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Obelix Build Log
- Thread starter Mucksmear
- Start date
3/16” thick vertical fins. Straightforward build with medium and hard balsa. Haven’t decided yet on whether to glass or Ultracote on the fins, but I’m leaning towards glass. They will probably be glued onto the wing with e6000 or some other semi-flexible shock resistant adhesive.
Now that I have all the major pieces, it’s mandatory pre-assembly time so I can have a look-see.
Now that I have all the major pieces, it’s mandatory pre-assembly time so I can have a look-see.
Dunno about the colors yet. When I redrew the plans I gave it a smallish, elongated bubble canopy that implying an apparent scale size similar to a B-57 or a B-47. I was thinking some scale-like USAF SAC or NASA test flight markings. Bare metal would be neat, but I’m wondering about visibility. Or I could just go with sporty colors. I still have lots of time before I have to decide!
The 50” Obelix build resumes!
I’m doing the same edge treatment I did on my Coyote to create just a little bit of an inside corner fillet of epoxy/Cabosil where the glass on the wing surface meets glass on the vertical face of the sub-trailing edge cutout, ie. along the hinge-lines. This starts with sanding a tiny 45 deg bevel along the normally 90 deg edge at the sub-TE
A strip of tape along the sub-TE and the previously sanded bevel form a little valley for the inside fillet
In this last photo you can see the little fillet of epoxy/Cabosil. Once I pull the tape off, the back face of the fillet should be relatively straight and flat a I’ll need to do a little sanding to get top flush with the wing surface.
I’m doing the same edge treatment I did on my Coyote to create just a little bit of an inside corner fillet of epoxy/Cabosil where the glass on the wing surface meets glass on the vertical face of the sub-trailing edge cutout, ie. along the hinge-lines. This starts with sanding a tiny 45 deg bevel along the normally 90 deg edge at the sub-TE
A strip of tape along the sub-TE and the previously sanded bevel form a little valley for the inside fillet
In this last photo you can see the little fillet of epoxy/Cabosil. Once I pull the tape off, the back face of the fillet should be relatively straight and flat a I’ll need to do a little sanding to get top flush with the wing surface.
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Nowdays I tend to glass the face of the subTE separately from the wing surface to avoid the glass trying to pull away from the sharp bend around the edge (almost 90 degrees) before it’s cured.
In this build I’m using silicone glue hinges where the control surface is adhered to the top edge of the subTE. This seems like a potential area for the glass to delaminate or peel away.
The interior fillet of epoxy/cabosil strengthens the corner and firmly ties the glass from the wing surface to the glass along the face of the subTE
If you’re using traditional mechanical hinges like hinge-points, etc that get inserted into the subTE then this isn’t even an issue
In this build I’m using silicone glue hinges where the control surface is adhered to the top edge of the subTE. This seems like a potential area for the glass to delaminate or peel away.
The interior fillet of epoxy/cabosil strengthens the corner and firmly ties the glass from the wing surface to the glass along the face of the subTE
If you’re using traditional mechanical hinges like hinge-points, etc that get inserted into the subTE then this isn’t even an issue
I believe I read on either the Barcs forum that he passed in Dec of ‘23.
The epoxy/Cabosil fillet (bead) needs to be done first because the fillet is on the interior corner of the glass. Other than that, it doesn’t matter which order you glass the top, bottom and subTE surfaces.
The sketch at the top of post #68 shows from left to right:
Frst sketch:: the basic section through core, veneer sheeting and balsa subTE.
Second sketch: the beveled top edge of the subTE and a strip of tape on the face of the subTE. The V channel created between the bevel and the tape gets filled with epoxy/cabosil and then sanded flush with wing surface.
Third sketch: the completed structure with the glassed top, bottom and subTE including the epoxy/Cabosil fillet on the inside of the corner
The sketch shows the fillet on the upper corner which is for a top hinged control surface attached with a silicone/glue hinge.
On this build I’m actually putting a fillet on both the top and bottom corners since I had already beveled them before I realized I only needed to do it to the edge where the hinge attaches.
Doc J
Very Strong User
Unfortunately yes, but a fitting tribute to Chas (and many others) that their designs are still being built and flown.
Started glassing. Decided to go with 1.5 oz/yrd^2 cloth for a little more surface durability.
I clamp wood clothes pins to the edge of the overhanging excess cloth along the LE and tip and then either lean them inwards or push them under the LE with a block to ensure a small overlap with the cloth from the other side.
Incidentally, I discovered if you tape one end of a single edge razor blade and leave some extra tape overhang the end, the overhanging tape makes a nice “grip tab” so you can wield the blade close and shallow to any surface without your finger tips getting in the way. I find it allows for a lighter touch and more delicate control.
Started glassing. Decided to go with 1.5 oz/yrd^2 cloth for a little more surface durability.
I clamp wood clothes pins to the edge of the overhanging excess cloth along the LE and tip and then either lean them inwards or push them under the LE with a block to ensure a small overlap with the cloth from the other side.
Incidentally, I discovered if you tape one end of a single edge razor blade and leave some extra tape overhang the end, the overhanging tape makes a nice “grip tab” so you can wield the blade close and shallow to any surface without your finger tips getting in the way. I find it allows for a lighter touch and more delicate control.
Doc J
Very Strong User
Really nice tidy build Mucky - Chas, would have been happy.
Have you ever flown one?
Not sure about the double size, but the smaller giveaway plan version was a real handful and great fun to fly - especially if you got the CG a tiny bit wrong.
Are you going to leave it a wood finish?
Really nice.
Doc.
Back in the mid 80’s two buddies and I regularly flew the 36” built up ones from the pull out plans. I think I built 3 of them back in the day. We found them to be well behaved. Interestingly, with the CG and trim dialed in, the model could be flown inverted or right side up with no trim changes.
As far as I know, he only published the 36” one but a fellow named Pete Burnett published the “Masterix”, which was a development of the Obelix with a few design differences and span of 48”. Both plans are on Outerzone.
This 55” is my own upscaling of the original 36”. It will be painted. There’s a big ugly scar on the top left panel.
Doc J
Very Strong User
Hey Mucker,
yes, we found much the same on the inverted flying side. The biggest problem I remember was figuring out which way up the damn thing was at times. I put two higher fins on my second plane to help with that, which it did a bit. I put two "L" plate learner driver stickers on the bottom too - do you still have "L" plates in the UK?
The inverted performance was always surprising, but if you asked Chas why he would just tap the side of his nose and say "It was designed that way" He was a real character. I don't think he knew why actually.
Looking at it now with a bit more experience I think in flight the center and outer wing sections are quite well separated by those "wing fence" fins on the upper surfaces and the bulbous nose will drive the isobars to each side. That would have had quite an effect on the pressure and spanwise flow profile.
Is there a wing section given on the drawing or is it one of the traditional RCM&E "Size Ten" sole of the shoe sections? As I remember Chas told me it was a "reflex" section that he'd dreamed up with some ancestry from another earlier model. I made one with an E180 section which was a lot thinner and so faster but with little inverted performance. Killer rolls though.
I think the Obelix might have been among the most built of the RCM&E giveaway plans.
Great fun for me right now as I'm making forays back into balsa right now with AWD.
Cheers,
Doc.
So I’m in the USA - we don’t have L plate stickers here, but some learners will put a note or sticker on the back to ward off road ragers.
Yes, we had orientation issues. I’ll have to put some thought into the color scheme.
The Obelix sections are not reflexed as far as I can tell, but the center section is rigged at a more negative angle than the outboard panels. Based on the plan write up, I got the impression that Chas developed the sections himself (with a shoe?).
