April 1, 1985

                    Peppy Pipers

         

        

How to turn a Cherokee 140 into an Archer for $3,200.

A speed boost of 20 mph is pretty impressive in a 170-mph airplane like a Mooney Executive. Such an increase would be absolutely astounding in a 130-mph turtle like a Cherokee 140. However, that's what Laminar Flow Systems, the Virgin-Islands-based Piper mod shop, is claiming for its souped-up prototype Cherokee trainer. And several Aviation Consumer flights in the LFS testbed suggest that the ratty old 1966 140 with its 2,300-hour engine is indeed a 150-mph-plus airplane that will outperform a Cherokee 180 and perhaps even nip at the heels of a 200-hp retractable Arrow.

Over the past two years, LFS has developed a set of wing modifications (flap and aileron gap seals, flap track fairings, wing rivet fairings and leading edge contour smoothing) for the Piper Seneca, Lance, and Cherokee lines. The wing improvements usually add 10-17 mph cruise speed on these aircraft.

LFS chief Robin Thomas has now come up with two more engine and airframe modifications which, combined with the wing mods, improve the lowly 140 to a startling degree. At this writing, neither new mod was FAA-approved yet, but Thomas anticipates approval soon.

Fancy Pants

The first improvement is a set of fairings for the standard-issue Piper wheel pants on the 140 and all the other early Cherokees. (About 1979, Piper offered a much more refined main wheel pant; the LFS pant fairings won't fit those.)

The standard Cherokee wheel pant, like most others, seems to defy all logic. Piper put the pant around the tire, which is already curved and smooth, but left the dangling sharp-cornered brake mechanisms, compression struts and nose wheel forks exposed to the airflow. The LFS fairings cover up these gaping airflow interrupters and fair them smoothly into the wing and the Piper pant.

Mod number two is a tuned engine exhaust system. In a tuned system, Bedecked with wing and landing gear fairings, this lowly Cherokee 140 can cruise at l5O-plus mph and rival an Archer in vigor. In a tuned system, all the exhaust pipes are carefully dimensioned so that reflected exhaust pressure pulses "scavenge" the exhaust and improve engine breathing. A properly designed system can increase power to a surprising degree. (Much of the Piper Malibu's excellent performance is credited to a tuned exhaust system, but no other aircraft that we're aware of has one.)

Bow-Wow

Taken all together, the wing, wheel pant and exhaust mods do wonders. The LFS prototype airplane, in its original stock form, was always considered a terrible dog around the St. Thomas, Virgin Islands airport where LFS is based. "Every time I took off in it, I prayed," commented one previous owner of the plane. "It barely cleared the pass at the end of the runway." Thomas bought the plane for practically nothing, set to work modifying, and has turned the former dog into a greyhound.

This metamorphosis was rather graphically demonstrated when Thomas and an Aviation Consumer reporter flew the LFS testbed side-by-side with a standard Cherokee 140 now owned by the former dogowner.

We allowed the standard airplane to take off a minute ahead of us. But within eight minutes, to the great astonishment of the other Cherokee pilot, her former dog had made up both the one-mile head start and the 500-foot altitude advantage, and was climbing away from her at a very smart clip.

"Pretty Impressive"

After leveling off at 6,000 feet, we tried a side-by-side speed race. It was no contest; we passed the standard airplane easily. The other pilot, as she watched her former dog zip by, radioed, "Okay, Robin, you've made your point." Later, on the ground, she commented, "That was pretty impressive."

Our indicated airspeed had been 140 mph, hers about 117. Our indicated 140 mph worked out to a rather phenomenal 155 mph true. (We later calibrated both airspeed` indicators to confirm these readings.) It's hard to escape the conclusion that the LFS mods add at least 20 mph.

Are we to believe that this lowly ancient Cherokee 140 can actually outpace a brand new 180-hp Archer II with tapered wing and hi-htech Piper pants (book speed 149 mph)?

PR Race

To erase all doubts, Thomas, a master of public relations, organized an air race for the principle purpose of demonstrating the merits of his Cherokee mods. "The Caribbean International Simple Airplane Race" took Place at St. Thomas on February 24, and was open to all fixed-gear, fixed-pitch airplanes. The idea was to lure in a bunch of standard Cherokees and blow their doors off in the name of LFS product promotion.

Ten planes entered the race, including six Cherokees of various types. A Cessna Hawk XP (technically ineligible because of its constant-speed prop) was allowed to enter because the owner was a buddy of Thomas' and because the ever-confident Thomas secretly believed he could beat the 195-hp XP as well.

He was almost right. The LFS Cherokee 140, with an Aviation Consumer reporter aboard, stayed right with the XP, in both climb and cruise, until late in the race. We finally finished 45 seconds behind the XP over the 77-mile course. Our average speed for the race was 126 mph, which included take-off and climb but no high-speed descent (the finish line was at 6,000 feet.) The LFS Cherokee burned 7.9 gallons of fuel, compared to 11.8 for the XP.

Thomas feels he would have beaten the XP but for an unexplained drop in indicated airspeed in the latter part of the race. Under the same conditions in which the plane had indicated 140 mph a few days previously, the plane showed only 133-35 during the contest. Thomas immediately did a compression check on the engine and says he found two cylinders way down. He vows to fix the engine and challenge the XP to a match race.

King of the Cherokees

As expected, the LFS 140 beat the other Cherokees in the race--two stock 140s, an old 180 and two taper-wing 160-hp Warriors, one with the latest Piper wheelpants. The Warrior owner had gone to great lengths to prepare for the race, pre-running the course several times, waxing his plane to a high sheen, and (he claimed with a semi-straight face) rubbing the wing leading edges with chicken fat. Nevertheless, the grungy LFS 140 averaged three mph faster for the race and used less fuel to boot.

The LFS·140 soundly trounced the pair of stock 140s by an average of 16 mph, burning 20 percent less fuel in the process. Using the CAFE formula for fuel efficiency (speed x miles per gallon), the LFS ship handily beat all the four-place planes in the race, including the Hawk XP.

20 MPH

Engine perturbations aside, it's clear to us that the LFS wing, wheelpant and exhaust mods add at least 20 mph to the Cherokee 140, and perhaps as much as 26 or 27. (That's the figure claimed by Thomas, based on a comparison of the original unmodified dogplane to the finished speedster.) We couldn't vouch for a 27-mph speed increase, but 20 looks pretty good, based on what we saw.

Dave Noland

REPRINT

May 1, 1984 issue

Lance Speed Mod

Flight Test of the Laminar Flow Systems STC Kit

Last year, we reported on a speed mod for Piper Senecas developed by a small company called Laminar Flow Systems Inc. (See the March 1, 1983 issue of Aviation Consumer for details.) We found the mod to perform pretty much as advertised, increasing speed on the Seneca II we test-flew by about 15 kts and boosting climb rate by over 200 fpm.

In the meantime, LFS has adapted the kit to fit the single-engine Pipers, and now has STC approval for virtually the entire PA-28 and PA-32 lines. (At this writing, only the PA-28-201 Arrow III and IV are not approved for the kit; that approval is expected shortly.) Price of the kits range from $1,272 to $2,454, depending on the model being modified. (Installation is extra, typically running from $500 to $1,000.) Due to wing variations among the various models, not all parts of the full Seneca kit apply to all of the single-engine models.

The complete kit consists of flap and aileron gap seals, fairing strips to cover wing leading edge rivets, flap hinge fairings and, on the retractable models, wheel well fairings. (Some leading-edge re-contouring with body putty has also been approved, and may be done at the owner's option.) LFS's Robin Thomas has claimed that a modified Lance has clocked over 200 mph. and another modified Lance finished second (to Mike Smith's superslick Bonanza) in the Dulles efficiency race, a contest that measures speed, fuel economy and payload.

We were recently able to test-fly a 1978 T-tail Lance freshly modified with the LSF kit. Is the 200-plus mph Lance a reality? Can Piper's boxy load-hauler, when outfitted with the LFS speed kit, actually outpace a stock Bonanza? Based on our flight test of one airplane, the answer is no, but the modified Lance's performance was nevertheless impressive.

Unfortunately, we did not get a chance to do complete before-and-after testing of the same plane, which is the only really accurate testing method. By comparing the "after speed figures with the handbook performance numbers, however, we felt we could get a decent approximation. (This method is also subject to airspeed indicator errors.)

Our first performance test was rate of climb. The stopwatch started at 3,000 feet, the lower limit of smooth air, and stopped at 12,000 feet. Power was set for cruise climb, and we chose a climb speed of 105 mph, 13 mph above best rate-of-climb speed, for improved engine cooling. Total time from 3,000 ft. to 12,000 ft. was 14:18, for an average of 630 fpm. At 4,000 feet, rate of climb was 800 fpm; at 8,000 feet, 650 fpm; and at 12,000 feet, 500 fpm. All of these figures more or less matched the hand-hook climb figures for our weight and temperature conditions-but the book numbers were predicated on full available power (2700 rpm) and best-rate-of-climb speed. In effect, the LFS mod allowed this Lance to achieve full-power best rate performance while cruise climbing at 2500 rpm. The payoff: more ground covered during the climb, less fuel burned and better engine cooling.

Once at 12,000 feet, we set up 59 percent power (20 inches my, the max available, and 2400 rpm). According to the book, the T-Tail Lance should flv 139 kts under these conditions. We indicated 128, for a true airspeed of 157 kts, a startling 18 kts above the book number. Fuel flow under these conditions, leaned to best economy, was 12 gph.

At 10,000 ft. we set up 65 percent power. Speed worked out to 159 kts, 13 over the book figure of 146. At 6,500 ft. and 75 percent power, the speed was 168 kts, 10 better than the book predicts Robin Thomas reports a similar pattern in the other Lances he has modified; the speed bonus seems to increase with altitude. He has no explanation for this odd state of affairs.

The owner of the Lance we tested later confirmed the general accuracy of our figures after completing the long trek from the Virgin Islands installation center to his Texas home. He says he's having his engine checked out to it is achieving rated power at the higher settings. Overall, he sounded happy.

We don't blame him. Even taking the most pessimistic figures, he's getting 10 knots better max cruise for about $3,500. The speed bonus is only about half that of the more elaborate Smith Speed Conversion for Bonanzas, but the cost is a quarter of the tab for a Smith job. By our reckoning, that's double the value. The LSF Lance we flew could achieve the book speed for 75 percent power while leafing at 59 percent--and burning 12 gallons per hour instead of 18. This fuel savings amounts to about $12 per hour, and will pay off the cost of the kit in about 300 hours--little more than a year of average flying. Not a bad bargain, as we see it.

Dave Noland

Reprinted from the May 1. 1984 issue of The Aviation Consumer. Copyright 1984 Belvoir Publications, Inc.. The Aviation Consumer is published twice a month by Belvoir Publications, Inc. 1111 East Putnam Ave. Riverside, Conn06878. Subscriptions are $48 annually.