Newbie to the forums here. I just joined these forums a few days ago, and only discovered the ugly rocket thread late last night. After reading "Da Rulez", specifically section 8 and I quote
"Entries will be taken first 3 weeks of month and after the 21st of every month the contest closes." I figured I could go to bed and submit during the day today.
So the contest is closed,
and one of the moderators has submitted an entry? Foul!
Anyways, here is my submission. Maybe I can get a people's choice award or something.
[ WARNING: I am rapidly becoming one of those old farts who likes to ramble. If you just want to see the pretty (er, ugly!) pictures, scroll down to the bottom. ]
So, a bit of background here. I am a BAR. I did the Estes rockets 25-30 years ago when a teenager. I got back into rocketry about 18 months ago when I discovered sugar propellants. Most of my work has been developing "small" (by ex-motor standards) single use motors. My upper limit is 62.5 grams of propellant to avoid BATF regulations. My lower limit is set by the tolerances of my tools. I'm one or two steps above the Amish lathe -- I use a file
and a drill press. And an angle grinder. Nonetheless, I have been able to make tooling for motors down to about 8 grams of propellant.
Relatively speaking, my motors are quite crude. Bentonite and concrete nozzles are hardly light, and PVC prevents running at the pressures required to max out Isp. Nonetheless, I have been able to achieve 120 seconds Isp (delivered) which is within 10 percent of what is generally considered quite good for a well-designed "proper" motor. Most recently I have been working with low pressure PVC (3/4" SDR 11) and truncated nozzles to get the weight way down without sacrificing performance.
I have done extensive static testing (well over 200 now) and I have had no failures (so far) in my final designs. Over the past few months I have begun to launch extensively to increase my sample size. With about 50 successful launches now I can only say my motors are at least 98.0% reliable. Ideally I would like to accumulate a lot of nines to the right of the decimal point.
My motors fall squarely in the mid-power area. I am using 1/2" SDR 13.5, 3/4" Sch 40 , 3/4" SDR 11, and 1" Sch 40. I have tooling for several different nozzle sizes for each casing material. I also have several different propellant recipes which give me a rather broad range of burn rates. This "toolbox" allows me to create just about any thrust curve I want. Generally, the 1/2" motors span the E class, the 3/4" motors the F class, and the 1" motors the G class.
In order to test these motors in a small field without losing them, I have been building short, high-drag, minimally built airframes. This keeps the danger down should the motor or parachute deployment fail. I have a number of good sources (dumpsters) for kraft tubes of various sizes. Fins are made from corrugated cardboard. Nosecones from chunks of packing styrofoam covered with paper mache. Don't laugh on this one -- an *amazingly* strong, light, and beautifully finished nose cone can be made from these materials!
I have always been a fan of the Mosquito. I have made a number of upscales so far. There are two problems with upscaling a mosquito. The first is that to really make the thing move (at least with a 120 second Isp propellant!) you need a motor that goes all the way up to the nose cone leaving no room above for a chute. The other is that if you do cram a chute up there, it will almost *always* break a plywood fin on landing.
So, I have decided to address these issues. The idea is to pack the chute and recovery harness in the space between the motor and body tube, and then eject the chute out the rear, with an attachment point at the base of the body tube. This allows the rocket to touch down nose first, allowing for the use of much more minimally-built fins.
The solution is a motor cartridge system that ejects the motor out the rear. This also functions as a piston, and as a double-plus bonus, motor cartridges (a majority of the construction work) can easily be swapped in an out, and even between multiple airframes.
That was the theory, anyways, the the rocket submitted below is essentially a "rapid prototype" designed to test all of these ideas, as well as my Ex motors. She was designed as a "one launch" test vehicle. Some 30 launches later she is still flying. She will get off the pad with a mid E motor and slow-ish propellant. It is a nice slow and low launch. Guaranteed recovery within a small ball-field. A fabulous way to *watch* chute deployment as it happens. A mid G will send her up to about 500 feet. On a dead-calm day I have had multiple recoveries of G launches within 100 feet of the pad.
She has come in hot a few times as a result of poor chute packing. I got a little sloppy and tested a new forward closure mod on the pad. Not a good idea. It completely gutted the inner core. Fortunately, fixing that was a 5 minute job. Slap in a new bulkhead plate and throw a new block of foam on the nose.
This rocket has been a blast to fly, but boy is she
UGLY! Here are the pics:
Here she is in all of her glory.
The business end. Poor lighting here. The body tube is, in fact, empty.
Here is the nose cone. That is packing foam from the dumpster of an appliance store down the road. It isn't even glued in. The shoulder is on the main body tube, allowing for easy replacement of the forward section with a bare tube of any length, as seen in the next photo.
Here the rocket is stretched with a longer tube. That's a different nose cone, too.
Here is a closeup of an alternate nose cone for stretched tubes.
Here are the motor cartridges for 1/2" PVC, 3/4" PVC and 1" PVC.
Here is a close-up showing the construction of the motor cartridges. The motor tube is hand-rolled from builders' paper using my own paper mache glue recipe. The core is more styrofoam. At the side ends are discs cut from cereal boxes. Everything is held together with urathane ("Gorilla") glue. The cutout is to allow for the recovery harness to pass through to the attachment point. (see next photo.)
Here is a closeup of the recovery harness attachment point. That is a coathanger, fiberglass drywall tape, and the only epoxy used on the model. You cannot really see it in the picture, but the ends of the coathanger wire and bent and go through the BT and are flush at the interior wall.
The way things look at launch-time.
The cartridge/piston with recovery harness attached. Initially I used one of the large wal*mart shopping bags. Yes, that really worked, even under high-speed deployment. This one is made from the plastic sheet you can take for free to cover your loads at the exit from the local big-box hardware store. The shroud lines are braided surveyer's line. They are knotted onto tabs protruding from the plastic chute. I have found this to be far stronger than tape.
Close-up of above.
A shot of the patch-job to fix a hot landing. Also note the packing tape over the "end grain" of the laminated cardboard.
Cardboard fins may bend easily, but they don't break. The rocket can be launched just like this with low impulse motors. Not with the fin bent, just set to straight at launch. Obviously this will cause flutter with higher impulse motors.
But here you can see how the bent fins are easily patched. That's just another piece of cereal box there. Urathane glue works best here, but CA can be used in a pinch in the field. In the picture, you can see how this particular patch has begun to fail.
A shot of the forward bulkhead. Initially this was made with styrofoam and cardboard which appears to be sufficient for an ejection charge. It is *not* sufficient to contain a motor bulkhead shot through it. In this photo, you can see the plywood disc inserted via the bottom end for replacement.
Hey, look, I made a message longer than the system can take. More in the next message...
