Gas vs Electric

Gasoline has a far higher energy density than that of a lithium polymer battery. One pound of gasoline has 50 times more energy than a pound of lithium polymer batteries. In 2002 Maynard Hill flew an RC plane weighing 11 lbs. 1,882 miles across the Atlantic in 39 hours on 3 quarts of gasoline.

So why aren’t all sUAS gasoline power?

• High maintenance – spark plugs, fuel lines, carburetors and gasoline engines require lots of maintenance. Spark plugs are changed every 25 – 50 hours for instance.
• High vibration – takes its toll on all components. Servos wear out quickly. Autopilots and other sensitive electronic components cannot tolerate vibration.
• Noisy – 4-stroke engines are used more due to the lower noise, though they are much more complicated having a camshaft and valves. 2-stroke engines cannot be effectively silenced because the back pressure from the muffler creates inefficient operation. 2-stroke engines are far less fuel efficient than 4-stroke engines, though 2 stroke are more reliable and lighter due to fewer moving parts. Most gas drones in the 50 to 250 lb. range are 2-stroke.
• The FAA has a limit of 55 lbs. all up weight including fuel. There are no efficient, reliable gasoline engines which are small and inexpensive. Most gas engines are in the string trimmer size of 25 to 30cc which weigh a couple lbs. and are used on aircraft around 55 lbs. Most drones like the Phantom or eBee weigh 2 or 3 pounds. Tiny gas engines to operate 3-pound aircraft have not been developed. Glow engines are used for these type models which operate on alcohol instead of gasoline. They are messy, high vibration, high maintenance, unreliable, and not particularly user friendly.
• Throttle response is poor, and power is nonlinear. These traits are especially bad for synchronizing multiple engines on one aircraft.
• Altitude changes the air density, and air density changes on a daily basis, both of which cause engine issues due to changing fuel air mixture.
• Temperature changes affect the usability of gasoline engines.
• Fuel injection resolves many of these issues of gasoline engines. The power is more consistent, fuel economy is greatly enhanced, reliability goes up, air density and temperature have less effect and more. This works great though it adds complexity and is very expensive. A fuel injection system (today) for a 30cc engine can cost over $15,000. The engine itself might cost less than $1,000 normally. It’s a large premium to pay for extended flight times.
• Electric motors can operate maintenance free for up to 100,000 hours. They are quiet, reliable, low maintenance, and very user friendly.
• Drones (today) cannot fly out of the line of sight. While a drone can be made to fly for many days on gas power there is little point to it because it’s easy enough to land, swap batteries and go back up again. The aircraft can’t be very far away. Once we start flying beyond line of sight and are many miles away where it must fly for several hours then gas will be a viable option.