Crobe 2 scratch build - RC Groups
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May 12, 2008, 02:42 AM
Just a test glide...
mkeveney's Avatar
Build Log

Crobe 2 scratch build

My Crobe 2 build is now underway.

If you've never heard of the Crobe 2, please see the general discussion thread here:

It will direct you to the original Crobe site, with plans, etc.

I thought I'd contribute a build log, since I've learned so much from other build logs. I'm scratch building from the plans, since I aleady had most of the material on hand.

I think it would be a good idea to keep general discussion of the Crobe2 on the original thread... but please feel free to add any questions or comments about my build in particular here.
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May 12, 2008, 02:43 AM
Just a test glide...
mkeveney's Avatar
I have had bad luck trying to transfer printed plans to balsa. I've tried carbon paper, a hot iron to transfer heat-sensitive copying machine toner, and acetone to dissolve the toner. None have worked for me. Things always seem to smear, transfer incompletely, or get distorted.

Instead I simply make an extra copy of the plan and cut the parts from it. (In this case the Crobe 2 designer has helpfully included a parts sheet separate from the plan.) Then I stick the paper to the balsa; cut the part out; and remove the paper.

To attach the pattern, you can use rubber cement if you like... it leaves a gummy reside that has to be rubbed off when you're done. I don't care for it particularly.

The stuff I currently use is called 3M Remount. I got it at an art store ages ago. I'm still on my first can.

You spray it on, let it dry, and then stick it to whatever you want, over and over again. It comes off without leaving any residue. I think it's the same stuff as on the yellow Post It notes.

An advantage of this approach is that you can put the part anywhere on your balsa stock you like: Align straight edges on the part with straight edges in the stock, or hold your wood up to the light to find the absolute lightest (or strongest) portion of the wood.

You can stick the patterns to a piece of waxed paper and save them for future use too.

This photo shows some patterns cut out and sprayed (sitting upside down on an overspray sheet...rather hard to see).
Last edited by mkeveney; May 12, 2008 at 03:01 AM.
May 12, 2008, 02:45 AM
Just a test glide...
mkeveney's Avatar
These shots show the fuselage sides, doublers, and tailfeathers... the remainder of the parts are similar.

I had to arrange the grain on the doublers lengthwise (contrary to the plan) since the part wouldn't fit any other way on the stock I found.
May 12, 2008, 02:45 AM
Just a test glide...
mkeveney's Avatar
I did wet and clamp the sides as described in the build instructions, but forgot to photograph that step. This shot shows the doublers glued in place, with the clamping re-established. (Right now that can of dope is just a weight, but I'll be using it for covering later )

I glued the doublers with CYA, and will probably be using CYA instead of PVA for most of the construction. (I'm patient enough to cut out my own parts, but not enough to wait for glue... go figure).
Last edited by mkeveney; May 12, 2008 at 02:57 AM.
May 12, 2008, 02:50 AM
Tearing the Skies a new one...
Sensiblenick's Avatar
That's a lovely job you've made of those parts..

Since reading the Crobe2 thread I've been itching to see one of these go together. Now sat on the edge of my seat awaiting more pictures



PS.... Sand it round!!
May 12, 2008, 06:21 AM
Closed Account
no one trying a glass or vac formed fuse yet..

seems possible for this size model

May 12, 2008, 08:58 AM
Gravity gets me down.
wingbeat's Avatar
Beautiful work. I need to go get some "reading glasses" to cut parts... my near vision is shot, and those wing parts tiny!

I like that spray you found. I did the same technique, only with 3M77 sprayed in a light coat.

WTG on starting a plan build. Subscribed.

May 14, 2008, 02:42 AM
Just a test glide...
mkeveney's Avatar
Oops.. forgot to post stuff yesterday. Today's entries actually cover two days of off & on work.

I added the extra skinny doublers in the hatch area. As I mentioned before, the pattern calls for the main doublers to be arranged with vertical grain. Since I had to arrange them horizontally, it would've made more sense to combine them with the hatch doublers as a single piece of ply.
May 14, 2008, 02:44 AM
Just a test glide...
mkeveney's Avatar
The triangle stock is installed. I had to cut my own, since I could find no 4mm stock at the hobby shop.
May 14, 2008, 02:45 AM
Just a test glide...
mkeveney's Avatar
Gluing the forward bulkhead in place. The servo mount rails were cut to size and simply held in place by the clamp in this shot.
May 14, 2008, 02:46 AM
Just a test glide...
mkeveney's Avatar
The servo rails are now in place. It was tricky to get everything clamped in place properly for this step. Slow drying glue would've probably been smarter than cyano, but I managed to pull it off without gluing the servos in!
May 14, 2008, 02:48 AM
Just a test glide...
mkeveney's Avatar
Forward sheeting now installed. The plans and instructions did not specify whether the sheeting was to be arranged with grain crosswise or lengthwise. I opted for crosswise, since it's easier to bend this way, and it's the way I've seen it done on other planes.
May 14, 2008, 02:49 AM
Just a test glide...
mkeveney's Avatar
I tapered the triangle stock before installing the rear bulkhead. I figured it would be easier to get the knife in there before the fuse was pulled together.

Here's my trick for marking a line to taper stock when it runs around curves: use a piece of tape for your line.

You can easily reposition the tape until it eyeballs exactly straight. If you trim very gently, the tape also seems to guide your knife when you get down to the last little slivers.
May 14, 2008, 02:50 AM
Just a test glide...
mkeveney's Avatar
The rear bulkhead is in and the sides are now joined. They aligned perfectly, which is rare for me. Usually some kind of twist has worked its way in by now, and I have to persuade the wood to line up before gluing. This time I seem to have nailed it pretty well.
Last edited by mkeveney; May 17, 2008 at 12:57 PM.
May 14, 2008, 02:52 AM
Just a test glide...
mkeveney's Avatar
With this much complete, I started to worry about how I was going to insert the servos. It's a little tricky to insert the second servo with the arm already screwed on -- and there's no room to attach the arm once the servos are in there.

I figured out the following technique:

First get the servo arm on the splines so it's 90 degrees from the case at neutral.

Then plug everything in and move your transmitter sticks so the arm goes all the way toward the top side of the fuse. (Or just force the arm over by hand if you're not worried about stripping the gears.)

When inserting the servo you'll have to tease the arm into the slot, and might have to turn it back a little bit before you can get the servo seated properly.

By the way... I had to increase the width of my fuse by about 3mm to accommodate my 6.4 gram Blue Arrow servos.

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