Wings

Big Project	Project	Project Manager
Post-comp fixed wing	Wing design	Nathaniel Li

Task Description

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

Constraints	Written By	Append Date
Design integrates an 0.75”x0.75” aluminum box tube	Nathaniel Li	Sep 8, 2024
Airfoil is based on a selected NACA airfoil	Smile Khatri	Aug 26, 2024

Subteam	Contact	Contact Description
Subteam collaborating with	@ of contact	what is the contact responsible for?

Assignee	Asana Task	Date
@ assignee	link to asana task assigned	Date assigned

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

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

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

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.

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

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
https://www.allrockets.ca/Balsa 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

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

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

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 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
https://www.rcgroups.com/forums/showthread.php?2881437-Monokote-vs-Ultrakote
- 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)

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)

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

Updated the wing cut outs, including spar, and the assembly
- The cutout clearance is sketched below