Canard Control System for Aircraft

The present invention concerns canard equipped aircraft and particularly such aircraft wherein canard lift may be varied.

In canard type aircraft, the small forwardly located wing termed a canard, provides lift forward of the aircarft center of gravity while the main wing center of lift is rearward of the center of gravity. When the canard and wing lift forces are in equilibrium the aircraft is stable, with no movement about its lateral or pitch axis. Currently provision is made in light aircraft of the canard type for altering canard lift for purposes of trimming the aircraft for stable flight, which is typically accomplished by a trim setting of the canard elevators, which incurs increased drag and lowers aircraft performance. Additionally, such trim positioning of canard elevators incurs the risk of "running out of elevator" when large trim adjustments are required, thereby precluding additional elevator movement for steep turns or approach and landing pitch changes.

A drawback to light aircraft of the canard type is that for the most part they do not utilize wing flaps since the trailing edge of the main wing is rearwardly remote from the aircraft center of gravity and would cause severe forward pitching of the aircraft as a conventional, fixed canard cannot counteract such forward pitching. Accordingly, light canard aircraft are usually without flaps and thus require greater landing and take-off distances than other light aircraft of comparable size and weight.

A still further problem with light aircraft of the canard type is that when the same are flown with less than an optimum weiqht distribution in the pilot, passenger and baggage areas, the aircraft must again be trimmed by setting of its elevators with the resulting increased drag and reduced aircraft performance. To resolve this problem, it is often necessary to carry deadweight in a seat or baggage area to keep the aircraft center of gravity within allowable limits. This practice is highly inconvenient and greatly reduces efficiency of operation.

The prior art on aircraft with positionable canards discloses such aircraft are of the military type and for the most part utilize swingable canards for changing canard lift forces. One such patent, U.S. Pat. No. 4,010,920, discloses a canard that is a primary flight control and positionable fore and aft along the longitudinal axis of the aircarft to change the canard moment arm as well as being positionable about said axis. The arrangement disclosed in the patent clearly does not lend itself to utilization in light aircraft by reason of weight, complexity and cost nor is it coupled to main wing flaps.

U.S. Pat. No. 4,569,493 discloses canards rotatable about a horizontal axis transversely disposed to the aircraft longitudinal axis. U.S. Pat. No. 3,778,926 discloses a toy aircraft having a manually settable canard. U.S. Pat. Nos. 3,883,094; 4,161,300 and 4,542,866 disclose canards positionable about multiple axes parallel and perpendicular to the aircraft longitudinal axis. U.S. Pat. Nos. 4,093,156; 2,924,400 and 3,926,389 disclose canards which swing about vertical axes to vary canard sweep and lift. U.S. Pat. No. 2,271,226 discloses a canard type aircraft with canard elevators connected to main wing flaps.

The present invention is embodied within a flight control system for canard type aircraft which permits the canard to be positioned throughout a wide range of movement to assure the aircraft stability regardless of aircraft loading and radical changes in main wing lift and drag forces resulting from wing flap use.

The forward portion of the aircraft fuselage houses canard carrier means which includes a canard carrier cage adapted generally for fore and aft movement along a rail arrangement. Provision is made in the carrier means for altering the canard angle of attack to preserve the highly desirable attribute of canard aircraft, i.e., the inability to stall. Such is automatically accomplished by an increase in the canard angle of attack when the aircraft is in approach configuration with stalling of the canard at all times occurring before main wing stalling. To assure simultaneous main wing flap and canard movement the canard carrier and the main wing flaps are synchronized to neutralize severe pitching tendencies. A trim control permits the pilot to finely adjust the canard to trim the aircraft for level, descending or ascending flight without the drag that would otherwise be incurred by the setting of the canard elevators.

Important objectives of the present system include the provision of a canard and flap control system which automatically maintains the aircraft in equilibrium about its pitch or lateral axis during wing flap deployment; the provision of a canard and flap control system which permits trimming of the aircraft by independent, incremental fore and aft positioning of the canard; the provision of a canard and flap control system which at all times maintains the canard angle of attack to retain desired stalling characteristics of a canard equipped aircraft, i.e., stalling of the canard prior to stalling of the main wing of the aircraft; the provision of a canard and flap control system amenable to incorporation within light aircraft of the canard type; the provision of a canard and flap control system wherein the canard may be positioned for trimming purposes independently of canard carrier means which positions the canard during main wing flap deployment; the provision of a canard and flap control system including carrier means which both positions the canard along longitudinal axis of the aircraft and ultimately increases the canard angle of attack to assure canard stalling prior to stalling of the main wing; the provision of a canard and flap control system which lends itself either to mechanical, electrical or hydraulic operation; the provision of a positionable canard and canard trim control means for positioning the canard wing fore and aft relative the aircraft center of gravity.

In the accompanying drawings:

FIG. 1 is a side elevational view of an aircraft embodying the present invention shown in landing configuration;

FIG. 2 is a schematic view of the present canard and flap flight control system in landing configuration; and

FIG. 3 is a view similar to FIG. 2 with the canard and flap positioned for normal flight attitude.

With continuing attention to the drawings wherein applied reference numerals indicate parts similarly hereinafter identified, the reference numeral 1 indicates generally an aircraft of the canard type having a main wing 2 equipped with flaps as at 3. A propeller 4 is shown as being of the pusher type.

Carried by the forward portion 5A of the aircraft fuselage 5 is a canard wing 6 hereinafter termed canard. Lift forces from main wing 2 and canard 6 act through different length moment arms from the center of gravity at C.G., to impart stability to the aircraft about its lateral axis. A change of the effective airfoil shape of the canard 6 or the main wing 2 by movement of elevators, deployment of flaps or by change of attitude of either one and/or by change of their moment arms relative to the C.G., will accordingly impart a pitch change to the aircraft about its center of gravity C.G..

With attention to FIG. 3, canard trim means are indicated generally at 11. Said trim means serves to advance or retract canard 6 for the purpose of altering the canard moment arm. Repositioning of the canard forwardly toward the nose of the aircraft increases the canard moment arm while avoiding an increase in drag which would otherwise occur upon airfoil alteration as for example by use of canard trim tabs and/or elevator positioning. One suitable mechanism for canard trim positioning is embodied in an internally splined shaft 12 universally coupled at 13 to a power source such as a crank 14 in the aircraft cockpit. Rotation is imparted thereby to a driven shaft 15 having a universal joint at 16. Shaft 15 has a forward threaded segment at 17 journalled at 17A-17B. A canard mounted traveller at 18 moves in response to shaft rotation to advance or retract canard 6 within a cage 20. A central portion of canard 6 is embodied in a slide 21 suitably entrained within a cage opening 20A for fore and aft movement. In aircraft without main wing flaps the above described canard and canard control means may be utilized for trimming purposes to establish pitch attitude equilibrium for level flight, climb or descent.

Canard carrier means are indicated generally at 19 and include the aforementioned cage which is of box-like construction and supported in place within the forward fuselage 5A by a fuselage mounted rail assembly having rails at 22 which are laterally spaced and with front and rear roller sets at 23 and 24 joined by shafts 25 and 26. Cage hangers at 27 and 28 depend from the shafts.

Flap and canard control means includes a cockpit located control member 30 for pilot actuation with a combination retainer and frictional drag member at 31. A first control rod 32 is pivotally coupled at its ends to said control member and canard cage 20 with clockwise movement of the control member advancing and eventually, as it approaches its forward extreme of travel, inclining the cage and canard to the FIG. 2 position. A second control rod 33 couples flap control member 30 to wing flaps 3 in a manner to effect flap deployment coincident with cage advancement and conversely flap retraction occurs with rearward cage and canard positioning.

While the foregoing system is shown and described in a manner suitable for use in light aircraft, it is to be understood that the system could be readily modified for use in larger aircraft such as by the use of servomotors for trim positioning of the canard within its cage as well as positioning of the cage and wing flaps. Such modification of the subject system would readily suggest itself to those skilled in the present field without departing from the scope of the present invention as defined in the appended claims.

In use, loading of the aircraft is accomplished in the usual manner with attention to maintaining the C.G., within fore and aft limits. The aircraft take-off roll may be reduced by partial flap deployment resulting in automatic advancement of the canard to an intermediate position between its extremes of travel. Normal or flight attitude entails full flap retraction with automatic repositioning of the canard rearwardly with lift forces from airfoils and moment arms in equilibrium. Trimming of the aircraft for level flight is achieved by incremental movement of the canard by canard trim means 11 which permits the canard elevators (not shown) to remain streamlined for minimum drag. For the sake of illustration of the present invention, the canard elevators and means for controlling same are not shown. Preparation for landing of the aircraft utilizing flaps 3 entails positioning of the flap control 30 clockwise so as to fully and rapidly advance cage 20 to forwardly locate and incline canard 6 to increase both the canard angle of attack and the canard moment arm to neutralize the tendency of the aircraft to pitch nose down as would otherwise occur by reason of the increased main wing lift and moment arm created by flap deployment.

While I have shown and described but a few embodiments of the invention, it will be apparent to those skilled in the art that the invention may be embodied still otherwise without departing from the spirit and scope of the invention.

Having thus described the invention, what is desired to be secured in a Letters Patent is: