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Tuesday, February 27, 2007

Tsotsi comes home

On Sunday the 18th Feb while I was testing my iTsotsi100 in preparation for the RES/100 Challenge I lost radio contact with the plane while it was climbing away in a thermal that was drifting across the field to the West. The plane went into a spiral decent and disappeared below the horizon, so I never saw exactly where it crashed. I don't know what happened and will have to try and find out exactly what went wrong now that I have the model back.

I took a bearing and Justice and I went looking. The grass on the field next to ours was armpit high and I knew it was not going to be easy finding the model in that. I also did not really know how far it had gone, but had a pretty good idea that it was right across the field and somewhere in the orchards on the far side. After a while Chris, Gordon and Tony joined us and we widened the search, but found nothing. Eventually we were all exhausted from the heat and lack of liquid refreshments and we gave up looking and went back to the cars to sit in the shade and recover.

Later in the afternoon Chris suggested we go and have another look, so Gordon, Chris and I, this time each armed with a bottle of water, set off to look again. This time we went right through the orchard but found nothing. We did another sweep through the grass on the way back, but again nothing turned up. By this time it was late and we had to get home.

On the Tuesday, while driving past the field I noticed that it was being cut, so I stoped and talked to the guy driving one of the tractors. He promised to keep a look out and let me know if he was able to find anything. By Friday they had finished cutting and I went and asked if they had had any luck, but they had not. So now I knew that it was definitely further west as I had suspected in the beginning.

While I was there I rode around in the Kombi, stopping every now and then to climb out and look. Another tractor driver, Johannes, came by and I asked him to keep a look out as well and that there was a reward of R100 for the person that found the plane. His eye (he only had one) lit up and he promised to look for the plane.

Anyway Sunday came and went and I was not able to fly the RES/100 as I didn't have a plane. I had given my 2 meter Tsotsi to Phil so didn't even have a back-up.

On Tuseday afternoon the 27th, at around 5pm I got a "please call me" from a number that I did not recognise. Normally I do not respond, but something said that I must call, so I did. And low and behold it was Johannes, the tractor driver. He had found my plane it one of the orchards even further west that the one we had searched.

I arranged where to meet him and went and collected my glider. Unfortunately it was a bit worse for ware. Both wing hold-down bolts had pulled loose and the wing was broken in two places. By the damage to the wing it is apparent that it had crashed into a tree and the sudden stop had done the damage to the hold down bolts and wing. The fuselage and tail feather were undamaged. Old Johannes was very pleased to receive his R100 reward. No doubt he is celebrating tonight, as I am that I have got my Tsoti back! At least the radio, (flat) battery and servos appear undamaged!

On the way home, the sun went behind a cloud and it was rimmed in a beautiful silver and gold. I wish I had my camera with. This reminded me again that "every cloud has a silver lining"!

I think I will play the Lotto today!


Spy Photos of the Stiletto Workshop

When one sees the fantastic models Mike is able to produce, it is even more amazing to see the workshop that these models come out of. There is hardly a workbench in site. The one table that is there is filled to overflowing with resins, scales, paint, cloth and all sorts of goodies. Most of the work is done on the floor and outside in the garden. The speed and tenacity with which Mike works is mind blowing! Producing a fully moulded model in 5 months is an achievement on its own. But what makes this even more remarkable is the fact that Mike produced the entire thing all on his own. Starting right from the conceptual drawings, then the plugs, then the moulds and finally the finished model . There was no fancy computer aided machining. It was all done by hand. In the face of disaster, he never gave up and simply put that behind him and started over. Most of us would have thrown in the towel and hit the Pub at that point, but not Mike! I take my hat of to you! Well done! You are an inspiration to us all and we now look forward with anticipation to your next project.

Monday, February 26, 2007

Stiletto Extreme

Never a dull moment with Mike. True to his philosophy of "Go Big or Go Home", he has now turned his attention to making the ultimate Cross Country ship in the monster 5,3 meter Stiletto Extreme. By adding another centre wing panel, he is able to create this model with an Aspect Ratio of 23:1 and 120sq dm of wing area. Very clever Sir!

I would love to see this beauty fly!

Stilleto takes to the Air

After Just about 5 months of hard work the Stilleto project came together when it flew for the first time yesterday at the BERG field.
Let me say this is a really good looking and big (3.8 Meters) span thermal glider and the first flights were very, very impressive.
Mike was a happy man and on my way back home I received the a SMS message on my
cell Phone. It read " Be scared very scared".

And the Emoyeni ? , well at least we saw the fuselage yesterday.

Making Horner/winglets for a Zagi

I have decided that my bagged Zagi must have good tip's/ winglets.

So to do this I used block balsa 15mm x 25mm wide and 175mm (tip cord).

On top of this I glued a 12 mm x 8mm x 145 balsa block.(see picture below) and shaped the basic plan form of one tip.

Next I rounded the lower part that will form the bottom part of the tip and glue the upright winglet to it.(1.5 mm balsa) and another 1.5mm piece cross grain to this on the inside .

Now I carve and sanded the tip to shape making sure that it matches the end profile of the wing.

Once satisfied I will glue it to the wing and glass it over with a light cloth for added strength.

Thursday, February 22, 2007

BERG Sub's 2006, 2007

Hi all BERG members,

Our club treasurer has informed me that there are still sub outstanding for last year and this year. If you still want to be a BERG member we have extended the grace period until the end of Feb after which you will have to pay a rejoining fee of R50.00.

BERG banking details:

Bank: Nedbank account no. 2988514461 (savings)
Branch code 19884100
Branch: Krugersdorp ..

When you do a money deposit in to the above account,
please put your surname and initials (in this order) in the reference block and if possible email Charl at your prove of payment.
(This is especially important when it comes to you yearly club fees.)

Thank you for you cooperation.

Piet Rheeders.

Monday, February 19, 2007

Zagi Goes Hi Tech

After cutting my second batch of Zagi foam cores I wanted to bag one for myself using the standard bagging techniques my friend Evan Shaw use.

I have built and bag one Zagi with Evan when he was still resident in Ladybrand and although we use brown paper instead of glass cloth, the end result was a very light and stiff air frame, and the performance a cut above the normal foami /come what ever covering Zagi.

So here are some pictures fresh from the vacuum bag this morning.

The basic construction after foam cores were cut is as follows:
a) The leading edges are reinforced with carbon tows and a thin layer of glass.
b) Carbon tows are wetted out and placed in length wise prepared groves in the wing to form spars top and bottom.
c) 4 x Mylar sheets are cut to size the left and right (top and bottom) are ram waxed and the color scheme spry painted on.
d) After the Mylar’s with the paint on has dried, I laid up one layer of 46-gram glass cloth, and another layer of 106 gram and wet it out.
e) After all the Mylar’s are wetted out, they get placed on the foam cores, and the whole wing is then
placed in the vacuum bag
f) Vacuum is applied and maintained over night.
g) If every thing goes well you can un bag your Zagi wing by the next morning, almost ready to fly
(radio installation and winglets sill to be done).
The Zagi done with this method is not combat legal, it is my goal to see how fast a bagged Zagi
can fly.
The zagi in the pictures shown weighed 430 gram (with out equipment) and I estimate an all up Wight of +/- 600 grams.
If you want to obtain a bagged Zagi or need more info on building your own you can email me

Wednesday, February 14, 2007


Dont fly these planes in a thunder storm the carbon fibre could attract lightning....... no jokes
On a quest to build strong and light, I tried a slightly different lay-up on wing no 2
These photos show the layup of the centre panel which is made up as follows.

Normal herex cut and sanded for sandwich.
1 x layer 49 gram glass cloth not at 45 degrees
1 x carbon cloth 96 gram at 45 degrees
These form the outer skin.
Inside there is 1 x layer 49 gram glass cloth.

the bottom panel has 7 x 60k tows with 4 x full length then spaced 5 x , 6 x and with 7 x across the centre about 40 cm . The top panel has 2 x more tows full length ending with 10 x across the centre 40 cm. Does this make any sense........well yes the top normally fails first as it is under compression on the winch, the bottom needs less tows as it is under tension.

The stepped layers of tows closely follow the curved load on the wing on its bending moment,
ie. greatest in the middle and less towards the tips , put very simply.
Next I have built a sheer web which holds the top and bottom spars together and or apart depending on what load the wing is undergoing.

This sheer web is made of 1 x 6mm balsa strip (normal grain) glued to this is a layer of 4mm
balsa end grain ( verticle) this resists crushing. This strip is sanded to fit between the skins when the moulds are joined, I have now pulled a carbon sock over this sheer web allowing overlap on the ends. The ends are wet out form a bond to the joiner boxes which are epoxy glued in place not with resin but structurel glue.(Sika-dur works fine)

The rear sheer webs for the flaps are made with balsa that has had a layer of 49gr glass bagged on each side and the cut into a strip , these are bonded in place with resin/flocks/microballons
which is "iced" on using the plastic bag as shown before. Dont forget to glue in hard points in this case ply wood for the wing bolts.
The estimated weight of this panel is 700gr about 180gr lighter than my 1st attempt, and considerably stronger, pop it from the mould tommorrow.

Another view of the STILLETO S in production.

Each time I layup a STILLETO there is a bit of an experiment going on so if you can add to this please dont be afraid to post a comment it would be constuctive and welcome.

See Ya Later.

Postals Report and scores - Feb 2007

The weather for both the 4th and 11th of Feb was far form ideal, but a few brave Bergies stuck to our guns and flew both weekends.

First Sunday

Evan became sick with tic-bite-fever the week before and by Saturday we were not sure that he would fly on Sunday. He opted to play it safe and stayed at home.
The wind turned out moderately strong from the West, forcing us to fly from the Eastern boundary of the field. Landings were difficult, coming in over telephone wires and boundary fence.
There was very little lift to be found and even with good launches due to the strong wind, it was more or less a straight glide home and most of us missing the spot all together.

Mike May Ellipse 1 1565
Piet Rheeders Makulu 1514
Peter Joffe Shongololo 943
Gordon Prahm Ava 589

Club score 4022

Second Sunday

Early in the morning we had a strong wind from the South West that must have been the tail end of a cold front passing by. It subside a bit at round about 11.30 and I managed 3 good flights before the wind started to pick up again at about 1.30 and only subsided again at round about 4PM.
Most of us flying this time round mange a fair score except for Evan who had some trim problems after repairs made to his Makulu.

Piet Rheeders Makulu 2073
Mike May Ellipse 1 1835
Evan Shaw Makulu 1267

Club score 5172

Friday, February 09, 2007


The last mould is complete as I write this it is ready to open but as I dont need it until sunday I think Ill wait a little longer, remember epoxy generally takes 7 days for a full cure.

Photo 1 shows the plug being polished(ram release wax) and the edges built up around the splitter board, prior to gel coat, this mould needed 100gr of gel coat per side.

Here I have started glass cloth work again fine weave first, this starts the moment the gel coat has gone hard enough not to fingerprint when touched.

I lay up thick carbon tow 2 x 60k in the corners and the leading edge a bit extravagent normal
glass tows or even a mixture of flocks and resin could be used, the reason for this is the thick cloth wont bend into a 90 degree corner and will make bubbles.

I have marked the centre line in the mould with 1 x plastic tape so that when building and later cutting the tips in half I will have an easy reference. The layups are made with pieces of cloth cut into manageable sizes ,the final thickness is about 4 mm , fairly light but these moulds are not going to produce more than about 20 gliders, I would double that for serious production.

Here I have layed in slices of the remains of a foam wing outers after the cores that were cut with a hot wire, I glass these in and they add strength.

The mould is turned over and the splitter board removed, carefully as you do not wish to release the plug .The bottom of the mould is now made against the first half , again the edges are built up(these made this box shape rigid) release wax polish off and gel coat-glass-etc.

totally aside I have included the photos of the STILLETO production line.

Fuselage 1 yellow purple 410 gr stab 120 gr.
fuselage 2 yellow black red 380gr stab 90 gr

fuselage 3 red yellow 310gr stab 84 gr
moral of the story .........practice makes perfect and the lighter it is the more perfect.
Once again I welcome any comments , the end is in sight.

Wednesday, February 07, 2007


The last posts of the tailplane covered the material preparation and the lay up to vacumn
bag stage, normally I bag overnight and can remove the vacumn the next morning, its good practice to leave the parts in the moulds for at least a day in summer and maybe longer in winter, to totally cure.
This series of photos cover the joining of the halves and the finishing off.

The joiner tube be it carbon, or aluminium for the main joiner is put in place slightly ahead of the centre of lift this keeps the forces nicely balanced and if no slop exists will not induce flutter(the situation where airflow forces create an oscillation around a neutral point or axis).
This should also ideally be between the tows.

I have made a balsa shear web not end grain, but have wrapped the tube in with some carbon tows, this is all tacked in place with cyano, and later painted lightly with resin.
The rear tube is thinner and for this I prefer brass , this thin joiner goes through the belcrank that the servo is going to actuate. The STILLETO design also has a small joiner in front of the tailfin leading edge to reduce twisting and help alignment between the tailplane halves.
Once the sheer webs are in place with the joiner tubes( important to have them all parallel)
we prepare the joining mixture.

Here I have mixed about 10 grams of resin /harderner with about half a teaspoon of cotton flocks(a fine form of shredded fibre glass still providing strength) a teaspoon of micro balloons
which adds volumne and is light but does not add much strength.

The mixture is well stirred and must be ever so slightly runny but not like paste, add micro balloons if required. This is then placed in small plastic bag and the very tip cut off, you now use this to squeeze a thin bead of mixture on the surfaces to be joined.

The moulds are now left overnight to cure , the next move once cured ,is to gently twist the moulds, a distinctive cracking will be heard as the part is released, normally one half will pop off , carefully twist the rest of the mould and the tailplane will come free.

It looks good , lightly sand the flash(excess) off the edges and race to the scale to see what it weighs (90 grams on the dot) it could be slightly better but still beats the 1st one at 120 grams ,
I am pleased ,its in the design weights.

Pretty colour scheme, remember to spray your stripes in the correct order ie outside in.
next post will be more detail on the wing tip mould which is currently curing.

Any comments are welcome as I am fairly new to composites / moulding and learning and teaching at the same time, trying to combine art with science.
So your input is welcome , please post a comment._

Friday, February 02, 2007


Work has taken centre stage so glider is now in the wings (get it) Ha , so we chip away with some of the little pieces in the meantime( it is like eating an elephant, one bite at a time)
I have shown some glass / epoxy layup detail , but this is more about each step , I am trying to achieve strength and weight saving in the stabiliser ,as lead in the nose in a ratio of 3 to 1 is required for balance, and this drives up total flying weight.

Photo 1 shows the waxed moulds, sprayed ready for layup( a recent problem of the stripes peeling off in places) may be overcome by lightly sanding the paint with 400 grit and a good clean up of paint dust. Other builders layup epoxy onto the paint the moment it is touch dry , this also aids adhesion . I dont always have enough time so lay up later. The balsa sandwich is light 1 mm cut to shape with space for carbon tows, the leading and trailing edges are champered with a sanding block , do this on a clean ,flat surface gently, the balsa is fragile.

Next I cut the glass cloth at 45 degrees to shape ,in this tailplane, I have 4 x 49gr layers . 1 X Inner and outer sandwich top and bottom, I also cut the carbon tows and some 96gr carbon cloth, which will strengthen the centre section for joiners.

The cloth and components are weighed and come to 39 gr .I think about 20gr of resin will do , so I mix up 10 gr to start. The resin is painted on in spots, with a smallish brush to hold the cloth in place, then using an old credit card or telephone card this is spread evenly, only adding more resin if areas remain dry(white in colour) at no time should the resin be thick enough to look shiny, any excess can be lightly mopped off with paper towel.

The wood goes on after it has been cleaned of all dust, I then wet out the tows , very little resin is needed, in this case I have 3x 12k tows layed 3 to 2 to 1 to the tips and 1 x tow around the leading edge.
Next the second layer of cloth is added and lightly wet out, total resin 10 gr per side, I mix fresh 10 gr resin and repeat the proceedure in the second side. The mould is now prepared for the vacumn bag , which sucks out all the air , this also pulls resin into and through dry areas and holds everything in place while it cures.

The mould and resin would stick inside the bag so a layer of nylon material called peel ply is placed over the layup, it is porous and will allow excess resin to escape , but once cured will peel off( tip peel back parallel to the surface) .
On top off this comes a release film(pink) it has tiny holes in it and allows air out ,and sits between the bag and the peelply. Clear as mud? no really its not that bad once you've had a bit of practise or been on a building group.

Carefully place in the bag , seal with caulking or tape and, pull some vacumn, then visually check for bubbles, creases etc. release the vacumn , rub out faults , realign if required, then apply vacumn and leave until cured. This tailplane will be joined shortly, and if the tubes and sheer webs can be kept light , will weigh around 80 grams , my 1st attempt was a hefty 120gr.

Maybe next week I get a chance to do the wing tip moulds I will take photos.

They say good things come to he who waits, I just want to fly this creation waiting is hard

Keep you posted, and oh yea you are welcome to post a comment , got a good one the other day
thank you.