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Old Mar 28, 2005, 02:08 PM
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Palo Alto, California, United States
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Mills 0.75 Diesel RC

A few years ago I purchased a K-Mills diesel motor with an RC carb for about $40. This an Indian-made copy of the popular Mills 0.75cc (aprox .049 cu inch) free flight motor and includes an RC throttle carb. I bench ran the motor and never really liked its performance. Construction quality is poor and it does not start easily (unlike the original Mills 0.75). It turns a Cox 7x3.5 prop at 8000 RPM and the throttle does not work very well on this sideport motor.

I decided to build a sheet balsa model for the engine and I threw together this twin boom motor glider that uses a Jedelsky all-balsa wing (see photo below). I decided to make it a pusher to keep the oil off of most of the plane, but I made the nose a bit too short and needed several ounces of nose weight to balance it. The wingspan is 50 inches and it weighs 16 ounces. The controls are rudder(s),elevator, and throttle.

The model flies great even with the wimpy Mills chugging away. It climbs at about 400 fpm and is easy to fly low and slow in the park. The Jedelsky wing is very efficient at low speeds and super-easy to build. If I were to build another I'd make the nose longer and use a little less dihedral. Maybe a more rounded fuselage would make it look less ugly.


Steve
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Old Mar 28, 2005, 08:31 PM
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Walla Walla, Washington, United States
Joined Sep 2003
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Neat design! I like the way it looks the way it is, the color scheme is especially elegant. I'm glad to hear that it flies well. That is a nifty little diesel, too bad it isn't a great runner. Where did you get it? Looks good,

Derek
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Old Mar 30, 2005, 01:59 AM
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Palo Alto, California, United States
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Derek,

I purchased the engine from Carlson Engine Imports. It was being sold very cheap and I have no complaints with them for selling it to me. Does anyone know if Carlson is still in business? Their web site is no longer working...


Steve
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Old Mar 30, 2005, 02:17 AM
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QLD, Australia
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Steve,
The Mills is a long stroke motor and has good torque try useing a 7X5 or 7X6 prop on it .
Stewart
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Old Apr 01, 2005, 06:08 PM
Barnwell, SC
Barnwell, SC
Joined Sep 2004
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I had one that was happiest with a Zinger wood 8-3 prop. Anything smaller and it vibrated. Once broken in it was an easy starter. I gave it to a friend who still has it.
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Old Apr 01, 2005, 06:19 PM
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Palo Alto, California, United States
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I put a trike gear on it and took out some of the dihedral. It flies better and is more fun to fly with the landing gear.

The 7x3.5 prop is OK and I probably won't try a bigger one. This engine isn't really the same as the original Mills and I think that is where its problems lie.

Steve
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Old Apr 01, 2005, 06:44 PM
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QLD, Australia
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Steve,
It is normal for lapped piston motors to be harder to start befor being fully run in , also they benefit from larger props dureing running in . As the motor runs in the max revs should increase to around 10,000 for the mills( even the curry mills) , I have not seen anyone use smaller than a 7x5 on these, and as hfen says they are quite happy on larger props .
I have used an original Mills, I own and use an indian k75, and a russian Mills75 , all perform closely. The russian took the longest to run in .
Stewart
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Old Apr 01, 2005, 09:15 PM
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Keremeos, BC Canada
Joined Mar 2004
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Good info. I, too, had a couple of the Indian version, and that was the first thing I found: inconsistent manufacture! Also have an original, much better. The Champion is my Doonside Mills 75, it is absolutely peerless; no one will duplicate that one, I'm sure. It started easily, breakin was effortless, power was excellent for it's design, and fuel economy was second to none. I nearly lost it on a freeflight biplane; scary!

Now I do freeflight less, and I will doubtless build another Bristol Scout for it, with a couple of miniservos in it, if for no other reason than to keep that motor...
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Old Apr 01, 2005, 09:34 PM
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Stewart,

Mine has several hours of bench running to its credit, so I think it's broken in. I purchased it in 1999 and ran it on the bunch just trying to see if would ever improve, but no good news yet. I don't think it's up to par with a properly built Mills .75. Even the prop nut is drilled crooked and wobbles when the crank rotates!


Stve
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Old Apr 01, 2005, 10:24 PM
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Rex, NC "Extreme Boonies"
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Your Mills..

Must have been made on an Indian holiday, (or the day after) where they did a lot of drinking! I purchased 2 of the r/c throttled Indian Mills replicas from Carlson a few years back, and everything on the ones I got was fine... including the performance. I guess I got a couple good ones off the line, made in the middle of the week! I thought they were a great deal at the price. I love your plane design, it's very appealing! Does she fly & handle as good as she looks? Bob
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Old Apr 02, 2005, 09:20 PM
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Keremeos, BC Canada
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Another thing I learned about running an Indian Mills as a pusher: it helps a lot to use a brass washer as a thrust bearing between the case and prop driver. I noticed that there was more and more endplay, so I eventually found a washer that took up almost all of it, and it seemed to pull better. This is not unique to the IMills, as most plain bearing engines end up with the same problem; has to do with steel prop driver agains an aluminum or potmetal case. Engines with proper (ball) bearings don't need this mod.
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