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Old Oct 07, 2002, 11:46 AM
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Robbe Gnat does not fly!

This is the first installment in a new series, entitled "XXX does not fly!!!", with - as first featured model - a Robbe Gnat on the (more or less) stock setup.

Doug's Gnat, Kyosho fan with AP29L on 8 x (3$) CP 1700 cells (t-33 & f-16 stock setup), jeti 50 controller, ca. 260 Watts and about 38 oz rtf. Spray painted only with tamiya acrylic italian red from the spray can (foam safe).

Video here of the Gnat (31MB, 3 mins):

Gnat video


brushless Astro 05 Gnat video
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Old Oct 07, 2002, 01:13 PM
SoCal, Year Round Flying!
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You're too funny Herb!
I wish my jet flew as well!
btw Theres no link to the video?
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Old Oct 07, 2002, 02:14 PM
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Old Oct 07, 2002, 05:30 PM
SJ
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I just ordered one.....
I have tons of rc2400 cells lying around.
Could I use 8 of them in the gnat with the ky fan and ap29l-V motor?

And, will it be hand launchable ?
As I can see, it has the same wing area of the ky F-16, so it should handlaunch ? right ?

SJ.
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Old Oct 07, 2002, 06:24 PM
SoCal, Year Round Flying!
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Are they still available? I thought they were discontinued? I watched Doug fly this and it really performs! It handlauched very easily.
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Old Oct 07, 2002, 06:59 PM
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Gnat

SJ

I would like to know where you ordered one from......
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Old Oct 08, 2002, 01:47 AM
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United States, CA, Lake Forest
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Quote:
Originally posted by SJ
I just ordered one.....
I have tons of rc2400 cells lying around.
Could I use 8 of them in the gnat with the ky fan and ap29l-V motor?

And, will it be hand launchable ?
As I can see, it has the same wing area of the ky F-16, so it should handlaunch ? right ?

SJ.
Dougs was flown on 8-CP1700s so an 8 cell 2400 pack will add about 4oz. It should still handlaunch ok but will need a good throw. He used a Kyosho fan and the AP-29 motor so you are ready to go!
bmiller, I think it slowed down after I threw it
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Old Oct 08, 2002, 06:33 AM
SJ
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I guess they dont sell like hot cakes in Denmark......
So a few hobby stores stil have them in stock.


ordered mine from http://www.el-fly.dk/

but have also seen them here : http://www.hobby-world.dk/

and here... http://www.avionic.dk/
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Old Oct 08, 2002, 11:54 AM
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Quote:
Originally posted by SJ
... I have tons of rc2400 cells lying around.
Could I use 8 of them in the gnat with the ky fan and ap29l-V motor? ...

SJ.
No, the 8x2400's are too heavy to get the CG right. 8-9 CP1700 is the absolute max on this model, unless you like your batts to lie inside the intake duct.
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Old Oct 08, 2002, 01:00 PM
Dude, where's My Plane?
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Quote:
Originally posted by Herb


No, the 8x2400's are too heavy to get the CG right. 8-9 CP1700 is the absolute max on this model, unless you like your batts to lie inside the intake duct.
Well Herb,,, remember this thread IS called Robbe knat dose NOT fly! So lets rethink our advice here. Of course, you could just not charge your CP 1700s or use a bad cell or two .
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Old Oct 08, 2002, 02:05 PM
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I'm the one that's responsible for getting Doug a brand new NIB Gnat for free . Because everybody says the Robbe Gnat don't fly ...

So I suggested the above power setup to Doug, and after a week of intense building (you know those sleepless nights thinking about how to sand the intakes, hourlong extenuating debates about which cyclovinylpolyurethanecyanoacrylates paints might be ultimately the lightest etc) he came to the field and tossed it into the air, and guess what?
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Old Oct 08, 2002, 02:23 PM
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hi everyone,

iam new to edf and i was woundering if the set-up above would fly a KC F18 w/ a minifan insted of the ky. sorry kind of off the topic.

janssen
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Old Oct 08, 2002, 02:41 PM
Dude, where's My Plane?
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Quote:
Originally posted by Herb
he came to the field and tossed it into the air, and guess what?
Lawn dart?
Salad shooter?
High speed bug blender?
Gravity test device?
ARF = ARC Almost ready to crash?
High price golf tee hole maker?
Worm burnner?
.
Good to here it did well on a stock type setup!
Its amazing to me how much all the little attention to detail adds up durring a build of a kit or from plans. Any time I catch my self deviating from the instructions and saying it will be ok because,,,,,,, I just stop and re-evaluate what im doing .
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Old Oct 08, 2002, 02:42 PM
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Quote:
Originally posted by Herb
No, the 8x2400's are too heavy to get the CG right. 8-9 CP1700 is the absolute max on this model, unless you like your batts to lie inside the intake duct.
I didn't realize his 1700 pack was shoved all the way rearward, my bad!
Unless of course the fan unit can slide back a few inches, you would indeed be limited to the 4/5 sub C cells.
SJ, 550 Kroner is about $72US. That's not too bad for a plane that doesn't fly
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Old Oct 08, 2002, 02:45 PM
Purple power
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Quote:
Originally posted by JANSSENM
hi everyone,

iam new to edf and i was woundering if the set-up above would fly a KC F18 w/ a minifan insted of the ky. sorry kind of off the topic.

janssen
yes, it will fly it. and with decent power. a good low dollar alternative to bl..........gregg
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Old Oct 08, 2002, 02:59 PM
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I second that. This flies great with the AP29L and the mini on 10 1700 zapped cells. Gregg was there to see it.
Steve
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Old Oct 08, 2002, 03:51 PM
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Nice!!! How come I never saw that one?
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Old Oct 08, 2002, 04:15 PM
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Thought you did. Didn't bring it to the show we were at, but I will next time. Thanks Herb.
Steve
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Old Oct 08, 2002, 04:43 PM
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So?

Does this little Gnat fly at all on the stock motor and fan?

Thats what I intend to use.

Or would it be better with a 480 BB?

Mine was NIB 45 and the mouldings look great.

Gary.
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Old Oct 08, 2002, 05:19 PM
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Herb would know the most about that. From what I've heard no or not very well. Herb?
Steve
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Old Oct 08, 2002, 05:36 PM
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The Robbe 410 motor that comes with the kit should be used as a paperweight instead, the RoJet fan can be used as a desktop ventilator in your garage. The 480 BB is too small & too hot, it won't fly the Gnat.
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Old Oct 08, 2002, 05:51 PM
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Cheers Herb

So now I have a mini extractor fan for my air brushing booth.
Why put them in the kit in the first place if they are not up to the job?

Thanks for the advice H.

Regards

Gary.
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Old Oct 08, 2002, 06:01 PM
SJ
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So you guys dont think it will balance with RC2400cell , even if I move the fan all the way to the rear ?

SJ
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Old Oct 08, 2002, 06:23 PM
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Hi SJ

Sorry I can not help. This is my first Gnat I I know nothing about them.

I know this does not help much but some one will get back to you I am sure.

Regards

Gary.
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Old Oct 16, 2002, 01:02 PM
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Probably not, although moving the fan all the way to the back does improve things a bit. Keep in mind that the Gant is made of flimsy very light foam, and breaks apart easily if you put too much weight in it...
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Old Oct 16, 2002, 09:59 PM
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Herb what were the control setups used for the Gnat in the video? Handled pretty nice.
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Old Oct 17, 2002, 10:57 AM
Epic Win or Epic Fail!
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2400's

My Gnat flys on 2400's in a eight cell pack but its specially made in this shape: [] = 1cell

[][][][]
[][][][]

I use the apl29 too and the weomtech 480 fan. It has good performance but I would like more (could be just me thought!). It will loop from a dive but not from level flight. I also bungee it to maximise my flight time. Looks grat on fast low (and I mean LOW) passes puling up into a roll at the end of the runway.

Alan
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Old Oct 17, 2002, 10:59 AM
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Cup

Also does the plastic cup trick restricting the exit help performance?

Alan
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Old Oct 17, 2002, 12:47 PM
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The control method is using one servo on the left to move the left aileron, the other servo on the right to move the corresponding right aileron, and a third servo placed next & behind one of the aileron servos for the elevator surfaces, linked by a rod that goes through the fuse. Seems to work very well.

If you use the WeMoTec MiniFan 480 & AP29L instead of the Kyosho unit, you need to add two extra cells, that is ten (CP 1700 or CP1300) cells. The MF480 on 8 cells delivers the same power as the original stock Robbe Rojet 410 setup, less than 200 Watts. On ten cells the MF will deliver roughly the same power as the Kyosho fan with the AP29L, that is around 300 Watts peak.

The MF480 is about 25% more efficient than the Kyosho fan in converting watts into mechanical work. But some already have an unemployed Ky fan & AP29L lying around.

If you use the MF (or even the Ky fan) a restriction at the tail will increase efflux (=faster model) but decrease static thrust (=less climb). If you have plenty of power you should add a restriction, but if you have marginal power it's pointless.

Doug btw could not resist the urge to go brushless, and stuck an Astro 805 K (?) in it. I think he needs to go to ten CP1700 cells now, the improvement was not so impressive...Maybe gyro hobby sold him a motor that's not really the 805k (kv=4750)???
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Old Oct 17, 2002, 01:29 PM
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Quote:
Originally posted by Herb


Doug btw could not resist the urge to go brushless, and stuck an Astro 805 K (?) in it. I think he needs to go to ten CP1700 cells now, the improvement was not so impressive...Maybe gyro hobby sold him a motor that's not really the 805k (kv=4750)???
Herb: i think the published kv is overestimated by Astro. my older 805k is close to 4000kv in reality.......gregg
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Old Oct 17, 2002, 01:53 PM
Big gov never Works
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New 805K 3-T #18 Kv 3,450. Steve
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Old Oct 17, 2002, 01:59 PM
Purple power
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Quote:
Originally posted by St. Martin
New 805K 3-T #18 Kv 3,450. Steve
Steve: where did that number come from? your measurements?
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Old Oct 17, 2002, 02:01 PM
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Oh I see... Disturbing. You mean AstroFlight does not have its kv figures correct ? Why would they claim figures which are totally off (kv 4750 vs 4000 or 3450)?

http://www.astroflight.com/Brushless.html
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Old Oct 17, 2002, 02:02 PM
Big gov never Works
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Gregg, No, from my astro paper that came with my 805W. Steve
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Old Oct 17, 2002, 02:04 PM
Big gov never Works
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805WKv4,750 805KKv 3,450 Steve
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Old Oct 17, 2002, 02:11 PM
Purple power
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lol........no wonder the built in controllers are under built!. well on 10x cp1700's i get 400w off the charger in a m/f 480. it would be nice if the manufacturer would get the facts straight.

maybe there is a california version, and then a 49state version?
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Old Oct 17, 2002, 02:14 PM
Big gov never Works
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MotoPinion;10-1700cp..284.1 watts mini fan Steve
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Old Oct 17, 2002, 02:25 PM
Purple power
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Quote:
Originally posted by St. Martin
MotoPinion;10-1700cp..284.1 watts mini fan Steve
this is moto calcs # in my application:
Motor: Astro Brushless 05 #805K; 4000rpm/V; 0.035 Ohms; 1.8A idle.
Battery: Cp1700; 10 to 12 cells; 1700mAh @ 1.2V; 0.0032 Ohms/cell.
Speed Control: Astro 805 Brushless; 0.012 Ohms; High rate.
Drive System: WeMoTec Mini Fan 480; 2.7x3.66 (1.3in hub); (Pcoeff=0.506; Tcoeff=0.807).
Ducting: 2.37in D x 6in L (1.6 taper) intake; 2.25in D x 6in L (2.1 taper) exhaust.
Airframe: F18; 195sq.in; 42.3 to 45.1oz; 31.2 to 33.3oz/sq.ft; Cd=0.035; Cl=0.21; Clopt=0.45; Clmax=0.88.

NC = 10
Weight (oz) = 42.3
Batt Amps = 36.2
Motor Amps = 36.2
Motor Volts = 10.4
Input (W) = 376.5
Output (W) = 314.3
Loss (W) = 62.3
Temp (F) =
Motor Ef(%) = 83.5
InPLd (W/lb) = 142.6
OutPLd (W/lb) = 119.0
Elect Ef(%) = 72.4
Fan RPM = 36569
Thrust (oz) = 27.2
Efflx (mph) = 140.2
Time (m:s) = 2:49
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Old Oct 17, 2002, 02:41 PM
Big gov never Works
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I agree , there are a lot of discrepecies. Mine is for the T-33. I don't own a whatt meter, wish I did. I believe I am getting higher watts than what motoPinion says. I am also using zapped cells. While I believe astro overdo its specs. I think motocalc can only tell us what info we feed it. I got on this thread because there is alway's a mix up between the old astro's and the new. Astro claims 400 watts on 10-2400, 300 watts on 9-2400. I don't believe 1 cell makes 100 watts. I do know that the astro 805W on 10 cells does everything that Bob Boucher said it will do, and does it better on zapped cells. Remember also that you are running the old mtr. Kv 4000, Mine is 4,750. would that make a diff. in the watt variation. Steve
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Old Oct 17, 2002, 06:35 PM
That should fly!
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Just looked at the video, nope, IT DOES NOT FLY

James
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Old Oct 17, 2002, 06:59 PM
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If the Minifan, and ap29l are more efficient than the kyosho unit, why does it require 2 extra cells?
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Old Oct 17, 2002, 07:09 PM
Big gov never Works
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Hi tripster, The The mini-fan w/AP29L is able to handle the 10 cells
vs the KY. The mini-fan has a much better potential for higher efflux veloc. because of the steeper pitch. This requires more torque, more cells, higher rpm. At less amp draw than the KY Steve
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Old Oct 17, 2002, 07:39 PM
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805W

Okay Guy's I have an older sensored 805W and the paperwork it came with says that the KV is 4000 rpm/v. And Moto Calc shows the motor as having a 4400 rpm/v. This is what I got in the Mini Fan on 10 cells. Fan RPM is 37,419 static. I am sure it will unload in the air.

MotOpinion - T-33 1
Sea Level, 68F

Motor: Astro Brushless 05 #805W; 4000rpm/V; 0.035 Ohms; 1.8A idle.
Battery: Sanyo RC2400; 10 cells; 2400mAh @ 1.2V; 0.0032 Ohms/cell.
Speed Control: Generic High Rate ESC; 0.003 Ohms; High rate.
Drive System: WeMoTec Mini Fan 480; 2.7x3.66 (1.3in hub); (Pcoeff=0.506; Tcoeff=0.807).
Airframe: Kyosho T33; 302sq.in; 44.8oz; 21.4oz/sq.ft; Cd=0.045; Cl=0.46; Clopt=0.67; Clmax=1.17.
Stats: 144 W/lb in; 120 W/lb out; 22mph stall; 29mph opt @ 42% (41:52); 35mph level @ 46% (34:54); 1321ft/min @ 31; -220ft/min @ -4.9.

Power System Notes:

The full-throttle motor current at the best lift-to-drag ratio airspeed (36.5A) falls between the motor's maximum efficiency current (16.1A) and its current at maximum output (73.1A), thus making effective use of the motor.

Aerodynamic Notes:

With a wing loading of 21.4oz/sq.ft, a model of this size will have flying characteristics suited to an experienced pilot. The plane will fly fast, and be readily able to handle fairly strong winds.
The static thrust (33.4oz) to weight (44.8oz) ratio is 0.74:1, which will result in very short take-off runs, no difficulty taking off from grass surfaces (assuming sufficiently large wheels), and steep climb-outs.
At the best lift-to-drag ratio airspeed, the excess-thrust (23.1oz) to weight (44.8oz) ratio is 0.51:1, which will give steep climbs and excellent acceleration. This model should be able to do consecutive loops, and has sufficient in-flight thrust for almost any aerobatic maneuver.

General Notes:

This analysis is based on calculations that do NOT take motor heating effects into account.

I will next post 12 cells because I may run 12 cells.
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Old Oct 17, 2002, 07:42 PM
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12 cells

Here is the 12 cell prediction based on what KV my motor is? I am changing over the stock speed control. I may not run 12 cells but its something I was interested in.
Joe

MotOpinion - T-33 1
Sea Level, 68F

Motor: Astro Brushless 05 #805W; 4000rpm/V; 0.035 Ohms; 1.8A idle.
Battery: Sanyo RC2400; 12 cells; 2400mAh @ 1.2V; 0.0032 Ohms/cell.
Speed Control: Generic High Rate ESC; 0.003 Ohms; High rate.
Drive System: WeMoTec Mini Fan 480; 2.7x3.66 (1.3in hub); (Pcoeff=0.506; Tcoeff=0.807).
Airframe: Kyosho T33; 302sq.in; 49oz; 23.3oz/sq.ft; Cd=0.045; Cl=0.46; Clopt=0.67; Clmax=1.17.
Stats: 197 W/lb in; 164 W/lb out; 23mph stall; 30mph opt @ 37% (44:30); 37mph level @ 41% (35:49); 1752ft/min @ 40.8; -230ft/min @ -4.9.

Possible Power System Problems:

The full-throttle motor current at the best lift-to-drag ratio airspeed (47.5A) is higher than the motor's current at maximum output (10.2A). A lower current level would actually increase available output power.
The steady-state battery temperature (approximately 141F) is higher than the suggested maximum temperature for this cell type (140F), which can result in battery pack damage. A lower current would decrease the battery temperature.
Current can be decreased by using fewer cells, a smaller diameter or lower pitched ducted fan, a higher gear ratio, or some combination of these methods.

Power System Notes:

The voltage (12.4V) exceeds 12V. Be sure the speed control is rated for at least the number of cells specified above.

Aerodynamic Notes:

With a wing loading of 23.3oz/sq.ft, a model of this size will have a very high flying speed, requiring the undivided attention of an expert pilot. The high weight will provide good penetration, even in strong winds.
The static thrust (43.5oz) to weight (49oz) ratio is 0.89:1, which will result in very short take-off runs, no difficulty taking off from grass surfaces (assuming sufficiently large wheels), and steep climb-outs.
At the best lift-to-drag ratio airspeed, the excess-thrust (31.7oz) to weight (49oz) ratio is 0.65:1, which will give steep climbs and excellent acceleration. This model should be able to do consecutive loops, and has sufficient in-flight thrust for almost any aerobatic maneuver.

General Notes:

This analysis is based on calculations that do NOT take motor heating effects into account.

As you can see 12 cells may not be healthy for the motor or cells So I am probably going to run 10 cells which allows me to use a 3-SL-40-6-18. More to come. As I do some real world testing for curiosity.
Joe
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Old Oct 17, 2002, 07:50 PM
Big gov never Works
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BRAVO!!
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Old Oct 17, 2002, 09:43 PM
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Which should I use. Kyosho w/ap29l or Mini480 with ap29l. Have both sitting here on the bench. The Mini took some work to slide over the motor. Had to remove some material. Guess the tabs would have to be removed from the Minifan also.
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Old Oct 18, 2002, 01:57 AM
Speed Demon
GregG's Avatar
Antioch,CA,USA
Joined Dec 1999
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Quote:
Originally posted by Gary M uk
So?

Does this little Gnat fly at all on the stock motor and fan?

Thats what I intend to use.

Or would it be better with a 480 BB?

Mine was NIB 45 and the mouldings look great.

Gary.


I covered mine with low temp film and sanded all of the internal ducting so as to smooth the flow.I just wish it flew as good as it looks. It came with the motor for 12 cells and the fan unit as part of the kit. I thought I'd get "More Power" out of it by adding a couple of cells. It ought to really move now that it has 14 of the old good 500ar's! Boy was I surprised, it barely even climbed out from a hand toss and every time I banked to make it turn back toward me it started losing altitude FAST! This thing even came right up to the advertised weight, (32oz.) no more. I ended up hitting a phone wire, yes wire. I couldn't do that again if I tryed. That was six years ago. Someday I vow to rebuild it and use something else for power. A clubmate of mine has one with the WeMoTec 480 fan and 10 cells pushing a Plettenberg and it flies with authority. Things have come a long way with EDF since I first tried this one.
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Old Oct 18, 2002, 04:52 AM
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Tripster, The gnat that I built had a mini-fan in it. It required filling in of the fuse. in front of the fan w/ balsa. I guess you would have to ask your self how much work yuo want to do. The KY falls into place and you should limit your cells to no more than 8-1700cp's. With the mini you can move the fan back and install 1/8by1/4" spruce to hold the mini. This will allow you more flexability w/ the cells.I made this in 1998, and used 800ar's. Now I would use 1300 or even 1700, 10 cells. I also used a tapered thrust nozzle, that tapered to 90% the diam of the fan. I believe it was 7-3/4" long. I also made the bottom rear of the fuse removable, for access to fan. Go through the threads on this forum there is a lot of input on this jet to help you make your dicision. Steve
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Old Oct 18, 2002, 01:55 PM
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Quote:
Originally posted by tripster
Which should I use. Kyosho w/ap29l or Mini480 with ap29l. ...
Doug's Gnat used the Kyosho fan with the AP29L because he had one lying around unemployed. It's a good fan with a very good ferrite motor (in fact one of the best as far as efficiencies are concerned).

The Minifan 480 is a more efficient fan (by about 25 %) so it's a better fan, at a cost.

The AP29L fits in the kyosho fan with no mods. In the MF480 you have to enlarge the motor hole.

The MF480 is a lighter load compared to the Ky fan, so if you use 8 cells in the Ky fan & AP29L (ca 33A), you will have to go to 10 cells with the AP29L in the MF480 (again ca 33A).

The MF is smaller diam (69mm vs 75mm) so you just move the fan a bit to the back inthe Gnat. This helps the CG problem as well.

To get the speed up, a restriction (ie rolled paper cone) is a good idea, exit cone about 60mm for Ky fan & 55mm for MF480. As St Martin says you can also use a cut down styro cup as a thrust nozzle, glued with silicone at the back end, this allows you to playe around with different restrictions. In the video Doug does not have any cone of any sort, the Ky fan is just siliconed at the stock location and that's it. Flies fine.

A restriction to increase efflux speed decreases thrust a bit, so you will need to toss it harder...
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Old Oct 18, 2002, 04:13 PM
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gregg, I think the problem is that the 500AR can't suply enough amps to the motor, usually 18 amps max.
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Old Oct 18, 2002, 05:52 PM
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Mine was pulling much less than 18 amps. It was running around 200 watts/lb. and could just barely fly. I was highly disappointed to say the least. I wouldn't bother with the stock fan in this plane. It'll probably be used to cool batteries.
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Old Oct 18, 2002, 06:05 PM
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Quote:
Originally posted by GregG
...could just barely fly. I was highly disappointed to say the least. ...
" ... The model climbs out of your hand and eagerly accelerates away. Rolls are no problem and loops can be achieved by diving the model to gain speed... I don't know what impressed me more, the quality of the kit or the performance of the power unit. The model's scale like-flight envelope ... is definitely a crowd pleaser."

S&E Modeler, June 1998 issue, page 24. (my italics, review of stock setup as distributed by Aveox).

Needless to say, that was just about the last issue of S&E Modeler I bought. And that particular review was not an isolated case.
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Old Oct 18, 2002, 06:18 PM
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I think that reading that exact article was what bugged me the most. I believe I was outright lied to and taken. The video you posted isn't with the stock powerplant and this is what the original poster wanted to know. I've heard of some of them working with the stock setup, but I've also heard many more trying the stock fan and motor didn't work.

They seen to fly great with other than stock motors and/or fans.
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Old Oct 18, 2002, 06:19 PM
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Hi, The first outing with our gnat saw two diff mtrs. First flights were with SP480BB, 8-800ar's. We then changed the mtr. to a HP200-20-6, 10-800ar's. Like nite and day. I still have the stock fan & mtr. somewhere, maybe it will work in my Ree's SAAB TUNNIN. Steve
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Old Oct 18, 2002, 06:31 PM
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Gregg, absolutely.

Your experience and mine on the original stock setup has been echoed by quite a few other people. They also were fooled by the above-mentioned article into believing that ... the article's description was actually accurate .

Yes, again, the setup Doug uses to fly his in the video, is "stock" but for the Kyosho T-33 & F-16, the Robbe stock setup that comes with the Gnat (speed 410 & RoJet fan) is pretty useless ...
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Old Oct 18, 2002, 06:36 PM
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This thread is really getting a workout thiss afternoon, isn't it? If I ever get mine going again I'd like too try the 1700AUP cells. They seem to be holding up under 30+ amp loads pretty well.
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Old Oct 19, 2002, 08:29 PM
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Australia, NSW, Katoomba
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I have a Robbe Gnat kit still undisturbed in its box.
I also have the Robbe stock fan and motor for it.
Thing is I really don't know wether to waste my time assembling the thing.
I also have MF 480 fans, Wemotec 480 motors, Kyosho fans and AP29 motors.
I even have a couple of Jetelec fans, and two low turn 550 buggy motors capable of spinning them at the V high revs needed to get the high eflux velocity they can produce.

All too complicated . Anyone want to make me an offer for the kit. (Don't all rush at once!!He He!!)

Cheers. Patrick.
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Old Oct 20, 2002, 02:32 AM
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I am interested in the kit. Sent you pm

Mike..
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Old Oct 21, 2002, 01:34 AM
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United States, CA, Lake Forest
Joined Feb 1999
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Today Doug flew his on 10-1700s with the Astro 805-K motor. He added some weight to the tail to balance it with the Kyosho fan in the stock position. It needs a little time to get on step from launch but once it's going it flies pretty quick "For a flying Beer Cooler" as we say
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Old Oct 21, 2002, 12:13 PM
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Here is some video of Doug's Gnat from last saturday with again Kyosho fan, astro 805k and ten regular $3 CP 1700 cells. ESC (located in canopy) gets barely warm so he's ok, ca. 35A.

To get the CG right, Doug had to add some lead in the tail. He'll try to move the fan a bit this week. He has no restriction at the back, I recommended he add a cut styrofoam cup to reduce the outlet to about 60mm to increase top speed. You can see the wings flex now close to the tips.

Level flight speed in fastest pass is around 81 mph.

http://aeneas.ps.uci.edu/edf/gnat/gnat_bl_short.mpg (6 MB, 1 min)

http://aeneas.ps.uci.edu/edf/gnat/gnat_bl.mpg (27 MB, 3mins)
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Old Oct 21, 2002, 12:22 PM
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Btw, with some ingenuity you can just replace the RoJet rotor with the Kyosho rotor, as I mentioned a couple of years ago...
At the time you could buy (from Tower) the rotor just by itself for about $9. Or of course buy the whole fan at $39 ...

http://www2.towerhobbies.com/cgi-bi...gm?Q=1&I=LXPW93

http://www2.towerhobbies.com/cgi-bi...=1&I=LXW938&P=V

If you just buy the rotors, you can make your own shrouds with rolled ply etc., you can do a search here on Chris True's excellent article on how to do that,

http://ezonemag.com/alist/By_Author/Chris_True/
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Old Nov 02, 2002, 06:22 PM
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MIKE

The E-mail address you gave me is not working.

Please mail me on mcgrathpatrick@hotmail.com

Thanks. Patrick.
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Old Nov 19, 2002, 08:58 PM
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Picture of Doug's Gnat taken this past weekend,
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Old Apr 07, 2006, 07:34 PM
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Irvine, Calif USA
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Here's a few pictures of my new COMPOSITE Folland Gnat - based on the Robbe kit.

What comes out of the box is a very nicely molded fuse & wings, with a nicely designed intake:


.
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Old Apr 07, 2006, 07:37 PM
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The location of the fan unit (lightweight Schuebeler DS-30 with Kontronic 480-33 & Kontronic Smile esc on 3S or 4S setup) will be determined by the location of the CG.

But it looks like it will end up just where the RoJet unit was designed to be. There's plenty of space in the nose for different pack configs (here $47 Apex Mk2 2100, in 3S or possibly 3S2P config).

.
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Old Apr 07, 2006, 07:43 PM
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Wings, tailgroup and fuselage are lightly sanded and spackled before the COMPOSITE makeover. The whole airframe weighs at this point 6.3 oz .

.
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Old Apr 07, 2006, 07:47 PM
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The next step in the COMPOSITE makeover involves covering applied with generous amounts of water-based polycrylic, in several coats. Sanding between coats is to achieve a reasonably smooth finish, good enough for final painting. Once this step is completed, another 2.0 oz have been added to the airframe.

.
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Old Apr 07, 2006, 07:52 PM
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Next the Gnat is airbrushed in red, using Tamiya (gloss) water based acrylics which are very light and very dense in pigments.

The idea is to try to replicate the Red Arrows scheme, as in these very nice pictures found on the internet:


.
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Old Apr 07, 2006, 07:54 PM
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So out comes the Tamiya airbrush, and after two coats of red it's ready for some drying time ...

.
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Old Apr 07, 2006, 07:59 PM
SoCal, Year Round Flying!
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Looks good Herb!
Maiden tomorrow?
I'll be there.
Bruce
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Old Apr 07, 2006, 07:59 PM
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Target weight is around 28 oz, power around 400 Watts depending on battery size. The Gnat will be handlaunched....
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Old Apr 07, 2006, 08:10 PM
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Herb, she looks good
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Old Apr 07, 2006, 09:23 PM
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HERB.

With that power setup she should fly really well.

I found the original fan and motor was a load of crap, to put it mildly.

Flew well as a slope soarer though. !!!.

Cheers. Patrick.
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Old Apr 07, 2006, 09:42 PM
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Herb, I'll practice my javalin throw!
Doubt it'll need it with a shubie....
which as you know is the only COMPOSITE in there!
Regards,
Bruce
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Old Apr 07, 2006, 11:00 PM
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Makes me want to root around in the closet cause I just know I got one in there.

Lookin' GREAT Herb
Randy
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Old Apr 07, 2006, 11:08 PM
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It's kinda fun to see the progress from the good old days to today with the Gnat. Cool!
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Old Apr 07, 2006, 11:17 PM
EDF all the way!
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Randy,
Better check for two.
Bob
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Old Apr 08, 2006, 02:01 AM
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It's looking great Herb! The ol' Gnat should fly like a whole different plane with modern power. BTW, who is carrying those Apex packs at this time?

I'd still like to see it with a thinner airfoil though........
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Old Apr 08, 2006, 02:13 AM
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GREG, I know what you mean.,

I thought the Robbe Gnat's wing was pretty thin at the time, but this afternoon I have been laying up the wing of a John Higgins Rodent, and it gives an altogether new meaning to the word "Thin".

Cheers. Patrick.
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Old Apr 08, 2006, 12:38 PM
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I saw one of these sitting on the ground at Best In The West 1996 or 1997 but didn't get to see it fly. I've yet to see one, but it's nice to see well designed ducting from back then. If only Kyosho had taken note of this airplane...the Europeans know their edfs, the far east however...

Looks great Herb!
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Old Apr 08, 2006, 01:45 PM
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... she's not ready yet - I have to fit all the servos and fan etc in it. The surface prep and lightweight covering is the most time consuming task.

There's quite a few of these Robbe Gnats still out there - Phil how's yours nib doing up in those garage rafters .

Even Chris had one (though he won't admit to it in public), I think he is still looking for his left wing somewhere in the woods

It's really a shame that Robbe stopped making the Gnat and the Bae-146, even after so many years they remain absolute classics: well designed and engineered, lightweight, no frills (but my head still hurts when I look at the instructions for the suggested Gnat linkages ).

It's funny that when you think of it there isn't really much available in this particular segment: handlaunchable, light weight, well designed, semi-scale (nice and rounded) foam jets in the MiniFan range ... Converted foam pushers made in china - pleeeeaaaze!

The Robbe Gnat is occasionally revived (I should perhaps say: pulled out of somebody's trashcan) in Germany as well, HWE brought out all his painting and detailing skills when he finished this one:

http://www.rc-network.de/forum/showt...highlight=Gnat

and the video is here:

Robbe Gnat with DS-30 on LiPos video


.
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Old Apr 08, 2006, 02:21 PM
SoCal, Year Round Flying!
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Newport Beach, CA
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Ok next week then! I hurt my shoulder warming up anyway!
Thanks for the link/vid.
That shubie makes it zoom!
Battery technology has moved forward alot since 2004. He had to 5P his lipos!
Bruce
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Old Oct 17, 2009, 01:41 PM
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Here's a more recent Robbe Gnat video (October 2006),

Early EDFs - Robbe Gnat (2 min 48 sec)


The Gnat gets progressively faster as the 4S 3200 Lipos warm up ...
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Old Oct 17, 2009, 08:07 PM
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vittorio veneto (tv)
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Very nice! I have bought one of this kit and I am going to build, any suggestion will be welcome in particular about propulsion.
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Old Oct 18, 2009, 12:45 PM
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Ehila' Robo,

http://www.rcgroups.com/forums/member.php?u=165&page=2

http://www.rcgroups.com/forums/showt...6&page=2&pp=46

Any half-decent fan with a half-decent inrunner brushless motor on 3-4S 2000-3000mAh batteries will fly this model very well!

Use this calculator:

http://www.s4a.ch/eflight/fancalc_e.htm

Some suggestions: WeMoTec Minifan, or any good copy of it
Also the Haoye 69mm fans should work ... Avoid anything
that looks shiny and weighs a ton.

eg. www.wemotec.com

Motorwise a good 29mm inrunner, Hacker Kontronic, Neu,
Mega, Het (Mega copy), Turnigy B28-xxx ...

http://www.hobbycity.com/hobbycity/s...v=l&sortlist=P


Another possibility is the Storm, fan & intergated motor now on sale for $99 ...

Speed controls Jeti Hacker Kontronic YGE, Hobbywing Pentium, Castle ... preferably with switched bec

.
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Old Oct 18, 2009, 05:11 PM
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Australia, NSW, Katoomba
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[Quote] Another possibility is the Storm, fan & intergated motor now on sale for $99 ...[Quote]

I can't find this set for $99.00 anywhere.
Can you please advise where.
Thanks. Paddy.
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