Kit Spit

This 220hp (164kW) Franklin engined version’s 1700ft/min performance are close to those of a 2937kg Battle of Britain Mk I Spit whose early Merlin developed 880hp (656kW) at sea level, giving it a 2500ft/min initial climb rate. Being lighter, the Mk 26’s span-loading and prop disc loading inevitably make it rather livelier in the sky than the original, while its lower climb speed probably makes its climb angle even steeper.

The Mk 26 also stalls nice and slowly. Its aerofoil is not the original NACA 2200, but Cessna’s more tractable NACA 2412. Because of this, the aeroplane’s a lot easier to control and generally more forgiving than a real Spitfire, while remaining a potent and thrilling performer.

But its biggest merit is price. Even after you’ve added engine, propeller, instruments, radios and paint, you’re still up for a small frac-tion of both the purchase cost and running expense of a full-sized one.

To summarise, this is a four-fifths scale Spitfire, and it flies four-fifths like the real thing. Oh, and this one has two seats, so you can show your mates first-hand just what a rip snorting machine it is.

The cockpit is nearly as roomy as its bigger Now, stop and ponder a moment. If this airframe weighs just a whisker more than a Cessna 152, but has a massive, 5. 7 litre, 220hp (164kW), six cylinder engine, what will happen when you open the throttle?

forebear’s, since you are lower down in the fuselage where it is wider, and there are fewer controls and systems, and less plumbing and equipment cluttering the sidewalls. It’s another thing in the back, where room is strictly limited – almost claustrophobic, even. The rear seater straddles the pilot as if in a gynaecologist’s stirrups, his head enclosed in a perspex tunnel with the pilot’s helmet and crossed shoulder straps immediately in front. Nevertheless, two full-sized men can be ac-commodated if necessary, and the forthcom-ing big-cockpit Mk 26B will be much better in this regard.

The Mk 26 pilot’s seating position is more comfortable than a real Spitfire’s, in which you sit with your legs hanging down below your body and treadle the rudder pedals at an awk-ward angle. In this slightly smaller aeroplane, your legs are nearly straight out in front of you in the tail-down attitude. The stick is nicer too. A real Spitfire’s cockpit is so cramped its con-trol column has to pivot side-to-side halfway up to prevent it hitting your knees. This makes right aileron application in particular a rather awkward backhanded motion. The Mk 26’s stick pivots right down on the floor, giving it a more normal arc.

Although not quite such ‘systems aeroplanes’ as its predecessors, this is still a complex type with retractable undercarriage, flaps, a constant-speed propeller and exhilarat-ing performance, so circuits-and-bumps can be busy, especially with someone in the back, for the rear C of G further erodes its already limited pitch and yaw stabilities. This kit Spit is not as demanding as a real one, but it’s still no Cessna. It’s best to brief your passenger to speak only when spoken to.

The run-up is done with extreme care, and strictly into wind, with mag checks at 1200rpm and exercising the prop at 1500. No more, or the tail lifts and she tips on her nose – Just Like The Real Thing (JLTRT).

During the pre-takeoff checks, I leave the canopy open. I don’t care how high the carbon monoxide is, you need to wag your head out from side to side to see where you’re going. You don’t want flaps, it’s best to leave the engine’s cowl flap open for circuits, and set the undercarriage switches up in advance to arm the mechanism; that’s three fewer things to think about in the air.

Now, stop and ponder a moment. If this airframe weighs just a whisker more than a Cessna 152, but has a massive, 5. 7 litre, 220hp (164kW), six cylinder engine, what will happen when you open the throttle?

Sorry, but whatever you imagined, it is that and more! The kit Spit accelerates like a scalded Jaguar and climbs like a homesick Space Shuttle. I timed its 0-60 (mph) time at a hair over five seconds, which is better than my old Caterham Seven. That big propeller gener-ates so much yaw you need at least half right rudder all the way up the climb. Luckily, the pedal pressure is light, so this is no hardship.

Line up precisely on the centreline. Roll forwards a little to ensure you’re pointing ex-actly along it. Take a deep breath, concentrate hard, hold the control column hard back, and then gently, progressively open the throttle, while pressing that right pedal to stay straight. There’s a growing crescendo from the ex-hausts just ahead of you (JLTRT), eye-water-ing fumes (JLTRT) and a trail of black smoke streams past the windscreen. The acceleration pushes you back in the seat (JLTRT). Carefully raise the tail and press on that right rudder. Aim that long cannon of a nose at a distant landmark. Control her! She lifts off cleanly around 60kt. Let her accelerate for a moment to 70, then raise that gunmetal snout skywards, swap hands on the stick, and pull back hard on the undercarriage up locks. Try not to let the nose bob about (JLTRT). The wheels take eight seconds to retract, so forget them now, and concentrate on flying her. Watch that speed! She’s unstable in pitch at full power with this aft C of G and you don’t want to exceed the undercarriage limit, nor to stall.

At 500ft, throttle back to 25in and 2500rpm. Reduce the right rudder to catch that nose before it swings wildly across the sky, grab the trim, and watch your speed. She still wants to accelerate, and 70’s quite enough because, although the undercarriage limit speed is 110kt, the flap limit is 80 and you will want them soon.

When the amber lights extinguish, the It is quite something to proceed across the airfield, waving back to the numerous onlookers, with this monstrous, lumpily rumbling power bulge protruding 2. 4m ahead from somewhere below your rib cage. wheels should be up, but stick your head out both sides to check the mechani-cal tell tales. Yes, they’re flush with the wings, so you can push the up locks home, switch off the undercarriage motors and bring your power back to 22 inches and 2200rpm. Rudder, airspeed, trim.

Approaching 1000ft (you’re unlikely even to be at the upwind threshold yet) and it’s time to make a wide 180 left. Throttle back some more to 20/2000 (adjust the rudder with every power change – JLTRT). Level off. Trim.

Heading downwind, roll the wings level, haul back the power further to 15in and wind out the prop pitch to 1500rpm, to stay under that 80kt flap limit while keeping positive pressure on those pistons to prevent ring chatter. Select carb heat, and wind out the mixture till the EGTs peak, then twist it back a bit. Watch that slip ball! Call downwind. Complete your checks. Keep ahead of it. The runway should be tracking along your aileron/flap gap.

Flip the undercarriage switches down, and pull the pins to lower the wheels, and then select 15 degrees of flap. The nose drops nicely. Trim back a little. Rudder.

Abeam the threshold select flap 30, bring the power right back (again adjusting the rudder), set the prop pitch to fully coarse (at idle with the prop in fine pitch she glides like a Leopard tank) trim fully rearwards, and start your left turn. This will be a continuous, curving, Spitfire approach (JLTRT) with a trickle of power to control that descent. Adjust your bank to keep the threshold nicely in sight.

Push home the undercarriage lock pins, check two green lights. Stick your head out of the cockpit to see both tell-tales are fully extended (to the accompa-niment of successive blasts of intercom), for those little protruding rods are too close to the fuselage sides to be seen from inside if you’re wearing a hard hat, then flip the undercarriage switches back to up for the touch-and-go.

Halfway around the turn you should be at 500ft and 70kt, nicely in the groove. Time for your final checks: reds, blues, greens – (mixture’s rich, prop pitch is fine and wheels down & locked). Remember to put the carb heat to cold for your touch-and-go or go-around.

Nearly there, tiny adjustments now: of bank to get you to the threshold; and in pitch to peg that speed at 70, bleeding back to 65 over the numbers. Perhaps a touch of sideslip to get on the glides-lope. Push her straight as the threshold flashes past, completely close the throt-tle, momentarily notice the exhausts pop and crackle (JLTRT) and start raising that long nose.

Now you can only see the runway margins, framed by those cowling flanks and the leading-edges. Hold them equi-distant as you keep raising that extended proboscis. All the way now, don’t let the stick force or its rearward position lull you into relaxing the backpressure, or you’ll bounce on those stiff, undamped legs, and you need your tailwheel on the ground to steer. Gently push off the drift, but be sure to keep those wings dead level. Remember that narrow undercarriage – not quite as narrow as the original, but you still don’t want a clipped-wing Spitfire do you? Finally, the stick hits its backstop and she settles, skipping once on those rigid legs and waddling just slightly. Let her run for a moment, pedalling precisely to stay straight, then raise the tail – you mustn’t lift off in the three-point attitude, just a whisker above the stall. Slowly, carefully, gradually open the throttle. Stand on that right rudder. Keep her straight at all costs. The roar increases to a bellow, more black smoke, a bit of a swerve, lots of right foot, and you’re back in the air and climbing like Spaceship One.

Let the speed build to 70, change hands, yank back the undercarriage levers, swap hands again, retract the flaps, hold the nose down, trim forward, watch that speed, catch the yaw, and you’re ready to do it all once more, but goodness knows when you’d have time to chat with your passenger! This six-cylinder Franklin sounds wonderful on full song, and its exhaust fumes make your eyes water (JLTRT). This lessens at higher speeds, when the propwash blows more directly aft, but it is important to keep the cockpit vacu-umed out and spotless, otherwise swirls of dust and debris blow up to sting your eyes, especially with any sideslip. Another reminder of the real Spitfire is to glance at a wing tip when it’s idling. That tip bobs as the engine throbs, reminding you of the high power-to-weight ratio (JLTRT).

Forward visibility is inevitably restrict-ed, but no worse than in a real Spitfire, Mustang or single-seat Pitts. Sitting high helps, and I take off and land with the canopy open to maximise visibility. The tailwheel steering is excellent, giving good control at most speeds. This is just as well because, with this long, high snout, it is vital to proceed in a classic tailwheeler weave to get glimpses of what’s in front. There could be a hangar in the way, but without weaving, you’d never know till you hear the clang.

Despite that disadvantage, it is quite something to proceed across the airfield, waving back to the numerous onlookers, with this monstrous, lumpily rumbling power bulge protruding 2. 4m ahead from somewhere below your rib cage.

Did someone say, “Phallic symbol”? I’m sure it wasn’t me! At faster taxi speeds, the aircraft might start a short moment, fore-and-aft trotting motion, but slowing below a walking pace soon cures this. Reduced tyre pressures also help; they make crosswind landings easier, too. The original brakes caused all sorts of problems, so those master cylinders were replaced with conventional Cessna units. Unfortunately, these have more piston area, requiring heavier pedal pressures, so the rudder linkages, brake pedals and floor beneath them had to be re-worked. When once I landed a little deep and used light braking to reduce the rollout, the tailwheel skipped off the ground twice. You need that tailwheel to keep straight so – as with all taildraggers but more so – these brakes should strictly be saved for manoeuvring. This is an anti-complacency aircraft, and it would be only too easy to stand it on its nose (JLTRT).

While probably not an aeroplane for the really inexperienced, the Mk 26 is not particularly demanding, provided you maintain concentration. However, during one takeoff from a grass airfield, I momentarily allowed myself to become distracted. When I mentally re-focused and corrected with a bootfull of right rudder, we skittered sideways towards the left verge like a startled filly. And that was with the tailwheel steering. Had I raised the tail, the outcome might have been worse. My tape said it all: “Bloody bucking bronco!” Once in the air, and above 100kt, the workload diminishes. Flying solo, she’s nice and stable, so you can relax and enjoy the privilege of observing the world unroll past roundel-adorned elliptical wings (at up to 170kt, her full-throttle speed at 700ft – what a hoon’s aeroplane!).

With such light ailerons, a cracking roll rate and great roll damping, medium and steep turns are a delight. This is a proper dogfighting machine, and woe betide anyone who strays into your gunsights! Even at the furthest aft C of G available, while solo I could not make it pitch up into a turn as the real thing often did, but two-up she’s a different beast, barely stable in pitch and yaw: you must concentrate, and fly her all the time (JLTRT).

Some of this pitch sensitivity is due to the higher power, and some to the three-bladed propeller, both of which inevitably reduce pitch and yaw stabil-ity. Also, this particular example has engine bearers 15 or 20cm longer than they need be (with the 10kg battery re-positioned above the tailwheel to compensate). Shortening the engine mounts would reduce the keel area ahead of the centre of pressure and enhance its stabilities, as well as significantly reducing weight, and making the aeroplane look more like a real Spitfire. It would also reduce the fuselage’s moment of inertia, potentially improving spinning behav-iour. Like this, I was not prepared to spin it, despite the Jabiru-engined prototypes having successfully undergone extensive spinning trials.

I timed the sea level solo climb rate at 1700ft per minute at 70kt (with lots of right rudder). This speed is much lower than the original’s, so this Mk 26’s climb angle is truly spectacular – it is a real interceptor! Unfortunately, during full-throttle climbs, even with the cowl flap open, and typically of a Franklin, while all six CHTs remained comfortably below 160°C, the oil temperature always hit its 110°C red line by 4000ft, forcing me to reduce rpm and increase speed to get the temperature back under control.

Subsequently, at maximum weight and with 100kg of rear seat ballast, an assess-ment was made of pitch, roll and yaw stabilities at 100kt in the climb. After any small elevator movement, the displace-ment increased and the nose diverged in pitch, evidence of static instability. The same was true in level flight. It was, however, just stable in roll and yaw in both directions, but slow to return to steady state flight, making it hard to fly, and very difficult to take notes, read a map, or in any way be distracted from the basic task of staying on top of it – a bit like a small helicopter.

At 4000ft, with 24in (the maximum available) and 2400rpm, the airspeed gradually accelerated (JLTRT) to steady at 149kt (165kt TAS) with a leaned 48 litres/hour fuel flow. Despite my high seating position, the nose still covered most of the forward view, with the cowling top just on the horizon. A more practical cruise would be at 20in and 2000 rpm, in a rather more nose high attitude, but at a convenient 120kt, burn-ing a neat 36 litres/hour. That gives a three hour safe endurance, or more than 400nm (740km) range on the standard fuselage tank.

This example also has the optional wet wing tanks, holding another 160 litres of fuel (but at the expense of a passenger, because of its weight). This would make its theoretical endurance seven hours, for an 850nm (1575km) range, but I suggest that’s beyond the physical tolerance of most folk.

Probably because excess filler has changed the wing’s original contours, stalling was rather exciting, and not at all like a real Spitfire – the most tractable of WW2 fighters. With the flaps at any setting, power off, and reducing speed gently, there was no prior warning except stick posi-tion and a changing whistle over the canopy, preceding massive wing drops of up to 110 degrees (that’s with the wings rotating through the vertical, and then another 20 degrees further), mostly – but not always – to the right. Height loss was considerable, sometimes more than 1000ft, and with the VSI on the ‘down’ stops during recovery.

Supermarine
Mk 26 Spitfire Kit

Technical specs
Powerplant
One normally aspirated
Franklin 6A-350 C-1R
six cylinder, horizontally
opposed piston engine, producing
220hp at 2800rpm.
TBO 1500hrs. MT V-12-D
193cm diameter, three
bladed, composite, constant
speed propeller.
Weights & loadings
Equipped empty 562kg
Max takeoff weight 810kg
Standard fuel 115 lit
Max fuel 275 lit
Load factors +6 / -4 g
Performance
(Manufacturer’s quoted)
Sea level Vne 193kt
Max speed (4000ft) 165kt
Max cruise 160kt
75% cruise 150kt
Stall, full flap 45kt
SL climb rate 1700ft/min
Service ceiling 18,000ft
(approx)
Max range (45 min reserve)
300nm (840 optional)
Max endurance (45 min
reserve) 3 hrs (7 optional)
Dimensions
Wing Span 8.43m
Wing Area 11.33m2
Length 7.24m
Height 2.08m
Manufacturer
Supermarine Aircraft,
Castle Bromwich, 388
Hawksbry Rd, Anstead,
Qld 4070. Tel/Fax: (07)
3202 9619. www.supermarineaircraft.
com.
Franklin Engine
Conversion: Langhill Ltd,
Perth. www.langhill.com,
e-mail: [email protected].
Price: Fast-build kit
A$118,250. Info Pack
US$30.

There were also a few seriously incipient spins when I investigated stalling at rear C of G. With this behaviour, I was not prepared to try stalling with any power, with quicker speed reduction, nor in a turn. Despite obvious tip-to-root spanwise airflow over them, the ai-lerons continued working in the correct sense down to around 1kt above the stall, but their effectiveness was seriously degraded within about 5kt of the stall at all flap settings.

The usual cure of fitting inboard, wedge-shaped leading edge stall breaker strips has gone some way towards taming this, but there is still work to be done with wider, longer, higher strips. There are now a couple of knots of warning buffet, and some nose nodding, before she eventually quits flying at around 52kt clean, or 47kt with any flap. I am told most other examples break harmlessly straight ahead, and generally at lower speeds.

Aerobatics are a true pleasure. The roll rate is fast (if not quite in the Edge 540 league) and although all controls, and the ailerons in particular, become heavier at speed, they remain very effective. In fact, despite its low weight, this aeroplane feels more like a heavier Harvard or Yak-11 (and with all the tendency of those types to flick under excess G). Most standard level manoeuvres can be accomplished fairly easily, and the combina-tion of low mass, clean lines and high power allow the Mk 26 to fly big figures without too much energy loss. Sure, there are neither an inverted fuel system, nor inverted lubrication (JLTRT) but with such an aerodynamically clean airframe, those need not be impediments to a spirited display.

I used conservative entry speeds of 140 to 150kt throughout (well below the 193kt Vne) and restricted myself to +4/-1g. Big, lazy chandelles are fun, and aileron rolls merely require a 20 degree pitch-up and clamping the pedals before whacking the stick to full deflection at Va. Barrel rolls are no more difficult (although you do need to work that little rudder), the high roll-rate giving you a quick and easy recovery if you let the nose drop through the horizon while inverted. Slow rolls are a bit harder, needing lots of pedalling in the first and third quarters (that tiny rudder again) and, of course, the engine stops when upside down. It is important to throttle back here, to prevent the prop over speeding when the motor barks back into life. I also noticed fuel spraying from the tank filler, but that could easily be fixed.

Loops use up to a thousand feet of airspace, but you have to swap from a little left rud-der at entry to almost full right rudder going over the top at low speed (40 to 50kt), when you must be careful not to pull too hard, or she gives every sign of wanting to flick out. Cuban eights and reverse Cubans are similarly straightforward, again thanks to that high roll-rate, although caution would be advised on a true 45 degree downward line to prevent a speed exceedence.

As I suspected, that small rudder makes stall turns rather more problematic. Going with the engine (to the left) and not wishing to tail slide, I started at what I thought would be a high ‘kick’ speed of 50kt, and the cartwheel started nicely, with no tendency to roll into or out of the turn. I was beginning to feel smug when, two-thirds the way around the rotation, the airframe shuddered, and she flicked 45 degrees left as the nose approached the verti-cal. I was already swapping to right rudder, and we still had full power pointing downhill, so the whole thing was over before it really got started, but I instantly decided the next one would begin at 55kt. This produced a similarly clean rotation, but there was still some un-bidden roll instability in the second half. I decided to call it quits before I frightened myself. Perhaps 60kt would work, but that rudder is just too small for competition style aerobatics.

The vertical up line before the actual stall turn went on so long, and the Spit’s roll-rate is so high, I tried a half verti-cal roll, both upwards and downwards. These were surprisingly straightforward, and it might well be possible to execute a full vertical roll, provided one limited oneself to a humpty-bump over the top rather than a stall turn, for which the airspeed would just be too low.

Having completed my investigation, I descended to 3000ft and busked a simple five minute sequence of loops, rolls, clo-vers, Cubans and wingovers until I’d had enough. Onlookers commented on the grace of these manoeuvres and the high, attention-grabbing noise levels of that MT propeller. This first acquaintance with Mk 26 aerobatics left me wanting more, but I thought it time to inspect the airframe for wrinkles. (There were none. ) So, what of the structure? It’s conventional all aluminium stressed-skin semi-monocoque, with 6061-T6 spar caps and 2024-T3 webs, ribs, string-ers and skins (of varying thickness) all fastened by blind or pulled (‘pop’) rivets. The wings have a six to one aspect ratio, five degrees of dihedral and two-and-a-half degrees of washout (JLTRT). Detachable outer panels leave the fuselage, tail and a 2. 36m span centre section standing on its steel undercar-riage, which uses a suspension of rubber and springs in compression and, like the flaps, has electric actuation. Supermarine says the wings can be removed and the aircraft trailered in under an hour.

The undercarriage mechanism is a little unusual. Each leg has its own motor, and the separate up and down lock pins are manually operated through Teleflex cables by twin, black-knobbed levers in a quadrant on the cockpit’s right. Above these are the two three-position switches (up/off/down). This example also has dual amber and green indicator lights, functioning convention-ally. Recommended operation involves selecting up before takeoff, then pulling the knobs rearwards once you’re unable to land back on the remaining runway. This both removes the down locks and completes the circuits via micro switches on the undercarriage legs, so the wheels retract, after which you can push the levers forward as up locks. Extension is much the same but in reverse.

The original Spitfire had single posi-tion split flaps, which were more air-brakes than camber-varying flaps as we now know them. This version has plain flaps, divided into two sections each side at the wing joint, and extending continu-ously up to 45 degrees. The consequent low stall speed enables almost STOL operations. You could safely operate a lightweight Mk 26 from most farm airstrips, which would be rather more of a problem with the heavier original.

With no cockpit indicator, flap posi-tion is currently deduced from painted lines on the ailerons’ inboard ends. Just one final point to emphasise the care this machine requires: when empty, and in the level attitude, the tail weighs less than 2kg. You can lift it with one finger! It would be only too easy to stand a Mk 26 on its nose, perhaps even easier than in the original.

So, while tremendously exhilarating, this kitplane may not be for everyone. The lower powered examples are probably not so demanding, but this high-powered one is a real performance aircraft, and not every pilot has the skills to fly it safely. Some have suggested the kit is expensive. Well, compared to with Vans RV, the price is admittedly high, but Supermarine only sells fast-build kits, so the Mk 26 comes with much of its main structure already complete. And, while most RVs might be more comfortable two-seaters, they will never attract such a crowd as this Spitfire.

Queensland based Supermarine has sold nearly 50 kits to date, with a produc-tion rate of one per month. Around a dozen are flying. The company recently announced (and started producing) the larger Mk 26B. Retaining the same wings and tail, this has a fuselage 36cm longer, 13cm wider and 10cm higher, making the cockpit much roomier – particularly for your passenger. Performance and han-dling should be little changed (although the extra tail arm will improve pitch stability at aft C of G) and this airframe is optimised for more powerful engines. Some builders are fitting V8s, which could make a very interesting aeroplane indeed. Personally, I would love to see (and, better still, hear) a Jaguar V12 in there.

With this kit, you get a brand new four-fifths Spitfire for a twentieth the price of a cranky, heavy maintenance nightmare; and its running costs will only be a fraction too. So, for less money than you might spend on a single, 60 year-old example of the real thing, you could have a dozen Mk 26s. Which would be more fun? Imagine a 12 ship airshow squadron scramble. You couldn’t do that with a single Spitfire, no matter how original. Yes, a Mk 26 is more expensive than an RV, and possibly less practical, but you won’t be mobbed in an RV, nor continu-ally waved at by the public. Neither will you get on national TV, nor be invited to air displays to dine in the pilots’ tent and watch the show from the VIP enclosure.

I know which I prefer. I loved it.