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Old Sep 10, 2002, 07:01 PM
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Cambridge, MA USA
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New 2m electric sailplane

Check out the teaser photo at
http://www.polecataero.com
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Old Sep 10, 2002, 08:28 PM
MKH
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Ohio
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Is that an electric Allegro, Allegro-lite, or something close to it? Let's hear the full scoop!
Marcus
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Old Sep 10, 2002, 08:39 PM
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chlee's Avatar
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Hmm, I think I do detect some Allegro-E-lite heritage...

(wiping drool off keyboard)
Chung
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Old Sep 10, 2002, 10:32 PM
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wings is built heavy ???
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Old Sep 11, 2002, 12:47 AM
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Quote:
Originally posted by MKH
Is that an electric Allegro, Allegro-lite, or something close to it? Let's hear the full scoop!
Marcus
Yeah, sorta. It has the AL airfoils, very slightly modified for the full-span flaps/ailerons. Denny's own new E-pod. AL boom with a new nifty molded stab mount.

The wing looks heavy, but it's not. It has VERY fast construction using large-diameter stepped hollow CF rods for spars, plus a few secret tricks. Don't want to say more without Denny's OK.

Unlike with typical carbon-tube wings, the airfoil fidelity on this one is excellent. Denny reports good speed range with reflex and camber.

It climbs well on the 2.5:1 geared S400 and 9x5 prop. This is a very inexpensive system, less than $50 I think.


The glider is very strong despite the simple construction. The same wing on a plain winch-glider version which may be offered (no promises, though) will take about 50 lb of winch pull. That corresponds to a brisk 65 mph climb.


Flying weight for the 5-servo E-glider will be about 26-27 oz. Poly 2-servo E-glider will be more like 22-23 oz. Winch glider (if offered) will be less than 20 oz. Note that these are for a 2m span and 540 in^2 of area. This glider will thermal much better than the usual 1.8m LMR stuff.
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Old Sep 11, 2002, 01:48 AM
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London
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Not another one!

No! Not yet another plane to add to my growing wish list!!

How do you guys decide which planes to buy?! Its driving me nuts...

When will it be available?

Aki
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Old Sep 13, 2002, 10:44 AM
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Anchorage, AK USA
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Now that looks like just the thing for F5J speed 400 competition... I'd been thinking about rebuilding my Lil Bird 2 HLG with a couple extra wing bays and a spoiler, but the "Polegra" looks better. Trailing edge control... good.

How about that X tail though... is it tough enough to take landings with a 27 oz plane on top of it, or are you just hand-catching it like a big DLG?

Doug
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Old Sep 13, 2002, 05:08 PM
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Quote:
Now that looks like just the thing for F5J speed 400 competition...
That's exactly the target application, at a low cost.


Quote:
How about that X tail though... is it tough enough to take landings with a 27 oz plane on top of it, or are you just hand-catching it like a big DLG?
The sub-fin doesn't see big landing loads because there is little mass back there. Everything behind the TE weighs less than 1.5oz. If you fly on abrasive surfaces, then a few layers of sacrificial tape over the bottom edge of the fin should do the trick.

Moving the whole vertical tail above the boom is possible, but not a good solution. The stab will then be close to the ground and at far greater risk. Better to let the sub-fin absorb the (small) punishment.
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Old Sep 13, 2002, 05:19 PM
MKH
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Ohio
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Denny emailed me with the basic specs of this design, and it sounds terrific. The maiden flight was a 25 minute flight after a 30 second climb. A poly version will follow, for those of us who's tx's don't have full TE control/programming. Finally, a super light 2m with good airfoils, and it will actually climb out on Speed 400 power.

Marcus
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Old Sep 14, 2002, 01:43 PM
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Anchorage, AK USA
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Mark,

How many cells are you running with the 2.5:1 gear drive? I've mostly seen something closer to 4:1 and 8 cells.

This does look like a winner... the closest commercial product I've seen so far is the Pulsar 2M F5J imported by Starflight... which looks very nice, but is also relatively expensive... and doesn't have a rudder.

Our local club has been mulling the idea of a electric sailplane contest next year, and this could be an ideal platform for it. I hope it is released soon!

Doug
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Old Sep 14, 2002, 02:24 PM
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Quote:
Originally posted by DRFranklin
How many cells are you running with the 2.5:1 gear drive? I've mostly seen something closer to 4:1 and 8 cells.
Most likely it will be a 6V S400 on 7 cells. Denny mentioned he might also try a 4.8V S400 on 6 cells. This may end up being dictated by the capabilities of the ESC.

A 4:1 gearbox on a clean S400 glider is overkill IMO. There is little climb rate benefit after 2:1 or so, and the bigger and heavier prop is a drawback in the glide.
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Old Sep 14, 2002, 02:42 PM
MKH
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Quote:
Originally posted by markdrela A 4:1 gearbox on a clean S400 glider is overkill IMO. There is little climb rate benefit after 2:1 or so, and the bigger and heavier prop is a drawback in the glide. [/B]
I'm glad to hear you say this, Mark. I've seen alot of AULD's, including Speed 400 AULD's, and the guys with 4:1 or higher, and big props, seem to climb so slowly. They climb out steep, but slow, then mush a bit, drop the nose, then pull up steep and do it all over. Meanwhile, the guy with a 6x3 folder on direct drive is climbing at a shallow angle, but faster airspeed, and is actually gaining altitude just as fast. I never understood it, but the big prop efficiency may not be what I thought it was.

As for Denny's new ship, his email to me said it was running on 8x500 size pack. He also said the 29 ounce weight could be easily reduced, as his plane was built in a hurry, uses a 4x300nimh rx pack, 5 servos, etc.

Marcus
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Old Sep 14, 2002, 06:45 PM
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Quote:
Originally posted by MKH

As for Denny's new ship, his email to me said it was running on 8x500 size pack. He also said the 29 ounce weight could be easily reduced, as his plane was built in a hurry, uses a 4x300nimh rx pack, 5 servos, etc.
Denny ordered a 6V motor, but incorrectly received a 7V motor. So he had to use 8 cells. With one less cell, lighter gear, and more careful construction, 27 oz is a realistic weight.

The separate 1oz RX pack may be unavoidable. There aren't any ESC's out there that will reliably drive 5 servos. The poly version will be soooo.. much lighter. You not only lose 2 or 3 servos and wiring, but the separate RX pack as well. At ~23 oz, it will be a real S400 rocket.
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Old Sep 14, 2002, 06:58 PM
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I've seen alot of AULD's, including Speed 400 AULD's, and the guys with 4:1 or higher, and big props, seem to climb so slowly. They climb out steep, but slow, then mush a bit, drop the nose, then pull up steep and do it all over. Meanwhile, the guy with a 6x3 folder on direct drive is climbing at a shallow angle, but faster airspeed, and is actually gaining altitude just as fast. I never understood it, but the big prop efficiency may not be what I thought it was.
It's simple. Doubling airspeed has roughly the same effect on ideal prop efficiency as doubling the diameter. If the airframe is clean so that the high airspeed doesn't chew up too much power, climbing shallow and fast on a smallish prop is a perfectly good alternative to climbing steeply and slowly on a big prop. It's lighter, gives less folded-prop drag in the glide, and is probably cheaper.

In any case, for any given airplane/motor/battery combination, there is always an "optimal" gearing and prop diameter which gives the maximum climb rate. In practice, you clearly want to have a smaller gearing and smaller prop than this optimum, because this gives a lot of secondary advantages. The 4:1 setup may be on the "wrong side" of the optimum. Dunno.
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Old Sep 14, 2002, 08:36 PM
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Portland, Oregon
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What's the expected release date and target price range?

Thanks,

Victor
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