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Clever landing gear design

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Jay Kempf

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For the retract gear design nerds out there just ran across this guys work:

CAD model animated:

Pneumatic bench test:

Hydraulic in place:

Just thought the over center in both directions with a single actuator mechanism was very clever.
 

Andy_RR

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Wow, that's quite beautiful! You have to see it on something bigger than a phone screen to figure out what it's actually doing though!
 

Scheny

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This design is used in most retractable that I know of.

I fly the Diamond DA42 which has a similar "one actuator pushes double overcenter". Also the DA50 and DA62 use it. If I am not mistaken, also the Piper etc. are built that way.
 

Jay Kempf

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Hard to see how the single actuator gets the lock link off of the over center position in both directions. That is what I thought was clever. Normally there is a second cylinder to pull the link out of over center and then locks it at the end. This gear doesn't have the second cylinder.

This is the pneumatic test. Better view of the mechanism:
 

wsimpso1

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Please tell us how you extend the gear when the primary actuator does not power it out of the over center up-lock position?
 

Jay Kempf

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Good question. Hand hydraulic pump in the cockpit? Cable to pull the up lock position out of lock so it will fall?
 

rv7charlie

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More to the point, if the cyl can move the link off 'overcenter' by simply rotating the pivot, why can't side load on the gear do the same thing? What are they not showing? (Unless it's not really an overcenter design, and they're depending on cyl pressure to keep the gear extended...)

Charlie
 

Jay Kempf

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There is something odd about the shaft and collars on the left of the video. One is attached to and rotates with the shaft. The other isn't. Looks like the actuator is off center or on a cam or something at that end. That may be what is rotating the link out of the over center condition. The link has a spring a lock on one side so it can only break in one direction.
 

TFF

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It’s an RC model not certified full size. Not same sort of redundancy. If you have ever flown RC with retractable gear they are prone to collaps. Easy to pop the up or down lock if they even had them. I would have to look at a Mooney or Viking to see if they double overcenter.
 

Hot Wings

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There is something odd about the shaft and collars on the left of the video.
Looks to me like the overcenter link is connected to, and phased with, the eccentric on the cylinder in such a way that when the link tries to return to linear the excentric is acting through the cylinder in the opposite rotation about the retraction axis.

In the first YouTube in post #1 the excentric is not shown as being attached to the link shaft and is stationary. It should be rotating with the link shaft.

No time to draw this up in SW.
 

poormansairforce

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You can see movement between the two socket head set screws on the shaft closest to the camera. There's a lever on that shaft and someone/something is manipulating that shaft which allows the locking link to collapse for a bit. The link joint appears to be spring loaded.
 

pictsidhe

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I think I get it. The over centre link has an offset shaft that the cylinder rides on. The phasing of that offset is different according to whether the gear is up, or down. So when the piston pulls the gear down from locked up, it rotates the offset the same way as when it pushes the gear up from locked down. Clever indeed.
I have an even simpler double locking mechanism for my Hurricane. It needs the actuating link rotated around 250 degrees. No problem for my cable operation.
 

pictsidhe

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Crude scribble, greatly exaggerated.

The small circle is the shaft. The large circle the offset shaft that the over centre is attached to. The cylinder pivots on that offset shaft. The angle between the over centre link and cylinder is different depending on whether the gear is up, or down. Pull on the cylinder causes the offset to rotate the same way as push does at the other gear position.

IMG_20201015_134834245.jpg
 

Jay Kempf

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This is supposedly a scale model of the actual landing gear assembly. Japanese fighters were a bit spartan. Maybe they just didn't care if the landing gear had safety down and lock option...?

Looking at it more closely it seems that because the link springs to straight only in one direction it goes over center against a stop with a spring to hold it straight. When the actuator starts pushing or pulling it breaks the link over center and starts moving the gear leg basically at the same time due to the large cam at the left end in the video. If it were hydraulic and accumulator against air pressure would be able to blow the gear down I guess.

Still think it is clever.
 

pictsidhe

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It would need to lock both ways. The Japanese were fine engineers and dogfighters. Can't do that if your gear is flapping around under gs. Landing with unlocked gear doesn't usually end well.

These are 'look at my cool gear' videos, not 'look at how I made my gear' ones.
 
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wsimpso1

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We are doing human carrying airplanes on here. It sure sounds incomplete without it handling nominal failure modes.
 

Jay Kempf

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Something must be omitted. This is supposed to be a scale model of the actual full scale gear design. I might ask the guy that built it how he got documentation of the design to work from. Still the simplest gear mechanism of this type I have ever seen.
 

cblink.007

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I think I get it. The over centre link has an offset shaft that the cylinder rides on. The phasing of that offset is different according to whether the gear is up, or down. So when the piston pulls the gear down from locked up, it rotates the offset the same way as when it pushes the gear up from locked down. Clever indeed.
I have an even simpler double locking mechanism for my Hurricane. It needs the actuating link rotated around 250 degrees. No problem for my cable operation.
This is the big pain in the rear on our full scale design...the retract design. Up and down leverage and movement not so much the issue. Just the locking part. We are getting there, though!
 
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