Tapered Blades

[Terry]

There seems to be a general idea that chord tapered rotor blades may be more efficient than rectangular blades on an autogyro.

Is this worth discussing on its own thread?

[Friendly]

Terry,
I asked Chuck about this several years ago. I don't remember his reply so I won't attempt to explain it. The net result of the answer was the extra work in building the blade would not be worth the marginal gain if any over the new smooth and high performance blades like dragonwings or sport rotors.

[RotoPlane]

If we are talking aluminum blades, I would heartedly agree….fiberglass….no problems…..
unless you want to include the extra material waste due to the taper.

[down under]

I do not think there would be any extra work in a composite blade, but they could not be made in an aluminium extrusion. For a fabricated aluminium blade the leading edge profile would require machining rather than a simple extrusion thus increasing the cost of the blade.
There are a number of people here in Aust that would buy tapered aluminium at the extra cost as the extra performance of these blades is well known yet they prefer to fly on aluminium rather than composite.

[SamL]

Tappering is very common on gliders with a high aspect ratio wings. It reduces the amount of vortex drag produced.

SamL.....

[Steve McGowan]

Greg Vallish was selling a blade that I think was called Stoley? or something like that.

It was originally made for windmills in Texas and I met (Loran ?)the person that had them Xtruded.. while I was there doing training with Brad King.. Yes they were tapered..

Greg told me at Mentone that a set 23' would carry the Black and two passengers 240lbs each... SHIIIISH

You have seen them on the Black haven't you.. I don't think so.

From my understanding of rotorblades the outter area is where the drive is, so if you taper it... ??

OK Chuck..... fill in all the blanks for me....

Steve

[Mike Schallmann]

I think the blades were called Avero Stolo --they were very dangerous --they have gone the way of the Dodo Bird --Greg Vallish has also left gyrodom--his whereabouts are unknown!

[Kevin_Richey]

Loren Stroup, I believe, was his name, according to posts by Chuck Beaty mentioning the blades.

[down under]

I have thought that the taper may more evenly distribute the lift along the blade rather than concentrating it at the tip. If this is the case tapered blades would be more suitable for lower airspeeds (depending in the amount of taper) due to the greater disymetry of lift on the inboard sections of blade as airspeed increases. I have not heard
of any problems with the Patroney tapered blades at higher airspeeds.

If the lift is more evenly distributed along the blade rather than being concentrated at the tip, this would also give a lower coning angle. I have found that a lower coning blade is more stable at very low airspeeds with stick back and power on. They also require less trim adjustment with changing airspeed. A low coning blade will also require more preset trim spring tension than a high coning blade.

I think this may be due to the blades angles relative to the air flow when in the for-aft position. If there were no cone on a rotor disc that is at an angle of nine degrees to the air flow then both blades would be at nine degrees to the air flow when in the fore-aft position.

If there is two degrees cone, the forward blade would be at 11 degrees to the air flow, the aft blade at 7 degrees. If there is 4 degrees cone, the forward blade is at 13 degrees to the air flow, the aft blade at 5 degrees. This makes a very noticeable difference in trim requirements and also some handling characteristics.

These tapered blades require more preset trim tension than a straight extruded blade which may indicate they are nose heavy in cord balance. They also show good lift in thermals which may indicate ballooning and tail heavy in cord ballance. It seems they are a well balanced blade with very low cone angle and good lift.

There may be two points that can improve performance in a tapered blade.
1 There may be a more even distribution of lift along the length of the blade.
2 A tapered blade would come closer to matching Cierva's calculations for blade loading and disc loading.

[RotoPlane]

Here are two 9' blades that are identical except for profile; one is an 8" rectangular and the other is tapered from 8" at the tip to 12" at the root. Also both have the same Cl of .3189 and 350 rrpm.

Note the lift curves.…the tapered blades curve is straighter and therefore has a more even lift. Its total lift would be greater than the rectangular one because of this and has of course more area for lifting.

The middle ~1/3 of the blade span is the driver for autorotation and the outboard ~1/3 is the driven or lifting section. A tapered blade has more area lift for driving than does the rectangular one. Therefore the tapered one should be more efficient.

[Passin' Thru]

Steve Mc said;

From my understanding of rotorblades the outter area is where the drive is, so if you taper it... ??

OK Chuck..... fill in all the blanks for me....

Steve, I ain't Chuck by any stretch, but here's a picture just for you!

[down under]

Looking at the diagram the driving region develops about 80% lift and 20% drive. A larger cord in the driving region would increase lift as well as drive.

[Gyro_Kai]

Hello,

I'm not quite following here. I was under the impression that DW blades were up-twisted towards the tip, which would increase lift on the outside, thereby have the same effect as getting broader wouldn't it?

A driven rotor is a totally different ballgame, here the blades are twisted the other way for the reason mentioned above, to get a more even load distribution, despite the much higher airspeed of the tips against the inner region.

In autorotation all is different, I thought.

confused,
Kai.

[RotoPlane]

On a blade with no twist, the outb'd 1/3 of the blade sees a shallower AoA than the middle 1/3 because its speed is much faster. Therefore the lift vector is angled further forward in the middle section giving more autorotative force/pull….as I see it.

[Passin' Thru]

No, you're looking at it wrong.The blade dipicted is non- twisted. The airfoils are not drawn on axis of rotation. Look at the relative air flow.

Click it a couple of times and it will enlarge more and is easier to read.