[Jeloff]

Hi, I am looking for some advice as to the effect on aerodynamics if a recess is cut into the lower surface of a wing. In a nutshell, the recess will be of circular shape (on plan) and is required to accommodate some components inside the wing and the recesses cannot be covered with film/sheeting. They will extend at least half-way into the thickness of the wing. This is actually on a model aircraft with a low aspect ratio delta wing/blended wing body.

Further question: would it lessen the impact if the recesses had smooth/rounded edges, rather then sharp edges?

I can provide details such as aerofoil, Reynolds Number etc. if needed.

Sketch image attached showing underside of the wing to give an indication of size/proportions/position of the recesses.

Thank you!

[aerosayan]

737's landing gears are open and under the belly of the aircraft.
https://aviation.stackexchange.com/q...d-from-weather

obviously there will be some losses, but if you're only making this wing for a model aircraft, nothing bad will happen.

hecc most model aircrafts have a Thrust/Weight ratio greater than 1, so they'll fly even without a wing. lol.

[Jeloff]

Hi aerosayan, thanks for your reply. My concern with this particular design is that the recesses are quite substantial in relation to the wing area and the wing also low aspect ratio, so much of the span will be affected. Also, I probably should have made this clearer that it is in fact for a fixed wing drone, rather than "recreational" RC aircraft, and flight duration/efficiency is therefore quite important. Admittedly, being low aspect ratio, it's not the best design for long duration but the airframe is heavily constrained by the payload and other components on the aircraft.

I'm a complete noob to CFD, so do you perhaps know how easily this can be modelled, and who can do that (happy to pay a fee, obviously)? I would be most interested to see the impact on L/D, for example, and at various angles of attack. I can provide a complete airframe design in CAD.

Thanks,
Jacques

[aerosayan]

Oh okay, if flight performance is important, then a large hole in the wing will cause flow disturbance below the wings.

The simplest solution would be to use a smooth plastic/carbon fiber cover that will go on top of the holes, and make your wing smooth.

I don't have a cfd model to prove it right now, but common sense dictates that the holes will cause a little bit of flow separation and reduce lift.

Even if there are some equipment like cameras mounted below the holes, you can design the plastic/carbon fiber cover to smooth out the wing.

Can't you do a simple home made wind tunnel test with some smoke ?

That might be better than CFD.

Just put a fan in front of the wing, set it to a low, mid then high speed, and introduce some smoke into the flow stream.

I'm not sure what source of smoke will be best, but we can figure it out.

If you see large flow separation, then that means your lift will be reduced, and drag will be increased.

[aerosayan]

I forgot to answer how you can model this, and get your L/D or CL/CD ratios.

Actually this is not that much difficult, if you have access to commercial CFD packages like ANSYS. There are many tutorials on youtube for it. Here's a 3 part tutorial : https://youtu.be/mpY0K4kDw1g

I would recommend first seeing a few of these videos to understand that's it's not difficult. There are literally thousands of videos on CFD simulations of wings.

Since you are serious about the performance of your UAV, I would highly recommend that you learn how to do the simulations yourself, as that will be more beneficial to your project.

It's not difficult.

If you don't have ANSYS, you can get a student license, but it's limited. Other opensource alternatives like SU2 ( https://su2code.github.io/ ) will be better if you don't want to use commercial codes. However the learning curve will be slightly high.

That's not really a problem, because whatever you're learning by seeing the ANSYS videos, can be applied when doing SU2 simulations. One difference is, ANSYS is primarily GUI based, but SU2 is primarily run from text configuration files.

For SU2 simulations you would use an opensource mesh generator like GMSH ( https://gmsh.info/ ). Using an unstructured grid (which has tetrahedral elements) will be the best for your case, since it's easy to use.

[Jeloff]

Thanks, really appreciate you providing those links for the tools and tutorials. I'll take a look at ANSYS shortly. Looks like I have a learning curve aheas

Thanks,
Jacques