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Author Topic: Carving Airfoils  (Read 617 times)
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Viking123
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« on: February 12, 2017, 03:15:13 PM »

Hi everyone!

After years of RC flying, I have recently discovered the delights of free flight - in particular free flight gliders. I have built a few basic HLG's with flat bottom airfoils, which has helped my cutting and sanding skills tremendously. I wanted to up my game to something that will really push my limits and teach me something new. I found a plan for a Cat 2 HLG which requires a under-cambered airfoil to be carved into the wing section, and as this would be a completely new skill and technique for me, I was wondering if anyone could help me with this? What would be your methodology for approaching carving airfoils with under-camber??

Many thanks in advance.   

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HoveToo
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« Reply #1 on: February 12, 2017, 04:37:19 PM »

The two ways that I have tried are to either glue/tape some sandpaper to a suitable bottle or can or to cut out the aerofoil section and glue to some suitable block balsa and cut a male profile to which you can glue some sandpaper.

To be honest, nothing that I have read indicates that an undercambered aerofoil is worth the effort for outdoor use as it is too draggy and harms the launch height. The designs by Tony Mathews and Lee Hines show the preferred aerofoils in use today.

Indoor is different but there the experts use a very thin section (flapper) that flattens out during the launch phase rather than a solid single piece of wood. In this instance see the postings of OlBill regarding his record breaking gliders.

Ian
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Olbill
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« Reply #2 on: February 12, 2017, 06:25:18 PM »

This is not meant to discourage you from learning a new skill but a Cat 2 glider with a fixed wing (not a flapper) probably doesn't need an undercambered airfoil. Flapper wings give you under camber without detracting as much from launch height as a fixed wing with undercamber would do.

A foam sanding pad on a round bottle would be a good tool if you must do undercamber.
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adanjo
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« Reply #3 on: February 13, 2017, 01:12:25 AM »

This is my convex sanding block and a convex plane that was modified from a normal flat plane.
I mainly use sanding block only for cat2 wing because the concave is not very deep.
I have one more convex plane but cannot find it.
Some use bent or curved cutting tools for this purpose.
Aki
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Re: Carving Airfoils
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Viking123
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« Reply #4 on: February 13, 2017, 12:57:42 PM »

Thanks for the advice and information! Its helped get a methodology into my head.

I did think the undercamber was a bit old even in RES gliders undercamber airfoils are uncommon these days. I had a look at the date of the plan and it's from 2007 which surprised me. But I think I'll still give it a go just for sanding practice.

I've been through the plan gallery and downloaded some other plans to get stuck in to.
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adanjo
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« Reply #5 on: February 13, 2017, 11:38:43 PM »

What is RES gliders?
These days, almost all indoor gliders have undercambered wing, some with latest Low Drug Airfoil others with old airfoil.
Aki
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iflyhlg
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« Reply #6 on: February 14, 2017, 09:28:46 AM »

RES stands for Rudder ,Elevator, Spoiler for one class of radio control sailplanes.
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packardpursuit
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« Reply #7 on: August 05, 2017, 03:27:27 PM »

Straining the "old gray matter" here, but I seem to recall an old "Hints and Kinks" featurette (American Modeler) showing to carve the upper surface first, then invert the panel and pin down LE and TE down to the board. The resulting "hump" is to be sanded off, level to both TE and LE.. Unpin the panel and a good start is made at an undercambered balsa section THEN finish shape/tweak with convex sanding block.
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