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Old Sep 15, 2003, 11:58 AM
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A little help--power for mini-telemaster

All my electric flight experience to date has been with s280 and IPS type drive systems, so this s400 mini-telemaster is giant-scale to me . Specs are: 45" span, 325 sq. in., about 8.5 oz airframe weight (I'm guessing). I picked up, for better of worse, a 6v speed 400, an MJ 4.1:1 drive, and a jeti 18a esc. I'm figuring on 7 or 8 cells. I'm figuring, from my motocalc guesses, I'll need at least 7, maybe 8 cells (600nicd/1100nimh) and maybe a 10x7 prop. Does this sound about right? This looks like about 6a max and about 12 oz. thrust. Possibly more prop would be better?
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Old Sep 15, 2003, 12:28 PM
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You are not far off. Pesonally I'd use a slightly lower ratio to get a bit more airspeed. 11x8 may suit you better - even up to 12x10 on 7 cells, but start with the 10x7. Lipoly e-tech 1200's 2s1p or 2s2p are a nice complement, if teh budget stretches.

Oh. On 7 cells an 11x10 is about perfect I'd say. And its very nice on 8 cells too.

Use the 10x7 on 9 cells or 3s Lipoly setups.
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Old Sep 15, 2003, 12:45 PM
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Thanks, vintage1. I was thinking after I got home that I should have gotten a lower ratio, but it's a little two late. I guess since props are cheap, I can experiment a little when I get this thing built. I've got two etec 1200 2s packs I could try, but I guess I was under the impression that would be under-volting the 400. I guess I've some learning to do here.
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Old Sep 15, 2003, 12:52 PM
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I have a lovely little plane = pictured below, that zooms around on 7 x600AE and a 6V sp400. This one is geared at 2.33 and uses an 8x6. Its startlingly good at climbing very high, despite AUW of about 20 oz.

The 10x7 prop is generally used with boxes in teh 3-3.5 area on 8 cells, the 4.1 is going to need a serious prop - thats more a box for sailplanes and folders.

Or use more volts on teh motor...but to be honest, they are happiest tootling around on 7-8 cells at 8-10A max. The 11x10 just drops into teh right sort of bracket with motocalc.

Over here tho, 5 APC props costs about the same as a battery pack

Those props are 4 each, and I have broken countless ones. At least youi can get em direct from APC in bulk
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Old Sep 15, 2003, 02:34 PM
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Man, that's expensive! APC's are about $3 here (gloating not intended). In the future, I'll have to make sure I know what I want before buying blind. I was guessing either 3.5 or 4.1, and in retrospect I would have been better off with 3 or 3.5. Oh well. Looks like I'll be either fabricating some extended LG legs or buying another GB. Very nice plane, BTW!
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Old Sep 15, 2003, 02:40 PM
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Oh dear. My favorite for 'sport' use is the Mpjet 2.33:1 ball race box. Very efficient and cheap. That runs 8x6 or 9x6 prop very nicely.

I'd get one of those, and save the 4.1 for somethig like a long can 480 on a bigger model.
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Old Sep 15, 2003, 03:00 PM
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Hmm, you're right. The 2.33 looks better in motocalc. 9x6 on 8 cells reads out at 12 oz static thrust at 10 amps. That should be enough to fly 'er if I keep the weight down. Thanks for the tip.
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Old Sep 15, 2003, 05:14 PM
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a 9x6 on that will fly a 220z plane very well. I'd actually try and 8x6 first. 10A is over the efficiency hump for a 400 6v. 7A is about right really - for most cruising around. Still try em all out!

I found that efforts to get up to the 10A plus region were dissapointing - more amps in and very little more power out. If you want over about 75W, its time for a long can 480, which is good for about 120W.
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Old Sep 16, 2003, 09:06 AM
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Thanks for all the info, vintage1! I think you've got me headed in the right direction now . The numbers all make a little more sense now. I just wasn't sure what to expect from the "400" class, I'm so used to 280 and smaller motors.
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Old Sep 16, 2003, 03:18 PM
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Vintage1,

Do the Ryanair decals mean it has to land in the next field over.
Only kidding!

Nice looking plane. Is it a kit/plan/OD?

Aidan
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Old Sep 16, 2003, 03:36 PM
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Its a west wings Beguine - fairly nice kit, except the fuselage is built like a brick ****house out of liteply, and I had an engaging afternoon hacking chunks out of it.

The wing, on the other hand, flexes alarmingly and is rather weak...

The reason for the ryanair stickers was I was using them to fly to a family wedding in sweden, and I wanted to frighten my mother ...

Sadly she never saw the model

However, I can absolutely recommend this as a bog standard (no offence intended) trainer on 3 channel. Stuart Marsden has a few of them and he has written up on various aspects of them in one of the mags.

If you have never bashed balsa before, its very easy to build.

I modded it with weight taken out of the fusealge, a hatch under the cabin to load the battery, and cut the nose off and faked a new cowl to fit the MPjet box rather than the FG3 it was designed for.

Flies exceptionally well with the dremel diet on 7x600AE - well its actually got a cheapo perkins pack in right now - not as good as 'real' 600Ae's but good enough.

I haven't flown it in a while, been busy with faster more aerobatic things.

Really I have given up tryimng to squeeze the last drop out ofcan motirs: Run them in their limits, get decent life and nice performance. Push them, they break, the batteries don;t have duratuion, and you end up in a spial of ever more cells, more wieght, low motor efficiency etc etc.

400's like to run at 35-60W cruise, 75W flat out and thats about it.
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Old Sep 16, 2003, 03:55 PM
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I've bashed plenty balsa. Probably too much. I end up spending too much time building and not enough flying!
I may have to go with a few kits to keep me flying while I procrastinate over my next scratch build.

I've got a 7.2V Speed400 geared 2.33:1 sitting doing nothing.
I might build something like your Beguine for it.


Have you come across the Aeronaut range of geared can motors?
I've got a Aeronaut Speed300 geared 4.85:1 that I'm putting into a small funfly type model. I was planning to run it on a 10*6" prop and either 7 600AE's or 8 500AR's but when I ran it on the bench with the 8 AR's it pulled 13.5A.
A bit much for a 300 I think!!!
It's obviously a higher kV motor than the Graupner Speed300 but I have no figures.
I'm trying to get up around the 1:1 power to weight but I think I'll need a higher gear ratio.

Aidan
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Old Sep 17, 2003, 01:50 AM
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I have a 7.2v 400, but I find it a bit gutless. I'd say you would need a 10x7 on that to get decent power, and 8 cells.

Worth a try tho. You could always slap in a 6v motor if you liked the plane.

I soprt odf built it for a friend to help get stickl time, but he seems to have lost interest..

No ideas on that 300, but 13A does sound high unless its a race wound motor. try propping it back ?
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Old Sep 17, 2003, 05:00 AM
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I got the geared 7.2V way back. I asked someone to grab me the 6V 2.33:1 but the shop was out so they got the 7.2V instead.
It's been lying there since because I have no high cell count packs at the moment and I reckon the numbers aren't too impressive up to at least 10 cells.
Might be okay in a lightweight floater though for just trundelling around.

I'll need to move down to about a 9"x 5" prop for the 300 and even at that avoid max throttle for long periods. I'll be down a bit on static thrust but should still have plenty for most things.

Aidan
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Old Sep 17, 2003, 01:34 PM
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If you can keep the model under 20oz, 8x6 or 9x7 on 7-8 cells will suit a trainer style plane on that motor and box.

On 3s e-tech 1200 8x6 is really rather nice. Almost aerobatic

As for the 300? the graupner/GWS sort seem to like at most 7A, better around 5A.
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