Flexible "self-variable" pitch props?
 

I should be doing something else but have a query - google does not reveal the answer nor does a pprune search...

Does anyone know if there any prop designs where the material is such that as you increase the engine rpm such as at take off, with zero forward speed and where the angle of attack of the blades is large, the prop "bends" under the resultant force of the airflow to provide a finer pitch, and when you enter the cruise and TAS increases, as you decrease engine RPM the prop bends back and coarsens? Sort of a self changing variable pitch prop dependant on engine rpm?

i'm sure I heard one of my old instructors talking about it years back about bush planes, but can't find anything on the web...could be using the wrong terminology.....

Sounds like a good, low maintenance idea to me, similar to the F1 teams who got banned from using "flexible wings" where more downforce was provided at low speeds, and less drag at high speeds.

as i said i should be doing something else but thought it'd be more fun to think about something completely random for a few mins...:}

cheers!:ok:

Check with the Experimental Aircraft Assn. There have been scimitar shaped props that tend to automatically adjust to airspeed and load.

The Aeromatic props of the 1940s and beyond have angled blades and counterweights that adjust blade angle automatically. The concept is great, but the wood blades in use at the time were clubs for airfoils. Planes like the Bellanca Cruisair with a large differential between cruise and landing speeds gained the most benefit from them.

GB
former owner of 1946 Bellanca Cruisair with Hi-Cruise Aeromatic prop.

CHeers GB interesting stuff hadn't really thought about that sort of setup. Thanks! So they do exist in some ways. Not hugely common though over here, not heard of that at all before. I'll have a look at the EAA.

Anyone know of any where the actual properties of a prop itself would cause it to bend/twist - i.e. with no counter weights/hub mechanism, just a single piece of wood where the blades twist under load?

Cheers!
Pheeel,
still putting off work:}

They also exist in the automotive industry as radiator fans...

I've flown a Globe Swift with an Aeromatic prop, too.

The scimitar shape has the end of the blade trailing, so air load flattens the angle of attack, somewhat akin to the wing warping of the Wright Flyer.

If I were to make such a prop, I would use only Shagbark Hickory or Osage Orange. Both are strong, yet flexible. Henry Ford made nearly a billion hickory spokes for the Model T's wheels. No other commercial wood has the strength, yet flexibility, of a true hickory. It grows only in the US and Canada, I believe, which is why other countries' cars were earlier to adopt wire wheels in quantity.

Osage Orange is even much tougher than hickory, but not widely available. I've seen hickory used for firewood.

GB

Interesting concept. Found this reference to research into ship propellors with this feature, with some discussion of required features

Wavelengths: Carderock Division to Study Flexible Propeller Blades

...and with a bit more looking found the same concept in research for aircraft

A Low-Noise 3-Blade Composite Propeller for General Aviation Aircraft

Seems to have sunk without a trace...

Some 15 years ago a German homebuilder developed a motorglider prop with automatic angle adjustment. It was a design where the axis of blade rotation was somehow angled with respect to the prop shaft and with respect to the blade axis, so centrifugal forces were turning the blades to high pitch while thrust was driving them to low pitch, thus giving a self adjusting feature. He extensively tested it (together with the rotary engine griving it) on a test bench and in windtunnels, obviously getting very good results.
Never heard about him to actually finish the plane.
And of course there are still autonomous fully automatic variable pitch propeller available on the market, testet in service for millions of flight hours, for example the V-503Afrom AVIA in Chech Republic.

They looked at the use of PZT material woven into Carbon fibre fan blades a few years back, but mainly used in turbofan engines I believe. Was "cutting edge" back in 01.

High Temperature Materials (Aerospace Research Institute - The University of Manchester)

bottom of the page.

There's a fairly complete description of the Aeromatic prop here.

Warnke :ok:

No, I'm not being offensive - there was an American prop called the Almost Constant Speed built by Mr W.

Any help?

Sir George Cayley

Anyone used a Warp Drive prop? [Archive] - VAF Forums

Several links there.