"A" model Hoerner wingtip design (updated)

[MidGenerationAL]

Within the limitations of me not being an aerodynamicist (or anything close to one) I think this design is closer to the conclusions of Hoerner's 1949 study.
The planform from above is square.
The cutback is obviously concave, but the cut profile is convex.
I moved the wingtip light up to where it is bisected by the outboard edge. There were some noisy-looking pockets the way I had it before.
Some of the transitions between cut sections will need a little bit of smoothing work with sanding or filler when this is out in real life.
Interested in comments/feedback/suggestions.

My idea is to make a reverse mold of this shape via 3d printing. Due to printer size constraints I will need to break it up into 6 pieces and glue them together. There is always some sanding and filling on a 3d printed mold but nothing like the work of making a plug from scratch.
The light bay will have to be a separate piece - the mold will have an uninterrupted leading edge.
My father has a vacuum pump and experience making composite race car parts but this is larger and a bit more complicated than what he's previously done. Will explore whether to try and make the parts myself vs having a professional lay it up.

There are some online CFD tools. Tempting to try this, but I am not sure I'd know what to do with the results and I think it's a bit pricey for an idle curiosity experiment.

[Battson]

That's the shape I have, I reckon it works great. We based our decisions on the available NACA research and later practical testing by Wittman and others who Bob recommended.

Unscientifically speaking, when rounding off the leading edge, to blend it into the outboard edge, you want to avoid the air having to deviate downward before it reaches the outboard side. In other words, if you view the wingtip from the front, there should be no part of the underside or outboard side which is hidden behind the leading edge "overhang", where you blend the shapes together.

Achieving that aim means either you need a complex curve on the underside of the wing tip, or you can achieve the same thing with a linear surface on the outboard by blending it appropriately at the leading edge.

[MidGenerationAL]

That's the shape I have, I reckon it works great. We based our decisions on the available NACA research and later practical testing by Wittman and others who Bob recommended.

Unscientifically speaking, when rounding off the leading edge, to blend it into the outboard edge, you want to avoid the air having to deviate downward before it reaches the outboard side. In other words, if you view the wingtip from the front, there should be no part of the underside or outboard side which is hidden behind the leading edge "overhang", where you blend the shapes together.

Achieving that aim means either you need a complex curve on the underside of the wing tip, or you can achieve the same thing with a linear surface on the outboard by blending it appropriately at the leading edge.

Can you please post a picture of your or other examples?
I think I follow you but a visual aid would help a lot

[Battson]

Sure - please refer to photos in this thread:

https://bearhawkforums.com/forum/bearhawk-4-place-plans-build/24611-hoerner-wingtip-build/page2

[MidGenerationAL]

That's the shape I have, I reckon it works great. We based our decisions on the available NACA research and later practical testing by Wittman and others who Bob recommended.

Unscientifically speaking, when rounding off the leading edge, to blend it into the outboard edge, you want to avoid the air having to deviate downward before it reaches the outboard side. In other words, if you view the wingtip from the front, there should be no part of the underside or outboard side which is hidden behind the leading edge "overhang", where you blend the shapes together.

Achieving that aim means either you need a complex curve on the underside of the wing tip, or you can achieve the same thing with a linear surface on the outboard by blending it appropriately at the leading edge.

What I had in my head from your description, and your linked pictures, and my latest updated CAD model, are all very similar..
There are a couple of the intersections on the underside of this model that aren't quite right, but extremely difficult to define in CAD.
However, the parts I don't like are "outies" on the model, thus will be "innies" on the mold - and therefore very easy to correct with a small application of body filler. After that I think what I came up with is very close to yours with the exception of the landing light window and the wingtip light mount (where this joins the upper airfoil I also have some corrections to make with filler)

[Bcone1381]

I curious if you made any progress on this?

Here is what I’m up to. I fabricated a model from foam and had it scanned. The “Scanner” printed a miniature model to inspect for errors. Next step is to print a full size what I’d call a “rib cap model” to verify the fit of the model to the wing.
IMG_4891.jpg
IMG_4955.jpg

[Bcone1381]

I am learning that a significant barrier to a printed wing tip is the material strength combined with the method of attachment. I think I will end up with a study mold to fabricate wingtips uisng a composite layup of Fiberglas or Carbon Fiber. The fragility of my foam mold is significant at the trailing edge and I'm going for a mold that is sturdy and re-useable.

[MidGenerationAL]

I curious if you made any progress on this?

I am very slow realizing I've had replies on here apologies for the delay.
We do have wingtips made but not installed yet - not quite to that stage in the build.
I 3d printed left and right plugs, then made molds, then used the molds to make wingtips. They are in upper and lower halves.
I did bond the uppers to the lowers but I left the leading and trailing edges unfinished to allow for fitting.
The wingtips I made are 3 layers of fiberglass cloth and one layer of carbon fiber, with epoxy resin.
We posted the progress in our YouTube channel - which has kind of a tongue-in-cheek tone, but you can see what we did and how they came out.
Skip ahead to 1:44 is where the wingtip update starts

https://youtu.be/yhUnQ5pnsBo?si=pZspydmDDHfZuTnS

We've done some more surface finishing since the last frame of the video, and also laid glass tape on the outboard edge, both from the inside and the outside.
I think they came out pretty well at this stage. The real proof will be when we try and fit them to the wings.

[MidGenerationAL]

ALTERNATIVE METHOD

This video is by SuperFastMatt - a project car guy, not project airplanes - but just today he goes and posts a method of turning 3d prints into finished composites.

https://youtu.be/nt85nTMnY1w?si=dp31AA1LtJbO0FCY

Quick Summary: he's making nylon 3d prints, then covering them with carbon fiber / epoxy.
I'm sure this method is plenty strong (stronger than needed for wing tips) but I do wonder about the weight.

There are two drawbacks to this method that would have caused problems for me
1 - you have to get the 3d model right. I wasn't able to get all the curves to blend properly in my 3d model, so there was a fair bit of sanding and filling work I had to do on my 3d printed plug to get the shapes I wanted. Someone who's a lot better with 3d modeling could get this right. For that matter, you could use Air Shaper like they did on this race car project to tweak your aerodynamics. (Air shaper is an online CFD thing - sort of like a wind tunnel simulator) - but these things all require real engineering skills that I decidedly do not have
2 - you need much better 3d printing capability than I have. I've got a consumer grade 3d printer that does an okay job with easy-to-print materials - but all the advanced materials that have real strength and UV and heat resistance are MUCH harder to print than your basic PLA or PETG. ABS is medium-difficult to print and I've gotten acceptable results on parts that are small and don't need to be dimensionally accurate. But getting big parts like this to fit together properly is a lot more difficult, and even more difficult with the materials they use in the video. You can get print quality with more difficult materials by being a deeply engaged 3d hobbyist who knows all the tricks and tweaks the machine to the nth degree, and/or by spending real money on higher grade equipment - neither of which is attractive to me
So I still think the way I approached the project was the right choice for me
We will see if this opinion is intact after I try to fit the wingtips to the wings

[Bcone1381]

A few days ago my 3D printer printed up a test piece of the airfoil....not the entire airfoil....just the front 1/3. We have a very very tight match. We'l check the reward 2/3 over the next few weeks. Ya know, Bob's CF wingtip that came with the kit has significant flex. Once it is secured, its light and plenty rigid. I guess its not more than two layers of CF, and the CF is not very heavy. I want that type of a finished product.....some flex and compliance but stiff when installed.