{"id":2515,"date":"2026-09-10T07:01:04","date_gmt":"2026-09-10T07:01:04","guid":{"rendered":"https:\/\/speed-reducer-gearbox.com\/landing-gear-retraction-planetary-reducer-reliability-overview\/"},"modified":"2026-09-10T07:01:04","modified_gmt":"2026-09-10T07:01:04","slug":"landing-gear-retraction-planetary-reducer-reliability-overview","status":"publish","type":"post","link":"https:\/\/speed-reducer-gearbox.com\/hi\/landing-gear-retraction-planetary-reducer-reliability-overview\/","title":{"rendered":"Landing Gear Retraction Planetary Reducer: Reliability Overview"},"content":{"rendered":"
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Electric landing gear actuation systems on modern aircraft \u00a1\u00aa from business jets and regional turboprops to large commercial transports experimenting with electrification \u00a1\u00aa use a planetary gearbox to convert electric motor output into the large mechanical force required to retract and extend the landing gear against aerodynamic loads, gravity, and gear door spring forces. The system must complete a full retraction or extension cycle in 5 to 15 seconds, hold the gear rigidly in the retracted or extended position without continuous power consumption, and be capable of gravity extension without any power if the primary actuation system fails. The planetary gearbox is the element that reconciles the motor high speed with the actuator need for very high force at very slow speed.<\/p>\n

Landing Gear Actuation Requirements<\/h2>\n

The force required to retract a main landing gear depends on the gear weight, the aerodynamic loads during retraction, and the spring forces from gear door actuators. For a business jet, the total retraction force on one main gear may be 15 to 30 kN applied over 0.4 to 0.8 m of actuator travel, at a rate of 0.05 to 0.10 m\/s during retraction. From a 400 W electric motor at 10 000 rpm through a ballscrew with 10 mm lead, the required motor torque is approximately 0.9 N\u00a1\u00a4m \u00a1\u00aa within a small servo motor capability when an appropriate planetary ratio is selected.<\/p>\n

\"Electric<\/p>\n

Self-Locking and Gear-Up Position Holding<\/h2>\n

When the landing gear is retracted and locked, the actuator must hold the gear in the wheel well against aerodynamic suction loads without continuous motor current. Three holding methods are used: a mechanical uplatch that locks the gear structure in the retracted position, a self-locking screw at low lead angle which is irreversible without powered backdrive, or a motor brake that is spring-applied when the motor is de-energised. Most aircraft use an uplatch as the primary holding device and the actuator as the force source only during retraction and extension.<\/p>\n

\n\n\n\n\n\n\n\n\n\n
Holding Method<\/th>\nMechanism<\/th>\nReliability<\/th>\nWeight<\/th>\nComplexity<\/th>\n<\/tr>\n<\/thead>\n
Mechanical uplatch<\/td>\nLatch hooks gear structure<\/td>\nHighest passive<\/td>\nLow<\/td>\nRequires release mechanism<\/td>\n<\/tr>\n
Self-locking screw<\/td>\nLead screw below friction angle<\/td>\nHigh passive<\/td>\nLow<\/td>\nLimited speed lower efficiency<\/td>\n<\/tr>\n
Motor brake<\/td>\nSpring-applied electromagnetic release<\/td>\nHigh electrical<\/td>\nModerate<\/td>\nRequires power to release<\/td>\n<\/tr>\n
Hydraulic lock<\/td>\nCheck valve traps fluid<\/td>\nVery high<\/td>\nModerate<\/td>\nRequires fluid circuit<\/td>\n<\/tr>\n
Continuous power<\/td>\nMotor holds continuously<\/td>\nLow power required<\/td>\nVery low<\/td>\nNot used in practice<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

Uplatch is standard on most fixed-wing aircraft; motor brake is common on electric actuation systems.<\/p>\n<\/div>\n

Backlash and Position Accuracy Requirements<\/h2>\n

Landing gear actuation systems do not require the sub-arc-minute positioning accuracy of CNC or robot joints \u00a1\u00aa the primary requirement is reliable full extension and full retraction within the timing budget, and positive lock engagement when fully extended. Backlash in the planetary gearbox is therefore less critical than in servo applications; 5 to 10 arc-minutes is acceptable. The more critical property is torsional stiffness \u00a1\u00aa the actuator must resist the aerodynamic loads that try to push the gear out of the wheel well without excessive compliance. The AB115 high-precision planetary series<\/a> provides the torsional stiffness needed to resist actuator compliance in landing gear applications, and the AD110 right-angle planetary series<\/a> serves installations where the actuator must fit in a constrained space requiring a perpendicular output shaft relative to the motor axis.<\/p>\n

\"Landing<\/p>\n

Emergency Extension and Gravity Drop<\/h2>\n

All aircraft landing gear systems must provide a means of extending the gear in an emergency if the primary powered actuation system fails. For hydraulic systems, this is a manual valve release allowing the gear to fall under gravity. For electric actuator systems, the emergency extension may be by manual hand crank that back-drives the planetary gearbox and actuator to release the uplatch, or by a dedicated emergency battery-powered motor. The planetary gearbox must be back-driveable by the manual crank at the force a pilot can apply \u00a1\u00aa typically 100 to 200 N at the crank handle \u00a1\u00aa which sets an upper limit on the gearbox ratio and the actuator lead screw efficiency that the designer must respect to ensure gravity extension remains possible. For comparable precision actuator drives in demanding applications, the VRV040 precision worm gearbox<\/a> illustrates the alternative approach where self-locking is used as the position-holding mechanism.<\/p>\n

\"Electric<\/p>\n

Frequently Asked Questions<\/h2>\n
\n
\n1. Why are electric landing gear actuators replacing hydraulic systems on some aircraft?+<\/span><\/summary>\n
Three advantages drive electrification: elimination of the hydraulic system including pipes, fluid reservoir, pump, and the risk of hydraulic fluid fire from a burst line near a heat source; reduced maintenance because electric actuators have fewer fluid seals and no hydraulic fluid to leak or degrade; and weight reduction for small aircraft where a dedicated hydraulic system is heavier than an electric alternative. For large commercial aircraft, hydraulic systems remain standard because they provide very high force density and inherent redundancy through the common hydraulic manifold serving multiple systems.<\/div>\n<\/details>\n
\n2. How is the landing gear retraction time calculated?+<\/span><\/summary>\n
Retraction time equals actuator stroke divided by actuator speed. Actuator speed equals motor speed divided by ratio multiplied by screw lead. For a 400 mm stroke at 0.07 m\/s: retraction time = 0.4 divided by 0.07 = 5.7 seconds. Verify that the motor does not overheat in this period \u00a1\u00aa a 400 W motor running 6 seconds at maximum torque produces 2 400 J of heat, well within the thermal capacity of a small servo motor at the rated duty cycle for landing gear actuation of perhaps 10 cycles per day.<\/div>\n<\/details>\n
\n3. What certification standard applies to electric landing gear actuators?+<\/span><\/summary>\n
EASA CS-25 and FAA FAR Part 25 for large aircraft, EASA CS-23 and FAR Part 23 for small aircraft. The actuator must demonstrate a specific probability of failure below 10 to the minus 9 per flight hour for loss of the gear-down function, which is a catastrophic failure condition. This requires redundant actuation systems plus the mechanical gravity extension backup. Australian CASA regulations for locally-designed and built aircraft follow the EASA\/FAA standards under bilateral agreements.<\/div>\n<\/details>\n
\n4. What motor type is used in an electric landing gear actuator?+<\/span><\/summary>\n
Brushless DC permanent magnet servo motors are standard for electric landing gear actuators in modern aircraft. They are compact, highly efficient at typically 90 to 95%, and reliable over the millions of cycles of aircraft service life. The motor controller is typically a dedicated brushless motor controller rated for the aircraft electrical bus voltage, which is 28 V DC for small aircraft or 270 V DC for larger aircraft with high-voltage DC distribution.<\/div>\n<\/details>\n
\n5. Can a standard industrial planetary gearbox be used in an aircraft landing gear actuator?+<\/span><\/summary>\n
For experimental and homebuilt aircraft under CASA RAAus or CASA Part 21 experimental certification, industrial precision planetary gearboxes in the AB115 to AB180 range are used in landing gear actuators by some builders. The key considerations are the temperature range from minus 40\u00a1\u00e3C at altitude to plus 80\u00a1\u00e3C on the ground in summer, corrosion protection from unpainted steel corroding rapidly in wheel well environments, and back-driveability for emergency extension. Document all specifications and justify all design decisions to the certifying authority.<\/div>\n<\/details>\n<\/div>\n
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Speak with a Planetary Drive Specialist<\/h3>\n

Share your torque requirement, ratio, and application environment \u00a1\u00aa our team at Condell Park NSW returns a sized recommendation and stock check within one business day. No obligation.<\/p>\n

\n
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ADDRESS<\/div>\n

27 Harley Crescent
Condell Park NSW 2200<\/div>\n

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PHONE<\/div>\n

+61 2 9708 3322<\/p><\/div>\n

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EMAIL<\/div>\n

sales@speed-reducer-gearbox.com<\/p><\/div>\n<\/div>\n

Send Enquiry →<\/a><\/div>\n<\/div>","protected":false},"excerpt":{"rendered":"

Electric landing gear actuation systems on modern aircraft \u00a1\u00aa from business jets and regional turboprops to large commercial transports experimenting with electrification \u00a1\u00aa use a planetary gearbox to convert electric motor output into the large mechanical force required to retract and extend the landing gear against aerodynamic loads, gravity, and gear door spring forces. The […]<\/p>","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_et_pb_use_builder":"","_et_pb_old_content":"","_et_gb_content_width":"","footnotes":""},"categories":[1],"tags":[],"class_list":["post-2515","post","type-post","status-publish","format-standard","hentry","category-uncategorized"],"_links":{"self":[{"href":"https:\/\/speed-reducer-gearbox.com\/hi\/wp-json\/wp\/v2\/posts\/2515","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/speed-reducer-gearbox.com\/hi\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/speed-reducer-gearbox.com\/hi\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/speed-reducer-gearbox.com\/hi\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/speed-reducer-gearbox.com\/hi\/wp-json\/wp\/v2\/comments?post=2515"}],"version-history":[{"count":0,"href":"https:\/\/speed-reducer-gearbox.com\/hi\/wp-json\/wp\/v2\/posts\/2515\/revisions"}],"wp:attachment":[{"href":"https:\/\/speed-reducer-gearbox.com\/hi\/wp-json\/wp\/v2\/media?parent=2515"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/speed-reducer-gearbox.com\/hi\/wp-json\/wp\/v2\/categories?post=2515"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/speed-reducer-gearbox.com\/hi\/wp-json\/wp\/v2\/tags?post=2515"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}