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    Curare dihedral...?

    Hey guys, I'm looking at doing plug in wings on my Curare build, for ease of transport. I want the dihedral to be right when the hole is cut for the sleeve, and I can't find my protractor. Not to mention I'm a little confused about where to reference an angular number from. I know from the cord thickness' on the plan and the note for dihedral each tip would have 1.5" and if the wing was on a flat surface inverted it would have .7" under the center, but as far as an angle to give the core cutter I'm stumped... Anyone know the answer?
    Blake

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    RE: Curare dihedral...?

    Hey Blake,

    Mr. Pythagoras has these answers but he hasn't been around lately. He left some notes with me though saying:

    Sin alpha = opposite (tip dihedral) / hypotenuse (panel span).

    He also said that,

    Alpha + Beta = 90 degrees

    David

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    RE: Curare dihedral...?

    David, Thank you. I divided the tip dihedral (1.5) and half the wing span (32.25) and got 0.0465. Would my answer be 4.65 degrees?

    BTW- I'm a wrench turner, and can do some cool stuff with balsa, no mathematician... but a quick google search on a hunch left me laughing Thank you for such a nice since of humor
    Blake

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    RE: Curare dihedral...?

    Blake,

    You're on the right road. Preferring to turn wrenches myself, the Greek left an impression on me as a boy saying his stuff would come in handy later when I got into building classics...

    Anyhow, for more accuracy, you should remove the wing tips from the span as dihedral is measured at the tip of the core (or at the tip rib as it were). Guessing, we're talking about ~1.5" of balsa out where the vortex lives. So, that leaves us with 30.75" panels at the fuse center line.

    Invoking the Greek, sin alpha = 1.5/30.75 = 0.049

    The dihedral angle is then alpha = arcsin 0.049 =~ 2.8 degrees

    I'm not sure to what decimal accuracy the cutter can set this angle but somewhere between 2.77 and 2.80 degrees should give you a reasonably uncoupled Curare (provided correct stab anhedral as well).

    Looking at it another way, the core cutter can cut that dihedral angle into panel roots at the fuse side (the proper length for your cores). Then, with the cores blocked up to put the roots perpendicular to the horizontal, the sleeve hole can be bored level and perpendicular to the root. Some cutters will cut the dihedral straight into the core so the root and tip are left square. This also makes it easier and more accurate to use the shucks as levelers when boring. It does result in slightly thicker foam blocks though - usually not an issue but it can increase the shipping I'm told.

    The thing to assess, is at what higher offset distance from the root chord centerline to enter the core. This offset will determine how long of a sleeve you can use without it exiting the bottom of the core. Inverting it, if you have a given wing tube you are comfortable with in terms of structural support, figure out whether the length might be getting close to the bottom at the ends if you enter the core on the centerline.

    Last but not least, this offset also determines where in your fuse sides (and doublers) you have to place the stub sleeve to position the wing where it should go.

    It's all good fun, isn't it!?

    David

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    RE: Curare dihedral...?

    One other thought:

    To reduce tip weight and avoid having to add pesky balsa wedges, you should have the cutter extend the cores to the very tip and then cut the right wedge angle downward into the blocks after the cores are cut. This will only necessitate some 3/32" sheet on the tips once the cores are skinned.

    The correct tip airfoil may need to be adjusted for this though depending on the wing plan design. I don't recall the two Magic plans at the moment. If the tip calls for a wood wedge (RCM&E?) then the tip airfoil needs to be "extended" further out to top tip span of the wing... If that makes sense.

    Edit: Disregard this - only applies to Magic cores.

    David

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    RE: Curare dihedral...?

    Thank you once again. Don will be cutting my cores, and I will link him to this thread. I have not converted to plug in wings before, and am not sure as to how far the tube would need to go into the panel. I plan on using 7/8" carbon tube from F3AUnlimited 10" into the panel. Is that enough?

    I also planned on raising the wing about .5" to help give room for the structure to support the tube. Will this effect the flight greatly? Would the dihedral need to be different for this change?
    Blake

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    RE: Curare dihedral...?


    ORIGINAL: doxilia

    One other thought:

    To reduce tip weight and avoid having to add pesky balsa wedges, you should have the cutter extend the cores to the very tip and then cut the right wedge angle downward into the blocks after the cores are cut. This will only necessitate some 3/32'' sheet on the tips once the cores are skinned.

    The correct tip airfoil may need to be adjusted for this though depending on the wing plan design. I don't recall the two Magic plans at the moment. If the tip calls for a wood wedge (RCM&E?) then the tip airfoil needs to be ''extended'' further out to top tip span of the wing... If that makes sense.

    David
    This does make sense, though I am building a Curare. Are you suggesting using a tip design like the Magic?
    Blake

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    RE: Curare dihedral...?

    Argh,

    Never mind that, I'm mixing up threads. That's what happens when you jump between two Prettner threads at the same time... and, if early senility sets in.

    Dismiss the Magic tip comments, core tips can be cut square. The aileron/TE design of the Curare (clipping) precludes Magic like tips. Besides, the clipping was his earlier anti-vortex no-flutter concept.

    BTW, Don will cut you cores with dihedral directly in the shuck. This allows him to bore with the blocks level - much better.

    Dunno about the tube length as I don't have the plans in front of me but I'd want to go to a ply stub rib on the tip side of the retract unit. Anything shorter and I'd be concerned with the wing buckling, particularly on a hard landing. Maybe I'm over cautious - let the early 90's F3A wing retract conventional gear guys tell you about it.

    David

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    RE: Curare dihedral...?

    Ok, Thanks. I am going to use convetional gear, and locate the mains in the fuse, this will take all of that force, and weight out of the wing panels. I will let Don determine the length.

    Any input on the dihedral angle or anything else concerning moving the wing toward the thrust line? I don't have it nailed down yet, but I was considering a half to three quarters of an inch for doublers to support the wing tube.
    Blake

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    RE: Curare dihedral...?

    If I've read correctly, then for the numbers given and the calculations provided you'd have the angle that the root must be cut relative to the bottom of the panel core NOT relative to the centreline of the panel core because the panel is tapered in thickness.

    Not a probem if the bottom of the panel core is parallel to the bottom of the schuck but I place my templates of the block centerline.

    Just one of things things to ask about and double check as part of the measure twice, cut once process.


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    RE: Curare dihedral...?


    ORIGINAL: LS171Malibu

    Ok, Thanks. I am going to use conventional gear, and locate the mains in the fuse, this will take all of that force, and weight out of the wing panels. I will let Don determine the length.

    Any input on the dihedral angle or anything else concerning moving the wing toward the thrust line? I don't have it nailed down yet, but I was considering a half to three quarters of an inch for doublers to support the wing tube.
    Well, going with fuse mounted LG does simplify the wing tube issue. Still, though, I'm not sure that less than a third of the panel span (10 out of over 30 in) is sufficient to support the wing when pushing high G's. However, it sounds like you have a ~24" tube on your hands with 4" within the fuse and 10" into each panel. What's the tube intended for? Then again, an almost 1" diameter tube is pretty stout. I'd probably favor a thinner longer tube.

    I didn't want to comment on your decalage proposition because it's one of those things that requires lots of testing. I know that it was done with the Illusion as an experiment on the Tipo 720 (the Illusion is a Tipo with more squares and a higher wing and reduced anhedral) and based on what I hear from the guys with ample experience (e.g., TonyF), the Illusion was not as good a pattern plane as the Tipo. Then again, people like Kimbro were of the school that wing and stab should be equidistant from the thrust line but that was for an altogether different kind of pattern plane (the Deception). My gut feeling tells me that vintage anhedral beasts like the Curare, Tipo, Magic and the like did better with a proper low wing position with respect to the pronounced stab anhedral. If you mess with that then you are getting into messing with the overall result of how the plane will end up flying - move the wing up, bring the stab down, change thrust angles, change the dihedral/anhedral and so on...

    One thing I know is that Hanno built and flew many, many Curare's as did many other people and the plane was considered good enough to be copied or "varied" to the point that umpteen different iterations and variations of the Tipo came out. In short, Hanno must have had things just where he wanted them. If it was me, I wouldn't futz with the aerodynamics of the Curare, but then again, that's half the fun of modelling.

    I'm not sure what you mean by 1/2 to 3/4" for wing tube support doublers. If you mean the thickness of the wall where the fuse sleeve is mounted, that's way overkill. The trick is to build it "torsionally" stiff. CF tubes are very strong but I wouldn't have a tube going across the fuse in a vacuum. I'd put a former just ahead or aft of the sleeve location across the fuse. The wall thickness of the sides for the tube can then be augmented with some simple 1/8" ply inside of the doubler essentially to support and bond the tube (and this is in addition to the already existing fuse side thickness and half length ply doubler).

    David

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    RE: Curare dihedral...?

    ORIGINAL: bjr_93tz

    If I've read correctly, then for the numbers given and the calculations provided you'd have the angle that the root must be cut relative to the bottom of the panel core NOT relative to the centreline of the panel core because the panel is tapered in thickness.

    Not a problem if the bottom of the panel core is parallel to the bottom of the shuck but I place my templates of the block centerline.
    BJR,

    regarding your first paragraph, that would be correct. The dihedral height is measured to the base of the wing tip root on the bottom of the panel. The vertex from which angular dimensions are taken (or applied) would be the bottom of the core at the root's thickest point on the fuse centerline (i.e., single piece wing core span) with the incidence set at 0 degrees. Someone who knows how to cut cores with dihedral into them would presumably also know how to fix the correct angle in the software.

    From what I understand, modern foam cutting CNC machines don't use hard root/tip templates for airfoil guidance, instead, you can instruct the cutter to "offset" the tip airfoil at the dihedral height. This results in a core that is cut "diagonally" into the block low at the root and high at the tip. This leaves one with a pair of core blocks that can be mated square to the table when the wing is joined. This, of course, also requires that left and right panels be cut (they can't be identical) and that the offset from the bottom of the block be even in both panels. It's nice though because if properly cut, the shucks take care of alignment if building a one piece wing (or for boring panels evenly).

    In short, the bottom of the panel core does not end up being parallel to the block bottom/table top if cut this way. Your point is a good one though because angular measurements are a delicate thing; shorten the block span (e.g., by cutting the cores to fuse side span rather than fuse centerline span) and the dihedral ends up being too much (and the converse). Likely the fuse side root airfoil thickness would also be incorrect in that case. Airfoil templates on these birds are provided for single piece wings generally.

    David

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    RE: Curare dihedral...?

    Thanks. F3a Unlimited sells a Gator 7/8" by 38.75" carbon tube with fiberglass socket. I think that would fit the bill, and Don can bore the panel up to 17" deep if it doesn't penetrate the bottom. The 1/2" to 3/4" comment was in regards to raising the wing in order to allow for more area under the tube for the 1/8" doubler... Otherwise, your description is what I have in mind.
    Blake

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    RE: Curare dihedral...?

    Thanks Dave,

    your comments re the panel length are important to consider. Just measuring off the two plans I have, the panel length along the bottom measures about 16mm more than the 30.75" you estimated in your example but the final numbers are still really close.

    I suppose technically there's 4 degrees of dihedral (each wing panel tilted up 2 degrees) using the centerline as a reference (as I would) but if the cutter's using the bottom of the panel as their reference then the bottom of each panel is at a 2.75 degree angle with the table.

    Again I'd ask and double check with the cutter because if there's two ways to do something I'm sure I'd do it the wrong way first time around. I'm more of a measure three times, cut once, THEN spot the mistake, throw it away and make another


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    RE: Curare dihedral...?

    ORIGINAL: LS171Malibu

    Thanks. F3a Unlimited sells a Gator 7/8'' by 38.75'' carbon tube with fiberglass socket. I think that would fit the bill, and Don can bore the panel up to 17'' deep if it doesn't penetrate the bottom.
    Blake,

    with a tube that length, you certainly have options. Over one half the panel span (17 in) sounds like too much with a CF tube that large. First I would check the position along the span where the airfoil reaches between 1.75" and 2" in thickness. I wouldn't bore a core deeper than that point with a tube which is almost 1" in diameter. At 1.75" airfoil thickness, if centered (which it won't be), the sleeve would only have 3/8" above and below it. I wouldn't want the foam much thinner than that. However, since the tube will be entering at an angle into the core (due to dihedral), you have to assess how deep you can go without getting too close to the bottom. I suspect that if you split the difference between your original 10" and Don's 17" max length, say 12-14", you may wind up at the correct spot along the airfoil thickness without getting too close to the bottom of the core. It's really a matter of scaling that root airfoil down as you move down the span of the panel. Check it at 14", if the core is good, use 14", if not, try 12".

    The 1/2'' to 3/4'' comment was in regards to raising the wing in order to allow for more area under the tube for the 1/8'' doubler... Otherwise, your description is what I have in mind.
    I see. Well, area under the tube for the 1/8" ply ring sleeve support is not so critical provided you have a good 1/8" ply former across the fuse in that area. If you look at many ARF's using CF tubes, they are built this way. The former and fuse bottom will stiffen this area up without you needing to raise the position of the wing. A problem you may encounter though is how to go about building the bottom of the fuse in this area without the root of the wing panel extending lower than the fuse bottom. I'd have to look at the plans again but I suspect that you might have to choose a position for the change of fuse bottom angle to transition from the fuse depth at the wing LE to the depth at the TE - the latter is typically shallower. I think I'd aim for a "follow airfoil" approach to building up the bottom of the fuse in the wing area so this might require a little care in assessing where to position the tube both with respect to the wing as well as the fuse. The former, if placed too far forward or too far back might result in the bottom of the fuse being harder to produce as desired.

    Many low wing design models were not designed with plug-in wings (other than for historical reasons) because it is a little harder to deal with the construction and support logistics. I take it you are going to build a fuse with a removable top deck if the bottom is to be closed? That too is of concern, particularly when using glow, as it tends to weaken the fuse structure unless properly accounted for. Will this be a glow or electric model?

    David


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    RE: Curare dihedral...?


    ORIGINAL: bjr_93tz

    Thanks Dave,

    your comments re the panel length are important to consider. Just measuring off the two plans I have, the panel length along the bottom measures about 16mm more than the 30.75'' you estimated in your example but the final numbers are still really close.
    Absolutely! My figures were really shown as a recipe rather than the final numbers. I just guessed that the panel, without wing tip, was ~30.75" - I certainly haven't measured it on the plans. That's for Blake to sort out.

    I suppose technically there's 4 degrees of dihedral (each wing panel tilted up 2 degrees) using the centerline as a reference (as I would) but if the cutter's using the bottom of the panel as their reference then the bottom of each panel is at a 2.75 degree angle with the table.
    As you mention, the added 16 mm of span (0.63 in), if that is the correct figure, only reduce the angular dihedral from 2.77" to 2.75" along the core bottom. I have no idea whether that translates to 2 degrees along the airfoil centerline as I don't have the airfoils but I'll certainly take your word for it. Feel wise, it does sound about right knowing generally how these airfoils transition. It is definitely important for the cutter to take into account whether the software uses the airfoil base or the centerline to dial in the angular dihedral. I would actually like to know how the software does this - centerline or base. It is also useful to know to what angular decimal accuracy the dihedral can be set (or rather, the CNC cutter can achieve). More than 2 decimal places aren't needed but two would be good.

    Again I'd ask and double check with the cutter because if there's two ways to do something I'm sure I'd do it the wrong way first time around.
    Don't we always!

    I'm more of a measure three times, cut once, THEN spot the mistake, throw it away and make another
    Somehow I suspect that Don won't prefer that route...

    David

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    RE: Curare dihedral...?

    I'm going to use the OS 95. They also have a 3/4" x 30", would that be better? BTW, the 17" max was just a number based upon tube length - fuse width/2. I don't know if Don has a max he can bore.
    Blake

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    RE: Curare dihedral...?


    ORIGINAL: LS171Malibu

    I'm going to use the OS 95. They also have a 3/4'' x 30'', would that be better?
    Generally, yes, it does sound like a better dimension. But you might want to check it with respect to the airfoil thickness at ~13" out into the core; this assuming a fuse width guess of 4" which may not be right. The 3/4" will give you more tolerance within the airfoil compared to the 7/8" so that it should be easier to avoid getting close to the bottom of the core.

    Frankly, it's worth sketching up on a piece of paper. Just draw it to scale so that it fits on the paper and you are using 1/5" scale or some such. It will tell you what you can and can't use. We're just talking about a few lines, nothing fancy.

    David

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    RE: Curare dihedral...?

    how will you acess inside of plane?

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    RE: Curare dihedral...?

    That is a good idea. I'll draw it up tomorrow.
    Blake

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    RE: Curare dihedral...?


    ORIGINAL: hrdflite

    how will you acess inside of plane?
    I'll fab an upper hatch.
    Blake

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    RE: Curare dihedral...?


    ORIGINAL: doxilia


    ORIGINAL: bjr_93tz

    Thanks Dave,

    your comments re the panel length are important to consider. Just measuring off the two plans I have, the panel length along the bottom measures about 16mm more than the 30.75'' you estimated in your example but the final numbers are still really close.
    Absolutely! My figures were really shown as a recipe rather than the final numbers. I just guessed that the panel, without wing tip, was ~30.75'' - I certainly haven't measured it on the plans. That's for Blake to sort out.

    David
    Thank you guys for bringing this up! Per the MK plan the panel is 31.375", and using the formula I learned earlier in this thread along with the plans call out of 75mm I have determined the per plan dihedral to be 2.33 degrees.

    Once again I want to extend my thanks to David for taking the time to assist me here. Time to order the wings and get to sniffin' glue!!
    Blake

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    RE: Curare dihedral...?

    Blake,

    I figured that rather than me continuing to guess measurements, having others point it out and you have to adjust for it, I pulled the MK Curare 60 plan to check things out.

    I redrew the wing planform in CAD and adjusted the core dimensions to accommodate a 1/4" LE and a 3/8" TE applied to the core once sheeted. Since the plan is metric, if one follows the "rib planform" to determine the foam core, one ends up with the requirement to use metric wood for LE and TE which is inconvenient.

    With the planform drawn, it was a simple matter to determine where the wing tube should go along with other details. It makes sense to locate the wing tube exactly on the CG for two reasons: 1) it permits you to easily balance the model without wings (or with partially inserted wing panels) by supporting the tube inserted through the fuse. 2) It also happens to be a good location within the airfoil thickness of the wing. I drew the tube according to the 3/4" x 30" tube you mentioned was available and it seems to be ideally suited. I don't think the dihedral will cause an issue with the tube perforating the bottom of the core at this location even if you enter the root on the chord centerline. It might still be worth triangulating the scaled 3/4" tube diameter at that location and at the proper wing dihedral. Gut feeling though tells me that all will be OK.

    I drew a 1/8" ply stub rib to be inserted into the core to support the tube/sleeve at the tip ends. I also drew the fuse side planform at the wing location and, as you probably know, the fuse is curved here. This curvature can be a little inconvenient when mating wing panels to the fuse as the cores are typically cut without curvature. I drew the correct location to cut the panels once they have been cut to fuse centerline - something I assume Don will do unless he has fuse side airfoils to use. Regardless, I would use the former approach anyway as the airfoils can be set square to the thrustline, so to speak. To accommodate for the curvature of the fuse and to mate the panels, once they are built, you can sand the root of the panels up and down against sand paper applied to the fuse side. This should produce the desired curvature to the panel roots. Once done, you can simply cap the roots with 1/64" or 1/32" ply. Because it's difficult to use thicker ply to allow the production of a retainer for wing bolts entering from the inside of the fuse, it might be preferable to fabricate some tongues anchored into the core that enter the fuse side and are then bolted top down from the fuse hatch you will produce. Several ARF's are made this way. If you position these tongues such that they enter the fuse just above a radio ply plate, you can use the plate to accept some blind nuts and then simply bolt the panels down with some thumb twist bolts on either side. There are many ways to skin this cat and I'm just dreaming this up as I write it so you may already have thought and figured this all out.

    I've attached the drawing (JPG and PDF) for reference. Depending on what Don has available or planned for cutting your cores, it might be worth showing him this drawing as well. If it were me, I'd locate that tube right on the CG - no reason to do otherwise.

    By the way, my per plan dihedral measurements are also shown on the drawing. I got an airfoil base angular dihedral of 2.71 degrees. I also didn't draw the aileron and flap details as they are not relevant to the core cutting. If you choose to have your cores feather cut, you could then take the core panel TE to be the rearmost magenta line rather than the cyan lines depicting a standard TE capped foam core which uses wood controls. The feather cut approach is preferable in my opinion. If you go with flaps, you might have to fabricate those out of wood since they extend beyond the aileron TE. Also, with flaps and plug-in wings, the best approach for controls strikes me as two servos per panel; one for aileron and one for flap each on ply plates mounted sideways. But now I'm getting into your build which is not my business...

    Glad I could be of help. The only catch is that now you are obligated to do a build thread!

    David
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    RE: Curare dihedral...?

    One more thought,

    it would be a good idea to also locate a small piece of 1/8" ply captured by the wing skins, top and bottom, where the sleeve enters at the root. This piece of ply can be inserted into the foam core about the sleeve bore after the root has been sanded to curvature but before the root is capped with thin ply. I suppose that likewise, you could produce your panel retainers in the same fashion if you wanted to go with the more traditional approach of inserting wing bolts through the fuse sides and into the panels to retain them.

    You probably will only need a single anti-rotation pin close to the TE of the wings but perhaps you have Gator incidence adjustors planned. If not, keep in mind that Hanno (or is it MK?) specifies 1 degree of positive incidence on the wing and stab. Man, Curare's strike me as a little tricky to build...

    David

  25. #25

    Join Date
    Jul 2012
    Location
    tucson, AZ
    Posts
    98

    RE: Curare dihedral...?

    why not re-invent the wheel while your at it!


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