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Building Tips and technical articles. => 1/2 A building. => Topic started by: Mark Mc on September 25, 2020, 09:44:01 AM

Title: Another Mid-70’s engine question.
Post by: Mark Mc on September 25, 2020, 09:44:01 AM
I was just reading the Gremlin 1/2A pattern plane article in the May ’75 issue of Model Builder by Tom Dixon, and it says the plane flies on a Cox “stunt special” engine.  The “stunt special” is a TD .049 with a Babe Bee piston/cylinder and a low compression glow head, a Kirn-Kraft NVA, and turning a Cox 6x4 prop on 5% nitro fuel from a Perfect wedge tank.  Tom says this pulls the 12 ounce model through the entire stunt pattern.  The KK fine needle would be the only thing I would have associated with “performance”.  A low compression head topping a single bypass/no boost cylinder with SPI doesn’t scream “performance”.  5% nitro on a 1/2A doesn’t scream “performance”.  A TD on suction from a standard plumbed wedge tank doesn’t scream performance.  And a Cox 6x4 doesn’t scream “performance” (unless you’re propping for torque).  And we all know Cox TD engines were made to scream.

What exactly am I missing on this?
Title: Re: Another Mid-70’s engine question.
Post by: Larry Renger on September 25, 2020, 10:01:52 AM
Sound all wrong to me! I went the other way with a Medallion bottom end and Tee Dee top. 15% Nitro. Great runs!
Title: Re: Another Mid-70’s engine question.
Post by: John Given on September 25, 2020, 02:05:04 PM
Sound all wrong to me! I went the other way with a Medallion bottom end and Tee Dee top. 15% Nitro. Great runs!

This is what I’d do.
Title: Re: Another Mid-70’s engine question.
Post by: 944_Jim on September 26, 2020, 08:02:46 AM
Oh, why did I see this? This plane is cute.  Now I want to build one! For all the concern about tail weight, I wonder how it would be scaled up about 5-8%, and flying a Norvel Big Mig .061.

Thanks for the tease.
Title: Re: Another Mid-70’s engine question.
Post by: Larry Renger on September 28, 2020, 08:20:45 PM
Go with it as is and just fly on longer lines. You’l love it.
Title: Re: Another Mid-70’s engine question.
Post by: Brett Buck on September 28, 2020, 08:24:59 PM
Sound all wrong to me! I went the other way with a Medallion bottom end and Tee Dee top. 15% Nitro. Great runs!

  Indeed, your method sounds a lot more plausible, the last things you want is to lower the compression or run the TD intake system

    Brett
Title: Re: Another Mid-70’s engine question.
Post by: Larry Renger on September 28, 2020, 08:33:10 PM
Nothing wrong with the Tee Dee in take system, it is the wild Tee Dee crank timing! A Tee Dee with a Medallion crank shoUld run just fine as a stunt engine, it is just easier to grab the entire Medallion bottom end. (Especially if you work in the factory 🤭)