CF188A
Topic Author
Posts: 680
Joined: Sun May 07, 2006 12:27 am

Engineering Of Landing Gear : Gear Transition

Thu Apr 26, 2007 11:29 am

I find that many aircraft in today's world, have a very unique cycle to their landing gear after take off and before landing. The F-16 seems to pivot the gear before retracting it forward on a slight angle inwards. The C172RG does some fancy hornet tail hook thing with it's landing gear, the F-15 eagle retracts it's gear in under two seconds. I find the C-17 has a very unique extension and retraction as well. So, my question is... from an engineering aspect; the method's and brains behind these transitions, does it simply only have to do with fitting the gear in the gear bay? Are other circumstances taken into effect? The F-16 for example, if it was to rotate its gear 90 degrees before retraction, you would have the entire surface area or the wheel acting as drag, as opposed to just the frontal width of the gear. I thought this would be a remotely interesting topic so, cheers. I look forward to some great info if it's available. This can be aimed to commercial aircraft as well Smile

[Edited 2007-04-26 04:30:06]
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FredT
Posts: 2166
Joined: Thu Feb 07, 2002 9:51 pm

RE: Engineering Of Landing Gear : Gear Transition

Fri Apr 27, 2007 1:43 am

As always, it is a world of compromises. Naturally you want the gear to retract fully into the fuselage without necessitating any bulges on the outside, which would cause drag. Aircraft today are crammed full pretty much to the last cubic inch, so space is at a premium. This means a pretty complicated retraction sequence/mechanism can be tolerated if it will allow you to save space in the aircraft.

On the other hand, the more complicated the mechanism the more likely failure becomes and the higher the cost and cost of maintenance. It also tends to add weight.

Quick retraction is good, of course, but how much more complicated are you willing to make it to get the gear in in half a second less? How much heavier hydraulic cylinders and mechanism are you preparing to lug around?

Do you want the aircraft to be able to perform short landings on unprepared runways? If so, the gear has to be sturdy. If you are only planning to operate out of ten-mile long runways which are smooth as glass, just teach the drivers to float down the runway and touch down gently and design a weak (but light) gear into the aircraft.

At what speed do you want to be able to have the landing gear out? At what speeds do you want to be able to extend or retract it?
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KELPkid
Posts: 5247
Joined: Wed Nov 02, 2005 5:33 am

RE: Engineering Of Landing Gear : Gear Transition

Fri Apr 27, 2007 5:27 am

Quoting CF188A (Thread starter):
The C172RG does some fancy hornet tail hook thing with it's landing gear,

I love the way Cessna's main landing gear retracts  Smile It has to go through a twisting motion before being put into the gear wells...The "Gutless" Cutlass (172RG) was designed well after Cessna decided to eliminate the gear doors and landing gear leg doors...good move on Cessna's part. I used to rent a 1962 Cessna 210B from a doctor, and the gear doors seemed to be the Achille's heel of Cessna's retract system (I had one flight where the main gear doors were stuck in the breeze all the way from ELP to HOB (Hobbs, New Mexico), and cycling the gear would not get them to come back up)  Sad Of course, when we took the plane back home, everything was normal again so that the mechanic could not witness the failure...eventually, the same failure happened to the A/C owner himself, and somehow the main gear doors got bent and scraped by contact with the ground that time (I guess he flares a little higher than I do  Wink ).
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