#18 Model Airplane Building Clinic >> Swanyshouse Primo 40 - RC Groups
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Oct 20, 2012, 10:28 PM
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#18 Model Airplane Building Clinic >> Swanyshouse Primo 40

Nothing to show except (at last!) a shipping notice for the kit. It was ordered on Sept. 21. Fortunately, I'm a patient guy. Heh. Stay tuned.

I don't have a power system picked out yet. That'll happen when it's framed up and I have a better idea of the flying weight. But certainly no less than 150 watts per pound. It's a 3D plane after all.

The decks are mostly clear for the build to begin. There's Formosa-II ARF in the works, but it's getting near the end.
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Oct 22, 2012, 07:23 PM
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A package arrives

Photos document the unpacking process.

I have to say I'm a bit intimidated by what I see so far. Tough to relate the low-contrast photos in the printed manual to the parts on hand and to the large plan sheet, which only shows a top view of the wing and side view of the fuse.

I've already asked Paul for a PDF of the manual, thinking the photos might be easier to decipher on-screen than in the laser-printed manual.

Parts that form the fuse should be easy to identify. But I found myself stumped with just the first few steps.

It seems the entire fuse, including possibly the root ribs, is built around the massive 3/4" thick plywood motor mount and fat CF rod that runs down the length of the fuse. However, since this will be an e-conversion, I know I'm going to have to hack the motor mount. I was hoping to save the hacking for later.

Well anyway, I was looking for "something different" and for sure that's what I got. This kit isn't like any other I've built so far.

UPDATE: Paul has responded (with lighting speed) with links to a PDF manual, full-sized photos of the build steps, and links to related build threads on the ProBro site (but not specifically a Primo 40 build.)
Last edited by rafe_b; Oct 22, 2012 at 10:43 PM. Reason: added update
Oct 22, 2012, 07:45 PM
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Should have added to last post... here's a scan of the motor mount plywood part. I mistakenly said in last post that it was 3/4", that was wrong -- it's 1/2".

But still, a massive bit of wood. 3.7 oz. right there.

Thought about the e-conversion hackery and realized that my usual motor mount technique (for profile planes) should work here as well.
Oct 23, 2012, 10:22 PM
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Root Rib Assembly

The photos illustrate Steps 1-4, center rib assembly. There are eight CNC cut balsa pieces involved.

Not sure why they don't do this in the manual -- but it does help to assemble this over the plans.

What you end up with is a square channel through the center of this assembly, that wraps nicely around the 1/2" (o.d.) CF dowel that runs through the motor mount plywood and the length of the fuselage.
Oct 28, 2012, 08:16 PM
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Wing In Progress

Okee dokey. Notwithstanding some hurricane preparations, got a few hours in on the Primo today, and the wing is definitely taking shape. The work shown in the pix gets me to the bottom of Page 7 of the instructions, though I missed a step: the shear webbing between the top and bottom main spar. No problem, I'll tackle that after the sheeting has set and after I've removed the tape that's holding it down.

All told, pretty straightforward. Follow the directions, think through each step, and you won't go too far wrong. Pinning down the ribs was the most laborious step.

I did find that I had to sand (open up) the notches for the 1/4" main spar a bit. No big deal. It might have worked without sanding but I didn't want to push it.

The only unusual bit is the main spar assembly itself, which involves a sandwich of very thin CF material, and 1/8 x 1/4" hardwood. (First two photos.)
Oct 29, 2012, 11:59 AM
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Shear webs installed. I chose to measure and cut them before installing them. That way I could apply beads of CA along their edges, rather than trying to apply the CA to vertical surfaces of the spars. Minor confusion here -- are there four webs per side or three? Photos and written instructions say three, but a note on the printed plans say four. I went with three.

Some decisions need to be made and probable departure from plans. What servo size? Primo's web page says "standard" servos. But what torque range? Some 40 mm servos have torque upwards of 150 oz-in, but weigh 2 oz. apiece. Then there are a bunch of 35-36 mm servos at 2/3 the weight and 65 oz-in.

Plans/instructions call for hatches in the two center bays, but do I really need hatches? What am I going to put inside the wing? This decision impinges on wing center bay sheeting. Obviously simpler and neater without hatches.

Home today on account of a hurricane. Oddly enough it won't be the wind that stops me today, it will be lack of CA. Almost out, and not really the right weather for a jaunt to the LHS. We're starting to get some serious gusts out there.
Oct 29, 2012, 08:24 PM
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Low-hanging fruit for now. Ailerons quite straightforward, with one little twist, as explained in the photo. Wing has been set aside for a bit. Tailfeathers next.
Oct 30, 2012, 01:07 PM
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JimTMich's Avatar
Hey Rafe_b, take a step back on the servos.... It's a 48" plane, so HS-65MG might be OK, or HS-85 like a 51" Slick. I strip HS-65MGs on 48" planes, So I think I would do HS-85MG or digital as the 85's are kind of slow. Just my 2 cents. Never built a 48" profile.
Oct 30, 2012, 02:54 PM
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Murocflyer's Avatar
Wrong plane size
Last edited by Murocflyer; Nov 01, 2012 at 01:17 AM.
Oct 30, 2012, 08:49 PM
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JimT: I may take another day or two to decide on servos. Considerations are: weight, size, cost mostly. $15 apiece is my limit. I really have little experience with servos larger than 11-14 grams. The hardwood servo rails are 43 mm apart, and it looks like I have about 36 mm of depth below the rails.

Frank: enjoy your Primo 15 build. Thanks to both of you for chiming in... I wondered if anyone cared....
Oct 30, 2012, 08:52 PM
Promoting Model Aviation...
Murocflyer's Avatar
Removed. Wrong plane size
Last edited by Murocflyer; Nov 01, 2012 at 01:17 AM.
Oct 30, 2012, 09:26 PM
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An hour or two this evening yields rudder and elevator. Each built from a combination of sticks and CNC-cut parts. Totally ordinary stuff. Pin major parts to plans, then cut & fit the ribs one by one.

I use thin CA for all these joints. After the glue has set and I peel the part off the wax paper, I put thin CA on the joints from the opposite side. I use a pipette tip on the CA bottle so the glue can be applied precisely.
Oct 31, 2012, 06:49 PM
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Just ordered four HS-485 HB servos from servocity.com. Must admit their site is well organized and very detailed.

67 oz-in, 1.6 oz. weight. More than I'm used to paying for servos, and I've hardly ever used Hi-Tec servos -- but my usual cheapo vendors didn't quite have what I wanted. HobbyCity did, but their shipping cost added 50% to the order, so fuhgeddaboudit.

Motor, ESC, battery and prop selection still far off. For that, I'll need to have the plane "in the bones" to mock up a power system weight-wise against CG requirements and all that.

Like, for example... sometimes it doesn't pay to economize on motor weight, when you're gonna need extra weight up front just to get CG right. You do what you can shifting the battery around... but there are physical limits. And it's always a nice touch if you can get the battery right on the CG, with lots of room to shift fore and aft.

Ideally she'll fly on 4S, since I have a few 4S/2600 and in that range. But if it needs higher voltage (and a couple new batteries) so be it. I'm thinking 800-1000 watts, in that range, based on a flying weight of 4 lbs. or a bit over.
Oct 31, 2012, 09:27 PM
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Horizontal stab. Note the inlaid thin 1/4" wide CF strip, at trailing edge and near leading edge. Pretty clever. Makes for a strong assembly, and it really needs to be.

Built mine a wee bit different from the plan because it fit better with the angles cut into piece #24. Should be obvious in the pix. I just can't see it causing a problem.

I really am running critically low on medium CA. Surprisingly hard to find online, and LHS charges waaay too much.
Nov 03, 2012, 09:26 PM
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Fuselage is mostly done. Certain details are now clear, viz.:

The black glass tube diameter is larger than the thickness of the fuselage. That means that the fuse has to be covered as two separate pieces. The tube "shows" in the final product -- it's not hidden by covering.

For the same reason, it makes sense to treat the fuselage as upper and lower halves until much later in the game, since it really is built around the fiberglass tube and won't be "one" until final assembly. Until that time, the only thing(s) holding the two halves together are those two short vertical ribs and the aft-most piece to which the rudder will be hinged.

There's a set of four ribs to which the R/E servos attach. Again, these items are deferred. I mean, why commit before it's necessary?

Also a pic of the shear web installed in the wing, even though that was done a few days ago. I'll get back to the wing as soon as I get hold of some fresh medium CA!

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