A boxcar designed to be a tough operator

Source:
This story is sourced from Flight International
Subscribe today »

Dave Higdon/HOUSTON

Houston's Ellington Field Airport can hardly be described as a bush environment, so it was not the perfect location in which to test the abilities claimed for the Gavilan 358 utility aircraft.

After a couple of hours flying the 358, just a few kilometres before my turn came to join the pattern, Ellington Tower's radio trafFIc alerted me to the fact that we were to share airspace with NASA astronauts sharpening their flying skills in high-performance jet trainers in preparation for flying with John Glenn on the veteran astronaut's recent return to space.

Not only was I concerned about the performance mismatch between our respective flying machines, but I had some trepidation about my ability to pick out a swift but small, white NASA jet through the vast luminescent Houston haze. In the reverse sense, I had few concerns, however. An offspring of the boxy-is-beautiful school of aircraft design, the Gavilan should not be hard to miss.

The eight-seat Gavilan 358 impressed me with an agility surprising for a utility aircraft. Early in an extended afternoon flight, I built up confidence in its ability to respond quickly and easily, whether to clear any perceived conflict or to manoeuvre through a tight approach.

In designing the 358, Bogota, Colombia-based El Gavilan wanted an aircraft capable of competing for established utility markets where there is a need for small package and cargo flights, haulage of heavy equipment and people to construction or exploration sites on short- to medium-length legs and to support relief efforts to remote disaster sites.

No doubt the size, shape, construction and configuration of this muscular, 260kW (350hp) "boxcar with wings" meets some very specific needs of those missions - a tribute to the company's 12-year development effort which culminated in May with the receipt of its US Federal Aviation Administration type certificate. This was the first FAR 23 approval awarded by the FAA in 15 years.

MARKETS PROSPECTS

The question is now: will the aircraft take off in the world market? The $365,000 fully equipped price seems right for a machine of its stated capabilities - able to carry 508kg (1,100lb) and carry out unsupported missions of up to 1,110km (600nm) on 75% power, 30min reserves, flown by a single pilot (there is provision for a co-pilot).

In terms of cubic volume alone, the Gavilan is unique in its price range, thanks to a fuselage 3.84m long, 1.42m wide and 1.49m high. Able to climb at a sustained 880ft/min (4.1m/s) is a credit to the big, strutted 12.8m-long wing and husky, 260kW Textron Lycoming TIO 540 flat six that powers the aircraft.

Rolls are easy, although adverse yaw is a factor in co-ordinating turns. Stalls win non-event status; slowing is a breeze. The biggest trick comes at landing, when the high vantage point of the pilot skews perspective when flaring an aircraft 9.15m long.

Thanks to the Gavilan's civilised handling, we managed to slip from the downwind pattern leg for Runway 17R to the downwind for 17L. "Cleared to land, Runway 17L, keep it tight," the tower advised, so we did. An unexpectedly light roll and pitch response combined well with the aircraft's large, single-slotted flaps and huge frontal area to make child's play of squaring the corners at 100kt (185km/h) before slowing down to our recommended final-approach speed of about 75kt.

Our final touchdown came slowly enough to let me make a 90¡ turnoff during what little roll-out was required. This is all part of the 358's design mission: short hops, up to 550km, carrying development supplies, medical aid or disaster relief to remote locations with 460m (1,500ft) of makeshift runway.

MISSION MADE, MISSION READY

The landscape may vary, but the mission has remained the same for El Gavilan - provide the world with a budget price aerial truck. The Gavilan's 770kg useful load gives an operator the ability to fly almost 454kg of payload on a round trip of 1,100km in about 4.5h, using only the onboard 395 litres (105 US gal) of fuel. Speed over such distances can be a significant factor, but shorter trips lessen the advantages of faster, more expensive aircraft, and 130kt certainly far exceeds any ground speeds over terrain with no proper roads. So the Gavilan should meet most utility requirements with aplomb.

But it is not exactly a short take-off and landing (STOL) aircraft, so rudimentary landing sites may need some improvement for the Gavilan to become a contender. Sea-level, gross-weight take-off requirements approach 550m to clear a 50ft obstacle, while landing demands 500m after a similar-sized object has been cleared.

Aircraft capable of matching the Gavilan's true payload, such as Cessna's ubiquitous Stationair 206, do not require runways this long. The Cessna, however, does not approach the Gavilan in cabin volume, a factor in many utility missions where bulk is more important than weight. Nor can it accommodate sheets of building materials measuring 1.22 x 2.4m (4 x 8ft). Cessna's bigger Caravan turboprop would have little trouble swallowing objects that size, however.

Similarly, the Caravan's 160kt-plus cruise speed carves more than 20% out of a theoretical 960km round-trip mission - or about 50min. But then, for the price of a single Caravan, El Gavilan could sell you three 358s. With three aircraft, an operator could have Gavilans landing every 40min, negating the speed advantage of the turboprop-powered Caravan.

To many bush pilots and cargo operators, the term utility aircraft is synonymous with durability, so it comes as no surprise that the Gavilan's designers made dispatch reliability one of their priorities.

This may help to explain the 358's construction - an aluminium-skinned fuselage supported by a lattice of 4130 chromolly steel tubing; aluminium monocoque wing and tail surfaces with aluminium control surfaces; simple, single-slotted, manually operated flaps; sturdy fixed main gear supported by steel tubing with elastometric shock absorption; and a beefy, fully castoring, trailing-link nose gear using an over-the-counter automotive shock absorber for damping.

El Gavilan has even incorporated flat Plexiglas windows to keep costs low and ease replacement. The overall design is geared to resisting damage, as well as easing repair when operating off-base. For example, the entire nose gear can be serviced in the field using normal hand tools.

As a clue to its durability, the Gavilan did not wince at the hard landing caused by my premature flare on our first touchdown. Plopping down onto the paved runway from a full stall at 20ft, the aircraft seemed to squat to the limit of the main legs, shaking off the abuse and rolling out with no bounce whatever.

On subsequent landings, the kiss of tyres to tarmac barely elicited a sense of touchdown from the big bird. In compliance with FAR 23, Amendment 46, the Gavilan wing is designed and tested to failsafe status, so apart from an impact with an immovable object, it is difficult to conceive of damage resulting from normal utility operations.

The single-slotted flaps work well, steepening descent angles and lowering approach speeds with an immediacy only available from a manual control system. With no electric motor or hydraulic powerpack to slow deployment, maintenance is also cheaper. Also, the lack of any nosewheel-steering linkage between the rudder pedals and the nose strut eliminates unnecessary complexity, while removing another potential source of damage in the bush.

Some old habits die hard. It took me practically my entire afternoon with the Gavilan to adapt to ground steering with differential braking. But Ilearned the advantage of this system - the ability to turn round in a space narrower than the aircraft's wingspan. By simply applying one brake and adding a burst of power, the nose gear unlocks, permitting turns about the inside wheel under 9m in diameter .

One small drawback is that the differential steering system causes greater wear and tear on tyres and brakes. Also, there is no simple way of reaching the FIller caps of each wing's 197 litre fuel tank. Even a simple, hang-it-from-the-strut step would help. As it is, ladders are the only way up to refuel or check the tanks.

No problems with the front office layout, however. With six-way adjustable seats in the cockpit, even aviators of moderate stature should FInd they are positioned high enough to gain an excellent front view from the 358.

The downslope of the engine cowling helps immensely when looking ahead. The twin front doors each sport a huge window with a view more than 90¡ off the longitudinal axis, thanks to the wings being mounted well aft of the cockpit. Inside, every switch and control falls easily within reach of the left seat occupant - an important consideration for a solo bush pilot.

Only the breakers check will force the short-armed pilot to adapt. The bank of breakers is located across the panel on the far right side - reachable, but only just. As equipped, the Gavilan 358 comes with two banks of three seats, which may be mounted "club style", with the front row facing aft, the back row facing forward. Behind the rear seat row is about 0.6m3 (21ft3) of space that can accommodate up to 910kg of gear.

Remove the seats and more than 2.84m of flat floor space with nearly 1.3m of height is revealed. A double cargo door on the left rear fuselage provides a 1.22m wide, 1.16m high access. If the cargo flts through the doors, the Gavilan should be able to lift it.

EASY IN, EASY OUT

The Gavilan weighs more empty than a loaded 172R Cessna Skyhawk and, when loaded, it carries about 1,000kg more. The aircraft brought to mind the ubiquitous Skyhawk. Apart from awkwardness in taxiing, its flight manners betrayed no clumsiness.

After a simple, uncomplicated preflight check, we climbed aboard with El Gavilan managing director Eric Leaver. Starting the big Lycoming required a bit of boost pump with the mixture at idle cut-off. As the engine tries to fire, the mixture is advanced to full rich, whereupon it catches and rumbles to life. In the time it took me to taxi to Ellington's Runway 4, all the engine gauges were in the green.

Leaver suggested adding some right rudder to help counter the torque of the big Lycoming and its 2.13m-diameter three-bladed McCauley constant-speed propeller. His suggestion worked well, considering that the rudder begins to bite before the Gavilan hits 30kt - and that my instinctive right-rudder was not stopping a drift to the left.

But the Gavilan 358 stayed with me as we reached the 60kt indicated, rotated and accelerated to 80kt. More right rudder was needed to maintain the heading.

Trimmed for 90kt and with the engine pulled back to 95% power, the lightly loaded Gavilan climbed easily at 700ft/min, even on a mid-October afternoon that was much warmer and more humid than standard conditions. The Gavilan's ample horizontal stabiliser made trimming a less sensitive task than I expected.

The wide-span NACA 4412 aerofoil exhibited the adverse yaw associated with old, tail-wheel aircraft such as the Aeronca Chief, Luscombe Silvair or Cessna 140 or 170. Keeping the ball centred required me to lead my turns with a touch of rudder, along with the yoke inputs. This worked well and resulted in minimal altitude excursions.

Keeping the ball centred for power-on and power-off stalls required little effort; the mush that passes for a stall brought no hint of wing drop, although there was less in the way of pre-stall buffet than I had expected.

AWKWARD STEERING

Only the adverse yaw in turns and the lack of nosewheel steering during high-power take-offs made flying the aircraft an experience in adaptation. Of the two, only the differential steering really seemed awkward. Otherwise, flying the Gavilan 358 was about as straightforward and uncomplicated as it gets.

So what does this mean for the company and its efforts to make the Colombian aircraft a real contender in the market? First of all, El Gavilan still lacks a US production certificate, so current customers are limited to national or regional operators, such as the Colombian air force.

The company also needs to finish off a couple of small items not addressed in the certification process, such as noise tests and crashworthiness of the passenger seats.

Winning the production certificate and passing noise tests are essential for success in the North American and European markets. With production certification and the field experience of a national operator, El Gavilan has the basics of a useful, affordable utility and cargo aircraft, air ambulance, regional, short-haul air taxi operator, research transportation - in short, any conceivable mission in general aviation.

El Gavilan executives must address the final barriers to US and European sales and then make the 358 as visible as possible. After that, its price, flying traits and payload potential should be all that is needed to make the sale.