Abstract:
A lift fan for use in short takeoff and vertical landing (STOVL) aircraft is disclosed and claimed. The lift fan is driven by bleed air from a main engine of the aircraft and may be controlled by an electromagnet. This eliminates the drag and torque on the main engine and reduces fuel cost and engine wear.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates generally to short takeoff and vertical landing (STOVL) aircraft and more particularly to an improved lift fan. 
       BACKGROUND 
       [0002]    A STOVL aircraft is a fixed wing aircraft that is able to take off from a short runway or even vertically in some circumstances, and land vertically. To achieve vertical lift, the aircraft uses a lift fan that to provide vertical thrust. The use of a short runway allows the aircraft to carry a larger payload than a purely VTOL (vertical takeoff and landing) aircraft, although the two types are closely related, particularly when it comes to achieving vertical lift. For the purposes of this application, STOVL should be interpreted as also including VTOL. 
         [0003]    Since STOVL aircraft are fixed wing, they have the need to provide vertical lift during takeoff and landing, but forward propulsion during flight. Prior art aircraft provide vertical lift in a variety of ways. One known method is to redirect some portion of the airflow generated by the main turbine used during forward flight in a downward direction using vectoring nozzles. This method is used, for example, by Hawker Siddeley Harrier aircraft. 
         [0004]    Another prior art aircraft is the F-35 Lightning which uses a separate lift fan that is connected to the main engine by a drive shaft. This type of system is shown, for example, in U.S. Pat. No. 8,910,464. However, this type of system creates a large load on the main engine, leading to breakage and other problems associated with extra torque on the engine. 
         [0005]    Thus, a need exists for a lift fan in a STOVL aircraft that eliminates the drag and torque on the main engine and reduces fuel cost and engine wear. 
       SUMMARY 
       [0006]    A lift fan for use in short takeoff and vertical landing (STOVL) aircraft is disclosed and claimed. The lift fan is driven by bleed air from a main engine of the aircraft and may be controlled by an electromagnet. The invention in one implementation encompasses an apparatus a lift fan for providing vertical lift to an aircraft, including a housing, which features a center mount, an outer rim, an inner circumference of the outer rim having a slot, an electromagnet mounted in the slot of the outer rim, an inlet for receiving compressed or bleed air from an engine of the aircraft and directing it into the slot and an outlet for expelling air from the housing; and a fan removeably attached to the center mount of the housing, the fan having a plurality of blades, each blade having a blade tip extending into the slot in the outer rim of the housing wherein the compressed or bleed air from the engine causes the fan to rotate. 
         [0007]    In a further embodiment, each fan blade further includes one or more magnets for engaging with the electromagnet. 
         [0008]    In yet another embodiment, the electromagnet is controlled to center the fan in the slot or to stop the fan. 
         [0009]    In a further embodiment, the invention encompasses a lift fan for providing vertical lift to an aircraft a housing with a center mount, an outer rim, an inner circumference of the outer rim further comprising a slot, an inlet for receiving compressed or bleed air from an engine of the aircraft and directing it into the slot, an outlet for expelling air from the housing and a coating of polytetrafluoroethylene (PTFE) on the slot; and a fan removeably attached to the center mount of the housing, the fan further comprising a plurality of blades, each blade comprising a blade tip extending into the slot in the outer rim of the housing wherein the compressed or bleed air from the engine causes the fan to rotate. 
         [0010]    In either of the above embodiments, each blade of the lift fan includes a curved support mounted perpendicularly to the blade and following the curvature of the outer rim of the housing, the curved support located inside the slot in the outer rim. 
         [0011]    In either of the above embodiments, the fan includes a center hub having a plurality of slots and a plate, each of the plurality of blades inserted into a slot and held in place by the plate, a bolt extending through the center mount, the center hub and the plate and a nut engaged with the bolt to secure the fan to the housing. 
         [0012]    In either of the above embodiments, the housing has an insulating material between the housing and the fan. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0013]    Features of example implementations of the invention will become apparent from the description, the claims, and the accompanying drawings in which: 
           [0014]      FIG. 1A  depicts a top view of a lift fan and housing according to the present invention. 
           [0015]      FIG. 1B  depicts an enlarged view of a portion of the lift fan of  FIG. 1A . 
           [0016]      FIG. 2A  depicts a top view of housing  12  from  FIG. 1A . 
           [0017]      FIG. 2B  depicts a cross-section view of housing  12  from  FIG. 2A . 
           [0018]      FIG. 3A  depicts a top view of a center cap in accordance with the present invention. 
           [0019]      FIG. 3B  depicts a bottom view of the center cap of  FIG. 3A . 
           [0020]      FIG. 3C  depicts a cross sectional side view of the center cap of  FIG. 3A . 
           [0021]      FIG. 3D  depicts a center cap plate for use with the center cap of  FIG. 3C . 
           [0022]      FIG. 4  depicts a cross sectional top view of the fan blade of  FIG. 1B . 
           [0023]      FIG. 5A  depicts a cross sectional side view of the housing and fan blade of  FIG. 1A . 
           [0024]      FIG. 5B  depicts an alternative embodiment of the housing of  FIG. 5A . 
           [0025]      FIG. 6A  depicts a side view of the fan blade. 
           [0026]      FIG. 6B  depicts a cross sectional view of the fan blade of  FIG. 6A . 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    Turning to  FIG. 1A , a lift fan  100  in one example comprises a plurality of fan blades  10  mounted in a housing  12 . In a preferred embodiment, housing  12  is made from magnesium or aircraft strength aluminum, although any suitable material could be used. Housing  12  includes front mounts  14  which allow lift fan  100  to be mounted in an aircraft by means of clamps, not shown. Rear mount  16  allows lift fan  100  to be attached to the aircraft using a pin (not shown) inserted along line  18 . Although specific front and rear mounts have been shown, one of ordinary skill in the art would readily understand that alternative mounting arrangements could be used. 
         [0028]    Housing  12  includes an inlet  20  for receiving high velocity air from an engine of the aircraft. In an embodiment, this air can be compressed air or bleed air. After air passes through the housing it is expelled through outlet  22 . Air exiting outlet  22  can be directed either back to inlet  20  or expelled to ambient air. 
         [0029]    Fan blades  10  are mounted to a center hub  24 , shown in more detail below. Each fan blade  10  includes an curved support  26  (shown in  FIG. 1B ) close to but not at the outer end of fan blade  10 . An extension  28  of each fan blade  10  extends beyond curved support  26  as shown in more detail below. 
         [0030]      FIG. 1B  shows an enlarged view of a portion of lift fan  100  of  FIG. 1A . Fan blade  10  includes curved support sections  26  which interconnect to form an annular ring within housing  12 . Extension  28  of fan blade  10  is located in housing  12  such that air from inlet  20  pushes against extension  28  so as to cause lift fan  100  to rotate. 
         [0031]      FIG. 2A  shows a top view of housing  12 . Similarly to  FIG. 1A , housing  12  includes inlet  20  and outlet  22 , as well as front mounts  14  and rear mount  16 . In addition,  FIG. 2A  shows center cap paddock  40  which is attached to the outer portion of housing  14  by arms  42 . A cross section view of housing  12  along line A-A in  FIG. 2A  is shown in  FIG. 2B . Center cap paddock  40  includes a bolt hole  44  and pressed precision bearing  46 . Center hub  24  ( FIG. 3C ) is bolted to the inner side of center cap paddock  40  next to spacer  52 . In an embodiment, spacer  52  is made of polytetrafluoroethylene but any similar material could be used. Housing  12  features a channel  48  around it&#39;s inner circumference into which blade tips  28  of  FIG. 1B  extend. Electromagnet  50  is mounted in housing  12  to provide centering and braking of fan blade  10 . 
         [0032]      FIG. 3A  shows a top view of a center hub  24  of  FIG. 1A . Mounting hole  54  will align with bolt hole  44  of  FIG. 2B .  FIG. 3B  shows a bottom view of center hub  24 . A plurality of slots  62  receive fan blades  10  of  FIGS. 1A-1B .  FIG. 3C  shows a cross sectional side view of center hub  24 . In an embodiment, bolt  66  extends through center cap paddock  40  ( FIG. 2B ), center hub  24  and plate  68  and is secured with nut  70 . Alternative methods of securing center hub  24  and plate  68  to center cap paddock  40  could be used as understood by one of ordinary skill in the art.  FIG. 3D  shows a bottom view of plate  68  of  FIG. 3C . 
         [0033]      FIG. 4  shows a cross sectional top view of fan blade  10  of  FIGS. 1A-1B . Fan blade  10  is connected to curved support  26  and blade tip  28 . Each end of curved support  26  ends in opposing tabs that interlock. Each tab  80  cooperates with tab  82  of an adjoining fan blade  10  to form a complete ring when all the fan blades are installed. Fan blade  10  is terminates in inner end  86 , which is inserted into slots  62  of center hub  24  as shown in  FIG. 3B . Magnetic material  84  cooperates with an electromagnet  52  of housing  12  (shown in  FIGS. 2B and 5A ). Although shown as a series of separate magnets, magnetic material  84  could also be made of a solid ring of magnetic material. 
         [0034]      FIG. 5A  shows a cross sectional side view of the housing of  FIG. 1A . Housing  12  encloses an electromagnet  50 , which is separated from housing  12  by an spacing  90 . In an alternative embodiment, spacing  90  is an non-magnetic material such as rubber or polytetrafluoroethylene (PTFE). It is necessary to separate and also insulate fan blade  10  from the environment and its corrosive properties. Blade tip  28  and curved support  26  ride inside electromagnet  50 . In operation electromagnet  50  is controlled through wiring  60  and cooperates with magnetic material  84  to provide braking of the lift fan. It also provides centering and stabilization of the fan in the housing  12 . The use of an electromagnet allows the polarity of the magnet to be changed. Giving electromagnet  50  an opposite polarity as magnetic material  84  results in a braking operation. The same polarity provides stability. 
         [0035]    An alternative embodiment is shown in  FIG. 5B . In this embodiment, the housing does not include an electromagnet. Instead housing  12  includes material  92 , for example, PTFE. This ensures that fan blade  10  rides smoothly in housing  12 . 
         [0036]      FIG. 6A  shows a side of fan blade  10  and blade tip  28 .  FIG. 6B  shows a sectional view of blade  10  along line B-B of  FIG. 6A . Arced support  26  ends in tabs  80  and  82  as shown in  FIG. 4 . Blade  10  includes a curvature typical of fan blades. The exact curve of the fan blade would vary along its length as would be understood by one of ordinary skill in the art. 
         [0037]    If used and unless otherwise stated, the terms “upper,” “lower,” “front,” “back,” “over,” “under,” and similar such terms are not to be construed as limiting the invention to a particular orientation. Instead, these terms are used only on a relative basis. 
         [0038]    An illustrative description of operation of the apparatus  100  is presented, for explanatory purposes. 
         [0039]    The steps or operations described herein are just for example. There may be many variations to these steps or operations without departing from the spirit of the invention. For instance, the steps may be performed in a differing order, or steps may be added, deleted, or modified. 
         [0040]    Although example implementations of the invention have been depicted and described in detail herein, it will be apparent to those skilled in the relevant art that various modifications, additions, substitutions, and the like can be made without departing from the spirit of the invention and these are therefore considered to be within the scope of the invention as defined in the following claims.