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Electrical Engineering/Retractable mechanism for Landing gear in airplanes.


QUESTION: Dear Prof Cleggsan

Are the Landing gears always retractable in all airplanes ?.


Once the airplanes takes off, the front and rear wheels are always
folded ?.
Once the airplanes wants to Land, the front and rear wheels are unfolded ?.

What are the Pros and Cons with and without having these retractable mechanism for Landing gears in airplanes ?.

Once the commercial airplane takes off by what time the front and rear wheels are folded ?. i.e. after 1/2 min, 1 min, 5 min, 10 min etc ....

Once the commercial airplane has to land before what time the front and rear wheels are unfolded ?. i.e. within 1/2 min, 1 min, 5 min, 10 min, 30 min etc ....

Are both these timings critical i.e. After plane take of and Before Landing and are these timings fixed globally as part of airplane operations ?.

Thanks & Regards,
Prashant S Akerkar


Is a good reference, of course.

And you can google around to find other discussions.

This is not an electrical engineering question so I offer only a personal comment.

The moment in time to pull up the wheels after takeoff is somewhat judgmental on the part of the  pilot.  Depending features are wind direction, load on the plane, airport geography and topography, type of aircraft and flight pattern that may dictate sharp radius.

On landing the same is true.  Judgment may dictate to drop the landing gear early to help slow down the aircraft caused by the need due to control tower asking for slight change of route.  Speed of approach may dictate some change in standard practice.  Pilot is in charge. The cockpit may get automatic signals to let the landing carriages down but the pilot has override depending on circumstances and flight conditions.  It has been known for aircraft to go down belly first because the pilot forgot to lower them; so I think alarms are now used to alert the pilot that the wheels are not down by a certain elevation, etc......

I don't think there are any international standards; but there are training manuals that give standard practices for the pilots to know what the variables are all about whilst flying the aircraft.

---------- FOLLOW-UP ----------

QUESTION: Dear Prof Cleggsan

Thank you.

Is it advisable for the pilot when the plane is in motion (flying) i.e. after airplane take of that in between they can also do "Wheels down" and "Wheels up" status ?.

Are there any specific advantages or disadvantages in doing Wheels down or Wheels up status when the plane is in motion i.e. running at specific speed in miles per hour ?.

Awaiting your reply,

Thanks & Regards,
Prashant S Akerkar

My guess is that the manual for operation of the aircraft gives cautionary advisors on when and how to extend the wheel  carriages when once in flight.  Emergency procedures and requirements aside there are probably severe restrictions on opening up the wheel  covers at high cruising speeds.  There may be automatic mechanisms that prevent opening the doors when in full flight and it would require an authorized override to allow the pilot to do so.

Please refer this question to an expert in the aviation field.  

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