Measuring airfoils

[Ralph Walton]

Has anyone got a method of taking an exising plane, and measuring and drawing existing airfoils for analysis? I've got various foamies that I'd like to know how close the built foil is to what its supposed to be. I've designed and built a couple of planes that I've been underwhelmed with in the performance dept. Others have performed well.

I believe that various layers of tape on the leading edge, gluing of spars etc etc should be compensated for in the cutting of the cores. Seems to me that the general building process removes quite a bit of camber too. I'd like to know rather than guess.

I guess I'm looking for the holy grail of an epp foamie that performs like a moldie.

[JetPlaneFlyer]

A profile gauge is probably the easiest /most practical way to do it: http://www.fine-tools.com/G309631.htm

You could go all high tech and use something like a laser scanner: http://www.leica-geosystems.com/corporate/en/HDS-Laser-Scanners-SW-Leica-HDS6100_64228.htm which could be used to produce a very accurate 3D model but unless you know someone in the trade who could do you a quick scan then that would be horrifically expensive.

[fnev]

You said very accurate… Photometry is the answer. But as it is stated above you will need to know someone with such measuring device. The beauty of this is that you can (almost) make molds strait from it… Ask the Chinese copy cats!

[JetPlaneFlyer]

You said very accurate… Photometry is the answer.

I think you mean ‘Photogrammetry’, which is when you use a special camera to take photos of an object from different positions then use triangulation to measure the object.. This is the way they make maps and yes it could be used on a model plane... Laser scanning is the newer technology that has superseded photogrammetry for much of this type of work. Laser scanning produces an actual 3D model made of millions of 3d points which form a 'cloud' that can be converted into a 'solid' 3d CAD model quite easily.

I'm hoping to very shortly have access to some of this kit (the actual scanner I linked to previously)... Should be great for producing CAD models based on scans of real planes.. No more debating the accuracy of 3-view drawings because a laser scan is accurate sub-millimetre.

Steve

[Brandano]

shine a laser line across the wing chord, take a picture from the wingtip. Scale the resulting line to thickness, bingo. Forget about laminar airfoils, though. Oh, and try taking the picture from a good distance with a zoom lens, to minimize perspective distortion.

[fnev]

Thank you for the correction Steve, I was in a hurry and wanted to mention a way that I am currently using to manufacture CNC molds from existing patterns or models. Actually I am dealing with a company doing it for the projects I am involved with.

This is an amazing way for creating tooling. Say you want to make a new fuselage for a glider. You could go strait into virtual modeling, but sometime it is preferable to have a “real” shape to visualize better the desire result. Now you digitalize this shape once you are satisfied and bingo you have the information needed to CNC the mold that will reproduce exactly your initial shape.

It goes even further: you can modify your digitalized shape. For example if you want to reintroduce the exact root section from the data base with its exact (desired) incidence you do it and now you have your perfect mould coming to life under the CNC 4 axis mill tool!!!

I have been dreaming of using such process for years and now that I am reaching the end of my professional activity I am lucky to be able to play with it… so cool…