Littlest BipeStik

[kdc914]

After realizing the challenges of my other idea, I decided to pursue a project that I had actually prepared for - a biplane based upon the Littlest Stik. Last year at Fall S.M.A.L.L. I purchased a Littlest Stik kit and and extra wing kit for it. When I told Doug my plan for it, he included a set of Q-Tee cabanes. Using my experience in building the fuselage of a Honker Bipe along with the Ed Larsen's EXCELLENT pictorial instructions of the Honker Bipe, this project theoretically has a reasonably high chance for success. Given that the Littlest Stik build is well documented elsewhere in this forum, my build photos and commentary will focus on the required changes to make it a biplane. Having already built a low-wing version of the Barnstormer, I am familiar with building a Stik design "upside down." Fingers and toes crossed...

[kdc914]

As a biplane, I have to invert the Littlest Stik fuselage as one would a Barnstormer to make it a low wing. The difference between the two is that the Littlest Stik has 5 degrees of downward thrust built into the shape of the fuselage sides whereas the Barnstormer does not. Therefore, an angle gauge and judicious application of Xacto blade is in order.
The first photo shows the unaltered side panels with notes indicating what must happen to them.

The second photo shows the angular difference.

The thrust angle mod completed.

Next: re-engineering the wing saddle for what is now the LOWER wing.

[kdc914]

OK. so now we tackle the saddle for the lower wing. Here's where the Box-o-balsa-scrap shines. Sometimes being a packrat comes in handy. Every conceivable shape and thickness just waiting to be used.

First we fit the odd angle

Then we cut/sand that flush and edge-glue more stock to accommodate the new curve

Now we take our newly created wing profile gauge and, measuring carefully to ensure zero incidence, draw out the desired new saddle

And, after a bit of carving and sanding (my favoritest thing EVER ), VOILA! I'll go back and add some extra for strength around the saddle and then we're ready to assemble the fuselage.

[kdc914]

Having completed the mods to the sides for an inverted fuselage, it's time to assemble. As with any project involving modification, I usually outsmart myself at least once and screw something up. Today I did it twice. Neither mistake was particularly bad but still annoying.

Everything in place. Fortunately, I remembered to flip the forward and middle former bulkheads before gluing them in.

close up of the assembled lower fuse mod for the wing saddle

And here's where the oopsies come in. I had to flip the forward and middle formers (not really, but yes from the standpoint of which way is "up"). In so doing, I thought I needed to do that for the aft former as well, so because one end is longer than the other I made a flipped image of it. Of course, I didn't realize that was incorrect until AFTER thoroughly gluing it into place. Not TOO terrible a mistake. At most, this will cost me slightly less than 2g of total weight for the carbon fiber stiffeners on the aft pushrods - that will now have to pass through the large hole rather than the small guide holes they were intended to use.

The other oopsie was a failure to RTFM. The last few WN kits I built called for gluing the aft end of the fuse sides together. This one does NOT, at least, not the way I did it. Easy enough fix with very careful application of the balsa saw.

And now it's beginning to resemble an airplane!

[kdc914]

Given that this bird will have twice the wing area of the normal Littlest Stik kit, I confirmed that lower wing loading meant I didn't need to use all the shear webs, thereby saving precious weight. After I completed the first wing, Dale Womack suggested saving even more weight by fitting the shear webs between the spars rather than in front of them. I did that with the upper wing. According to my presumably very accurate laboratory scale, I should have only saved a few tenths of a gram, yet the difference between the wings was a whopping FIVE grams. I can only attribute that to differences in wood density and/or moisture content.

Because of the inverted fuselage and battery placement, I need to put the landing gear in the lower wing rather than the fuselage. To do this, I borrowed from the method used on the Skylark and Sky Tiger kits - building a box for the wire to slip into adjacent to a wing rib. My only regret is not thinking of this BEFORE decking the lower wing. I should have extended the forward upper decking further beyond the inner rib to form the top of the box.
The rather complicated wire bend required to make this feasible

Next, I crafted proof-of-concept braces from relatively thin balsa

And here's how that looks with the wire in place

And finally a ballpark idea of the finished look. Now to go back and craft the outer braces in thicker balsa or ply. Then I'll quadruple check alignment and epoxy it all together

[kdc914]

Because I hadn't previously included the full-span trailing ailerons in the calculation, I had to revise my total wing area from 160in² to 170in². This new area measurement was used to create the new tail feathers, shown below with the kit originals on top for size comparison. At 29in², the horizontal tail is 17% of total wing area and a bit over 1/3 of wingspan. Not wanting to get too deep into geometry calculations, I used my calibrated eyeball to get the size of the vertical tail. Hopefully, it's enough.

Well, by gosh and by golly, it's starting to resemble an airplane!

Now, onto the cabanes. And then, even more [deleted string of expletives] SANDING...

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[kdc914]

The kit came with 7/64" balsa. My LHS didn't have that so I had to use 3/32". Given the extra area, that will help offset some of the extra tail weight. Here are the new tail feathers in 3/32" with the lightening holes cut. I used a quarter for the holes on the horizontal stab, a nickel on the vertical stab, and a dime on the rudder.

The original 7/64" tail feathers weigh 4.1g. My new 3/32" ones weigh 5.6g. Only 1.5g extra weight for the significant extra size. Not too shabby - IF they are strong enough. NOW on to the cabanes...

[kdc914]

When I ordered the Littlest Stik kit with an extra wing, I told Doug my plans for it and he graciously included a set of S-Tee cabanes. After playing around with those for a bit, I realized that I would have to recreate the saddle pieces for the upper wing anyway so I set the S-Tee parts aside and decided to do my own cabanes, using the example from my partially completed Honker Bipe. Step One was a trip to my local hobby shop for wood. I got both Balsa and Basswood.

The S-Tee cabanes from Doug are 9/64". My LHS doesn't sell 64ths and was out of stock on 5/32" so I sent with 1/8". Given that I was going with a material 1/64" smaller than what is presumably recommended, I opted to go with Basswood since it (theoretically) should be stronger.

Here is the mostly finished saddle and rough-cut vertical struts.

Pretty decent fit. Still some sanding to do on the upper wing AND the saddle BUT...

Now I have to figure out the vertical strut lengths, angles, and placement.

[kdc914]

I decided to use the horizontal pieces of the S-Tee cabane assembly as the forward verticals on my Littlest BiStik since they already had holes drilled AND happened to be more or less exactly the required length

After marking where the holes needed to be in the fuselage, I added some extra balsa inside for extra strength at the hole site

I needed to see of ironing covering over the cabane struts would be problematic so, I took some scrap and setup a test

Seemed to work out just fine. The upper parts that aren't touching the fuselage will have to be painted but, it looks like the lower end of the cabane struts can be covered at the same time as the fuselage side. I can glue the struts into place and then cover the fuselage. This seems to be preferable to covering the fuse sides, then marking where the struts go and cutting away covering from there to glue them in. IMPORTANT NOTE: IF ANYONE THINKS THIS WILL BE A BAD IDEA TO COVER THE LOWER STRUTS WITH THE FUSE SIDE, PLEASE LET ME KNOW ASAP.

The rear struts are next and then I can begin assembly of the full cabane structure.

to be continued...

[kdc914]

Now the hard part - alignment. Grid-marked cutting mat and calibrated eyeballs, this is your moment!

First, we add some 9/16th balsa inside the fuselage where the anchor/alignment holes will go. Next, using my angle gauge, I mark the lines for the rear strut to match the arbitrary angle set for the forward strut. Then it's time to drill.

Trial fit indicates "so far, so good" on the angle.

Now to set the holes for the upper saddle

And the more or less finished product. Given the crude methods used, I think I'm ready for admission into the TLAR Engineering group.