Tuesday, March 24, 2009
To retract or not to retract? That is the question.
Cruise performance obviously benefits the most from putting the wheels to bed. The early-1980s Cessna Skylane and Skylane RG are perhaps the purest examples of the difference between fixed and retractable gear. Both airplanes sported a 3,100-pound gross weight, constant-speed props and roughly the same horsepower. The RG model offered a 1,140 fpm climb and 156-knot cruise, whereas the fixed-foot Skylane had a 924 fpm climb and 140-knot cruise.
Bowen emphasizes that those differences may shrink to relative insignificance on airplanes that fly high to achieve their best speed. “Again using the Cessna 400 as an example,” he comments, ”we’ve applied computer modeling to evaluate a clean airplane with the wheels totally enclosed beneath the wing. We know we give away about 18 knots at sea level to a clean airplane with the wheels totally enclosed in the wing. As you climb higher, however, parasite drag comprises a smaller percentage of total drag. Up in the thinner air at 18,000 feet, we’re only sacrificing about seven to nine knots. At 25,000 feet, the difference is more like five knots. In other words, on turbocharged airplanes operating in the flight levels, there’s very little cruise penalty to fixed gear.”
The engineer feels retractable gear can offer some advantages in landing mode. “Rough turf or gravel runways aren’t kind to tightly faired wheel pants on high-performance airplanes. There’s less ground clearance, and the result can be damage to the fiberglass. Additionally, in the worst-case scenario, a retractable offers the option of landing gear-up in the event of an engine problem, and that may minimize the possibility of winding up inverted in rough terrain.”
Most pilots agree that a retractable-gear airplane looks better in flight than a fixed-gear version of the same machine. The Cessna Cardinal RG is an example of a design that was transformed from an admittedly attractive airplane to a work of art by simply retracting the wheels.
Tom Bowen is quick to acknowledge that retractable gear does offer some advantages, especially with rising fuel prices that encourage maximizing nautical mpg. But with proper design, fixed gear can achieve many of the same goals at a lower overall operating cost.
Page 3 of 3