Gear re-trackment speed


#1

Anybody notice that during take off a 737s gear is almost immediately re-tracked compared to the take off of a 777 the gear re-trackment speed is alot slower. These planes are just an example

Faster gear speed (737 CRJ B1900 Q400 E120) Slower (777 747 A380 A340 A330)

I’m looking for an answer to this, any one know? 8)


#2

Speed is a direct variable relation to the re-trackment velocity coefficient of the Prosser valve setting on the re-derackment setting on the rotary switch on overhead panel 3B.

Right JHEM?


#3

You know you’re going to Hell, right? :mrgreen: :smiling_imp:


#4

Who, me??? :open_mouth:


#5

There is no “reason” behind it, bigger planes have bigger actuators that take longer to operate is one reason, another reason is that there is a timing sequence for planes with gear doors compared to a 737 that has none. After maintenance to the systems, during operational tests, most of the manuals will tell you to time the extend and retract operation. There are many reasons, but no ultimate “this is way” reason.


#6

Ive always thought it was up to the pilots when the gear comes up, just wanted to dig deeper into my question. :wink:


#7

Thought you were wondering about the speed of the process and not the when does it start. LOL


#8

Correct 8)


#9

The size of the Captains Prosser valve…ah, never mind.

The usual way is for the PNF (pilot not flying) to call when a positive rate of climb happens on the IVSI’s (Instantaneous vertical speed indicators), the PF (pilot flying) then commands “gear up”. The IVSI’s are not really instantaneous, but better than the original VSI. The slight delay gives you a built in safety margin in case the airplane hits a downdraft immediately after lift off, you wouldn’t want to settle back onto the runway with the gear unlocked. JetMech is right, every type has a different system speed with the 737 being particularly fast without the gear doors.


#10

When I was in the Military and on Boeing test flights, Ive asked and it always seems to be 300 ft above the runway alt and Positive Rate of Climb as a general rule.


#11

I’ve never heard of 300’ but the military and test flights may have their own standards. Except for retracting the gear on the ground there is no wrong way to do it.


#12

Seen that more than once too :mrgreen: :mrgreen: :mrgreen:


#13

Oh and its Gear Retraction speed.

Which there is a max speed that you should try to drop and retract the gear and a max gear airspeed. But those are a horse of a different color.


#14

For GA, I’d always used the rule to retract once you’re past the (far) end of the runway. It’s always handy to have the gear in place when you have an engine failure and can still make the runway.


#15

I always thought it had more to do with whether you were using squirrels, chipmunks or something else to run the APU…


#16

We have been experimenting with camel dung mixed with water from the port. Mixed results so far, the APU seems to like it but when we need to run the air…not so good.


#17

If we’re talking about the speed of the retraction cycle, then my nomination for the fastest one is the DC-9 family. Pretty fast considering that type has full doors. Doors open, gear sucks up, doors close, all in less than 6 seconds. Usually it’s all done before reaching the end of the runway.
The slowest? I would have to go with the A340-500 & -600, as well as the A380. 20+ seconds, every time.

The above is among commercial jets. I know about the old Mooneys with the gear handle that you can retract in less than a second lol…


#18

Memories of throwing that handle is exactly what came to my mind as well. While it took a bit of beef to retract in under a second, you could drop it at ludicrous speed! :laughing: