. This often conflicts with placement of as-designed dual deployment systems as well as, for custom, shifting the balance point for rocket design. There's also the issue of lower average impulse so they need somewhat lighter rockets. The long burns make it all worthwhile though!
GSEI've scratch built my own GSE as I've been frustrated at my apparent inability to sync up with the right people with the right equipment at a particular launch. So for the last 4 launches or so, I've had my motors, but was unable to launch them for various reasons - that boiled down to not having my own GSE. This situation will certainly improve overall - but I want to fly! The GSE availability at Whitakers is resolved, and the equipment typically in the trailer.
I've built a master / slave relay control panel along the lines of the "12 volt relay launcher". I've modified it though to use CAT-5 cable (through DB-9 connectors) and by doing so I get power from the slave and can also add NOX dump/fill and O2 lines. I won't be using the GOX, but am adding support for it so that I can launch HyperTek's later (either mine or others). I will post plans, schematics, and progress.
I've completed my GSE for all extents and purposes. It's complete with respect to handling all fill/dump/gox relays and one pad. The launch pad box has installed relays for pads 2, 3, but those aren't wired to the second DB9 or the breakout strip. The LCO box will fully control the launch pad box with respect to pad 1 and the hybrid relays. It does not yet have ANY support for pads 2 and 3 nor does it yet support single box launching (using just the LCO box for a "close, non hybrid pad").
You can look at more details on my Hybrid GSE Page.
I occasionally find myself desiring or needing (sometimes out of field necessity) to adapt equipment to my own or from my own to others. In that light I'm starting to work out the Hypertek GSE Pinouts. Click on that link for what information I've got.
Fill Tubes, Relief Cuts, and SheethingOn U/C valve type motors it is important to get the fill tubing to burn through and separate as close to it's exit point from the injector. The lower the burn through the lower the average thrust, the higher the O/F ration, the higher probability of a burn through, esp if the tubing is slightly bent and pointing even slightly towards a side of a grain. (It's quite common for the tubing to have a slight bend and very difficult to eliminate it).
A common technique, that is really the minimun you should do, is to overwrap the fill tube, for the length of the motor grain and a bit more, tightly with an overlap to two thicknesses of electrical tape. Leave just enough of a gap to match the thickness of the pre-heater grain.
Dave Griffith of Monterey Machine (RATTWorks) now supplies cardboard tube sheaths for his 29mm motor reloads. These work great
Dave also came up with the idea of using some high temp fiberglass sheathing for, in particular, his 64mm K-240, Tribrid, and L/M motors.
Here's a picture of a K-240 TriBrid fill tube with fiberglass sheathing installed.
Dave: "For the Ratt K- 240 5/16 dia fill lines use 1/4 i.d. sleeving (part# 8819k44) mount about 1" below injector and long enough to reach past nozzle. use black tape to hold in place. On the Ratt TriBrid and L/M 600-900 motors with 3/8 fill lines use 5/16 i.d. sleeving (part# 8819k45) mount right at below groove and long enough to go past nozzle and tape in place. Price is only.31 per foot.
For the larger nylon fill tubings, 5/16" for his K-240 and 3/8" for his TriBrid and L/M combos, Dave cuts a relief groove in the fill tubing to further encourage U/C valve separation at the desired opint.
Here's a close-up of that same fill tube illustrating the relief groove.
This tubing is high pressure 3/8" nylon tubing. The ID is 0.25" providing a measured wall thickness of 0.065". The OD of the relief groove is 0.325" so 0.050" has been removed. providing a new calculated wall thickness of 0.065 - (1/2)(0.050) or 0.040" so we've removed about 1/3rd of the wall thickness.
Pyro-Free GSE (ignition)The HyperTek system seemed cumbersome requiring all the GSE. Now that I'm building out my own GSE, adding O2 seems only more of a slight additional expense.
Basically it's a flare fitting T. The leg would carry the "ignition gas" to the outer sleeve. One end of the T would have a compression with the larger ignition gas tubing; the other end of the T would have the N2O tubing running through it. The specific orientation is only to allow the N2O tubing, which goes through the fitting, to go straight through. The ignition gas tubes terminate at the fitting so can be on the leg and end of the fitting.
West Coast and Propulsion Polymers have been up to this. Here's the West Coast Hybrids instruction document and they're Pyro-Free GSE plans; and the Propulsion Polymer's instructions (well, one variant anyway) has pyro free info.
Here's a NOW Hybrids page on Pyro Free for RATTWorks Hybrid Rocket Motors.
Propulsion PolymersI've purchased a Propulsion Polymers I160 from Pratt Hobbies. I've since purchased the other tubes and floating injector in the set. I hoped to then use the larger J140 tube to attain my TRA L2 certification. But for various reasons that didn't pan out and I got my L2 cert on a solid. I bashed Periwinkle's Pride, my PML Black Brant VB, and re-christened her "Periwinkle's Pride Gets N2Oxious". The J-140 motor took up most of this kits's body tube I doubled it's length adding a recovery module and main chute bay.
I've flown Periwinkle half dozen times or so on the I-160 and J-140 tubes. both are sweet rides. Nice kick off the pad and nice long burns. They don't have the raspy "farty" note of the RATT Works motors, so some folks don't recognize it for a hybrid flight.
Propulsion Polymers now has a nice 54mm "Penta Max" motor with two tubes and configurable injectors.
Do see Designing Rockets for Hybrids down below and, in particular, my efforts at bashing Periwinkle.
Micro HybridI'm interested've received this motor and plan on building a rocket for it. Since the motor has no recovery provisions I'm planning on using a Magnetic Apogee Detector to fire the main chute. These are inexpensive (~$30) and quite compact. I've got a "Kinda Jayhawkish" LOC kit for it.
Update: I've picked up some N2O micro-cylinders from Ebay (cheap!), but haven't done anything with it yet. I think I'll try it first in a Art Applewhite UFO so I can test it in a rocket not requiring recovery (I haven't anything small that has electronic recovery - though I DO now have a MAD detector on my bench). And the LOC kit on the bench too.
Recovery ElectronicsThis page discusses rocket recovery electronics. The focus is on altimeters, timers, tracking transmitters, beepers, etc. Look elsewhere on this index page for other electronics.
Designing Rockets for HybridsDesigning a rocket for Hybrids is a little more challenging. Partly due to the longer motor tubes (very long in the RATT, particularly the M-900!) Also the need for electronic deployment. And, if one wants dual deployment, the weight of those components is shifted farther forward. For such a more neutral balance (vs short motors in the ends), either a longer rocket is required OR smaller fins. This to keep the rocket "stable" but not over stable. Small fins requires a longer launch rod/rail depending on the initial motor thrust. The other issue is the relatively low average impulse of hybrids. Long motor burns, yes, but lower average impulse. Fortunately, most thrust curves are regressive providing a nice kick off the pad.
Note that Apogee Rocketry's Hybrid Motors In RockSim page they erroneously state that the worst case scenario is when the motor is empty. This is not correct. The worst case scenario is when the nitrous level matches the CP in the rocket. It is at this point that the nitrous is "doing it's worst" making the CG/CP relationship unstable as it's at this point that the nitrous weight is pulling the CG back the most. The situation actually improves again as the nitrous is consumed.
So CG/CP is at it's best when motor is full
is at it's worst when nitrous matches CP
is, well, somewhere inbetween when nitrous consumed.
Here's a specific link to a cool rocket. It's built for the HyperTek, but the ideas apply. This link is from Star Rocketry. They also have some good build info.Todd Lumpkin's Sc