Gas RC helicopters (also called "Gassers") are commonly confused with the much more popular nitro RC helicopters . They are however completely different; or to be more precise, the engine is completely different.
RC gas helicopters themselves are more or less exactly the same as similar sized nitro, turbine, or large electric. Gas powered RC helicopters are fairly big with the smallest being roughly the same size as 90 size nitros or 600 to 700 size electrics.
Century RC's Radikal 20 Gasser seen below spins 600 to 660mm rotor blades, weighs in at about 4.5kg, and is powered by a 20cc two stroke gas/petrol engine.
These 2-stroke gas engines used in gas RC helicopters are very similar to all single cylinder two stroke gasoline engines, just like what you might find in your gas leaf blower or chain saw.
As far as fuel, they use regular - premium gasoline/petrol mixed with a quality racing two-cycle engine oil.
The sizes of these two stroke engines are also similar to what you might find in a gas powered weed whacker or small chain saw. The most popular 2-stroke gasoline engines for model aircraft are usually in the 20cc-30cc range.
Gas powered RC aircraft engines have some interesting differences over the garden tool variety. Click on that link to learn more about these engines and discover the advantages they have over nitro engines. When choosing your gas model engine, you will also be faced with what kind of ignition system to use.
Because gas powered RC helicopters are fairly large, and powered by rather heavy two stroke petrol engines, the power to weight ratio of Gassers is fairly low compared to that of nitro or electric. You won't find a gas powered heli for example performing the hard core 3D smacking you see the new electric stuff doing these days. That certainly doesn't mean you can't still throw them around; and for sport or lighter type 3D flying, they are very nice fliers as shown in the video below.
The big advantage with gassers is the flight times can be fairly long (up to 30 minutes with some of them), fuel costs are easily half to 1/3 that of nitro, and unlike electric, you don't have to cart a bunch of big expensive LiPo packs around for back to back flights. With a gas RC helicopter, you just land, refuel, and go flying again.
Lastly, if you want a large fuel powered RC helicopter and don’t want to spend many thousands of dollars on a turbine RC heli – gas is the way to do it.
As seen below on Century RC's Radikal G30; gasser mechanics are not much different than nitro. Perhaps the biggest noticeable difference is most gasser engines have side mounted carburetors allowing easier carb tuning access and the ability to fit an air filter if you wish.
large gas RC helicopter is obviously not your best choice for your
first RC heli because of the higher cost of the kit, complexities involved building it, and dangers involved when flying a large model. Gassers (due to the large reciprocating piston mass in the 2-stroke engines) are also vibration prone; so you have to understand how to deal with that on a model RC helicopter as well.
However, once you have mastered a nitro or larger electric
helicopter, a gas powered RC helicopter makes a lot of sense for some folks.
If your goal is large scale RC helicopters, gas power is also a very viable option. You don’t need the high power to weight ratios to perform scale type flying where your most extreme maneuver won’t be anything much more than a steep stall turn.
In fact, the added weight of the gas engine actually makes your heli fly a lot more scale like. More weight means more stability and longer, more pronounced cyclic commands to slow or change directions. The inside of your fuselage and windows won’t be covered in nitro oil residue either – a nice benefit.
As far as the equipment you will need for a gas RC Helicopter, it is pretty much identical to a nitro model other than not needing a glow plug power panel or driver. The radio equipment, gyro, or flybarless unit will be the same as in a large nitro or electric model (note, not all FBL units are able to be used in high vibration environments such as Gassers; so do your research when choosing an FBL system for a gas RC helicopter).
You will usually have the
option of starting a gas powered helicopter engine with an
external electric starter
(like on a nitro heli), or with a pull start recoil cord (like on a typical gas powered garden tool).
Unfortunately, gassers due to their narrow niche market are becoming harder and harder to find. No question, the direction of "main steam" RC helicopter manufacturers is toward grossly overpowered, hard core electric 3D machines leaving the gasser pilot with few options. That said, there are still options out there...
Century Helicopter Products
Bergen RC offers the 26cc powered Intrepid Gasser.
Vario Helicopter offers their line of Benzin gas powered RC helicopters.
These are the three most popular RC helicopter manufacturers (at least here in North America), that offer gas powered RC helicopter options; so sourcing parts is not an issue. I just placed a small parts order with Bergen RC this morning as a matter of fact and it's already showing as being mailed :-)
Bergen Intrepid Gasser In Action
The other gas RC helicopter option is to convert your larger nitro or electric into a gasser with a gas conversion kit.
These kits generally include new frames and base plate to accommodate the larger gas engine along with engine mounts. Fuel tank, pinion, clutch/bell housing, cooling fan, cooling shroud, and new main gearing may also be included depending on the kit & conversion.
HeliBug is one such company that offers a wide range of conversion kits for popular RC helicopter brands/models (Align's lineup of larger T-Rex's of course being likely the most popular). They have gas conversion kits for the T-Rex 550 all the way up to the 800 for example.
T-Rex 600 HeliBug Gasser Conversion Shown Below