Plane & Pilot
Tuesday, April 21, 2009

Looking For 200 Knots


Forty years ago, the goal was 200 mph. Today, it’s 200 knots.


knottsFast feels good. For those of us obsessed with clocking along at the velocity of a Lamborghini, speed is the kinesthetic equivalent of beauty.
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Mooney Acclaim S
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.



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