Bomarc (stomp) Missile with optional display detail

[Retired_for_now]

Next up was to fix the tail. I'd started the project by modifying an earlier rocket tube and for some reason just left the 1/4 marks on the tail end for locating the fins. This results in:




After a little thought (with me, probably very little) I realized the obvious. The horizontal stabilizer looks much like the wing and is positioned in line with the wing - so why not build and attach it the same way as the wing! And so I did.




The result is more accurate, stronger, and easier to keep aligned. It's no more difficult to make and you're doing the wing the same way anyway.

Yogi (I guess I'll need to update the file in the downloads - again)

[Retired_for_now]

And version 2 of the simple rocket with the tail modification is posted in the aviation download section.

[Darwin]

Yogi, taking a close look at the latest pics, I'm suspecting that the wings of the Bomark (and, I suspect, of the F 104 as well) serve more to provide stability to the model's trajectory than to provide aerodynamic lift for a glide. Also, I've gathered from the various stomp rocket discussions, wings need considerable beefing up (read internal framwork) for structural strength during the high stress of a launch. Also, (always true for flying models whatever the medium) weight is your enemy. Leading me to my point for pondering....when attempting to model a glider (such as a Mig-15 or F-86, as opposed to a projectile like an F-104, X-15, etc), should the model skin be made with 20-24 lb bond paper rather than cardstock?

[Retired_for_now]

Darwin,
With an easy, level launch the missile will glide stably for about 100 feet - so we are getting lift. Of course, the model is much lighter (scale) than an actual missile so we're getting proportionately a lot more lift than an actual missile would (but we're not going Mach 3 either). The only internal structure on this one is the "cereal box" card in the wing. It handles a hard launch well, probably because there is a lot of glue surface in the underside of the center wing and on the tabs for attachment (a special case for this design - your comments are likely correct for something with longer, thinner wings attached to the sides of the fuselage).
On the weight - for a world-record paper airplane I would agree. For something launched outdoors you gain more from the strength of card than it costs in weight. The weight (inertia) also helps keep this one stable.
Still working on getting a good, hard launch to transition to stable flight - four flights is about the limit before those neat looking engines start to break loose from the pylons on landing. Tiny tweaks and dents that aren't obvious on an easy launch become a source of excitement with a hard stomp. I should probably go back to the simple, more robust model for testing.
Print one out and give it a try - adjusting the CG by slipping card disks under the nose is quick and easy (as is the inevitable replacement of said nose after several landings) and you should be able to hand launch it easily, though 1/2 inch PVC pipe is cheap. The blow-gun technique works well.

Yogi

[Retired_for_now]

A prominent visual feature of the Bomarc missile is the dorsal cable run - modelled on the simple stomp rocket with a shaded stripe. I've rolled a lot of cylinders, but for some reason it took a while to figure out a good way to do a long half-cylinder.

I started with a rectangle that will curve into the surface with a couple of tabs on the long edges to both keep it straight (angle iron effect) and to provide gluing surface. Then, I thought about installation - glue it all at once and deal with the inevitable mis-alignment tremors and glue smears or glue it a bit at a time and try and poke the toothpick-glue applicator into that little gap. In both cases, trying to keep it exactly straight and correctly positioned. The missile's namesake might be able to do it (or build a cool jig), but I decided to punt.

I cut a strip of card the diameter of the finished part, slipped it inside the glue tabs, and squeezed the part. This trapped the card strip in the angle between the rounded section and the tab - ensuring the part was straight and consistent. Self jigging.



I revised the pattern to use one wide tab the width of the finished part that gets folded up inside a narrower tab on the other edge to get the same result.

The ends are half-cones and attach using internal paper joiner strips - on the prototype I just let the internal card strip run long and trimmed it to catch the bottom of the end pieces. I revised the pattern to do something similar to the tunnel section.




Of course, I glued the wing and tail to the top surface of the fuselage, so I needed a card strip to shim the gap in front of the wing and between the wing and tail. The front shim was glued to the finished cable run to aid in locating the part on assembly (you can see it on the first photo, above), the aft shim glued to the fuselage as you can see below.



Final result seemed to work OK.


Yogi

[Retired_for_now]

The initial Bomarc design was driven by simplicity, hence the simple cone for the nose attached to a collar so it could be replaced.





I looked at a couple of options for increasing the detail/fidelity of the part.

The actual nosecone is a narrow ogive/arched form. You can get close with paper (essentially a flat material) by making petals or by decomposing the shape into a series of conics. I'm not fond of petals (I'll do 'em if I have to, but ...). Modelling this shape with petals would give a very accurate profile, but it would still present a series of flat surfaces curving up to the point (though you could burnish them down a bit). Using stacked conics preserves the round frontal shape but gives you a less accurate profile.

I tried a quick compromise, cutting four petals just for the tip (the most difficult part to roll with a long cone). While the result might be more robust for a flying model, it really doesn't improve the fidelity.



I weighted my tradespace toward the easier shape to build. Closing up numerous long, thin petals would be difficult for most builders. Stacked conics require more parts, but are much easier to build correctly - and are a lot stronger than those long, thin petals. A note on proportions: a stack of anything usually looks best if the lower parts are larger than the upper (geometric ratios/golden mean/pick your ratio to use). To simulate a smooth form, you are also limited by the actual curve you're trying to match. I usually stack trapezoids over the actual picture on my drawing palette (OK, it's just PowerPoint but palette sounds better) and adjust to minimize the surface errors.

The result:



The topmost conics in the final form are almost the same height, but that was necessary to follow the curve. More conics could produce a more accurate shape - at the cost of more seams.

The final bit of the nose is the collar that fits over the pressure tube/fuselage to allow you to remove and replace the nose after incurring flight damage (well, actually landing damage).



For a more accurate model the collar can be left off and the nose cone (trimmed a bit) attached directly to the front of the model. I left enough extra material on the forward tube (under the collar) to provide a connection - or cut it off, add a connector or edge glue as you prefer. For the fliers, the removeable nose cone provides an easy place to add weight to adjust the flight path - obviously not a consideration for a display model.

Yogi

[Retired_for_now]

Getting good closeups of the missile is difficult (still pending my sortie out to Eglin). Most of the shots are like Tim's - good pictures but full frame of a missile painted for display.

I did find two sources - some shots taken at Hill AFB of the test and operational paint schemes
Hill Aerospace Museum - Outdoor Exhibits :: Boeing Bomarc surface-to-air missiles picture by Norman_Rockwell - Photobucket&

and some good aft and engine views from what looks like the AF Museum intensive care area
CIM-10A BOMARC Walk Around Page 1

Well, we work with what we've got. Add panel lines where we can find them, &etc.

Yogi

[Retired_for_now]

Bomarc launched on it's tail, the launch rail only supported the missile while stored and was used to erect it when fired. For launch, the missile was held by four clamps on the tail ring. Based on the photos I found, that's where most of the detailing was concentrated (I didn't try and add every rivet line as I would expect them to be flush and painted over on a production missile).




The booster rocket nozzle is mounted on a circular, removable plate that sits against a paper ring glued just inside the aft end. Removable so you can pull the plate and put the missile back on the stomp launcher - and then fix those danged pylons again after another hard landing.




Yogi

[Retired_for_now]

So, what do we get with all these tweaks?




And what have we learned over the past few months? You get better seams by using joiner strips instead of tabs, at a cost in extra parts and assembly time. You can edge glue parts (vertical and pylons on the above) if you won't stress them later.



There's always some jigging to do - a couple of Bomarc jigs (but hardly the quality of bomarc's jigs) for wing and engine alignment.




And you probably won't want to fly the display model ... nosecone and engines the first to go, followed probably by the edge glued attachments for the vertical tail and engine pylons.



But if you keep it simple you can knock out a battery pretty quick.



Yogi (probably need to do an erector/launch pad next ...)

[Retired_for_now]

If you can see it, you may as well do something with it.


Ramjet aft internal former disk.

The Bomarc erector is looking a bit obscure - no real reference or training manual diagrams found online so far. There are some photos, so the general shape is available. Details like the erector ram remain missing (but I think it has to go under the main pivot, anchored at the aft end of the launcher base).


Yogi