Tuesday, 21 February 2017 17:27

HellFire 22 Dates Announced

HellFire, sponsored by the Utah Rocket Club (UROC)  takes place this year August 3,4,5,6. Though HellFire is technically an amateur launch, we’re talking serious rocketry here. Participants from around the country launch rockets ranging from foot-tall wonders to towering monsters that weigh in at over one hundred pounds, feature high-tech electronics, use a propellant similar to that used on the space shuttle, and lift off with 750 pounds of pure thrust.

Now in its 22nd year, HellFire continues to grow. Many people attend not to launch, but simply for the thrill of watching. Between launches, visitors enjoy examining rockets and components close-up and speaking with the experts who build and launch them.

Spectator Admission to HellFire is free and the public is welcome. HellFire will be held on the Bonneville Salt Flats near Wendover, Utah. Take Exit 4 on Interstate 80 and follow easy-to-spot signs. The event takes place 9 a.m. to 5 p.m. Thursday, August 3 through Sunday, August 6.

Discounted registration for flyers is available for UROC members.

Many more details to come over the next weeks.

Tips for visitors:

  • According to UROC insiders, Saturday is the day “where it starts getting crazy” with “lots of flights.”
  • All launch plans are subject to weather. Visitors are encouraged to check www.uroc.org BEFORE driving out to the launch.
  • There are no food or drink vendors at the event, so UROC reminds visitors to bring binoculars, hats, chairs, shade, lots of sunscreen, food and snacks, and plenty of drinking water.
  • UROC strongly encourages spectators to leave their pets at home, this is not a pet friendly environment
Published in UROC News
Wednesday, 15 June 2016 10:24

HellFire 21 - Time to Register!

Hellfire 21 "Aces High" is shaping up to be a great launch. The Utah Rocket Club's premier High Power Launch for the year will take place Thursday, August 4, 2016  through Sunday, August 7, 2016.  We have folks coming in from all over and are expecting a fun time seeing old friends and making some new ones. We have received approval from the FAA which will allow us to grant flights up to 25,000ft AGL. Over the next week or two, all of our sponsors, contests, and lots of other surprises will be making their way on to this website. In the meantme, please take a moment to register for the event. If you are planning on flying at HellFire you do need to register.  Remember that Spectators are free. You only need to register and pay if you are planning on flying at HellFire.

 

Eventbrite - HellFire 21 - High Power Rocketry Event
Published in HellFire
Friday, 24 August 2007 06:57

Fiberglassing Body Tubes in One Easy Step

One thing I have found about rocket construction is that there’s not just one ‘right’ way of doing things, in other words there can be many different approaches that can work on a given application. Here’s one way I’ve come up with to fiberglass body tubes and come up with a nice smooth finish all at the same time. I usually fiberglass whole lengths of tubes at one time and cut them to the length needed afterwards. 

I generally use ‘flex phenolic’ tubing but the method works well on paper tubes also as long as you sand the gloss layer with a course sandpaper such as 80-100 grit to allow the epoxy to ‘soak’ in the tube. Some have recommended peeling the outer layer of ‘glassine’ off but I’ve never been that ambitious and have had good results just sanding. I lay out the fiberglass flat, roll the body tube up in it the desired number of layers (depending on motor impulse level anticipated), and cut the cloth with a little overlap on the joint and the ends. If you cut it straight with the weave in the cloth you will have minimal loose strings to deal with, if you have any pull these loose to avoid them causing lumps in the finished product.

The next step is where you may need a little help, roll the tube tightly in the cloth and while holding the cloth rolled up on the tube have your helper roll a leg of women’s nylons down over the tube to completely envelope the tube and the cloth

At this point I use a twist tie to hold the open end of the nylons leg closed. After you get it tied off you can go back and smooth out any wrinkles that may have shown up under the nylon ‘veil’. This is generally easier if you start with ‘queen sized’ nylons on the tubes 4”- 6”, but is fairly easy with ‘normal sized’ nylons on anything smaller. At this point you have the hard part done; you can don the latex gloves and mix up a batch of epoxy. I generally use the stuff that cures in 30 minutes or so. I’ve found using the cheap paintbrushes available at Wal-Mart on the smaller tubes or the smaller paint rollers on the bigger tubes minimizes the mess and makes epoxy easier to apply. Hold the tube horizontal and start laying that stuff on!

When you get the whole tube coated and the epoxy worked in so the cloth goes transparent work out any bubbles you have and hang it up by the twist tied end to cure. If you didn’t use too much epoxy it shouldn’t run down too much but after 15 minutes or so you can turn it over to even out the ‘flow’. After it’s cured just trim off the ends (I use a power miter saw because I’m lazy), and sand the entire tube with the orbital sander of choice in long smooth strokes while turning frequently. This usually goes quick since the nylons provide a nice smooth finish by themselves.

Well that’s it, this method may not be to everybody’s taste but it’s worked for me for years on a lot of rockets from ‘G’ power level up to full ‘L’ (I couldn’t find big enough nylons for 7.6” tubing).

Tracy “Woody” Wood - TRA#4828 L3

PS - If you don’t care for filling spirals on tubing but don’t feel your rocket needs the extra strength of Fiberglassing just pull a leg of nylons down over the tube with no fiberglass cloth underneath and epoxy coat the same as above (after sanding on paper tube). It will add some strength with minimal weight gain on the finished rocket and fills those nasty spiral marks.

Published in Learning
Tuesday, 07 August 2007 16:11

Thinking About Level 3? You Can Do It!

As the UROC club grows, there are more and more flyers that are progressing up the ranks of level 1 and 2. Some of you may be considering making the jump to level 3 and wondering if this is something that you might want to achieve. UROC has seen a big increase in the number of Level 3 flyers over the last couple of years. I remember when I first got into high power rocketry I thought that those guys putting up level 3 rockets must have a PhD in astrophysics or some other connection to NASA. Surely, Level 3 rockets were beyond my basement building techniques.

The purpose of this article is to demystify the Tripoli Level 3 process for anyone considering making the jump and to set forth guidelines to help walk you through the steps.

I am not a NAR member so I am not as familiar with their procedures but I understand NAR has adopted similar regs and rules. Currently, Tripoli has about 700 Level 3 members nationwide with more being added all the time.

First of all, I am a TAP (technical advisory panel) member for Tripoli. TAP members must be level 3 certified and must apply to the Tripoli board for inclusion on the membership list. I wanted to become a TAP member because there was nobody in Utah at the time that could help certify Level 3 members at our launches. Also, I enjoy seeing the nuts and bolts of other Level 3 projects and I learn something new from each and every one. To date, I have flown or been very involved in about 50 M and N motor flights. That's some AP poundage!

Why does the TAP committee exist? Because Tripoli believes that as the rockets get bigger and the total impulse goes up, the potential danger also rises. These rockets should have more than one pair of eyes looking at them to ensure that they are safe and the construction and design techniques make them flight worthy. After the flyer has demonstrated the ability to construct and successfully fly a large M motor rocket, he or she is free to fly other Level 3 rockets without TAP approval.

Myth #1

Level 3 rockets are technically much harder to fly than level 2 and 1 rockets. Not necessarily true. In fact, many level 2 rockets, especially multi stage or clustered J-K rockets are tougher to fly and more technical than basic Level 3 rockets. For your Level 3 attempt you may want to employ the KISS method (Keep It Simple Stupid) to have a greater probability of success.

Myth #2

The Level 3 process is a lot of bureaucracy. Not true. There are some basic steps that you have to follow but with friendly TAP members (like me) guiding you, this should pose no problem.

Myth #3

Level 3 rockets cost a lot. Actually, this one isn't a myth. Level 3 rockets are definitely a step up in the cost factor depending on what you decide to do. But, if you can borrow somebody's motor hardware (with the typical lose-it-or-dent-it, you-buy-it policy) you can help bring the cost down. The 75mm reloads are also a lot more cost effective than the 98mm loads. Still, it is not uncommon for a level 3 rocket to cost over $1000 when you consider electronics, parachutes, motor hardware, motor reload and airframe parts. Everything but the reload is reusable but you still have to ask yourself, "What will this cost if it crashes and I lose everything?"

OK, so how do I get started on my Level 3 project? First of all, you need to select a project to build. It can be an upscale of an old estes kit or a Level 3 kit from some of the various rocket vendors or your own design. Some of the basic Tripoli rules for the design are as follows:

  1. Single stage design only.
  2. No clusters allowed.
  3. The project must be constructed principally by the flyer.No team projects allowed.
  4. Electronic recovery is required and must function as designed. A redundant (backup) recovery system is also required. This can be motor ejection but not recommended. I always advise that either two altimeters be used or one altimeter and a timer backup.
  5. Two-stage recovery is not required. If you want to keep it simple, blow the main parachute at apogee. A lot of Level 3 rockets don't go that high anyway.
  6. Currently, Tripoli is allowing kits from manufacturers to be used. There is some discussion among the TAP committee that only scratch built rockets will be allowed in the future. More to come on this issue

Next, you should contact a TAP member to discuss your project. He'll tell you what you need to do in order to get your paperwork signed off. In my case, I tell the flyer that I would like to see the following:

  1. Overall written description of the project with specification such as length, weight (loaded and dry), diameter, electronics involved, recovery systems, expected altitude, etc.
  2. A schematic of mechanical drawing showing all components of the rocket.
  3. Some photos of construction are nice if you can take them as you build.If not, then details of construction and materials used, etc.
  4. Some computer simulated flight profiles with the motors you expect to use.
  5. Tripoli paperwork.

For Level 3 certification, you need to have two TAP members sign off on your project at least one month before you actually make the flight. This is to allow time for minor changes that TAP members may suggest. If you would like to use me for one of your TAP members, I can suggest others that would be happy to serve as your second committee member. Rich Evans of UROC is also a TAP member in Utah and is happy and willing to serve as a second TAP member for UROC level 3 projects.

Finally, you need to launch your project. The day of reckoning! For the actual flight, a TAP member must witness the flight and survey the rocket upon recovery. The TAP member witnessing the flight can be one of the first two preliminary members that you used or it can be a third member. If the flight is successful, he will sign your paperwork at the site and mail it in to Tripoli headquarters.

In my case, I define a successful flight as follows: The rocket must work as designed and sustain only cosmetic or minor damage. Example: If you design in a level of complexity such as two-stage recovery, then the rocket must work that way. Damage such as zippers may mean that recovery was somehow compromised or structurally the rocket couldn't withstand the forces encountered during chute deployment.

What's the success rate? The Level 3 projects that I've been involved in have had about a 65% success rate. 2 successes for each failure. That's not bad. And for the failures, most were able to launch again at a later date and have a successful flight.

Hopefully, this article will encourage some of you who are thinking about Level 3 to go for it. If you want to call me to get started, my phone number is 277-9006 hm or you can catch me at a meeting or launch.

Published in Learning
Tuesday, 07 August 2007 04:03

Fin Fillet Construction

As with many aspects of rocket building, there are many ways to do things. This is how I make my fin fillets and can be used on both methods of fin attachment, direct body and through the tube attachment.

I use balsa wood for the fillet material in the profile shape of a triangle. Square material could be used, but it would require more sanding. I cut the balsa a little longer than the fin root chord length and sand the sides to make it fit. The balsa is cut at 90 degrees and the area for the fillets is more than that, so some sanding is needed.

I disregard the fact that the fin is flat and the tube is rounded at the glue joint area. This small difference is filled in with the adhesive and is less noticeable with the larger rockets. I use slow cure epoxy for the adhesive. I have tried to use wood glue to save money, but when it dries it shrinks and makes huge gaps in the fillets when even using pins to hold the balsa in place.

I force epoxy in the fin/tube joint for through the tube attachments, apply epoxy to the balsa and attach the fillets. Be careful not to get epoxy on the fin or the tube outside the bond area. While curing, examine the fillets to make sure they are staying in place. Pressing on the fillets during curing a few times makes the fit better.

After cure, sand the fillets using a sanding drum tube held between the fingers. I use a 1/2" X 2" drum on the smaller rockets less than 2", and 1" X 2" on the larger rockets. While sanding, and as the flat side is becoming concave, be careful not to cut into the fin or the tube. It will make a groove that will have to be filled later. Stop sanding just as the edges of the balsa meet the tube or fin. While sanding, compare all fillets to make sure they are coming out even in shape.

The forward part of the fin/tube attachment is the hardest to shape. I use a pencil wrapped with sand paper to make this transition smooth, again making sure that all joints are identical. If the tube extends aft past the fins this procedure must be used again. If the fins end with the tube, sand this area flat and fill any voids with filler. I always glass the fins and tube for strength.

Published in Learning
Saturday, 24 June 2006 10:07

Making a Foam and Wood Nosecone

After trying several ways to create the nosecone for the ASP (Atmospheric Sounding Projectile), I've decided I won't use any of those methods again. Here are some notes and photos of what I did, and a few suggestions for what I'd do differently. Any input would be welcome.

We (Luke, Ian and I) had earlier experimented with gluing up just the foam (styrofoam insulation), turning it to shape, splitting it and then gluing it to the wooden ribs that were to support it. Bad idea all around in my opinion. It was a pig to put (and keep) on the lathe and cutting the finished product into four equal pieces would be a pain. Maybe it'd be OK for a smallish cone but not for this one. By the way, gluing a piece of styrofoam to a wood disc and attaching that to a faceplate on the lathe works pretty good for pieces up to maybe a foot long and a foot in diameter.

Image

The next experiment was to create a wooden support structure with a 1” dowel at the center and 1/4” plywood ribs for support. The dowel had four 1/8” deep dadoes cut into it to hold the plywood.

Image

I then cut the ribs so that, when glued to the dowel, they would make a structure defining the size and shape of the finished nosecone. Stacking the rib blanks and taping them together made it fairly easy to cut them the same size and shape.

Image

I drilled and cut foam circles just a little bigger than the wooden structure and quartered them.

Image

A 3/4” center hole worked great and careful quartering produced a pretty good fit when I began gluing the pieces to the ribs.

The first attempt I made at this procedure can be seen on the lathe in the background of the picture above. I thought I might be able to do it cheaply by using liquid nails to hold the foam together. - -Wrong.- - The liquid nails ate the foam from the inside out and the whole thing blew apart under stress on the lathe.The assembly in the foreground has wood glue for the wood joints and Devcon epoxy for sticking the foam. I used 5-minute epoxy but I had extra hands there to put the cable ties on and help mix the epoxy. Working alone would definitely require slower epoxy. 

This attempt went well. I planned on using a skew (angled knife) to turn the foam down until I hit wood and figured I'd get the right shape and a nice smooth finish that way. The first time I nicked the wood I could tell I'd have to change plans. Even with a razor sharp skew, the difference in density between the foam and the wood made the knife catch and pull. I ended up using a drywall sanding block and paper to get the finished shape while the lathe was running. One downside to sanding instead of cutting was that any amount of pressure applied to the sanding block wore the foam more than the wood resulting in a dip along one edge of the rib. Another downside to using the sanding block was that I couldn't get the nice crisp corners I wanted on the angles in the lower portion of the ASP's cone.

Image

The Finished Product - Next time I'd make the wood ribs smaller than the finished cone size and fill in with 1/4” strips of foam. It would take some careful work with a skew and calipers to get the exact shape but I'd prefer that to sanding and I think I'd be happier with the results. Turning the foam on the lathe is easy and that's nice, but the stuff is so soft I ended up looking for a filler to take care of some nicks. Lightweight vinyl spackle seemed to do the trick.

Something else I'd like to try would be to turn a wooden form and create the cone out of fiberglass. Maybe glue a wooden support structure in later after the cone was removed from the form. That kind of glass work is beyond me right now but I'd love to learn. More to come, Evan

P.S. You can find out more about this project on Jim Yehle's pages at http://www.xmission.com/~jry/rocketry/projects/asp/asp-group-project.html.

 

 

 
 
 
 

 

 

 

Published in Learning
Thursday, 11 November 2004 10:25

How To Interpret Rocket Motor Codes

motorclass1Sport rocket motors approved for sale in the United States are stamped with a three-part code that gives the modeler some basic information about the motor's power and behavior. For example, a "C6-3" designation indicates that the total impulse of the motor ("C"), This number specifies the average thrust ("6"), and finally, the last number indicates the time delay between burnout and recovery ejection ("3").

Total impulse is a measure of the overall total energy contained in a motor, and is measured in Newton-seconds. The letter "C" in our example motor above tells us that there is anywhere from 5.01 to 10.0 N-sec of total impulse available in this motor.


In a typical hobby store you will be able to find engines in power classes from 1/2A to D. However, E, F, and some G motors are also classified as model rocket motors, and modelers certified for high power rocketry by the NAR can purchase motors ranging from G to K.

Since each letter represents twice the power range of the previous letter, total available power increases rapidly the further you progress through the alphabet.

Average Thrust

Average thrust is a measure of how slowly or quickly the motor delivers its total energy, and is measured in Newtons. The "6" in our example motor tells us that the energy is delivered at a moderate rate (over about 1.7 seconds). A C4 would deliver weaker thrust over a longer time (about 2.5 seconds), while a C10 would deliver a strong thrust for a shorter time (about a second).

As a rule of thumb, the thrust duration of a motor can be approximated by dividing its total impulse by its average thrust.

Keep in mind that you cannot assume that the actual total impulse of a motor lies at the top end of its letter's power range -- an engine marked "C" might be engineered to deliver only 5.5 Newton-seconds, not 10.

Time Delay

The rocket is traveling very fast at the instant of motor burnout. The time delay allows the rocket to coast to its maximum altitude and slow down before the recovery system (such as a parachute) is activated by the ejection charge.

The time delay is indicated on our sample motor is 3 seconds. Other typical delay choices for C engines are 5 and 7. Longer delays are best for lighter rockets, which will coast upwards for a long time. Heavier rockets usually do better with shorter delays -- otherwise the rocket might fall back down to the ground during the delay time.

Motors marked with a time delay of 0 (e.g., "C6-0") are booster engines. They are not designed to activate recovery systems. They are intended for use as lower-stage engines in multi-stage rockets. They are designed to ignite the next stage engine immediately once their own thrust is finished. Often their labels are printed in a different color to help prevent you from using them in a typical rocket. In a multi-stage rocket, you would usually select a very long delay for your topmost engine.

https://en.wikipedia.org/wiki/Model_rocket_motor_classification

 

Published in Learning
Thursday, 07 February 2002 17:00

Rocketry Rules of Thumb

First, please read the fine print... There are many different solutions to the rocket design challenge. Rules of Thumb simply provide a solid starting point that many have found useful in the past, and that will, in many cases, provide a suitable solution for your design problem today. Rules of Thumb are guidelines. They're not laws. They are nominal solutions that usually, in many cases, most of the time, get the designer in the right ballpark. Once a rocket designer's judgement has been formed by lots of experience, some Rules of Thumb can be stretched, bent, stood on their head, or ignored completely.

Using Rules of Thumb certainly does not take the place of stability tests, or attention to safety. Proof of stability and a constant focus on safety are the most fundamental and unchangeable Rules of Thumb I know. If you know Rules of Thumb that are not mentioned here, e-mail them to Tom Savoie and they could appear in a future update with your name as the contributor. Comments are always welcome.

General Design

Motor Mount Size
Build your rocket for the largest motor you might want to fly in it. You can always adapt down, you can never adapt never up.

Paint Selection
Whatever your choice, use a primer, finish and clear coats that are compatible. Many times this means sticking to the same brands-e.g., Krylon primer, Krylon finish coat, and Krylon clear coat.

Airframe

Diameter And Length Of The Rocket
The ratio of rocket length to diameter, sometimes referred to the aspect ratio, should be from 10 - 20:1. For example, a six inch diameter rocket would mean a length of 60 -120 inches.

Reinforcing the Airframe
The larger the rocket, the more important reinforcement becomes. Two layers of a lighter fiberglass fabric work better than a single heavy layer. Two layers of 4oz fiberglass works well for 3-4 inch rockets, 2-3 layers of 6oz for 5-7.5 inch rockets. A final wrap of 2 oz glass provides a good sanding veil. Glass a rocket measuring 2.56" or greater that will reach equal or greater than 0.85 Mach.

Fins

Fin Dimensions
A fin that is 2 diameters of the airframe in root length and span and a chord length of about 1 diameter will be effective.

Fin Shape or Planform
The shape you see more than any other is called the clipped delta, and is known for its effectiveness. The clipped delta resembles a parallelogram, with the fin swept somewhat to the rear. The root and chord lines are near parallel, and the leading and trailing edges are near parallel. There are many, many shapes that will get the job done. Some look cooler to me than others. One of the most efficient fin designs looks like a simple rectangle attached to the tube.

Shaping the Fin
The leading edge of the fin should be rounded, the trailing edge shaped like a V. The chord edge should remain square.

Number of Fins
Three fins will almost always do the job. Four fins work too, but only marginally better as far as improving CP. Some have said that four fins reduce wind-induced spin.

Recovery

Black Powder Ejection
Use enough BP to yield a 15 psi pressure within the airframe. See article on Ejection Charges for a detailed discussion.

Sizing The Parachute
You want your rocket to descend at about 15 feet per second under nominal conditions. Slow it up over playa and concrete. Use 3.5 square feet of chute per pound of recovered rocket weight. Determine chute size by doubling the square root of the weight of the rocket. For example, a 16 pound rocket would use a 2X4=8' chute. A 49 # rocket would use a 2X7=14' chute.

Streamers should be 10 times as long as they are wide.

Drogue recovery descent should be about 50 ft/sec.

A full-hemispherical canopy has very little performance gain over the more efficient and less bulky quarter-spherical--the top-half of a full-hemispherical chute.

Recovery Harness Strength
Tensile rating for recovery materials should be at least 50 times the static weight of the rocket.

Sizing Tubular Nylon
9/16" serves well in rockets up to 15 pounds. Go with 3/4 up to 30 pounds. 1" up to 50 pounds.

Length of model rocket shock cord
Make shock cords for model rockets a minimum of 2 to 3 times the overall length of the rocket. Middle or high power rockets should use tubular nylon at least 5 times the rocket length.

Wadding
Use enough wadding to fill 2 x the diameter of your BT. Any more is probably overkill. Any less may allow hot particles through to hit your chute. Do not pack it tight.

Knots, Loops and Sharp Bends in Shock Cord or Bridle
Knots, sharp bends, including sewn loops, in the tubular nylon or flat webbing will weaken its load capacity by 50%.

How Tight is Tight?
Many people use masking tape to finesse the fit between an airframe and a coupler that must separate at deployment. A common question is: how tight do I want it to be? Use enough masking tape so that you can pick the rocket by the nose cone without the rocket coming apart. If you vigorously shake the rocket up and down, and don't see any movement off the coupler, you've probably got too much tape on, Jack.

Piston Deployment
Use 25% less Black Powder if your deployment system is piston driven.

Piston Maintenance
Running a damp cloth through your airframe after flying will clean out powder residue and keep your piston moving freely.

Shear Pins
Use shear pins on any rocket where you need a little extra piece of mind to know everything will stay in place until the proper time. Use 1/16" styrene rod or #2 nylon screws on almost any high performance rocket. For example two styrene shear pins each on a 2.6" phenolic airframe, 4 nylon screws on a 6" bird. See the article on Shear Pins in the CONSTRUCTION area for more detail.

Shortening Delay Elements
Note: Adjusting the delay as described below is considered a modification to the motor and is therefore against the rules in a TRA/NAR sanctioned launch. Delay grain burns at the rate of 1/32" per second. Shorten delay time by drilling a 1/16" bit to drill a hole into the ejection charge end of the delay. Drill to a depth of 1/32" for every second you want to shorten the delay. A piece of tape wrapped around the drill bit at the proper depth will help ensure an accurate depth. Don't drill more than 25% into the length of the delay.

Stability

Margin of Stability
The CG should be forward of the Center of Pressure by 1-2 calibers. A caliber is simply the diameter of the bird. One caliber of stability is also known as a margin of stability. In other words, in a four inch rocket, the CG must be ahead (closer to the nosecone) of the CP by 4 - 8 inches. More than .5 but less than 1 margin of stability (less than one caliber) and a rocket is "marginally stable'. More than two calibers of stability is known as "over stable". An over stable rocket will tend to dramatically turn into the wind. A marginally-powered, over stable rocket can end up almost horizontal.

Adjusting the Center of Gravity
To move the CG forward, add weight to the nose, lengthen the rocket, or lessen the weight in the aft end of the rocket. To move the CG aft, (for example, if your rocket is overstable), do the reverse.

Adjusting the Center of Pressure
To move the CP aft (more stable), increase the size of the fins. To move the CP forward, decrease fin size.

How Long is Too Long
A rocket must maintain its rigidity in flight. Any tendency to bend will be magnified in flight resulting in a kinked tube and likely a failed flight. If you hold a rocket horizontal by its tail section and notice any curvature in the rocket, your bird probably isn't stiff enough. Sorry, rocketeers, Viagra will not cure this problem.

Propulsion

Sizing the Motor
In selecting a motor to power your rocket, you need to have at least a 5:1 thrust to weight ratio. See a detailed discussion of this guideline Motor Selection in the PROPULSION area.

Launch Operations

Launch Rod Diameter
Determine by motor size:
A,B,C - 1/8"
D,E - 3/16"
F,G,H and a body tube less than 2.6" - 1/4"
F,G,H,I w/ 2.6" to 4.0" body - 7/16"
I,J - 1/2"

Over J and body tube over should use rail buttons

Minimum Speed for Stable Flight
44 fps (30mph) is generally accepted as a minimum safe speed for stable flight. Faster speeds are necessary to achieve stability in windy conditions.

Mounting launch lug(s)/button/s
When mounting a single lug, cover the center of gravity with the lug. Always mount at least two rail buttons. When mounting two lugs or buttons, mount the lower piece at the rear of the airframe. The second should be on or just behind the center of gravity.

Submitted by Tom Savoie

 

Published in Learning
Sunday, 02 February 2003 17:00

The Importance of Procedures

Originally printed in Extreme Rocketry Magazine

Rocketry is one of those things you do in life that has no in-between. You have either a complete success, or an unmitigated disaster. Every flight, including failures, is a new andunforgettable learning experience. While some of the disasters can be attributed to bad or defective equipment or materials, a lot of failures can be attributed to incorrect preparation.

You certainly feel bad when you forget wadding in your Big Bertha, but it pales in comparison to forgetting something when flying your Big Kahuna. And the more we pay attention to the successes and failures of others and ourselves, the more we learn and the better our chances are for successful flights in the future.

Flights with a regular model rocket are basic. Wadding-parachute-motor-igniter-plug and you're off to get a launch pad. Mid- and high-power rockets are more complex, so more things can go wrong. The lack of proper preparation reminds me of one flight I saw. The rocket represented a considerable investment of time, effort and money for this person. The lift-off, boost and coast were perfect, and separation charge fired at apogee. However, during separation, everybody saw the one little "oops" this rocketeer forgot: to fasten the shock cord to both sections of the rocket. The upper part of the rocket came in under parachute, but the booster came in ballistic. Ouch.

Trying to document all of the possible ways to go wrong would fill a James Michner novel. Here is a small list of failures what I have either witnessed or been guilty of myself: All it takes is something like a forgotten O-ring in the motor and you get a CATO. Or there's not fastening the shock cord correctly and you get more pieces coming down than went up. Forgetting to arm the recovery electronics gets you a ballistic rather than parachute recovery. Using the wrong size launch rod will send your rocket off in unwanted directions, if it cleared the rod at all. Forgetting wadding turns your parachute into either a melted wad or the equivalent of a screen door, both bad for future flights. Not verifying your CG on assembly can turn your vertical flight into a horizontal one. That's not a good way to get the crowd to do the Wave.

Since we are all rocket scientists, I decided to take a "page" from the professional rocket scientists and write check-off lists, or "procedures" as they call them, for rocket preparation and launch evolutions. Even in the middle of the Apollo 13 disaster, everybody had a procedure for everything. If there wasn't one, you wrote it to make sure everybody was clear on what they needed to have and what they were supposed to do. This made sure everybody was "on the same page."

Procedures are essential to a person like me. I would forget my head, as the saying goes, if it wasn't permanently attached. I run down a procedure to make sure I don't forget something every time I leave the house. If I didn't, I would leave at least one essential thing behind, every time. I started using procedures years ago when I was SCUBA diving. It is embarrassing to get to the dive site and discover you forgot your weight belt, regulator or fins (or all of them) as I did on several occasions.

The source of my organization comes from my Palm Pilot. Not only do I use it to help keep me organized, I can also recover flight data from my onboard computer into it while on the flight line as well. I mention Palm specifically because there is a shareware program called HandyShopper that I use for these lists. I use the Aisle #'s as step #'s so that I can easily adjust the order of things in a procedure if I have to. In practice, after completing a step, I merely check it off, just like if I had just grabbed the bread or eggs. If you don't have a handheld computer, clipboards and paper served the professionals for years.

The best way to develop your own procedures is to sit in a quiet area and go through everything in your mind, start to finish. After you have imagined them, write them down and go through the list again. Then go and perform the procedure, adding notes and adding/changing steps as you go. As with all endeavors in our lives, your mileage may vary. The standard that you should aim for is that anybody can understand and complete your procedures. Imagine yourself in a full body cast with your jaw wired shut. A fellow rocketeer of approximate experience should be able to get you to the range, prep and fly your rocket without any "input" from you.

The first list is the material preparation procedure. You make sure your rockets are ready, double check you have everything, test electronics, dip a few igniters, whatever you need to do to make yourself ready. This will prevent the proverbial running around like a headless chicken the morning of the launch, which cuts into flying time. Doing this over an evening or two during the week gets you 90% ready. All you have to do the night before is quickly check everything before packing it into the car to make sure no one has "borrowed" something. I verify my range box, motor box, etc. are properly stocked by writing in the bottom or on the cover of every compartment what is supposed to be there, so anything missing jumps out you.

Next you can concentrate on the family. Lay out clothes for everybody, make sure your club ID's, cash for range fees and so on are on hand (preferably packed in your range box).

The next procedure is car-packing. The order that I use to pack the vehicle is the opposite of what I will need on the range. Things that have to come out first (tables, chairs, etc.) go in last. If you pack everything but food and drink the night before, you can do it calmly and you have the time and leisure to double-check and properly secure the items. You also make sure the vehicle is up to the job. Check the fluids, tires, gas and so on. If your alarm doesn't go off and you wake up late on launch day, you can jump into your clothes, dash out to the car and drive off, with the worst consequences being you have forgotten food, drinks and family members.

Once you are on the range and set up, you can relax a bit and take a break. Fly some model rockets, catch up with club members, volunteer as RSO/LCO for a shift, whatever. Your prior planning has given you this break.

Once you are ready to launch a big rocket, pull out its' pre-flight procedure. You will probably need an individual procedure for each of your HPR rockets. This procedure should take your rocket from cold (unprepared) to warm (ready for RSO and the launch pad). The number of individual steps is not important. Clarity of the steps is important. Thirty-seven steps to load and secure the motor into the rocket might be a bit of overkill, but you don't want to have just "stick it in and tape it down" either. Make sure your flight card is filled out, electronics are installed and ready, your CP/CG ratio is good and everything is connected and ready to go.

Now comes the final countdown. Get your rocket approved by the RSO, draw a pad from the LCO, and head out with the rocket and your final preparation procedure. Verify the launch pad can handle your rocket, put the rocket on the pad, insert the igniter, arm the electronics, take the rocket from warm to hot (ready) and head back to the range head to ready your cameras.

If you have invested the time in developing your procedures, you have eliminated 98% of human error on your part. You have done everything you could to ensure a safe flight that ends in a recovered rocket.

The investment of time you spend at home developing these procedures will save countless hours and rockets on the range. As the military puts it, "The more you sweat in peacetime, the less you will bleed in wartime."

Safe and successful flying!

Remember, the things you need FIRST go in LAST.

Range Box Procedure

  • Check drawers
  • FRS Radios, load with fresh batteries
  • Forceps
  • Scissors
  • Hammer
  • Wet Wipes
  • Weather Station
  • Talcum Powder
  • Tempura Powder
  • Club ID Badges
  • Cash for Range Fees
  • Cash for Concessions

Car Loading Procedure

  • Check vehicle fluids (gas, oil, collent, etc.)
  • Rocket Box
  • Motor Box
  • HPR rockets
  • HPR launch pad(s)
  • Camera bag
  • Camera tripod
  • Laptop and AC inverter
  • Weather station
  • Tent/sunshade
  • Chairs
  • Table

Departure Procedure

  • Load Food, sodas and ice into cooler
  • Fill canteens and place into cooler
  • Load cooler into vehicle
  • Load family members into vehicle

HPR rocket Prep procedure (Cold to Warm)

  • Remove and disassemble electronics bay
  • Install fresh batteries in all electronics
  • Activate flight computer(s), verify units are operational
  • Mount computer(s) into bulkhead
  • Prepare ejection charges
  • Mount ejection charges; wire them to flight computer(s)
  • Reassemble electronics bay
  • Attach shock cord from booster to electronics bay
  • Attach shock cord from electronics bay to payload bay
  • Attach parachute to payload section
  • Attach streamer to electronics bay
  • Assemble motor(s) per manufacturer's directions
  • Slide motor(s) into motor mount tubes
  • Secure motor(s) by using MMT hardware
  • Verify launch weight
  • Verify Center of Gravity
  • Verify projected apogee doesn't break waiver
  • Fill out Flight Card
  • Take rocket to RSO

HPR Rocket Pre-Launch Procedure (Warm to Hot)

  • Take rocket to assigned pad
  • Verify pad will hold rocket properly
  • Mount proper rod/rail onto pad
  • Tilt pad, slide rocket onto rod/rail
  • Tilt pad/rocket upright
  • Insert igniters into motor(s)
  • Activate and final check electronics
  • Verify pad power is OFF
  • Attach launch clips to igniter(s)
  • Return to Safe Area
  • Ready cameras
  • Give final GO to LSO
Published in Learning
Tuesday, 07 August 2007 04:33

Using Artist Acrylic Paints for Rocketry

I enjoy painting plastic models and pewter miniatures used in games. I've used many different kinds of paints, so when it came time to paint another rocket, I decided to try some of them, rather than another can of Krylon. I've settled on using artist grade acrylics for my miniatures, so I decided to start there.

I chose acrylics for a variety of reasons. Typically they are non-toxic, they clean up with soap and water, can be thinned with water, are permanent, durable, and are readily available.

I purchase most of them from either Robert's or Michael's craft stores (don't forget the 40% off coupons in the Sunday newspapers).

The brand I like best is Liquitex, but I have had good luck with Golden and Winsor & Newton. The Liquitex paints come in a little wider color range, and are a little cheaper. Experiment yourself and see what works best! The model acrylic paints (like Testor's Model Master Acryl line) do come in a wider range of colors and are already thinned, but they seem fragile-any little scratch seems to take them right off.

Most of the artist paints can be heat-treated to improve their durability. Usually baking them at 200 F for about 30 minutes works, however, my wife would not appreciate an Alpha in the oven, so I put them on the dash of my car, and park in the sun.

Acrylic paints consist of two parts: a pigment and a binder. Usually the pigment is a naturally occurring mineral that is finely ground, and the binder is a plastic resin. Most artist acrylic paints across brands are compatible, but not all. Some very interesting colors can be mixed together. Get a color wheel and experiment. Also, there are a wide variety of pearl colors, or interference colors. Pearl colors appear as metallics, and interference colors change color depending on the angle you look at them

Make sure to buy the artist-grade, and not the student-grade paint. The student-grade paints are about 2/3 the price, but have less pigment in them, and come in fewer colors.

These paints have different viscosities between brands, and even between lines in the brand. High-viscosity paints have almost a peanut butter type consistency, and need large amounts of thinning for our purposes. The lower viscosity paints typically have the same amount of pigment as their high-viscosity counterparts, but need less thinning, so they go further. I use the medium-viscosity Liquitex, or Golden's Most of these paints have 2 ratings on them: Lightfastness and Opaqueness. Lightfastness refers to the pigment's ability to withstand fading. The highest grade of Lightfastness means the paint will stay it's original color for 100 years when exposed to museum-quality lighting. Most paints fall into this category, however many of the fluorescent colors shouldn't be used-they will break down in a few days of outdoor light.

To thin these paints, a variety of items can be used. Water is the most common, but don't use too much. As the water dries, the paint shrinks, and can crack. Add a drop or two of dishwashing detergent to the water to lower the surface tension. Windshield wiper fluid is another thinning agent, however I have had the alcohol react with the plastic binder in a few brands. Do not use mineral spirits or turpentine! Unfortunately, the best thinner for acrylics is not the cheapest--mediums. Mediums are sold for different types of thinning, from brushing to airbrushing, to giving a very glossy or dull finish without any overcoat. Most mediums are the plastic resin in a nonvolatile suspension. One thing I have learned, is to use the same brand of medium for the paint - different resins can react with each other. You can use several mediums, like combining airbrush medium with gloss medium. As a rule of thumb, do not user more than 25% medium in the paint. Try thinning to different levels, but remember, it is easier to thin the paint more than thicken it back up. A little medium goes a long ways.

I have applied these paints using brushes, rollers, and airbrushes. The best results have been with an airbrush, although a roller or brush can be used equally well with a few cautions. For brushing, use the highest quality, softest, synthetic fiber bristle you can find. Natural bristles tend to absorb the moisture in the paint, so it doesn't dry naturally, and can crack. Softer bristles leave less of a brush mark. Don't skimp on a quality brush, you wil thank yourself later.

If you don't have access to an airbrush, a spray bottle (like the kind for misting plants) can work too. Find the finest spray pattern you can, the finer the spray, the more uniform the paint will be. Pump-style hairspray bottles can work, but very little paint will go down per pump. Even though the paints are labeled non-toxic, I would still recommend using a NIOSH approved paint mask for any airbrush work. To use this paint in an airbrush, thin the paint to the consistency of heavy cream. Set your air pressure to about 20-23 lbs., and hold the airbrush as perpendicular to the rocket as possible. Start the spray before the rocket, and use a smooth stroke, ending the spray after the rocket. I practice on an old piece of cardboard, so that I can get the color and consistency that I want.

If you have spirals in the body tube to fill, I've used a product called Gesso with some success. Gesso is used to prime canvas for acrylic or oil paints, so that the paint does not soak through the canvas. It looks like a thick, syrupy material. I thinned it using water, then applied it using a brush directly onto the spirals. I had to let it sit overnight for complete drying, though. After that, I sanded the Gesso smooth. You can apply masking tape about 1/16" from each side of the seam, to make a guide if you like. It may take more than one coat, try to apply thin coats. If you want to use a primer, I've used whatever I had handy-spray cans of Krylon, airbrushing model paint primer, or an acrylic primer made by Designs From the Heart, or thinned Gesso. Each seemed to work equally well, but I let the oil-based primers dry for about 48 hours before I tried to apply acrylics over them. The solvents in the primer should be completely outgassed, or the paint will bubble later.

As a top coat, I have used either Liquitex's Solvar gloss varnish, the Gloss medium, Future floor wax, or simply left it alone. Some of the paints leave a little rough surface, and do need topcoating. Future has worked well, and it is cheap. The varnishes are a little on the expensive side, but very durable. Solvar is also removable with turpentine, so you can repair the paint easily. Solvar also has some UV inhibitors in it, which helps the paint resist fading.

Liquitex has a website with good technical information at www.liquitex.com. Golden's is www.goldenpaints.com. Winsor & Newton's website is www.winsornewton.com, but it seemed to concentrate more on their oil paints. Each has technical contact email, which I have found to be fast, friendly and expert advice (Liquitex put me in contact with their chemical engineer when I had a question on heat curing!). Acrylics have been a good alternative for me. They are more versatile, cheaper, easier to use than oil based enamels, and I because of their non-toxic nature, I can paint inside my house with them. Experiment with them, and see if they work for you.

Have fun, and keep the pointy end up! This article originally appeared in the December, 2002 issue of the Ballistic Beehive.

Published in Learning

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