Hi Guys
I want to build a model called Chilli Wind, by Mike Delacole. I have the plan but it only shows root and tip profiles for the wing, assuming using a foam wing.
I want to do a built up wing so I need profiles for the intermediate ribs.
It has been suggested I use either Profili or Compufoil, but I am a computer novice and don't even know where to start with either of these.
Could someone please give me a simple (I mean really simple) guide to how to do this?
Thanks
Jeff

This gets discussed often in Modeling Science and Balsa Builders. I recommend having your thread moved to one of those forums.

Andy

Hi Andy, good point.
Wonder if one of the moderators could move this to the balsa builders forum?
Thanks
Jeff

Click on "Report this thread to the moderator"

This can also be done in XFLR5, if you have the airfoil coordinates for both root and tip.

If you just have a drawing on the plans for the two ribs, do it old school, like this:
https://www.airfieldmodels.com/infor...ribs/index.htm

I think you're looking at the old stacked rib template method unless the plan or article specifies what the airfoil truly is. A lot of these designs used airfoils drawn around french curves or done by the TLAR method or taken off previous successful designs. The computer option would only work for you if the airfoil on the Chilli Wind is a "brand name" type with proper name and coordinates.

Yea I would just go old school. Use the two ribs as templates..just stack balsa blanks and sand to match the profile. You can make them 1/16th over size than you can sand the edges square after

Hi Guys, thanks

Wazmo and Turbonut
The old 'stacked ribs' method, or sandwich, only works with parallel, or very slightly tapered wings. This one has sharply tapered ones, such that the root chord is 12"and the tip is 8". Also, the whole taper is on the leading edge, the trailing edge is straight.
That's a 4" change, or a 4" overlap on front of the stack. Works ok on the rear part, but virtually impossible to do at the front.
I know, I've tried.
What is XLFR5?
Aerofoil is NACA 63012A.
Either Compufoil or Profili will do what I want, but I have looked on sites for both, and as a computer novice I have a problem understanding how to use them.
What I'm looking for is someone familiar enough with these to give me a simple (read idiot proof) guide to the process.
Jeff

Actually, you CAN do it stacked providing you give some spacing in there. Bob Hunt's "Lost Foam" method works great.

Do you have access to a copy machine with a scaling function?

Since you're converting a foam core to a built-up wing, you will need to do some stuff by hand, but it's not hard.

Start by getting a full-size print of the root rib onto a piece of paper. Since it's 12", you would be best served by doing it at Staples or FedEx Office.

The 12" rib is going to be 100%. The 8" rib is 67%. The ribs in between will range between those two numbers depending on position within the span. I suggest that you plan on an odd number of ribs - you'll see why in a second.

The rib in the center will be halfway between the other two. You calculate that as the average, so it'll be (100% + 67%) / 2, or 83.5%. 84% will be close enough. It will be halfway between those two sizes in chord as well - (12"+8") / 2 = 10" - that way you can verify the calculations are correct.

So there you have 3 ribs defined.

This works fine as long as you have (powers of 2) + 1 ribs (3, 5, 9) but that doesn't always fit well with common rib spacings of 2.5 - 4". So instead, figure out how many ribs you want in a half span. For that plane I would go with 9, but you are free to choose what you want. If 9 is good for you, then do the same thing as you did before, averaging between two defined ribs to get the center rib.

The more general method is to lay the ribs out on the plan for the spacing you want, and then work the percentages of span to scale it to the appropriate size.

If you have Paint (comes free with Windows) you can do this inside your PC. Just use the Resize option to enter those percentages, then print.

Andy

Originally Posted by Border Lord

What is XLFR5?

It's an airfoil analysis program, based on Drela's XFoil.

Originally Posted by Border Lord

Aerofoil is NACA 63012A.

If both root and tip use the same airfoil, that's pretty easy to generate. If you can post planform details (including span), rib spacing, and spar position(s), I can post a PDF with the ribs.

Hi Wazmo

If that's ok, I'll definitely take you up on the offer.
Will PM you with the details.

Thanks

Jeff

Hi Wazmo
PM sent
Jeff

Hi Andy
See you found me, even after I got the thread moved.
So, like your method, even more because it can be done in Paint, which I have.
However there is one issue inherent in all the systems that use percentage reduction rather than plotting.
That is that the percentage reduces all dimensions by the same proportion.
I'm thinking of the trailing edge depth, which starts at the root at 14mm, but by the percentage method would end up at the tip as only 9.25mm.
Really don't want to have to taper off the aileron stock along its length, especially as I would have to try to keep the width the same.
Any way round this?
Jeff

My favourite (and now only) method for constructing built up wings, is the so called "Laser method". Foam ribs, balsa capping, carbon main spar.
Quick, easy and accurate.
Do a search for details. Some pictures of examples on my blog.
If you are interested and stuck trying to find details, ask again here.

Jim.

Actually quite easy.

Start with un-sheated rib profiles. Using your reduced print outs, you know the thickness of your trailing edge so draw it on each print out. then use a straight edge to connect the top of the TE to the closest tangent point on the top of the printed out airfoil. Do the same for the bottom of the TE. For spars select either the forward or rear vertical surface and move the other vertical surface per your spar thickness. Always select the same vertical.

Vola , you have an airfoil.