Flight Test

Originally built in the US in 1962, and imported into the UK in the early 1990s, this Smith Miniplane is the sole example of this diminutive biplane here in the UK. Its full ‘name’ or type designation is a Smith Miniplane DSA, the DSA is the tautological emphasis of a ‘Darn Small Aeroplane’. Golf Juliet’s wingspan is just 17ft, the fuselage is just over 15ft long, and the tip of its upright propeller stands just six feet from the hangar floor. It has to be said, it is one dinky aeroplane. One with an intriguing character though, promising a certain amount of enjoyable agility, coupled with its Continental C90. Its owner and caretaker is Adrian (known locally and colloquially as Ad, pronounced ‘Aid’) Eves who, at 6ft 3in tall, is not very small at all. I was a smidgeon under 6ft 1in, but with life’s gravity and perhaps the constant compression of aerobatics, I am now a straight 6ft. So, on meeting the Miniplane, my question wasn’t, would I fit in, but rather, how do you go about getting in…? More on that later…

The Smith Miniplane was designed by Frank Smith and made its first flight in October of 1956, just more than 65 years ago. Smith would go on to produce plans for like-minded and motivated constructors. The staggered wings have spruce spars and ribs, and a welded steel tube fuselage and tail group, all fabric covered. Glancing at it quickly, you might understandably mistake it for an early Pitts, but with large tyres. True, it shares a similar layout and dimensions, but then so do the Mong Sport and the Meyers Little Toot of the same period within the United States.

The Pitts, which first flew in 1944, would grow in popularity from the first and earliest 55hp-powered machine, and way beyond in the power to weight ratio game. There were only a few S1s – the earliest model –when the Miniplane first took to the air, though that would change when Curtis Pitts started selling plans for the S1-C 1962. This was for their ‘flat wing’, as was and still is, the Miniplane. Frank Smith, however, was ahead of the marketing game and by 1977 had reportedly sold 350 sets of plans. After Frank’s passing his son worked on a two-seater version the Miniplane+1 and later Sky Classic Aircraft produced plans for a wider and longer fuselage, as well as incorporating a refined wing section with a tailored change of incidence. While the burgeoning growth of the various Pitts variants and its capabilities has proved a boon to the aerobatic world, in the world of recreational aerobatics the Miniplane offers enjoyment for a modest outlay and a fun way to swap the horizon for the sky, and back.

Below The Miniplane was fitted with a new Hercules propeller for this flight test. It’s 70 × 47 (diameter and geometric pitch in inches).

Acquisition and adaption

You may remember a Meet the Members article from the July 2020 issue of Light Aviation of a serial builder, or perhaps a rebuilder, Dave Howell. I first met him when I had the good fortune to fly his Taylor Titch for a flight test article, which I admit to particularly enjoying. He acquired the Miniplane after the then owner had a landing upset.

’GJ suffered a collapsed undercarriage, a splintered prop and a scuffed belly and right wing tip.

The repairs included fitting a new wooden prop and a freshly rebuilt Continental C90, reconstructing the undercarriage, and repairs and spraying to the fabric and paint where needed. Dave says he bought her to fix and if he found he could fit in the aircraft then, OK, well, so much the better! Well, he did, and whatsmore flew her for a further two years before selling her to Ad, who moved her to Dorset. Dave replaced the Miniplane with a half-scale WAR Focke Wulf 190. There are not too many of those either…

While Ad was pretty happy with the Miniplane, he wished for a prop which was slightly coarser to improve the cruise speed. He turned to Rupert Wasey of Hercules Propellers to replace its current French Evra prop, which had a diameter of 70in and a pitch of 44in. Hercules makes its props from laminated blocks of European Beech from Eastern Europe, bonded with aerodux. Each one is 3D modelled using its own software then machined by CNC (Computer Numeric Control). The leading edges are embedded with a section of polyurethane, which according to Rupert, makes them impervious to stone chips and rain. The finishing process sees the application of a polyester lacquer produced by an Italian firm, which Rupert says is also used on vintage Ferrari steering wheels – a nice touch. Each individual propeller’s parameters are fine tuned for the specific engine and airframe to give performance gains. In the case of the Miniplane’s new prop, the diameter has remained at the original 70in, but the pitch has deepened by 4in to 47in. Ad was hoping for a higher cruise speed to enable him to manoeuvre from straight and level, rather than having to waste altitude diving to increase the speed for aeros. So when I was asked to help with the propeller test flights, and in turn judging an aircraft through its aerobatic capabilities, it was an invite that was right up my street.

Propeller test flight

Look around on the LAA website under the Engineering section and then ‘Flight Tests’, and you’ll find a new propeller flight test check. This includes all aspects of engine handling, noting ‘t’s and ‘p’s, indicated speeds and performance, rpm at every aspect from the tick over to take off distance, time to climb, cruise figures, a Vne dive and landing distance had to be recorded. A change of propeller can make a significant performance difference, with both gains and losses, but hopefully provides the pilot’s desired increase in the area of tailored performance. A fixed-pitch prop means having to find that fine balance between climb or cruise. Propeller balance is of real importance as vibrations are not only awkward, but an indication of potential damage soon to occur. Blade tracking is also pertinent. Like all such flights, it’s wise to study the requirements of all of the form boxes before getting airborne to ensure every section is completed correctly. It is rarely just one flight, as sections may be investigated separately. A chat with Andy Draper at LAA Engineering, reminded me that a thorough submission should prevent protracted toing and froing. One other note, the final flight is undertaken with the loaded weight within 90% of the max take-off weight.

Almost 40 years ago I was engaged to test fly a two-seat, tailwheel Sonerai. It was thought that the prop needed more revs to help move the actual performance nearer to the anticipated brochure figures. The prop’s chord was shaved back. I certainly got the revs on departure and certainly got a different performance, but not quite what had been hoped for. The revs were higher but, what I could only describe as the ‘pull’ had somewhat diminished. The Sonerai and I vanished from view over the runway’s slight upslope in a very low rate of separation from the Earth. Air traffic’s query of ‘have you got a problem?’ went unanswered, not because of ill manners, but because the throttle lacked any friction and dropped the much needed revs as soon as I took my hand off to try and press the remote RT button. We both arrived back after a low, low circuit and I, a little bit wiser on an aspect of prop theory, and applied operational practice, i.e. reality. I later ended up in the same aircraft on my back in a barley field while heading to an LAA Rally, with ever-reducing revs being unable to clear carb’ icing. But that, as they say, is another story.

So, with this experience in mind, our agreed test schedule for the Miniplane considered possible scenarios of vibration, under or over speeding, as well as the more common considerations of partial and full engine failures. Along with Ad I was one of two nominated Miniplane test pilots and I had an early shot. There was no need just yet to be at nearly all up max weight, as the plan called for the first flight to establish some general everyday figures without going too far into the corners of the envelope. The 60 litre tank was half full, and under normal circumstances would give an hour and a half at a generous 20 litres an hour. We agreed how long I would be and where I was to operate.

In the cockpit

Because a pilot completely fills the Miniplane cockpit, Ad gave me a cockpit brief – before we got in.

Pride of place in the centre of the panel is the ASI marked in mph with a green line starting at a stall speed of 55mph, up to a Vne of 150. Helpfully, there is a blue best rate of climb line at 75mph. Scanning anti-clockwise is the VSI, a G-metre still recording three and a half from the last flight, an altimeter, a cylinder head temperature gauge, the rpm gauge with green permissible bands and red warnings, then a small rotary switch and cylinder temperature selector 1 to 4, and above is the combined oil pressure and temperature circular dial. Good to know the original builder was so keen on monitoring the engine. A small slip ball completes the set up.

The keyed mag switch is on the left and at first glance looks for the world like those found in all commercially built trainers, except the fourth click position for the starter is missing. Starting will be a hand-propping exercise. The weight of a starter and battery might also have been an early determining factor as the centre of gravity was first considered. Beneath on the left fuselage sidewall is the red mixture lever, which is suggested to only be used to stop the engine, the black throttle knob and a grey carb heat selector with a short pull range. The control column is topped with a hand-fitting grip and the expected ‘press to transmit’ button on top. The Kigass primer is far right on the panel next to an iCOM sidemounted handheld. In a good nod to safety, the cockpit is edged with neatly bound and laced leather-esque cushioning.

A fairly recent trick of mine has been using my phone to take pictures in the tight and invariably darker recess of the inner lower forward cockpit, so as to get an idea of the rudder and brake pedals. I find it gives a useful heads-up seeing where, and knowing how, the brakes are applied. In this case they are heel operated levers similar to those found in both the Piper J3 and L4 Cubs. While knowing the position of the lever arm and how far it extends across the span of the floor and width of the rudder base may seem an unnecessary fact to gather, my flying boots have a lip where the sole is stitched onto the leather and, in the past, this has momentarily snagged when changing the position of my feet from rudder to brake on other types. That moment lost might be at minimum embarrassing, and worse, costly. Also slow rolls require a near extension of full rudder pedal to both slow down the aileron input for roll, while holding the nose on the horizon. Any snagging here is a bit detrimental to the flow and calibre of the manoeuvre. I flew for a collection in Northern Germany and the owner kindly presented me with two flight suits, one black and the other a desert tan as well as a pair of ‘pixie’ boots as used in car racing circles. I wore them, but honestly they were not me, and I felt, well, a bit of a prat in them…

As a complete serendipitous result of the picture taking, I got a good view of the fuel selector. The fuel tank is between the firewall and the instrument panel, just above the pilot’s knees, and the lever sits at the lowest point in the fuel pipes.

Lastly, the cockpit headrest opens to reveal a small stowage area for chocks and a small overnight bag, well maybe a tube of toothpaste and brush. I once ferried a Laser aerobatic aircraft and was not asked to roll on the flight to the Republic of Ireland as the chocks in the locker might dent the turtle decking. I didn’t, but thought it a weak excuse to prevent me enjoying myself and defeat the boredom of so much straight and level…

Externally the front pair of flying wires angle downwards from the outer top of the N struts to the main undercarriage legs, while the closely spaced twin landing wires rise from the outer wing forward N strut base to the rear of the fuselage cabane struts. The front metal cabane struts are useful visual cues for steep turn aiming points to align with the horizon, and the bracing wires directly in front of the cockpit offer the same for 30° banks. Mind you, those tyres do seem oversized and draggy, although handy for uneven strip

Hands-on

The start is against chocks and positioned on the grass. I had the five point harness strapped tightly, hugging into the cockpit confines and a headset on my lap so that I could hear Ad’s starting instructions. As prop-swinger, he is in charge. After the primer has squeaked in some shots of UL91, Ad calls, “Throttle set, contact.” I answer with the same, and she fires first swing. The warm up gives time to run through checks and orientate myself one last time. The view over the nose, through the rotating disc is pretty good as I can see the horizon. Well, not much but I can see it. The curved windscreen surprises me in its ability to keep the slipstream at bay.

The 1,800 rpm against the chocks allowed for power checks, including a comforting drop and rise as I used the carb heat. With the chocks waved away, a bit of taxying on the grass showed a good turning circle with the castering tailwheel disengaged. Flexing my heels onto the pedals, the drum brakes were effective, although I needed a little practice and anticipation. Onto the tarmac, where I felt prepared enough to backtrack and line up for what I hoped for was a controlled departure without visiting the edge of the runway. After all, she is short-coupled and potentially prone for a squirrely character on a smooth surface under power and speed. I would try not to over control and keep the tailwheel on the ground for as long as practical on the take-off roll. “Drop your shoulders, relax, feel the aeroplane.” I need not have been worried as she remained in the groove, up and running along the centreline at quite a surprisingly increasing pace, with the ASI needle rising as I counted four seconds before easing the stick smoothly forward to what I thought was neutral, prepared for the slightest of swings. It didn’t though, and we lifted cleanly from the ground without any encouragement from the stick, to accelerate in ground effect. A little gentle rolling action, a bit of up and down pitch and a light 'pedal' of the rudder, – I felt connected and at home. We climbed away at the helpfully marked blue line speed of 75mph. I was definitely grinning.

Above It’s rare that the top wing of a biplane may be inspected on a walk ’around, but on the Miniplane it's below eye-level!

Left Adjustment of the rudder and elevator trim tabs give a feet and hands free cruise of 100mph at 2,300rpm.

Below On the break! The Miniplane is one of those machines that just wants to help you have some flying fun.

Below Pretty proportions, but those wheels (which are from a Cub) do look quite chunky compared to the rest!

Aloft

Although bright and sunny there was some thermal activity with the odd developing Cu about. The sort of feature to be avoided during any time to climbs or the high speed dives. Clear of cloud and any updraughts, our light weight at 75mph / 2,300rpm returned an indicated climb rate of just under 1,000ft per minute. The cruise at the same figure, 2,300 rpm, gave 100mph and the light stick force that had to be held in the climb was now missing. Trimmed out, she appeared stable in pitch, but not markedly. Directional stability was fair, but lateral was lacking with both wings ponderous in their return to level. The frise ailerons have side stepped most of an ailerons deficiency of adverse aileron drag, but any slight yawing away from the turning is helped along by gentle squeezes on the rudder.

After a scan around the sky to look for traffic, I rolled her. Nothing exotic, just a few aileron rolls. A pitch up to a guessed attitude nose high, checked with neutral stick to stop before a full rolling application. First left, then to the right. Without the benefit of a stop watch I thought the left took just over three seconds at four to the right. Stick forces were light.

Stalling showed a rattle through the stick at 60mph and flat wobbling wing shake, letting go at 55mph. Fine, that confirmed my approach speed of 75mph. And for my enjoyment, over-pitched climbing turns with cruise power showed that she rolled out of the right turn levelling the wings. However, aided by the same influence of torque, she juddered at the high angle of attack and fell away when I tried to the left. Promptly moving the stick forward with some balancing rudder solved all.

Wide open throttle while maintaining altitude brought the rpm to 2,650 and 120mph, with temperatures and pressures stable and in the green. What did cause me to down on the dial and having to check for parallax. Looping from the cruise, she came up and over and down again, ‘working’ her over the top and easing the stick as the air over the elevator was thinking of detaching. So, just a bit slow, perhaps pull harder initially or start from a higher speed. The G-meter read three and a half. A couple of languid barrel rolls, arcing up and over in both directions and a Cuban… I ought to take her home. In clear sky now away from hills and clouds, with the throttle eased back to save the dear C-90, we nudged to the Vne of 155mph.

Back on the ground with a three pointer I read off the numbers. All very satisfactory. No tremors. No vibration. All areas satisfactory. All with a high fun factor without using much airspace either. The debrief left Ad with the more in depth examination to complete and then the Permit flight test.

I later flew in formation with Ad after his Permit issue, and after splitting away I climbed to give myself a view as he flew some aeros. Two manoeuvres impressed me, as with each he broached the horizon at my level from a barrel roll and a stall turn. Marvellous to be able to grandstand such aerobatics with an elevated viewpoint.

I flew the Miniplane again for the photos for this article, and after breaking off from that sortie, I tried some more aeros. Spinning her from straight and level with throttle fully closed, decaying airspeed and with stick fully held back, left rudder increasing to full deflection – and around we went. She used the first rotation to settle and on the next two she spun rather like a top, quickly. Well, I should have expected that with such short wings. I counted the appearance and disappearance of my straight road line feature and after two full stabilised rotations, applied opposite rudder. I could feel the right foot pressure against the rotation, paused and eased the stick forward of neutral. More by luck than judgement we exited on our road now with no deflections and fortuitously pointing homeward.

Having seen Ad from the air and his stall turn I felt happier now to try one. One time, flying a Cuban in an aeroplane without a starter, I had an engine stop and my subsequent dirty dive couldn’t prompt an air start… I had asked Ad what speed had he used to kick at the top? He shrugged, saying, “When it felt right.” I too kicked when it felt right, and it worked beautifully. Nevertheless, I had still checked and positioned high above some newly mown fields as insurance! A quarter clover – a three quarters loop with a 90° change of direction on the vertical downline, found me throttling right back, as the speed built, my roll rate slower than the last machine in which I had tried this. Perhaps I should do the roll on the upward line first?

Back home on the ground with the Miniplane easily rolled into the hangar, I thanked Ad and said we should do some more formation. He smiled and readily agreed. I would love to get some video of him repeating his aerobatics. A spectacle indeed.

And should you be wondering, after all that, how I got into the cockpit, it was really quite simple to swing a leg over the rear decking as if mounting a horse.

Getting out though, was a struggle… unless you have double jointed knees. A feature I sadly lack… Happy landings! ■

Smith Miniplane Specifications

General characteristics

Length: 15ft 3in (4.65 m)

Wingspan: 17ft (5.18 m)

Height: 5 ft (1.52 m)

Wing area: 100 sq ft (9.29 m2)

Empty weight: 616lb (279kg)

Gross weight: 1,000lb (454kg)

Powerplant: Continental C90 90hp

Performance

Maximum speed: 135mph (117kt)

Cruise speed: 100mph (87kt)

Stall speed: 56mph (49kt)

Range: 260 nm

Service ceiling: 13,000ft

Rate of climb: 900fpm