Jim.Thompson's blog View Details
Posted by Jim.Thompson | May 04, 2019 @ 07:02 PM | 2,244 Views
I have adopted the routine of modifying the templates for hot wire cutting from that produced by (in my situation) Profili2.
Profili2 template print outs show a sharp change of gradient from the airfoil to the chord line at both the leading edge and the trailing edge.
I shape the LE with a curved, smooth entry to facilitate easy starting of the wire transit. It is inclined to get stuck with a sharp change of template shape here (or anywhere for that matter).
The very small extra foam can be quickly sanded off after the cut is done. If care is taken with the shaping of this curved starting section, little or no extra foam is left uncut.

At the TE, I continue the airfoil contour gradient beyond the TE, as distinct from sharply changing the contour to the chord line. This minimises or avoids any "scalloping" (loss of foam mid panel) of the TE and provides a faithful result.

One other practice that I am at variance with Phil Barnes vac bag instructions is in the type of top template used. If I recall correctly, he advised the use of a bottom template with a full airfoil template sitting on top of that to do the top cut.
Not only does this obviate the above advantages, but also can result in the wire slipping between the two template parts and completely ruining the foam blank.
This at least, was my experience, and I now only use a separate top cut template.
A typical one can be clearly seen in the foam rib hot wire cutting video posted in this blog below.

Posted by Jim.Thompson | Dec 25, 2018 @ 07:38 PM | 6,137 Views
This is my very first Arduino project.
Thanks to Hans Meijdam on this site for the design, guidance and assistance: http://www.modelbouwforum.nl/threads...-vario.199904/

The only problem I encountered along the way was Linux Mint permission problems. Once I got around them, all went according to the instructions.
I have encountered "Permission Denied" problems before in my otherwise excellent Linux Mint 17.3 operating system. Don't ask!.............

It is amazingly sensitive and sounds like a full size sailplane vario.
Posted by Jim.Thompson | Dec 10, 2018 @ 04:19 PM | 5,108 Views
The advantages of this method are:
1. Light and strong.
2. Ease of construction.
3. Quick and cheap. Foam for the ribs can often be found from recyclers.
4. Accuracy. All ribs cut together in the one set up. Cannot get them better aligned than that.

For my next constant chord wing using this method, I plan to construct the spar first. It will go something like this:

1. A foam core tapered in thickness will be hot wire cut. Dimensions will be the airfoil thickness minus the carbon caps, minus 1 mm for sanding/fairing balsa. Lets say, nominally 35 mm high and 8mm tapering to 4mm thick, (for example sake only).
2. This core will be faced in 1 mm Pauwlonia ( but could be balsa or basswood et. al.) with vertical grain orientation.
3. End grain of the timber is then sanded down to the foam.
4. Pre-made carbon spar caps are then added to the top and bottom of the assembly. These will be layed up using common uni-carbon/laminating epoxy which is cheap.
The thickness of these caps are tapered out to the tips.
5. The caps are glued on and the assembly wrapped with Dyneema, Kevlar, or other similar high strength braided line. Then all given a light application of thinned epoxy resin.
6. The "laser method" hot wire cut ribs are cut with a slot to take the spar. The building board might be in two parts, to enable separation of the two halves to allow the spar to be lowered into place, glue applied, then the two halves brought together.
7. The joiner boxes will be glued into the main spar and the assembly wrapped again.

I fully expect this assembly to be super light and super strong.

Video of a top cut:
Top cut left wing (1 min 35 sec)

Posted by Jim.Thompson | Dec 02, 2018 @ 03:37 PM | 5,955 Views
Link to the vimeo video here:
Silicone Hinge Demonstration (8 min 19 sec)

Posted by Jim.Thompson | Oct 25, 2016 @ 04:19 PM | 9,151 Views
This is the last method I have tried successfully. The advantage of it is that it can be moved on the mandrel before investing any composite materials in the job.


I will take some pictures next time that I do one this way.
Posted by Jim.Thompson | Sep 02, 2016 @ 05:37 PM | 10,683 Views
I've been deliberating for months on how to build a dolly for launching gliders when aerotowing. I finally got around to making one, this is the result.
It needs a bit of adjustment to provide a slightly increased angle of attack to lift the glider off the dolly positively.
Some form of suspension would also be good; it would prevent the possibility of the glider being bounced off the dolly prematurely due to the bumpy ground.
Posted by Jim.Thompson | Mar 14, 2016 @ 03:52 PM | 11,179 Views
Here for reference and ease of finding. I get asked now and again for this and have to do a search.

Posted by Jim.Thompson | Mar 14, 2016 @ 03:51 PM | 11,118 Views
Here for reference and ease of finding. I get asked now and again for this and have to do a search.

Posted by Jim.Thompson | Jul 21, 2015 @ 08:01 PM | 11,872 Views
This is my latest project; a lightweight version of this model. I have the heavy one, as can be seen earlier on in my blog.
This one has foam core/vacuum bagged wings and tail surfaces. All hinges are kevlar, so called "live hinges".
The wing airfoil is the same as my Entropy airfoil, which is basically a TP 29 variant.
Four servos, servos in the wings as can be seen in the picture.
I like a rudder on these little models; it assists braking during final approach while landing using crossed controls, just like the full size often resort to. Besides, it is good for aerobatics including fully developed spins.
At this early stage without paint, it balances out at around 800 gram. I expect it to gain at least another 100 during painting. It will still be a good light to medium air weight.
Posted by Jim.Thompson | Jun 28, 2015 @ 03:56 PM | 12,527 Views
As most builders have found, or will find, supplied tube and rod of whatever material (carbon, aluminium or steel), come in a nominal size only. There is always, or mostly, a size discrepancy or variation from the specified size.
I now make my own receiver tubes to suit any supplied rods or joiner tubes, for this very reason.
However, there comes a time when a hole needs to be drilled in a bellcrank (for example), to fit a 3 or 4 mm factory made rod. Without a full set of numbered drills sitting in the shed on hand, it can be frustrating to drill/file/ream a hole out that will be a good fit with near zero slop.
One way around this, is to reduce the size of an off the shelf, hardware store twist drill. I use a disc sander as per the video. For final polishing, a grind stone works well too.

Reducing twist drill diameter (0 min 28 sec)

Posted by Jim.Thompson | Apr 07, 2015 @ 01:44 AM | 14,697 Views
I am building a replacement set of wings for my old Passer Thermo.
I used some yellow XPS foam from Bunnings here in NSW Australia. It cut extremely nicely using my gravity hot wire cutter.
I'll attach a .pdf document. Unfortunately, the dimensions did not come out in the file transfer from the .dxf file.
Each side is a two panel wing. The first panel is 600mm long. 200mm chord at the root and 160 mm at the break. The end panel is 300mm long with a tip chord of 120mm. The TE is straight like the original. Technically a swept back wing.

Video of the hot wire cutting of the wing cores here:

Cutting wing cores. (1 min 33 sec)

Posted by Jim.Thompson | Feb 15, 2015 @ 05:25 PM | 14,596 Views
Posted by Jim.Thompson | Dec 07, 2014 @ 02:50 AM | 14,122 Views
This is a link to a report and pictures of my gravity powered hot wire foam cutter:

Posted by Jim.Thompson | Oct 29, 2014 @ 02:24 PM | 14,064 Views
Description and pictures posted here:

Posted by Jim.Thompson | May 21, 2014 @ 04:48 PM | 15,538 Views
I have been busy learning to draw in 2D LibreCad, which is an open source CAD drawing system designed specifically for Linux. That has been a challenging but very rewarding adventure in itself.
Also, I've been working on the design of my next project; Entropy build thread here:

Also I have been doing a bit in the shed building another light plank out of the remaining scrap foam that I salvaged from the tip. This one will be very similar to the 1200 I finished recently (flew again yesterday - very nicely too), but will be 1400 span. The max size panel that my gravity cutter can cut is 700mm, so that determined the size. I expect to be able to make this one to an even lighter wing loading that the smaller one. I've learned a few more tricks along the way, as happens.
Posted by Jim.Thompson | May 02, 2014 @ 04:17 PM | 15,328 Views
I built this foam plank heavy with view to Dynamic Soaring it. I hope to travel up to one of the DS sites where some of my flying pals fly regularly. There are no DS sites to be found around where I live.
This plank has an AUW of 1850 grams, which makes it a bit of a heavyweight.
Span: 1500mm
Airfoil: PW51

The finish method went as follows:
1. After the wings were shaped and sanded, I applied powder filler (not the pre-mixed type) in the usual way. Sanded, then another coat etc. till smooth. Usually three applications.
2. Then I screeded a coat of PU glue over the surface with a hard plastic spreader. This really made the spackle nice and hard and formed a smooth glazed surface. Sand, second coat. Sand. Very little sanding required this way.
3. Spray adhesive applied, then two layers of crossweave tape diagonally opposing. (45/45 orientation).
4. Degrease, then lay flat with covering iron. Sand lightly with coarse paper to scuff it up a bit.
5. Spray adhesive applied again, then covering film to decorate.
6. Finally, another mist of spray adhesive and a layer of 30 micron laminating film applied..
7. The elevons were bagged glass over balsa, with some light uni-carbon strips top and bottom at the TE. This made for nice and stiff elevons.
8. The fin is vac Bagged foam core. Carbon/glass.

I hope to get out to Mt. Borah for a test fly tomorrow actually! Great forecast.
Our winter season of westerlies has begun.
Posted by Jim.Thompson | Apr 09, 2014 @ 12:30 AM | 15,511 Views
These pictures show how I build the box section fuselages - I hope!
The EPP beds that the foam cores come in is cut down to 10mm sheets using a hot wire and a couple of spacers on the bench.
After the sides and top are cut out, I line the inside with 80/20 glass and epoxy.
The wood that I'm using for the bulkheads is recycled Douglas Fir venetian blinds that I have cut into strips. These are glued together and first tacked in with CA.
The final assembly is done with PU glue.