LoonyBob

'Course it has to be rotating; by "autorotation", I was referring to the condition whereby the velocity distribution across the disc gives such a low AoA near the centre, that the lift vector drives the blades around - as per gyrocopter, or helicopter in a tizzy. What about adding a "choke" to the compressor inlet? Once flamed out, if no air was allowed into the compressor, the rotor would be spinning in close to vacuum, so not braking the prop...

Errum, a small radius LE may give a quick break-away, or it might give short-bubble separation - which in turn may result in a LE stall character, or a TE stall character, depending on what's behind it... the "original" CY, about 9.3%? T/C, has quite a small LE radius. Certainly a lot of WW1 airfoils w/tight LE radii gave bitey stalls. The Gottingen 398 (from memory) is a bit of a weirdo; it has a high maximum lift coefficient at lower Reynolds numbers, which works out quite well for the Thruster T300/500... Va, Vb, and Vc are very close! Interestingly, if you use the NACA system to expand the ordinates of CY to 12% thick, it becomes astonishingly close to 4412. As a speed freak, I don't like 4412's pitching moment; but for a STOL aircraft, that scarcely matters. Yes, planform, twist, and Reynold's number, dogteeth, slots, slats, VGs... HS size and position... the Jodel wing is quite a sophisticated solution to the challenges of a small runaround. WRT section changes, yes indeed - the Jodel uses a 5-digit section for the constant chord bit, then transitions to (ignoring the aileron) what looks like Clark Y at the tip. This combination was popular for a while; there are a few gliders with the same mix (can't remember which, offhand!). Interestingly, most such transition by straight generators, meaning the intervening airfoils are unknown/untested... there is no telling where along the span, the separation may transit from TE to LE. Caproni made a few gliders that used "step" transitions, and seem to lose no performance as a result.

Idiot-resistant is the best I can do! The energy to be disappated is calculable, and not particularly huge for a wooden prop on a 150-kt 600kg aircraft - bearing in mind that it's an emergency device, not a frequent-use item. Consider how long a wooden J2200 prop keeps spinning if you close the throttle at 90kts. I'd favour a featherable unit myself, but weight and cost are factors. If it meets an airworthiness design standard, the engine failed criteria will be specified. Nev, we may be using different definitions of drag coefficient... if the pitch setting is coarse enough to avoid autorotation (partial reverse flow), the mean drag should be of the order of 4~6 times the maximum full-power thrust, which is still less drag than a solid disc of 1.15 times the actuator disc area. With an adjustable pitch prop, which will feature less blade twist, it will be higher; indeed, at several hundred knots, such would likely begin to autorotate; but without autorotation, I can't see how the prop can transfer the momentum.

The Clark Y, and 43012, were far and away the best low Reynolds number sections tested by NACA... 43012 doesn't have the most benign stall, but as used in the Jodel D18, the upper surface fabric bulges just enough to give it a trailing edge first-stage stall, nice and easy. The Austers with 23012 (j5?) were capable of stol performance, and the stall was manageable. CY and CYH both have very progressive TE stalls...

How about fixed pitch wood & a brake?

Shortage drives up prices; simple Free Market economics... The sun is nuclear, and it does shine all the time, just not continuously on any one bit of the earth's surface... the solutions are there, but the economic incentive is not.

Never had to do that in a Thruster... I suppose whatever worked for a Spitfire would work for the LK1. By the numbers, it's a pretty efficient solution for the science of the day.

Whatever the factor of the rated thrust, the Cd surely won't be more than ~1.15?

Soz for the delay, local electrical storm... Yep, CS with feathering ability pretty much a must. Or a high-bypass fan!

Where to begin? New principles? I thought the 1950 Rover JET1 used regeneration; I'm sure the 1965 GM Turbine truck did. Good on 'em for having an R&D effort, anyway. I though heat engines gave a maximum possible thermal efficiency approximating to the expansion ratio by cycle temperature ratios, divided by the absolute ratios. Williams persued this, and ran into stability problems with 3-spool engines. A single turbine ain't gonna cut it... Because a gas turbine is only burning ~4% of the air passing through it (I believe the more recent airliner burners better this, but nothing small), a lot of the energy in a turboshaft is returned via the exhaust jet; and the efficiency of the jet is directly proportional to the speed, which light light aircraft ain't meant to have. The Dreher Baby Mamba was inspirational, but a wee bit wee for what we want. I confess to being fascinated by the possibility of affordable micro gas turbines - burning alkylated electrolised hydrogen? - but the challenges are very real.