Sunday, April 5, 2020

Building Model Rockets Out of Order - When I Deviate from the Instructions


I often build model rockets out of order.

The Handbook of Model Rocketry emphasizes time and again "Always read the instructions!" And while this is good advice, after you've built a number of rockets, you might find it helpful to deviate slightly from those instructions from time to time. Here's an example.

Estes' instructions usually have the build order go as such:
  1.  Prep fins
  2.  Assemble engine mount
  3.  Mark the body tube for fin placement
  4.  Glue the fins on
  5.  Glue on the launch lug
  6.  Glue the engine mount into the body tube
Et cetera...


I don't like doing it this way! You'll notice numbers 3-6 in the above list are italicized. That's because I always, always do those steps out of sequence when building a model. I do this for a few reasons.

I want the launch lug to line up with the engine hook. Many models have the motor tube flush with the base of the body tube, which means I'll often use a tool, such as my sanding block, to push the engine mount flush with the back of the rocket. I like to give the motor mount a twist when installing it, to ensure there's a nice bead of glue all the way around the centering rings for a good bond. And, because I'm a fussy builder, I often use a tool to make sure my launch lug is on perfectly straight.

Now, I find it easy to forget to pay attention to the marks on the outside of the body tube when installing the motor mount. Some models, especially those like the Big Bertha, have fins that are far swept back, meaning it can be hard to get a tool up to the base of the rocket if the fins are already glued on. And if the glue catches when the motor mount is only partway in, you may have to give a bit of a push - I don't want to break any fins off while installing the motor mount! Sometimes far swept fins can make it tricky to get even your fingers up in there to do some adjusting. And the fins would usually be in the way if I wanted to use a piece of aluminum angle to check the alignment of the launch lug.

The order I usually do the steps above is: 6, 3, 5, 4. I build and install the motor mount before anything else.

Before I make any marks at all on the body tube, I install the motor mount. Once it is glued in place, and the glue is holding (so that the mount won't slide in or out or rotate in place), I will mark the launch lug line.

I line up an aluminum angle with the engine hook and make a line all the way up the tube.


Now I know that the launch lug will be in line with the engine hook. I'm not going to accidentally forget to turn the motor mount so the hook is lined up with a launch lug I've already marked and glued on.

There are two reasons it's best to put the hook and the launch lug on the same side. First, it's neater. The launch lug is essentially the back side of the rocket. With the rocket on the launch pad - or on display - you won't see a hook sticking out the bottom if it's on the back.

But the second reason is more critical. If the launch control clips touch the hook, they'll create a short circuit. Electrons are lazy - they take the easiest route. Since a metal hook has less resistance than the bridge wire of a starter (or igniter), the current will flow from clip to hook to clip again, and back to the launch controller without passing through the starter. The rocket motor won't ignite!

Keeping the engine hook on the back side makes it less likely you'll get a short.

So, I glue in the motor mount, not worrying one bit about aligning things. Then I mark the launch lug line. And then I wrap the fin marking guide around the rocket. I line up the marks for the launch lug with the line I've already made, then mark the fin line locations with a small pencil mark.


Then I remove the fin marking guide and draw the fin lines up the tube. You can use a door jamb for this, or a drawer's edge - either of which you might find in the instructions. But I prefer to use a piece of aluminum angle.

Cheap, and widely available at home improvement stores and online, aluminum angle is a great tool for model rocket builders.


Because of its shape, it sits perfectly on a tube, giving you a nice straight edge. It's like a ruler which won't move when placed on cylindrical stock.


Aluminum angle is thin and makes a sharper, straighter line than a door jamb. It comes in 3 foot lengths or more, so you can mark all the way up the body tube.


Some instructions suggest making a mark only a few inches long, but I always prefer to make my fin lines and launch lug line all the way up the length of the tube.

Someone at a club meeting recently asked me why I do this.

The reason is that it's easier to make sure things are on straight if you have a reference line going all the way up. You can sight through the launch lug and over the tips of your fins once their glued on, but before the glue has dried. This will help you determine if things are truly in line, or if they just look like they're straight.


So, my tip for you is to mark the whole length of the tube.

In the case of some kits, such as the Estes Nike-X, the instructions actually tell you to do this, because you're going to glue on some forward fins and some canards up near the top end of the rocket. But I recommend it for every build. It's just a helpful way to check your work.

Next, I usually glue on the launch lug. I do this before gluing fins on, because it enables me to use a piece of aluminum angle to ensure the launch lug is perfectly straight. I glue the lug on, and while the glue is still somewhat wet, I gently slide the aluminum angle in place next to the lug, and I can adjust the straightness of the lug using the angle as a straightedge.


If the fins were already glued on, this wouldn't really be possible, because they'd get in the way of the aluminum angle.

Now, I don't find this step too critical. It's not hard to get a launch lug on straight by siting up the line through the lug. But, as I said above, I'm a fussy builder, so I like the added assurance I've got the lug on nice and straight. And in the case of rockets with two lugs, I always do this.

I glue the first lug on, making sure it's straight with the aluminum angle. Once the glue has dried, I glue the other one on, pressing the angle gently against the dried lug, and using it to guide placement of the second lug. This ensures that the two lugs are perfectly in line.

If you don't want to bother with that, or don't have an aluminum angle, my tip of drawing the fin and launch lug lines all the way up the rocket will help you, because you can sight up the rocket through the launch lug, to make sure it's nice and straight.


When everything is lined up, I finally glue on the fins.

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Tuesday, March 24, 2020

New Podcast - The Model Rocket Show!


I'll be doing a new podcast, called The Model Rocket Show. It should be debuting the weekend of March 28. It's from LittleBeth Media, and is a spinoff of The Rocketry Show podcast.

The Rocketry Show tends to deal mainly with high power rocketry and really advanced stuff. But there's a need for people whose main interest in rocketry is in low power rocketry, whether they are beginners or longtime rocketeers who prefer model rocketry. And then there are those rocketeers who enjoy both sides of the hobby, and would like to hear more episodes focused on the model rocket side of things.

It can be difficult to address both ends of the hobby with one show. Some advanced rocketeers are no longer interested in model rockets, and some beginners may have a hard time following some of the more advanced episodes.


Look for all kinds of stuff on the new show - build techniques, interviews with people in the model rocket industry, TARC, listener questions, and maybe some first steps toward high power certification - like "what's a good first kit" type stuff.

So, whether you're a Rocket N00b or a longtime modeler, I hope you'll check out the new podcast when it comes out. You can hear the trailer by clicking here.

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Tuesday, March 17, 2020

Update from the National Association of Rocketry re: COVID-19

Well, two posts in one day. A lot of stuff happening these days.

From the Facebook group of the National Association of Rocketry:

March 17: Update on COVID-19 for National Association of Rocketry

Recently, the recommendations from the White House and CDC on minimizing the risk and spread of COVID-19 have been updated to ask that all “Avoid social gatherings in groups of 10 people.” (Reference)

This recommendation is pretty clear and should be followed by all to help slow down and stop this rapidly growing health concern.

Based on the recommendation of the President and CDC, as the President of the NAR Board, I am instituting the following policy to take effect immediately and be in effect for a minimum of 15 days (March 17 -April 1, 2020):

1. All NAR Sections shall postpone or cancel Section launches, meetings, and other group activities during this period.

. There should be no organized launches, meetings, and other group activities of 10 or more persons during this period.

I will send an update on the policy on or before April 1.

I ask that all members please adhere to the intent and spirit of this policy and help to protect all who would be attending a launch from the possible infection of this virus. TARC launches have been suspended indefinitely by AIA and the NAR, so there will not be any TARC teams needing our help with qualification flights. I understand this is a potential hardship for some, but the desire to fly rockets in large groups does not supersede the potential risk of infecting someone attending a NAR launch.

Thank you and please be safe!

John N. Hochheimer
President National Association of Rocketry

These are indeed interesting times.

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TARC Suspended Due to COVID-19



From an email issued by The American Rocketry Challenge, or TARC:

Hi Rocketeers, 
As always, one of our priorities is to ensure the safety and wellbeing of our entire community. Therefore, we ask that you follow all guidance you are receiving from your schools, as well as state and local health departments, on COVID-19. 
We are closely monitoring the situation with school closures across the country, as school groups compose a great number of our teams. Due to the growing number of extended closures, all qualification flight submissions are suspended effective immediately. At this time, we ask that you do not submit any additional qualification flight scores and cancel all scheduled launches. 
We are still determining when and in what form the National Finals may take place. We will keep you updated in the coming days regarding resumption of launches/submission of qualification flights. 
Additionally, we are also indefinitely extending the submission deadlines for the Engineering Notebook and Marketing Competitions. Please follow the instructions on the competition pages on our website to learn how to submit. 
Please let our team know if you have any questions in the meantime. 
Best, 
Jeremy Davis 
Program Manager, The American Rocketry Challenge

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Friday, January 3, 2020

Test Shots


Happy New Year!

If you've listened to the latest episode of The Rocketry Show podcast, you know that I recently bought myself a nice, entry-level digital SLR camera. I'm hoping to get better photos of my family, of my rockets for this blog, and better video for my YouTube channel.

Here are just a few of my first shots - taken without totally knowing what I'm doing yet - that I took with my Canon Rebel SL3 - or 250D.

(It's known as an SL3 in the US and Canada and a 250D elsewhere. I bought it from a discount distributer in Brooklyn from eBay, and I got a non-US branded 250D. It's the same camera.)

No real sense to these. I'm mostly just playing around with the focus and depth of field.



With a wide aperture, I can focus on a specific point, separating it from foreground and background objects. See here how I focus on the N00b Tube in the first photo, then on the Astron Sprint XL decal in the second. This will be good for showing specific details in blog posts.



Shooting through the fleet to pick out just the Dr. Zooch Saturn V.


Even in pretty low light, I think this closeup of R2D2 looks pretty good. This action figure is only about 2 1/2 inches tall.


Some of Mrs. N00b's giraffes, mentioned on the show. Again, I'm just trying this thing out here. I don't even know how to do any post-production stuff on photos yet, so I have to say, I'm pretty pleased how well a quick shot like this comes out.


This fidget spinner was moving quite fast, but even in relatively low light, I was able to nearly freeze it with a fast shutter speed. If this were a rocket, and outdoors in brighter light, I'd probably get a nice still shot - if I managed to actually catch it with the shutter!


An artsy-fartsy photo of the Rocket Room (it's finally organized and clean!!)


Andy the Penguin hopes you had a good holiday season. Now, get to building rockets!

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Friday, December 13, 2019

Estes G40-7 Is Discontinued


I knew this was coming. I knew it for a couple years. I expected it to come sooner, and when it didn't, I started to think maybe it wasn't happening.

But it has happened. The Estes G40-7 composite motor is gone.

This 29mm single use motor was manufactured by AeroTech, like all Estes composites. The G40 was the highest impulse Estes motor you could purchase. I really like the motor, especially for flying Estes Pro Series kits, as well as for things like my North Coast Rocketry SA-14 Archer.


It was a simple motor to use, and performed really well.

I'm pretty sure I heard that the motor had been discontinued a couple years ago, when we spoke with Estes' designer John Boren on The Rocketry Show podcast. They had some left in stock - a couple thousand, perhaps - but when those were sold, the G40 would be gone forever.

Then Estes changed hands, and the G40 did not sell out as fast as I had assumed it would. Because of that, I was secretly hoping that they had decided to continue producing it. I bought a small stockpile of them, just in case, but I hoped I'd be able to pick some up for a long time to come.

Well, my stockpile is the last I'll be able to fly of this motor. I checked AC Supply today, and they finally had the motor listed as Discontinued. You can no longer find them on the Estes website. It's really, finally gone.

There are plenty of other mid power composites to choose from, of course. And I still have a stash of G40's, so I won't be out for a while.


But I really like this motor, and I'm sad to see it go. It makes me wish I'd grabbed even more when I could. I don't think it was a terribly popular motor, but I love it. In fact, I've probably flown more G40-7's than any motor other than the C6-5!

It's simple, has a relatively long burn, and you can fly it without a waiver or high power certification.

G40 thrust/time curve, from thrustcurve.org

It was also cheap, if you got it from the right source. AC Supply sold them at 40% off, which put them at just above $16 per motor. There was a HAZMAT fee to pay, but if you bought a large bundle of them, the shipping was free, so the HAZMAT became negligible. $35 is a lot of HAZMAT to pay for one motor. But if you buy a lot of, say twenty (I did that once), you're only paying an additional $1.75 per motor.

Time will tell if Estes gets back into composite motors. I won't hold my breath on this - I don't think Estes motors were as popular among APCP flyers as AeroTech or Cesaroni. But Estes definitely has plans on releasing new motors, and who knows what the future may bring?

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Wednesday, December 11, 2019

Estes Nike-X - Part 2


This is a little tool I made. I made it to help me create perhaps a dozen or so little rockets and build them all as close to exactly the same as I could. It's just a used motor casing with a 1/4 inch length of BT-20 body tube glued around the base of it. A second 1/4 inch length of body tube is not glued on, but can slide on and off the motor casing.

See, I have a project I've been thinking about for this blog, which may never come to fruition, but it's been in the back of my mind for a long time. And for it, I need multiple rockets built as close to precisely the same as I can get. This tool is to help me build multiple copies of Flechette, a skinny, high-flying two-stage rocket I designed.


I flew - and lost - the prototype a couple seasons ago, but the proof of concept flight went well, and man, did it go high!

The booster stage of Flechette has a motor overhang - that is, the motor hangs out the back - by 1/4 inch, while the sustainer (upper stage) has an overhang of 1/2 inch. Since I wanted all my Flechette rockets to be the same, the tool I made is for pushing an engine block or thrust ring up into the tube a precise distance. With the basic pushing tool, I can get all my boosters to have the engine block set into the tube so all booster motors hang out 1/4 inch. If I slide the loose ring onto the pushing tool, now I can install a thrust ring that will leave 1/2 inch overhang. It'll be exactly the same every time.


I like precision, if I can manage it. I was never good at precision before I started building rockets. Making stuff was not something I was good at. So, while I don't have the knowledge of a maker who's been using tools or crafting things for a couple decades, I do my best to make things more precise if I can think of a way to do it.

Which is why I did this:


The Estes Nike-X instructions say to place the engine block inside the motor tube with a 3/8 inch overhang. My little pusher tool wouldn't work for that.

Look, friends, I know. I know... This is fussy and silly, and a totally unnecessary step. I'm not suggesting that you need to do this.

But wanted to, because I like precision, so I did it.

I measured the pusher tube supplied with the kit, marked 3/8 inch from the bottom, and wrapped it with tape. No need to put my thumbnail on the pencil mark - I could push the engine block precisely into place, and now that I have this in my tool box, I can use it for another build which uses the same measurement.



Look, don't make fun of me. Just use your thumbnail and you'll be fine.

Or, if you like this idea, use it.

Actually, this isn't a terrible idea if you're building with kids for the first time. More than one of my rocket camp kids pushed their tubes all the way into their rockets, leaving no overhang, because they forgot to keep their thumbnail on the mark. Your thumb is supposed to be what stops you from pushing the engine block too far into the rocket. Kids - or sloppy adult builders - might forget this and shove it all the way inside. You really need the motor to hang out the back a little bit, or you won't get it back out of the rocket after its first flight. If you're teaching a rocket class to kids, making a few of these with used casings might come in handy.

Anyway...


If you look at the motor mount for the Nike-X I'm building, you'll notice that the engine hook has no thumb tab.

I first learned that people sometimes cut this tab off from Chris Michielssen's Model Rocket Building blog. I didn't understand why you'd do that when I first started building rockets. I used to like the tab. It made it easy to pull the hook out of the way and insert an engine into the rocket.

But the more rockets I built, the more I realized that the tab can be in the way more often than not.

If you buy motor hooks from other vendors, for building your own, you usually won't have a thumb tab. And some companies' kits don't come with them - Semroc, for example.

You can cut the tab off, which involves using some wire cutters and a lot of force to score the bend in the hook where the tab starts, then wiggling it back and forth until it breaks off. I use needle nose pliers for this.


You can then either sand or file the rough end you've cut, or use that as the top end of the hook. The tabless end now becomes the bottom and holds the motor in.

I used to file the rough cut, but I found it tedious. I followed Chris' advice and simply turned the hook around on this one, and it works great.


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