Airtest – Speedtwin

A couple of years later he demonstrated Beagle’s Husky in Denmark, moving on to become sales manager for the Victa Airtourer. When that also foundered he went on to be a commercial instructor, then an airfield manager, charter manager and CFI, and continued to put on spirited displays, now in his tiny Andreasson BA-4B biplane, to which he had bought the World manufacturing rights.

In the early seventies he joined Britten-Norman as training and demonstration captain, displaying their Islander, Trislander and Defender in 65 countries worldwide and becoming famous for a Bob Hoover inspired routine of loops, barrel rolls and stall turns (sometimes with a feathered prop). When Britten-Nor- man went broke (to be taken over by Pilatus) he worked for a while for the enigmatic warbird collector Doug Arnold and then rejoined Desmond Norman as chief test pilot for the Norman Aeroplane Company. Taking their innovative Fire-cracker military trainer, Fieldmaster giant crop sprayer and Freelance tourer through to final certification, in the process learning all there was to know about test flying and the various authorities’ statutory requirements.

Who would be a test pilot? To the outsider the job seems glamorous, exciting, thrilling and rewarding, but in reality it is often tedious and frustrating. Having honed their flying skills to perfection, test pilots spend their lives detecting and establishing the handling and performance characteristics of new aircraft, only to find that the fixes to these snags so often cause further problems.

Their pay is generally poor, the risks undeniable and the job can be infinitely disheartening, for development funds are frequently limited, while manufacturers constantly push to get a new type into production as quickly as possible. Once a machine will just meet the requirements, its design is promptly finalised to rush it into production, when a little extra time, effort and money might make it near perfect. Peter led this frustrating sort of life with NAC so, in 1981, wanting sparkling, uncompromised handling, he starting building his own aeroplane in the garage. Seeing no point in making a conventional machine and knowing that the trainer market was over subscribed, memories of Meteor aerobatics led to the Speedtwin’s unusual configuration. In 1988, a year before NAC ceased trading, he and his ex-parachutist, air racing wife, Sue, moved to Wales to refine the machine until it was as flawless as he could make it. Determined that this perfectionist’s aeroplane would be just the way he liked it, everybody else could admire or ignore it as they wished.

Wanting near perfect visibility, excellent handling and two seats to take Sue with him, Peter chose the low drag tandem configuration, with the rear seat raised for a good view, both outside and of the single front instrument panel. Twin engines conferred safety and a carefully spatted and faired fixed tailwheel undercarriage minimised drag. The structure was kept light and as simple as possible with all aluminium wings and a sheet alloy clad steel tube fuselage so that modifications could be made in the light of experience with minimum effort and disruption.

Choosing the ever popular NACA 23012 aerofoil because of its good CofG tolerance and low trim drag, his wing has a 1:5. 5 aspect ratio with taper and washout. Although taper is said to be more expensive to mass produce, it can be made lighter, allows better roll response and is much more aerodynamically efficient than constant chord, the lift distribution curve more closely conforming to the elliptical ideal. Ailerons and flaps do not meet on the trailing edge, there being a foot long piece of fixed surface between them. Experiments to find the best aileron size suggested that anything bigger than those now used would twist the wing, reducing high speed roll effectiveness. The definitive production version will have a stiffer outer wing and bigger ailerons for an even better roll rate.

Controls and flaps are corrugated for rigidity, the elevator’s blunt trailing edge increasing the stick force per g to statutory levels. Still an inventor at heart, Peter has incorporated his own self devised and patented aileron force lightening system. Keeping the other systems simple, the props are fixed pitch and there are no cowl flaps, while the single fuel tank feeds both engines at once, eliminating the need for a crossfeed. The prototype was designed to be semi-aerobatic, allowing manoeuvres up to +4. 4 and -2. 7 g, but production versions will be fully aerobatic.

On a test pilot’s limited income (and, later, pension) Peter had to keep the costs way down, so he scavenged and searched for second hand components to fit his vision. The engines, a pair of rather tired hundred horsepower Continental 0-200s are neatly cowled with plenum chamber cooling for minimum drag. The main undercarriage legs came off a junked Chipmunk, instruments and fittings were obtained wherever he could find them, and the first propellers were hand carved, wooden, ex race leftovers lent by Formula One air race champion, Steve Thompson.

Unashamedly designed for pleasure (and originally for com petition aerobatics), the Speedtwin’s development was protracted as Peter refined his design, fixing this to find it affected that, then changing that only to discover it altered something else. Not for nothing do the cowlings bear the legend E2E, Peter’s copyrighted insignia, meaning “engineered to excel” (or two pilots with an engine each side). But, with the loyal help of engineer Larry Gane, he persevered, flying, modifying and perfecting his baby until he was prepared to launch his pride and joy on an unsuspecting public.

The blue and gold beauty’s debut was at the 1992 Biggin Hill Air Fair, where he put on a spirited aerobatic display to the astonishment of the gathered crowds, but the Speedtwin was most admired at the Popular Flying Association’s Wroughton homebuilders’ rally, where it was surrounded by an inquisitive crowd throughout the weekend.

Evoking vague visual memories of the de Havilland 88 Comet racer and likened variously to a miniature tailwheel Pucara, a Tigercat and a Westland Whirlwind, the jaunty, Disney dolphin looking Speedtwin does appear a trifle unconventional. But to see just how revolutionary it is you have to get down on your knees and peer under its belly, where a pair of forward facing flag like projections rotate from side to side with movement of the ailerons. These are the external components of Peter’s patented RAP (Remote Aerodynamic Power).

An improvement on the aileron spades seen on competition aerobatic mounts, RAP similarly uses the airflow to aid control movement. But, while spades unfortunately affect control surface balance (possibly inducing flutter), and occasionally cause over balancing and an unnaturally light feel at low speeds, RAP does not have this problem. It can also be tuned to fight the greater forces at the top end of the range, yet leave normal response at low speeds.

More importantly, these ‘flags’ aid lateral stability, avoiding the need for the springs commonly interconnecting ailerons and rudder, and a small modification will reduce their effect below a certain aileron deflection. Unlike spades, they are immune to icing induced flutter, but most importantly they can be tuned in a few minutes to suit the individual, so that forces can be feather light or as heavy as you want, without altering stability. Of course there is an art in perfecting their shape, and this has taken up much of the project’s development time.

Thanks to RAP, unlike more short coupled homebuilts, the Speedtwin does not rely on reduced stability for its exceptional liveliness. Despite its remarkable manoeuvrability, it is inherently stable in all axes, and will fly hands off for long periods. Indeed, Peter has gone to great lengths to ensure that his aeroplane’s handling meets or surpasses all stability requirements in BCAR 23 and FAR 23 even at its rearmost CofG – something achieved by few, if any, other kitplanes-because he knows these to be the minimum for safe flight.

Most aircraft have light elevators and heavier ailerons, with the rudder heaviest of all. But the accepted ideal control harmony is for ailerons to be lightest, elevator next and rudder the firmest. The Speedtwin is one of very few aircraft actually meeting this ideal and it has the most remarkable aileron feel I have ever encountered. These are light and very responsive at near stalling speeds, but remain so right up to the over 200 knot Vne (370km/h), getting not one jot heavier with speed.

But enthusiasm causes me to get ahead of myself. The Speedtwin can be flown from either cockpit, so after a brief demonstration sortie in the elevated rear seat Peter let me loose in the front to confirm my initial impressions. You enter from the left wing root, climbing a short portable aluminium ladder laid against the leading edge and using a rubber mat to protect the wing’s glossy surface. From here it is an easy step down into the fuselage after lifting the one piece, tube framed, sideways hinging canopy which is held by a cable with a neat restraining bungee cord. With the canopy closed, the front occupant’s head has a full 13cm of clearance, more than enough for a bone dome. The rear seater’s feet stretch alongside the front pilot, but there is plenty of room within the fuselage’s 66cm width.

Visibility from the back is fine, while from the front the vista through the one piece, curved, demisted windscreen is superb. Both seats are slightly reclined, with firm cushions and sturdy, military four point harnesses for aerobatics, the front one having inertia reels on its shoulder straps. For simplicity there is no seat movement, but both rudder and brake pedals are ground adjustable (a neat innovation, the latter, how often have the brake pedals been at the wrong angle for you?) The cockpit is prototype spartan, cluttered by the externally flush air vent’s box, black heater ducts, elevator trim and teflon lined throttle cables running between the sidewall tubing, but pro- duction machines will have a conventional flush rivetted, stressed skin fuselage, so customers can easily refine the interior to their own requirements. The twin throttles are high on the left sidewall with the quadrant trim lever just below them.

With self aligning ball races throughout, all controls are very light and remarkably free of friction, although there is a noticeable spring in the elevator circuit to provide the 4. 5 pounds per g stick force required in a 4. 4g aeroplane. The rear column is cutdown slightly to allow sufficient clearance from the back of the front seat but the front one is nicely placed. In the upper aft fuselage an enclosed 60cm long baggage compartment carries 45kg (and the boarding ladder).

The whole composite nose cone is quickly removable to get at the controls, battery, brakes and the back of the panel, which holds the usual flying instruments in standard layout. As a remarkably sensible innovation, the T handled mixture and carb heat controls, magneto switches and engine dials (including four position CHT gauges) are ‘handed’, with those for the left one grouped at the left of the panel and vice versa. (However the system falls down slightly in this prototype with both fuel boost pump switches and the vacuum gauge on the left and a dual pointer rpm dial and ammeter on the right, while the vacuum pump is on the right engine and the sole generator on the left one!) Two big supplementary manifold pressure gauges between the front pilot’s feet are for test purposes only and the old Collins radio above them is supplemented by a transponder and Sigtronics voice activated intercom.

The single fuel gauge is also on the right of the panel, the split master switch at top left and two small red fuel cocks below the forward edge of the front seat rotate ninety degrees anti-clockwise into view for on. There is no need fora crossfeed since both engines are supplied from the single 102 litre tank beneath the rear seat.

At 629kgs this proof of concept demonstrator is slightly more heavy (or should I say “less light”) than production models will be, nevertheless it can be pushed out of the hangar by one man, and with two 75kg occupants and ninety minutes fuel (77 litres) is still below the 839kg maximum aerobatic weight. It has a wide CofG tolerance, accepting a 110kg solo pilot with minimum fuel as the worst forward case, or a lightweight 65kg front seater with an 80kg passenger in the rear, full fuel and 15kg of baggage. The Normal Category weight limit is 885kgs, but I wanted to see (and Peter wanted to show me) some fun.

With typical Continental reliability both engines fired up immediately after priming with two pumps of the throttles so we were soon ready to taxi. Bearing in mind this machine has a tail wheel, I was surprised to see the ground in front as close as three metres ahead. A function of the steeply sloping nose and the raised seating position, the superb view was utterly atypical of a taildragger.

Releasing the park brake plunger, I opened up the left engine a little ahead of the right to exit from our tight parking spot, but the steerable Maule tailwheel needed little assistance, although it does feel a trifle heavier than on a single. The differential Cleveland discs can be used to pivot about one mainwheel for an incredibly tight turn if needed. The suspension is a little firm but the current, rather heavy, ex Chipmunk main legs will be replaced by similarly spatted, purpose built, trailing link units on production machines. The Cessna motor slowly ground out fifteen degrees flap, to be confirmed by aligning a yellow line painted on the leading edge of the left flap with its counterpart on the wing’s upper surface. A similar, longer line denotes full flap.

Most twins need significantly larger runways than singles but, being light, this one definitely does not. In fact it qualifies as a STOL plane. On opening the throttles for takeoff, the response was immediate and the brisk acceleration over the muddy grass nothing short of remarkable considering the aeroplane’s limited power. The tail rose as the speed passed 25kt (48km/h), while the merest pressure on the right rudder counteracted a very slight leftward tendency. Since the fixed pitch props only allow 2200 static rpm, the engines are only pulling about 80 horsepower so one would not expect much swing. Unsticking at fifty (96km/h) after an impressively short hundred yard ground run in the ten knot breeze, we climbed like a bird at a surprisingly steep angle at 65kt (120km/h). The whole thing was remarkably easy and quick.

Retracting the flaps at 300 feet (90m) produced no trim change and, in a steady 75kt (135km/h) climb, still with a little right rudder, I timed the initial rate at over 1200fpm (365mpm). Later Peter showed me that it is possible to calculate a theoretical rate of 1827fpm (557mpm) from a pair of very ordinary O- 200s with good constant speed props. We reached 5000 feet in well under five minutes and solo, with half tanks, Peter has climbed from 1000 (365m) to 6000 (1830m) in just over four minutes.

Airborne visibility is quite unbeatable, better, I think than from any other propeller aeroplane. The nose sits surprisingly low in level flight so not only can everything above the horizon be seen within a 350 degree panorama, but most of the ground around is visible too. As you sit fairly high over the wing neither it nor the engines obscure much of the view below. (Of course, in this aircraft, if you really wanted to see what was directly underneath, you would roll inverted!) Even the outer half of each tailplane and the top part of the fin are visible from both cockpits.

In the air that elevator spring is no longer noticeable, but what is immediately apparent is that the Speedtwin handles like no twin you have ever flown before (unless you were on Mosquitoes in the war). Its elevator is not Spitfire light, be- cause that would no longer be permissible under current regulations, but it is remarkably effective, with a linear stick force per G and just the right feel for folk used to modem machines (although, to be honest, I personally like an elevator to be just a bit lighter than is legal).

Those incredible ailerons are peerless. The smallest movement has an immediate effect and, as I mentioned before, their feel is the same throughout the speed range. Only the smallest stick travel is required for normal manoeuvres, and when it is moved more than a couple of centimetres sideways the force actually seems to reduce slightly as the roll rate increases, yet if you completely let go of the control column the aeroplane stays exactly where it was left, such is its stability. In calm air it will fly straight and level apparently forever, a remarkable achievement for so manoeuvrable an aircraft.

Comfort within the roomy cockpit is fine, and ample warm air from the effective heater is ducted to both seats. The low drag air vent provides plenty of cooling breeze and the internal noise is reasonable for an unsoundproofed twin. I noticed surprisingly little vibration considering the four cylinder engines, but did have a little trouble synchronising them to cancel the propeller beat. Leaving the throttles as they were when we levelled out, the speed built up, in a two degree nose down attitude, to a maximum of 141kt (262km/h) with 2750rpm at 6000 feet (1830m) which, with an OAT of -6 degrees C gave a TAS of 152kt (280km/h). (At this altitude this is around 75% power). Later, at 2800 feet (854m) and zero degrees C a reduced setting of 2300rpm gave 120kt IAS (22km/h) (122 TAS [226]), and Peter will guarantee 130kt (241km/h) at 60% power on the flush rivetted production model.

There is very little trim change with power reduction and not much with variation in speed. Throttled back to 2150rpm we still indicated 110kt (200km/h) at a greatly reduced sound level for a fuel consumption of a whisker over 18 litres per engine per hour (match that in any other twin!) This would give a dry tanks range of around 300 nautical miles (555kin) in around two and three-quarter hours on the prototype, and a planned 590nm (1093kin) with 45 minutes reserve in the definitive machine (to meet Peter’s requirement of London to the South of France in one safe hop).

Reducing power completely, the clean stall came in a near level attitude at 59kt (60km/h), preceded by obvious natural airframe buffet starting at 65kt (120km/h), and accompanied by a very slight but completely containable left wing drop. With fifteen degrees flap the onset of buffet was reduced to seventy and the innocuous stall occurred at 56 (104). Full flap lowered these speeds to 56 (104) and 52kt (96km/h), still with lots and lots of warning and a straight ahead g break. Holding the stick hard back rather than recovering only induced a high sink rate in heavy buffet, with no sign of a wing drop.

The story was the same with power on and, pulling into a tight turn, one could accurately hold the aeroplane on the edge of the buffet, to coax the most lift out of the wing for at maximum rate turn – you can tell that this is an ex-fighter pilot’s aircraft. Pulling up to 3g under full power simply causes pitching up and down in unmistakable buffet, with no sign of a desire to flick.

Peter has carried out four turn spins both ways and full-power spins for up to two turns. Normal entry produces a stable spin, although the rotation rate is quite high, with the nose fifty to sixty degrees below the horizon. The aeroplane responds to standard RAF recovery within half a turn thanks to the tiny triangular dorsal fillet ahead of the tail. Before that was installed the spin was rather more oscillatory and sometimes took a full turn to stop after applying opposite rudder.

Having got the routine stuff out of the way, Peter could not wait to show me some aerobatics. The Speedtwin’s Vne is 179kt (331km/h) (and during testing he has dived it to 200kt (370km/h) IAS) and its Va is 120kt (225km/h). Starting his jet like demonstration, Peter flew a lovely smooth loop with a 3g pull from 147kt (275km/h) with his feet clear of the rudder pedals throughout and only the slightest movement of the slip ball as the speed changed. The minimum speed over the top was 56 (105km/h) with no divergence and he exited through his slipstream straight into a 150kt (275km/h) barrel roll. For future reference I just had time to note that the drooped nose was a long way above the horizon while inverted, before he pulled up hard into a stall turn. Deceleration in the vertical was noticeably slow before, at 60kt (115km/h), he pushed full left rudder while simultaneously throttling the left engine and applying a little right aileron. Around we went in a half cart-wheel reminiscent of the great Zurakowski. All standard aerobatic manoeuvres are possible and Peter has even demonstrated his machine’s ability to safely recover from a tail slide. When he had finished I made the error of commenting on the sparkling roll rate, suggesting it must be around 180 degrees a second. This was a mistake for two reasons. First Peter treated me to a discourse on how journalists so often over estimate roll rates without properly timing them, saying the Chipmunk’s is about seventy degrees per second and the Pitts’ little more than 180. (The poor old Cherokee and Tomahawk barely make thirty degrees per second).

Secondly, while he was explaining that the reason for the apparently high rate is simply the aeroplane’s almost instantaneous roll acceleration, without warning he demonstrated this, cracking my head against the canopy as he whipped his machine through a fast aileron roll. I quickly submitted. Later, using my stopwatch, I timed the rate at a remarkably brisk hundred degrees a second. Whatever it is, the effect is nothing short of startling, especially when the aileron feel does not change, however fast you fly.

This took a little getting used to, as did the need for only the tiniest touch of rudder to coordinate turns, but with practice I quickly got to like these controls, marvelling at the way fast pitch and roll action stopped dead beat as soon as you let go because of the aeroplane’s basic stability. It must be the perfect formation mount, something Peter later demonstrated by inch perfect positioning during the photographic sortie. (He also demonstrated its superior controllability, his fighterpilot background and the sheer exuberance engendered by such a machine, attacking our Champ from all angles while I changed films during the prolonged session).

To try out his twin’s performance on one engine, I throttled back the right one and switched off its mags, having to reduce below 60kt (115km/h) in the start of airframe buffet to get the comparatively coarse prop to stop rotating (even then I could see it disobediently flick over the occasional compression when it thought we weren’t looking). At 4000 feet (1220m), with an OAT of minus three, I was able to coax a steady, if gentle, climb from the remaining engine at 78kt (145km/h). With a little left bank and full left rudder (but not a particularly high foot force thanks to the close-mounted engines), reducing the speed back below 60kt (115km/h) into quite marked buffet, I found the Vmcato be well below the clean stall of 65kt (120km/h). The prototype lacks a rudder trim, but future airframes will have an electric one with its motor inside the rudder.

Remembering how hard one has to dive a Cessna 150 to windmill start the same type of engine, it was a surprise to see the dormant prop begin turning as soon as the speed rose above 85kt (160km/h) until I remembered the comparative coarseness of the faster Speedtwin’s props. Flying with the dead engine running, but windmilling, the performance was just the same as with the prop stationary, so one need not try to stop it at low altitude. Closing both throttles for descent at 75kt (137km/h) we indicated 800fpm (245mpm) in a near silent glide, the extreme quietness of the airflow further testimony to the very low drag of this incomparable blue beauty.

The circuit can be flown clean at 90 to 105kt (170 to 195) and as close as you like to the airfield, since it is clearly visible at all times, whichever direction the circuit. The flap limit speed is 95kt (177km/h), the spring loaded switch returns to off, and extension takes five seconds, allowing base leg to be flown at 78 (145). Selecting full flap just before turning final and reducing to 75kt (137km/h), the visibility is peerless, better I think than anything else I have flown. It was remarkably easy to position the untwinlike Speedtwin for a pulse quickening curved approach and it proved agile right down to the last second.

There is plenty of elevator control for a full flare, and the flat topped coaming is very useful for confirming wings level. Even at minimum speed these matchless controls are extremely effective, but the aircraft is not at all twitchy. During the round out its nose is surprisingly low, so the hold off is over before you would expect it, the aeroplane settling gently to the ground in the three point attitude like the thoroughbred it is. There is no trim change as you close the throttles and absolutely no difficulty in keeping straight on the rollout, which was, like the takeoff, satisfyingly short even without using the brakes. There is not even any noticeable trim change on the go around. Peter was politely fulsome in his praise of my flying but, to be honest, this is not a difficult tailwheeler to handle. In fact it is a delight. After a couple more careful circuits, I began to relax and enjoy myself in this entirely predictable and very sprightly machine, occasionally using rather more bank than I ought, and flying an ever tighter pattern. I was having fun flying round and around the airfield, getting to know the aeroplane better and better until Peter pointed out the sun to horizon ratio and gently asked me to stop. It was a very long while since I last got such true pleasure from simply flying circuits.

Peter does not pretend to be a major player in the kitplane business, but he is more honest than some. To reserve an airframe, the customer sends a 10% ($3,800) deposit. This is held by the bank safely in escrow (earning good interest) and not transferred to Peter until construction has started. Then each of the four kits is paid for in turn. Having kept the project a secret for twelve years, the carefully tested design is now finalised, much of the more difficult production tooling is completed and Peter’s small workforce intend turning out kits for half a dozen aeroplanes per year.

Twenty dollars gets you an information pack, while demonstration rides are available for $300 (discounted from the price) to genuine prospective purchasers. The ‘kits’ will be more a collection of completed major components requiring assembly. The entire fuselage will be constructed, along with a pair of wings, empennage, flaps, control surfaces and undercarriage. All composite and plastic parts are included (full canopy, cowlings, wing tips, spats and nose). To meet the homebuilder’s ‘fifty per cent’ rule the purchaser bolts this lot together, installs control runs, instruments and electrics, adds engines and propellers and paints the lot. No special skills should be needed, an instruction manual is supplied and teach- ins could be available. Mind, this will easily absorb the allotted time.

If the builder substituted Norton rotaries, Rotax 912s or similar powered lighter engines it would perform even better, and variable pitch props would further increase performance. This airframe might be ideally suited to a pair of Teledyne Continental’s new 125hp 10-240s, while two 160hp Lycoming 0-320s with v/p props would treble its performance. In the future a three seat version with retractable tricycle undercarriage is a possibility, while Peter talks of military applications and the potential of installing two 400hp Allison turboprops weighing the same as the present O-200s. Although expensive, the thrust to weight ratio of this combination would be greater than unity! Development is expected to allow ‘fully aerobatic’ status and since the aircraft could be self maintained it would cost far less to run than a conventional twin.

There are people who buy an aeroplane for its looks. Some concentrate on the performance specs. Others like the feeling of freedom and power over their destiny conferred by flying. Yet more like to impress their friends with an obviously expensive toy. Some, like the little boy who always wanted to be a train driver, see themselves as fledgling airline pilots. But for many of us aviation is a drug, an addiction to be served at all cost and in any way. Since flying is my sport, my hobby as well as my career, to me no recreational aircraft is worth considering unless actually flying it is a pleasure in itself. Pure delightful handling is the ultimate accolade, and this is one of the few aircraft I have sampled meeting this criterion.

For the connoisseur of fine handling, the Speedtwin is a singular aircraft from a remarkable man.