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niart17

F-18 Landing Gear Retraction Sequence

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Hey all, I was considering doing a build of the Blue Angels high performance transition using the Academy F-18D as a number 7 aircraft. Since the landing gear in the kit is broken into individual parts it shouldn't be too hard to get the landing gear set-up. The only problem is I haven't been able to locate any really good references of what that sequence looks like in mid retraction state like the photo below. Is there anyone here that might have some pics of something like that? Maybe a plane on stands doing landing gear repairs or something where you can get close up?

 

This is the look I'm after, except it will be the 2 seater. (pic coming soon, sorry)

 

 

blue_angels_low_takeoff_by_gtxcrusader-d31de4h.jpg

Edited by niart17

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Thanks Onigiri. I saw this video but unfortunately it doesn't get in close and doesn't really show the main gear. The nose gear is likely pretty straight forward but the main gear makes a funky rotation to get the wheels parallel to the body. 

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It wouldn’t be easy as the oleo extends and the gear extends when the gear is weight off wheels.

 

I may have the gear sequence in one of my technical manuals but I don’t think the pictures would help.

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HI 🙂 The easiest thing to do is perhaps to just glue the MLGs at a slight angle backwards, by pivoting them on their actual spots for gluing. There should be 2 pins at the base of the pylons (where they fit in the bays). If i remember correctly, these two spots (little pins) per pylon are in a slightly angled position inside the bay so if you just "retract" the gear - it should perfectly fit inside the bay. Of course it doesnt, because the oleos are extended and the gear has the shape as for a parked model sitting on its wheels. I would go with further cutting of the main joints and  gluing them back as they should be extended without the weight of the plane, and then do the gluing at a slight angle from the provided pivots. When all dries up solidly, just cut the tiny little hidraulics (1 per gear) for the retraction, to shorten them, until they fit in the shortened distance. 

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13 hours ago, Scooby said:

It wouldn’t be easy as the oleo extends and the gear extends when the gear is weight off wheels.

 

I may have the gear sequence in one of my technical manuals but I don’t think the pictures would help.

Hey, anything MIGHT help. I think the main parts of the gear are pretty straight forward as to where everything bends at the joints and how the oleos extend etc and rotates up into the well... my main confusion comes from if the lower main section has to rotate around it's axis at all and what happens with all the smaller actuator parts below the knee. You can tell they either extend or contract because they have travel to them, but it's hard to imagine what does what.

 

So yeah, if you have tech manual drawings or something, or even written description might help.

 

Thanks guys for all your help!

Bill

Edited by niart17

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1 hour ago, eraucubsfan said:

Does this one help?

It most certainly DOES! THANKS!

 

Assuming the Super is basically the same as the legacy gear, I think I can get enough information out of that video. If anyone is interested in having fun exploring this a little, take a look at the above video around the 21-22 second mark if you watch it frame by frame. The wheel hubs do some sort of a jump, almost as if they push off the centerline of the axle. That doesn't seem right but it's doing something wonky at that part of the retraction. Anyone have any ideas what's going on there? That's a very interesting study in mechanics.

Edited by niart17

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6 hours ago, niart17 said:

It most certainly DOES! THANKS!

 

Assuming the Super is basically the same as the legacy gear, I think I can get enough information out of that video. If anyone is interested in having fun exploring this a little, take a look at the above video around the 21-22 second mark if you watch it frame by frame. The wheel hubs do some sort of a jump, almost as if they push off the centerline of the axle. That doesn't seem right but it's doing something wonky at that part of the retraction. Anyone have any ideas what's going on there? That's a very interesting study in mechanics.

 

I do, I’ve been involved in a lot of retraction tests on Hornets. I honestly don’t think it will be easy to replicated. 

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8 hours ago, niart17 said:

If anyone is interested in having fun exploring this a little, take a look at the above video around the 21-22 second mark if you watch it frame by frame. The wheel hubs do some sort of a jump, almost as if they push off the centerline of the axle. That doesn't seem right but it's doing something wonky at that part of the retraction. Anyone have any ideas what's going on there? That's a very interesting study in mechanics.

I watched the video several times but can't see what you are seeing but what you might be seeing is the anti-skid (brakes) locking.

 

It is common on USN/USMC aircraft that when the gear retracts the anti-skid kicks in to stop the tire from rotating as it goes into the wells, sometimes it causes the tire to move slightly.

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On 11/9/2018 at 6:59 PM, Scooby said:

 

I do, I’ve been involved in a lot of retraction tests on Hornets. I honestly don’t think it will be easy to replicated. 

So Scooby, would it be somewhat accurate to just try to replicate the gear in the same configuration (angle) of it hanging in-flight and just rotate it upward into the wheel well to whatever position I prefer (about 3/4 of it's travel) or does something else happen to get it up into the well? I know it's just a model and know one would likely know if Its not perfect, but I am curious about it and would like to maybe get it close accurate. 

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21 minutes ago, niart17 said:

So Scooby, would it be somewhat accurate to just try to replicate the gear in the same configuration (angle) of it hanging in-flight and just rotate it upward into the wheel well to whatever position I prefer (about 3/4 of it's travel) or does something else happen to get it up into the well? I know it's just a model and know one would likely know if Its not perfect, but I am curious about it and would like to maybe get it close accurate. 

 

Probably be easier to replicate it hanging, you’d need to change the extension on the planing links too.

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Just now, Scooby said:

 

Probably be easier to replicate it hanging, you’d need to change the extension on the planing links too.

Thanks, I know that means something but....planing links? :dontknow: 

 

Sorry, I don't want to be a nuisance. The position I'm hoping to get it pretty much just like that first picture I posted of no. 6. 

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6 minutes ago, niart17 said:

Thanks, I know that means something but....planing links? :dontknow: 

 

Sorry, I don't want to be a nuisance. The position I'm hoping to get it pretty much just like that first picture I posted of no. 6. 

 

This paper has some pretty good labeled pictures explaining the links on main gear

 

https://trace.tennessee.edu/cgi/viewcontent.cgi?referer=https://www.google.com/&httpsredir=1&article=1110&context=utk_gradthes

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Awesome Saber! Thanks! I'm sure most of this is above my grade in understanding, but I can maybe follow the gist of some of it.

 

Bill

Edited by niart17

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What an interesting and strange(?) subject for a thesis paper. As Bill said above, it is beyond my ability to understand it, but fascinating none the less.

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12 hours ago, Sabre Freak said:

 

 

This paper has some pretty good labeled pictures explaining the links on main gear

 

https://trace.tennessee.edu/cgi/viewcontent.cgi?referer=https://www.google.com/&httpsredir=1&article=1110&context=utk_gradthes

 

I was going to send him that link but for some reason the pictures weren’t visible when I tried.

 

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11 hours ago, niart17 said:

Awesome Saber! Thanks! I'm sure most of this is above my grade in understanding, but I can maybe follow the gist of some of it.

 

Bill

 

You’d need to adjust the length of the connecting link too. As I mentioned it wouldn’t be an easy task to model the gear retracting.

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11 hours ago, Mstor said:

What an interesting and strange(?) subject for a thesis paper. As Bill said above, it is beyond my ability to understand it, but fascinating none the less.

 

We had a lot of planing link failures, I dragged a few jets into our hangar with mangled gear due to a planing link failure.

 

We couldn’t push them, we had to drag them. 

 

Not a strange thesis at all. 

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1 hour ago, Scooby said:

 

You’d need to adjust the length of the connecting link too. As I mentioned it wouldn’t be an easy task to model the gear retracting.

So I take the odds are against me and the fate of the model rest in my hands; and failure could result in certain peril and ultimate humiliation?  SOUNDS GREAT! I want some of that. 

 

Worst case I ruin a perfectly good set of landing gear, punt and buy some of the brass or other metal gear sets out there. OR maybe try to model it in CAD and print it? Hmmm...either way. I may never finish the model but the prospect of getting this gear thing worked out has me hooked.

 

Thanks for everything guys!

Bill

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1 hour ago, Scooby said:

 

We had a lot of planing link failures, I dragged a few jets into our hangar with mangled gear due to a planing link failure.

 

We couldn’t push them, we had to drag them. 

 

Not a strange thesis at all. 

 

I figured that there was a reason the modification was done in the first place. I didn't really read the paper. Took one look at it and went cross-eyed. Without lots and lots of pictures, I'm lost (I know there are pics in an appendix and great ones too, but not enough for my mind to grasp how it all worked together). Thanks!

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ok, I THINK I got a rough idea of what's going on. The axle of the wheel is not perpendicular to what looks like the center line of the axle is. I'm thinking the axle itself has a bend or at least is mounted, maybe around 30 degree or so from the center line perpendicular to the strut? So when the gear goes up, those planing arms pull on that plate, which I assume is rigidly mounted to the part of the axle assembly that's perpendicular to the wheel hub. because it is attached the lower gear arm at that 30 or whatever degree angle, when the that plate rotates 90 degrees it pulls the wheel in tighter and closer the whole assembly, It also pulls the shock in a bit so the gear can fit into the well. If I'm close to being correct, I think that's the funky shift I'm seeing at the beginning of the sequence. It does make it look like the wheel is pulling off axis, because it never was on that axis, it was some amount of degrees off. At least I think. I guess that's why the landing gear never really looks correct on the models. Some mold the wheels axle perpendicular to lower part of the strut and it's clearly not.

 

Anyone confirm or deny my thoughts?

 

I'm going to have to play with this.

 

Bill

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