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Aircraft Topics related to WWI aircraft, aircraft engines and armament

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Old 8 October 2004, 01:59 PM   #1
antiquegunsmith
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Rotary Engine throttle?

How do-
... somehow, I had gotten the impression that the rotary engines used during this time frame had no throttles- yet I see referances to the use of such a control by no less than Captain Eddy in his 'Baby Nieuport'. Certainly there is evidence that the early war rotarys had only two settings- off and on- yet I have seen pictures of a Camel cockpit that show devices labeled 'mix' and 'spark'- perhaps this is a later development? Perhaps not a 'throttle' in the true sense of the word, but a device that allows some margional tweeking of one's airspeed?
Anybody know?
Thank you,
Gregory F. Howard
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Old 8 October 2004, 03:07 PM   #2
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Rotary throttle

Not a throttle like in your car, but a way of increasing or decreasing the amount of fuel mixture fed to the engine, in three separate steps.

There was an engine air intake pipe that used something like a ball valve to regulate the amount of air going to the engine. This was generally operated via a linkage from a handle in a "throttle quadrant" located on the left side of the cockpit. The amount of fuel going to this intake pipe was regulated by a "fine fuel" valve from the pressurized fuel tank, or from a gravity tank, to a jet inside the ball valve, where the incoming fuel was atomized. The air ball valve acted like a Venturi tube, supplying suction to help move the fuel. This "fine fuel" valve was operated by a separate handle located in or near the "throttle quadrant". The Germans seemed to favor locating the "fine fuel" control on the control column and operating the valve by a twist knob via a Bowden(?) cable. Castor oil was carried in a separate tank and pumped from this tank thru a sight flow regulator in the cockpit to the fuel mixture feed line as it entered the crankcase.

Both air and fuel had to be increased or decreased in steps to avoid leaning or flooding, either one resulting in a dead engine. As the aircraft climbed and the air became less dense, the fuel had to be cut back to avoid flooding and a dead engine. As the aircraft descended the fuel had to be increased to avoid leaning out and a dead engine. Oil regulation didn't seem to be quite as demanding of immediate attention as the air/fuel mix, but still necessary.

The coup button, or "blip" switch, allowed quick changes in engine speed by cutting ignition to all cylinders. On landing, for example, the engine was adjusted to take-off power then the coup button used to cut the engine for brief intervals to decrease air speed for landing. If the button was held too long the unburned fuel/oil mix would flood the engine to where it wouldn't restart when the button was let go, and/or worst case the expelled unburned fuel mix would catch fire in the cowling.

Wooden airplanes and iron men!
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Old 9 October 2004, 07:33 AM   #3
EricGoedkoop
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Gregory -

Have a look at this thread from a few years back.

Tripehound's explanation is very good. I would only add that some makes and models of rotaries had different methods of control in addition to the mixture adjustments and coup button. The 160hp Gnome, for example, could be set to fire all 9, 7, 5, or just 3 cylinders on each revolution. The cylinders that were not firing still cycled, but had no spark. They filled with fuel/oil and then expelled it, unburnt, into the cowl. Messy and primitive, but it worked. Mostly.

There are photos in Mike Vine's Return to Rhinebeck of ORA's repro rotary-powered Caudron G3 being overhauled. The mechanic has the nacelle up on sawhorses with the cowl and engine removed - you would not believe the GUNK on the firewall. It's as thick as cake frosting.

Last edited by EricGoedkoop; 9 October 2004 at 07:36 AM.
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Old 9 October 2004, 09:21 AM   #4
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Rotary Engine throttle

I just read the old thread. It seems to me that the throttle on a rotary works much like the throttle on an R/C model airplane engine, with which I've had some experience. It especially resembles the old Fox throttle from the early 70's. However, there is no oil regulator on a model engine, as castor oil dissolves in the alcohol fuel which carries the oil to the cylinder. Castor oil won't dissolve in gasoline and must be metered separately in a rotary.

In an article a LONG time ago I read about a replica Camel using a Bentley rotary that had "no throttle", but a switch panel that could be used to cut the ignition on from 1 to all 9 cylinders! The article further stated that the Bentley system was random; for example, if one cylinder was selected, it cut the ignition to one cylinder, then jumped to another to cut, letting the first one fire to avoid oiling the plug. Only eight cylinders fired, but the cut one was different every time. Same with selecting 2, 3,etc. I can't comment on this one way or another, except to say that this seems a bad waste of fuel, and really flirting with disaster in the form of an in-flight fire.

Something I've frequently thought about but never done is to talk with the people at the Naval Aviation Museum in Pensacola (an hour from here) to see if I can't "get under the ropes" and locate these cylinder ignition cut-out switches that are supposed to exist. The Museum has a Neiuport 28, Hanriot HD-1, Sopwith Camel (Bently, I think), and a Thomas-Morris Scout. There's also a Fokker D-7, but it's hanging from the ceiling and not accessible. The others are on the floor.
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Old 9 October 2004, 12:34 PM   #5
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Rotary Engine Throttle? (Rube Golberg design, no doubt)

YAAAAAAAAAAAUGH!!!!! AND THEY FLEW THESE THINGS?!?
... I driven steam locomotives that were easier to control! OK, so the pilot is paying more attention to this... 'throttle' situation when he is changing altitude or holding formation, then 'blipping' when the *&%* hits the fan or he's landing... all the time building a molotov cocktail under the cowling... I do NOT want to fly a rotary! (not that I could afford one...)
...another thing- Rickenbacker talks of his 'Baby Nieuport' until about June- yet there is no record of him having anything other than the N-24, the N-28 then the SPAD. I am not convinced that he is talking about a N-11, but rather a N-17 as he talks later of MG synchro and clearing a jam, unless the 'Bebe' saw such gear... but then the 17 is an 11 with bigger wings & engine, right? I wonder if some of the N-17's weren't canabalized N-11's....?
... just a thought.
GFH
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Old 9 October 2004, 02:04 PM   #6
EricGoedkoop
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Quote:
Originally Posted by antiquegunsmith
YAAAAAAAAAAAUGH!!!!! AND THEY FLEW THESE THINGS?!?
... I driven steam locomotives that were easier to control! OK, so the pilot is paying more attention to this... 'throttle' situation when he is changing altitude or holding formation, then 'blipping' when the *&%* hits the fan or he's landing... all the time building a molotov cocktail under the cowling... I do NOT want to fly a rotary!
And don't forget about the gyroscopic effects of a few hundred pounds spinning in the front of your aeroplane, not to mention wing fabric that will shred and spars that will break if you dive too steep, oxygen deprivation if you fly too high, guys shooting at you and, if you manage to make it back to your aerodrome, ground-looping. War is hell, right?

The rotary may be unconventional by today's standards, but it was an ingenious solution to one of the biggest problems facing early aero-engine designers. They simply didn't have an effective way to cool the things - remember that the only reason Louis Bleriot made it across the Channel was the rain. The rotary was one way to solve the problem, and because it was a success it was developed and used far beyond the point when technology made it unnecessary - kinda like how the British were still designing pushers in 1918.
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Old 9 October 2004, 02:57 PM   #7
Paul914
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other danger of rotary engine blipping?

Perhaps someone can answer this question for me. While discussing rotary engines with someone who has a little bit of first-hand flying experience, he told me a pilot he knew that flew a rotary pusher said one danger of engine "blipping" to slow down for landing was that if the engine was cut out for too long you stood the chance of it backfiring upon re-starting and it could run backwards. Could this happen? Thanks.
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Old 9 October 2004, 04:07 PM   #8
R Pope
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Paul-- It probably couldn't cause the engine to run backwards because it would have to come almost to a complete stop for this to happen, and the windmilling prop would prevent this. The whole thing could easily go up in a ball of flame, though. By the way, one reason why the throttle control--actually a disc with holes in it that could be turned to restrict the air to the engine--didn't work better is because much of the combustion air entered the cylinders through the exhaust ports. Wierd enough for you? And You're right, not many people today would run a rotary on a regular basis.
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Old 9 October 2004, 05:28 PM   #9
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Quote:
Originally Posted by R Pope
Paul-- It probably couldn't cause the engine to run backwards because it would have to come almost to a complete stop for this to happen, and the windmilling prop would prevent this. The whole thing could easily go up in a ball of flame, though. By the way, one reason why the throttle control--actually a disc with holes in it that could be turned to restrict the air to the engine--didn't work better is because much of the combustion air entered the cylinders through the exhaust ports. Wierd enough for you? And You're right, not many people today would run a rotary on a regular basis.
Thanks Rich, that would make sense. Let me ask another question I have from your answer (I am a fan of WW1 planes, not a pilot or expert by any means!) - If combustion air enters through the ehaust ports, are rotary engines 4 stroke instead of 2 stroke engines? If they are 4 stroke, then on the non-combustion downstroke, they would draw in outside air if the exhaust valve timing and function wasn't perfect.
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Old 9 October 2004, 07:47 PM   #10
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Yes, they are 4 stroke engines. The fact that they draw air in the exhaust port isn't an imperfection, it's the way they were designed.The exhaust valve stays open after TDC to draw in air, then closes so the intake can draw in a rich gas-air mix from the carburetor, which is leaned on mixing to the proper ratio for firing.I'm not sure why they did it this way, but it worked, and that's what counts!
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