Airtest – Beechjet

Beech had limited success in the early seventies with the Beech Hawker 125, having delivered 65 aircraft before they terminated the sales agreement in 1975. The company felt that this aircraft type represented too great a step up from the King Air. During their search, several aircraft appeared to be available. These included the Canadair Challenger and the Gates Learjet; however, whilst both these aircraft were excellent products, Beech was looking for an aircraft, not a production facility. Their search ended with Mitsubishi Aircraft in Texas. These aircraft had their airframes manufactured by Mitsubishi Heavy Industries in Japan, one of the most experienced airframe producers in the world. The airframes were then shipped to the USA for completion. This was an ideal set up so Beech acquired the Mitsubishi product line. The MU2 would be discontinued but the Diamond II was just what the doctor ordered. Here was a strongly constructed seven passenger light to medium jet transport with further development potential, excellent performance and carried a long standing Beech characteristic – an oval cabin.

When Mitsubishi first considered participating in the entry level jet market they wanted an aircraft that could compete with the two market leaders – the Cessna Citation and the Gates Learjet 20 series.

The design perameters were for a 14,0301b gross takeoff weight aircraft capable of 435kts. A standard day range of 1,500nm with a balanced field length of 4,100 feet and a 1,000nm range after a hot and high departure. It would be a swept wing design with a roomy cabin and powered by Pratt & Whitney JT 15D-4 powerplants of 2,500lbs thrust each. This all looked great, however, during the certification process the aircraft managed to increase its empty weight. Part of this was due to requests made by the FAA and part of the blame lay with the manufacturer for not paying close attention to weight saving details. So to maintain their desired range projection the engineers increased the gross weight by 6001bs, making the new GTOW 14,630lbs. The increased weight naturally had a detrimental effect on the aircraft’s wing loading and power loading. Whilst standard day sea level performance was quite acceptable, higher temperatures and elevations placed an unacceptable second segment climb penalty on the Diamond I. Indeed with an 800lb payload and full IFR reserves, the aircraft had a range of about 350nm!

The Diamond I received its FAA Part 25 Type certificate on 6 November 1981. Sales were sluggish and the aircraft consequently attracted a reputation as a poor performer. The Mitsubishi engineers quickly set about rectifying this situation and through their performance enhancement programme introduced a number of retrofitable fixes. Obviously power to weight ratio was a priority. The most significant change was the use of the Pratt & Whitney JT15D-4D engine. Whilst this engine still produces the same 2,5001bs of thrust that the -4 produces, the -4D can produce maximum thrust under ambient conditions of 10°C higher. In addition there were a number of operational changes to enhance performance, the aircraft was thus certified for takeoff with its environmental control system switched off thus leaving more power for thrust on a hot day. Additionally, the FAA granted Mitsubishi approval to increase their V speeds to produce a better second segment climb on a hot day albeit at the expense of runway length. There were also a number of detailed changes involved with the aircraft and it virtually became a mature and developed model of the Diamond I which is now known as the Diamond IA.

From the outset Mitsubishi were looking toward a family of business jets. The Diamond IA had its market but now it was time to introduce the vastly improved Diamond II. Whilst this aircraft bore a strong resemblance to the IA it differed significantly in the areas of powerplant and performance. This aircraft would be an honest competitor to the Learjet in terms of performance and the Citation in terms of economy. The Diamond II earned its FAA Part 25 Type Certificate of 30th April 1985. And with just two STC’d modifications (external baggage and additional fuselage fuel tank) the aircraft is now known as the Beechjet 400. The original agreement still had Mitsubishi Heavy Industries producing the basic airframe, albeit out of American aluminium, however the Beechjet is now wholly produced in North America.

When Beech first acquired the Mitsubishi Aircraft operation, they took delivery of five assembled airframes, of these one was painted and sold as a Diamond II. One was stripped and gutted and had a new Beech designed interior installed in it as did the remaining three aircraft. This interior is now the standard for all Beechjet 400 aircraft.

Beech have always had a very high standard of finish in their interiors and the demonstration aircraft that I flew was no exception. Of instant recognition to King Air owners are the polarised windows which allow a passenger to permit just the right amount of sunlight into the cabin. The standard interior arrangement has a three place bench at the rear, a club seating arrangement of four individual chairs and a forward potty that is partitioned, with solid sliding doors, from the rest of the cabin when in use. There is a carry on baggage area ahead of the main entrance door and opposite the toilet. Directly opposite the entrance door is the galley area, the whole layout is well planned and quite roomy for an aircraft of this size. In fact, the Beechjet provides 26% more cabin volume than the Lear 35A and 24% more than the Citation SIi. Additionally, the Beechjet has more headroom than either of these aircraft even though it has a flat floor. Through clever use of noise absorbing materials and with the installation of the one piece headliner and sidewall on non-rigid mountings, Beech have significantly reduced internal noise levels.

Moving forward to the flight deck, Beech have lengthened this compartment by 2 inches making it large enough to accept even the tallest of airframe drivers. The general panel layout is standard and easy to follow. Most circuit breakers are on the lower left hand panel next to the captain and most system switches are located in a well laid out overhead panel. Visibility on the ground and in the air is excellent. Auto-pilot, navigation and communication radio controllers are located in the extended centre pedestal and are easily accessible. There is room for a dual long-range navigation system installation at the front of the pedestal, although most aircraft would carry only the one unit.

The Beechjet does not have a tiller as a means of directional control on the ground which is achieved directly through the rudder pedals. This is a simple and very effective system. The overall feel of the flight deck is quite comfortable.

The fuselage is of conventional semi-monocoque construction, and like all Mitsubishi aircraft structures, built with extreme strength. The swept wing is of an advanced design, again of semi-monocoque construction, but it has a milled carry through structure and twin u-shaped carry through beams. Fowler flaps also extend for 80% of the spar to provide lower approach speeds. Roll control is achieved through spoilers as per the MU2, and these, as are the rudder, and elevator are actuated through steel cables and pushrods. The spoilers can also be activated hydraulically. Roll control is very positive and easy to manipulate and the spoilers produce the same feel on short finals at V Ref as they do at high altitude and M. 78. There is however, a very marked difference once the speed brakes are extended, roll control is suddenly heavy but still manageable. Another unique feature is the yaw damper. This is actually a separate control surface above the rudder, although the aircraft flies quite well with the yaw damper disengaged. Trim is electronically actuated by a convenient four directional switch located in the top of each control column.

There are two separate engine driven hydraulic pumps providing 1,500psi to the modular hydraulic system which powers the landing hear, gear doors, flaps, anti-skid/power brakes, speed brakes, lift dump and thrust reversers if installed.

The electrical system based on a dual parallel bus power distribution system is fed by a single 24V DC 36 amp-hour Ni-cad battery, and two 30V DC 400 AMP starter generators. AC power is available from two 450 VA solid state inverters. Management of this system has been simplified through the use of colour coded circuit breakers, automatic load shedding and single switch control of essential equipment.

The undercarriage of the single wheel, tricycle type is hydraulically actuated and held up by mechanical positive uplocks. Emergency extension is a free fall system. As mentioned earlier, nosewheel steering is accomplished through a direct mechanical linkage with the rudder pedals giving a turning circle of just 40ft, curb to curb. The anti-skid system is hydraulically actuated with a pneumatic back up.

The fuel system has a capacity of 4,904Ibs and is stored in two independent integral wing tanks and an aft fuselage tank. Two jet pumps with back up electric boost pumps feed the two engines whilst the electric pumps also provide crossfeed and transfer capabilities.

The 9. 1psi pressurisation system provides a sea level cabin to 24,000ft and a 6,400ft cabin at 41,000ft. An air cycle machine provides environmental temperature control in the air and there is an optional freon airconditioning system for ground operations. There are separate climate controls to allow the temperature in the cabin to be varied from that on the flight deck.

The heart of the Beechjet’s performance comes from its Pratt & Whitney JT15O-5 turbofan engines. This engine is flat rated to deliver 2,900Ibs of thrust at sea level up to a temperature of 27°C. The fan blades are of a wide chord design for optimum high altitude performance and proof of the efficiency of these engines is evident when one compares the -5 with the -40 fitted to the Diamond IA. At FL410 the -5 will actually produce 25% more thrust whilst providing a 5% lower specific fuel consumption. Pratt & Whitney have also redesigned the nozzle allowing the mixing of the secondary fan airflow with the core’s primary hot airflow aft of the powerplant exhaust exit. The engineers claim that this new system provides more thrust and also reduces specific fuel consumption. To enhance reliability the -5 also incorporates directionally solidified first stage turbine blades capable of absorbing higher ITT temperatures. This should prove to be an excellent airframe powerplant match.

Meanwhile, Hawker Pacific’s Beechjet demonstration pilot, Captain Rod Mendham had lodged a flight plan that would take us over Katoomba and Parkes, thence Cowra for some circuit work then home to Sydney, the flight outbound would be at FL410. Rod and I strapped ourselves in and proceeded with the checklist. The start was a relatively easy procedure – depress the start button, wait for the airflow to stabilise and at 10% N2 bring the power lever forward out of idle cutoff. We started the second engine and completed our checks and obtained a taxi clearance. The visibility out of the Beechjet is excellent and that together with the direct nose wheel steering makes the aircraft very easy to control on the ground.

Standard takeoff procedure requires 10° of flap, and as there wasn’t too much traffic around so I opted for a maximum rate climb departure out of Sydney. With a deck angle in excess of 25° the Beechjet was climbing like a homesick angel. This performance was excellent and what may have been an ordinary flight in another aeroplane suddenly became a very pleasurable experience. The handling of the Beechjet is excellent – it is so easy to fly precisely that instrument flying actually becomes a real pleasure. The pilot’s workload is minimal and the Supervisory Electronic Fuel Control System makes it even easier once one sets the power. This system maintains the desired setting without any tendency to creep. automatically compensating for temperature and density. I would like this system introduced on our Garrett TFE731’s.

After clearing the Sydney zone and leaving 10,000ft we settled to a normal climb of 220 KIAS until it read M. 64 and maintained that Mach number to FL41O where we quickly accelerated to M. 78. This cruise translated to 445 KTAS with a total fuel flow of about 1,000lbs/hr – very impressive. I spent quite a bit of time hand flying the Beechjet and found it without vice in all regimes of flight. The spoilers offer precise roll control even when conducting steep turns at 41,000ft. We also had the opportunity to sample the speed brakes on our descent into Cowra. This gave a rapid controlled descent with only slight pitch trim required. The roll control, however, was now quite heavy by comparison. Incidentally, the windshield on the Beechjet is made of glass and permanently heated thus visibility remains excellent from high altitude to saa level – Learjet pilots would appreciate this.

Handling at low level was just as it was at FL410 – precise. After some more handling trials and a few viceless stalls, we continued our descent into the Cowra circuit area. 200 KIAS is the speed at which you can lower the gear and deploy 10° of flaps. Landing flap can be lowered at 170 KIAS. The wind at Cowra was light and variable so we could choose either runway. We decided on a full stop landing on runway 33. The aircraft handled very well and I was quite surprised at how quickly we pulled up. The demonstrator did not have thrust reversers fitted, yet stopping on brakes alone was more than adequate. We did a few more landings and then departed for Sydney where I flew an ILS. With the aircraft stabilised and the power set at 60% N1 the Beechjet will virtually fly itself down the ILS. The Beechjet should prove to be an excellent entry level jet for Australia. King Air pilots will have very little trouble in upgrading to the senior member of the Beech family and they will certainly enjoy the extra performance of the jet. The demonstrator has since been sold to Hornbill Skyways or Sarawak in Malaysia. This is a pity for Australian operators as this aircraft did represent excellent value. However, life must go on and Hawker’s have already ordered a replacement demonstrator and this one will have a full EFIS flight deck.