Supermarine Aircraft Mk 26B

The 90% Spitfire captures the essence of what made the original so appealing, at a fraction of the cost.


“Don’t touch anything!” These words were reported to be the first spoken by the pilot of a new Experimental fighter prototype at an English airfield three-quarters of a century ago. The prototype (Supermarine Aviation Work’s model K5054), with its artfully shaped elliptical wings and powerful Rolls Royce Merlin engine was, in the hands and mind of test pilot Joseph “Mutt” Summers, perfect. While changes were made along the way, it was this airplane’s offspring that became the archetypal British fighter of WW-II: the Supermarine Spitfire.

Born in the Australian outback, Supermarine owner Mike O’Sullivan grew up with war surplus aircraft at his local airstrip. Is it any wonder he fell in love with the Spitfire?

The “hoop ” on the top of the stick mimics that of the original Spitfire, but the controls of the Mk 26B operate conventionally.

Every red-blooded, aviation-crazy American boy who grew up in the decades after the war (myself included) took it as an article of faith that the ultimate piston-powered fighter was the P-51 Mustang. Powerful, fast, long-ranged and lethal, it was clearly the ultimate aerial combat machine, flown by heroes who swept the skies clean for democracy. With youthful simplicity and innocence, we locked our attention on the airplane we saw at airshows, and it was only later (with maturity comes wisdom) that we learned of the elliptical-winged wonder that flew so heroically in the Battle of Britain and beyond, the Spitfire. While the P-51 was power itself, the Spitfire was both quick and nimble, a perfect combination as an air defense fighter. It is no wonder that today we list it among the ranks of the “best of the best.” Through all of its versions, it maintained the heart of the British lion within its subtle curves. It was an inspired design.

Few will ever have the chance to fly a real Spitfire, but that doesn’t mean that a modern pilot can’t experience the thrill of handling one of these amazing machines. Through the efforts of an Australian-born company, Supermarine Aircraft—now of Cisco, Texas—a modern-day Spitfire, true to the original but built in a slightly smaller size for practicality, is available as a kit for those who want to know what it was like for that early test pilot who implored the engineers not to change a thing. R.J. Mitchell (the original designer of the Spitfire) had indeed gotten it right, and today’s modern kit company has been careful not to ruin the formula.

The cockpit of the Mk 26B reflects the “steam gauge” heritage of the original Spitfire, while hiding a few “digital age” enhancements.

The Aircraft

Mike O’Sullivan built his first Spitfire replica in the early 1990s, as a 75%-scale version of the original, which he called the Mk 25. Several of this type were built before he came out with a slightly larger model (80% of the original) that added a (small) second seat behind the pilot and was called the Mk 26. The current production kit is a 90% version called the Mk 26B. This airplane faithfully reproduces the beautiful lines of the original while providing a passenger seat and giving the modern builder an opportunity to own a flying version of the legendary fighter for a price far less than a real one. It is an all-metal, monocoque design with a fiberglass cowl. The recommended engine is a V-8 auto-engine conversion produced by Supermarine to perfectly match the airframe (at least one project is underway to incorporate a Mazda rotary, and British customers favor an Isuzu V-6 that is also produced by Supermarine). The under-wing radiator housing found on late-model Spitfires is used to house the engine radiators on the Mk 26B, and the radio compartment behind the seat is now a baggage area.

The low-drag elliptical wing is enough to set any aerodynamicist’s heart aflutter, and its history is enough to give a pilot goose bumps.

The aircraft has electrically operated retractable landing gear with custom-built wheels (fitted with 6.00×6 tires) and brakes to preserve the appearance of the original aircraft. The propeller used on the factory demonstrator was custom designed for Supermarine by MT-Propellers to match the characteristics of the prop on late-model Spitfires. It is a constant-speed, electrically controllable prop that can be operated either automatically or manually from the cockpit. Earlier versions of the Mk 26 have used different props, but Supermarine seems to be settling on the MT as its preferred design.

The side-entry door makes entry and exit easier and more elegant. It also enhances the historical mystique of the cockpit and helps the pilot envelop himself in the role. Leather helmet and oxygen mask are optional.

The cockpit of the Mk 26B is almost spacious, with plenty of elbowroom. In fact, while the entire airplane is scaled to 90%, Supermarine actually built the cockpit slightly larger to accommodate modern pilots comfortably. The back seat (as has been added to many full-size fighters that survive to this day) is a bit short from front to back, but it is not claustrophobic. The pilot seat is ground adjustable to optimize the pilot’s position relative to the rudder pedals, and cushions can be used to vary height and comfort. Climbing in is facilitated by the little “door” that swings down on the left side after the bubble canopy is slid back, a feature found on the original Spitfire and carried through for both nostalgia and practicality (no climbing in over a tall cockpit longeron for the proper British pilot). The instrument panel in the factory airplane is an interesting mix of old and new, the round gauges of the traditional VFR panel contrasting with the large electronic engine monitor LCD at the top of the panel. There were no attitude instruments, but O’Sullivan said that some builders are opting for modern EFISes in their aircraft. Accentuating the “old and new” theme in the demonstrator is a TruTrak autopilot and the control panel for the MT prop. The switches for electrical and engine controls are in easy reach across the bottom of the main panel, circuit breakers are ahead of the stick, and the all-important landing-gear controls are on the right. The stick has the classic “Spitfire hoop” handle on top, but it operates conventionally. The throttle is a single lever on the left side, sharing a quadrant mount with the lever used for pitch trim.

The two levers on the right side of the cockpit operate the landing gear (in coordination with switches on the panel). You could retract only the left or right by itself if you had a good reason.

All in all, everything fell easily in place for me, an average-size pilot, and the visibility was quite good, as you would expect in a plane designed to find and shoot down other aircraft. Supermarine has even duplicated the Spitfire’s iconic external rear-view mirror to help with that “bogey at your six.” Truth be told, according to O’Sullivan, many of the pilots in WW-II removed the mirror because, as I found out, it was pretty much blocked by the canopy latch and essentially useless. For those modern pilots used to fully blown Plexiglas bubbles, the window frame might seem to be an impediment to vision, but if you are coming from a Cessna, the view will astound you. Sitting on the ground, that big, powerful snout blocks considerable real estate; I added an extra seat cushion to bring my head up close to the canopy and give me a little better view but was reminded once again that taildraggers will be taildraggers, and S-turns are not optional. It had been a few years since I had flown from the back seat of a Cub, but some things are hard to forget, and it felt like home in just a few minutes. One visibility item I noted that was a bit unusual was that (as in most fighters of the era) the cockpit is almost even with the trailing edge of the wing, so the leading edge can effectively block your view of the horizon in the three-point attitude. This makes it seem just a little more blind during ground operations, not much different than most vintage taildraggers. It is, however, something to remember in the landing flare, when forward visibility to judge height can suddenly become useless.

The steerable tailwheel gives good control on the ground, whether on pavement or the Spitfire’s natural element: turf.

While most of the controls in the cockpit are quite standard (electric cowl flaps, electric flaps, a switch to toggle propeller speed up and down, and standard prime plus backup fuel and ignition systems), the landing-gear operations will seem a bit odd, a term Americans often use to describe British machinery (and, I suspect, the other way around). Most modern pilots are used to a single gear handle or switch that is either up or down, plus indicator lights for each retractable gear (in this case, the two mains; the steerable swiveling tailwheel remains hanging in the breeze). In the case of the Mk 26B, there are actually three lights, a selector switch and a lever (on the side of the cockpit) for each of the maingear. They can be operated independently, though I am not sure when you would want to do that. The selector switch is a three-position toggle with the center position off and the up or down selecting the direction of travel. There is an up (blue) light and a down (blue) light, plus a central red light to indicate that the system has power.

To raise the gear, the pilot places both left and right selector switches in the up position before takeoff. Once a positive climb rate has been achieved, the pilot reaches over to the right sidewall (switching hands on the stick, of course), and pulls back firmly on both gear levers, which unlocks the pins and causes the electric gear motor to drive in the direction selected by the switch. After 5 to 10 seconds, the gear has gone full travel up into the wells, and the up indicator light comes on; the pilot then pushes the levers forward to lock the gear in the up position. O’Sullivan advised against using too much force to lock them up, as it wouldn’t be fun to have a pin jam in that position. Lowering the gear is the same procedure, with the switch in the opposite position. To cycle the gear, you pull the levers back until the position has been achieved, and then push them forward to lock. This will take some getting used to for new pilots, and gear operations need to be quite deliberate. (Emergency gear extension is achieved by pulling release cables, but I didn’t experiment with this in our flight.)

Almost all of the maingear components (struts, wheels and brakes) are made in-house at the Supermarine factory. The gear is retracted with electric linear actuators.

The aircraft flown for this report is the factory demonstrator, with about 65 hours total time on the airframe and engine at the time. Over the course of our discussions, I learned that several details were still in development. For instance, the landing-gear operating system had recently been rewired and updated. The braking system is under evaluation, and the factory pilots were still working out their operating philosophy on the new MT prop (I was instructed to leave it in manual and set the pitch to specific values that they had worked out). The fit and finish on the aircraft was excellent, and the engine compartment showed an unusual attention to detail for an early model machine. A number of controls and switches still needed proper labeling, and these were covered by a preflight briefing to avoid confusion. The airplane was also ballasted aft to keep the tail from getting too light in solo flight.

The nicely balanced rudder makes it easy to yaw the nose left and right, a reminder that the original aircraft was primarily a gun platform that needed to be aimed.

Flying It

Engine start was a breeze: master, ignition, fuel, and hit the starter. Because this is basically an auto engine, it starts like a car, but it sure doesn’t sound like one. With the three-blade MT prop swinging around up front and the short exhaust stacks crackling alongside the nose just behind, this is clearly something different. Because the prop is geared down, applying throttle changes the exhaust note and the prop sounds in a somewhat exotic mix, a wonderful combination that clearly tells the pilot (and anyone within earshot) that power is available whenever you want it; just push the knob forward. It is interesting for an inveterate Lycoming driver to have so much oomph available with only a single lever (no mixture or prop controls), but if you think turbine, you’re not far off. In fact, it is hard to think of another modern non-round piston engine that can give you 430 horsepower, so to get the same effect you probably need to be burning Jet-A.

Count the exhaust stacks. For exterior authenticity, the V-8 becomes a V-12 through the use of a short manifold. The sound is beautiful.

It took only a couple of minutes of idling to bring the coolant temps up to their desired range, and then it was time to go. The airplane is stable on the ground, due to a long fuselage and an aft-mounted “little wheel.” The steerable tailwheel is familiar, moving with the rudder to about 30˚ either side of center, then breaking free to full swivel to allow swinging the tail around in close quarters. I was cautioned that the custom-made brakes were not very effective (something that is obviously high on the factory’s list to correct) and therefore approached taxi speed and turns with care. In fact, the braking action reminded me somewhat of the old bladder-style brakes from the ’30s and ’40s, drum brakes actuated by rubber expansion bladders that had nowhere near the stopping power of today’s disks. As long as you know this, it is simply a matter of planning for it. Don’t expect to make sharp ground turns, and certainly don’t depend on them for significant steering corrections. I elected to operate off the grass beside the paved runway, on the recommendation of the factory guys, to give me some natural braking effect, and this worked out well.

All of the intakes are authentic; the radiators under the wing are actually radiators.

With flaps up, canopy locked and the engine checked and stable, there was nothing to it but to put the coals to the “old kite” and let her rip! With horsepower galore (4500 rpm gives about 350 hp), the airplane leapt into the sky with almost no time (or need) to correct heading after raising the tail. Initial directional control with the tail on the ground was excellent, and there was only a slight bobble to the left as the little wheel lifted off, easily corrected with rudder alone. Airborne acceleration was equally quick, and I pulled back to nail the 120-knot best climb (and maximum gear extension) speed while I deliberately operated the undercarriage. By the time that task was compete, I was out the top of the traffic pattern (there was, in fact, no traffic) and headed crosswind to go find some Messerschmidts…I mean, to give myself some altitude and room to maneuver.

I leveled off at 4000 feet MSL and set the power as recommended at 3200 rpm, 42% throttle position (yielding about 23 inches MAP), and saw the speed stabilize at about 161 KIAS, which computed to 172 KTAS. The demo plane didn’t have a fuel-flow indication, and the company is still quantifying performance with the new MT propeller, so it is hard to say what it was burning. Customers will have to wait until better fuel-burn numbers are confirmed to get actual endurance and range data.

Two-piece electric flaps provide a great deal of drag, and the airplane has a wonderfully slow stall speed in keeping with its sod runway roots.

This is a fairly clean airplane with plenty of power, and it likes to show off. My initial impression was of a nicely controllable airplane, with moderate (not too light, but far from heavy) stick control forces. Rudder forces were delightfully light, and it was easy to point the nose left or right by up to 10. I could quickly see that the original airplane’s intended purpose was to be a good gun platform; it was point and shoot. At cruise, the airplane was stable in all three axes and returned to the trimmed speed quickly when disturbed. In roll, you got just what you asked for—no more, no less—and it took no significant aileron to hold it in a turn. Aileron forces were slightly heavier than pitch forces, but not objectionably so. I only flew the airplane in one weight and balance condition, so I’m not able to say how pitch forces would change with loading. I was told that the airplane was intentionally built to balance much like the real Spitfire, which was nose heavy (or “tail light” as O’Sullivan preferred to say). It would be interesting to see how it handles with a passenger in the back seat. As it was, some ballast in the tail had been added to bring the CG into the range for a pilot of my size.

Whether you are looking in or looking out, the Spitfire cockpit is a classic. The mirror, however, is mostly for show.

After a few turns with bank angles up to 60 (very little back pressure was required to hold altitude), I slowed the airplane to see how it stalled. The stated stall speeds are remarkably slow (45 knots dirty, 51 knots clean) for a high-performance airplane, but I found them to be accurate. It was explained to me that the original Spitfire was designed in the mid-1930s to be pilot friendly, operable by low-time pilots off of unimproved fields. Aircraft designed once the war was truly underway tended to be more weapons-oriented, and the pilot was expected to adapt to the speeds that resulted. For the modern civilian pilot, low stall speeds are a definite plus if things get dicey, or if an off-airport landing is required. Lower speeds will always help survival, and I felt that the Mk 26B would give you every advantage in that event. (I was instructed to leave the gear up if I had to land off-field, as experience during the war showed the airplane to survive with little damage in this configuration.)

There is little fiberglass to be found on this kit airplane. With the exception of the cowl, the curves are all executed in metal by the factory.

While the airplane flies slowly quite well, a pilot flying in this regime needs to be careful to not let the airplane get too slow, as the stall warning itself was almost unnoticeable. It was flying, and then it broke; there was no buffet or shudder. I did several power-off stalls and got the same result each time, with a significant roll off to the left and a steep drop of the nose (as you would expect in a forward-CG airplane). Recovery was simple with the power available, but the altitude loss was significant, so I would caution that this is not an airplane for beginners. I made a mental note to add a few knots in the traffic pattern my first time around.

Because of the nature of this solo flight, I had decided not to attempt any aerobatics (even though the airplane is stressed for +6/-3 G), but I did want to sample the handling qualities beyond normal turns, climbs and descents. After accelerating from the slow-flight tests, I tested the Dutch roll characteristics and found the airplane to be stable, with no tendency to wallow around. Next, I cranked in some bank and pulled back into a chandelle. I gained quite a bit of altitude without putting in additional throttle. Even though the speed change in this maneuver is considerable, the pitch and roll forces remained balanced, and the airplane felt natural. Next up were a few Military Eights (“lazy eights with gusto,” as a former instructor liked to call them). Again, the airplane felt natural with one wing pointing high to the sky and the other low, and the fighter-like visibility was obvious as I swept the blue for bogies. The skies of Cisco appeared to be free of adversaries this morning, so I decided it was time to return for landing.

O’Sullivan and his team prepare the Mk 26B for its next mission. It could be over the plains of Texas, or the cliffs of Dover.

I planned a gentle pattern entry and slowed the airplane gradually. I had been warned that it was slippery, and that planning far ahead was required to get below the 120-knot gear speed. But I found it to be no different than most RVs, and easier than many glass ships, to bleed off airspeed. I was entering a wide downwind when I cycled the gear levers back and held my breath until I saw those two blue lights in the “down” position, then pushed the levers all the way forward into the locked position, knowing I was home free. The airplane was easy to fly in the pattern. I flew the recommended 10 of flaps on downwind (after slowing to 80 knots), held 80 on base and then slowed to 70, putting out full flaps (they are mostly speed brakes, according to O’Sullivan) on final. The winds were only slightly cross, but I wanted to make a three-point to be sure I had good steering at touchdown. My only surprise was a slight gust during the final flare that caused a bit of a balloon. The touchdown, however, was acceptable and predictable, and I noted no tendency to tip left or right on the somewhat narrow gear. (O’Sullivan said everyone flies it a bit too fast the first time, and only a few knots extra in the flare will cause that balloon. It simply continues to fly slower than you would expect from a fast airplane).

Roll-out was easily controllable, and the only problem I had was getting turned around in the fairly narrow grass area with a ditch on one side, weeds on the other and brakes that were hard to lock up. A nice blast of power over the rudder solved that, and I was quickly taxiing back, canopy open, happy to have returned from my first Spitfire mission.

Summing Up

Few modern pilots will ever get the chance to fly a full-size fighter from WW-II. Fewer still will get to fly a Spitfire, as there aren’t many of them compared to their famous American cousin, the P-51. But the Supermarine Mk 26B can put the experience much closer for a builder with a passion for fine flying machines and the skills necessary to complete the airplane. This is not an inexpensive kit by any means, but it is well built and well designed, and it flies wonderfully.

The demo plane clearly had a few items that are still under development, and this should be understood by buyers considering the kit. As mentioned, the factory team is still characterizing the new MT prop, and additional development work may be done in this area. The company is still working on finding the best power and prop settings for cruise flights; accurate cruise numbers should be available from the company soon. My experience showed that the airplane seemed to faithfully achieve the numbers the factory provided.

No, the cannons aren’t real, but does your opponent know that?

The factory also said it is working on improving the brakes and has recently changed the landing-gear controls. I would like to see gear operation simplified to the modern standard, and I would not be surprised if that is the way the system evolves in future kits. The firewall-forward package seems to be mature, but the airframe wiring harness may change slightly as the gear and avionics options are developed. I did not have a chance to look at the schematics or wiring diagrams, so I can’t say clearly how the airplane would support glass cockpits and other avionics. However, modern panels draw relatively small amounts of power, so it should adapt well. And there is nothing wrong with a steam-gauge cockpit, which in this case seems almost appropriate.

The Mk 26B should not require extraordinary pilot skills, but it is, by definition, a high-performance airplane with retractable landing gear and a lot of horsepower, so it is not for the raw beginner. Operation of the liquid-cooled V-8 and electric prop will take transition training for pilots new to the equipment, but nothing seems to be particularly tricky or counterintuitive. From my sample of it, this seems a good airplane for those who enjoy gentleman’s aerobatics or maybe a little “air combat maneuvering” with like-minded individuals.

The choice of an alternative engine (something other than a Lycoming or Continental) may give some pause, and I admit to being cautious about auto-engine conversions in aircraft. But I am an engineer who believes in picking the right machinery for the job and am open-minded enough to know that sometimes boundaries need to be pushed. The LS2 conversion produced by Supermarine matches the airframe well, and the company has done considerably more analysis and testing than some engine-package manufacturers. Buyers should still be aware that they are not flying a powerplant with millions of operational hours, however, and they need to accept that they are at the cutting edge with this engine. Aviation does not advance without some risk, and while that risk appears to have been minimized by Supermarine, it is something that each potential builder will need to evaluate for himself.

In the end, there is the experience of looking out of a vintage cockpit at a set of beautiful elliptical wings, pulling back on the stick and freeing yourself from the earth with a stunning rate of climb. There is the harmonious feel of well-balanced controls that allow you to point the airplane where you want to go with little effort, movement or thought. And there is nothing like realizing that you are getting to fly an airplane whose heritage, looks and handling harken back to the days when young men flew them in the skies over Europe. The Spitfire lives up to its legend, and so does this incarnation.

For more information, call 254-442-1800, or visit

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Paul Dye
Paul Dye, KITPLANES® Editor at Large, retired as a Lead Flight Director for NASA’s Human Space Flight program, with 40 years of aerospace experience on everything from Cubs to the Space Shuttle. An avid homebuilder, he began flying and working on airplanes as a teen and has experience with a wide range of construction techniques and materials. He flies an RV-8 and SubSonex jet that he built, an RV-3 that he built with his pilot wife, as well as a Dream Tundra they completed. Currently, they are flight testing a Xenos motorglider. A commercially licensed pilot, he has logged over 6000 hours in many different types of aircraft and is an A&P, EAA Tech Counselor and Flight Advisor; he was formerly a member of the Homebuilder’s Council. He consults and collaborates in aerospace operations and flight-testing projects across the country.



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