RE: Curare Build
 

OK, that is alot to digest. Like many people, I tend to stick with what I know until forced to make a change. Since I'm on my last bottle of Sourghum and it is no longer in production (I believe), I'll have to learn a new trick soon.

I'll decide after I get the landing gear and cutouts installed.

Here's a pic of the nose blocks. I had a senior moment and cut on the wrong side of the block the first time. The blocks were too narrow. Fortunately the block supplied is twice as long as it needs to be. I can't see any other use in this kit for block balsa, so I just cut them again.

RE: Curare Build
 

Greetings,

I've been thinking about how to make a Curare stab plug-in and adjustable for some time. The amount of anhedral (4 1/2 under one tip, with one stab flat on the building board) is a challenge. Anyone have any ideas about how to do this?

Best regards,

George

RE: Curare Build
 

the only possible advantage that i see to skinning wings with the PU glue, as it appears that all methods hold just fine, is that just an ounce or so of glue can be rolled out over the entire wing until just a shiny wet look occurs. very, very little glue is required.

RE: Curare Build
 

Mitch,
We almost used Southern Sorghum (later Dave Brown's productI believe) exclusively back in the day. It did not matter at all whether we glassed with thinned epoxy, resin, or just monkoted the wings, all worked fine. I have a Dirty B wing in the garage attic that was sorghummed and covered with M-kote in 1979 (it is very sound and looks very useable today), hhmmm. Good looking build project too, keep up the work.
Mark

RE: Curare Build
 

George,

is your concern the anhedral in the stab?

The issue with plug-in flying surfaces and incidence adjustment is that it is hard to have both this feature and fillets going on at the same time. If your stab were built and installed flush with the fuse sides, then I can't see a problem with adjusting incidence whether the stab has anhedral or whether it is flat. In the case of an anhedral stab, the angle of the cut is just acute rather than square.

David.

RE: Curare Build
 

I received a pm request for a wing sheeting layout. This drawing was made by measuring the MK plan. It is the dimensions of the wing sheeted area only, from the leading edge to the aft face of the rear spar, from the center line to the outboard edge of the foam.

I hope this helps. Of course, you'll have to allow for the curvature of the airfoil and expand these dimensions a bit. I would also allow myself a little margin all the way around. It's easier to trim than to add!


edit: second pic corrected for missing dimension (I need a drawing checker)

RE: Curare Build
 

Mitch,

thanks for the nice template. If I may add a couple of comments to cutting sheeting...

A very sophisticated method (not :)) is to simply take your joined sheets and after having sanded them smooth, lay them on the table with the shuck over top and put some weight on it at the tip and root so it doesn't move. The tendency is to line up the LE or TE with the sheet grain (i.e., root at 90 degrees to grain), but a better method (particularly on classic wings - a little different on modern F3A wings) in my opinion is to sweep the sheeting with the LE.

This means that your LE template (or shuck) will be parallel to the LE which results in the TE being at a ~20 degree angle (depends on taper) to the grain. Why do this? Because it helps to avoid the TE from warping over time and keeps the wing truer. A TE which has grain parallel to it can have a tendency to warp up or down. Together with the LE proper which is applied to the core (either before or afterward - reasons for either technique exist) once sheeted, the whole wood structure interlocks nicely with differing grain directions. Sort of like how fuses are built. Sides with grain lengthwise and formers with grain heightwise.

So, with your shuck canted on the sheeting leaving a healthy 1/2" at the LE of overhang, mark the root, tip and TE lines by drawing with a straight edge at another 1/2" separation. This overhang need not be as much on the root and tip. The overhang at the LE/TE is to account for the airfoil using more material than the flat shuck would (as Mitch pointed out).

The couple of pictures show sheeting for a Tiporare (the Curare's evil twin [>:]) wing and stab cores being prepared. As can be seen the first sheet is always intact width wise. Depending on whether one uses 3" or 4" sheeting one may end up with several whole sections of sheeting until the last one is cut at an angle. The only time when the sheeting LE and TE grain actually ends up parallel is when they are both swept back equally or in the event of sheeting a simple rectangular wing (e.g., Quick Fly) span wise. The last few pictures show how the surfaces look once sheeted (note the angle of the grain), the sheeted core sandwiches prepped (wax paper between sheeting and shucks) for loading and the sheeting sanded flush to the core/shucks in the stacked pancake (note reference to cool engines...[8D])

In short, use the template (or the shuck) by laying the LE of it parallel to the front of your sheeting prior to cutting.

David.

RE: Curare Build
 

Hi David,

Thank you foryour input re. making a plug-in, adjustable Curare stab:

I'm concerned that, with this much anhedral, the joiner tube can't extend into the stab halves sufficiently to take the bending load. That's if the usual method is used, with a single joiner tube going through the fuselage from a socket in one stab half to a socket in the other stab half. I attach a diagram I quickly freehanded to show what I mean: the three piece socket (one piece in the fuselage, two in the stab halves) is in red, the joiner tube is in green. I don't have enough experience to devise an alternative method. Any input will be very much appreciated.

Best regards,

George

RE: Curare Build
 

You could use flat plates of aluminum, cut to the anhedral angle. This would require rectangular cross-section sockets in the stab and some reinforcement at the upper and lower surface.

I think this would also require a fixed portion of the stab at the center to be permanently fixed to the aircraft with the aluminum joiners locked in place.

I think to make this also adjustable would require adding significant weight in the tail.

RE: Curare Build
 

David,

Excellent input, thank you.

The person that requested this drawing via pm is waiting for a kit and wants to get a head start.

Mitch

RE: Curare Build
 

Mitch,

I was going to ask if I should remove those pics. Didn't want to detract from your excellent build sequence. Since the wings are very similar, I thought it might lend to the thread. Anyway, I'm glad you approve.

Thanks, David.

RE: Curare Build
 

George,

That certainly is an extreme case of anhedral. Just by looking at it, I'm not sure the Curare has that much but still it's worth figuring this thing out. Mitch's idea of using aluminum panel/fuse doublers is one good method. This wouldn't require a cross-stab CF/glass tube. Using two screws in tabs under each panel to fuse junction, you could make the TE screw fixed so that the stab rotates about this pivot when adjusting. The front screw would allow vertical adjustment to change the incidence. The tabs would require an arc opening in the fuse plate - vertical arc in the LE and horizontal arc in the TE. This way, the arc in the LE permits the stab to rotate up and down while the arc in the TE permits the screw to move horizontally (mostly) very slightly. The extent of adjustment is very small so the rotation is typically also not extensive and the arcs can be cut to slightly over sized rectangular openings. This, off the top of my head without having drawn it out.

Another, perhaps less elegant method would be to use permanently fixed CF inner tubes bonded into the fuse stab plug (the center portion that would fill the fuse opening). By drilling out the cores - say half way - with a center outer phenolic tube held in place by a 1/16" ply rib in the stab panel (another at the root), you wouldn't have to worry about the cross-stab CF tube. In the case of a stab, it is sufficient that the panel doesn't flex from the fuse C/L. It isn't necessary to cross-join the stabs with the tube. Of course, it is less elegant because you'd have the inner CF tubes permanently afixed to the fuse. However, if you think of the fuse/stab assembly as a single unit rather than a fully removable stab concept, this isn't an issue. The tubes are merely there to provide adjustment. The LE of each panel then is adjusted with standard Central Hobbies incidence adjusters (which allow rotation about the CF tubes in each panel).

Basically one builds the stab in a conventional manner except that each panel is fitted for its own phenolic tube through the rearward end of it inserting the ply rib(s). Once, the front adjusters are in place, you join the stabs in a conventional manner with the required anhedral. With the stab inserted through the fuse and aligned, you mark the stab plug section on the side of the fuse. You then cut each panel off through the phenolic and cap them at the root as well as the plug (this latter only needs a 1/64" ply cap to cover the foam). Insert the inner CF tubes into the plug where they will be permanently bonded once re-aligned. In a nutshell it's the same idea as would be done with a flat stab except that you are using two CF tubes rather than a single one going through the fuse.

Also, as drawn your CF tube appears much larger than needed. A Curare stab root might be ~1-1/2" thick. You probably only need a 1/4" inner tube. It can be done, it's just a matter of figuring out the right geometry.

I'll certainly watch if you decide to do it! :D

David.

RE: Curare Build
 

Don't worry about that, I'm doing this build thread to both provide knowledge and to gain knowledge, and it's certainly working.

RE: Curare Build
 

I decided to deviate from the plans on the nose construction. I wanted an easy way to ensure that the nose is straight and symmetrical. I cut a block that fills in the space between the fuse sides and the upper and lower nose blocks.

This way, I can just glue and clamp the fuse sides to the block and everything should be straight.

Most of this block will wind up being hogged out.

As can be seen in the pictures, I had to add material to the block to get the dimensions right.

It's important to have all of the grain running fore and aft in the nose, this makes it easy to shape with a razor plane.

Also, the shape of the lower nose block has changed from the previous pics due to a difference between the plan and the supplied fuse sides.

RE: Curare Build
 

Hi David,

Many thanks for your considered input. I hope Mitch won't be annoyed with us for using his build thread to discuss plug-in adjustable stabs for the Curare. I think it's relevant, as the Curare was the design that started the anhedral bandwagon rolling in the first place, and modelers today might want to have the benefits of a plug-in adjustable stab.

I freehanded the drawing to show the principle; it's certainly not to scale. In any case, the Curare stab has about 10 degrees of anhedral as measured on the top surface. Looking, for example, at ACP Composites' web site, a suitable joiner tube and sleeve assembly is a .230in OD carbon tube and a .278in OD glass tube. Even if we thicken the stab to be 15mm at the fuselage side, doing the maths shows that the sleeves can only extend less than 2in into each stab half. Even if we play tricks with fillets at the fuselage side to get a little more space, we can't get much more than 2in. I think you'll agree that won't be enough.

It looks like we're going to have to seek a different solution, perhaps along the lines of the alternatives proposed by you and Mitch. You both gave me some good ideas to consider. Many thanks!

Best regards,

George

RE: Curare Build
 

I'm attaching two Curare articles I grabbed from the internet a while ago. Interesting read.

Mitch, have you thought about which of two flap/spoiler setups you are going to use? The setup from the RCME article seems cool but I would have no idea how to do that (besides using two servos: one for flap and one for spoiler).

Ordered my kit and retracts yesterday! Can't wait and follow along!

RE: Curare Build
 

Why does the joiner have to be round?

Why not build a ply BOX into the stab where you were thinking of putting a TUBE, and then cut a piece of 1/8" CF or ply to join the two sides together. You could use different joiners to obtain different angles.

Two boxes (one for anti-rotation) and you'd be set.

Or am I missing something?

Andy

RE: Curare Build
 

Hi Andy,

Thanks for providing another suggestion for the Curare plug-in adjustable stab.

You're right, a flat joiner in a box section spar is a good solution for joining the anhedral stab halves, and this arrangement can be used to vary the anhedral with different joiners too.

I want to make the stab incidence adjustable, so the probable solution is to find a way to combine a flat joiner with a system that will allow for adjustable incidence. Your suggestion, combined with some ideas from Mitch and Dave, has got me thinking of some possibilities.

Best regards,

George

RE: Curare Build
 

If the center of the joiner is thicker than the stab airfoil, you can make adjustments by changing out the flat joiner. Simply make the part that extends into the stab higher or lower on the center.

Some CRUDE graphics to convey the idea:

RE: Curare Build
 

Andy,

I don't think I follow. Are you suggesting a square/rectangular CF section or a basically flat "spar doubler" like section?

The technique with square section was used by Matt on the Arrow (see his plans) which of course has no anhedral. A square section is nice because it is very strong. However, a circular section is equally strong and distributes stress uniformly. I think CF also produces more reliable circular sections. A flat section on the other hand would be prone to flexing unless overweight.

But I must be missing something now.

David.

RE: Curare Build
 

Hopefully the attached will present the concept in enough different manners that all will grasp.

There are several different views and they all show the same thing.

Start with a flat sheet of ply or CF sheet. Think an old-fashioned dihedral brace/joiner that is actually removable from the plane. It slides into a box in the wing just like your standard joiner tube does today. Instead of being just one width (height, viewed from front), it has a center area which is a little oversized.

It looks like a flattened Sponge Bob - a square with two arms sticking out. The angle of the arms adjusts the di/anhedral of the stab. The vertical location of the arms adjusts the incidence.

Instead of a tube that goes thru the fuse, you stick Sponge Bob in so only his arms stick out, then you slide the stab panels onto his arms.

If you make a stack of a bunch of these for different anhedral and different incidence, it kind of looks like some Hindu god waving its arms.

Andy

RE: Curare Build
 

someone has kids.:eek:

RE: Curare Build
 

Andy,

Now I see what you mean - nice approach. The only thing that strikes me as needed is that the anti-rotation pin should actually be a rotation axis. Sponge Bob would effectively alter the height of the LE. Unless the TE is kept at a fixed height position and allowed to rotate, the height of the entire stab would be altered as opposed to just the LE.

Making this from ply with CF mat on each side sounds quite easy. The box in a foam stab sounds a little more laborious - built up would be easier.

David.

RE: Curare Build
 

FOAM!?!?! GAG! It would need to be built in before sheeting, but other than that it should be pretty easy.

Would a 1/4" peg do OK for anti-rotation?

As for being the pivot, I think it would do better to be the adjusting item for incidence while the forward one carries the flight loads and acts as the pivot.

Keep in mind, we aren't talking about a large amount of adjustment. If you're moving the stab angle more than a very few degrees, something else is much farther off up front. It's a proven design that is being tweaked, not something off the wall.

Andy

RE: Curare Build
 

7, to be exact, plus (as of last weekend) one granddaughter.

I only know of Sponge Bob from friends and junk in stores. I watched it once and it was the stupidest show I ever saw. We actually don't have cable TV (no cable in our town), satellite TV, or even off-air (by choice).

Andy