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Jul 19, 2006, 03:13 PM
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Keil Kraft Gypsy

Hi guys,

Have inherited a KK Gypsy in completed wood state.....about 4.4 ozs less prop / rubber / wheels and uncovered. Not too keen on rubber, thinking about an electric conversion but want a real slow big folding prop , somewhere about 12-14 ". Does anyone have any ideas or practical experience for a power unit spec for free flight??

Am thinking about 20-25 gms outrunner with gearbox for 2 cell LiPo about 120 gms thrust for 20 watts. i.e. cruising gently about the sky as it would in rubber spec.

Anybody done this ??


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Jul 19, 2006, 08:09 PM
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vintage1's Avatar
Not with an outrunner, but I have come close...

If you are happy to carve a prop, the GWS IPS BRUSHED motor on 3s LIPO geared as deep as it will go - 11:1 for the 'F' gearbox - with a prop something like 11x11 prop would suit..about 2300 RPM..on 2s LIPO you could use up to about 15" but pitch needs to be VERY coarse, and power is lower.

Current draw on these is about 2A, so a 300 mAh pack is more than enough. Two servos, a motor/gearbox, and ESC and a pack should add about 3.5oz in all to teh basic airframe weight.

There are very few brushless motors that are actually sufficienty low power to work here..the best of te stiock motirs are teh PJS 300 IN and the AXI 2204/54..but these are both more interested in about 5000 RPM than 2500..its probably better to use at least the IPS gearbox, and one of the small Feigao or Medusa inrunners which fit straight in, if bushless is what you want.

I would expect you to be able to keep the weight under 6oz AUW..this will make for a very rapid climb on 20W or so.
Jul 19, 2006, 09:48 PM
Registered User

KK Gypsy or is it Gipsy?

Keil Kraft Gypsy or is it Gipsy?

Seems both are correct by my dictionary, and also even KK spelled it both ways in various advertisments.

Great Bill Dean design that I can trace back to 1949.

Built this one in 1996, and as you may see the tissue repairs has been flown plenty---freeflight of course.

This one now weighs 112 grams without the rubber.
Rubber is 100 grams of Tan2, 16 strands of it wound to about 1000 turns.
17 inch prop. Esaki Light Japanese tissue covered. Very good flyer.
Jul 20, 2006, 12:19 AM
Registered User
Nice one Gossie, i have the plan here, but am just waiting another 18 years or so for the kids to leave home before i build it...
Jul 20, 2006, 10:58 AM
Registered User

Thanks for an interesting and encouraging response.
If I have understood you correctly.....

1. Consider a good old 'everybodies got one somewhere' GWS IPS brushed motor running the largest reduction g'box that you can find. Interesting that you mention carving your own prop. Would have done this years ago as a matter of course but have just got out of the habit. To cool a hot motor down I can carve a real bad one and I can make it look like a 'rubber' prop .
Great idea and very , very slow.

2. Strange coincidence, but I have just bought a PJS 300 IN for a 2F electric Tomboy, running on 2s LiPo and a 11 x 4.7 APC slow fly. So, with a few measurements and experimentation and an additional gearbox, I might just get there with this one.

3. Have been hanging my nose over the 12 mm Feigao for some months as the quoted weight is impressive. Whether this is a solution will depend on my ability to make or adapt a gearbox to give 2500-3000 rev/min prop speed. I wonder if 1 cell would be an option?

4. Was wondering why you were insisting on very coarse pitch, then it clicked....required pitch is a function of rotational speed. Make this slow and pitch must increase to get your velocity triangles correct?

Great ideas and a high play factor.


I would have thought that a fellow living on the Aussie Gold Coast would have enough of the readies to splash out on a couple of sheets of Esaki to give a fine old lady a well deserved recover.


Get the kids building?

Jul 21, 2006, 01:03 AM
Registered User
Aw 'bofin', she who must be obeyed keeps spending it on me-----the house is nearly full-----will need to get a bigger one soon so she can keep stocking up.

The Gypsy is covered with light Esaki all over, but since then I have learned that for that size rubber ship the fuselage and one layer of Esaki is not quite enough---it holes fairly easily.
I have a couple of other big ones , Jeckyl & Hyde's for example, and cover them with 2 layers cross grained----very strong indeed.

Give the Gypsy a couple more years though, and I shall give it 'the double treatment'.
Have plenty of Esaki light here. All colours except that awfull green.
Jul 21, 2006, 04:47 AM
Registered User
Malc's Avatar

Electric gypsy

Mine is fitted with a cheap Bell outrunner turning a 10 x 6 prop two micro servos 2 cell 1500ma lipo.
Climbs like a homesick angel and is my most flown vintage
Jul 21, 2006, 04:49 AM
Registered User
Malc's Avatar

Electric gypsy

See my post in this forum 'Gypsy Transformed '
Jul 21, 2006, 05:40 AM
Registered User
vintage1's Avatar
Boffin: Of ALL the outrunner motors I have looked at on paper to replace a geared IPS, that one comes closest (PJS 300 IN)

If you don't want to go prop carving, that on a 9x7.5 (3s LIPO) or 10x7 or 11x7 SF (2s LIPO) slow fly prop should get it all in the air.

I am trying to wind a motor with those general charactristics myself..Its pretty poor efficiency wise but it will swing a large prop slow..
Jul 21, 2006, 09:43 AM
Light and floaty does it
Work in Progress's Avatar
You may be interested in my experiences scaling up a KK Competitor to Gipsy size (40" span) and with some structural refinements.

That flies nicely on 2s on a Feigao 4100, A gearing and 8x6 prop. On 3s it goes like a rocket on the 8x6.
I went with relatively shallow gearing and a small prop to make it easy to fly and because I wanted to avoid a steep deck angle, weight and drag associated with the super-length undercarriage and enormous prop. But I did have to trade-off some of the "rubber powered" character and I can definitely see the attraction of doing it with a monster super-coarse rubber style prop.
A deep-geared IPS gearbox and brushless 12mm would be my choice for that application.
Jul 21, 2006, 09:47 AM
Light and floaty does it
Work in Progress's Avatar
By the way, I reckon you will end up with a flying weight of 8-9 ounces depending on choice of LiPo, and that's no weight at all for a model like this.
Jul 28, 2006, 03:08 PM
Registered User

Thanks for your input....always a great help and encouragement.
I fancy the carve your own (balsa) prop route.
Not too bothered about efficiency.
Going to go for a PJS 300 IN and a home brew gearbox.
I want the (electric) Gypsy to look like a rubber model.
So no servos and a Zombie for flight scheduling, so 4 amps tops and hopefully a lot less.
Will post when I have something to shout about.

Am I going to get good at prop carving, or what??


Jul 29, 2006, 12:21 AM
Voices through wires? Ha!
Chas's Avatar
Try the laminated method! Great for high pitch, large diameter props at cheap prices.
Jul 29, 2006, 02:42 AM
Registered User
A great trick I remember seeing, was to add a water based dye to the PVA.

When the prop. was all carved and finished, the coloured lines were quite visible, and looked great.
Aug 13, 2006, 01:24 AM
Sir Jasper
zl3vml's Avatar
I have converted three vintage models so far to electric.
All fly well indeed. Both the Simplex and the Baby Bombshell were built for 1/2A Texaco (10 oz/sq ft wingloading) and then converted to electric so are a fair bit heavier than if I had built them for electric only.
The centre model, the Sparky is a rubber model that I built from start for electric instead of rubber.

Initialy I was going to fit a GWS - IPS system but it would not fit in the front without some serious modifications to the model, so I rewound a mini cdrom motor to a current draw of 2A, and with two LiPo's of 350mA (for our club SOS events in which the weight of LiPo's may not exceed 20g) I get two flights of around 10-12 minutes each.

After the initial burst of power to get a bit of height 30 or 40 ft or so I throttle back to just above tickover, just enough to maintain height at a very slow and rubber like pace.

The all up flying weight is just a tad over 5oz, not much more than the original model with rubber.

I am using a GWS prop, I know it does not look genuine and I had thoughts of carving a balsa one to the same dimensions but have not done so yet.
Maybe sometime....


By the way, the Sparky has micro RX and two servos for rud/elev

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