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1Repair Windows errors before they cause bigger problems2Scan for outdated or missing drivers - takes under a minute3Clear out junk files and repair common Windows errorsThe Allbon Bambi is the best-supported answer to “What is the world’s smallest diesel engine?” It is a 0.15 cc (0.009 cubic-inch) model-aircraft diesel designed by Alan Allbon and manufactured by Davies-Charlton (D-C) Ltd. Its power was sufficient to fly a small free-flight model, making it a genuine flying engine rather than a bench-top novelty.
The wording needs care: the Bambi is the smallest-displacement model engine documented as entering series production, not the smallest miniature piston engine ever built. A custom 0.05 cc engine was smaller, while the often-mentioned Cox Tee Dee 0.010 used glow ignition and therefore was not a diesel.
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What makes the Allbon Bambi the leading answer?
Adrian’s Model Aero Engines describes the Allbon Bambi diesel as “the smallest-displacement model engine every to enter series production.” The engine’s displacement is 0.15 cc (0.009 cubic inches). Alan Allbon designed it, and Davies-Charlton (D-C) Ltd. produced it for the model-aircraft market.
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How small is it compared with other miniature engines?
“Smallest” changes depending on whether the comparison is limited to diesel engines, mass-produced engines, or any working piston engine. The table separates those categories instead of treating them as one record.
| Engine | Ignition and fuel type | Displacement | Production status | Documented use or performance |
|---|---|---|---|---|
| Allbon Bambi | Diesel model-engine type | 0.15 cc (0.009 cu in) | Series-produced by Davies-Charlton | Power reported adequate for a small free-flight model |
| Cox Tee Dee 0.010 | Glow ignition | 0.1634 cc (0.00997 cu in) | Mass-produced miniature aircraft engine | 13 g without tank; 15.3 g with tank, according to a 2006 University of Maryland dissertation |
| Rova Blitz by Ronald Valentine | Diesel | 0.05 cc | Limited custom engine, not widely produced | No published performance data established |
| D-STAR 0.050 | Micro-diesel | 0.050 cubic inch | Laboratory micro-engine project | 0.12 hp at 18,000 rpm; a coupled generator produced 50 W net output in the reported system |
The Cox Tee Dee 0.010 is slightly larger than the Bambi at 0.1634 cc, despite its name suggesting a 0.010-cubic-inch class. It is a glow engine, so it is not evidence that the smallest diesel and smallest mass-produced working piston engine are the same thing. The University of Maryland dissertation identifies it as a benchmark for miniature mass-produced engines.
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Ronald Valentine’s 0.05 cc Rova Blitz is smaller by displacement than the Bambi, but it was a custom build rather than a broadly manufactured product, and published performance figures are not available. It is therefore best described as a smaller custom miniature, not as a replacement for the Bambi’s production record.
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A model diesel engine compresses an air-and-fuel charge until the heat of compression ignites it. Unlike a glow engine, it does not rely on a continuously heated glow plug for ignition. At 0.15 cc, each combustion event releases very little energy, but the engine can run at high rotational speed and turn a propeller sized for a very light aircraft.
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Small free-flight models are designed around that limited output. Their low mass and low aerodynamic drag let a brief powered climb produce a useful flight. The engine does not need to lift a person, carry a battery, or provide sustained thrust for a full-size aircraft; it only has to accelerate a lightweight model and establish its flight pattern.
Why miniaturising a diesel is so difficult
Tighter machining and sealing
As cylinder bores, pistons, crankshafts and ports shrink, ordinary manufacturing tolerances consume a larger fraction of the available dimensions. A clearance that is insignificant in a larger engine can cause compression loss or seizure in a miniature. Sealing also becomes harder because leakage through a tiny gap can represent a substantial share of the total charge.
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Fuel-air mixing
The fuel and air have less physical distance and time in which to mix before ignition. Small passages can make mixture settings unusually sensitive, and a minor change in needle position or fuel composition can move the engine from weak running to an overly rich or lean condition.
Friction and heat
Surface friction and bearing losses do not shrink in perfect proportion to power output. In a tiny engine, those losses consume more of the available work, while the small mass and surface area make temperature control and lubrication more demanding.
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The University of Maryland work cautions that laboratory measurements of hobby engines were often below manufacturer claims. Fuel formulation and mixture settings affected the results, so a published horsepower figure should always be tied to its test conditions rather than treated as a universal rating.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What the historical records do—and do not—prove
- The Bambi is a documented 0.15 cc diesel that entered series production and was capable of powering a small free-flight model.
- The Cox Tee Dee 0.010 is a 0.1634 cc glow engine and a separate mass-production benchmark.
- The 0.05 cc Rova Blitz demonstrates that a smaller diesel was built, but not that it was commercially produced or better performing.
- D-STAR figures show what a larger 0.050-cubic-inch micro-diesel system achieved under reported laboratory conditions; they do not establish a world record for the smallest aircraft engine.
Can you buy one today?
The Allbon Bambi and Cox Tee Dee 0.010 are vintage engines. Current stock, pricing and ongoing production were not established in the available records, so a listing should not be assumed to represent regular manufacture. Collectors generally encounter such engines through specialist vintage-model channels, estate sales or restoration projects, and condition varies substantially.
For restoration, verify that the piston, cylinder, crankshaft, compression screw and fuel fittings are present before attempting a run. A seized or incomplete antique engine can require specialist machining, and forcing the compression screw or propeller can cause permanent damage. Treat any surviving performance number as historical unless it is accompanied by a modern test setup and fuel specification.
Bottom line
The Allbon Bambi is the most defensible answer to “world’s smallest diesel engine” when the claim means the smallest-displacement diesel model engine that entered series production and flew a model aircraft. Smaller custom engines existed, and the Cox Tee Dee 0.010 is an important but glow-ignition comparison. The achievement is not just the 0.15 cc number; it is making a diesel that could be manufactured and deliver enough reliable power to put a real aircraft model into the air.
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