Looking For 200 Knots

Unfortunately, speed in an airplane is less telegraphic than in a supercar, unless you're running the pylons at Reno. Granted enough altitude, speed becomes all but invisible. While you may be covering ground more quickly, it's hard to tell.

Years ago, when I had the once-in-a-lifetime opportunity to fly the McDonnell Douglas F-15 Eagle at 37,000 feet and Mach 1.6---roughly 1,050 mph---the big speed was simply a number on a dial, not that impressive from seven miles up.

Similarly, if you're flying peacefully in a single-engine private airplane, operating in clear air and sunshine 10,500 feet above Kansas, the difference between 200 mph and 200 knots may be difficult to spot. It's hard to tell if one silo is drifting by faster than another.

But make no mistake, speed is still the ultimate aphrodisiac for many pilots and, therefore, the target du jour of many manufacturers. Two hundred knots has become the new improbable dream that 200 mph used to be. Range, payload, climb, endurance and all the other parameters shrink to relative insignificance compared to pure, unbridled speed.

That's not to demean 200 mph (or if you'd rather, the less numerically significant 174 knots). Even today, you can count the number of single-engine airplanes capable of max cruise at 200 mph on one hand. Among production machines, there's only one Piper, one Cessna, one Cirrus, one Beech and the inevitable Mooney.

These days, the search for ultimate knots above 200 among piston singles is led by a similar quintet of contenders, at least two of which will give the bottom-rung turboprops a run for the money (and a lot less of it, at that).

For the purposes of this analysis, we've limited our search to piston production airplanes. The four primary factors that dictate an aircraft's ability to fly fast are aerodynamic efficiency, power, air density and weight.

It's significant that all these models utilize turbochargers and must operate in the relatively thin air of the flight levels to achieve their top cruise speeds. While it's true that all five could probably manage near/over 200 knots at breathable altitudes, turbo boost and an oxygen mask (for four of the five) are all mandatory in order to reach the big numbers.

High-performance turbocharged airplanes aren't necessarily operated in the flight levels, however. Much of the time, owners of unpressurized turbo singles prefer to fly in the bottom three miles of sky. The climb to big altitude can be long and frustrating, wearing an oxygen mask is a nuisance, and some of the other physical symptoms of high-altitude flight aren't much fun either.

To that end, the entire quintet will touch 200 knots at semi-breathable VFR cruising altitudes below the flight levels, typically above the weather but below the mandatory Class A restrictions, where most pilots operate turbocharged singles most of the time.

The standard mantra for airplanes capable of cruising at 200 knots has always been that given enough power, you could push the Queen Mary through the Mach, but the power required would, indeed, be prodigious.

As the late Roy LoPresti proved back in the '70s, it is possible to wring hidden speed out of a good design without a power increase. (After all, some gliders fly very well and very efficiently with no power at all.) LoPresti extracted 16 additional knots from the old Mooney Executive with the same 200 hp engine out front to create the 201.

Perhaps the better approach to ultimate speed, however, is to employ every possible advantage. Back in the '60s at Compton Airport in Southern California, I watched a pile of junked warbird parts in the hangar next to mine slowly transform into the world's fastest piston airplane. The warbird belonged to TWA Captain Lyle Shelton, and it was to become the remarkable Unlimited Class Grumman F8F Bearcat Rare Bear.

Shelton knew he needed both plentiful power and an extremely aerodynamic shape to go fast. Accordingly, he sandwiched an 18-cylinder Wright R-3350 engine onto the firewall, generating more than 3,000 hp with the benefit of water injection, nitrous oxide and 70 inches of manifold pressure.

Shelton understood that power alone wouldn't allow him to overcome the Bearcat's draggy barrel shape and produce a winner. To that end, the airline pilot modified the Bearcat's drag profile, chopping 2.5 feet from each wingtip, removing the flaps and flushing the wing, redesigning the canopy to an extreme low-drag configuration and eliminating anything nonessential that might contribute to drag.

Eventually, Lyle's Bearcat became the world's fastest propeller-driven airplane, setting the three-kilometer prop/piston speed record at 528.33 mph, winning Reno's Unlimited Championship 10 times and winning or placing well in practically every other race he finished.

In a more moderate sense, the airplanes in the 200+ knot category are veritable masters of their own brand of aerodynamic art. They utilize engines as strong as 350 hp and employ airframes and wings as optimized for aerodynamic efficiency as production requirements will allow.

The manufacturers also know that weight is the final ingredient that constrains speed. Any airplane will fly faster if it flies lighter. Some aerodynamicists suggest the improvement may be as much as one knot for every 100 pounds reduced on aircraft lighter than 6,000 pounds. Here's a quick rundown of the specs on the five airplanes in the 200+ knot class.

The Mooney Acclaim S leaves virtually nothing hanging in the wind. It's a truly slick design that sports a drag coefficient of about 0.0190, nearly as good as the famous P-51 Mustang, which logged an amazing 0.017.

I flew an Acclaim S last year that couldn't have been much cleaner and scored 240 knots at FL250, only two knots off the book promise. That's 276 mph, far out in front of the goal and easily the equal of some turboprops' best efforts. Even the step was missing, not necessarily a major inconvenience since the aft inboard section of the wing is close to the ground.

A development of the original (2006) Acclaim, the new "S" variation has a new prop, flap gap seals, improved gear doors, cleaner hinges and a low-drag cowling.

For motive force, the Acclaim S employs a severely derated, 280 hp Continental IO-550-G engine, breathing compressed sky through a pair of Kelly Aerospace turbochargers that maintain full power all the way to 25,000 feet. The Continental is approved for as much as 350 hp in other applications, so 280 hp is a bare 80% of the max rating. Accordingly, the big IO-550 carries a TBO of 2,000 hours.

Cessna's Corvalis 400TT, formerly known as the Columbia 400, is all the more amazing considering that the quick Cessna is a fixed-gear design. The Cessna Corvalis 400TT is the logical extension of the original turbocharged Columbia 400.

As a fixed-gear airplane, the 400 couldn't be much cleaner. A composite design with no rivet heads, section lines or any of the other inconsistencies of aluminum airplanes, the Corvalis 400TT is about as slick a machine as you'll find, probably scoring a drag coefficient close to the Mooney.

The turbocharged Corvalis benefits from the same engine as the Acclaim S, but it's rated for 310 hp rather than the Mooney's 280. TBO remains 2,000 hours, and Cessna claims a cruise of 235 knots at 25,000 feet---with fixed gear.

The Cirrus SR22 TN easily races along at better than 215 knots up high, 200 knots down low. Cirrus's SR22 TN employs the identical engine rated for the same horsepower, but boosted by a turbonormalizer produced by Tornado Alley Turbo (www.taturbo.com) of Ada, Okla. The brainchild of Alan and Dale Klapmeier, the Cirrus features all-composite construction plus a whole-plane parachute, the latter is a feature none of the other models offer.

The Cirrus' combination of a clean design and essentially the same 310 hp Continental IO-550 engine results in an optimum cruise speed of nearly 220 knots, making it easily competitive with the Acclaim S and 400TT.

Semi-finally, the venerable Piper Malibu and Mirage have been 200+ knot airplanes since the type's introduction 25 years ago, longer than any of the others. The new Piper Matrix, at its roots a depressurized Mirage, is the latest airplane to join the 200+ club.

The Malibu represents the old order of 200-knot machines. Introduced in 1984, it was the result of the dedicated efforts of a design team led by aerodynamicist Jim Griswold. The original Malibu featured a roughly circular fuselage, designed from the outset for pressurization and high-altitude operation. Better still, there was no taper, as the fuselage translated aft, so all six occupants enjoyed the same head and elbow room.

The Malibu first flew with a Continental TSIO-520-BE engine churning out the familiar 310 hp, and once again, the fuselage and wing were as slick as Piper could make them. The wing was 43 feet wide (try fitting that into a standard T-hangar), designed with a relatively short chord to provide a glider-like high aspect ratio, and optimized for high-altitude flight.

Piper's original spec for the Malibu was 216 knots, and most of the airplanes would reach that number in the thin air at FL250. The newer, heavier, post-1989 Lycoming-powered Mirage features 350 hp and can manage more like 213 knots.

Perhaps equally impressive to many of the older folks who can afford the currently million-dollar Mirage is the fact that the airplane's 5.5 psi pressurization system allows the airplane to fly at nearly 200 knots at 12,500 feet, where the cabin altitude is still practically at sea level. Similarly, the Malibu/Mirage offers a six-seat, semi-cabin-class environment with a double-clamshell door for entry/exit.

The Piper Matrix enjoys all the benefits of the Mirage except the inflatable cabin and offers a lower empty weight, improving payload. Cruise speed is in the same class, 210 to 215 knots, with almost 200 knots available at 17,500 feet.

Despite the above, not everyone is willing to pay the penalties associated with flying fast. Climb can be laborious and subject to ATC step-ups; all the aformentioned models burn between 19 and 22 gph at high cruise, and engine-overhaul shops suggest that engines run at max cruise and high altitude have less chance of making TBO. Still, there's little question that speed sells. For many pilots, speed isn't the most important thing. It's the only thing.