Sherwood’s Kub — Fun, Light Recreational Aircraft from Across the “Pond”

While occupied on some travel, I am pleased to provide a pilot report on a Part 103-type from across the Atlantic in the United Kingdom. Who better to report this to you than my counterpart in Britain, Dave Unwin. Dave has flown a huge number of aircraft of all sizes. When he writes about lighter aircraft, I enjoy presenting his views. Comments in italic are my amplifications. This time I present Dave’s article with minimal editing so you can enjoy his British style. This means it is longer than our usual fare but I found it a fun read and I hope you will, too…

All the great pictures were shot by photographer extraordinaire, Keith Wilson. Thanks to Dave and Keith for a great story. —DJ

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As I turn onto final James Milnes’ voice suddenly crackles in my headset, “Golf Oscar Kilo Uniform Bravo, don’t forget it’s a tailwheel today!” The reason for James’ timely reminder was that when I’d flown the same aircraft a few weeks previously it had been configured as a trike, but today it’s a taildragger! Like most things in life, sport flying isn’t getting any cheaper. Hangarage, insurance, maintenance and fuel are all getting more expensive. But what if you had an aeroplane that lived on a road-legal trailer and fitted in your garage? One you could fly from practically any friendly farmer’s field while burning only eight liters (about 2 gallons) of mogas an hour and that you could do all the maintenance on?

I give you the Sherwood Kub. Built by The Light Aircraft Company (TLAC) at Little Snoring Airfield in Norfolk, the Kub is a high-wing, single seater which falls into the snappily-titled Single Seat Deregulated category, or SSDR. As the name implies, an SSDR aircraft can only have a single seat, and in the UK it must stall at less than 35 knots and have a MAUW (maximum all up weight) no greater than 300 kilograms (some countries alternatively specify an empty weight of either 115 or 120 kilograms — the U.S. Part 103 number of 254 pounds or 115 kilograms).

Before going flying, a look around the TLAC facility reveals quite a few Kubs in various stages of construction, and the large lift (which wouldn’t look entirely out of place on an aircraft carrier) that conveys completed aircraft from the production line on the first floor down to the ground. Unlike some of the SSDRs that I’ve tested over the years, the Kub looks very well made, and also quite robust. TLAC boss Paul Hendry-Smith explained that although SSDR aircraft don’t need specific approvals from a national aviation authority or administration, as the Kub is descended from the Reality Aircraft Kid, it is built to British Civil Airworthiness Requirements, uses aircraft-quality materials and is “a proper aeroplane.”

Kub, the Machine

Wandering out to look at the test machine reveals an interesting anomaly; unlike any other aircraft I’ve ever flown (but similar to the Kolb TriFly), “Golf Oscar Kilo Uniform Bravo” appears to have both a nosewheel and a tailwheel! TLAC’s Chief Pilot James Milne explains that the Kub shares several similar features as its big brother the Scout, including being offered with different engine options, having quick-folding wings and being easily reconfigured with either a nosewheel or tailwheel undercarriage. “The mainwheels are set up for a nosewheel” he explains, “but we thought we’d leave the tailwheel on for a laugh; to see if you’d notice!”

Currently offered by TLAC as either a basic kit, “Fast-Build” kit or as a RTF factory-built SSDR microlight, the Kub is of classic rag ‘n’ tube design. Construction is primarily of TIG-welded 4130-gauge aircraft grade steel tube that is then powder-coated. The fuselage has a triangular cross-section aft of the cockpit, while the wings use Avid Flyer/Kitfox-style tubular aluminium spars and plywood ribs. Oratex UL600 covers the fuselage, wings and tail, with composites used for the cowling, which half-covers the Hirth F23 engine.

The Hirth F23 is an air-cooled horizontally-opposed two-stroke twin, which produces 50 horsepower at 6150 rpm and turns the three-blade, fixed-pitch prop via a wide Polyflex V-belt drive with a reduction ratio of 2.2:1. James explains that initially G-OKUB (British “N-numbers” start with a “G”) had been fitted with a Hirth F33 single-cylinder two-stroke of only 33 horsepower, but this was soon replaced with the F23, which, he grinned, “has transformed it!”

Now, I’m not a huge fan of two-stroke aero-engines. In fact, even my lawnmower’s engine is a four-stroke, so I regard the F23 with a slightly jaundiced air. It’s quite an interesting, almost contradictory little engine, as despite Hirth having replaced the old-school magnetos with dual Capacitive Digital Ignition (CDI) units you still must mix the two-stroke oil into the petrol by hand. I believe automatic oil injection is an option, but even my Yamaha RD400 motorcycle had the oil automatically injected as standard in 1978. The Hirth does have an excellent power to weight ratio though – 50 horsepower from an aero-engine that only weighs 35 kilograms (77 pounds, including the electric starter and twin expansion-chamber exhaust) is not to be sniffed at. It’s fed from a pair of wing tanks with a combined capacity of 47 litres (12 gallons) via a fuselage-mounted four-litre (1 gallon) header tank.

The main undercarriage is of the split-vee type fitted with chubby low-pressure tires and heavily slotted Shimano cable-actuated disc brakes. Bungees are used for shock absorption. As both ‘third wheels’ were fitted, it made this particular preflight unique, at least in my experience. The large pneumatic nosewheel is carried by a welded steel-tube frame and free-castors, while the small solid tailwheel is suspended from a single leaf spring and steers via springs through the rudder pedals, up to about thirty degrees each way. A mixture of struts and wires brace the tailplane, which carries separate elevators with a large trim tab set into the trailing edge of the starboard one. The big fin is pleasingly rounded and carries an equally large rudder.

The constant-chord wings are braced by vee-struts and fold aft using a similar system to the Scout’s, but what really catches my eye are the large, single-slotted mechanically-actuated flaps. These have four positions, 0°, 10°, 25°, and 40° but are they really necessary? This thing has a MAUW of only 300 kilograms (661 pounds) and with a wing area of 10.5 square meters (113 square feet) the wing loading is very low, so why would it need flaps? It’s obvious that without some sort of hinged trailing edge it wouldn’t be possible to fold the wings, as they’d foul the fuselage. But does it really need lift-and-drag producing aerodynamic flaps? Only one way to find out: fly it!

In-Flight Evaluation

Access to the cockpit is via a split window/door on the starboard side. The door opens forward and is quite small, while the upward-opening window is big. Most Kubs also have an identical window to port. Unsurprisingly, neither the seat nor pedals adjust, but luckily it fits me quite nicely, so once firmly strapped in with the well-made Willians four-point harness I study the surprisingly large cockpit’s controls and instruments. Quite predictably it’s an exercise in minimalism. The tall stick carries twin bicycle-type brake levers, while levers for the throttle, trim and flaps are on the port sidewall by your left knee, hip and elbow respectively. The panel continues the minimalist motif with a centrally-mounted MGL Stratomaster Xtreme EFIS as the primary instrument for both flight and engine information, with a back-up analog altimeter and ASI below it and a slip-ball between them. The ASI reads in mph and somewhat optimistic (about a third of the scale is basically superfluous) and the altimeter not ideal, as it only has a single pointer.

There are only four circuit breakers and four toggle switches (for the master, avionics master and CDI units), plus a large button for the starter — and that’s pretty well it for the electrical services, as the handheld-type Icom transceiver doesn’t count as installed equipment.

Now it’s time for my mea culpa moment. James had turned on the master and avionics to brief me on the EFIS, and then said, “off you go,” so I set throttle and choke, shouted “clear prop” and pressed the starter. The propeller whirled most convincingly, but the motor didn’t even cough. Further attempts were equally unsatisfactory, then realisation dawned on James and I simultaneously – maybe turning on the dual ignition systems might help? This was the first time I’d ever made this fundamental mistake on a test flight! Lesson learned: if someone else has turned on some of the systems it’s always best to turn off everything and then start from the start, before trying to start! Incidentally, the choke isn’t great (but they’re working on it). It’s spring-loaded to the off position and as there’s no parking brake, you run out of hands as you also need to press the starter and guard the throttle. Taxiing out using the hand-operated differential brakes is quite easy, once I’d remembered that — as with all aircraft fitted with a castoring nosewheel — its easier if you keep the speed up a bit.

As you may readily appreciate, the pre-take checks continue the simple theme because the F23 is a two-stroke so it doesn’t need warming up and you can’t even check the oil temperature or pressure. Consequently, my generic SEP “flow check” is quickly completed but — as it always does when flying a two-stroke — the small “Master Caution” light in my brain flickers once or twice. “Have I missed something,” I wonder? To be certain, I waited until the CHTs rise slightly then run through the pre-takeoff checks again. Finally convinced I really haven’t forgotten anything, it’s time to fly.

I saw no need to taxi round to runway 25; I simply set the flaps to 10°, opened the throttle and took off from the taxiway. Ambient conditions are above ISA, with an airfield elevation of 196 feet and an OAT of 20°C (68°F). With both tanks full G-OKUB is about 44 kilograms (97 pounds) below the 300 kilogram MAUW. I had a slight crosswind from port but the acceleration is so brisk that the Kub is up and away after about fifty meters (165 feet). The climb rate is equally impressive, the Vy of 45 knots producing over 1,000 fpm. The weather was not good for air-to-air picture taking, so photographer Keith stayed on the ground while I headed off to the west to explore the general handling, control, and stability. Initial impressions were all good. Kub handling is fine around all three axes, with low break-out forces and little “stiction.” Unsurprisingly, slow flight is slow. The strut-braced wing uses a relatively high-lift aerofoil and the loading is quite light, barely half that of a Cessna 150.

Stalls — power on or off — are very benign. There is no artificial stall warner, but adequate natural pre-stall buffet.  Furthermore, as you approach the stall a reasonable amount of backpressure on the stick is required.  Recovery is quick and easy – just release the backpressure. Flaps up Kub stalls at around 28 knots, and although with full flap and some power you can get it down to around 22 knots it’s almost academic, as a sensible approach speed is well above stall. Trim is quite precise, although it did seem to run out of aft trim at my weight.

Regarding stick-free stability, the Kub is stable around all three axes, being quite positive longitudinally, softly positive directionally and just barely positive laterally. The roll rate is, as you’d imagine, quite nippy while the visibility in the turn (and most phases of flight) is quite good for a high-wing aircraft.

Cruise performance is also pretty well what you’d expect. A comfortable cruise speed is 50-55 knots, and although you can bump it up to 60 knots, the engine is buzzing quite frenetically and you’ll be burning (relatively) a lot more fuel. For example, at 50 knots you’re only burning around 10 liters an hour (2.6 gph), so the full 51 liters (13.5 gallons) provide a still-air range (including 30 minutes’ reserve fuel) of around 250 nautical miles. If you pull the power right back you can certainly improve the endurance; it’s just that if there’s any appreciable headwind at all then you won’t actually be going anywhere! However, when flying an aircraft like a Kub the journey is at least as important as the destination.

For my first landing I opt for runway 25, which is wider, longer, and directly into wind. This goes well, and as I can see Keith has positioned himself by the mown grass strip (Runway 28) next to the taxiway to shoot some take-off and landing shots I fly several for the camera. This is great fun. The simple pleasure of a well-flown approach never grows old, while the subtle and seamless transference of weight from wing to wheel and back again has never paled, especially if you’ve got an open cockpit (or large window open) and the runway is grass. (This sentence alone is enough to appreciate Dave, don’t you think?) As mentioned earlier the test aircraft had a third wheel at both ends and just for laughs (and with a bit of application) I even managed a three-pointer.

I typically use about 45 knots on final, and although if it’s flat calm you could probably safely shave off another five knots, I’d advise against it. A Kub has plenty of drag and not much inertia; the speed soon washes off. Plus, it sideslips superbly.  Furthermore, when landing into just a stiff breeze the speed at touchdown is very slow, possibly less than 10 knots. Brakes are only for taxiing.

I also examine the take-off and landing performance with various flap settings and eventually tried the ultimate test by inverting all normal procedures by taking off with full flap and then landing with no flap. Conclusion: you don’t need any flap at any time, except when folding the wings! My experiments had convinced me that the weight and complexity of the flap system’s lever, cables, pulleys and bell cranks is unnecessary and that — and particularly for the 50 horsepower version — simple pip-pins could be used to hold the flaps in place when rigged for flight.

A few weeks later Keith and I are back, and the weather is great. This time G-OKUB lost the the “training [tail]wheel” and is configured as a taildragger. It looks a lot better, I think. In fact, it looks a little bit like a single seat miniature Aeronca Champ. Slightly chubby and cheeky-looking, it exudes fun. Taxiing out was if anything (and unusually) easier in the taildragger then the trike. S-turning is unnecessary, as visibility over and each side of the nose is good and the tailwheel steers through the rudder pedals whereas the castering nosewheel requires differential braking. While best rate of climb is 45 knots, once I rose above 500 feet I sped up to 55, as this not only improves the view over the nose but also gets me clear of the airfield and chasing the camera Cessna 152 a bit quicker.

The air-to-airs with the C-152 carrying Keith and James were not easy as the Kub has practically no overtake, so I have to use a lot of geometric cut-off for the re-joins. With all the pictures recorded I briefly re-flew some of the items off the flight test card to see what — if any, changes in performance and handling had been produced by removing the nosewheel. Unsurprisingly, directional stability is stronger (less keel area in front of the center of pressure) but longitudinal stability weaker (more weight aft of the centre of gravity, exacerbating the limited aft trim). It also seems slightly faster (less drag). It’s also definitely better looking!

During my two test flights I had a lot of fun with the Kub — it’s an absolute hoot! Even the two-stroke engine impressed me; it really does pull well and the rate of climb is spectacular. It really was great fun to bumble about the sky with my elbow out the open window. The handling is crisp, the roll rate nippy and its just… well, fun, for there’s something very special about flying rag ‘n’ tube taildraggers from grass; something that is difficult to explain and hard to resist.

So, would a Kub work for you? Ultimately, the only question you need to ask yourself is, “Do I go flying for sixty miles, or for sixty minutes?

(At this time, TLAC’s Kub is not offered for sale in the USA.)

Sherwood KUB Specifications

• Price as tested — £34,250 (about $42,000 at current exchange rates)
  • Aircraft can be fitted with a variety of engines and a nose or tailwheel undercarriage.
• Length — 16 feet
• Height — 5.2 feet
• Wing span — 29 feet / 8 feet (folded)
• Empty weight — 297 pounds
• Gross Weight — 661 pounds
• Useful load — 364 pounds
• Fuel Capacity — 13.6 gallons
• Baggage Capacity — 22 pounds
• Vne — 86 knots
• Cruise — 50 knots
• Stall — 22 knots
• Climb Rate — 1000 fpm
• Takeoff over 50 feet — 325 feet
• Land over 50 feet — 325 feet