1/2A Model Flying

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Written by Fitz Walker
Big fun with tiny engines
As seen in the March 2021 issue of Model Aviation.

many coxpowered models do not have a throttle so dead-stick landings will be the norm
01. Many Coxpowered models do not have a throttle, so dead-stick landings will be the norm. Fortunately, most aircraft in this class have benign gliding performance. Photo by Lee Ray.
this quickie dragonfly was designed in the 1980s for .049 engines
02. This Quickie Dragonfly was designed in the 1980s for .049 engines. The model was scratchbuilt from Radio Control Modeler plans.
flying 1/2a-size models will hone your hand-launching skills
03. Flying 1/2A-size models will hone your hand-launching skills. Even those that have wheels will likely be too small for grass takeoffs. Ray photo.
like this mini mamba many 1/2a models tend to be kitor scratch-built and are relaxing to fly
04. Like this Mini Mamba, many 1/2A models tend to be kitor scratch-built and are relaxing to fly.

As a wee lad—that is, in my preteens—I was introduced to the world of model aircraft flying. This was in the form of Control Line (CL) airplanes. Not surprising because this was in the late 1970s when such flying was still popular.

My then-stepfather had a history of aircraft modeling—Free Flight (FF) and then CL—so he sought to give it a try with me. His method of training was through the venerable—no, legendary—Cox PT-19. For the uninformed, this was a nearly ubiquitous CL trainer entirely made of plastic and held together by rubber bands and wishful thinking. It was quite durable, which it needed to be. Its flying qualities were likely mediocre at best, but I didn’t care. It was a cool model airplane that I could fly (assisted), even if it wasn’t RC.

At that point, I was hooked. Although my mother’s and stepfather’s marriage didn’t last, my interest in model aviation did. I don’t really recall flying that old PT-19 much after that, but I eventually did get another CL wonder—the awesome, spaceship-looking Testors Galax IX. This was a pusher-configuration piece of "plastic fantastic," which I remember flying quite often with my neighborhood friends, much to the chagrin of my neighbors who complained about the noise in the cul-de-sac in which we flew. Thus began my lifetime love of 1/2A-powered models.

some.049-powered cl models can get quite exotic, such as this old testors galax ix
05. Some.049-powered CL models can get quite exotic, such as this old Testors Galax IX. Despite its unusual configuration, this model can be flown by kids.
this out-of-production rc helicopter was initially powered by a cox
06. This out-of-production RC helicopter was initially powered by a Cox .051. It was later upgraded to an NV Engines (formerly Norvel) .061 engine.
cox made a variety of ff helicopters for its engines
07. Cox made a variety of FF helicopters for its engines. Expect to get a lot of exercise when flying these!

Technically, the term "1/2A" refers to methanol-fueled glow engines of .010 to .049 cu. in. displacements. The .049 was the most common size. Although 1/2A refers to a specific size and class of competition engines, most modelers use the phrase in generic terms to mean anything with an engine size of up to 0.061 cu. in.—basically, small models with really loud engines. When an engine is this small, mufflers are often not used.

These engines typically swing a 5- or 6-inch propeller at approximately 20,000 rpm or so, which is roughly equal to 400-class electric motors of approximately 60 watts. What they lack in power they make up for by turning propellers really fast. Of course, these power and rpm numbers vary, depending on the engine and its manufacturer, and the fuel used.

An overwhelming number of these engines were made by the now-defunct Cox engine company, named after Leroy Cox, which manufactured millions of them from the 1950s to the late 1990s (estimates put it at tens of millions of units made). Simply saying "Cox-powered model" is synonymous with saying ".049-powered model," despite the fact that there have been many other manufacturers of similar-size engines such as Wen Mac, MP-Jett, Testors, and Norvel, to name a few.

These little gems were inexpensive to buy and economical to operate. If you were like me—a starving student living at home—Cox-powered models were the primary means of flying model airplanes. Fortunately, there were countless models designed for those small powerplants. Practical, small, electric power wasn’t practical at the time, so budget flying options were limited to these tiny glow engines.

My first Cox-powered RC model was actually a glider conversion. I took a Goldberg Gentle Lady glider and added a power pod to it. The little Cox .049 engine mounted above the wing did surprisingly well for such a large airplane. I essentially taught myself to fly with it. I literally flew the wings off of it because I found out that Gentle Lady models are not strong enough to perform high-speed rolls in flight.

The huge variety of these engines is too great to explain in this article, but there are some common engines you will see on the used market. Names such as Baby Bee, Black Widow, and Tee Dee represent the bulk of the models you commonly see. They are often found for reasonable prices—heck, I’ve even been given some for free!

Engines made by the Cox company typically fall into two types: rear reed valve and front venturi. The reedvalve engines typically (but not always) have integrated fuel tanks, while the front rotary-induction ones usually (but not always) use an external tank. Confused yet? That doesn’t include the rotary-valve and rear-venturi models.

The Cox company constantly tweaked its designs and developed new models. Engine differences can be subtle to the newcomer. Many of the company’s products also went into ready-to-fly CL models (such as my old PT-19), cars, boats, and even helicopters. These small, inexpensive engines were also extremely well made, with manufacturing tolerances that are still the envy of machinists to this day.

Unfortunately, changing economics and the rise of electric power caused the Cox company to cease sales in 2009 after being bought by the Estes model rocket company in 1996. All of the remaining stock was said to be sold off to various small vendors. It was truly the end of an era.

Those who have never flown a 1/2A-powered model might wonder what it is like to operate one. Starting a Cox engine is often an exercise in frustration, persistence, and exhilaration when you finally get the little bugger running well. They are noisy, messy, cantankerous, and incredibly fun. You also learn a lot about priming, tuning, and troubleshooting small engines.

These little engines also require special glow fuel that contains significantly more lubrication (mostly castor oil) than their larger brethren. Using the same fuel as a typical .40-size glow engine will work but will cause premature wear and likely overheating. Instead, you need fuel with at least 20% lubrication and 15% to 30% nitromethane. Although I have seen people use 40% nitromethane for speed competition, that is not recommended for normal flying because it is hard on the engines.

So why, in this modern age of quiet, clean electric models or big, powerful gas airplanes, would I want to mess with small, messy throwbacks to a bygone era? The best reason I can think of is a mixture of nostalgia and a sense of accomplishment.

nv engines are russian manufactured and offer higher performance and more amenities than a typical cox engine
08. NV Engines are Russian manufactured and offer higher performance and more amenities than a typical Cox engine. These include a pressure-tapped muffler, throttled carburetor, and ball bearings.
this nv engines .061-powered herr aqua star seaplane is also capable of taking off from short grass
09. This NV Engines .061-powered Herr Aqua Star seaplane is also capable of taking off from short grass.
the diminutive cox tee dee .010 is the smallest massproduced engine in the world
10. The diminutive Cox Tee Dee .010 is the smallest massproduced engine in the world. Despite their tiny sizes, .010 and .020 engines can have a higher power-to-weight ratio than larger engines.
this shows a small assortment of cox engines from .010 to .074 cu.in
11. This shows a small assortment of Cox engines from .010 to .074 cu.in. displacement.
not all 1/2a engines are glow powered. an mp jett diesel l is posed next to a norvel
12. Not all 1/2A engines are glow powered. An MP Jett diesel (L) is posed next to a Norvel .074. Both engines provide more power to 1/2A-size models.

In a world of ARFs, it’s still nice to fly a model you or someone else built from scratch (or at least a kit). Something that is as unique in its own way as a 1/2A ARF is fairly rare. Other than the occasional engine di¶culties, flying 1/2A models can be sheer joy.

Modern equipment is far lighter and more reliable than in decades past. Gone are the days of a little .049 struggling to carry a pair of heavy, full-size servos and a large NiCd battery pack.

In the early 1990s, I converted a 27-inch Guillow’s FF Mitsubishi Zero to RC using a Cox reed-valve .049. I made several concessions to make it fly well, such as shelling out the cash for a couple of what would now be considerd mini servos (they were not cheap) and making my own battery pack using 50 mAh NiCd battery cells taken from a disassembled, rechargeable 9-volt battery.

The battery pack was only good for approximately two or three short flights before it needed recharging, but the weight savings was worthwhile. Now, for the same weight, I can have 200 to 300 mAh LiPo packs and fly all day on a single charge. And the servos? Submicros now cost and weigh roughly a third of the old Airtronics mini servos I used at the time.

My "modern" Q-tee, a scratch-built, late-1970s design that I discussed in a previous issue of Model Aviation, has a throttled Tee Dee .049. It has incredible performance, is surprisingly aerobatic, and will easily cruise at half throttle or less, all because of miniature, lightweight, modern electronics. The super-tiny Cox .020- and .010-powered models also gain significant performance with modern equipment. These 1/2A model designs, which were only single-channel or two-channel aircraft, can now be four or more channels and still weigh less than their designers originally planned.

A surprising number of modelers still take pleasure in flying Cox-powered models. A yearly event in Arkansas, called S.M.A.L.L., attracts 1/2A fliers from across the country. CL modeling has apparently seen a resurgence. Several companies continue to sell Cox engine parts, both original equipment and custom.

Engines sales are brisk on the used market. New-in-the-box engines can command hefty prices for some of the rarer examples. Although I think most are sold to collectors, many people still fly them as well. These pilots are hidden away in every corner of the world, quietly having fun and making lots of noise.


Cox International

(877) 769-1779


Ex Model Engines

(860) 681-2451


Brodak Manufacturing

(724) 966-2726


AMA Plans Service

(800) 435-9262, ext. 507


Sig Manufacturing

(641) 623-5154


NV Engines


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