It’s been almost 20 years now that diesel technology has been a promising alternative for light general aviation, though the adoption of compression engines has taken longer and has suffered more teething pains than its proponents anticipated. I’ve had the chance to fly five different airplanes with four different diesel engines — the original Thielert, the Centurion 2.0, the Austro AE300 and the SMA SR305 — and my experience in every case was good, if not ideal.
Somewhat surprisingly, Redbird Flight Simulations has introduced a new diesel-engine airplane refurbishment project it calls the RedHawk, based on an existing Cessna Skyhawk. We flew the new airplane last week to see how well the concept works in the real world. Like Agent Mulder in The X Files with his belief in alien life, we want to believe in diesels, but can we?
As you likely know, Redbird has made a name for itself with its lineup of simulators, from high-quality desktop game-level models to full-motion certified training devices. It’s also a mover and shaker, no pun intended, in the flight-training game. At its Skyport FBO/laboratory in San Marcos, Texas, Redbird not only trains a lot of pilots, it also keeps track of every bit of data it can during the learning process, such as how long it takes each of its customers (not “students,” mind you) to reach every one of his or her milestones.
The flight school opened for business just over 18 months ago, starting out with a fleet of four brand new Cessna Skyhawks. Redbird founder and chairman Jerry Gregoire told me that he loves Skyhawks as training platforms, even though they’re pricey. Though the standard gas piston Skyhawk is no gas guzzler — burning well under 10 gph for most training missions — the higher fuel costs go, the bigger possibility there is of an improvement, especially on airplanes that might fly 100 hours per month.
Skyport’s Skyhawks also suffered from nagging maintenance problems with their Lycoming engines. So Gregoire and his team at Redbird set out to see if they could reduce the impact of all three areas — purchase price, maintenance and fuel costs — not by finding a new airplane to rival the Skyhawk but by building an airplane of their own. The result is the RedHawk, a refurbished Skyhawk that features a 135 hp Centurion engine.
The RedHawk I flew was a 2002 S-model, which is one of the new-production Skyhawks built in Independence, Kansas, after Cessna’s decade-long hiatus from the piston airplane game. When Redbird bought its S-model 172 to rebuild, the airplane had steam gauges and a pair of Garmin GNS 430 navigators. The airplane was not in particularly bad shape, which meant it would be a good subject on which Redbird could cut its teeth. When it comes time to produce RedHawks for retail customers, however, Redbird won’t use later production Skyhawks but instead mid ’80s airplanes originally built by Cessna just before the hiatus.
While I’m writing in terms of “producing” RedHawks, Redbird won’t actually be manufacturing the airplanes in any regulatory sense. It will, instead, extensively overhaul the original, stripping, corrosion-proofing, and adding a paint job and new interior. Everything will be done via STC, meaning the cost of getting into the RedHawk project will be workable, Gregoire says.
Redbird hopes the end result will be an airplane that costs less to buy — the company is shooting for at least $100,000 less than a new Skyhawk, which goes for around $340,000 — while costing less to operate and maintain.
The RedHawk’s engine, a reworking of a Mercedes automotive turbo-diesel with an aviation gearbox turning a three-blade composite prop, is a thing of beauty. Featuring single-lever power, advanced computerized engine control and turbocharging (which gives it excellent performance up into the low teens), the engine is in theory a godsend for GA.
It’s hard to understate the advantages of jet-A, a fuel that costs about a buck a gallon less than 100LL. More importantly, the diesel burns very little fuel compared to a gas-piston engine, so the savings are compounded. On my test flight with Redbird’s FBO head Roger Sharp, we were seeing anywhere from around 2.5 gph at a reduced power setting to around 7.5 gph at 100 percent power. Speeds are typical of a Skyhawk or slightly better down low. As you climb, they get a lot better. We were seeing almost 130 knots true at 4,500 feet at 7.5 gph. The RedHawk will likely cut fuel consumption by around a third while adding in the lower-cost of jet-A compared to 100LL.
Operators of the Centurion 2.0 rave about the fuel efficiency, while also railing against the engine’s maintenance issues, most notably the need to replace the gearbox clutch plate with an overhauled unit every 300 hours or less. The plan these days is for Continental and its network of U.S.-based service centers to oversee maintenance of the engine, something that was done in Germany. The gearboxes, according to reports we’ve heard, will still need to be overhauled in Germany, though schools can stock spare parts to cut the airplane’s downtime to a couple of days. Continental’s hope, Gregoire says, is for the TBO on the gearbox to eventually go up to 2,400 hours, an interval that will make the Thielert, unknown issues aside, a lot less expensive to operate than a Lycoming. Continental has already announced it is seeking to increase the first inspection interval to 600 hours from the current 300.
Another disadvantage is that the Thielert produces less power than the Lycoming — 135 hp compared to 160 hp for the vintage Skyhawks Redbird will be refurbishing.
I flew out of San Marcos with Sharp recently in the proof-of-concept bird. Starting the Centurion engine was beyond easy. Push a button, let it crank over — a couple of turns is all it seems to take — and then monitor the gauges — green is good. After that, you push and hold a test button that checks the health of the engine-control units, which are redundant computers that set all the parameters for you, except percentage of power, which you do with a single lever. In terms of engine operations, it’s a piece of cake, meaning student pilots will have one less thing to worry about while learning to fly the airplane.
The airplane itself is more utilitarian than a new-production Skyhawk, with its leather seats and big displays; Gregoire says the RedHawk will be intended specifically for training. The seats and upholstery were all redone in nice but durable synthetic material. The overall effect was very impressive.
It was hot out — at least 100 degrees on the ramp — and with full fuel, Sharp and myself on board, I wasn’t expecting a rocket ship. The RedHawk surprised me though with if not comparable then at least very representative performance on a lot less horsepower.
The avionics in the proof-of-concept airplane were nice: dual GNS 430Ws with dual Aspen displays, the Evolution PFD and MFD. The panel also included a number of upgrades including the switches and controls necessary for the diesel operation. Gregoire tells me that his folks are evaluating a number of different avionics options still, and he, like many others in the manufacturing game, is intrigued by the possibilities of the new Part 23 regulations.
Once out to Runway 13 at San Marcos Municipal, we got our takeoff clearance from the tower controller and rolled.
When I advanced the power, I got the sudden realization that this wasn’t any old Skyhawk but something different. The sound, the feel of the engine — it’s smooth and quiet — and the quick acceleration all feel distinctly different from the venerable gas piston 172. Yes, I’m a fan. Still, the takeoff roll in the RedHawk was about what I’d expect from any Skyhawk on a hot day with two guys on board and full tanks.
One thing I really liked about the RedHawk was the sound of the engine or the lack thereof. Several folks watching our departure from the ground said they couldn’t hear the airplane go out. We could hear the engine, but just barely above the wind noise of flying it. It’s a much quieter engine than the Lycoming, no doubt about it.
At 2,000 feet, we were seeing around 120 knots at 100 percent power and 7 gph; bringing back the power to just over 5 gph saw a drop in true airspeed of about 12 knots. At 4,500 feet, as I said previously, we were getting nearly 130 knots at around 7.5 gph, a figure Sharp later told me is good all the way up to 9,000 feet, something that would not be the case in a conventional, normally aspirated Skyhawk.
In the pattern, the RedHawk was great. Engine control is smooth and very precisely responsive, almost like a jet but without the spool-up time. It felt as though I needed to carry a little extra power on final, compared to the Lyc-powered bird, but Sharp thought it was roughly compar-able. My sense of more thrust required could be a function of the constant speed prop.
After a touch-and-go, we climbed in a right-hand pattern to do a full-stop landing. The performance of the RedHawk was clearly affected by the heat and our relatively heavy weight. Still, climb performance seemed a little less than that of a 160 hp Skyhawk.
Redbird plans to start manufacturing RedHawks at a new factory on the San Marcos airport, which is scheduled for completion by the second quarter of 2014. It will build the first four Aspen-equipped RedHawks for use in its own school. After that, it will sell them to flight schools, though Gregoire says his company hasn’t yet determined a final price or equipment list.
As with everything else Redbird does, the RedHawk is a learning experience. The final product will benefit from what it learns along the way, Gregoire says.
As it is, the RedHawk is a satisfying product. There are questions about the operating costs associated with the former Thielert engines, but once they get straightened out, as Gregoire expects to happen over the next couple of years, the cost of operation of these airplanes could make the RedHawk an attractive alternative for flight schools looking to give students a combination of a proven airframe and an advanced engine.
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