digital_trucker

I've finally buckled down to CAD and begun designing a 1/2A sport plane. The design features true elliptical wings, in that the leading edge, trailing edge, and thickness are all ellipses. This means the wing is going to have to be built on a jig, and I've decided to follow full-scale building techniques. Each wing rib inboard of the outer end of the aft spar is divided into 3 pieces, the ribs outboard from there are two-piece. The wing is all balsa, except for the dihedral braces joining the wings at the spars. The spars will have to be built first, then jigged up and the rib sections (made of 1/32 balsa) attached. The leading and trailing edges will be laminated. Cap strips and center section sheeting of 1/32" balsa completes the wing. It has built up barn-door ailerons.

I'm still working on the fuse and tailfeathers. The wing is roughly 230 square inches, with 5 degrees of dihedral on each side (it's a low wing, with a 13% symmetrical airfoil, so the ailerons should be highly effective even so).

blvdbuzzard

Looks good. Lot of work to build. I think it would be easier to build if the ribs were 1 piece and you sheer webbed between. The spars would still fit the notches on the ribs. Are the leading and trailing edges built up with thin strips around a form to get the shape?

I have built 1 and only 1 elliptical wing, it was from RCM or AMA plans. I had no jig so I had to make one. I used aluminum tubing for the rods and pine blocks for the ends. It was a hard wing to build. After it was all built it had a strange tendency to drop a wing tip in a turn. You would start the turn and you watched the tip keep dropping. At the time I was told that is the way that type of wing flies. I am no expert but it was a fun plane once you got used to it dropping the tips. It did have a VERY low stall speed. It would hang on the wing. Once it let go, you better be ready for the snap. It was a blur.

I would like to watch the build thread on this one.


Dru.

Andrew

DT

That wing looks like it would be a booger to build, but a beauty when done. Look for some threads by Dickeybird - he built an elliptical wing for one of the 1/2A build contests a couple of years back.

ChicaWolverina

Very nice indeed, and it should have some dihedral, but 5 deg for each panel is about 3 times what it should be.

IMHO.

K...

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Tomasina

digital_trucker

I thought about using one-piece ribs, but the problem arises from a few different angles. It's going to have 1/32" balsa ribs, and I'm not sure how well they'd stand up to having a the 1/8" x 3/16" balsa spars bending across them (the thickness of the wing is ALSO elliptical down the wing...bottom and top). One other unusual thing I'm doing is that the ribs will have vertical grain as opposed to chordwise grain. Essentially the ribs will be built like miniature spars, with the body of the rib acting like shear webbing and the cap strips acting like spars. Yes, the leading and trailing edges will be laminated around a form. There's two reasons why I'm building so much dihedral into it; for one thing, every full-scale low winger has a fairly large amount of dihedral (even warbirds). I've also heard about the 'tip tuck' issue elliptical wings sometimes have, I figure dihedral will help that out too. Ultimately though, I think it just looks better with the dihedral

I'm working on the tailfeathers now, they're also going to be symmetrically airfoiled instead of flat slabs...and the stab leading edge will also be a laminated bow.

I'm going for a very sexy look with this thing, hopefully I can achieve that and get something that flies acceptably well too.

combatpigg

My Feedback: (3)

Great looking project DT! Don't forget the elliptical fuselage, too [8D]

planebuilder66

My Feedback: (8)

Looks like a spitfiire wing to me, if you add inboard split flaps it would be a clone.

digital_trucker

It's definitely 'spitfire-ish', but it has a much greater aspect ratio. I was looking at spitfires when I laid out the planform, and spit wings are surprisingly stubby.

cp - the fuse lines are based on ellipses, at least in the nose and turtledeck area.. The stab and elevator are elliptical, along with the rudder, but the fin isn't. I couldn't come up with an elliptical fin that I liked the looks of, so I blended it into the fuselage instead. The fuse lines are very sleek, and I can't help but wonder if it might actually be easier to fabricate out of fiberglass. I'm also giving serious thought to having the wing permanently attached to the fuse, I'm just not sure about the best way to go about that. I've never built an R/C model that's had the wing permanently attached - any ideas on how to engineer that?

This is DEFINITELY going to be a builder's project...no slab sides and Stik clones here! (I admit to going with fairly standard moments and ratios though). I swiped the airfoil from the Ultra Sport, but thinned it down to 13%. My experience with these smaller models is that they tend to do better with thinner wings. Not sure why, but maybe it has to do with the fact that the air itself doesn't scale down? In the end, I'm using a highly technical process based on precision TLAR design parameters .

combatpigg

My Feedback: (3)

DT, someone mentioned something about elliptical wings "dipping". Just like any other wing if over loaded, but they will snap roll with even greater efficiency So leaving out as much wood and detail as possible is a good approach. I've never seen it demonstrated that fiberglass is as light a way to go on this scale as balsa stick is. There was a huge "old timer" hanging up at the LHS that your plane will look related to, it was a masterpiece.
You're on your own with radio access, just consider all your options.

planebuilder66

My Feedback: (8)

I vote to unitize the structure and use flush hatches to access the radio equipment, if the fuse has a belly pan then just incorperate the fuse formers through the wing and tieing into the spars, sheet the fuse and unitize the structure, the only problem will be fairing it all together and repairing the occasional mishap to the structure. But in the end it will save some weight by reducing reinforcements and hold down blocks to mount the wing.

Entropy

My Feedback: (2)

It reminds me a bit of the Sig Rascal's wing. I only say that because right now I'm in the process of converting a Lil' Rascal to glow. But the Rascal has a straight leading edges until the tips.

soarrich

My Feedback: (98)

Beautiful design so far.

The complexity is part of the beauty. I went over to a friends house the other night, he had Proctor Antics, two sizes, they where so cool to look at. I think the ARFers wouldn't get it though, because they probably don't fly any better than a light ply laser cut arf.

Back to your plane, could you put up a spar, rib, shear-web section? I tried to blow up what you have up, but it was really pixallated.

digital_trucker

Rich, I'll be submitting a PDF when I get 'er done. Basically the main spars and one-piece shear web are built as a unit and jigged up. The 1/32" balsa ribs are in three pieces with fore, center, and aft sections that glue between the leading edge, spars, and trailing edge. 1/32" balsa cap strips and center section sheeting go over the whole mess. A little bit of balsa makes up the wing tip.

combatpigg

My Feedback: (3)

The ARFers are happy with their Wonderbread, bologna and Bud Light, while us sophisticated 1/2A scratch builders are able to savor the artistry, craftsmanship and the splendor of a true masterpiece [8D]

digital_trucker

I have the stab structure wore-or-less worked out, just not sure yet exactly how I'm going to actually assemble it yet. Here's an image, with a teaser of the fin/rudder and fuse shape.

beenie

My Feedback: (9)

That is a good looking airplane. I think that this may be one of those planes that it would be a shame to cover.
Ben

digital_trucker

I've nailed down the fuse shape, it's going to be old-fashioned former-and-stringer on a crutch construction. You can see a hint of the fin/rudder in this render.

hogflyer

DT –

That looks great.

What software are you using for the design and rendering?

Hogflyer

digital_trucker

I'm using TurboCAD 14.

combatpigg

My Feedback: (3)

Looks like it might have hit 550 mph back in the 1940s? [8D]

planebuilder66

My Feedback: (8)

I likie, want one!, wait,.... another plane to build, I have too many to finish or fix right now, maybe later on.

eroc144

My Feedback: (1)

DT - How are you generating the 3D views? So far I've only bothered to work with 2D views in Turbo CAD.

EG

digital_trucker

Eroc, as far as I know, it's just a matter of switching to 3D mode and making solids. Maybe the version might make a difference, I'm using TurboCAD Pro.

lildiesel

Those renderings have a very 30s racer look to them. Put it on floats and it would look like what Reginald Mitchell might have designed to follow up the S.6b if the Schnieder Trophy hadn't been won outright and retired.

Just for kicks, a Spitfire Mk. V on floats:

BMatthews

The Pro version makes a huge difference on the 3D stuff. I'm running V15 deluxe and while I can do a fair amount of the easy stuff like wings with no problem I can't do curved sides or a sexy shape fuselage like your drawing. When I look in the Help I find the commands or options I need and the cryptic "This feature available in Pro only".

I gave up and I'm back to 2D which I understand better anyhow.....

Speaking of "anyhow" the paramour looks fantastic. Obviously very Spitfire like and it's just begging for a canopy or perhaps a canopy and turtledeck. Maybe place it back in a more race plane like position to avoid the obvious "Is that a Spitfire mister?" comments that would invariably come from placing the canopy in a normal position.