[NRV Rocketry] How To Get into High Power Rockets

[Charles Albright]

Thank you, Tom , for your effort to provide a comprehensive picture of what's involved in the building and flying of 
high power rockets. There is much good information there.

I'm concerned, however, that someone new to high power will find all that information hard to swallow in one gulp. I 
hope I can help simplify some of it and pare down the list to that which applies to one's first high power rocket.

First, I highly recommend that you start by building your first high power rocket from a kit. This will provide you with 
hands-on experience with a well designed (stable) rocket and allow you to learn new building techniques without having 
to worry about acquiring all the right parts on your own. However, while the kit may provide a parachute, it may not 
provide a (Nomex or Kevlar) parachute protector. You should purchase and use such a protector. You may also have to 
provide your own motor retention hardware. And some high power kits will come with launch lugs, which may work just 
fine. But if you prefer rail buttons (as I do), you'll have to supply your own.

There are a number of high power rocket kit manufacturers. As just one example, take a look at LOC Precision to see some 
of what's available.

http://locprecision.com/

You may want to start with a smaller "large" rocket kit designed to fly on a G motor as a way to ease your way into all 
this. Such a rocket will probably be somewhat like a scaled-up "Estes" rocket with some high power attributes. A G motor 
is the most powerful one you can buy without certification.

For your first pure high power rocket, I recommend one with a 4" diameter body tube. Sometimes construction requires 
reaching down into the body tube to attach or glue (i.e. epoxy) a part and, in my experience, it can be very difficult 
to put your hand in a smaller tube and still be able to see what you're doing. And speaking of epoxy, in general the 
slower the cure, the stronger the bond. I use 30-minute epoxy most of the time, both because of the stronger bond and 
due to its more forgiving nature in that it allows you more time to get the glued part into its proper position before 
the epoxy "seizes" it. This can be especially important when inserting and fastening the motor mount to the inside of 
the booster body tube.

Concerning materials, I recommend you stay away from fiberglass in the beginning. It can be messy and even dangerous, 
requiring breathing protection while cutting, drilling, and sanding it (think surgical masks). It is completely feasible 
to complete both Level 1 and Level 2 certifications without ever touching fiberglass. I know because I've done it using 
only cardboard-type tubing.

Concerning electronics, Level 1 certification can easily be achieved without any electronics, using only motor ejection 
to deploy a single parachute. More advanced techniques such as altimeter-controlled recovery, dual-deploy parachutes 
(drogue and main), shear pins, etc., can be left for higher certifications.

I recommend using rocket design and simulation software to verify the performance of any high power rocket. One 
excellent example is the OpenRocket program which is available via free Internet download (no need to pay over $100 for 
Rocksim).

http://openrocket.sourceforge.net/

Such software can help you get the ejection timing right (i.e. at slow speed near apogee), which along with a long shock 
cord, is the best way to "zipper-proof" your rocket (i.e. avoid having the shock cord rip a slot down the side of the 
rocket body tube). Generally, zippering occurs because of bad recovery deployment design and timing, not because of a 
weak body tube.

Finally, look at rockets successfully flown by others, ask for advice (from more than one person), and read and learn 
using the Tripoli and NAR websites and the excellent book by Mark Canepa, "Modern High-Power Rocketry 2." There is one 
copy available in the local public library system (on the shelf in Christiansburg).

Charley Albright
Tripoli # 14063, Level 2


----- Original Message ----- 
From: "Thomas Weeks" <tweeksjunk2 at theweeks.org>
To: <nrvr at nrvr.org>
Sent: Friday, August 30, 2013 1:46 AM
Subject: [NRV Rocketry] How To Get into High Power Rockets


Someone at the meeting the other night asked me,
        "Tweeks.. how do I 'graduate' from fun little model rockets to these
         big ones that I've seen fly at some of these local NRVR launches?"

What's the Same, and What's Different for High Power?
============================================================
For those who are wanting to move to, or even just dabble in High Power
rocketry, here are some of the most common differences between model rockets
(A, B, C, D motors), medium power (E, F and G motors) and bigger beefier High
Power (generally, H, I and up motors):

Some construction and flight principals stay the same as low power/model rocketry:
-What makes a rocket stable
  -Center of Gravity in front of Center of Pressure by 1.5 Body tube diameters
   (remember the string, "spin test"?)
  -You need a 5:1 thrust(N) to weight(N) ratio
   or weight of rocket(lbs) x 4.45(N/lb) x 5   ~ or < avg thrust of motor (N)
   Ex: 1lb rocket needs at least 22.25 Newtons of thrust motor, something
    like an F23 or bigger
    http://www.apogeerockets.com/Rocket_Motors/AeroTech_Motors/29mm_Motors_Single_Use
-Undistracted attention to packing your own chute
 (feels to tight.. do it again)


The biggest differences between model/low-power and what you need to do for
high power rockets construction and design wise are:
-Higher speed flight = MUCH more violent component stresses
-More stresses = Design Changes: "Beef-Up" everything
  -Move from glue to epoxy
  -beef up motor mount/bulkhead strength
  -move from elastic shock cords to nylon/kevlar shock cord
  -move from 2ft shock cord to 20ft shock cord
  -move from chute snap swivels to 1/4" quick links
  -zipper proofing your design or body tube
  -reinforce body tube strength (fiberglass/kevlar/carbon fiber)
  -reinforce fin root edge/mounting strength (through tube mounting)
  -use BEEFY fin fillets (epoxy, metal putty epoxy, etc)
  -high speed = greater internal pressure = popped nosecones = make vent holes
  -for chute protection move from paper wadding to kevlar cute cover
  -move from launch lugs to rail buttons
-If in doubt, over design (to a point :)
-Bigger rockets = more weight (more violent launches & ejections)
-More weight requires slower/safer recoveries = larger chutes
-Larger Chutes = more drift and...
  -need for smaller drogue chutes (more toward L2) to slow them down first
  -need for altimeter controlled drogue & main chutes ejections
  -need for Ebay/electronics and static port holes
  -need for secondary/backup ejection systems
  -ground ejection system testing
-Higher speed/altitude/mass = MUCH more violent ejections
  -need for nosecone sheer pins to hold main chute in until needed
-Preflight check list(s) (due to added ejection system complexities)
-Compare notes, ask questions, learn from the experts (end THEIR mistakes ;)

Also.. this is a great illustrated book to much of what I list above and more:
"Modern High-Power Rocketry 2", by Mark Canepa
http://www.amazon.com/dp/1412058104
(we just gave a copy away at the last meeting!)


What High Power Certification Is, And What's Required:
========================================================
To even purchase these high power motors though requires a certification. So
that's one reason why people even bother getting certified.
You want to fly big rockets?
You need to get certified (which is the industries way of keeping everything safe).

Here is some info on what certification actually means:
https://en.wikipedia.org/wiki/High-power_rocketry#Certification_in_the_USA_.26_Canada

This means that you'll first need to either become a formal member of either NAR or
TRA (Tripoli):
http://www.tripoli.org/Certifications/tabid/80/Default.aspx
http://www.nar.org/NARjoin.html

NRVR is currently a TRA group(#143), but we can certify NAR members also,
and the certifications are cross group compatible.

You very first HP motor purchase is allowed, but you'll want to contact our
group's RSO (rso at nrvr dot org) to go over your rocket, the motor you want,
and announce that you desire to do a certification launch attempt. At this
point, you do not have to be a member of NRVR, VAST, or any other local
"club", but this is where most people go ahead and do join, as we will be
helping you a lot during your journey to becoming certified. Here's how
to join NRV Rocketry (our local club in the NRV):
http://nrvr.org/membership/


Get Your Level-1 Cert with a Rocket That Can Fly Both Medium & High Power:
==============================================================================
I always recommend that folks in the NRV start off with a dual purpose rocket
that can fly as either medium power (F-G) or high power (H, I etc).  Especially
since some of our launches are medium and model rocket flights only, while only
some (at this point) allow for high power flights. Here are several good
Rockets to choose from, many of which can handle both medium power (F & G)
as well as starter High Power (H) motors:
http://www.apogeerockets.com/Rocket_Kits/Level_1_Certification_Kits

NOTE: Personally, I recommend getting one with a 38mm motor mount. Cessaroni
motors are the easiest (and cleanest) to work with.  And they have a deal
right now.  If you're buying a "cert motor refill", the y give you the metal
motor casing (a $40-50 value) for free! Just mention it when buying your
Cessaroni motor refill grains. :)

Also. here are a few really nice little videos (from Apogee) on the
ins and outs of "Level-1" HP rocketry and certification:

Intro to Level 1 Certification Rockets
http://www.apogeerockets.com/Advanced_Construction_Videos/Rocketry_Video_60


and then if you really want to see what building a Level-1 Rocket is like from
start to finish, here's a really nice ten part video series on how to construct
high power rockets, from beginning to end:


Building Your First High Power Rocket - Part 1
http://www.apogeerockets.com/Advanced_Construction_Videos/Rocketry_Video_61


these videos above make for a really of useful set of starter videos to help
those interested in moving a bit beyond the basic Estes model rockets of our
childhood.

Any other certified members have anything similar to share? Suggestions?
Gotchas? Lessons Learned?

Tweeks
NRV Rocketry Founder
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