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Scratchbuilt Foamie Pusher For AP

Old 11-19-2007, 01:57 PM
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Default Scratchbuilt Foamie Pusher For AP

Last night, after a full day of yard and other work around the house, I decided to start cutting out my third attempt at an AP plane. My first attempt was pretty much a disaster (pusher with the motor mounted high on a post, causing major motor thrust issues). Big'N was number two and, while it WILL fly again (minor damage from it's maiden hasn't been fixed yet), it's simply too big to hand launch if I'm alone and have no runway to take off from.

I've currently got three camera setups I plan to use, a 1.2ghz 800mw with CMOS camera, a 2.4 ghz 2000mw CCD camera, and my Aiptek 5100M 5 mega pixel pocket camcorder. I'll be ditching the two AA batteries that the camera uses and powering it off the plane's battery via a 3V regulator to save extra weight. When using either of the two wireless setups they'll be powered by the plane battery as well, but won't require any voltage regulator. Since I've done almost zero AP thus far (a few minutes on a Stryker once), I'm pretty anxious to finally build something air worthy specificly for it.

Although I've got a thing for dual boom pusher designs, I didn't want the dual boom this time to keep the tail as light as possible, allowing me to shorten the nose length. In keeping reduced tail weight in mind, I'll probably only have a skid plate at the tail, but two normal landing wheels at the front.

My general requirements of the design were this...

Engine Setup: Pusher for durability.

Plane Size: Small enough to hand launch on my own if no runway is present, but big enough to see at a good distance for AP. Plane also needs to be able to launch and land in fairly small areas, which means lower wing loading so it doesn't have to come in fast.

Key Design Advantage: The required fuse height to clear the boom with the prop also serves to give me the needed fuse height (and then some) to allow my Aiptek 5100M pocket camcorder to stand up inside the fuse. There will also be plenty enough room for a hxt500 servo to mount on top of the camera to fire the shutter switch if I'm doing still shots. Video won't require the servo since I'll just press record before launching. Camera will sit exactly at the COG point so the plane will fly the same with or without it.

Fuse Width At Camera Area: 4". With the camera sitting for side views it's length from front to back (fuse side to fuse side) is 3". I may reduce this width via ply or balsa as right now with just foam I'll need the extra half inch of foam for strength on the sides of the fuse.

Fuse: Two 2" wide slabs of EPS foam glued side by side. It'll be tapered to a narrow nose roughly as seen by the marker lines on top of the fuse in the pictures. It's length will be cut down as short as possible once COG is determined with all the gear in. Pretty much shooting for the fuse look of the Busy Bee (link below).

Tail Feathers: The ones in the picture were just quickly cut and thrown on for evaluation/pictures. I already know I want a bigger verticle stab and rudder to compensate for the large front fuse surface area. Input on size of that and the horizontal stabilizer needed as well. I know the elevator, hanging off the tail of the fuse and past the rudder, will need to be bigger as well.

Wing: Cut by Alex for another plane (glider) that he gave me. I believe it's close to 9" at the root and 7 or so at the tips. I think he said it's got 2 and 1/2 feet of surface area, and should handle up to about 28 ounces of flying weight while still landing at not too high of a speed. Not sure (?) what airfoil it's using. The wing will be removable via nylon bolts/basswood, so if I need a larger or different style wing it'll be easy enough to hot wire out a new one.

A few more stats:

Fuse Length: 36"
Controls: Rudder/Elevator for simplicity and smooth flat turns for AP.
Motor: Probably a 2409-18 swinging a 10x5 APC E. Might go to a 9x6 or so to reduce the total fuse height from it's whopping 6 & 1/2" to 5 & 1/2" or even less.
Battery: 2200ma 20C lipo 3 cell, or may use 2000ma 10C 3 cells
Speed Control: 30 amp Tower Pro
Servos: HXT900s, or maybe HS81s

I always liked the look of the Busy Bee and, without even realizing it, I've pretty much copied the design. It gives me some comfort that something as tall and fat as the Busy Bee can fly. Anybody know the fuse height and width of it? I'd like to know those and other general fuse dimensions of it for comparison purposes. They only list the fuse length. Here's a link...

http://www.hobby-lobby.com/busybee.htm

I threw it all together with some toothpicks just to take a gander at the concept. Very rough, unsanded, tail feathers aren't to size or shape I want yet, fuse size/shape will change and be tappered, etc...But it gives you a general idea of what I'm shooting for...
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Old 11-19-2007, 01:59 PM
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Default RE: Scratchbuilt Foamie Pusher For AP

Here's a repost of a message on my AP build, along with the initial concept drawing/notation...

Alex recently dropped me off a copy of a fuse and wing for a glider he built. I was intending to use it for some AP work as well but figured I'd better design something specificly for that, leaving the nice glider to do what it does best.

The first AP build attempt I ever did was a pusher with the motor mounted up on a post which had major motor thrust issues. My second attempt was Big'N , which did show promise while *I* was flying it (handed the controls over to Alex halfway through it's maiden) The damage to it can be fixed within an hour (which I haven't done yet) and, while I haven't given up on it, I do need something smaller that I can manage to get into the air on my own. Lacking a proper runway for take off, Big'N requires a second person to throw it into the air with a running start. This build won't. It'll be small enough to throw on my own should I not have a runway.

So, having two wireless setups (1.2ghz 800mw CMOS, and a 2000mw 2.4ghz CCD camera setup) along with a very light pocket camcorder, all of which really haven't been used yet, I figured attempt number three was in order.

Since I've always liked pusher prop setups for their durability, but I didn't want the added tail weight of a dual boomer (requiring extra nose length), I thought I'd try a somewhat "different" design.

The added plus (and key to this setup) is that the height of the fuse to allow the prop to clear will also give me the needed height (and then some) for the pocket camcorder to stand up inside a fuse chamber for side view video and still shots. In fact, the extra fuse height needed by the prop length will also allow me to mount a servo on top of the shutter button for doing the stills.

Being a "unique" design, I'd prefer a little input on this bugger before I build it. Criticism welcome. It aint to scale, either...

PS- Alex, Planning on maybe using the glider wing you gave me for it, setup as removable with nylon bolts/basswood.
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Old 11-20-2007, 11:31 AM
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Default RE: Scratchbuilt Foamie Pusher For AP

A little update from another website on this build...

Quote:
Originally Posted by skymind
I don't think it is, I think the nose is too long. If the tail goes longer, and I think that's unnecessary, you'll only have to keep more weight on the other side of the wing.

The tail seems adequate to for the elevator to work. The rudder size and arm may have a challenge keeping that big schnoz under control. The rudder does seem a little short and blocked by the boxy fuselage. Reduce the nose and the rudder should be ok and help keep it lighter.

END:

Agreed. Longer tail means longer nose. Actually, the tail boom is longer than it looks in the pictures, and when I use bigger tail feathers (with the elevator hanging off the tip of the tail boom) the tail will get a bit longer. The ones thrown on for the photo were just hacked out, and not meant as permanent or to desired size. I plan to oversize the tail feathers to keep the frontal surface area from giving me any problems. A quick question: When the tail moment gets shorter, will larger tail feathers help stability?

As said in the post, the nose is too long on purpose for right now. It's going to be slimmed/rounded/trimmed/tucked/whatever. The entire fuse is only a rough cut out for now, with more foam than needed so I can slim it down as I go. In fact, I'm thinking of adding ply/bass/or balsa to the sides of the fuse where the camera sits inside it. That'll eliminate the need for foam there so I can reduce the 4" thick fuse down to about 3 and 1/4". This will be the thickest point of the fuse (big enough to house the camera sitting sideways). The rest of the fuse will still be foam, and the front and back of the body will contour down from the camera chamber.

Fuse height right now is a whopping 6 & 1/2". 5 & 1/2" to clear the prop over the boom, plus another inch for the boom it's self. The best prop for max thrust on the 2409-18 is a APC 10x5E. However, I may opt for a different motor and/or a smaller prop in the 8 to 9" range. This will allow me to lower the height of the fuse another inch or so. Got to run those numbers on the Busy Bee to see just how high and thick it's fuse is as a general guideline. My camera height, even with a shutter servo on top of it, is still much shorter than the current fuse height anyway.

I was thinking of using a carbon tube to strengthen the tail boom foam but probably have decided on thin balsa to cover the foam. A friend does this and I'm amazed at how strong it gets with just a thin sheet of balsa spray glued to both sides.

Thanks for all the input and keep it coming.

Old 11-20-2007, 05:02 PM
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Default RE: Scratchbuilt Foamie Pusher For AP

Some more repost material:

The current dihedral wing I'm sure work fine. What I'm trying to get at is what wing style is going to work best in windy conditions without ailerons. That's where the current wing leaves a big question mark, though it may perform decently even in stronger winds. Fly and see, I guess.

I'm also wondering about the airfoil? Since this plane isn't going to be fast, I'd rather have an airfoil on it that is designed to play to very low speed strengths, to the point of almost stalling the plane. That should give me the ability to slow it to a crawl and linger over desired AP shots.

As long as we are talking about wings and things, I'd say despite whatever options are available, I'd rather hold off on any new wing construction until I get the plane built and see what it's AUW is. That way I can figure out the needed wing length (max of about 9 or 10" wide at the root) to keep the wing loading low enough for slow speed landings. I'm betting the current wing is going to be plenty big enough to keep it low, but might as well build the plane and run the numbers first.

Looks like I'm not the only one to think this design style lends it's self perfectly to AP work. Look at the EyeSpy....Free plans but you can also by some of the hardware pre-made...

http://www.windandwavemodels.com/Eyespy.html

Again, another Busy Bee look alike. By the way, this guy is using a carbon golf club shaft for the tail boom. Good idea to prevent twist when trying a carbon only tail boom. I've never had the issue of twist before with EPP/carbon booms, but then again those were a bit thicker foam than what I'm shooting for on this build. What I'm looking at now is sheeting the foam tail with thin balsa to stiffen/prevent twist. Camera area sides of the fuse will be either balsa/ply/bass to keep it as thin as possible there. Rest of fuse is going to be just the foam because it'll be too hard to shape the balsa over the curves, and don't need the strength there. Might use Tyvek paper or tape over the rest of it if I don't want bare foam.

Old 11-21-2007, 01:41 PM
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Default RE: Scratchbuilt Foamie Pusher For AP

Here's the latest photos of the AP ship. Sanded the fuse down a good bit. The nose will be lopped off more once I know where the battery has to sit for COG. Total fuse height now is 6".

I may raise the motor a half inch to an inch above the fuse so I can swing a 10x5 APC E prop should I decide to go with the 2409-18 motor. I'm probably going to go with a motor a friend has sitting around that he says will swing up to an 8 or 9" prop, getting rid of the need to raise the motor anyway, or use a 8 or 9" prop on the 2409-18.

Fuse width at it's widest point where the camera sits is about 3 and 1/8". The foam on the sides of the fuse in that area will be removed and some kind of wood will be used to provide the sides there, keeping the body as slim as possible.

All the side foam where the camera sits won't be gone. The camera will be inserted into the plane from a hole in the belley, so there will still be a good bit of foam (2 to 3") above the camera chamber under the wing, keeping the body foam well connected from front to back of the fuse.

Reason for belly insertion is this will also double to provide an access view for down video shots. Other reason is if I made the wood on the side some kind of door I think it'll weaken the side of the fuse too much not being glued to the foam?

The body is regular EPS foam from Home Depot, but the boom is the denser EPS a friend gave me. It's a stronger foam. The length you see will change, probably being shorter.

My current thinking is to sheet the boom (top, bottom, and sides) with thin balsa. I'm hoping this will be enough to make it real stiff and prevent flex. I've seen a friend sheet foam this way and the strength is pretty incredible. Eliminates the need for carbon or other strength mods. The boom, balsa and all, will be glued into the fuse several inches to provide a good joining.

I thought about using a carbon golf club shaft or even a thick dowl rod for the tail boom, but hitching the tail feathers up to a smaller surface area like that can be a pain to keep from flexing. I've heard people have good results with Goop to glue them on. Still, routing control rods down a shaft like that isn't easy either, so I think the foam/balsa is probably the best way to go. If anybody has any other suggestions to make a strong tail boom I'm open to it.

Not sure if I'm keeping the foam you see behind the wing where the motor mounts. I may lop that off because the motor can sit under the wing, or through a notch in the wing if it's going to be raised somewhat above it. The whole plane is still in it's rough design stages, obviously.

Tail feathers are still just hacked mockups. I'm planning on increasing the final size of them and using Cell Foam 88, which is stronger than blue foam.

More input welcome...

By the way...I tried 3M spray gluing the two fuse halfs together and it worked fine. I put 3 or 4 coats on them, letting it dry between them, and then one final coat and stuck them together right after spraying that one on. I normaly use Gorilla glue to join two fuse halfs for a thicker fuse. That works great, but when doing drastic sanding on the fuse afterwards the Gorilla glue can get in your way and make it hard to sand things down. I'd still opt for the Gorilla glue to join the two halves if there wasn't going to be much sanding involved. When I do that I just keep the gorilla glue away from the edges so I don't run into it while sanding.
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Old 11-22-2007, 11:37 AM
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Default RE: Scratchbuilt Foamie Pusher For AP

Still toying with other ideas for the boom on the AP plane. Does anybody think that two aluminum arrow shafts spaced parallel and about an inch apart inside the tail boom foam (as in in the above pictures) will be enough to keep the boom from twisting/flexing? I'd melt two channels into the tail boom foam and use gorilla glue to glue them in place. I could then add a few "X" struts in the foam to connect the two, or perhaps just melt one channel and glue both tubes touching side by side? Keep in mind it isn't strength I'm concerned about (I know they'd be plenty strong enough), it's left/right twist of the tail that bothers me. If I go that route I might not need to sheet the boom in balsa.
Old 01-04-2008, 03:14 PM
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Default RE: Scratchbuilt Foamie Pusher For AP

Got a little more work done.

The first fuse I posted a picture of a while back for the AP bird was using Home Depot foam. Since it's going to get a chamber carved out pretty deep at COG to house my digital camcorder, I figured I'd re-do the fuse using stronger foam. Reason why two peices are glued together is his foam comes in small blocks.

Picture doesn't show it well but I sunk two thick dowl rods on to of the fuse for the wing's nylon bolts to thread into. I always used a big piece of basswood to glue to the top of the fuse for that, but I'm thinking the dowl rods will work much better. Less weight and no gap between the fuse/wing. The tail boom is a strong plastic that is smaller and lighter than PVC. I'll cut down the boom's length to achieve COG with the battery sitting as far into the nose as possible while still protecting it.
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