Tuesday, June 1, 2004
An Enthusiastic Cherokee
Maybe it isn’t the fastest 140 in the world…but then again it might be
The very nature of Cherokee 140s wouldn’t seem to lend itself to speed. After all, the airplane made its reputation based on a docile stall and some of general aviation’s most benign flying qualities. The littlest Cherokees have always been regarded as among the gentlest of trainers, so universally respected for their predictable manners that some instructors actually criticize them for being too easy to fly. " />
Every feature of the airplane was aimed at simplicity. Designers John Thorp, Fred Weick and Karl Bergey concentrated on creating an airplane that was easy to build, easy to fly and easy to service. The flaps were manual, activated by a Johnson bar that pulled up from the floor in three clicks. Engine cooling was so good, there was no need for cowl flaps, and the first Cherokee 140 made do without toe brakes. (Braking was via a lever mounted beneath the panel). Pitch was the only axis of trim, and the control was mounted on the roof and activated by a horizontal crank. The Cherokee used a low wing, so Piper did mount an electric fuel pump to deliver fuel to the engine in case of an engine-driven pump failure.
There was only one cabin door at right front. Baggage had to go aboard from the front and manhandled into the back. The Cherokee airfoil, unlike the semi-tapered Warrior wing, was a constant-chord, laminar-flow design. It used large, one-piece skins that wrapped around the leading edge and were riveted into place at the trailing edge. Just as the nickname suggests, the Cherokee wing really did resemble a Hershey bar. The empennage carried the theme of simplicity to its logical conclusion. The horizontal tail was a single-unit stabilator rather than a conventional stabilizer plus a movable elevator.
Apparently, Piper got it right. They sold over 10,000 of their PA28-140s, and in some respects, the model is still with us, although the current 2004 New Piper Warrior III has very little resemblance to its 1964 ancestor. There were very few 140-hp Cherokee 140s produced (most were 150-hp models), but the name was to identify Piper’s entry-level airplane until the advent of the Tomahawk in 1978.
I first flew Jim Rhoads’ airplane in Long Beach, Calif., in stock trim, then a day later, at the same temperature and weight after Tom’s Aircraft had fitted the Cherokee with the Power Flow exhaust. The Power Flow system requires five to seven hours for installation, costs $3,675 and modifies the airplane’s exhaust to significantly reduce back pressure, optimize induction airflow and improve horsepower.
Power Flow’s Robin Cook and Darren Tillman discovered long ago that many aircraft exhaust systems are relatively inefficient, often failing to evacuate burned gases in the exhaust cycle. The result is that a portion of the following power stroke is wasted, trying to burn already deoxygenated exhaust.
The Power Flow unit is more efficient at scavenging exhaust gas from the cylinders, so the engine burns a more volatile mixture of fuel and air, rather than trying to reburn a portion of the previous combustion cycle. The bottom line is more horsepower at all altitudes and a higher altitude for 75% cruise. That translates directly to more cruise speed, since thinner air offers less drag.
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