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).
Mike
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
www.borgeltinstruments.com
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
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