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Rising Star: The Rotary Engine of the Thomas-Morse S-4

Posted September 19, 2018 9:00 AM by dstrohl

I have been a World War I aviation buff since I was a boy, but it wasn’t until recently that I came to really appreciate rotary engines.

I had been working on a Restoration Profile of a 1917 Thomas-Morse S-4B for the September 2018 issue of Hemmings Motor News, when it came time for me to describe for readers just how its engine worked. This happened to coincide with my encountering a comment from a misinformed fellow on a message board vehemently asserting that rotary engines do not spin (that would be crazy!).

While, in a way, it does sound akin to turning the house to screw in a lightbulb, I assure you rotary engines do indeed spin. And far from crazy, or primitive, it turns out it’s a brilliant, albeit ultimately limited, solution.

What's the difference between a radial and rotary engine? And why were rotary engines perfect for planes?

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Re: Rising Star: The Rotary Engine of the Thomas-Morse S-4

09/19/2018 12:26 PM

The pilot would definitely gain an insight on how a gyroscope behaves with that much spinning mass.

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#2

Re: Rising Star: The Rotary Engine of the Thomas-Morse S-4

09/19/2018 3:50 PM

You think the plane would have one wing longer than the other to compensate!

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#3

Re: Rising Star: The Rotary Engine of the Thomas-Morse S-4

09/19/2018 5:35 PM

1) RADIAL means 'round'; ROTARY means 'goes around' ...there's quite a difference.

2) The really good (lived) WWI pilots used the gyroscopic effect to THEIR advantage in dog fights; the poor (dead) WWI pilots didn't.

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Re: Rising Star: The Rotary Engine of the Thomas-Morse S-4

09/19/2018 7:26 PM

The rotary engine is inside out. The crankshaft is stationary and the engine rotates around it.

Here is an animation that shows how it works:

http://www.animatedengines.com/gnome.html

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#5

Re: Rising Star: The Rotary Engine of the Thomas-Morse S-4

09/19/2018 10:41 PM

Actually these planes had a nasty characteristic due to the gyroscopic effect of the engine: turn right and the nose would pitch up; turn left and the nose would pitch down. (or visa-versa.) These planes were pretty light so the effect could be drastic. Not good if you're close to the ground.

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Re: Rising Star: The Rotary Engine of the Thomas-Morse S-4

09/20/2018 9:04 AM

In modern planes, there is normally some interaction between the yaw axis and roll axis. When you roll using the ailerons, the wing that is lifted also has more drag, causing the plane to yaw in that direction. Also, to some extent, yawing the plane with the rudder causes more lift on the wing that is moved forward causing some amount of roll.

The pilot, of course, when banking into a turn instinctively cancels out this interaction by coordinating the rudder and aileron controls. So I suspect the WWI ace in one of these flying gyroscopes would develop a different skill set incorporating the coupling of the pitch axis as well.

It would be very interesting to learn to fly one of these planes. Maybe there is a flight simulator for one.

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