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Electric power for KeilKraft Gaucho.

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Jeffrey Cottrell 203/06/2020 22:26:07
207 forum posts
33 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

DCW04/06/2020 08:17:08
98 forum posts
66 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.


Peter Miller04/06/2020 08:54:19
11334 forum posts
1330 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
21 forum posts
20 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.


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
207 forum posts
33 photos

Hi Guys, and thanks for your help.
Here's what i have so far:
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.
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?

John T04/06/2020 17:05:03
21 forum posts
20 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.

Jeffrey Cottrell 205/08/2020 07:41:19
207 forum posts
33 photos

Hi Guys

Sorry, it's been a while since I posted on this thread. Mind you, it's been a while since we had conditions suitable for the maiden.
Anyway, today was the day, and I'm well pleased.
Here's the detail:
Got so fed up with the model sitting on the shelf and making me feel guilty, that I set my alarm for silly time,and was down the field at 6am.
Not sure if I'm allowed to be there that early, but nobody to notice so took a chance.
Also, confession time.
No-one around to help so didn't do a range check. In my defence I use the FS-i6/iA6 combination on many of my models, and never had an issue. Figured it was a chance worth taking.
On glide tests at the local park, I found a distinct right turn, so fed in as much left trim as I could and that proved to be enough.
So, deep breath, quick prayer to the model gods and launched into the wide blue yonder.
Needn't have worried. Climb out tracked straight and true and soon at speck height.
During my tests the home built motor I started with decided not to play ball any more, so I re-motored with a CF2822, same as John T but fed with 3s.On this motor, and an 8 x 4 Aeronaut Cam prop it climbed vertically and would probably have continued to the ISS if I had not got cold feet.
Bench tests showed this prop/motor combination only pulling 7.5a static, so there is leeway for a larger prop if I need it.
Now, the only downside, and something I could use some advice on.
On the glide it seems to want to stall all the time. To me, looks like c/g or incidence issue.
C/G is exactly where it should be, maybe slightly forward, since the new motor sits a little further out than the old one.
If I fed in a little down at the bottom of the stall it sorted itself out, and glided (glid?) flat if very slow, which was to be expected.
So, my thinking is a little packing under the front of the tailplane.
What do you expert glider guiders out there think?
Have to say, for such a radical departure from the models I normally fly, maiden went well, and I'm happy so far.
P.S. Did three climbs to height, and the charger only put back in 109ma. That on a 900 pack.
Given the stall issue, glide performance wasn't anything to write home about, but timer still registered 7m 29s for that first flight.

So far, so good

EarlyBird05/08/2020 08:24:40
345 forum posts
265 photos

Hi Jeff,

Thinking back to my free flight towline glider days in the early 70s.

It sounds to me like you have it trimmed on the point of stall which is nearly perfect. There are two solutions either add some nose weight or very slightly pack up the LE of the tail plane. That is what I used to do but why not add down trim on the elevator?

Cheers beer


John T05/08/2020 09:40:38
21 forum posts
20 photos

Hi Jeff,

Glad the maiden flight went ok,

The C of G on my Gaucho is 4 3/8th" (or 112mm) back from the LE, which works out as about 70%. If yours is no further back than that I would try packing up the LE of the tail a touch. Don't forget the original free flight design would have been trimmed to glide in a large circle on the glide, which would have tended to kill any slight stalling that might occur in straight flight.

I normally use the dive test to check the C of G. If you dive the model at about 30 degrees and let go of the elevator, the model should gently nose up on it's own. If the dive increases, the C of G is too far back.

Have fun trimming.


Jeffrey Cottrell 205/08/2020 13:43:07
207 forum posts
33 photos

Hi Guys, thanks for your thoughts

Think you might be giving me too much credit.
'nearly perfect trim' All I have done so far is build it as close to the plan as possible.
Having said that, I am sufficiently encouraged by the maiden to do some more work on it.
I can see some more clandestine visits to the field in the wee small hours.
Not keen on adding any more nose weight. I already have a chunk of lead on there.
Mind you, I worked out the wing loading with that lead and it comes out at just under 7 oz/sq ft, so I do have leeway.
I am using my FS-i6 transmitter, which has very little trim range.
On the whole, from a drag point of view, I'm thinking packing under the le.

I set the c/g as per plan, but I have since changed motors.
Out of interest the plan says 2" forward of the trailing edge, which makes it about 4mm further back than yours. Got a little job to do first, then I'll get it back on the c/g machine, see where I stand.
If it looks ok, I'll do a dive test next time out.
Take your point about the free flight version being trimmed to fly in circles.
However the stalls I was getting were pretty violent, so I'm looking for an aerodynamic cause.
Either way, loads more work to be done. Looking forward to it.


John T05/08/2020 15:02:53
21 forum posts
20 photos


My memory must be going or something. I just had a look at my Gaucho and remembered that I'd initially had similar issues with stalling. I resolved mine with a 1/16th ply plate under the tailplane LE. I know it was 6 years ago that I did this, but I fly the model every couple of weeks or so and have to band the tail on each time!smiley


Jeffrey Cottrell 205/08/2020 18:27:20
207 forum posts
33 photos

Hi John

Thanks for the thought, and the picture, but I don't think that's the answer.
Bear in mind that the plan shows this ply plate, as a support for the front of the tailplane, and also, in the free flight version, to hold the tailplane at an angle as the plan requires.
So it would have been there in the build stage, not for packing purposes.
However, packing under the leading edge still remains an option, but in addition to the plate already there.
C/G check shows it in the correct position as you have yours.
Next time out I'll take some packing with me for a real time test.



Jeffrey Cottrell 214/08/2020 14:36:21
207 forum posts
33 photos

Hi Guys

Story so far:

Done a fair bit of flying with the Gaucho. Pretty much cured the stall tendency by adding 1/32" packing under the tailplane leading edge.
Still slight when turning upwind, but nothing a stab of down won't cure.
Overall, despite being a competition model it's a real pussycat to fly, and I'm enjoying it very much.
Now, the insect in the unguent.
Earlier in this thread I posted a link to a Sam 35 competition which the Gaucho is ideally suited to.
I have no intention of competing with it but it's a useful benchmark for how mine is performing.
The task is a 20 second motor run, then longest glide with a 5 minute max.
I'm currently nowhere near that, my best is 2 min 15 sec, but I think the issue is the initial climb is not as high as I would like. Seems to go up ok, but runs out of steam halfway up.
My suspect is the LiPo's I'm using. They are 1000 ma, 15c., so in theory should be good enough, but a bench test shows the terminal voltage going from 12.3v at rest to 10.5v at full chat. That's some voltage lag.
So, what I'm looking for is the holy grail (perhaps that should be unicorn).
I need a small, light lipo, but capable of maintaining a reasonable terminal voltage under a 10-11a load.
Checked with George at 4-Max, and he does a 800ma 40c, but I have a problem with £9.49 shipping fee.

Other than that, any ideas?


Bob Cotsford14/08/2020 17:15:38
8744 forum posts
487 photos

A Hobbyking 800mAh 2S 40C would only be £5.67 postage from the UK warehouse.

Jeffrey Cottrell 214/08/2020 17:32:48
207 forum posts
33 photos

Hi Bob

Thanks for the quick reply, but I'm running 3s not 2s. Also as you say shipping from UK warehouse is £5.67 but if you order from the EU warehouse, it's only £2.19.



Bob Cotsford14/08/2020 18:49:12
8744 forum posts
487 photos

I'm not surprised about the Eu postage, I just did a quick search for comparison. I see the Turnigy 850mAh 70C is listed as in stock at both Eu and UK warehouses. I have had good results with the Zippy Compacts and the Graphenes but the Turnigy blue's seem ok too so far.

I've got a Slicker Mite kit that I'd thought about building for electric, I think it's quite a bit smaller than the Gaucho iirc.

Edited By Bob Cotsford on 14/08/2020 18:50:46

Jeffrey Cottrell 214/08/2020 20:13:03
207 forum posts
33 photos

Hi Bob

Wonder if you might have a link to that TGY 70c? I can find Turnigy Blue in 60c, or NanoTech in 70c.

Another thing to consider is this. If I'm flying to a contest format, do I really need 850Ma?

Probably not a good guide, but the cells I am using now only use 100ma or so for a 20 sec climb. Maybe I ought to consider 450 or so in the frame as well. Benefit from the smaller size and weight.

I can see this getting complicated.

As regards the Slicker Mite, it's 32" compared with 44" for the Gaucho. but it does have a full fuselage compared with the profile one on the Gaucho, so you should be fine.

Go for it


Edited By Jeffrey Cottrell 2 on 14/08/2020 20:23:39

Bob Cotsford14/08/2020 22:34:14
8744 forum posts
487 photos

Sorry Jeff, my mistake, as you say the TGY blue is 60C. I managed to mix it's specs with the NanoTech (shudder!).

I have some smallish motors and escs, fibafilm and balsaloc and a selection of small servos and receivers, maybe I will dig out the SMitewink

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