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General control line discussion => Open Forum => Topic started by: petermick on July 05, 2023, 03:56:16 PM
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I managed to purchase a complete Magnum kit in the box for $50. I plan on powering this plane with a Super Tiger 60. i happen to have three of them so I might as well use one. ( I will sell the other two if anyone is interested.) All of the Magnums I have seen in the past have always weighed more than 70 oz. Does anyone have any suggestions for weight reduction? I have a couple ideas that I am toying with. Because most of the extra weight seems to be in the foam wing any reduction in wing weight should be my goal. Idea one is to use the idea Ted Fancher had a number of years ago with the Time Machine. This was to eliminate a large section of the balsa sheeting. By doing this would I be weakening the wings? The second idea is to substitute the foam wing with a built up ribbed wing. I have a Bob Hunt Lost Foam setup for a Geo wing which is slightly smaller than the Magnum. Does anyone think this would work? Any suggestions will be appreciated.
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I have never seen the Magnum foam wing. Is it "cored out"? That is, are there three hollow sections, from root to tip, with a foam spar left between the sections? If not, maybe you can have it cored to remove some weight.
After building foam wings for quite a few years now, I have come to the conclusion that you save very little weight, if any, by doing the "partial sheeting with capstrips" method. You then have to cover it with something, like poly span, fill it with dope or some other product, and then go thru the typical finishing. It is much easier and faster to simply fully sheet the wing. It will be stronger and not much heavier.
That said, I have done the partial sheeting method, but on smaller planes only. Anything larger than, say, a Nobler, and I would be worried about that wing holding up with partial sheeting.
One area to be careful here is the amount of adhesive used to attach the wing sheeting. I use epoxy, but there are other adhesives that work. I stay with epoxy because I use Bob Hunt's method for attaching the sheeting, which uses much less epoxy, but you still get a very good bond line. It works well for me and I am not about to experiment with anything else now.
I would weigh the kit wood and see if you can find lighter wood. That might be impossible these days since contest wood is very hard to find, and very expensive if you do find it.
You can certainly do an all-wood wing. It should be a bit lighter, depending on the wood you use and your building and finishing skills.
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I managed to purchase a complete Magnum kit in the box for $50. I plan on powering this plane with a Super Tiger 60. i happen to have three of them so I might as well use one. ( I will sell the other two if anyone is interested.) All of the Magnums I have seen in the past have always weighed more than 70 oz. Does anyone have any suggestions for weight reduction? I have a couple ideas that I am toying with. Because most of the extra weight seems to be in the foam wing any reduction in wing weight should be my goal. Idea one is to use the idea Ted Fancher had a number of years ago with the Time Machine. This was to eliminate a large section of the balsa sheeting. By doing this would I be weakening the wings? The second idea is to substitute the foam wing with a built up ribbed wing. I have a Bob Hunt Lost Foam setup for a Geo wing which is slightly smaller than the Magnum. Does anyone think this would work? Any suggestions will be appreciated.
At the end of the day, light models always seem to be about the wood used. You could consider that a $50 set of templates and replace all the wood with something lighter. That doesn't have to mean hunting down rare and expensive contest wood. Have a look at this post from Bob Hunt. He discusses an alternate strategy for building light without using contest wood.
https://stunthanger.com/smf/open-forum/what-to-do-with-heavy-balsa/msg657166/#msg657166
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Peter,
I have built two Magnums and they were around 67oz with OS VF46 and pipe. The Magnum wing is a little weak in the back half. What I did was to add a 1/2" wide foam vertical spare between the main spar and trailing edge. This gives it the support in needs to hold shape. One way to reduce weight is use 1/32" hard sheeting for the leading edge to the spar then use geodetic 3/4" wide cap type strips from the leading edge sheeting to the trailing edge sheeting. Trailing edge should be 1" wide down the hold span. Also do full sheeting over the center 12" and use 1" fiberglass tape over the wing half joint. Now if you really want to save weight Monokote the wing and stab and paint only the fuse. Use a molded top block (I used two shells of 1/16" sheet with some formers inside) and bottom block. You will likely need 6 - 7oz tank.
Best, DennisT
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P'Mick,
There have been lots of threads here on the Magnum and its weight. Mikey has informed us of his experiences building multiple different copies of the Magnums. He has also provided some suggestions on how he would build a more modern version today. All good stuff.
Many that were seriously overweight have been attributed to the sheeting installation--too much adhesive and not the best type. That is likely the single biggest weight sin.
One thing that you can do right now to help you make up your mind is to take the wing components: cores, sheeting, everything and weigh it. You will likely see--unless you have cementwood--that if you keep the weight of the glue to a proper minimum, you will be ok. Don't include the weight of the finish in this estimate. You are going to have to finish the wing no matter how you build the structure.
My own version of the Magnum is in primer now, awaiting more sanding. I look forward to getting a flight on it!
Dave
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Peter,
Weight reduction in a stunt ship requires paying attention to everything. It also take years of experience to know how minimal one can fabricate the many parts and have them be adequate. Here are some thoughts that might be helpful.
Buy a good gram scale
Keep weight records.
Review every part How can we do this lighter??
Wood selection
Lite Balsa of course
plywood use should be kept to a minimum. Will Balsa suffice?
Plywood should be as small and thin as possible. 1/64 fuse doublers are more than adequate.
Hardwood Landing Gear mounts should be as small as possible.
ALL parts should be hollowed and have lightening holes to the greatest extent possible.
Hardware selection
Pay strict attention to EVERY piece of hardware weight.
Measure and compare weights of the many hardware options before making a selection.
Finish many stunters become overweight due to finish.
A simple clear dope finish, with minimal primer and minimal pigmented paint can save a lot of weight.
MonoKote is not a bad choice for open bay surfaces
Polyspan without paint is a good choice for open bay surfaces. Strong and reasonably light.
Glue
Cyanoacrylate adhesives can add weight because nothing evaporates.
Titebond and Ambroid solvents evaporate and leave minimal material behind
Epoxy should be used sparingly and applied only as a very thin film.
Make all joints clean and accurate. No sloppy work of excess material
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Build a Millennium Wing and ditch the foam. It will be much lighter. Just an idea if you are concerned about the weight .
Mike
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(https://outerzone.co.uk/images/_thumbs/plans/10272.jpg)
(https://outerzone.co.uk/images/_thumbs/plans/7493.jpg)
Hurumph : Could do a tom Morris style MAGNUM wing , Geo even VD~ if you wanna save the Geo wing for a Geo .
But it depends what the Aeroplane is supposed to Do . A every day field basher , and a STOCK Magnum should be fine ,
if built straight & good stiff flaps & controls . Was a Jack Sheeks kit review where He'd momocoated the flaps , which is
good if you dont like flaps , and bad if you want effective flaps . good Stifff quater grain 1/4 / sheet might be needed .
Go through thewoodb and skewer the less suitable . Every iota counts . Detroiter whale bone type ribs in a built up wing,
maybe perhaps possably , if your aiming for the Walker Cup Fly Off .
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Hi Guys
There are a lot better engine now than when the Msgnum was designed, I used the tried and true ST G21 46. Still one on the best engines found out ther in my opinion. Many have used this engine for years and installed them in everything from a Nobler to a Super Chipmunk with good results.
Now with the ST 51s, and other Such as the Magnum 52 and electric power that has become so popular for good reason. If I was to design a new Magnum there would be a long list of things to change.
1) increase the tail area to 25% of the wing area.
2) lengthen the tail moment to 17.5 to 18.
3) build up the wing or use a triple cored foam wing with 1/16 balsa sheeting (in my opinion foam wings are only slightly more weight than a built up wing).
4) make upper and lower blocks and cowl from molded 3/32 balsa.
5) fuselage sides from 3/32 balsa with 1/32 plywood doublers. The fuse could use either aluminum landing gear, or wing mounted landing gear (which I prefer they look better).
6) this is where you can save a lot of weight, three or four coats of nitrate dope and cover everything with light carbon Vail, the three or four more coats of nitrate dope., assemble the model making sure it aligned properly and add fillets after block sanding. Give the model two coats of gray as a base and block sand again, everything should be smooth and flat awaiting its first color coats, if not add another coat of gray. Now you can paint and add trim colors until your finished. Once your happy with base color and trim, spray two coats of clear to seal the edges of the trim and allow to dry a few days. Block sand again, with a lighter 600 grit w/d sandpaper until its perfectly smooth with an even dull gloss to it. Apply the lettering, ink lines, and added trim. Spray the clear coats use a high quality (Omni) poly clear with hardner and allow to dry, the clear should be be shinny and smooth and require very little buffing. You guessed it, block sand again with 1500 WD sandpaper and use a high quality buffing compound and Hand rub the finish to a deep luster, apply two coats of wax to preserve the deep shine.
Ill try to show this method with a step by step with the proper part number for the products
Mike Pratt
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Looks like someones already done one . S?P
https://www.youtube.com/watch?v=-bm4i5HriQ4&list=PL58x9x2vgja-ZWy8PipziF2JRlctym3Uw
Pile of ' Build Tapes ' for all the tricks .
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"Ill try to show this method with a step by step with the proper part number for the products."
I'd be VERY interested in reading that!