Vortex generators boost Meridian’s useful load

 - October 8, 2007, 9:45 AM

When Piper introduced the Meridian in 2001, it marked the return of the Vero Beach, Fla.-based manufacturer to the turboprop market and the end of a nine-year hiatus since the Cheyenne production line went quiet in 1992. Reflecting the shifts in the market since the Cheyenne died, Piper put its new eggs in a turboprop single, leaving the market for building turboprop twins (also abandoned by Cessna, Mitsubishi and Rockwell/Gulfstream) to Raytheon Aircraft with the venerable Beech King Air line and to Piaggio with the still futuristic Avanti.

Piper’s was a smart move for at least two reasons: the low end of the turbine market had changed drastically in those nine years with the arrival of the CitationJet and the emergence of development programs for very light jets that, we are told, will sell for around a million bucks; and by basing its turboprop single on the existing Malibu Mirage pressurized piston single, the development task was less daunting technically and financially for a company that had been steadily rising from the ashes of bankruptcy in 1991.

As emphasized in AIN’s pilot report on the Meridian (March 2001, page 24), however, it would be a mistake to see the Meridian as simply a Mirage with the 350-hp Lycoming removed and a Pratt & Whitney Canada PT6 put in its place. The 1,076-shp thermodynamic PT6A-42A delivers 500 shp to the propeller, and the airframe was suitably enlarged and strengthened to handle the additional 150 hp beyond the Mirage rating.

Weightlifting Course
The Meridian as first delivered was a well designed and well engineered project that, with a price tag of $1.6 million, took the entry-level rung in the market for turbine singles. However, as also noted in the same pilot report, it suffered from a sharply limited full-fuel payload and a disappointing autopilot. With full fuel, the typical Meridian could carry 350 pounds in the cockpit and cabin–sufficient for little more than a couple and their weekend bags. Among pressurized turbine singles, the original Meridian was the BMW Z3 of the fleet and the Pilatus PC-12 was the Chevy Suburban. Saddled with the FAA requirement that no single-engine airplane shall stall at more than 61 knots in the landing configuration, Piper could not simply raise the mtow to find the extra pounds to boost useful load. It could have demonstrated improved crashworthiness to gain a couple of knots’ exemption, but the most expedient way to accommodate the need for added weight would be to reduce the stalling speed so that a weight increase could bring it back to the 61-knot limit.

Through clever application of vortex generators, that is exactly what Piper was able to do. Meridians now being delivered (S/N 149 onwards) offer a full-fuel payload of almost 560 pounds (an increase of 210 pounds) and a max ramp weight of 5,134 pounds (up by 242 pounds) while still staying within the 61-knot stall speed. The empty weight of the airplane I flew at Vero Beach in 2001 was 3,418 pounds; the upgraded Meridian I flew this summer (S/N 144) with Piper chief pilot Bart Jones from Caldwell, N.J., weighed just 18 pounds more, at 3,436 pounds empty. Max usable fuel capacity remains unchanged at 1,140 pounds.

In addition to 96 vortex generators affixed to the upper surface of the wings and another 80 affixed to the underside of the horizontal stabilizers, the upgrade includes tougher gear attach points and some wing strengthening. The mods are not retrofittable to older Meridians, Piper having deemed them too complex for field installation.

In an installation devised by Micro Aerodynamics of Annacordis, Wash., the vortex generators keep the airflow attached to the wings and tailplane at high angles of attack but have essentially no effect at cruise angles of attack. They have also allowed the deletion of one stall strip.

There aren’t many things in airplane design that give something for nothing but, if you dismiss the process of having to buy and affix the tiny vanes, these vortex generators work their magic for free, allowing a 242-pounds-heavier airplane to meet its original stall-speed limit and (once some of the extra weight has been shed by fuel burn) retain its original book cruise speed (260 knots true at 25,000 feet). With its previously stunted full-fuel payload, the Meridian was a fine candidate for the vortex-generator treatment, which on multi-engine airplanes has enhanced low-speed and engine-out controllability and therefore safety.

A Better Autopilot
As I discovered while flying N5361A this summer, the shortcomings of the S-Tec (Meggitt) 550 autopilot have been banished by adoption of the Meggitt Magic 1500.
Where the original 550 had dithered, the new Magic 1500 nailed altitudes and headings and courses with a precision appropriate for a turbine airplane. The 550 was a rate-based upgrade of the S-Tec 55, but the new Magic 1500 is rate and attitude based; it will provide a standard-rate turn or 30 degrees of bank and is integrated with the ADHRS and EFIS, making it operationally more intuitive. With the old autopilot, one push on the nav button initiated needle-driven guidance, but two pushes were required to initiate GPS guidance. The Magic 1500, conversely, automatically recognizes what is driving the navigation function and follows that guidance with just one push of the nav button. Annunciations are also larger on the 1500, and the new autopilot has a go-around button where the 550 had none. The altitude alerter is integrated into the system, meaning that the 1500 automatically arms itself to capture whatever altitude was dialed into the alerter, with no more action required of the pilot.

The bumpy, puffy-cumulus mid-summer weather that had settled over New Jersey for the day of my flight gave the autopilot a good workout, and it generally behaved well, nailing headings, holding altitudes to within 10 or 20 feet and performing nav tasks with aplomb. It flew the ILS into Allentown, Pa., with precision, and the autopilot’s integration with the Garmin GNS 530 nav system made for smooth turns that are calculated to lead any course kinks for precise tracking. Programmed for banks of 30 degrees, it rolled into turns with gusto but nailed and held the bank angle accurately enough to inspire confidence quickly. There was a bit of Dutch roll with the yaw damper switched off, and the trick on reapplying the damper is to engage it at a moment when the airplane is steady.

Base price for the Meridian is now $1.75 million, and the typical delivered price is $1.8 million.