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GNieuwoudt's blog
Posted by GNieuwoudt | Jun 29, 2008 @ 01:46 AM | 10,894 Views
I took a long break from building but here I am back with a bang!

In the resent Nats I saw my 1.8m Cumulus with S400 brushed motor is losing the technology war in the F5J competition and is not performing as well as in the past. I was flying this little model for 8 years now and will prolly pass it on to my little boy as it is still far from retirement.

I had a pair of beautiful built-up 2.5m wings from many years back of a model that flew well, but the fuz was useless and I disposed of it. The airfoil is the old E205 but still very useful for this purpose. The plan was designed round a 350-400 Watt setup. For F5J with brushless the launch time with motor on, should be not more than 15 seconds to be competitive. I believe as the technology is catching up (or is that the checkbook war) this time will decrease closer to 5 seconds. There is a balance between battery capacity and AUW of the model. One of my goals was to prove that I can build a competitive model on a relative low budget. The electric equipment now readily available do make this possible. An outrunner with a 3 sell 2100mAh Lipo would be the power train. The aim was a model weighing not more than 1.2kg. MotoCalc show that I can prolly go vertical with this setup. The logic is that a light airframe needs less power for launching which imply lower cost setup.

And so a model built from Spare Parts was born. The fuz consists of a boom and pod. The boom is from a Bubble Dancer which I replace after I found a...Continue Reading
Posted by GNieuwoudt | Feb 27, 2008 @ 01:51 PM | 10,639 Views
Yes I am guilty! Have not updated my blog for some time and I have not finished the Supra as promised. But I have a new toy. I took the plunge with last years bonus and bought a molded Supra. Any way here is some photos taken by Johan Snyman. Thanks Johan

I flew my postals on the Friday 1st Feb ! 14H30 the afternoon. My weekends
is very full and on the first day of February I saw we had good air and
decided to do it. At that stage my new moulded Supra (the homebuilt Supra is
still to be finished) was not properly setup for landings. The first landing
was 15m, then 10m, then 6 m short then I went 6 meter past the spot with the final landing on the spot. After each flight I was changing flap curves
until I got it "spot-on". At this stage I am very satisfied with the new
model and it suits my type of flying (slow and cautious) very well.

Cheers
Gert
Posted by GNieuwoudt | Sep 24, 2007 @ 08:35 AM | 11,297 Views
By the time I am finished with this Supra there will prolly be a new toy on the horizon. It is part of the hobby/sport for me to do the building so I can just as well take my time, but I need a tool for next years HTL. I gave the league a skip this year but miss all the old friends and healthy competition atmosphere, so be warned I may be back soon!

I have finished the fuz and all of its parts during the past 2 months. After much consideration and some experience from my previous Supra project I decided to change the pylon at the base of the wing. I have added a wider flange/faring. The reason is to improve the strength of the pylon. Due to torsional twist during hard landings the pylon is prone to damage. I have made a base for the wing from 200g Carbon which was done on the finished wing. The next step was to glue this base to the fuz and added a fairing with lots of carbon tow and some filler. The base have tows running 45 degrees and the carbon tows running parallel along the fuz sides. I hope this will add enough strength in the needed directions when the fuz stops movement and the 3.4m wing want to twist. The added weight for this modification was well worth it.

The push rods is 2mm carbon and sleeves supplied by Dion Liebenberg. I could
not get the teflon sleeves in time and decided to use the white sleeves. The rest of the installations is not rocket science and I think the pictures tell the story.

The completed fuz with rudder and elevator and servos...Continue Reading
Posted by GNieuwoudt | Jul 14, 2007 @ 12:53 PM | 12,427 Views
Due to the extreme cold here in Secunda I can not continue with the Supra as my workshop is too cold in the evenings to work with epoxy resin. I decided to finish the CNC cutter as it is already a three year project. I have collected the parts over a long period but finally with a bit of effort in the warmth of my study I did the last few solder joints and it is working.

The cutter consists of a table which have the mechanics driven by 4 stepper motors, a electronics board which is the interface between the PC software and stepper motors, a old Pentium 100 which is still useful for this purpose and a powersupply for the foam cutter bow. For the interface board I used the MM2001 board design which was made for me by a electronic shop in Vdb. I had to solder all the components to the printed circuit board and program the PIC processor integrated circuit. Details of the electronics and
software I used is here http://gm.cnc.free.fr/en/index.html. This board is connected to the PC via a parallel cable. There is various sources for ready built or kit form stepper motor drivers.

I have seen and used other CNC foam cutters previously and I have tried to built other mechanics previously. It took me a while before I found this simple design which is also very solid (see photos). I am very happy with the results as it is very accurate and the cuts is very smooth. The stepper motors have 200 steps and one rotation on the screw will move the wire 1mm. The sliders is ordinary...Continue Reading
Posted by GNieuwoudt | Apr 08, 2007 @ 11:49 AM | 12,547 Views
In previous installments I have shown the plug for the pod with the pylon. I have done the mold now after many roundabouts. At first I made the plug with two halves thinking that it would be easier not to make a parting board. The result was two plug halves which were skew. I had to glue the two pieces together and do the finishing again (read lots of elbow grease). So now you know I am really not an expert and learn all the way. I made a parting board and the rest can be seen in the photos. I did not cut the board very accurate so I had to fill the cavities with clay between the plug and parting board. The complete setup took me less then an hour. What worked for me is to wax the plug and parting board and buff it by hand until it is shiny. I cover it with PVA mold release from Mica using a foam brush. When Dry I coat it with epoxy resin and fill the corners with a Carbosil mix. I found the carbosil mix should not be to thick as the bubbles do not escape then. I wait some time for the epoxy to get sticky and start with the layers of glass. I use a brush to tap it into all the corners and to make sure there is no bubbles trapped between work piece and glass.

After many thought I made a six piece mold for the fuz, nosecone and the servotray. This helps when you have to join the halves as you have access to epoxy the seam. The servotray was still a difficult shape and I made a joggle plate in order to create a offset for the one halve to fit inside the other. I fitted the...Continue Reading
Posted by GNieuwoudt | Apr 08, 2007 @ 11:17 AM | 12,197 Views
For those who is still following here we go with the wing center section. I am progressing slowly and hope to pick up speed and still make the Nats with this model. My available building time is only a fraction of what it used to be as I have endless lists of handyman jobs to do at my new house.

I have used 62g Kevlar as the main part of the skin on Supra #2. The center section have a double-up piece on top and bottom. The bottom center where the wing would rest on the fuz I have added a piece of 90g carbon and also on the top skins where the flap servos will be mounted for reinforcement.

Kevlar do not like to be sanded afterwards so in order to get a smooth leading edge I did the following. Add a carbon tow to the leading edge using spray glue. Cover that with a strip 2cm of 86g glass along the leading edge and iron the glass to the foam core with the spray glue. This will prevent it from sliding off when resin is applied. The Kevlar skin will be placed such that it is 2-3mm from the edge of the leading edge. So when the epoxy is cured after bagging you will not sand into the Kevlar, but only the glass. I tried to take pictures of this, but it do not show clearly how it come out. The small patches of Kevlar that did land under the sanding block I used foam safe cyno to harden the frays and sanded till smooth. Overall I was pleased with the outcome.

Back to the skins: I sprayed the maylars with the colour scheme I planned for this model. I was a bit too...Continue Reading
Posted by GNieuwoudt | Jan 21, 2007 @ 12:33 AM | 12,445 Views
I have relocated with "Vrou, kind, hond en 'n wavrag aardse besittings" to Secunda during December. There was no house available with a 6x6m workshop/store room like I used to have in Vaalpark, so I still have to find holes for all my hobby equipment. In this process I found a few things which was gone for the past few years and I got rid of a few things which was never used.
Secunda is about 170km from Johannesburg and 150km from Pretoria on the way to Volksrust. It is mainly the Sasol petrochemical factory that provide income in this area with the Billions of $$$'s projects going on. It is a typical "kokolol" town, but very hobby friendly. The model RC car and airplane clubs is very active and both have excellent facilities. The weather is not that friendly towards thermal gliding as it is situated on the Highveld RIDGE. Wind is blowing most of the time and for some reason we have 4 seasons on a normal day.

I have joined the local TRMC club (TEKS Radio Model Club [TEKS = Trichardt, Evander, Kinross & Secunda the 4 towns in this area). This is mainly a power flying club, but there is some interest in glider thermal flying and slope flying. The club have a beautiful facility close to town with tar runway, clubhouse etc. I am in the process to locate a separate field for gliding. We will be flying the postals.

During this period I did not do nothing, as I built a Fokker DVII foamy with Depron and a Slope wing in order to have some social stick time and acquired a Jazz F5B model (see reference to wind above).

I am now about to continue again with the Supra building. I have finished the Rudder and Elevator and the Center section of wing. The plug for the fuz mold is with Mark Stockton where I think it got less priority at the moment due to Tabooish DLG production. The tips should be easy and I will take you through the process of alignment once I get started again soon.

Cheers
Gert
Posted by GNieuwoudt | Oct 11, 2006 @ 06:16 AM | 13,389 Views
It is always wise to test your procedures and tools for vacuum bagging on a smaller piece like the Rudder. The booboo will be less painful that way and provides for a learning curve. I have sanded the Rudder and Elevator cores to shape as the CNC cutter can not do the rounded tips. The Elevator get an easy spar system. My first Supra had only unidirectional carbon on top and bottom for spar. The #2 get a carbon rod top and bottom. Both systems would work fine. A small block of balsa is layed in for the hold-on bolt and a balsa flange to fit the V-platform is added. The Rudder do not get a spar. A final finish with the sanding block and it is ready for the vacuum bag.

There is lots of info on the net for vacuum bagging and this is really not difficult to get under the belt with spectacular results. First the "mylars " is cut to size. I use clear PVC which I can get locally. I spray paint the mylars with colours I want the wings to appear, dark colour on bottom of elevator and white on top. Make sure you have cleaned the mylars before painting otherwise you will have some marks on the final finish. I used Plascon spray cans this time. Do not use the metallic colours as for some reason the result is awfull. It looks like the silver and colour seperates, I can show you an example in my booboo box.

I have some 60g Kevlar available and will use this on #2, 86g fiber glass will also work here. Cut the material to fit (yea right I said cut and not chew). I bought...Continue Reading
Posted by GNieuwoudt | Sep 12, 2006 @ 03:03 PM | 14,277 Views
Ok I survived the Nats and all of my model as well, so there is no restoration work and I can make time to continue with the Supra wing before I move house in December. As you can see I spend time when available and it often happens that my workshop do not see me for days or weeks. I am lucky to have a family as well so priority is not always Supra only.

If your eyeball technique of sizing the spar worked then the wing cores will fit with the spar a little smaller in height than the beds. The first thing to do is to cut the channel for servo wiring in aft part of cores. I made a simple tool for my "Dremel" type tool so it can operate like a small router. It is made of a small piece of flat bar aluminum with appropriate holes at right places and screws onto the tool, look at the picture. Keep the slot size small as it may create a dent in the wing under vacuum. Test fit the cores and mark and cut, cut-outs for bolt beam. Glue the foam cores to the spar. Be careful with glue as you do not want the glue to seep trough to the other end and make a bulge and you do not want the glue to fill the slot for wiring harness. I like to keep the bottom of spar flush with the bottom of the cores with a small gap on the top. Usually I would first place a piece of packing tape on the foam core beds for incase the glue would run through. I have tried many types of glue for this process and had many booboo's. You do not need high strength here and obviously keep the weight low....Continue Reading
Posted by GNieuwoudt | Sep 12, 2006 @ 02:43 PM | 14,232 Views
The Wing Spar

Once the spar caps is cleaned with sanding paper the rest of the spar can be done. Cornelius cut the foam cores from Isoboard for me with his CNC cutter. The center panel consists of two parts with a dihedral break in the middle of 2.5 degrees each side according to the plan. To do the construction for this is most difficult as the center panel is 1.6m long. The way I do this is to cut the foam cores with the dihedral in the foam beds. Due to the thickness of the foam we had only 1.5 degrees was possible. This will effect the EDA slightly, (4.9 degrees i.s.o. 5.9 degrees) , but from my first Supra I found that it works fine. You line up the foam core beds on a work bench and glue with spray glue to the bench. Now this can be used for all the preparation work on the foam cores and spar and can also serve as the beds for the wing when vacuum bag is done. It is important to get this very accurate as this will determine if your wing comes out "straigh" or like a propellor. So spend some time to measure it out and adjust according to the plans. I cover the TE with a piece of masking tape for protection during the building process, and yes remeber that cyno eats the foam so be careful when you spill some on your perfectly cut cores! (more filling and sanding to do for me)
Next step is to measure the spar in the wing cores and cut the gaps in the cores for the spar with your foam cutter, wire running against a guide on the ends. Place the pieces of foam...Continue Reading
Posted by GNieuwoudt | Aug 26, 2006 @ 01:39 AM | 14,633 Views
Spar caps
The wing spar will consists of a web in the centre made of balsa and foam with carbon fibre runners called the "spar caps" and the whole lot is then covered with fibre glass whith strands running 45 degrees. The spar caps is used on the top and bottom of the wing spar to provide the pull and compression strength for the wing spar system. Taking into account the length of the wing and thickness this is one of the critical areas for failure. I have found in the past if the total spar weight can be kept low then the wing total weight will be low. This will also determine what type of launch you can achieve before failure, a fine balance!. The original plan call for prefabricated taper carbon fiber stock. This however is very expensive if you have to import. I use Uni-Directional Carbon Fiber tape and make my own roughly tapered. Obviously I compromise by doing so and it may be not of a similar uniform strength and weight, but hey! I am building a toy plane on a limited budget. See photo of the type of carbon I used this time. Now, I am not a structural engineer, so I use "What Looks Right" rules and previous experience (not a lot) to determine how much carbon is enough and how much I put in, is my secret, so do not ask.

In previous attempts I found it difficult to keep the tows straight when I vacuum the spar caps. The reason for vacuum curing is to force most of the unnecessary resin out. I made a jig from aluminum square tubing and flat bar....Continue Reading
Posted by GNieuwoudt | Aug 26, 2006 @ 01:23 AM | 14,397 Views
The Supra have a pod and boom design for fuselage. The carbon boom help to keep the total weight to a minimum and with sufficient strength for the application. Booms are available from Polecatearo.com for around R300 landed cost. The pod design of Mark Drela is optimised for F3J gliders but can be used for many other purposes. You may even use this for a RES model and by changing the layup materials you have a means to control the strength and weight for your application.
I am no expert and document as I learn for my own future use. There are many ways to achieve the same or better results and I will be glad to hear of the other ways.

Ok to do the pod you first find a pensioner in Potchefstroom with a lathe. Some Yellowtong wood and instructions to the oldtoppie who is complaining heavily, only used to do coffee table legs, and a week later you go for inspection. To make things even more interesting I want the pod to consist of two pieces split in the middle, length wise. Any way it came out close to the original plan. With some wood filler you cover most of the grain and holes in the round plug. Add the pylon and file it nice round to blend in with the fuz. Sand the plug as smooth as you can. Cover with varnish to seal the wood. Spray paint it with epoxy paint. By now it should be fairly smooth if you do some fine sanding (600 grit paper) but there will still be some imperfections and wood grain showing only slightly. Now for the final step to sand and buff the thing...Continue Reading
Posted by GNieuwoudt | Aug 26, 2006 @ 01:10 AM | 14,160 Views
Ok here we start.

The plans are at: http://www.charlesriverrc.org/articles/supra/supra.htm

A building thread with many ideas and photo ilustrations are at: http://www.rcgroups.com/forums/showthread.php?t=437733

Material list with options available locally:

Foam Cores: Cornelius du Plessis for Isoboard CNC cut cores [Cordup@telkomsa.net]

Fuz mold and plug: I am busy with a plug according to the Drela F3J plan, will be ready by mid Aug.

Composites: Talk to AMT
Wing Spar:
Carbon UD 2LM x 600 wide. See what is available. Even carbon tow can be used, it is just more work.
Glass sock 3m x (35mm dia)? Light stuff Should fit over spar.
Or Carbon sock (heavier but stronger)
Or rap with 2 layers 49g glass (from off-cuts)
10mm Balsa x 1 sheet (will be cut for endgrain spar in sections)

Wing Skins: (see layout diagram) <<...>>
Option 1 (glass)
Centre 1 layer 86g + 1 layer 49g and some dubble layers for centre,servo bays and flap
Tips 1 layer 86g and some dubble layers for root,servo bays and ailerons
86g = 1m x 2.7Lm , 49g = 1m x 2Lm
Option 2 (kevlar)
61g with some double layers for root,servo bays and ailerons 1m wide by 2.7Lm long
(I find that this come out quite soft with Isoboard and dents easily, and would personally use CF doublers iso. Kevlar)
Otion 3 (Carbon)
90g with some double layers for root,servo bays and ailerons 1m wide by 2.7Lm long

(Obiously many derivatives in between can be done)
You...Continue Reading
Posted by GNieuwoudt | Aug 26, 2006 @ 01:06 AM | 18,450 Views
I always wanted to fly a full house glider. You see, here in upcountry you must keep up with the neighbors flashy "glass slippers". The cost of these "babies" however made my wife think twice, taking into account the unknown expire date of these models with my flying skills. I have been following the evolvement of the Supra design after building my Bubble Dancer from the same designer Dr Mark Drela of MIT and AG airfoil fame. Mark designed the Allegro and Allegro Light 2m gliders and followed that up with the 3m Bubble Dancer. I am not sure what was first but in the same time the SuperGee DLG glider was designed by him and many of the lessons learned in the DLG was carried to the designs that followed and hence the "big" gliders that looks like overgrown chukies. Mark designed a 2m full house glider and called it the Aegea. He was requested by club mates to stretch this wing to 3.2m for the Manis which was very successful in USA TD competitions. The Mantis design ideas originated in a car traveling back from a seminar by Dr Selig which Tom Kiesling attended. Anyway the 3.2m Aegea wing together with a "Pretty Mantis" fuselage was used by a few scratch builders. One of the ideas from the Dr Selig talk was to mount the wing on a pylon. It was found during launches with the 3.2m Aegea wing that due to the spar not being straight that wing would twist and cause washout and hence launched not optimal.
Mark was approached by Tom Kiesling (...Continue Reading
Posted by GNieuwoudt | Jul 25, 2006 @ 09:34 AM | 14,267 Views
Hi. My name is Gert and I fly mainly RC gliders in South Africa. I live in Sasolburg in the Freestate and work as a control system engineer for petrochemical projects. I like building my airplanes and spend a lot of time in the workshop. I have built all sorts of gliders and other airplanes over the years. Below is a few photos of the latest airplanes still in service.

I have scratch built a Supra from the Mark Drela plans and is currently busy with #2. I enjoy flying this model most of my fleet. I use it in the local TD competitions. I may add info of the local building group later to this area.

I have built a Bubble dancer. First with a builtup wing and then later upgrade with a foam and glass bagged wing. I flew this model for 2 years in the local competitions.

I also have a 2m RES glider with a Kevlar wing and a glass fuz which perform very well. This model was built light but strong for "dork" landings in competitions and have special reinforcement to handle rough abuse. It can take full pedal zooms (almost).

I use a modified Graupner Cumulus for F5J S400 competition. The motor is a S400 6V with 4.5:1 GB and 12x7.5 carbon prop. I use a 3S 1500mah Lipo battery which works well and seems the motor lasts with this setup.

I like to play with a DL50 DLG when on the beach during holidays. A really nice kit for building a DLG which was well thought out and performs well for the low cost.

I have recently completed a Minimoa scale glider of 2.8m...Continue Reading