During the interwar period, attractive silver parasol aircraft occupied the fighter arm of the Swiss Air Force. Dewoitine D.26 HB-RAG ‘286’, owned by Hangar 31 and based at Grenchen in Switzerland, is just one of two remaining airworthy Swiss parasols from that period – they are as rare as Edelweiss.
The D.26 was manufactured further to a requirement for a training version of the Swiss Air Force’s first all metal aircraft, the D.27 fighter, which had brought the air force up to date in the early 1930s. Having been largely neglected since the First World War and made up of a myriad of unreliable and outdated types, and being a militia force comprised mainly of civilians who served only a number of weeks a year or when called up, the air force needed urgent improvement. In 1929 a bill was put forward to the Swiss Federal Assembly to update, standardise and expand the air force with more modern types and permanent personnel. This eventually passed, with a 20 million CHF budget approved for use, including the purchase of 65 French-designed Dewoitine D.27 fighters and the manufacture under licence of 40 Fokker C.V.E reconnaissance and light bomber aircraft.
Émile Dewoitine founded the Dewoitine company in Toulouse in 1920, utilising the design experience he had gained working at Latécoère during the First World War. His company had produced a range of parasol types, and whilst these had been largely ignored by the French Air Force, interest came from export orders in Switzerland, Italy and Czechoslovakia. Émile was forced to liquidate the company in 1927 and moved to Switzerland to oversee the final assembly of the country’s orders, and was able to re-establish his company in Paris the following year. The D.27 purchased by the Swiss was a parasol fighter with a 500hp Hispano-Suiza 57 12Mb V-12 engine that far outstripped anything in Swiss service at that point. As such, there was a requirement for a lower-powered version of the aircraft that would be used as a trainer.
For this the D.27 airframe was mated with a 340hp Hispano-Suiza 9Q radial engine (a licence-built Wright R-975 Whirlwind) and initially called the D.27-II, later re-designated as the D.26. Ten of these were ordered and built by Dewoitine, undergoing final assembly at the Swiss K+W plant in Thun. Two further examples were ordered and a slightly higher-powered version of the radial fitted, whilst one of the original batch was also re-engined. The lower-powered D.26s were used for general training, formation flying and gunnery practice with the uprated examples utilised for air combat training, both officially entering military service in 1931.
The D.26 is a fairly compact aeroplane, sitting fairly squat and stocky. The Hispano-Suiza radial engine sits up front, attached to the semi-monocoque metal fuselage which becomes more bulbous towards the middle of the aircraft before tapering off nicely to the tail, giving a length of 22ft 1in. Being a parasol design, the wing is not in contact with the fuselage and is secured in place by two main and one supporting strut on each side of the fuselage, standing the aircraft at 9ft 1in tall, with a wingspan of 33ft 10in. The wing, horizontal stabiliser and all control surfaces are fabric covered.
Just two of the 76 D.26s operated by the Swiss Air Force remain in airworthy condition. One of these, HB-RAG ‘286’, is owned by Hangar 31 and based at Grenchen, in the Canton of Solothurn at the foot of the Jura mountains in north-west Switzerland. The Hangar 31 association was set up with the aim of operating the D.26 and promoting both local and national aviation history – ’31’ pertaining to 1931, the year of the D.26’s manufacture and the establishment of the airport at Grenchen. ‘286’ spent some of its military career at Grenchen itself, latterly serving as a glider tug at the local Aeroclub after its retirement in 1948. Following an engine failure on take-off, the aircraft ended up in various forms of storage; first a barn, then in a children’s playground at a school, and finally in a covered shelter next to a hangar on the airfield. After many years, Aeroclub Grenchen president Peter Brotschi arranged for the aircraft to be saved and for a restoration to airworthiness to commence. Retired Swiss Air Force mechanics from Interlaken airbase spent more than 11,000 hours restoring the aircraft to flight, culminating in a post-restoration flight in 2000. ‘286’ then passed into ownership of the Swiss Air & Defence Force Museum at Dübendorf airport, where it spent most of its time on display in one of the hangars and was seldom flown. The aircraft was then sold to collector Albert Zeller, who invested 40,000 CHF in restoring the aircraft to pristine airworthy condition. In 2015, ‘286’ came full circle and was purchased by Hangar 31, who christened it ‘The City of Grenchen’.
Hangar 31’s chief pilot Paul Misteli has flown the D.26 frequently since its return to Grenchen. “I learned to fly as a civilian when I was 17”, he says. “I did go into the Swiss Air Force, but not as a pilot. At first, I was an officer responsible for the maintenance of jets – Venom, then Hunter, and then the F-5 Tiger II.” After 20 years in that role, Paul moved to Air Battalion 6, comprised of Super Pumas, as an intelligence officer and then an engagement officer. In tandem with his military career, Paul racked up considerable tail dragger experience in civilian life, owning a red Jungmann for many years and accumulating over 1,000 hours on Bückers alone. Since 2015, he has spent a significant amount of time at the controls of the D.26; an impressive feat, given that the Hangar 31 association limits the D.26 to no more than 25 flying hours per calendar year. “I have logged about 70 hours and 97 landings so far,” he says, “and each time it is a huge honour to fly it!”
Careful pre-flight maintenance of the 90-year-old engine is essential: “We have to grease the rockers every five hours of flight time. The cylinders on the upside of the engine are not greased well due to gravity, compared to those on the lower part of the engine. This is very important, but for the first flight afterwards you have to try and make sure to keep your head inside the cockpit behind the windscreen or else you get covered in grease!” Being powered by a radial engine and thus susceptible to hydraulic locking, the D.26’s propeller must be pulled through before start-up to distribute the oil pooled in the lower cylinders. “That is very important, like with all radial engines, and we have to turn it a minimum of 12 times. We normally do this with two people because the compression is very high and [the propeller] is a big chunk of wood!”
Cockpit access is achieved by stepping into the footstep part way up the side of the fuselage, and using the loop of leather secured to the trailing edge of the wing above the cockpit to pull oneself over the rim of the fuselage and down into the seat. “You must fly with a parachute,” adds Paul, “not just for safety, but because the seat is fixed in position and without it you are sitting too low down, disappearing into the fuselage, and can’t see!” The cockpit is snug, but of a reasonable size by comparison to contemporary vintage types, and most of the controls are within easy reach. In front of the pilot is a small windscreen; ahead of that, periscope and auxiliary gun sights.
The D.26 is a fairly basic aeroplane from a systems perspective, and the cockpit is accordingly uncomplicated. To the lower left of the pilot’s seat is the large elevator trim wheel, and forward of that on the cockpit floor is the brake lever. On the port cockpit coaming is a quadrant containing the mixture and throttle levers, and just forward of this is the magneto switch. The instruments are split into two banks on a semi-circular instrument panel. On the left side of the panel sit the altimeter, clock, stopwatch, a large airspeed indicator, and the tachometer. In the gap between the two panels is a turn and slip indicator and a compass. On the starboard bank are oil and fuel pressure dials, as well as oil temperature gauges for both the engine and the oil tank. On the right hand cockpit coaming are a map holder, and slightly behind the pilot is a metal bracket where an engine hand crank would have been stowed in days gone by. A fuel and oil tap and a hand crank for generating ignition current are found level with the pilot’s knee, mounted on a metal rib. Another quadrant on the right hand cockpit coaming contains the cowl flap and engine ignition levers on the top, and underneath, a lever for a quirky fuel tank release system incorporated into the design by Émile Dewoitine. The 220 litre tank sits in the belly of the fuselage, held in place by leather straps that are in turn secured with pins. Says Paul, “The idea was that if you were in a dogfight and then received an impact in the tank which began to burn, you could drop it from the aircraft and glide to a forced landing. Thankfully we have secured that function so it is no longer active!” Finally, on a metal crossbeam above the pilot’s knees and below the instrumentation are four pull rings, all related to the fuel system and engine starting process, and the engine primer. The one-piece control column has a gun trigger on the handle, whilst two basic rudder pedals lie on the cockpit floor.
There were various methods of starting the D.26 – these included swinging the propeller by hand, operating a hand crank in the side of the fuselage with the assistance of the ground crew, and a combination of internal and external hand cranking by both pilot and ground crew. Today, the D.26 has an electric starter motor for ease of operation. With the aircraft chocked due to limitations of the brakes, Paul begins the engine start-up sequence. With the engine ignition lever pulled back and set in low ignition, he will open the fuel and oil tap and proceed to pump fuel into the carburettors using the two right-hand pull rings in an alternating action. The single-plunge primer is then used to inject fuel into the intake ducts. Paul cracks the throttle, switches the magnetos on and presses the small retrofitted silver button below the left-hand instrument bank to engage the electric starter motor. This slowly winds up with a whining sound, and when the inertia has reached its peak, Paul pulls the second pull ring from the left which engages the engine starter. “Normally the engine starts very nicely first time, then it is important to check immediately that the fuel pressure comes up within 60 seconds to the 130 psi mark. If not, it is imperative to shut down immediately”.
The ignition lever is then advanced fully forward, and the running becomes smoother. Before Paul can open the throttle, he must first wait for the oil to warm up. “It can take between 10-15 minutes to warm the oil to the 40°C mark, although sometimes on a hot day it will be faster. If you increase the rpm before that it will damage the engine. So we are very kind to the engine and give it time.” With the oil warmed, a power check is conducted at the parking position with the wheels still secured by chocks to avoid putting undue pressure on the weak brakes; first, the throttle is opened to 1,600 rpm for the magneto check, then to field power of 1,850 rpm. Once completed, Paul will signal the ground crew to release the chocks, and can begin taxying to the runway.
“As is normal for a taildragger like this with a relatively long nose, and that big radial which is wide and tall, the forward visibility is absolutely zero!” says Paul; thus, a slalom taxy is required. “Normally we have one or two ground crew who aid the pilot during start-up and taxying, which can be very helpful, particularly manoeuvring on the ground in an airshow environment where space is tight”. Once underway, the quirks and the quality of the brakes become evident, as Paul explains: “Most aircraft have toe brakes on the rudder pedals. With the D.26 we have the lever down by the left side of the seat on the floor of the fuselage, much like a car handbrake. If you need to use the brakes you have to bend down to use it, and of course when you do that you lessen your visibility temporarily!” Pulling the lever applies brake pressure, but Paul notes that the brakes are not particularly impressive, even for an aeroplane of the D.26’s vintage. “When you have a small grass airfield, this is not a big problem, but if operating at a large military base with hard taxiways where we can have as much as a 2km taxy to the runway, brake action can reduce to virtually nothing! When they heat up the action can dull to zero.” Even after an air display of around 10-12 minutes, Paul knows that the brakes still will not have cooled down fully, so their action will remain limited, making landing and taxying a challenge.
On take-off, centreline positioning is vital as the aeroplane’s poor visibility precludes any forward view until the tail comes up. Throttle advancement on the initial take-off roll is slow and smooth for a number of reasons, as Paul explains. “Firstly, this is just to take better care of the engine, to reduce wear by being gentler, but mainly this is because there really is little directional control from the rudder during the early stage of the take-off. The engine has a compressor which, if power is applied too quickly, will see too rapid an increase in torque at the stage when the rudder is less effective.” Paul will let the speed build until he feels the rudder gain authority, and will then continue to open the throttle to take-off power of 1,850 rpm.
Despite the careful approach the D.26 will still get airborne in 150 metres once it reaches 100km/h, and from there, it goes like a rocket. “The climb out with the D.26 is very steep. The original manual says to climb at 120km/h, but when you do that the nose is angled so steeply upwards – I don’t like that! In that attitude, if you have an engine failure it could become a critical situation, so we have made our procedure that we climb at 140km/h, so it is not so steep and engine cooling is improved. Even then it is still seven to eight metres per second, and steeper than most aircraft!
“Normally it runs with the oil temperature a little too high and the cooling system is not very effective, even though we fly with the oil cooler flap fully open. During a display it can move towards the red line, but as long as it is monitored it is not a problem. Today we use modern aviation oil, compared to what they had in the 1930s, which got hotter and burned more quickly. Modern oils are more efficient and we can better predict their behaviour.”
Paul concedes that from a handling perspective, “the D.26 flies like a truck… OK, maybe a small truck! But it is nowhere near as fine in handling as, say, a Bücker”. The thick airfoil and shallow ailerons impede lateral control; by contrast, the D.26 is much more pleasant in pitch, with lighter stick forces and better pitch sensitivity afforded by the parasol wing. “When you fly in an air display with higher speeds it is a good idea to have both hands on the stick, as you do have to roll with considerable force. In pitch it is lighter, so the aircraft controls are not harmonised particularly well.”
Stalling is a benign affair, and reducing the airspeed to 100km/h with a high angle of attack leads to a gentle nose drop from which the aircraft regains airspeed quickly. “There is no wing drop,” says Paul, “it does not diverge, and it really is no problem to recover, which is very good”. Whilst no D.26s were lost in service through low-level stalls on approach to land, the D.27, with its heavier engine, was a little less docile with more pronounced stall characteristics that could bite if the aircraft got too slow.
The D.26 cruises at 1,600 rpm and 170-180km/h, burning “about 60-70 litres of fuel per hour, compared to about 100 at display settings”, says Paul. The aircraft has a range of approximately 500km, or an endurance of roughly one hour 45 minutes. “It is not very effective,” Paul says of the mixture control, “as it is semi-automatic, and the carburettor has an automatic altitude corrector system. We crossed the Alps going to the Ambri airshow one time, and I experimented with the mixture settings but there was no real difference in fuel consumption”.
For several years, the two airworthy D.26s have been marketed as a pair for air displays. Titled ‘Patrouille Dewoitine’, the duo has appeared at events in France and Germany, as well as their native Switzerland. “Flying the only two airworthy D.26s together is huge fun!” Paul exclaims. “They both have the same performance, so it is very nice to make these formation flights together.” Paul’s wingman for the displays is Laurent Calame, flying HB-RAI ‘284’ of the Association pour le Maintien du Patrimoine Aéronautique (AMPA) based in Lausanne on the shores of Lake Geneva. “Laurent is an excellent pilot, but the visibility afforded by the parasol wing is really bad for formation flying, so it is very important that he is always in the correct position so that he can see me. When we are in close formation that is absolutely key, so he has a tough job.” Paul will set 1,800 rpm for the display so as not to overspeed the propeller beyond the permitted maximum of 2,000 rpm in a dive. The paired display begins with a topside pass in formation, reaching about 260km/h, turning back onto the 45° axis and then completing a flat 360° turn. “Then we change to a tail chase including wingovers”, he says, only ever reducing the airspeed to about 180km/h at the top of the manoeuvres. “We try to keep yo-yoing and turning to keep it interesting for the crowd, as we cannot do aerobatics. We do not like to be pulling heavy G either in these aircraft, so it is fairly smooth with no more than 3G.” Against a blue sky, the sight of the two silver parasols with the attractive red bands and Swiss crosses on the wings looks magnificent. For the final manoeuvre, the pair form up into a loose echelon formation, with Laurent off Paul’s right wing: “I lead us round into a shallow dive towards crowd centre, coming straight at the crowd, and on my signal, I pull up and to the right, and Laurent pulls up and to the left, making a nice final crossover break.”
Breaking into the circuit, Paul aims to reduce the airspeed to 140km/h, keeping some power on so as not to shock cool the engine. Of utmost importance before landing, Paul says, is setting the correct trim, “or else it will be very difficult to settle the aircraft into a three-point attitude”. The trim wheel requires considerable force to make the necessary adjustments, but Paul has found and marked the sweet spot for landing for ease of reference. “In the base [leg] the speed will come back to about 130km/h, and on final 125, and then on short final 120”, he says, with the approach made straight in and with a side slip to improve forward visibility. To maintain the side slip, a modicum of power is required: “Power off is not advised; if you pull off the power completely, the descent rate becomes too much. Then, over the hedge, once everything looks good, you can straighten up and slowly close the throttle. The stall speed is 100-110km/h, so the margin is small. On the flipside too, if you have more than 120km/h the aircraft will not land and will just float, so it is a bit of a balancing act”.
Being of interwar vintage, grass runways are preferred for the Dewoitine, and hard surfaces prove to be more difficult to operate from – even more so with a crosswind element. The aircraft has been fitted with a tail wheel, replacing the original skid, to facilitate operations from hard runways. “It is castoring, so cannot be locked,” Paul adds, “and has about a 30° movement in either direction”. If sudden movement forces the tail wheel past 30°, it can pop out of place and cause a ground loop; avoiding strong rudder input and pilot-induced oscillations is key, as Paul explains: “When you land, particularly on a hard runway, you have to hold your nerve – if you see the aircraft begin to turn slowly to the left or right, let it do that. Don’t use lots of big rudder inputs to try and remain on the centreline”. Having battled with the fading brakes on the taxy back in, the ground crew will chock the aircraft at the parking position whilst the engine is cooled down by pulling the ignition lever back and running the engine for around three minutes at 400 rpm before shutdown.
Paul was the first to fly the D.26 under Hangar 31’s ownership, delivering the aircraft to Grenchen in 2015. “That was an epic day!” he remembers fondly. He went to Sitterdorf, a small grass airfield in the north-west of the country near Lake Konstance, where the D.26 had been based under the ownership of Albert Zeller. There the mechanic who looked after the aircraft showed him all of the controls and talked through the involved engine start-up procedure. “He lay on the fuselage behind me, like our ground crew have to do sometimes in windy conditions, pointing over my shoulder! I started the engine on the first attempt and he told me to taxy to the fuel station. This was when I first realised the brakes were very bad, and the taxiways at Sitterdorf were very narrow! Once you have gone about 20 metres you realise you don’t have much to work with and just have to get used to it!” With the aircraft refuelled, Paul prepared for his first flight in the aircraft – intended to be a short local flight with some circuits at Sitterdorf. “‘No, no, no! That is not a good idea’, the mechanic proclaimed”, Paul recalls. “‘Once you take off you must go direct to Grenchen!’ I thought to myself, ‘Oh, OK, he thinks I will crash the aeroplane, and would prefer it if I crash at my home base!'” So off Paul went, “climbing like a rocket”, direct to the D.26’s new base, meeting with a Jungmann and Jungmeister from the Aeroclub en route to escort him in.
At Grenchen, Peter Brotschi, the president of the association, had organised an event to celebrate the Dewoitine’s arrival; it was a considerable ‘do’, with the Mayor of Grenchen, politicians and about 300 members of the public and TV and radio stations in attendance. “I had discussed with Laurent before about flying the D.26, and he said I must use the grass runway. I contacted Grenchen tower requesting landing on the grass, and they said they had closed the grass runway! Anyway, I tried to convince them to let me land on the grass but they wouldn’t. I thought, ‘This is not good! All of those people, and TV cameras, about to watch my first time landing in this aircraft and it will be on a hard runway!'” A slight crosswind further complicated matters, but Paul set landing trim, made a steady approach and “it landed wonderfully! After the event, Peter suggested that we put the D.26 in the hangar and go and enjoy a bottle of wine, but I said no, I’ll sit in the aircraft, start up again make another flight and when that landing is good, then we go and enjoy two bottles of wine!” Paul flew for another quarter of an hour, and after a second nice landing, the Dewoitine was duly wheeled into the hangar and the wine flowed. Since then, Paul has converted more pilots onto the D.26, including the next generation – his son, Nicolas, and son-in-law, the latter of whom is an F/A-18 pilot. Nicolas also flies a Beech 18 with Hugo Mathys’ Classic Formation display team comprising of DC-3 Dakota and three Beech 18s, and is the youngest member.
Not all of Paul’s flights in the D.26 have been so pleasant; in 2018, he had to act fast to save the aeroplane when the crankshaft broke in flight. “We had just taken off for a formation display and there was a huge bang”, he remembers. He immediately instructed Laurent to turn away from him and made a downward left turn away from the crowd. Thankfully, he was able to circle back to the airfield. “One turn, down and land. The vibration became so heavy I had to completely close the throttle”. As it stands in spring 2020, the replacement crankshaft has also been found to have a crack in it, throwing the future of the D.26’s airworthiness into question. Work is underway to machine a new crankshaft out of more modern materials, however the cost is significant and it is uncertain whether Hangar 31 will be able to afford to continue running the D.26. A new chapter may therefore lie ahead for the Dewoitine. “All things have an end. But, that’s OK… That’s OK”, Paul says as he reflects on his time flying the D.26 over the mountains, lakes and pastures of Switzerland. “We’ve had a lot of fun with this plane and if we have to sell it, a new collector may bring new possibilities for the Dewoitine. We could instruct them on how to operate it, of course, and this piece of Swiss history will go on.”
Paul’s affinity with the little silver parasol shines through as he enthusiastically recounts his experiences flying the aeroplane. He has had many memorable flights in his long time as a civilian pilot, including an epic trip to Scotland with his son-in-law in their pair of Bücker Jungmann and Jungmeisters, but his fondest was a once-in-a-lifetime experience with the D.26. “We were invited down to Payerne airbase by Fliegerstaffel 18, the Panthers, because our aeroplane has their black cat squadron emblem from the 1920s on the side”, he continues. The squadron was formed in 1928 and its first aircraft was the Dewoitine D.27 fighter; in 2018, the unit held an event for staff and families to mark its centenary and both airworthy D.26s were invited to Payerne to participate in the celebrations. Today the Swiss Air Force’s frontline fighter is the F/A-18 Hornet, and much as the Dewoitines did in the 1930s, the Hornet’s role is to guarantee Swiss air sovereignty and air defence. The Panthers are one of the F/A-18 squadrons, and their emblem has now been upgraded from a cat to a black Panther. The unit has something of a fixation on the number 18 – being Fliegerstaffel 18 and flying F/A18 Hornet – and the squadron commander accordingly requested that Paul arrive overhead Payerne at 11:18 on the dot. “We approached and managed to overfly the crowd dead on 11:18. Upon landing the squadron commander, Major Bernhard ‘Beni’ Kocher, greeted us and said, ‘That was amazing, you were exactly on the second! How did you do that, do you have iPads in the cockpit?’ I said no, we have Swiss watches, they are really exact! It really was a great event and the Swiss Air Force commander-in-chief asked us to make a commemorative flight the following day together with an F/A-18.” The jet in question was serial J-5018, adorned with Fliegerstaffel 18’s black Panther emblem on its fins.
Following a thorough briefing the evening before, Major Kocher flew the F/A-18 himself, whilst a second F/A-18, a two-seater flown by Captain Marc Zimmerli, acted as a photo-ship flown with on-board operator and photographer Lieutenant Colonel Aldo Wicki there to document the formation. The four aircraft flew out over Lake Neuchâtel for the 90-minute sortie. “It was a very emotional moment and an overwhelming sight when the Hornet appeared next to us”, says Paul. “I was leading and could look right to see Laurent in ‘284’ and then look left to see the mighty F/A-18!”
Matching the airspeeds of the Hornets and the Dewoitines was difficult; with the parasols flying close to their maximum speed at 230km/h, the Hornets would be at the fringe of their performance. With the F/A18s flying very slowly at a high angle of attack, the vapour forming beside the cockpit would impair the photographer’s view in the camera-ship – taking pictures would be practically impossible. To remedy this, the second F/A-18 would have to fly faster, taking photographs as it passed the formation. Major Kocher wanted photographs where the F/A-18 was deploying flares, and coordination between the camera-ship and Major Kocher was key to ensuring he would fire the flares at just the right moment when the second F/A-18 was passing by. “That was really something!” says Paul. “The F/A-18 was shooting flares and we could smell the cordite from our cockpits! I said over the radio to Major Kocher, ‘Hey, not too close, my wings are fabric covered!’
“I think that was the best flight of my life!” Paul offers enthusiastically. Swiss Air Force past and present; that formation showcased the air force’s advancement over the last 90 years into the highly skilled force it is today. The charismatic little parasols are a small but significant part of telling that story. The black cat really has grown up into a Panther.
With thanks to Paul Misteli, Cornelius Braun photography and Ian Lienhard photography. For more information on how to donate to Hangar 31, please see the society’s website.