This story about the Quest Kodiak by Owen Zupp first appeared in the April 2019 edition of Australian Aviation.
In aircraft design, beauty is more than skin deep. While some airframes are particularly aesthetically pleasing, many hide their strengths beneath aerodynamic fairings or engine cowlings and only on closer inspection is their true purpose revealed. The Quest Kodiak is a classic case study of this fact.
Before pen was ever put to paper, the Kodiak was conceived with a very specific role in mind. The aircraft was to serve humanitarian aid groups in the field and therefore called for short takeoff and landing (STOL) performance as a critical requirement. Furthermore, as many of these groups operated in remote and relatively inaccessible regions, the Kodiak would not only have to operate on unsealed runways but into areas where there was no runway at all. And overly complex systems would also be a disadvantage, as spare parts and support may be many miles away. Reliable, rugged and simple was the basic three-pronged criteria that gave birth to the Kodiak.
Previously, piston-engined aircraft such as the Cessna 206 had been the backbone of air transport in this role, however Avgas is becoming increasingly difficult to obtain on many parts of the world. Additionally, the ever-reliable Pratt and Whitney PT-6A turboprop engine added a level of performance that a piston engine simply cannot match.
To this backdrop, the Kodiak evolved as a single-engined, high-wing turboprop. Inevitably, constant comparisons to the Cessna Caravan were made and continue to be discussed. However, Quest’s Chief Demonstration Pilot, Mark Brown, emphasises that he sees the Kodiak’s strength in its rugged design and STOL performance as a step up for Cessna 206 operators. As we take a closer look at the Kodiak, its various design features speak volumes to its suitability for its primary task.
What lies beneath
The Quest Kodiak sits on the ramp and cuts a nuggety figure rather than a glamourous one – and that’s okay. At first sight, the Kodiak looks like a workhorse, standing tall with solid fixtures, big doors and the unmistakable PT-6 engine. Offering more than a 9:1 power-to-weight ratio, the choice of a Pratt and Whitney PT-6 as the powerplant is of no surprise, but the “dash 34” variant was selected with a very clear purpose. Producing 750shp, it is suited to the low altitude operations that the non-pressurised Kodiak undertakes. Additionally, it has been in continuous production longer than any other single-stage PT-6 which equates to proven reliability, broader parts availability and lower operating costs. These are all definite advantages for an aeroplane operating in the ‘back blocks’ of the planet.
The engine’s inlet sits very high, away from foreign matter waiting to be ingested from an unprepared runway. Meanwhile, the PT-6 is turning a four-bladed all-metal Hartzell propeller. By somewhat bucking the trend and selecting four blades, the blade length is shorter than a propeller with three blades. In practical terms, this equates to greater propeller clearance – 19 inches in fact – well clear of the rocks and dirt.
While examining the engine bay, Mark draws attention to the rather concealed nose gear support structure. It resembles a small anodized girder rather than your typical aircraft component and beneath the cowling the torque tube is thicker and sturdier than others I have seen. Mark describes the nose gear as having a “9-inch stump load”, referring to the size of concealed stump it could strike and survive. This same nose gear has steering to 17.5 degrees either side of centre but can castor up to 55 degrees, allowing the aircraft to effectively pivot on one main landing gear and turn in very confined spaces. Again, every design feature has a purpose, even if it is not obvious at first sight.
Perhaps this is most poignantly present in the Kodiak’s main landing gear. The two legs extend from the fuselage, with large 29in tyres at their end. However, the true strength of the main gear is concealed by the aerodynamic fairings that streamline the leg and the join between the fuselage and gear. Each gear leg is mounted upon a substantial steel trunnion and rather than a single carry-through tube running through the fuselage between each gear leg, the Kodiak has two x 3in tubes. It is an undercarriage designed to take the shocks an unprepared surface can deliver.
The fuselage is functional from every aspect. Of all-metal construction, other than a few panels at the front of the aircraft, the Kodiak displays its rivets like a badge of honour. In no way is it masking what it was designed for and the near-industrial appearance of the skin gives an air of durability.
Mounted beneath the fuselage, the external baggage compartment (ECC), or “cargo pod”, provides additional cargo and baggage space of up to 750 pounds with a maximum floor loading of 65 pounds per square foot. Divided into three compartments, its forward section is cleverly faired, meaning that for the extra carrying capacity there is 1-2 knots reduction in cruise speed.
The fuselage’s near-square cross-section permits the maximum loading of boxed freight without the corners of a curved fuselage eating into the available space. An individual crew door allows easy access for the pilot via a substantial step and handle, independent of the passengers and parcels to the rear. Standing at the crew door, it is easy to survey the Kodiak’s upper wing surface and importantly, the security of the fuel caps.
Passenger access is to the rear on the port side through a generous two-piece door, whose lower half folds down to provide in-built steps, held in place by two lanyards. These lanyards can easily be detached, allowing the lower door to fall vertically from the door sill and allowing loaders to get right up against the airframe to place their cargo on board, rather than being obstructed by the air-stair.
The fin sits high at over 14 feet and features a sizeable horn-balanced rudder which undoubtedly offers a high level of authority at low speed and in crosswind situations. Beneath the aft fuselage, there is an “upsweep” created as the rear of the cargo pod merges into the airframe, which generates an area of low pressure. To counter this and enhance directional stability, the Kodiak has two ventral strakes – an aerodynamic feature more frequently associated with Learjets and the like.
The horizontal stabiliser is fitted with “vortex generators” on its upper surface, just ahead of the hinge line. This row of small metal blades enhance the effectiveness of the elevator and improves low-speed stability, both of which are valuable qualities to the Kodiak operating in the STOL regime.
At every turn, every feature is optimised for performance in the STOL realm. And there is still one critical element in the success of an aeroplane that flies in the world of low and slow – the wing.
A working wing
From the design phase, the Kodiak’s wing span was targeted at a minimal 45ft. The driver behind this requirement was that many of the remote airstrips are 45ft width, hence offering the Kodiak a margin that some larger winged aircraft don’t benefit from. Like the Kodiak’s wing struts, main landing gear legs, and empennage, its wing’s leading edge incorporates porous titanium panels that seep anti-icing fluid and permit flight into known icing, or FIKI. However, the wing hosts a number of other features that contribute to its profile.
Firstly, and most noticeable, is the fixed, discontinuous leading edge. At around two-thirds of the span, the step in the leading edge is aligned with the inner edge of the aileron on the trailing side of the wing. The purpose is to further deliver a wing that not only stalls at the wing root first but retains aileron authority throughout. Furthermore, the leading edge is void of any “stall strips” which are often an indicator of a wing design that required ‘fine tuning’ in post-production.
At its root, the aerofoil cross-section is thick as one would expect for a STOL aircraft that calls for high lift production over speed. That being said, the Kodiak has a respectable maximum cruise speed of 183kts TAS, although normal cruise is closer to 174kts. Within the wing, 320 US gallons of fuel are held within two tanks that gravity feed the engine. These tanks also feature a drop-down Magnastick for easy confirmation of fuel quantity. Another requirement at the design stage was that these tanks remain aft of the main wing spar to offer a barrier of protection in the case of an impact on the ground roll.
On the trailing edge, the flap hinges are again of a rugged construction and the marketing department boasts that they are ideal for tethering a hammock. Extending to a maximum deflection of 35 degrees, the large single-slotted Fowler flaps offer a stall speed of only 60 knots at the maximum weight of 3,290kg.
On the inside
By virtue of its square cross-section, the cabin of the Kodiak is spacious. The Kodiak can carry up to 10 people with a centre aisle allowing passengers to move through the aircraft. The interior package can be one of three options ranging from a resilient, lightweight option for everyday passenger and freight operations through to a luxurious corporate-style interior. In addition to being comfortable, the passenger seats are tested to a force of 26G! These same seats are easily removed from their rails and fold to fit within the cargo pod, allowing an easy transition between passenger and freight operations without having to leave the seats behind. The walls are lined and fitted with conventional brackets to attach cargo nets and straps.
The cockpit is fitted with a Garmin G1000 NXi suite with synthetic vision, vertical situation display and an autopilot, all of which have a clean appearance and greatly enhance situational awareness. The Kodiak 100 is equipped with an angle of attack (AoA) indicator allowing the pilot to visually target a desired angle of attack for different phases of flight. Providing instantaneous AoA trend information, the ARINC 429 also alerts to impending stalls. Still, beyond the smooth finish of the avionics, the rest of the cockpit assumes a well thought out appearance for remote operations.
The rudder pedals are solid and housed in a bay that is lined with metal and not carpet – ideal for dirty boots. The toggle switches that line the instrument panel are substantial and the throttle quadrant is similarly built for work. One luxury is the leather-covered control column which has a sports car feel but is very comfortable in the hand. Overhead, the fuel selectors are big, colour-coded and unambiguous with a simple mechanism preventing an inadvertent selection to “off”. And while the Kodiak is certified for single-pilot operations, the selectors and all primary controls are easily accessed from either pilot’s seat.
Inside and out, the various design features of the Kodiak are aimed at providing a STOL aircraft that is resilient in rugged, remote operations. Quantifying that ability, at maximum weight the Kodiak has a certified takeoff roll of 285m and only 233m on the landing roll. In the context of its role, that is impressive.
Flying at the cruise speed of 174kts, the Kodiak can span 1,005nm, burning around 33gph (125lph). Should time on station be what is required, the aircraft can set a best endurance speed of 95kts and burning a miserly 28gph (108lph), it can remain aloft for nearly 10 hours. In all aspects, the Kodiak has been designed to possess a flight envelope that is ideal for its prime task and other roles as operators may see fit.
When the hardest to reach areas of Ecuador were devastated by an earthquake in 2016, humanitarian groups, Samaritan’s Purse (flying bulk supplies into major airports in Ecuador) and Alas de Socorro del Ecuador (ADSE), a Mission Aviation Fellowship (MAF) affiliate, relied on the Quest Kodiak to aid those in need. With roads and bridges destroyed by the magnitude-7.8 earthquake, the Kodiak was still able to deliver aid to the injured and homeless.
It was a scenario that closely resembled the genesis and foreseen purpose of the Kodiak and the aircraft performed admirably. Its ability to do so is a combination of a clear vision of the aircraft’s STOL role, combined with the integration of design features to best execute the task.
From common sense selectors to aerodynamic devices and rugged construction, the Kodiak is a born and bred backcountry specialist. At every turn, the aircraft is well thought out and dedicated to its mission. This is not by chance or good fortune, but like so many successful aircraft, it is by design.
VIDEO: An introduction to the Quest Kodiak 100, Series II from the QuestAircraft YouTube channel.
This story first appeared in the April 2019 edition of Australian Aviation. To read more stories like this, become a member here.