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It was originally made for windmills in Texas and I met (Loran ?)the person that had them Xtruded..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... ?? :confused:

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

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.

[RotoPlane]

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.

Pete's post #11 is NOT showing a helicopter blade :sorry:…..sorry about that Pete…I now see the airfoils are depicting the relative airflow they feel, NOT the pitch from twist. That's the best depiction of autorotation I've seen.

[Master Roda]

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.

Ok, since you posted this, I whipped out a sample for tapered blades. All aluminum, 8.5 at the root, and 7 at the tip.

My intent is too produce a 25' rotor with that aspect ratio. Then test it on our Vortex. When I get the results, I will post a new thread. I will be comparing them to our 8x25 rotor.

Jon

[down under]

I will be very interested in the results. I have been interested for some time in trying Sportcorter blades for mustering.

One thing that is importent in a mustering blade is the correct amount of inertia. If the blade is too light it responds quickly to turbulance and a rough day can be tiring. If it is too heavy it is slow to respond to control inputs. The inertia of an extruded blade seems a good compromise.

A 12'x8" extruded blade weighs approx 15 kg with even weight distribution. A fabricated blade may need some tip weights to achieve the same inertia.

[Master Roda]

After showing Jim an example of my idea, he has graciously allowed me to produce a set of tapered blades with the parameters in my above post.

As I said before, I will post the results of the testing. This may take awhile, but it will be worth it I think.

We will offer these blades at an additional cost ONLY if they prove better performance.

As a side note, I will offer these blades to forum members at a discount. Just submit your screen name, I will confirm, then you get the discount.

Alternate sizes will have to be tested before we produce them.

I thank everyone for your interest, this is exciting for me as well.

Jon

[Master Roda]

I bonded the tapered blades yesterday.

Pulled them from the oven this morning and they look great!

Flight testing will begin next week sometime!!

Jon

[RotoPlane]

Gosh Jon, you don't mess around! I can't wait to see how they compare to your standard blades.

[Master Roda]

I can't either!

I built the tapered ones to have the same square area, and airfoil. So it will be very interesting to see in the real world how this works. My prediction is higher top speed. I don't want to speculate much further than that.

Jon

[RotoPlane]

I'll go further ;).

A somewhat higher top speed makes sense to me because your blades will have more autorotative force (over a standard blade), which will reduce the disk angle and therefore its drag.

You should also notice a somewhat higher retreating blade stall limit.

I'll even say you will notice a faster spin-up during the takeoff roll.

There......

I'm assuming your standard blade chord is 7.5". I believe the blade would have even better performance if it started at 7.5" and it was shortened to the same area….but I could be wrong.

[Master Roda]

The comparison will be against 8x25, but should also be compared against our 7x25 to be fair. After all, it will be 7 at the tip.

If this first test works well, I will build others with different parameters.

Jon

[Joe Pires]

I cant believe your going to make us wait till next week, slacker.

[Master Roda]

I cant believe your going to make us wait till next week, slacker.

If we don't get some sun, it will be longer :wacko:

Thanks for the laugh :)

[All_In]

I love the spirit of this forum.

Someone suggest an idea, and one of you guys like Jon just builds it!

[StanFoster]

Jon- While you have some spare time this next week...whip me out some blades for my Helicycle....:)

Stan

[down under]

Not much grass growing under your feet Jon.
It will be very interesting to see the results.

[OzyRuss]

Just a quick follow on here guys................you blade makers should get to know each other, hava chat etc etc............we got a guy here in Oz, makes composite blades and props etc........guys swear by them, he produces a "twisted....tapered" blade for those wanting the characteristics of that "type".
As well he makes the conventional profile. Even moulds into the leading edge a " protector thingo"........great for rain damages.

My point is...............some of you guys have some great "great ideas", if you bounce them off knowledgable same guys..........we............flyers, get the very best of technology, and singularly each of you don't have to reinvent the wheel, so to speak.

This same guy was approached by "Robinson" re him making blades for helos.......he's that good. I've witnessed his blade building, the different types of matting / materials / resins, that go into a single blade was amazing.
Certain fibres go into certain sections of the blade, and certain resins go into particular areas of the blade...........it was a real eye opener.

[down under]

[ This same guy was approached by "Robinson" re him making blades for helos.......he's that good. I've witnessed his blade building, the different types of matting / materials / resins, that go into a single blade was amazing.
Certain fibres go into certain sections of the blade, and certain resins go into particular areas of the blade...........it was a real eye opener. ]

Russ, I always had a worry about how the glass blades would hold together if I had to drop into the trees. There was an accident here a few years ago. The mast broke off in the accident and I was told the blades and hub cartwheeled across the paddock and finished up a hundred meters from the machine. Apparently the only damage to the rotors was a bent hub bar and a few scuff marks. Strong blades.

[OzyRuss]

A quick follow up............testing these blades to "destroy" was way and above metal blades.
try setting your metal blades up between 2 stools.....a stool at each end, then climb up on them and stomp around, walk up and down em..........he does.
Then grab a half decent dolly hammer............and belt the hell out of em after you place them on a concrete floor..........he does.

and yes........they trim timber reeel good.......just get stained green on the leading edges:)

Only downside............tad heavy.
Cost........................$3500 Oz

[Master Roda]

OzyRuss,

Thanks for your input. Your right about communication between pilot and builder. I happen to be both. And I talk to myself all the time....does this count?

I'm doing this test using the same construction methods we have for years. I just wanted to produce something new to this company, not that it hasn't been done before, just that WE have never done it. Making a bonded aluminum blade into shapes other than standard is a bit tricky.

The strengths and faults of aluminum and composite blades are known so I won't get into that.

Jon

[Joe Pires]

Welllllllll??? How did they fly?

[RotoPlane]

I want to know too! I've been checking your weather and it has been fine, so........

[C. Beaty]

No discernable difference.

Not enough taper to do much of anything and tapering width without also tapering thickness may do as much harm as good. But probably a wash.

[RotoPlane]

I don't know for sure Chuck, but I understood they were using the same airfoil, which means to me they would be tapered in thickness. If the blades aren't, then I agree they will have less performance than a standard blade. I too wish the chord had more taper, but I'm happy they are trying something different :).

[Gyro_Kai]

Hello,

I still don't get it. If the blade is narrower at the tips, it produces less lift, right? But DW which are best renowned, have a twist upward to produce MORE lift at the tips. Why are tapered blades more effective?

Kai.

[Master Roda]

I'm painting them today. Assembled tomorrow. Flying Friday.

Ed,

If we don't try new things, then we aren't living anymore. Thank you for your support.

Chuck,

Let's just say that maybe were not after higher this, or better that. Did you ever consider I might change the pitch in accordance with the airfoil? Or whatever? Maybe I'll start twisting my nipples in flight to see if that changes my flight experience. That's positive twist of course :)

[RotoPlane]

Hello,

I still don't get it. If the blade is narrower at the tips, it produces less lift, right? But DW which are best renowned, have a twist upward to produce MORE lift at the tips. Why are tapered blades more effective?

Kai.

Hi Kai - Check out posts #9 & #10. If the outboard 1/3 of the blades have the same area, all other parameters being equal, they will have about the same lift. In my humble opinion the taper both in chord and span, compared to a rectangular blade, will produce higher Reynolds numbers for each chord station. At the correct taper angle the lift will be linear along the span and not logarithmic as with a rectangular blade. This will give more drive to the middle 1/3 of the span and more able to power the outboard 1/3 driven lifting section. Also a wider chord at the inboard 1/3 will stretch out retreating blade stall.

[Master Roda]

I forgot to explain that I had to take care of my customers first. That's why it's taking a little longer. Sorry.

PRA 73 will be here Saturday, so they will be the first to see them. If I have definite results by then, I will post. I'll post anyway, what the heck.

[OzyRuss]

Welllllllll??? How did they fly?


If you are asking re me................they were definately different, good different.
Could feel better lift, less power for same cruise........downside..........they just wanted to keep flying on roundout / flare, but with more time, one would adjust technique to control that.
My main concern with blades in general, is weight..........big blades are getting damn heavy ( 30 footers and bigger ) composite is even heavier than same alloy.
This "heavy" getting into our perameters now, is possibly entering into the unknown, we could rue this venture............maybe not:noidea:

[down under]

[ This "heavy" getting into our perameters now, is possibly entering into the unknown, we could rue this venture............maybe not ]

Russ, once you get past centrifigal force and coning flex in the book on 2 blade rotors its like the rest of the pages are missing.
There's a lot of different thoughts and theorys, none of them proven - mine included.

I am hoping to get my theory tested by maths and strain gauges so it can be laid to rest or proven.
If it is disproven there will still be a black hole in rotor theory.

[RotoPlane]

If it is disproven there will still be a black hole in rotor theory.

Black Hole?.....Black Hole?......Ask, and I will give you solid ground....:humble:....:wacko: ;)

[down under]

Possibly the wrong thread for it but if you can nail down the exact cause of a number of low hour hubbar failures due purely to fatigue, I would consider that solid ground.

Some common factors appeared to be heavy machines, heavy blades, take off and landings. From what I make of the way the cracks developed it was due to both cone flex and inplane flex. Some possibly just inplane flex.

[Master Roda]

Well Peter, since you asked......

I believe the problem to be a combination that involves resonant harmonics. The material simply cannot dissipate the energy frequency. What I mean is, if you vibrate something at it's resonant frequency, it will tear itself apart. This is pure speculation.

And, yes this is the wrong thread....albeit a good one. You should start one.

[OzyRuss]

Would like to add........i was privy to limited information the other week, A chap here is doing a thesis on metal fatigues, all part of his "degree"
Anyway a gyro buff got onto him to maybe look into our situation, chap agreed to include our hub bars in his research..........cut a long story short, already he has identified matters we must address, will be interesting to see the final outcome of his research.
His access to knowledgable folks, equipments, etc, and all for zip...for us, is great news indeed.

Stay tuned.................

[Gyro_Kai]

Hi Kai - Check out posts #9 & #10. If the outboard 1/3 of the blades have the same area, all other parameters being equal, they will have about the same lift. In my humble opinion the taper both in chord and span, compared to a rectangular blade, will produce higher Reynolds numbers for each chord station. At the correct taper angle the lift will be linear along the span and not logarithmic as with a rectangular blade. This will give more drive to the middle 1/3 of the span and more able to power the outboard 1/3 driven lifting section. Also a wider chord at the inboard 1/3 will stretch out retreating blade stall.

Hello,

if you taper, than you have less surface area per running length, don't you. Again, I would achieve a similar effect with down-twisting the tips wouldn't I?

Kai.

[RotoPlane]

Kai - It depends on what chord length you start with at the tip. If you have two 9' blades, one an 8" rectangular blade and one tapering blade that starts at 8" at the tip and ends at 12" at the root, the tapering blade will have more lifting area. Comparing the lift these two blades I found I could reduce the span of the tapering blade by about 1'.

[Master Roda]

I've started a new thread for tapered blades

http://www.rotaryforum.com/forum/showthread.php?p=298657#post298657

[tyc]

..we got a guy here in Oz, makes composite blades and props etc........guys swear by them, he produces a "twisted....tapered" blade for those wanting the characteristics of that "type".
As well he makes the conventional profile. Even moulds into the leading edge a " protector thingo"........great for rain damages.

This same guy was approached by "Robinson" re him making blades for helos...

Certain fibres go into certain sections of the blade, and certain resins go into particular areas of the blade...........it was a real eye opener.


I know that Robinson had a bad problem with outsourcing when it came to rotor blade manufacturing, so much so that now Robinson makes his own blades. If the individual is NOT the one Robinson had problems with, who is this fellow? What is his business/mailing address?

tyc

[OzyRuss]

Not the same guy..........he said no to Robo ( too busy with what's on his plate in general )

Re contact..........drop me a "PM"

[RotoPlane]

Moved this post here, from the "Skinny Blades" post.

These 0012 blades start tapering from 7" at the tip (for the reasoning in this thread and Peter's post #28), and .5" per foot to the root at 11". I have found this shape will lift as much at 22' dia. as a 24' rectangular blades and the autorotative vector forces are also higher. The rotor is rigid and the blades are fixed at zero degrees. The collective and cyclic controls cause the servo tabs to twist the blades. The collective controls the amount of positive pitch and the cyclic controls both positive and negative pitch. This allows for higher pre-rotation rrpm, jump takeoff, soft landings, etc.

This will give those that asked, some idea of what these tapered blades look like…. Note that you can zoom in and out....

[RotoPlane]

Welcome Jordan, to the club of getting your head around it!

I look at failure of the servo-tabs in the same way I look at FW aileron failure….chances are good that there will be some exciting moments. The servo-tabs are interconnected to the swashplate and on to the flight controls. The inside blade control path is by two bellcranks and cables. The cables are run inside UHMW urethane tubing. I'm using four Morse cables from the flight controls to the swashplate and control rods for everything else.