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Jan 30, 2019, 10:04 AM
lurking in the HOLE :)
KCV6's Avatar
I meant removing purely in the 3D model, sorry it's really late here and I'm a bit tired.

Yeah I have been professionally using ProE/Creo for years now and I still find myself learning new stuff often. It's all there. I'm more in the optronics field but I have good contacts in the aeronautical and automotive fields so I may ask a few questions.

When I 3D model I tend to start with a base part and then remove material so my design intent sort of follows how a part may be machined from a solid. So with the lattice I'd be tempted to extrude a base lattice part that was oversized from the finished airfoil and then extrude away back to the desired airfoil. Easy on a uniform taper, more difficult on a complex taper with washout. Again I'm purely talking in the 3D model realm here to then convert to high res STL
Last edited by KCV6; Jan 30, 2019 at 10:15 AM.
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Jan 30, 2019, 10:11 AM
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Extreme Sports's Avatar
Quote:
Originally Posted by charentejohn
I tried a tapered wing and can do it in Freecad, sort of. It is the Loft command where you do a small chord and a larger chord as distance apart then tell it to Loft them. You end up with a solid figure which tapers, or even curves between the different chords. If you Loft between 3 chords and they don't line up along one edge freecad curves it. So you can make a curved tapering wing but not easy.
I have made wing tips using this but haven't figured how to get a second airfoil in the same model. Just haven't asked around yet, sure it is possible.
Tapered wing is very easy in Sketchup - I'd have thought that proper CAD packages have similar functionality:
1) Draw the root profile
2) Extrude for a half span
3) Scale just the tip profile to the required size and move it about to get the required sweep and dihedral
4) Rotate the tip profile to add washout

If needed draw in a flat plane to work out how much the ribs need to be shimmed on the building board (less important if printing a full structure)
Jan 30, 2019, 10:17 AM
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Extreme Sports's Avatar
Quote:
Originally Posted by KCV6
When I 3D model I tend to start with a base part and then remove material so my design intent sort of follows how a part may be machined from a solid. So with the lattice I'd be tempted to extrude a base lattice part that was oversized from the finished airfoil and then extrude away back to the desired airfoil. Easy on a uniform taper, more difficult on a complex taper with washout.
Pretty much the approach I took:
1) Built up a generic lattice larger than the intended wing
2) Placed it on top of the wing and intersected everything
3) Manually deleted any surfaces and lines not needed. Tedious - I would assume there are better ways
4) Discovered the holes and other issues

Conceptually simple. Frustrating as hell in practice
Jan 30, 2019, 10:27 AM
Registered User
Thread OP
First a question for Quorneng about the 2mm (thought not possible but obviously is) foam. I can find 3mm paper covered foamboard here, covered in normal printing paper I think. Can't get any for another week or so. Is it just shaped and glued as shown.
Your model seems to work with large spacings of the airfoil shapes, can you confirm it is just as shown (with balsa spars) as great to know that will hold.

My plan is a 3mm sheet with the grid infill stuck to it and small ribs underneath just to give shape. Then wrap a piece of 3mm foamboard around, as people do with all foamboard wings. Possibly add some spars, more to attach wing to a plane than anything else.
Ailerons same principle, small triangles covered in foamboard. When I have something usable I will post it in thingiverse and people can try it.

In the spirit of print it and see, I will do a mockup in the next few days. Just realised I don't have foamboard but can use cardboard as a test setup.

I agree this is no faster than traditional methods but I am just fascinated by the possibility of doing it. Why do it, because I can
Jan 31, 2019, 06:00 AM
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japim's Avatar
Quote:
Originally Posted by charentejohn
My plan is a 3mm sheet with the grid infill stuck to it and small ribs underneath just to give shape. Then wrap a piece of 3mm foamboard around, as people do with all foamboard wings. Possibly add some spars, more to attach wing to a plane than anything else.
Ailerons same principle, small triangles covered in foamboard. When I have something usable I will post it in thingiverse and people can try it.
This is great idea.
By merging the 3D printed parts with foam boards you can achieve great results.

If you are workingon this - please consider for example incorporating the simple stearing arms/hinges/pivots into the printed ribs. By doing this you can get an aileron triangle with stering arm. Or a rib with a small section sticking aft where the aileron can be attached to.
Jan 31, 2019, 09:30 AM
Registered User
charentejohn
Yes I can confirm the wing is built exactly as shown with 2" rib spacing and balsa spars.
This view from the tip (short rib to give space for the aileron) shows the construction.
Name: LHwing2.JPG
Views: 45
Size: 135.3 KB
Description:
The sequence is:-
Lower balsa spar glued in between the front and rear lower skin sections. The front lower skin is preformed to account for the wing section.
The ribs are glued on to the lower skin and Depron shear webs glued between them. The webs are 6 mm thick at the root to 2mm at the tip.
A front Depron shear web is glued to the nose of the ribs.
The top front skin which includes the top spar is glued on.
This creates a D box so the wing is rigid enough to be lifted from the board and the aileron servos to be installed and wires to be run through the wing.
The rear top skin is added.
Finally a 6 mm Depron solid leading edge is glued on and carefully sanded to shape.
The result is stiff and very light but then it is used on a plane that only weighs 24 oz ( 650 g) all up. Not intended for 3D aerobatics but it can safely be looped.

It is perhaps worth noting that conventional Depron has denser outer skins which means it is significantly stiffer than normal foam board, or Aero Depron, of the same thickness so it can tolerate a wider rib spacing. The fact the skin is curved over the rib greatly increases its resistance to crumpling under compression which is the most likely failure mode. I have used 5 mm 'soft' foam board on a similar wing with 2" rib spacing. The result is a bit heavier and a touch more flexible.

You may have noticed in my first post an EDF Airbus A350 in the back ground. Its wing is built using a similar printed rib/balsa spar/Depron skin although 3mm thick as far as the EDFs.
Last edited by Quorneng; Jan 31, 2019 at 09:36 AM.
Jan 31, 2019, 02:33 PM
My planes plow into the field
farmertom's Avatar

Density of Palight


HI,
I ordered a free sample of the Palight - foamed PVC Sheet. I never heard of it so I was curious. Came in the mail today. Nice colors and fairly stiff. If my math is correct the stuff weights 0.6 gr/cm3 (9 grams for a 50x100x3mm sample), were balsa is about 0.16 gr/cm3. It is hard to compete with Balsa Wood.
As a reference point ABS filament is 1.04 g/cm3.
Jan 31, 2019, 06:14 PM
Registered User
Thread OP
Good info all round.
Just ordered some 3mm foam board from hobbyking as I had to do something, too much theory. The palight seemed similar weight to foamboard etc, and is available here, does it bend with a bit of heat though ? Should do as most of this sort of sheet seems to, just a matter of learning how. I bent a piece of extruded polystyrne (about 5mm thick) I cut off a larger piece. Used a heat gun, it was trying to shrink to nothing but did work, patience is the key.

I am hoping the 3mm hobyking stuff will fold. Thanks Quorneng as I reckon this will do based on your experiences. I will try the tape, crush with a pen, rolling pin curve methods I have seen online. Ordered all this inc some glues and should be here in a week or so. From your wing I should just need to glue paper to the middle sheet of foam, for rigidity, and use the grid to give shape. Sounds like the grid squares will be enough support for the outer skin, grid is 4mm / 1.5" squares in the previous photos.
To stick I will try this - youtube "Gorilla Glue Gap Filling Usage" where someone shows a nother way to use this. He was repairing a foam wing but.... Mixed before applying allows a little foaming before joining the surfaces, could be an interesting technique. Think mixing 2 part epoxy except G Glue and water instead.

I have a design with integral ailerons centrally pivoted, photo attached, but heavier than I would have liked. Currently 500g when filled with hot wire cut extruded polystyrene, TLA provides framework and strength. Not helped by aluminium brace which may not be necessary. Part of another project, the overall weight is the same as a 3d printed wing from 3dlab so not excessively heavy just could do better with another method. Much easier to print though as small parts.
Feb 01, 2019, 02:43 AM
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Extreme Sports's Avatar
Quote:
Originally Posted by farmertom
HI,
I ordered a free sample of the Palight - foamed PVC Sheet. I never heard of it so I was curious. Came in the mail today. Nice colors and fairly stiff. If my math is correct the stuff weights 0.6 gr/cm3 (9 grams for a 50x100x3mm sample), were balsa is about 0.16 gr/cm3. It is hard to compete with Balsa Wood.
As a reference point ABS filament is 1.04 g/cm3.
If my calcs are right, that 3mm sheet of Palight weighs 1800g per m^2 (9g/(.1m x 0.05m). That is WAY WAY heavier than foamboard or any other regular build material (on par with GRP/CF, but we never use those at 3mm thicknesses). All our common build materials are essentially cellular structures - foam, balsa, correx, and proper composite structures are mostly air. My material table has 3mm Depron at 130g/m^2, 2mm correx at 345g/m^2, foamboard a bit more and balsa all over the place depending on thickness and grade. This Palight type material has come up in the SPAD forum several times and it has never caught on as a primary construction material. 3D printing similarly tries to mimic the cellular structure with thin walls and minimal infill. Would work great if seam strength was higher and the plastics were as ductile as molded equivalents As you say, it is hard to compete with balsa!

Charentejohn, remember aluminium's density....not a good choice if you want to keep the build light The SPAD guys use it regularly, but mostly for larger, heavy glow powered builds.
Feb 01, 2019, 06:07 AM
Registered User
Thread OP
I don't know the palight source but a place that sells it did an unscientific 'weigh in' for me as below. Seems little difference except ironically palight is 50% heaver than foamboard but is it stronger ?
PVC FOAMED 'PALIGHT' 210 297MM Weight: 45gr
FOAMBOARD, WESTFOAM WHITE 5.0MM 210 x 297MM Weight: 30gr
Plasticard We stock styrene plastic in white at 0.5. x 220 x 340MM. Weight of styrene: 43gr

I did think aluminium was not a good choice but these were light (not as light as they should be though) and available locally. I think I will use 5mm dowel next time.

Just did a higly scientific structural test using the finest quality cereal packet (genuine kellogs) and hot glue that I have Photo attached, very roughly glued and not everywhere. The top is just tagged at the X junctions. Tried twisting it, bending it and leaning hard on it and all solid. Won't bend lengthways or front to back and wont move if I try to propeller twist it. I think if I really tried it would break but so would anything.
I am hoping that my proposed structure will be much better, especially with a shear web installed.
Feb 01, 2019, 07:26 AM
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Extreme Sports's Avatar
The right question is not which is stronger, but which is strong enough. I'd put to you that, unless you envisage a >2m span circa 5kg plane, all are too strong and far too heavy for the park-flyers size that I expect you have in mind. Your foamboard, the lightest on the list tips the scales at a decidedly tubby 480g/m^2 and is used very successfully by hoards of builders without complex and redundant weight adding rib structures.

For comparison, a 0.4mm single layer PLA 3D printed skin would weigh about 500g/m^2, (ABS about 420g/m^2) so it is effectively the second lightest option on your list.

No need to build any test samples on these - the maths already tells you they will be heavier than 3D printed (which is already heavy). But keep searching - there are lighter options for the skin and they must be available locally. For example, have you thought about making just the D-box area from Foamboard and skinning the rear section with normal iron-on or laminating film? How about slicing up ceiling insulation to 2mm sheets ala Quorneng's method? Would seem silly to go to all this effort just to end up with something that is worse than existing techniques.

Attached is a brochure for Palight....specs are near the back. Definitely not something that I'd consider using.
Feb 01, 2019, 09:46 AM
Registered User
Thread OP
Can't find a weight in the brochure may be calc from density, they do lots of types, the type they gave the weight for is here http://modelshop.co.uk/Shop/Item/PVC...-603mm/ITM6958

I have ordered some 3mm foam sheets and wing tape. Plan is to build the wing from this and the pla grid etc. then cover in wing tape (part of how to bend it anyway).

So assuming my 20x100cm wing 3 layers of palight would be about 450g. In 5mm foamboard this would be about 270g, I will be using 3mm so assuming pro rata will be about 180g ? Add in the plastic at an estimated 60g for a 100cm wing, based on a top grid infill piece 20cm long weighing 7g, plus any extra bits. So my basic wing without servos and bracing struts should weigh about 240g.

I did a PLA and extruded polystyrene one and it ended up at 500g, hence my pursuing this concept, I used too much PLA, and the aluminium. I have a wing from a 3dlab P47 in pla, same area more or less and that is 500g without servos etc. and a real oinker to print. 500g wing with about 400g of parts in the bin.
I am getting better at printing these forms now though but still not easy.

I am hoping this wing will give me a 200-250g head start on the same wing area. I know I could just use a KF airfoil like in the flite test video (10 mins in), as they say takes seconds to build and really light. But where's the fun in that Their wing uses 3 layers of 5mm foamboard so should be about 260g ? If palight is stroner than foamboard then should be under 400g for the same wing area using KF airfoil, if it is stronger, higher density I would guess so ?

I think it will be a couple of weeks before I finally get the materials but I will start printing a box of wing sections I think ready for the foamboard's arrival.
Like I say, doing it because I can. I like alternative systems. I know I could take a balsa spar, wrap some foamboard around it to give a sort of airfoil shape but this can reproduce actual airfoil shapes, which I like the idea of.
Feb 01, 2019, 10:35 AM
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Extreme Sports's Avatar
Please don't get me wrong, I fully support what you are trying to do and this thread has got me thinking about all sorts of alternatives (just don't have time right now to start another build). I'm just prodding you to set your aspiration as high as possible. That way I can just copy whatever you come up with

The problem with foamboard is that the paper is the heavy part, it is on both sides (the reason 3mm is not much lighter than 5mm) and it does not come off easily.

So, to set you a challenge, how about this for a base target:
  • Ribs: 30g (15 at 2g each). Given the proposed skin method, a ~75mm spacing between ribs is absolutely fine, and 2g/rib should be easy
  • Spar: 20g. Thinking two thin strips of pine (6mm x 2mm) and a foam web
  • Skin: Slice of ~3mm foam covered with a single layer of newsprint paper (the clear sort without printing on it) plus a coat of paint - 100g (2 layers of 0.2m^2 x (130g/m^2 (foam) + 80g/m^2 (paper) plus 40g/m^2 (paint) = 100g

So the wing could weigh just 150g, be very strong, and there are no unobtanium materials in it. That is a little under what a 2mm correx wing would weigh (160g), and correx is supposed to be heavy. Tinker around with other materials and I recon you could beat this. Light weight is everything in planes this size

PS: Kfm wings really are cr*p relative to what you can potentially achieve. Please don't lower your standards that far
Feb 01, 2019, 11:23 AM
Registered User
Thread OP
Don't worry I will get there, and anyone is welcome to the results, if any
The Hobbyking stuff has no covering, hence thinking of the wing tape. No idea of the actual weight of a sheet, they only give shipping weight inc packaging.
It is something foam sellers never seem to do, give the weight of a foam sheet. Especially areomodelling stuff as that is a main consideration.
If I can get the wing to 200g I will be well pleased. Just got a mail from hobbyking saying all is on it's way so hopefully next week, let printing commence
Feb 01, 2019, 11:50 AM
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Extreme Sports's Avatar
HK foam is just XPS foam, density around 38kg/m^3 IIRC so expect something close to depron weights (130g for 3mm). May differ a little as not all foams are exactly the same. I discovered that our local ceiling board manufacture throws the off-cuts away, so I get a free supply of this stuff - just need to hot wire slice it and no shipping cost.

Packing tape is actually a better covering than iron-on films as it sticks better and does not require heat which can distort the foam. Just have to take care not to get too many wrinkles. IIRC mass is around 30g/m^2. So you should easily beat even the 150g target Running the tape spanwise will add additional strength, and if your airfoil profile is deep enough (> 10%), you may find that just a single depron web is enough for a spar. All depends how how light your final plane is planned to be.

I really like the rib lattice concept - just gonna have to wait until I have lots more free time to raise my CAD skills to the point where I can do the CAD work. Until then I'll just have to remain a spectator...


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