A BT-55 with a BT-70 could work ?
I would love to build an Estes version but their so expensive :cry:
Do you have the actual dimesions of the Mercury Atlas?? Got "Rockets of the World"?? (HIGHLY recommended!) If you don't, dimensioned drawings aren't too hard to find on the internet, for some stuff at least... NTRS (NASA Technical Resource Server) has a lot of NASA studies and reports available for download (and I've summarized more than a few of them in the scale section...) Rockets of the World is available from NARTS...
Just how detailed of a model are you shooting for?? Are you looking to make a very realistic close to scale as possible model, or are you looking for a general-shape and more-or-less correctly proportioned "semi-scale" rocket for flying fairly often?? If the latter, then you have a lot more options... If you can tolerate the looks of it, (proportions perhaps being a bit off) then you can make do with some standard size parts... but it all starts with doing a little math.
As I said, the Atlas was 120 inches (ten feet) in diameter... if you wanted to use the BT-80 tube, which is of course readily available (and a nice size IMHO) which is 2.6 inches in diameter, if we divide 120 by 2.6, we get 46.15, or roughly 1/46 scale. Divide it the other way around, and we get 2.6 divided by 120, or .02166, which is your scale conversion factor... multiply all the sizes/lengths/diameters (NOT angles!) by this number to get the size they'll be on the model... (basically this equates to a 2.16% model). The Mercury capsule was 74.5 inches in diameter (IIRC) and so multiplying that out, your capsule should be 1.614 inches in diameter... (rounded to the thousandth of an inch). Now, a BT-60 tube is 1.637 inches in diameter (outside) so that's only 0.023 inches off (23 thousandths of an inch, which is about the thickness of several sheets of paper... IOW, pretty darn close... (not close enough for internats, but if you're building an internats model, you should already know all this stuff... )
If you wanted to use a BT-70 tube, which is 2.21 inches, then that works out to 54.30 rounded, or 1/54 scale... and the conversion factor would be 0.0184, or about a 1.8% scale... the capsule (which is 74.5 inches in diameter, remember) would be 74.5 times 0.0184, which equals 1.371, rounded. Comparing that to the BT-60 size of 1.637, that's 0.266 inches smaller, or 266 thousandths of an inch, or a little over a quarter inch smaller than the BT-60 size... IOW, not a common size... if you use a capsule nosecone made for a BT-60, it's going to be pretty oversize and a little funny looking.
Now, I know Semroc offers some pre-made mercury capsule shaped nosecones... what sizes, I dunno exactly, but you can look it up on their website. You'll need the rest of the dimensions of the rocket, but you can find those yourself.
You got me curious, so I dug out my Estes Mercury Redstone and measured the capsule shoulder on it... it's for about a 500 mm tube (the battery was dead in the digital caliper so I had to just read it off the scale, but if we convert (254 mm per inch) that works out to a 1.968 tube or thereabouts... (you could probably find the exact size on Jim Z's site, but I'm not going to that much trouble for an example... this kit is the "plastic wonder" with stickers version that was out a few years ago, dunno if it's still available or not). If you used this capsule as your starting point, measuring the actual capsule ring diameter above the tube shoulder (might be able to get a 50 mm tube from Semroc or Quest for the capsule to slide into-- it's not a typical Estes size so you won't get it from parts from them...). The capsule base ring is just shy of 550 mm (call it 545 mm) dividing by 254 mm per inch, we get 2.146 inches... (the capsule will slide down completely inside a 2.21 inch diameter BT-70, so this is about right). This is 131% of a BT-60, which we know is a pretty good fit with a BT-80 size rocket body, so if we upscaled the 2.60 inch BT-80 to 131% of it's size, we'd know what size tube this would work well with... we come up with a 3.406 inch tube, roughly speaking (proportionately).
Let's figure it by the scale... the Estes Redstone capsule is 2.146 inches in diameter, dividing by the 74.5 inch actual capsule size we get 0.0288 conversion factor, or the inverse, 34.7, which is about 1/35 scale. Figuring for the 120 inch diameter Atlas, we get 120 times 0.0288, or 3.456 inch tube... pretty close to our rougher figures above. Now, I don't know of anybody who makes a 3.456 inch diameter tube, so if you go this route, you're on your own... you can downsize a BT-101, which is right at 4 inches in diameter, or you can make a homemade tube.
FWIW, if I were doing this project (and I've kinda had it in the back of my mind, to be honest, but have enough irons in the fire right now) I'd get a Dr. Zooch BT-60 size Mercury Redstone, and use the capsule and tower off it. Heck build the whole kit and maybe buy an extra capsule blank from Wes and you'll have a Redstone and an Atlas in the same scale. Since we already did the math and found that a BT-60 capsule would go pretty darn close to a BT-80 size Atlas main body, then that eliminates a lot of parts hunting... the Zooch capsule is already BT-60 size and has all the guts and parts to make the tower and stuff as well... and instructions! Plus the wraps are in there as well... which you might have to "redecorate" to your liking, depending on which Atlas flight or capsule you're trying to model, but that's not a big deal anyway. Basically the full-size BT-60 Zooch Merc Redstone is a "reinventing" of the classic 60's Estes BT-60 Merc Redstone, which required a lot of work to make the multi-piece built up fins... (yeah the tower is work too, but this isn't a turn key deal anyway unless you want to just spend the dough on the Estes Merc Atlas with its plastic tower...)
That'd be MY first choice for this project... plus basically you get 2 fer one when you're done, in the same scale... How cool is that??
Later and good luck with your project...
OL JR
