I am to the point where I am putting everything together. No matter how careful I was trying to be when constructing the wing, there is some misalignment with my booms - I have to pull them together to contact the stab. The plans say that I can use 1/4" balsa to widen the stab to solve this exact problem.
How common is this? And how bad is it to use those balsa spacers? Should I try to do something with alignment first to get it closer or should I not worry about it? I am uncertain as to what kind of effect all this has on flying characteristics. I would imagine if it's still symmetric, it should only be a tad slower - that's all.
Nikita.

Hi Nikita,

It's common. When I built my first one (std bobcat), this was before the spacer even existed. I found that I needed about 1/8" added to each side to make the stab touch the booms at their closest point.

I checked with some other builders (including BVM rep Tony F.) at the time, and they too had needed to add approx 1/8" spacers. In my experience, any of the top pattern guys who actually build their own planes tend to be extremely accurate builders.. Tony comes from that background, so if even he had to use a spacer, then I don't feel bad about using one.

Right now I'm building an XL, and again found that I need about 1/8" on each side, so I shaped the 1/4" spacers so that they are about 1/8" wide at the narrowest point and flare out to their 1/4" width at the front & back of the stab. Shaping the 1/4" spacers is a better way to do it than the completely straight 1/8" spacers I used on the first cat, as it means that less filler is needed to get the correct shape... and less filler = less weight.

Personally, I'd caution against trying to pull the booms together to decrease the amount of spacer needed. Doing that would put stresses all over the place. Get the centre-section to boom fit as good and as straight as you can, then pad the stab as necessary to fit whatever gap that makes naturally.

If putting spacers in was bad, they would not have included them in the kit.

The above is just my non-professional opinion of course - check with a rep, or with Dana or David at BVM if it makes you more comfortable.

BTW, if you have not finished the fuz yet - check the BVM website, as there is a new "addendum" entry posted there today, regarding the positioning of former F2 for the XL kit.

Regs,
Gordon

Hey Nikita.

I just finished this step a few weeks ago. Here is how I went about it.
First asemble the center section with the booms pulled tight against the center section. Measure the front of the booms from center to center(I marked the center of the booms on a piece of paper to get a more accurate measurement.)
and the rear edges of the fins. You should be at least within 1/8"

Now you can determine if you need to use the balsa fillers. I'm 99% sure you will still need them, but it is no big deal. Since the bolt holes aren't on the center line of the stab, mark their location before you glue them on. Once you get them glued on you will still have to sand and carve them down to fit the curve of the fins.

If you use Evercoat 408 to fill the small gap that is left, cover the inside of the fin with wax paper and NOT masking tape.
My fillet stuck to the tape and not the wood. So I had to re do it.

Good luck
Jeremy Smith

Thanks for the help on the stab, guys, I now feel somewhat better about the situation. I am almost done glassing the wings, I will soon put it together and fit the stab according to your suggestions.

I have a question about the battery. Is it desirable to have two batteries in the plane? Would I just use a Y-harness to plug two separate switches into the receiver? What about CG issues?
Also, what kind of battery is best - regular A-cells or something like SC-cells? I guess I will go with a 4-cell battery (or two) for now, since dealing with regulators and voltage issues is too much for me for now. It's 5 times more complicated than my previous projects already. I know that with A-cells I can get a 1700mAh battery, which is around what the manual suggests. I used that in an Edge540 and worked well for me.
Nikita.

If you want a really tight gap, pitch the tape, waxed paper, saran wrap..... al of it and use parting wax. put that on the booms and fill. Pop it loose and you have a perfect fit.

David Reid

David, where do you get this parting wax?
And do you have any suggestion on my battery question just above?
Thanks. Nikita.

Dunno where David gets his, but I get mine from the local Tap Plastics store.

Gordon

I think I got my parting wax from Composite structures technologies, but any store that sells fiberglassing materials should have it. (It's the green wax)

Batteries, in both of the BC's that I have built I have used 5 cell 1800 mah packs I am about to finish stuffing the batteries into mine today as I finish the engine installation (and the plane ...... Halleluah!!!!) but in the first one I built it took absolutely no ballast to get the CG right on the money. I did not use a voltage regulator but it is a simple matter of plugging the thing in after the switch and before the reciever. I have not used 2 packs on any jets yet, but in a larger aerobatic plane I simply plugged the second pack into a switch then into an unused channel in the radio and it worked fine.

I too loose the tape, saran wax, etc.

A thin coat of 'vaselene' smeared on with a finger works great. Just apply sparingly to the part you don't want bonded,
then putty, let dry and pop appart. Works every time.

I agree with David, I have tried everything, and the wax is the best.


I just saw VERY large parts (over 90 inch long fuse parts for a military UAV) popped out using pure carnuba wax.

It must be PURE, I guess they put some other stuff in it for furniture or whatever that use that stuff for.

Matt