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Constraints | Written By | Append Date | |
|---|---|---|---|
Design integrates an 0.5”x075”x0.5” 75” aluminum box tube | Aug 26Nathaniel Li | Sep 8, 2024 | |
Airfoil is based on a selected NACA airfoil | Aug 26, 2024 |
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Designed a cut-out for the ribs. Based on this research article, elliptical cut-out shapes result in lower stresses in the aircraft ribs (studied using ANSYS) since sharp corners was what leads to higher stresses. Hence, I used elliptical cut-out shapes for our ribs. I also used a similar design in their studies (e.g., 3 ellipses) and chose the size in respect to their ratio between ellipses.
But…I did read on reddit that this doesn’t matter if your wingspan is greater than 6 inches…but that’s also from a random redditor 🤣
The placement of the ellipses solely depended on the spar cut-out and the thickness of the outline. There is at least 2-3 mm distance of clearance and 12.5 mm distance from the outer edge of an ellipse to another ellipse.
The ellipses and spar cut-our follow (or on) the camber line.
I wasn’t sure if the main spar and rear spar will be the same so I just made a cut-out with the one Evan Janakievski added in the Wings file. This is welcome to change
I’m curious if we should fillet the corners to reduce stress but idk if the spar will fit
Thickness is 5 mm but we can def slim it down to 2-3 mm like Nathaniel Li suggested
Wings Update
8 ribs are spaced 80 mm apart and the wing skin is 600 mm (all are estimates rn)
LE and TE Concave Issue
3D prints that cover them is one solution but I was also considering a long wooden rod like in the images below and we can cut-out a circle in the front to insert it. But this will only for the the LE issues.
Control Surface Idea
I thought this idea was pretty cool, where the servo to control the flaps are inside the wing (attached to the ribs): Aileron Servos on my Guillows Sopwith Camel. I’ll prob look into it more tho
Author: Nathaniel Li Updating Date:
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These are looking great!
Disagree on 12g being a small weight savings! 16th ribs > 1/8th ribs imo → this is 24g overall for the drone!
Don’t design around prusa dims, we should have bambu labs printer back
Unless you have a reason not to, I would make the cutouts larger but keep more vertical supports (more material in the vertical direction will help reduce bend more than more material in the horizonal direction, think like beam bending)
How are we thinking of adding ailerons to these?
How are we spacing out the ribs?
maybe LW PLA spacers?
TE print could probably be bigger, LE slightly thicker
How are the LE and TE prints attached? → glue
End cap + print that bolts to spar to keep wood on aluminum (shoutout Sohee)
You may want to make a test rib to check tolerance of the square cut-out after laser-cutting, talk to the person who does the laser cutting to find out what tolerances you can expect → exact sizing almost never just works for mating parts
tbh you addressed most of my concerns in design updates (no more second spar)
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Following deflection calculations for 1/2” box tube aluminum for 25 N (half of current lift force needed for cruising) and 68 N (calculated for just under half of lift force on take off), decided to update size of box tube to 3/4”
Deflection was up to 2 cm
Repeating tests (changed 68 N to 80 N for greater safety margin) with 3/4” box tube, deflection decreased to 2 mm
Files for sims on PDM in Fixed Wing → Wings
Author: Sohee Yoon Date:
Updated the wing cut outs, including spar, and the assembly
The cutout clearance is sketched below
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Author: Nathaniel Li Date:
Currently waiting on aileron design as it may end up splitting ribs into 2 pieces
Will still want to some test cutting of ribs next week
Need to ask RPC about tolerance for spar
The laser cutter has a kerf (thickness of cut) of 0.1-0.175mm
For manufacturing, start with tolerance of -0.175mm, test for fit with box tube and try again
Need to keep pitot tube design in mind
Half on the wings to avoid prop wash
Need to keep gps mounting in mind
Most likely at the tip of the wing
Author: Nathaniel Li Date:
Meeting with Joshua Perry (WatArrow) about Wing Manufacturing
Discuss manufacturing process (iron)
What are your post-comp takeaways?
3kg plane
Tail very heavy since it was fully 3d printed
What iron did you use? Was it CSA approved?
Hangar 9 sealing iron
Not CSA approved
It was pretty simple to use
What material was the heat shrink laminate?
MonoKote (same as the one we are trying)
Why are you moving away from heat shrink laminate wings?
Manufacturing is too difficult
Heat applied for monokote (300 f) will easily damage other components like foam and ABS prints
What is your new wing being made out of?
Foam
Using a carbon fibre tube (about $10 each, might be worth a try)
Author: Nathaniel Li Date:
Manufacturing Update:
All materials in now for first initial trial of 3 ribs
Waiting for new rib spacer CAD for manufacturing
8 ribs with a negative 0.175mm tolerance (for laser cutting)
Easiest way seems to overshoot the negative tolerance and sand down until we get the desired fit
DWG of ribs found in:
WARG_CAD\Fixed Wing\Fixed Wing Design\Wings\DWG
FW_WINGS_P006_RIB_UPDATED.dwg is the original file
FW_WINGS_P006_RIB_UPDATED_4INx36IN_SHEET_0.175MM_TOLERANCE.dwg is the file I created with 8 ribs and the tolerance applied → This is the file I’ll give to the RPC
Author: Nathaniel Li Date:
Initial Wing Manufacturing Trial
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1/16” ribs are too thin → 1/8” or even 1/4” should be tried
Fragile and break easily when sanding and assembling
Ribs warp and deform from shrinkage of ultracote
Very little surface area for bonding to ultracote
-0.175mm tolerance for laser cutting can be reduced to -0.1mm and 0mm in future tests to get a more precise fit
Sanding is almost always inevitable
LE and TE covers work
Doesn’t melt even at high temp of 350F (used CF PETG but ABS should be fine)
TE cover is pretty small → make larger (further back on chord)
Easier manufacturing
Prevent top and bottom layer of ultracote from sticking together
Need to use rib spacers on spar for even spacing
Iron works well but shrinking technique can be improved
At lower temp of 242F, adhesive starts melting and is pretty easy to deal with
Risk of burning and over melting is rare; just keep the iron moving
Best to slightly tension each section as you iron it
At higher temp of 350F (shrinking temp), it can be harder to work with and requires special attention
Staying in one spot for even slightly too long will overshrink
Gets rid of almost all wrinkles
Best to slightly tension each section as you iron it
A little concaving as shrinking starts
Causes: Thin ribs, not enough tensioning
Can possibly be mitigated by tensioning more during shrinking
Need sharper knives or xacto knife to make cleaner edges/seams
Overall feedback about process:
Long and tedious process to make
May not be suitable for small control surfaces (like ailerons and stabilizers)
Any mistakes accumulate and require a full redo to correct
Design Changes
Thicker ribs definitely needed
Super simple and lightweight internal spacers (for manufacturing)
Jig for manufacturing wing?
Holding the larger full size wing can be tiring and difficult
Larger overall wing (changing height/thickness of rib)
Prevent sticking of top and bottom layer of ultracote
Fit servos and other components
Author: Nathaniel Li Date:
Overall Size Increase
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Increased the size of ribs (and appropriate LE and TE spacers) to have a 50% larger footprint
This should help accommodate components like servos
Still retains the NACA 4412 profile