Design, Engineering and Manufacturing | General | Forum

Post edited 9:13 pm – January 16, 2011 by Dave

Design, Engineering and Manufacturing is here to consolidate all construction related topics and discussions. This is only an idea started by me (Dave) too assist people in learning how to design, engineer and manufacture a rocket. This section should also contain the following in no particular order: 

1/ Materials and Equipment choices

2/ Rocket dimensions and characteristics

3/ Parts needed and required 

4/ System Design and testing

5/ Ancillary equipment and testing 

6/ Construction and transportation

7/ Communication and electrical systems

8/ Drawings/ blue prints and re-design suggestions

9/ Any research documentation found helpful please note it

10/ Launching a rocket and other 

Drilling-

#The limiting angle for any average drill is around 50 degrees. A drill has an angle of 59 degrees on each (rounded) face. Inclusive 118 degrees (59 x 2). 

#You can buy a drill set that has different angled tips for drilling at an angle. Or just grind your own and experiment with that machine and material. 

#A center drill is used to start the drilling process (speed and feed calculations are required depending on material) then use a spotters drill. Basically a short drill. The further away the tip of the drill is from the chuck the more tip movement you get. Accuracy reduces as distance increases. 

#Best done in a vertical milling machine with an angle table (can be magnetic) and vice with parallel plates. 

Valves-

#Depending if the motor requires gradual oxidizer flow at the beginning or full flow will depend on the type of valve required. 

#Typically an "/ off" valve can be solenoid operated 2/2 valve. Using about 2 Watts of power. You could latch this valve open using some relays thereby reclaiming your 2 Watts. 

#You can buy solenoid operated 3-port valves that might also do what you are after? 

#"IF" the oxidizer is in liquid form then a TX-valve would be required first. TX-valves are used in refrigeration systems to "boil" a liquid into a gas. 

#Preference is given to welded joints over mechanical compression fitting in this instance. Limits leak potential. Material would be seamless high pressure gas pipe. NO elbow joint as this affects fluid/ gas flow. Radius corners with no joints are best where applicable. 

Fuel system-

#As there will be a requirement to mix the fuel and oxidizer in certain mixture ratios (stoichiometric ratio), I am guessing the tanks would empty into a pre-combustion chamber first (swirl chamber) allowing for adequate mixing of the fuel components. Then onto the actual continuous combustion chamber? 

#"IF" liquid oxidizer is used maybe a shore supply fuel delivery system can be used to fuel the rocket motor on start up and then internal fuel supply system takes over once motor start up and warm up is achieved. The internal liquid oxidizer can then be "boiled off" using the heat on the thruster cone. This also aids in cone cooling. 

#A bladder inside the tank will require a bleed valve on motor start up. Plus alternate valves for the bladder and oxidizer/ fuel refill system. 

#Curious – how cold is this system going to get? Or how hot? 

Material Choice- 

#I choose materials this way

1/ What is that part going to do? (factors – size, weight, forces, stress, piping, mounting, where is it, pressure issues, vibration etc)

2/ What environment is the part going to be in? (what properties does it need – thermal, corrosive, pneumatic or hydraulic, chemical, electrically conductive, insulative etc)

3/ What properties does the material require – see (1 and 2) and make list!

4/ Check properties against probable materials choices (cost and availability are always included) 

5/ Can we manufacture what we need using that material. (skills and equipment)

6/ Decide and then just experiment with chosen material(s) choice. 

Dave 

For the choice of the combustion chamber and oxidizer tank material, we made the decision by determining the requirements and constraints, similar to how you laid out, but then followed through with a plot of these materials and then a design analysis (OpenOffice spreadsheet). You can see the process from here.

All these materials are readily available and I have welded all of these materials on more than one occasion. All can be welded using GTAW or Tig welding. Different shielding gases are required as well as an oven to recover the properties lost during the welding process.

The Al 6061 T6 will require the most post weld heat treatment as welding normally takes it down to a T4 (temper). The material will age harden naturally "if" the proper post weld processes are undertaken. Al 6061 T6 is very prone to "hot cracking". Hot cracking occurs as the weld is solidifying and cooling. To avoid this problem I use a 4043 filler metal which has Si 5% added to it. Silicon allows for fluidity in the weld pool and allows for better stress relieve on cooling. 

304L (L = low carbon and is better to avoid carbide precipitation during welding). 304 Stainless steel is a very common material and has excellent weldability. Welds beautifully… 

Nickel Chromium or in the trade better known as Ni Chrome. This material requires someone who knows what they are doing regarding the welding of it. Welds great but caution is a must at every step and cleanliness is the top priority. You need to use a shielding gas with about 10% Hydrogen to reduce the effects of porosity (holes in the weld). Furthermore, the weld settings must be set correctly for that material size to avoid weld metal cracking and the welding speed must also be accurate to allow for the right amount of time for weld pool solidification.  

Pre-weld treatments for all materials will need to be assessed depending on the type of forming process that they have undergone. 

Hope this helps.

I have also copied all of the above links including the spread sheet… very interesting! 

Thanks 

Dave