Single engine turbo-props have established themselves as the new darlings of the charter companies and feeder airlines, consigning the faithful piston-engined singles and twins largely to history books and aviation magazine retrospectives.
Operators have been forgotten in the manufacturers' stampede for faster turbine aeroplanes that carry more people or cruise at higher flight levels; each development widening the gap between can-affords and the can't-affords.
But relief it seems is now here, as Mahindra has leapt into the empty space with an SETP designed to fit perfectly between a Cessna 206 or their own Airvan 8, and the out-of-reach C208 Caravan or Quest Kodiak.
The Australian-designed and built ten-seat Airvan 10 turbo-prop may just be the puzzle piece that smaller charter operators have been missing for decades: economical, robust, spacious, hardworking and has flying characteristics that make it only one small step above an Airvan 8 rather than the giant leap needed to get to a Caravan.
A long time coming
Although the Airvan 10 prototype first flew in May of 2012 as the GA10, the aeroplane has been on the cards for a lot longer than that. Gippsland Aeronautics was sketching SETPs even before the piston GA8 was certified. The project gained sudden impetus in late 2009, when Indian conglomerate Mahindra & Mahindra bought a controlling share in the company.
From the firewall backward the aircraft has a distinct Airvan flavour, appearing at first perusal to be very much like the iconic Airvan 8, but longer. Forward of the firewall it's a different story completely. The nose tapers down each side to meet the prop spinner in a very typical SETP way, encasing a 450 shaft horsepower Rolls Royce M250 turbine engine.
Hanging from the front is a three-bladed Hartzell constant speed, reversible and full-feathering metal propeller that completes the impression that this aircraft is something above your standard Airvan.
"What we've got now is a viable product we can go to market with," GippsAero test pilot Dave Wheatland explains. "With regard to the performance, flight handling and capabilities of the aeroplanes, the configuration and design of the aircraft is locked in.
"It has a lot of the characteristics of the Airvan 8, particularly in flight handling, functionality and capabilities.
“One of the benefits of the turbine engine of course is that the additional power gives it a more positive rate of climb, it hangs on the prop a bit during approaches, which means it’s very suitable for getting in and out of small airstrips; but the big benefit is that it runs on jet fuel.”
In Australia we are not yet suffering from an avgas drought, but in many countries the supplies have all but dried up, and it seems those countries are the ones that benefit the most from utility aeroplanes with star-quality performance on goat-track style runways. And, so long as there are heavy jets nearby, the fuel supply is guaranteed for SETPs.
As remote-area operators are Mahindra’s bread-and-butter market, the company shored up their share by producing the Airvan 10, but even so, it had to be the perfect fit for the niche they designed it to go into.
Going with the Roller
One of the questions that had been simmering was why go with the Rolls Royce engine? The rest of the world seems to be operating the Pratt & Whitney PT6A turbine: Caravan, Kodiak, PC-12, PAC 750XL and Beech King Air. Right there is a roll-call of the aircraft currently dominating the paddling pool that Mahindra wants to play in.
“This is a 450-shp engine, which is the size our aeroplane needs,” Wheatland said. “Even though it’s a relatively old design [it has heritage back to the Allison 250 of 1961] it has been refined. It’s now producing reliably higher power on less fuel, which it doesn’t use a lot more of than an equivalent piston engine. A 450-hp piston engine will use around 100 litres per hour, and so does the Rolls Royce M250.
“A PT6 would have to be significantly de-rated, which is good for ongoing reliability, but it’s a significantly bigger and heavier engine and it has a higher fuel consumption rate. So for the same endurance in hours you need bigger fuel tanks, and that means more weight that has to come out of the payload.”
“Most operators typically want to have a maximum of five hours endurance available in an aeroplane,” chimed in GippsAero co-founder George Morgan, “even if they fly only one-hour sectors most of the time. If we put a PT6 in this thing, we’d have to increase the fuel load so much to get the five hours that we’d have to put the rest of the aeroplane on steroids to carry it … and suddenly you’re staring straight at a Caravan or a Kodiak!”
Time to aviate
From the moment I hauled myself into the left seat of Airvan 10 VH-XMH I knew I was not going to be suffering a lot of cockpit shock: there was much similarity with the Airvan 8 I had flown before. The control column, trim wheel, overhead panel, centre console and seats were pure Airvan, but there were some mysterious things that set this cockpit apart.
Firstly, there was a lever missing from the console. Instead of the traditional three power levers omnipresent in CSU aircraft, there were only two: power and condition. Also there were strange switches and buttons on the panel that didn't make a lot sense to a dedicated piston pilot like me, such as start interrupt, prop overspeed, engine master, airframe master and Bus 2 Auto/Override.
The power lever controlled the thrust coming from the turbine, and had three regions placarded on the slide, from the bottom: Reverse to GI, GI to FI and FI to Max Thrust. Ground Idle (GI) is the lever position for developing just enough thrust to taxi easily and Flight Idle (FI) is the position for developing not a lot of power in the air. No matter where you position the power lever, the engine RPM stays the same, controlled by a governor just as a CSU would be.
Pilots set that prop speed via the condition lever, which is placarded max RPM, Min RPM, feather and fuel off. Sliding the lever enables the pilot to choose an RPM somewhere between 2030 and 1900, which are the limits on the three-blade Hartzell out the front. It also enables the prop to be feathered just as they are on twin-engined aeroplanes, and facilitates fuel flow to the engine.
Although the Garmin G500 avionics were nothing to sweat about the Auracle Engine Management System (EMS) showed some measurements that were not immediately familiar: tot, trq, np and Ng. It was becoming clear to me that I was about to learn a whole new way to set engine power to get the desired performance from the aeroplane.
Wheatland stepped me through the start procedure, which bore almost no common actions to piston engines at all, and the Hartzell started slowly rotating, settling soon into a smooth roar. With the start-up check list complete and stowed, it was time to taxi.
Now here's a bit of magic: all I needed to do was slot the power lever into GI, which is the top of the Beta range, and release the brakes to get XMH rolling. Realistically, there was no need to touch the power lever again during taxi. If we gathered a tad too much momentum, a quick stab of the brakes was enough to check the speed without needing to reverse the prop.
Ground handling was a heavy as I expected; the Airvan 10 is a long aeroplane and has large tyres on the main undercarriage. However, the response to pedal input was excellent and I got no impression of wrestling with directional control. That was evident at the threshold when I swung her through 180 degrees to line-up for take-off.
"When you're ready," Wheatland said, "put your feet on the brakes and advance the power lever until you get 35 psi torque (trq), then release the brakes and move the lever to about 70-80 psi."
Take-off power in the Airvan 10 is 111 psi, which can be held for only five minutes before being reduced to a maximum continuous power (MCP) of 92 psi, which delivers 380 horses.
With take-off flap set, XMH didn't demand a lot of runway before reaching the required 60 kt rotation speed, and with a bit of back stick we were soon climbing out with our nose held high. I retracted the flap, pulled the condition lever back to 1900 RPM (np) and got on with the job of flying.
We turned south towards and climbed 84 kts, which gave us a climb rate of over 1100 fpm. We could have done even better; 2030 RPM and flaps one would have given us over 1250 fpm.
We leveled out at 10,000 feet, where Wheatland displayed great delight in showing me exactly what his creation could do. He coached me to set condition to 2020 RPM with 82 psi torque. Trimmed out, the cruise TAS beat 150 with ease, but the 104 lph fuel flow had me frowning a bit until Wheatland put it into perspective.
"That's one engine," he pointed out. "To do the same in something like a Chieftain you'll be going through around 85 lph per engine."
Mahindra has positioned the Airvan 10 as a low-cost turbo-prop, so you can imagine they are very keen to emphasise the fuel flow. Accordingly, Wheatland had me set up XMH in a loiter mode with the engine wound down and the aeroplane trimmed for 70 KTAS.
"Now look at your fuel flow," he said from behind a cheeky grin.
The Auracle was saying 65 lph. "That's Bonanza territory," I exclaimed.
Amazingly, there was no sloppiness of controls at loiter speed, and Wheatland assured me the characteristics don't change much even with a decent payload on board, something the emergency services and law enforcement users will be very interested to hear.
We reconfigured the Airvan 10 for cruise and threw it around the sky a bit. As I rolled into the customary 45-degree turns, I felt an initial resistance on the ailerons that actually abated as the angle of bank increased, but once the roll was on, the stick got lighter. The turbo-prop version has also retained one of the classic Airvan 8 behaviours: you can roll it back and forth around its longitudinal axis without the aircraft actually turning in the air.
“Parachute operators are going to love this aeroplane,” Wheatland predicted happily.
I could see why, we were descending underneath the control step with the power at flight idle, prop up to 2030 RPM and 130 knots on the clock. The G500 was telling me that we were going downward at over 2500 fpm. The Airvan 10 was solid in this profile, with the prop out the front acting like a large brake to prevent us from getting too fast. Jumps operators love planes that will carry a lot of people to height quickly, get the out quickly and return to get the next load even faster. This might just be the perfect machine for doing that!
We leveled out smoothly at a good altitude for some stalls on an inbound track to Latrobe Valley. Mahindra’s Airvan 8 is renowned for stall characteristics as mild as Sunday morning, and I was keen to see if big brother could replicate them.
With the power back to flight idle, no flaps out and the spinner glued to the horizon, the ASI tape fell rapidly until we started to get some slight buffeting. Around 70 knots, we stalled. But, I knew that only because Wheatland pointed out the rate of descent on the G500. I released the back pressure and we were flying again.
We repeated the performance with landing flap set; the only difference being a slight rotation to the right that rudder took care of crisply.
Asked and answered: the Airvan 8 stall characteristics have carried over to the Airvan 10.
By that time I knew the aeroplane was not going to be very insubordinate when it came to landing; as a rule no Airvan product is. Even though I was dealing with the largest aeroplane I’d ever flown, I felt the rock-solid performance and stability would compensate for any dodgy handling on my part. I was proven right.
After turning base onto 03, Wheatland had me set landing flap, reduce power and trim for 70 knots. That done, the Airvan 10 should have flown straight into the flare … and would have done had I not tried to fly it myself. We got a bit fast, and my inexperience with the turbine engine had me trying to land it like a C172.
Wheatland wasn’t concerned, he knew the plane would behave anywhere between 70-80 knots, but that I would go through more runway on landing than I needed to.
At 50 feet I closed the power to flight idle and XMH found her way to the tarmac. No aerodynamic braking here, once the nose wheel was on the ground I closed the power to ground idle to slow us down.
With only half the runway left ahead, Wheatland took control back from me and set XMH up for a performance take-off. With his feet firmly on the brakes, he brought the power up to 35 psi and let her roll. As the speed passed 55 knots he pulled on full flap and the Airvan 10 sailed into the air like a sunhat caught by the wind. He’d used less runway on the take-off than I’d used to land!
What do we have?
Mahindra’s Airvan 10 has been a work in progress for a number of years, but its arrival as a developed machine stands to change the businesses of many operators in many sectors. It’s a tough aeroplane with fantastic take-off and landing performance, great visibility out the windows, a large cargo door and it runs on turbine fuel. It could very well be the aeroplane some operators didn’t even know they wanted until now.
You can tell from talking with Wheatland that he is chuffed to bits with the machine. From the pilot’s point of view, the Airvan 10 is not a huge handling step above the Airvan 8 or Cessna 206, which means operators looking to make the leap to a turbine now have the ability to do so without a substantial outlay in money or re-training costs.
Wingspan 12.41 m
Length 10.17 m
Typical Empty Weight 1066 kg
Max Takeoff Weight 2166 kg
Usable Fuel Capacity 572 litres
Max Cruising Speed156 KTAS
Typical RoC @ SL ISA 1300 fpm
Typical Take-off Ground Roll 340 m
Typical Landing Roll without reverse 255 m
Engine Rolls Royce M250-B17F/2
Engine Power Take-off 450 bhp, continuous 380 bhp