DEEZIL!
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Tiny Diesel RC Plane Engine

Tiny houses. Tiny cars. Tiny diesels. Now you’ve seen it all. We’ll bet you didn’t know that diesel engines have long been a part of the model aircraft world. In the early days of the hobby before World War II, the intricate spark-ignition engines were the biggest expenses. Simplified engines didn’t enter the market in a big way until after WWII, and here comes the diesel content. WWII saw advanced diesel engine technology and exposed many more people to it, so it was no wonder the model aircraft engine hobby took a stab at downsizing it once the war was over.

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Deezil: The diesel engine that lives in infamy! The manufacturing year of this engine is unknown, but it comes from the most infamous years. Owned by Dan Badger, curator of the America’s Packard Museum in Dayton, Ohio, it’s shown nestled in the valley of a legendary full-sized aircraft engine, the Packard Merlin. Badger, a private pilot as well as an RC aircraft modeler, keeps the engine as a curiosity piece. He’s never tried to start it, saying he doesn’t want to blow it up… assuming it would even start. The bronze flywheel is there to simulate the weight of a propeller, leading one to conclude this engine may have actually run at some point.

Among the many companies working on diesel model aircraft engines was Gotham Hobby of New York City. Gotham Hobby was founded by two WWII veterans, brothers who had once been part owners of a long-running New York hobby store, America’s Hobby Center (AHC). AHC was founded in 1931 by the four Winston brothers, but for whatever reason the two veteran Winston brothers weren’t welcomed back to AHC after their service. After a little family feuding, the brothers started Gotham Hobby. The Gotham Hobby diesel story begins soon after, although ironically AHC was also working on a diesel at nearly the same time but never got past the prototype stage.

The Gotham Hobby “Deezil” made it to production in 1947 and was initially sold at the outrageous price of $12.95 (about $149 in 2019). According to various model engine historians (yes, the model aircraft hobby has its own history geeks), this wasn’t out of line for a quality engine of the period. Too bad the Deezil didn’t remain a quality product. In fact, it’s become notorious in the model aircraft community as one of the worst model engines of any type ever built.

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The rear view shows the “carburetor.” The engine inhales through a rear-facing port in the crankcase and exhausts via ports to either side of the crankcase. The compression screw is on top of the head and is screwed in to raise the compression and out to lower it. Raising the ratio has the effect of advancing the timing and vice versa.

The Deezil was a good design and of decent quality when first built. Model engine guru and historian, Adrian Duncan, says this engine was likely designed and initially built by someone outside Gotham Hobby, someone with more than a little knowledge and skill. It displaced 0.124 cubic inches from a 0.473-inch bore and a 0.708-inch stroke and weighed 5.22 ounces. It was advertised for 8,000 rpm using a 6×10 propeller (6-inch diameter/10 pitch). It had a variable compression ratio, which you could tune as the engine ran or for starting. Induction was via ports (much like a loop-scavenged diesel) with a simple carburetor-like device. The prescribed fuel was either a 60/40 mix of castor oil and ether, or a 60/40 mix of SAE Grade 60 or 70 engine oil with ether. In later years some modelers used a mix of 75/25 mix of diesel fuel and castor oil.

We weren’t able to find any advertised power figures from back in the day, but blueprinted NOS or repro engines of recent times have produced between 0.077 and 0.084 rip-snorting horsepower between 6,700 and 6,900 rpm, and as much as 0.112 horsepower at 8,800 rpm. According to Adrian Duncan, who made the upgrades and published his test results in a 2011 Model Engine News article, these are very good numbers.

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The first Gotham Hobby Deezil ad appeared in 1948.

Not long after its introduction, the Deezil went into a tailspin. Sales were low initially, so Gotham Hobby decided to cut manufacturing corners in order to cut the price. The price was dropped from $12.95 to $2.95 and eventually to $1.95. This is when cheesy three-piece brazed crankshafts and excessive piston clearance entered the picture. You never knew if a new engine would have enough compression to run or not. If it did run, it might’ve done so for a few minutes and then grenaded. By 1955, Gotham Hobby pulled the plug on the Deezil and it was tossed on the trash heap of history.

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Soon after the Deezils were built, model aircraft engine manufacturers settled in on nitromethane-fueled engines that employed a glow plug. The glow plug is heated by a battery for starting, but once the engine is warmed up, the glow plug retains enough heat to ignite the compressed air/fuel mixture. In many ways these engines work like the old hot tube/hot bulb semi-diesels of the past. There are still model aircraft diesels out there today, but they’re very intricate, complex, and expensive.

In recent years, collectors have revisited the Deezil and there are hilarious YouTube videos of people trying to get vintage NOS Deezils to run. More serious individuals like Adrian Duncan have re-engineered the Deezil, replacing the most failure-prone parts with dimensionally correct ones made from better materials. The results have yielded a good running compression-ignition model aircraft engine.

The ’47-55 Deezil remains one of the most talked-about model aircraft engines of all time, but that talk is generally laced with profanity. It’s become the model aircraft equivalent of the Yugo, with a level of infamy that rises to legendary status. Like the Yugo, it’s a poster child for ruining a basically good design with poor manufacturing quality.

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This small scale machine was a building block for diesel engines. It’s highlights and blunders aided the development of diesel engineering seen today.

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The Deezil featured a die-cast crankcase, bronze connecting rod, composite cylinder and head (two-piece steel sleeve and aluminum head), and a ringless steel piston. The first crankshaft design was a nicely machined once-piece steel part supported by a bronze bushing. It was later downgraded to a brazed three-piece unit supported by a cheap brass bearing. Piston fit was vital for adequate compression, but during most of the Deezil’s production run little care was taken to clearance-fit pistons to bores. Many, if not most, wouldn’t start from day one due to low compression.


SOURCES

Adrian’s Model Aero Engines
AdriansModelAeroEngines.com

America’s Packard Museum
AmericasPackardMuseum.com

Model Engine News
ModelEngineNews.org