Reprinted from: AOPA PILOT
Pilot Products
August, 2002

Laminar Flow speed mods
By Julie K. Boatman

Speed rules. And with all the mods out there to turn your bugmasher into a rocket, you may wonder how money turns into speed. There are speed enthusiasts who argue that you should see one knot of speed gain for every $1,000 spent on modifications. If only it were that easy.

Some mods work well on particular airframes, and some don’t work at all. You may spend thousands on contraptions with funny names and the glue to stick them on, and come up empty-handed. And you’re almost never going to get money back when it comes time to sell.
So why do pilots go for the elusive speed? Because like the Holy Grail, the Fountain of Youth, and the Lost Dutchman Goldmine, we’ve heard tales of riches- and speeds that leave their hangar buddies in the dust. And enough of these stories are true to keep us in the quest for speed.
We had the opportunity to follow an airplane through two iterations of power and speed mods—a rare chance to witness firsthand the rebirth of one very average Piper Cherokee 140 into , yes, a 140 that can reliably beat 140 mph true airspeed.

Laminar Flow Systems, a division of Power Flow Systems, borrowed N140HC from customer Jim Rhoads to develop modifications to boost performance in PA-series aircraft

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No aircraft that’s been flying for more than 30 years, as OHC has, comes without flaws. We reviewed the Power Flow Systems’ tuned exhaust last winter (see “Pilot Products,” February Pilot),, and we found the power increase produced by the system to be substantial.

At that time, the airplane worked flawlessly. During the testing for the review, however, a carburetor heat cable that had been previously repaired began binding, leaving the valve progressively farther open each time the carb heat was applied. This affected our tests of the Laminar Flow speed mods, since the problem wasn’t addressed until after the airplane was returned to the company’s headquarters.
Even with this underlying problem, the airplane gained notably with the speed mods. These mods included aileron and flap gap seals (to cover the space between the fuselage attach points and the flight controls), flap hinge fairings, wing-smoothing and fuel-tank fairings, a nose-gear fairing, and main-gear speed pants (with FAA certification pending during the test—the rest of the mods were certified at the time of testing).

We followed roughly the same profile during our climb as in the previous test, but flew a 92 to 95-mph target speed for better engine cooling (Vy is 85 mph). We leaned the mixture after passing through 5,000 feet, according to Piper’s recommendation. Our average rate of climb, with the extra 7 mph, was 475 fpm from 5,000 to 7,500 ft-only 25 fpm less than the prior test. The company reports up to 100 fpm additional climb at Vy from the speed mods in their own testing. For better cooling, visibility, and greater groundspeed, it seems like the extra speed is an adequate tradeoff.
However, the Laminar Flow mods are optimized for cruise and performance at top speed. Prior to installation of the aerodynamic mods, the tuned exhaust system-equipped 0HC topped out at 118 mph indicated, and 134 mph true at 8,500 ft msl, minus 1 degree Celcius, and 2,645 rpm. The Laminar Flow-equipped 0HC gained 50 rpm (even with the carb heat cable problem) and indicated 124 mph, with a TAS of 140 mph.

Down lower, with increased rpm available, we saw the TAS climb to 147 mph (at 4,500 ft, minus 4 degrees C, and 2,750 rpm). Fuel flows were 11.4 gph at this lower altitude, versus 10.8 gph at 8,500 ft. We had flown the airplane from Frederick, Maryland, to Lancaster, Pennsylvania, for the test, and on the way back, there were times when the airplane nudged 142 mph, for a TAS around 150 mph.

However, we couldn’t hold this speed the 147-mph figure is an honest conclusion.
One big question: “An rpm above 2,700 says “redline,” and some may argue that it’s not fair to claim speed gains at unsustainable rpm. Darren Tillman (sic.Tillman) of PowerFlow/Laminar Flow responds: “Because speed mods enhance performance so greatly, it is more likely the engine will exceed the redline limitation up to a much higher altitude than they are used to. It is possible to repitch the propeller to more of a cruise pitch.” The owner can trade climb performance for extra speed in cruise and keep the prop below redline at the same time. The prop was left in the original pitch during both tests.
Before any modifications were made, the airplane performed well below pilot’s operating handbook values. With both the tuned exhaust and Laminar Flow mods, the airplane matched book speeds at 75-percent power—but only using fuel flows commensurate to 65-percent power. The package added a little more than 17 pounds to 0HC’s empty weight.
If you want the fastest 140 on the block, the Laminar Flow mods make a good argument. We gained 6 mph (roughly 5 kt) at cruise, were able to climb at faster groundspeeds, and added some low-speed handling improvements in the process. The total cost of the Laminar Flow mods to 0HC comes to $3,410 (estimated retail price; discount kits will be available). So if every Cherokee 140 on the ramp takes to mods like the 0HC, the $1,000-to-knots ration is easily beat by the package.
For more information, contact Laminar Flow Systems, 1585 Aviation Center Parkway, Hangar #104, Daytona Beach, Florida, 32114; telephone 877/693-7356; fax 386/248-1587; or visit the Web site powerflowsystems.comor laminarflowsystems.com