Why don't we use rotary engines in aircraft?

Question

In my opinion, a pistonless rotary style engine would be ideal for an aircraft engine. They are smaller and weigh less than a piston engine of similar power so less drag, are reliable and most importantly can get much higher RPMs than pistons, and RPMs are what gets airspeed. Whats the deal?

I guess I was looking more into the smaller general aviation stuff. I know why a larger plane wouldn't use them, but putting one in a Cessna or Piper seems like a good idea.

Answer 1

There are some people who have put Wankel engines in homebuilts and the like but they need a gear reduction system to run the propeller at a usable speed. The Wankel is also unreliable compared to conventional engines, otherwise it would have caught on with more car manufacturers or in applications other than a powerful but impractical sports car.

Also, even though the Wankel engine is capable of producing high power at high RPM, it wasn't designed to run this way continuously. In an aircraft application it would be run a lot harder than a car (high RPM is only used for brief periods of acceleration). Imagine in your car going from a stoplight at full throttle, and then cruising steady at 100-120MPH for five hours, and doing it every day for a year. This is how an aircraft engine is operated (nicely).

Aircraft engines may seem archaic but they get the job done. Most aircraft engine failures are highly publicized (car engines blow up every day) and their reliability is excellent considering how hard they are pushed.

Remember too that the basic construction of car engines hasn't changed that much over 50 years either (except for going to aluminium components which aircraft engines have had for 80 years). Also FADEC and electronic ignition has come to some newer versions of aircraft engines to narrow the technology gap.

Answer 2

Rotary Aircraft Engine

Answer 3

This Site Might Help You.

RE:
Why don't we use rotary engines in aircraft?
In my opinion, a pistonless rotary style engine would be ideal for an aircraft engine. They are smaller and weigh less than a piston engine of similar power so less drag, are reliable and most importantly can get much higher RPMs than pistons, and RPMs are what gets airspeed. Whats the deal?

Answer 4

First off, propellers do not like being spun at high RPMs. Depending on the length of the propeller blades, the prop tips will go supersonic between 2700-3000 RPM, and cause the prop to make more noise and less thrust. That's why all turbo-props and many piston driven airplane engines use prop speed reduction units (gear boxes) to reduce the propeller speed.

Airplane pilots tend to be more conservative than most, and one of the cardinal rules of aviation is "If it works, don't fix it!" Rotary (Wankel) engines have been used in a few experimental aircraft, and they have performed reasonably well, but are typically less fuel efficient than regular piston engines, and also require more maintenance. Not the best combination if you want to convince anyone to use a rotary engine in your airplane.

Answer 5

I assume you mean for small GA aircraft?

First, you can only drive a propellor so fast, when the tips start going supersonic that's your lot. So running the engine at higher speed for the same power just means you need a bigger reduction gearbox, which is not good.

It is very difficult to get a new type of engine into aviation use. Despite significant reliability and handling issues the Lycoming flat fours and sixes and their like are still the defacto standard. They are light because they are air cooled, but you can crack a cylinder simply by throttling back and diving in cold weather. There have also been many cases of crank shaft failure which are almost unheard of in other applications regardless of engine size.

Then there were the initial weaknesses of Wankel engines, the rotor tips wore rapidly and it was difficult to maintain compression and sealing. They are alse difficult to fuel inject and by their nature burn less than 100% of their fuel along with some oil. Wankels are oil injected because there's no other way to lubricate the rotor tips, conventional engines are lubricated from the crank case. They heat and cool unevenly, the combustion is always on one side and the inlet on the other, so the area nearest the inlet stays cold but the combustion and exhaust get very hot.

However, they have been in limited use since 1968. They are likely to continue to be of limited interest.

Answer 6

Yada Yada Yada!

The real reason is that the FAA and GA community are so insular and in bred they haven't developed anything approaching a new engine since the 1950's. Mooney went out and certified the Porsche 911 engine and the FAA treated them like pariahs and weighed the thing down with gear driven accessories till it no longer had a weight advantage.

A modern auto engine is 20 times more reliable and generates far more power and economy than the Crap Lycomings and Continentals.

Experimental Aircraft have been using SMB Chevies for years!
I have worked on alternators with an FAA certification that were exact matches for a Ford Taurus but cost 5 times as much! It is totally Government interference in the industry.

Ret. USAF SNCO, Aircraft Environmental and Electrical Systems

Answer 7

a rotary engine was fine for a small aircraft, but Jet engines came along and the rotary was up for grabs and it was put into a car by Mazda in the 70's. Oil was the problem and cooling for the cars location of the engine. This brought the engine down for cars.

Answer 8

We do. I've heard of people using rx-7/rx-8 engines in small planes.

Answer 9

Two major problems:
#1 is reliability. The rotary engine does meet the test.
#2 is power to weight ratio - Jets do it better

Answer 10

gasoline vs aircraft fuel
hmmmmm
I'm pretty sure aircraft fuel wins there.
Also come on that engine cant produce the RPM to get that huge fan in the engine to the speed to blow the air that fast there is no way it could do that ... this question isnt even worth answering bye