5" x .12" tube weighs .0403 pounds per linear inch
| Grain # | Tube Length | Recess Length | Propellant Length | Gross Weight | Tube Weight | Propellant Weight | Density | |
| 1 | 7.0 | .2 | 6.8 | 5.2470 | .2821 | 4.9649 | 4.9649/7.00 | 0.06176 |
| 2 | 6.97 | .2 | 6.77 | 5.2452 | .2809 | 4.9643 | 9.9292/13.97 | 0.06203 |
| 3 | 7.0 | .2 | 6.8 | 5.2893 | .2821 | 5.0072 | 14.9364/20.97 | 0.06229 |
| 4 | 7.0 | .2 | 6.8 | 5.2724 | .2821 | 4.9903 | 19.9267/27.97 | 0.06207 |
| 5 | 7.02 | .2 | 6.82 | 5.3129 | .2829 | 5.0300 | 24.9567/34.89 | 0.06239 |
| 6 | 7.0 | .2 | 6.8 | 5.2309 | .2821 | 4.9488 | 29.9055/41.89 | 0.06156 |
| 7 | 7.0 | .2 | 6.8 | 5.264 | .2821 | 4.9819 | 34.8874/48.89 | 0.06197 |
| 8 | 7.0 | .2 | 6.8 | 5.2492 | .2821 | 4.9671 | 39.8545/55.89 | 0.06179 |
| 9 | 7.0 | .2 | 6.8 | 5.23 | .2821 | 4.9479 | 44.8024/62.89 | 0.06155 |
| 10 | 7.0 | .2 | 6.8 | 5.2225 | .2821 | 4.9404 | 49.7428/69.89 | 0.06145 |
| 11 | 6.95 | .2 | 6.75 | 5.2069 | .2801 | 4.9268 | 54.6696/76.84 | 0.06174 |
| 12 | 5.5 | .2 | 5.3 | 4.1104 | .22165 | 3.8686 | 58.5382/82.84 | 0.06174 |
| Totals | 82.34 | 80.04/6.67 | 61.8807 | 3.32235 | 58.5382 | 0.06186 |
Kn: 430 initial, 454 max, 407 ending
Propellant Weight: 58.5382 pounds
Density: .06186 pounds per cubic inch
Propellant Diameter: 4.375"
Casting Tube Diameter: 4.615"
Throat Diameter: 1.53"
Assembly of the motor took place a full two weeks before launch date. But I had the propellant cast, and decided the casing was as good a place to store the propellant as any.
Forward closure still had a layer of high temp RTV covering it, so I applied another thin coat over the old and allowed it to cure. A new steel 1/4" pipe plug was inserted into the transducer tap with a generous winding of PVC sealant tape. The RTV on the inside also filled the remaining cavity of the port. 2 new o-rings were made from standard buna o-ring material, lubed with silicone grease and installed in the bulkhead o-ring glands.
The casing had just about exactly 84" of internal length between the forward bulkhead and the nozzle. I cut my EPDM (.045" thick) sheet to 14.75" x 84". The propellant grains were all trimmed to the appropriate lengths, then the outside cardboard surface of the casting tubes were painted with sodium silicate solution and allowed to dry. I mixed up a new batch of pyro starter mix, consisting of 100 grams of black powder green meal, 5 grams of magnesium particles and 2 grams of red iron oxide. A binder of dissolved ping pong balls in acetone was then added to dry pyro mix and painted on the cores and ends of the upper 6 propellant grains, the lower 6 grains were painted on the ends only.
The EPDM thermal liner was laid out on the floor, and the grains arranged in a line on the EPDM. Starting in the middle I used a piece of Scotch tape at each grain to loosely hold the liner in place, then I applied a single layer of heavy aluminum foil tape the entire length of the seam. I coated the inside of the motor casing, and the EPDM liner outside surface with talcum powder to aid insertion of the propellant package into the casing.
I must say, insertion of the propellant package went very smooth. I suppose it helps that I've done this twice before, but sliding the 60+ pound package into the casing had been problematic in the past. No problems this time though, after carefully measuring for the bulkhead and nozzle clearance, I arranged the package so it would just touch the forward bulkhead at one end, and the nozzle at the other end. I did run into the same situation I did last time, in my quest to load as much propellant as possible, I didn't leave enough free space between the propellant grain and the EPDM liner. So same as last time, I cut 1/2" off the end of one propellant grain, costing me .365 pounds...
Cutting that 1/2" off the last grain did give me a chance to do a test of my pyro starter mix though. So I went outside, laid the slice of propellant on the ground and threw a wood match on it. Nothing, the match went out. The second match I laid next to the first, it went out too. I was getting a little worried, I know most of the heat goes up, but I really thought it would light a little easier than that! The third match did the trick. I was surprised to see the entire surface ignite almost instantly. There was one little pop, or fizz when it lit, then the whole surface was burning. I really think it's a result of the magnesium particles throwing very hot sparks. It was wonderful to see the whole surface ignite and burn so smoothly, exactly what I'm looking for in an ignition aid.
Back to motor assembly, I painted a new coat of the pyro mix on the cut grain, allowed it to dry and continued with assembly of the motor. I applied a coat of RTV to end of the EPDM liner on the bulkhead end, and onto the inside of the casing about 1/2". The inside of the casing was lightly lubed with silicone grease and the forward bulkhead inserted. Being careful to stop exactly where the bolt holes lined up between the casing and the coupler/retainer. Ideally, the bulkhead will push into the RTV slightly as it's inserted, and form a perfect flame proof seal between the thermal liner and the forward bulkhead. The retaining bolts were then installed and I allowed time for the RTV to cure before moving on to the nozzle.
After about an hour, I did the same procedure with the nozzle, RTV between the casing and EPDM, silicone grease on the inside casing, then inserted the nozzle and bolted it in place. The nozzle uses two larger diameter silicone o-rings.
Pre Launch:
This launch represents the largest rocket and motor I have launched to date. The "O" class motor with over 58 pounds of propellant is intimidating by itself, now add a 14' long 5" diameter rocket and the entire project takes on a bit of a surreal atmosphere. It's hard for me to believe I've built, tested, and now going to launch such a project. It's been incremental steps for me over the past 5 or 6 years, I've learned from mistakes and successes. Now it's time to put it on line so to speak.
I was originally targeting 25,000' with this project. But I cut down the original length of the motor somewhat, so apogee is now expected just under 25,000'. Depending on the drag coefficient, a nominal flight should put me in the 24,000' to 25,000' range. Another consideration that will cost me a little altitude is my launch location. The launch site is about 2 miles from a small town. So I'm going to have to angle the rocket away from the town, to eliminate any possibility of the rocket coming in ballistic and landing in the town. The launch rail will be set to 3-5 degrees from vertical, and the azimuth set to a flight path that takes the rocket over uninhabited land.
Wind will also be a consideration come launch day. Of course surface winds speeds in excess of 20 mph will scrub a launch, but wind direction can not be from the Southeast either, I don't want the rocket landing or even drifting over the town. Pre launch preparations include gathering upper level wind data, I use this data to plot on a map the likely landing location of the rocket.
Every bit of data I can acquire goes into a launch book binder. I gather information from various software programs to predict apogee, downrange apogee, ballistic impact range, speed, thermal heating, drag coefficient vs. mach number, center of pressure data... This binder also contains copies of safety standards, set up check list, ground support personnel duties, FAA waiver, contact phone numbers, county road maps, satellite photos of the launch and recovery areas, wind data plot, really any and all information I may need on launch day. In most cases I don't need to use all that data, but it's nice to have just in case.
Component Weights:
Lower Body Tube/Fin Can, Loaded: 96.0 pounds
Nose Cone: 2.2 pounds
Deployment Module: 7.6 pounds
Upper Body Tube: 9.0 pounds
Lift Off Weight: 114.8 pounds
Launch Day:
Almost all of the equipment I had loaded the night before, and had gone over my checklist at that time. When John
and Joel arrived in the morning all we had to do was install the transmitters in the nose cones and load up the
rockets. About noon we headed out to the launch site. Set up went fairly well, as the small launch rail was on
a trailer of Joel's and quick to set up. The launch tower for the Defiance took a little longer, as we ran guy
wires to help support the tower. John laid out the 700+ feet of ignition wire, at the 500' mark we placed the launch
rail for the Prelude, then at the end was the Defiance launch tower.
At T-1 hour we called in to activate the waiver. Both the Minneapolis ATC and I were a little concerned about aircraft at upper altitudes, as it would be difficult for us to ground spot any aircraft that high up. So it was decided that I would call in immediately before the launch, to make sure there were no aircraft in the area.
Final set up was finished right at about 2pm and on schedule. A couple of minutes after 2:00 the Prelude was launched (Launch Test 135). Then we reset the ignition leads for the Defiance and I went out to arm the flight electronics. The weather turned out to be great, lower 60's and light ground wind. Although upper level air currents were very strong. I had downloaded the upper level wind speeds prior to leaving for the launch site. I'd use this data later to determine the approximate landing site of the Defiance.
Here's John and I with the Defiance after set up.
There were actually a few people at this launch, although not nearly as many people as had said were going to show up. One of those spectators was my mom and my uncle, so my mother had the honor of pushing the launch button for both launches. I had intended to use an external 12 volt battery to fire the igniters, but for some reason the battery wasn't powering the launch controller. So I used the internal nicad power supply, as it turned out even with over 700' of wire, the igniters lit instantly. My uncle also presented me with a little present, it was one of my original T-2 motors that I had lost in a field years before! Odd how things like that can just turn up...
Everything was now set for the Defiance launch. To be honest, I really didn't have time to think about everything leading up this point, I was pretty much concentrating on the job at hand. But the months of work, all the testing, were about to put on the line. One little push of a button would determine either utter failure or glorious success. I had visualized this moment many times in the preceding weeks, now my mind was numb. The next few seconds would tell the story.
Joel was time keeper, and responsible for the countdown and calling out flight event times. John took a camera and drove to the opposite side of the launch tower to get a different camera angle, he also started the camera close to the launch tower on a tripod. Joel started the countdown, big rocket, so more drama in a 10 second count down.
10,9,8,7,6,5,4,3,2,1 and launch!
Click Here
for an edited video containing all the camera angles. 6.2 MB for 1:27 video. It's highly compressed so quality
is only fair.
Click Here for the same video in higer quality. 62.9MB wmv file.
It happened so fast, the motor lit instantly and in a fraction of a second was off the tower accelerating to mach
1.9. It was beautiful, straight as straight could be, thundering loudly with a huge trail of pure white exhaust
trailing behind. The edges of the fins even leaving little vapor trails behind them. The motor burn was perfect,
I released my breath. Everyone was silent for a few moments, literally shocked and stupefied by the sight and sounds
they had just witnessed. I wasn't relaxed just yet, Joel was calling out time to apogee, then he announced apogee.
I grabbed my RDF receiver and pointed it in the last known direction of the rocket (straight up). Joel was now
calling out the time to expected ballistic impact, then he called out we had passed ballistic impact time, I still
had a strong signal on the receiver. At this point I did relax, the signal was still coming from high above and
I knew the rocket was under at least one drogue chute.
Ignition!
Half way up the tower.
Tower cleared, notice all the dirt kicked up!
Here's liftoff from another angle.
Nothing left at the tower but lots of white smoke.
Well into the motor burn now.
Motor burn out.
We stayed at the launch control table and tracked the rocket with the RDF receiver for over 6 minutes, until I lost the signal. That was another good sign, if only one drogue had deployed we should have lost the signal sooner. So at that point it seemed both drogues at least had deployed. Now we set out on the search. I had maps printed up, and charts made up to calculate the rocket drift direction and distance. At first, we started looking for an RDF signal closer to the launch site, about 1.5 miles out. Hoping to pick up the Prelude signal as well. After about an hour, neither signal was picked up within about 1.5 to 3 miles. So I plotted out the drift course on the map and we headed to that location. Within several minutes I picked up a weak signal from the Defiance! We zeroed in on the location by driving around the section where the signal was coming from.
Here's the landing site, dead in the middle of a section. John thought he had seen the rocket from 1/2 mile away from the other side of the section with my binoculars. He was right, and won his bet with Joel for $10 and donuts that it was just on the other side of this fence!
Here's a closer shot showing exactly how the rocket was found.
You maybe couldn't tell from looking at me, but I was ecstatic. The Defiance had been found intact, and had deployed all chutes perfectly! I tried to read the altitude beeps from the altimeters, but with two altimeters beeping at the same time, I couldn't do it. All I could make out was the first two beeps. So the Defiance made it to 20,000' at least. All we had was my Blazer to load the rocket into, as we decided not to drag the trailer along during the search. So I decided to break down the rocket in the field, that would also give me a chance to read the altimeters better.
Once the deployment module was out of the rocket, I placed a finger over the ARB3D speaker to hear the RRC2X. John wrote down the beeps as I read them. First was a two (20,000'), next was a nine (9,000') wait... Could that be right? Start over. 2 then 9 then 3 then 8 lastly 9. Ok, let's see, that's 29,389'. Holy cow, twenty nine thousand feet! I had to check the ARB3D, it always reports a lower apogee than the other altimeters, after carefully counting the beeps, the ARB3D read out an apogee of 28,867.3'. Oh my, the Defiance had exceeded expectations and did indeed fly to 29,000' AGL! While I did have somewhat mixed feelings about busting my waiver by 3,739', I was pretty pleased with the rocket performance.
Joel and John load the disassembled rocket.
After we got back to the launch site with the Defiance, I took this picture of the crater the exhaust had created. What makes this even more impressive is the fact that this ground was very hard.
To sum things up, this flight was picture perfect, with everything working exactly as planned. It really is gratifying when all the work you put into a project comes to fruition in a successful flight!
Technical Data:
Burn Time: ~6 seconds
Time to Apogee: 38.8 seconds
RRC2x Reported Apogee: 29,389'
ARB3D Reported Apogee: 28,867.3'
Peak Velocity: 1,397.6 mph/ mach 1.9
Maximum Acceleration: 14.77 g's
Rocket Cd: .553 (best estimate)
Here's a capture from the Accelograph software.
This is another screen capture showing the thrust curve.
It's interesting to note that I couldn't get the data from the ARB3D to fit the expected motor performance unless I dropped the drag coefficient down to under .4, or increase the Isp to nearly 149. Which makes me wonder where the extra performance came from. Even increasing the propellant Isp to almost 138, I had to drop the Cd down to .553 on flight simulation software. For whatever reason it looks like I hit the nail on the head with this rocket, as the performance blew away all expectations.
Looking at the thrust curve of the motor, it's apparent it too performed flawlessly. I had wondered if the g forces of flight would accelerate the burn rate, but that doesn't seem to be the case. The burn looked just as good and stable as the last static test of this motor. After disassembling the motor, the liner and casting tubes look just like the last static test as well. All the casting tubes are in great condition, and the EPDM thermal liner has only slight burn through between grains 1 and 2 from the forward closure. That slight burn through is likely caused by erosive burning causing the lower grains to burn out first, with the last couple of grains burning a second or two longer because of the drop in Kn of the motor. I still think a little Fe2O3 in the top grain or two would solve that... Right Bob?
Aside from some melted paint on the nose cone and fins, the rocket has no damage from the flight at all. On the recovery system, one drogue chute had one small burn spot, but not enough to even require repair. The only anomaly to report was that the ARB3D apogee charge did not go off. After testing, it was determined there was a bad e-match, so the ARB3D was not at fault. So the RRC2X performed apogee deployment, and my homemade timer backed it up by deploying the second drogue.
There really isn't a whole to say here, because everything worked just as expected. I looked over the flight computer data in Excel, and didn't find anything there out of the ordinary either.
Click Here for the spread sheet (csv) file from the ARB3D.
Click Here for the ARB3D native file.
Here's the liner and casting tubes after cutting it open. You can see everything survived quite well. The red circle indicates the location of one of my notches in the casting tube to allow pressure behind the grains. The red circle to the right indicates a small burn through in the thermal liner. It didn't seem to cause any casing damage, as the hole is small and likely occurred late in the motor burn. I should probably make a wrap of aluminum foil tape over the grain joints for insurance.
Here you're looking down three casting tubes. Very nice...
Here is the nozzle. You can see some loss of the o-ring gland surfaces nearest the convergent end of the nozzle. I suppose some pressure in the gland and the RTV sealant caused this. There was a small longitudinal crack as well. The crack started at the convergent end and went about 1/3 of the way down the nozzle. The convergent cone and throat are starting to show some erosion now as well. Two firings on the nozzle seem to be about it. This is low grade graphite, and only costs about $30 a nozzle. So on a motor this size I think I could consider the nozzle as one use and expendable. Moving to a higher grade graphite would run into the hundreds of dollars...