Rotary Engine

[thewoo1 0]

I read in abook about the Laf Esc that stated all rotary engines were run full out or not at all rpm were controlled by ignition switch... true even for later models ?...... fuel mixture adjustment?

[Bullethead 12]

I read in abook about the Laf Esc that stated all rotary engines were run full out or not at all rpm were controlled by ignition switch... true even for later models ?...... fuel mixture adjustment?

 

Later models had multiple throttle positions, but as I understand things, none of there were every totally analog.

[Stiffy 1]

There is a myth that rotarys didnt have carburettors... this isnt true, it just want advanced enough to control mixture. This quote explains better than I could.

 

 

"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 rotary engine'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 more difficult, "throttling", especially when landing, was often 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.^[1]

 

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.^[4] 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.^[5] 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.^[1]

 

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.^[4] 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."

 

 

[Bletchley 8]

Excellent summary, Stiffy :)

 

The Oberursel (Fokker Eindecker) selector switch could be used to cut out just one cylinder at a time - it was not a form of engine control, I think, like that for the 160 hp Gnome mono. (N28) but was used instead to isolate a faulty cylinder that might be running rough or misfiring. Even the earliest Oberursel rotaries had both the throttle and fine adjustment controls (as well as a blip switch) extended into the cockpit for pilot use - as compared to the early French Gnome types that they were based on, which appear to have been run full-out in the air (not usual to have throttle or fine adjustment controls in the cockpit, just a blip switch, although these could be added) but could have throttle and fuel controls adjusted on the ground. The Le Rhone rotaries also had a mechanical linkage between throttle and fuel controls so that, in theory, opening the throttle also increased the fuel supply to the engine to automatically supply the correct fuel/air mixture for each position of the throttle - but in practice this was sensitive to wear, temperature and pressure changes and did not work well unless constantly re-adjusted.

 

I don't think any flight sim does a good job of simulating rotary engine control (I think even ROF ignores this), although if you want to have a taste of what it might have been like to control these engines in flight (and you still have RB3D on your system) try Gabi's ReLoad mod for RB3D and set the engine type to 'Type 1' for the early Gnome, 'Type 2' for the Gnome Monosoupape, or 'Type 3' for the later rotaries (Clerget, Le Rhone, Bentley, and Oberursel) :)

 

Bletchley

Edited October 28, 2009 by Bletchley

[OvS 8]

A true 'BLIP' switch is impossible within the confines of OFF

 

However an extremely 'serviceable' Blip is possible

 

By reprogramming, F10 & F11 to 10% & 100% Throttle respectively

 

Although this is totally true with OFF, and you can 'turn-off' the trottle from 10 to 100% to compensate... the new Fokker E.V will sound more like a Rotary should. I was able to tweak the sound curves tight enough so that it goes from one stage to the other without any fading. What that means is at 100% throttle, you're full out, at about 80% you'll beging to blip at 3/4 ignition... and so on. It actally sounds like a the ignition is clipping the motor... then the further down you go, the less smooth the engine runs. So now you'll get the high... cough.. cough... run-up to high.. high... cough... run-up to high.. high..... choppy... choppy... run-up to high.. etc.

 

OvS

[RAF_Louvert 101]

.

 

Outstanding info in this thread for those not familiar with the throttle controls on these early rotary-powered kites, (and it is an important part of their "charm"). I use a variation on uncleal's approach and have a key on my joystick set up to toggle between 10% and 100% throttle, which gets me pretty close in control and feel to a real blip switch.

 

Cheers!

 

Lou

 

.

[Bullethead 12]

Which is the reasoning for use of two adjacent keys, with a "rocking action" you can come pretty damn close to a toggle. Needed because with a Force Feedback Joystick, buttons are in great demand

 

Using the Saitek software, you can set up your throttle handle to work like various types of of rotary engine control. What you do is tell it that the throttle is no longer a control axis but instead is set up in "banded" mode for keyboard entry.

 

"Banded" mode is where you divide the range of motion of the throttle handle, joystick, rotary, etc., into however many segments (bands) you want (and they don't all have to be the same size). Then you assign different keyboard commands to each band, so that when the throttle handle moves into that position, it generates that keyboard output. You can also assign bands to have no output. Anyway, what you do is define bands to have the various keyboard commands that put the engine at specific power levels.

 

NOTE, however, that this is just the theory, to give you the idea of how it works. In practice, you actually have to do things a bit differently because of how joystick buttons send constant streams of their keyboard characters if they're kept pressed down. When you put the throttle on banded mode, each band you create is in effect a new joystick buton, which acts like it's being pressed continuously as long as the throttle handle is in that position. This can lead to all sorts of problems both in and outside the game, so it's best to avoid it using null bands over most of the arc of travel.

 

For example, suppose you want to set up the throttle as a 10%/100% "blip switch" for an early rotary. The best way would be sorta like this:

 

|---------------------------Null-------------------------------|-10%-|----------Null----------|-100%-|-------------------------------------------Null------------------------------------|

 

 

The idea here is that the bands with the actual commands are very, very narrow so the throttle handle will usually be in a null area not giving any commands. The commands are triggered like brief button presses as the handle moves across the narrow command bands moving from 1 null position to another. Adjust the size, spacing, and position in the arc of movement to your taste. Also note that you can "safety" your throttle by moving it all the way to either end, so that it won't be generating its output while the profile is loaded but you're not playing the game.

 

I've never bothered to look, but if CFS3/OFF has more engine commands than 10% and 100%, you'd be able to do the above using several of the other commands to replicate the control over later rotaries.

[Bletchley 8]

One of the problems not already mentioned so far, is that these rotary engines had a very high "idle" speed of around 800 rpm in the air (somewhat lower, at 500-600 rpm on the ground), and the effective range of power control was not therefore 10% to 100%, but was more like 60% to 100% (or from 80% to 100% for the early monosoupape) when in flight - so your throttle controls should be calibrated to give this narrower range, if possible. This is the reason that they had the blip switch - as this (or switching off the fuel flow via the 'fine adjustment' or fuel cock) was the only way to slow the engine rpm and reduce power for landing or whilst taxiing on the ground. The pilots would then remember, or mark their throttle quadrant, with the positions of the throttle and fine adjustment levers for a small number of preset engine conditions (usually 'idle plus' at about 60%, 'cruise' at about 80% and 'full power' at 100%), and then move the fine adjustment lever for any necessary small increases or decreases in power (using this mixture control to control the power output) or for altitude adjustment. These engines were also run 'full rich' for full power, and so were more sensitive to altitude changes than most of the stationary engines of this period (with the exception of the 'fuel cooled' Renault and RAF engines, which also ran on the rich side).

 

Bletchley

Edited October 30, 2009 by Bletchley

[Bullethead 12]

One of the problems not already mentioned so far, is that these rotary engines had a very high "idle" speed of around 800 rpm in the air (somewhat lower, at 500-600 rpm on the ground), and the effective range of power control was not therefore 10% to 100%, but was more like 60% to 100% (or from 80% to 100% for the early monosoupape) when in flight

 

It wasn't just rotaries that were like this, but even at least some stationaries. For example, the Beardmore of the Fee didn't much change in RPM from idle to full power. Or so I learned from watching vids on flying a reconstruction with and original Beardmore.

 

What you describe for rotaries reminds me of all the tweaking necesary to get proper throttle response out of an R/C model engine. Adjusting the throttle and idle stop screws, the needle valve, and the throttle control pushrod from the servo. It might take a few hours, even longer if you had to get broken-off stop screws out of the carb after a bad crash