Month: November 2016

So we’ve got a length of Kevlar shock cord and a fixed anchor point on our rocket. Unless our shock cord has a sewn loop, I guess we’ll need to tie a knot.  Certainly we know how to tie the simplest of all knots, the overhand knot, sometimes called a granny knot.  During ejection of a chute and when that chute opens, this knot is stressed in tension, exerting hundreds of pounds of force or more, and after the chute opens, the knot will be stressed in torsion.  In all likelihood, a simple overhand knot will fail, probably resulting in the anchor, and whatever is attached to it, going one way and the shock cord going the other.  Adding a couple of half hitches is an improvement but still not very reliable.

Most rocketeers who’ve been at it for a while have a “go to” knot they use to attach shock cords to anchors. Three knots seem to excel for this application:  fisherman’s, bowline, and figure eight.  All three of these work well with rigid anchors like screw eyes or U-bolts.  All can be untied even after being subjected to a load.  And all three are fairly simple.

As its name suggests, the fisherman’s knot is normally used to attach a hook to the end of a line.  It is good in tension and torsion.

Notice that the fisherman’s knot tightens its loop as the line is loaded.

The bowline knot is used to make a loop on the end of a line. It is used in sailing and is recommended by the FAA for lashing down light aircraft.  There are a number of variants but the standard knot forms a loop that will not close when loaded.

My personal favorite is the figure eight. Most technical climbers trust their lives to figure eight knots.  We should be able to trust our rockets to them.  The figure 8 also produces a non-closing loop, even when the line is loaded.

Although knots may be small, they are not trivial. Maximizing the reliability of your knots will make your rockets a little bit more reliable, more likely to be recovered intact and ready to fly again.

 

Several years ago, my six year old son, asked me if we could build a model rocket. I had flown Estes and Centuri rockets as a kid and so I thought I was an expert. He and I made a visit to Hobbytown USA in Longmont, Colorado. Being typical male shoppers, we went right to the Estes rockets, missing the much larger PML and Loc rockets farther down the aisle. He picked out an Estes Viking and I opted for the Estes Redliner. Kits in hand, we headed to the cash register.

While waiting in line to pay, I spied a rocketry magazine. On the cover of the magazine was a rocket that stood at least two feet taller than the man holding it. I thought to myself, “Whoa, what is THAT!”, and added the magazine to our purchases. Nineteen years later, my son has long ago lost interest but I’m still actively involved in the hobby. Although I enjoy building and flying the big birds, I still fly several of A through E powered rockets. I’ve often considered why so many people, myself included, move up the power scale as quickly as their available resources will allow.

With twenty three flights before it was retired, my Redliner was a good investment. Twenty three flights is a lot of air time for a rocket, especially a $9 kit built from kraft paper tube and balsa wood. I should be saying, “Wow, twenty three flights is GREAT!” But I don’t. The problem has to do with what we call the WOW! factor, that heart pounding thrill of a really big motor roaring off the pad, delivering its payload, the rocket, to the mercy of the sky demons.

What is the WOW! factor? I believe it is a combination of sensual inputs, mostly sight and sound, combined with an appreciation of the complexity and risk involved. Would it be possible to rate rocket flights based on their visual, audible, and technical merits?

Visually, my 2.5 oz Estes Redliner is nearly identical to fellow club member, John Wilke’s 23 lb, level 3 rocket, Argos. They both have airframe aspect ratios roughly 20:1, clipped delta fins, and ogive nosecones. Of course, he is dwarfed by his 10 foot tall rocket while my Redliner dwarfs only the spiders that inhabit its basement home.

More important visually is the flame to airframe (F/A) ratio. When I decide to go for it and stuff a comparatively large C6-7 in my little Redliner, the result is a relatively short flame several inches long, lets say 2″, emanating from the rear of a 20″ tall rocket. The F/A ratio is, therefore, 2/20 or 0.1. At left we see Ed Dawson’s and Joe Hinton’s Saturn V lifting off on an M650 and four K185’s at Mile High Mayhem in 2011. Ignoring the soundtrack leading up the launch, the last 60 seconds of the Apollo 11 countdown, I think most people present would have called this a “cool launch”. I measured the picture and determined that the airframe is 2.875″ long (in the picture) with the white portion of the flame a mere 1.75″. That gives us an F/A ratio of 0.61. So it is probably safe to say that any boost with an F/A ratio approaching 1 is a pretty cool rocket.

Now consider the next picture, a Titan IV launched in 2000 from Vandenberg AFB in California (photo courtesy of Ron Evans). Once again, I measured the picture to ascertain the F/A ratio’s critical dimensions. At .875″ for the rocket and 1.875″ for the white portion of the flame, the F/A ratio is a whopping 2.14. No doubt, if you were anywhere in the same county when this bird took to the sky, you would have thought, “WOW!, that was really cool!!”

The second criteria is the audible input, more commonly known as the roar. My Redliner merely hisses into the sky and tops it off with a diminutive pop to eject the parachute. Compare, this with the roar of four K185 with an M650. Even the relatively small I284 puts out over 100 dB. According to Ron Evans, the previously mentioned Titan IV rattled windows in nearby towns and that it was painfully loud from his vantage point 8 miles away from the launch site. So I think we can conclude that a lot of noise is good if you want to do a really cool rocket.

Finally, there is technical complexity. Typically, only rocket scientists appreciate technical complexity. For much of the general public, a big flame and a loud roar is enough. For those in the know, however, dual deployment, hybrid motors, flight computers, and other such stuff are enough to evoke excitement even if the rocket doesn’t leave the ground. Rate the rocket from 0 to 1 on technical complexity, an Estes Sprite being 0.000 and NASA’s Space Shuttle ranking a good solid 1.000. Agreeably, this is a subjective rating but it will suffice.

To obtain a rocket’s WOW! factor, though, we need to combine the three values. Take the product of the rocket’s F/A ratio, the sound level at the viewing distance in decibels, and the technical rating.
Wf(Redliner) = .1 x 50 x .01 = .05
Wf(Saturn) = .61 x 100 x .5 = 30.5
Wf(Titan IV) = 2.14 x 150 x .99 = 317.8

Although the combination is somewhat arbitrary, if you apply it to a wide variety of rockets you will find that it works. A rocket with a high score will be one that folks will stop what they are doing to watch as it roars skyward. Rockets scoring in the hundreds will be ones that folks will travel across the country to watch.

As far as my Redliner is concerned, sorry Vern, it may be fun but it isn’t a heart stopper.

By Chris Kraft
2001, Dutton Publishing, $25.95, ISBN 0-525-94571-7

In Flight, Chris Kraft pens both his autobiography and a brief history of NASA’s early years. It is the tale of a young man who grew up at the right place and time, had the right tools, and went on to do accomplish great deeds.

The time was the early cold war. America had just won World War II but had found new enemies in its wake. Competition with the Soviets was fierce.

A bright young man, Chris Kraft excelled in school and took advantage of the breaks that life dealt him. It resulted in his being the Flight Director through all of the Mercury program as well as most of the Gemini flights. He then managed flight operations during the heyday of the Apollo moon landings.

His reputation of as a no-bull leader shines through his often dry writing style. After dispensing with the not too interesting but relevant story of his life before Mission Control, he tells many a tale about the astronauts, engineering the spacecraft, the missions, and the many, many problems that were handled along the way.

But there are deeper messages in his book. Although one could glean the information from just about any compendium of space flight, it was impressive to realize just how much had to be done to enable Mercury to fly, even more for Gemini, and the monumental task putting an American onto the moon had been. And all of that occurred between October 4, 1957, when the Soviets shamed the U.S. by flying Sputnik I, and July 20, 1969, when Neil Armstrong reclaimed our national pride by taking that first step on the moon. We can do great things working together and when sufficiently motivated.

It also became apparent that various small events had huge and long lasting effects on NASA and its programs. Those early Sputnik flights and Kennedy’s challenge to our nation were the catalyst that started it all. But foremost among those is the fire on Apollo 1 that took the lives of Gus Grissom, Ed White, and Roger Chaffee. Kraft claims that the fire was tragically avoidable but gave the program a technical focus that it had been previously lacking. And then, during the Apollo 12 moon landing, Al Bean inadvertently aimed their only TV camera at the sun, burning out the electronics and depriving many millions of the highly anticipated real time, color images of men walking on the moon. With nothing but audio feeds, the networks ceased prime time coverage of the mission. It was the kiss of death for public support of the space program.

Finally, hidden deep in his 355 page narrative is the real reason why this book is a “must read”. The people who worked to make it possible to land a man on the moon were nothing short of passionate for what they were doing. Somewhere in his book is the reason why we load our equipment into our cars at 6am and drive hours out into the empty prairie, why we spend huge amounts of money for a few moments of flight that may result in a beautiful success or a resounding failure, why we do rocketry. Is it the quest for the unknown or simply the joy of making a big stick burn into the heavens? Each one of us has a different reason but, regardless of which end of the spectrum we are on, one thing is certain, given the chance, every one of us would have jumped at the opportunity to participate in man’s quest for the moon.

Whether you want to take your rocketry showmanship to the next level or just watch others do so, big launches are the place to go. If you are in Colorado, there are a number of excellent regional launches within a day’s drive of Denver.  Starting close to home, the three clubs with high power waivers sponsor a half dozen big launches.

One of the oldest Tripoli Prefectures still in business is Tripoli Colorado, www.tripolicolorado.org.  They have a very scenic launch site at about 8800 ft above sea level located on a buffalo ranch about 5 miles east of Hartsel, CO.  Their Spring Fling is usually the third weekend in June and Fall Frenzy is the third weekend in September.  Aside from mountain vistas, crystal clear skies and miles of recovery range, the ranch’s heard now features three white buffalo.

Northern Colorado Rocketry, www.ncrocketry.club, puts on Mile High Mayhem, High Skies in July, and Oktoberfest at its Pawnee Grasslands launch site 45 miles northeast of Ft. Collins, CO.  NCR boasts almost 100,000 acres of treeless recovery range.  Mile High Mayhem is around, but not necessarily on, Memorial Day weekend.  High Skies in July is usually the weekend after 4^th of July.  And Oktoberfest is in the beginning of October.

Southern Colorado Rocketry Enthusiasts, AKA SCORE, www.scronline.net, has been host to two NARAMs and an NSL in recent years.  Their annual regional launch, Chile Blaster, is usually scheduled around the end of July.  Located 4-H property 15 minutes from downtown Pueblo, CO, they are probably the most accessible of any high-power capable club.

Going west on I-80, Utah Rocketry, www.uroc.org, puts on their Hellfire launch every August about 12 miles east of Wendover, UT on the surreal Bonneville Salt Flats.  Although visual recovery is pretty easy on the pool table dry lake bed, the salt is hard and can damage rockets on landing.

South on I-15 through Utah, past Las Vegas and to the dry lake bed east of Jean, NV is where Tripoli Las Vegas, www.tripolivegas.com, does their Spring Fest in mid-March and Oktoberfest in mid-October.  Although they constantly share the lake bed with a variety of other wheeled and flying things, there is plenty of room for recovery in this classic desert launch site.

Near Tuscon, AZ, Southern Arizona Rocketry Association, www.sararocketry.org, has a launch site in the Sonoran desert.  Early April is when their  Desert Heat launch is held.

At the end of September, Tulsa Rocketry, www.piedmontrocketry.shutterfly.com, puts on their High Frontier launch in the Oklahoma prairie.

Last but not least, with a 50,000 ft waiver, Kloudbusters, www.kloudbusters.org, hosts three regional launches every year from their site outside of Argonia, KS:  KLOUDBurst in mid-April, AIRFest on Labor Day Weekend, and Distant Thunder in mid-November.

Rocketeers in the west tend to be very friendly, helpful, and open. Some launches might have special restrictions.  Be sure to consult the club’s website before making the long drive to one of these launches.

Fly high, fly often, and have fun.

The simplest mid and high powered rockets use the rocket motor’s delay and black powder charge for parachute deployment. Usually very reliable, ejecting the parachute near apogee can result in a long walk and possibly a long search for your rocket once it is on the ground. Jolly Logic’s latest addition to its innovative line of rocketry avionics is the Chute Release. It keeps a deployed chute from opening until a pre-set altitude is reached during descent. Therefore a simple rocket flying to several thousand feet altitude or higher can have its chute open closer to the ground to ease the effort for recovery.

Skeptical as to its efficacy and dubious to its hefty price tag, I tried the Chute Release at Tripoli Las Vegas’ Octoberfest last month. My 2” fiberglass rocket flew on an I161 with a projected altitude of 2900 ft. Normally, this rocket would deploy a chute at apogee and then float downwind, the distance depending upon the wind speed. On this flight, in a 5 mph wind, the overstable rocket weather-cocked slightly into the wind. The chute deployed just after apogee but didn’t open. The rocket tumbled quickly down to the release altitude of 300 ft where the Chute Release let go its grip on the chute. Then, as planned, the chute opened and the rocket made a soft landing about 200 yards from the launch pad for an easy recovery.

Before that flight left the pad, I’d already developed a very favorable opinion of the Chute Release. It is a product that is well implemented. Opening the sales package, the Chute Release and its standard accessories are all nicely displayed. Only a few pages long, the manual describes operation with clear and simple instructions aimed at getting the device into your rocket and up in the air in minimum time. The device is even powered by a built in battery recharged through a standard USB cable.

Using the Chute Release is really simple. One just presses the right hand button. After a short, 4 second, initialization, two banks of lights indicate the battery charge and the current release altitude. From this point, pressing either button increases or decreases the release altitude. Setting the release altitude higher than 1000 ft turns the device off, below 100 ft starts a test release. The one downside is that the device cannot be turned on or set without direct access to the chute bay.

Although most seasoned rocketeers will already have tried and true methods for folding various sizes or types of parachutes, a good folding method is even more important with the Chute Release. Once folded the parachute is held tightly closed by a rubber band with a pin on the end. When the set altitude is reached the pin is released and the chute opens. Several sizes of rubber bands are supplied to accommodate the full range of parachute sizes.

The Chute Release costs $130, which is more than most commercially produced two event rocket altimeters. That sounds like a lot of money until you add up what it costs to put your $80 altimeter into an avionics bay add shock cord, a drogue chute, and the additional size of your rocket.

The device in the images has only flown once but it is not difficult to imagine that being repeatedly packed into a tight chute bay and vigorously ejected might result in significant wear. Jolly Logic even has an answer for that with an accessory, a little Nomex pouch that fits over the Chute Release.

The Chute Release is probably the most significant development in rocketry technology since readily available downlinked GPS. With the Jolly Logic Chute Release, every rocket can have dual recovery.