karandir
Topic Author
Posts: 3
Joined: Sat Oct 09, 2010 3:11 am

### Airfoil Interfacing

Let's suppose I am building an aircraft wing that is really long --- a wingspan of 10 metres.

From root to halfway outboard -- 5 m -- I want to use a 28% thickness airfoil.

From halfway to the tip, I would like to use 15% thickness airfoil.

How would I interface the two airfoil types at 5 m point.

For simplicity, I assume that the chord is, say, 1 metre throughout the entire span.

I need help on this topic to understand manufacturing better. Any help, please? Thank you in advance.

tdscanuck
Posts: 8572
Joined: Wed Jan 11, 2006 7:25 am

### RE: Airfoil Interfacing

 Quoting KARANDIR (Thread starter):How would I interface the two airfoil types at 5 m point.

The short answer is, any way you want. Any shape that matches your 28% airfoil on the inboard edge and the 15% airfoil on the outboard edge will work. There are obviously some that are easier to manufacture, and some that are easier to model, and some that are lower drag (and these probably aren't all the same thing).

What is your design criteria? What are you trying to optimize?

Tom.

ANITIX87
Posts: 2983
Joined: Mon Mar 07, 2005 4:52 am

### RE: Airfoil Interfacing

 Quoting tdscanuck (Reply 1):Any shape that matches your 28% airfoil on the inboard edge and the 15% airfoil on the outboard edge will work.

I think the goal, if I understood correctly, is to try and have a constant 28% thickness from root to mid-span, and then a constant 15% from midspan to tip. In which case, the interfacing becomes significantly more complex. I assume having a step in thickness would be unacceptable due to lateral flow across the wing (assuming it's swept at all).

TIS
www.stellaryear.com: Canon EOS 50D, Canon EOS 5DMkII, Sigma 50mm 1.4, Canon 24-70 2.8L II, Canon 100mm 2.8L, Canon 100-4

karandir
Topic Author
Posts: 3
Joined: Sat Oct 09, 2010 3:11 am

### RE: Airfoil Interfacing

======================================
I think the goal, if I understood correctly, is to try and have a constant 28% thickness from root to mid-span, and then a constant 15% from midspan to tip. In which case, the interfacing becomes significantly more complex. I assume having a step in thickness would be unacceptable due to lateral flow across the wing (assuming it's swept at all).
======================================

Exactly my thoughts and, therefore, questions. For now, assume straight wing, no sweep, no twist, no dihedral/anhedral.

ANITIX87
Posts: 2983
Joined: Mon Mar 07, 2005 4:52 am

### RE: Airfoil Interfacing

This does make things considerable easier. Remember that a swept wing will have lateral air flow along its span. A straight wing will have much less, but there will be a component there because of the pressure differential and vortices. The sudden change in wing section thickness will create big issues with separation of flow on the outer half of the wing, and will cause drag issues, too.

However, keep the Vickers VC-10 in mind:
View Large View Medium

That "fence" along the wing creates similar problems to what I'm describing, but is very near the root and away from any control surfaces or lift devices so its negative effect is reduced. Your section thickness changing at the midspan will cause some major problems.

There isn't any reason on this planet I could think of that would make the wing you're describing actually work, so I really don't think it's a practical example.

The only non-continuous wing I can think of is the one on the F4-U Corsair, but that wing's cross-section was the same before and after the kink (called the "gullwing").

Tdscanuck can correct me if I'm wrong, but I think that, given the above statements, there's no way your proposed wing would work at all.

TIS
www.stellaryear.com: Canon EOS 50D, Canon EOS 5DMkII, Sigma 50mm 1.4, Canon 24-70 2.8L II, Canon 100mm 2.8L, Canon 100-4

Fly2HMO
Posts: 7184
Joined: Sat Jan 24, 2004 12:14 pm

### RE: Airfoil Interfacing

Ignoring construction issues, would it be correct to assume that if you did the opposite, (15% root to mid and 28% mid to tip) the step itself would be like a wing fence?

After all, many bush planes seem have leading edge devices effectively thickening the airfoil or lengthening the chord of outer portions of the wing.

tdscanuck
Posts: 8572
Joined: Wed Jan 11, 2006 7:25 am

### RE: Airfoil Interfacing

 Quoting karandir (Reply 3):Exactly my thoughts and, therefore, questions. For now, assume straight wing, no sweep, no twist, no dihedral/anhedral.

It's possible...the simplest way, from a manufacturing point of view, would be to run spars that match the 15% section through the whole wingspan, and just change the ribs for the inboard section. Not the lightest solution, by a long shot, but simple and it would work. This is vaguely how Spitfire spars were done.

 Quoting ANITIX87 (Reply 4):Tdscanuck can correct me if I'm wrong, but I think that, given the above statements, there's no way your proposed wing would work at all.

It would work in the sense that it would fly...it's almost certainly not the lightest or least draggy configuration, but there's no inherent reason it wouldn't work at all.

 Quoting Fly2HMO (Reply 5):Ignoring construction issues, would it be correct to assume that if you did the opposite, (15% root to mid and 28% mid to tip) the step itself would be like a wing fence?

Basically yes, although it wouldn't be as effective as a fence because the size of the step wouldn't get significant until you got partway back on the chord.

Tom.

karandir
Topic Author
Posts: 3
Joined: Sat Oct 09, 2010 3:11 am

### RE: Airfoil Interfacing

Ok, I have mis-stated the problem itself, and therefore the misunderstanding begins.

All I want to do was to model a HELICOPTER BLADE (in CATIA, Solidworks, etc.), that had 29% airfoil from root to midspan and 15% from there to the tip.

I said no sweep, no diherdral, etc., etc., to keep complexity at a minimum and because most blades don't have any of those except at the tips

I want to know how one would model such a wing and then manufacture it using the models. I know it can be done, and has been for the V-22 Osprey's blades, which have 4 different airfoil sections through its span.

tdscanuck
Posts: 8572
Joined: Wed Jan 11, 2006 7:25 am

### RE: Airfoil Interfacing

 Quoting karandir (Reply 7):I want to know how one would model such a wing and then manufacture it using the models.

Are you asking about how to model the airfoils themselves, or just the transition?

The simplest way I can think of would be to just model the two airfoils as two separate extrusions and stick'em together. To build them, you could build each part separately and bolt them, or just mill (or mold) from a single block. If you mill it, I'd use a ball-mill for the transition, which will automatically give you a radius even though that's not in the modeled part.

Tom.

dynamicsguy
Posts: 442
Joined: Tue Jul 08, 2008 9:24 am

### RE: Airfoil Interfacing

 Quoting karandir (Reply 7):All I want to do was to model a HELICOPTER BLADE (in CATIA, Solidworks, etc.), that had 29% airfoil from root to midspan and 15% from there to the tip.

Do you want to have a sharp change in the cross-section, or a smooth transition? If the latter, then all you'd need to do is to sketch the cross section at the points where you want to enforce a certain shape, and let CATIA deal with how to smoothly transistion between them. You may need, or want, to sketch a couple of guide curves at the leading and trailing edge, but if it's straight then there's probably no need.

It's ages since I've used CATIA much other than to extract geometry for FEM, but there are plenty of tools under shape design to do this sort of thing.

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