GEAR UP OR DOWN? A senior project engineer with Cessna, Tom Bowen weighs the costs and benefits of flying above fixed gear versus retractable gear (as with the Globe Swift above).
My first airplane was a retractable, but it was sometimes hard to tell.
It was a purely stock 1946 Globe Swift GC1B, and while the main wheels would retract— eventually—there often seemed to be little effect on performance. Though the airplane was a cute little devil and a fairly primo example of its kind, its performance was a country mile behind the “book.” Globe’s manual bragged of a 1,000 fpm climb at gross and a 120-knot cruise speed, but that was an ad writer’s dream. The reality was more like 500 fpm and 110 knots, all on a perfect day with optimum biorhythms and a full moon. On a hot day, the tiny electric motor that drove the gear would work its heart out trying to levitate the wheels into the wells, sometimes without success. Occasionally, the gear would get stuck about halfway up and refuse to retract the rest of the way. Other times, it would require 30 seconds to two minutes to lever the wheels into the wells. Fortunately, with help from gravity, the wheels always came back down.
As a result, I received a new pilot’s involuntary education into the difference between retractable and fixed-gear airplanes. The half-dozen airplanes I’ve owned since that first Swift have all been retractables, but over the years, I’ve had reason to question my choice.
Roy LoPresti’s Grumman American Tiger and Cheetah from the late ’70s were startling examples of efficient airplanes with fixed gear, but discounting homebuilts, they were pretty much alone until the ’90s. Today, there are a variety of production airplanes that offer near-retractable cruise speeds with fixed gear. The Cessna 350/400, Cirrus SR20/22, Diamond DA20/40 and Liberty XL2 all deliver excellent performance with the wheels down and welded.
I have a list of sources on all things aviation, and one of the best on aerodynamics and aircraft design is Tom Bowen with the Bend division of Cessna Aircraft. I first met Bowen when he was chief engineer at Mooney, then worked with him after he moved to Columbia Aircraft in Oregon and now deal with him as senior project engineer at Cessna Bend. Bowen has worked for major manufacturers of pistons and jets, retractable and fixed-gear airplanes, so he’s conversant with both sides of the argument. These days, his opinion favors fixed-gear designs.
Bowen feels general aviation retractables have their place, but he questions whether they’re worth the price in weight, utility, complexity and dollars for some pilots. “Properly designed wheel pants can go a long way toward recovering the performance advantages lost to retractable gear,” says Bowen.
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.
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.
Bill Cox is in his third decade as a senior contributor to Plane & Pilot. He provides consulting for media, entertainment and aviation concerns worldwide. E-mail him at [email protected]