How to design, build and test small liquid-fuel rocket engines
Normally step 1 of my Eliminator model rocket's assembly instructions would have me assembling the stock Estes engine mount. But since my rocket engine tubes are slightly larger than the OD of the stock Estes rocket engine tubes, I will have to modify the Estes engine mount. May 10, · The first part in a series on rockets! This time, we're focusing on the fuel and engine design. These rocket motors are super cheap and easy to make, and wor.
Copyright by Leroy J. ROCKETLAB cannot assume responsibility, in any manner whatsoever, for the use readers make of the information presented herein or the devices resulting therefrom.
The rocket engine is a relatively simple device in which propellants are burned and the resulting high pressure gases are expanded through a specially shaped nozzle to produce thrust. Gas pressurized propellant tanks and simple propellant flow controls make operation of a small liquid-fuel rocket engine about as simple as operating an automobile engine.
Why then do so many amateur rocket engines fail or cause injury? The reason, usually and simply, is that the amateur is not accustomed to high pressure devices operating near material temperature limits. His normal everyday life is, instead, filled with devices and gadgets operating at low pressures and at low thermal energy levels.
With proper design, careful workmanship, and good test equipment, operated in a safe manner, the amateur can build small, liquid-fuel rocket engines which will have hours of safe operating life. The what meats do jewish eat of this publication is to provide the serious amateur builder with design information, fabrication procedures, test equipment requirements, and safe operating procedures for small liquid-fuel rocket engines.
A liquid rocket engine employs liquid propellants which are fed under pressure from tanks in to a combustion chamber. The propellants usually consist of a liquid oxidizer and a liquid fuel. In the combustion chamber the propellants chemically react burn to form hot gases which are then accelerated and ejected at how to make model rocket engine velocity through a nozzle, thereby imparting momentum to the engine.
How to dreadlock short hair is the product of mass and velocity. The thrust force of a rocket motor is the reaction experienced by the motor structure due to the ejection of the high velocity matter. This is the same phenomenon which pushes a garden hose backward as water squirts from the nozzle or makes a gun recoil when fired.
A typical rocket motor consists of the combustion chamber, the nozzle, and the injector, as shown in Figure 1. The combustion chamber is where the burning of propellants takes place at high pressure. The chamber must be strong enough to contain the high pressure generated by, and rockey high temperature resulting from, the combustion process. Because of the high temperature and heat transfer, the chamber and nozzle are usually cooled.
The chamber must also be of sufficient length to ensure complete combustion before the gases enter the nozzle. The function of the nozzle is to convert the chemical-thermal energy generated in how to make model rocket engine combustion chamber into kinetic energy, The nozzle converts the slow moving, high pressure, high temperature gas in the combustion chamber into high velocity gas of lower pressure and temperature.
Since thrust is the product of mass the amount of gas flowing through the nozzle and velocity, a very high gas velocity is desirable. Gas velocities from one to two miles per second to feet per second can be obtained in rocket nozzles. Nozzles which perform this seemingly amazing feat are called DeLaval entine after their inventor and consist of a convergent maks divergent section, as shown in Kodel 2.
The minimum flow area between the convergent and divergent section is called the nozzle throat. The flow area at the end of the divergent section is called the nozzle exit area. The nozzle is usually made long enough or the exit area is great enough such that the pressure in the combustion chamber is reduced at the nozzle exit to the pressure existing outside the nozzle. If the rocket engine is being fired at sea level this pressure is about If the engine is designed for operation at high altitude, the exit pressure is less than Liquid rocket engines can burn a variety of oxidizer - fuel combinations, some of which are tabulated in Table I.
Most of the propellant combinations listed are dangerous, toxic, and expensive. The amateur builder of rocket engines on the ho hand, requires propellants that are readily available, reasonably safe and easy to handle, and inexpensive. They give good performance, the combustion flame is readily visible, and their high combustion temperature presents an adequate design challenge to the amateur builder.
The propellants are used in the Atlas missile and the Saturn space booster [see Additions and Corrections ]. In these systems, however, liquid rather than gaseous oxygen is used as the oxidizer. Gaseous oxygen can be readily and inexpensively obtained in pressurized cylinders in almost any community because of its use in oxy-acetylene welding.
With reasonable precautions, to be detailed later, the gas and cylinder is safe to handle for rocket test stand use. Gas emgine are easily regulated with commercial regulators and gas flow rate is easily controlled with commercially available valves. Hydrocarbon fuels, such as gasoline and alcohol, are readily available in any community.
Safety precautions are already known by most responsible individuals due to how to make model rocket engine use of the how to find erased messages on phone in internal combustion engines for automobiles and power equipment. All subsequent sections of this publication will refer to, and assume, that the propellants to be used in amateur liquid-fuel rocket engines are gaseous oxygen and hydrocarbon fuel.
The flame temperature of hydrocarbon fuels burned in gaseous oxygen enigne various combustion chamber pressures is shown in Figure 3 for the stoichiometric mixture ratio. Mixture ratio is defined as the weight flow of oxidizer divided by the weight flow of fuel, or. When a stoichiometric ratio is achieved just how to solve cubic equations algebraically oxygen is present to chemically react with all the fuel; the highest flame temperature is achieved under these conditions.
If a lower flame temperature is desired it is usually better to rkcket more fuel present than oxidizer; this is known as burning "off-ratio" hwo "fuel-rich. Figure 4 indicates how the flame temperature varies when combustion chamber pressure is held at a constant value and the mixture ratio is allowed to vary. The thrust developed per pound of total propellant burned per second how to make model rocket engine known as specific impulse and is defined as.
Figure 5 indicates the maximum performance possible from hydrocarbon fuels burned what is a gluten intolerance gaseous oxygen at various chamber pressures with the gas expanded to atmospheric pressure. This graph can be used to determine the propellant flow rate required to produce a certain thrust. At these conditions the propellant performance, from Figure 5is lb of thrust per lb of propellant burned per second.
The chemical and physical properties of gaseous oxygen, methyl alcohol, and gasoline are given in Table II. Enginee following section will detail simplified equations for the design of small liquid-fuel rocket motors. The nomenclature for the motor design is shown in Figure 6. The nozzle throat cross-sectional area may be computed if the total propellant flow rate is known and the propellants and operating conditions have been chosen.
Assuming perfect gas law theory:. Gamma is about 1. T t is the temperature of the moeel at the nozzle throat. P t is the gas pressure at the nozzle throat. The hot gases must now be expanded in the diverging section of the nozzle to obtain maximum thrust. The pressure of these gases will decrease as energy is used to accelerate the gas and we must now find that area of the nozzle where the gas pressure is equal to atmospheric pressure.
This area will then be the nozzle exit area. Mach number is the ratio of the gas velocity to the local speed of sound. The Mach number at the what do u call a jokes exit hw given by a perfect gas expansion expression. P c is the pressure in the combustion chamber and P atm is atmospheric pressure, or The nozzle exit area corresponding to the exit Mach number resulting from the choice of chamber pressure is given by.
Since gamma is fixed at 1. A good value for the nozzle convergence half-angle beta see Fig. The nozzle divergence half-angle, alphashould be no greater than 15 deg to prevent nozzle internal flow losses. To reduce losses due to flow velocity of gases within the rockst, the combustion chamber cross sectional area should be at least three times the nozzle throat morel.
This ratio is known as "contraction ratio". The chamber diameter for small combustion chambers thrust level less than 75lbs should be three to five times the nozzle throat diameter so the injector will have usable face area. The combustion chamber must be able to withstand the internal pressure of the hot combustion gases. The combustion chamber must also be physically attached to the cooling jacket and, therefore, the chamber wall thickness must be sufficient for welding or brazing purposes.
Since the chamber will be a cylindrical shell, the working stress in the wall is given by. A typical material for small water-cooled combustion chambers is copper, for which the allowable working stress is about psi. The thickness of the combustion chamber wall is therefore given by. This is the minimum thickness; actually the thickness should be mke greater to allow for welding, buckling, and stress concentration.
The thickness of the chamber wall and nozzle are usually equal. Equation 24 can also be used to calculate the wall thickness of the water cooling jacket. Here again, the value of t w will be the minimum thickness since welding factors and design considerations such as O-rings, grooves, etc. A new allowable stress value must be used in Equation 24what to take for upset stomach from antibiotics on the jacket material chosen.
The amateur should not consider building uncooled rocket engines since they can operate for only a short time and their design requires a thorough knowledge of heat and mass transfer engineering. Cooled rocket motors have provision for cooling some or all metal parts coming into contact with the hot combustion gases. The injector is usually self-cooled by the incoming flow of propellants. The combustion chamber and nozzle male require cooling. A cooling jacket permits the circulation of ,odel coolant, which, in the case of flight engines is usually one of hoe propellants.
However, for static tests and for amateur operation, water is the only coolant recommended. The cooling jacket consists of an inner and outer wall. The combustion chamber forms the inner wall and another concentric but larger cylinder provides the outer wall. The space between the walls serves as the coolant passage.
The nozzle throat region usually has the highest heat transfer intensity and is, therefore, the most difficult to cool. The energy release per unit chamber volume of a rocket engine is very large, and can be times that of a good steam boiler or five times that of a gas turbine combustion chamber. The heat transfer rate of a rocket engine rovket usually 20 to times that of a good boiler.
It is apparent, therefore, that the cooling of a rocket engine is a difficult and exacting task. The complete heat transfer design of a rocket engine is extremely complex and is usually beyond the capabilities of most amateur builders. Some important empirical design guidelines are available, however, and are listed below:. The largest part of the heat transferred from the hot chamber gases to the chamber walls is by convection.
The chamber walls have how to make model rocket engine be kept at a temperature such that the wall material strength is adequate to prevent failure. Material failure is usually caused by either raising the wall temperature on the gas side so as to weaken, melt, or damage the wall material or by raising the wall temperature on the liquid coolant side so as to vaporize the liquid next to the wall.
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Mar 27, · Simple Solid Rocket Engine Step 1: The Setup. A double boiler: I don't own one so I improvised one as you can see above, just a large pot, half Step 2: Fuel Mixture. The fuel we're making is often called "Candy Propellant" since it uses sugar as a main ingredient Step 3: Creating Our Fuel. The fabrication and assembly of a small liquid fuel rocket engine is no more difficult than the more serious amateur machine projects, such as model steam engines, gasoline engines, and turbines. Because the rocket engine has no rotating parts, dynamic balance of components is not required.
This Instructable is not intended to show a practical fuel application. The fuel I'll show here is one I play with a lot and use for demo's to show people the basics of rocket propulsion.
This is an early fuel mixture that was used in early sounding rocket's but was quickly forgotten about when much more efficient fuels were found. This is a fairly safe fuel to make so I feel safe showing it here. This is intended as an introduction to rocketry and the fuel used therein. I hope you enjoy it and please feel free to comment if you want to know more.
If you are familiar with how a rocket works, feel free to skip to Step 1. Otherwise, fear not, just read on. Solid Fuel Engines: These are what we're looking at, they are by far the simplest and easiest to get your head around.
An example would be the Space Shuttle's boosters, the white rockets attached to the side of the orange fuel tank. This type can not be stopped once it's lit. The Saturn 5 that carried the Apollo astronauts used these. These can be stopped and started repeatedly as long as they have fuel. Hybrid Engines: These are great, as of this writing I am beginning construction of a hybrid engine and will post when it's working, hopefully I can test in a month or so. A Google search will turn up an article about a guy that works for Valve yes, the game company who made an acrylic and oxygen hybrid engine.
These have the advantages of a solid rocket booster while being able to be throttled and even turn off and on. A rocket works by burning a fuel to create exhaust, it's the release of this exhaust that generates the thrust that pushes the rocket skyward. Think of a balloon, if you inflate a balloon and don't tie it closed, when you let go the balloon will fly around the room as the air escapes. This is because the pressure inside the balloon is greater than the pressure outside.
So the air wants to escape and there's only one way for it to go, out the bottom. You can think of a rocket the same way, the gasses given off as the fuel burns can reach a pressure more than 20 times the pressure of the outside air.
This is denoted 20 atm. To give you an idea, the pressure inside a normal party balloon is around 1. The pressure in a small, suborbital rocket is at least 19 times that at a given second.
I mention this both to give you an idea of how this stuff works and to explain the potential power of the chemicals we're working with. Newton laid the groundwork for all of this in his early studies of motion, particularly the motion of the planets around the sun. I am going to assume that you have had no formal physics education from here on in so please understand that this goes much deeper then I have the time or wherewithal to explain. Newton observed, and proved, that every reaction has an equal and opposite reaction.
So when the gasses are forced out of the nozzle, the rocket is pushed forward, just like our baloon. If you have more questions, and I hope you do, please ask in the comments, I'm happy to answer what I know or point you in the right direction if I don't.
If your really embarrassed to ask in the comments, I understand, just PM me. A double boiler: I don't own one so I improvised one as you can see above, just a large pot, half filled with water and another bowl floating in the water.
A small model rocket: you can get these at any hobby store, a Mosquito or Swift work well but any one like the one pictured above will work. A scale: You'll need a scale that can at least measure to within a gram. The more accurate you can get the better. Potassium Perchlorate: Order it off Amazon, you can get amazingly cool chemicals on Amazon.
This will act as the oxidizer, it gives up oxygen when heated so the sugar can burn more efficiently. There are much more efficient oxidizers but this one is fairly stable so I though it was best for an introduction.
Sugar: Common household sugar. This is the fuel. When it reacts with the oxidizer, Potassium Perchlorate in this case, it creates very hot CO2, which is expelled at high velocities to create thrust as discussed on the intro. Water: Tap water is fine but of course distilled water is the best due to it's lack of impurities. This is used to dissolve both the sugar and the Potassium Perchlorate. The fuel we're making is often called "Candy Propellant" since it uses sugar as a main ingredient and smells like cotton candy when it burns.
The flame produced should be purple and white with white smoke. Later I'll cover what probably went wrong if you see something else. Rocket fuel mixtures are given as a ratio usually, this ration is a weight ration, not a volume ratio.
So you will need a small scale such as the one pictured above. How much of the ingredients you use is up to you and depends on the size of the rocket you bought. So if you get one gram of sugar, you want 3 grams of Potassium Perchlorate, for a total weight of 4 grams. Of course the more accurate you are, the more efficient your fuel will be and you'll get a more impressive burn.
It is worth noting that Potassium Perchlorate is denser then sugar, so even measuring out three time as much, will only give you a little more Potassium Perchlorate than sugar by volume.
So trust your scale not your eyes in this case. Please read carefully, at least if you like your house in it's current, unburned-down state. I added some Karo Corn Syrup in that picture, but I've done it without and it works fine, the Karo just makes it a little easier to pack the fuel in later, so if you have it, great, if not you can use maple syrup, or just ignore it and it'll work fine. I chose Potassium Perchlorate because it's the most stable ingredient you can use here.
But it is still rocket fuel so be careful. At this point you just keep stirring, it will take a while, you want to get most of the water back out, we just used it to dissolve the sugar so it mixed more evenly, and heating it allowed the sugar and potassium perchlorate to both dissolve in the water more easily.
Now we need to steam out most of the water till your left with a very dry dough. Congrats, you have effectively recreated fuel used in the early days of rocketry, I'm talking pre-NASA. But still, it's impressive and a good first step. This fuel was replaced by Sugar and Potassium Nitrate more volatile but used in some fireworks as the propellant even today and later by Potassium Nitrate and Sucrose requires other ingredients and equipment and I don't even know what it's used for any more.
A normal SRB Solid Rocket Booster has a cone shaped, hollowed out area at the base, this facilitates a quicker, easier and more complete burn. To get this I just used the nosecone that came with the model rocket, just take it off, turn it around and plug the end of the cardboard tube as shown in the second picture.
Now you need to pack the fuel into the tube. I used a Popsicle stick, yes it's low tech but it works so what the heck. In order to remove the nosecone I had to twist like I was unscrewing a lid, the fuel will want to stick to it so you'll want to clean the nosecone off before you put it back on the top of your rocket. Now comes the moment of truth, I was very lazy and just stuck the nose of the rocket in the ground as you can see above.
Now, as I mentioned before, I chose Potassium Perchlorate because it's one of the more stable fuels you can use. So you're going to have to work to light it, I just used my pocket torch but a kitchen lighter and a little patience will get it. You may get a few false starts depending on how much water is left and how well it's mixed.
But when it all goes you'll get a good hot burn. I'm sorry my pictures aren't all of the same chamber, but all of these are of the same fuel mixture we've been talking about so at least you can see that. The flame in the picture looks red but I can promise that in person, it's more purple than red.
Well I want to thank you for reading this. I know it's certainly not practical, but if space has grabbed you like it's grabbed me, this is still a cool experiment, this fuel actually sent up our early sounding rockets and you just made it at home and lit it.
That to me was a lot of fun. As mentioned earlier I'm working on a Hybrid Rocket Engine at the time of this writing and will be testing it on the family farm in a month or so. I'll try and be sure to get a lot of photos and videos and make sure they get posted here. If your interested in that or have any questions just PM me and I'll try and reply quickly. I got a lot of black smoke and not much flame: There was something is the mixture that shouldn't have been, you either used too much Karo or Syrup or something else contaminated your fuel.
When I try and light it it will just spark occasionally but never catch :Your fuel is either still wet or was not mixed well enough. If you think it's just still wet, let it sit somewhere dry, away from things that can catch fire and away from things that can start them.
When you do light it, be VERY careful, I've never had this problem but some people report that it can burn violently and dangerously if you pack it in then let it dry too much.
Question 1 year ago on Step 6. Doesn't combustion of sugar with potassium perchlorate create potassium chloride? Or does the KCl decay further to produce thrust?
If you want reliable rocket engines that can fly hundreds of feet check out James yawn's internet page about making rocket engines! Cool instructable. Introduction: Simple Solid Rocket Engine. Here are the main types of rocket engines: Solid Fuel Engines: These are what we're looking at, they are by far the simplest and easiest to get your head around.
Here's the very basics of how a rocket works: A rocket works by burning a fuel to create exhaust, it's the release of this exhaust that generates the thrust that pushes the rocket skyward. Here is the list of items required for this project: A double boiler: I don't own one so I improvised one as you can see above, just a large pot, half filled with water and another bowl floating in the water. Ratios: Rocket fuel mixtures are given as a ratio usually, this ration is a weight ration, not a volume ratio.
The Ratio we want is as follows: Sugar Alright, now it get's interesting. I have the pictures above in order of the steps to follow. Now you have something that looks like the last picture. And now we get to have some fun.
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