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SS1 Airframe Assembly
A lot of very visible progress happened between Thanksgiving and Christmas of 2007. I had some vacation days to burn at the end of the year, and the Arizona weather was absolutely irresistable. So naturally I spent the time in my garage. But the day I finally assembled all the pieces I managed to move the work out into the Arizona sunshine.
It took a very long time to get to this point, and when the final assembly finally came together I was extremely pleased with the results. I spent a lot of time planning and preparing for this particular operation, and it paid off.
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This photo was taken just after I completed glassing the lower joint attaching the airfoils to the fuselage. The airframe is inverted on the alignment jig I built to help me keep everything straight. I also used a laser level with a crosshairs to assure that the airfoils were perfectly aligned with each other.
The white coils of wire you see hanging from each wingtip is the servo wire. I fed it through a hole in the wing, then through a hole in the fuselage. I used six-strand CAT-3 cable; each horizontal stabilizer will used two servos, and each servo uses three wires.
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Here is the main reason that this assembly step went so smoothly: I had installed threaded inserts into the ends of the aluminum spars that span the airfoils (Look [HERE!] for details).
I attached blocks of wood on each side of the airfoils and tightened the screws down to pull the airfoils snug to the fuselage. This pulled the joints tight and kept the parts from moving around, which made the alignment and installation extremely easy.
I glassed the lower joint first. I used one layer of 1-inch fiberglass tape and let it cure. I then applied another layer of 3-inch tape over that.
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Once the resin on the lower joint cured I flipped the assembly over and glassed the upper joint. I first applied 1-inch tape, then a layer of 2-inch tape over that. Once the tape is sanded it will virtually disappear.
Why the fascination with fiberglass tape?
I have found that it is lighter than any fillet material - why fill a gap with ounces of goopy fillet material when you can span it with tape? It is also stronger. Fillets often crack on a hard landing, but these layers of fiberglass are much less brittle. Finally, if the tape is installed properly the only fillet work required is minor cosmetic blending.
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Before the vertical stabilizers could be attached, I needed to run the Cat3 cable through to the servo compartment.
I didn't take pictures of the step where I drilled a hole from the front tip of the vertical stabilizer back to the servo box. I used a really long 1/4" drill bit I bought for a buck at Harbor Freight. (It was a pretty barbaric piece of surgery. Gerald Meux was there helping to decide where to put the servo box, and I think it kind of freaked him out the way I went after the stabilizers with that drill.)
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After I removed the blocks of wood that I used to snug up the airfoils (don't need those anymore) I ran a piece of string through each hole and then pulled the cable through. Then I attached the vertical stabilizers to the airfoils using screws into the ends of the aluminum spars.
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I aligned the left and right airfoils with the markings I had previously drawn on the vertical stabilizers. I also took meticulous measurements to make certain that everything that should be parallel or perpendicular was. I moved carefully and slowly around the airframe with the next steps so I wouldn't bump anything before the epoxy cured.
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Once I was satisfied that the alignment was correct I proceeded with the application of fiberglass tape at the joints.
The photo at the right show the vertical stabilizer attached, and the epoxy resin curing. Something about that photo seems terribly undignified.
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The last detail added to the airframe was the canard fin and the extension on the airfoil. I used 1/8" aircraft plywood for the canard and added a layr of 3oz glass. The extension is shaped out of some fin material I whipped up once upon a time when I needed some G10 on a Sunday afternoon.
The extensions will look a lot better once they are blended into the airfoil.
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Dry Fit
The big moment -- the dry fit of all the airframe parts, including the horizontal stabilizers.
Just for comparison, I stand five-foot eight.
Here is the best part:
- Everything on the rocket that you see here weighs only 23.6 pounds!
- The Center of Gravity is located in the same spot as the successful reduced-scale glider.
- This means that no significant ballast will be required to make this bird airworthy.
The final weight is likely to grow with the addition of paint, fillets, RC components, etc. However, for this large airframe to weigh in at less than 25 lbs is extremely engcouraging. I normally overbuild everything; this craft is lightweight and not underbuilt at all.
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Access Port
I really don't like cutting into these fiberglass airframes once they're finished, but sometimes it is unavoidable, like the cutting of fin slots. I decided I would have to include a large access port in order to install the RC controls, but I put off the operation as long as possible while I planned where to put it and how to make it.
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The most sensible location seemed to be an opening similar to the egress port on the starboard side of the SpaceShipOne. I thought about purchasing a 6" hole saw for this operation, but decided the $40 for roughly 3 seconds of cutting was too steep. Also, ahole saw would leave a gap nearly 1/8" wide anyway, so I would still have to fille the edges with Bondo anyway — a clean edge would be nice, but would still need to be modified.
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I used a trepanning cutter I bought at Harbor Freight for $1.99 instead (partially shown in the lower left of the photo). It wasn't as clean a cut as a hole saw would have been, but I knew that going in. The chunk missing from the top edge of the hole is a missing piece of bondo filler. The hole spans the joint beteen the main body tube and the front transition.
The SS1 is topside-down in this photo, in case you don't recognize the orientation.
Once the hole was cut I needed a way to re-install the cover plate, so I made a backing flange.
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- I cut three O-shaped pieces of 1.5-ounce fiberglass mat (8" outside diameter and 5" inside dimeter) and applied these to the inner edge of the opening.
- Then I took an 8-inch disc that I had cut from 1/8" polypropylene stock and applied it to the back side.
- I bolted these together to hold them in place
The photos below show the assembly while it cures — from above the access port and from inside the airframe. The cover plate is covered in masking tape to prevent it from being cemented into place.
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Below left is a photo of the completed flange. Through the opening you can see the core tube running through the center of the rocket. Below right is the access port with the cover installed.
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INDEX
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