Rotary Engines

W

Wildfowler

Guest
Did rotary engines have throttles?

I am currently have a debate with a friend over this. He claims many rotary engines had no throttle control. They ran at full speed or nothing. You shut the engine off to reduce power and used the windmill effect of the prop to restart. For example the engine would be "bliped" when coming in to land.
He said some had throttles which were closed, half power or full power.

I am interested in what you experts out there think.

Thanks
 
If you notice, the discussions are all about ignition squences and engine adjustments, nothing about a true fuel/air control of the rotary as there is none.

It's a perpetual motion machine... it just keeps running, and if you could add more fuel beyond the size of the intake ports and system, it would overspeed till it exploded. It has to due with the way the fuel and air are pre-mixed in the crankcase, then pulled into the combustion chamber.

A throttle does NOT control fuel... believe it or not... it controls the amount of AIR rushing into the carb, which then pulls more fuel, adds more power, adds more suction... etc.. etc..

When I studied them in college (ERAU A&P School), we studied how to control them and keep them from over-speeding, which is done solely by ignition and mixture controls. There is no real throttle as there is in a normal horizontally, or V-type engine.

Same goes for a Turbine engine, it's a constant explosion. The only thing that stops it is to cut the fuel flow. The ignition runs but is only there as a precaution in case of a flame-out for immediate restarts. Otherwise it's a never-ending bomb-blast.

OvS
 
Thanks both!!

Thats great. Even a technophob like me can understand!!
 
This video states the method used to THROTTLE his camel

http://www.youtube.com/watch?v=qtprTL66-FY

Due to the fact that NO supercharger is used, the same amount of AIR/FUEL/OIL is pumped into the cylinder all the time

As the man said, it's throttled by the amount of fuel actually burned by the spark provided

If you listen as he attempts to land, 'he Blips the throttle'

I simulate that action by F10, and F11 the ONLY available side by side keys in OFF.

F10 - 10% Throttle

F11 - 100% Throttle

A little quick back and forth, you're basically doing the same thing . . With a little cheating of course :wiggle:
 
Rotaries do have mixture controls, though, so it's not always the same amounts of all the components. The total volume is the same, it's composition differs.
Rotaries also had a rich mixture in the crankcase which was leaned out in the cylinder by keeping the exhaust valve open on a slight delay during the intake stroke. The crankcase mixture of fuel and air was just rich enough not to ignite. Some of the early Gnomes had the mixture perfect and the first bit of spark off-timing usually resulted in a big bang, which in turn usually blew the front cover and prop off.
 
Here is a description of rotary engine control which I like:

Rotary engine control

It is often asserted that rotary engines had no carburettor and hence power could only be reduced by intermittently cutting the ignition using a "blip" switch, which grounded the magneto when pressed, shutting off power to the spark plugs and stopping ignition. However, rotaries did have a simple carburettor which combined a gasoline jet and a flap valve for throtting the air supply. Unlike modern carburettors, it could not keep the fuel/air ratio constant over a range of throttle openings; in use, a pilot would set the throttle to the desired setting (usually full open) then adjust the fuel/air mixture to suit using a separate "fine adjustment" lever that controlled the fuel valve.

Due to the Gnôme's large inertia, it was possible to adjust the appropriate fuel/air mixture by trial and error without stalling it. After starting the engine with a known setting that allowed it to idle, the air valve was opened until maximum engine speed was obtained. Since the reverse process was difficult, "throttling" was accomplished by temporarily cutting the ignition using the blip switch.

By the middle stages of World War I some throttling capability was found necessary to allow pilots to fly in formation, and the improved carburettors which entered use allowed a power reduction of up to 25%. The pilot would close off the air valve to the required position, then re-adjust the fuel/air mixture to suit. Experienced pilots would gently back off the fuel lever at frequent intervals to make sure that the mixture was not too rich: a too-lean mixture was preferable, since power recovery would be instant when the fuel supply was increased, whereas a too-rich mixture could take up to 7 seconds to recover and could also cause fouling of spark plugs and the cylinders to cut out.

The Gnôme Monosoupape was an exception to this, since most of its air supply was taken in through the exhaust valve, and so could not be controlled via the crankcase intake. Monosoupapes therefore had a single petrol regulating control used for a limited degree of speed regulation. Early models also featured variable valve timing to give greater control, but this caused the valves to burn and therefore it was abandoned.

Later rotaries still used blipping the ignition for landing, and some engines were equipped with a switch that cut out only some rather than all of the cylinders to ensure that the engine kept running and did not oil up. A few 9 cylinder rotaries had this capability, typically allowing 1, 3, or 6 cylinders to be kept running. Some 9 cylinder Monosoupapes had a selector switch which allowed the pilot to cut out six cylinders so that each cylinder fired only once per three engine revolutions but the engine remained in perfect balance. Some documentation regarding the Fokker Eindecker shows a rotary selector switch to cut out a selected number of cylinders suggesting that German rotaries did as well.

By 1918 a Clerget handbook advised that all necessary control was to be effected using the throttle, and the engine was to be stopped and started by turning the fuel on and off. Pilots were advised to avoid use of the cut out switch as it would eventually damage the engine.

The blip switch is, however, still recommended for use during landing rotary-engined aircraft in modern times as it allows pilots a more reliable, quick source of power that lends itself to modern airfields. The landing procedure using a blip switch involved shutting off the fuel using the fuel lever, while leaving the blip switch on. The windmilling propeller allowed the engine to continue to spin without delivering any power as the aircraft descended. It was important to leave the blip switch on while the fuel was shut off to allow the spark plugs to continue to spark and keep them from oiling up, while the engine could easily be restarted simply by re-opening the fuel valve. If a pilot shut the engine off by holding the blip switch down without cutting off the fuel, fuel would continue to pass through the engine without combusting and raw fuel/air mix would collect in the cowling. This could cause a serious fire when the switch was released, or alternatively could cause the spark plugs to oil up and prevent the engine restarting.
 
[FONT=Times New Roman, serif]The early Gnome 50-80 hp 7 cylinder rotary aero engines introduced from 1908 onwards had no throttle control, and the fuel/air mixture could only be adjusted for fine tuning on the ground by a mechanic. The engine was therefore either on or off, although there was a blip-switch for the pilot to temporarily cut ignition. The development of the 100hp Gnome Monosoupape (or 'Mono') in 1913 introduced pilot-control of the fuel-air mixture for the first time, with a lever that regulated petrol flow to the engine. This permitted the pilot to make small adjustments to the RPM, or lean the fuel mixture at higher altitudes to maintain engine efficiency. Lt. R.T. Leighton provides a very good description of this in his pilot notes published by the Shuttleworth Collection: "The engine should give 1,150-1,200 rpm, as height is gained, then petrol should be cut down until engine is giving 1,050-1,100 rpm, when machine [Avro 505K] flies level at 65 mph. The machine at full revs flies level at 85 mph...[to descend] shut petrol off...glide down at 55 mph...do not 'buzz' engine...taxi in by buzzing the engine with petrol about 1" on adjustment". Pilots were now discouraged from using the blip-switch, as over-use could stress the engine and (in the mono) cause an engine fire. In the 100hp Monosoupape the engine rpm could only be reduced by about 10% or 20% without risking engine cut-out. In 1916 the 160 hp 14 cylinder version of the Gnome Monosoupape introduced another refinement in the form of a second magneto switch that could be used to cut ignition temporarily to two or more of the 14 cylinders in any one cycle to give reduced power rather than no power at all: a switch that could be used to reduce engine output by approximately 1/8, 1/4 or 1/2.[/FONT]


[FONT=Times New Roman, serif]The Le Rhone and Clerget engines introduced a second mixture control, to control the air added to the mixture (often referred to as the 'throttle' by WWI pilots) although the petrol adjustment lever was also retained (referred to under a number of different names, but most usualy as the 'fine adjustment' by RFC pilots). There has been quite a bit written on the Le Rhone, which was much liked by pilots. Cecil Lewis, in 'Sagittarius rising' comments "The rotary was an 80hp Le Rhone. It was a beauty, the sweetest running rotary ever built. It throttled down and ticked over like a water-cooled stationary, and was as smooth as silk over its whole range". The Le Rhone was also ahead of its time in linking the throttle to the needle valve which regulated the petrol supply: Lt. Leighton comments in his pilots notes that "Theoretically, the position of the fine adjustment can be found once and for all for every position of the throttle, so that having set fine adjustment once, it need not be moved again. The throttle lever then being worked as on a stationary engine". He adds, though, that "Practically, the engine will run if worked this way, but better results are obtained by varying the position of the fine adjustment with varying positions of the throttle lever". The two levers were positioned together normally on the left of the cockpit, on a quadrant marked from 1-10.[/FONT]


[FONT=Times New Roman, serif]The Clerget had the same arrangement of throttle and fine adjustment levers, but dispensed with the unreliable linkage between the two - it was much liked by ack emmas, as it was easier than the Le Rhone to maintain in the field, and by the War Department as it was slightly cheaper than the Le Rhone. In both the Le Rhone and the Clerget (and the later Bentley) the combination of a throttle and a fine adjustment did take some getting used to, and RPM could not be changed rapidly in flight even by experienced pilots. I do not believe the 'throttle' was used much, if at all, in combat - it was used mainly to ensure optimum endurance at altitude, to make formation flying easier, and to reduce power on landing. Engine rpm could not, in practice, be reduced below 50% or so of engine power, however, so a powered landing would still require use of the blip switch unless the pilot was confident enough to bring the airoplane in by gliding down with the petrol switched off. Robert W. Bradford (An Associate Director of the [Canadian?] National Aviation Museum) is quoted as saying "the 110/120 hp Le Rhone rotary has the characteristics of all early rotary engines - they have a high idling speed in proportion to the full power rpm. They simply do not 'tick over' as a radial or inline engine would do - in fact with the fixed pitch wooden propeller, they idle at about 45% of full engine speed (500 rpm as against 1150 rpm for take-off at full power)" [billybishop.net/bishopF.html]. I have seen a variety of other figures for the safe idling speed of Le Rhones and Clergets, from 600 rpm up to 800 rpm, and there is some evidence that the Bentley rotaries might have idled at a lower rpm [Blakemore,1986] - in practice, I suspect each engine would be slightly different depending on the make, length of service or time between overhauls, the skill of the fitter, maintenance standards in the field, etc. It does seem clear, however, that most pilots would be reluctant to risk an engine cut-out (particularly in the final approach to landing) by cutting rpm back further than 50% of engine speed.[/FONT]
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[FONT=Times New Roman, serif]So these rotary engines could be 'throttled' up or down, but it was certainly not a simple procedure and pilots report that it took considerable practice before it became second nature (engine failure on take-off was often caused by the pilot getting the mixture wrong and then choking the engine). Also, these engines could not be 'throttled' up or down quickly - it took about 7 seconds before the change in the mixture setting had any effect on engine power [Nahum, 1987]. Using such a 'throttle' in combat was therefore unlikely to be practicable. Most pilots would continue to use the blip-switch to produce sudden changes in engine power, mostly on the final approach to landing (although they were officially discouraged from doing so, particularloy at full engine power, as it damaged the engine).[/FONT]






[FONT=Times New Roman, serif]German rotaries were similar to the early Gnome and Le Rhone engines, although German pilots had both throttle and mixture control for even those engines based on the early Gnome design (so the Fokker E.III/E.IV had both a throttle and a mixture lever). I think that the most interesting of the German rotaries is the late war contra-rotating 160hp SH III fitted to the Siemens Schuckert DIII and IV. This was "fitted with twin magnetos and speed was governed by a proper throttle control, sensitive down to about 350 rpm" [Profile 86].[/FONT]


[FONT=Times New Roman, serif]Blakemore, L N. [/FONT][FONT=Times New Roman, serif]Bentley BR2 World War 1 rotary aero engine[/FONT][FONT=Times New Roman, serif]: building the one quarter scale working replica. Yalanga, 1986.[/FONT]


[FONT=Times New Roman, serif]Leighton, R T. [/FONT][FONT=Times New Roman, serif]Pilots' notes for the handling of World War I warplanes and their rotary engines[/FONT][FONT=Times New Roman, serif]. Shuttleworth Collection. [Pamphlet. Notes originally written in 1917 by an RFC pilot. Covers the Monosoupape, Clerget and Le Rhone rotaries, with notes on flying Avro, 1 1/2 Strutter and Pup]. [/FONT]


[FONT=Times New Roman, serif]Morse, William. [/FONT][FONT=Times New Roman, serif]Rotary engines of World War One[/FONT][FONT=Times New Roman, serif]. Nelson and Saunders, 1987[/FONT]


[FONT=Times New Roman, serif]Nahum, Andrew. [/FONT][FONT=Times New Roman, serif]The rotary aero engine[/FONT][FONT=Times New Roman, serif]. HMSO, 1987.[/FONT]


[FONT=Times New Roman, serif]Profile Publication 86: [/FONT][FONT=Times New Roman, serif]The Siemens Schuckert DIII and IV[/FONT][FONT=Times New Roman, serif]. 1966.[/FONT]


[FONT=Times New Roman, serif]Lewis, Cecil. [/FONT][FONT=Times New Roman, serif]Sagittarius rising[/FONT][FONT=Times New Roman, serif]. Peter Davies, 1966. [/FONT]



[FONT=Times New Roman, serif][/FONT][FONT=Times New Roman, serif][/FONT]
[FONT=Times New Roman, serif]On a related note, it is interesting that very few of the German stationary engined aircraft with either the Daimler Mercedes or Benz engines (Alb. D.II, D.III, D.V, D.Va, Pfalz) had any mixture control until altitude compensating carburettors were added to these engines in early 1918. Both the British and French stationary engined aircraft, with Hispano Suiza or RAF engines, had altitude compensating carburettors of the Zenith or Claudel/Hobson 'vacuum' type added from around mid to late 1916 onwards, and therefore had both throttle and mixture control[/FONT].
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http://www.theaerodrome.com/forum/aircraft/31874-altitude-compensating-carburettors-pt-1-allied.html

http://www.theaerodrome.com/forum/aircraft/31875-altitude-compensating-carburettors-pt-2-german.html

Bletchley
 
[FONT=Times New Roman, serif]So these rotary engines could be 'throttled' up or down, but it was certainly not a simple procedure and pilots report that it took considerable practice before it became second nature (engine failure on take-off was often caused by the pilot getting the mixture wrong and then choking the engine). Also, these engines could not be 'throttled' up or down quickly - it took about 7 seconds before the change in the mixture setting had any effect on engine power [Nahum, 1987]. Using such a 'throttle' in combat was therefore unlikely to be practicable. Most pilots would continue to use the blip-switch to produce sudden changes in engine power, mostly on the final approach to landing (although they were officially discouraged from doing so, particularloy at full engine power, as it damaged the engine).[/FONT]
Click to expand...

Hence my point that there is no 'true' throttle to a rotary. Throttle being the single mechanism to control the force of the engine quickly. From a mechanics point of view, throttle is the key to producing HP and power. If you can't control that effectively, and quickly, then you are not really controlling the engine. You are adjusting it.

These are some fantastic references you guys have posted. Really great stuff. If there is one thing this forum will NEVER be shy of is knowledge!! :)

I know some will disagree, but from my personal experiance working on everything from 2-Stroke marine engines, small-block Chevy's, 2/3/4 cylinder motorcylces, and cumbustion/jet power airplanes.... the rotary is a motor you simply can't control other than turning it on and off. The only other thing like it is a turbine engine. As I said before, you don't really control a turbine engine, you adjust it, then shut it off.

The rotary reacts in the same way, it 'spools' up and down when you adjust the fuel/air mixture. Unlike a normal engine, whereas it reacts immediately. A turbine does the same thing, you jam the 'throttle' up, it dumps more fuel in, but it takes a little while for the engine to react, hence the spool-up time, then when you pull back the throttle, it takes time to spool-down. However, cut the fuel, the engine stops poducing power instantly. Same for the Rotary.

That's the reason why the 'blip' is the best way to control the power of the rotary. You're really not controlling the engine per say as a true throttle, you're controlling the engine by limiting it's power output by cutting the ignition.

The best way to give this as an example is to hook a Rotary (a true rotary, not the 3-cylinder Mazda engine) to a Drag racer....

Assuming you could transverse the power of the rotary into an axel without is blowing to pieces when you start it. The car would have to be constantly turned on and off to keep it in one place. When the light turned green, the car would be at full-throttle, with no transmission to shift... gone... no chance to push in a clutch, nothing... just balls to the wall.

That's the same idea as it being attached to a propeller, you see this in the amount of torque it throws out when the ignition it switched on.

Anyhow... it's a great subject, and certainly worth the 'debate' :)

OvS
 
No 'debate' from me!

I just offer the little bit of information that I had copied and stored away...
When I used to sit in a classroom with other students, I would turn the pages in my course book when I saw that everyone else was turning the page, just so no one would know how completely baffled I was....:costumes:

Thanks for all the good information presented here. It all helps to understand the workings of these unique engines.
 
ovs said:
The best way to give this as an example is to hook a Rotary (a true rotary, not the 3-cylinder Mazda engine) to a Drag racer....

Assuming you could transverse the power of the rotary into an axel without is blowing to pieces when you start it. The car would have to be constantly turned on and off to keep it in one place. When the light turned green, the car would be at full-throttle, with no transmission to shift... gone... no chance to push in a clutch, nothing... just balls to the wall.
Click to expand...


Thus the need for a transmission. Rotary or inline, reguardless, the crashing of gears would make one heck of a racket, and the smoke cloud from the damage to drive train and rubber......... I don't even want to think about it. And agreed, the Wankel was not a true rotary in the sense of the term. It was more a hybrid than anything else, but I understand the principle behind it trying to get the most power for fuel consumed. I worked on one and after that I refused to touch them. The way they were designed in the engine bay, other than simple maintenance, the best way to work on them was to remove said engine, roll the car out of the shop, roll the dumpster in, drop said engine in dumpster, and install a new one.

A benefit of the aero-rotary design, in that it was light in weight for power developed, so in comparison to vee or inline engines the rotary in principle should allow more time running when tuned properly compared to it's inline or vee counterparts with equal ammounts of fuel, due to fewer working parts, which translates into less friction and since the crank was a solid mount and the cylinders rotated, cooling the engine in principle should be easier than liquid cooling whether water or polyethylene glycol is used to transfer heat. So in essense they were more fuel efficient than their inline and vee counterparts, and should have been easier to coll although the latter was dependent on ambient temperatures for both designs.

An interesting note even though it applies to a radial design was when Professor Kurt Tank was having trouble with the BMW 801 A radial overheating in the Focke Wulf 190A series, it was eventually cured by mounting a fan on the propshaft behind the propeller, that forced airflow into the cowling and circulated through the engine cowling to alleviate the problem.

This is definitely a cool thread. Very interesting for sure.
 
Thanks everyone for this input it really is fantastic. I am seeing my friend over the weekend and I am going armed with all this. He is going to be very interested!

He servered in the Royal Air Force and clocked hours on the Lightning. Thats the English Electric Lightning not the P38!!
 
Hylander,

Believe it or not, that was the same problem that plagued the Harley engines for years. The rear cylinder would overheat immediately in traffic, or at low speeds due to lack of cooling air. Seeing it was blocked by the front cylinder and covered by the tank, it suffered.

The Evo engine slightly cured that with some ducting using rubber and a slight shift in the cylinder placement.

Hence why Jap bikes last longer... but aren't as nice looking/clean. ;)

OvS
 
Hey, OvS
This may not be the right thread, but as you mention Harleys: do you know, which Harley that was, Michael Douglas was driving at the beginning of "Black Rain" ? (I'd like to ride that one some day...)
Cheers; Olham
 
Hey OvS, I just looked at my 02 HD Heritage Classic with Evo engine and the rear cylinder is in-line with the front, no off set and no rubber ducting. Are you talking about a different engine or year of make?

I have ridden this bike in 100F degrees ambient air, plus sitting at 3 minute long stop lights, with no over heating issues ever. I will say the only thing that did over heat was me!

As with any engine design fluid dynamics, thermal, has a leading factor in the overall configuration of the engine. One much remember that engines run in two thermal environments, forced convection cooling i.e. water, fan, forced air ... and convection cooling i.e. just still ambient air, modes.

It all equals surface area for thermal transfer and heat lose based on design requirements.

Rice Rockets .... ?

Good thread.
Cheers,
WF2
 
Don't mean to hijack (sort of)

If you look at the four main Harley engine designs (excluding the Flathead and the K model) you will see that the Evolution engine uses an aluminum cylinder with a steel sleeve as opposed to the cast iron cylinder and has larger cooling fins than the Knucklehead, Panhead, and Shovelhead, thus virtually eliminating the overheating problems experienced by the three earlier OHV models. One way Harley riders of the past alleviated the rear cylinder overheat was to run a cooler plug in the rear cylinder. This practice did reduce the performance of the engine, however, not enough of a reduction to be noticeable. I haven't owned a motorcycle in 20 years because after I had to sell my FXR (pictured) I figured that I had ridden the best and will not settle for less. I know I'll probably have numerous folks disagree, but that is my opinion.

CJ
 
Yes, as I said the design requirements dictate cooling solutions i.e. material selection, fin design, surface area ... etc. Aluminum having a better thermal transfer rate then steel. This is why Stainless steel pots have a very bad heat distribution even with a copper bottom, cast iron a bit better.

This was one of the issues with rotary engine design, material. They did have radial engines at the time but as history tells us there were big over-heating problems to over come, hence why they spun the engine for cooling.

WF2
 
Hi all,
Like the explanations OvS - reminds me of my early days in the RAF:

Daniel Bernoulli (Swiss 1700 - 1782) - Extract from:

http://en.wikipedia.org/wiki/Bernoulli's_principle

  • The relative air flow parallel to the top surface of an aircraft wing or helicopter rotor blade is faster than along the bottom surface. Bernoulli's principle states that the pressure on the surfaces of the wing or rotor blade will be lower above than below, and this pressure difference results in an upwards lift force.[14][15] If the relative air flows across the top and bottom surfaces of a wing or rotor are known, then lift forces can be calculated (to a good approximation) using Bernoulli's equations — established by Bernoulli over a century before the first man-made wings were used for the purpose of flight. Note that Bernoulli's principle does not explain why the air flows faster past the top of the wing and slower past the under-side. To understand why, it is helpful to understand circulation, the Kutta condition and the Kutta–Joukowski theorem.
    Besides, Newton's third law states that forces only exist in pairs, so the air's upwards force on the wing coexists with the wing's downward force on the air, which results in a downward acceleration of air.
  • The carburetor used in many reciprocating engines contains a venturi to create a region of low pressure to draw fuel into the carburetor and mix it thoroughly with the incoming air. The low pressure in the throat of a venturi can be explained by Bernoulli's principle - in the narrow throat, the air is moving at its fastest speed and therefore it is at its lowest pressure
:mixedsmi:http://en.wikipedia.org/wiki/Bernoulli's_principle
 
This is the best video of a rotary engine having its RPM deduced by varying the air/fuel mixture. Watch as Gene DeMarco varies the air/fuel mixture and note the engine RPM in response. This is all the throttle a rotary had, not with standing the selector switch on later engines or blip-ping the ignition.

OBERURSEL ENGINE RUNNING

Cheers,
WF2
 
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