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Posted by Jim.Thompson | Mar 14, 2016 @ 03:52 PM | 1,551 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 | 1,542 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 | 2,473 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 | 3,131 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 | 4,742 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 @ 04:25 PM | 5,119 Views
Posted by Jim.Thompson | Dec 07, 2014 @ 01:50 AM | 4,545 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 | 4,767 Views
Description and pictures posted here:
Posted by Jim.Thompson | May 21, 2014 @ 04:48 PM | 6,087 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 | 5,926 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 fuse and wing were shaped and sanded, I applied spackle in the usual way. Sanded, then another coat etc. till smooth.
2. Then I screeded a coat of PU glue over the surface. This really made the spackle nice and hard. Sand, second coat. Sand.
3. Spray adhesive, then two layers of crossweave tape diagonally opposing.
4. Lay flat with covering iron. Sand lightly.
5. Spray adhesive, then covering film to decorate.
6. Finally, a layer of 30 micron laminating film.
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 | 6,188 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 | 6,045 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 | 6,221 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 @ 01:03 PM | 5,802 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 | 6,644 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!
Posted by Jim.Thompson | Apr 03, 2013 @ 10:31 PM | 7,198 Views
I'm posting this here for my own reference and for anyone else who may be looking for it:

"K Factor" for tailplanes.

K= (Stab Area)x(distance between 1/4 chord points) divided by (Wing Area)x(Average wing chord)

Really nice flying planes have K~0.5
Trainers have K~0.6
Racers and high aspect ratio sailplanes K~0.4
K~0.3 is almost unflyable.
Posted by Jim.Thompson | Feb 14, 2013 @ 04:07 AM | 7,339 Views
I have the two wings ready for closing now.

edit: They are joined up and removed from the mould. It was a difficult release; I used wax only and no paint. Not a good idea. I'll at least prime the moulds next time when using wax only.
The weights are both around 390 grms. Not much lighter than the first prototype.
I was hoping for a lighter one, but don't mind much. The previous plane was a hoot to fly @ 2kg in big air! Given a guess, I would say this one might finish up at around 1.8 kg.
Posted by Jim.Thompson | Jan 05, 2013 @ 01:39 AM | 7,945 Views
I layed up one fuselage yesterday and there is another in the mould today.
I have 25 psi pressure in the bladder and the excess resin is audibly being pushed out.
I had success with the orange coloured Bunnings drop sheet plastic for the bladder. I found out my accident that it does not even require the wing fillet silicone plugs in place to suppor the bladder. It is sufficiently stretchy enough.
This plastic welded very easily using an 80 watt iron with the tip shaped into a sharp cone. I can move along the seam quite quickly and where required, I will go over a stretch if there is some doubt about the seam integrity. I know I have it right when it tears freely from the waste edges.

This fuse is layed up as follows:

1 layer of 100 gsm plain weave glass fabric @ 0/90 orientation.
1 layer of 100 gsm plaind weave glass fabric @ 45/45 orientation.
1 layer of 200 gsm uni-directional glass @ 0 orientation.
1 layer of 76 gsm kevlar back to about half the fuse length.
Extra pieces of glass to face the wing fillets etc.
Extra Uni-glass @ 90 in the fin for stiffness.
Carbon tow in the wing root arris's.

Finished weight for the first one: 200 grams.
I mixed approx 100 grams of resin.

This fuselage is nice and stiff and quite light for the service it will be put too. Given that planks land hard and fast, I need them strong!

I'm pleased. I'll try another layup after this second one is out of the mould. Maybe with a layer of 165gsm crowfoot glass, one layer of the 100 on the bias, and a part layer of the uni.

Posted by Jim.Thompson | Dec 22, 2012 @ 07:19 PM | 8,633 Views
I did my very first vac resin infusion tests yesterday and the results were quite good. I had leaks on the first tests, but it did not seem to spoil the composite plate that I was making. Probably because the leak seem to bypass the layup.

I waxed up some thick glass plate after taping the edges to keep them clean so that the acrylic filler would adhere to retain the bag later. Then I cut out two cores, one out of 1.5mm LRC (low resin content) Soric.
The second one, I cut the same size core out of Coremat, which is a regular fibreglassing core filler which I just happened to have in stock. I place a layer of heavy glass cloth (295 gsm) on top and bottom of each of these and positioned them on the glass plate. Then added a layer of peel ply, with the ends wrapped around pieces of spiral wrap in the usual way. I finished off the stack with a layer of infusion mesh. Inlet and outlet hoses were inserted the spiral wrap, one to pull the vacuum and the other to supply the resin.
I used a spray paint pot as a resin trap, copying "Ant's" example described in an earlier infusion thread.
I used Araldite LC3600 (it goes by several numbers??), and the ambient temperature at the time was 35 deg. C, so I didn't bother warming the resin.

I had some difficulty chasing leaks, but after they were (mostly) tracked down, the infusion went smoothly and plenty quick enough.
The bag was opened and the samples stripped from the glass this morning and look good. What was...Continue Reading
Posted by Jim.Thompson | Dec 08, 2012 @ 02:08 AM | 8,137 Views
I made a quick joiner mould today using two pieces of 12x12 RHS aluminiun and one piece of 40x40 aluminium RHS.
I used the 40x40 to space the smaller sections accurately. I waxed this to ensure it would stick to the assembly. Then I cleaned a piece of 8mm plate glass with acetone and masked off the 40 mm wide strip that would form the mould interior. Then I carefully ground the glass slightly to provide a good key for the epoxy that I was to glue the 12 x 12mm strips to, with my angle grinder. The 12x12 strips were cleaned with acetone and sanded rough on one face to provide a key.
Then I removed the masking tape and glued and clamped the thinner strips to the glass using the large piece as an accurate spacer. I glued them with epoxy and West Systems 403 added.
When the glue had mostly set, I removed the 40 x40 and cleaned the surplus epoxy that had exuded slightly out the inside corned of the joins with a chisel.
Now I have my mould for a 12 x 40 joiner bar!
Any combination of scrap sized material could be juggled to suit the application. This saves much time and money.


When fully cured, I waxed and PVA treated the mould. Then when the PVA was totally dry, I layed in the bottom of the mould 12 rows of 50k carbon tow, suitably wet out with laminating resin and rolled as flat as possible.
The next day, I glued in a foam core with included plywood shearweb that I have previously cut to 9x36mm using my hot wire gear. This was carefully spaced equidistant from...Continue Reading