Dave Higdon/WITCHITA
In developing the Meridian, a turboprop derivative of its Malibu high-performance piston single, New Piper Aircraft is counting on the fact that customers will find the transition to turbine power both attractive and manageable.
To test this premise, Flight International evaluated the Malibu turboprop conversion developed by JetProp of Spokane, Washington. On paper, the JetProp DLX and Meridian are close in speed, range, payload. The biggest differences are in runway and climb performance - and price and availability - areas in which the JetProp outpaces the Meridian.
Performance differences are the result of the propulsion choices made by the two companies. Both use the popular and reliable Pratt & Whitney Canada PT6A turboprop, but Piper derates the powerful -42A to the same 260kW (350shp) as the piston-powered Malibu, while JetProp extracts 415kW from the smaller -34 and fits a four-blade propeller, instead of the Meridian's three-blade unit.
As for price and availability, it takes about 12 weeks to convert a customer's PA-46 into a JetProp DLX, at a cost of $589,000, whereas deliveries of the $1.35 million Meridian will not begin until 2000. While many customers will opt to wait for the factory-produced Meridian, waiting did not interest Wichita-based businessman Jeff Greenberg, whose aircraft, flown for this report, was the first Malibu Mirage, and the fourth PA-46, to be converted to a JetProp DLX when he took delivery in March.
FAR FROM MILD
Putting a 415kW turboprop in an aircraft originally built to take a 260kW piston engine should be expected to produce some changes. But the adjustments facing the pilot stepping up from a Malibu or Mirage to the JetProp DLX are far from mild. The first 10min flying demands the biggest adjustments and doles out the toughest lesson - things happen faster in the re-engined Malibu.
Climb rate more than doubles to over 3,000ft/min (15.2m/s) at normal loads, and an otherwise-unchanged best climb speed of around 110kt (200km/h). Take the JetProp to its higher service ceiling of 27,000ft (8,200m) and maximum speed is 270kt - 45kt faster than the already swift Mirage.
While the JetProp climbs quicker and cruises faster, it also consumes more fuel, around 115 litres (30USgal/h) compared to 83-90 litres/h, but it does consume less-expensive Jet-A. For trips up to 2,400km (1,300nm), at lower power settings and airspeeds, per-mile costs should actually be slightly lower with the JetProp.
Initially, a pilot familiar with the Malibu may have problems managing the same machine at the higher velocities possible after turboprop conversion, but the JetProp should not overtax any pilot already competent on the piston-powered Malibu or Mirage. Anyone already comfortable flying a high-performance, high- altitude, pressurised piston single should easily make the transition to managing the turbine engine and its power output.
The JetProp repeats a philosophy creator Darwin Conrad proved at Rocket Engineering, which specialises in uprating Mooneys: take a fast, sturdy, used airframe, add enough power to make it decidedly faster, and equip it with systems to make the pilot smarter and the package more reliable.
Conrad's shop takes a standard Mirage or Malibu, removes the 260kW turbocharged Textron Lycoming or Teledyne Continental piston engine and installs a PT6A-34 turboprop, flat-rated to 415kW from its 560kW thermodynamic capability.
The conversion increases higher fuel capacity, adding a 52 litre header tank; and incorporates a new cabin heating system, dual 24V batteries, new controls and gauges, engine inlet anti-icing, and redundant vacuum sources and electrical generation.
The result is not so much hugely improved capability, as more utility and operational flexibility - and torque, a lot more torque. The turbine engine also means greatly reduced take-off rolls and a faster climb rate that is sustainable to a much higher altitude - still exceeding 1,000ft/min at the 27,000ft service ceiling.
Flying the aircraft and operating its systems demands little more skill than many turbo-charged piston singles, including the original PA-46. Like the Malibu, the JetProp is pressurised, requiring the pilot to keep tabs on the manual cabin-pressure control. The PT6A-34 installation entails some engine gauges that may may seem foreign at first, but there are no mixture and propeller controls to manage. The power lever can be moved relatively freely, with little worry about overheating or shock cooling.
A Shadin trend monitoring system, installed as part of JetProp DLX modification, includes a fuel-flow system that tracks consumption from the 615 litre supply. The unit also supplies a wealth of air data useful to the cross-country pilot, plus digital power readouts to augment the easy-to-read analogue dials.
ENGINE TREND DATA
Engine trend data is recorded on interchangeable storage cards, and allows on condition inspection of the turboprop's hot section. The time between overhauls is 4,000h, twice that of most piston engines. One reason for this is that the engine is flat-rated to more than 25% below its thermodynamic capability and remains well below its design limits.
The conversion includes a bank of annunciator lights high on the instrument panel that warn of changes in the electrical supply - the JetProp has both a 250A starter/generator and 70A stand-by alternator - as well as low fuel and even a change in the instrument vacuum source from the installed pump to one powered by the engine's bleed-air system.
Redundancy is enhanced. There are multiple fuel pumps and back-ups. The new header tank is the direct fuel source for the engine and is refilled from enlarged wing tanks. Run a wing tank low and an annunciator warns of low fuel; run it dry and the PT6 continues to feed off the header tank while you change the fuel source to the opposite wing tank. Run both wing tanks dry and the full header tank provides about 20min more flying. Other redundant systems include heated pitot tubes on each wingtip, and dual independent airspeed indicators.
The JetProp weighs slightly less empty than the unmodified PA-46 and provides a slightly larger useful load, largely because the PT6A is lighter than the Lycoming TIO-540 originally installed. A forward luggage compartment nestles between the firewall and the forward pressure bulkhead. Fuelled and loaded, payload and maximum cruise range are nearly equal to the unmodified Mirage, meaning that a decision to upgrade to turboprop power will likely come down to speed.
Until the Meridian becomes available, the JetProp DLX may be the most time-efficient way to move up to six people between two points up to 2,400km apart - and not get into serious seven-figure prices and three-figure hourly operating costs. Based on buying then converting a recent, low-time Mirage, the JetProp programme can provide a new level of performance for just over $1 million. With ample older PA-46s available in the $250,000 to $400,000 range, the $580,000 conversion's appeal is easy to appreciate.
UP FRONT
While expensive up front, the turbine transplant makes the JetProp DLX a higher-performance cabin-class single with barely higher operating costs.
As noted before, the JetProp's climb and cruise numbers demand some adjustments from the pilot. The first comes in flight planning: for the Malibu pilot used to a 225kt airspeed, the 45kt jump means a dramatic reduction in elapsed time. The next comes when you advance the power and a 635kg (1,400lb) torque load, applied through the Hartzell four-blade propeller, assaults your right foot.
On my first take-off, I had to fight hard to hold the centreline, even with three turns of right-rudder trim cranked in before adding power. But the fight was brief; the JetProp lifted off about 1,000ft up the runway. Clear-ing a 50ft obstacle would have required no more than 1,200ft.
Getting a feel for required rudder should be an easy adjustment for any pilot coming from a high-performance piston single. Subsequent take-offs held none of the surprise of the first and holding the centreline required no special tricks or sensitivities.
While the most likely JetProp customers would seem to be business fliers unlikely to use the smallest, most-remote fields, some adventurous pilots undoubtedly will use the aircraft's ability to launch and land in under 1,500ft. And the JetProp's take-off and landing capabilities do add a great deal to its operating margins at longer airfields. Pilots already comfortable in the pressurised, 225kt Malibu will find nothing surprising about handling a turboprop version. Speeds remain basically unchanged for rotation, climb, descent and approach.
Similarly, the Mirage's overall handling is unaltered by the shift to turbine power. Roll, pitch and yaw response is unchanged. Power-off stalls exhibit are no more dramatic than they when when the windmilling powerplant was a piston engine.
Except as noted already, the initial adjustment to how quickly things happen was the only taxing aspect of flying the JetProp. There are steps to learn, differences to discern and new systems to monitor - and the speeds and altitudes possible demand more in judgment skills during everything from flight planning to flight operations - but Flight International's evaluation suggests that any competent pilot of a Malibu will like turboprop power.
Source: Flight International
