Jim.Thompson's blog View Details
Posted by Jim.Thompson | Dec 10, 2018 @ 04:19 PM | 639 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.

I fully expect this assembly to be super strong 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 | 1,458 Views
Link to the vimeo video here:
Silicone Hinge Demonstration (8 min 19 sec)

Posted by Jim.Thompson | Oct 25, 2016 @ 04:19 PM | 4,899 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 | 6,043 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 | 6,851 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 | 6,818 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 | 7,558 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 | 8,269 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 | 10,305 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 | 10,295 Views
Posted by Jim.Thompson | Dec 07, 2014 @ 02:50 AM | 9,774 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 | 9,826 Views
Description and pictures posted here:

Posted by Jim.Thompson | May 21, 2014 @ 04:48 PM | 11,256 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 | 11,059 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 | 11,222 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.
Posted by Jim.Thompson | Apr 06, 2014 @ 12:56 PM | 11,175 Views
I flew my new little 3 servo plank out at our favourite beach headlands. It flew just fine without an problems. Smooth and agile. I did make a very slight CG adjustment, but ended up setting it back to where I had it from the bench set up. I look forward to flying it out at Mt. Borah in some good lift.
My flying buddy Andrew even took a short video of the launch here:

Jims Plank (0 min 11 sec)

Posted by Jim.Thompson | Mar 24, 2014 @ 07:26 PM | 11,403 Views
During the short breaks in the humid rainy weather of our wet season, I've designed and built a new 1200mm span 3 servo plank.
The wing core was cut from some low density scrap foam scrounged out of a skip at the dump to a PW106 airfoil. I chose the higher camber PW section as I want this one to be as light as I can achieve and be a bit of a floater. Also, I wanted something that will turn a bit quicker than my larger planes, fly in light conditions and be suitable for one of our local beach headlands.

Root Chord: 220mm
Tip Chord: 160mm
LE sweep around 16 mm to keep the 22% chord line straight.
I first applied a 20mm strip of bias woven carbon (using a double carrier sheet), to the LE of the wing and allowed 3 - 4 hours for it to start to cure. Then proceeded with the layup below:
Layup is two layers of 76 gsm plain weave, one @ 0/90 and the other @ 45/45.
Approx 1/3 span overlap of each of the second layers to constitute 3 layers for this inner part of the wing.
Three servos to separate the ailerons a bit and provide better efficiency.

This is made from scrap depron sandwiched between layer of glass/epoxy. I cut out the depron and lined it with 80/20 Fin:100 gsm glass. Then built it up into a box section structure using bulkheads where required. Then sanded to a rounded sort of shape and covered with two layers of 50 gsm glass plain weave fabric/epoxy.

This was hot wire cut to a NACA06 section from some scrap blue foam. Then bagged with two...Continue Reading
Posted by Jim.Thompson | Jan 23, 2014 @ 02:03 PM | 10,777 Views
I've been fitting outboard bearings to the servos in my flap installations in the last couple of builds. It makes for a very tight servo installation with residual backlash and slop down to the absolute minimum. In fact, it is only the slight bearing backlash remaining; with very good quality servos, such as MKS, this would be absent.
I'll submit a picture of one out of one of my Wompoo's. It's difficult to take pictures of them in a new operational wing, due to access difficulties etc.
This was a very cheap DIY way of doing it. I just made up a laminate sheet and cut out the bearing supports from that. The bearing is a press fit into the little laminate block and it is glued to top and bottom skin. I similarly link both skins to my servos to avoid flexing of the skin where the servo mounts.
I've tried several bearings from several sources. Very mixed quality and availability and cost. The ones I have now are cheap and available from Banggood. A$2.32 each delivered. These are 3x8 mm and will suit the bigger metal geared servos with a 3 mm horn retaining screw. All that is then needed is a longer screw and a suitable spacer between the bearing the horn. And of course, the support block as above.


I've already posted a picture of one bearing installation on my Wompoo build thread, but here it is again:
Posted by Jim.Thompson | Sep 04, 2013 @ 06:35 PM | 11,755 Views
I'm planning on putting together a light 1500 mm span EPP plank at our coming Manilla Slope Festival. It will have a PW75 airfoil and I'll cover it with laminating film. This will be my first attempt at using Lam film.
I decided on the spur of the moment to make up trial fuselage using 12mm sheet offcuts from a former EPP wings sliced down using my hot wire.
I cut out the sides using a fibreboard template and laminated 200 gsm uni-carbon to one side of each (to become the inside of the assembly). In hindsight, I would use uni-glass instead due to any 2.4 ghz shielding concerns.
I then cut some more sheet to form the top and bottom of the fuselage and laminated this with 200 gsm uni-glass.
Some formers were made with some carbon strip which I had made some time previously to fit several stations.
The assembly was a bit of a fiddle, and some more thought is needed to get this sorted. But I used some hot glue for the first bottom/side join. Not a good idea, as this caused some sanding problems later on. However, it did provide a good start. The battery pack (4 AA cells) was hot glued into place and well supported as far forward as possible. The remaining side and bottom was glued up using PU glue and spiral wrapped with tape overnight.
I shaped and sanded the corners this morning and the result looks quite presentable! Nice and light and very stiff!