Tuesday, March 24, 2009
To retract or not to retract? That is the question.
Bowen outlines a number of advantages of flying above fixed gear: “First, in the design phase, retractable gear can limit airfoil design to a section that’s thick enough to enclose the wheel. A thinner wing is usually more efficient, but that’s sometimes inimical with retractable gear. The Bellanca Viking, for example, retracts its gear directly forward into the thickest part of the wood wing, and while the double clamshell doors do cover the wheels, they leave a major bump beneath the wing.
“Similarly, you can place fixed gear in the optimum position under the wing rather than have to adjust its location with concerns about compromising structural elements in the fuselage and wing,” Bowen explains. “Gear support and structure can be less robust with fixed gear, and the surrounding structure doesn’t need to be heavily reinforced to maintain the load carry-through. Placing the wheels in the proper geometric position can make a big difference in ground control, especially during crosswind landings.
“A retraction system exacts a penalty in weight and complexity, and unless you increase gross weight to compensate, that may subtract from payload. It also translates directly to cost, so a retractable of a given seating capacity and horsepower will nearly always be more expensive than a fixed-gear model.”
Insurance can be more of a hassle with a retractable, simply because it’s one more system that may be mishandled. “Insurance costs aren’t necessarily prohibitive with retractables,” Bowen admits, “but it’s one more factor that weighs against airplanes that hide the wheels.” Repair costs can be considerably exaggerated with retracts, according to Bowen, and simple system maintenance is more costly.
The most often quoted benefit of retractable gear is better performance, and cleaning up the underwing does reduce drag and allow the aircraft to climb and cruise faster. The climb delta is a little tougher to quantify, but Bowen suggests the difference may be as much as 10% to 15%. In the case of the Cessna 400, the plane would probably levitate 150 to 200 fpm quicker with a clean underwing.
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