70mm F-106 3D Printed Jet

[telnar1236]

I have flown the living snot out of this plane in RealFlight!

LB

Didn't know this was in RealFlight - I'll have to check it out

 

[telnar1236]

Turns out I'm just bad at designing wing apex fences. I reread the NASA paper and realized I'd missed a couple things about the geometry. The redesigned wing fence creates a 16% boost in lift which is closer to what I was looking for (the equivalent of cutting 360 grams out of the weight in terms of landing speed). It also reduces the pitching moment by 36% which will reduce the needed deflection of the elevons and result in an even greater increase in lift. Paired with weight reductions and the increased drag from the wing fence I think this design will make the plane much easier to handle. I'll still include the current wing design with the final STLs for people with 500' runways since it will bleed less speed in turns and handles very nicely once in the air, but for most people I think the wing with the retractable fence will work better.

You can see how much better developed the vortex is with this new design and how the flow stays attached for most of the length of the wing as opposed to just closer to leading edge as on the previous designs.

 

[JetCrafts]

what software do u use

Turns out I'm just bad at designing wing apex fences. I reread the NASA paper and realized I'd missed a couple things about the geometry. The redesigned wing fence creates a 16% boost in lift which is closer to what I was looking for (the equivalent of cutting 360 grams out of the weight in terms of landing speed). It also reduces the pitching moment by 36% which will reduce the needed deflection of the elevons and result in an even greater increase in lift. Paired with weight reductions and the increased drag from the wing fence I think this design will make the plane much easier to handle. I'll still include the current wing design with the final STLs for people with 500' runways since it will bleed less speed in turns and handles very nicely once in the air, but for most people I think the wing with the retractable fence will work better.
View attachment 246900
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You can see how much better developed the vortex is with this new design and how the flow stays attached for most of the length of the wing as opposed to just closer to leading edge as on the previous designs.

what software do u use

 

[JetCrafts]

I don't think I'm going to manage to reduce the landing speed as much as I want just based on reducing the weight, so I've been looking into ways to improve the aerodynamics. Delta wings aren't really compatible with conventional flaps since they would just make the plane pitch down so I need another option.

One possibility is to put a set of split flaps in the middle of the wing where they won't cause much pitch change.
View attachment 246883
The issue with this kind of flap design is that they don't actually do that much. Wings fly primarily due to the low pressure on top of them and the low pressure on top of the flaps is shared with the bottom surface of the wing. Therefore, they are mostly air brakes, only boosting lift by about 5% and slightly making the plane want to nose up decreasing the loss of lift due to trim forces on the elevons. They may be worth adding still since every little bit helps, though, especially if combined with reduced weight and other high lift devices.
View attachment 246884

I did some reading and also stumbled on a second possibility. Wing apex fences look very strange, but like flaps they increase the lift at a given angle of attack.

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View attachment 246878

Since the wing has enough lift to fly slower, just while at a higher angle of attack than the plane lands at, the apex fence could be a good option and easier to design and more effective than the flaps. It works by generating and capturing a vortex similar to what delta wing generates at higher angles of attack which increases the lift at the cost of drag. Here's a paper from NASA describing how they work: https://ntrs.nasa.gov/api/citations/19940019630/downloads/19940019630.pdf

Here is some CFD showing it a little more clearly. The wing with no fence doesn't generate much of a leading-edge vortex at all at 12.5 degrees AOA.
View attachment 246879
Adding in a small partial fence creates a vortex over the inboard part of the wing and boosts lift by about 5%.
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And adding in a fence over most of the span generates a much larger and stronger vortex and boosts lift by about 10%.
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The NASA paper shows that the lift increase should be able to be much bigger (about 20%) at least at the Reynolds numbers they tested, so I'm still trying to refine my designs. I'm trying to keep them relatively low profile to reduce how much of the wing the mechanism to deploy and retract them would take, but I think I should be able to improve performance by increasing the height and angle of the fence closer to 5 degrees or possibly by splitting the fence into a couple smaller ones. Tilting it back by 10 degrees should also help a tiny bit. In the last CFD of the full fence, the outer section of the fence doesn't actually generate much of a vortex, probably due to its smaller angle. I was trying to replicate a gothic wing fence with a smaller outboard angle (amazing name on the part of whoever designed it) that should get better performance, but that may not work the same on this particular plane. It's also possible that wing apex fences just work much better on full scale planes or I did a bad job designing it.

View attachment 246882
(From the NASA paper I found)

u can try dog teeth aka leading edge extensions https://en.wikipedia.org/wiki/Leading-edge_extension

 

[telnar1236]

what software do u use

what software do u use

For the analysis shown above, the free version of Simflow to run the analysis and Paraview to generate the plots. It's a bit of a learning curve to use, but for wings that generate things like vortices it's the only way to get particularly accurate results.

u can try dog teeth aka leading edge extensions https://en.wikipedia.org/wiki/Leading-edge_extension

Those mostly improve the high angle of attack characteristics of a wing but don't do much to boost lift at lower angles of attack. As a delta wing, this wing can already reach 40 degrees AOA and get plenty of lift to slow down, but the issue is that the plane cannot land at those angles of attack because the tail would hit before the landing gear. So what I'm looking for is a way to shift the lift curve to the left so that it generates more lift at lower angles of attack. Basically flaps on a delta wing. That's what the wing apex fence does very effectively. This is an incomplete plot from an earlier iteration of the wing fence that shows what I'm trying to do.

 

[L Edge]

What, you mean you can't do this?

 

[telnar1236]

What, you mean you can't do this?

If only, I wish I could do that

 

[L Edge]

What, you mean you can't do this?

If only, I wish I could do that

If only, I wish I could do that

Yeah, if you do my a+b approach, you could come close. Want to hear it? Guaranteed less than 150 ft for landing. And that includes acrobatics including the "Cobra" if you can practice enough.

 

[telnar1236]

What, you mean you can't do this?

Yeah, if you do my a+b approach, you could come close. Want to hear it? Guaranteed less than 150 ft for landing. And that includes acrobatics including the "Cobra" if you can practice enough.

The issue isn't so much that the plane can't perform that maneuver as the height of the landing gear and how brittle 3D printed structures are. I can't land at more than 14.5 degrees AOA and I can't come it at a higher AOA and then drop the nose and let it "plop" down since it would break