Which sustainer system would you chose for your sailplane?

I wonder if nose cone in trailer has to be changed?

I think there is little doubt that the FES system has lower drag
(thus better performance) than a pylon mounted electric
motor. Pylons are weight and complication that the FES just
doesn't have. With the pylon stuck out and the engine not
running the drag will be much greater than a failed FES. Failed
pylon mounted engine/props also produce turbulence at the
elevator, masking feel, not a nice scenario.
Are there performance figures for pylon mounted electric
sustainers? Do such gliders exist?
I know it's not a correct comparison (as the props are so much
larger being self launchers) but with engine out and a
windmilling prop the 18m DG800B goes from 48:1 to 16:1; the
20m Antares20E goes from 55:1 to 30:1.
Anybody have figures for a failed FES? I'd guess the glide
angle would still be pretty good.
Dave Walsh

On Wednesday, January 13, 2016 at 5:30:05 PM UTC-6, Dave Walsh wrote:
I think there is little doubt that the FES system has lower drag
(thus better performance) than a pylon mounted electric
motor. Pylons are weight and complication that the FES just
doesn't have. With the pylon stuck out and the engine not
running the drag will be much greater than a failed FES. Failed
pylon mounted engine/props also produce turbulence at the
elevator, masking feel, not a nice scenario.
Are there performance figures for pylon mounted electric
sustainers? Do such gliders exist?
I know it's not a correct comparison (as the props are so much
larger being self launchers) but with engine out and a
windmilling prop the 18m DG800B goes from 48:1 to 16:1; the
20m Antares20E goes from 55:1 to 30:1.
Anybody have figures for a failed FES? I'd guess the glide
angle would still be pretty good.
Dave Walsh

If the FES fails, the blades fold back. Or, don't unfold in the first place. Only drag penalty would be on an SH if it didn't align so the nose cone isn't faired with the fuselage behind it. That is another part of the beauty of the FES.

Steve Leonard

On Wednesday, January 13, 2016 at 1:44:05 PM UTC-8, Casey wrote:
I wonder if nose cone in trailer has to be changed?


Photos of the new nose cone:

https://www.facebook.com/lzdesign.si...31887170295631

On Wednesday, January 13, 2016 at 3:30:05 PM UTC-8, Dave Walsh wrote:
I think there is little doubt that the FES system has lower drag
(thus better performance) than a pylon mounted electric
motor. Pylons are weight and complication that the FES just
doesn't have. With the pylon stuck out and the engine not
running the drag will be much greater than a failed FES.
Dave Walsh

Dave,

I don't think so. A small prop is not as efficient as a large prop. In terms of thrust, it's better to move a lot of air slowly than a small amount of air faster. The Wright brothers got that part right, big props turning slowly are most efficient. In most glider applications, a pylon allows for a larger prop that does a nose mount. So if available energy limited, a pylon mounted larger prop offers significant advantages. Other examples are the human and solar powered aircraft

With the pylon prop stowed, there is essentially no drag penalty. The same cannot be said for FES, though I don't know what any drag penalty might be. On MKIV customer contacted me because his yaw string did not stream straight back in flight but stayed off to the side. We determined it was due to flow disruption from the stowed FES blade/s. Moving the yaw string further aft on the canopy apparently solved the problem. The point being that the stowed blade was not just tripping laminar flow behind the blade (I think stowed at roughly 3 and 9 o'clock) but was influencing a much larger area, as the string was obviously at 12 o'clock. Strange.

I agree a failed FES should have less drag than a failed and still extended pylon and prop. And the risk of being stuck with an extended but non functional FES should be near zero. Whatever degree of risk, for a stuck extended pylon, one might assign, my understanding is it's fairly rare in the ASH26E community (self launch, but the idea is the same). The engine's been running, so when it's time to get rid of the noise, the battery has adequate capacity to drive the linear actuator to lower the pylon - and the actuator has an easy time of it as it's not fighting air flow as it would be when extending the pylon in flight. I imagine there have been more instances of failure to extend pylons than getting them stowed.

Well, the main problem I see with FES is that it's plain ugly. Stemme has at least found a solution that keeps the blades out of sight.

Bert
Ventus cM TW

On Tuesday, January 12, 2016 at 1:52:08 PM UTC-8, wrote:
On Tuesday, January 12, 2016 at 3:16:41 PM UTC-5, Andy Blackburn wrote:
On Thursday, January 7, 2016 at 10:40:33 PM UTC-8, Surge wrote:

How about FES in an EDF (electric ducted fan) configuration instead of pylon mounted FES? The EDF could be mounted in the fuselage with doors than open and close for the inlet and exhaust.
Would this make any sense or be simpler than a pylon mounted system?
Would a smaller prop size make it less efficient and impractical?
The one advantage would be the removal of most of the pitching issue associated with pylon mounted systems.


FES is by definition the front mounted ('F') variety not pylon mounted - just to nit-pick.

As to EDF, you might be able to get one big enough to climb a glider, but the efficiencies would, I suspect, be poor and electric sustainers already face a weight/range tradeoff that is marginal for many pilots. I expect the pylon-mounted sustainers with a larger prop would be the best compromise (reliable and fast deployment, minimal drag, acceptable range, low enough weight for an 18m glider to not face too much of a weight penalty. Whether it is appreciably more efficient than an FES prop would be interesting to know - my guess is they'd be a bit more efficient. FES wins for pure simplicity.

I'd rather carry batteries around than gasoline any day. Internal combustion engines (and turbines) are a recipe for lots of mechanical fiddling and maintenance in my experience.

9B

There are plenty of retractable engine gliders that, due to geometry changes to fit the engine etc, and/or poor doors, may well have as much drag rise over a pure glider as those 2 prop blades.
The down side to front motor is that, for almost all but the light gliders, there is not a good way to get enough ground clearance for a prop that will apply the power needed for self launch.
It is a very clever concept.
UH

To solve the prop size problem, would there be any way to "extend" the props once the glider is off the ground a few meters? And thus turning a FES into a "FEL" or "FEM" (no good acronyms here...)? Surely there is some mechanical way to do this? Has it been or is it being considered?

IMHO, this plus a small 4-stroke generator of 10-20 hp is the perfect system:
https://www.facebook.com/gpgliders/v...5333550523888/

No noticeable drag if it fails to start, electric reliability and extreme range due to the generator.

On Thursday, January 14, 2016 at 4:19:13 PM UTC-6, J. Nieuwenhuize wrote:
IMHO, this plus a small 4-stroke generator of 10-20 hp is the perfect system:
https://www.facebook.com/gpgliders/v...5333550523888/

No noticeable drag if it fails to start, electric reliability and extreme range due to the generator.

Looks nice, but could the drag caused by all those doors (even closed) not equal the drag of a closed FES prop?

Speaking of FES, why not have a single blade? Counterweight in the spinner (it's been around for a long time), fold the prop into a recess under the nose of the plane, cover with a door if you want to be really Gucci...

Kirk
66

Was wondering how the Arcus E's (electric motor from Lange) are selling compared to the gas engine model?