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Tuesday, April 29, 2008

Ventus no4 ZS-SWT

So much for recycling..... Ventus no 4 contains the following recycled parts, from no 3
Carbon fibre canopy
Carbon fibre wing joiner (survived a full tilt impact )
And no small amount of knowledge other than that, this is a totally new aircraft, the recycled parts are probably 3 days worth of work to build.
Because this was a quick build project I needed to try new ideas , one shown above was the wing wiring. Because the HQ/3/12 is fairly thick I decided to wire the wing servos as follows, I cut out the flap and the aileron , then routed a grove into the foam with my Dremel tool , the servo wire was fitted into this slot and then a piece of balsa strip pushed into place to cover it, finally a mix of resin/flox and micro/balloons sealed everything into place it worked well.
While the wing was completed with its wiring , I next routed out a hollow where the control horns attach and made up a plywood tongue, this was bonded in with the same mix and provides a strong point to bolt onto, you can see I have sanded this back down to shape. Note also the ply blocks for the servo in the servo bay epoxied to the top and bottom carbon spar and skins.

Having learnt a valuable lesson with tailplane/elevator linkages, this time I am going for direct drive from a servo mounted in the fin, nothing to bind or snag and easy to adjust.

Attention to detail is important because this fuselage has carbon tows, the arial for the receiver is routed in a plastic tube down the fuselage away fron the tows, visible behind the rudder servo which is now pull/pull with steel cable no more pushrods. A thick wooden dowel forms a compresion strut between the wing leading edges and it is this that probably saved the wing joiner last time.

There she is.. I managed to save about 1.2kg on the last one and with a thicker wing she should fly at a lower speed which should make launches a little easier.
This glider was build in under 2 weeks and is the best one yet in terms of finish, good planning and project management aid in getting such results.
So for those slow coaches out there you have more than enough time to prepare for next years Sungazer.
Cheers for Now

New Emoyeni takes to the Sky

Evan's new 3,7 Takes to the air on its maiden flight.

The Berg field yesterday bussed with activity as pilots for the upcoming nats this weekend did their practice roundup. Many new planes were observed including our new local challenger Evan's 3.7 Meter Emoyeni.
The first flights even in strong wind look very promising. The Berg Team will be represented by Evan, Piet and Derek

Friday, April 25, 2008

Ventus no4

The progress on Ventus no 4 has been rapid to say the least, this has been one of those projects were everything has just gone smoothly(or is it practice).
In the photo below the servo tray has been bonded in and below it you can see a strip of 200gr carbon cloth which ties the two sides together and stiffens the belly which takes strain in the landings.The forward cut out is for a tow release servo , aerotowing being a new field for me altogether but worth a try later in the year.
In the photo below you see the blue foam cores being prepared , A tip here is to mask up the grove on one side and place your straight edge on the masking tape, once the grove is correct(ie, wider or deeper at the root to accept more carbon tows) Then you mask the other edge, wet out the tows and layup the spar being carefull not to get any resin on the cores, normally these drips get wiped but leave hard areas which show up on the bagged wing. Now once the wet tows are all in, use a plastic card to flatten them but screeding across the masking tape , once happy remove the masking tape and leave to cure. If you grove is slightly hollow/deep you can fill with a mix of resin and balloons and again screed to get a level finish.

This photo shows the fuselage being modified for the thicker airfoil , you can see the infill on the wing shoulder, this was done by cutting two balsa root ribs , sanding the area and then gluing them onto the fuselage, I then filled the contour with a mix of resin / balloons /and flox finally sanding to shape and then respray with 2k.

Boxing smart not hard, the end ribs (ply-wood)are cut to size, bonded on and then sanded to match the cores, I normally glue them on afterwards but this is better as it will now have glass across the join, lighter and stronger.
The leading edge is strengthened with 3 x 12 k carbon tows and smoothed prior to vacumn bagging on the skins, which are 1 x 104gr and 2 x 163 at 45 degress I use Epolam resin system on the wings. As I post this the wings have already been bagged with no problems and appear to be in the weight region of 2000grams, but need final cleaning up and control surface cutting, this is about 500 grams per wing lighter than no 3 but they feel as rigid, this may also be due to the thicker foil section.
I will post the final pictures of this build early next week.
What next? It has to be a built up vintage glider after seeing these at the Sungazer,
I have already picked a subject and need to get some drawings and rediscover the smell of balsa-wood and white glue.
Cheers for now.

Monday, April 21, 2008

20,000 and counting

The B.E.R.G. blog has reached 20,000 hits recently, and the build up to and article on the Sungazer Scale gliding event drew a very wide audience.
Most interesting is that only about 1 in 5 visitors , were from South Africa ,the balance all overseas visitors from countries including the U.S.A., Canada,U.K. Germany ,France, Portugal, Italy , France , Brasil, Columbia , Croatia, Turkey, Singapore, Uganda, Australia and even Iceland .
The internet truly exposes our local activities to a wide and very interested number of r/c gliding aeromodellers.
Hopefully some of our inactive contributors can once again become active...nudge,nudge, wink,wink.

Air Crash Investigation

Well the loss of my Ventus at the Sungazer raised plenty of questions , most prominent being what went wrong , followed by could I have done anything differently and finally what has been learnt by this accident.

My flight started with the usual checks, including the correct radio program and movement on all the surfaces, I asked Charl when he launched to really push out and slightly nose down(did not wish to have a missfire like Peter). The Ventus went off well and accelerated at quite a dive I let it build speed and then eased in some up, there was very little response , I pulled full up and the glider went into a verticle climb, I adjusted the trim(normally 3 clicks would put it into level flight). It stalled ... my brain working overtime to establish the problem, had the nose weight shifted? something broken? she started downwards gaining speed , only full up brought it back into a verticle climb and a second stall.

This was becoming a roler coaster ride and I wanted off, third stall and dive and it went into the hill with a thud.

I asked the guys who went to collect the pieces to bring everything back and already started trying to understand what had happened, this glider had flown 3 times before , two flights of about 45 mins , had been pushed a little (recorded a speed of 189km on the logger)and flew well, so what happened.

The weights were checked ,I sometimes fly a five cell battery pack , the weight is marked as such, but I then substitute a sinker of a similar weight if I fly with a four cell pack. Both correct weights in and judging by how they got bent still attached at impact, so weight had not shifted.

Paul Carnell made a comment" looks like your elevator may have been jammed".

This is what it felt like but I still had full up and full down movement. When I studied the elevator linkage things fell into place. The silicon keeper which holds the clevis in place was possibly binding on the cutout.

Sure enough when I checked it, it was torn , it was ok before the flight , so why had I not picked up this problem, one explaination is that I move the sticks full travel when testing and it was sticking/binding in the midrange and locking on top or underneath the cut out.The long pushrod linkages taking up the stain before pushing past the sticking point. I like this theory and will put down the loss of this plane to a small piece of silicon. (Sorry about the photo quality but you get the picture)

Now with all the pieces I had a good look at what failed and how, it verifies your construction techniques, I dont build using a computer and theoretical loads. I build and add a safety margin
on experience and gut feel. Here below is a test of the wing inner panel in this photo the weight(me 80kg) this panel only has one side of carbon tows and the sheer web , no skins, it bends but did not break , so with both sides and skins it is well........over engineered by a fair margin.

I feel that I could do well to build these gliders lighter, but still strong so I started with Ventus no 4, this is to be based on the HQ/ 3/12 airfoil much used on scale ships as opposed to the slippery Mh 32 and Sd 7037 used previousely . So far I have saved 700 grams on the fuselage 100 grams by going the balsa foam route on the tailplane, this equates to a saving of 300 grams in the nose, and it looks like I will get a saving of 1000gram on the pair of wings by carefull layup and choice of materials.
Ventus no 4 will fly soon and if it can have an all up weight of 7kgs it will be a winner
Ventus no 3 ZS-VCX weighed in at 8.7kg A.u.w.
It flies next weekend weather permitting, I just have to get back on the horse after the fall.

Thursday, April 17, 2008

Sungazer 2008 Report & Pics - Sunday 13th April

Mist on the slope from the cosmos fieldsSunday morning started off overcast and misty. Before Oom Louis wonderful breakfast spread, Martie and I took a walk out into the fields. Cosmos was abundant and very pretty: above a shot of the south slope from the farm.

Mist on top of the slope
After breakfast everyone packed bags and models and headed up the slope to wait for the mist to clear. Some lesser type aircraft were periodically launched into the mist to test conditions and it wasn't long before the visibility was good enough to fly.

Unfortunately the wind was not quite strong enough for the heavier scale models but Chris demonstrated some really smooth and graceful flying in the light conditions.

Above, Chris flying, his landing approach and where the model came to rest after the slide! I'm not too sure of the model he was flying there, but he has a full set of moulds for this one and it is a very impressive flyer.
Ken and Chris working light lift on the south slope
ASH26V flypast

Above, the ASH26V of Ken Kearns and Chris's scale model cruising the slope in the light and misty conditions.

Left, Ken's ASH26V was very light: fibreglass fuselage and open structure wings. Ken again got the most airtime with his ASH26V and Slingsby models, often handing the transmitter over to other pilots while he either took a break or went off to prepare one of his other models for flying.

Below, Ken readying his ASH26V and posing with the Skylark.

Ken Kearns ASH26VKen Kearns Slingsby
Andries Videoshoot
Above, Ken flying, Andries taking videos of a close flyby. Below, Craig Baker getting ready to launch Johan Bruwer's ASW28 and Ken Kearns putting just a wee bit of electric power on for a safe single handed launch.

Craig ready to launch Johan Bruwer's ASW28Ken Kearns launching his Skylark

Below very cute sequence of young Jason Weber launching his model.

... and that's all for this year, folks. I bet everyone is already looking forward to Sungazer 2009, but now got to get back into the workshop to get some models prepared for the Nationals.

Tuesday, April 15, 2008

Sungazer Photos/Report another view

The 2008 Sungazer met all the goals set, other than one minor incedent it went off as advertised, .......perfect. The conditions on friday were absolutely calm with smoke nearby rising vertically, and predictions were for the less favourable south slope.
Friday saw Charl and I decide to clear all the bushes on the north and south slopes after the farmer gave us the go ahead(the chainsaw is the way to go). Friday night, no saterday early morning 03.00hrs the windows started banging from a gust of wind... our prayer blew for 5 minutes and stopped, I lay awake waiting its return ,nada.
What to do all day with 25 fanatics, well there was always the beer and food to calm the masses if there was to be no flying.
Saterday the pilots briefing got underway on the south slope ,but the wind just kept comming from the north west, stronger and stronger. Formalities over we all moved and then started what was to be the best scale slope event most had ever been to.
Stunning gliders, excellent flying, new friendships made, we estimated that at least 50 scale gliders were present , some hidden away and others not unpacked, probably the biggest collection ever in South African scale gliding history.
Unfortunately a few casualties ,either through nerves, or equipment failures about 6 aircraft crashed but all were well away from the pilots and spectator area.
These pilots (hmmm myself included) all received the Captain Chaos Awards at the evening braai, these were epoxy resin and glue as well as carbon tows and glass cloth, kindly sponsered by A.M.T. the supplier of the composite materials used in the construction of our models, this was organised by Paul Carnell the now famous Fox pilot.

All the pilots are wearing standard issue Sungazer headgear it would look like a field of daisies from outer space.
Not Barbie but Ken Jnr. readying his nerve for his first flight off the Tamatieberg southside.

Ken Jnr is all safely strapped into his SKYLARK 1.

Ken Kearns readies his superb Minimoa scratch built and nicely detailed.....unfortunately he is quickly surrounded by the modelling "paparazzi".

Chris Adrian built this tiny scale trainer glider used in the early days for short flights or more accurately "hops" Chris was telling us these flights were measured in seconds and recorded in the log books as such .. imagine flight times of 5 seconds then building up to 11seconds.

It is a ZOEGLING SG-35/38 (I think)and it flew...... also short flights.
Sunday saw a southerly wind blowing through but at start time the slope was still in the morning mist. Marginal winds meant only a few with faith ,dared fly as thermal activity was light and recovery from way down the slope was always going to be a risk.

The picture above shows Chris on finals landing in what can only be described as tight and challenging landing zone.

All in all this was a great event bringing a group of R/C glider pilots together in a beautifull
setting at Volksrust . May some of that inspiration that I experienced there 2 years ago , have rubbed off on others ,who will also now want to be a part of this magical pursuit.

The Sungazer team.