Rotary Engine

[Nigel Taylor]

A short video showing my miniature rotary compressed air/CO2/steam engine.



In rotary engines the crankcase rotates with the propeller. The conrods rotate about the crank pin. These two rotational axes are parallel and half the length of the stroke apart. In this way the early engines removed the need for a heavy flywheel by using the mass of the engine as rotational inertia.

This model rotary engine might look good on an indoor Sopwith Pup and powered by a CO2 canister.

 

[D_W]

I never realized those engines rotated around a point that wasn't at the center! I guess I never even considered it - interesting!

 

[AES]

No, neither did I D_W!

A while back there was a post on here from a bloke who made a wooden rotary (purely to explain the principle). I'll see if I can dig it up and post the link. Fascinating those old WWI engines - did you know that many did not have a throttle at all, just a "blip switch" which cut off the magneto as required - i.e. full revs or "nothing at all ( flywheeling actually). AND a lot of those old rotaries were (of course) total loss lubrication, which is OK I suppose (common enough perhaps), EXCEPT that the lubricant was castor oil which in turn lead to pilots having constant fits of the runs!

P.S: VERY nice work Nigel.

 

[Inspector]

Hats off for making a cool little engine.

Pete

 

[AES]

Re above: Here you are folks, it's from 2013:

https://worldwarwings.com/carpenter...but-when-you-see-it/?a=mk&var=ww2-wood-radial
Can't remember now, but not sure if it's a rotary or a radial (BIG difference)!

Just checked, it's a RADIAL. When I worked at Swissair we had a glass case electrically-powered P&W Radial (DC 6 I think) which was sectioned by the apprentices from one year. Of course, when the "modern managers" took over it was decided it was too old-fashioned for the main foyer and was discarded. Would love to know what happened to it (hopefully in the Transport Museum in Luzern).

 

[Spectric]

I never realized those engines rotated around a point that wasn't at the center!

That must have required some balancing, that could have been a large offcentre mass.

 

[dickm]

There's a nice line in the link posted by the OP.
" The impact of the rotational inertia on the flying characteristics is quite another story. "
Have said elsewhere that my Father flew Camels in WW1 and, possibly surprisingly, lived to tell the tale!

 

[AES]

Yeah, from all I've read (NO, I wasn't around at the time - a visitor at a recent tour I gave at the Zeppelin Museum asked me if I'd worked on Spitfires in the RAF!) the effect of the mass of the engine (plus propeller don't forget) all rotating together made the whole business of turning in one direction very much a job for the experts (OR the incredibly lucky) - whilst turning in the other direction was apparently akin to moving an ocean liner around the water.

Don't forget the effect of all that rotating mass also had a marked nose down moment effect too. Apparently Sopwith Camels were particularly noted for all that (especially the later higher-power Bentley rotaries with, I think 140 hp), but many other types with rotaries apparently also needed to be handled with "respect".

I should think the "possibly surprisingly" bit in that article is probably about right!

 

[Farm Labourer]

Precession (p-factor) must have been quite a significant factor whenever Bloggs used any of the flight controls - less so with aileron.

 

[AES]

Yup, exactly. That's what I was talking about (inadvertent nose down moment when turning).

 

[Farm Labourer]

Don't forget the effect of all that rotating mass also had a marked nose down moment effect too. Apparently Sopwith Camels were particularly noted for all that (especially the later higher-power Bentley rotaries with, I think 140 hp), but many other types with rotaries apparently also needed to be handled with "respect".

We're saying the same thing and our posts crossed. I fly a 260hp sports biplane with a 1.78m prop, so genuinely understand this but I've had the advice and experience of lots of blokes in the past hundred plus to learn from. Hardly surprising that the aviator death-rate in WWI was so high.

To counteract the effect of castor oil, Doc dosed them with brandy - so that really helped, too!

 

[mikej460]

Unfortunate name but remember these?
50 YEARS OF ROTARY REVOLUTION | We are Mazda

 

[Farm Labourer]

"(inadvertent nose down moment when turning)" - when turning one way. Nose up - potentially leading to a inadvertent stall in the other direction. I don't know which way the prop turned when seen from the cockpit so can't determine which direction would command a pitch or a descent!

 

[D_W]

No, neither did I D_W!

A while back there was a post on here from a bloke who made a wooden rotary (purely to explain the principle). I'll see if I can dig it up and post the link. Fascinating those old WWI engines - did you know that many did not have a throttle at all, just a "blip switch" which cut off the magneto as required - i.e. full revs or "nothing at all ( flywheeling actually). AND a lot of those old rotaries were (of course) total loss lubrication, which is OK I suppose (common enough perhaps), EXCEPT that the lubricant was castor oil which in turn lead to pilots having constant fits of the runs!

P.S: VERY nice work Nigel.

If the cylinders fire in order around the same time at the crank, it actually makes sense. i'd never thought about it, but if it weren't that way, the whole engine would have to burble around in some spirograph pattern the length of the stroke ...that'd shake the airplane apart in short order.

It's really interesting looking, though.

 

[AES]

We're saying the same thing and our posts crossed. I fly a 260hp sports biplane with a 1.78m prop, so genuinely understand this but I've had the advice and experience of lots of blokes in the past hundred plus to learn from. Hardly surprising that the aviator death-rate in WWI was so high.

To counteract the effect of castor oil, Doc dosed them with brandy - so that really helped, too!

Yup, as you say posts crossed. And yeah, I'm only an engineer, not a pilot, but I guess with 260 hp (a Pitts or something?) you must get that too, quite a lot (BTW, I presume your prop is metal. Is that heavier than the laminated wooden ones back then? And I wonder how all that that would compare with a Camel?). And yup, to turning the other way too (but upwards - supposedly to a stall if not careful)?

Interesting that thing about the brandy, wonder if it was the brandy or "P" that caused so many accidents back then???

P.S. Does this mean that next time I get the runs I should ask wifey for brandy?

 

[Kittyhawk]

That is a beautiful little rotary engine, one I'd be proud to own.
We have a lot of exact replica WW1 aircraft here in NZ, many owned by Peter Jackson, the Lord of the Rings man. We are meant to have the biggest collection of these aeroplanes in the world but take that with a grain of salt - kiwis reckon everything here is the biggest/best in the world.
Mention has been made of rotary engines and Camels and in the collection there are a couple of replica Sopwith F1 Camels, one powered by an original Clerget 9B rotary engine and the other by a replica of the same engine. According to the owners and other pilots that fly these machines they are a little tricky to control but not excessively when compared to other aircraft of the era which then calls into question why the Camels were known as pilot killers. And they were. From the Imperial War Museum records, 413 Camel pilots killed by enemy action, 385 pilots killed due to problems controlling the aeroplane.
So this creates something of a dilemma which in turn leads me to research, a favorite past time of mine which also should be taken with a grain of salt as I have only basic training as a researcher but this is what I think.
From the beginning of the war though to early 1917 when the Sopwith Camel entered front line service allied pilots were on the back foot against the plainly superior German machines. With the agile Camel allied pilots were in the ascendancy until mid 1918 when the Fokker D.V111 came along and reversed the situation again and the once superior Camel was relegated to the role of trench fighter.
1916 was terrible year for losses for the RFC and they put out a call across all branches of the military for volunteers to undertake pilot training. Furthermore, this call was to all ranks and not just to officers as was previously the case. It was said that a few commanders saw this as an opportunity to rid themselves of some of their more troublesome subordinates, encouraging them to volunteer for service in what was known as the Suicide Brigade.
So a new pilot just out of training finding himself strapped into a Camel sounds like a disaster in the making and especially so when you consider the official training schedule that I found in a private memoir. Because of the desperate shortage of pilots ( and also training aircraft) in 1917, aside from the classroom work, two and a half hours dual flight time until first solo and another 8 - 12 hours solo to be deemed combat ready. Compare this to the RAF in 1939 which was 40 hours to first solo and a further 200 hour to combat readiness. It is said that the Camel was an unstable aeroplane but I read that a degree of instability is a desirable feature in a fighter as it equates to agility. Perhaps this instability coupled with the centrifugal forces generated by a rotary engine were more that a barely trained novice could be expected to handle. And so I think that the bad press associated with the Sopwith Camel is undeserved and it was not greatly worse than any other aeroplane of the period.
And the reason I'm fascinated by the Camel is that I have two 1:20 scale models just about ready for oiling.

 

[Nigel Taylor]

That must have required some balancing, that could have been a large offcentre mass.

The animated engines website shows the Gnome rotary: Animated Engines - Gnome Rotary - you can slow the animation down.

Effectively you have two off centre circular objects (one being the crankcase and cylinders, the other being the pistons and conrods) rotating at the same speed. The propeller is bolted to the front of the crankcase.

If you turned the engine around and fixed the crankcase so it didn't rotate then the crank would rotate and the pistons would just move up and down the respective cylinder. The lower end of the master conrod and slaves would move in a circle.

I think the rotary is quite fascinating when you realise there are effectively two flywheels in parallel, but space apart.

 

[AES]

The animated engines website shows the Gnome rotary: Animated Engines - Gnome Rotary - you can slow the animation down.

Effectively you have two off centre circular objects (one being the crankcase and cylinders, the other being the pistons and conrods) rotating at the same speed. The propeller is bolted to the front of the crankcase.

If you turned the engine around and fixed the crankcase so it didn't rotate then the crank would rotate and the pistons would just move up and down the respective cylinder. The lower end of the master conrod and slaves would move in a circle.

I think the rotary is quite fascinating when you realise there are effectively two flywheels in parallel, but space apart.

Thanks for the link Nigel. Fascinating stuff.

 

[Nigel Taylor]

That is a beautiful little rotary engine, one I'd be proud to own.
We have a lot of exact replica WW1 aircraft here in NZ, many owned by Peter Jackson, the Lord of the Rings man. We are meant to have the biggest collection of these aeroplanes in the world but take that with a grain of salt - kiwis reckon everything here is the biggest/best in the world.
Mention has been made of rotary engines and Camels and in the collection there are a couple of replica Sopwith F1 Camels, one powered by an original Clerget 9B rotary engine and the other by a replica of the same engine. According to the owners and other pilots that fly these machines they are a little tricky to control but not excessively when compared to other aircraft of the era which then calls into question why the Camels were known as pilot killers. And they were. From the Imperial War Museum records, 413 Camel pilots killed by enemy action, 385 pilots killed due to problems controlling the aeroplane.
So this creates something of a dilemma which in turn leads me to research, a favorite past time of mine which also should be taken with a grain of salt as I have only basic training as a researcher but this is what I think.
From the beginning of the war though to early 1917 when the Sopwith Camel entered front line service allied pilots were on the back foot against the plainly superior German machines. With the agile Camel allied pilots were in the ascendancy until mid 1918 when the Fokker D.V111 came along and reversed the situation again and the once superior Camel was relegated to the role of trench fighter.
1916 was terrible year for losses for the RFC and they put out a call across all branches of the military for volunteers to undertake pilot training. Furthermore, this call was to all ranks and not just to officers as was previously the case. It was said that a few commanders saw this as an opportunity to rid themselves of some of their more troublesome subordinates, encouraging them to volunteer for service in what was known as the Suicide Brigade.
So a new pilot just out of training finding himself strapped into a Camel sounds like a disaster in the making and especially so when you consider the official training schedule that I found in a private memoir. Because of the desperate shortage of pilots ( and also training aircraft) in 1917, aside from the classroom work, two and a half hours dual flight time until first solo and another 8 - 12 hours solo to be deemed combat ready. Compare this to the RAF in 1939 which was 40 hours to first solo and a further 200 hour to combat readiness. It is said that the Camel was an unstable aeroplane but I read that a degree of instability is a desirable feature in a fighter as it equates to agility. Perhaps this instability coupled with the centrifugal forces generated by a rotary engine were more that a barely trained novice could be expected to handle. And so I think that the bad press associated with the Sopwith Camel is undeserved and it was not greatly worse than any other aeroplane of the period.
And the reason I'm fascinated by the Camel is that I have two 1:20 scale models just about ready for oiling.

thanks and interesting research

 

[HamsterJam]

That must have required some balancing, that could have been a large offcentre mass.

Not sure there is much balancing required as the engine mass is central about its point of rotation. Granted that is not the same centre of rotation as the big ends (I don’t think it can be called crankshaft as it isn’t cranked).
Maybe Nigel can confirm.