New! Bletchley's Notes on Throttle Control in Rotary Engines of the Great War (April 2005) 

There is some uncertainty and confusion over the authentic use of the throttle in RB3D when flying a plane powered by a rotary engine. Some players choose not to use the throttle on their joystick or the throttle settings on the keyboard, in the understanding that Great War rotary engines had no throttle control. Other players have found references in pilot manuals or memoirs to the use of a throttle. The historical reality is complicated, and it depends very much on the type and makes of engine in use. These appear to fall into three broad categories: those that had no throttle control at all; those that had one or more taps, levers or other devices to regulate and fine tune the fuel/air mixture to the engine; and just one (the contra-rotating SH III) that had full throttle control like the stationary engines of the period. The notes that follow are my own attempt to analyse and synthesise information from several sources (the main ones are listed at the end) and apply them to the game.

Those with no throttle [Type 1]

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 (hence the nickname of the DH2 - the 'spinning incinerator'!). 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 in just two or more of the 14 cylinders 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.

 The early German Oberursels fitted to the Fokker E series were built under licence from Gnome, and later ones were exact replicas of Gnome engines (possibly not quite as well made), so in RB the EIII would be controlled as for the 100 hp Gnome Monosoupape, and the EIV as the 160hp Monosoupape (the earlier unarmed EII had either the 80 hp Oberursel copy of the Gnome, or the 100 hp copy of the Monosoupape).

 TYPE 1: If you are flying a plane with the 80 hp Gnome rotary, I would suggest you run them at 100% and use the TAB key to simulate the blip-switch. If you are flying a plane with the 100 hp Gnome Monosoupape (such as the DH2), I would suggest that you run them at 80%-100% (from 8 to 0 on the keyboard) and use the TAB key as the blip switch. If you are flying a plane such as the Nieuport 28 that is fitted with the 160 hp Monosoupape I would suggest that you use the 0, 9, 8, 7, and 5 throttle settings only, and continue to use the TAB key as a blip-switch.

Those that have fuel/air regulators [Type 2]

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 usually 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 (very convenient for us, as this equates nicely to the 1-0 on our keyboards!).

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 aeroplane 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. I thought at one time that the Bentley BR1 and BR2 might have been a bit different, but recent research (I have looked at a surviving example in the RAF Museum, Hendon, and I have recently read W.O. Bentley's autobiography) leads me to believe that mixture control in these engines was the same as the in the earlier Clerget.

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, particularly at full engine power, as it damaged the engine).

The later Oberursel engines (fitted to the DR1) were either poor copies of the Le Rhone, captured Allied Le Rhones, or Le Rhone engines built under licence at the Thulin works in Sweden and smuggled into Germany via Holland [Weyl,1965]. For RB treat as Le Rhone rotaries.

TYPE 2:  In RB terms this would equate to a minimum power setting of '5' on the keyboard for landing, a setting of between '5' and '0' for climbing and cruising, a constant '0' at all times in combat, and sparing use of the TAB blip-switch, used mainly for landing.

The German Contra-Rotating SH III Rotary Engine [Type 3]

I think 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 engine "was fitted with twin magnetos and speed was governed by a proper throttle control, sensitive down to about 350 rpm" [Profile 86].

Type 3: treat in the same way as a stationary engine, with full throttle control.

Bletchley April 2005 Version 2

Blakemore, L N. Bentley BR2 World War 1 rotary aero engine: building the one quarter scale working replica. Yalanga, 1986.

Leighton, R T. Pilots' notes for the handling of World War I warplanes and their rotary engines. 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].

Morse, William. Rotary engines of World War One. Nelson and Saunders, 1987

Nahum, Andrew. The rotary aero engine. HMSO, 1987.

Profile Publication 86: The Siemens Schuckert DIII and IV. 1966.

Lewis, Cecil. Sagittarius rising. Peter Davies, 1966.

Weyl, A R. Fokker: the creative years. Putnam, 1965.

[plus various contributions to the forum at www.theaerodrome.com, and other internet sources]

Rotary Engined Aircraft in RFC, RNAS and RAF Squadrons 1914-1918

(From Appendix XXVIII of The War in the Air by H A Jones)

Avro                                        80 hp Gnome               Type 1:Squadrons 1, 3, 5

B.E.8                                       80 hp Gnome               Type 1:Squadrons 1, 3, 5, 6

Bleriot                                     80 hp Gnome               Type 1:Squadrons 3, 5, 6, 9, 16

Bristol Scout                           80 hp Gnome               Type 1:Squadrons 3, 4, 5, 6, 8, 16

Bristol Scout                           80 hp Le Rhone            Type 2:Squadrons 1, 7, 8, 9, 10, 11, 13, 15,                                                                                                    18, 21, 25

Caudron                                  80 hp Gnome               Type 1:Squadrons 1, 4, 5

D.H.2                                      100 hp Monosoupape  Type 1:Squadrons 5, 11, 18, 24, 29, 32

D.H.5                                      110 hp Le Rhone          Type 2:Squadrons 24, 32, 41, 64, 68AFC,                                                                                                      2AFC

F.E.8                                       100 hp Monosoupape  Type 1:Squadrons 5, 40, 41

Henri Farman                         80 hp Gnome               Type 1:Squadrons 3, 5, 6

Martinsyde  S.1 Scout           80 hp Gnome               Type 1:Squadrons 1, 4, 5, 6, 16

Morane Monoplane               80 hp Gnome/

                                                80 hp Le Rhone            Type 1/2:Squadrons 4, 60

Morane Monoplane               110 hp Le Rhone          Type 2:Squadrons 60

Morane 'Parasol'                   80 hp Le Rhone            Type 2:Squadrons 1, 3, 60

Morane Biplane                     80 hp Le Rhone            Type 2:Squadrons 60

Morane Biplane                     110 hp Le Rhone          Type 2:Squadrons 1, 3, 60      

Nieuport Scout N11               80 hp Le Rhone            Type 2:Squadrons 8RNAS (208)

Nieuport Scout N17               110 hp Le Rhone          Type 2:Squadrons 1, 11, 29, 40, 60

Nieuport Scout N17bis          130 hp Clerget             Type 2:Squadrons 6RNAS (206)

Nieuport Two-seater              110 hp Clerget             Type 2:Squadrons 1, 46

S.E.2                                       80 hp Gnome               Type 1:Squadrons 3

Sopwith '11/2 Strutter'           110 hp Clerget             Type 2:Squadrons 43, 45, 69AFC, 3AFC,                                                                                                      8RNAS (208)

Sopwith '11/2 Strutter'           130 hp Clerget             Type 2:Squadrons 43, 45, 69AFC, 3AFC,                                                                                                      8RNAS (208)

Sopwith 'Pup'                          80 hp Le Rhone            Type 2:Squadrons 4, 46, 54, 66,                                                                                                          3RNAS (203), 8RNAS (208), 9RNAS                                                                                                (209)

Sopwith 'Camel'                     110 Le Rhone              Type 2:Squadrons 3, 46, 54, 71AFC, 4AFC,                                                                                                  73, 80, 151, 152, 17American

Sopwith 'Camel'                     130 hp Clerget             Type 2:Squadrons 28, 43, 45, 54, 65, 69AFC,                                                                                                3AFC, 71AFC, 4AFC, 73,                                                                                                                  148American, 6RNAS (206), 8RNAS                                                                                                 (208), 9RNAS (209)

Sopwith 'Camel'                     150 hp BR1                 Type 2:Squadrons 1RNAS (201), 3RNAS                                                                                                      (203), 4RNAS (204), 8RNAS (208),                                                                                                   9RNAS (209),10RNAS (210)

Sopwith 'Snipe'                       230 hp BR2                 Type 2:Squadrons 43, 71AFC, 4AFC,                                                                                                            8RNAS (208)

Sopwith 'Tabloid'                    80 hp Gnome               Type 1:Squadrons 3

Sopwith Triplane                    130 hp Clerget             Type 2:Squadrons 1RNAS (201), 8RNAS                                                                                                      (208), 9RNAS (209), 10RNAS (210)

Vickers Fighter                      100 hp Monosoupape  Type 1:Squadrons 2, 5, 7, 11,16, 18

NOTE: The Nieuport 28 used mainly by the Americans was powered by the 160 hp Gnome Monosoupape (TYPE 1, but see note about using the second magneto switch).

Settings for Ground Gunners Initial Aim in FCJ or CM11 (April 2005)

The first table is based on three assumptions:

1. That the stock Red Baron 3d setting of around 800 for Initial Aim is probably about right for the early period of the war (1915-16), but not effective enough for the later periods (1917-18).

2. That the default Full Canvass Jacket setting of 25 for Initial Aim might be OK for the late period, but is far too effective for earlier periods.

3. That these assumptions are based on a third assumption, that the effectiveness of ground fire increased as the war progressed  (I have no historical data to support this, but anecdotal evidence from RFC pilot accounts would suggest that this is so).

In producing this table I have started with a simple regression from 1000 in August 1915 to 25 in November 1918, representing a progression from very inaccurate initial aim in August 1915 to very much more accurate initial aim by November 1918.

I then developed a second table that superimposes over this simple regression a matrix for July 1916 to July 1918 based on historical figures for deviations in total hours flown / losses incurred to ground fire that I derived from H A Jones ‘The war in the air’ and Trevor Henshaw’s ‘The sky their battlefield’. It has the effect of further increasing the hazard faced by low-flying aircraft during the main ground battles of the war.

Bletchley          April 2005  Version 3

Bletchley's Other Red Baron 3D Aids for:

• Engine Failure, Gun Jams, and RFC Leave
• Rotary Throttle Settings and Use
• AI Settings [Requires FCJ Control Panel]
• Mission Type Changes during the course of the war [RFC/RAF Flanders Front; for other nations see Mark Hutchinson's tables, below]