Homebuilt Helicopter Engines
Two Stroke Helicopter Engines
- Pros
- ▷ Low weight
- ▷ Low parts count
- ▷ Small size
- ▷ Availability
- Cons
- ▷ Tight operating parameters
- ▷ Fuel sensitive
- ▷ Medium fuel usage
The age old "discussion" over the viability of a two stroke engine for the purposes of powering a helicopter will never end. What we can say is that some ultralight helicopters such as the Mosquito ultralight helicopter using the Compact Radial Engines MZ202 two stroke engine and Angel CH7 using the Rotax 582 engine have a recognized reliable history while other kit helicopters such as the Mini 500 by Revolution Helicopters using the same Rotax 582 (same as the Angel CH7) under different conditions have a less than favorable performance history.
Our opinion is that you should consider the overall purpose of your helicopter design and its intended flight envelope. While a two stroke engine certainly could take you the distance, it would be more suited as a paddock hopper rather than a serious cross country contender. They are more sensitive to old fuel/fuel contamination issues. Always oversize your two stroke helicopter engine requirements for an added margin of safety. Also see Mosquito Helicopter.
Four Stroke Helicopter Engines
- Pros
- ▷ Proven history
- ▷ Low fuel usage
- ▷ Availability
- Cons
- ▷ Heavy weight to HP ratio
- ▷ High parts count (more to break down)
This is the one engine that you can count on. It has a known history with many proven hours so operated within their limitations, they are a solid choice. Aviation specific engines are still quite expensive though now there are many other options including auto conversions and some motorcycle options. The most popular motorcycle engine conversions currently are the BMW's while the auto conversions are generally BMW motorcycle, Suzuki or Subaru engines (though the Aeros used a VW conversion with success). There are many other engines that can be used though keep in mind their weight to horsepower ratio. Look for the more compact and lighter alloy block engines and consider reduction drive or transmission mountings required to couple the engine to the rotor shaft. Also see Rotorway Helicopters.
Rotary Helicopter Engines
- Pros
- ▷ High power potential
- ▷ Smooth running
- ▷ Low parts count (like two-stroke)
- Cons
- ▷ Heavy weight
- ▷ High fuel consumption
- ▷ Noisy
- ▷ Very high RPM's
There have been a few successful helicopters powered by the rotary style engine including a Rotorway Exec powered by a Mazda 13b and a Scorpion 2 powered by a Mazda 12a plus a few others powered by unknown rotary engines. Others have experimented with smaller rotary engines such as the British Norton motorcycle engine in the Revolution Helicopters Mini 500 though with little success.
The fixed wing community have done much for proving the rotarys viability, especially in the Vans RV type homebuilt aircraft. Some of the issues they have faced were high frequency vibrations, cooling and noise control. Also see Fly Rotary and Neo Helicopter.
Turbine Helicopter Engines
- Pros
- ▷ Reliability
- ▷ Low weight
- ▷ Small size
- ▷ High power output
- Cons
- ▷ Initially expensive
- ▷ High Fuel Cost
- ▷ Specialized maintenance
- ▷ Availability
The ultimate rich-mans engine, primarily due to their fuel consumption as their lower maintenance would somewhat overcome the higher initial purchase cost. Military surplus turbine engines have been popular on ebay over the years though gaining higher asking prices and lower availability. There are also now a few after-market modifications available to convert them appropriately for running in small aircraft installations. Military often are looking for "heavy fuel" engines so they do not have to worry about shipping in different fuels while in combat.
It is important to note that many still challenge the use of non-aircraft turbine being used in higher duty cycles such as for helicopters. On the plus side, these concerns are gradually being answered with increasing reliable flight hours gained with the many in service today in both small helicopters and fixed wing aircraft. Also see the Helicycle Helicopter.
Diesel Helicopter Engines
- Pros
- ▷ Reliability
- ▷ Low fuel consumption
- ▷ Low parts count
- ▷ High power output
- Cons
- ▷ Initially expensive
- ▷ Fuel sensitive
- ▷ Heavy weight
- ▷ Availability
- ▷ Initial cost
Relatively new to the homebuilt aircraft arena is the aircraft diesel engine. There have been a few non-starters as the development costs of any engine is excessivly expensive. The few that have made it to testing and production also come with a significant price tag and as yet, no sound long-term history of performance. Another popular option are the european diesel auto conversions. They have found some success in fixed wind aircraft though there use in rotary wing aircraft has yet to be proven.
Some of the issues include increased compression vibrations and duty cycles. The diesel engines introduction to the aviation world will be welcome once proven it could certaily find its place in the homebuilt helicopter market. Also see Delta Diesel Helicopter. On the downside, diesel engines are known for their higher that average pollution levels.
