The Body Tube

 The Thrifty Rocketeer blog continues....

It's about time that this blog got back to it's mission...saving you money in this hobby.


There are lots of flavors in the hobby to keep everyone satisfied.

Some build scale model rockets... some build families of identical rockets, scaled up or down.. some build kits.... while other prefer scratch builds and experimental designs.

Recently, I've stumbled onto a series of old Estes kit plans that apparently taught rocketeers to build their own rockets from plans... or to supplement their kits by cutting their own fins according to the plan.

Many of these older rocket plans are hosted on various websites.  One is SpaceModeling.org    , where the webmaster makes the PDF files available for download, and just asks you for a donation to keep it going and to make it worth his while.

I have downloaded two so far, and will be sending him a little something shortly.
http://www.spacemodeling.org/jimz/est2038.htm 


But I was having trouble finding some of the parts that looked pretty standard, really.

Now, some rocket websites and vendors have slick pages and web pages that hawk only their own kits.  And some manufacturers have various categories of rockets...by skill... or design... or other sort-able theme.  The point is that most are all user friendly, and market to the general public, allowing you to navigate and shop with your eyes.

But there's one site that offers mainly supplies, and lots of them.  The system is organized and efficient, but it's not always intuitive or user-friendly to the general public.  You're shopping for PARTS... not glossy packaged kits...although they are available there also.  But there are LOTS and LOTS of parts on this site, and most of them don't have photos, but stock parts drawings.

Anyway, my point is that I was looking for a cheap BT-80 body tube 9" 15/32" long for this rocket.  I had most all the small parts, or could make and cut them from scrap I had accumulated.  I found by searching for BT-80...dozens of listings..most of which were BT-80 tubes of various lengths.  I found 8" and 9" tubes for about $4.39 each...but when it came to a 9.3" tube, the price shot up to $8.19 each.

I couldn't understand the sudden price jump.  So I wrote to the owner to ask why the sudden jump in almost double the price.  After all, I just wanted a cheap BT-80 body tube.

I wondered if maybe the material the craft tube was made of was somehow better or more expensive.  I couldn't figure out why 1/3" more of tube would cost so much.  My target was 9 15/32" length, though I could not figure out why it wasn't just 9.5" and be done with it.

I also looked at the quantities on hand.  There were almost 83 units of the 8" length available.  There were more than 86 of the 9" on hand.  But the 9.3" length had only 4 units available.  Could it be that the price depended on supply and demand??

It turns out the answer is even simpler than I had imagined.

I got a very nice e-mail back from the owner who patiently explained that the price for some parts was a function of the cost to produce it. That is, they cut their craft tubes to length, stocking most of the standard lengths, but willing to cut custom lengths if necessary.  Custom orders would reflect the time and effort to generate the number of parts that were being ordered....like tens or hundreds for assembling various kits for other vendors and rocket sellers.

But the answer for why the price would suddenly double is even simpler than that.  They cut their lengths from 18" craft tubes.  Therefore, a 9" tube is very easy to cut. They get two of them for every cut that they make on their machine.  However, a 9.3" produces one usable tube, and leaves about 8.7" scrap.  Now, that 8.7" length can then be cut into an 8" length or two 4" lengths, etc.  But there's still about .7" scrap left over due to the initial cut.  

That's why the price nearly doubles to get that extra fraction of a tube... you can only get one per 18" tube.

It's so simple and so obvious, now that he explained.  I felt almost foolish to not have seen it.

I appreciated his patient answer and placed my order for ONE 9" BT-80 tube, and a few other things like a PNC-80 nosecone, a BT-20 motor mount, some centering rings and a thrust ring stop.  I was glad to shell out for those lower priced parts, but drew the line at 9.3"....and the higher price.

After all, this IS the Thrifty Rocketeer blog...

**Footnote:  Since writing this, I have discovered that the cheapest PNC-80 nosecone is a bit taller than an ogive, and more pointed elliptical...and it's translucent in color.  That's good for me, cause if you push a glow stick into it, it will glow for night launches!  But the ogive that I originally wanted was quite expensive...until I discovered that it's the nosecone used on the Mega Mosquito model.  And low and behold, I've got three at my disposal...one white, one yellow and one lime green.  Now, I don't want to paint it bright red to match my Alien Probe rocket, so I'm going to settle for the translucent nose-cone and call it square when I can launch it in the daylight before the upcoming "night launch" for Halloween!


Comments

Post a Comment

Popular posts from this blog

The End of the Line

Image
 The Thrifty Rocketeer blog continues... Well, for years, the state of the model rocket industry relied upon plans and patterns that were photocopied or printed out, and then applied to standard sheets of balsa to be cut out. Eventually, the various parts for various sized rockets were packaged in groups or blister packs, and sold at hobby shops across the nation.  The emphasis was on home brew or building a rocket to specifications and plans. Eventually, entire kits were pre-packaged, with all the parts that one would need.  And then, laser cut shapes, fins or parts were already pre-cut, doing away with the need for most of the patterns and tracing. So what happened to all those bags and bister packs of parts of rockets?  That is, a baggie of various nose cones... or connectors... or transitions or more ?   Many of  those packages remain at your local mom and pop hobby store, just waiting for someone to come in and buy some of their pegboard stock.  And the number and frequency of the
Read more

sleeping with the enemy

Image
 The Thrifty Rocketeer blog continues... First thing I did when they put in a Hobby Lobby in my smaller metropolitan town, 40 miles away, was to grab an application to work there.  Now I know what you're thinking... "How could you?  Who would want to work for that conservative corporation?".. as my daughter would say.  And you'd be partially right. I saved the application and took note of the mailing address. Within the first month or so, most of the initial buying frenzy was over, having sold out of some things, but not everything.   But it seemed nothing new was getting restocked. So, I got on my word processor and wrote a letter to the store management, THANKING them for bringing the store to our isolated metro area. I pointed out that many of the items had sold through completely, and how much we had appreciated their stocking rockets. Then I also encouraged them to restock and consider expanding the display, pointing to the fact that as rocketeers grow older, the
Read more

Death of a Hobby

Image
 The Thrifty Rocketeer blog continues... No, this is not a column about how Model Rocketry is a dying hobby.  It's actually about another sister hobby that sometimes overlaps into Rocketry. I'm talking about Amateur Radio. Just this last weekend, our local Ham Radio club held a "swap meet" which is commonly called a Hamfest.  These gatherings to buy and sell used equipment, parts and visit old friends typically happen just once a year and in the absence of the late Radio Shack, is one of the only places to find parts and electronic elements. There is also testing held to advance to higher licenses. The admission varies depending on the club, their overhead, expense of renting the hall or venue, and the number of tables that they can sell to area vendors who will drive across state with their wares to set up for the half day show. It's not uncommon for amateur radio operators to drive across state to attend, pay admission and get a single entry into the door prize
Read more