E-Props ...who has first hand experience with these

[LoonyBob]

Under static conditions, propellors are running with a very high degree of recirculation, which remains significant up to 20~30kts foward speed (light aircraft). Recirculation gives a weird spanwise inflow velocity distribution on the blades, and so a weird lift (thrust) distribution - not very representative of flying conditions..

A look at fixed pitch props on TC'd aircraft (Cherokees, 172s etc) shows that a maximum static RPM of ~85% of full power RPM, will allow a healthy RoC, and WOT level flight without engine overspeeding; a 65% cruise of 1.5~1.6 Vs1 is typical, but 75% gives not much increase, as the prop is becoming depitched. This can be tweaked by adding a bit of pitch - a "cruise" prop - at the expense of a longer TOD.

Fitting a CS prop to such a beast will give markedly better TO performance, simply because the engine is allowed to develop near full power for the entire TO roll and initial climb. At the top end, the CS prop will not change the airframe's power needs, but should offer 5~8% better cruise.

Whilst Cherokee 172s are somewhat draggy, RAAus machines range from very draggy to very clean; however, a static WOT RPM of ~85% of full power RPM is a good starting point.

Note that most fixed pitch props for TC'd aircraft have "overtwisted" blades (twisted beyond optimal performance for the speed range in question), because (a) tradition [most propellor makers still don't use blade element theory!], and (b) it tends to meet the overspeeding requirements for certification without much difficulty.

Most (all?) composite RA blades are a tad undertwisted, which limits the propellor's efficient speed range.

 

In summary: a CS prop will yield near-optimal TO performance for any aircraft, though not much if Vs1 >= 30kts; and should give optimal cruise, but not huge increases, subject to blade twist. A VP prop is a step in the right direction.

The D18 gets a ground roll of ~110m, a healthy climb, and will cruise at Vno on a fixed pitch prop. The climb and fuel burn can be improved by drag reduction, and reducing the TO roll by ~15m is not worth the weight of a "live" prop...

[LoonyBob]

1 hour ago, skippydiesel said:

Hi Kyle,

 

Three questions:

• Is there a CS (Glorious) E-prop in Australia?
• Why have E-Prop opted for hydraulic pitch change, rather than one of the electric systems?
• Is there an In-Flight-Adjustable variant of the Glorious (or plans to offer one)?

Electric props tend to have slow actuation (the forces can be quite high), and I do know that an early version of a well-known German VP prop on a 503, used to "hunt" when using a CS controller, and sometimes allowed engine overspeed at the end of climbout. Hydraulic actuators give both more force & more damping...

[skippydiesel]

My limited experince is with the Airmaster electric system and way back when I was in GA, hydraulic .

 

So far (about 60 hrs) I can say the Airmaster is not at all slow to move between changes, seems to have no problem adjusting pitch, whatever the situation and neither hunts or allows overspeed.

 

The Airmaster can be used like a traditional CS, with the pilot controlling all pitch changes or in semi automatic ie preset Takeoff , Climb, Cruise.

 

[facthunter]

Adjusting the pitch stops is the only way to be safe with overspeeding.. Nev