allflight57

Why is it that Vlo is always lower than Vle, is the gear stressed more during retraction than extension?

Thanks,
Tyler

III Corps

Gear doors?

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tangoindia

Well......here is something to think about. Depending on the type of plane (the direction the gear retracts....forward or backwards) if the gear retracts forward it would be fighting against all that relative wind. In other words, the retraction system would have a "great force" pushing in the other direction. When you extend the gear (assuming backwards) the relative wind is actually going to aid the gear get into the lock position.

Does it make any sense?

TI

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HSLD

My simple brain has always thought of the difference between the ability of a hydraulic actuator (or electric motor) to overcome flat plate drag -VS - the ultimate strength of a mechanical down lock.

allflight57

yea that makes sense, the wierd thing about it tho is that in particular i was thinking about the Piper Arrow where the mains retract sideways and the nose gear retracts going backward, so one would think Vle would be lower cuz the nosegear has to push against all that wind, its not that big of a deal, Im just kinda curious. By the way what are the gear speeds on the 777?

USMCFLYR

Like III Corps said - on my airplane it has nothing to do with the gear itself - the limitations have to do with the gear doors. I've heard the second-hand stories of a Hornet's gear coming down at over 400 kts and nothing happened to the gear. Now the doors were another matter

USMCFLYR

the King

Vle is usually about the gear doors. On light airplanes, Vle is usually greater than Vlo. However, you may be confusing the two speeds for Vlo on the Arrow.

There is a higher extension speed in the Arrow due to a mechanical advantage of the system. Hydraulic force is measured by the hydraulic pressure multiplied by the area the force is applied to. In the case of extension, you have the entire surface area of the piston head inside the actuator cylinder.

During retraction, you have the same amount of pressure, but it is being applied on the opposite side of the piston head. On this side you have a smaller area since the piston rod is also present. This limits the amount of force the piston can produce. Thus, retraction is disadvantaged and must occur at a lower speed. It also works since we are usually slow when retracting the gear (climbout), and we have a higher speed when extending the gear (pattern altitude and level usually).

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Brendan

Am I missing something here? I have always thought it was like this:

Vlo: Maximum gear OPERATION speed; the maximum airspeed the gear can be operated, whether that be extension or retraction.

Vle: Maximum gear EXTENDED speed; the maximum airspeed with the gear in the extended position.

Therefore, I have always thought the reason Vle is higher than Vlo is because the landing gear and/or gear doors are certified to withstand a higher speed while stationary (extended) than when in motion (extending or retracting).

Anybody agree or disagree?

SB2K

This was always my understanding also.

Rama

That is correct, also was told the limit is due to the doors.