How to scale airfoil coordinates to achieve the required size?

Question

I'm using airfoil data that is generated by a program. The generated airfoil has a chord length of 1 unit. I want to know how to scale up this airfoil to required chord length. My airfoil series number 638xx. NACA five digit series.

MountainClimberi · Accepted Answer · 2017-02-28T16:47:42.630

3

This is a simple math question. Multiply your x and y coordinates by the scaling factor you want. Say your chord length is 100mm. To make it 150mm, multiply all your values by 1.5. If you have a picture of an airfoil, just scale the image by 150%.

edited Feb 28 '17 at 16:47

answered Feb 28 '17 at 16:00

MountainClimberi

166
7

What about the y coordinates ? – papabiceps Feb 28 '17 at 16:09
Multiply both x any x values by your scaling factor. – MountainClimberi Feb 28 '17 at 16:11
Did that do the trick? – MountainClimberi Feb 28 '17 at 16:13
No, I was a following a video tutorial done by some guy on youtube. He shared his airfoil section coordinate files. When I check the scaling factor for the airfoil coordinates, it is different for x and y coordinates. For reference I'm adding pastebin [link](http://pastebin.com/4gybQCfV) and the original coordinates [data](http://m-selig.ae.illinois.edu/ads/coord/naca4415.dat) – papabiceps Feb 28 '17 at 16:23
he is using NACA 4415 – papabiceps Feb 28 '17 at 16:23
I thought the scaling factor would be same like you. But this is showing its different for x and y coordinates. – papabiceps Feb 28 '17 at 16:33
That's interesting. If you scale both values differently you are going to get a different airfoil aren't you? – MountainClimberi Feb 28 '17 at 16:59
Let us [continue this discussion in chat](http://chat.stackexchange.com/rooms/54508/discussion-between-papabiceps-and-mountainclimberi). – papabiceps Feb 28 '17 at 17:01

score 2 · Answer 2 · edited May 23 '17 at 12:38

MountainClimberi is correct. Multiplying both x and y coordinates by the same factor will scale your airfoil correctly. Using a different factor for each will result in a different aspect ratio and a different(stretched) version of that airfoil that will not match its published properties.

Also remember that after scaling the data, your reference location will have moved if it was not (0,0). This may require a translation operation if you need to adjust it.

Per Scaling(geometry) wiki: "The scaling is uniform if and only if the scaling factors are equal (vx = vy = vz)"
Willamate.edu has a good article on 2D transformations including scaling.
Python would be a good language to manipulate this data with. Here is an SE python scaling question.

How to scale airfoil coordinates to achieve the required size?

2 Answers2