Hobbico Electristar Select
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| 10/25/2008
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Posts: 2537
Joined: 9/24/2004 From: Brook Park,
OH, USA Status: offline
I've been working on a huge dual boomer (6 foot wingspan) for AP. Made from 2" thick white "box" foam. I've figured out a way to secure the two-piece wing to the fuse and booms. In the picture it's already held to the fuse using basswood glued to the top of the fuse and some ply sitting on top of the wing. I threaded the basswood for four nylon bolts. The two booms will be secured in a similar manner with two bolts per boom. Right now the booms are resting on the ground so they are lower than they will be. I'm planning to use two carbon tubes (one in each wing) that will slide into a sleeve in the other wing for strength. The tubes will reach out past the booms to prevent the wing folding. The tappered 6' wing (10" at fuse, 8" at tips) is positioned so the leading edge is straight and they tapper is in the back. I decided on coruplast for the horizontal stabilizer. I'm probably going to install a flat piece of carbon across the leading edge of the coruplast to prevent flexing and reduce prop wash vibrations (it's going to be a pusher). The 3" wide balsa elevator isn't in the picture yet, but that should help stiffen the trailing edge of the coruplast. Of course the fins/rudders are also absent in the picture. I may also install carbon tubes in the booms and connect those to the flat carbon across the horizontal stabilizer to prevent them from bending. Sorry about the dark photos (bad lighting). She's all sanded down and ready for more assembly.
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Posts: 2537
Joined: 9/24/2004 From: Brook Park,
OH, USA Status: offline
Some more work and info on the build...
The digital pocket camcorder is going to go into a chamber under the belly right at COG and be held via velcro straps and some soft foam. I'm going to make the chamber so the camera can be held for a side vide (through a hole in the fuse) or a straight down view. The 2000mw 2.4ghz CCD setup will also go in the same chamber when I'm not using the pocket camcorder. My third 800mw CMOS unit is so light I'll just slap it on anywhere that strikes my fancy when using that.
Reason for the 4" thick fuse (6" tall) was to provide a large and safe enough chamber for the pocket camcorder. I don't care if the larger fuse costs me some drag, I just want to make sure the camera is probably going to remain safe even in a bad landing or worse.
Played hookey from work today because I have to do my taxes, which I still haven't got to yet. So, did a little more work to the plane.
Right now the rods are drying in the wings with gorilla glue. I ended up opting for fiberglass rods rather than carbon tubes since I've got so many of those things sitting around from the garbage picked patio umbrella. A bit heavier than carbon and a little more flexible but they'll work fine regardless. I mounted them in channels about 2" from the leading edge of the wing and their extra weight should help me with getting COG right. They run the entire length of a wing and then sleeve into aluminum tubes (from an arrow) in the other wing under the ply/basswood area. When the ply is torqued down onto the wing via the four nylon bolts threaded into the basswood it should provide a pretty strong wing structure. Will post some pictures later.
I've also got a piece of flat carbon drying to the leading edge of the coruplast right now. Later today I'm going to groove the top of the booms for their carbon tubes for strength there. It'll be glued from under the basswood on the booms and run to the tail. Decided to use carbon back there to keep the tail as light as possible. After that I hope to drill and tap the boom bolts and then install the verticle fins/rudders. Should be able to complete the body today to where it's ready for electronics.
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Posts: 2537
Joined: 9/24/2004 From: Brook Park,
OH, USA Status: offline
More progress:
The fiberglass rods and aluminum sleeves in the wings worked out well. Secured the wing to the fuse to check flex. Bad news is the wing will bend pretty far due to the fiberglass but the good news is there was no problems with the foam. Reminds me of a fiberglass sail plane's wing that flexes in flight. It will stiffen up a good bit more when I put Extreme strapping tape over the tubes and on the top for dihedral.
Got the rudders cut out of the fins and hinged with heavy duty dubros. Did the same with the balsa elevator joined to the coruplast horizontal stabilizer. Booms are drilled for the nylon bolts. Next will be installing the carbon tubes in the booms, glue the fins/rudders on, and she'll be just about ready for electronics.
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Posts: 2537
Joined: 9/24/2004 From: Brook Park,
OH, USA Status: offline
The original plans were for a 3 foot "So" series plane designed by FoamFlyer. I've built three of those planes so far with some modifications to get COG easier to achieve on those builds. For this upscaled one I used my mods done to my smaller build and a few new ones. The thread and plans can be found in the foamies section under a thread called "Here's A Simple & FREE First Foam Build Plan! Cool Looking Plane Too..." More pictures when finished with the body. Maybe today.
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If you believe in Global Warming then shut your mouth. All that hot air is warming up the planet, remember?
Posts: 2537
Joined: 9/24/2004 From: Brook Park,
OH, USA Status: offline
Here's an updated picture of my dual boomer with the 6 foot wingspan. I've got fiberglass rods in the two wing pieces to join them already and used basswood glued to the top of the fuse/booms that nylon bolts go through the ply on top to thread to. I did this so I can break the wing down to two pieces and pull the booms off for transport. The wing has a good bit of flex to it but I'm sure that will stiffen up some when I use Extreme strapping tape over the rods and on various other places.
Still, the coruplast horizontal stabilizer and balsa elevator appear to be sticking out too far for the weight. There is a good bit of flex there, as you can see in the picture by how the tail is not level with the nose. I'm considering gluing carbon tubes into the tops of the booms and attached to under the basswood on them to stiffen the tail up. Not sure if that will cure the problem. I am also considering cutting off the booms at the trailing edge of the wing and then just using carbon tubes for them all the way to the tail and no foam. That will make the rear end very light and stiffen it up, though I think it will distract from the looks of the plane not having foam back there. I might also ditch the coruplast in favor of foam on either modification above. Could use some input.
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Posts: 2537
Joined: 9/24/2004 From: Brook Park,
OH, USA Status: offline
Here's a new picture of the scaled up dual boomer with it's 6 foot wingspan next to the "original" (I changed some of the dimensions) plane with a 3 foot wingspan. Gives a good idea of just how big this monster is. Still dwelling on the wing flex problem between the fuse/booms. My best idea yet is basswood just laid across the fuse/booms on top of the existing basswood that is already glued to them. I'll drill some holes in it so the nylon bolts can pass through it and thread into the glued basswood on the fuse/booms. Can't find any long enough (roughly 28" long x 5" wide or so). Anybody know of a source or a possible lightweight wood substitute I could use? I'm sure this will eliminate the flex and make the fuse to boom areas rock solid but am not sure if that's going to play havoc with lift since it will be laying on top of the bottom wing surface?
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Posts: 2537
Joined: 9/24/2004 From: Brook Park,
OH, USA Status: offline
Thanks. The wing is a USA27. A friend brought over the jigs and we cut it out using my hotwire bow. There is very little one can find on this airfoil. I did a search and could only find some obscure military memos from WWII on it. My friend says its a less drag/but almost as high of lift wing as a Clark Y. Here's a re-post of more progress on it...
(MESSAGE ONE)
I finally got around to testing the wing fix for the huge dual boomer to see if the flex is gone...And it works! Originaly I had two aluminum arrow shafts glued into the two wing sections that would sleeve over the fiberglass rods I also have glued (full length into the wings). The two wing halfs would come together and the fiberglass rods would slide into the aluminum tubes. The wing sections would then be bolted to the fuse via four nylon bolts, plywood on top of the wing, and basswood glued to the top of the fuse tapped for the bolts to thread into. The booms also bolt to the wing via plywood/basswood and two nylon bolts per boom. There was too much forward/backward flex of the wing with this setup.
So, I removed the aluminum shafts and cut new ones that were long enough to reach just past the booms. That way they'd we sandwhiched between the bass/ply on them just like they are on the fuse. I then added to more aluminum tubes further back on the wing to also do the same thing, though they don't have anything sleeved into them (yet). Bolted the bird back together and the wing and booms are rock solid! They'll get even stiffer once I put some Extreme strapping tape over the tube channels and such. Very happy this bird is going to be possible, 6 foot wingspan and all. Will throw some pictures up this week of the wing strength mods.
Since this is going to be my AP plane and I've had three camera setups collecting dust for a couple of years now, I'm very anxious to get it into the sky.
(MESSAGE TWO)
Here's a few pictures of the big dual boomer with the 6 foot span along with the wing mod. It's a little hard to see it but there are four aluminum tubes glued into each wing half (2 per half), two of which have a fiberglass rod that slides into them as the wing slides together. The fiberglas rods are glued the full length of each wing section and stick out a good 7 or 8 inches to slide into the aluminum arrow shafts. The back two arrow shafts may also get fiberglass rods to slide into them that will be full wing length, though at this time it's plenty stiff enough...even without the Extreme strapping tape I plan to cover the channels with, not to mention the Extreme tape I'll use to hold the tempered dihedral I'll be putting in the wing for stability.
The basswood glued to the top of the fuse/booms along with the plywood on top of the wings that the nylon bolts go through really helps to sandwhich and hold the tubes/wing as "one". The one piece plywood section that goes on top to join the two wing halves will remain unglued (of course), but the two pieces of ply for the booms are going to get glued to the top of the wings for even more strength. Took a lot of head scratching but I am real happy with figuring out this simple mod to join this wing. The booms don't currently have any carbon or tubes in them yet they are very strong with not much flex if you push down near the tail. I was worried this would still tork the wing. I'll either add carbon or glass tubes inside the booms or just rely on Extreme strapping tape to make sure they stay stiff. Might have to order my Hextronicks 35/36 1100 k/v motor pretty soon for this bird. Anybody have an opinion on the two servos (one for the two rudders, one for the elevator)? I was thinking HS81 non-MG versions but perhaps I should go bigger?
Excuse the dirty look of the foam along with a few odd chunks taken out of it. Dirt is from the floor, dings are from a curious nephew. Nothing the paint and tape isn't going to hide. The clear tape on the wing was just to keep the gorilla glue from escaping foam and will be taken off later.
Here's the thread with the original design this plane was based on...
Posts: 2537
Joined: 9/24/2004 From: Brook Park,
OH, USA Status: offline
More progress and pictures on the "BIG'N" dual boomer...
I was so happy with the wing strength mod, even though the tail seemed plenty stiff enough, that I decided to go all out on them too with carbon. I figure, why not build a tank like a tank? There shouldn't be anymore worries of body/boom/wing flex now...
In a few of these pictures, you can get a better idea of the wing strength mod. I also have the ply glued on top of the wing now. The middle square of ply that joins the two wings is glued to one of them for an added touch of strength.
I did have a flat piece of carbon on the horizontal stab but wasn't happy with that, so I took that off and inserted two carbon tubes through the coruplast near the leading and trailing edges with some gorilla glue. I had a great idea for these. I was going to heat the coruplast with a heat gun to allow me to push the tubes through the channels without having to slit it. It was working but I quickly realized I'd need an extra set of hands, so I just slit a channel.
The carbon tubes in the booms are being inserted under the basswood a good few inches, so they will be "one" with it once the gorilla glue is used. The two tubes in the h-stab cross over the tail boom tubes and will be glued as well to form a kind of skeleton.
She should hold up to some pretty rough landings, which I never have of course...
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If you believe in Global Warming then shut your mouth. All that hot air is warming up the planet, remember?
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Homemade Dual Boom Pusher Foam AP Build - 
