Yes, Matt.

Mainly that the limited diameter of the prop limits prop efficiency. In the chain Battery->motor->prop-> useful thrust, prop efficiency is the single largest loss. You'll get around 50% at the power/diameter/airspeeds we are dealing with here. More blades aren't necessarily better. I'm no fan of sustainers. For a little extra trouble make the damn thing self launching. I am a little surprised at the willingness of glider pilots to accept ANY performance loss from the FES though. BTW a TE probe typically causes about 0.7% of the drag at 100 KIAS on a 400 Kg modern glider.

The Peszke GP glider designer has his views on the matter and has made it clear where he stands as the GP series self launchers have retractable propulsion units. Having seen video of it in action I wouldn't expect any trouble. Seems to take about 4 seconds to extend and retract. Given the number of manufacturers making linear actuators in all sorts of sizes I doubt there is a generic problem with them. Seems to be that both Peszke and FES get their motor/controller/battery tech from the same source. Yes there is a drag penalty for the extended engine on a pylon. With proper design it can be minimised (I'd close the doors with the engine extended). The FES drag penalty in powered flight is more subtle. To produce thrust the air has to be accelerated through the prop. Now VERY APPROXIMATELY we are talking around 1.4 times the flight velocity which gives twice the drag and this air passes over the entire fuselage, wing root, fin and probably part of the tailplane, though at reduced velocity for the latter. With the retractable pusher of the Peszke system, only over the fin and tailplane. Interestingly both the Peszke designer and the FES designers come from a model aircraft R/C glider background. As does the electric propulsion tech.

A few other considerations:

The system appears to weigh 40 Kg. Better have motor glider or turbo wings on the glider as it is all non lifting parts. Probably not an issue with recent gliders as I suspect all of them are built with the stronger wings to prevent embarrassing mistakes. They do seem to have learned about Murphy's Law since the Libelle aileron drives were designed.

You can bet some idle idiot will try to unfold a prop blade on the ground. Will this be OK or will it cause a problem? The TOP certainly could have a problem if ONE of the three blades was manually opened. Two simultaneously was OK.

What happened to the Australia required nose release? Only self launch on lightweight gliders so you'll need a tow.

From the website: "Cell manufacturer claims that at discharging with 1C rating (horizontal flight) life expectancy of batteries is around 1500 cycles. After that the battery will still have 80% of the original capacity" . At full power they are pulling 200 amps, around 5C., not 1C.

DO remove the batteries for charging and put them where the house/hangar etc won't burn down if things go wrong. The R/C people have burned down a few houses and I heard of one near new VW Transporter carrying models where batteries were being charged and it had to stop, be abandoned and burned to the ground.

I do agree with Richard Frawley that outlanding sucks for many reasons. After 62 real ones in farmers' fields I've had enough. Mr Lycoming willing, there won't be any more. Besides with the consolidation of agribusinesses, agricultural quarantines (remember the foot and mouth outbreak in the UK where cross country gliding was banned for a season?), foreign ownership and contamination issues with GM crops you may find that the "social licence" for outlanding will go away(as much as I hate that term).


At 09:31 PM 9/19/2016, you wrote:
I think what Mike was referring to was not the drag of the blades in gliding flight but the efficiency of the nose-mounted propellor in climb. Reliability through simplicity is definitely a factor, but the FES is not much good if you want to self-launch (prop clearance).

Borgelt Instruments - design & manufacture of quality soaring instrumentation since 1978
tel:   07 4635 5784     overseas: int+61-7-4635 5784
mob: 042835 5784                :  int+61-42835 5784
P O Box 4607, Toowoomba East, QLD 4350, Australia  
Aus-soaring mailing list

Reply via email to