Duke B60

Fast class

Lovely to behold and rewarding to fly, this sleek six-seat pressurised, turbocharged twin has real presence. Enter a circuit, and all

So, leading with the left throttle and lots of right rudder, I gradually increased the volume to a high-pitched howl and concentrated on keeping the wilful brute on the centre-line.

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Enter a circuit, and all eyes follow that powerful drone. Taxying in, the Duke’s purposeful, nose-low and tail-high stance makes it look as if it is still belting along, but otherwise it is similar to its larger stablem-ate, the King Air. Its proud owner can expect to start answering questions as soon as he parks, for this elegant eye catcher is comparatively rare. Five hundred and ninety six examples of Beech’s macho Model 60 were built during the 14 years between 1968 and 1982, but produc-tion ceased after Beech was taken over by the giant Raytheon corporation. The basic design mated a beefed-up version of the established Bonanza/Baron wing and undercarriage with a new pressurised fuselage, a taller, sharply raked fin and swept tailplanes. The icing on the cake was the use of more powerful (and rather more tolerant) 380hp (283kW) Lycoming engines rather than Beech’s traditional Continentals. These are housed in necessarily substantial squarish cowlings.

From 1971 the improved A60 Duke got lighter, more efficient turbochargers, a better instrument layout, a 23kg gross weight in-crease (to 3075kg) and other minor improve-ments. Incorporating the original optional outboard fuel tanks into the standard system raised fuel capacity from 538 to 765 litres. The final and definitive B60 version, intro-duced in 1974, cost $600,000 and had slightly more interior room, gained by levelling the previously sloping rear floor. Further optional tip tanks gave a 878 litres fuel capacity, and a more reliable King Air type AiResearch pressurisation system headed the list of other minor improvements. The first B60s had an expensive NiCad battery which suffered from poor cooling and only lasted a couple of years, so a lead acid battery conversion soon became available.

I was introduced to the breed by Graham Tickton, a South African enthusiast who has owned several examples. His latest is pristine. It previously had one meticulous owner from new, and even its gleaming paintwork is the un-touched quarter century old original. The Baron-like wing is familiar but with wider flaps. Its skins are flush-riveted to one-third of the chord. Graham had a Boundary Layer Research vortex generator kit, to be fitted once the aircraft was back on the US register. This improves the maximum gross weight to 3177kg (enough for another passenger plus 27kg of baggage), and yet at this higher weight the stall speed is claimed to be 7kt less.

The engines are similar to those in the much larger Navajo Chieftain. They are fitted with beefy 125 amp Lear Siegler generators, either of which provides enough power to start the other engine direct, even if the battery is flat. Each has dual belts for redundancy. The big, three-blade propellers have only 23cm ground clearance, but Graham says this has never proved a problem, even off un-paved African airstrips.

The airframe has full de-icing, with pneu-matic boots on its wings and tail and electric prop mats, and the aircraft is certified for flight into known icing. The workmanship is excellent. Strong as any Beech, the Duke’s structure is certified to 30,000ft, with cabin pressure kept down at 10,000ft while the aeroplane cruises at FL 250.

Everybody boards through a tall door at the left of the rear cabin. Pressing a catch and turning the sturdy handle first rotates retract-able hinges out from under a couple of sprung fairing plates, then releases the latch. Below the door, a single step on a long arm extends with the landing gear. The cabin is quite roomy, with inward-facing club seating for four. This 1980 model B60’s blue and white vinyl upholstery and trim are original equipment, and still in good condition, but now perhaps seem a little dated. The windows are double-glazed and have curtains, and a small table folds away into the right cabin wall. All occupants have lights, air vents, cup holders and (a sign of those times) ash trays, and there are storage bins under each seat. Below the right rear place is a chemical toilet which curtains can be drawn around for privacy. Behind the rear seats a narrow coat compartment will carry up to 32kg (or 64kg with only two cabin seats occupied). Expensive aircraft like Dukes tend to be fitted with all available options. This example was no exception, and its com-prehensive array of equipment (includ-ing air conditioning and full de-icing) pushed its empty weight up to 2155kg. But it still had a very good useful load of nearly a tonne, although payload inevitably has to be balanced against fuel. Full-mains payload is 370kg, allowing carriage of four mixed-sex occupants with 62kg of luggage, giving 1000nm range in five hours at 220kt. Filling the aux tanks as well would limit passengers to 288kg (three big men and a few bags) but would allow a tremendous 1200nm to dry tanks at 65 per cent power. Alternatively six people with 68kg of baggage could still carry fuel for over 700nm. Mechanical sight gauges on the upper wings outboard of the nacelles help greatly with such partial-fuel loads.

The aircraft has a tolerant centre of gravity range, helped by the restricted capacity of the rear coat space. Instead the cavernous 0. 9m3 baggage compart-ment in its long nose holds a whopping 227kg (including avionics). You could get a couple of people in here, and it is even big enough to take several sets of skis or golf clubs, thanks to a neat nose-wheel retraction mechanism, which twists the wheel to lie flat below its unobstructed floor.

Undoubtedly the pilots have the best seats in the house once they have squeezed into the cockpit, thanks to the neat collapsing armrests. Their backs have large pockets, and a storage space below these is large enough for even the biggest chart folders and flight bags. Between them on the spar carry-through are the two three-position (on, off, crossfeed) fuel selectors. The seats are comfortable and adjustable, and the forward view, although limited by the high coaming and low windscreen tops, is quite adequate, and not unlike an airliner’s. At first sight the cockpit seems a trifle crowded, but all the controls and switches are systematically grouped on black sub-panels round the light blue instrument panels.

This Duke has two full panels, with a comprehensive array of Collins Micro- Line avionics in two stacks in the middle. The five main engine gauges are spread across the top, where they are easily seen, and there is an eight-light annunciator panel directly above the left ADI. The engine levers share a compact central quadrant with the Century IV autopilot controls. They are laid out as in modern twins with, from left to right, throttles, pitch controls and mixture levers. (Earlier Beechcraft had them aligned in the piston airliner order of props, power and mixture).

The landing gear switch is left of centre on the lower sub panel, while the three-position (up, approach, land-ing) flap switch and its three indicator lights are to their right. The gear, flaps and cowl flaps are electric, and the wheels extend and retract with typical Beech rapidity in just four seconds. They can be dropped with fifteen flap at up to an amazing 175kt for a quick speed reduction or descent.

A heavy, three-tonne aeroplane must put a strain on its landing gear, and undercarriage collapses have been a problem from time to time. One cause is inadequate maintenance of the mo-tors, which lose torque if the brushes become worn, causing the circuit breaker to trip just before the wheels are fully locked down. Firing up the big six-cylinder Lycomings is no more difficult than starting a car, provided you wind them up with the mixtures in lean, then go to rich once they are turning. They sound a great deal better than any road vehicle, so you can revel in the impatient thrum of their three-bladed props. Release the park brake hidden behind the yoke and apply a squeeze of power and the Duke moves off majestically. The steering is quite light, but a spring in the system gives it a slight lag. This makes a dab of differen-tial brake and a burst of outboard engine power useful on the tighter corners.

This brawny beast was built before the advent of namby-pamby counter-rotat-ing props, so when you open the taps the combined thrust of the full 760hp (567kW) all wants to drag you off to the left of the runway. That weak steering spring does not help, and Graham’s solu-tion is to start the takeoff pointing ten degrees to the right of runway heading. So, leading with the left throttle and lots of right rudder, I gradually increased the volume to a high-pitched howl and concentrated on keeping the wilful brute on the centre-line. There is no need to modulate power, the automatic waste-gates do that for you, and the Duke just thunders away, nose-down and bellowing, like a bull at the charge.

I had suspected such a heavy aeroplane might use a lot of runway, but Graham again showed me the solution. He counters the negative angle of attack by holding the weight off the nose slightly as the elevator came alive. With this technique and rotating positively at 85kt, we used perhaps 600m of runway. Whipping up that speedy gear and setting the cowl flaps to trail helped us accelerate rapidly to the 120kt best climb rate speed. Reducing power to a smooth but vocal 36in and 2750rpm, we thrummed up-wards at a very respectable 1700ft/min. With just three men aboard and 218kg of fuel, we weighed perhaps 2650kg, or 450kg less than the 3073kg maximum. The published full-power climb rate at top weight is 1600ft/min, and the Duke will maintain this well up to the mid tens of thousands of feet. Graham says he routinely climbs to 24,000ft in under 30 minutes from a max weight takeoff.

At 5000ft with 30in and 2500rpm we ate up the countryside at 167kt IAS (175 TAS) using 51kg per side per hour (the fuel flow dials are also calibrated in percentage power). Normal cruise is a highly competitive 220kt (TAS) with 70 per cent power at 24,000ft, still using 51kg/hr a side, or 144 to 151 litres/hr to-tal. Reducing to 55 per cent power burns just 114 litres/hr, but the speed drops to 185kt (which is still fast), and there can be a problem keeping the cabin pres-surised at high altitude with such a low power setting. The air conditioning works well (and does not have to be switched off on takeoff) while the optional propel-ler synchrophaser eliminates annoying prop beating.

The aircraft is smooth and comfort-able, with almost no vibration, and its high wing-loading ensures it rides the bumps well.

Because the engines and props are set well forward the internal sound level is never high, and quickly drops as the pressurisation gets to work. It was soon possible to hold a normal conversation between the cockpit and rear seat occupants. The Duke is very stable in flight, although its controls are perhaps a mite heavy. With classic harmony, the ailerons require the least pressure to move, the elevator is heavier, and the rudder, while highly effective, is the heaviest. If you make enough effort (and add a touch of rudder) the aeroplane will roll quickly, but at its normal high cruise speeds it does have a large turn radius. Elevator loads are soon relieved by the electric trim, and visibility is fine at up to 45 degrees of left bank, but is restricted by the roof at over 30 degrees to the right.

Stability is good in all axes, even in yaw without the yaw-damper (which comes as standard). Switching it back on immedi-ately kills any wiggle which might take a second or so to stop naturally, and roll stability is dead-beat, meaning that after rolling on some bank, once you let go of the wheel it stays put.

To sample its single-engine handling, we reduced power on the left engine (the critical one) to zero thrust by pull-ing its pitch lever to the feather detent and setting 12in of manifold pressure. At the Vmca of 85kt a significant right rudder pedal pressure was needed, but this was quickly trimmed out. At the 110kt blue line speed (for best single-engine climb rate) the VSI showed a steady and most impressive 600ft/min climb at 4000ft at our weight of approximately 2630kg. Sea level ISA single-engine climb rate at max weight is claimed to be over 300ft/min, which is unusually good. The rudder force, although high, could be held without trimming, and it was easy to pin the exact speed. Single engine ceiling is 15,100ft.

Stalling revealed no surprises. The Duke has a high wing loading, so the comparatively high 73kt clean stall speed and 20 degree left wing drop were expected. The horn preceded this at 83kt and there was some aerodynamic buffet just a couple of knots before the break. With gear and full flap the horn stayed quiet until 80kt, and the shuddering break came (after a high pull force) at 60, again with a sharp, but easily controlled wing-drop.

Descent is made at cruise power to retain engine heat, and it is wise to anticipate slow-ing this fast, heavy machine before sweeping imperiously into the circuit. Downwind is best flown at 120kt, using 25 to 30in and 2400rpm, with gear and approach flap (15 degrees, indicated by a blue light). Both gear and flap extension cause minimal pitch changes, and the flap switch has to be pulled out to get the second setting (30 degrees, indicated by an amber light – the red light means in transit). Visibility is fine in a left hand circuit. Initial approach is established at 110kt with 24in, in a slightly nose-down attitude, reducing to 85 on short final. The aeroplane seemed to be a good, solid instrument platform, and was very speed-stable and surprisingly easy to control. The Duke’s mass coupled with the engines’ high 1000rpm idle (set for Johannesburg’s 6000ft altitude) meant we in-evitably floated a couple of hundred metres after my flare (which needed quite a pull). The gear legs are surprisingly short and stiff, so when we finally settled we contacted the ground with a bump, but easily stopped within 700m with little braking, and no directional problems.

These sleek, sexy aeroplanes usually have proud pilot-owners, who love them dearly. But (like any other powerful pressurised twin) a Duke can be costly to run, most of this expense being incurred by the avionics. The early cast iron turbocharger housings used to crack, but most of these have long since been replaced by an improved stainless steel type. There have also been problems with cylinder head cracking, but this is mostly due to unsympathetic engine handling. The original engines were ‘throwaway units’, only expected to last 1200 hours between overhauls, and early (pre no 781) crankcases tended to crack, but motors built since 1974 have a 1600 hour TBO, and some last as long as 2000 hours. Early 60 and A60 models had short exhausts, causing flap corrosion problems, but the later B60’s longer tail-pipes give the flaps better (although not absolute) protection.

Exclusive and highly desirable, the Duke is a fast, nice-to-fly, stratospheric mini-airliner which clearly means business. It has long been known as “The Mercedes Benz of twins. ” Although a little costly to maintain, this just adds to its exclusivity in the eyes of its devotees. For me this splendid aeroplane remains `the twin with attitude’.

Beech Duke B60

(Technical specs)
Powerplants
Two six-cylinder, turbosupercharged,
horizontally
opposed 541cu in
Lycoming TIO-541s, each
producing 380hp (283kW)
at 2900rpm. Propellers
Hartzell fully feathering,
constant-speed, threeblade
aluminium.
Performance
(Manufacturer’s stated)
Max speed (TAS, midweight,
25,000ft) 246kt
(74%) cruise speed (same
conditions) 233kt
Long range cruise @
15,000ft 199kt
Stall (full flap) 72kt
Range at 74% power
(std tanks) 1045nm
Service ceiling 30,000ft
Takeoff distance 800m
Landing distance 934m
Weights
(test aircraft)
Equipped empty 2155kg
Max takeoff & landing
weight 3073kg
Useful load 918kg
Useable fuel 764l
Optional fuel 878l
Baggage 227kg
Dimensions
Length 10.31m
Height 3.76m
Wing span 11.96m
Wing area 19.78m2
Cabin length 3.61m
Cabin width 1.27m
Cabin height 1.32m
Manufacturer
From 1968 to 1982,
Beech Aircraft
Corporation, Wichita,
Kansas, USA.