Flying With CO2

When I first started power model aircraft flying back in the1950s we only had the ic engine generally available,items did appear in the model press from time to time in the 1960s about the use of CO2 motors,

Unfortunately ic engines had a few drawbacks mainly in the fact they where noisy, there where no silencers for them in those days and as control line flying was in its heyday many complaints about noise started to roll in, causing the loss of several flying sites,manufactures started to produce silencers for many of the bigger engines and there where attempts to produce early electric powered planes, The drawback being these proved very heavy due to batteries, the size of the motor and the radio gear at the time,

A few CO2 motors had started to appear in the UK about this time, Bill Brown in the USA had built he’s first CO2 engine that ran in 1942, apart from The American Brown the English Shark ,Telco, and the Czech Modela, became available,and until around the early 90s this is how things remained,

Enter Stefan Gasparin. Until the first ‘Interscale’ in Nottingham in 1991, this name was known only to a very few people outside of the model fraternity in the then Czechoslovakia for whom Stefan made a very few tiny motors for his friends.

The advent of the Velvet revolution enabled him to consider selling his motors to the west and with this in mind he got together with a small firm which made instruments for full size aircraft (mostly Russian, this company at that time was suffering from a sudden drop in orders) the idea being for the factory to mass produce a new design of motor for him.

At Interscale, Gasparin motors were shown by the editor of the Czech model magazine, Otakar Saffek, also an international F.A.I. judge, to a stunned group of modellers who couldn’t believe a model airplane could fit into a 2oz tobacco tin, let alone have a working motor fitted to it that actually worked.

So today there is now an opportunity to build quite a variety of small, light scale, sport, competition model aircraft, either for free flight or RC, indoor & outdoor. You name it. A safe, clean, and satisfying way to fly. The power produced for their size is astonishing.

A word about how they work. The CO2 and steam engine work on the same principal. They are expansion engines. The main difference, the fuel. The CO2 engine uses gas generated from liquid CO2, as opposed to steam. The gas vapor under high pressure is fed through a small tube from the tank to a chamber with a ball and valve seat in the cylinder head. When the piston, which has a post centered on top, pushes the ball out of the seat (at top dead center), gas rushes in, pushing the piston down. The gas exhausts through ports as the crankshaft swings around toward bottom dead center. As the piston comes back up, the cycle is complete. The engine will run either direction.

The information presented here is quite general and is intended to help the newcomer to CO2 eliminate some problems that can arise from not following a few important procedures. By following these procedures a great deal of satisfaction and good old fun will be yours.

Servicing the engine: When there is a need to open your engine to clean out dirt or foreign matter from a bad landing, replace a damaged seal, etc., assemble parts just finger tight, lock nut, cylinder head, tank lid, nozzle, etc. NEVER use pliers or any kind of wrench.

Lubrication: It’s very important to keep your little gem well oiled. For the oiling procedure, see mfg. instructions. Every six or eight flights should do it. A small amount with a needle oiler will do. Don’t over oil. Extra oil won’t hurt the engine but will, if done repeatedly, mess up your aircraft.

Chargers for C02 Motors.

There are currently 5 types of charger available.

In the UK we generally use only 2. The simple `spartlet’ type which uses the 8gm bulb used for making soda water is cheap to buy but can be very expensive to run, a box of 10 bulbs only holds 80gms of gas, and anyway, for the larger motors the small fillers are impractable as the tank has a larger capacity than the bulb filling it. In this case by far the most economic way to charge the motor is to use the bulk adapter that fits onto a `Sodastream’ cylinder. These are generally available in some form worldwide, but do make sure if you use a non `Sodastream’ cylinder that the pressure release valve is on the side of the cylinder and NOT built into the head valve.
In countries where the `Sodastream’ cylinders are not available it is often possible to get 12gm bulbs, usually used on airguns. In order to use this size of bulb it will be necessary to use the deluxe Gasparin charger which takes either 8 or 12gm bulbs.

In the UK the `Sodastream’ cylinder can be obtained from Boots, Tesco etc, it is only necessary to purchase the cylinder once, from then on take the empty one back and exchange for a filled one for less than the cost of a box of bulbs. Each cylinder contains 250 gms of gas and can last for ages. Installation of C02 motors is quite simple, the tube from the motor to the tank can be gently bent to almost any shape required, in the case of Gasparin tube, it can be wound round a pencil to take up unwanted slack. The only rule to bear in mind is that the tank must not be mounted more than 45¡ off vertical. It makes no difference to the motor which way up its installed.

Filling the tank can be done in two ways. With the filler nozzle of the motor facing down and the charger nozzle up, a `gas’ charge is made, this is used for trimming and flight testing and also, in conditions of very high humidity. This is to prevent very rapid burning off of the gas which can lead to freezing of the motor cylinder and hence very poor performance.

The other way to charge is a `liquid’ charge. This is with the charger facing down and the filler nozzle from the motor facing up. Liquid gas is introduced into the tank and takes longer to burn off than a gas charge resulting in much longer motor runs. Beware! It is possible, if the pin on the piston is lifting the ball in the head valve at the time of charging, that liquid gas can get into the cylinder. If this happens and you swing the prop, the result is a ruined piston ring which will have been frozen to the cylinder wall by the sub zero gas. Always make sure that the piston is not at the top of its travel before filling the tank.

Should you be unlucky and freeze the ring, it is very simple to change it, simply unscrew the whole cylinder, locking ring and all and lift it off the piston. You will see the ring on the top of the piston, flick it off and fit a new one, don’t forget to put a little C02 lube on the ring before carefully re-fitting the cylinder, remember to slacken off the locking ring before putting the cylinder back, put a gas charge in the tank and screw the cylinder down flicking the prop between turns until the correct speed is set , then lock off with the locking ring. Simple really! BUT! If you attempt to fit a ring to one of the smaller motors, G24 down, I do recommend that you wear a jewellers glass so you can see what you are doing!

C02 motors are now both reliable and relatively inexpensive to buy. They look good on a model that should have an engine and, most of all, although they are virtually silent, the noise they make is most realistic and won’t cause offence to neighbours or the public when in use

Engine speed adjustment: RPM can be changed by rotating cylinder. Loosen locknut, turn cylinder clockwise RPM is increased. Counter clockwise RPM is decreased.

Selecting engine size for your model: Refer to mfg. operating instructions. However, it is wise to install a slightly larger engine throttled down than a smaller engine that has to be run wide open for desired performance.

Mounting tank in model: Locate the tank on the center of balance, or slightly forward. The weight of tank varies with the amount of liquid and if too far from the center of balance it can change the trim of aircraft in flight.

Model weight: Build light. Keep wing loading down. Light models, especially scale, look better as they fly slower.

Good Luck And Happy Landings