Flight Test: B&F FK9 ELA-SW
- Credit: James Lawrence Photo 2012
An excellent example of how a good aircraft evolves over time into a great one
Whilst chatting to FKLightplanes CEO Roland Hallam at AERO, I was particularly taken by the elegant-looking taildragger on display. Even amongst the myriad of microlights on show it looked good. It was actually the latest iteration of one of the most successful light aircraft of the last twenty years, the B&F? not, as has appeared in error elsewhere, ‘Funk’?FK9.
The FK9 is one of the original modern microlights ? the first generation to blur the line between the flexwings powered by two-stroke engines and conventional light aeroplanes, fitted with three-axis controls and an enclosed cockpit. Designed by Otto Funk and his son Peter, the prototype first flew in 1989 and made its debut at AERO Friedrichshafen the following year.
Over the next two decades the type continued to evolve, and is now available in a number of different permutations. There are long-wing, short-wing and folding-wing options, while the landing gear configurations available include tricycle, taildragger and floats.
I was able to test the ELA-SW version while I was at Sebring, courtesy of the Hansen Air Group (East). The ELA-SW is essentially a short-wing MkIV that has been specifically tailored to meet EASA’s new European Light Aircraft category. As ELA is very similar to the FAA’s LSA classification, this is the version currently being marketed in the States. Two models are available: the Professional (aimed at flight training schools); and the Executive (targeted at the owner-pilot). I flew the Executive model, which has leather seats and a comprehensively equipped panel.
Before beginning the preflight I like to stand back and study the aircraft from a distance. The FK9 shares the same features as many other successful LSAs. These include a wide cockpit that tapers into a slim-waisted fuselage, a relatively short wheelbase/narrow track undercarriage, a windscreen which stretches from the cowling to the wing and gull-wing doors.
As you approach the aircraft one of the most obvious differences over earlier marks is the elegant winglets. These are claimed to reduce fuel consumption, although I suspect that their primary purpose is to reduce the stalling speed and improve the handling on the slow side of the speed envelope by constraining spanwise flow. (As the aircraft has evolved, not only has it got heavier but, contrary to expectation, the wingspan has been reduced. The angle of incidence has also changed over the years, although the aerofoil used ? a Wortmann section? remains the same.)
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One option that I really like is the folding wing mechanism. I’ve always been a keen exponent of folding wings. As most aircraft spend a lot more of their time on the ground than in the air, hangarage represents a significant cost. An aircraft that can reduce its span from around ten metres to less than two has to be a good thing. This is of course not a new idea: when the Daily Mail sponsored a series of light aeroplane trials at Lympne in the early 1920s, part of the specification required the aircraft to be able to pass through a narrow wooden frame. Consequently, in the 1930s the Avro Avian, de Havilland Gipsy Moth and BA Swallow all had folding wings, as have literally tens of thousands of naval aircraft.
Although we didn’t fold the wings on N611SP I am reliably informed that it is both quick and easy. However, the controls do not auto-connect and ? having lost two dear friends in accidents involving aircraft with manually-connected controls ? I fervently believe that they should.
The FK9 is constructed using a fascinating fusion of materials and techniques. The fuselage has a chromemoly steel-tube ‘cage’ as its core, which is covered with a GRP/honeycomb sandwich skin. The wing is completely composite, being a mixture of carbon and GRP, with a carbon main spar. About two-thirds of the wing is taken up by the large, single slotted, electrically-actuated composite flaps. These have three settings: position 0 on the selector somewhat confusingly reflexes the flaps to -10º; 1 (take off) equals 5°; and 2 (landing) is 30°. The fabric-covered ailerons extend right out to the tips and feature a horn balances. Large LED position lights are built into the tips.
The forward fuselage and cockpit are large, while aft of the cockpit the rear section tapers elegantly. In common with most LSAs, a BRS is fitted: it fires upwards through a frangible hatch in the top of the fuselage.
The tail unit consists of a mildly swept back fin and broad-chord rudder, a large tailplane, separate elevator and small ventral fin. This features a small wheel as well as a position light and I assumed that, as the wings fold aft, this must help manoeuvre the aircraft on the ground. Pushrods are used to actuate the ailerons and elevator, while the rudder uses cables Pitch trim is provided by a spring-bias system, the ailerons and rudder are fitted with ground-adjustable trim tabs.
Power is supplied by the near-universal 100hp Rotax 912S, which turns a Duc composite three-blade, ground-adjustable, prop. There is a hatch on the top of the cowling through which it is possible to check the oil and coolant. If you prefer to inspect the engine in greater detail, the top half of the cowling is quite easy to remove as it is secured by Camloc fasteners.
The fuel is carried two wing tanks with a total capacity of 76 litres. A single 60 litre fuselage tank is the preferred option if the wing-fold mechanism is installed.
The tricycle undercarriage consists of three closely-spatted wheels suspended from fully-faired undercarriage legs, and I noted with interest that the nosewheel spat has plenty of keel aft of the pivot point. The composite main undercarriage is of the cantilever type, and is made from a single piece of carbon. This is a very simple arrangement, which requires minimal maintenance. It’s also very robust ? in fact Peter Funk has one in his office that has logged more than 80,000 landings! The nosewheel uses a spring for shock absorption, while the mainwheels are fitted with hydraulic disc brakes.
Excellent build quality
Overall, I would rate the build quality as excellent. Cockpit ingress/egress is good as the sills are low, while the large gullwing doors open wide and are well supported by gas struts. However, I did think that perhaps the pitot tube looked slightly vulnerable (it’s half-way up the port wing strut). The cockpit is quite roomy and seems even more so, as the big, wrap-around windscreen, large windows and small skylight combine to produce an airy, well-lit interior. The comfortable seats adjust fore and aft and the seatbacks adjust for rake. I also approved of the four-point harnesses ? if I were king they’d be mandatory in all light aircraft that weren’t fitted with fivepoint restraint systems!
In the cockpit, many of the ergonomic errors associated with LSAs have already been addressed. For example, the choke lever is sensibly sited away from the throttle and all the controls are clearly labelled. I especially liked the dual throttle arrangement.
The panel is available in three different options ? ‘analogue’, ‘Garmin’ or ‘Dynon’. The test aircraft was equipped to the latter standard, and very smart it is too. It features a Dynon EFIS D100 on the left side of the panel, an EMS D120 on the right and a Garmin 696 in the centre. Above the 696 is a MID engine data logger, while an analogue standby ASI and altimeter are directly above the EFIS, with round 57mm transceiver and transponder above the EMS. This arrangement gives the panel a pleasing symmetry. All the really important electrical services? such as the master, ignition, starter, fuel pump, generator warning light and associated circuit breakers? are all located in a neat block to the left of the EFIS. The lights and their CBs are in the centre pedestal that extends down from the centre of the panel and joins up with a console, which continues aft between the seats. The pedestal also carries the T-handle for the BRS and two neat little air vents, while the console contains the electric flap selector and co-located position indicator, levers for the trim and wheelbrakes, plus park brake selector. A neat touch was that the test aircraft had green tape on the trim lever and the slot it travelled in to delineate the correct setting for take off.
Excellent build quality
I was impressed with the instruments and control layout, although I didn’t like the hand-operated brakes. In the USA, toe brakes are an option for the nosedragger (one I’d exercise) and standard for the tailwheel version. However, if you must have hand brakes (and I am aware of the advantages) why not use a motorcycle-type lever on the stick? I prefer to have one hand on the stick and the other on the throttle whenever any aircraft that I am piloting is moving on the ground.
If I were going to be picky ? and I will, as that’s my job ? I would say that the tumbler switches for the electrics looked a bit flimsy. I’d prefer rocker switches, and for the fuel pump one of those rockers that lights up to show when it is on. As the flap limiting speeds are rather low, I think it would be a good idea for them to be marked adjacent to the selector. However, the only items that really let the side down were the rather cheap Velcro straps that secure items in the glove box. While we’re on the subject of stowage, as well as the glove box in the panel there are rigid pockets in the doors and plenty of space behind the seats. Up to 35kg can be carried in the baggage bay; there is a hatch on the port side aft of the main door to facilitate the loading of larger items.
Typical Rotax 912 reliability
The engine started with typical Rotax 912 reliability, and we set off on the short taxi to Runway 18. The nosewheel steers through the rudder pedals, and although I didn’t particularly like the brakes, they worked well. The aircraft can be taxied with the doors open, which is a nice feature on a warm day. A single lever in each door actuates two locking pins, while a light on the panel illuminates if a door is unlatched.
With all the pre-take off checks completed, the BRS armed and the flaps set to 1, I lined up the FK9 with the runway centreline and smoothly opened the throttle. The acceleration was excellent, and I doubt that we used much more than 100m of the 1,500 available. The climb rate was equally impressive, at around 1,000fpm.
The general handling was good, and a couple of steep turns and reversals revealed crisp, authoritative controls with delightfully pleasant stick forces that firmed up nicely as the speed increased. The control circuits all seemed light and reasonably frictionless, with low breakout forces. Control harmony was also ideal, and though I’d once read that the rudder was slightly sensitive it seemed fine to me. Visibility was very good for a high-wing machine. However ? as you’d expect with any side-by-side aircraft of this configuration ? it is restricted by the wingroots. An exploration of the FK9’s stick-free stability around all three axes revealed it to be strongly positive longitudinally, neutral laterally and also positive directionally. Opening the throttle from idle to full produces a slight pitch-up moment with the trimmed speed dropping from 55 to 50kt.
Slowing down to examine the stall took a while, the FK9 being quite slippery. As the airspeed bled away it occurred to me that the glide angle seemed very flat. Once the speed tape on the PFD had finally dropped into the white zone, I began extending the flaps, down to their maximum of 30°. As the flaps went down they produced a slight nose-down pitching moment that was easily trimmed out. However, care must be taken to avoid exceeding Vfe, which at only 62kt is somewhat on the low side.
Very subtle stall warning
There is no artificial- and only a very subtle aerodynamic stall warning, but the speeds are so slow and the deck angle so high that it’s obvious that something isn’t going well. In fact, with a little bit of power on, the Dynon EFIS simply gave up and read zero!
A slight wing drop accompanied the actual stall to the left, which was easily contained by the rudder. Having retracted the flaps to the take-off setting of 10°, I increased power for a look at a departure stall. As expected, this manoeuvre did provoke a slightly more vigorous response, although the ensuing stall was easily recovered from, with minimal height loss.
I also examined the FK9’s side slipping characteristics. As mentioned earlier, it has a considerable amount of keel area in front of the Centre of Pressure, which can be detrimental for sideslips. In practice, it slips well and recovers promptly.
An examination of the cruise on the way back to Sebring revealed that 5,000rpm at 3,000ft produced a 110kt TAS, for a fuel flow of around 21lit/hr. This means that the range at ‘fast cruise’ is around 275nm, with at least thirty minutes’ fuel left. Pulling the power down to 4,000rpm sees the fuel flow drop to only 9lit/hr, greatly increasing range and endurance. Nearing the airfield both Mike Hansen and I had our eyes on stalks, as a lot of aircraft were arriving for the show. I was grateful that the FK9 has relatively good visibility, while the fact that we also had an armed BRS did provide an extra level of comfort.
As with just about every other aspect of flying the FK9, I found it to be a very straightforward machine in the circuit, with perhaps the single caveat that proper speed control is important. Even being just five knots too fast would probably result in a rather prolonged float, but this would only be an issue on a very short runway. An airspeed of 55kt with ‘Flap 1’ seemed about right, bleeding back to fifty over the fence. In calm conditions and with ‘Flap 2’ set you could comfortably shave off five knots, with the caveat that machines such as the FK9 have low inertia and tend to bleed energy rapidly. If you do use ‘Flap 2’ and 45kt don’t flare too high, because there’s not much energy left.
A great all-rounder
In conclusion, I was very impressed by the FK9. It’s a great all-rounder, and it should be. I’m a big fan of evolutionary theory, and this machine is an excellent example of how a good aircraft evolves over time into a great one. It would make a fine personal aircraft and, as a trainer, can you imagine if your flying club had the tricycle, taildragger and floatplane versions? now that would be a fantastic fleet!