GB2214989A - Mounting blades on rotors - Google Patents

Abstract

One or more rigid blades 12 are connected to the rotor shaft 32 by plates 14, 28 with interposed packing 34 which are subject to twisting forces due to blade rotation whereby the blade pitch changes. A shackle 24, 26 is adjustable radially or removable to vary the flexibility of the blade fixing. The bolt connection of the plates 14, 28 to the shaft 32 includes elongate holes (20, Fig. 1) whereby the angle of the blade may be varied. The blades may be aircraft or marine propellors or prop-fans or used in gas turbines, gas or liquid pumping, wind generators or tidal flows. <IMAGE>

Description

Initial Application for a Patent concerning IN-FLIGHT AUTOMATIC PITCH-ANGLE ADJUSTMENT of a WORKING AIRSCREW; Simple, Lightweight, Cheap and of no moving parts.

Suggested nomenclature to be 'TRALFLEX' Propellors.

History This invention stems from the hypothesis proposing the advantageous flexing to be derived from a backwards-curving propellor blade. It's torsion, flexing and subsequent pitch- angle reduction when under strain. Commonly known as Scimitar propellors. Construction of such propellors is extremely Labor -ious, and the later tailoring of the blade and itS built-in flexibility adjustments can be so delicate ( & dangerous) that the idea is dropped. Scimitar propellors have fallen into disuse.

The newness of this invention, the Trailflex, is a modern -isation of the original hypothesis but separating the flexibility tailoring problem from that of hhe aerodynamic qualities. The tip and outter half of a propellor blade produces the thrust ;- we displace the flexing to be only at the blade root fixing. Flexibility adjustments can now be made at the root very eail. Similarly relegated to antiquity are the constant 3 equalisations to be made before each test flight, By use of identical (fibre compo -site) single blades, the repeared static, dynamic and aerodynamic balanc -ing of the standar @@@@ are no longer necessary.

Description From the technical drawing it can be explained that 3 devices will give us control of the flexibility.

a) The Blade, & variSweepback to produce torsional forces b) The Root/Web assembly @) The Shackle Not affecting @@exibility but derived from the use of these root tie-bars, is a fourth advantage claimed in this patent, that of; d) Stagger, of the webs on the prop-shaft to give univer -sality and plural-ity of a common, cloned blade to construct sets of 2,3,4, and 6 blades if required.

Even a single blade is possible.

a) The Blade;- Bolted-on and set with a trail angle, or sweep -back,of 18 degrees is a normal prop blade, less a radial 15% at the root. Contrary to the scimitar, this blade must have no built-in Sexibility. It should be as rigid as possible.

b) Flex-Web Stack ;- All flex control is desired in this assem -bly of 4 root WebS. Packing is held inbetween the webs, as are also the equal and opposite blade webs. An oversize thrust-plate secures, via the usual 6 bolts, the whole assembly. The length of the webs is the missing 15% of the radius.

Cut into the webs at-~the hub bolt-holes, are 5 curved slots of 5 different lengths. The master bolt-hole needs no modification. From this,trail angle adjustments up to an addit -ional 8degrees can be made. To a total of 26 degrees.

c) The Shackle ;- Self-explanatory in the diagram. After trials and the final position has been decided,a very thin bolt can be run through the middle as security holding against centrifugal for testing, inside snag-teeth should suffice rorces.AAlsoat this stage Ilard pellets can @@ positioned in the different bolt@hole slots to take care that no catastrophic dis -placement takes place after a bird strike in flight.

OPERATION ; Thrust loads from the rotating blade are transmitad through the root along with a strong torsional/twist force. This -torsional flexing in the root can be controlled in 5 ways. One is an installation/hangar job, but the other two can be done in the field-if downed at a short and muddy airfield.

a) Interchangeable Flex-Webs ;- Different materials can be used in manufacture of these simple items. Plus width, thicknes and radial length can be varied. Probably using composite fibres the lay-up can vary warp/weave angles, Percentages and different quality fibres.

b) The Shackle ; Can be adjusted radially along the web.

Having reached the innermost available position (for max flex) the shackle ,and packing can be removed.

c) Sweep-angle ;- Increasing angle will increase torsion and decrease working pitch angles.. This will give better accel -eration on ground and better climb-out but the cruise @speed and economy will suffer until reset at the next landing. Although a torque-wrench will be required to re-tighten the hub bolts, this is also an in-field adjustment where a piece of string can align both tips and hub axis to check equal trail angle.

d) Blade Stagger ;- is self obvious once rigging work has started, Pac a gust be cut to suit.

For a brief description of the different pitch settings assumed by the blade, it must be remembered that on a normal tour- -ing flight only 4 changes will take place after the initial fined -out (min.angle) Take-off & Acceleration phase. Listed as Climb -out, Cruise (some 90% of.the flight time) Descent and a possible Go-Around from a baulked landing... Similarly, angle shift is no greater;than-5 or 6 degrees, in mOst cases.

The conking forwards will strain the blade to take up a very small pitch angle for T/off and acceleration on the ground.

This is because although receiving maximum engine power/torque there is no forward Speed to bend back the blades. The cruise position is very different with only 659t economy thrust setting and the important cruise speed achieved, the blade can move rear wards and assume it's designed coarse pitch position. Without (at this stage)producing graphs of Torque,R.P.M., Flexing, Pitch angles and forward relative Airspeeds ; it is fairly clear that the other 3 conditions of this flight will get the suitable angle necessary.

ADVANTAGES ; Pessimistically viewed it can be asserted that from the especially expensive fuel we are pbliged to use in general aviation. only some 15 is transmitted to motive power. This is because our 50 year old (in design) reciprocating engines give only a 25% mechanical efficiency and the common 2 blade fixed pitch prop is only 600 efficient over the flight envelope. The old-fashioned mechanical electro-hydraulic pitch changing mech -anisms can cost more to fit than the small aircraft they are designed to complement.

Currently, our major producer, the USA is able to sell only a tiny fraction of itta previous decade'sai ctions. Their 2 largest aircraft factories (Piper & Cessna) have shut down.

except for a sparce trickle of the large models.

I believe that the Trailflex principle can help break this stale-mate of inefficiency and high prices.

IFASTIR,fuPTR does WorKlng as lt does in the field of fluid dynamics, extensions of this controlled flexing principle will find applications in Marine screws, gas-turbine and prop-fans along with gas and liquid pumping. Conversely energy can be extrected for use in wind generators tidal flows etcetera. These claims will be clarified at a later stage, when required.

Follows 2 Diagrams.

Claims (11)

1. A self-adjusting blade of a rotor comprising a rigid outer blade of fluid dynamics design mounted on an auto -deformable root such that the problem of torsional flex -ing control is completely isolated from the dynamic thrust, or energy extraction, properties of the revolving blade.

2. A self-adjusting blade of a rotor as claimed in Claim 1 wherein the correct torsional force in the blade root fixing is originated by mounting the blade at a trail sweep angle.

3. A self-adjusting blade of a rotor as claimed in Claim 1 or Claim 2 wherein a flexible connector is provided as the blade root fixing to give the material rigidity along with the desired degree of flexibility, and such that installation corrections can be easily made by web interchangeability and pruning in length, width and perhaps, thicknesses.

4. A self-adjusting blade of a rotor as claimed in Claim 1 or Claim 3 wherein the flexible connector has its flexibility controlled by means of a clamping shackle.

5. A self-adjusting blade of a rotor as claimed in Claim 1 or Claim 3 wherein the torsion force at the root assembly is varied by a change in the sweep angle of the blade.

6. A self-adjusting blade of a rotor as claimed in Claim 1 or Claim 3 wherein the flexible connection is included as a leaf or web into the hub itself, and by interposing these webs the blades are offset or stagger-mounted along the rotor axis.

7. A self-adjusting blade of a rotor as claimed in Claim 1 or Claim 6 where the plurality in attaching a different number of blades is made possible by this stagger-mounting.

8. A self-adjusting blade of a rotor as claimed in Claim 1 or Claim 4 or Claim 5 wherein an emergency high-trust setting is available,with the shackle discarded, and maximum sweep -angle chosen. This Claim is of primary importance for a downed aircraft threatened wit total dismantlement because available take-off distance is too short for a normal lift -off and flight.

9. A self-adjusting blade substantially as described herein with reference to the Figures 1 - 2 of the accomp -anying drawings.

13. A self-adjusting blade of a rptor, as claimed in Claim 2 but where additonally,or alternatively, torsion is originated by off-setting the centre of gravity of the blade to be out of the plane of rotation of that blade.

Amendments to the claims have been filed as follows

1. A self pitch-adjusting blade of a rotor comprising a rigid outer blade of fluid dynamics design mounted on an auto-deformable root, such that the problem of torsional-flex control, about the pitch-rotational axis, is completely isolated from the dynamic thrust, or energy extraction, properties of the flying blade.

2. A self-adjusting blade of a rotor as claimea in Claim 1 wherein the correct torsional force at the blade root and about it's axis, is originated by mounting the blade at a trail sweep angle.

3. A self-adjusting blade of a rotor as claim in Claims 1 & wherein a flexible connector is provided as the blade root fixing to give the material rigidity, along with the desired degree of flexibility.

4. A self-adjusting blade of a rotor as claimed in Claims 1. and Claim 3 wherein the flexible connector is of fibre composite material or similar, such that the undesirable immutability of the propellor(along with it's fixed performance), can be overcome, and some degree of performance control becomes possible. By this is meant web-r@ot flexibility adjustments by either tailoring and cutting-away of material to decrease rigidity, or conversely the simple bonding-on of more fibre laye@s to increase ligicity.

5 A self-adjusting blace o@ a rotor a@ claime@ in Claim 1. or Claim 3 wherein the flexi@le connector has it's flexibility controlled by means of a clamping shackle.

@. A self-adjusting blade of a rotor as claimed in Claim and Claim 2 wherein the @@rsion iorce at the ro@t- -asse @@y is @ari@@@@ @@ a change @@ @@e t@@ll @@@@@ angle of the bla@e.

7. A self-adjusting blade of a rotor as claimed in Claim 1. and Claim 3. wherein the flexible connection is as a leaf or web to form the hub itself, and by interposing these webs the blades are slightly off-set from each other, or stagger-mounted along the rotor axis.

8. A self-adjusting blade of a rotor as claimed in Claim 1. and Claim 7. wherein the blade plurality is no longer fixed immutably at manufacture. Instead subsequent change: in plurality is now possible, from the webs and off-set stagger-mounting feature.

9. A self-adjusting blade of a rotor as claimed in Claim 1. and Claim 5 and Claim 6 wherein an Emergency Hi Thrust Pitch setting is now available to an aircraft down in a too-short field for lift-off. With shackle discarded and maximum sweep angle selected, complete aircraft dis -mantlement could be avoided.

10. A self-adjusting blade of a rotor as claimed in Claim 1. and Claim 4. wherein the undesirable i > wutability of propellors can be further overcome by the introduction of safe shimming at the web/blade changeover point allowing adjustments in set angle of incidence

11. A self-adjusting blade of a rotor substantially as described herein with reference to the Figures 1. and 2.

of the accompanying drawings.