Retractable Landing Gear Features and Installation
Landing gear is the undercarriage of aircraft that allows pilots to takeoff, taxi, and land with ease. It is designed to absorb and dissipate the kinetic energy of landing impact; thus, reducing the impact loads imposed on the airframe. On small aircraft, landing gear consists of three wheels, two of which are on either side of the fuselage and one is positioned at the front or rear of the aircraft.
The arrangement of the wheels is mission-oriented and highly dependent on the aircraft type. There are three basic wheel arrangements: conventional, tandem, and tricycle-type variations. Other than this, landing gear can also be classified as either fixed or retractable. In this blog, we will be looking at retractable landing gear in particular and how it is installed in an aircraft.
The installation of landing gear is fairly straightforward, wherein the main gear retractable unit is mounted perpendicular to the centerline of the fuselage and parallel to the lower surface of the wing. Meanwhile, the nose gear is usually mounted directly to the firewall. However, for some aircraft, like WWII fighters, the gear is arranged so the struts rake forward relative to the wing chord line when extended, and rake away from the span line when retracted.
To better understand how landing gear is installed, we will outline the process for a hypothetical model with the strut raked forward 10 degrees in side view, raked aft 20 degrees from a bird's eye view, and perpendicular to the flat center section of the wing. With this configuration, it becomes clear that you must tilt and rotate a part of the assembly to get the strut where it belongs.
By tilting the entire mechanism 10 degrees forward in the side view and 20 degrees backward in the bird's eye view, a 20 degree toe-in on the extended wheel is created, but it can be fixed by twisting the strut 20 degree counterclockwise in the trunnion. This configuration is optimal, depending on the size of the aircraft tire and the thickness of the wing.
At this point, you must add a cover door to the strut. Usually, it must be parallel to the tire, but with this arrangement, it may be unaligned with the lower wing skin in the retracted position or angled to the slipstream when the gear is extended. The required retraction angle can be calculated using solid geometry, trigonometry, and a calculator.
Begin by calculating the distance between the lower end of the strut in the extended and retracted positions, and then plug this number into the Law of Cosines to derive the retraction angle. The resulting value is only an approximation since it does not take the kink angle into consideration. Keep in mind that commercial retractable landing gear is available with retraction angles varying in 5 degree increments.
As the aforementioned example is for a smaller aircraft model, installation for a full-scale aircraft may slightly differ. Nonetheless, the process is pretty simple and can be carried out on small models to perfect one’s method of installation. During installation, if you find that you require aircraft parts, such as axle landing gear parts, seat rails, gear mounts, wheel fairings, and more, rely on a dependable distributor like Cogent Sourcing.
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