You don't. If you need to ask the question, you're not likely to be able to handle the complicated conversion process (also, I don't think you can find gasoline engines that are small enough; you can buy liquid fuel engines, but they don't run on gasoline, the fuel they use is more like diesel fuel).
Battery powered remote control cars are more efficient and economical.
There are many retailers where one can purchase a gas-powered remote control car. One can purchase a gas-powered remote control car online at Amazon, eBay, and XenonProject.
The average entry level remote control car will cost about $75.
For someone looking to purchase a gas powered remote control car, websites such as Amazon, eBay, Nitro RCX (which claims the lowest prices),and Xenon Project.
A great site for buying gas powered remote control cars is hobby-estore.com. You can put together a gas powered rc car with your ideas there. The cheapest one I found was about $390.
Gas Powered RC Boats are exactly what they sound like. They are remote control boats that are powered by gas. Check them out here! gas-powered-rc.buycheapr.com
In the past it used to be very hard to fly gas powered remote control airplanes. However these days, they come 90% assembeled, and are generally easy to fly! http://www.raidentech.com/arfnigasai.html
Some gas powered remote control airplanes are suitable for six or seven year old children, however, many rc airplanes are advisable for ages eight and up.
Gas operated remote control cars are faster, but require much more maintenance and care.
Drones are powered by lithium-polymer batteries and use a remote control or smartphone app for piloting.
To convert a remote control ceiling fan to switch operation, you will need to remove the receiver unit in the fan and directly wire the fan to a wall switch. This will allow you to control the fan using the switch instead of the remote. Be sure to follow safety precautions and consult a professional if needed.
I had a difficult time finding this information. This link gives several different gas powered planes for sale. The specifications for each plane are listed. Hopefully this helps.http://www.nextag.com/remote-control-gas-planes/stores-html?nxtg=38230a28050c-593B61A4F52745FD