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Dec 05, 2006, 07:58 PM
magic612's Avatar
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Build Log

"Little Go Bipe" - 5-6 oz foam biplane; new design, free plans!

Hey everybody -

Okay, so it's not exactly a "new" design in the sense that it's just a foam biplane with a stick fuselage. Nothing "new" or "revolutionary" about that. It's just "new" in the sense that I designed it by myself, using the acquired knowledge I've gained by reading a lot of stuff here, and trying different designs at home (some succeeding, some failing).

Anyway, I've been playing around with the basic biplane design for about the last 3 or 4 months. My goals were simple enough:

- Made from inexpensive materials, including radio and power system
- Able to be made from a single sheet of foam
- Capable of both slow flight and decent aerobatics
- Lightweight and (relatively) quite small
- Forgiving of less than perfect landings
- Easy to cut out

First, I started out using the foam from the foamboard with paper on it (paper stripped off, though). It flew "okay", but I was also using a GWS 280 direct drive and a 1.4 oz NiMh battery. Next, I redesigned it using Cellfoam 88 - worked a bit better, but the tail still kind of hung down relative to the wing and nose.

I've redesigned what (I think!) should be a great little flyer. The wing is a 4-40 chord (From LE, 4% up, at 40% of the chord), and has a 3% "up" incidence on the upper wing. Also, because I got tired of fixing foamies with fixed wings, this one employs a rubber band to hold the wing onto a balsa fuz spar, .375" square. A "wing stabilizer" is attached to the fuselage using some wing supports, and matches the airfoil of the lower wing. The rubber bands go underneath the wing, allowing for very forgiving "less than ideal" landings.

I've switched the motor to a GWS ISP "A" drive, assuming a 9x7 prop, and a 200 mAh - 350 mAh LiPo to keeps the overall weight to between 5 and 6 oz. I really like having landing gear, since I prefer "touch and go's", and also because many of the areas I fly have hard surfaces (and not much long grass for landings).

It should fly nice and slowly, but the previous versions I made would also do snap loops and fairly snappy rolls too. I'm not an aerobatic expert by any means yet, but I think this plane will offer quite a bit of gentle response for newer fliers, yet plenty of fun for more advanced fliers (I hope!!!). Of course, a brushless motor will make this into a real screamer, but I don't think that's necessary, since I really designed it for small backyard or indoor use.

I'll add pictures of the build shortly. Hope you enjoy!

I should note my appreciation for the article by Jef Raskin about small plane airfoils - the airfoil for this plane is derived directly from that article (even though it's Re number is just slightly over 50,000). And also, props to everyone here that posts their plans, tips, and insight - your thoughts along with my own interests coalesced together are how this design came into being. So thank you to everyone one here - this is my way of "giving back", I guess.

Plans for all parts on 11x8.5 pages, here:

EDIT: Here is golem's initial flight report in post #46, using a brushless setup:

EDIT: Plans for a 3 oz, 14" wingspan version can be found here in post #92.

EDIT: Added tiled plans below on 6/7/07
Last edited by magic612; Jun 06, 2007 at 11:08 PM.
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Dec 05, 2006, 08:55 PM
magic612's Avatar
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Foam parts layout

I originally had this plane at a 20" wingspan. Then I realized that Depron comes in 1 meter lengths, or 39". So, to get two wings from one sheet, I knocked it down to 19.5" - and the rest of the parts (horiz / vert stab, wing supports, wing stabilizer & supports) will all fit on the remainder of a 39" x 13" sheet of Depron after the wings are cut out.
Dec 05, 2006, 09:04 PM
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Horizontal stabilizer is epoxied directly onto fuselage spar. Vertical stabilizer is designed to fit on top of horizontal stab, and is epoxied directly to it. I colored the pieces before gluing - MUCH easier to do that way!!
Dec 05, 2006, 09:20 PM
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Wings, and wing supports

Well, I discovered that bending the Depron to the desired airfoil shape was not quite as easy as I had hoped (and it was nearly impossible with the Cellfoam 88). The Cellfoam kept breaking when I tried modifying my old plane to this new shape, and when I was working with the Depron, I realized that I was trying to bend it "across the grain".

So - word of caution: GO SLOWLY. Bend the foam a little at a time, working from the edge, all the way across the wing. Then bend it about .75-1.0" further up, again, moving across the entire wing span. Continue this so that the whole wing is "flexed" with a start to a basic airfoil curve.

Next, the leading edge will likely require some additional curve, as the front 40% of the airfoil is a tighter radius curve than the remainging 60%. Try to match the wing's airfoil to that of the plan's side view as best as possible. The wing supports will help the wing keep it's shape, but it is important to bend the foam to get as close to it as possible FIRST.

Mark the location for the wing supports, making sure they are square with the leading edge. Epoxy them to the lower wing, then while the epoxy is curing, start bending the upper wing for it's shape.
Dec 05, 2006, 09:23 PM
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Upper wing attachment

Epoxy the upper wing to the wing supports, after the epoxy for the lower wing has cured. I found that I really need to bend the leading edge quite a bit, to get it to match the curvature of the wing supports. I placed a rather large, soft-cover book on top of the wing after I had the epoxy applied and wing in place, to keep the leading and trailing edges in place while the epoxy cured. It did a nice job of keeping the wing surface right on the entire length of the top of the wing supports.
Dec 05, 2006, 09:41 PM
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Rudder and horz. stab servos, wing stabilizer assembly

The wing stabilizer assembly is a key component of this design. It keeps the fuselage in the proper orientation relative to the main wings, as well as forcing the entire plane to roll when ailerons are applied. Without it, the design falls apart. Plus, with the rubber bands underneath the plane, it allows for more forgiveness under landings that are less than ideal.

First, make a mark on the fuselage 4.937" from the tip. This is where the wing stabilizer supports will be glued. Before gluing them, determine where your servoes will be placed underneath the fuse, based on their size. I tried to allow space for most any 5-6 gram servo. Placement is not critical - just be sure to leave enough space in front of and behind them, so that the stabilizer supports will have sufficient strength when attached to the wing stabilizer surface. Cut stabilizer supports to allow for servos as needed.

Use double sided adhesive tape to attach the servos - one facing one way, the other the opposite direction - effectively "nesting" them together. I taped my two servos together with clear tape, going completely around them, before attaching them to the fuse and the double sided tape, for strength.

Next, epoxy the wing stabilizer supports to the fuselage - the front edge of the supports should be glued 4.937" back from the tip of the fuselage spar, and the tops of the supports should be flush with the top of the fuse. Then, center the wing stabilizer underneath the supports, and epoxy it in place.
Dec 05, 2006, 09:49 PM
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Remaining radio equipment, pushrod guides

Completed wing stabilizer assembly, and radio gear (ESC not pictured). I used .032" piano wire for the pushrods, but the distance between the servos and the tail assembly is far enough, I decided to add some pushrod supports to avoid pushrod "flex" when the servo was pushing the rods instead of pulling them.

The pushrod support is simply a piece of balsa wood CA'd to the fuselage, and some pushrod tubes epoxied to it.
Dec 05, 2006, 09:54 PM
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Underside of plane

There are several ways to attach the rubber bands to keep the wing in place, but I've chose what I think is the lightest method. Since I use Dubro MicroLite servo pushrod attachments, I slid the rubber bands onto the fuselage BEHIND the servos/radio. After attaching the pushrods to the servos for the tail surfaces, I placed the fuse through the wing. Pulling the rubber bands all the way forward over the end of the fuse, I then pull the rubber bands back to just in front of the stabilizer supports. Center the wing stabilizer on the lower wing, and Voila! Strong wing, with plenty of forgiveness when landed less than perfectly!!
Dec 05, 2006, 09:55 PM
magic612's Avatar
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I should be able to finish this up later this week.
Dec 05, 2006, 11:52 PM
ToxicToast's Avatar
Looking good! Love to see video when you get things worked out. Nice small design!
Dec 06, 2006, 02:50 AM
Registered User
I agree ! fantastic !
Dec 06, 2006, 07:01 PM
magic612's Avatar
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Single sheets - full plan

PDF files that have sufficient info to use to trace the outline for all necessary foam parts for this plane. Wings are only 1/2 of total wing; simply flip the cut-out design over to trace the other half.

These should make it easier to print all parts of the plane.

EDIT: A tiled version which prints all these parts is now in post #1.
Last edited by magic612; Jun 07, 2007 at 08:22 AM.
Dec 06, 2006, 07:24 PM
Got more toys than my kid
macr0t0r's Avatar
A cute little bugger for a ParkFlyer. Looks like it'll land on a dime. I've grown a tad tired of the wonky 3D-style, so it's refreshing to see a something built to fly rather than flutter.

Subscribed. There's just something about a biplane!

- Jim
Dec 07, 2006, 12:44 PM
magic612's Avatar
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Thanks Jim! I agree - I just like biplanes. Besides, it makes it easier to get more wing area into a shorter wingspan, for more lift.

I'll have more to post (pictures, build info) later on, and hope to have a possible video by the weekend. Not sure if our digital camera's video function will show it at much more than a dot (no zoom), and that'd be the only way I could upload a video to my computer - at present, anyway.
Dec 07, 2006, 10:12 PM
magic612's Avatar
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Aileron servo placement and pushrods

I struggled with this. I really did. I've tried several variations on where to put the darn aileron servo, and this is, I think, the best placement. My first design, I double-sided taped it to the bottom of the fuse-spar, which forced it to stick through the lower wing, exposing not only the servo arm, but the pushrods, etc., to the "elements of the ground". I didn't like that too much, especially for 5 gram servos.

Next, I placed it up on top, similar to what I've done with the present design, but the wing stabilizer supports were as short as possible, and the tail / elevator servos were back behind the receiver and aileron servo. This made balancing the plane challenging, since two servos were relatively far back.

Which leaves me with present placement. It's probably the best spot, though it has it's drawbacks, but they aren't horribly objectionable. First, make sure that the servo arm for the ailerons is in a centered position BEFORE placing the wing structure over the fuse. So, turn on your radio system, connect a battery, and center it as much as possible now. Next, attach the pushrods to the servo arm - I really like the Dubro E/Z links. They give a good solid connection to the servo arm, and since this servo is in a hard-to-reach spot when the wing is on, one needn't mess with this connections once they're in place. I didn't bend my pushrods at a full 90 degrees, more like about 70 degrees (or should I say 110 degrees, since it's an obtuse angle?) for easier pushrod movement on the arm.

Now, put the wing on, attaching it with the rubber bands as described previously. I drew light lines on my lower wing so I can instantly see if it's centered with the wing stabilizer. To attach the pushrods to the wings, I use Dubro Micro Horns and the Mini E/Z Connectors. Reason being, when the wing is on, it's not easy to mess with the connectors. By using the EZ Connectors, and most importantly, FACING THE SCREW HEAD TOWARDS THE OUTSIDE OF THE WING ON EACH SIDE, it makes it snap to slide the pushrods into the connectors, and adjust them with ease.

See the pictures here for some closeups.
Last edited by magic612; Dec 08, 2006 at 05:08 PM.

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