Booster.  Strength is the objective of this design.  So the concept is a variant of the flying case model.  Shown below assumes a Pro98 6xl case with the boattail option.  An aluminum fin can slid over the case will provide the direction control  The electronics bay will be mounted to the forward closure.

The interstage coupler will be a CNC machined aluminum piece with an integral mounting of a Peregrine CO2 system for stage separation.  Not show in the picture is is short length of G12 thickwall coupler tube that connects the interstage coupler to the top of the motor case which transfers the compressive load during flight.  Another length of thickwall airframe tube bridges the coupler tube and the outside of the motor case to support any bending load that upper airframe may experience during flight.


Next:  Some simulations

Haven't had a blog entry in a while....

After reading reports on BALLS 25 flights, I got really interested to see what it takes to design a serious altitude attempt, something above 100K.  This would also have the side benefit of considering altimeter features and functionality needed for the select range of flights that very few people attempt.

So here are my parameters for this project:

  • Doable with "commercial motors'
  • Don't want to be an R&D project on new materials, composites etc
  • Be able to design components and everything on Autodesk Inventor (my CAD program).

So the lmiitation of using commercial motors would drive the concept to a 2-stage rocket, most likely an N to M design, minimum diameter for the booser and sustainer.  Rough simulations of provisional designs in RASAero suggest target altitudes could be attained with this concept.

Next entry, the booster concept.

My Honest John flew at LDRS34.  The on-board electronics was 2 Marsa54L's and 2 MrfPyro units in the nosecone to remotely fire the CO2 chute cannon.  Separating the nosecone after the apogee deployment was 47 feet of tubular nylon.  Fortunately for the rocket and MarsaSystems the MarsaNet system successfully fired both main matches for a perfect recovery in the middle of the field at LDRS. 

In a few days I will be making available a new member of the Marsa54L altimeter family.  This will be a heavy duty version dubbed the Marsa54LHD.  This model was inspired by several customers whose cracked LCD's I have repaired due to hard landings for various reasons.  The Marsa54LHD lywill have the following design changes:

1. The LCD module will be removable before flight.  For programming the LCD module will plug into the board and work as normal.  Remove before flight as the LCD is the most fragile part of the system.  If you have multiple Marsa54LHD's this can be a cost savings because you will only need on LCD module.

2. The electrolytic can capacitors have been removed and replaced by surface mounted low profile capacitors.  The old capacitors were relatively tall and heavy relative to their solder mounting pads so occasionally they would detach from board during rough treatment.

3. The board will receive an acrylic conformal coating to seal the board and provide addtional mechancial protection. This will make the board waterproof.  For those rockets that occasionally spend time in trees or land in irrigation ditches.  All the traces and connections will be protected and washable (with care).

One other feature will be that the LCD module will be usable on other MarsaNet products to be 2016 including a ground receiver for Marsa54L telemetry data.

On my 7.6" Honest John project I am using a CO2 powered chute cannon to deploy the main from the nosecone using a  MrfPyro unit.  Why CO2?  Because its something I wanted to play with.  This blog entry will discuss what I have learned about CO2 systems.

Below is a pic of the cannon.  It is a 5" fiberglass tube with a bulkhead that mounts the electronics and chute attachment point.  I will be using a 12' elliptical chute with pretty much takes up the entire length of the tube.  Inside a piston is used to push out the chute.

Initial tests without the piston showed there wasn't enough energy to eject the chute reliably with an 8g CO2 cartridge.  My thinking was that gas was leaking around the chute and escaping.  First test with the piston was dissappointing with the result that the chute was halfway ejected from the tube.  I increased the CO2 to a 12g cartridge and the chute ejected (clearing the tube) but the piston was dissapointedly still about 1" from the end of the tube.

CO2 Learning #1: CO2 (cold gas) provides pressure to separate airframes well but does not energetically expel chutes like a projectile.  Conventional BP (hot gas) would probably be a better choice.

However I decide to push on because I want this technology to work and like the idea of cold gas ejection.

Here a pick of the chute cannon and CO2 components (Peregrine system).

And the electronics end


To solve the question on why the piston only travels to the end of the tube and stops perhaps as a last resort we will try and do some physics. My daughter who is studying chemistry in high school was task with the problem to detemine how much pressure will a 12g CO2 cartridge generate on the piston of my chute cannon.  Her analysis follows:

12g CO2 has a molar mas of 44g (2 O's at 16 and one C at 12).  So the 12g CO2 cartridge has 0.273 moles of CO2.

Now the chute cannon has an inner diameter of 5" or 12.7cm.  The length of the cannon is about 18" or 45.7cm.  So the total swept volume of the piston in the cylinder is 5788cm2 or about 5.8L.

The pressure on the piston at any position in the tube can be calculated from the gas law: pv = nRT.  For instance when the piston halfway down the cannon the volume of the CO2 will be around 2.9L.   At 25C or 298K the pressure on the piston will be:

p = 0.273moles * 0.082 *298K / 2.9L = 2.3 atmospheres or about 34.4psi (absolute) or about 20psi net.  20psi on a 5" piston generates about 392 pounds.  So there is a healthy force on the chute on the way out.

When the piston reaches the end of the tube the pressure will be

p = 0.273*0.082*298/5.8L = 17.2psi (abs) or about 3psi net (not alot).

Now these calculations assume no leakage of gas around the piston which there is.  So physics explains why the piston doesn't "fly" out of the cannon. But I think it will work.....We'll see at NYPOWER and/or LDRS.