Slow grind

Been building one day and one dollar at a time. Infrastructure is my new game. Couple grand in but still much to be done. Lathe and mill bought. Cylinders for brazing aluminum acquired. Materials ate in. Designs have been designed. My new rocket is going to be a 250lbf flyable model. It's a bit of a living mess for the time being but more to come.

The Pause of an Era

The month of June has been a very eventful one. Most significant is my career shift. I got a new job in Cape Canaveral working on rockets...imagine that! I packed up and moved down so now I am located in the rocket capital of the world! Sadly, this takes me away from the machine shop where I spent the past few months slaving over the tools building rockets. For the time being I will have to put my rocket engine building on hold until I can find a new home to get back to work. It does give me time to start developing a flight ready design with the knowledge I have gained.

The final tests before I had to see my baby go. These were the best/loudest tests yet so at least I left off with a wooooooosssshhhhhh and not a bang!
Fortunately, my rocket has a good home where it will serve as a demo model for Advanced Engine Technologies back in Dayton. I did manage to get a regenerative chamber designed and hastily machined so the next big step in that build will be to get an injector plate drilled up. So if there is anyone in the state of Florida that has access to machine tools please let me know and we can make
some sparks fly! I have a youtube playlist with all of my engine tests that can hopefully help inspire other to keep up the good fight! Please continue to share and offer me some feedback so that the next one will be even better!

This is the 100 lbf regeneratively cooled chamber! Coming eventually! I'll have more pictures as soon as I get unpacked.

Day 29: WE HAVE IGNITION!

I spent the morning battling the leaky connection monster. After that war was finally won, I dragged everything out to the holding bay where we typically store the race team's tractor trailer (plenty of room) and gathered everyone who has been apart of the journey so far. The first test was with 91% IPA straight from the store. When I would run the fuel, there was a great flamethrower effect until I hit the nitrous. Then the flame went out... I tried a couple different combinations with the propane torch across the injector as my ignitor and I couldn't get the combination to burn. I then realized that my nitrous tank was almost empty and that very little liquid N2O was actually getting out of the injector. Coupled with the fact that there is only supposed to be a 100 psi drop across the injectors, the mixture was off balance. Since I can't dial back the pressure on  the N2O to anything less than about 400 psi, I let the gaseous nitrous flow and reduced the injector pressure to 45 psi to try to reduce the richness caused by the, now gaseous, nitrous flow. All this tinkering cause my crowd to dwindle.

I paired the correct flows with first fuel followed by oxidizer and IGNITION! The 10-15 foot flame roared to life with a thunder. The deep rumbling sound vibrated that whole building and then the masses poured back into the holding bay. There is no question about it. This is a real rocket.

After a couple tests of 91% IPA and 99% methanol (HEET fuel system cleaner), I had to get my nitrous tank refilled ASAP. I called around and it isn't as easy as I thought it was. All of the big companies like BOC and Praxair need either a letter from a race track or league documenting that you are using it for a racing application or they need to send a representative to your company to see that it is legitimate. Even though my company name is Advanced Engine Technologies....? I called around to a couple performance shop where I was finally able to find a company that would fill the tank today. The quote of $6 per pound was like hearing fingernails on a chalkboard. I did some research and found that price to be a little high of the average $5.50 per pound so I went to get it filled. Then the real tests began.

I tested 91% IPA, 99% IPA with some proprietary chemical that makes it turn yellow (Iso-HEET), and 99% methanol. There is no doubt that methanol burns the hottest. Methanol is on an completely different level compared to the more energy dense IPA. The biggest contrast was between the 91% and 99%. The 99% FAR surpassed the 91% in terms of intensity and burn rate. I expected a difference but not that big. The pictures help but the videos say it all.

99% IPA

99% IPA

91% IPA

91% IPA

99% Methanol

99% Methanol

99% Methanol

99% IPA

91% IPA

99% Methanol

99% Methanol Injection Pattern

Day 26: 1 extra hour in each day is what I'm asking Santa for this year!

The 80/20 law is in full swing! 20% of the work got me 80% of the way there. Its getting down to the last couple pieces and now comes the hard part.

Drilling the injectors has proven to be more difficult than I anticipated. The oxidizer holes (inner ring) are 0.033 inches where as the fuel holes (outer ring) are 0.015 inches which is the smallest drill bit in the world. It is a #80 drill bit. I broke 2 of them before ordering one made of carbide. That broke too. I am convinced that it is simply not possible for me to drill these holes with the tools I have so I will be changing to a 6 hole pattern which will allow me to use 0.038 and 0.017 inch bits for the oxidizer and fuel, respectively. I am also going to start by drilling one small hole to start that way if I can't get the 17 thousandths bit to work I can go to a 4 injector set up.

The bottom left hole on the outer ring contains the offender!

This is the new injector plate.

Since I couldn't work on my injectors until I got a new plate finished, I started to test my electronic systems. I learned that not all nitrous solenoids are created equal. My fuel solenoid is not powerful enough to open against the 400 psi charge pressure. Should have figured that since car fuel pressure is only ~20-50 psi. So ordered a new one that is on the way now.

I  took the time to just sit down and learn everything there is to know about DC circuits and capacitor banks. Turns out that even though the steady-state requirements of my coolant pump is only 110 watts at 5 amps, the start-up surge can top 50 amps. Even if it is only for a split second, it still shuts my set-up-down. Geoff comes to save the day yet again with lawn mower battery that I can use to run the pump separate from the rest of the system until I can get a capacitor bank put together.

 Testing of the cooling system with the battery. Everything checks out.

 This is the man himself! This is Geoff helping me get my solenoid to seat properly.

 For some reason, our horizontal band saw has been taking FOREVER to cut so while I got the stock for the injector plate cut, I started to shape my next next rocket! This one will be 100 lbf and regeneratively cooled. More on that later!


Quick design notes for my capacitor bank (Warning: Hand-wavy math incoming):

The governing equation is Charge (Coulombs) = Capacitance (Farads) x's Voltage (Volts)

Capacitors in series have additive voltages. A common voltage is a 2.7 volts so I will need 5 of them to get higher than my 12 volt power supply. 2.7 x 5=13.5 volts maximum.

They need to all be able to store the same amount of total charge.

So the equations break down to:

Vt=V1+V2+V3+V4+V5
1/Ct=1/C1+1/C2+1/C3+1/C4+1/C5
Qt=Q1=Q2=Q3=Q4=Q5

It (amperage)=Ct*dV/dt
Stored work potential in the capacitor (joules) is W=1/2*Ct*V^2

So my pump needs 50 amps at 12 volts minimum. My PSU supplies 12.3 volts. Ebay has cheap capacitors that are 80 farads at 2.7 volts. Combining them in series gives me a maximum of 16 farads at 13.5 volts.

dV/dt is going to be limited by the rate at which my power supply can recharge the capacitor.

300 watt power supply can supply 300 joules/second.
If the total joules of energy in my full charged capacitor is W=1/2*~16*12.3^2=1152 Joules
If the total energy in the capactiors can be kept above W=800 Joules (~300 joules less than the full charged one), solving for V=sqrt(2*W/Ct)=sqrt(2*800/16)=~10 volts shows that my psu can supply about 2 volts/second to the capacitor. So my dV/dt is 2 v/s.

The amperage that my ebay capacitor can supply amounts to
It (amperage)=Ct*dV/dt=16*2=32 amps psuedo-continously but it is ok if the voltage drops for a little while until the motor gets spooled up so I think it will work.... "in theory"