Thursday, May 1, 2008
Flying With Speed Brakes
Speed brakes can ease the process of descent and landing, and they can even decrease engine wear and tear on piston aircraft
Some piston pilots have a philosophical objection to speed brakes, arguing that it’s a cardinal sin to deliberately fly a fast airplane slow. In the VFR world where pilots can pretty much do their own thing, that’s partially true. Most pilots of unpressurized piston airplanes plan their descents for 500 to 700 fpm, dependent upon such factors as wind, terrain, turbulence and temperature.
This means if you’re descending from a 10,500 cruise altitude to a near sea-level airport, you’ll need to start down somewhere between 19 and 14 minutes out. Letdowns quicker than about 800 fpm may cause some passengers problems in equalizing air pressure in their ears. A properly executed descent and approach can recover some of the time lost in climb and improve block speed.
Spoilers commonly come in two varieties, depending on aircraft type. Most piston singles employ a pair of bridgework-style brakes that rotate up out of each wing (they’re usually mounted to the rear spar just forward of the outboard flap hinge). This allows for maximum lift disruption with a minimum of structure and weight, but not in the critical forward portion of the chord. Larger aircraft such as 421s and other corporate twins employ larger, rectangular “boards” to block more air, but produce the same result.
(Military airplanes may mount spoilers practically anywhere, on the sides or top of the fuselage, on top and/or bottom of the wing, even on the vertical stabilizer. These can be huge and have dramatic effects. I flew with the nine-plane Canadian Snowbirds team many years ago, and their little Tudor jets mount large speed brakes on the sides of the aft fuselage, providing them with spectacular braking action for rejoining formation after breakup maneuvers.)
The concept and design of speed brakes is so simple that flying with spoilers installed doesn’t demand a nuclear brain surgeon. Unlike flaps that may be partially extended in piston aircraft, spoilers or speed brakes are all or nothing. You either need them or you don’t. Glider pilots learn to use spoilers in their first hour of training, and without the benefit of power, they must rely on them to help regulate descents on practically every flight. Extending the boards is a little different than operating with a clean wing, but there are rarely operational problems.
Asymmetric deployment is an obvious concern, though it’s a highly unlikely event. If one brake begins to deploy and the other doesn’t, a sensor will automatically clue the rising brake to stop and retract. Even if you did suffer a full asymmetric deployment, the companies that produce spoilers are required to demonstrate easily controlled flight with one up and one down. Icing is sometimes a concern and can cause delayed deployment or only partial extension.
Sadly, the principle of TINSTAAFL (there is no such thing as a free lunch) still rules. Nothing is free, and installing speed brakes will subtract from both your payload and your bank account. Payload reduction is minimal, about nine pounds, and there’s little or no performance loss (although the brakes do require cutting a slot in the top of the wing, it’s so far aft that airflow is usually long since separated). There’s no noticeable drag penalty when the brakes are stowed.
The brakes themselves and the actuation mechanism aren’t too expensive, but installation is fairly labor intensive. My Mooney mounts a set of electrically activated Precise Flight brakes, and installation required about 40 hours of labor. Fill in your own shop rate, but you’ll probably pay at least $3,000 for the install.
Speed brakes are approved for a wide variety of airplanes. As mentioned above, Precise Flight of Bend, Ore., is perhaps the most prolific producer of GA speed brakes. Precise Flight has certified several dozen aircraft models for speed brakes and has delivered some 6,000 systems since 1982. Another prominent manufacturer is Spoilers Inc. (www.powerpacspoilers.com) of Gig Harbor, Wash., which specializes in spoilers for corporate twins like Cessna 300/400s, Dukes and Aerostars.
Call them what you will, speed brakes, spoilers or boards definitely aren’t for everyone. They wouldn’t offer any significant advantages installed in a Warrior or Skyhawk, and it’s unlikely you’ll see them on any LSA. If you fly anything from a Lear to a Bonanza, however, speed brakes can help control glidepaths, reduce shock cooling, facilitate speed reductions to maneuvering, flap or gear limits and lend a welcome assist when it’s time to return to the runway.
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