And now for something completely different:

From Budd Davison's writeup regarding the Zlin526:

http://www.airbum.com/pireps/PirepZlin526.html

"The local tire-kickers usually start conversation with one of two
questions. Is it a Chipmunk, and what're the gizmos on the spinner? I
skipped the first question, but my own opening remark was that the
spinner looked like a bomb fusing device. In reality, the two-piece
spinner with the fins around it is part of the best constant-speed
propellers either side of the Iron Curtain.

If you press on the spinner, where it says "do not press" (I couldn't
resist), you'll find it moves in and out a half inch or so. It also
rotates, independent of the propeller, driven by the little vanes
around its circumference. This rotation drives a hydraulic pump
contained within the hub, and when the spinner dome is pushed fore and
aft by dynamic air pressure (proportional to airspeed), it actuates a
valve that bleeds hydraulic pressure to the prop blades, changing
their pitch. While you're flying, you set your power with the throttle
(there is no propeller control) and forget about it. Even at full
power, straight down, the engine will only turn up to the preset 2500
rpm, but you'd be doing 9,000 mph, pronto. If you watch the spinner
while you're flying, it looks pretty weird because it will stand still
for a while, then back up or move ahead, but it's always moving in
relation to the prop. The Avia propeller people came up with a better
mouse trap on this one."


Regards,

Matt-

This has been around for years and it never really caught on.
I think even Cessna offered it on the 172 but apparently there were no takers.

Avia was founded in 1919 and produced aircrafts until 1960, aircraft engines until 1988 and propellers ever since the company's foundation.


The company Avia-Hamilton Standard Aviation Ltd. was founded in 1992 year, as a joint venture with foreign majority capital investment, created by joint forces of the important aviation firms. On the Czech part that were Avia.a.s., Walter a.s. and Aeronautical Research and Test Institute a.s. and on the foreign part the world-wide known producer of aircraft propellers and other major components - company UTC Hamilton Standard Division.


The new company inherited the tradition, experiences and trade mark of Avia a.s., one of the most important producers of the aviation technics in the central and Eastern Europe, founded in 1919 year and the same features from the company UTC Hamilton Standard, founded in 1918 year.


That connection is resulted into more than 150 years of combined engineering, research and development experiences in the field of the aircraft propellers guaranteeing goodwill and reliability to the products in world-wide scale.


The possibility to use the Hamilton Standard trade mark known in a great majority of the aviation population world-wide played an important role, especially for the "heritage" propeller blades manufactured by Company under license agreement.


Further ownership structure change was performed in the end of 1998. Mr. Gerd Muehlbauer, the owner of aircraft propeller manufacturing company MT PROPELLER Germany, replaced the Hamilton Standard company and became the majority shareholder. During the year 1999 the company name was changed to AVIA PROPELLER.

The new AVIA PROPELLER is strong and modern company able to deliver the highest quality products and to develop the most up to date aviation technologies.