15
$\begingroup$

What happens to the spinning landing gear right after V2 on takeoff? Are they automatically or manually braked to a halt before gear retraction? Or are they allowed to spin to a halt in the wheel wells?

I am asking this question in the context of common passenger planes, such as the Boeing 737-800 or the Airbus A320.

$\endgroup$
26
$\begingroup$

The question was formulated in the context of a jet liner such as the Boeing 737-800 or the Airbus, I do not understand why there are persons responding to this question in the context of a smaller less complex aircraft.

With that being said, I will like to expand the answer by DeltaLima. Boeing uses a device attached to the Brake Metering Valve Module called a De-spin Actuator. This device directs controlled hydraulic fluid to the brakes when the landing gear lever is set to retract to stop the spinning of the wheels. More information can be found in the AMM ATA 32 (Aircraft Maintenance Manual Chapter on Landing Gear).

https://www.facebook.com/aviationisawesome/videos/1598830786833154/

Video of a 737-500 from inside the main gear wheel well shows:

  1. After becoming airborne, the landing gear suspension unloads and the wheel hangs down, still spinning
  2. Once the main gear arms begin retracting, the wheel stops within a second
  3. The gear has fulled retracted in 6-7 seconds.

De-Spin Actuator

Source: http://www.eaton.com/ecm/groups/public/@pub/@eaton/@aero/documents/content/ct_194202.pdf

$\endgroup$
  • 1
    $\begingroup$ Welcome to Aviation.SE Andres! Very interesting answer, I hope you come back with more of those. $\endgroup$ – DeltaLima Jun 27 '15 at 0:08
  • 1
    $\begingroup$ I especially like how you can see the RH main wheels "push" downwards when the aircraft rotates. Very nice video; thanks for sharing (and answering). $\endgroup$ – pr1268 Nov 24 '17 at 23:52
  • 2
    $\begingroup$ Video is unavailable. In the future, it would be nice if the content of the video are described so that if a link goes bad, the answer here is still useful. $\endgroup$ – mahboudz May 14 at 20:50
  • $\begingroup$ @mahboudz agreed, I've managed to find a copy at facebook.com/aviationisawesome/videos/1598830786833154/…, and I submitted an edit to this post to add a description of what happens in the video. $\endgroup$ – zymhan Aug 16 at 14:09
29
$\begingroup$

In most common passenger aircraft brakes are automatically applied when the gear is retracted. The wheels stop spinning before they enter the wheel well. This is particularly important because a spinning damaged tire may cause damage to hydraulic and fuel lines which are usually routed near the wheel bay.

The nose wheels have no brakes, so they are spinning while they are being retracted. Most aircraft have rubber brake pads (snubbers) fitted in the nose gear bay that stop the spinning of the gear once the wheels are retracted.

$\endgroup$
3
$\begingroup$

These are the "nose wheel spin brake linings" (the braking pads) that stop the spinning of the nose wheel after retraction.

enter image description here

$\endgroup$
2
$\begingroup$

I fly retracts and have heard this question a dozen times. Some people say to tap the brakes, other people (like me) never do. I have asked certified mechanics, and they have all said it doesn't matter.

My advice is to follow the POH. If it says tap the brakes, then do so. Otherwise do or don't it doesn't matter.

$\endgroup$
  • 1
    $\begingroup$ I was checked out in a Cessna 172RG Cutlass, and the POH did indeed specify applying brakes before retracting gear. $\endgroup$ – Fred Larson Dec 15 '14 at 17:51
  • $\begingroup$ There you go. The 177 I flew probably said the same thing but I don't recall. $\endgroup$ – rbp Dec 15 '14 at 18:03
2
$\begingroup$

General policy when operating a retractable gear aircraft is to apply brake pressure after becoming airborne and prior to commanding the retraction of the landing gear. This causes the wheel to cease spinning, removing gyroscopic precession loads on the landing gear during retraction (remember a spinning tire acts like a big gyroscope and wants to maintain its orientation in space) as well as reduces the chances of damaging components inside the wheel well when the gear is stowed.

$\endgroup$
  • $\begingroup$ What does this answer add that isn't in any of the other answers? $\endgroup$ – Notts90 Jul 23 '17 at 9:03
  • 2
    $\begingroup$ Correctly noting that spinning wheels create gyroscopic precession loads on the gear during retraction? $\endgroup$ – Carlo Felicione Jul 23 '17 at 9:53
  • 1
    $\begingroup$ No they didn't. That poster described it as centrifugal force. It is not. $\endgroup$ – Carlo Felicione Jul 23 '17 at 17:15
  • 1
    $\begingroup$ Could you have notified the poster of the misnomer in a comment to their answer? $\endgroup$ – Koyovis Jul 23 '17 at 17:46
  • 1
    $\begingroup$ No. I make my own comments in this case. $\endgroup$ – Carlo Felicione Jul 23 '17 at 19:34
1
$\begingroup$

Follow the POH is always the best and most correct answer because it is different on different models and types.

I have a 1971 C177RG POH in front of me right now and it says:

Landing Gear Retraction Before retracting the landing gear, the brakes should be applied momentarily to stop wheel rotation

$\endgroup$
  • $\begingroup$ Yabut in FAA parlance "should be" is not required, and "must be" or "shall be" is required. So this POH language is a suggestion not a requirement. $\endgroup$ – Skip Miller Dec 18 '14 at 16:47
1
$\begingroup$

On the 737, the main gear gets gear retract braking pressure when the gear lever is placed in the UP position. It also doesn't hurt that a heavy brake stack will close up under gravity as the wheels are turned horizontal during retract. The nose wheels are free to spin up into the wheel well, where they contact a friction brake that drags on the tires; slowing and stopping nose wheel spin.

$\endgroup$
-3
$\begingroup$

Actually, the main reason brakes are applied to stop spinning wheels is the centripetal and centrifugal forces. These forces are a reaction to the spinning of wheels. As the gear is retracted, the forces that would be generated would cause uncontrollable vibrations throughout the aircraft. The result would be catastrophic. Want an example of how this works, find a fidget spinner. While it is spinning, rotate the spinner on an axis. You will feel the spinner "wobble". Now imagine the landing gear and the speed they are rotating at.

$\endgroup$
  • $\begingroup$ I believe you mean gyroscopic forces. $\endgroup$ – Koyovis Jul 23 '17 at 22:14

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.