Landing gear being lowered due to combat damage

[Jenisch]

Hello,

One type of failure that occured at least in WWII planes, was the landing gear some times coming down after the plane suffered combat damage. I don't know why this occured, someone can explain?

 

[tyrodtom]

If the locks that hold the landing closed fail for whatever reason, then the weight of the landing gear is going to tend to pull it down.

 

[Airframes]

Or if the hydraulic system, or emergency Co2 landing gear system was seriously damaged, on some aircraft types this could cause the gear to drop.
Also, lowering landing gear was the international signal for surrender - lowered gear was not always caused through damage.

 

[stona]

Also, lowering landing gear was the international signal for surrender - lowered gear was not always caused through damage.

Voila!
Surrendering aircraft (though not in the heat of combat) made their intention clear by lowering their gear,waggling their wings and in one case firing off every colour of flare they had onboard.
Cheers
Steve

 

[tyrodtom]

I know they used hydraulics, electric, or manual methods to retract the gear. But surely they don't depend on hydraulic, etc. to keep them up ?
The locks are automatic and require what method to unlock ? Manual ? Electric ? I'm sure there's many different systems, but just in general ?

 

[FLYBOYJ]

I know they used hydraulics, electric, or manual methods to retract the gear. But surely they don't depend on hydraulic, etc. to keep them up ?

Most of the time and depending on the aircraft - no.

The uplocks usually engage through sequenced hydraulic pressure. Once the gear reaches a certain point and engages the uplock a sequencing valve "may" retain pressure to the uplock remains engaged if hydraulically actuated. Here's a key, again depending on the aircraft - once the gear is up and locked and the pilot has "two or three greens" indicating the gear is up, the landing gear handle is placed in a neutral position, removing pressure from the system. This will vary aircraft to aircraft...

If the uplock is damaged or a pressure line keeping the uplock in place is ruptured. the landing gear may extend. Sometimes the landing gear doors are locked too and may support the landing gear, again, this will vary aircraft to aircraft.

The locks are automatic and require what method to unlock ? Manual ? Electric ? I'm sure there's many different systems, but just in general ?

Depends on the country and aircraft. The aircraft I mainly work on (L29s, 39s and most recently MiG-15UTI are all hydraulic

 

[Balljoint]

Not military, but I remember being on a Convair 880 that was pretty much buttoned up shortly after takeoff when a pronounced THUD and wind noise announced that the landing gear had fallen back down. Probably had something to do with copious hydraulic fluid streaming from the wing.

I suppose a down default is the better option.

 

[FLYBOYJ]

Not military, but I remember being on a Convair 880 that was pretty much buttoned up shortly after takeoff when a pronounced THUD and wind noise announced that the landing gear had fallen back down. Probably had something to do with copious hydraulic fluid streaming from the wing.

I suppose a down default is the better option.

That in the case of a larger aircraft may involve the landing gear dropping and a hinged drag strut extending into an over-centered position and locking the landing gear down.

in 4:18 of the video you could see the drag struts operate when the gear is lowered.


View: https://www.youtube.com/watch?v=ChPLaXqO0eQ

 

[Milosh]

What keeps the landing gear inner covers up on a P-51 up/closed? Iirc they close after the landing gear extended to full down but gradually lower after the a/c has been on the ground for awhile.

 

[FLYBOYJ]

I believe it was a combination or hydraulic pressure and locks with flow going to each component in sequence. Here's a link to a basic diagram

Hydraulic Landing Gear System on the P51 Mustang

 

[gumbyk]

I thought on the Mustang that the gear was held up with hydraulic pressure alone, so that the gear would free-fall in the event of a loss of hydraulic pressure. Hence, you always see them with gear doors and flaps down.