What do I care about speed? Aren't I the one who likes to stare out the window and enjoy the countryside at a snail's pace?
But I recall the number of times I, too, have sat at 11,000 feet, heading home, staring at the groundspeed on the GPS, willing the airplane to top whatever airspeed it met.
Every pilot likes to go fast at least some of the time, so I talked with several experts to find out how to wring every available knot from a flight. Aircraft modification, loading, climb profile, power setting, altitude selection, airspace negotiation — they each play a role in going fast.
The land of mods
Some aircraft are faster than others, either by original design or later modification. Since few of us channel the engineering genius to design our own aircraft — and Darwin takes care of those who only think they do — aircraft owners look to modification to streamline their ships.
Mods do more for some airframes than others. Gap seals, which smooth seams and cover holes between control surfaces and the fuselage, can offer up to 5 knots of speed gain. On fixed-gear airplanes, the gear account for up to 15 percent of the total drag associated with the airframe, according to Robin Thomas, president of PowerFlow and LaminarFlow Systems, producer of speed mods for light production GA aircraft. "Good fairings can reduce this by over two-thirds and make a fixed-gear plane practically Is fast as a retractable. The Cirrus [SR22] comes to mind," says Thomas.
An altered cowl that allows for better airflow through the engine compartment can also post significant gains, as demonstrated by the LoPresti speed cowls for such aircraft as the Grumman Tiger, according to Curt LoPresti, president of LoPresti Speed Merchants, another maker of aircraft mods. The mod includes smaller, round aircooling intakes, moving the engine air intake to an external NACA duct on the right side (from just above the right rear cylinder), and replacing one of the two lower cooling air exits with a larger one. Greg Amy installed a LoPresti cowl on his 1977 Tiger — and at the same time gave the airplane much-needed new paint. Whether the 5- to 6-kt gain in airspeed at redline (2,700 rpm) he's seen is attributable to the new cowl or the paint, or both, Amy isn't sure. "It's fairly well-accepted [in the Tiger community] that the cooling air intakes were more than large enough (many say too big), but that the air couldn't escape fast enough out the bottom, and thus the change in pressure across the cylinders was insufficient," he says.
Some manufacturers use wing flaps that move up, into what's known as the "negative" range, as well as down. Negative flaps, or reflex flaps, are installed in certain models of Maule MX-7 aircraft, and deflect upward about seven degrees. This action reduces the effective wing area and changes the camber of the airfoil to produce less lift, and therefore, less induced drag. When deployed on the Maule in cruise, negative flaps supposedly add 2 to 3 kt to the airspeed. In fact, some users report as much as a 5-kt gain. However, because the Maule has relatively large wings, the experts interviewed debated whether such flaps would produce results on other airplanes with smaller wing areas relative to their gross weight. Thomas tested negative flaps on a Piper Cherokee 140 and reports that the flaps didn't alter the cruise speed in a recordable way.
Speed sans mods
There's a lot you can get from old-fashioned clean flying. We tested several of the following methods to determine their relative value, and all had some effect on overall cruise speed.
Loading. A good test not only measures your skill but also teaches you something. Ten years ago, during my commercial checkride, I learned about aircraft loading from Bill Bacon, a designated examiner in the Denver Flight Standards District Office. He asked me during the oral if I knew how to make an airplane go faster. I drew a blank — no one had ever approached the subject with me, or if someone had it flew in one young ear and out the other.
As Bacon patiently explained to me how an airplane behaves when loaded toward the aft end of its center-of-gravity envelope, I got a peek into how understanding certain aerodynamic relationships can mean the difference between flying an airplane safely and flying an airplane well. The airplane goes faster as the center of gravity (CG) slides back toward the center of lift because less tail-down force, generated by the horizontal stabilizer, is needed to offset the nose-heavy condition created by a more-forward CG. Grossly simplified, you waste less energy maintaining aircraft stability.
Testing this trick in a Beechcraft A36 Bonanza, we saw some extra speed — at times. Lightly loaded, with full main fuel tanks and two average-size people up front, the Bonanza rides CG forward. Would it be a good platform for the test? Perhaps. Even with the CG to the front end, the Bo cruises into the yellow arc at altitudes below 5,000 feet msl. We followed a speed run profiled by Curt LoPresti similar to one that he uses to determine speed gains given by the company's modifications. We averaged 179 KTAS (knots true airspeed) at 2,000 feet msl and 25 inches at 2,500 rpm in light chop, and 190 KTAS at 5,500 feet in smooth air at full throttle (about 24 inches) and 2,500 rpm. The 190-kt figure was a little suspect, though — two earlier flights showed average true airspeeds at 5,000 feet to be around 182 KTAS.
A second trip was made with the front-seat occupant (who became 190 pounds of movable ballast despite his skills as a copilot) changing position to the far aft seat of the Bonanza. While we made time at lower altitudes (going 185 KTAS at 2,000 feet), we lost ground at 5,500 feet, showing only 181 KTAS.
We had moved the CG aft by just over four inches; we could move it back another five inches and still be within limits. Whatever we did, it wasn't enough to gain a consistently measurable amount of speed — but the airplane handled better with the CG in the middle of the envelope. Copilot notwithstanding.
Climbout. In a normal level-off, a pilot leads the target altitude by 10 percent of the rate of climb. So if you're climbing at 500 fpm to 5,000 feet, you'd begin your level-off at 4,950 feet.
Perhaps you've heard of the technique that involves overshooting your altitude by 100 feet and zooming down to the target altitude to reach top speed faster — but does this really work? Every demo pilot showing off a new airplane to us has suggested some version of this move, so I asked LoPresti. He verified that overshooting by 200 feet and leaning properly as soon as you get close to the target altitude help the airplane "get on the step" faster than just leveling off — a couple of minutes faster. Sure, it doesn't seem like much, but that's two more minutes at top speed, and four or five miles covered in many airplanes.
Some airplanes speed up more quickly than others. We tested the trick in the Bonanza, known to take its time reaching cruise, and we saw top speed within a minute or two — as opposed to five with the usual level-off procedure.
Altitude. You can speed up the miles by carefully consulting the winds aloft and deriving the time to climb to a given altitude and your net gain. Several brands of flight-planning software, such as RMS Technologies' Flitesoft and Jeppesen's FliteStar, have "optimize altitude" features that do a pretty good job of selecting the best altitude — if the winds aloft information you give the program is correct. Remember, garbage in, garbage out. With FliteStar, you start with the winds aloft forecast and make sure the information from each station along your route has been imported or entered. Then you can fill in other stations, such as those in the wind profiler network if you live in areas of the country where these stations are located. Profiler stations report actual readings, whereas winds aloft forecasts predict winds at a certain time. Both have associated caveats: The profiler stations don't give you predictions — but they do verify or debunk trends. Conversely, the winds aloft forecasts don't tell you what is, and forecasts can be wrong. A thorough preflight analysis plays one off the other, but you probably won't have time to do this before every flight. However, you should have a record of the predicted winds aloft to take with you in the airplane to compare to the winds that you get — a significant change from the forecast can not only alter your speed dreams, but it can also cut into your fuel reserves.
When we looked at winds aloft forecasts and wind profiler notes, we found another mixed bag. The closest wind profiler station to our home base is at Fort Meade, Maryland. On one flight, while flying a box pattern about 25 nm northwest of this station, we noted winds that had picked up by 10 or 15 kt from the last reading. The direction was right on, and the increase wasn't out of the blue, as the velocity had been on the upswing all morning. On another flight, we saw headwinds that were a good 25 kt more than the winds aloft forecast for a station directly on our route. Again: Direction, good. Velocity, not so much. Hey, we all have bad days.
Altitude also leads to faster speeds if you use it correctly. Maintaining a given indicated airspeed at a given altitude and a given aircraft weight requires a given angle of attack and the lift it generates. As fuel burns, aircraft weight decreases, and less angle of attack is required to maintain a given altitude. You can translate that extra oomph to knots by allowing the airplane to climb as fuel is burned and taking advantage of the higher true airspeeds available at higher altitudes — unless the actual winds aloft put more on your nose as you climb.
Trim and use of the autopilot. It's as simple as this: Trim the airplane to straight and level in all axes before setting the autopilot. Fuel imbalance can cause the autopilot to trim for the imbalance, allowing the airplane to fly through the air sideways. Monitor fuel loads closely and retrim periodically and reset the autopilot. If you have roll trim, set the roll axis level by using a point on the horizon. Also, a level airplane starts on the ground — the turn coordinator simply tells you where your CG is in a turn. Get the aircraft on the level to see where the ball is on the ground.
Be smooth. A close corollary to &mart use of the autopilot is to mimic its grace when you're hand flying. Sloppy airplane handling robs you of 'peed as surely as anything mechanical. What's the gain if you go to great lengths to have the airplane tightly rigged and then waste it by flying with a drooping aileron or a rudder out in the slipstream? In our test flights, we gained a few knots when we stayed coordinated.
Lean for best power. According to Thomas, "The easiest way to go fast is to put the throttle to the wall and lean the mixture for best power. You'd be surprised at how many pilots don't do that." Some aircraft are limited by the rpm gauge from running longer than a few minutes at full throttle, and some pilots argue that a firewalled engine won't meet time between overhauls. Thomas has had different luck. "My own Cherokee 140 only knew two throttle positions, fully open or fully closed, except on final. Its engine lasted well over 3,000 hours." However, some props are tuned to work best at a given rpm, so any additional juice is wasted at the prop hub.
And don't forget to close the cowl flaps after the climb, once engine temps warrant. Open cowl flaps can cost you 3 kt or more. Check yours to ensure they don't sag, too, by closing them after you shut down.
Check airspace for route planning. A little bit of preliminary sleuthing paves your way to the most timesaving route. For example, I plotted a flight last summer from Hampton Roads Executive Airport in Norfolk, Virginia, back to Frederick, Maryland. A quick scan of the chart showed that a direct route would cross right through the Washington, D.C.-area Class B airspace. I'd spent months avoiding the area — with its brick wall of temporary flight restrictions. But I had heard that the controllers at Dulles Approach were allowing VFR traffic to transition their chunk of the tri-area pie just east of the airport — and just west of the 15-nm TFR around the Washington metro area.
Going around the Class B on this leg was no small task — it would add about 30 nm and 20 minutes to the trip. And a climb to 10,500 feet to avoid the Class B? Another 20 minutes in this vintage Piper Archer. So I changed my routing to go direct to the Brooke VOR, 37 nm south of Washington Dulles International Airport — and see what transpired.
Listening to the approach frequency, I heard controllers vectoring the airliners for landing to the south. My call was answered with a brisk clearance to maintain 4,500 ft and proceed direct to an uncharted intersection, which translated to a heading of about 10 degrees. Controllers called out my Piper speck to one Boeing 737 pilot after another as they descended from 6,000 to 4,000 ft on their way past me. After a compliment from the controllers for precise navigation and with a local "mountain" in sight, I departed the Class Bravo 20 quick nm later, saving time, avgas, and about $17.50 off my aircraft rental.
Ah, the rewards of going fast.
E-mail the author at [email protected].
Related Articles
