Experiencing sticker shock at the avgas pump these days?
Beyond cruising at reduced power settings to conserve fuel, what else can be done? Perhaps Power Flow Systems (PFS) of Daytona Beach, Fla. has the answer, providing more speed for the same fuel consumption or the same speed you now enjoy at a reduced burn.
No upstart with a whiz-bang idea, PFS has been around since 1997, designing tuned exhaust kits for a variety of aircraft on an STC basis. Company founder Robin Thomas began researching ways to improve aircraft exhaust systems back in the 1980s while selling speed kits for several models of Pipers through his company, Laminar Flow Systems Inc.
The concept of a tuned exhaust is not new. Race cars and motorcycles have had tuned exhausts for years to develop maximum power for a given sized engine, generally utilizing straight pipes. But for cars and motorcycles, noise is not a consideration, as any racing fan will attest. The big question: How to get maximum efficiency from an aircraft engine and still be a good neighbor?
PFS will provide anyone technically minded with chapter and verse on how it all works but, basically put, a stock reciprocating airplane engine does not deliver rated horsepower because of degraded combustion in the cylinders. When the inlet valve opens to introduce fuel and air, there are still exhaust gases in the cylinder that contaminate the next combustion cycle due to an overpressure condition. The PFS system creates a partial vacuum in the cylinder, sucking all the exhaust gases out before the inlet valve opens. This is achieved by all individual collector tubes being the same length before they go to a collector box and out the muffling pipe, called a “secondary.” Determining the exact length of the collector tubes is the key to the design.
The entire PFS tuned exhaust system only weighs about five pounds more than a stock system. Sole options are a shortened exhaust stack (9 versus 33 inches) to more closely resemble the stock exhaust and a ceramic coating of the exhaust stack. While this is purely cosmetic, PFS reports 90% of buyers add this option for an extra $200.
Since the first FAA-approved STC on a Cessna 172 in March 1999, PFS has acquired subsequent FAA blessings on the Cessna 175 and 177, four models of the Piper PA-28, four variants of the Grumman American AA5 series, as well as seven of the Mooney 180 and 200 hp models, B through J. Kit prices vary from $3,425 to $4,790 depending on the model.
Installation times run from three to seven hours and may be done at Daytona Beach or at the owner’s home base by a qualified mechanic. PFS warrants the system for one year or 500 hours (whichever occurs first) and the buyer can get a complete refund if not satisfied during the first 60 days after installation. With more than 2,000 kits sold to date, one could say public acceptance has validated Thomas’ dream.
Obviously, GAN wanted to experience what everybody was talking about, so we contacted Darren Tilman, general manager/chief test pilot and one of PFS’ first employees, to set up a demo flight in the company’s Mooney 201. He agreed to bring the Mooney to Kissimmee, Fla., for the moment of truth.
We would first fly the aircraft with the stock exhaust system at various altitudes and power settings to establish a base line. Then the PFS tuned exhaust system would be installed (it took less than two hours) and the same flight profile would be repeated to record performance improvements.
The flight profile consisted of flying with ram air door open, wide open throttle, mixture leaned to 50° on the rich side of peak, using 2,700 rpm, then 2,500 rpm at each of three altitudes — 2,500 feet, 7,500 feet and 11,500 feet — while measuring OAT, airspeed, fuel consumption, oil and cylinder head temperatures. Comparisons would then be drawn between the stock exhaust system and the PFS installation.
With Tilman in the left seat and yours truly writing down the numbers, easily and exactly done thanks to the electronic engine instruments, we departed Kissimmee in the stock Mooney toward broken clouds above, timing our climb to 11,500 feet and leaning the engine as we transited 9,500 feet.
Two speed runs were done at each of the three altitudes, using 2,700, then 2,500 rpm, engine leaned on the rich side of peak for best power. Numbers noted, we returned for landing. Then Tilman and PFS mechanic Victor Rodriguez began installing the tuned exhaust system.
Back in the airplane, we went out for our second set of runs. Though not exact because of turns, climbs through holes, vectors from Orlando Approach Control, etc., our rate of climb appeared to be about 10% better than the first flight (PFS claims a 15% improvement). Also noticeable were cooler cylinder head and oil temperatures. Fuel flow was about the same.
AT 2,500 FEET
- Two speed runs. TAS increase: 3-5 knots over stock exhaust.
- Fuel flow: 0.3 to 0.8 gph less than stock.
- Cylinder head temperatures: combined, 4° to 22° less than stock.
- Oil temperature: 3° to 10° less than stock.
AT 7,500 FEET
- TAS increase: 4 knots over stock. (Recent tests run in California for Mooney dealers yielded 7 knots faster than stock.)
- Fuel flow: 0.3 less to 0.2 gph more than stock.
- CHT: 10° to 17° lower than stock.
- Oil temperature: 6° to 9° cooler than stock.
AT 11,500 FEET
- TAS increase: 4-5 knots faster than stock.
- Fuel flow: same as stock.
- CHT: 8-18° lower than stock.
- Oil temperature: 6-9° cooler than stock.
Improvements were evident throughout all parameters with the PFS system. Fuel flows were the same or almost a gallon less per hour, but yielding up to 5 knots faster speed. With the PFS-equipped airplane no attempt was made to match the true airspeed of the stock airplane by reducing power. Obviously, this would have resulted in even lower fuel consumption and lower temperatures — and lower operating temperatures contribute to extended engine life.
After the second flight, Tilman talked about the company, which has just 13 employees.
“But it’s sized right for what we do,” he said.
“Except for the Mooney 200 hp series, which is fuel-injected, all our conversions are on four cylinder carbureted engines,” he continued. “But right now we’re working on some six cylinder models and the results are promising.”
How does Tilman characterize the PFS product in a nutshell?
“Better speed, better fuel consumption, lower engine operating temperatures, better climb performance and safety,” he said. “With our system we were able to get almost 24 extra horsepower out of a Cessna 172. With a high density altitude, or operating out of a short field with trees at the end, I think you’ll agree that could make the difference.”
For more information: 877-693-7356.