Foam magnum wing weight

[P Maset]

Hi all. I have a quick question about the weight of my Magnum wing. it is a foam wing straight from the box. I weighed one wing panel today out of curiosity. leading edge and trailing edge are on but not shaped, no wing tip on yet. The weight of that one panel was 206 grams (7 1/4 oz) it just FEELS heavy, any body have insight as to if I am going off the rails on this? Thanks!

[Ken Culbertson]

Hi all. I have a quick question about the weight of my Magnum wing. it is a foam wing straight from the box. I weighed one wing panel today out of curiosity. leading edge and trailing edge are on but not shaped, no wing tip on yet. The weight of that one panel was 206 grams (7 1/4 oz) it just FEELS heavy, any body have insight as to if I am going off the rails on this? Thanks!

14 1/2 for an unfinished wing with no controls, flaps, etc IS heavy. 

Ken

[Gerald Arana]

Use the cradles and do a lost foam wing. Very easy, See Robins view for a tutorial.

Good luck, Jerry

[Dan McEntee]

   Don't get too worked up about weight at this point. You still have some sanding and shaping to do. You can put in some extra effort on the wing tips to lighten them up, even replace the blocks if you think have to. As you finish the wing, pay close attention to how you sand it, and don't forget to re-enforce the center section joint. At this point, concentrate on the rest of the airplane. If you haven't sheeted the tail surfaces yet, make sure you have good wood for that. As you assemble the model and get ready for finish, just keep the finish simple so you don't add a lot of weight there. I have a Magnum that weighs 72 ounces and was powered by an ST G.51. How it got that heavy was my fault and a long story, but I found that the airplane carried the weight very well. It was with this model that I started to get consistent 500+ point scores, and I also won my first Expert class contest with it. I have seen many more fly well that were a bit porky. The Magnum is a durable model and if you focus on building it straight, (I think that is more important than obsessing over weight) I think you will be very happy with it.  Just because the wing came out a bit heavy doesn't mean that the rest will and the effort will be a waste. Good luck with it and have fun!!
  Type at you later,
   Dan McEntee

[Brett Buck]

Hi all. I have a quick question about the weight of my Magnum wing. it is a foam wing straight from the box. I weighed one wing panel today out of curiosity. leading edge and trailing edge are on but not shaped, no wing tip on yet. The weight of that one panel was 206 grams (7 1/4 oz) it just FEELS heavy, any body have insight as to if I am going off the rails on this? Thanks!

    It's pretty heavy, but not way out of bounds, and pretty typical of Magnums build from kits. Build on - and remember, this is a big-boy ST60 or similar airplane, it's not going to be flying around on a 40LA, and the *loads* on these big airplanes are also high.

    What engine are you planning on using for this airplane?

      Brett

[P Maset]

Mr. Buck,

I have a NIB Super Tigre .51 for it. I am not super concerned at this point, because I know I have to shape the LE and TE. I already bought new wood for the tips, and plan on them hopefully lighter than what is shown on the plan.

[Dan McEntee]

Mr. Buck,

I have a NIB Super Tigre .51 for it. I am not super concerned at this point, because I know I have to shape the LE and TE. I already bought new wood for the tips, and plan on them hopefully lighter than what is shown on the plan.

     It will be good carving practice to hollow out the tip blocks. Don't put your tip weight box in the tip, put it at the edge of the wing tip. The ST.51 will do the job. I think I was flying mine with 12-5 and 12-6 BY&O at that time. That was before I discovered the APC 12.25-3.75. Now that you have some idea of where you are going, I don't think you will have much trouble coming in under 70 ounces, maybe even closer to 65. Make provisions for a 6 ounce fuel tank of your choice. The only fuselage blocks are the top block for the nose and the fuselage bottom. Don't go too light on the top block, and on the bottom block just hollow it out behind the trailing edge. You need that stiffness in the nose and wing joint area. Don't glue the bottom in permanently until you have the wing fitted in and installed. You may want to consider fuselage mounted aluminum or carbon gear a little further forward for grass gear, unless you are really sure about the wing gear mount blocks. I have a couple of Magnum kits stashed away and want to revisit the airplane soon and even use the Aeroshell airshow paint scheme I used. The Magnum was a popular model and did well for people. The kits go for high prices on eVinBay so you know there are some out there that respect the design. It got a lot of pilots through advanced and well into expert class, including me. Keep us posted on your progress, please.
   Type at you later,
   Dan McEntee

[BYU]

I once had a long lecture from a top 10 competitor who showed me first hand how to get excess weight off a foam wing.

The weight build up on your wing will be the heavy sheeting and the glue. It is too late to deal with excess glue but not too late to deal with the sheeting. SIG were rarely able to put sufficiently light wood for sheeting in it’s Magnum kits. For a light foam wing you need 4-5Lb density 1/16 wood or thinner 3/64 – 1/32 higher density wood.

So  .  .  your solution now the wood has been affixed to the core is to lightly sand the sheeting down to 3/64 – 1/32. If the wood is where the excess weight has come from, you will be able to remove an ounce or more in each wing. Use a semi hard foam sanding block with medium grit and after most of the excess thickness is off, final finish with finer grit. The tips can carry less sheeting (1/32) and you can leave more at the root, be careful to make your sanding as even as possible using a block as you don’t want to change the airfoil.

Yes this takes a bunch of time, but it is worth it.

[MikeyPratt]

Hi all. I have a quick question about the weight of my Magnum wing. it is a foam wing straight from the box. I weighed one wing panel today out of curiosity. leading edge and trailing edge are on but not shaped, no wing tip on yet. The weight of that one panel was 206 grams (7 1/4 oz) it just FEELS heavy, any body have insight as to if I am going off the rails on this? Thanks!

P Maset,
Lots of good information here, I’ve built a bunch of them, the weight I shooting for was 14 ounce with the controls flaps installed, lead-out guide and tip weight box.  The Magnum on the box label was 60 ounces with a dope finish and powered by an ST 60.  Later on, I put OS 40 VF and pipe set up in it and that raised the weight up to 65 ounces, but still flew pretty good even though the the pipe tunnel looked odd (kind of funny).

For power I would look at the Magnum 52 XLS (Randy Smith) from Aero Products (Killer Motor for the Magnum), lots of power and easy to set up and very consistent.  It’s ok to ask lots of questions, maybe we can stop a few headaches you might get.

Later,
Mike Pratt

[Brett Buck]

Mr. Buck,

I have a NIB Super Tigre .51 for it. I am not super concerned at this point, because I know I have to shape the LE and TE. I already bought new wood for the tips, and plan on them hopefully lighter than what is shown on the plan.

   Listen to Mikey, it's his airplane!

    At any rate, don't be so worried about this, it might be a bit heavy, but don't resort to extreme measures, you do not have an extreme problem. For sure, round off the LE at least as much as is shown on the plans, that will keep you out of trouble.

    What finish do you expect to use? That will greatly affect the weight, the lighest finish might save 8 ounces or more over a heavy finish.

       Brett

[Dennis Toth]

PM,
I assume the wing is fully sheeted at this point so you can do the sheet sanding as BYU suggests, just go slow so as not to get to thin. I've built two of them they had piped OS 40VF and 46VF, coming in around 65oz. I did deepen the fuse to have a pipe tunnel and added some extra formers to add stiffness to the back end. The first one I did a dope and clear finish but instead of full sheeting I did a 4" leading edge sheeting and 1" trailing ledge strip then used geodetic 3/4" cap strips over the foam. On the second I did a take-a-part using Paul W's Impact approach and cut out the foam between the geodetic cap strips, I covered the second with MonoKote and did the fuse with LusterKote. It also came in around 65 - 66 oz. On both ships I increased the stab/elevator area a bit to around 27% of the box wing area. This mod works well for the Magnum, do a search on this forum for the Magnum and you will see what others have done.

Best,   DennisT

[Dave_Trible]

I’ve read where NASA is looking to shoot something heavy into an asteroid moon.....or you might try something to really help lighten the finish.  At any hardware or Home Depot you can buy that feather- light drywall spackling. It’s totally worthless for fillets or anything else we do EXCEPT!  It is fabulous to fill all the balsa wood grain and small holes or dings with virtually NO measurable weight gain from bare wood- and it doesn’t shrink or later soak in deeper into the wood like anything with dope will.  Just scrape it on heavy with an old credit or playing card on the entire airplane.  When dry sand most all of it off and the fill job is done and might save you 3-4 ounces.  Proceed with your dope finish or whatever.  I think most finish weight gain comes in filling the wood.  This should offset the extra weight in that foam wing..

Dave

[Ken Culbertson]

I’ve read where NASA is looking to shoot something heavy into an asteroid moon.....or you might try something to really help lighten the finish.  At any hardware or Home Depot you can buy that feather- light drywall spackling. It’s totally worthless for fillets or anything else we do EXCEPT!  It is fabulous to fill all the balsa wood grain and small holes or dings with virtually NO measurable weight gain from bare wood- and it doesn’t shrink or later soak in deeper into the wood like anything with dope will.  Just scrape it on heavy with an old credit or playing card on the entire airplane.  When dry sand most all of it off and the fill job is done and might save you 3-4 ounces.  Proceed with your dope finish or whatever.  I think most finish weight gain comes in filling the wood.  This should offset the extra weight in that foam wing..

Dave

I have done this several times and Dave is right.   One cautionary note though is that since it does not sink deep into the wood fiber it also does not adhere to the wood as strongly as dope would.  Be careful masking over this method.  It pulls easily.  I would use tissue OVER it before applying the final finish.  Another trick I have used was to use the dope itself as a filler.  Instead of blowing or wiping off the sanding dust on the early coats, I leave it in the grain and spray a coat of clear over it to seal it in.  Learned that trick from a hand launch glider guru.

Ken

[Dan McEntee]

I’ve read where NASA is looking to shoot something heavy into an asteroid moon.....or you might try something to really help lighten the finish.  At any hardware or Home Depot you can buy that feather- light drywall spackling. It’s totally worthless for fillets or anything else we do EXCEPT!  It is fabulous to fill all the balsa wood grain and small holes or dings with virtually NO measurable weight gain from bare wood- and it doesn’t shrink or later soak in deeper into the wood like anything with dope will.  Just scrape it on heavy with an old credit or playing card on the entire airplane.  When dry sand most all of it off and the fill job is done and might save you 3-4 ounces.  Proceed with your dope finish or whatever.  I think most finish weight gain comes in filling the wood.  This should offset the extra weight in that foam wing..

Dave

   I think if you get into one of the late Allen Brickhaus' construction articles that has a detailed description of his rattle can finishing system, I think you will find that he did this also but thinned the spackling compound down with water until it was in a slurry type consistency and can brush it on. This lets it penetrate deeper, and pulls the grain a bit like a coat of dope or sanding sealer would. Sand it off and apply a second coat and sand smooth again. this was the base for the thinned finish cure epoxy that was brushed on, allowed to cure, then sanded smooth. If need be touch up areas where you may hae sanded through with some more thinned epoxy. When satisfied, this is the base for your primer and or base coat.  Once you are past the slurry mix step and sanded smooth, tissue or carbon vail can be doped on then and progress from there. Lots of possibilities, really but try not to mix too many chemicals. This would make a good base for doing a dope finish on the wing and fuselage, or a rattle can finish on the fuselage. I wouldn't do a rattle can finish on a sheeted wing. Too much area and too much weight build up.
  Type at you later,
    Dan McEntee

[MikeyPratt]

Hi P Maset,
I went and dug up the build info on my last Magnum I built, as I had incorporated a few changes over the stock Magnum (I wrote about this a this 20 tears ago) maybe longer lol.

Wing built stock with following instructions:
Cut off the foam of the outboard wing panel .625” and don’t hollow the outboard wing tip.
Add 1/8” light ply landing gear clips at each end of the landing gear block before gluing the light ply spar is glued in place. (Make sure you cut out an opening in each of the clips for the lead-outs to pass through).  Glue the light ply spar, landing gear clips, and foam pieces in place with white glue or epoxy.

Make 3/32” balsa spar that extends the full length of each the foam wing panels vertically (use the leftover foam wing core plug in the wing as a guide.) this gives you a triple cored wing (sort-of) and reinforcing back hall of the foam wing.and glue in place with white glue.  Sheet the entire wing with 1/16” Balsa, as light as you can find.  The difference between super light 4 pound wood and 6 pound wood it very little maybe .75 ounce at the most.  Sheet the wings cores with slow drying epoxy (Note: brush one coat of nitrate dope on the inside of each wing skin, this keeps the epoxy from penetrating into the balsa wing skins) and lightly sand the with 320 grit sandpaper.  This alone saved about and ounce just on the foam wings, maybe more.

At this point let’s talk about controls.  Use the best quality controls items you can find, 1/8” wire horns with the top hole set at 1-3/8” from the center of the 1/8” wire to the center of the flap push flap horn, the second hole set at 1”.  Bell-crank 4” (I like Brett’s idea with a captured lead-out).  Carbon Fiber push rods with ball-links make sure they work smoothly and free from binding, if they are not, don’t use them. 

Flaps:  The flaps should be made from solid balsa flaps, if you have built them already then sheet them with 1/32” sheeting, double cover the flaps with silks-pan or a single layer of light weight fiberglass, to make sure they are stiff and won’t flex (ask me how I know).

Stab & Elevators:  Using the stock stabilizer, cut in half and add a 1” piece of balsa and carve the balsa to match the foam core, in addition add a 1” end rib to the tip of the foam, again carve to match the foam.  Then drill three 3/4” holes equally spaced in the foam to lighten it.  Sheet the foam core with 1/32” light balsa and add the 1/4” trailing edge and stabilizer tips.  We just increased the stabilizer span 4”, so now we have to increase the size of the elevators to match, building over the plans, increase the the span 2” of the elevators by moving the ribs out to match the stab, this sounds harder to do than it really is, just make the ends of the elevator from sheet balsa.  You don’t need to Sheet the elevators they will work as intended.

Fuselage:  I wanted to increase the side area of the Magnum so I changed a few of the fuselage block sizes.  The top of the turtle deck from 1/4 sheet to 1/2” balsa sheet.  The bottom block was also changed from 1/4” balsa to 1/2” balsa, the blocks were hollowed inside to about 3/32” thickness (I would mold them now).

Fin & Rudder:  increase the size of the fin by adding a 3/4” X 1/4”  sheet of balsa to the back of the fin to increase the overall size of the fin.  Set the rudder at 0 degree of off set or make it adjustable if you want, but mine did need it.

Finishing:  I tried something new on this model and it worked like a champ.  With the model fully assembled lightly sand it with 320 grit sandpaper and vacuum off,  Brush on one coat of clear epoxy paint (I used K&B), then wipe off the clear with paper towels.  Let the epoxy dry overnight  and lightly sand with 320 grit sandpaper again and remove the dust.  All surfaces should look smooth and even.  Next, add a coat of nitrate dope and sand off when dry.  It should be ready to silk span and dope.  Note:  Back then the carbon fiber matt wasn’t available (at least I didn’t know of it yet) the .2 c/f matt is what I’d use now finished in dope.  Ready to fly it came in at 58 ounces with a heavy Rossie 40 in it and the added tail weight to balance it.  After that I installed an OS 40 FSR with hand built three blade props that flew very, very nicely with that combo. 

Sadly I lost it flying in (crazy)  winds way too strong, but I wanted to see what it could do in crazy wind, the engine quit in just the wrong place and the wind rolled it across the runways shedding parts as it went, bummer!
It was the best flying Magnum I built but it didn’t last very long, so on to the next, the Magnum Force with a different shaped body but the same wing as the Magnum.

I hope this helps,
Mike Pratt

[MikeyPratt]

Gary,
I was flying at the Sig airport, the winds were coming out of the west directly over a row of T Hangers at 25 to gusting to about 30 +, it was a very bumpy flight from the start.  The engine ran out of gas just before down wind side side of the circle, I tried to whip to land it next to the T hangers below the wind turbulence, just as I was getting to the end of the hanger about to touch down when the wind caught it, it looked like a invisible hand smacked it out of the air and tumbled it across the runway.  I was in total shock when that happened.

Later,
Mikey Pratt

[Dennis Toth]

Mike,
Interesting summary for the Magnum updates. You should consider doing "The Magnum Story" for the model library section. This model is part of many stunt pilots history and is certainty worthy of being memorialized here on Stunthanger. Would also be great for an updated 2022 version.

Best,   DennisT

[MikeyPratt]

Mike,
Interesting summary for the Magnum updates. You should consider doing "The Magnum Story" for the model library section. This model is part of many stunt pilots history and is certainty worthy of being memorialized here on Stunthanger. Would also be great for an updated 2022 version.

Best,   DennisT

Dennis,
Thanks for your encouragement, I wish I had photos of all the versions I built over the years.  If I build another Magnum I’m going back to the i bean version (without the sweet forward flaps) I did in the late 70’s with updated for a modern stunt model with electric, larger tail group, lots of molded parts, twin rudders and call it Double “Barrel Magnum” lol, that should be really fun.

Later,
Mikey

[P Maset]

Thank you to everybody, especially Mr. Pratt! I am poking along, and making slow progress. Thanks again for the insight, advice, and encouragement.

Pat