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How to use Liquid fuel in a standard model rocket

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McBingus

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For a project for my world history class, I'm supposed to complete standards about the progression of technology and the development of rockets and nuclear warheads. My plan was to build three. One for the types of fuel during the cold war (still working on) 1 for between the cold war and the present ( solid mixture of potassium nitrate and other reactants.) and 1 for the current era. My question is fo the new era how you I make a standard model rocket compatible for liquid combustion. Since liquid hydrogen isn't the easiest to acquire, I was instead going to use liquid nitrogen to freeze the air around it and get some liquid oxygen. I can't seem to find a way to modify a model rocket without going over budget and taking too much time. Any and all help is appreciated and questions are more than welcome.
 

JohnCoker

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In terms of history, I think it's important to understand what you mean by the term "rocket." The oldest propellant is black powder which has been used for centuries for fireworks and military rockets. During the developmen of rockets in the 20th century, liquid fuels were common. (Goddard used liquids.) Different methods have different trade-offs and are used for different purposes.

The first large-scale deployment of military rockets was by Germany against Great Britain in WW2. Many sounding rockets after that time were propelled by solids and liquids.

So I don't think you can make the case for a progression from solid to liquid. I suggest you read more on the history (either long-term or just the 20th century).

Hydrogen has been used as a fuel (notably by the Apollo program) because it, burning in liquid oxygen (LOX), has the highest ISP. However, handling of liquid hydrogen is hard and many rockets, at the time and today, substitute other fuels such as kerosene. I think you will find building a hobby rocket with liquid fuel to be impractical because of the complexity. The tanks, valves and plumbing will weigh too much. These engines are great for very large rockets, but don't scale down.
 

Steve Shannon

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For a project for my world history class, I'm supposed to complete standards about the progression of technology and the development of rockets and nuclear warheads. My plan was to build three. One for the types of fuel during the cold war (still working on) 1 for between the cold war and the present ( solid mixture of potassium nitrate and other reactants.) and 1 for the current era. My question is fo the new era how you I make a standard model rocket compatible for liquid combustion. Since liquid hydrogen isn't the easiest to acquire, I was instead going to use liquid nitrogen to freeze the air around it and get some liquid oxygen. I can't seem to find a way to modify a model rocket without going over budget and taking too much time. Any and all help is appreciated and questions are more than welcome.
At age 15 you really cannot do a liquid rocket that uses combustible liquids. Don’t let that make you feel bad; at age 63 I can’t either. They are just too dangerous for the average hobbyist. Instead, you might want to illustrate the difference between historic blackpowder rockets using commercial Estes model rocket motors and more modern rockets which use ammonium perchlorate composite propellant (APCP) such as commercial motors produced by Quest Model Rockets. You can easily demonstrate in two similar rockets (or even one using the two different motors) the difference in “Specific Impulse” which is the amount of energy released for a particular mass of fuel.
Black powder motors are similar to what was used in the earliest rockets made by the Chinese and in military rockets throughout time (see https://en.m.wikipedia.org/wiki/Congreve_rocket) including those mentioned in the star spangled banner.
APCP motors are a much newer development. APCP is still used as the preferred propellant for solid rocket boosters because it is relatively safe to handle.
Best of luck!
 

prfesser

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Dear McBingus,

Your project is roughly the equivalent of someone wanting to build a Formula 1 race car that could win the Indy 500, while having no experience with machining or metalworking or engineering, and not yet having earned a driver's license. I'm serious. Liquid fuel rockets look simple on paper, but they're anything but.

I think your classmates and teacher would be more impressed with a nicely constructed, fairly large non-working model of a liquid-propellant rocket. Find a cardboard tube of the right size, cut it in half lengthwise to show the parts. Paint and label 1 liter soda bottles as fuel/oxidizer tanks. Maybe 3D print something that looks like an engine with combustion chamber. Small dowel rods to represent fuel/oxidizer lines, etc. This is 2019; consider that a very large fraction of schools are removing chemistry lab from the curriculum. Even if it was possible to make a small working liquid-propellant rocket, do you really think that a teacher is going to allow it to be demonstrated in flight? (One word: liability)

Oh, and any discussion of propulsion that does not involve commercial certified rocket motors goes in the Research forum, which is restricted to certified high-power fliers.

Best -- Terry
 

G_T

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Even the liquid nitrogen extraction of oxygen from the air is VERY dangerous. Rule of thumb - when you see it start to happen, run!

Please carefully consider what Terry has posted. If the teacher has issues, please refer the teacher to here and we'll try to help. Rocketry does look simple, but it is the hairier side of aerospace engineering.

Gerald
 

Bat-mite

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The problem with liquid fuel, and why we don't use it in hobby rocketry, is the problem of containing the burn. It burns rapidly and explosively. NASA can do liquid fuel because they have thousands of engineers working full time on containing and controlling the burn.
 

McBingus

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Dear McBingus,

Your project is roughly the equivalent of someone wanting to build a Formula 1 race car that could win the Indy 500, while having no experience with machining or metalworking or engineering, and not yet having earned a driver's license. I'm serious. Liquid fuel rockets look simple on paper, but they're anything but.

I think your classmates and teacher would be more impressed with a nicely constructed, fairly large non-working model of a liquid-propellant rocket. Find a cardboard tube of the right size, cut it in half lengthwise to show the parts. Paint and label 1 liter soda bottles as fuel/oxidizer tanks. Maybe 3D print something that looks like an engine with combustion chamber. Small dowel rods to represent fuel/oxidizer lines, etc. This is 2019; consider that a very large fraction of schools are removing chemistry lab from the curriculum. Even if it was possible to make a small working liquid-propellant rocket, do you really think that a teacher is going to allow it to be demonstrated in flight? (One word: liability)

Oh, and any discussion of propulsion that does not involve commercial certified rocket motors goes in the Research forum, which is restricted to certified high-power fliers.

Best -- Terry
Thanks for the advice, Instead of the liquid rocket. I'll take use your idea of just building a non functioning model instead. I never realized how dangerous liquid fuel actually was, it'll still work for my project but at least I get to keep my hands.
I'll still work on the other one but I'll be a lot more careful now that I have received feedback. Thank you for the information.
 

boatgeek

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Thanks for the advice, Instead of the liquid rocket. I'll take use your idea of just building a non functioning model instead. I never realized how dangerous liquid fuel actually was, it'll still work for my project but at least I get to keep my hands.
I'll still work on the other one but I'll be a lot more careful now that I have received feedback. Thank you for the information.
If your teacher has any issues with not demo-ing liquids, you could always show them the SpaceX blooper reel*. Even experts blow stuff up when building liquid fuel rockets.

If you're willing to shift your goals a little bit after some research, you could look at any of the following solid fuel rockets:
Chinese fire arrows (~900 AD, black powder)
Congreve rockets (early 1800's, black powder, see link posted by Steve Shannon)
German R4M (late WW2)
Arcas sounding rockets (1959-1991)
AIM-9 Sidewinder (1956-present)

If it's important, all but the Arcas are weapons. The information above is enough to find quite a bit of data from the Internet.

* This is a bit unfair to SpaceX since all of those explosions were on failed landings rather than in flight. Still, it gives a sense of how badly things can go wrong.
 

sghioto

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How about a water rocket, that's liquid!:)
SG
 
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