boundary layer control diffusing means includes slot means connecting the duct on each side of the fan whereby downstream boundary layer air is bled to the duct upstream of the fan.

5. Apparatus as described in claim 3 wherein the boundary layer control diffusing means includes slot means in the body directing high pressure air jets along the lower body surface to induce the fan discharge to spread along the lower surface of the body and produce a flow area downstream of the fan larger than the duct.

6. A VTOL system including a body having a substantially vertical duct therethrough, fan means disposed in the duct substantially in the plane of the lower exit of the duct to direct air downward through the duct and create a lift force on the body, and boundary layer control diffusing means adjacent the fan periphery on the downstream side to controllably spread the fan discharge along the lower surface of the body and produce a flow area larger than the duct cross-sectional area.

7. Apparatus as described in claim 6 wherein the body is a wing of an aircraft.

8. Apparatus as described in claim 6 wherein the body is a fuselage of an aircraft.

References Cited in the file of this patent UNITED STATES PATENTS