"The wildest 'stick and rudder' experience"
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Mastering the ‘Dreidecker’: Mikael Carlson on the Fokker Dr.1

Mastering the ‘Dreidecker’: Mikael Carlson on the Fokker Dr.1

“After landing the Dreidecker you should be exhausted and dirty; it’s when you’ve cleaned it and put it to bed that you can have your Cognac and enjoy the moment. With enough time you can do anything in it, which makes it the wildest ‘stick and rudder’ experience.” So says Swedish aviator and engineer Mikael Carlson of his Fokker Dr.1 ‘Dreidecker’, an authentic reproduction manufactured to original specifications using predominantly the same materials and processes utilised more than a century ago.

“You have to learn what is and isn’t achievable in the Dreidecker. It isn’t difficult or dangerous to fly, it’s just unlike any other aeroplane. If you don’t understand how to handle the aeroplane and the engine through every second of a flight, you will get it wrong and it will bite you without warning at any point, and bite hard.”

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The Dreidecker first flew on 5 July 1917, the prototype F.1s reaching Manfred von Richthofen and Werner Voss at Jagdgeschwader 1 for combat testing later that summer. “People who know nothing about aviation have heard of the Red Baron”, says Mikael. “By association, the Dreidecker is a true aviation legend.” Von Richthofen scored his sixtieth victory, and his first in F.1 102/17, on 1 September 1917. With four of his Jasta he attacked and downed an R.E.8 artillery observation aeroplane near Zonnebeke in Belgium. “Most probably the English pilot had taken me for an English dreidecker,” he wrote, “as the observer stood upright in the plane without thinking of making use of his gun”.

Two days later he achieved his sixty-first, a Sopwith Pup fought down to an altitude of just 50 metres, noting, “The Fokker Dreidecker F.1 102/17 was undoubtedly better and more reliable than the English machine”. In the Fokker Dr.1 he claimed a further 17 kills (one of them ‘probable’), amongst them Sopwith Camels, SE5as and a Bristol F2b. Von Richthofen’s final victories – his seventy-ninth and eightieth, both Sopwith Camels – were flown in his red Dreidecker on 20 April 1918. He was killed in action near Amiens the following day.

48-victory ace Werner Voss officially downed 11 aeroplanes in F.1 103/17 and, in his final sortie on 23 September 1917, damaged several SE5as in a remarkable seven-on-one dogfight before he was shot down and killed. Ace James McCudden was amongst the British pilots: “The German triplane was in the middle of our formation, and its handling was wonderful to behold. The pilot seemed to be firing at us all simultaneously… His movements were so quick and uncertain… He was very low… still being engaged by an SE. As long as I live I shall never forget my admiration for that German pilot, who single-handed fought seven of us for ten minutes and also put some bullets through all our machines. His flying was wonderful, his courage magnificent, and in my opinion he was the bravest German airman whom it has been my privilege to see fight”.

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Production Dr.1s had been active on the front from October 1917 and achieved great success with comparatively few operational units. In the right hands the Dreidecker had the capacity to outmanoeuvre its contemporaries in a turning fight, but its climb performance degraded at higher altitude and it was quickly superseded by faster fighters. “The Dreidecker was my favourite fighting machine because it had such wonderful flying qualities,” appraised Jasta 6’s Franz Hemer, “and could avoid an enemy by diving with perfect safety. The Dreidecker had to be given up because although it was very manoeuvrable, it was no longer fast enough”.

The disparity in performance is further touched on in the diary penned by Jasta 7’s Josef Jacobs. His third flight in the Dr.1 came on 24 March 1918. “It is slower than the Albatros D.V,” he wrote, “hence not very useful.” Within days, his opinion of the Dreidecker had warmed somewhat, and in early April he wrote that, “At 2,000m it is better than Pfalz and Albatros, much more manoeuvrable, but it requires more flight training as it is very unstable, especially when firing”. By the war’s end, Jacobs had become the Dreidecker’s highest scoring ‘ace’, having downed more than 30 aeroplanes.

Manoeuvrability was paramount at the time of the Dreidecker’s design; by late 1917, however, an aeroplane’s ability to climb quickly, surprise the enemy with a diving attack from the rear and climb away from a confrontation to strike again was deemed superior to its ability to dogfight at close range. The rapid advancement of technology and the evolution of air combat rendered the Dreidecker largely obsolete, and the limited production run of a little over 300 aeroplanes ended in May 1918. By the Armistice in November 1918, hundreds of them had been shot down or written off.

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Mikael’s Fokker Dr.1 was built at his workshop in Sweden over three and a half years, making its maiden flight on 2 November 2008. It is part of his fleet of Piper L-4 Cub, Tummelisa, Fokker D.VII and two Blériot XIs (Thulin As) and flies out of his private grass strip in the Swedish countryside. It wears the Jasta 6 markings of an aeroplane flown by Johann Janzen in March 1918. Mikael’s extensive experience building and flying First World War fighters afford him authoritative insight, allowing him to cut through the conjecture that has mired the Dreidecker’s reputation to offer a definitive account of its operation and handling.

The original restored 1917 110hp nine cylinder Le Rhône 9Jb rotary engine is largely responsible for the challenges inherent in flying the Dreidecker; it requires constant engine management to fine tune the fuel/air mixture throughout each stage of a flight, whilst the gyroscopic effects of the rotating engine combine with the aeroplane’s design features to produce the lively and occasionally volatile handling characteristics that made the Fokker Dr.1 such a notorious fighter. The Le Rhône’s cylinder block is arranged in radial fashion around a stationary crankshaft that is bolted to the airframe and rotates with the crankcase and wooden propeller. The crankcase and cylinder block act as a flywheel, with the airflow created by the rotating engine offering satisfactory cooling even on the ground.

The Dreidecker’s fuel system is fairly primitive but requires explanation to contextualise the pilot’s role in fine tuning the mixture. A single 75 litre fuel tank sits between the engine and the cockpit. The fuel is fed through a fine mixture needle valve into the bloctube “carburettor” mounted to the rear of the crankshaft, mixing with air drawn from the bloctube air intake. The air/fuel mixture then passes through the hollow crankshaft and into the crankcase, which is utilised as a distributor chamber from which the mixture is drawn into inlet manifolds by the vacuum in the cylinder heads and the rotating force of the engine. Each cylinder has two valves opened by a centrally-pivoting rocker arm: the mixture enters the cylinders via an inlet valve, whilst the other vents the exhaust after the mixture ignites. A basic total loss oil system sees lubricant fed from a 13 litre tank into the crankshaft via an engine driven pump and then directly into the cylinders at a rate of six to eight litres per hour.

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Before each flight, up to four shots of fuel are sprayed directly into the cylinders through the exhaust valve with an oil can and the propeller is turned through two revolutions after each spray to vapourise the fuel. “It’s better to have too much primer than too little,” Mikael says, “as some fuel is needed to keep the engine running on start-up before fuel is introduced from the fuel tank. If you under-prime, the engine will catch but it will die before it can receive fuel from the tank”.

The Dreidecker’s compact cockpit features minimal engine instrumentation and no flying instruments, save for a compass. “I wouldn’t even want to have them”, Mikael says. “I would never look at them – you have to fly these aeroplanes by feeling, and you’d make a critical mistake if you tried to fly by the numbers. In the Dreidecker, you’re truly flying by the seat of your pants – flying with your ass!” The only instruments are limited to a single magneto switch on the port cockpit wall, a tachometer tucked down by the pilot’s left foot, and the fuel gauge, which sits between the two reproduction Spandau machine guns directly in the pilot’s line of sight. “They’re the only instruments I need,” says Mikael, “and I only look at the tachometer once, when tuning up the engine before take-off to achieve the maximum static rpm I want for the flight.”

As is customary in rotary aeroplanes, traditional throttle and mixture controls are absent and the pilot uses ‘bloctube’ and ‘fine adjustment’ levers to regulate the air/fuel mixture and obtain the desired engine performance. The left hand grip on the control column is a hinged Bowden lever that operates, via Bowden cables, the bloctube and moves its air slide to govern the air/fuel mixture delivered to the cylinders; as more air enters the bloctube, the volume of air/fuel mixture ignited within the cylinder and the piston’s power stroke increase exponentially. An auxiliary T-handle bloctube lever sits low on the starboard side of the cockpit for use if the cables connecting the Bowden bloctube lever on the control column are compromised. A ‘blip switch’ at the top of the right hand grip cuts the ignition to all cylinders when actuated by thumb, allowing a degree of power control on the ground and at lower airspeeds.

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The fine adjustment lever is positioned on a small toothed quadrant mounted on the port side of the cockpit, with which the pilot controls the fine mixture needle valve upstream of the bloctube. Optimisation of the air/fuel mixture at each bloctube setting is required; where the mixture contains too much or too little fuel, the engine will cut out. This arrangement allowed the pilot to fly the aeroplane, use the blip switch and fire the machine guns with his right hand, whilst controlling the bloctube and fine adjustment levers with his left hand.

A small rod on the lower left of the cockpit is twisted to open the fuel tank tap before the start-up sequence, and the bloctube is opened to the midway point of the lever’s travel. The propeller swinger leads the start-up, giving the command of ‘Mags on’ for Mikael to switch on the single Bosch magneto, waiting for the return call of ‘Contact’ before swinging the prop. If sufficiently primed, the engine should fire immediately and run initially on the primer charge whilst the bloctube is brought back to idle power and the fine adjustment lever is moved forward to increase the amount of fuel in the mixture and keep the engine running as the primer diminishes. “After start-up the way to check that the engine is receiving oil flow is to blip the engine on the ground at idle power of 500 to 600 rpm and look for white smoke puffs”, Mikael adds. “You can also look at the lower wing root, and should see oil streaking along it. As long as the engine runs, the pump will deliver oil to the engine.”

Pre-flight power checks see the manipulation of the bloctube and fine adjustment levers to attain the maximum rpm and smoothest running at full power with the aeroplane chocked. “You lean the mixture for best performance in a rotary engine, whereas radials and inline engines perform best with a rich mixture at low altitude”, Mikael explains. “These bigger rotaries are not made for idling and perform best at high power. They run roughly at mid-range power settings due to the imbalance in air/fuel mixture. I set the bloctube to full power, which will be in the upper end of the lever’s travel, and lean the mixture as the engine starts to cut out to achieve peak static rpm at that bloctube setting, which is in the region of 1,200 to 1,300 rpm – the tachometer needle wobbles and if it settles around that range, I’m happy. I won’t check the tachometer again after that static rpm check; I’ll feel even a small decrease in rpm, and there’s no risk of over-speeding the propeller for more than a few seconds, so I don’t need it in-flight.”

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These power checks should take no more than one minute, after which Mikael will position the aeroplane for take-off and get airborne immediately. Taxying is kept to a minimum, in part owing to the total lack of visibility present in the three-point attitude. “There is virtually no forward view as that middle wing sits right in your eye line”, Mikael says. “Keep taxying to a minimum, use wingtip walkers and ensure that the path ahead is clear before you point yourself in that direction. You cannot weave and must taxi straight unless it’s a very wide field with no obstructions. The key in tighter spaces is to sit stationary, blip the engine, push the stick fully forward, feed in full left or right rudder and then apply power to unload the tail skid. That method gives you reasonably good directional control, but if you really opened the power you could turn 360° in a stationary position!”

He continues: “I’ll have the high power bloctube and fine adjustment lever positions in mind when I bring the engine back to idle power immediately before take-off, and know that returning to those positions will give me the rpm I want once I’m airborne. I also know that the engine runs smoothly without risk of a rich cut or lean cut at those power settings. If the mixture is on the rich side and you start pulling g, the gravity feed from the fuel tank will increase the flow and the engine could receive too much fuel. That can flood the engine and give you a rich cut, and you’d notice a sudden deceleration. It could take 10 to 15 seconds to get the engine back, which can put you in a critical situation.”

As the bloctube and fine adjustment levers are adjusted to full power settings at the start of the take-off run the tail comes up immediately and forward visibility drastically improves. The nose is immediately hunting and anticipatory full right rudder is required to counteract any divergence, the aeroplane getting airborne in around 40 metres. “The aerodynamic noise is so bad, it’s like being in an inferno”, says Mikael. “You have to get to a point where you are comfortable enough in the aeroplane to feel any changes in rpm and be reactive with the fine adjustment lever to seek better performance, as you’ll never hear the engine. Even with triple ear plugs I could be nearly deaf for an hour after a flight.

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“The Dreidecker is completely unstable and needs to be flown all the time”, Mikael continues. “It must be flown preemptively, not reactively.” With no fin and a large horizontal stabiliser, the aeroplane is highly sensitive in pitch and all yaw stability comes from an all-flying rudder that offers no feedback through the rudder pedals. Pronounced characteristics in all three flight axes mean elevator, rudder and aileron inputs can induce massive directional changes that need to be anticipated. This made the Dreidecker a skittish, incredibly versatile fighter for its time, with exceptional handling in the mid and high-speed range. It can turn on a sixpence and can be demonstrated to its fullest capabilities within a display box of only a few hundred metres. Benign low-speed handling characteristics and the thick airfoil mean there’s no chance of flicking in a stall and the Dreidecker begins to mush as it approaches the stall, giving the pilot plenty of feedback.

“You should be concentrating on managing the engine and moving the fine adjustment lever if you feel a drop in rpm, so the flying needs to come instinctively”, Mikael says. “My feet do not stop moving on the rudder pedals from the moment I’m airborne. I couldn’t even tell you what I’m doing with the rudder with each manoeuvre and each turn, as it’s always different and it’s just so instinctive. Generally it pitches quickly with a little back stick, then you need to be heavier on the ailerons and dancing on the rudder pedals to turn as it’ll be pulling one way then the other as you change your elevator and aileron inputs, but the turns aren’t really coordinated, they’re usually flown out of balance.

“If you need to think about the physical flying of it, it’s going to bite you. You don’t have a turn and slip indicator so it’s all done by feel and is a constant feeling out process. When I first flew the Dreidecker I felt like I had been flying sideways the whole time, and it took a good ten hours for me to have a more complete impression of the aeroplane and feel comfortable flying aerobatics. You’ll feel the buffet if the aeroplane isn’t tracking straight. If you let go of the control stick, it will yaw immediately to the left into in an ‘X’ position, flying sideways out of balance with the airflow hitting you hard on the side of your face. You could use that to your advantage in a dogfight. It feels unnatural to do it now but flying out of balance in combat meant you could outperform other fighters and get yourself into a shooting position from all kinds of crazy angles, sitting the Dreidecker on its nose, flying flat turns, turning with the nose down and tail high, or horizontally shooting almost sideways at a target.”

“...you’ll be almost stationary at the top of the loop with full power on and high rpm. The torque will twist the aeroplane at the apex and you’ll fall out to the left or right in a yawing side slip...”
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This inherent instability makes aerobatics in the air display arena particularly challenging. Mikael flies a dynamic routine comprising loops, rolls and split-S figures, as well as rapid turn reversals and tight turns. “It’s crazy!”, Mikael enthuses. “If you enter a loop with the wings level and manage to keep it in balance with constantly alternating left and right rudder in the climb, you’ll be almost stationary at the top of the loop with full power on and high rpm. The torque will twist the aeroplane at the apex and you’ll fall out to the left or right in a yawing side slip, regardless of what you do with the rudder. It just spits you out in either direction and you could exit at 90° to how you entered.

“To reduce that problem,” he says, “I lean the loop a little to the side. That allows me to spiral out of the manoeuvre in the direction I have chosen if I lose rudder authority. There’s more control that way and it isn’t so wild. In diving figures I also pull back the power and allow the propeller to windmill the engine at the same rpm, but with no thrust in the cylinders.”. Aileron rolls require an equal level of fine-tuned control coordination. The Dr.1 features large horn-balanced ailerons on its upper wing, with the wider part of the aileron extending outboard of the wingtip and forward of the aileron hinges. The effect of this is that the stick forces required to roll the aeroplane are lighter. “You can fly a nice roll with full aileron and a small amount of corresponding rudder. Too little or too much rudder and the aeroplane will stop on its side, yaw heavily upwards and depart in an inverted flick. That happened to me at an event in Sweden when I tried to use more rudder to increase the roll rate, but it kicked me right out of the manoeuvre. It took five to ten metres to regain control.”

In the circuit the bloctube is brought back to high idle power, around one third of the available power, and the fine adjustment lever is pulled back in tandem to lean the fuel and prevent a rich cut in the event of a go around. The Dreidecker’s wings lack rigging wires and the clean profile makes it slippery in straight and level flight – unlike biplanes with draggy rigging, power reductions do not bring an immediate drop in airspeed. The deceleration and descent are accordingly controlled by judicious use of the blip switch, which Mikael says is an art in itself as even when the ignition is cut, the fuel feed to the engine continues and overuse can risk oiling the spark plugs (which could prejudice reignition) or even a fire on reignition. Blipping at high power is also to be avoided, such is the risk of shock loading and damaging the engine. As the aeroplane is flared in a three-point attitude for landing, the engine is momentarily cut with the blip switch, which is then disengaged to bring the engine back to life once the aeroplane has touched down.

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“That pulls the aeroplane straight and creates some airflow to allow responsiveness from the rudder,” Mikael adds, “and you need to do that to avoid a ground loop or diversion. I’ve landed the Dreidecker with a dead engine during testing and almost every time it ended up in a small ground loop. The mass of the aeroplane is behind the undercarriage and there’s no control of the rudder if the engine has stopped, so nothing is pulling you straight and the aeroplane will turn in one direction with no rudder control to stop it.

“I would also never dream of flying a wheeler landing – it’s a three-point aeroplane, and if you wheel land it the airspeed could be too high as the tail comes down. The energy in the aeroplane will cause a swing or a group loop, which can be quite violent. If you three-point it the proper way, it should stop safely in 70 metres”. Engine shut down is a simple affair, with the bloctube and fine adjustment levers brought to idle power, the magneto switched off and the fuel tank tap closed in turn.

Since 2008, Mikael has taken the Fokker Dr.1 all over Europe. At the time of publication, he is believed to be the only pilot flying a full aerobatic sequence in what is essentially an authentic Dr.1. “I don’t look at the Dreidecker in a scientific way and apply modern standards to it. The pleasure comes in it being a challenging aeroplane. Why would you apply modern standards to it? I don’t want it to be fully balanced and pleasant like a Cessna 150. I want a true Fokker Dr.1. To fly First World War aeroplanes isn’t a pleasure at the time, it’s hard work, but when you land you think, ‘Wow, I’ve flown something historic here’. It’s not an aeroplane to go flying in on a Sunday morning to look at the clouds and the forests. For that, you’d take a Piper Cub.

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“I have started flying the Messerschmitt Bf 109G for Hangar 10 at Usedom”, he muses. “That’s a similar aeroplane in that it has a powerful engine and a small airframe with unconventional handling characteristics and an engine you need to constantly manage. The Dreidecker and Bf 109 will both bite you if you don’t fly them as they need to be flown. It takes a few hours to get used to that – I have that luxury, but the guys in the First World War didn’t and they suffered for it. The Fokker D.VII was a stable aeroplane that could take a poor pilot and make them a mediocre pilot. By contrast, the Dreidecker could take a mediocre pilot and make them an excellent pilot in time.

“With experience, you can do anything in the Dr.1”, repeats Carlson. “Nothing gives you such a wild ‘stick and rudder’ experience as the Fokker Dreidecker.”

“After landing the Dreidecker you should be exhausted and dirty; it’s when you’ve cleaned it and put it to bed that you can have your Cognac and enjoy the moment.”
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