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Joined: 7/20/2005 From: Bairnsdale, AUSTRALIA Status: offline
That Macchi looks alot cooler than the 326 - never noticed how podgy the old Roulettes were. Living up the road from Sale means the Roulettes are regulars in our skie which is nice. There's a straight stretch of road south from Sale where, if you're driving your car and there's no "witnesses" around, they take great delight in doing simulated "strafing runs" over you from behind - scared the manure out of me the first time! Also had them fly UNDER me in formation once whilst paragliding...but I digress.
Will be watching your progress with interest. Good to see "Miss Behave" lurking back there too.
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Paragliding? Had my first go at that in NZ recently. Very serene & peaceful. My 'captain' (dual gliding) is an aeromodeller so we had plenty to talk about on the way down. Sometimes when he's taking another modeller along for the ride they take a Zagi RC glider for some formation flying.
As mentioned before my Macchi is a close relative of the Thunderbolt, as is the jet trainer coming up soon!
Miss Behave sends her regards. - John.
< Message edited by Boomerang1 -- 12/25/2007 11:45:55 PM >
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With the top sheeting on part of the box it becomes more rigid so the sides can be pulled in at the nose & formers fitted.
When I build fuselages I put marks on the middle of the formers with a pencil & draw a line down the centre of the building board. If the formers will not be sitting on the board I extend the centre marks down with little balsa tabs like you can see on the front former. When the sides are joined I tape them top & bottom to hold them together while the glue dries, line the lines on the formers up with the centre line on the board & hold them there with bricks. No more banana shaped fuselages!
As this model relys on the wing tube for alignment I block the tube up every time I am working on the fuselage to ensure it all stays square.
< Message edited by Boomerang1 -- 12/26/2007 9:27:45 PM >
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The little tabs sticking out through the top sheeting are to support the rudder & elevator pushrods. The stainless steel ring below supports the outlet of the jetpipe & the back end of the outer pipe. Two small scews will go into the timber blocks to stop the ring sliding through the former. - John.
< Message edited by Boomerang1 -- 12/26/2007 9:30:27 PM >
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I've started on the wings. The first job was to make some sockets for the aluminium wing tube. I began by marking out how long I want the sockets to be on the wing tube. Then I smeared vaseline on the tube & wrapped 2 layers of sandwich plastic around the tube making it longer than where the socket would be starting, applying more vaseline between the first & second layer. The outer surface of the second layer has no vaseline on it.
I then wrapped 2 layers of 4 oz woven mat around the tube, applied polyester resin & then scraped off as much resin as I could.
The first one took some getting off the tube so I applied more vaseline to the second socket layup. Once it was sanded smooth on the outside I pulled out the plastic wrap, cleaned the inside out with acetone & sanded it inside with a dowel with a square of sandpaper taped to it in the electric drill. The result is below, a perfect sliding fit and it weighs about 1/2 oz.
There is also a short piece that goes through the fuselage. This will help spread the load of the wing tube & make it easier to slide through. This one's not quite set yet but I can tell already it will be easy to remove from the wing tube. - John.
< Message edited by Boomerang1 -- 12/28/2007 12:30:43 AM >
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Wing ribs are now cut except for the plywood ones (run out of wood) and the tailplane is started. I was not sure of the spar positions so I will cut them to suit later when I'm ready to fit them. The elevators have seperate mass & aerodynamic balances. Retracts are on the way, Robart 630 heavy duty jobbies with a 95 degree retract angle. The Macchi main gear retracts outwards like a Spitfire or ME 109 so the greater angle is needed so the gear can follow the extra angle of the dihedral. - John.
< Message edited by Boomerang1 -- 12/28/2007 12:36:20 AM >
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Almost time for the Macchi to go back on the front burner! The trainer has flown & is a nice stable flyer! This is very encouraging as the Macchi uses the same wing section, tail section, about the same moments, rigging angles, is about the same size and should be quite a bit lighter. Really, it's just another Thunderbolt variant but scaled up quite a bit. It's 2.1 metres span, 2.2 metres long & weighs 9.5 kg. It's amazing how well the tiny engine pushes this thing along, top speed was radar timed at 175 km/h in level flight & it will easily break the 200 mark in a gentle dive. Only have to paint this one & it's back on the board. - John.
< Message edited by Boomerang1 -- 12/28/2007 12:44:34 AM >
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The trainer is painted & Macchi is go again! I'm glad I built the trainer as it has made obvious a few shortcomings I have made with the Macchi due to my inexperience with turbines. Mods to make from the original design are:
The turbine manufacturer, Wren, now recommends a larger distance from the engine nozzle to the jet pipe, this will be moved back.
The air tank for the Robart 630 units is too big, I'll fit a smaller tank in each wing.
After a small fire on the trainer (no damage at all, just some pooled fuel ignighting) I'm going to fit a top engine hatch to keep an eye on the engine at start up & provide better access for a fire extinguisher. I'll line the rear fuselage with aluminium tape and leave the start gas tank out to save some weight and eliminate one more thing that can explode!
The engine now has an intake screen fitted so these can be left off the airframe.
Even at 21 pounds + fuel with full flap the model slows down enough to land on our club strip so I can leave off the belly mounted air brake.
The manufacturer of my turbine (Wren) have informed me that a stronger jet pipe for my model engine, the Supersport, is now recommended following a couple of failures of the standard pipe with this more powerful engine.
I now have a new pipe & am fitting it to the model, this was originally a difficult job so thankfully the new pipe is almost the same. The manufacturer of the pipe has also suggested it be relocated rearwards 20 mm. I'll machine up some spacers rather than move the former. The pipe & the outer pipe will have to be trimmed 20 mm at the other end.
Fin & rudder are under construction, the two fin spars sticking out of the fuselage were wrong & had to be modified, D'OH! - John.
< Message edited by Boomerang1 -- 12/28/2007 12:50:10 AM >
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I've reached the point where the old thread is finished & the RCU thread begins in 'real time'. The trainer is racking up the hours & flys great.
The Macchi fin is half built, new pipe installed, rear fuselage lined with fire resistant aluminium tape & fully sheeted. I have also fitted the nosewheel retract & sorted out the mounting, the original formers (spaced for Rhom Air units) were wrong of course & had to be moved/modified. The nosewheel will not retract forwards like the full size but backwards. Much more room & much simpler steering linkages are the reasons. - John.
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Views of the work done since the last post. The fin is now fully sheeted, once the tip is added I can sort the hinging, counterbalance & shrouds & it will be put aside while the wings are built. - John.
< Message edited by Boomerang1 -- 1/12/2008 6:07:22 AM >
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Thread back from the dead!
I bought an damaged ARF Bobcat 50 with 2 turbines at a bargain price & have been working on that for a couple of months.
Now it's flying & only needs paint I'm back on the Macchi.
Now, where was I up to....................
One thing that's come to light is that the Bobcat is a slippery little sucker & was difficult to slow down until I fitted an airbrake. The Macchi has a belly mounted airbrake & I was not going to make it functional so I'll have to have a rethink.
It would be far easier to fit one at the start & fasten it shut if not needed than it would be to leave it off & hack into the model & fit one later if I do need it.
John.
< Message edited by Boomerang1 -- 8/17/2008 5:07:30 AM >
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All Forums >> RC Airplanes >> RC Scale Aircraft >> RE: Aermacchi 339 build thread. 
RE: Aermacchi 339 build thread. - 
