Peter Henley/MOSES LAKE, WASHINGTON
Embraer's RJ-135 is a logical and economical derivative of its successful stablemate - the 50-seat ERJ-145 - with the fuselage shortened to reduce the capacity to 37 passengers.
The ERJ-145 has taken the regional airline market by storm. Following the trail blazed by Bombardier's Canadair Regional Jet, it has offered the passenger appeal of a turbofan-powered aircraft to a marketplace that is accustomed to the compelling economics of turboprops. At the same time, Embraer claims operating economics which can rival those of the turboprop. Its decision to base the design around the fuselage of the EMB-120 Brasilia 30-seat turboprop reduced development and production costs, while keeping systems as simple as possible reduced operating costs. Now, the Brazilian manufacturer hopes to repeat the formula in the even more cost-conscious 30/40-seat market.
The ERJ-145 grabbed the attention of the regional airlines and has sold well, with 172 orders and 67 aircraft delivered to date. There is no doubt that Embraer had a degree of luck on its side. By the time the ERJ-145 entered service in December 1996, public opinion had hardened considerably and a preference for jet-powered regional aircraft was rapidly becoming a demand. Embraer was also aware that regional airlines were enjoying significant increases in load factors after introducing jets.
All this was sufficient encouragement to launch a further onslaught on the turboprop by aiming at the 30/40-seat sector of the market with a smaller regional jet. Embraer decided to shrink the ERJ-145's fuselage (which it had so recently stretched from that of the Brasilia) by removing the two plugs that had been inserted and substituting shorter ones. The overall reduction in fuselage length is 3.5m.
DESIGN TARGET
The design target was 95% commonality between the ERJ-145 and -135. The advantages are enormous. First, there is the economy of scale - the predicted production run has been doubled, allowing Embraer to negotiate lower prices with suppliers. Minimum change also means minimum certification costs and, by minimising upfront investment, Embraer is able to sell the ERJ-135 at a competitive price while keeping the cost of ownership low. For ERJ-145 operators, the benefits are even greater: the same spares stocks can cover both models and pilot type ratings can be common to both.
Reflecting the minimum changes, the new aircraft, for certification purposes, is referred to as an ERJ-145 Model 135, although it is marketed as the ERJ-135. The commonality is exemplified by the first development aircraft, which was once the first ERJ-145 prototype and, as such, was used for Flight International's flight test (3-8 July, 1996) when the aircraft was still known as the EMB-145.
Certification is scheduled for May 1999, with deliveries beginning in July. The $12 million ERJ-135 can be considered already to be a success, with commitments received for over half of the 500 aircraft Embraer expects to sell. While orders stood at 73 (and options at 122) by early August, including 25 (plus 50) for existing ERJ-145 operator Continental Express, American Eagle - another -145 customer - is expected to announce at Farnborough orders and options for up to 150 aircraft. Even before the Eagle order, Embraer is close to its 80-aircraft break-even point on the ERJ-135 programme with first deliveries almost a year away.
After surgery to shorten the fuselage, the aircraft first flew as the ERJ-135 prototype on 4 July. Apart from the airframe length, it is otherwise unchanged from the original EMB-145 configuration. Production aircraft will have minor changes, such as different valves for the pressurisation system (as it will have to serve a smaller volume). Certification flying is concentrating on handling and performance because the commonality of systems between the two aircraft means little work is needed here.
Aircraft 801 was dispatched early in its new life with a team of pilots, flight test engineers and maintenance personnel from the Embraer plant in San Jose do Campos, Brazil, to Moses Lake, Washington, USA, to carry out runway testing. The long journey was undertaken because Moses Lake is an erstwhile US Air Force B-52 base with runways 3,965m (13,000ft) long by 106.8m wide - over twice as wide as a standard runway. These vast runways are ideal for trials to establish minimum control speeds on the ground and minimum unstick speeds (VMU). The area is also relatively sparsely populated and there is only a nominal amount of local flying.
The runway trials require still air, so development flying tends to happen early in the morning and in the evenings. Flight International was invited to fly the ERJ-135 during the day, when both it and its crew were not too busy.
It has to be said that the ERJ-135 looks better proportioned than its longer brother. Although a development aircraft, 801 has been refinished to a high standard in Embraer house colours. The only blemish to its elegant looks is the large and robust tailskid attached to the underside of the fuselage to protect it during VMU tests. The cabin is packed with the usual test paraphernalia - flight test engineer stations and water ballast tanks. The cockpit is as it was two years earlier for the ERJ-145 evaluation, including development instruments indicating g, angle of attack and sideslip.
It is worth emphasising the strong points that the ERJ-135 shares with the -145, which were explored in more detail in Flight International's technical description (18-24 October, 1995) and flight evaluation of the 50-seat aircraft. First, there is the obvious thought that has gone into making turnround servicing easy by facilitating simultaneous access for refuelling, catering, baggage handling and lavatory servicing. Then there is the cockpit: both attractively snug and relatively small, but easy to enter and leave because the seats swing outward at the limit of their rearward travel; there are electrical controls for seat height and recline and for rudder pedal reach. The cockpit is compact and its suite of five Honeywell Primus 1000 display panels make it feel more like a business jet.
Taxiing the ERJ-135 is a delight; it is even nicer than the -145, presumably because it has a shorter wheelbase; the -135's nosewheel steering has greater deflection than that of the -145, tightening its turning circle.
| EMBRAER RJ-135 | ||
| SPECIFICATIONS | ERJ-135ER | ERJ-135LR |
| Length overall | 26.33m | |
| Wing span | 20.04m | |
| Height overall | 6.75m | |
| Powerplant | R-R Allison AE3007A | |
| Power (each) | 10,000lb | |
| Basic operating weight | 11,130kg | 11,230kg |
| Max payload | 4,770kg | |
| Max take-off weight | 19,000kg | 20,000kg |
| Max cruise speed | 450kt/Mach 0.78 | |
| Range (37 passengers) | 2,200km | 2,930km |
NOTE If no figure is given for the ERJ-135LR, then it is the same as the ERJ-135ER
DEREATED ENGINES
The Rolls-Royce Allison AE3007 engines are available in two standards - the basic A or uprated A1 - exactly as with the -145, but, in both cases, derated because the -135 is lighter and has less drag. The derating is about 5%, but varies in different flight phases (take-off, climb and cruise, for example). The A1 engine is retained to offer longer range as a customer option. The A1 has no derating of climb thrust, which enhances the ERJ-135's rate of climb in the extended range profile. A good rate of climb together with high airspeed is seen as an advantage in high-density airspace, providing quicker times to cruising altitude and an earlier escape from more-congested lower levels. Programming of the full authority digital engine control (FADEC) is consequently slightly revised in the ERJ-135 to accommodate these different thrust ratings. In practice, however, the ERJ-135 behaves exactly like the -145 on take-off.
Moses Lake's elevation is about 1,100ft, the temperature was +36°C, the weather was fine and there was a southerly breeze. The aircraft weighed 15,300kg (33,700lb) against a maximum take-off weight of 20,000kg. Embraer test pilot Sergio Mauro Costa occupied the right seat, and I flew from the left seat, while Luis Rodrigues sat on the jump seat as safety pilot. Alexandre Figueiredo, the flight test engineer, was at his console in the cabin. There was 3,000kg of fuel on board. Flaps were set at 9í and the resultant take-off speeds were V1/VR (decision speed/rotate) 118kt (220km/h) and V2 (climb safety) 126kt. The centre of gravity (CG) was just aft of the mid-point.
The engine power was set for take-off, the engines spooled up rapidly and the ERJ-135 accelerated smartly. The aircraft was rotated easily and then unstuck cleanly. The control force to rotate seemed lighter than I remembered for the ERJ-145, probably because, on this occasion, the CG was more favourable. The climb attitude of about 14¼ nose-up pitch was easy to establish, maintain and trim. Retracting the undercarriage and flap after take-off caused no discernible trim change. Pressing a mode button behind the power levers, on the centre console, commanded the FADEC to set and maintain climb power.
The aircraft was flown manually to 37,000ft. During the climb it was obvious what a pleasant aircraft the ERJ-135 is to fly. The aileron break-out force is low and the roll control light and powerful. The pitch control forces required were slightly higher than those for roll, but not unpleasantly so. The rudder was powerful and required forces similar to those for the elevators. At 15,000ft and 250kt, with the yaw damper off, a Dutch roll mode was excited with a rudder pedal "doublet", and was damped naturally in about three cycles. With the yaw damper operational, the result was dead beat. Passing through 27,000ft at a temperature of ISA+11°C, 500kg of fuel had been used since engine start.
At 37,000ft, two 60°-bank turns were flown at Mach 0.7 and 1.8g in an attempt to provoke stall buffet; none occurred. The aircraft was then accelerated, wings level, to M0.775 and pulled up at 1.5g, which caused no Mach buffet. It would seem that the ERJ-135 can be flown confidently at these altitudes without risk of encroaching on the buffet boundaries.
Descending towards middle altitudes for further handling evaluations and with the power levers closed, at M0.7 and 35,000ft, the airbrakes were selected out (they are either in or out, with no intermediate setting). There was a small trim change and a little burble. The rate of descent was 5,500ft/min (28m/s).
In a block of airspace between 15,000ft and 17,000ft, the aircraft was trimmed at 250kt, with power to maintain that speed, and then rolled from 45¼ of bank to 45¼ of opposite bank. The roll acceleration and rate of roll were impressive; the manoeuvre took 2s.
Next, two stalls were carried out. The first was clean, power off. The trim speed was 138kt, the stick shaker activated at 112kt and the stick push came at 108kt. The second stall was with undercarriage down and full 45° flap. The trim speed was 121kt, the stick shaker activated at 96kt and the stick push came at 91kt. In both instances, aircraft handling was good, with roll control remaining effective to the stick shaker. Care had to be taken during the standard recovery not to provoke a dynamic stall at about 135kt by pitching up into the climb too aggressively.
TRIM CHANGE
While at these middle altitudes I took a look at trim change with acceleration. Starting at 135kt, with take-off power selected and the aircraft trimmed, the ERJ-135 was allowed to accelerate to 250kt in level flight. As expected, the nose tended to pitch up. Level flight was maintained with down elevator, held and not re-trimmed. At 230kt, the stick force required was 15kg, rising to 20kg at 250kt, when this stick force was quickly and easily trimmed out.
A designer has to consider handling characteristics at high speeds and altitudes and at speeds low enough to enable the aircraft to use a 1,500-1,800m runway - while being conscious of characteristics when the aircraft moves from one regime to the other. The issue is how much trim change results with acceleration and how easy it is for the pilot to hold the stick force, and how quickly he can retrim the aircraft as it accelerates. In the case of the ERJ-135, this characteristic was acceptable. It may be that automatic longitudinal trim will eventually become available to pilots, possibly using the autopilot servos and capable of being switched in or out manually in the same way as yaw dampers usually are.
Exploring the trim change found that the flaps and undercarriage were extended in turn at slightly less than their limiting speeds. The undercarriage can be lowered at 250kt or less - a usefully high limiting speed - and caused a slight pitch change. The extension of flap to 9¼ at 250kt, 22° at 200kt and 45° at 145kt caused very little pitch change or ballooning.
For the recovery to Moses Lake, the autopilot was used, although it is not yet to production standard. Radar vectors to the instrument landing system, using the autopilot and manual power control, worked well. Following a touch-and-go landing, Costa simulated an engine failure by closing the left engine power lever to flight idle, after which a visual simulated asymmetric circuit (traffic pattern) was flown, followed by a final two-engine circuit and full-stop landing. On this last landing, reverse thrust was selected at about 90kt by lifting latches on the power lever stems. Reverse was cancelled at about 50kt. The aircraft was smoothly retarded.
During the lower-speed handling in the circuit (typically between 130kt and 180kt) a little of the magic deserted the handling. This seemed to be because of roll-induced yaw which had not been evident at higher speeds. Co-ordinated use of rudder in lower-speed turns helped to restore the precision of the handling. It is not a technique commonly required with modern jets under these circumstances, but should easily be acquired by pilots regularly flying the ERJ-135.
An obvious rival is the Fairchild Dornier 328JET, and much is being made of the different rates of climb of the two aircraft. Flight International's evaluation of the 328JET (1-7 July) indicates that the aircraft is going to have an impressive rate of climb to cruising levels: Embraer clearly intends to enhance the ERJ-135's climb performance by scheduling the maximum thrust in this mode with the optional AE3007A1 engine. With both due to enter service next year, the 30-seat regional airliner market will be fascinating to watch.
Source: Flight International
