Wednesday, February 28, 2007

Injector Version 2 flow tests

Based on my previous testing and some advice I received on Arocket I built a new injector.
Its got a smaller pintile and a tapered out area behind the annular gap. the annular gap is only 0.050 deep. the new pintile is only 0.400" across. I flow tested it tonight and the Fuel came out perfectly within 1.5 % of where I wanted. Well within my experimental error! The oxidizer is about 10% low (Meaning I'll need to run my pressure 20% high) Its good enough to test as is. The visual quality of the combined spray cone is very good. I took a fast flash picture of the result its on the left.

I also took a picture of just the fuel orfice

I also tried to take a picture of just the lox spray and got everything in the entire shop wet. Sorry for the bad quality, but after wiping the water off of my Lathe and Mill I was not about to try to take the picture again.

Thursday or Friday I'll try to braze the igniter mount on the the assembly and I'll have a new motor by the end of the week end!

Monday, February 26, 2007

How I got started...

I realized that normal mortals could do liquid rocketry after spending some time with the SDSU rocket team. They have also started a blog, only one post so far.

After watching them build and fly stuff and discovering the Armadillo blog I was hooked.

Update on the week end:
  • Bob welded up two tanks and was almost finished with the third. When the tanks are ready we will have them heat treated and test one to failure.
  • My son went into production mode working on making a batch of 12 of the tonegowa servo valves.
  • I worked on designing and fabricating a new pintile injector based on our flow tests and some feedback I received on Arocket.

Wednesday, February 21, 2007

Some Hardware.

Here is a picture of my Pintile injector.
To give you an idea of scale the tip sticking up in the middle is 0.675 inches across. The small holes are 0.029" I don't have a water proof digital camera so I was unable to get pictures of the injector flowing.

I went to harbor frieght and bought a small sandblasting unit to use for pressurized flow testing. It has a large pressure tight opening on top to rapidly refill with water. It makes a heck of a squirt gun. Using that I flow tested both my lox and fuel flows for my injector. (I tested using water and adjusted the numbers for density) The fuel flow was about 35% low, and the lox flow was about 11% low. The 11% is close, but the 35% is off more than I would have expected. I'll try opening up the annular gap a tiny bit in next few days. It will be very hard to get it re centered. I'll probably end up making another one in the next few days .

Lastly here is a not quite ready to be fired picture of my igniter. The Aluminum box it's leaning on is the electronics for driving the shielded sparkplug.

Tuesday, February 20, 2007

Quick clarification

Carl asked what keeps the fuel plate from moving back and collapsing into the pintile. The cut away view did not show the arms very well, but this view with the pintile turned tranparent does. the three arms are a solid part of the fuel orfice plate. They also align the two plates. The outer aluminum casing is turned off in this view.

Monday, February 19, 2007

A New chamber design

I put together a short outline of my vehicle and the safety systems to present to the faa/ast when I was in DC. There are some typos, and a couple of things missing, but its probably worth publishing. astpresnt.pdf.

I have a bunch of new hardware that I will post pictures of in the next few days. I've designed a 250 lb thrust chamber. Its a copper tube with an outer aluminum shell. I've designed the pintile injector and and I built one this weekend. The hard part for a motor this small is keeping the annular alignment between the pintile and the fuel plate the gap is nominally 0.0062" all around. This seems insanely small,(The 25 #69 lox holes in the pintile aren't exactly large) but I did the calculations a bunch of times and it seems to be correct. I machined an alignment step on the pintile and a corresponding recess in the plate that forms the annulus. Goal was to hold the annulus size to +/0.0005" and I think I got it. That is the limit of my measuring equipment.
The alignment recess and step are close enough that if you heat the the plate to slightly warm and cool the pintile to slightly cool they slide together. At the same temperatures they are a tight press fit.

The O-rings I had on hand were not correct to seal in my injector test fixture so I did not get the satisfaction of seeing the injector work. (the o-ring sealed enough for my to try it and get all wet... again.) In the next two days I will be flow testing the injector and I'll post pictures of the hardware.

On the left is a split rendering of the chamber design. To give an idea of scale the inner copper tube has an ID 0f 2 inches. I still have not decided if the throat will be copper or Graphite.
I will try both. The chamber needs to throttle from 80 lbs to 250 lbs. so I set this up to be 50 to 150 % of nominal. Thus the chamber is nominally laid out for 166 lbs of thrust at 166 psi expanding to 12.5 PSI. (the ambient pressure at Las Cruces.) Theoretical ISP at this low pressure is 216 frozen, I'm hoping to realize 180+. The pintile orifices are designed for 32 PSI of pressure drop at the desired flow rate. The orfice sizes were calculated with a discharge coefficient of 1.5. We will see how close I got when I do the flow testing this week. I'll gladly post my notes and spread sheets for all of this, alas I fear they probably won't make any sense to anyone but myself.

I resurrected the lrd (liquid chamber design program ) from the rocketworkbench. I modified it with two additional parameters. water_percent to allow you to add water to your fuel/oxidizer and exit_pressure to set an exit pressure other than 14.7 psi. The program executable is here and an example input is here. If anyone wants the modified source code I'll send you the microsoft visual C 6.0 project with all the files in it. (this also builds cpropep, but the cpropep I built seems to go bboom when I try to run it. I haven't taken the time to figure out why. In the end it turned out easier to use the output from cpropep and a spread sheet.

Sunday, February 11, 2007

Saturdays Testing(updated II)

From the lunar lander project perspective everything on Saturday went perfectly. The systems all worked as designed, we had no frozen vales, instrumentation or computer problems all of that was flawless.

The real story is we were testing an older engine design that used a pyrotechnic igniter and we and that failed to get it lit. So some time in the next 24 hours I'll post a very boring video of Lox and alcohol coming out of a motor in unburned form.

If we had more Lox we would have tested again, but we were using the left over Lox that had been delivered for a different project. By the time they were done there was less left than expected. My son was very disappointed we did a lot of work and got no flames, booms or other intersting pyrotechnics. I was happy with the result because the components of the test that apply to the XPC project all worked flawlessly.

Here is the test video, kind of boring, I've also uploaded an unrelated video of other rocket things...

Saturday, February 10, 2007

Its 2am the thrill is gone....

A number of knowledgeable people keep telling me to start fireing a Motor, any Motor to get experience with liquid rocket motors. This summer my son and his friend Jason built a test stand and rocket motor. I built the Injector Plate for it. Due to valve issues it was never run.
We have put new valves on it and its ready to test. Since our test site has a lot going on this weekend and we decided this would be the weekend. Alas everything takes longer than expected.
One minor example... I'm a founder at Netburner, so the electronics that runs the test stand is all based on Netburner modules. Well the sample code that I brought home this evening to use uses a relatively new NetBurner feature so the code release that is running on my laptop does not support it. So step one is download a large file and reinstall tools... It went down hill from there,I think were finally ready to go, but the garage looks like there was a tool explosion...

It's 2am and I get up in 4 hours, as the song says its 2am and the thrill is gone....

Sunday, February 04, 2007

Quick Update

A quick update before I catch a plane.
  • Tanks: I found a place where I can order thicker T0 aluminum, the aluminum for thicker end caps will be here on Feb 7th. I also found a local place to do post weld heat treating, this should get me to my goal of 500 PSI with the aluminum tanks.
  • Igniter: I fabricated an Igniter using orfice sizes and the basic construction concepts that John has documented on the Armadillo updates. The Igniter, solinoids and ignition system is lighter than the weight allocated on my virtual vehicle. Having something tunr out lighter is always a good thing. I'll test it late next week.
  • Paperwork:I'm flying out to DC to attend the AST commercial space conference, I have a meeting with AST on Monday I'm going to try real hard to learn something and be diplomatic.