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Nov 25, 2008, 02:20 PM
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Twomosa - 4 oz pattern plane for 10 gram brushless power

My last few builds were long drawn out scale projects that resulted, in some cases, with planes I was afraid to take out in less-than-perfect conditions. How often do we have perfect conditions? I didn't want to spend a lot of time on another hanger queen.

What I needed for the next project was a sport plane I could throw together quickly and take out in most any flyable conditions. Something with so little time and money invested that I really didn't care too much what happened to it. Something I could get a lot of use out of.

Since I already have too many planes laying around I needed to decide which plane in the fleet would sacrifice its life to provide the donor organs. The victim would have to be my prototype Zeke's Whim Fokker D-VII. I find 3 channel planes to be of limited entertainment value and I also suspected that the little 10 gram outrunner in it was poorly suited for that type plane. Even with a fine-pitched prop the little motor would do nothing but make more noise when pushed above 1/2 throttle. My guess was that motor was best suited for something much sleeker than the WW1 bipe.

So the criteria for the next build was a sleek four channel sport job in the 4 oz range. One of my all time favorite planes was a Tiporare pattern ship I rebuilt from someone's wreck years ago. It tracked like an arrow, climbed like a rocket, rolled perfectly axial and made me look like I knew what I was doing. That era of pattern planes included such classics as the Curare, Dirty Birdy, Kougar and Super Kaos that have continued to have a following to this day. A little version of one of those planes would be perfect for this project.

A few years back I needed a disposable plane to test some flakey power system/radio components in, so I picked up a GWS Formosa because it had the sleek lines of those classic birds. The test components actually worked fine and the Formosa performed just like the old classic ships it was patterned after. The "test" lasted a whole season because the plane was so much fun to fly. I figured something with the general outline of the Formosa, but 1/2 the size, would be just right.

1/2 of a Formosa = a Twomosa
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Nov 25, 2008, 04:34 PM
Perpetual Hobbiest
nice build so far reminds me a bit of this little pattern,

i want to build the above linked plane eventually. seems like the pattern stuff in electric is all foam profile or 40 size and above not many people building balsa pattern under 30 ounces.
Nov 25, 2008, 04:46 PM
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Very nice. Thanks for sharing this project with us.
Nov 25, 2008, 04:48 PM
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[QUOTE=carlosponti]nice build so far reminds me a bit of this little pattern,

I had always meant to build a Jelly Bean! I'll remember that one the next time I splatter one of my 200 watt planes.
Nov 25, 2008, 04:56 PM
Huh?! well waddayouknow!?
Great stuff! What is the ws?length?
I am ready to go on this one!
will you be posting some easily downloadable files?
Nov 25, 2008, 06:54 PM
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Watching this one with great interest! I had started work on a scaled down Formosa about the same size and planned to use the same power set-up. My wing was a bit simpler--more like a double sided "whim" type wing since I was in the middle of the "whimified" Spad and Stearman designs at the time. I bet this will be a boatload of fun! If it flys anything like the foam Formosa it will be a sure winner.

Nov 25, 2008, 08:03 PM
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Thanks for all the interest so far guys.

Danno, wing span is 18", length is about the same. I hope to clean up the plans and have a pdf. after working out the bugs. You can see the notes accumulating on the plan sheets in the pictures. Cutting parts this small by hand is a pain too. I may draw up parts sheets with the laser kerf and retention tabs and send it out to be cut accurately.

Ron - You are probably on the right track doing the wings in a simplified manner. I just always draw my wings the same way. It helps me get my "gluing-sticks-together" fix. I loved your Whim Stearman.

Time to make the canopy and sheet the top. The top and bottom stringers extend 1/32" out from the formers. This is so the 1/32 sheeting can be trimmed to size and fit in between them. That way any trimming inaccuracies can be hidden with filler. The same is true for the turtledeck. The turtledeck sheeting butts with the fuse sides and top stringer.

Once the sheeting was in place I put the fin in place and tacked a couple of blocks in place for the fin fairing. I then took the fin off and carved and sanded the blocks to continue the contour of the turtledeck.

The front end design is a function of the motor size and available spinner. I couldn't find any hard plastic spinners small enough for the task, so I decided to use one of the GWS IPS rubber spinners kicking around in the spare box. It is a bit floppy, but the right size and shape. The GWS DS001 2mm prop adapter allows you to use the GWS props with this motor and shove the rubber spinners on the end. With a prop and spinner installed I measured from the motor mount to the rear of the spinner and decided I needed the cowl to extend 1.2" from the firewall. So I cut a 1.2 inch length from the end of a 2 x 2 x 12 balsa block. It took some trial and error to get this right. I learned that I needed to paste the outline of the nose block onto the middle of the 2 x 2 block and cut the 7/8" motor hole with a spade bit before cutting out the outline of the block. You need all the supporting wood around the hole to prevent the spade bit from shattering the block. A 7/8ths hole saw would cure this, but a spade bit is only $3.99. I did go through a few pieces of block before getting a usable nose.

The 1/32" plywood firewall was placed over the nose block and holes were drilled for the 1/16th dowel locating pins and the 1/8th diameter button magnets. The firewall was also drilled for the 15mm three hole circular motor mounting pattern. The firewall was then glued to F1 on the front of the fuse. No thrust angle futzing around here. This is a pattern plane. Motor is mounted 0 degrees up, 0 degrees right.
Nov 27, 2008, 10:41 AM
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The main spar slides through the holes in the six inboard ribs to begin wing construction. Building tabs on the bottom of the ribs allow the wing to be built flat on the bench. The tabs are then cut/sanded off. The ailerons are built in place and cut out afterwards. The trailing edge is shimmed up 1/4" to aid in assembly.

The second shot shows completed wing with aileron servo in place. Holes for the torque rods were drilled before wing assembly. 1/64th ply bearing surfaces were added to reinforce the holes. The torque rods are bent to an L shape and slid in from the outside. Then the 90 degree vertical bends are added. The ailerons and wing hinge area surfaces are covered and the monofilament hinges are added, but the hinges are not glued in place yet. The ailerons must be left off until final assembly so that the vertical bends in the torque rods can be pushed back down flat with the trailing edge to allow the wing to be slid into the fuselage. The torque rod ends and the linkage to the servo arms have their ends bent back 180 degrees and are then pushed into sections of 1/2A fuel tubing that is notched in the middle for strain relief. Credit goes to Chris parent for the linkage design.
Nov 27, 2008, 08:35 PM
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The tapered wing requires a bit of figuring to arrive at the mean aerodynamic chord. Using CAD to do the geometry, I determined the MAC to be 3.75". 30% of MAC is the starting point CG for flight testing. The diagram shows that 30% of MAC is 43mm back from where the LE meets the fuse.

The parts were all slapped together for final fit before covering. All surfaces to be covered were prepped with a coat of thinned nitrate dope and finish sanded with 400 grit. My normal procedure is to do this twice, but this thing is starting to get heavy. I had initially planned for a removable wing, but that would have added to the complexity and weight. The wing simply slides into the hole. After final assembly, balsa scraps are to be glued on the inside fuse sides to trap the root ribs in place. The width between the root ribs is exactly the width between fuse sides. These could break away to disspate energy in a hard crash or be cut out if wing removal was necessary.

All the covering except for the fuse bottom and aileron bottoms was completed prior to final assembly. The fuse bottom remains open to assist in placement of gear for proper CG. The monofilament fishing line aileron hinges were roughed up with 400 grit sandpaper and CA'd into the wing. After the wing is slid into the fuse, then the ailerons will be CA'd to the hinges and the aileron bottoms covered.
Nov 27, 2008, 10:58 PM
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Nov 28, 2008, 03:22 PM
Chess club geek with wings
blunight's Avatar
Great looking plane, cant wait to see the plans or better yet - a short kit!
Nov 28, 2008, 05:43 PM
John 3:16
Daddy-O's Avatar
Now we just need a video!
Nov 30, 2008, 06:19 PM
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Thanks for the encouragement guys.

The elevator and rudder servos were installed and .032" push rods were fashioned to connect to the 1/32" ply control horns on the control surfaces. I used Z bends at the servo arms, V bends just aft for fine tuning and 90 degree bends at the control surfaces that are held in place with Dubro micro clevis keepers. Holes were drilled in Former 3 to allow the rods through and supply support and slits were cut in the rear fuse sides to allow the rods through there.

The receiver and speed control were placed to see how I could make this balance. With the long tail and light motor, it is necessary to move things as far forward as possible. The ESC got stuffed in the nose. I tried to keep the receiver back away from the speed control and motor, so glued a stick from the aileron servo mount to the wing trailing edge and stuck it in place with foam tape. The bottom could now be covered.

After all the radio components were in their logical places, I needed to find a spot for the battery. Test showed the 350 mah two cell pack needed to be just forward of the desired CG point and directly over the servos. I needed to provide access to the servos for maintenance, so the battery platform had to be removable. I had very little room between the rudder and elevator pushrods and the fuse sides, so the battery tray supports need to be thin. 3/16" wide carbon ribbon was cut to length and glued to the fuse sides. Balsa gussets on the carbon pieces support 1/32" ply pads that the battery tray screws on to. The tray itself is 1/32 ply with 1/32 reinforcement running laterally to prevent the battery from bouncing. Some velcro hook material was glued to it and a rubber band provides secondary restraint. The canopy fits over it all and is retained by 1/16 dowel pegs and 3/16" diameter rare earth magnets.
Last edited by Mike Tully; Nov 30, 2008 at 06:25 PM.
Nov 30, 2008, 06:57 PM
Headed to Naval Flight School!
PiperCub49's Avatar
Yes...a video would make it complete! It sure does look deserving!

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