Chamber failures explained.

Tonight I made a chamber liner by silver soldering it at high temperature.
In my pressure test fixture it failed between 380 and 400 PSI.
So this explains my motor failures, but does not really give me a huge amount of comfort. It means I can never get the liner hot enough to anneal it and I am Dependant on the annealed condition of commercial water pipe for my strength.

We are going to test fire again the weekend.

Simulating Chamber failure at home.

Any time I can run an experiment at home that replicates things I see at the test site it's a huge win. Tonight I fabricated a plugged injector plate and soldered up a chamber inner liner and throat. I used the plugged injector plate to Hydro test the chamber to failure. The chamber liner failed at 1750 PSI. It failed in exactly the same way as the chambers that failed in the field did. This liner and throat were soldered with normal relatively low temp solder.

Thursday I will solder up a throat with high temp silver solder and test that to failure.

As part of doing this test I also abused my o-ring seals, no lubricant and hammered them together. I even got o-ring slivers sliced off the injector end o-ring. Still the o-rings held and did not leak at 1750 PSI.The Snap ring retainers and the fuel feed plumbing also held the pressure. All in all a good test.

For one last reality check Plain old un alloyed copper has a work hardened to fully annealed yield strength ratio of ~5. So 1750/5 = 350PSI we were running the fuel feed at around 375.
At some level it all makes sense.

Chamber Failures

This weekend we had two chambers fail identically. We set out to verify we had solved our ignition problems. So for our first test we ran a few seconds , purged a few seconds and ran again. Both ignitions were perfect. On the second start we saw a big green copper flash. We thought this chamber failure was due to too short of purge. But in reviewing the video I see we got a green flash on shutdown. We ran a second motor and it failed on startup.

Thoughts on the failures:
The first chambers we built we used high temp silicon to seal to the carbon throat and had the spiral wires soldered on with normal solder. The chamber to aluminum jacket tolerance was so tight we had to assemble the motors with a sledge hammer.

The motor we ran for 106 seconds had the copper throat soldered into the chamber wall with normal solder and spiral wires soldered on with normal solder. This motor was tight, but only needed light taps, not the full sledge treatment.

When we disassembled that motor we discovered that some of the spiral wires were loose, we did no know if that was an issues with getting hot of breaking the wires loose on assembly / disassembly.

As a result we decided that we should silver solder the parts together. So the last two motors we built with silver solder. This requires that we get the copper liner much hotter and probably removes the temper. As we have been using copper water pipe the temper is a side effect of the forming process and is not guaranteed to be in any particular state of hardness.
My current set of hypothesis is as follows:

1. We are softening the chamber walls when we silver solder the parts together.
2. The Hotrod igniter is making a soft spot on the chamber side leading to local buckling.
3. We got a different batch of water pipe and is is less tempered.

My corrective actions are:

1. Switch back to normal solder for the throat and spiral wires.
2. Rerun our flow rate tests we ran on the first chamber to verify we have not drifted off of nominal.
   
3. Do a hydrostatic collapse test on the pipe we have to see if the batches are different.
4. Build up 4 chambers for testing, hopefully, next weekend.
5. One of these chambers will use thicker pipe wall.
   

My verification tests are as follows:

1. Run a test where we run the igniter and then hit the chamber with full fuel pressure, but no lox if this collapses then we have the igniter too hot or oriented wrong.
2. Rerun the tests we tried this weekend.
3. If both of these fail retest with the thick wall chamber.

Murphy Wins!

We went testing this weekend....
The game was not even close, Murphy won.
Video Summary here

1)Saturday Afternoon Very little lox, almost none.
Masten Space was nice enough to sell us some of theirs.
Thank you thank you thank you!


2)Saturday late ran the test chamber twice
Melted the test chamber in a new way. Video and pictures Monday.


3)Late Saturday set up telescope.
One axis is broken and drive motor makes grinding noises.
Used it in manual mode looked at moon and Jupiter, very cool viewing.


4)Sunday Morning test stability and control air lander...
No stability no control we now have pieces...video later


5)Sunday noon time...Tested 2nd chamber failed immediately with the center copper chamber wall buckling and collapsing inward. Same failure as #2 above.


6)Sunday just after noon help SDSU students with telemetry for their rocket.
SDSU has spectacular hard start and fireball. (video Monday)

7)Early Saturday Successfully flew my RC helicopter.
Saturday Afternoon flew it again, tail rotor belt failed.
Failed in low hover, no other damage.


8)Sunday about 3:30 got flat tire.
Spare was flat. The road to the test site is rock and dirt, very hard on tires.
(Had a 12 V compressor with me, dodged Murphy a bit)


Murphy 8 unreasonable rocketeers ZERO.

No one was physically injured, when I got home the house had not been leveled by a stray meteor, its all part of the process.

I've received the first Tee Shirts

I've just received the first Unreasonable Rocket Tee's and they look good.
So feel free to order some at the Store.

Learning Curve/Frustration...

I brazed my last injector myself, but it got really oxidized.
I was worried about the black oxide flakes plugging up the injector.
So I thought I would step up to the plate and have the next one furnace brazed.

So I did about 30 hours of machining making all the parts and took it to a company that specializes in furnace brazing. As I did it all myself I had the peice part drawings, but did not have an assembly drawing. The parts only fit together one way.

So I carefully showed them how it all goes together with the warning that it was very important that the gap between the pintile and the injector face not be brazed....

Unfortunately the person doing the work was not the person I presented the parts to. The person I presented the parts to came from the shop end of the building so I figured he would be doing the work.

I got it back today and the gap between the pintile and injector plate is brazed shut. $200.00 of telerium copper and more importantly 30 hours of work are scrap. Argggh!

Key learning point.... If the shop is used to detailed assembly drawings provide them one. Even if it is self explanatory to you it may not be so to them.

FAA Permit Application

I've just finished printing the two copies of my experimental permit application. I'm on my way out the door to send them.

As I've stated previously I would make anything I formally submit available.
Here is the Application and the Cover Letters.

I'm a tiny bit queasy making all of this public, but one of my main goals is to try to demystify the process of doing rocketry as much as possible. The regulatory aspects are a key part of that process.

AST News.

I got a chance to chat with my AST representative today and I'm pleased with the discussion. He indicated that I should probably formally submit my next revision and not just send them a draft for review. While not a formal endorsement, it at least implies that I'm close to "complete enough". I hope to finish up and Mail the Fed-X the formal application on Monday or Tuesday.

In a past life I was responsible for negotiating the technical engineering aspects of a significant subcontract. whenever we found ambiguity in the contract it was good news because we could exploit this to get more money from the prime. As a result I have a fine tuned "ambigious nit sensor". I have to fight this impulse to pick these nits when working with the FAA.

A simple example:
One of the comments I received on my draft application was :

AST understands that there are no hazardous materials asociated with the vehicle.
However for the purposes of documentation completeness, the application still needs to state positively that there are no hazardous materials used in the suborbital rocket.

Seems like a simple statement and they are really looking for a statement that I'm not using hydrazine or some other really nasty substance. This seems really simple,but my "ambigious nit sensor" goes off and I start wondering ....

Is Lead solder Hazardous?
Is the Lead in Brass Hazardous?
Is the gallium arsenide in the GASFET RF amplifiers hazardous?

So I write the following:

Unreasonable rocket will not be using any environmentally hazardous substance, we are only using benign non-toxic propellants . The non- consumable portions of the vehicle will be constructed with aluminum,copper, stainless steel and normal composite structures. The only components of vehicle that might contain nominally hazardous materials are the trace elements in the electronic components and lead containing solders that are part of these assemblies. The commercial components will all be RHOS compliant lead free, but the non commercial components assembled for this effort will use lead solder for reliability purposes.

What I finally put in the application is:
Unreasonable rocket is not using any hazardous consumables.

Fabricating our first vehicle....

Our test stand used flight weight tanks and valves.
Our first vehicle is going to look a lot like four of these test stands.

Toward that end my son and I have been fabricating and buying parts, we hydroformed and machined 17 tank ends (1 spare ),

We had Thunderbird Water jet cut some valve parts and brackets.

We ordered and received a batch of tonegawa servos from Tokyo hobbies.

Tube services sold us some aluminum tubing to make tanks.

We ordered all the tank weld on AN fittings from Iindustrial liquidators They are a dealer for Earls Fittings.

Lots of Valves, snap rings and parts from McMaster Carr.

I have enough Tellirium Copper to build 20 or so Motors purchased from Cambrdige Lee.

3 Vehicles of solinoids from Predyne.

1.25 Vehicles of ignition modules from CH-Ignitions.

2 Vehicles worth of Composite helium tanks on Order from SCI.

O-rings from Real Seal.

On Friday I pick up a furnace brazed Injector assembly from Certified Metal Craft.

Flowers for my understanding wife from ProFlowers.com....
(Delivered some time Wednesday Morning. Shes' usually home in the mornings, so I've asked her if she can be home Wednesday Morning to receive a very important package for my project, she just doesn't know its flowers for her...yet....)

I'm sure I've left off and forgotten a million vendors.

Our New Logo....

What would a new logo be without a Tee shirt Shop...
Buyer Beware I have not yet seen this printed on a Tee shirt.
The colors may not work... I've ordered a few I will update
the blog with a good/bad review later this week when they arrive.

A trip to DC

On Monday I flew to DC to meet with AST to discuss my draft experimental permit application and to attend the Experimental Permit workshop. After this series of meetings I'm feeling pretty good about the paperwork side of the process. AST did not ask for anything that was at all unreasonable. The comments to my draft application were entirely reasonable and I'm very hopeful that my next submission will be judged as "Complete enough" to start the 120 day permit clock. Now back to actually building a vehicle capable of competing.

While I was in DC I went to visit the Aerospace museum. It was really sad that the only launch hardware advances in the museum newer than 35 years old was Spaceship one.
We made incredible advances in the 50's 60's and early 70's, since that time we have done nothing to extend that legacy of development. What we have instead is an entrenched NASA bureaucracy striving to get funding for a development boondoggle of biblical proportions.

Testing 5/12 (sort of)

After the last test sequence I did some more igniter test work and made a few changes:

• Increased the orfice sizes raising the igniter chamber pressure from 80 to 160 PSI.
• Changed the check valves to metal seat check valves and moved them closer to the igniter.
• Added a sintered fuel filter to keep from plugging the fuel orfice.
• Changed the orifices from steel to stainless.

After verifying all of these changes with some igniter tests using GOX/Ethanoal I fabricated a new injector and chamber assembly. I also took Sunday the 6th off and went up to help Kevein weld on the Large vertical test stand. It was a really busy week, we finished up and headed to the test site about 19:30 on Friday.

We have been bringing our own LOX out to the test site, but this time we were bringing two barrels of Ethanol and did not want to carry both on the highway at the same time. So we had the LOX delivered. We arrived at the test site about 00:30 Saturday morning. As we unpacked and got ready to camp we noticed a loud hissing noise and discovered it was the lox dewar venting, It was completely empty. The short version is no LOX no testing.

Saturday was scheduled to be a FAR work party weekend, so we spent the day working on the facility. We shovled the sand out of the block house, and laid out and leveled the Emergency Medical Evacuation Helipad. (Just happens to be a 10M diameter circle.)

On Monday the 14th I fly back to DC to talk to the FAA about my experimental permit and to attend the experimental permit workshop.

Testing 4/28

I'ts been 4 weeks since I last offered an update. We have been testing every 2 weeks, two weeks ago we went out to test with the goal of improving our ignition reliability and doing some throttle testing.

After reviewing the data from our earlier test series we learned that the fuel and LOX pressures were not coming up evenly to the commanded start position. The end result is that we tried to start at idle and then powered up to full throttle. We probably did this before the chamber was 100% lit causing harder starts. So we modified the software to change this sequence and went out to try again. The only physical change to the motor was a change from bolted to snap ring closures on the motor.


We tried to start the motor 4 times with only one successful light. After the first two failures to light we changed the software back to its origional condition and tried a third time, still no light.
So some diagnostics showed that the igniter fuel solenoid was dead. We replaced that and tried a fourth time. We did not switch the old software back to the new so for the forth attempt we successfully lit the motor but it started a bit hard. At this point we were suffering for the 3 failed attempts as we were running low on presurant gas. The video camera had also been running for more than an hour and it gave up the ghost so we got no video of the 4th run. The 4th run was a 30 second throttle test.

As we had been messing with the igniter connections diagnosing the no-light issues the igniter plumbing connection at the fuel solinoid was loose so we got chamber gas flow backwards into the igniter at about 20 seconds into the run the fuel solenoid decided it had had enough of hot gases leaking at it and let a burst of fuel into the aluminum line between the chamber and igniter. The mixture was just right to detonate in the line. So we have a small bulge/hole in the fuel line between the igniter and the fuel solenoid. At or near the same time the chamber pressure transducer disassembled it self. We did not notice any of this from the block house the only thing we knew is that the chamber pressure went to zero. The motor continued to run
and did its throttle steps for another 10 seconds or so. This chain of events is pure speculation based solely on the visual state after the run and the data we collected.

When we returned home and disassembled the motor we also determined that the injector plate was bent.