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Jul 24, 2013, 12:43 AM
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Build Log

Electrified Oly III Full-House (plus a V-tail!)

]There are a quite a few build threads/discussion on electrified versions of the Oly III from Skybench Aerotch. See for example:
In this and the following few posts are some details of my electrified Oly III (full-house) that had its maiden flight last weekend after 6 months of construction.

Motor: Scorpion SII-3014 1040 kv
Battery: 3s 2200 mAh Lipo 45C discharge rate (Turnigy Nanotech)
ESC: ZTW 70 amp with switching 4 amp BEC
Prop: 11 x 7 or 12 x 6.5 Aeronaut Folder
Spinner: MPI Maxx Products 40 mm with Hub
Servos: HS-85mg everywhere except flaps; HS-5085mg on flaps

Design Changes
With ailerons you can decrease dihedral/polyhedral to zero if you want, but since this is a thermal glider I elected to retain most of the polyhedral called for by the plan. I tried out different polyhedral arrangements using SailplaneCalc ( and settled on angles that gave an effective dihedral angle of 6.5 degrees, which yielded a reasonable value for spiral stability but hopefully would be a little more stable than the stock glider when landing in gusty conditions. Some output from Sailplanecalc are below.

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Flap (and aileron) chords are 25% of the total wing chord along their lengths, which is significantly more than called for. I wanted to be sure the flaps would be really effective and the ailerons would do their job without needing a big hinge gap. I pretty much copied the layout of the Supra which has plans available online: Also, I made the tail parts removable as a single unit.

Highlights of the Build
The Scorpion outrunner motor I had is 2.5mm wider than the ones most people have used, which is not optimal but I had the motor already. A geared inrunner is the best choice for keeping the nose as skinny as possible. You have to replace the included liteply bottom sheeting to accommodate the widened nose and since the local hobbyshop doesnít carry anything longer than 24Ē, this length determined the location of the motor mount, which I cut from 2mm fiberglass plate laminated to 1/16" ply (to be sure there is lots of contact between the motor mount and sides of the fuse. The nose length seemed reasonable given the extra nose weight that the motor, ESC and battery would add, not to mention the extra plywood I would epoxy under the motor. I probably should have mounted the motor lower so that the nose shape would be closer to the original. Too late now. Downthrust and right thrust are ~ 4 degrees and 3 degrees, respectively.
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Tomorrow Iíll post more.

Last edited by mitchcb; Dec 23, 2014 at 10:50 PM. Reason: Corrected error in wing chord for SailplaneCalc
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Jul 24, 2013, 09:48 AM
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Sir Dumb Thumb's Avatar
I am building a electric Oly2S and I am almost done. This is my first wood sailplane I have built and the learning curve was not a steep as I thought. I mounted my motor lower on the horizontal centerline, a little too low. I didn't think of the spinner till the end and I had to use a smaller spinner on the front. I ended up with a 36mm spinner but I think a 40mm would have been better. I didn't want the spinner to be lower than the nose because I thought it would be a problem landing and breaking the motor mount. Live and learn. I only have 2 degrees of right and down, but I put in a smaller motor than other builders. I will be interested in your flap and aileron setup, mine just has flaps. I did not know how to make mine so I guessed from looking at other planes. I really enjoyed the building process and could see a Oly3 in my future, especially a full house version. Mine is on the last page of this thread.
Jul 24, 2013, 05:04 PM
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More Nose Photos of the Oly III Electrified

Here are some more pictures of the nose construction. That pile of plywood sitting next to the fuse in the first photo was epoxied together first, ground out to conform to the underside of the motor, then epoxied in with J-B Weld because I needed a thick strong glue to fill in the gaps. I added a plywood nose ring so that the motor mount screws would be hidden and to get a small gap between fuse and 40 mm diameter spinner. A Dremel tool helped a lot with removing all that extra plywood on the bottom. Later I ground away more wood inside to allow the motor wires to sit further away from the motor. Cutting the front end of the hatch at a forward angle worked out nicely as it holds the hatch in place pretty well even before adding a retainer pin at the front and a pair of magnets at the rear.

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Jul 24, 2013, 05:27 PM
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Pushrod Replacement Oly III Electrified

The included pushrod wire is pretty heavy so I replaced it with teflon tubing that I had. I had to buy some 72" long 1 mm (0.038") straight music wire, from Small (Amazon). Good luck trying to straighten coiled music wire yourself. I tried and failed miserably. The teflon tubing has to be secured with a bunch of balsa pieces so that the pushrod can't flex. I didn't cross the pushrods at the tail because I needed room for the nylon bolts for the removable tail.

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Jul 24, 2013, 05:53 PM
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Removable Tail - Oly III Electrified

I epoxied 10-32 blind nuts (ground down some to save weight) into the horizontal stab, aligning them with the center line as best I could. Centering in the stab doesn't have to be perfect. The receiving holes in the top of the fuse were drilled after the blind nuts had been glued into the stab. The hole positions are a little cockeyed, but the stab itself is centered. The holes in the bottom were drilled first in some loose plywood pieces. These were glued to the bottom of the fuse with the stab centered and level, bolts holding the stab to the fuse while gluing. Later I added the balsa bottom sheeting, and also some 1/32" x 1/2" ply strips (not shown) on both sides of the fuse to help support the horizontal stab.

Those ugly blind nuts were later hidden underneath some balsa corner stock that also helped to support the vertical fin. No pics of that. In case you decide to use this method for a removable tail, DON'T USE 10-32 BOLTS. This size is being discontinued at the hardware stores.
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Description: Bottom ply pieces gluing in with horizontal stab centered and level.
Last edited by mitchcb; Dec 22, 2014 at 01:51 AM. Reason: Added comment about 10-32 size no longer available
Jul 24, 2013, 08:05 PM
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Full House Wing Issues - Oly III Electrified

To get deeper flaps (and ailerons) than shown on the plan (25% of wing chord) you have to cut deeper notches in the ribs for the deeper trailing edge sheeting. That's easy on the the center sections since all the ribs are the same size. But the outer sections are tapered and therefore trickier, especially since the rib locations on the plan are said to be less accurate than the laser cut ribs. So you are supposed to adjust the rib locations left or right to get all the laser cut notches lined up straight. I ignored those instructions and just lined up the outer section ribs as shown on the plans, then cut the sheeting notches. Name: small P1000391.jpg
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Description: Use a straight edge to mark locations for cutting the ribs to allow for deeper sheeting in the outer wing panels
This seemed to work OK, but it would be nice to have exact rib spacing distances/locations provided in the instructions. Maybe they are posted somewhere.

The wing servos need sheeting of the ribs top and bottom, so the ribs on either side of each servo need to be cut to allow for the 1/16" sheeting thickness. The bottoms are easy (just extend the existing rear sheeting notch forward). For the tops I used the rib from the left side to draw cutting guidelines on ribs from the right side (and vice versa). No photos of any of this. I did scan all the ribs and made some notes on a printout in case I had to make a replacement rib.
Last edited by mitchcb; Jul 24, 2013 at 09:19 PM.
Jul 24, 2013, 08:29 PM
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Wing Tube Alignment - Oly III Electrified

Here's how I dealt with the wing tube alignment business. My local hobbyshop (Franciscan Hobbies in San Francisco) carries precisely cut 2" x 2" square basswood blocks. Perfect right angles, smooth finish. When I questioned the accuracy and straightness, they said the guys from "Mythbusters" use these blocks for their engineering exploits (in other words, "Just shut up and buy the block, buddy"). Anyway, I checked them carefully and then bought one, applied masking tape on one face, then epoxied a section of brass tubing onto the tape using a right triangle to get it glued on straight. When gluing in the wing tubes, the wings were aligned perpendicular to the block.
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[Note: In Post 12 (below) Ray Hayes points out that the innermost ribs (No.1 ribs) are not supposed to be glued in at this stage, and the plywood sheer webbing on one side of the wing tubes should be glued in. Later on the No. 1 ribs should be glued in while the wings are mounted onto the fuse, so that the No.1 rib can be aligned precisely with the side of the fuse. Good advice. Do as he says, not as I did.]
Last edited by mitchcb; Jul 25, 2013 at 07:52 PM.
Jul 24, 2013, 09:05 PM
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Major Blunder - Oly III Electrified

I spot glued the wing tubes in place and went to bed. Then woke up at 2 AM in a cold sweat and checked my calculations again. Oops! 1.6 +1.8 does not equal 2.4. Name: small P1000373.jpg
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Description: Just when I thought I would get through this project without a major blunder, an arithmetic error bit me in the butt.

The next day I ground out the glue joints (along with a bunch of rib) and re-did the gluing with the correct angle.Name: small P1000372.jpg
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Description: Next time I'm going to have someone check my calculations before I mix up the epoxy.
Last edited by mitchcb; Jul 24, 2013 at 09:23 PM.
Jul 24, 2013, 09:39 PM
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Front Top Sheeting - Oly III Electrified

I used Titebond to glue the top sheeting.Name: small P1000392.jpg
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Notice the brown discoloration on the sheeting? That's because I used a hot covering iron to speed up the Titebond gluing process. Thanks to Keith (aka IHAVAWDY) for illustrating this technique.

Gluing on the top front sheeting induced a small bow in the trailing edge for some reason. The bow disappeared after I glued on the trailing edge sheeting. But the bow came back after cutting the through the trailing edge sheeting to make ailerons and flaps. I was able to correct the bow by overnight suspension of the wing with strategically placed weights to create a reverse bend.
Jul 24, 2013, 09:59 PM
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Cutting Out Flaps - Oly III Electrified

The instructions describe cutting a 1/4" wide slot in the top sheeting, into which you insert two pieces of 1/8" balsa which become the rear face of the fixed part of the wing and the front face of the flap. To allow for a little reflex (upward movement) of the flap, Ray Hayes suggests inserting some pins between the two pieces of 1/8" balsa to make a small gap. Instead I spot glued two 1/8" pieces of balsa with a wire placed between the two at the top. This was inserted into the slot cut into the top sheeting and was glued to the bottom and top sheeting and the ribs. BEFORE this step I glued in a 1" long section of trailing edge stock between the top and bottom trailing edge sheeting at the location of the flap control horn. The control horn needs this for support.
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Description: Face pieces glued in, flap ready to be cut out of the wing.
Jul 24, 2013, 10:23 PM
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Cutting Out Ailerions - Oly III Electrified

On one outer wing panel I tried the same method used for flaps to make the front face of the aileron and rear face of the wing. Here's a drawing of how the two pieces of 1/8" balsa were temporarily glued together.
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Description: 1/8" thick balsa strips with a 3/16" spacer placed to create a 25 degree hinge gap angle
And here it is inserted into a slot cut in the top sheeting of the right outer panel.
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Description: Glued into a slot cut in the outer panel
The problem is that the pivot point of the hinge is at the top side of the bottom sheeting instead of the bottom of the bottom sheeting. When the aileron deflects upward, a gap opens at the bottom. It's not a problem on the flap because the angle of upward deflection is so small that the gap formed at the bottom is negligible.
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Description: This drawing shows that the pivot point sits at the top of the bottom sheeting rather than the bottom of the bottom sheeting.  So when the aileron moves up a gap opens in the bottom sheeting. No good.

Enough posting for today.
Last edited by mitchcb; Jul 24, 2013 at 11:54 PM.
Jul 25, 2013, 05:41 AM
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Here is the link to my web's "Wing Construction Tips" located on the front page, note the steps concerning the plywood horizontal shear web install before the brass tubes are glued in and the absents of ribs #1 prior to gluing in the brass tubes. Wing Construction Tips.

Woodys Forever
Last edited by Ray Hayes; Jul 25, 2013 at 05:47 AM.
Jul 25, 2013, 08:24 PM
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Aileron Issue Resolved - Oly III Electrified

After botching the right side aileron (fixed later) I made the left aileron by cutting a slot for 1/8" balsa and glued that in to form the rear face of the fixed part of the wing. The balsa was glued to the forward part of the wing (not the back). To mark where to cut the bottom sheeting I inserted pins as shown. Then I cut the "pre-aileron" using a long straight edge for guidance (straight edges are your friend; use liberally). After the pre-aileron is separated from the wing, 1/8" needs to be cut off the front bottom, and a bunch more from the top to make room for the 1/8" front face balsa and to get the desired angle. I was trying for 25 degrees, but in the finished glider I can only get 18 degrees - not sure what happened there but 18 degrees is enough.
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Description: Gluing the front face of the aileron.
The aileron ends at the last rib because I had already shaped the wingtip block per the plans (bottom slanted upward towards the tip). If you want the ailerons to run all the way to the end of the wingtip, the bottom of the wingtip must be in line with the aileron hinge line. Shaping it per the plans makes an upward "kink" that cannot be nicely hinged.
Jul 25, 2013, 08:35 PM
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Wing Servo Mounting - Oly III Electrified

1/8" balsa sheet sanded to a wedge shape sits under the servos to make clearance for the servo arms (servo arms do not exit the wing). Cutting and sanding 16 hardwood blocks for servo hold-down screws was "fun". I think I made ~ 24 blocks, 8 of which were failures. The pictures tell the story.
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After completing everything except pushrod installation I covered the wing and attached flaps and ailerons. See the over-under/barn door tape hinge method in the next post.
Jul 25, 2013, 09:11 PM
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Over-Under Tape Hinges - Oly III Electrified

This style of hinging with tape seems to have many different names (barn door, over-under, X). Make them by putting one strip of 2" wide packing tape with adhesive side up onto a glass sheet, fixing in place with some masking tape at each end. Then apply a strip of 2" packing tape with adhesive side down, overlapping with the first piece to make an overlap section that is a little narrower than the thickness of the surfaces to be hinged. Use a Sharpie pen to mark the overlapped section, then mark the widths and lengths you want. Finally, use a knife blade to cut the hinges. Apply a couple pieces of masking tape to hold together the surfaces to be hinged. Then thread the hinges through the hinge gap. I use groups of 3 hinge pieces; some people do groups of 2. If you mis-align the surfaces you can pull off the offending hinge and reapply it.

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Description: Overlap region and widths marked.Name: small P1000456.jpg
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Description: Ready to be pulled off the glass one at a time.
The hinge gap is sealed with a strip of Ultracote.
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Description: Covered with Corsair Blue Ultracote.  Hinge gap sealed with Ultracote.Name: small P1000460.jpg
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