Synthetic rotor blade
 

Looking at the idea of a rotor blade that can have its surfaces moved by an internal venous system, a bit like certain parts of ones body! Has anyone else tried out this concept Bug

ONERA (France) are doing research into tip servos moved by piezo-electric to damp out blade vibration. Problem is getting power to system - AC contactless slip ring transformer makes sense to my mind.

bugdevheli;
Since you asked: :)
I once considered developing a control arm that acted like a snake. It had 3 compartments with flexible walls mounted radially about the central longitudinal axis of the arm. This set of three compartments was repeated many time down the length of the longitudinal axis. The motion of the 'arm' was to be controlled the volume of fluid that was inserted or extracted from each of these compartments.

Your idea:
I assume that you may be thinking of threading tubes into the diagonally laid-up flexible skin (fiberglass) of the blade to provide active blade twist. And/or spanwise tubes to change the profile or camber of the blade. If so, it might just work.

Dave

Air Muscle
 

The issue I would have is what happens when the fluid (air/oil) leaks? The idea worked in an air muscle manufactured by The Shadow Robot Company.

http://www.efunda.com/sponsors/inven...scle_Intro.cfm

It's definitely an interesting concept!!

How about an Electric Muscle?

1. Iron filings in a liquid are inserted into a mold.
2. A large magnetic field aligns the filings.
3. The liquid cures into a gel.
4. This gel is then located between the poles of an electromagnet.
5. Applying power to the electromagnet will realign the filings and thereby change the shape of the gel.

The real issue is asking how much gain for the complexity and weight. The shape of the airfoil is not a big driver, but the chord certainly is.
Any bright ideas for making a variable chord blade are worth lots.

Skinny blades for hover, fat blades for high speed cruise could add 5 to 10% to the payload of a typical helicopter.

Electric motors and piezo actuators work for me. The difficulty for direct blade actuation is always designing for high g and supplying control signals and power. Slip rings are bad news, but brushless AC makes sense.

There would be large benefits in a blade with variable camber, particularly if system was fast enough for a cyclic control. Thin cambered aerofoils prefer a narrow range of AOA, with the point of stagnation right at the leading edge. If blade could be pitched to keep front aligned with incoming air, camber would produce lift control. Ideal operation would have blade operating close to stall (Ct/sigma = 0.125).

The downside is varible pitching moment, which puts more load on swash plate and hydraulics. Perhaps for this reason a better design is variable chord in a constant camber design.

By the time this has been optimised it will likely need many CFD/Tunnel/Tower hours to produce a marketable solution. Best a privateer can do here is to demonstrate a concept system...