24.12.2008, 22:00
"The Bf109 is a fascinating aircraft. It was produced in greater numbers than any other fighter aircraft, and was the main single-engined fighter opponent of the Spitfire and Hurricane in the Battle of Britain. Ever sinec I first flew a Spitfire I had a great desire to fly the '109. I soon had the opportunity to fly a Hispano HA-1112M1L Buchon and this made me even more curious about what a real Bf109 was like to fly.
John Allison did not have to ask me twice if I would like to be the other pilot to fly the Bf109G-2 that had been rebuilt by Russ Snadden and his team at RAF Benson. I still feel very privileged to be able to fly this aircraft so when I was asked to write an article for Warbirds Worldwide on flying it, how could I refuse!
The Bf109G has conventional elevators, ailerons, and rudder. Pitch trim is achieved by a variable incidence tail plane, and there is a ground adjustable fixed tab on the rudder and on the aileron for yaw and roll trim. The wing trailing edge incorporates manually operated simple flaps and radiator cooling is controlled by split flaps on the trailing edge which droop with the main flaps to increase flapped area. The outboard half of each wing leading edge incorporates an independent automatic slat, which extends at low speed or in hard manoeuvres. The main undercarriage legs retract outwards and when fully lowered the mainwheels feature a marked toe-in, i.e. the wheels are closer together at the front than at the rear. I believe that this unusual characteristic is caused by the problems of fitting the wheel well and undercarriage leg pintle into the wing due to the position of the main spar. The tailwheel is lockable from the cockpit. The engine is a Daimler-Benz DB605, driving a VDM variable pitch propeller which rotates clockwise when viewed from behind.
On approaching the aircraft it looks sleek, compact, and quite small compared to other World War II fighters. These characteristics are emphasised by the cockpit, which is small, cramped, and neither the seat nor rudder pedals are adjustable. Once the canopy is closed, there is very little headroom either. I am 6feet 3 inches tall, and to the question "How do I fit in it?" all I will say is that 'where there is a will there is a way!' However, the cockpit of this particular airframe is almost totally original, the only significant difference being that the gunsight has been removed and a Becker VHF radio and standby magnetic compass fitted in its place. This degree of originality adds much to the feel and character of this airframe and sets it apart from many rebuilt warbirds that have modernised cockpits, a practice that I dislike greatly. It must be added that this original cockpit has all of the labelling in German, airspeed in kilometres per hour (kph) and altitude in Kilometres. Manifold air pressure is in atmospheres (ata), 1 atmosphere being 30 inches of mercury.
Starting the engine requires one or two willing helpers standing on the starboard wing root to wind up the inertia starter with a crank-handle. The engine is then primed with about 10 strokes of a Ki-gas type pump, the fuel pump switched on and the starter handle pulled which engages a clutch connecting the inertia starter to the engine; hopefully the engine starts! There are two points about this starting procedure. Firstly, you cannot overprime the engine. Secondly it is not feasible to take the aircraft away from Duxford without the groundcrew!
Taxying is achieved using differential braking via rudder pedal mounted toe brakes. The aircraft is reluctant to turn sharply and my technique is to apply full rudder in the required direction of turn to give me better leverage and to then stamp on the toe brake. This is aided by pushing the stick fully forward to unload the tailwheel, an action which is totally unnatural to someone used to the Spitfire! However, the '109 is tail heavy and the tail never lifts. It is during taxying that the very poor forward field of view is first realised. You can see virtually nothing within 30 or 40 degrees either side of the nose, definitely worse than anything that I have ever flown.
Take off is made with 1 degree nose up tailplane trim, 20 degrees of flap lowered and always with the tailwheel locked. After lining up the throttle is smoothly opened to 1.1 ata, controlling the moderate left swing with rudder. Once the take-off power is set and the aircraft is directionally under control, the tail is gently raised just clear of the ground. The aircraft lifts off at around 150 kph with slight back pressure on the stick. This may sound simple, but is one of the most difficult tasks in flying the '109. If any swing is allowed to develop the toe-in on the outside wheel turns the aircraft even more i.e. it is directionally unstable. It will then roll about the outside wheel, leading to the classic ground loop. This problem is accentuated because the forward field of view is so poor that it is difficult to detect any swing starting. The only saving grace is that the lockable tailwheel gives some directional stability, and so it is kept on the ground for as long as possible. The gyroscopic effect of the propeller and loss of directional stability from the tailwheel once the tail is raised is marked, hence the tail is raised very gently and only slightly.
Once airborne, engine handling is markedly different from similar British and American engines, due to the lack of a constant speed unit on the propeller. The operating philosophy is that the engine has a running line of optimum rpm for a given manifold pressure; 2000 rpm at 1.0 ata, 2300 rpm at 1.15 ata (max. continuous) and 2600 rpm at 1.3 ata (30 minute limit). These rpm are also the minimum for the manifold pressure without overboosting the engine. The pilot sets the manifold pressure with the throttle, and engine rpm is controlled either automatically (when it is governed to the running line) or manually. Manual control is by a rocker switch on the throttle and this varies the propeller blade pitch. Once set, the propeller runs with fixed pitch, RPM increasing with increasing airspeed and vice versa. Cockpit of blade pitch is on a clock. For example, 12:00 is set for take-off and 11:45 for landing. Initially, we always flew the aircraft with manual RPM control, until we were happy with the automatic control functioning. In a display, 1.15 ata is set and RPM controlled manually to 2400-2500 to prevent overboosting. This requires a setting of around 11:05 at high speeds such as for loop entries, and an increase to around 11:20 over the top of a loop. This results in a lot of head-in-cockpit time and propeller adjustment during a display, greatly increasing the workload.
The Bf109G is heavy to manoeuvre in pitch, being similar to a Mustang. At 520kph it is possible to pull 4g with one hand, but I find it more comfortable to use both hands on the stick for looping manoeuvres, normally entered at 420kph and 3g. Pitch trim changes with speed are moderate, and the tail plane trim wheel mounted abeam the pilots' left hip is easy to use. For a display, I run it at 420-450kph in trim, and then do not retrim. This causes no excessive stick forces during the display. Overall the aircraft is straightforward to handle in pitch.
Roll performance is similar to a Hurricane or elliptical wing tipped Spitfire. A full stick roll through 360 degrees at 460kph takes 4 to 4.5 seconds without using rudder, and needs a force of around 20 lbf. One interesting characteristic is that rolls at lower speeds entered at less than 1g, such as a roll-off-the-top or half Cuban, have a markedly lower roll rate to the right than to the left. Therefore, I always roll left in such manoeuvres.
There are two problem areas in yaw control with the '109. Firstly, directional stability is low and marked slip ball excursions occur with any changes of speed or power. Also, there is moderate adverse aileron yaw (right yaw when left aileron is applied, and vice versa). The rudder force to centralise the slip ball is low, but constant rudder inputs are required during manoeuvres to minimise sideslip. If the slip ball is not kept central, the lateral force on the pilot is not uncomfortable and no handling problems occur, but it looks very untidy in a display. At the top of a left wing-over, you are very cross-controlled, with left aileron and lots of right rudder applied. This lack of directional stability makes it hard work to fly the aircraft accurately and neatly, although there are no safety problems. However, it must have made accurate tracking for a guns 'kill' very difficult. I suspect that many '109 kills were made at very close range! It also says a great deal about the shooting skills of the Luftwaffe Aces. The second problem is the lack of a cockpit adjustable rudder trimmer. The fixed tab is set so that the rudder is in trim during the cruise, reducing footloads during long transits. However, for all other airspeed and power combinations, a rudder force must be applied. This is an annoying feature, and I am surprised that a rudder trim tab was never fitted to later models such as the Gustav.
The idle power stall characteristics of the aircraft are very benign and affected little by undercarriage and flap position. Stalling warning is a slight wing rock with the stick floating right by about 2 inches. This occurs 10klph before the stall. The stall itself is a left wing drop through about 15 degrees with a slight nose drop, accompanied by a light buffet. All controls are effective up to the stall, and recovery is instant on moving the stick forward. Stall speeds are 155kph clean and 140kph with gear and flap down. In a turn at 280kphwith display power set, stall warning is given by light buffet at 3g, and the stall occurs at 3.5g with the inside wing dropping. Again, recovery is instant on easing the stick forward. One interesting feature is the leading edge slats. When these deploy at low speeds or in a turn, a 'clunk' can be heard and felt, but there is no disturbance to the aircraft about any axis. I understand that the Bf109E rolled violently as the slats deployed, and I am curious to know the difference to the Gustav that caused this.
Back in the circuit, the '109 is straightforward to fly, except that it takes around 25 secs to lower the flaps, using a large wheel mounted next to the tail plane trim wheel and on the same shaft. A curving final approach is flown at 200kph, and once aligned with the runway the forward field of view is poor. The threshold is crossed at 175kph, the throttle closed, and the aircraft flared to the 3 point attitude. The '109 floats like a Spitfire and controls are effective up to touchdown. After touchdown, directional control is by using differential braking. The three point attitude is easy to judge, and although it bucks around on rough grass it does not bounce significantly on touchdown. however, the landing is not easy. From approaching the threshold up to touchdown the forward view is very poor, and it is difficult to assess drift. if the aircraft is drifting at touchdown, the toe-in on the wheel towards which it is drifting causes a marked swing, and you are working very hard to keep straight and avoid a ground loop. Each landing is a challenge, and just a bit unpredictable. Hard runways have higher friction than grass surfaces, and so the wheels dig in even more if drifting on touchdown, making ground-loops more likely on runways than on grass. The possibility of drifting on touchdown increases with a crosswind, and so for these two reasons, we are only flying the Gustav off grass and with a 10kt crosswind limit. I have flown the Buchon off the runway, and landed with a 10kt crosswind on concrete, but it is something that I would never do out of choice!
The Buchon flies very much the same as the Gustav, although directional stability is even worse. The biggest differences are engine handling and cockpit noise levels. The Buchon is very noisy due to the high exhaust stacks of the Merlin, the low exhausts of the DB605 giving a considerably quieter cockpit.
In summary, the Bf109G is a demanding aircraft to fly. The workload is high maintaining directional control on take-off and landing, although in flight the stalling and pitch characteristics are god. I would advise anyone planning to fly a '109 to get lots of experience and confidence in other large piston-engined taildraggers first. However, if its peculiarities are understood and the take-off and landing limits are strictly adhered to the '109 can be operated perfectly safely. I treat the '109 with greater respect than anything else that I fly, but the challenge of trying to fly it well gives me greater satisfaction and enjoyment than probably any other aircraft. But I am never satisfied- I now have an ambition to fly an Emil; the Bf109E."
John Allison did not have to ask me twice if I would like to be the other pilot to fly the Bf109G-2 that had been rebuilt by Russ Snadden and his team at RAF Benson. I still feel very privileged to be able to fly this aircraft so when I was asked to write an article for Warbirds Worldwide on flying it, how could I refuse!
The Bf109G has conventional elevators, ailerons, and rudder. Pitch trim is achieved by a variable incidence tail plane, and there is a ground adjustable fixed tab on the rudder and on the aileron for yaw and roll trim. The wing trailing edge incorporates manually operated simple flaps and radiator cooling is controlled by split flaps on the trailing edge which droop with the main flaps to increase flapped area. The outboard half of each wing leading edge incorporates an independent automatic slat, which extends at low speed or in hard manoeuvres. The main undercarriage legs retract outwards and when fully lowered the mainwheels feature a marked toe-in, i.e. the wheels are closer together at the front than at the rear. I believe that this unusual characteristic is caused by the problems of fitting the wheel well and undercarriage leg pintle into the wing due to the position of the main spar. The tailwheel is lockable from the cockpit. The engine is a Daimler-Benz DB605, driving a VDM variable pitch propeller which rotates clockwise when viewed from behind.
On approaching the aircraft it looks sleek, compact, and quite small compared to other World War II fighters. These characteristics are emphasised by the cockpit, which is small, cramped, and neither the seat nor rudder pedals are adjustable. Once the canopy is closed, there is very little headroom either. I am 6feet 3 inches tall, and to the question "How do I fit in it?" all I will say is that 'where there is a will there is a way!' However, the cockpit of this particular airframe is almost totally original, the only significant difference being that the gunsight has been removed and a Becker VHF radio and standby magnetic compass fitted in its place. This degree of originality adds much to the feel and character of this airframe and sets it apart from many rebuilt warbirds that have modernised cockpits, a practice that I dislike greatly. It must be added that this original cockpit has all of the labelling in German, airspeed in kilometres per hour (kph) and altitude in Kilometres. Manifold air pressure is in atmospheres (ata), 1 atmosphere being 30 inches of mercury.
Starting the engine requires one or two willing helpers standing on the starboard wing root to wind up the inertia starter with a crank-handle. The engine is then primed with about 10 strokes of a Ki-gas type pump, the fuel pump switched on and the starter handle pulled which engages a clutch connecting the inertia starter to the engine; hopefully the engine starts! There are two points about this starting procedure. Firstly, you cannot overprime the engine. Secondly it is not feasible to take the aircraft away from Duxford without the groundcrew!
Taxying is achieved using differential braking via rudder pedal mounted toe brakes. The aircraft is reluctant to turn sharply and my technique is to apply full rudder in the required direction of turn to give me better leverage and to then stamp on the toe brake. This is aided by pushing the stick fully forward to unload the tailwheel, an action which is totally unnatural to someone used to the Spitfire! However, the '109 is tail heavy and the tail never lifts. It is during taxying that the very poor forward field of view is first realised. You can see virtually nothing within 30 or 40 degrees either side of the nose, definitely worse than anything that I have ever flown.
Take off is made with 1 degree nose up tailplane trim, 20 degrees of flap lowered and always with the tailwheel locked. After lining up the throttle is smoothly opened to 1.1 ata, controlling the moderate left swing with rudder. Once the take-off power is set and the aircraft is directionally under control, the tail is gently raised just clear of the ground. The aircraft lifts off at around 150 kph with slight back pressure on the stick. This may sound simple, but is one of the most difficult tasks in flying the '109. If any swing is allowed to develop the toe-in on the outside wheel turns the aircraft even more i.e. it is directionally unstable. It will then roll about the outside wheel, leading to the classic ground loop. This problem is accentuated because the forward field of view is so poor that it is difficult to detect any swing starting. The only saving grace is that the lockable tailwheel gives some directional stability, and so it is kept on the ground for as long as possible. The gyroscopic effect of the propeller and loss of directional stability from the tailwheel once the tail is raised is marked, hence the tail is raised very gently and only slightly.
Once airborne, engine handling is markedly different from similar British and American engines, due to the lack of a constant speed unit on the propeller. The operating philosophy is that the engine has a running line of optimum rpm for a given manifold pressure; 2000 rpm at 1.0 ata, 2300 rpm at 1.15 ata (max. continuous) and 2600 rpm at 1.3 ata (30 minute limit). These rpm are also the minimum for the manifold pressure without overboosting the engine. The pilot sets the manifold pressure with the throttle, and engine rpm is controlled either automatically (when it is governed to the running line) or manually. Manual control is by a rocker switch on the throttle and this varies the propeller blade pitch. Once set, the propeller runs with fixed pitch, RPM increasing with increasing airspeed and vice versa. Cockpit of blade pitch is on a clock. For example, 12:00 is set for take-off and 11:45 for landing. Initially, we always flew the aircraft with manual RPM control, until we were happy with the automatic control functioning. In a display, 1.15 ata is set and RPM controlled manually to 2400-2500 to prevent overboosting. This requires a setting of around 11:05 at high speeds such as for loop entries, and an increase to around 11:20 over the top of a loop. This results in a lot of head-in-cockpit time and propeller adjustment during a display, greatly increasing the workload.
The Bf109G is heavy to manoeuvre in pitch, being similar to a Mustang. At 520kph it is possible to pull 4g with one hand, but I find it more comfortable to use both hands on the stick for looping manoeuvres, normally entered at 420kph and 3g. Pitch trim changes with speed are moderate, and the tail plane trim wheel mounted abeam the pilots' left hip is easy to use. For a display, I run it at 420-450kph in trim, and then do not retrim. This causes no excessive stick forces during the display. Overall the aircraft is straightforward to handle in pitch.
Roll performance is similar to a Hurricane or elliptical wing tipped Spitfire. A full stick roll through 360 degrees at 460kph takes 4 to 4.5 seconds without using rudder, and needs a force of around 20 lbf. One interesting characteristic is that rolls at lower speeds entered at less than 1g, such as a roll-off-the-top or half Cuban, have a markedly lower roll rate to the right than to the left. Therefore, I always roll left in such manoeuvres.
There are two problem areas in yaw control with the '109. Firstly, directional stability is low and marked slip ball excursions occur with any changes of speed or power. Also, there is moderate adverse aileron yaw (right yaw when left aileron is applied, and vice versa). The rudder force to centralise the slip ball is low, but constant rudder inputs are required during manoeuvres to minimise sideslip. If the slip ball is not kept central, the lateral force on the pilot is not uncomfortable and no handling problems occur, but it looks very untidy in a display. At the top of a left wing-over, you are very cross-controlled, with left aileron and lots of right rudder applied. This lack of directional stability makes it hard work to fly the aircraft accurately and neatly, although there are no safety problems. However, it must have made accurate tracking for a guns 'kill' very difficult. I suspect that many '109 kills were made at very close range! It also says a great deal about the shooting skills of the Luftwaffe Aces. The second problem is the lack of a cockpit adjustable rudder trimmer. The fixed tab is set so that the rudder is in trim during the cruise, reducing footloads during long transits. However, for all other airspeed and power combinations, a rudder force must be applied. This is an annoying feature, and I am surprised that a rudder trim tab was never fitted to later models such as the Gustav.
The idle power stall characteristics of the aircraft are very benign and affected little by undercarriage and flap position. Stalling warning is a slight wing rock with the stick floating right by about 2 inches. This occurs 10klph before the stall. The stall itself is a left wing drop through about 15 degrees with a slight nose drop, accompanied by a light buffet. All controls are effective up to the stall, and recovery is instant on moving the stick forward. Stall speeds are 155kph clean and 140kph with gear and flap down. In a turn at 280kphwith display power set, stall warning is given by light buffet at 3g, and the stall occurs at 3.5g with the inside wing dropping. Again, recovery is instant on easing the stick forward. One interesting feature is the leading edge slats. When these deploy at low speeds or in a turn, a 'clunk' can be heard and felt, but there is no disturbance to the aircraft about any axis. I understand that the Bf109E rolled violently as the slats deployed, and I am curious to know the difference to the Gustav that caused this.
Back in the circuit, the '109 is straightforward to fly, except that it takes around 25 secs to lower the flaps, using a large wheel mounted next to the tail plane trim wheel and on the same shaft. A curving final approach is flown at 200kph, and once aligned with the runway the forward field of view is poor. The threshold is crossed at 175kph, the throttle closed, and the aircraft flared to the 3 point attitude. The '109 floats like a Spitfire and controls are effective up to touchdown. After touchdown, directional control is by using differential braking. The three point attitude is easy to judge, and although it bucks around on rough grass it does not bounce significantly on touchdown. however, the landing is not easy. From approaching the threshold up to touchdown the forward view is very poor, and it is difficult to assess drift. if the aircraft is drifting at touchdown, the toe-in on the wheel towards which it is drifting causes a marked swing, and you are working very hard to keep straight and avoid a ground loop. Each landing is a challenge, and just a bit unpredictable. Hard runways have higher friction than grass surfaces, and so the wheels dig in even more if drifting on touchdown, making ground-loops more likely on runways than on grass. The possibility of drifting on touchdown increases with a crosswind, and so for these two reasons, we are only flying the Gustav off grass and with a 10kt crosswind limit. I have flown the Buchon off the runway, and landed with a 10kt crosswind on concrete, but it is something that I would never do out of choice!
The Buchon flies very much the same as the Gustav, although directional stability is even worse. The biggest differences are engine handling and cockpit noise levels. The Buchon is very noisy due to the high exhaust stacks of the Merlin, the low exhausts of the DB605 giving a considerably quieter cockpit.
In summary, the Bf109G is a demanding aircraft to fly. The workload is high maintaining directional control on take-off and landing, although in flight the stalling and pitch characteristics are god. I would advise anyone planning to fly a '109 to get lots of experience and confidence in other large piston-engined taildraggers first. However, if its peculiarities are understood and the take-off and landing limits are strictly adhered to the '109 can be operated perfectly safely. I treat the '109 with greater respect than anything else that I fly, but the challenge of trying to fly it well gives me greater satisfaction and enjoyment than probably any other aircraft. But I am never satisfied- I now have an ambition to fly an Emil; the Bf109E."