MTA Launch Event, 2022-07-21

by Chris Kobel and Larry Hoffing, Reaction Research Society


On Tuesday, July 19, 2022, 31 interns from various departments within Aerospace’s Engineering Division gathered in the Building D8 cafeteria to construct mid-power rocket kits. The kits were based on the LOC Precision company’s HyperLOC-160 model kits which utilize a 1.6” diameter airframe, plywood fins, and a 29mm motor mount, along with other requested custom modifications.  Under the tutelage of Aerospace Corporation, Astrodynamics department retiree, Chris Kobel, along with his son James (both RRS members), VDID’s Isaac Goldner, Jeff Lang and his son Chase, and the Propulsion Science Department’s, Andrew Cortopassi (former RRS secretary and member), the interns successfully constructed the kits over a 2.5 hour period, while discussing various aspects of aerodynamics, propulsion, stability, recovery, and construction techniques.  A second session was held the next day for three interns who couldn’t make the first session.

                On Thursday, July 21, 2022, approximately 35 interns left Aerospace early in the morning on chartered buses and made the journey to RRS’s MTA facility in the Mojave Desert.  They were accompanied by the Aerospace Corporation build team, along with VDID’s Jerry Fuller and Sophia Martinez as well as Carah Fukumoto from University Relations and Recruiting.  The RRS treasurer, Larry Hoffing, acted as the Pyrotechnic Operator in charge for the event.

Under calm and clear skies, but with increasing temperatures reaching a high of 106 degrees Fahrenheit, approximately 45 flights were made, mostly successful.  A new 5-rail launch pad provided by Aerospace Corporation was paired with the RRS MTA’s Cobra Wireless firing control system to handle the rocket flights.  A few of the early flights indicated some slight instability which was addressed by adding ballast to the nose cones of the rockets (using desert sand!) moving the center of gravity (CG) forward to increase the margin of stability.  The sight of some rockets were lost as they departed the launch wires in a somewhat sideways direction out over the desert or on a direct trajectory towards a blazing sun. 

Jeff Lang and Chris Kobel with the five station launch rail system built by Aerospace

A demonstration flight of Aerospace’s C-LINK technology was marginally successful as the booster performed flawlessly, but the payload separated incorrectly and ended up powering into the ground. 

Following the launch activities, the interns were treated to a terrific launch at the Voyager restaurant at the Mojave airport, welcoming the cool air-conditioning and ice cold drinks. Overall, it was a long and hot day, but a very successful outing with an enthusiastic response from the interns.


Biconic Nosecone Geometry and Sizing

by Dave Nordling, Reaction Research Society


One of the most common nosecone geometries I have seen in model and amateur rocketry is the tangent ogive. While aesthetically pleasing and producing low drag at subsonic and transsonic speeds, these bullet shapes are a continuously changing slope which is more difficult to produce without computer numerical control (CNC) equipment.

Tangent ogive shape with a rounded tip

Although CNC is much more available than ever before, there are many who use manually controlled lathes. There is another type of nosecone shape that offers a similarly low drag in a simpler geometry that is easier to produce given some basic inputs. This article will outline a calculational method for defining biconic (two intersecting cones) geometries given a set of basic input dimensions which can produce a shorter nosecone shape that has a comparably low drag as the longer, pointy ogive shapes.

Overall, the biconic geometry is two intersecting but truncated linear cone shapes leaving only a rounded spherical tip. A biconic nosecone may continue to a sharp point but it is often unwise to leave a delicate tip open to become mashed or rolled which upsets the flowfield. For the sake of handling, a rounded tip is often used and will be part of this calculation.

It is important to follow the calculation steps in order. The variable names are given in the photos taken of the derivation.

The general sizing dimensions of a biconic nosecone.

The first input is the cone base diameter or radius ”R3”. This is what mates to the rocket body tube. Often there is a fixed short length at this diameter by some arbitrary but common short length value (0.25 inches, 6mm, etc.). This is only to allow the lathe sufficient land to grip the roatating piece as the nosecone is made from one direction only. The base radius, R3, would match common body tube sizes (e.g. 54mm diameter or 27mm radius).

The second input is the tip diameter or radius ”R1”. This is much smaller than the cone base, “R3”, but typical a modest fractional value. Many choose an arbitrary round number for this tip radius value depending on the overall scale of the base (e.g. 0.375 inches, 8mm).

The third input is the overall biconic length, ”H1+H2”. This does not include the extra rounded tip length. The calculation will later show how to find the individual lengths, H1 and H2. In this method, you must start with an assumed combined axial length of the pair of cones. It is likely to be significantly greater (1.5x, 2x, 2.5x) than the base radius, R3. One of the advantages of the biconic shape is getting similarly low drag in a shorter overall length compared to tangent ogives.

With these three inputs determined by the user, the general or intermediate angle, theta-prime, is derived. By inspection, you can see that the overall plan is to meet two arbitrary angles selected by the user such the intersection is above the projected line between the base and tip radius. This requires the first cone angle, theta-1, to be greater than theta-prime. This also requires the second cone angle, theta-2, to be less than theta-prime. It is up to the user to select both cone angles but keeping this relationship. Typically, round numbered angular values are selected (e.g. 5, 10, 15, 20, 25, 30…). Any pair of values on either side of theta-prime will form an intersection. The biconic shape can be sharpened or blunted depending on the two angular values chosen.

Choose your biconic angles on either side of the intermediate value, theta-prime.

Now that all three dimensions and the two cone angles are chosen, the phantom length, b, is calculated. This is a projected, fictional value that is useful in subsequent calculations but has no physical meaning. The user should notice that the left side is simplified to being only the difference in base radius to the tip radius (R3-R1). This will make the calculation easier.

Calculate the phamtom length, b.

With the phantom length (b), two cone angles, the biconic length (H1+H2) and the radius difference (R3-R1). the two cone lengths can be individually calculated (H1, H2) and the intermediate radius difference (R2-R1) determined. With intersection point determined, the travel distance to cut each cone is known.

Calculate the individual cone axial lengths and the middle radius, R2

The last segment of the calculation is to get the rounded tip. The tip radius is not the same as the spherical tip radius. Because the first cone intersects the sphere at a tangent point, the true center of the sphere is recessed inside the cone. The true spherical radius value, phi-1, is greater than the tip radius, R1. This recessed length or offset, H0, is calculated by trigonometry using the existing tip radius, R1, and the first cone angle, theta-1. The projected tip length, A1, is the result from the rest of the resulting geometry.

Get the nosecone radius, recess depth, and tip projected length

The biconic nose shape is still used on launch vehicles today likely for its ease of manufacture. This calculation process should make production of biconic nosecones easier to do. The actual drag from this family of shapes is a complex subject all its own, but it can be inferred that this family of shapes are useful to amateur rocketry.

Atlas V vehicles by United Launch Alliance, biconic and ogive fairing shapes

MTA Launch Event, 2022-05-21

by Frank Miuccio, Vice President, Reaction Research Society


The RRS held a launch event at our private testing site, the Mojave Test Area (MTA) on Saturday, May 21, 2022. Larry Hoffing was the pyrotechnic operator in charge. Temperatures were still mild and below 90 Fahrenheit. Winds were very slight for the entire event,

The main event was the launch of a number of student built model rocket kits using commercial motors. The second planned event was a member project, the two-stage Gas Guzzler ramjet, by Wolfram Blume. The third event was a cryogenic liquid tanking test at the vertical test standt of a portion of the Compton Comet liquid rocket overseen by Dave Nordling and Waldo Stakes.

Students prepare to hear the safety briefing after their arrival at the RRS MTA

The RRS teamed up with Boyle Heights YMCA and taught the students about rocketry over several weeks before the launch event. These students were the ones involved with the YMCA’s robotic program. We had 22 students come out to the MTA. During this launch day, we launched 23 Baby Bertha rockets all built from kits and custom painted by the students.

Students and mentors observe the safety briefing and propellant burn demonstration.

These rockets were launched first with smaller A8-3 engines. The students then retrieved their rockets and went into the Dosa Building and reassembled the parachutes for their next launch. The next launch was done with a larger C6-5 engine. All went well for the day.

Larry Hoffing and Frank Miuccio prepare the new launch racks for the Boyle Heights flights.

We were able to use the new launch racks built by Dimitri Timohovich which gave us the capability to set up 18 rockets at a time which was our channel limit of our Cobra launch system. We have made a great investment with this safe and convenient product and more of our pyrotechnic operators are getting trained in its use thanks to Keith Yoerg.

The Boyle Heights YMCA wants to continue doing classes with the RRS. The students had a great experience.

Boyle Heights students observe the launch of their rockets from the observation bunker.

The second event of that day was Wolfram Blume’s next attempt to launch the Gas Guzzler for its second flight. Significant design improvements were made. This very ambitious project is the result of a lot of complex design and 3D-printed parts which must fit correctly into their respective assemblies. Unfortunately, a critical fit problem with the nose piece prevented Wolfram from completing the build despite some on-the-spot adjustments. He postponed the flight to conduct minor repairs back at his home workshop. Wolfram plans to return to the MTA on June 4th at our next launch event with the UCLA Capstone Project.

The gasoline fueled ramjet upper stage and solid motor powered booster sit ready for inspection.
L-sized high-powered motor to the left, ramjet second stage to the right.

The third operation at the MTA was a cryogenic liquid tanking test. The Compton Comet is a large liquid rocket being built by students and former students of Compton College. Led by Dave Nordling and Waldo Stakes, it is a project supported by the RRS and each person on the team is a member of the society. The Compton Comet describes both the vehicle which will be built and flown by the student members of the society and the team, itself. The ethanol/LOX vehicle uses a surplus 1500 lbf thrust chamber from an RM6000-4-1 engine once used to power the Bell X-1. The project is still in the latter parts of the design phase and important component testing is essential before committing more resources to construction. Bill Inman assisted with some of the operations that day.

Waldo Stakes (sleeveless, to the right) explains the goals of the cryogenic testing.
Schematic of a cryogenic liquid cylinder from Chart Industries literature
Identification of the parts on a cryogenic liquid cylinder, medium-pressure unit, Chart Industries

The Compton Comet uses a pair of surplus stainless steel oxygen aircraft tanks. With the two tanks joined in series, a cold shock test with liquid nitrogen was done to verify their integrity after some minor welding was done. These tanks are decades old but have passed hydrotesting and visual inspection at the welded connections. These operations gave the student members hands-on experience with the safe transfer of cryogenic liquids. The society has acquired personnel protective equipment (PPE) such as polycarbonate faceshields, long elbow-length gloves and long cryogenic aprons to help future projects.

LN2 cryogenic liquid cylinder and vacuum jacketed transfer hose connected to the dual propellant tanks supported vertically
RRS members Drake Pearson and Aarington Mitchell, observe the start of cryogenic liquid loading wearing their PPE. All others stand back.

RRS member Diana Castillo recorded the time of each event and observations of the team as the tanking test progressed. The cryogenic liquid loading in uninsulated tanks is a slow process that loses much liquid to boiling. Eventually liquid nitrogen does accumulate in a tank if sufficient flow and capacity is available. The tank was vented at the top throughout the testing. A cryogenic rated relief valve to be used later in the full static fire was also present.

Filling from the top tank, the lower tank never reached full. The design is being reconsidered.

The second objective of this test was to demonstrate the pilot-operated solenoid valves intended for use as the main propellant valves of the vehicle. One of these high-pressure rated, normally-closed angle valves was connected at the bottom of this dual-tank setup. Cryogenic temperatures have been known to cause failures in electrical equipment. After attempting to fill the lower tank and having a significant amount of liquid nitrogen sitting at the inlet, the solenoid valve was well chilled for this functional test.

End view of the 2-prong Bendix (Amphenol) electrical connector.
Unable to get a suitable two-prong plug to the MIL-SPEC interface, the connector wires inside were used to manually actuate the 24 VDC 1Amp valve.

Before cryogenic loading, the valve was tested at ambient conditions using a pair of 12 VDC gel cells strapped in series to get the full 24 VDC needed to actuate the pilot solenoid. The circuit was switched by manually connecting the positive terminal by alligator clips. The distinct popping sound of the core stem moving inside was easily heard and very repeatable.

With the valve fully chilled after 40 minutes elapsed, the valve was tested again and functioned reliably. This is an important validation of the solenoid working in a relevant environment. The angle valve’s internal spring is very large and will require significant inlet pressure (150 psi?) to open. It was decided to leave the tanks vented at all times during this initial cryogenic liquid filling operation and leave a flow test for later. There were no signs of leakage from the valve outlet which was also a good result.

The Compton Comet project team recorded and discussed their findings. Leaving the tank vented, the liquid nitrogen boiled away in the warm afternoon. The remaining members enjoyed some time in the Dosa Building eating grilled burgers and hot dogs made by Waldo Stakes. Dimitri was able to reinforce the metal support legs of this donated propane gas grill to continue its service to the society.

The society cleared the areas and stored our gear. The next MTA event will be June 4th with the UCLA Senior Capstone Project. Wolfram Blume will return to fly the Gas Guzzler for a second flight. Dave Nordling will be the pyro-op in charge. Any other member projects are welcome and they should contact the RRS president to schedule them.

president@rrs. org