The Internet Craftsmanship Museum Presents:

Leroy Cox

Added to museum: 2/5/09

1906—December, 1981

Leroy Cox checking parts on the engine assembly line.  Photo courtesy of Pegasus Hobbies archives

Leroy M. Cox, L.M. Cox Manufacturing Co. Inc.

(Based on a more detailed biography by Evan T. Towne that can be found on the Academy of Model Aeronautics web site at

Bringing powered model cars and airplanes to millions of enthusiasts

Leroy Cox developed an early interest in mechanical devices while working around his father’s bicycle shop in Placentia, CA. Once out of school he spent 20 years as an electrician, running his own electrical business part time. Efforts to branch out into a photography equipment business were unsuccessful due to shortages of materials caused by World War II.

In 1944, he came up with a superior design for a wooden popgun and produced it on a small budget it his garage with the help of neighborhood women as his workforce on an initial investment of $2200. Like some of his later products, its success was based on the fact that it was better built than the existing competition. Sales took off rapidly and the product was a success; however, the renewed availability of metal for toys at the end of the war meant that wooden toys were soon to be a thing of the past. Cox recognized this and along with a friend, Mark Mier came up with a design for a metal model racecar to take advantage of post-war America’s fascination with cars. By August 6, 1946 he and a crew of 20 people were turning out 1500 unpowered model cars a day.

A fire that totally destroyed the factory on August 7th brought an end to production after 4 months. The destruction was almost total and there was no insurance, but they still had orders on hand, so he did some fast talking and bought a nearby vacant lot. A military-type Quonset hut was set up in 4 days, and by October 15th he was back in business filling orders for Christmas. He even managed to double his production capacity with the emergency change.

He introduced the Cox Thimble Drome Champion racecar in 1947. This model was not a pull toy but included a handle and cord that attached to the side so it could be swung around in circles at high speeds. The 9-1/2” long metal car had rubber tires and an attractive paint job, adding to its success. The $4.95 car ushered in the start of the popular fad of tether car racing and the “Thimble Drome” name was soon to be applied to future products as well.

Cox noticed that customers, fascinated with the realism of the Champion racecar were installing engines from model aircraft in it. He contracted with Cameron Brothers model engine company for a .25 cubic inch engine that could be installed in the Champion using a direct drive. The confined cockpit area dictated vertical cooling fins rather than horizontal as was the convention. A later engine called the “Doodle-Bug” was similar but smaller with a displacement of .099 cubic inches, and a larger .19 engine was also developed. By 1948 he was ready to introduce a ground-breaking engine powered racecar. It was the first under $100—WAY under $100—at only $19.95. Sales that year were over $500,000 for cars with and without engines. He also developed and sold his own brand of Thimble Drome racing fuel.

In 1949 the company added a smaller car called the Special. The .045 cubic inch engine was made up from a piston, rod, cylinder and head from the Mel Anderson Company but produced in his own factory so he could better control the quality of production. Other engine manufacturers at the time were experiencing quality problems because often they could not afford produce all the parts themselves. They would source out production of certain parts to others and then do the final fitting and assembly themselves. Cox recognized that in order to get high production quality and consistency he wanted, he would have to control all production himself and even designed the manufacturing equipment needed to do so. Eventually the entire racecar and engine were made within his own facility, although he later outsourced production of plastic parts for some products.

1949 saw a rapid decline in the popularity of tether cars, but engines were still in demand in the rapidly increasing model airplane market. Cox spent the next year working on an engine that would overcome some of the problems (hard starting, lack of dependability) that plagued existing engines. He felt a better running, easy to start, high quality engine would bring many more people into the model car and airplane hobbies and came up with an .049 cubic inch glow engine called the Thimble Drome “Space Bug” that hit the market about October, 1950.

This engine featured a glow head with built-in coil of Cox’s own design, but the main advance was the steel piston and cylinder that were machined to very close tolerances for the time. The compact crankcase was cast aluminum and attached to a large cast aluminum gas tank which was mounted to the firewall with four screws. Inside the tank was a reed valve fuel induction system. The Space Bug sold for $6.95. With the heavy tank removed it was called the “Thermal Hopper” and also sold for $6.95. The “Space Bug Junior” featured a plastic tank and sold for $3.95. An engine review in Model Airplane News magazine in 1953 sparked a new wave of enthusiasts.

Cox offered their first complete airplane in 1953. The Thimble Drome TD-1 was a U-control model weighing 10 ounces and had an aluminum wing that was 24-1/2” long. The plastic body was 18” long, and it sold for $19.95 ready to fly including an accessory kit with a Skyon control reel, battery wires, connecting clip, control lines, filler hose and finger guard.

Leroy Cox (second from right) and staff from the new plant. (Click on photo to view a larger image.) Photo courtesy of Pegasus Hobbies archives

By the time the engine was winning almost all the ½-A flying contests and a new factory was built in Santa Ana, CA where 250 people were employed. In 1955 they introduced the second generation .049 engine which was called the Babe Bee. The engine now featured a spun aluminum tank in place of the cast tank and a signature black glow head and cylinder. The engine initially sold for $3.98, but you could also buy it mounted in several different plastic U-control plane. It had a spring starter making it easy for even a novice to start properly.

Cox later introduced the Pee Wee, which was an exact scaled down copy of the Babe Bee displacing .020 cubic inches. Interestingly, despite the smaller size it put out almost as much power as the larger engine. It was billed as “The World’s Smallest Model Engine” and sold for $3.98. These two engines were to remain in continuous production for well over 50 years, a remarkable achievement in itself.

For 1961, Cox took the line of reed valve sport engines and expanded it to include contest or high performance engines. They had engine designer Bill Atwood come up with a front rotary valve induction system to increase RPM and came up with what was called the Space Hopper*. The new method was applied to four engines for 1961 release: the .010, .020, .049 and .15 cubic inch models.

*Bob Beecroft notes, "The front rotary induction engines were the Tee Dee series I think is what is meat here."

The .010 had no fuel tank so it could be used with light, thin-wall brass tanks. It could turn up to 30,000 RPM and sold for $7.98. (It was sometimes offered with a brass tie clip in case the user wanted to wear it to work instead of use it to power an airplane—a testament to its tiny size.) The .020 sold for $6.98, the .049 for $7.98 and the .15 for $12.98. These engines have sold in huge numbers and brought the company a lot of financial success.

The slot car fad did not go unnoticed by Roy Cox, and in 1962 they established Cox International in Hong Kong to meet this demand. However, the sudden collapse of the slot car fad in 1967 left the company with a cash flow problem. At this same time Roy’s wife died and he experienced health problems, so he sold the company in 1969 to Leisure Dynamics, Inc. who continued production of the engines until the company was purchased again by Estes/Centuri in 1996. The company celebrated its 60th anniversary in 2005.

Leroy Cox died in December, 1981. His company over the years produced so many engines (sometimes over 1 million a year) that it is said their total output exceeded that of all model engine manufacturers in the world put together. That is quite a remarkable achievement, and many modelers today got their start with his products.

Marketing successes

Early Disneyland visitors in late 1950's may remember the flying circle near Tomorrowland where young pilots gave demonstrations of U-control aircraft hourly, doing some fancy flying and teaching others how to fly. Cox managed quite an advertising coup when he got his aircraft and employees chosen for these demos, seen by hundreds of thousands of visitors to the popular amusement park. The "Flight Circle" had previously been manned by flying club members initially and then by the Wen-Mac company, but Cox's reputation as a more reliable manufacturer got them the into this premium space starting in the summer of 1958 until it closed in 1965. The young flyers would sometimes fly two or three aircraft at a time or bring people from the crowd in to try their hand at flying Cox aircraft. Tether cars ran in circles and powered boats also ran in a pond. For more on the Flight Circle at Disneyland CLICK HERE.

Cox employees gave hourly flight demonstrations in the Flight Circle in Disneyland's Tomorrowland from 1958 to 1965. The second photo shows Lee Heinly, one of the Cox pilots, at the display after the last show in 1965. Behind him is the model boat pond. (Click on a photo to view a larger image.) Photos courtesy of Second photo thanks to the CoxPilot, Lee Heinly.

Roy was also well attuned to what the public wanted, and was always ready with the right product at the right time in history. However, the basis of his success in each product he offered was quality. His engines were successful because he insisted on standards of production excellence not previously achieved by other manufacturers, despite the large numbers of engines he produced. He developed his own manufacturing and testing equipment to achieve this level of excellence. It is claimed that piston/cylinder tolerances of over 25 millionths of an inch (0.0000025”) would result in rejection.

Roy Cox was also one of the first hobby manufacturers to exhibit at the Nurenberg Toy Fair and the first American company to have a booth there. This gave his company world-wide exposure and resulted in exporting his engines to over 50 countries.

More sources of information on Cox products and history

For a more complete discussion of the development and specifications of various Cox engines see This site includes diagrams of how the engines work and photos of the various glow heads.

Additional information from the Cox museum can be found at This site from Germany has quite a collection of Cox specs and details and is probably the most complete source on Cox products and history available.

An article about Leroy Cox including a photo of him from Mechanix Illutrated, November, 1958 can be found at

Comments from others

"I hadn't realized it was Bill Seltzer who came up with the machined bar stock concept to replace the earlier castings. Man, he was there a very long time! I met him in 1995 when Cox agreed to manufacture the Medallion .051 especially for NFFS (National Free Flight Society). We made a contract that was sealed on nothing more than a handshake and the motors were made. It's really a shame they are now gone."

--Bob Beecroft

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Photos of Leroy Cox and some of his products:

Leroy Cox (Right) receives and award from the Hobby Industry Association. Photo courtesy of Pegasus Hobbies archives
Leroy Cox on the factory floor with a production worker. In front of them is a pile of parts to be assembled. Another photo shows more of the production area. Photo courtesy of Pegasus Hobbies archives
  Leroy Cox (Center) with other company officials.  Photo courtesy of Pegasus Hobbies archives
A letter from 1970 announcing the appointment of William Selzer as president of the LM Cox Manufacturing Company, then owned by Leisure Dynamics, Inc. after Mr. Cox had sold the company and retired. Mr. Selzer was the company engineer who had originally come up with the idea of machining bar stock crankcases rather than using less reliable castings. The second photo shows Mr. Selzer. (Letter courtesy of Pegasus Hobbies archives)

Donated by Joe Martin

The .010 cubic inch Tee Dee was the smallest engine made by Cox. The photo on the right shows a tie tack sold as a place to mount the engine in case you wanted to attract attention to your hobby at work or social occasions that called for a tie. Photo: Joe Martin Foundation
A Cox Pee Wee .020 is shown in the original packaging. It has a needle valve at the rear of the aluminum gas tank for fuel adjustment. This engine was donated to the Joe Martin Foundation museum by Denny Bevis, who also included a glow plug, starting kit and several props—all new and in their original packaging. Photo: Joe Martin Foundation

Donated by Joshua Vest

A Cox Tee Dee .020 in its original packaging, a clear plastic box, also includes the original instruction sheet and two spark plug wrenches. It was donated to the museum by Joshua Vest. This engine has a red plastic gas tank and a carburetor with needle valve in front of the cylinder. Photo: Joe Martin Foundation

Donated by Tom Boyer

The Cox .049 Babe Bee may be the highest production engine in the world. Some years saw production on this engine top 1 million, and it was produced for many years. The one on the left was donated by Tom Boyer. The one on the right with the spring starter was donated by Bill Holcomb along with an original bubble pack card showing a sale price of $4.69. Photo: Joe Martin Foundation

Donated by Joe Martin

The Cox Tee-Dee .051 was made in 1961 and was basically an .049 with a slightly longer stroke. (Bore: 0.410", Stroke: 0.386") The packaging refers to it as a front rotary valve contest engine.

This example is still in the original packaging, which consisted of a folded cardboard base and molded plastic cover which were enclosed in a slip-on cardboard cover. Inside the base were glow plug wrenches and an instruction sheet. A yellow sheet stating "Special Notice" says that this engine was fitted with a new high compression glow head with three .005" thick copper head gaskets installed at the factory. The idea was to remove one or two of them after the first few runs, which would result in about a 250 RPM increase in speed for each gasket removed. This increase came at the expense of ease of starting as the compression was increased with each gasket removed. Cox racing fuel (red can) was recommended for this engine. Photos: Joe Martin Foundation

Paul Cords sent this photo of a Cox P-51, typical of the scale realism of the .049 powered aircraft models offered by the company. Paul Cords photo
An ME 109 stunt plane based on the famous WWII Messerschmidt fighter.
A PT-19 control line trainer. Many real pilots learned to fly in the full-size version of this plane, and many kids took to the air for the first time with the Cox version. The wings were attached to the fuselage with rubber bands that would come off in case of a crash.
A TD-3 with the "Sky Reely" control line handle.
A 1/2 A combat plane with a Tee Dee .049 engine.
Two Sea Bee speedboats shown also with the engine cover open to expose the Cox Babe Bee .049 engines. The marine version of the engine in the blue boat featured a head with large cooling fins.
A stock and a modified Water Wizard.
 A Shrike propeller driven car and a 1/32 scale Corvette slot car. The Cox slot cars featured an aluminum frame and high quality molded bodies in several popular styles. A factory was built in Hong Kong to meet this expected demand, but they hit the market near the end of the slot car craze, leaving the company with a cash flow problem.

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