29mm vs. 33mm

[Senior Space Cadet]

When I decided to move up from 18mm motors and 24mm body tubes, the obvious next step seemed to be 33mm body tubes. Partly, maybe entirely, because that was the smallest size available with pre-slotted tubes (at least from Apogee).
One of you remarked that he thought 33mm was an odd size. Now I'm starting to see what he was talking about.
29mm is actually the next size up from 24mm and though I may not be able to get pre-slotted tubes in 29mm, there are other things that are available in 29mm that aren't available in 33mm.
Obviously, 29mm will have less drag than 33mm.
So now, once again, I need to buy a whole bunch of building supplies for 29mm. Well, I don't have to, but it looks like, in the long run, this might be the better size.
So, for anyone thinking about moving up from 18mm motors and 24mm body tubes, you have a choice. 29mm or 33mm. Right now, I'm thinking that, in the long run, 29mm might be the better move.
If you have counter arguments, I'd love to hear them.
Jeez, I hope I don't have to do this all over again.

 

[Charles_McG]

I design in the reverse direction. I pick the body tube for the look/scale I’m seeking and then think about motor mount sizes for the weight of the rocket and the T:W and impulse options available to me.
The only time I put the motor mount as the first design criteria is when I’m down scaling existing kits.
Using the metric sizes instead of the classic tube sizes is -slightly- unusual. 33mm looks approximately like BT-55.

I don’t build for altitude, so that would be skinny for a 24mm mount for what I like to fly. Not ‘wrong’ but not to my taste.

 

[Charles_McG]

Lots of 41mm rockets (BT-60) have 18mm mounts.

 

[lakeroadster]

A good sharp X-Acto knife makes DIY tube slots easy peazy...

These are on a BT-60 that has a full length internal C-60...

 

[dhbarr]

Almost no nosecone variety available in 29mm, a constant source of irritation. The Aspire NC from Apogee is a favorite, but their matching tubing is very short.

 

[dr wogz]

Motor mount & tube dia are not related. I have minimum dia. 18mm & 24mm rockets, and one favorite that is a BT-80 (2.6" dia) with an 18mm mount (Fat Boy - I've also scratched one with a 24mm mount). Mix & match..

Buy a kit or two. build said kit or two. Basically, look at what others have done, learn from that, use that as inspiration.. (Go back thru the years of Estes catalogs even! Look what Canaroc did back in the early 80's!!)

Then buy a few more kits, and toss the instructions & face card. Toss the 2 or 3 (or 12!) kits into a box, and use that as your source for a new scratch build. I do that repeatedly; buy "ugly" kits on sale & add them to my parts box (The Mean machine is a great source for tubes & couplers!!) You get the basics this way: Tubes, NCs, MMTs, and of course, fins (usually pre-cut) Along with a bag of other useful parts: shock cord, lugs, chute, etc.. and some decals / sticker to boot! If you buy on sale or use the Micheal's 40% off coupon (is that still a thing?) you'll probably save in the long run, than buying each piece individually.. And, personally, I find buying kits on sale yields a better assortment than buying the Estes Designer's box..

Not all LPR require TTW fins, in fact, most don't [thinking Estes kits]. And, cutting slots is pretty easy once you get the hang of it.. Cutting tubes to length is also pretty easy once you get the hang of it.

Something to think about: the pre-cut fins that comes with a kit can be modified. You can remove some material, and you can add material, Add a triangle to a fin, and you go from a basic trapezoid to a fin with a strake on its leading (or trailing) edge, (Combine different shapes, so that your leading edges are all with the grain in the proper sense.. This can make for a much stronger fin, than trying to cut a complex shape in one shot from a sheet of balsa..)

 

[kuririn]

33mm is not an odd size. It is a BT-55 tube. Pretty much standard and used in many kits, even 13mm powered ones. Apogee uses a metric system of tubing designation, most others use the original Estes BT classification.:
13mm = BT-5
18mm = BT-20
24mm = BT-50
29mm = motor mount tube for 29mm engines or minimum diameter airframes.
33mm = BT-55
41.6mm = BT-60
56mm = BT-70
66mm = BT-80
My Goony clones have a 41.6mm (BT-60) airframe but fly on 13mm motors.
Do not equate tube size with motor size in a design. Rockets are designed with a purpose first ( cool looks, maximum apogee, whatever) then the motor is matched according to weight, drag, etc.