Wings

Task Description

Design the wings of the post-comp fixed wing plane.

Constraints

Relevant Contacts

Assignees

Task Progression/Updates

Author: @Nathaniel Li Updating Date: Aug 5, 2024

Updates from 2024-07-31 Mechanical Meeting Minutes and Designs

• Plan to use 1/2” aluminum box tube for spars (also being used for frame)

• @Sohee Yoon working on a design for balsa ribs

• RPC laser cutters cuts up to 9.5mm thick pieces

  • If too thin, can glue two pieces together

• Should keep in mind control surfaces that also need to be added (ie. ailerons and possibly flaps)

• My current WIP design:

  • 0.23m chord length, 1.5m wingspan, NACA 4412 based on fixed wing calculator

    • Wingspan is end-to-end length but will most likely break into 2 sections so that it can connect to fuselage

  • 5mm rib thickness although 2-3mm (1/8”) seems common for rc planes with wingspan around 1-2m

    • Will look into what kind of Balsa sheets we can get, anything within 2-5mm range will do but should be able to get away with thinner side

    • Also can save lot of weight by cutting out material

  • Rib spacing is kinda unknown but ~ 2-3” and up to 5” is common

    • 5-10cm seems like a good range

  • Main issues to tackle:

    • Supporting LE and TE to prevent concaving issues

      • Thinking of doing a 3d print that covers them to give rigidity

    • Positioning of main and rear spar as discussed with @Smile Khatri → seems like 25-30% of chord length is ideal for main spar

      • For simplicity, usually a spar at LE and TE would suffice and also give the desired profile (and rigidity) but cutting the profile is very hard for Balsa tubes

Author: @Sohee Yoon Updating Date: Aug 6, 2024

Balsa Ribs Update

• 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

Open

Ribs

Wings Update

• 8 ribs are spaced 80 mm apart and the wing skin is 600 mm (all are estimates rn)

Open

Wings

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: Aug 10, 2024

Balsa Selection

• Many hobbyists prefer 1/16” or 1/8” (~1.5-3mm) for wingspans of around 90” (over 2m) rib thickness Rib Thickness and Spacing - RCU Forums

  • 1/16” is thinner and saves weight

• Ribs are approx 30mm x 230mm

• Balsa : Canadian retailer of Estes, Aerotech, Quest, Rocketarium, Madcow, Public Missiles, Aeropack, LOC Precision, PerfectFlite, Jolly Logic, rocket engines/motors, launch supplies and electronics many sheet thicknesses (1/32”, 1/16”, 3/32”, 1/8”) and sizes

  • Balsa Sheet 1/16" x 4" x 36" 1.5875mm thick: 101.6mm x 914.4mm

LE and TE Concave Solution

• Working on making a 3d print that would cover both LE and TE to preserve profile

Author: @Nathaniel Li Updating Date: Aug 19, 2024

3D Print Cover for LE and TE

• 200mm length (print bed is 210mm x 210mm x 250mm for prusa)

• LE follows curve profile and is 1mm thick into the rib

  • Not sure if 1mm is too thin/will fail easily but can always change to be thicker

• TE is a triangular piece as following the curve profile would be too thin

• Modelled in assembly

Weight Savings - 1/16” vs 1/8” ribs

• Currently have 1/16” modelled

• 1/16” rib weight: 0.795g

  • 0.795g x 8 ribs/wing x 2 wings = 12.72g

• 1/8” rib weight: 1.591g

  • 1.591g x 8 ribs/wing x 2 wings = 25.456g

• Total weight savings of 12.736g if using 1/16” instead of 1/8”

  • Tbh, this isn’t much of a weight savings so to be safe it might be better to go with 1/8” for more rigidity

Monokote and Ultracote

• Monokote Covering This appears to be the monokote that other teams were talking about at comp

• UltraCote White Ultracote is another material that kept coming up in my searches, it’s essentially the same product as monokote, it is the american name for Oracover (previously mentioned in our research)

• Any hobbyist store would sell it, I found that Ricky's Hobby Corner has a lot of selection and is in Canada, they sell a variety of UltraCote

• Monokote vs Ultrakote - RC Groups

  • Seems like most people find Monokote harder to apply compare to Ultracote

  • MonoKote vs Ultracote?? - RCU Forums However, it seems like Monokote holds up better long-term

• I think it’s worth using Ultracote for development as it’s easier to get started and will be faster for making a bunch of wings

• In the future, we can look at using Monokote for a final product to make it more durable and look nicer (more colour selection apparently)

Author: @Alison Thompson Date: Aug 26, 2024

WING SYNC

Alison’s thoughts so far:

• 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)

Author: @Evan Janakievski Date: Sep 8, 2024

• 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: Sep 11, 2024

• Updated the wing cut outs, including spar, and the assembly

  • The cutout clearance is sketched below

Author: @Nathaniel Li Date: Sep 26, 2024

• 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: Oct 3, 2024

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: Oct 29, 2024

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: Nov 3, 2024

Initial Wing Manufacturing Trial

• 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: Nov 3, 2024

Overall Size Increase

• 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