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Author Topic: Macchi M5 (Co2 powered)  (Read 568 times)
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Radek J
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« on: June 06, 2022, 01:47:50 AM »

Hi.

I'm new here. After visiting the site now an then for a few years and watching the fantastic builds here,  I took a deep breath and ordered some balsa myself. Previous experience being the usual 'used to build them comet and guillows kits as a kid' -40 years ago. So basically have very little of an idea of what I'm doing. However, with age you get to know yourself better. So this build will most definitely be a slow one, it might not ever get finished either, but it will be a good learning experience full of mistakes and wrong turns. By sharing, hopefully someone else can also learn from those Smiley

-radek


« Last Edit: June 06, 2022, 02:09:14 AM by Radek J » Logged
Radek J
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« Reply #1 on: June 06, 2022, 01:57:13 AM »

Found some Keith spark drawings online. Not sure how Keith Sparks feels about his plans floating around online so I've sent him an email asking if I can pay for myself borrowing like this.

Resized the plans to 1/14 scale (85cm span) and started building a stab/fin. 3 grams for those and another gram for the bottom pylon. 4 in total.
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Radek J
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« Reply #2 on: June 06, 2022, 02:03:54 AM »

A g300 gasparin engine arrived.

Instructions for it state a maximum model weight of 140 grams, the engine being 30g itself. Might have to revert back to electric if I cross those 140 grams too much.

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Radek J
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« Reply #3 on: June 06, 2022, 02:05:45 AM »

And, with the tail framed up I made a start on the boat. So far, a very enjoyable build.
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Prosper
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« Reply #4 on: June 06, 2022, 03:56:42 AM »

Welcome Radek,  and good luck with your interesting project.

Stephen.
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DHnut
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« Reply #5 on: June 06, 2022, 06:38:19 AM »

Hello Radek,
                 The GM300 should fly that with ease but watch out for the need of upthrust for the Macchi with the high set motor.

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skycafe
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« Reply #6 on: June 06, 2022, 08:51:38 AM »

Cool project!

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Radek J
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« Reply #7 on: June 07, 2022, 03:30:09 AM »

Thank you all!

Dhnut. You have experience with this engine? I'm trying to weigh everything and keep it all to a minimum but without experience it's just guesswork really. For instance as to how thick of a trailing edge I need for the covering not to warp it. Or how much weight the 'lightweight' polyester tissue I'll be using is after a few coats of dope and some paint. Hoping for the best though.

Regarding thrust line. I'm actually aware of that after reading build threads on the dare kit and keith Sparks larger version. Been eyeing the lake buccaneer thrustline also. But thanks for the heads up!


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USch
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« Reply #8 on: June 07, 2022, 04:20:24 AM »

... For instance as to how thick of a trailing edge I need for the covering not to warp it.

...Or how much weight the 'lightweight' polyester tissue I'll be using is after a few coats of dope and some paint.

For a balsa trailing edge, I would not go under 0,8-1,0mm to be on the safe side. On later models you may decide to go thinner, using jap like Esaki for covering.

About covering weights a table I found years ago somewhere, it does not cover all possible coverings but will give you an idea. The second pic is a conversion table from myself as I am not used to oz, sq. in, sq. ft ecc. Notice that the white jap with butyrate bears some hidden error.

Urs
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DHnut
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« Reply #9 on: June 07, 2022, 05:01:52 AM »

Radek,
         I have an interest in CO2 and have built a numbe rof models powered by Telco, Brown and Gasparin motors. A 650 mm span Comper Swift weighing 90 gm powered by a G160 Gasparin flies that well and on a small tank will do inexcess of 35 sec. It is probably the upper limit. I also have a similar Comper Swift powered by a GM120 and that is a bit marginal. A friend has a Piper Super Cruiser that is GM300 pwered and that will do over a minute. Span is in the region of 750 mm and weight unknown. Pleased you are aware of the upthrust factor, it can be a bit of a trap.
Ricky 
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Radek J
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« Reply #10 on: June 18, 2022, 05:22:46 AM »

Baby steps.

I cut out the fuselage sides from 1mm balsa. Strengthened the wing/motorpylon attachment area with some 0.4mm plywood and sanded the edges on those for smoother transitions

Proceeded with making fuselage formers after spending some time in photoshop checking the shape and angle of those for errors. Looks like a basic box fuselage but has few straight lines or angles. Then with the help of my rudimentary fuselage jig (a 6mm balsasheet with a center line drawn along the length of it. Visible in picture 1) I glued it all up as straight and true as I could. Looks alright. 15.2 grams as it is right now. Heavy, but lots of balsa there. Once planked and I get a feel for how rigid it is by then, might start carefully thinning the balsa a tad.

So,, deck and bottom planking next. That will be interesting Grin


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« Last Edit: June 18, 2022, 06:52:46 AM by Radek J » Logged
Radek J
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« Reply #11 on: June 18, 2022, 06:01:08 AM »

USch thank for sharing that table! Find the weights a rather usefull eyeopener, dope and laquers adding considerably much to the total. I received the ’lightweight poyester” I had intended to cover it in but the weave just had too many open pores that would allow water in in the case of a ”wingtip gently catching a wave” i.e., me landing at a 45 degree descent. So ordered som litespan, some airspan and some mylar&esaki to fall back on in case I don’t like the other stuff.

Ricky thank for sharing that. Very encouraging hearing your thoughts on it as I doubt I can get close to the recommended model weight of 140g rtf. The macchi m5 has lot’s if wingarea though and I don’t mind underpowered but would love it if it could manage a water take off.
« Last Edit: June 18, 2022, 07:35:57 AM by Radek J » Logged
g_kandylakis
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« Reply #12 on: June 18, 2022, 10:25:07 AM »

looks like a verly clean job!

looking forward to the rest...

George
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ironmike
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« Reply #13 on: June 18, 2022, 10:25:34 AM »

Watching Keith Sparks fly his Macchi on water it required the e powered system power
to break the surface tension to ROW.
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TimWescott
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« Reply #14 on: June 18, 2022, 12:42:05 PM »

... and some mylar&esaki to fall back on in case I don’t like the other stuff. ...

Esaki tissue is, in my experience, very different from all the other tissues I've sourced here in America over the years.  Basically, it's a much tighter grain -- which means it needs much less dope to seal.  I've never done the tissue & mylar thing, so depend on others for suggestions there, but that size plane is about as big as I'd go for just covering with Esaki.  It'll cover it, it'll fly nice, but it'll be just a bit fragile if you land in grass or whatever.
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Radek J
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« Reply #15 on: July 04, 2022, 04:44:03 AM »

Bit more progress and managed the bottom planking.

The shape of the Macchi hull.. Going from regular v-bottom to a concave section at the end of the 'step' - I just couldn't figure out how to orient the grain. In the end decided for this hybrid solution and think it turned out ok. The tail section behind the step is slightly convex and I strip planked that (4x1 mm strips). The convex:ity of this section really contributed to the torsional strength of the fuselage. Also, added some diagonal stringers in the cockpit area for a more scale look.

Next step will be top formers and top planking. Haven't hollowed out the nose balsa block yet but weight of the fuselage krept up to 25grams at this tage. With tail surfaces, an all up weight of 29.9 grams.

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« Last Edit: July 04, 2022, 05:06:12 AM by Radek J » Logged
Radek J
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« Reply #16 on: July 04, 2022, 05:59:05 AM »

Watching Keith Sparks fly his Macchi on water it required the e powered system power
to break the surface tension to ROW.

Ironmike are you saying he too was on co2 power at first? I myself doubt it will ROW but really want to give it a try. Converting it to electric will be rather straight forward, routing the battery wires through the cabanes the complicated part. Would likely save some weight also but just lacks that co2 puttering.

... and some mylar&esaki to fall back on in case I don’t like the other stuff. ...

Esaki tissue is, in my experience, very different from all the other tissues I've sourced here in America over the years.  Basically, it's a much tighter grain -- which means it needs much less dope to seal.  I've never done the tissue & mylar thing, so depend on others for suggestions there, but that size plane is about as big as I'd go for just covering with Esaki.  It'll cover it, it'll fly nice, but it'll be just a bit fragile if you land in grass or whatever.

Thank you for the advice Tim. Received all the covering materials and after examining decided to first give the litespan a try for all open structure. The fuselage, doped esaki though.
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ironmike
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« Reply #17 on: July 04, 2022, 01:07:29 PM »

Nah he went right to RC electric.
He started out ROG, as in rise off short grass, The RC
short grass runway easier than water.
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