RixKillian

We Built a Real Rocket Engine! [Video]

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Hello all!

Over the past year I've been part of an internship (sort of) that's hosted by my high school, in which we work with volunteers from Aerojet/Rocketdyne to develop a liquid fueled rocket that we're planning on launching as the IREC (InterCollegiate Engineering Competition) sponsored by ESRA in Utah this June.

Last year we had our first engine test, but due to fuel/oxidizer ratio issues and combustion blowout (the propellent burned outside the nozzle), we only got fifteen of the expected hundred pounds of thrust. Discouraged and frustrated, we left the project over the summer and continued in October. Finally, this Saturday, after weeks of analysis, engineering, and assembling, we were ready for our second engine test. Here's the highlights:

We replaced the solenoid valves with servo valves so they could open slowly to allow combustion to build up, and adjusted the propellent mixture, to glorious results!

Unfortunately the avionics team had some trouble with the load cell data acquisition system, so we don't have thrust data for the engine as of now. Therefore we'll have another test in a few weeks, and hopefully we'll get the engine starting more reliably as well.

Playing KSP, you don't always think about all the pieces that go into every component of a rocket, but this process has undeniably filled me with respect for NASA, SpaceX, Blue Origin, Aerojet, and everyone who works on these systems. Keep up the incredible work!

-RixKillian

Edited by RixKillian

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Uhhh I like it! Good project!

I'm curious, can you give some kind of dimensions, expected trust? The engineer in me wants some data!

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For gods sake, my stupid Canadian highschool doesn't even do things like that. I'm literally the only one in my grade 9 class who studies grade 11 at home, while everyone else is struggling on basic integers. I have ADHD, and am still trying to read The Design of Liquid Propellant Rocket Engines. But I can't even get past the first page without losing focus.

Then, I see future geniuses, like you guys, and I want to cry my face off.

Anyway, what's the thrust, in kilos, of the engine? Have you considered adding a nozzle? How did you do it, and what did you guys use to start studying the design of rocket propulsion systems? What are some easy-to-get chemicals that can combust in that fashion?

Edited by Matuchkin

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18 hours ago, Streetwind said:

Those are some beautiful shock diamonds :)  Congrats to figuring it out!

Thank you! Yes, the diamonds were a victorious sight for sure.

2 hours ago, Matuchkin said:

For gods sake, my stupid Canadian highschool doesn't even do things like that. I'm literally the only one in my grade 9 class who studies grade 11 at home, while everyone else is struggling on basic integers. I have ADHD, and am still trying to read The Design of Liquid Propellant Rocket Engines. But I can't even get past the first page without losing focus.

In later years of high school look for internship opportunities, or clubs and the like. Especially in college, there are countless opportunities to work on aerospace, even if it isn't part of a company or directly through the school. I'm impressed by your endeavor, though, that sounds like a dense read!

17 hours ago, kunok said:

I'm curious, can you give some kind of dimensions, expected trust? The engineer in me wants some data!

 

2 hours ago, Matuchkin said:

Anyway, what's the thrust, in kilos, of the engine? Have you considered adding a nozzle? How did you do it, and what did you guys use to start studying the design of rocket propulsion systems? What are some easy-to-get chemicals that can combust in that fashion?

As for the technical aspects of it - The expected thrust is around 100 pounds, or a little over 45 kg. I'm unsure of the engine dimensions, but it operates at a chamber pressure around 300 psi (2070 kPa). The rocket is 8.75 ft (2.67 m) tall, and has avionics systems and a parachute to collect data and deploy at the right altitude and speed. The contest has a hard altitude limit set by the FAA of 25,000 feet (7600 m) so we're aiming for 23,000 ft (7000 m), which is where we receive the most points. 

The nozzle is actually the constriction and expansion portion of the engine just below the combustion chamber - every engine has one by definition. I assume you mean a bell nozzle, which is what's seen on most KSP liquid engines. The bell nozzle's advantage comes in that it directs exhaust straight out of the engine by converting non-axial gas momentum to axial, making the engine much more efficient. Due to the size of our engine, machining a bell nozzle would be much more expensive and would not provide significant improvements on this scale. We had the engine machined at Aerojet/Rocketdyne, but could likely be done with a nice metal lathe if the materials are available.

Most of our knowledge came from our mentors, a few of which have worked directly in the engine department at Aerojet/Rocketdyne. 

For propellent, we use 75% ethanol and 25% water for the fuel (by mass) and liquid oxygen for the oxidizer. The fuel on it's own isn't very dangerous, it should be treated just as one would do with gasoline, but LOx can be incredibly dangerous to handle - it can rapidly accelerate a spark into a fire if it comes into contact with any carbon (like if you spill some on the ground), and generally requires professional cleaning of any lines and valves before filling. I would wait until you can work with organizations for a liquid rocket, but solid motors are rather easy to make and use. (Keep in mind that I'm not endorsing freelance rocketry, it's still very dangerous and we have a strict safety protocol for every procedure in the firings.)

1 hour ago, insert_name said:

oww my ears

whats that whine from the engine at the end?

That's been puzzling me as well - I'll talk to people at the meeting tomorrow and get back to you. I have my theory, related to different thermal expansions of dissimilar steel alloys but I keep running into logical problems. :confused:

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Cool! I do rockets too (see profile pic), but I've never tried building anything liquid-fueled.

A quick mind-sim tells me that a rocket mostly fueled with heavy liquids in heavy tanks is going to weigh a lot. Keep in mind that to prevent weathercocking (turning into the wind) and the resulting loss of altitude/potential problems with the parachute, the rocket should have a thrust-to-weight ratio of 3:1 at an absolute minimum. This means your tanks, pipes, nozzle, airframe, electronics, and all of the other fun stuff you're putting on the rocket should not exceed 33 lbs at launch.

I would also love to see any simulation files you have of this thing. I'm sure you've played around with OpenRocket, Rocksim, or some other design software that tells you how your rocket will fly. What will the rocket look like, and what's its flight profile?

Finally, I wish y'all the best of luck. Please keep me posted!

-Upsilon

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17 hours ago, RixKillian said:

I would wait until you can work with organizations for a liquid rocket, but solid motors are rather easy to make and use. (Keep in mind that I'm not endorsing freelance rocketry, it's still very dangerous and we have a strict safety protocol for every procedure in the firings.)

Check your local laws too. In Britain making your own solid rocket fuel is probably illegal unless you meet onerous regulatory requirements, but a bipropellant rocket is less troublesome. (It's because the solid fuel, with its oxidizer mixed in, falls under the same laws that regulate explosives). The USA seems to be more lenient, and I've no idea about Canada.

Edited by cantab

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47 minutes ago, UpsilonAerospace said:

Cool! I do rockets too (see profile pic), but I've never tried building anything liquid-fueled.

A quick mind-sim tells me that a rocket mostly fueled with heavy liquids in heavy tanks is going to weigh a lot. Keep in mind that to prevent weathercocking (turning into the wind) and the resulting loss of altitude/potential problems with the parachute, the rocket should have a thrust-to-weight ratio of 3:1 at an absolute minimum. This means your tanks, pipes, nozzle, airframe, electronics, and all of the other fun stuff you're putting on the rocket should not exceed 33 lbs at launch.

I would also love to see any simulation files you have of this thing. I'm sure you've played around with OpenRocket, Rocksim, or some other design software that tells you how your rocket will fly. What will the rocket look like, and what's its flight profile?

Finally, I wish y'all the best of luck. Please keep me posted!

-Upsilon

Weathercocking, while it does depend on gaining enough speed at the beginning, is more an issue of aerodynamics and mass distribution. We want the center of pressure to be just behind the center of mass of course, but not far enough to weathercock. The thrust ratio really only affects weathercocking at the beginning of the flight, when the rocket isn't going fast enough for the fins to stabilize it. By the time our rocket clears the rail though, at 40 feet, it will be going 100 ft/s, plenty fast enough to be stable. I believe it will be about 50-55 lbs, including an extra payload in the nose (a category requirement of the contest) but we have solid motors than boost it to 100 ft/s by the end of that 40 feet.

We've been using RASAero, but I haven't run any sims on it (someone else's job) so I only have a rough idea of the flight profile. We estimate it'll reach about mach 1.2 max, and 22,000 to 23,000 feet altitude.

LiquidFueledRocket.png

This is the basic design, which we've changed slightly for mass and new arrangements. The picture's from my physics teacher's website.

Also, we did a thrust calculation based on the exhaust speed and the fuel flow rate, and we found that the engine was producing about 200 lbs (91 kg) of thrust! of course, this was due to a higher flow rate and higher pressure than we want, as a sustained burn at 200 lbs would heat the engine to the point of a blow through. Therefore, we'll be adjusting it to lower the thrust and heat. This does mean we may be able to step up our thrust slightly, maybe to 110-120 lbs and get a shorter burn time (Nice!).

Back to @insert_name's question. The squealing was from the check valves - as the engine burned through fuel and reduced tank pressure, the pressure gradient on either side of the valves equalized until the valves (which are spring-loaded) started oscillating at their resonant frequency due to the passage of gas, making that sound.

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18 hours ago, RixKillian said:

As for the technical aspects of it - The expected thrust is around 100 pounds, or a little over 45 kg. I'm unsure of the engine dimensions, but it operates at a chamber pressure around 300 psi (2070 kPa). The rocket is 8.75 ft (2.67 m) tall, and has avionics systems and a parachute to collect data and deploy at the right altitude and speed. The contest has a hard altitude limit set by the FAA of 25,000 feet (7600 m) so we're aiming for 23,000 ft (7000 m), which is where we receive the most points. 

Wait, do you really use Imperial units in technical aspects in high school? Uhh, I thank (or maybe hoped) that currently you would use only metric system in science education.

18 hours ago, RixKillian said:

The nozzle is actually the constriction and expansion portion of the engine just below the combustion chamber - every engine has one by definition. I assume you mean a bell nozzle, which is what's seen on most KSP liquid engines. The bell nozzle's advantage comes in that it directs exhaust straight out of the engine by converting non-axial gas momentum to axial, making the engine much more efficient. Due to the size of our engine, machining a bell nozzle would be much more expensive and would not provide significant improvements on this scale. We had the engine machined at Aerojet/Rocketdyne, but could likely be done with a nice metal lathe if the materials are available.

If you are using a CNC lathe I don't see the point of not programming a bell nozzle, it won't be difficult, and you can use a CAD/CAM software if you don't know programming. And an old lathe operator knows how to deal with strange trajectories in manual lathes.

56 minutes ago, cantab said:

Check your local laws too. In Britain making your own solid rocket fuel is probably illegal unless you meet onerous regulatory requirements, but a bipropellant rocket is less troublesome. (It's because the solid fuel, with its oxidizer mixed in, falls under the same laws that regulate explosives). The USA seems to be more lenient, and I've no idea about Canada.

In Spain too, a solid rocket will be categorize as an explosive (because it is...). There it's a little company developing a little rocket and they only use liquid motors because the regulations.

Edited by kunok
typos as always

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1 minute ago, kunok said:

Wait, do you really use Imperial units in technical aspects in high school? Uhh, I thank (or maybe hoped) that currently you would use only metric system in science education.

We use only metric in class, but the rocket is in imperial for some strange reason.. I agree though

2 minutes ago, kunok said:

If you are using a CNC lathe I don't see the point of not programming a bell nozzle, it won't be difficult, and you can use a CAD/CAM software if you don't know programming. An and old lathe operator knows how to deal with strange trajectories in manual lathes.

I'm not sure what was used - it was machined long before the internship started, and regardless the bell curve wouldn't make much difference, especially since the difference in air pressure throughout the flight will be very small compared to rockets sent to space.

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That's almost like October Sky... 

Except with liquid fuel.

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Just now, Bill Phil said:

That's almost like October Sky... 

Except with liquid fuel.

I love that movie!

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How high up do you estimate this can go? Is there any possibility/logic in clustering/ staging when making these things?

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12 minutes ago, Matuchkin said:

How high up do you estimate this can go?

3 hours ago, RixKillian said:

We estimate it'll reach about mach 1.2 max, and 22,000 to 23,000 feet altitude.

Of course, we're launching from 4300 feet to begin with, which gives us an extra 1000 feet in addition thanks to the lower air pressure.

16 minutes ago, Matuchkin said:

Is there any possibility/logic in clustering/ staging when making these things?

We aren't clustering or staging in our rocket, but generally you would use explosive rings that shear pins to separate the stages. As for clustering, one has to be sure the engines won't burn through or produce asymmetric thrust. Not to mention the tangles fuel lines and equal flow rates... (Nightmare!)

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We'll be having another rocket engine test in two weeks, I'll keep you all updated with what we find out as for thrust and engine durability.

Edited by RixKillian

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That's beautiful. :)  How is your MCC/nozzle cooled?  What books do you recommend reading for a good background in that kind of stuff?  How much calculus was necessary?

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The fuel lines will wrap around the combustion chamber and nozzle, both to preheat the fuel and help cool the engine. (I believe preheating it helps with efficiency?) 

I haven't read much about it in books, but I bet you could find some aerospace engineering books at a library or secondhand bookstore.

As for calculus, I haven't had to use much because I'm on the Launch Rail team (I had to use a little for stress and torque optimization calculations), but I think the other teams, especially engine and feed system, would be using a lot more.

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8 hours ago, RixKillian said:

(I believe preheating it helps with efficiency?) 

Yes, it lower entropy loses, progressive heating it's always a good thing, and in the nozzle you want a gas with velocity not heat so stealing heat in the nozzle should improve the overall efficiency.

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7 hours ago, kunok said:

Yes, it lower entropy loses, progressive heating it's always a good thing, and in the nozzle you want a gas with velocity not heat so stealing heat in the nozzle should improve the overall efficiency.

Ah thank you, I didn't know the details of it but that makes a lot of sense :D

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I wish to be on that stage, i have some financial planning goals and money management course soon so i will motivate myself more to buy some parts from ebuy and do first rockets or join existing tgeam. 

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Nice work! I think O/F ratio is good, not too much fuel. I think my engine is more fuel rich. And your engine has 20 times more thrust. Great!

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Nothing wrong with discussing this project here in this thread... just a gentle reminder, though, that the thread is from nearly four years ago, so do bear that in mind.  ;)

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