Mikael Carlson has been flying the Thulin A for almost 30 years. The first, registered SE-XMC, took to the air in 1991. The second, SE-AMZ, flew 13 years later. Alongside his collection of First World War types, comprising FVM Ö1 Tummelisa, Fokker Dr.1 and Fokker D.VII, he flies the two aeroplanes from his private grass airstrip in Sweden, and frequently transports them by road to air displays across the continent.
This is Mikael’s third interview for The Vintage Aviation Echo and, as ever, he talks authoritatively with palpable respect and enthusiasm for his aircraft. We’re speaking by telephone in the early stages of the Covid-19 pandemic, and Carlson’s native Sweden has just been placed under lock down. “I’ve been self-isolating in my shed building aeroplanes for the last 30 years,” he jokes, “so this is no different to me!”
Both Thulin As are licence-built Blériot XIs originally manufactured by AB Enoch Thulins Aeroplanfabrik in Sweden, though throughout our interview Mikael refers to them as Blériots and they are hereafter named as such for simplicity. He has restored four of the type, three of them to airworthy condition. In his two Blériots, Mikael has flown at events across Europe, and as far afield as the USA, UAE, New Zealand, Russia and Turkey. He has crossed the English Channel in both of his aeroplanes, in 1999 and 2009, to commemorate Louis Blériot’s landmark 1909 flight.
The Blériot XI is a beautifully constructed flying machine, the intricacy of its tapered fuselage, formed by wooden longerons, uprights and crossbeams held together by ‘piano wire’ trusses, belying its strength. Wooden panels cover only the forward half of the fuselage, quite fascinatingly revealing both the wire trusses and the control cables running from the frightfully exposed cockpit to tail feathers comprised of a small ‘all flying’ rudder and, attached beneath the rear fuselage, a large horizontal stabiliser. The heart of the aeroplane, the original seven cylinder 50hp Gnôme-Omega rotary engine, is mounted to the forward part of this wooden frame, to which two large castering main wheels are also attached. The design pre-dates ailerons, marginally effective lateral control achieved instead through wing-warping that changes the incidence of the entire fabric-covered wing to induce bank.
It is a supremely demanding aeroplane to master, with no margin for error; more so than any other aircraft Mikael has flown, the ambient weather conditions and aerodrome layout are critical to its safe operation. Though familiar with the nuances of the Blériot’s demanding engine management and counter-intuitive flying characteristics, Mikael approaches each flight with singular focus. “If I know I’m flying the Blériot, I think about it all day,” he says, “and will withdraw into myself an hour before the flight. I’ll be trying to visualise the flying arena and how the wind might react to its surroundings, identifying suitable ground on the aerodrome and outside the airfield boundary to put the aeroplane down if I need to”. Each sortie is preceded by a methodical pre-flight. Mikael looks over the whole aeroplane at least twice, checking that all wires and cables are rigged correctly and that the connecting turnbuckles are locked – every Blériot flight is made at low altitude, with no margin to survive loss of control from a structural fault. Attention then turns to ground management of the Gnôme-Omega.
The engine’s fuel and oil delivery system is basic, but warrants explanation to contextualise the pilot’s role in governing the fuel/air mixture. Fuel from a 30 litre fuel tank mounted forward of the cockpit is gravity fed through a fine mixture needle valve into the T-shaped bloctube ‘carburettor’ to the rear of the hollow crankshaft, mixing in the crankshaft with air from the bloctube intake. The air/fuel mixture passes into the crankcase and is delivered to the cylinder via a spring-loaded flutter valve at the top of the piston. The valve depressing rocker then opens the exhaust valve to vent the exhaust from the chamber after the mixture ignites. The total loss oil system sees lubricant fed from an eight litre tank into the crankshaft upstream of the bloctube via an engine driven pump, and then directly into the cylinders and bearings.
“The early Gnôme-Omega had one critical part,” adds Mikael, “which is the intake flutter valve spring on each piston crown. The springs balance the weight of the valves and the book says the spring should work for 12 hours. I use mine for 10 hours before replacing them with new ones I’ve manufactured. Losing a spring in-flight would lose you 50 rpm instantly, and that could be critical. You’d have enough power to stay airborne, but nothing more. You’d need to land straight ahead, and it could be a hard landing – so those springs need to be intact.”
As a precursor to each flight, the distributor plate on the crankcase is wiped down with a rag to remove the film of oil that could impair ignition from the magneto. Each cylinder then receives four shots of fuel primer, injected directly from a small can before the engine is turned over by hand. “It is better to start over-rich and lean the mixture as you turn the propeller through two slow revolutions to vapourise the fuel,” adds Mikael, “as too little primer in the cylinders means there will be a delay on start-up as the primer burns off before the fuel reaches the engine via the bloctube. That can take a few seconds and you can lose the engine charge in that time.”
The cockpit is wonderfully spartan. Engine controls consist of a single magneto mounted on the top of the control stick, which doubles as a ‘blip switch’ to allow the pilot to exercise a degree of power control on the ground and on landing. Bloctube and fine adjustment levers sit in a quadrant to the left (via which the pilot manually regulates the air and fuel mixture by adjusting the air slide in the ‘carburettor’ and the fuel mixture needle upstream of the ‘carburettor’ respectively), whilst an early oil pressure gauge indicates that oil is flowing from the tank to the engine. Flight instrumentation is limited to a tachometer. The flying controls are standard, but have their quirks – notably the circular non-turning wheel mounted on the control stick, to which the lateral and longitudinal control cables are attached.
The propeller swinger leads the start-up, their call for ‘contact’ prompting the pilot to move the bloctube to the midway point of its travel, and open the fine adjustment lever to draw fuel from the tank to the ‘carburettor’ via the mixture valve. The pilot readies himself with one finger from his right hand on the magneto switch, and his left hand on the fine adjustment lever, and replies, “Contact”. As the propeller swinger turns the engine over the magneto is switched on, and as the engine catches, the fine adjustment lever is moved fully forward to increase fuel in the mixture. A one minute warm-up at idle power increases the cylinder head temperatures before the full-power run, whereby the bloctube and fine adjustment levers are opened fully and then moved slowly back across their travel to alter the air/fuel mixture delivered to the engine. As the fuel mixture leans, the rpm should increase, eventually illustrating the bloctube and fine adjustment lever positions required to achieve full power in-flight.
With no brakes and practically no controlled ground handling capability, taxying is achieved only with the assistance of two wing walkers. Mikael describes the take-off: “Full power using the lever positions you mentally noted during the run-up, and stick fully forward to get the tail up for more efficient airflow over the rudder. The castering undercarriage means the rudder can be sloppy on the ground until the airflow stabilises. Maintain positioning with rudder input to the extent possible, but accept that you will not have full directional control at any time. It should fly off the ground within 50 metres of so, then you need to build up the airspeed and maintain acceleration before you attempt to climb. You cannot raise the nose on take-off – even a few degrees of pitch-up will induce drag and wipe out your airspeed, and you could enter a deep sink rate.
“It is very pitch unstable at all airspeeds and you’re constantly pitching up and down, even on a calm day with no wind, and you are constantly on the rudder pedals to keep in balance. There is no such thing as straight and level flight in the Blériot!” Being a tail-heavy aeroplane with a large rectangular horizontal stabiliser, the elevator provides very effective deflection for pitch axis control. “Though we call the tail a horizontal stabiliser, it really isn’t – it is a rear wing. It’s a lifting device and the incidence is trimmed to balance the aircraft to the airspeed and rpm at maximum power settings.”
Manoeuvring the Blériot is something of an art, with even the gentlest turns requiring forethought. The fabric-covered wings are 8.6 metres in span and have a surface area of more than 16 square metres. Each wing consists of a rigid front spar mounted to the forward fuselage with a steel tube mount, and a second, flexible rear spar hinged to the fuselage perpendicular to the cockpit. Three lateral ribs (two between the spars and one aft of the rear spar) and 11 longitudinal ribs form the rest of the strong, light wooden structure. The leading edge of the wing drops away steeply forward of the rigid front spar, thus airflow is curved downwards to increase its speed and create lift.
A pair of control cables run from the base of the pilot’s stick to an actuating horn mounted to an inverted pylon beneath the fuselage. Attached to the actuating horn is a pulley from which two warping control cables run to the wings. Under each wing, two of these cables connect to the flexible rear spar between the fourth and fifth, and eighth and ninth of 11 ribs. Two more bracing cables run from the bottom of the steel undercarriage mount to the rigid front spar of each wing, again connected between the same ribs under-wing. A vertical pylon mounted above the fuselage connects further warping balancing cables to the top of both spars, with additional bracing cables running to the steel tubing of the undercarriage mount and the longerons of the wooden cockpit frame. Each wing’s angle of incidence is changed by simple left and right stick movements that move the two rearmost under-wing warping cables, differentially twisting the flexible rear spar to induce bank.
“Before you turn, you must put the nose down first to gain some airspeed to make the wing warping more efficient,” says Mikael, “and you must never try a climbing turn. This will stall the aeroplane. You need to climb with very little pitch up – today we call this a cruise climb – to build some airspeed, and then lead the turn with rudder whilst descending gently, being ahead of the aeroplane at all times and appreciating that each turn has a long lead in time; the flying controls do not respond immediately as they do in other aeroplanes, and you could move the stick to wing-warp left and it will not be an instant movement. For example, if I want to turn left, I will fly a shallow climb and then lead the bank with left rudder, using left wing-warping to balance the aeroplane through a shallow diving turn.
“So a left turn means left rudder and left wing-warping – that sounds simple enough, yes? Like a conventional aeroplane. But this is not a conventional aeroplane, and you need to unlearn what you know about conventional flight. At certain airspeeds, often in the lower to mid-range for the Blériot, if you turn with left rudder and left wing-warping the aeroplane will slide into the turn. It will effectively side-slip and fall out of the sky at an increasing speed. All turns are uncoordinated, and you will need to fly cross-controlled to maintain the bank with left rudder and full right wing-warping to stabilise the aeroplane so it behaves conventionally. This is why you shallow dive in the turn, as more airspeed makes the wing-warping more effective and gets you out of the range where, for example, you need right wing-warping to turn left.
“With no airspeed indicator I cannot say what airspeed you need cross-controlled turning, as it is all done through feel – you can feel the aeroplane beginning to slip, it’s like it’s falling away from you and suddenly conventional control inputs are ineffective. You have only seconds to counteract this with opposite wing-warping, which is why you need to anticipate that and be ahead of the aeroplane. The method of turning is all about minimising the effects of drag from a very draggy aeroplane.”
As with so many aspects of the Blériot’s handling, things are rarely that simple. “One scary aspect is that you cannot descend with the nose down and high airspeed. Proportionally, the tail creates more lift than the wing as the airspeed increases. The faster you fly, the nose wants to drop – it’s like it’s trying to tuck its chin under – and you have to hold the stick aft more and more. As the nose drops and the aeroplane is ‘tucking under’, you could either run out of back stick or run out of altitude. I experienced this during flight testing. I climbed, turned in a steep dive and tried to pick up some airspeed. The faster it went, the more the aircraft wanted to dive and I was bringing the stick further and further back. It got to the point where I was worried that the increased loading would cause a structural failure of the elevator.
“I had to blip the engine to get the airspeed down and raise the nose again. It was a scary experience. The lesson is: dive gently in the turn to stabilise the turn, but don’t dive steeply to gain airspeed. When I’m talking about diving, it is only a few degrees of nose-down descent – but the margin between giving yourself enough airspeed to successfully turn and being too fast to pull out at low-level because of the lift from the rear wing is very small, probably only a few kilometres per hour.”
Mikael describes how throughout any flight, he is constantly checking the tachometer to see that the engine is still producing the desired rpm. That might involve moving the fine adjustment lever to lean the mixture and eek out a small increase in rpm – even five to 10 rpm more, he says, can be useful and offer a little more margin in the event of an engine failure. “You’re always hunting for the maximum revs. If you lose the engine, you don’t have any slipstream over the tail and you can’t put the nose down to maintain airspeed to land. I don’t know what would happen if the engine failed, but I would imagine it’d involve a rapid sink rate and hitting the ground hard and fast.
“Engine management is a constant feeling out process. You don’t want to flood the engine and cause a rich cut, or lean it too much and risk a lean cut. I fly at full power, in the region of 1,200 rpm, the whole time I am airborne, but of course, full power is not always maintained with the bloctube and fine adjustment lever in the same position as they were when you set full power for take-off, and you need to feel the rpm changes in-flight and adjust the mixture to increase the rpm. Allow the rpm to decrease and you will lose your airspeed far too quickly to do anything effective about it.
“I only reduce power by blipping the engine 10 to 20 metres from touchdown as I lean the mixture more to avoid a rich cut. Landing is simple in the Blériot, as you fly the aeroplane almost to ground level at full power and then blip to slow down, settling at a three-point attitude directly into wind. It really lands by itself, and has never ground looped on me. You must never take-off or land with a crosswind. Ever. The dihedral of the wings will turn the aeroplane to one side, and you’ll wreck the aeroplane and bring yourself to harm. It’s a good, strong undercarriage and you can operate from rough ground, as long as it’s into wind. That is not negotiable, and if I cannot do that, I will not fly.
“Wind itself is not necessarily a problem when flying the Blériot,” Mikael adds, “but it depends on the site you are flying from. I have flown at an airshow on the Swedish coast with a 16 knot wind and it was absolutely stable, no turbulence, and wasn’t dangerous at all. It is trees and other obstructions that cause turbulence and make things dangerous. In turbulent conditions, you would not hold the aeroplane. It could fall out of a turn or catch a downdraught and you would not be able to climb or turn. That’s the key to all Blériot flying – do not paint yourself into a corner. Say you are flying towards trees. You are low-level with low airspeed, as ever in the Blériot! You catch a downdraught – you cannot climb, you cannot turn. You do not have the space ahead to land. You cannot do anything. Never fly yourself into a position you cannot safely escape from.”
Though the rapid advancement of aviation quickly rendered the Blériot obsolete, it was a groundbreaking machine in its day and its list of accolades is an indictment of the design’s rigidity: becoming the first heavier-than-air aircraft to fly in Norway; flying the first aerial reconnaissance sortie, during the Italo-Turkish War of 1911; pioneering the world’s first regular airmail service, and later flying Australia’s first airmail service; making the first successful flight from the United Kingdom to Ireland in 1912; crossing the Pyrenees and the Alps in 1913, and crossing the North Sea from Scotland to Norway in 1914, in doing so setting the record for the longest flight over water. Beyond that, the aircraft won several air races and set numerous world altitude records, all in the span of just a few years. That it was such a demanding aeroplane to fly makes those feats all the more impressive.
Twice Mikael has commemorated the aircraft’s most famous of records – Louis Blériot’s 25 July 1909 flight from Les Baraques on the French Channel coast to Northfall Meadow, near Dover Castle on the Kent coast, in which the Blériot XI became the first heavier-than-air aircraft to cross the English Channel. On 25 July 1999, Carlson launched from Marck airport near Calais, successfully crossing the English Channel and landing on a 200 metre strip of land near Dover Castle, close to the site Blériot came down on 100 years prior. There Mikael dismantled the aeroplane in the field, enlisting the help of keen onlookers to lift it over the fence. The second commemorative flight came a decade later – delayed by one day due to restrictions imposed by the French authorities, Mikael once again flew cross-Channel and landed safely at the Duke of York’s Royal Military School, a stone’s throw from Dover Castle, shortly before 9am on 26 July 2009.
“For both flights, I cruise-climbed for 30 minutes and then cleared the chalk cliffs by maybe 50 metres. As soon as I was airborne from France, I could see the white cliffs – you couldn’t miss that target! Both times it was a very simple flight, a little over half an hour flight time. The Blériot performed well and there were no issues. The weather was good and I had no troubles at all. Flying very slowly over the deep blue water, my mind was focused on the engine and the aircraft, but of course coming over those cliffs was an amazing feeling. On my first flight in 1999, I flew one orbit around Dover Castle. That was not wise – if I lost the engine on the western side of the castle, there is nowhere to go. But it is a once in a lifetime opportunity. I couldn’t not!”
In 2006, Carlson commemorated the 95th anniversary of Jan Kašpar’s 100km flight from Pardubice to Prague. “I departed Pardubice during the airshow and flew the Blériot to Prague, landing on the horse racing track. My scarf came loose after five or ten minutes. There was no way to tighten it in-flight as you can’t take both hands off the stick, it’s too unstable for that. I flew for an hour and 20 minutes with my head tilted to one side and my chin pinning the scarf to my chest. The flight took longer than I expected and after 90 minutes in the air, I ended up landing in near darkness at twilight, with the race course lit by car headlights to guide me in. I was absolutely frozen when I landed and literally had to be lifted out of the aeroplane. They dragged me into the bar and warmed me up with a pitcher of Cognac!
“Those flights were eye-opening,” he reflects, “and gave me even greater appreciation of the pioneers who flew Blériots over a century ago. What sticks with me is the photograph of Louis Blériot before his Channel flight. Look at his face. There is no smile there, it does not look like someone about to set off on an exciting record breaking flight. It’s the face of death – a man who knows he’s not going to make it. No one expected him to make it. Then he went and did it, and he will be remembered forever. Jorge Chavez crossed the Alps in his Blériot [in 1910], but crashed at the very end of the flight and died. Harriet Quimby [the first woman to cross the English Channel solo, and the first licensed female pilot in the USA] was killed when her Blériot pitched forward and she was thrown from the aircraft.
“Not all of the pioneers made it”, Carlson muses. “Many of them pushed the Blériot to do amazing things and set records that no one could have imagined even a year before. I have been lucky to have completed some anniversary flights under blue skies and sun with no wind, but they were a true challenge even with decades of Blériot experience. In time I have learned you fly only when the weather is calm – early morning or late evening are ideal. Never fly in a crosswind. Keep your thought process ten seconds ahead of the aircraft at all times. Never turn in the climb, as you might not have the airspeed to continue. Never dive with full power or bank steeply close to the ground – you might not be able to recover. Don’t paint yourself into a corner by flying towards obstructions, as a lack of power or a downdraught might mean you cannot turn or climb to clear them. Always fly over open ground. Always search for the maximum rpm and have an escape route – you cannot glide if you lose the engine.”
It’s an almost breathless précis; lessons learned from three decades’ Blériot XI experience. “Do all of these things, and the Blériot will still be the worst aircraft you will ever fly. You could fly it for 30 years and most of the flights will not be fun. But after the flight you have the huge satisfaction of knowing you’ve flown an authentic first generation aeroplane that is a pioneering design dating back over 110 years.”