# US 11,440,644 B2 · Download reducing winglets for aircraft having a rotor producing downwash and method of operating the same

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- Number: US 11,440,644 B2
- Document ID: US11440644B2
- Status: Granted
- Kind: B2
- Application number: 16/797,342
- Filed: 2020-02-21
- Published: 2021-08-26
- Granted: 2022-09-13
- Earliest claimed: 2020-02-21
- Assignees: Textron Innovations Inc.
- Applicants: Textron Innovations Inc.
- Inventors: Kent E. Donaldson; Kyle Smolarek; Lynn Francis Eschete
- Web page: https://patentgrep.com/patent/US11440644B2

## CPC

- B64C 23/069: {using one or more wing tip airfoil devices, e.g. winglets, splines, wing tip fences or raked wingtips}
- B64C 27/26: characterised by provision of fixed wings
- B64C 21/10: using other surface properties, e.g. roughness
- B64C 23/06: by generating vortices
- B64C 27/32: Rotors
- B64C 2230/26: by using rib lets or hydrophobic surfaces
- Y02T 50/10: Drag reduction
- B64C: AEROPLANES; HELICOPTERS
- Y02T: CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION

## Abstract

An exemplary aircraft includes a wing positioned below a vertical rotor, the wing extending to an outboard end, and an anhedral winglet extending from the outboard end through an angular transition to a tip, the anhedral winglet having an external surface exposed to the rotor downwash and the external surface is contoured to generate local wing lift in response to the rotor downwash.

## Claims

### Claim 1

An aircraft, comprising:
a rotor in operation producing a rotor downwash;
a wing positioned below the rotor and extending to an outboard end;
an anhedral winglet extending from the outboard end through an angular transition to a tip, the anhedral winglet having an external surface exposed to the rotor downwash, wherein the external surface is contiguous with a top surface of the wing and contoured to generate local wing lift in response to the rotor downwash; and
a turbulence feature located on an upper side of the external surface and oriented to induce turbulence in the rotor downwash passing across the external surface,
wherein the turbulence feature is located on the angular transition.

### Claim 2 (depends on 1)

The aircraft of claim 1, wherein the turbulence feature is a surface roughness feature.

### Claim 3 (depends on 2)

The aircraft of claim 2, wherein the surface roughness feature comprises a plurality of dimples.

### Claim 4 (depends on 1)

The aircraft of claim 1, wherein the turbulence feature is a vortex generator.

### Claim 5 (depends on 1)

The aircraft of claim 1, wherein the turbulence feature comprises a ridge extending generally longitudinally.

### Claim 6 (depends on 1)

The aircraft of claim 1, wherein the turbulence feature is a ridge oriented generally parallel to a forward flight airstream at a cruise speed.

### Claim 7 (depends on 1)

The aircraft of claim 1, wherein the turbulence feature is a ridge oriented obliquely to the rotor downwash.

### Claim 8 (depends on 1)

The aircraft of claim 1, wherein the wing comprises a cutout of an aft portion of the wing proximate to the outboard end.

### Claim 9

A method, comprising:
operating an aircraft in a hover, the aircraft having a rotor producing a rotor downwash directed vertically downward onto a wing extending to an outboard end, and an anhedral winglet extending from the outboard end through an angular transition to a tip, the anhedral winglet having an external surface exposed to the rotor downwash; and
triggering turbulence in the rotor downwash on the external surface of the anhedral winglet in response to a turbulence feature located on an upper side of the external surface, wherein the external surface is contiguous with a top surface of the wing, wherein the turbulence feature is located on the angular transition.

### Claim 10 (depends on 9)

The method of claim 9, comprising the anhedral winglet generating local lift in response to the rotor downwash.

### Claim 11 (depends on 9)

The method of claim 9, wherein the wing comprises a cutout of an aft portion of the wing proximate to the outboard end.