Rotary Engines... Why??

timjnf · 20 June 2002, 08:02 AM

Does anyone have any thoughts on why rotary engines became the popular design choice they did?

One fact, that they appear to have had the greatest power to weight ratio in their day, seems to provide a simple answer to this question.

But the answers I'm looking for is why did the rotary configuration provide such a substantial performance gain over other designs?

Was there something in the metal alloys available at the time that required the rotation of the entire engine for cooling purposes? (I actually think I remember Cole Palen, or one of his henchmen, stating this at ORA years ago, but I can't find any liturature to support it.)

Thanks,
Tim

AchimEngels · 20 June 2002, 12:31 PM

Hi,

The main reason why the brothers of Séguin in France developed their rotary engine - as well as others did - was the fact that at that time there was no real aero engine available. Most engines have been adopted from cars. Weight was one of the most concerning things and in order to reduce weight many of these former automobile engines had their heavy flywheels reduced in size.

This reduction limited the safety of the running of the engines. With a car this was not even a problem since the mass in motion of the vehicle itself helped to overcome any sudden ignition problems. With an aircraft this was something different and resulted in many forced landings due to a suddenly stopping engine.

The rotary engine was a welcome solution to this problem since the engine itself provided a large revolving mass that made any flywheel uneccessary. In addition, the heavy water cooling that was neccesary with the stationary engines was also no longer needed which increased the reliability of the rotary engine. It should be noted that these advantages often have been considered even to justify the high consumption of gasoline and oil compared to stationary engines.

The rotary concept can be considered being the first real aero engine and had a great success after the introduction by the brothers of Séguin in 1908.

By the way, the company of Societè des Fonderies de Cuivre was founded by the Séguin brothers of Lyon. This company aquired the rights to produce a gasoline industrial engine that was invented by a man called Will Seck. This engine has an underpressure activated inlet valve and was called the "GNOM" by Willy Seck. the Ségiun brothers made big with that license production and used its working principles to develop the rotary from. In memory to that engine they called their rotary the "Gnóme" which was the French translation for that little creatures from old German fary tales.

Later the company that was founded formerly by Willy Seck became famous as the "Motorenfabrik Oberursel A.G." which in turn took license to produce the French "Gnóme" before the war begun and continued so after the war has started. That way the German industrial "Gnom" returned to Germany as the aero engine "Gnóme".

Best

Achim
*

P.S. Make sure to wait for the English translation of my book on the Oberursel Motorenfabrik. Or if you are able to read German, make sure to get your copy here:

http://www.collectors-edition.de/f-t-s_buc...ung_english.htm

chip55 · 21 June 2002, 12:41 PM

Hello

The rotary also added quick turns due to their torque effect. And it would be possible to have a shorter fuselage putting the pilot closer to the center of gravity. Also the view from the cockpit wouldn't be obscured by cylinders, radiators and exhaust stacks etc. My thoughts anyhoo.

be well
chip55

timjnf · 21 June 2002, 03:40 PM

While it's true that experienced pilots learned how to exploit certain handling characteristics caused by the rotary, don't forget that the over-all handling of the aircraft was severely, negatively impacted by the combination of torque and gyroscopic effects caused by that large spinning mass of an engine. I don't suppose the p-factor from that large propeller helped you much either when you were slow and at high angles of attack.

I love the smell of the burning castol oil, and the sound of a rotary is music to my ears, but I would want to fly an airplane with one often.

I've heard a lot about the quick turns, but it only allowed quick turns to the left. Right turns suffered severely. Unless you count a left snap roll, stopped 3/4 the way around, then levelling out, allowing you to quickly achieve a heading near 90 degrees to the right of your original heading, a normal method of doing right turns. If so, then right turns were fast also.

Or, I suppose, if you blip the ignition as you start your right turn you would to roll more quickly to the right than if the engine is going full throttle.

Quote:

Hello

The rotary also added quick turns due to their torque effect. And it would be possible to have a shorter fuselage putting the pilot closer to the center of gravity. Also the view from the cockpit wouldn't be obscured by cylinders, radiators and exhaust stacks etc. *My thoughts anyhoo.

be well
chip55

Shooter · 22 June 2002, 06:33 AM

Tim:

Every recip engine imparts a certain amount of torque effects to a/c performance. These effects were particularly pronounced with rotary engines because of the mass of moving metal at the front of the ship.

The Camel was noted for the torque effects of its power plant, but the Dr1 had a similar engine and does not seem to have been as effected. Dunno why.

Shooter sends

Shooter · 22 June 2002, 06:39 AM

Tim:

Every recip engine imparts a certain amount of torque effects to a/c performance. These effects were particularly pronounced with rotary engines because of the mass of moving metal at the front of the ship.

The Camel was noted for the torque effects of its power plant, but the Dr1 had a similar engine and does not seem to have been as effected. Dunno why.

Shooter sends

Ron_F · 22 June 2002, 02:14 PM

the camel turned better to the right than the left due to the gyroscopic forces. down and to right, up and to left. the camel is the only one that gets the press for this, how much it affected the others, Dr1 included, has been a debate for several years at least to the RB3d community.. :-/

<I've heard a lot about the quick turns, but it only allowed quick turns to the left. Right turns suffered severely. >

timjnf · 22 June 2002, 02:51 PM

To Shooter,
I am a pilot myself, and I'm aware of the effects of torque and p-factor caused even by the low powered engines and small propellers we use today (low powered by today's standards (< 200hp) though I realize they far exceed the power of the average WWI fighter.)
Never having flown anything with a rotary I can't comment from first hand experience as to what it would be like. I can only speak from what I've read and from a theoretical point of view.

To Ron,
Please don't go there. Don't compare a PC simulator to the real thing. As sophisticated as some of them are, and I've tried nearly all of them, they all have their short comings, especially when it comes to the flight model in the slow flight and stall areas of the flight envelope.

And to everyone I reiterate: a skilled pilot will always take advantage of the characteristics of any given airplane's handling abilities. But that doesn't mean that a torquey engine that produces ton's of gyroscopic forces can be considered to have a desirable effect on controllability or maneuverability.
Rotary's were used because their benefits (power to weight, and reliability) out weighed the adverse effects the caused to the over all performance of the machines on which they were used.

Shooter · 22 June 2002, 03:31 PM

Tim:

Hey, I wasn't trying to be condescending, pal. One never knows the capabilities of those he talks to on the Forum. Me, my experience runs toward the ground side of things, but I have a few hundred hours under my belt. Ran outta money before I got IFR qual'd so you might have the edge on me.

Shooter sends

Ron_F · 22 June 2002, 09:54 PM

Tim,
if you read again, i was NOT comparing RB3d to real life experience, only the DEBATE on the characteristics of ww1 crates and how they perform by RESEARCHING how they fly, performance etc for us when were trying to make the flight model better.

I know that they pale in respects to R/L a/c. but we/I researched as much as i could on how they flew.

camel turned better to the right than left. Flight journal august 1998, and various other camel sources.

Quote:

To Ron,
Please don't go there. *Don't compare a PC simulator to the real thing. *As sophisticated as some of them are, and I've tried nearly all of them, they all have their short comings, especially when it comes to the flight model in the slow flight and stall areas of the flight envelope.