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Landing Gear (Undercarriage) Arrangement

Landing Gear (Undercarriage) Arrangement. 1. Single main gear Pros Simplicity: this the reason why it is used in many sailplanes. The wheel can be either forward of the cg or aft of the cg. In the latter case a skid is required under the cockpit. Saiplane landing.

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Landing Gear (Undercarriage) Arrangement

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  1. Landing Gear (Undercarriage) Arrangement 1. Single main gear Pros • Simplicity: this the reason why it is used in many sailplanes. The wheel can be either forward of the cg or aft of the cg. In the latter case a skid is required under the cockpit.

  2. Saiplane landing

  3. Landing Gear (Undercarriage) Arrangement 2. Bicycle gear: 2 main wheels, fore & aft of the c.g. small outrigger wheels required on the wings to prevent the ac from tipping sideways Pros • Can be used on ac w. narrow fuselage(B-47, U-2). Cons • Aft wheel is so far behind the c.g. that the ac must takeoff and land in a flat attitude (cannot rotate). This limits the use of this type of LG to ac w. high L at low aoa (high AR wings w. large camber and / or flaps).

  4. B-47

  5. U-2

  6. Landing Gear (Undercarriage) Arrangement 3. Tailwheel (taildragger) Pros • Tailwheel is small, light, and simple to design. • AC lands in a flat attitude, hence the D is low. • Easy attachment of the main LG on the wing. • Good for rough field operation (allows the wing to generate more L and get off the ground sooner). • A 3-point LND can be made by stalling the ac. The resulting D is desirable when airfield is unsuitable for full brake application. • When brakes are applied, the vertical load on the main LG increases, reducing the risk of skidding. • Provides greater clearance for a front propeller or wing LE-mounted props.

  7. Lockheed Electra

  8. Lockheed Electra

  9. Landing Gear (Undercarriage) Arrangement 3. Tailwheel (taildragger) Cons • Inherently unstable: • Violent braking will tip the ac to its nose. • Braking force acts ahead of the cg and has a destabilizing effect when the ac is moving at an angle of yaw. This may cause a ground loop (ac drags wingtip, collapses the LG, or turns off the side of the runway) • In a 2-point LND a tail-down PM generated by the impact force on the LG, increases L and causes bouncing. • Difficult to taxi in strong winds due to the high wing incidence. • Inclined cabin floor is uncomfortable for passengers and inconvenient for loading. • Reduced pilot visibility over the nose during taxiing. • High D during the initial TO run until the tail can be raised.

  10. Beech Staggerwing

  11. Landing Gear (Undercarriage) Arrangement 4. Tricycle Landing Gear (Nosewheel) Pros • Inherently stable: braking force acts behind the c.g. so it is stabilizing, allowing full use of brakes. AC can be landed w. large “crab” angle in a crosswind. • Fuselage is level when the ac is on the ground. • The pilot has good view while taxiing. • Nosewheel protects the ac (especially the propellers) from turning over. • Low D during the initial phase of TO. • In a 2-point LND the LG generates a nose-down PM.

  12. C-182

  13. F-14

  14. L-1011

  15. Landing Gear (Undercarriage) Arrangement 4. Tricycle Landing Gear (Nosewheel) Cons • Nosewheel tends to be heavy because it must take 20-30% of the W under steady braked conditions. • Special structural provisions are generally required to accommodate the LG. • Difficult to find storage space for the nose gear in light ac. Note: Nosewheel must not be placed too far forward. If it bears less than 8% of the W the ac cannot be steered!

  16. Landing Gear (Undercarriage) Arrangement 5. Tandem Undercarriage (Quadricycle) B-52 Pros • The main legs are placed at nearly equal distances ahead and behind the c.g. Thus, there is locally a space for placing PL close to the c.g. • The wheels are retracted inside the fuselage w/o interrupting the wing structure. • Allows the cargo floor to be very low, close to the ground.

  17. B-52

  18. Landing Gear (Undercarriage) Arrangement 5. Tandem Undercarriage (Quadricycle) Cons • Outrigger wheels are necessary to balance the ac, resulting in 1% W increase. • Solution: Use 2 pairs of main wheels to get some track, so that outriggers do not take much W (B-52) • Pilot must carefully maintain proper touchdown attitude to avoid overstraining the LG. • Large tail-down PM is necessary to rotate the ac. • Solution: Design ac attitude (wing incidence) to fly off by itself (i.e. w/o the need to rotate) • Requires flat TO and LND attitude. • Solution: swivel wheels.

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