IL44661A

IL44661A - Helicopter blade for high speed forward flight

Info

Publication number: IL44661A
Application number: IL44661A
Authority: IL
Original assignee: United Aircraft Corp
Priority date: 1973-06-04
Filing date: 1974-04-17
Publication date: 1976-12-31
Also published as: IL44661A0; JPS51116599A; CA988906A; FR2231565B1; IT1014735B; FR2231565A1; DE2426689A1; GB1477490A; BR7404568D0

Claims

44661/2. ' ■X What we claim is:

1. A helicopter blade having a span dimension , a chord dimension, a tip and including: < A) a blade root section adapted to be connected to a rotor hub for rotation therewith in both lower and forward flight modes of operation, B) a blade central portion connected to said blade root portion and extending outwardly therefrprn, C) a blade tip portion connected to said central portion and constituting the blade outer extremity and coopera ting with said blade root portion and said blade central portion to, define the blade span and shaped to have : 1) a generally negative non-linear twist of values ranging between -1 ant? about -8 degrees, 2) a substantially constant chord dimension throughout most of its span, 3) a thickness between 6' and 10% chord dimension, 4) and being cambered with the maximum camber forward of the 50% chord station.

2. A blade according to claim 1, characterized in that said tip portion constitutes the outer 18% of the blade span plus or minus 2% blade span for three bladed rotors, the outer 15.5% of the blade span plus or minus 2% blade span for four bladed rotors, the outer 14% of the blade span plus or minus 2% blade span for five bladed rotors, the outer 13% of the blade span plus or minus 2% blade span for six bladed rotors, the outer 12.5% of the blade span, plus or minus 2% blade X-. span for seven bladed rotors and the outer 12% of the blade . span plus or minus 2% blade span for eight bladed rotors.

3. A blade according to claim 1, characterized in that said blade central portion has a twist ranging from 0 to -20 degrees and said generally non-linear tip twist commences at about the 88% mark span station ί 2% span station and extends to the blade tip for eight bladed rotors, at about the 87.5% span station - 2% span station and extends to the blade tip for 7 bladed rotors, at about the 87% span station - 2% span station and extends to the blade tip for 6 bladed rotors, at + about the 86% span station - 2% span station and extends to the blade tip for 5 bladed rotors, at about the 84.5% span station ΐ 2% span station and extends to the blade tip for 4 bladed rotors, and at about the 82% span station - span station and extends to the blade tip for 3 bladed rotors, at about the 77.5% span station - 2% span and extends to the blade tip for two bladed rotors, and at about 71% span station ΐ 2% span and extends to the blade tip for a one bladed rotor.

4. A blade according to any one of claims 1 to 3, characterized in that the blade central portion has a twist of -14 degrees and a thickness of about 11% chord dimension.

5. A blade according to any one of claims 1 to 4, characterized in that the thickness of the blade ti portion is about 9,5% chord dimension.

6. A blade according to any one of claims 1 to 5, characterized in that the maximum camber of the blade tip portion is about 0,8% chord dimension and at about 27% chord station.

7. h blade according to any one of claims 1 to 6, characterized in that the blade tip portion has a trapezoidal tip.

8. A blade according to claim 7, characte ized in that the trapezoidal tip commences at the 95% span station ΐ 2% and reduces uniformly in chord dimension so that the blade tip chord is about 60% of the blade chord dimension and so that the tip aerodynamic center remains at the same chord station-.

9. A blade according to any one of claims 1 to 6, characterized in that the blade tip portion has a rearwardly swept tip shaped to establish a tip lift vector offset from the blade elastic axis to produce e. nose-up moment on the advancing blade during high speed flight.

10. A blade according to any one of claims 1 to 9 , characterized by having a solidity of .115 wherein said blade tip portion twist is -4.67 degrees at the 100% blade span station, with a tolerance of +3 degrees and -1 degree twist and + a tolerance of - 2% span for the span station for blades used with rotors having between 1 and 8 blades j is _4.67 degrees at the 71% span station for one bladed rotors, at the 77.5% span station for two bladed rotors, the 90% blade span station for three bladed rotors, at the 92.5% blade span station for four bladed rotors, at the 94% blade span station for five bladed rotors, at the 95% blade span station for six bladed rotors, at the 95.5% blade span station for seven bladed rotors, and at the 96% blade span station for eight bladed rotors, and having 12 degrees twist tolerance and ΐ 2% span station tolerance; is -2.62 degrees at the 74.5% blade span station for one bladed rotors, at the 80.5% blade span station for two bladed rotors, at the 84.5% blade span station for three bladed rotors, at the 87% blade span station for four bladed rotors, at the 88.5% blade span station for five bladed rotors, at the 89.5% blade span station for six bladed rotors, at the 90% blade span station for seven bladed rotors and at the 90.5% blade span station for eight bladed rotors, and having twist tolerance between +3 degrees and -.5 . degree, and a span station tolerance of - 2% span; and -1.2 degrees at the 71% blade span station for one bladed rotors, at the 77.5% blade span station for two bladed rotors, at the 82% b1o.de span station for three bladed rotors, at the 84.5% blade span station for four bladed rotors, at the 86% blade span station for five bladed rotors, at the 87% blade span station for six bladed rotors, at the87.5% blade span station for seven bladed rotors, and at the 88% blade span station for eight bladed rotors, and with a twist tolerance of - 1 degree and a span station tolerance of ΐ 2% span, and varies substantially linearly between these span stations.

11. A blade according to any one of claims 1 to 9, characterized by having a solidity equal to .115 wherein said blade tip portion twist is equal to; the blade basic twist -1.83 degrees at the 100% span station for blades used with one to eight bladed rotors, and with a tolerance of +3 degrees and -1 degree; the blade basic twist -2.33 degrees at the 80% span station for one bladed rotors, at the 85.5% span station for two bladed rotors, at the 90% span station for three bladed rotors, at the 92.5% span Nation for four bladed rotors, at the 94% span station for five bladed rotors, at the 95% span station for six bladed rotors, at the 95.5% span station for seven bladed rotors, and at the 96% span station for eight bladed rotors, with a twist tolerance of + 2 degrees and -1 degree; the blade basic twist -1.2 degrees, at the 74.5% blade span station for one bladed rotors, at the 80.5% blade span station for two bladed rotors, at the 84.5% span station for three bladed rotors, at the 87% span station f or . four bladed rotors, at the 88.5% span station for five bladed rotors, at the 89.5% span station for six bladed rotors, at the 90% span station for seven bladed rotors, and at the 90.5% span station for eight bladed rotors, with a twist tolerance and of =3 degrees and _.5 degree; /the blade basic twist at the 87% span station, - 1 degree.

12. A blade according to any one of claims 1 to 11, characterized in that said tip portion local twist can be particularly defined for six bladed rotors with a design blade loading, in hover of about .09 as follows: ® Beta Tip, X = Base, X +Δ for span station ranging from .71 ^ X ^ 1 for one bladed rotors, .775 ^ X i 1 for two bladed rotors, .82 ^X^l for three bladed rotors, .845 for five bladed rotors, .87 ^X^1 for six bladed rotors, 87.5 X l for seven bladed rotors, «88 ^ X «^ 1 for eight bladed rotors. Where _ . _. „ equals the Beta Tip twist at span station Beta Tip , *· X, andA^x equals change of twist between blade basic twist, & Base, X ' and & Beta Tip, X at station x< and where the blade basic twist for the linear case at span station X is defined: ® , x = Θι

13. A blade according to any one of claims 1 to 12, characterized in that said blade tip portion has an airfoil cross-sectional shape with two dimensional aerodynamic characteristics such that at tip Mach numbers of .3 and .6, the maximum lift coefficient, max,, is at least 1.41 and 1, respectively, and has a drag divergence Mach number of at least 0.76 at a lift coefficient of 0.2, and that the blade cambe is shaped to produce a blade pitching moment coefficient of less than .03 before moment divergence at subsonic Mach numbers.

14. A blade according to any one »of claims 1 to 13, characterized in that said blade tip portion is of airfoil cross where X is a chord station measured from the blade leading edge, C is the chord dimension, t is maximum blade thickness, Yu is the upper airfoil location at station X, and Y is the L lower airfoil location at X and where the leading edge radii can be defined by the following equations; where is the leading edge radius of the blade upper airfoil and is the leading edge radius of the lower blade airfoil, both taken from a point on the blade chord, and within a range of - 3% of the values of Y , Y_ , lculated. U JU « U , _ so ca Ju

15. A blade according to any one of claims 1 to 13, charac terized in that said blade tip portion is of airfoil cross section defined by the coordinates: x/c Y /t YL/t^ u' .0125 .1863 -.1526 .025 .2737 -.221 .05 .387 -.2993 .075 .45 -.3395 .1 .4926 -.3642 .15 .5442 -.3937 .2 .5734 -.4087 .25 .5842 -.4147 .3 .5815 -.4122 .4 .5578 -.3959 .5 .51o9 -.3627 .6 .4434 -.3145 .7 .3553 -.2509 .85 .2486 -.1745 .9 .1345 . -.0905 .975 .0345 -.0244 where X is a chord station measured from the blade leading edge, C is the chord dimension, t is maximum blade thickness, Y is the upper airfoil location at station X, and YT is the u L lower airfoil location at station X, and where the leading edge radii can be defined by the following equations: where u is the leading edge radius of the blade upper air~ foild section taken from a point on the blade chord, wherein C is the chord dimension, wherein t is maximum blade thickness, and where ^L is the leading edge radius of the blade lower airfoil section taken from a point on the blade chord, and within a range of t 3% of the values of Yu/t# Yi/t, Pu and P so determined. ' L

16. A blade according to any one of claims 1 to 15, characterized in that said central portion is of airfoil cross section defined by the coordinates: x/c Y u /t YL/t .0125 .1863 -.1526 .025 .2737 -.221 .05 .387 -.2993 .075 .45 -.3395 .1 .4926 -.3642 .15 .5442 -.3937 .2 .5734 -.4087 .25 .5842 -.4147 .3 .5815 -.4122 ■Λ .5578 -.3959 .5 .5109 -.3627 .6 .4434 -.3145 .7 .3553 „.2509 .85 .2486 -.1745 .9 .1345 -.0905 .975 .0345 -.0244 where X is a chord station measured from the blade leading edge, C is the chord dimension, is maximum blade thickness, Y is the upper airfoil location at station X, and Y_ is the U L lower airfoil location at station X, and where the leading edge radii, can be defined by the following equations: leading edge radius upper: fit s ^"^^ 40 where r air- foil section taken from a point on the blade chord, wherein C is the chord dimension, wherein t is maximum blade thickness, and where is the leading edge radius of the blade lower airfoil section taken from a point on the blade chord, and within a range of - 3% of the values of Y /t, YT/t, i U L P and so determined, u ' L

17. The method of improving helicopter rotor performance-comprising selectively twisting the blade tip to reduce blade tip loading in hover operation, and selectively applying sweep to the blade tip to produce, a tip aerodynamic center aft of the blade elastic axis to generate dynamic twist to thereby A) reduce tip twist and hence reduce tip loading on the advancing blade in high spaed flight, E) increase tip twist and hence reduce tip loading on the retreating blade in high speed flight, and* C) increase blade twist and hence reduce tip loading in hover.

18. A blade according to claims 1 to 16 substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

19. A method according to claim 17, substantially as hereinbefore described with reference to the drawings.