Posted by Matty on April 17, 2010, 22:43:07 Message modified by board administrator August 4, 2011, 20:48:21
Although pioneered by one or perhaps two naval aircraft (most notably the RN's Short Folder seaplane, whose very name derived from it) during WWI, wing-folding, like most other carrier-related developments, didn't really come into its own until just before- and during WWII, whence it has remained in use, essentially unchanged, ever since:
Ultimately, three main approaches to wing-folding were adopted, as could be termed "overhead", "swept-back" and "tucked-back" schemes.
OVERHEAD FOLDING
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Examples of overhead folding include the AD SkyRaider (left) and F7F TigerCat (right), whose wings of course fold straightforwardly upward/inward - regardless whether the tips actually fold clear over the fuselage, as in the former, or don't, as in the latter - or may not even fold past the vertical, as in, for example, the F2H Banshee (not shown). The hinges are aligned with the fore-and-aft (longitudinal) axis of the aircraft - with the S2F Trackers, at top, representing a minor variation, in which the hinges are skewed very slightly off-axis, to allow the wingtips to fold past each other, reducing overall height. Other variations have ranged from, on the one hand, restricting folding to only the wingtips - such as on the A6M Zero, or F-4 Phantom, etc. - to, at the other extreme, folding not just the entire wing but additionally folding the wingtip downward/outward, in an accordian-like double fold, as on the Fairey Gannet.
SWEPT-BACK FOLDING
This approach, such as implemented on the Fairey Swordfish (top) or F-14 Tomcat (bottom) is a again a straightforward rotation, except now around the vertical axis, leaving the wings more or less parallel with the fuselage. The hinge axes are vertical (or nearly so) - on the Swordfish, for example, running along the inboard aft wing struts. Additional variations, such as that seen on the Fairey Barracuda, have included lifting and/or dropping inboard sections of the wing- and/or flaps above or below the wing plane, to allow the wing to scissors past them, during folding.
TUCKED-BACK FOLDING
Click on Image to Enlarge
The third, last-invented and by far the most elegant and ingenious approach (IMHO) - as attested by its immediate and longstanding success, being still in use to this day - was the backward-tuck scheme, as originated with the classic Grumman WWII trio of F4F(-4) Wildcat (not shown), TBF/TBM Avenger (left) and F6F Hellcat (right). Much like an actual bird does, this scheme rotates almost the entire wing simultaneously about both the above axes - plus the third perpendicular axis, the lateral - to twirl (properly, to "pitch") the leading edge down, while sweeping the wing in a curving downward, backward and finally upward arc, coming to rest not only parallel (again, more or less) with the fuselage but also flat against it (or nearly so). To address this three-axis rotation, rather than employing multiple- or universal joints, the system ingeniously combines all the needed contributions (vectors) in a single hinge, which is simply tilted: raked slightly backward from the vertical and canted outboard significantly. Accordingly, the break-plane of the wing is also canted outboard - not only to allow the rotation, but also such that in-flight stresses from lift serve only to compress/lock the wings more tightly in place.
A more useful wing-fold for carrier storage could scarcely be imagined - note above how tightly the Avengers are clustered aboard an escort carrier - each one practically packing itself up in a crate! Likewise, shipboard helicopters, such as the HSS/HUS Seabat/Seahorse (not shown), while often folding the tail swept-forward, used tuck-back folding for their main rotor ("rotary wing") blades - two folding on each side - while others, such as the SH-3 SeaKing (not shown), appear to have used a combination of tucked folding for the outermost blades, and swept-back folding for the (inboard) remainder.
If even the simplest of the above wing-folding took some engineering before making their appearance in operational use, neither are they trivial to engineer - working, yet still decently accurate-looking - in miniature. As I have been learning the hard way in, for example, my 1/48 F2H Banshee build, delayed substantially by even its simplest of overhead-folding schemes. Accordingly, the start of a planned Avenger build, with its much more complex and demanding mechanism, has been postponed until I can really get "on top of" just how to design and install these things, (starting) in 1/48 scale.
Therefore, appended below will be references and examples of progress to engineer the best-looking and -working wingfold installations - of all three types, above - in various builds of naval aircraft, going forward. I hope you will find it as interesting, useful and challenging as I do...
This type of folding is really straightforward - pretty much the way living birds fold their wings - however a diagram(s) to really illustrate the way Grumman implements it on aircraft would be so complex that I won't (yet) even try. Suffice to say the examples to be appended as "replies" below, will show exactly how to engineer and install this type of wing-folding - and pretty realistically, at that - on models of the appropriate aircraft.
I can now make the above prediction with high confidence, as I just engineered my very first, successfully tuck-back-folding wing:
This is the starboard wing of my Accurate Miniatures 48-scale TBF Avenger (Thanks, Donny!). Stand by for a photo-primer(s) on just how to do these, and the tuck-back-folding wings of other aiarcraft which had them...
Still a lot of writeup yet to do - it was a LOT of work - but it WAS successful, as I can now demonstrate, in engineering the above pair of fully-compatible, working tuck-back-folding wings for the Accurate Miniatures (or really, any) 1/48 TBF Avenger!
So, stand by for all the details on how to create exactly the same, on your own bench...
Cheers,
- Matty
Overhead Folding: Not (always) That Simple!
Posted by Matty on August 5, 2011, 14:32:54, in reply to "Carrier Aircraft WING FOLDING" Message modified by board administrator August 5, 2011, 17:07:56
Much as I hate to accommodate yet more complexity, I have by now been forced to conclude there are really (at least) three sub-categories of Overhead wing-folding - each determined by how far the hinge is buried into - or beyond - the wing surface:
The simplest (from a geometric viewpoint, hardly needing explanation), is when the hinge is mounted atop the wing surface (left), over the fold joint: the outboard wing section (red) simply rotates up around the hinge, just as on a typical door. As one starts to bury the hinge halfway or more into the wing (right), rotation becomes limited due to binding against the inboard root (blue), depending on how deeply-sunk into the wing it is.
Obviously, burying the hinge deeper into the wing improves aerodynamics - and such a progression was indeed seen between development of, for example, the pre-war TBD Devastator and mid-war SB2C HellDiver - the latter arriving at complete burial of the hinges entirely below the wing upper surface:
Albeit among the most desirable overhead-folding scheme - and thus one you'll need to install among the most frequently - this variant is unfortunately also the most complex, as inboard- and outboard wing surfaces won't clear each other at all (left) - unless employing offset joints (right), straddling the hinge on opposite sides and connected by (some form of) cantilevered arm(s) - at least one, most often two - which ride on it like a see-saw. Typically each arm is fixed to the outboard wing, while the hinge is fixed inboard, so that during folding the arm's inboard tip drops down, while the outboard wing lifts up - to clear the opposing surfaces in both instances, as shown.
This latter scheme, which I will call "Lifting-Arm", remained in use post-war on the F2H2 Banshee - on which build I struggled repeatedly - until finally realizing that this installation (and probably all of the above) would be most easily and reliably achieved on wings which have not yet been separated along their fold-lines! Indeed - and completely counterintuitively - it turns out the easiest models on which to install actual, folding wings are those not designed to depcit wings folded! (Oiy! ) Although my Banshee started out as such a kit, it has long since been repeatedly bashed-upon, its wings not only separated but significantly crapped-up, as well.
Therefore, the examples below will use other kits to demonstrate how to "get it right" (or very nearly so) for the above types of Overhead Wing-Folding, on the very first time around.
After success on my SkyRaider wings, chance to try slightly more complex overhead-folding, on one of most expendable kits in my stash:
Revell (nominally) "1:48" Cougar is what Garry would've called a "humble" kit - not even quite 48-scale, judging by comparison with the Monogram 1:48 Panther (not shown) - but overall shapes and proportions look decent, so useable for this trial.
Wings come already separated - and not even along fold lines - so first step was to glue them on:
Click on Image to Enlarge
Entire, thick F9F wing roots molded into fuselage halves, so in addition to attaching wings (left, top), bottom center section was removed (left, bottom), to provide required access. Cutouts for lifting-arm insertions were transferred from Monogram Panther mold, presumed very similar if not identical, but further work along fold line would have to wait for "fully-cured" date, labelled with tape (bottom). At right, on undersides ridges along hinge axis could be flattened (top), and aluminum axle tubes cemented in (bottom) using CA-putty.
Two weeks later, progress could resume:
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At left, lifting arms sculpted from solid blocks - again, just like on SkyRaider - except this time arms anchored inboard, as outboard wing too thin, and also at less than 90degrees, to follow sloping wing root (bottom). Conversely, wire ends now anchored on outboard wing (right), except complexity of trapping under plastic strips, done for portside wing (top and middle), was found to be not only redundant but an impediment. Outboard wing is so thin there is no room for the buildup, meanwhile the bottom wing pieces (not shown) will provide (more than) the same support. So on starboard installation (right, bottom), wire ends simply glued down with heavy CA-putty - that's the way to do it.
Wish I could report that at least the folding came off without a hitch, first time - but that was not at all the case. The thick wing-root of the F9F (Cougar or Panther) represent a hugely-exaggerated wing camber: more camber requiring longer clearances - greater clearance requiring longer lift-arms (though I don't yet have a way to predict/calculate this precisely).
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Incremental whittling-away of the fold joints on the first wing, until it opened (not shown), finally established the basis for success on the second wing (left, top) per the following:
Fold-joint line: 0.7" inboard of air dam on wing Arm Length (same for both): 0.3" Hinge Axis: midpoint under arms (0.55" inboard of air dam)
Note I maintained a perfectly straight-line fold joint. This may or may not be accurate - I really don't have sufficient references to know.
The next step is integrating the bottom wing pieces - already started for the port wing (right) - however when that fold-joint had to be re-established substantially further inboard, it became aparent that further progress would require the bottom wings be attached to the bottom cutout and their joints relocated inboard, as well:
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Thus work came to rest in this state, to wait another (at least) two weeks, before restoration of the port wing, and completion of the undersides for both wings, can be addressed.
Meantime (out of impatience) I drilled out all the holes in the belly dive brake (right foreground). But - although I think it can look good with folded wings - it could take an almost unlimited amount of further detailing/correction, which I'm not sure would ever be worth the effort.
Still, I'll definitely keep you posted on the lower-wing installations, and final result.
I know you've rarely if ever seen me completely and deliberately give up on a build, no matter what difficulties may have piled up. However this particular installation, on this particular kit, is leaving me no rational choice but to do exactly that.
The insurmountable obstacle really comes down to the unusual (and entirely too casually-made) decision to anchor the lift arms inboard, instead of outboard - where they really MUST go, I've now learned (the hard way). The problem is that, with arms attached inboard the outboard wing, instead of entirely lifting up, rotates so that (as we've seen) the inboard edge dives downward:
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Let us note first of all that this is simply flat-wrong for this aircraft - as I've just recently been able to verify with this pic of a TF-9 Cougar trainer, at the Lexington-II museum in Corpus Christi:
Click on Image to Enlarge
Clearly, ALL of the outboard wing lifts up - more or less just as on my SkyRaider installation: i.e., with lifting arms fixed outboard. Doing the reverse causes ALL of the problems just encountered - especially for this thin-winged (Panther or) Cougar, where the diving edge needs to clear not just the top surfaces of the wing root, but also its BOTTOM surfaces - these latter being next to impossible to access, since the top surfaces are all fixed permanently in place.
The result: a fatal combination of near-impossibility to trim/adjust the inboard edges, along with severe stresses on the parts, while trying generally to get everything to work:
Particularly for the portside wing, whose whittled-away sections I had beautifully (if I may say so) restored (white) and smoothed-flush between strips of protective aluminum tape.
Then surface-checked with a coat of silver paint:
Click on Image to Enlarge
This was the last gratifying sight of this build, as the above conflicts with the undersides utterly ruined sections along the joint-line: twisting and even breaking out parts of the above restoration, the problem only exacerbated by discovered weakness of repair areas due to insufficient curing time. (Which should have been more like 3-4 weeks, instead of 2.) But - more than that - to fit within the lower wings, lift arms - solid, unadulterated plastic - required so much thinning that, again subject to greatly-increased stress, one even broke clean through! Again: FAILURE. Utter. Complete. This installation not only did not work, it CAN NOT work - ever - IMHO. I've already conceived an scheme* which I think WILL work, however at this point, with this kit, it would still require a complete "reset": re-attachment (and repair) of the wings, whose inboard areas still remain "hot" - in fact, now more than ever - saturated with glue solvents. Meantime, this mold - a real dog, flagged "expendable" from the get-go - is not even true 1/48 scale, thus can never be truly compatible with my others. So buying another copy seems likewise a waste of money - yet there are NO other decent 1/48 scale Cougar kits in styrene, AFAIK.
There does at this point seem to be one acceptable option: use the outboard wings (and one or two other pieces) for easy conversion of my Monogram Panther - whose wings come separated OOB and would thus have to be re-attached anyway - to get a real, 1/48-scale Cougar. (Later, and yet easier for a Panther, I can buy one the several 1/48-scale kits available with wings already attached.) For this project, however - at least for now - the final straw is that my Panther kit is already packed away in storage, pending the "Interminable Move-Out" (IMO), to a new apartment - so that appears to be F-in' THAT.
For now the best I can leave you with, are the above findings and admonition to Heed my Tale, Oh Youthful One(s) - and learn from the Mistakes of Your Elders!
Cheers,
-Uncle Matty * SOLUTION: Anchor lift arms outboard as required, but now for these use extensions of the STEEL AXLE WIRES - both very thin AND stong - and plastic block only for bushings, to minimize play and optimize friction.
Overhead Folding: "LIFTING-ARM" Type - Case Cracked!
The following is an installation of Lifting-Arm wing-folding in my Revell 1/48 Skyraider A1-H (AD-6), a mold which it appears once offered wing-folding, but was reissued with wings fused:
At left, top-left, the kit plausibly indicates two lift-arms, straddling three plates looking like flaps to accommodate the wing-fold over the highest points on the wing - later concluded to be exactly that (see below). However, all things being equal - an assumption required, to get started - begin, as I did (top-right), by drilling tiny holes exactly halfway down each arm. Flipping the wing over (bottom-left), size- and place an aluminum tube for the hinge directly connecting the two holes. Set with a drop of superglue, and then massively reinforce in place, using CA-putty (bottom-right), duplicating this on the other wing as well.
At right, top-left, very precisely cut out the arm areas - on just one wing (and not both, as mistakenly shown). From a thick piece of plastic (top-right), sculpt a one end to present a plug fitting through the cutout as perfectly as possible and very snug - and the cut-back edge butting flat on the wing plastic (bottom left). Held firmly in place by hand (removed for clarity of the pic), mark the center of the tube on the block - preferrably by poking throught the tube with a sharpened wire, as shown, but otherwise by marking lines pointing to the center of the tube, and noting their point of intersection. Through this point (bottom-right), drill a hole the same or slightly smaller diameter as the wire, perpendicularly through the block.
At left, top, on each arm whittle further the obvious area of contact with the slot - but leave it to flare out onto the wing, retaining maximal surface for attachment there. Chop down the arm height (bottom-left) - leaving a generous excess - and insert a wire through the hole and into the tube (bottom-right), to check for position/fit when also plugged into the slot, and butted down on the wing.
At right, top-left, insert the actual "L"-shaped wire to be used - one leg extending just under halfway into the tube and the other long for secure anchoring on the inboard wing - but cement only the outboard end of the lift-arm in place. Only after this cement is fully hardened, secure the ends of the wires (top-right), by first tacking each down with a superglued strip and then flooding the attachment with (concrete-like) CA putty. On top of the wing (bottom-left), unwanted gaps can be shimmed - note, glued on one edge only - before chopping and sanding the arms flush with the surface, aided by tempory protective tape (bottom-right).
It is only now that the wings should be separated along the fold-lines: scribe carefully, all the way through (and don't tear up the arms). Conservatively whittle each arm in the obvious contact areas, gently flexing the wing and noting all points of binding, to remove the minimum and leave the block as heavy - and fit as tight - as possible, without undue stress on the hinge. Leaving substantial friction will eliminate the need for any "locks" to keep the wing from flopping down when folded, or up when extended. (The only "downside" being that any paint will quickly rub off, exposing the white plastic (so paint the exposed wing interior white!) Past 90 degrees (top-right), look for binding to start with the outboard wing (on a SkyRaider) - and confirm it using backlighting (bottom-left) - and later involving the arms themselves (middle- and bottom-right). To make a long story short, ultimately the entire joint between both arms had to be carved back outboard - and then the arm slots also needed to be extended inboard slightly, as well. Both of these introduced inaccuracy, however installing some sort of yielding flaps - undoubtedly those three plates seen originally - was simply not realistic. So, the whittled-away surface would later be restored on the inboard wing - the wing still folded perfectly - and the final appearance not unduly compromised.
At right, top, the folding wing can now be dry-fitted for clearance past the bottom wing. The forward arm - over the thickest part of the wing - meets no obstacle(s), but the rear arm does - and this will be typical. Rounding and tapering the arm to a (near) point minimizes the contact, and the rest is eliminated by gouging the inside of the lower wing (bottom-right). Other aircraft might require a slot be opened completely through the lower wing, but again this would have minimal impact on the final appearance.
The second wing can now be done much more efficiently - avoiding all missteps of the first one - by directly transfering markings between them (top). Locate the proper ends with the help of a piece of tape, wrapped around just like painting a stripe, or waterline on a ship, and drill these end-points (bottom-left). In fact, the relevant dimensions (no doubt workable for any 48-scale SkyRaider mold) turned out to be:
Arm Length (same for both): 0.37" Hinge Axis (from outboard fold-line): 0.20"
Likewise, the workable (outboard) fold-line is just the continuation of the aft joint, between both arms (bottom-center). Simply tranferring these marks and repeating the above constructing accordingly, resulted immediately in a very plausible-looking fold (bottom-right), without further adjustment!
How well did it really match the other wing? Take a look:
Click on Image for FULL RES
Pretty damn close, IMHO - certainly close enough for the needs of this build. This result for the second wing - on the "first try" - was so encouraging, that I plan to duplicate it on an ERTL/ESCI 48-scale SkyRaider - even possibly other planes (which appear to have a very similar wing).
But the above - assuming your model has anything near accurate details indicating the lift-arm(s) and fold-lines - is the general approach recommended, for any aircraft with Lifting-Arm wingfolding.
Meantime, it looks like my Revell A1-H is going to get finished before my Banshee!
Cheers,
-Matty
Re: Carrier Aircraft WING FOLDING
Posted by Mike Kozlowski on April 18, 2010, 16:03:09, in reply to "Carrier Aircraft WING FOLDING" Message modified by board administrator April 19, 2010, 10:13:59
Matt,
I have the Monogram Avenger re-release with the folding wings and everything - would a pic or drawing of the wing fold mechanism from that beast help?
That's a nice offer - but I am already adapting "tuck-fold" joints molded from my own Revell Avenger, as I posted recently (though I didn't go into detail). I'm very busy lately, so haven't been putting a lot of explanation into my updates (but if you look closely at the pics and think a little, you should be able to read a lot "between the lines"). There was once a thread showing the start of my Grumman-type wingfold jig project - long since dropped off the board - but it will reappear as part of this thread.
Meantime, congrats on finishing your Boston - where was the Region 12 show held?
Be advised: another thing which lately I don't have time to mess with is fuzzy (or otherwise lousy) pictures - so, whatever you may send in, first make sure the pics are (at least) in focus, and at least decent, OK Mikey? Thanks again, buddy.