The retractable landing gear on high-wing Cessnas that have them (172RG, 177RG, 182RG, 210, 337) remind me of the feet of a duck, the way they retract. Rather than simply folding into the wing like a door, they drop down, dangle for a second or two, and then fold backward. Video.
How do they work? I’d like to see the mechanism, if anyone has a link to the drawings.
Until someone more knowledgable comes along.
I don’t know the exact mechanism, but looking at the above video it appears that once the down locks are released they hang in a position dictated by gravity and drag, then once the hydraulic pressure is adequate they hinge back into the fuselage. The hinges would be off from perpendicular so that the gear moves inward at the same time as moving rearward.
Edit: My girlfriend used to fly them. She doesn’t remember anything particularly special about the sequence. Just that they were hydraulic and hinged back into the fuselage. Unfortunately she has thrown her C210 books out.
found a description of it as a simple “ball joint like hinge”. here’s what the RC people built which is about how I imagined it. It swivels on an angle.
It’s a term I haven’t heard in years but it used to be called the “limp grasshopper” retraction method.
Good video. I was rushed last night.
It’s the hinge I’m curious about. To start, the gear legs are perpendicular to the fuselage. Obviously if they simply retracted like a door hinge or like the mains on a typical low-wing aircraft, they’d be sticking out to the side. This would be true even with an angled hinge. As can be seen, they drop vertically first before folding backwards.
If I were going to build a model, I think I might do it like this: The legs are on a hinge, and there re down locks to keep them in place when they are extended. The down locks are unlocked, and the legs drop on the hinge like a door. The hinge is attached to a stout tube, and the tube is rotated to bring the gear back and up.
That’s if I wanted to replicate action without knowing how it works. It’s just such a funky-looking retraction method, I’d like to see the mechanism.
Magiver: That’s a pretty good solution for an r/c model! 
The arrangement, or at least the action, of the landing gear reminds me of the wing folding action that Grumman used on a number of their carrier-borne aircraft, namely the F4F, F6F, TBM, and most recently the E2-C Hawkeye. The wings fold by roatating both aft-wards and to a more upright position at the same time. The mechanism that allows this is simplicity itself. The axle that bears the wing is inclined two directions: it is canted away from the vertical axis of the aircraft aft as well being tilted inward. This allows the wing to rate in two directions as the wing is folded, backward to align itself with fuselage, and longitudinally to have the upper wing surface facing away form the fuselage.
I heard the Grumman Ironworks designer who originally came up with this got the idea after playing with a paper clip and a pink pencil eraser. As proof concept (80 years after the fact) I just goofed around with a paper clip and a block of Styrofoam. It’s quite fun, actually.
The Cessna’s axis is pointed in a different direction (inward and forward) but allows the gear to swing back and rotate outward at the same time. And since there is really one direction of rotation relative to the axis (bearing wither the wing or landing gear) only one actuator is needed to effect the motion.
I volunteer aboard the USS Midway and there is an E2-C with its wings folded and sure as shit, there is just the one shaft bearing the wing and just one actuator. Now that’s good design!
I had model F6Fs when I was a kid. They accomplished the wing folding by having a ‘T-bar’; with the wing hinging upwards on the T, and rotating backwards on the shaft. No doubt that’s where I got the ‘model’ for the Cessnas in my previous post.
On the Grummans, I can almost visualise the mechanism; but I’d have to see it in a diagram and/or animation/video. On Cessnas, I don’t see how the movement could be accomplished with a single hinge, as the gear definitely drops down before folding back.
Well, get a block of styrofoam and a paper clip and start playing!
I think it’s a function of an angled pivoting joint. Here’s a video of the actuator. looks like a regular piston action. still looking for a closeup.
That was reputedly Leroy Grumman himself.
I found a Cessna 210 maintenance manual available online. (Very large .pdf file.)
The pivot assembly (Figure 5-1) is V-shaped, with the part connected to the pivot shaft attached perpendicularly to the main gear actuator. The bit that protrudes at an angle holds the strut (landing gear leg). Figure 5-2 shows an exploded view of the actuator. It appears to be a rack-and-pinion unit that rotates the gear aft.
I’m still not clear how the initial ‘drooping’ is accomplished. Perhaps someone more mechanically-inclined than I am (which would be just about anybody) can point it out to me?
When it droops it is just hanging from the pivot without hydraulic pressure. There is nothing special happening mechanically, it is just in an intermediate state where the uplocks are no longer holding the gear in the fully down position and the hydraulic pressure hasn’t yet been applied to retract the gear. The natural hanging position of the gear is not the same as the down/locked position.
Not if the hinge is angled correctly. In the RC model you can see the hinge is at about a 45° angle. The detail from the C210 manual shows the hinge at a similar angle. It means that when rotating rearward the legs are also rotating inward.
OK, I’m… ‘maybe almost’ seeing it. In Fig. 5-1, the tire seems to be parallel with part #4, the outboard support. I assume, therefore, that the outboard support is parallel to the outer skin, and the actuator is an an angle. (I couldn’t see the actuator, or I didn’t know I was seeing it, in Magiver’s video.) So when the down-locks are released, the gear drops under their own weight. They bob around for a couple of seconds until hydraulic pressure is great enough to push the rack within the actuator, turning the pinion, and tucking the gear in. So the rotation of the pivot assembly is the only thing going on mechanically (ignoring the down-lock).
When I looked at the model, I thought it was a ‘good enough for a model’ solution. The initial hanging of the real undercarriage fooled me. Now that I see the angle between the actuator and the outboard support, it makes much more sense.
Maybe someday I’ll get a chance to see it up close IRL.
It seems clearer in Figure 5-7 of the 177RG maintenance manual from the same site.
Yeah, that is a different version of the same principle. The axis of rotation is much clearer.
Thank, everyone, for your answers.
Next question:
Earlier 210s had doors over the mains. Later ones did away with them, instead having close-fitting depressions in the fuselage for them to tuck into. I think I’ve seen pictures of 177RGs that have been retrofitted. Obviously, this arrangement reduces complexity and the potential for failure. Without the mechanical components to operate the doors, it’s lighter too. If the doors are mis-rigged, you may have ‘droopy doors’ that will cause drag. Removing them in favour of the fairly clean depressions seems like an excellent way of configuring the main undercarriage, and perhaps it should have been done that way from the outset.
ISTM that the doors would make the airframe slicker, and the depressions would make it draggier. Is top speed affected? Or does the reduced weight counterbalance any additional drag?
Follow the money.
It doesn’t necessarily add drag. The openings are back and up at an angle to the slipstream of fuselage. Think in terms of a NACA duct.
I just wanted to add that the Cessna retractable is notorious for it’s number of parts and micro switches. Taking out the back doors is a major improvement.