Automatic variable pitch props

Eric Page wrote:

DUC Hélices also offer all carbon fiber CS props, in both electric-over-hydraulic (controller similar to the Airmaster) or pure hydraulic (blue push-pull knob).  I have the pure hydraulic 72" 3-blade FLASHBLACK-M.  I haven't installed or flown it yet, but my best estimate is that the total installed weight, with governor and control cable, will be in the neighborhood of 21 lbs (9.5 kg).  Quality of the parts I received appears excellent.

European website: http://www.duc-helices.com/

USA website: http://www.duc-propellers-usa.com/

It seems that the DUC inflight/constant speed propellers are much like many other European designs, in that they use a linear actuator (electric or hydraulic) to move a lever (s), connected to a rod (within hollow prop shaft), which then moves the in hub pitch change mechanism.

Airmaster have the pitch change motor in the hub - power/signals is via a slip ring, that in my case delivers its message through the same hollow prop shaft.

Intuitively I would have thought (wrongly) that the Euro system would be heavier of the two concepts.

I would speculate that the Euro system, with its rods & actuator on top,  may require a higher cowling than for the Airmaster.

Airmaster have a, deservedly, excellent reputation for quality workmanship & durability of their systems. My props fit & finish is outstanding.

Hi Sean,

I thought your comment that you would not again install a CS prop on a light aircraft was interesting, and it’s nice to hear that honest evaluation from an owner who has one.   I have a 912iS on a Bristell and I have considered if I would install a CS prop once they are allowed on LSA here in America (likely in late 2024)   

Currently I’m running a DUC Flash 3-blade ground adjustable prop and I’m quite happy with the performance. A CS prop might provide a few extra knots and marginally better climb, but the trade off is extra weight, complexity and cost.  I have come to the conclusion it’s just not worth it on a 100 HP LSA.  It seems like certified aircraft manufacturers came to that conclusion long ago. The Cessna 172 is the most popular piston single ever produced, and with the exception a couple special models, they have always been fitted with fixed pitch props. Cessna, and their customers, decided the small performance gain just did not justify the extra cost and complexity.  

Hi Jeff - On small light aircraft, like my Sonex, the performance gain, in fitting a CS,  is real but marginal.

Having said that, you might like to read up on http://worldrecordplane.com/. Robins record beating Sonerai VH-SGS and now his highly modified Sonerai VH-SRS, both use CS props to help in achieving astonishing Max & Cruise, Climb speeds, with standard Rotax 912ULS.

What I take from this is - if you have the right airframe/engine combination, a CS may do wonders. If you are like most of us, lacking in  the aerodynamic design field,  your every day baby will only gain a few knots for a lot of dough expended.

Also - most Rotax 912 powered aircraft are in, what I would term, the recreational end of the aircraft species - they are all about relative simplicity and economy. True many of us (me included) are seduces by fitting our baby out just like the big boys (CS / Glass Cockpit / Autopilot/ Retractable undercarriage / etc ) but I admit this is sort of corrupting the initial concept.

I own a Sling 2 which is powered by  a Rotax 912 IS

An  Airmaster  constant speed propellor and Electric controller (Whirlwind propellor)

I have found that this configuration combination delivers good alround performance

Very happy with my setup.

Hi Glen,

Yes of course they work BUT it's the cost versus benefit question, in our usually, small, relativly low power, simple aircraft. Then there is a weight, complexity (potential failure) penalty on top of that.

Similar Sonex/Rotax 912 ULS aircraft to mine, with fixed pitch props perform almost as well - slightly longer ground role & slower in cruise (for a given rpm).

I won't be removing my Airmaster but as I said before, in the unlikly event there will be a third small aircraft in my life, I won't be going to the expense of a CS prop.