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Schweizer Main and Tail Rotor Blades


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Are the main and tail rotor blades symmetrical or asymmetrical?

According to Helicopter Performance, Stability, and Control by Ray Prouty (p 697), the main uses a NACA 0015 and the tail a NACA 0014. Both of those airfoils are symmetrical.

 

Bob

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OK PF, my ? is why R U asking this in the first place?

 

There is another instructor here, he is an A&P with IA, who insists that the tail rotor uses asymmetrical blades. I told him otherwise...he said "prove it." I set out to prove it, but the RFM, HMI, and Parts Schematics don't describe the shape of the blade, only the construction. Took it further, and googled for an hour, but the only NACA resources I could find related to sailing (in a boat, not an aircraft), and had no information about symmetrical/asymmetrical. So I knew the NACA numbers for the blades, but couldn't find the info I needed.

 

--PF

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This is a ridiculous question, but I can't actually find a document to back this up.

 

Please, don't laugh...too much...

 

Are the main and tail rotor blades symmetrical or asymmetrical?

 

--PF

 

Dont think that is a ridiculous question at all. When i was at the Schweizer school in 1990, i remember that the main blade is a 0015, dont remember what the tail is tho, but 0014 as relyon pointed out is probably true. The double O series are symmetrical airfoils & the second 2 digits are how thick the airfoil is in relation to it's cord in percent.

 

It is fairly easy to prove: 1) trace the tip of the blade on a piece of thin cardboard, carefully cut the tracing in two along the cord line & then cut out the airfoil shape. 2) match the cutout on both sides of the blade----i'm sure you will find it is symmetrical, & you can do the math & verify that it is a "fourteen"

 

OK: i measured a C Model blade & came up w/ this: thickness=0.690 cord=4.740 the percent works out to be 14.557 so ? voilla !

 

The blades do have a "twist" to them, maybe this is what your A&P friend is referring to?

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Hi --PF

 

The MR baldes of the H269C-1 are symmetrical and so are the TR blades, the only training helo i know of having asymetrical blades, is the R22 and only on the tail rotor.

 

By the way... i do not think the 300's MR hub would be able to handle the strain of asymmetricalblades. Mabye if it had a titanium hub like the BO-105.

 

Tried to find you some documentation, but had some problems. I'll get back to you on that one.

 

Best regards

2rst1

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By the way... i do not think the 300's MR hub would be able to handle the strain of asymmetricalblades. Mabye if it had a titanium hub like the BO-105.

 

Tried to find you some documentation, but had some problems. I'll get back to you on that one.

 

Best regards

2rst1

 

I would be very interested in this documentation. Why does an asymmetrical blade create more load on the hub?----as far as i see it? the lifting load would have to be the same, the centrifugal load all depends on the weight & speed of the blade.

 

As far as i can remember from aerodynamics class, the reason for symmetrical blades is the center of pressure tends to stay in the same displacement along the cord line--thereby eliminating blade forces being transmitted back into the controls during pitch change.

 

 

As far as the tensile strength of titanium compared to some hi -alloy steels? The steels will usually come out ahead-----titanium is known for its "strength of steel,--but the weight of aluminum"

 

BTW 206 blade isnt symmetrical

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I would be very interested in this documentation. Why does an asymmetrical blade create more load on the hub?----as far as i see it? the lifting load would have to be the same, the centrifugal load all depends on the weight & speed of the blade.

 

As far as i can remember from aerodynamics class, the reason for symmetrical blades is the center of pressure tends to stay in the same displacement along the cord line--thereby eliminating blade forces being transmitted back into the controls during pitch change.

As far as the tensile strength of titanium compared to some hi -alloy steels? The steels will usually come out ahead-----titanium is known for its "strength of steel,--but the weight of aluminum"

 

BTW 206 blade isnt symmetrical

 

Hi,

 

I never said it would increase the load due to increased lift. But i have to agree, that the impact of asymmetric blades is more on the controll side.

 

Asymmetric blades will result in putting more strain on the controll transfer due to the added twisting moment created by the big movments in Center of pressure as the center of pressure moves forward.

This is also the center of lifting force acting on the airfoil. So as you said it will affect the controlls.

 

As far as the 206 goes... i do not know, but i would be very supprised if it had asymmetric blades. The new 407 yes, 206 no

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As far as the 206 goes... i do not know, but i would be very supprised if it had asymmetric blades. The new 407 yes, 206 no

 

saaprize saprize ! :rolleyes: (my Gomer Pyle imitation) ((no offense Gomer Pylot)) ;) But the 206's are among many helicopers that use a "droop snoot rotor blade" Not exactly sure if the very early 206's had this, but i worked on a few of the early 1980's vintage & they did.

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saaprize saprize ! :rolleyes: (my Gomer Pyle imitation) ((no offense Gomer Pylot)) ;) But the 206's are among many helicopers that use a "droop snoot rotor blade" Not exactly sure if the very early 206's had this, but i worked on a few of the early 1980's vintage & they did.

 

I'll be the first to admit it when i'm wrong. :blink:

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Asymmetric blades will result in putting more strain on the controll transfer due to the added twisting moment created by the big movments in Center of pressure as the center of pressure moves forward.

This is also the center of lifting force acting on the airfoil. So as you said it will affect the controlls.

The moment about the aerodynamic center is actually pretty constant over a reasonable range of angles of attack for most airfoils. Torsional strain over the entire blade span and through the attachments (grips and dampers) is a bigger structural issue than control force, however, and I suspect the main reason symmetrical airfoils have traditionally been used on light helicopter main rotors. It's much less of an issue over the span of a small tailrotor that also has no cyclic control mechanism (eg. the asymmetrical airfoil on the R22 tailrotor).

 

Bob

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