Carbon Fiber Wingtips for a Jet Fighter

As I mentioned recently, I got the chance to see some serious carbon fiber work in action–building a set of wingtips for a jet fighter. To be precise, these wingtips are going on Czechoslovakian L-39 Albatross planes destined in some cases for the Reno Air Races:

Talk about a cool project!

This is Sky Greenawalt’s project, and I want to walk you through it a little bit. I’m hoping to get Sky to do some guest blogging here too, especially to talk about how he did the CAD work for this project, so let’s start there. Here is the wingtip in Rhino3D:

If you know much about CAD, designing these kinds of smooth flowing shapes can be extremely difficult. But, Sky is a very talented guy and he has mastered a new power tool called T-Splines that he says revolutionizes this kind of work. I can believe it from the short demo he gave, so that’s what I want to see him guest blog about. You should check out Sky’s posts over on the T-Splines forum if you like this kind of thing. He has the L-39 wingtips, a custom turboprop cowling, and a design for a Reno air racer he wants to build (couldn’t resist posting this one):

Let’s back up a step, because these wingtips weren’t just created from nothingness. First, there were handmade tips that used to take a solid month of skilled craftsmanship and labor to produce:

Next came the idea of doing carbon fiber wingtips, pulled from molds. To get started, Sky had to digitize the existing wingtips. You can see the control points on the top photo from Rhino. He used a Faro CMM arm to do the digitizing work:

Faro CMM Arm

Think of the Faro as a portable CMM (Coordinate Measuring Machine). It’s not motorized, but you have to know what you’re doing to capture accurate and valuable point clouds to feed your CAD software. These photos show Sky’s setup for measuring the light lenses that go on the wingtips. Note the heavy bags of salt to make sure the Faro is completely stable as measurements are taken.

Once all the measurements were in, and Sky had built the CAD model, the next step was to fire up Madcam (his weapon of choice since it plugs into the Rhino CAD program he uses) and produce the g-code. Next, the g-code went to the large router Sky uses (belongs to another gentleman–hi Dana!–whom I have consulted with from time to time to help keep it tuned up):

I should note that this router is a very cool machine and should be the subject of a blog post all by itself. It was created specifically for making molds for aircraft parts, its all hand built, and it does an amazing job with Mach3, servos, and an Ajax motion controller. The neat thing about it is that it has huge Z-travels to make creating tall parts possible.

Evntually, with a 1/2″ ballnosed endmill, 20 thousandths stepover, and hours and hours of patience, a very nice mold is created:

The mold quality was just gorgeous. The material was heavy tooling foam. The foam billet he cut the wingtip mold from weighs about 60 lbs and cost $1200, but it sure is nice material. One nice thing about the material is that it is easy to fix any minor imperfections with a little gentle sanding or filling. For example, Sky filled some pinholes in the material with spackling before the mold was put to use:

That concludes the CAD and CNC portion of the work. Next step will be the actual carbon fiber process.

In part 2, we go through the process of doing the carbon fiber layup and vacuum bagging.

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Related posts:

1. Carbon Fiber: UFO Quality Material

6 Comments

• Carbon Fiber Wingtips for a Fighter Plane, Part 2 « CNCCookbook 2011/04/12 at 5:17 am

  [...] I recently wrote about a project a friend was doing to create a set of custom wing tips to improve the aerodynamics of an L-39 Albatross jet fighter. To refresh your memory, here is the shape he was looking for: [...]

  Reply
• Carbon Fiber Wingtips for a Fighter Plane, Part 2 « CNCCookbook 2011/04/12 at 5:17 am

  [...] I recently wrote about a project a friend was doing to create a set of custom wing tips to improve the aerodynamics of an L-39 Albatross jet fighter. To refresh your memory, here is the shape he was looking for: [...]

  Reply
• 
  Karl 2011/06/15 at 1:29 am

  Hello thanks for the informative blog. Did you ever do a post about the CNC router mentioned above? If so, can you please provide a link here in the comments? Thanks.

  Reply
• 
  Karl 2011/06/15 at 1:29 am

  Hello thanks for the informative blog. Did you ever do a post about the CNC router mentioned above? If so, can you please provide a link here in the comments? Thanks.

  Reply
• 
  Bob Warfield 2011/06/17 at 6:20 pm

  Karl, I haven’t yet done a post on the router.

  Best,

  BW

  Reply
• 
  Bob Warfield 2011/06/17 at 6:20 pm

  Karl, I haven’t yet done a post on the router.

  Best,

  BW

  Reply