Wide cord blades

[deebee]

I recently picked up a set of 430mm Maverick blades. http://www.ebay.com/itm/391100889454...%3AMEBIDX%3AIT
When I got them I found that they are an extremely wide cord blade. From reading some other posts, I learned a little about increased solidity and what that means, as well as increased weight.

Question is what should I expect with these wide chord blades from a standpoint of drag and efficiency, as well as response to cyclic and pitch?

How would a wide chord compare to a narrow chord of the next size up?
I.e. 430mm wide chord vs. 470mm thin chord.
I gather that staying with 430mm the disc loading remains the same regardless of solidity. Yet would the lower disc loading of a skinnier than normal 470mm overcome the lower solidity? Or am I looking at disk loading all wrong.


Going from align 425D or Revo 430 fbl to these wide chord blades I am certain that my fbl gain settings will need to drop a bit. Should I also expect that the increased responsiveness will lend to a need to make other adjustments, (headspeed, agility, etc.) or should the effects of increased blade weight mostly even things out.

Sorry for all the questions, I know aero is a very complicated subject, and it's not as simple as tossing a couple numbers into an equation. I suppose I should familiarize myself with Reynolds numbers, and such. Maybe one day I will have the time to get into advanced rotary wing theory. I will probably end up going back to school to finish my engineering degree, (only got a year towards it. Chem1, calc 1 and 2, Physics 1) either EE or ME.

[Jmann841]

I myself and still learning so will do my best and I'm sure much more knowledgeable people can chime in.

Increasing solidity will give you more lift, however, also more drag. The requirements on your motor will increase substantially.

Generally speaking, if 2 blades have the same airfoil and wetted area, the higher aspect ratio one (longer and skinnier) will be considerably more efficient for a given amount of lift generated. IE Lift/drag ratio.

I would argue that generally speaking a thicker chord 2 blade setup is more efficient and a better solution than a 3 blade setup. The disadvantage of a 2 blade over a 3 blade setup of equal solidity is your cyclic response, since your RPM on a thick chord 2 blade setup is going to be similar to the 3 blade setup of equal solidity, but, your control frequency is at 180 degree's instead of 120.

But, since it is a hobby and these are not designed for pure efficiency, the best way to find out is to test it and see how you like it. Generally speaking a larger disk for a given airframe without changing weight will make it "feel" more floaty while increased solidity will make it "feel" more powerful if your power system can handle it.

Just be mindful of the increase in demand on your power system. Just like when changing props on an airplane, as lift and drag goes up, so does the required power to drive it.

[deebee]

I have put them on my Protos 500 Carbon, factory scorpion/yge 60/ stretch boom/ 15t pinion.
It has enough power to drive 430mm Revo. Blades at 2900rpm and just under 14° Pitch. Should be enough power to run the wide chords at least with a little lower HS and pitch. Might have to drop to 14t.

That should leave me.... with a max HS of 2750 governed.

[R_Lefebvre]

I did some testing with the Spinblade Asymmetric blades on my Protos, which are very wide chord, and found they did no offer any increased efficiency compared to standard blades. This is on a very heavy UAV airframe (3200g!) running on 4S giving about 1800-1900 rpm. What I found was that, the Spinblades did provide more lift all-else-being-equal, but not more efficiency. Standard blades are capable of flying fine in this condition, but they require more maximum collective pitch to do so. I found they required pretty much the same power to hover. Due to the increased cost, I stopped using the Spinblades.

One thing that is not helping the Spinblades, is the really horrible flat leading edge they have, due to the manufacturing process. It's really bad, and might be creating quite a bit of drag. Hard to say if nicely made blades of the same profile would perform better.

[Smoggie]

Yep, the last post sums it up. Wide chord blades will give you more lift for a given RPM and pitch, but at the expense of more power absorbed.

To get better efficiency you need to increase disk area (longer blades) and decrease RPM

[R_Lefebvre]

Yes, exactly. Forgot to mention that.

There is a theoretical limit, where increasing disk size and decreasing RPM won't work anymore, and would begin to decrease efficiency (imagine somehow fitting 1m blades to a 450 frame) but for all practical discussion, the rule holds true.

[Smoggie]

Actually there is no 'theoretical' limit. Efficiency increases to the square of rotor diameter and it does so indefinitely until in theory you approach infinite efficiency. However in the real world practicality comes into it, the blades would become heavy, 'floppy' and fragile.

But you can get some idea of what can be done with very large, very slow turning blades by this human power helicopter that can lift around 130Kg (286lb) with only the power of a human cyclist (about 400W):
http://www.popularmechanics.com/flig...rize-15682369/

Atlas Human-Powered Helicopter - AHS Sikorsky Prize Flight (1 min 45 sec)

[R_Lefebvre]

Yes, fair point. I was actually going to use the example of a 450 with a 1 Mile blade, but that's so extreme that I toned it down a bit.

I think the truth lies somewhere between your example, and the 1 mile blade. And not just because of structure.

At some point, the skin friction would be so high, I don't think that a human could rotate the blades.

[Icanfly]

really horrible flat leading edge they have,

*

Thickness in the blade will cause drag, angle of attack too, not enough aoa and the airfoil is pushing more air than it is using to lift. Does wide always mean thick? In the case of mavs yes, I have some of them 700x 70mm, 1cm thick (?).

I once saw a vid where an airplane was at a greater angle of attack than cruising and before stall. The streamers placed on the wings showed more attachment at the greater attack angle and showed detachment at cruising angle.

When your talking airflow you have to think about compression and vacuum of a fluid mass. Move any other mass through it and it has to go somewhere temporarily. Move a solid through it and it can be manipulated, that's what blades do while looking to OPTIMIZE what the things can do to your benefit.