Patrick F

My Feedback: (17)

Looking to see if there is any interest in building built up wings and stabs for Mach-1,Curare,EU-1 and others i am working on these and would be offering the fuse wing stab fin in a short kit. You would be able to use the wing and stabs for fiberglass fuses, i will offer wing and stab short kit for these also. Pricing should be quite reasonable
Any feed back would be appreciated.

Thanks Pat
Lasercut USA

pimmnz

Yeah, when you design them try to keep the mainspar straight tip to tip, makes any joining/dihedral bracing much easier and stronger, and therefore lighter. Try to make one of the retract beams line up touching/epoxied to the mainspar. This makes the mounts much stronger, easier to attach the rib doublers to, and again lighter than hanging the U/C mounts in a rib somewhere.
Evan, WB #12.

Patrick F

My Feedback: (17)

Thanks Evan, don't quite understand lineing up main spar tip to tip, as far as the retracts i an making a plywood box that will fit in that location.Oh that is the Mach-1 wing!!!


Pat
Lasercut USA

doxilia

My Feedback: (3)

Evan,

these sound like interesting ideas but I don't quite see how one would use a main spar as a retract support area as well. It's easy to do in terms of design but then, at least the bottom spar needs to be cut in order to allow the wheel to retract. Cutting spars doesn't sound like a great idea.

Also, using a spar which is perpendicular to the ribs (e.g., Kaos) is a nice approach but it doesn't work too well with swept back wings. Even single LE tapered wings (e.g., Escape) don't benefit greatly from such an approach, the spar wants to run in such a way to produce a reasonably constant D-tube section.

Maybe I misunderstand though.

David.

pimmnz

The shape of the wing doesn't mean that the main spar cannot be straight tip to tip, it simply means that it might not line up with the max thickness on all the ribs. It does mean that you can make the spar in one piece without breaking it in the centre to build in any forward or rearward angle. This means you can splice the dihedral into the top and bottom caps, and you then only need light bracing for the dihedral angle. The UC retract 'problem' is only apparent, when you do the forward (or aft) retract beam you simply make it a bit wider, or add a tapered doubler to the spar cap, to give sufficient clearance for the wheel. In practise, given the width of the retract side flange and the beam, there is enough room to retract the wheel without cutting the spar. I know this cause I've done it on Curare, Sicroly, Atlas, Superstar...all fitted with Hobbico mechanicals. The 'D' tube argument doesn't really stack up, as you still produce the tube, only now it tapers in width as well as height, there is no loss of torsional stiffness, and it could be argued that with partially sheeted wings the reduced amount of wood at the tips is actually good...I think Kaos (I have a fixed gear SK) has straight spars? As I remember anyway.
Swept wings (where both the leading and trailing edges are swept back) are entirely different, my Blue Angel needs a swept mainspar, but you can still make one end of the retract beam touch the spar, and pack a wedge between the beam and spar to take the landing forces through to the spar. I only posted here to make the OP think a bit about the structure as he is doing the thing in CAD, and this stuff can be done easily and produce both a stronger, and lighter, structure than before. For aerobatic models, lightness is rightness. Bunging a ply box in a wing to carry the retracts is fine, but you must give some thought to transmitting the landing loads to the rest of the structure, and a ply box might not be the most efficient way of doing it. It might be easy, but it might not be right. Just FWIW.
Evan, WB #12

Patrick F

My Feedback: (17)

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Here's an update on the wing and stab the almost completed CAD work

Pat
Lasercut USA

doxilia

My Feedback: (3)

Evan,

I'd like to understand your approach but I don't think I quite follow your explanation. Perhaps a sketch or a photo of a wing might help.

For reference here's a wing plan of a modified Kaos. This being one of the simpler pattern wings I've come across, I thought it might serve as a basis for the discussion. As we can see, the Kaos is designed with a spar that meets your suggestion - it's perpendicular to the ribs. If we take the location of the LG (UC) as being fixed per design, in your post above you are suggesting to move the spar back so that the spar itself (or some hardwood addition to it) forms the bearer for the front flange (the one closer to the LE) of the retract. Other than the fact that one ends up with a larger sheeted D-tube section, all is fine. The wing would just be somewhat heavier due to the additional sheeting. In this particular CAD drawing the retract installation wouldn't work too well due to the rib spacing since the mains would retract into the side of the fuse (I never conceived the plan for retracts so I made no provision for them) but this would be simple enough to change by re-lofting ribs in different locations or producing a non-constant rib layout. In any case, it seems clear to me that when retracting, the spar would end up interfering with the wheel and would prevent it from tucking into the wing.

In several designs this is taken care of by either moving the spar forward, tapering it, moving the LG centerline back somewhat or a combination thereof. Another solution is obviously to build on a foam core where you can put the LG wherever you want for all intensive purposes.

Perhaps you could help me understand how the Kaos wing would be modified to fit your design suggestions.

I'm always interested in learning new or different approaches to design.

David.

P.S. Pat, nice work. Apologies for the detour - your thread seemed to lend itself to a discussion of wing design since that's what you are working on. I look forward to seeing more progress on these wings and stabs.

Patrick F

My Feedback: (17)

Hi David, Thanks for the feed back, i am trying to understand what is said,let me try to explaine what i did:
I took the original drawing of the Mach-1 using Compufoil i was able to get the correct wing rib configuration from the basic foam templates,
then plotted out for the ribs and wing design
then superinpossed that drawing over the oringnal Mach-1 drawing to get the retract box set up,
now i can still move the spar to just about any location within that wing.
My question to you is should i move the spar?? I am making a retract box to insert in the location where it shows on the plan.

Thanks
Pat
Lasercut USA

DLQ5088

I think it is a great job. as a SPA pilot, the built up wing would be a nice addition. What you have done so far looks very light and from my experience would be quite strong enough to stand the rigors of flying. I wouldn't need the retracts, but it would not be a hard job to put them in if I wanted. This wing would be strong enough when sheeted. We have a propensity to build for heavier than necessary. Weight is everything. Either placement of the gear, whether attached to the main spar or to ply doubled ribs would be strong enough for most pilots who would be flying a performance plane. Thanks for doing this. Please PM me I would be interested in the possibilities.

Dan

doxilia

My Feedback: (3)

Patrick,

thanks for your understanding regarding the detour on the topic of your thread. It sounds like Evan has some interesting ideas on design so I am curious to better understand what he is proposing.

As far as the M1 design, I haven't spent much time studying those original plans (I'm not even certain I have them) so I might not be the best person to ask regarding the position of spars and retract boxes. Your approach to get the original drafted plan into CAD form sounds like the typical approach - that's how I go about it too. Actually, I tend to draw my planforms first and then I "fill" them in according to what I have in mind. Much of the re-design work I have done involves reductions in scale so I tend to loft lighter than the original.

That aside, I would go ahead and place the retracts in their original position unless there is a particular reason to move their location. If the spar gets in the way, then that would be what I would likely taper a little more in order to clear the wheels when retracted. But this brings us back to what Evan was proposing so that's why I am curious to hear more about it. Aside from those alternate approaches, I find that one of the conventional ways of using ply rib doublers to transfer the stress to the wing structure is fairly effective and simple to build. Using an additional ply box which is laser cut is that much more elegant as it provides a designed space for the retract unit. Of course, it can also limit the choices of retract units unless it is designed to be "variable" when constructed in terms of flange width and retract unit length. As you know, mechanical units have a small footprint but pneumatic and particularly electric units have a much larger footprint.

I quite like the technique that MK used for rib doublers when it came to LG. They would cut them so they were "reversible". You would glue them in one orientation if you were using fixed gear but if you were using retracts, you would flip them 180 degrees and glue them in that way. This accommodated either a slotted HW fixture for standard gear or two HW bearers for retracts.

The attached picture provides an idea of how large the foot print of a retract unit can be. These particular wells are for vintage Kraft/Multicon electric retracts - about the largest units I've come across. Of course they are rather heavy and no longer in production so not much of an issue but there are units that are still being made that are roughly equivalent in terms of footprint (e.g., Lado). With a retract box, you could also make 3-4 variations to accomodate different brands and have those as a separate item to the wing/stab kits themselves. This way, the modeler could choose which box they need according to the retracts they plan to use. You might only need 2-3 designs; one for mechanicals, one for electrics and possibly one for pneumatics. These last might work well in the mechanical units with a slight modification to the box.

When planning for the size of wheels in these 60 size classic designs, I would aim for wheels as large as 2.5". Most will use 2.25" mains but some may use 2.5" and others may even drop to 2". I think the M1 might have been one of those designs where the wheels might have been 2" instead of 2.25". I'd say most conventional gear 60 size models would likely go with 2.5" wheels (e.g., Prettner designs post Magic) whereas trike models would use 2.25" mains (e.g., Prettner designs pre Magic).

Just some thoughts.

David.

pimmnz

doxilia, the Kaos I have is fixed gear, built as per the plan. In this case the wing centre sheeting helps support the u/c blocks, and the blocks themselves are supported by three ribs, being nice and long. Retracts tend to concentrate all the loads in a small area, that of the mounting plates of the unit itself. If you were to fit retracts you would probably have to move the strut pivot outboard to allow inward retraction. Here's how I would do it. Draw the wheel in its retracted position. Allow 1/8" clearance all round. At the most forward point this will be the back edge of the lower spar. Now draw the retract mounting flange bolt holes in the position they will be when fitted. The distance between the retract side plate and the new spar position now gives the size of the forward retract support. Taper it nicely, or use a nice curve to spread the load to the spar, and it only needs to be a bit of 1/4" thick spruce. Fit the rear mount in the usual way, the two 1/16"ply rib doublers carry the loads from the support to the spar, so design the doublers to lock into the spar. Again the rear mount only needs to be a bit of 1/4 spruce wide enough to fit a couple of blind nuts. The only problem is now that the gear mounts are so 'embedded' in the structure a bad landing won't pull them out, but it will cause all sorts of damage to the retracts themselves. (Don't ask how I know, just accept this as the 'voice of wisdom'). The cure is to replace the usual 4 x steel caps screws with a couple of nylon bolts the same size, fitted diagonally, of course. All my models have been retrofitted with 3mm nylon bolts. Naturally, since then I haven't been able to test the theory... If you don't want to move the top spar, for any reason, you should note that all of Wolfgangs early models use staggered spars, the web between them being vertical and glued to the back edge of the bottom spar and the forward edge of the top one. The Taurus uses the same idea.
Evan, WB #12.

Patrick F

My Feedback: (17)

Hi, If you look at the orignal M1 drawing i did not move anything form it's orignal position the retract location is where it is on the drawing did not want to fuss with the C/G as far as the spar i look at other built up versions ang kind of average it out on where to put it, unless somebody has a formula that they use please inform me. I do appreciate all the help you guys offer.

Pat
Lasercut USA

pimmnz

There really isn't any formula for spar positioning, put it at the thickest part of the wing, modify its position to suit the mechanical bits you need to support. KISS works, if you keep the spar straight, the the joining can be kept simple, and light. That's about all there is to it. Where the mainwheel (trike) ends up when its 'down and locked' does depend on the balance of the airplane, ideally the axle centre line should be just behind the balance point. How it gets there is in the designers hands, the leg does not have to line up with the spar, so you can point the retract wherever you want, so long as the down position is in the right place. Same general observations about the stab, why use an extra (swept) spar when you have a perfectly good (straight) one along the elevator hinge line? Why not just use that one as the main spar? A small surface like the tailplane is not subject to anything like the flight loads of the main wing and the curve of the sheeting over the ribs is way more than is needed for both bending and torsional stiffness, so by just adding local blocks where the hinges are placed is entirely sufficient for that spar. Same with the elevator, unless you can get some very light 1/4 grain wood thick enough for the elevators, you might as well just have a built up elevator with 1/16 sheeting top and bottom, a bit of 1/4 for the leading edge and some diagonal balsa triangles for ribs, and a bit of block where the joiner goes, light, stiff and warp free. It might not be the same internally as the original, but from the outside you won't be able to tell.
Evan, WB #12.

MTK

You fellas care much about weight? Wings this small shouldn't weigh more than 1 1/2 lbs RTF, right?

doxilia

My Feedback: (3)

Matt,

I think this conversation has been had before but 24 oz is roughly the weight of a 60 size 65" classic wing, unfinished and unequipped. Remember that classics typically have a much thicker airfoil than your average 2m pattern wing. A wing from a model such as a Curare is quite possibly twice as thick as that of many 2m pattern ships. That additional thickness might begin to compare to the volume of a 2m wing given it is a fair bit larger.

All up weight of a wing depends on whether it is covered or painted - and if it painted, how. How many servos and what type of retracts are in it also matter clearly. But of course you know all this.

My latest build (a Tiporare) has a 23 oz hinged wing unequipped. Since the retracts are vintage electric units weighing 5 oz each, the expected AUW of the wing will be in the 40-42 oz ballpark - about 6-8 oz lighter than the designers target weight was in 1980.

I don't think anyone has a functional finished classic 65" wing with retracts that weighs 24 oz. Maybe 30 oz...

David.

pimmnz

Matt, Curare wing, mechanical retracts, 3 servos, (aileron, flaps, retract) Solarfilm covered, 23 oz. Sicroly ditto, 24 oz. Built up, balsa and ply structures, following the basic structures per the RCM&E drawings, with my usual internal mods. Taking them both flying tomorrow, oh, thats today! Forecast is good, minimal wind and the flying field is open...
Evan, WB #12.

pimmnz

Lord, it must be late, can't read my own scales...Curare wing 36 oz, Sicroly 37 oz. Both models just under 7lb RTF.
Evan.

Patrick F

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OK Here is a 1st drawing of the EU-1 Wing this was a challenge.

Pat
Lasercut USA

doxilia

My Feedback: (3)

Yup,

that sounds more like it. Without using contest sheeting, a built up classic wing might weigh 2-4 oz less than a foam core wing using vintage foam. Using today's foam and contest balsa, the built up and foam core might be closer to each other in weight.

The lightest large classic wing I'm aware of from this forum is Jeff's electric plug-in wing Aurora. Built on foam cores, his wings, combined, weighed 22 oz if I remember correctly. He made some mods to the airfoil making it a tad thinner but since it is a larger classic at 68" span, it still came in at 22 oz for the pair. Mechanical retracts were used in that wing but the servo was in the fuse. Ailerons were controlled by individual servos. The finish was also exceptionally light using water based low gloss paint. Gloss was had in the form of a final clear coat. Total AUW was under 30 oz I believe - 3 oz for servos, 5 oz for the finish. I have never lifted a lighter classic wing. It was also the first plug-in classic I had come across.

Anything under 2.5 lbs for a classic sounds pretty good to me - This can probably only be done effectively with mechanicals. Well done Evan.

A very few classic models such as the EU-1 might be the only ones resulting in more than 24 oz unfinished weight, so I guess you are right on Matt saying 1.5 lbs., but not RTF.

David.

MTK

I see....electric retracts are heavy. Thought you guys were using mechanicals but I see it's electrics. I never used electrics back it the day, only mechanicals. Started on Southern Pros (Dave Browns eventually) and then later used much lighter Japanese units; I forget the name. One servo drove everything including the gear doors.

Almost always glassed and painted my stuff.... still do. If you guys have not tried Klass Kote epoxy paints, especially their clear/satin catalyst to bed the glass or silkspan, you might want to give it a try.

doxilia

My Feedback: (3)

Matt,

Good tip regarding the KK clear. I'm considering different options for the next paint job and was planning on using polycrilic as I found it amazing to work with on a table I built some years ago. It did require a lot more work (coats, filling and sanding) though.

Since the return of electric retracts a year ago or so, I think folks are using all three types of retracts. With the smaller units, using mechanicals isn't necessarily a lighter solution. There are also a number of folks who would use nothing other than Spring Air pneumatics. The Japanese units have always been very light but not necessarily very rugged - a little more maintenance is required in my view. The larger Asian electrics have some issues too but hopefully they will get resolved with the second generation of production.

I'd still be interested in reading your article on finishing techniques with silkspan and dope - sent you a PM a couple of days ago or so.

Regards, David.

pimmnz

Doxilia, I note that both Matt and Prettner were using foam core wings, even back in the '60's. The English plans always showed a built up wing, even as late as Arrow and Magic. What is interesting is that, in spite of individual aileron servos, extra retract servos, air tanks etc we are still ending up a pound or two lighter than the originals, or at least I am, and the models all fly really well, just like a smooth arrow...yep, just back from the field, and blown all the cobwebs away (Winter down here).
Evan, WB #12.

Patrick F

My Feedback: (17)

OK Here is the first kit that will be on the market,the ATLAS this already is a built up all wood model,here are some pic's;

Pat
Lasercut USA

Patrick F

My Feedback: (17)

Next Short Kit we are working on is the MACH-1

Pat
LasercutUSA

Gene Margiotti

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Keep it going Pat!! I want a kit of the Atlas. Best flying plane my feable skills ever saw!!

Gene