West Point Beemer Final Report for SLI

Vehicle Performance/Flight Analysis

Overall, launch operations went well with only about two unexpected surprises. Vehicle prep went smoothly with no unexpected occurrences. Original concerns about interference with tracking devices were worked out Thursday, and a potential interference problem with the video transmitter was solved before the transmitter was in the rocket by changing channels when it was noted that a group across the road was using the same channel. Motor installation went smoothly, even thought there were concerns that without a motor mount tube, some of the nearby wires would get caught in the way. This concern could be eliminated in the future by advanced communication about when the motors can be installed and planning ahead. The first time the rocket was loaded on the rail, both rail buttons popped off partly due to bad mounting that had worked on smaller rockets and partly due to the team not knowing that the rocket needs complete support until it is vertical. New mounting holes were drilled relatively quickly, the buttons were re-installed and the rocket was put on the pad a second time. Power up of all three altimeters, the video transmitter and the data recording went nominally with no unexpected continuity problems. Concerns over the wind led us to orient the rocket with the rail facing the wind to partially shield it. This, along with not wanting to pop the buttons off again made us reluctant to rotate the pad to achieve a precisely vertical flight. The launch rail was pointed with a slight angle toward the south. The onboard video before launch showed that the rocket was rotating back and forth on the launch pad about 45 degrees due to the wind. This made us concerned that the buttons may come out or the rocket could fall off the pad, fortunately, this did not happen. Countdown went nominally with both tracking devices and the video camera working properly. The igniter fired and chuffed. About 1 second later, the motor came back up to pressure and the rocket took off on a strait trajectory at the angle it was launched at. Liftoff occurred at around 3:00 pm.  Motor burn was nominal (more on that later). At apogee, all three altimeters fired their 3 gram charges in sequence as planned. Unfortunately, the Tether device designed to retain the main parachute until 900’ released early without activation from a charge. This is proven by the fact that the patterns of residue on the metal do not match the patterns from a normal firing. The rocket descended at roughly 18.85 feet per second under the Rocketman R14 main parachute. After drifting for nearly a mile, it touched down in a tree surrounded by a swamp. The video feed cut out shortly before touchdown. The nose cone separated from the rest of the body, as intended, when the main came out, and landed in a forest area in a 10 foot diameter gap in the canopy. The rocket was recovered within a half an hour and placed in the back of an unknown white pickup for about 2 to 2.5 hours as seen in the video. At approximately 5:30, the rocket, minus nose cone, was returned in good condition. A few small chips of paint at the top of the tube were missing, but everything else was perfect. The nose cone was later found in good shape by Army personnel with the help of Kevin Trojanowski and the Beeline tracker in it. The altitude of 5094’ was read off the backup MAWD approximately 45 minutes after launch when video feed was reestablished. The other MAWD read 5104’ and the ARTS reported 5045’ on the barometric sensor and 5323’ on the accelerometer, showing that the flight was not exactly vertical. One half of the Tether was no longer connected to the rocket when we got it back and it likely fell off during decent after a 1” long screw worked its way out. This is likely unrelated to the main coming out at apogee, which was probably caused by insufficient tape holding the device together.

Overall, the only problems were the rail buttons coming off, the main parachute at apogee and the motor burn.

The thrust curve generate by the ARTS is shown below:

The nominal thrust curve is below:

The difference between the two was obvious when examining the ARTS data and investigation of pictures of our test launch and the launch in Huntsville showed that the motor we test flew on had 6 shorter grains and the motor we flew in Huntsville had 4 longer grains. Animal Motor Works was contacted and it was determined that the K975 we flew in Huntsville was old stock that they were taking back from a dealer who had been in trouble with the ATF about the same time they were shipping our motor. The K975 used to consist of 4 grains like the one we flew about 4 years ago and was changed to the 6 grain version a couple of years ago. No damage was done to the motor case or rocket and the only reason it was noticed was because we had the ARTS data.

The flight data graph from the ARTS of the first 82 seconds of flight that it recorded data from follows:

The boost portion of the flight, including deployment is below:

Finally, the portion showing only the motor burn:

The maximum acceleration was 448 ft/s/s or about 13.93 gees. Maximum velocity was 681.4 ft/s or 464.3 mph. It should be noted that this is nearly 70mph slower than our test flight. Altitude on this flight was also almost exactly 1000 feet lower than on our test flight. Reasons for this include more drag from a lower launch site, added weight of the paint, the video camera, and the hat we took from Kevin Trojanowski that also went along for the ride.  

Overall, the team was extremely pleased with the flight and would much rather have had this flight than one of the major failures seen during the day.

Scientific payload final report.

We filled our gas tubes the night before launch with the four gasses we had chosen hydrogen, oxygen, carbon dioxide, and air.  We chose those gasses because 1 – we wanted to test a variety of gas types, and 2 we could generate those gasses in our motel room with a limited amount of equipment and locally obtainable raw materials. (Thanks Dawn!)  Hydrogen and oxygen are both elemental gasses, carbon dioxide is a compound, and air a mixture.  Since we were going to measure a pressure differential between inside of our tubes and the outside we knew that filling them the night before would not be a problem. 

At launch time we set our custom data recorder to start recording data as soon as the rocket left the pad by using a break wire attached to the pad.  The recorder sampled 6 channels at a rate of 15 Hz for 3 minutes and stored the data in onboard memory.  The data was recorded in a hexadecimal format. 

We knew we had some problems during launch when our main chute deployed at apogee instead of at 500 feet as planed.  This problem is discussed in the rocket section.  We downloaded the data into a spreadsheet in its raw hex format.  We then converted that into a decimal format, following that by converting it into the corresponding output voltages.  These voltages were then converted into their representative pressures using the conversion graph from the manufacture of the pressure sensors. (Freescale)  This data was then graphed for visual representation.  We had originally planned to have six gas samples to work with, but found payload space limited our gas tubes to four, so our data acquisition had 2 extra ports that we did not use.  This results in our spread sheet having 6 columns of data, 2 of which are discarded for our graph.  The raw data and conversions are available as a spread sheet on the web page.

In analysis of our data we found some very interesting things.  First it would appear that our carbon dioxide tube sprung a leak and opened to the outside air pressure partway up.  We did not know this until a week later when we downloaded and graphed the data, and our payload had been disassembled, so could not find where the leak occurred.  Second we could see the anomaly in our data at apogee, when our ejection charge fired and changed the ambient pressure in our payload bay.  This showed up on our leaking tube as well.  Third it seems that the hydrogen tube was at a lower starting pressure and maintained that consistently lower pressure through out the flight. The carbon dioxide tube seems to start low also.  We had planned on a quick decent to 500 feet instead of the slow on-chute decent we got.  This resulted in not having enough time in our recorder to record the full decent.  This slow decent did not affect the outcome of our experiment.

We feel that the three successful tubes show complete agreement with the expected ideal gas law predictions.  There was no difference between elemental gasses or the gas mixture (air), and none was expected.

Some personal reflections of the project

Shawn:
-How to prepare for an event
-The different steps to proposing a design
-How to design a rocket
-Not to loose your cell phone
-Ignore old people
-Rockets don't always go up
-Watch the person with the zip-ties and shrink wrap

Tessa:
During my SLI experience, I have learned of course, the science stuff. After learning about our fellow SLI team's rockets, it was interesting to see how impressive rockets can fail. The tours were very educational. But I learned the most in the hotel rooms. Coffee will keep you up doing late night projects. All in all, it was a good and enjoyable learning experience.

Andrew:
-Good video and good data and analysis can lead to conclusions that couldn't be figured out otherwise
-NASA personnel may be looked at by some by heroes, but they aren't
-Not everything goes as planned
-People do not always perform assigned tasks as assigned
-Some teams encountered more challenges than others, especially during flight
-Communicating details is essential early on, especially from organizers
-Precision cut parts in general are great
-People not knowledgeable in certain areas shouldn't express their "knowledge" in those areas
-Watch the person with the zip-ties and shrink wrap