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Electric power for KeilKraft Gaucho.

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Jeffrey Cottrell 203/06/2020 22:26:07
117 forum posts
16 photos

Hi Guys
Here's one for all you motor gurus out there.
Planning stage of my next build and I'm thinking of a KeilKraft Gaucho, 44" contest duration model from the late 50's.Just for the challenge, I'm also going electric.
Reading up on the model I find it will 'potter' about on a Mills .75, shown on the plan is a DC Sabre 1.5cc, and it has been flown on a Oliver Tiger 2.5cc.
Rooting through my old engines box, I found a motor I built many years ago, but still going strong.
Slapped it on the bench, and measured 10860 rpm on a 7 x 5 apc-e prop.
So, of the three motors listed above, which would my motor be closest to in terms of performance?
I would guess it has more oomph than the Mills, good news, I don't really want to 'potter', but how would it compare with the other two?
Only looking for a subjective opinion, not hard and fast rules, but I'd like to know if I'm on the right track.
Your thoughts
Jeff

DCW04/06/2020 08:17:08
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95 forum posts
64 photos

Hi Jeffrey.

Coincidentally A few weeks ago at the start of 'lockdown' I thought about radio conversion and electrification the KK Gaucho, I built one in my early teens. Back then I was not interested in using it as a contest machine, so I did not bother with the Elmic Universal timer, valve and de-thermaliser, I just wanted to fly it. I fitted it with my Mills 75 which at that time was fitted into a KK Snipe, not contest performance but just right for my purposes. I still have that Mills and ran it up last year, it fired up after just about six or so flicks of the prop. More details and a plan download of the Gaucho can be found on 'Outerzone' , together with a link for the wing rib profiles.

I have already electrified the KK Halo and the KK Chief which with it's long nose lends itself for the installation of a 3 cell LiPo. The Gaucho would only need a two cell system, but a Mill 75 I think would be a nicer option. As with the description in Outerzone the wing tip dihedral would need to be reduced a little and the tilt on the tailplane would not be needed.. The fuselage is of profile build, but a lightweight radio system could be built into the fairing blocks just behind the engine.

Hope this helps, keep in touch.

David

Peter Miller04/06/2020 08:54:19
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11104 forum posts
1309 photos
10 articles

At a rough Guess I would say half way between the Mills and the Sabre.

The Mills was normally run on an 8" prop

The Sabre used a 8X6 or 8X4 for free flight at 10 to 12000 rpm. The 8X6 for sport FF and the 8 X 4 for contest flying

The Oliver Tiger used either a 10 X 6 or 8X4 at 8000 to 18000 rpm The 10X 6 was for sport,the 8X4 for free flight contest work

Quoytes from a very old Plans handbook

John T04/06/2020 11:05:00
7 forum posts
19 photos

Hi Jeffrey,

About 5 years age I made an electrified Gaucho which i still fly regularly, in fact I last flew it 2 days ago.

Gaucho

Mine is powered by an Emax CF2822 motor with a JP Green 8 x 4.5 folding prop and a 2 cell 800mAh LiPo. This gives quite a reasonable climb, although not exactly "contest" level. I'm guessing your set up would be similar or slightly more powerful. As Peter said, somewhere between the Mills and the Sabre.

As for the model itself, I widened and extended the side cheeks slightly so there was room for the battery, receiver and elevator servo. The pylon was also widened fractionally and I've mounted the ESC and rudder servo there. I extended the trim tab to the full height of the fin to use as the rudder, but if I were to build another one I would make it a bit bigger. The dihedral is pretty much as designed. I needed a bit of nose weight in mine so try and keep the gear as far forward as possible.

For a relatively small model it thermals really well, and it will cope with surprisingly strong winds.

Jeffrey Cottrell 204/06/2020 13:37:40
117 forum posts
16 photos

Hi Guys, and thanks for your help.
Here's what i have so far:
DCW
Back in the day I had an Irvine Mills .75. Little jewel of an engine, but I sold it on, along with my others, when I went electric.
Already got the plan from OZ, plus the rib link. In fact the ribs being flat bottomed, convinced me of the project.
Peter
Pretty much what I thought, thanks for the confirmation. Performance on the Mills is described as 'pottering'. Not what I have in mind. Probably won't get 'contest' performance, but I would like something more positive.
John T
That's a pretty model you have there. Notice you have quite a sizeable elevator. Do you use all of that?
Both you and DCW suggest a 2s system. What's the thinking behind that?
HK used to sell NanoTech 900ma tubular LiPos. Sadly now discontinued but I do have a spare set. These can be arranged in any format you choose, so could be tailored to fit behind the nose cheeks. A 3s pack would take up very little more space than a 2s one.
That's all I have so far. Your thoughts?
Jeff

John T04/06/2020 17:05:03
7 forum posts
19 photos

The main reason I used a 2S pack was to try and keep the bulk down as much as possible to avoid widening the fuselage much. It's a bit tight in there! If you can cram a 3s pack as far forward as possible it might help with the C of G.

The elevator is hinged at the original rear spar line in the rather optimistic hope that it wouldn't really show up when it was flying (It uses an internal wire yolk which engages in a slotted sliding plate). Both halves are used, but there's only about 15 degrees each way and it's not particularly sensitive.

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