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Old Sep 05, 2003, 08:21 PM
mattski is offline
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GWS Spitfire - does this sound right?


Hi,

I have more or less finished my GWS Spitfire now, it only needing final setting up of CG and radio trim etc.

I've been doing some powerup tests with everything connected to make sure everything is ok.

Upon throttling up the motor _sometimes_ sounds as though it is struggling and, at full power, has once or twice sounded as though it is losing power.

My setup is as follows:
Stock 300 motor and GWS 1080 prop (right way round)
GWS ICS100 Speed controller.
3 x Pico servo's.
Futaba micro receiver, aerial is currently just unravelled and runs to the back of the plane.
Enjoy Model Lithium Ion 10.8V 0.7A (3.6V x 3 cell) battery.
Futaba FF6 transmitter.

_If_ there is a problem, the only think of is that the battery isn't fully charged, I am using an Ikarus Lithium Ion 3 cell 800mA charger. The charger turns itself off, presumably, when the Li-Ion is charged ok.

Any thoughts as to what could be the problem, if any?

ta,
Matt
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Old Sep 06, 2003, 05:56 AM
brobin1 is offline
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First off - You must not let Lithium Iron drop below a certain voltage - I think it is 3.2v - Otherwise you will damage the cell beyond repair. I use Enjoy Lithium Ion cells but I also use the dedicated ESC whic ensures that the motor cuts before any damage is done - It weighs about the same as your current ESC & I would suggest you use it or buy a lot of cells!
Old Sep 07, 2003, 07:32 AM
kensp is offline
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Re: GWS Spitfire - does this sound right?


Quote:
Originally posted by mattski
Hi,

I have more or less finished my GWS Spitfire now, it only needing final setting up of CG and radio trim etc.

My setup is as follows:
Stock 300 motor and GWS 1080 prop (right way round)
GWS ICS100 Speed controller.
Enjoy Model Lithium Ion 10.8V 0.7A (3.6V x 3 cell) battery.
Futaba FF6 transmitter.

Matt
I have been using the Enjoy batteries since November 2002 and have found that they do not work well when asked to deliver a currents over 5 Amps. MotoCalc predicts, that when using 3 Cells, a stock EPS300C-C motor with the 5.33:1 gearbox and the GWS 10x8 slow fly propeller, the current will be 11 Amps static and 8 Amps when flying. This is way too much current.

Try using an 8x6 slow fly propeller. This propeller should have a static current of 6.6 amps and a flying current of 4.5 amps. Top speed should be 42 mph and static thrust 11.5 oz.


Ken
Old Sep 07, 2003, 08:57 AM
brobin1 is offline
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Ken,
What would happen with an 8 X 4.3 prop?
Old Sep 07, 2003, 02:46 PM
kensp is offline
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Quote:
Originally posted by brobin1
Ken,
What would happen with an 8 X 4.3 prop?
MotoCalc predictions for GWS Spitfire.

3 cells Enjoy1.4 Battery
4.33:1 Gearbox
8 x 4.3 Propeller
(Note that this propeller requires the use of a 4.33:1 gearbox for speed to be high enough for the ailerons to work properly)


At Top Air Speed = 32.0 MPH
(In flat and level flight)
Motor Amps = 2.94
Motor Volts = 10.5
Input (W) = 35.0
Motor Temp = 43.1 C
Motor Eff = 73.2 %
Motor RPM = 50333
Elect Eff = 70.9 %
Prop RPM = 11362
Total Eff = 36.6 %
Time = 28 minutes 36 seconds

At Manoeuvring Air Speed = 24.0 MPH
(In a loop or tight turn)
Motor Amps = 5.72
Motor Volts = 10.2
Input (W) = 68.4

At Static Air Speed = 0 MPH
(In hand ready to launch. Only run motor for max 5 seconds before launch)
Motor Amps = 7.45
Motor Volts = 10
Thrust = 13.6 oz



The static thrust (13.6oz) to weight (15.1oz) ratio is 0.904:1, 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 (7.22oz) to weight (15.1oz) ratio is 0.48:1, 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 manoeuvre.

Ken
Last edited by kensp; Sep 07, 2003 at 02:52 PM.
Old Sep 07, 2003, 03:21 PM
Happy|Harry is offline
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veni,vidi, roto volubilis
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Quote:
Originally posted by kensp

The static thrust (13.6oz) to weight (15.1oz) ratio is 0.904:1, 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 (7.22oz) to weight (15.1oz) ratio is 0.48:1, 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 manoeuvre.

Ken [/B]
Sounds good to me and on a GWS300C but i don't think the 300 will hold on for long at the 10.8V(12.6) a 3S pack provides

phil
Old Sep 07, 2003, 04:23 PM
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Quote:
Originally posted by Happy|Harry
Sounds good to me and on a GWS300C but i don't think the 300 will hold on for long at the 10.8V(12.6) a 3S pack provides

phil
The thing that has always put me of using 3 cells lithium on a 300 C is not the amp draw but the 50 000 rpm that the motor spins at.

My GWS Warbirds use 2 servos and no U/C. Using this configuration the weights with the 2 cells Enjoy 1.4 and 2 cells E-Tech 1200 are between 12 and 13 oz. At these weights 2 cells gives excellent performance, especially the E-Tech. For this reason I have never tried 3 cells Li on the 300C

The MotoCalc figures for the Multipex 280 BB used with 3 cells looks promising but unfortunately this motor is not easy to obtain in Australia.

Ken
Last edited by kensp; Sep 07, 2003 at 04:29 PM.
Old Sep 07, 2003, 04:57 PM
brobin1 is offline
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Ken,
I am trying something a little different - An Orion Modified "Big Block" engine - Suposed to be a hot motor - Slips straight into the GWS gearbox - First test flight tomorrow - I will let you know how it goes
Old Sep 07, 2003, 05:35 PM
AndersO is offline
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No parachute? Wow!
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GWS 300c motor and GWS 1080 prop with 3s lipo's at full throttle will hold about 1-2 minutes.. Tried it some months ago
Old Sep 07, 2003, 07:32 PM
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I'm with kensp. 2cell etec 1200's can deliver the amps you need. I run them in my GWS Mustang with no problems.
Old Sep 07, 2003, 08:17 PM
LuckyArmpit is offline
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Rehab is for quitters
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Just got back from the field with my spitfire. This was the 2nd maiden attempt with the first being too tail heavy. This time,
I didn't use the clay, just a bolt taped to the bottom. Made the CG just about at the spar. A tad nose heavy. Used 8 cell 720 nimh's. Flew great!!!! I decreased the EPA on my Eclipse radio for the elevator and ailerons. Couple of tics down and to the left and it was trimmed. My spit with batt pack weighs exactly 16 oz.
Now the bad part. After last batt pack (I have 8), tried to throttle off and land. Spit would not shut off motor and it landed and cartwheeled. Fuse is now being probonded cause it snapped in half. Also missing a foam piece out of elevator.
If your using e-tecs, I'd advise you to make sure that model balances!!!! If your tail heavy, plan on doing some gluing!!!
I'd make it nose heavy until you get used to flying it.

Dave...


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