There may not be a really strong benefit to be gained from putting retractable landing gear on an airplane, but most builders and pilots have nevertheless felt the heat of desire when a sleek retractable-gear aircraft cruises past. That cleaned-up airframe just looks right. Flipping the gear switch or handle to “up” delivers a satisfying severance from the ordinary mortals who are stuck with dragging their wheels out in the breeze.
In truth, economics and common sense support fixed gear. When Cessna put retractable landing gear under the 182 Skylane, it picked up a mere 12 knots of top speed (as measured by the brochure), but the mod added nearly $20,000 to the base price, in 1978 dollars. A Glasair Super II FT (fixed tricycle) homebuilt can cruise at 210 mph, barely 11 mph slower than the RG version of the same design. There will be weight and maintenance penalties to be considered when installing retractable gear, and rough field operation should be avoided to a greater degree, given all the added stress on wear points like joints and linkages.
The landing gear indicators on the SubSonex jet are LEDs located above a guarded toggle switch.
And so, why do we do it? In the spirit of innovation, seeking to maximize every drag-reduction advantage, in order to maximize speed and range, we opt to fly with our wheels up. But in the final analysis, we do it because we want to. Even though a well-designed set of skinny fixed landing gear can approach the drag reduction of simple open-well retractable wheels, it’s just not aesthetically the same. Every Piper Cherokee owner wants an Arrow, even if he won’t admit it publicly.
The SubSonex main gear features two tires per side—just like the Space Shuttle and many large aircraft.
Putting It Together
It makes sense, however, to carefully weigh the pros and cons of retractable gear. From a design standpoint, we have to provide for a means to actuate the gear’s retraction and extension, which inevitably adds complexity and extra weight. There are three common methods of moving the gear up and down: manual, electric, and hydraulic, the latter sometimes involving an electrically driven pump. A simple manual system, using a lever or crank to move the gear, requires smoothly operating linkages and strong mechanical advantage to avoid overtaxing the pilot’s strength. In most cases, no backup extension method is provided, the manual system supposedly being failure proof.
When retracted, the main landing gear on this Velocity is almost entirely concealed by simple gear doors.
An electrically driven gear system uses a set of straight-run torque tubes to swing the gear, driven by a centrally mounted motor and transmission (or chain drive), typically bringing the main gear inboard and the nose gear aft during retraction. There must be a provision to disconnect the motor from the system to allow for a manual backup extension, in case the drive mechanism locks up. Seldom do such backup systems provide for retraction.
Designers of hydraulic gear systems have the advantage of being able to run the lines carrying pressurized fluid through Byzantine twists and turns, around corners, and through bulkheads, terminating with an actuator at each gear leg to motivate the gear in and out of its wheel well. The engineer is thereby freed from having to find a way to route a stiff actuating tube through a wing or fuselage. A source of pressure for the hydraulic fluid can be an engine-driven pump, an electrically driven power pack, or even a hand pump. The weakness of hydraulics is loss of the system’s fluid. Proper design makes provision for a standpipe, separate from the main reservoir, that will retain enough fluid for an extension cycle if a rupture occurs elsewhere. Most often, hydraulic pressure holds the wheels up, so emergency extension can be done by releasing the trapped pressure and letting gravity do its work, but springs may be needed to move forward-rotating gear legs over center to securely lock down. A standby “blowdown” bottle of compressed gas is used in some systems to force the gear into place.
However the gear system works, it needs regular attention, including placing the plane on jacks and observing its cycle, in order to keep it rigged properly and check for wear in bushings, joints, and attachments. Gear doors, switches, and motors are subject to periodic adjustment and maintenance. Fixed gear, on the other hand, is largely forgotten about between tire changes.
Velocity nose gear viewed through an access panel. In flight, the gear is completely covered by tight-fitting doors that match the contours of the forward fuselage.
There’s Those Who Have… And Those Who Won’t
Misoperation of retractable gear, resulting in a gear-up landing, adds to insurance costs and affects resale value of the aircraft. While mechanical failures do account for some of the gear-up landing incidents, most of the time it’s a simple lapse of pilot attention that contributes to an ignominious termination of the flight. System failures might manifest themselves as having one gear not locking into position, but when a landing occurs with all the wheels up, it’s more than likely an “oops.” Later on, I’ll be telling you about how I made my first gear-up landing.
It is not true that every pilot flying a retractable will eventually slide to a stop on the airplane’s belly. We can, and we must, take measures to make sure it never happens to us. A properly designed retractable gear system will include mechanical or illuminated position indicators, actuated to show a gear-down indication only when the cycle is fully complete. To make sure the pilot is aware that the wheels are still up during a landing approach, a throttle-actuated switch should sound a warning tone if power is reduced below a throttle position corresponding to 12 to 15 inches of manifold pressure with the gear up. Recently certificated airplanes will also have a flaps-extension warning that actuates when flaps are extended beyond the approach setting with wheels retracted.
These are all excellent safeguards, but the ultimate safeguard has to be a participating pilot. It is not enough to say “I always do a GUMP (gas, undercarriage, mixture, prop) check on the downwind leg” or “I never fail to use the checklist.” Gear-up landings occur because we didn’t pay attention, despite the checklist. When we encounter a break in the normal routine, a distraction, or a hurried approach, the warnings and indications may be overlooked. Headsets can do a fine job of masking a weak warning horn.
The transition from draggy gear-down configuration to sleek, fully enclosed gear-up turns the Lancair into an entirely different airplane. (Photos: Doug Henson)
You might habitually do the GUMP thing abeam the airport, but what about those times when you don’t fly a downwind? An unexpected traffic conflict might require a reapplication of power during a spacing turn, silencing the gear-up throttle switch. Doing a go-around heightens the risk of landing gear-up on the next attempt; because you were distracted by the sudden reversal of fortunes, you may think you left the gear down, but you didn’t.
A friend of mine had to reposition a few miles from one airport to another after a long day of flying. In his tiredness, he intended to leave the gear down as he essentially flew a parabolic arc across town. Instead, his right hand followed his regular habit: gear-up, power to cruise-climb, prop pitch tweaked, trim rolled in. He didn’t verify gear-down because he knew it was already down—until the prop blades bit into the concrete.
Extension of the landing gear should be done anytime the destination airport is neared: entering the pattern, descending to pattern altitude, passing the final approach fix, or lining up on base leg or a long straight-in final. Anytime landing is on the agenda, putting the wheels down is a priority, earlier being better than later.
Moving the gear control is not equivalent to extending the gear; check that the wheels actually made the trip, noting the “gear down” indication and passive backups like mechanical indicators and gear-position mirrors. Any pilot familiar with his or her aircraft should be able to tell by the added drag, noise, and trim change that the gear has extended. In the absence of such normal changes, start double-checking. An abnormal reduction of power to stay on the glideslope probably means the gear isn’t down.
No matter what I’m flying, I always sit up straight and do a short-final check of landing readiness. Is the gear down? Is the prop pitch set for go-around power? Did the tower give me a “cleared to land”? You may not always fly a downwind leg or base leg, but you always have to fly down final. Make that short-final check as the end of the runway approaches.
In any checkout involving retractable gear operation, I invariably obscure a gear-down indication while the student is distracted. I can turn down a dimmable green light, flip the instrument lights to low-intensity night mode, or just hold my hand over the indicator. If the student fails to look for a gear-down indication on short final, the landing is deemed unsatisfactory. He or she should have gone around to troubleshoot the problem.
Having said all this, I will now tell you about my first gear-up landing. I flew a perfect approach to the touchdown zone, I leveled off normally, I eased the yoke back to reach the right attitude, and then let the aircraft settle onto the surface. The touchdown was as smooth as glass, and as I came to a swift, sliding stop, I opened the Lake Amphibian’s windshield to dabble in the water lapping at my elbow. Then I grinned and asked my instructor, “Can I do that again?” No, I haven’t made a gear-up landing on a runway.
Nice article. I guess it’s fixed tricycle 90% probability; conventional 9% probability; retractable 1% probability.