Summer Buildoff: Roc n Roll Flying V guitar

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Getting the fins cut from spare foam packaging I had left over from some furniture boxes. Free! Nice! Laminating two of them will be close to the diameter of the BT-55, so I need to cut four of these.

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While the body fins are sitting under a pile of books during lamination, I started the cut on the head. So far the outline is cut and it is tapered, but there is more shaping to go on that.

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Razor blade to cut the outline, then a band saw to do the tapering on the head.
 
Flyfalcons said:
Getting the fins cut from spare foam packaging I had left over from some furnature boxes. Free! Nice! Laminating two of them will be close to the diameter of the BT-55, so I need to cut four of these.
Click to expand...

Good to find a productive use for that stuff, because as a packaging material, I loathe it from the depths of my very soul. When I open a box and find those sheets I wanna... well, let's just say I wanna do "bad things".

Maybe I just need to make a bunch of guitar rockets out of it! :)
 
Yeah that stuff is the scourge of my garage while I gather more stuff to make a dump run (takes up too much room in my garbage bin).

I pulled the weights this morning and the fin laminations look good. Just some sanding to make sure they are identical before gluing them in place is needed. Before that, I had to do a dry fit to see how it's all coming together. I left the BT-20 long until I figured out the head fitting. I'll probably just butt-glue it on, so the BT-20 will get trimmed down a bit.

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Flyfalcons said:
Yeah that stuff is the scourge of my garage while I gather more stuff to make a dump run (takes up too much room in my garbage bin).

I pulled the weights this morning and the fin laminations look good. Just some sanding to make sure they are identical before gluing them in place is needed. Before that, I had to do a dry fit to see how it's all coming together. I left the BT-20 long until I figured out the head fitting. I'll probably just butt-glue it on, so the BT-20 will get trimmed down a bit.
Click to expand...

Use an old 18mm motor as a coupler for the nosecone.
 
Work continues. I edge-sanded the two fins to be identical and they are now waiting on the epoxy to cure after being joined to the BT-55 tube. I was pretty sure I wouldn't get any epoxy on my weights, but just to be safe, I used my wife's books. I have the guitar head ready to glue to the neck, but I want to have easy access to the main body first, so that'll come tomorrow. Then I can add the neck pieces and begin final shaping of the parts.

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I think I might use a balsa nose cone embedded into the guitar head, if it were me.
 
I just went back and watched the test video. Is there really enough base drag from the thick fins to stabilize it in the, ah, sideways direction? Certainly the test flight looked darn near perfect...
 
I've flown the POC four times now, including in a light breeze. All flights were perfect. The actual build brings some new questions and challenges, but I have ways to mitigate them. There will probably also be a test flight once I get the final shaping in to see if there are issues before I go to the effort of making it pretty.
 
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TangoJuliet said:
I think I might use a balsa nose cone embedded into the guitar head, if it were me.
Click to expand...

I'm using Rich's idea of an old motor as a coupler. Besides, once the side pieces and covering are on, the whole will be much stronger than just the body tube and guitar head.
 
Epoxying the head on. Some weight to hold it level, and craft sticks to account for the taper. A quick CG check showed, unsurprisingly, the CG further aft than I want. I still have more weight to add up front with the neck pieces but in the end, some lead weight will probably be required.

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The head of the guitar is going to act as a destabilizing canard. Additionally, the main body fins are swept back much further than the fins on my proof of concept. This could mean less yaw stability than the proof of concept, and in addition, I may not be able to get the CG as far forward as I really want without adding excessive nose weight. The good news is the main body fins are twice as thick as the proof of concept. I'm going to round/taper the neck and head sides a bit to help decrease drag in the yaw axis above the CG, so that should also help. But the real test to see how we're doing aerodynamically is to just chuck the thing in my horse pasture and see how it does.

[video=youtube;zxswvZkWY4A]https://www.youtube.com/watch?v=zxswvZkWY4A[/video]
 
Sides for the neck have been cut and epoxied on (the rocket is built upside down with the top of it against the work bench). Tomorrow I'll start with the shaping. Kinda really not looking forward to that.

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Looks like you are good with canard like forward fins as is.
IIRC (did a search but couldn't find it. May have been in Handbook of Model Rocketry) there was a model rocket version of an Israeli missile, the Python. Had big forward canards. The modeler mounted these on swivels. The swivels were attached forward of each canard CP, so the canards angled to maintain orientation with the air stream. Again, IIRC this worked well to correct an otherwise unstable situation. Might be more than you want to do on your bird, but just an idea.

Lookin' Good!
 
Shaping on the neck and head is pretty much done. Balsa wood is going to hate those compound curves on the head and I'm half-tempted to just sheet the neck with cardstock and smooth the head out with spackle, then paint. The last inch of the neck was left flat so I could add the body - neck transition after sheeting. Not much shaping to do on the body; I'll just break the edges a little after sheeting and before paint.

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A quick search through my balsa box netted me some 4" wide 1/16" balsa sheets; perfect for sheeting foam. Kind of surprised to see how well the 4" sheets cover the body; I might not need nearly as much wood as I thought I might!

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If you cap the edges of your foam fins with a thicker balsa you can round over the edges. ;)
 
Keeping the "body" fins square is the key to succeeding with this design. I'm just going to break the edges a little bit so they don't look too jagged, but I need to play it safe this time and leave them as square as possible.

Do I wish I had kept the foam smaller on the neck and head, to allow for thicker balsa for shaping, maybe a bit. ButI shouldn't have a problem tackling that part with multiple, smaller pieces of balsa sheeting.
 
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I was able to make sheeting for one side of the body with just one 36" x 4" sheet of balsa. Nice!

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Top and bottom sheets have been sprayed with 3M 77 and are now in place and drying.

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Flyfalcons said:
The head of the guitar is going to act as a destabilizing canard. Additionally, the main body fins are swept back much further than the fins on my proof of concept. This could mean less yaw stability than the proof of concept, and in addition, I may not be able to get the CG as far forward as I really want without adding excessive nose weight. The good news is the main body fins are twice as thick as the proof of concept. I'm going to round/taper the neck and head sides a bit to help decrease drag in the yaw axis above the CG, so that should also help. But the real test to see how we're doing aerodynamically is to just chuck the thing in my horse pasture and see how it does.

[video=youtube;zxswvZkWY4A]https://www.youtube.com/watch?v=zxswvZkWY4A[/video]
Click to expand...

That's a pretty great flight! Wish I had a back yard I could launch in. This is an awesome project!!
 
The straight cap strips were glued on last night. Today I sanded those even and glued on the curved cap strips on the main body. The weight is going up with the balsa sheeting (maybe 2mm depron would have been a better choice), and now I'm shooting for a 10oz finished weight minus motor. So a D12-3 will be the bare minimum to fly this.

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Sheeting is on the top of the neck and head. I've decided to add an ounce of nose weight, so I'm going to carve into the back side of the head and add epoxy and fishing weights there, then sheet over that with balsa.

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