January 12th, 2012
Hybrid propulsion update
In the past few months the hybrid propulsion group has been working along with other fellow students in a minor at the TU Delft. A minor is a semester during which students can choose to specialize in a field or discover new areas non-related to their field of study. The minor not only allowed more students to discover rocketry but to get closer to a flight ready design.
One significant improvement was the design of a vertical test bench with reduced friction and restrains movement in the vertical direction thus allowing for more accurate data gathering and analysis. Further integration resemble to a ready design was made by designing an in house developed tank to hold the oxidizer. To ensure the safety one tank was tested up till its burst pressure at 147.9 bars and the second tank was tested to be leak tight to at least a pressure of 95 bars. These test were performed at the company Advanced Lightweight Engineering
A heating system was added to be able to heat the tank to an operating pressure of 60 bars and obtain comparable data. To perform this a coil of heating wire was wrapped around the tank and epoxy was applied to the outside of the tank and the tank was insulated. The coils were equally spaced to prevent spot heating. Once all design and production was completed hot fire test were performed as shown in the picture below.
Hot test fire on veritcal test bench
Three successful hot fire tests were performed with HDPE and sorbitol both fuels using nitrous oxide as oxidizer. Problems were encountered with the ignition of the engine, as it did not behave in the same way as in horizontal test setup. In the following weeks this problem should be resolved. The hybrid propulsion group will now work further to integrate this propulsion system into a rocket.
January 10th, 2012
Solid propellant – last PTD tests
Today, the solid propulsion group performed their last tests using Pressure Test Devices (PTD). Although there were some problems with the data logger, we may call them a success (see DARE’s youtube channel: lrdare). The ignition was good, and the burns were very powerful. During the second test, we reached a chamber pressure of 75 Bar. We have sufficient data now to be able to design a solid rocket motor using our ALAN-7 propellant. This is exactly what we are going to do at the start of the new year!
The motor will be a large K or small L-class (about 2500 Ns) and contains 1.2 kg of ALAN-7 propellant. It will be reusable, so that several concepts may be tested. We can for example alter the nozzle geometry and material. This will provide more insight into the propellant characteristics, as well as suitable nozzle materials. Later, we may replace the casing, which is initially manufactured from aluminum, by carbon fiber or glass fiber, to decrease its mass.
For now, the solid group wishes you a merry Christmas and a happy new year!
September 7th, 2011
Solid propulsion update
After the successful tests of 16th to 18th of August, it was decided to fire the PTDs (Pressure test devices) just once more, to gather more data points. This was done on Thursday, September 1st. We assembled two core-burning PTDs, with nozzles of 4.1 mm and 5 mm respectively, to obtain Klemmung values of 325 and 220. Both PTDs ignited well, but unfortunately, the safety valve of the first test was activated, due to the high pressure inside the combustion chamber. Next to that, the voltage gain of the data logger was set to a too high value, so that it clipped. Therefore, we only have some data regarding ignition and burn time from this test.
The second test, however, was more successful. After a good ignition, it burned in a steady manner until all 90 grams of propellant were consumed. Post-test analysis of the nozzle showed that it did not suffer from erosion or clogging, and hence had a constant throat area. This makes the pressure data of this test, which were successfully recorded this time (See Figure 1), very suitable to calculate the Characteristic Exhaust Velocity (or C*), an important performance factor of the propellant. It turns out that we reached a C* of 1452 m/s, where 1504 m/s is the theoretical maximum. This means we reached a combustion efficiency of 97%, which is quite good!
Figure 1: Chamber pressure in time
Again, some nice video footage was recorded as well. This will be published at our YouTube channel as soon as possible.
What remains now is the analysis of the data, of which we now have plenty. The preliminary results are looking good: we have a nice Pressure-Regression rate curve from 1 to 80 bars, which very nearly resembles a power function, as was expected. The graph is displayed in Figure 2.
Figure 2: Pressure regression rate
After we found from the analysis that the performance of this propellant is what we expected, we will continue with building a small rocket motor with it, to obtain more experience with materials and constructions that can be used with this propellant.
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May 27th, 2011
Another successful hybrid motor test
Last Friday, the 20th of May, the hybrid propulsion group had three successful system tests of the hybrid propulsion system under development for Stratos II.
The test engine had been redesigned to overcome leakage problems experienced with the previous generation of test motors.
The first test using a conventional axial oxidizer injector system ignited successfully and burned for 8 seconds creating remarkable 275 Newton of thrust. The nozzle unfortunately was damaged irreparably, but the rest of the motor stayed intact.
The second test featured a swirl injector that was tested earlier. The engine ignited properly but then blew out for yet unknown reasons.
Finally the first pyrovalve prototype was tested for leakage using nitrogen. At a pressure of 60 bar the only leakage found occurred at the threaded connection to the feed system proving the leak-tightness of the valve mechanism itself.
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May 15th, 2011
Not 1 but 2 successful tests on launch day
By Hein Olthof (only uploaded by Frank)
On Friday, May 13th 2011, the solid propulsion group reached a great milestone at ASK ‘t Harde: the first rocket powered by an ammonium nitrate rocket propellant was successfully launched. After a year of thorough theoretical studies and testing, it is now proved that the newly designed ALAN-7 propellant has the potential to reach its most important requirement: delivering enough thrust to lift a rocket out of the launch tower.
After some initial burn tests under atmospheric conditions, the solid propulsion group was confident that the ALAN-7 propellant had all the necessary characteristics to be used in a rocket motor. To prove this, a test motor was designed and built.
The very simple motor consists of an aluminum casing and a steel nozzle and endcap. All parts are connected together with threading, for easy loading and assembly. The motor casing is shielded from the heat of combustion by an ablative liner. It houses four propellant grains, which form a bates-grain configuration (circular propellant blocks with a circular port in the middle). It weighs approximately 500 grams and contains 112 grams of propellant.
The motor was tested two times on the ground and from these tests, a thrust curve was deduced. This curve shows that the performance of the motor is beyond expectations: it reached a specific impulse of 191 seconds, a little above the 185 seconds which we aimed for. Unfortunately, the heat shielding during the first test, which was made of cardboard, proved to be insufficient to protect the casing from the heat of combustion. The motor casing got hot and its crystal structure changed. Due to the cheap type of aluminum that was used, this lead to weakening of the structure, so that it failed spectacularly during the second test. A lesson was learned and a new, thicker liner was produced of PVC to provide better shielding.
We decided that it was worth the risk of building a rocket around this motor and fly it on the next launch day as an ultimate technology demonstrator, proving that it could launch a rocket. A lightweight body tube, made of glass fiber composite material was produced. To this tube, four fins and a nosecone were added, as well as two bulkheads, made of aluminum. No recovery mechanism was used, but the rocket was designed such that the upper part of the body tube would act as a crash barrier, protecting the motor for too much damage. We painted the rocket with a fluorescent orange color and called it Fulgor (lightning flash), after the bright orange flame that the motor produces and later the Flaming Tiger, because of the pattern of stripes that was found on the body tube after curing. The rocket was only 74 centimeters long and weighed 300 grams, motor excluded.
The motor was prepared for launch and fitted inside the rocket on the day prior to the launch day. Because of the highly experimental nature of the launch, the Flaming Tiger was scheduled for the last launch window of the day, right after the Stratos Concept Launcher. Finally, the tiny rocket was placed in the tower and connected to the ignition wires. After the relief of the successful launch of the Concept Launcher, the adrenaline started pumping again: would we have another casing failure? Or would the propellant fail to ignite? All these possibilities crossed our minds. But finally, the red button was pushed and after some hesitation, the rocket leapt off the pad with a roar and a bright trail of sparks! The motor thrusted for three seconds, accelerating the rocket straight into the clear blue sky. When the rocket reached its apogee of 750 meters, the rocket was barely visible. It turned over plummeted towards the ground at terminal velocity, as planned, with a whistling sound. It impacted very close to the launch tower. A recovery group of military personnel was dispatched to try and find the remains of the rocket back. However they did not find a trace and assumed that the rocket was buried deep in the ground. However, after some searching by team members, the rocket was found only 25 meters from the tower. Its front end was completely shredded, but the important back part, containing the motor was still intact! This was a 100% mission success!
With a great feeling of happiness, we accepted congratulations of the fellow rocketeers and shared some cigars in good DARE tradition. Now, we are ready to scale things up and make bigger, better rockets powered by ALAN-7.
