View Full Version : Build Log - Guillow's B-17G Electric Conversion
04-10-2006, 08:10 PM
I've just started my build, and have gotten to the point where I have the left side fuse formers attached to the top/bottom/left side stringers.
I have not yet fully decided on power systems or covering, but I know I want 4 working motors (so I will probably go brushed to keep costs down, and use 2S TP1320 lipos). I'm hoping for a final AUW of no more than 24oz.
Now I need some advice. I have seen other people talk about removing excess balsa from things like the fuse formers, wing ribs, etc. I'm wondering if I should do the same? It would be easy for me to still do the formers as I only have the left side attached at the moment. I can cut down the right side formers before attaching. I can also remove a lot of balsa from the main stringers as they are about 3/8" thick. I have a dremel and want to put it to good use.
Is this advisable? I want to come in as light as possible, but don't want to weaken the structure too much, or remove balsa where it might be needed later in the build. Also, I will have fixed gear, and don't plan on adding any extras other than what is included in the kit. I plan on using 4 channels only (speed, elev, rudder, ailerons).
Appreciate any suggestions you guys may have. I will post pics as I progress.
04-10-2006, 09:34 PM
Hi Pat, good luck with the B 17! That's an ambitious project. You might want to check out Ozzieflyers' "Lancaster" build thread, I believe it's on the "Indor + Micro" Forum. He's using 4 motors also.
One of the reasons many flyers don't use the Guillows kits for conversion is that thay have a reputation for supplying heavy and/or too hard balsa. Their die-cutting used to leave something to be desired also but I think they're laser-cut now. Since you've built a Stevens Aero kit, have you noticed a difference in wood selection? If the wood in the "Fort" kit seems too heavy, it is possible to cut away some, but I would limit it to the formers; Replace the strip wood. It's almost impossible to reduce strip stock without weakening it. Just make a list of the sizes and quanities needed (bear in mind, balsa only come in 36" lengths unless it's a very well-stocked shop) go to the shop and hand-select every single piece. Strip wood is fairly cheap, you can replace everything for about $10.00. Later, if you want to keep building and maybe "Scratch" build, a "Balsa Stripper" is a worthwhile investment.
Not only will this save weight and time, the airframe will be stronger, since you won't have any cut-away sections on the long pieces.
While you're at it, check the rib stock. Too heavy? Buy a sheet or two of 1/16" x 3 x 36 and cut your own. Check the spars, leading edge, trailing edge. Replace as needed.
I'm sure you've seen these electric models with transparent covering showing artfully cut-out pieces, holes, etc., but remember, they started out with light ("contest") balsa. That's where the real weight savings comes from. Balsa selection and less glue are the two biggest weight savers in models.
04-10-2006, 10:20 PM
Thanks for the kind words. Yes, this will be an ambitious project, and look at my signature to see what's next in line (B-29!). I may use the B-17 build as a learning process, and apply the knowledge gained to the B-29 build.
I think the kit I bought was produced fairly recently, as the die cuts are all clean and no crushing is evident (but not laser cut, that would have been nice!). But I did notice that some of the balsa sheets are pretty hard, almost like lite ply.
I'm using thin CA instead of epoxy and hitting each glue joint with insta-cure, so I save a little there, but I will probably use 30-minute epoxy on the major joints (tailfins, wing root, etc).
I'm sure I will be going to Michael's for replacement balsa. They sell the same stuff as the LHS, but cheaper.
04-12-2006, 02:15 PM
.........I'm using thin CA instead of epoxy and hitting each glue joint with insta-cure, so I save a little there, but I will probably use 30-minute epoxy on the major joints (tailfins, wing root, etc).
Why use epoxy at all? I would use thin CA, than add some thick at any joint that might need added strength.
It seams that a lot of people don't trust CA: they think it's bonding ability is less than epoxy. I beleive that is all wrong, and one of the few reasons we would want to use epoxy (instead of CA) would be to fuel proof something (CERTAINLY not needed here).
Otherwise, epoxy tends to be:
1) heavier ( because it usually has a bigger 'blob' than CA)
2) more labor intensive.
I have one of these kits also, and plan to build someday using E-power/ 4 motors, and possibly retracts, so I am following with interst. Awhile ago, I figured out that scale prop size is somewhere around 5" dia, so I was looking for those old Cox 3 blade props. Hopefully tho, by the time I get around to building it, a newer generation of small, scale looking electric props will be available.
And I don't think that sanding and replacing balsa will reduce weight by a signicant amount, if the projected final weight is 24 oz. These are designed to be light to begin with: for rubber power and CO2 power? In fact, I started a Guillows SBD Dauntless build, and deciced to substitute the 1/16" balsa strips with 1/16" SPRUCE strips, for added strength.
So I just don't think they can be lightened by much more.
Just my 2 cents.
04-12-2006, 07:36 PM
Yeah, I've thought about skipping epoxy all together, and after making recent repairs on my Super Cub with thin CA and Insta-cure, it has me thinking CA is the only way to go.
And I think I will skip removing extra balsa too. If weight is going to be a few ounces more than I plan, then I'll just compensate with more powerful motors. Although with the efficiency of todays motors, I don't think that will be a problem. My biggest obstacle will be finding those magic 3-blade props! If I find good ones, I'll be sure to share my source.
I haven't touched it since last weekend, but more building will be happening over the next 4 days. I will post pics of the progress. Maybe a full set of bones by the weekend!
04-15-2006, 03:32 AM
Here's a quick update on progress so far. The fuse is completely framed and ribbed. I will eventually take the dremel and slice off the top portion of the fuse for use as a hatch. It will be secured with small dowels in the front, and magnets in the back.
Working on the wings now.
07-07-2006, 07:21 AM
Any progress Pat?
I'm doing the Guillow's Catalina at the moment (an "on-the-side" job)
07-14-2006, 09:25 PM
Sorry, was out of town for a few weeks with limited internet access, so I am just now seeing your post. I had actually set the B-17 aside in favor of other projects. I will be getting back to it soon now that the summer heat is driving me inside. I will update as I progress.
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