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Acro Magnum Reloaded

Old 10-15-2014, 05:36 AM
  #1  
rtfm
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Default Acro Magnum Reloaded

Hi,
Despite the Magnum Reloaded having become a cult plane in Europe (mainly in Germany), and the fact that it has spawned the "Acro" version, produced in great numbers by a number of manufacturers over there, a Google search will turn up only the barest of references in non-European RC forums.

I hope to change this.

The plane is amazingly easy to build, and almost ANYONE can fly it. It is, I think, the best all round (meaning: slow flyer, circuit flyer, and right up to 3D flyer) aircraft currently available. Best of all, it costs very little, and has an amazingly rich forum presence (you've got to use the German forums, and ask Google to translate for you).

I have recently received my Acro Magnum from the US, ex Germany. And despite having travelled more than half way round the world to get here, it STILL only cost me under $50

My plan is to document my build here, with plenty of pictures. Keep in mind, however, that I can't fly. I'm a complete newbie. So when you see me maiden it, it'll be as a complete novice, with only some simulator time.

Here are some photos of the Acro Magnum to enjoy in the meantime.

Regards,
Duncan
https://www.google.com.au/search?q=a...e%3B762%3B1024
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Old 10-15-2014, 05:54 AM
  #2  
CHELLIE
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Hi Duncan does the pretty blond come with the Plane, I need to get my youngest son married off and out of the house but i will keep the Plane for myself LOL

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Old 10-15-2014, 05:57 AM
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Ha ha. Nice one. But I was hoping to keep her for myself...

Duncan
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Old 10-15-2014, 04:34 PM
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Duncan

Subscribed.
Looking forward to your endeavor.
Good luck!

Regards
Jimmy
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Old 10-15-2014, 05:51 PM
  #5  
Wildflyer
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Both models look very good.

What is the construction of the plane, it looks like EPP foam.
Is the wing airfoiled? There seems to be a carbon fiber spar in top, probably bottom also, is this accurate?

Could you give us the measurements ? (just the plane) we have to stay focused.
What size motor ?
Sorry for all the questions, I have a flying field very close to my house for that size of plane. one last one, Where did you buy it.

Thank you
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Old 10-15-2014, 05:53 PM
  #6  
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I like that plane alot......followed builds at RCG, so many options.

Here's a link I found most usefull....no sound or comments, but awesome step-by step.....Don't have one yet, but it's an itch I'll need to scratch for sure....:

[media]http://vimeo.com/64267999[/media]
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Old 10-15-2014, 10:50 PM
  #7  
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Originally Posted by Wildflyer View Post
Both models look very good.
:-)

What is the construction of the plane, it looks like EPP foam.
Is the wing airfoiled? There seems to be a carbon fiber spar in top, probably bottom also, is this accurate?
Yes, EPP. The wing has a symmetrical airfoil. Looks like one of the NACA variants (possibly NACA 0010). The wing doesn't come with any CF spar, but CF rods/strips are provided. As a full-scale aircraft designer/builder I have always thought that the common RC practice of inserting a single beefy (ie heavy) CF rod down the centre of the wing panels is a relative waste of time. For a really rigid wing, one MUST bond in a CF rod on both sides of the wing. So I simply cut a slit (top and bottom) at the 25% chord line, and slipped in a 3mm x .5mm CF strip. Then ran some thin CA onto the slit. It wicks down into the groove really well, and when both strips have been bonded on place, the wing is as stiff as a piece of wood.

Could you give us the measurements ? (just the plane) we have to stay focused.
ha ha. I'll do so today and post all vital statistics this evening, if that's OK.

What size motor ?
Well, it all depends on the type of flying you want to do. I intend progressing from almost instant crashes all the way to 3D, so I need something which will enable vertical flight. The plane (without hardware - ie foam and CF spars) weighs 165g. Add to that the weight of the ESC (10A Turnigy Plush), battery (2S, 450mAh) and HXT500 servos (x4). And of course, the servo control rods. That will give you the all up weight minus the motor. I have two candidates, and a number of prop choices in the workshop. I'll try both by powering up, and holding the plane vertical. And then see which motor/prop combination will tug the play vertical under full power. My two motors are both E-Flite. Park 300 and Park 370. I suspect the Park 370 will end up the clear winner, simply because it weighs almost the same as its smaller brother. But I'll report on this when I get there.

Sorry for all the questions, I have a flying field very close to my house for that size of plane. one last one, Where did you buy it.
I got mine from wmparkflyers.com Great people to deal with, and they have both variants in stock (ie the Magnum reloaded (3-channel) and the Acro version (4-channel)). I plan to start building them here in Australia for local guys. I have some modifications I'd like to try first though. Besides, local guys won't want to wait the 4 weeks it took for the model to arrive from the US.

Happy flying,
Duncan
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Old 10-16-2014, 03:58 AM
  #8  
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HI,
Back from the workshop, and here are some build photos. The fuse is 600mm long, and it has a wingspan of 820mm (including the wing tips). Haven't done the thrust test yet.

Regards,
Duncan
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Old 10-16-2014, 04:07 AM
  #9  
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Next, the wing.

I simply cut a slit along the 80mm (back from the LE) line, and slipped a 3mm x .5mm CF strip into it. Then I did the opposite side. Then I added some thin CA into the cut. It disappears immediately, creating a no-nonsense bond between the CF strip and the foam. The wing can easily handle a 2kg load almost without bending, which is about 8G. It could probably take double that before failing.

Here's what it looks like...
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Last edited by rtfm; 10-16-2014 at 07:11 AM.
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Old 10-16-2014, 04:12 AM
  #10  
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The wing is bonded to a removable part of the fuse. This allows the wing to fit snugly to the fuse with rubber bands. You could use magnets, too, if you wished.
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Old 10-16-2014, 04:19 AM
  #11  
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Finally, the undercarriage.
First, each u/carriage piece (ie left and right) comes as three pieces, which have to be gliued together like a sandwich. The reason for this is because the middle piece is cut away to accommodate a wheel (supplied). Couldn't be simpler.

The recommended glue is Foam-Tac, but from personal experience, UHU Por is indistinguishable. In fact, and foam safe contact adhesive would do just as well. Check out your local hardware store or art supplies shop and buy something local (at a fraction of the rather steep cost).

I stiffened the gear with a 3mm x .5mm CF strip on either side.

The rectangular cutout is for the aileron servos (HXT500) This makes for a very short (ie light and rigid) control rod.

Next, gluing the undercarriage to the wing, attaching the tail feathers, attaching the motor and the electrics.

Cheers,
Duncan

Regards,
Duncan
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Old 10-16-2014, 05:47 AM
  #12  
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Very interesting, I haven't seen full solid color EPP foam before. You could smooth the wings with some sharp sandpaper without going through the paint job like I have done in the past, if the wings needed it. I have an EPP plane that if you go below 100 watts it wants to stop in midair. The wings are very rough.

I have done the embedded CF strip before, in EPP and styrofoam, it really adds strength with out much weight.

I fully agree with you about a centered spar being less useful than 2 spaced spars even though the 2 may be smaller than the 1 centered spar.
That is the same logic as an I beam steel or a TJI floor joist.

What type of full scale planes do you design and or build?
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Old 10-16-2014, 06:03 AM
  #13  
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Hi,
Strangely enough, while it is called EPP, it certainly isn't what I have come to know as Expanded Polypropylene. It looks like, feels like and behaves like polystyrene. EPP has a waxy feel to it, and one can drive a car over it without worry.

But it is called EPP by the community, so I guess I'l just give in and go with the flow.

Sanding it is problematic. It doesn't like to be sanded. Someone on another forum suggested covering the foam with a wax paper, and ironing it (200 deg I think was mentioned). This smooths the surface. Haven't tried it yet, but I'll do a few experiments on some offcuts. I'll have to pinch the wife's iron for a bit.

The nice thing about the Magnum is that it is not supposed to be quick - so I guess a rough wing surface is OK. Won't know till I've tried it, though...

I do sexy little single seaters. Composite. In fact, the reason I'm getting into RC is because I want to try out my latest design in scale. I'd rather crash and burn a model than have my bum sitting in the seat when it all goes wrong...

http://rtfmaero.wordpress.com/

Regards,
Duncan

Last edited by rtfm; 10-16-2014 at 07:14 AM.
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Old 10-22-2014, 03:10 AM
  #14  
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Quick update on ironing EPP:
It works beautifully. I grabbed my wife's iron, set it to somewhere in the middle (half way between "silk" and "wool"), placed some tin foil (shiny side down) on the wing surface and ironed it a few times back and forth. The tin foil came off leaving a mirror-finish on the foam. Brilliant.

I also glued the aileron servos to the undercarriage, glued the undercarriage onto the wings (used Foam-Tac for both), and routed the aileron servo wires along the bottom of the wing and up through a little hole next to the fuse.. These go into the Rx which I've placed just in front of the little windshield. The standard HXT900 servo wires fit perfectly. The elevator and rudder servos are also bonded in place, and the engine is mounted.

Looking good so far. Still to do: servo linkages, and then check servo centering etc.

Duncan
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Last edited by rtfm; 10-22-2014 at 05:39 AM.
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Old 10-22-2014, 07:05 AM
  #15  
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Thanks for the tip about ironing with tin-foil.

I will have to try it.
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Old 10-22-2014, 08:45 AM
  #16  
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Lest I cause you to melt your wing - please experiment on some scrap first...

Duncan
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Old 11-19-2014, 10:03 AM
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Hi again,
Sorry for the long period between posts, buy I'm back to report on progress.

Power woes:
My first attempt with the Magnum wasn't that successful. Suffice to say, my Turnigy 2204-14T (19g) motor was underpowered, and my inexpert attempts at hand launching (full throttle) saw repeated nose-dives into the grass.

My second motor (Turnigy 2836) which I happened to have in my toolbox, was WAY overpowered, and this time the plane took off like a rocket, I over-controlled it managed to dig quite a nice hole in the turf, break the prop and that was that.

My third motor (I had to go out and buy this one) is a Turnigy D2822/14 which has been widely recommended as a "perfect" motor for the Reaktor (about the same weight and same mission as the Magnum). But I now need to get another prop. My existing 8x4 props won't fit on the prop shaft, so I either get a prop which will fit, or I ream out the prop to make it fit. Either way, I have to return to the LHS.

So my progress has been short, sharp and spectacular.

However, since the weather has been lousy, I've been spending some considerable time at the CAD screen working on what will be "my" version of the Magnum. It consists of a 3mm plywood "strongback" which runs down the centre of the fuse, and to which a sheet of 10mm EPP is bonded to either side. To this sandwich, two additional pieces of EPP are bonded, giving the fuse a distinctly three-D look, plus providing internal space for storing the battery, ESC and receiver. I'm having to get the plywood laser cut, but this should arrive shortly. It follows the external shape of the plane, with most of the internal area cut away to save weight. For receiver I'll be using the FrSky micro 5 channel (only 2g in weight). The aim is to produce a really light yet strong Magnum. We'll see... If things work out OK, I might even be able to use the original Turnigy 2204 motor.

Until then, happy flying.

Duncan
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Old 11-27-2014, 02:07 AM
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Default Maiden flight

HI,
Well, today I took the little Magnum down to the flying field, and got one of the guys to take it for its maiden flight. She flew beautifully, and he commented that it flew straight and true, required very little trimming, and did loops and rolls effortlessly. It was a bit breezy, but the Magnum didn't seem to mind.

So I'm chuffed.

At 395g all-up (with a Zippy 800MaH battery) it gets airborne in less than 10ft, and stays aloft for just over 8 minutes. Landing was very docile and slow. I couldn't be more pleased. My test pilot suggested I come and join them at their indoor flying venue, because it flies so slowly and with such good manners it would fit right in. Seems I got the motor just right third time round...

My next step is to learn to fly it myself.

Vodeos as soon as I can get some flying skill, and find a volunteer cameraman. Probably my wife...

Duncan

Last edited by rtfm; 11-28-2014 at 12:22 PM.
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