GB2331972A

GB2331972A - Ice protection system for aircraft

Info

Publication number: GB2331972A
Application number: GB9725708A
Authority: GB
Inventors: Christopher Yardley
Original assignee: Individual
Current assignee: Individual
Priority date: 1997-12-05
Filing date: 1997-12-05
Publication date: 1999-06-09
Also published as: GB2331972A9; GB9725708D0

Abstract

The application describes an aircraft deicing system comprising an inflatable wing envelopment 1, for an aircraft flying surface, a source of warm air 6, a releasable ducting system 7,8,9, to connect the warm air source to the envelopment, the envelopment including an exhaust duct. Multiple envelopments provide for wings and the tailplane. The exhaust duct is preferably arranged so as to maintain a substantially constant internal pressure sufficient to keep the bag inflated and thereby ensure application of hot air to all external surfaces. The envelopment preferably includes a pressure relief valve or blow-out panel to prevent excessive internal pressures arising in the event of failure of the exhaust duct. The system acts by (a) effecting a reduction of the relative humidity of the air inside the envelope, (b) increasing the temperature of the aircraft skin, and (c) providing a physical barrier to prevent freezing precipitation (snow, sleet or freezing rain) from coming into contact with the aforementioned critical surfaces. A corresponding method is also described.

Description

(4 - 2331972 1 ICE PROTECTION SYSTEM This invention relates to an ice

protection system for aircraft.

Ice, frost, snow and similar freezing substances must be completely removed fromthe mainplanes tailplane and control surfaces of aircraftbefore flight. This is because such contaminants adversely affect an aircraft's flying qualities and performance and would therefore, if allowed to remain, cause a reduction in flight safety.

Several accidents have in the past been attributed to wing ice, including instances in which de-icing steps were taken. Attempts continue to reach standards for essential de-icing operations and equipment, but full agreement has not yet been reached.

Current practice in the prevention or removal of freezing contaminants is to keep aircraft inside heated hangars, or to spray them with a de-icing fluid. The usual fluid is a mixture of glycol and hot water. However, hangarage space is often limited and de-icing spray is both expensive and damaging to the environment when the run-off finds its way into ground water. Many airports and airlines are forced to recycle or process glycol runoff and this imposes significant costs.

The present invention therefore provides an inflatable wing envelopment for an aircraft flying surface, a source of warm air, a releasable c 2 ducting system to connect the warm air source to the envelopment, the envelopment including an exhaust duct.

It is clearly preferable for there to be multiple envelopments, in particular three such envelopments for each wing and the tailplane.

The source of warm air should be controllable so as to compensate for excessively cold occasions without wasting energy at other times.

The exhaust duct is preferably arranged so as to maintain a substantially constant internal pressure sufficient to keep the bag inflated and thereby ensure application of hot air to all external surfaces.

The envelopment preferably includes a pressure relief valve or blowout panel to prevent excessive internal pressures arising in the event of failure of the exhaust duct.

The primary purpose of the system is to prevent or remove the formation of ice or frost on the critical surfaces by:- (a) effecting a reduction of the relative humidity of the air inside the envelope; (b) increasing the temperature of the aircraft skin; (c) providing a physical barrier to prevent freezing precipitation (snow, sleet or freezing rain) from coming into contact with the aforementioned critical surfaces.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which:- Figure 1 illustrates an aircraft in plan view with a wing envelopment fitted to the left mainplane; i 7 3 Figure 2 illustrates in front elevation an aircraft with a wing envelopment fitted to the right mainplane; Figure 3 illustrates a tailplane envelopment; Figure 4 illustrates a wing envelopment fitted to an aircraft with tail mounted engines; and Figure 5 illustrates in plan and cross-section an envelopment incorporating an internal spanwise duct.

Referring to the illustrations, the system comprises the following parts; Fabric wing enveiopments Wing Restraining means for the envelopment Fabric tailplane envelope Closure means for tailplane envelopment Controllable pneumatic source Envelopment inlet ducting Releasable couplings Wing envelopment outlet ducts Overpressure protection feature Internal spanwise duct 1 4 5 6 7 8 9 11 The wing envelopments 1 are fabric bags which are fitted by being pulled over each wing 2 from the tip inwards. They then fit loosely over each wing. They may or may not envelop the engine(s) when these are mounted on wing pylons. At or close to the wing root each wing envelope is held against its wing surface by a means of restraint 3, e.g. a tensionable strap, to restrict warm air loss. Drain holes (not shown) are provided in the lowersurface of the wing envelopmentsto drain off moisture accumulations.

c.l 4 Warm air from the inlet ducting 7 enters its envelopment via an inlet coupling 8 attached to the fabric of the envelopment close to the wing root. This air flows outboard towards the wing tip where it exits the envelopment via a further coupling which attaches to outlet ducting 9 incorporating an electrically or mechanically driven outflow valve, e.g. a butterfly valve, to restrict the flow of exhaust air thereby creating a small positive pressure differential between the envelope and ambient. The envelope is therefore maintained at correct inflation either by a pressure sensor within the envelope sending electrical signals to open or close the outflow valve, or by an operator positioning the valve by hand. Blow out panels in each wing envelopment protect against overpressure damage in the event of malfunction of the outflow valves. The inlet and outlet ductings are mechanically supported, e.g. by stands (not shown) close to their respective couplings to prevent excessive gravitational forces on the envelopes. Outlet ducting may either discharge exhaust air to atmosphere or direct it to the inlet side of the warm air source thereby saving energy.

On larger aircraft correct inflation of the wing envelopments may be prevented by adhesion between the upper wing surface and the envelopment material. This may be prevented by the inclusion of one or more spanwise ducts 11 within the envelope as shown in Figure 5. The duct(s) may be fashioned from the same material as the envelope. Warm air from the inlet coupling enters the envelope via outlets spaced along the internal duct(s). The combined area of all the outlets is such that a positive pressure differential exists between the inside of the duct(s) and the inside of the envelopment. This pressure differential serves to inflate the duct(s), thereby assisting main envelopment inflation.

The tailplane envelope 4 is positioned over the entire fin and tailplane, its opening then being reduced in an area by a drawstring or similar arrangement 5. Warm air is then introduced via inlet ducting the open end of which is directed inside the envelope by being suspended on a stand or i n being attached to points within the envelope adapted for the purpose. There is less need for outlet ducting for the tailplane envelope.

The source of warm air can be a trailer mounted blown air pneumatic source similar to those well known for heating large areas such as factories, aircraft hangars, and the like. Adapted for use on an airfield by consideration of spark suppression and other safety considerations well known, the source may be powered by its own fuel supply or by the airfield supplied ac electrical source. Alternatively, currently used airfield ground pneumatic units may be adapted for use, or possibly in the future, an airfield supplied ring-main of air could be envisaged. Three outlets are required, one for each wing envelopment and one for the tailplane.

The temperature and volume of the outputs are initially set by the system operator. However, temperature sensors may be installed within the envelopments which send electrical signals to the warm air source to modify these parameters when necessary.

Consideration may need to be given to fuel tank vents. Most aircraft include fuel tanks within the wings, which are of necessity vented in order to prevent a vacuum forming in the fuel tank above the fuel. It may be necessary to seal the vents temporarily during de-icing, or to provide a further vent which allows the fuel tank vent to communicate with the atmosphere outside the envelope. Alternatively, if the exhaust air is recirculated, it may be occasionally necessary to vent the atmosphere within the bag to prevent excessive build-up of fuel vapour. For example, the exhaust air could be vented for five minutes out of every twenty-five.

It will be appreciated that many variations can be made to the abovedescribed embodiment without departing from the scope of the present invention.

6

Claims

Aircraft deicing apparatus, comprising an inflatable wing envelopment for an aircraft flying surface, a source of warm air, a releasable ducting system to connect the warm air source to the envelopment, the envelopment including an exhaust duct.
2. Aircraft deicing apparatus according to claim 1 wherein multiple envelopments are provided.
Aircraft deicing apparatus according to claim 2 wherein three such enveiopments are provided, being one for each wing and the tailplane.
4. Aircraft deicing apparatus according to any preceding claim wherein the source of warm air has a variable output.
Aircraft deicing apparatus according to any preceding claim wherein the exhaust duct is arranged so as to maintain a substantially constant internal pressure sufficient to keep the bag inflated.
6. Aircraft deicing apparatus according to any preceding claim wherein the or an envelopment includes a pressure relief valve or blow-out panel thereby to prevent excessive internal pressures arising.
Aircraft deicing apparatus substantially as herein described with reference to and/or as illustrated in the accompanying drawings.
8. A method of deicing an aircraft, comprising the steps of; placing one or more envelopments over an airframe section bearing ice; i 11 -.

7 connecting the envelopment to a source of air at elevated temperature; and injecting the air into the envelopment thereby to raise the temperature in the vicinity of the ice.
9. A method of deicing an aircraft substantially as herein described with reference to and/or as illustrated in the accompanying drawings.