Peter Henley/MARIETTA
The C-130 Hercules has been in service with military and commercial operators around the world since the 1950s. Demand for the type has been such that it has stayed in production throughout that period. It has appeared in various guises since the original A model. The major reincarnations have been as the H model for the US Air Force and the K model for the Royal Air Force, but there have been other less prolifically produced models and several specialist modifications such as gunships and weather-monitoring aircraft. The Hercules has, at various times, been fitted with skis to allow it to be operated from snow-covered terrain, stretched by implanting an extra 4.6m in the length of the fuselage and been equipped for airborne refuelling.
Most military customers have bought the C-130 as a tactical transport. The aircraft's roles include airborne assault - paratrooping, platform delivery of weapons and supplies and freefall delivery of small, robust items. Rugged construction and excellent short-field performance have given it an outstanding air-landed assault and resupply capability. Its combat successes have been achieved during the Vietnam War and in numerous lesser skirmishes, and the aircraft has starred in many television reports in its humanitarian roles, being used to deliver food and supplies. Its range of just over 3,200km (1,740nm) with a useful payload has endowed it with a useful capability. Military and commercial owners have successfully used it as a medium- sized cargo freighter.
SOUND DESIGN
Such pre-eminence throughout more than four decades says much for the aircraft's original concept and design. It also reflects the absence of any serious competitors during that time. The European Future Large Aircraft (FLA) has yet to become a cohesive, defined and funded project. Like the Douglas DC-3, the DH Chipmunk and the Boeing 727, the C-130 Hercules is a difficult aircraft to better.
Modern technology has now given the C-130 yet another lease of life. Starting from the premise that the airframe remains more than adequate for the roles it has traditionally filled so well, Lockheed Martin has concentrated on improving mission effectiveness. The heart of this improvement is a mission computer allied to electronically controlled engines and propellers, 1553B databus architecture and digital avionics. The result is a two-pilot cockpit that is without the customary air engineer and navigator (although the flightdeck retains a third seat for an additional crew member if required), modern systems management, improved navigational capability, better situational awareness and enhanced short-field performance.
Situational awareness and mission capability are specifically improved by head-up displays (HUDs), station-keeping radar with three-dimensional separation cues (ie distance from other aircraft in the formation in cloud or at night shown fore and aft, laterally and vertically) and a topographical-map display. The C-130J is intended to be flown using the HUD as the primary instrument reference with the head-down cathode-ray-tube (CRT) displays for altitude and horizontal situation as back-up.
The C-130 flight line looked almost identical to that of the mid-1960s when I first saw it during the procurement phase for the RAF's fleet of C-130Ks. The only immediately obvious difference today is the six-bladed, composite Dowty R391 propellers which are fitted to the C-130Js awaiting flight test before delivery.
Entering the cargo compartment of the C-130J brings no surprises as it is much like earlier versions. The cockpit is still approached via a near-vertical ladder, and the two crew-rest bunks are still at the rear of the cockpit, and there is still a crew position where the navigator traditionally sat. There is no fold-down floor panel to cover the ladder well: the galley has been turned through 90í so that the working aspect faces into the cockpit - instead of over the ladder as before. The wonderful "windows-everywhere" concept is retained, so that the C-130's exceptional field of view remains undiminished. The control yoke, the nosewheel steering wheel and the parking brake handle are discernibly traditional C-130 items - otherwise the cockpit is very different.
The main instrument panel is large, angular and uncluttered - almost spartan. There are four large vertical-format cathode ray tubes (CRTs), two side-by-side in the centre of the panel, with one in front of each pilot. The wide centre console is retained, but the engine-condition levers have gone and four tall and unadorned power levers rise above it. The overhead panel has been lowered so that it can be reached comfortably by the pilots, but most of the systems panels are still equipped with toggle switches rather than pushbutton indicators. A fairing above each pilot's head houses the HUD symbol generator and there is a HUD screen (the "combiner") attached to the upper windscreen frame in front of each pilot. When not in use it folds flat against the cockpit roof.
TRADITIONAL STRAPS
Strapping in is still a fairly traditional C-130 procedure. The seats are similar to those of earlier-generation aircraft and are adjustable fore and aft, vertically and for rake. They are fitted with foldaway, adjustable arm rests and four-point harnesses. The essential criterion when positioning the seat is to achieve the proper eye position for viewing the HUD symbology. Incorrect positioning could mean that not all the symbols are visible or in focus. The screen itself is latched down in a predetermined position and angled relative to the symbol generator, and is not adjustable. This seat position was quite easily achieved, but it did seem as if short pilots might have to have their seats so high that reaching the rudder pedals effectively could be difficult or impossible. Lockheed Martin is aware of this and is pursuing a solution. The seat is being redesigned to allow the occupant to sit higher, the rudder pedals are being given more rearward adjustment and the control yoke is being positioned higher on the column and being made smaller to allow clearance from the pilot's knees. An obvious penalty from the smaller yoke will be an increase in aileron control forces. It is expected to be about 10%.
The majority of the pilots converting to the J model, when it enters service, will be experienced in the earlier models. Because the airframe is virtually unchanged from a pilot's point of view (there have been changes to materials, finishes and manufacturing processes), they will find the C-130J very similar in terms of handling qualities; that is, it will feel the same to fly. The latest-technology avionics, system management by the pilots and, above all else, using the HUD from take-off to landing, will be new experiences for most, however.
I found the HUD to be extremely "user friendly". The symbology is clear and compelling and the presentation is much less cluttered in all modes than of some earlier HUDs. I imagine that most pilots unfamiliar with HUDs might need a couple of simulator training sorties to become used to the presentation, to become certain of where to find the particular cue they need and how to "set up" the HUD for specific purposes, such as instrument approach. Thereafter, I predict, they will become increasingly comfortable with it to the point of feeling deprived if forced to cope without it. This is of course, important because competent use of the HUD enables the pilot to fly the aircraft to finer limits than would be possible using conventional instruments. Approaches to airfield instrument runways in poor weather can be flown to lower limits while clandestine landings at unequipped, unlit strips at night become a reality. In all phases of flight, the HUD allows the pilots to increase their situational awareness..
The C-130J is being manufactured in standard and stretched versions. The aircraft I flew from Lockheed Martin's site at Marietta, Georgia was a C-130J-30 (stretched variant) destined for the Royal Australian Air Force, although it was being used for development testing and had undergone 15 test flights. It was not fitted with the optional underwing fuel tanks. I had not flown a C-130J-30, although I had flown the USAF C-130E, RAF C-130K and the Lockheed High Technology Testbed version.
Once airborne in the J-30, the differences between the two variants became largely academic; perhaps the rudder was a little more powerful, possibly as a result of the longer fuselage. There is, however, a difference required in the technique for a "max-effort" - or short-field - take-off. This is because of the risk of clouting the rear fuselage on the ground during rotation in the longer aeroplane. Both C-130J variants have better short-field performance than that of their predecessors through their more powerful engines and electronic-thrust control, but the long aircraft suffers a penalty in rotate speed because of the risk from "over rotating".
It was largely for these reasons that I was invited to fly the aircraft from the right seat rather than the left and that the max-effort take-off was demonstrated by two company test pilots. The Lockheed Martin Engineering Flight Test Plan written for our flight carried a medium-risk level overall because the max-effort take-off and stalls were both assessed as medium risk while all the other events were considered low. C-130J chief test pilot Wayne Roberts was in command from the left seat; the total crew complement was seven, including a flight-test engineer and observers.
FADEC CAPABILITES
The Lucas Aerospace full-authority digital engine-control (FADEC) for the Allison AE2100D3 engines provided automatic starting cycles with automatic shutdown for overspeeding and warnings should other malfunctions occur. Taxiing the C-130J seemed much the same as for any model. Low-speed ground-idle for the engines still exists (to reduce engine power and therefore taxi speeds without the need for reverse pitch or wheel braking when the aircraft is light - and to reduce outside noise), but is controlled by four push buttons immediately behind the power-lever quadrant.
The pre-take off checks were completed and the flaps set to 50%. The max-effort take-off reference speeds were calculated, although eventually the flight-management system (FMS) software will provide reference speeds. The aircraft was light (43,600kg) all-up weight (AUW) - against 70,300kg maximum take-off weight (all figures are for aircraft not fitted with external fuel tanks). There was 6,350kg of fuel, but no cargo. Marietta is about 1,000ft (300m) above sea level and the temperature was 16¹C.
The fadec allows rapid power lever movement and "carefree" engine control. Thus, for a max-effort take-off, the power levers are moved rapidly to the forward limit of the quadrant and held there. The engines spool up to maximum power quickly and evenly. A quick glance at the top row of engine instrument displays on the centre CRT panel (which show horsepower) indicated full power had been achieved by all four engines. At brake release the aircraft leapt forward and accelerated rapidly. At 80kt (150km/h) the nose was raised to 7¹ nose-up and the attitude held until the aircraft was airborne. The pitch was then increased to about 20¹ nose-up, at which point the airspeed stabilised at about 100kt. The undercarriage was retracted, the aircraft climbed to 1,000ft above the ground and the flaps were retracted during acceleration towards an en route climb speed of 180kt. The climb angle achieved was probably about 15¹ and the rate of climb was of the order of 4,000ft/min (20.32m/s) in the initial climb.
Roberts briefed me on the HUD in a development simulator, which enabled me to settle down with it in the climb. At 14,000ft, the aircraft was manoeuvred, including steep turns up to 60¹ bank. It was possible to fly these turns accurately using the HUD, which gives good flightpath indication against the artificial horizon line. The technique is similar to flying a familiar aircraft in steep turns, using a clear natural horizon. Speed control using power was easy throughout all flight regimes because of the help provided by the speed-trend arrow or "carrot"; if the aircraft is accelerating, the carrot is above the flightpath symbol; if decelerating it is below. When the speed is stable, the carrot is against the left tip of the symbol. The HUD was straightforward to control (ie, change modes or presentations) using controllers arranged along the glare shield. There are also FMS controllers along the glareshield so that it is possible to fly the C-130J in visual or instrument conditions without looking "head down", except for glances at the engine instruments. Even here, the fadec and the crew-alert system permit a much more "carefree" attitude to engine parameters. There is, for example, no longer any need to line up all four engine powers by setting each power lever - the fadec does that. The alerting system warns if all is not as it should be with the engines - or other systems.
The HUD display was free from extraneous reflection and was easy to use when wearing prescription glasses. If one's head was moved to look through a side window or into the cockpit, the HUD symbologies were immediately re-acquired when the head was turned back to look through it. There is a small controller next to the combiner's hinge point which sets the brightness as required; thereafter it can be left to adjust itself automatically with changes of ambient light or it can be controlled manually. When rolling out of a turn to face directly into bright sunlight, the display compensates, but greater brightness is easy to select manually.
UNEXPECTED PROBLEMS
The C-130J development programme was beset by unexpected problems with the stalls. Lockheed Martin quickly established that the traditional C-130's benign and predictable stalling characteristics had been upset because the six-bladed propellers caused the airflow over the upper-wing surfaces to separate. The aerodynamic devices which were tried were leading-edge stall strips, wing fences and vortex generators. The extremely complex flows over the wings were traced by using "tufting" and endless photographs from a chase aircraft. As a result, it was possible to find a satisfactory cure for the problem under any one set of conditions - eg, power off or full power, but not both, because the propeller effect was found to be so varied. Eventually, the only viable solution was a stick pusher. Although the stick pusher now installed meets both the military- and civil-airworthiness requirements, it is viewed as a temporary solution. An aerodynamic cure is still being sought.
It has been this problem with the stall which has caused the most significant delay to the C-130J programme and has pushed back production-aircraft deliveries. The phenomenon also obviously begged the question about other serious consequences. If the airflow over the wing was upset, was it also disrupted around the aft fuselage, with serious repercussions for the aircraft's vital paratrooping role? At the time of writing, no live jumps have been made, but more than 200 dummies have been dispatched.
Because of this aspect of the programme, it was particularly pertinent to see how this C-130J-30 behaved at and near the stall. With the C-130J, there are no dire consequences from using aileron near the stall and, indeed, the technique is recommended to counter any tendency for a wing to drop. The first three stalls undertaken were wings level, power off; the aircraft was trimmed at 1.4 stall speed in each case, from which point the airspeed was reduced at 1kt/sec. The airspeed display on the HUD combiner provided by the mission computer, shows a carrot for the relevant stall speed for the configuration and shows digitally the predicted stall speed. As the airspeed decreased towards the stall there was a clear audio warning of "stall, stall", but no natural stall-warning buffet. The airspeed is shown digitally throughout the stall sequence and the carrot is a useful aid during recovery. Once the angle of attack has been reduced by the stick-pusher, the carrot moves to a new, higher predicted stall speed. The aircraft can consequently be flown safely out of the stall and into the climb with minimal loss of height by keeping the airspeed just above the carrot speed without risk of entering a dynamic stall.
The fourth stall was a turning stall with approach power; in this case the mission computer again generated predicted stall speeds on the HUD display. The aircraft had to be fairly ham-handedly abused to provoke a stall and, in this dynamic approach to the stall, there was a re-assuring natural buffet which would be difficult to miss. In none of the approaches to the stall, nor during the stick push, was there any tendency for a wing to drop (see table).
The aircraft was then descended to about 3,000ft above ground level to examine the authenticity of the automatic thrust-control system (ATCS). This system provides autofeather of the associated propeller should an outboard engine fail and automatic control of the resultant asymmetric thrust. This means that if an outboard engine were to fail at full power during take-off, its propeller would automatically be feathered without any action by the crew and the power would automatically be reduced, if necessary, on the opposite outboard engine so as to improve directional control while ensuring that the sum total of the power on the three remaining engines was sufficient for safely continuing the take-off and climb out. This means that the minimum-control speeds are lower for the C-130J than those on earlier models under identical conditions, and that the short-field performance is consequently superior.
The relevant conditions were simulated by setting flap at 50% with the gear down, setting take-off power on all four engines and flying the aircraft at the relevant safety speed. The left outboard power lever was then retracted to flight idle. Monitoring the four top-engine indicators (horsepower) revealed maintenance of take-off power on the two inboards, but a decrease to the right outboard power. Accelerating caused the power to be smoothly restored to the right engine; decelerating reinstated the power decrease. Throughout the changes, the ATCS controlled the power changes smoothly and progressively. A manually flown return and instrument-landing-system (ILS) approach to Marietta was then flown - as always, using the HUD. The requirement was entered using the FMS controller on the glare shield. The head-down CRT map display then showed the direct track to Marietta and the HUD displayed a corresponding track "needle" indication. The track, the localiser intercept and the glideslope capture were all a pleasure to fly through the HUD. The aircraft was rolled (touch and go) and climbed into the visual circuit (traffic pattern). It was flown like any other, using visual reference points for the downwind positioning and finals turn while the HUD provided horizon, attitude, airspeed, barometric altitude and radio altitude.
The C-130J is typical of all C-130s to handle in the circuit, on the approach and in the flare, the controls requiring only moderate forces for a large aircraft of the period - albeit with higher forces in pitch than in roll. Also, the C-130J inherits the fairly large pitch trim changes with flap selection - particularly between 50% and full flap. The electric pitch trim, controlled by a double pole switch on each pilot's yoke is quick to respond. For selection from full flap to 50%, the C-130J has automatic trim.
The final item was a demonstration of a short landing by Roberts. A concrete strip on the edge of Marietta's main runway was used. This strip is 600m long, with plenty of undershoot and overrun and no obstructions. A 3¹ approach slope was programmed into the HUD. The threshold speed was 105kt and the touchdown was at 99kt. Full reverse thrust and maximum wheel braking were applied immediately after landing and brought the aircraft to rest in about 1,500ft (460m) of ground run.
STEEPEST APPROACH
Three degrees is about the steepest approach path which can now be used. This is because the C-130J's propeller creates less drag than the earlier four-bladed versions. To approach more steeply, Roberts hopes that it will be possible to certify the use of a modest amount of reverse propeller pitch in the air. This may not be easy bureaucratically because the C-130J has had to incorporate safety devices to prevent selection of reverse pitch in the air either unintentionally or deliberately. Earlier legislation required only that inadvertent selection should be prevented, but the present regulation for US Federal Airworthiness Requirements (FARs) and European Joint Airworthiness Requirements (JARs) demand additional balking against deliberate selection. The C-130J is designed to meet FAR and JAR rules (as well as military requirements) so that it can be used commercially.
By endowing it with more-powerful engines, more-efficient six-bladed propellers and modern electronic technology, the C130J-30 proved to be a convincing update of a much older airframe. The main motivation for doing so has been the absence of any viable alternative in the form of a replacement designed from scratch. Even if such an aircraft were available, it is hard to envisage how it could be significantly better. I found it a convincing tactical transport to serve into the next century, or at least until a next-generation replacement does appear.
Source: Flight International
