Model Rocket Launch Igniter Diagram

Model rocket motors, also called "engines", are what make a rocket go. The propellant, a slow-burning delay cap, and then black powder used as the ejection charge. These are all wrapped up in a casing that is made of paper, plastic or aluminum. Motors are all single-flight use, though the casing may be reusable.

Model rocket motors are made up of a fuel and an oxidizer, this is the propellant. These two ingredients can vary but both are required to produce the appropriate thrust. The most common model rocket engines are made of black powder and have only three ingredients: charcoal, potassium nitrate, and sulfur.

Read on, or click the jump links below for more information.

• What do all the numbers and letters on a motor mean?
• What is a "Black Powder" vs "Composite" motor?
• What is a "Low-Power" vs "Mid-Power" vs "High-Power" motor?
• What is a "Single Use" vs "Loadable" vs "Reload" motor?
• What are the differences between the rocket motor brands we sell?

To read model rocket engines, you just need to understand the simple code they use in the manufacturing process. It consists of a letter and two numbers. The letter, at the front of the code, corresponds to the total amount of energy contained in the motor, this is measured in Newton-seconds. The first number, directly beside the letter, is the average thrust of the motor. The higher the number the faster it burns through the propellant, the more thrust per second. The third number, located after the dash, represents the time delay from ignition to the time the ejection charge fires and deploys the parachute.

Let's take an example so you can see how to read the charts.  We'll look at AeroTech's"E28-4T" motor.

Breaking it down, we have four bits of information. "E," "28," "4," and "T"

Power: The first letter

This, "E," in our example, is the power level classification of the motor, measured in impulse of Newton-seconds.  If you look at the chart at the right, you can see that "E" motors range between 20 and 40 Newton-seconds of "Total Impulse" Each letter classification's maximum total impulse is twice that of the prior. For a full chart of impulse classification levels, check out the Wikipedia page.

In our example, the E28-4T has 39.69 N-s of total impulse per the manufacturer, so it would be considered a "Full" E motor since it is so close to the maximum of 40 N-s.

Average Thrust: The number after power

This is the average thrust level of the rocket measured in Newtons, each unit of which is equivalent to 0.225 pounds of force. That means in our example, the motor has an average thrust of 28 Newtons.

Delay: The value after the dash

OR

This is the length of time in which the "delay charge" burns before it allows the flame to reach and ignite the ejection charge, which deploys your parachute. Delay allows time for the rocket to coast and slow down so the parachute doesn't rip out of the tube at ejection. In our example, the rocket would coast for 4 seconds before deployment.

Most single-use motors give a hard number for the delay, and you will need to purchase the appropriate one for your kit. Some loadable, larger single use or reloadable motors will often have a maximum delay that, with a specially designed tool, you can use to shorten the delay to what is best for your rocket. Look at the "Max Delay" statistic for that particular motor.  If the delay is missing but there is a letter such as "M," it stands for "Medium" which is typically around 10s.  If it is an N/A, or not listed, you cannot adjust the delay. A "P" stands for plugged and requires electronics to deploy the parachute because there is no ejection charge in plugged motors.

Color:  The letter after the delay, maybe.

 OR

This notation is optional, and depending on the brand, may actually come before the delay indicator, such as with an H123W-M.  This denotes the propellant type, or color, of the motor. The exception to this is Estes, who uses a "T" to denote a "Tiny" 13mm motor.

Black powder motors do not have color choices, whereas composite motors have a variety.  Each brand uses a different lettering scheme.  Our example is an Aerotech motor, and the "T" tells us that it is a Blue Thunder propellant. Propellant type doesn't affect the way your rocket flies, it just affects the way it looks at takeoff.    For more information on motor flame-color, see Peak-of-Flight Newsletter #217.

At Apogee, we sell rocket motors of two different types:  Black Powder and Composite.   There are others available, such as Hybrids (liquid and solid combination), but we do not sell them, nor do we have the knowledge to give to you about them.

Black powder

Black powder is also called gun powder and has only three ingredients: charcoal, potassium nitrate, and sulfur. The advantage of black powder propellant is that it is cheaper compared to more exotic propellants. The downside is that it doesn't create a lot of energy per kilogram of fuel. The easy way to tell a black powder motor from other motors is that it comes in a paper casing. That is one reason it is so inexpensive compared to other fuels.

Pros:

1. Easy to come by. They can be found in nearly every hobby shop across the country, making finding the motors easy if you're in a time crunch.
2. Relatively inexpensive. The base components, clay, black powder, and paper (used for the casing) are all easily acquired and low-cost materials.
3. Easy Ignition.Black powder is rather flammable, so ignition is very consistent.
4. Easy to stage.  Black powder motors only require intense heat to ignite, so you can stage the motors without direct flames, such as with direct- or gap-staging techniques.
5. Ready to use.All black powder motors are ready to slide into your rocket and fly!

Cons:

1. Lower energy density.Compared to a composite propellant, you cannot fit as much oomph into a given diameter casing.
2. Can crack internal propellant if dropped.  Because the propellant is just hydraulically compressed black powder, if you drop the motor, it can crack.  Cracked propellant doesn't burn correctly (too fast) and the pressure increases in the wrong spots, potentially bursting the casing and thus ruining your rocket.
3. Limited sizes. The volatile nature of black powder, combined with the increased risk of cracking as the length and diameter increase, means that there is an imposed limitation on how big you can go.  It's just too risky to go any larger.
4. Shipping on larger motors is risky.Again, because of the volatile nature, some of the black powder motors require HAZMAT shipping, particularly those of E and F power.  All the motors on our site say if they require HAZMAT shipping, so pay attention when purchasing your motors.

Composite

Composite, basically, means that the propellant is a mixture of ingredients (fuel and oxidizer substances) that when mixed together, solidify by means of a chemical reaction, similar to a two-part epoxy or resin.  They can be ready-to-use "single use" style, or they may require assembly as a "reload."

Pros:

1. Higher energy density.The chemical composition is similar to those used by big rockets and shuttles. It has more than twice the energy density of black powder, which means you can fit a D motor's worth of power into 18mm, whereas black powder can only fit a B or C.
2. Composite material is rubbery, so very low risk of propellant fracture upon impact.Here's where the money saver kicks in.  The material is very resilient, so it will take the bashing of the shipping process, potholes on the trip to the launch site, and rolling off your prep table with stride.  This means safer launches and fewer catos and lost rockets.
3. Available in nearly all diameters and power levels.That rubbery, low-risk texture means that you can go bigger and better with the motors.  The safety factors of the composite propellants mean you can make, ship and fly motors that are 18mm, 38mm, 98mm and even bigger.
4. Optional flame colors.When mixing composite propellants, the manufacturers can add additional chemicals to create different colors of flame, much like they can with fireworks.  You're sure to please the crowd this way.

Cons:

1. More expensive than black powder.To get the higher energy density, the manufacturers need to use more expensive and higher quality components.  Also more expensive would be the heavier-duty casing used to contain all that extra pressure that makes your rocket soar.
2. Harder to come by in hobby shops.While most hobby shops you can find a small selection of composite motors, to get the full variety available you will need to shop online.  The amazing online selection of rocket motors (particularly at Apogee!) comes at a price of shipping, and the fact that we HAVE TO ship rocket motors by ground.  FIAA and other government organizations will not allow such flammables onboard an airplane.
3. Can be more difficult to ignite, particularly with staging & clustering.Composite motors require a direct flame to ignite.  While this is a great safety feature (as in, heat itself isn't enough, like it is with black powder), it does make things such as direct staging and gap staging impossible, as those methods use only the heat of the ejection charge to ignite the second motor.  You will need electronics to stage any composite motors in a rocket.   Similarly, clustering is possible, but you need to make sure all of your starters are properly inserted so that they ignite simultaneously and none of the motors have a delay in ignition causing your rocket to veer.

As mentioned in the previous section, the power of a rocket is denoted by the initial letter in the rocket's common name.  A6-4 has an "A" power, H255 has an "H" power.   The motor powers, A through O and higher are divided into three classes, generally indicating what sort of performance you will get.  There are some gray areas at the cusps of the classes, but general rule is as follows:

• Low-Power: A, B, C, D motors.  Typically 18-24mm.
• Mid-Power:  D, E, F, most G motors.  Typically 24-29mm.
• High Power: A few F,  a few G, all H and higher, all thrust higher than 80.  Typically 29mm and up.  Requires Certification and 18+.

The transition from Low to mid-power motors is a gray area.   There are some D motors that are considered low power, some high.  The key with low and mid-power motors is that these do not require any sort of training or certification to fly.  As long as the motor is a combination of having both a power of "G" or less and a thrust of "80" or less, you can fly it without certification.  A first-time flyer can fly on an F or G motor, but we recommend you work your way up and use larger motors as your experience provides.

High power motors, though, require certification.  Anything that is "H" or higher, or a fraction above a thrust of "80" will either require a certification through the National Association of Rocketry (NAR) or through the Tripoli Rocketry Association (TRA), or it will require a qualified individual to watch your flight to see if you retrieve it back intact and immediately ready to fly again.  For certification information, talk to your local rocketry club or visit one of the association pages linked above.   If you need to find a club, those registered with the associations will be listed on their sites.

The NAR runs a "Junior Certification" program, which allows 14 through 17-year-old rocketeers to certify and fly high power motors, but they are still required to have a parent or mentor over 18 purchase their high-power motors.  The TRA does not have a junior program, and all high power members are over 18.

Some model rocket engines are reusable however the propellant and oxidizer will always need replaced. There are three types of motors that Apogee sells:  Single-Use, Loadable, and Reload.  At the mid-power level, it becomes more common for motors to come in the loadable or reload styles, and high-power motors are almost exclusively reloads.

Single-use

• Cannot screw up in assembly
• Cheaper initial setup, as there is no casing to purchase
• More expensive in the long-run. If you'll be launching mid-power more than 3 times, it's a better investment to get a reload system.
• No casing to replace if you lose your rocket
• Available with both black powder and composite propellants.
• Easily found at hobby shops, at least in smaller sizes.
• Most (with a few exceptions on high power varieties) don't require age 18+
• No age requirement for low and mid power SU motors
• No control on delay times (with a few exceptions on high power varieties) -- Delays are pre-set, so you need to purchase the correct delay.
• Expensive to ship in larger diameters or lengths due to HAZMAT requirements (check motor info to see if required).

Loadable

• Composite propellant only
• Similarly priced to single use motors
• Designed to be shipped through the post office without incurring HAZMAT fees.  Basically, the post office has a maximum weight for individual, continuous propellant segment.  Loadable motors have their full propellant broken down into certain length slugs so as to qualify for non-hazardous shipping.   There is no restriction on the number of segments that can be shipped.
• Assembly required.
• Age of 18+ verification required (due to access to propellant itself)

Reloads

• Cheaper propellant means lower cost-per-flight.  You typically save $6-10 per flight.
• Requires casing purchase, so there is a higher initial investment.  That investment is paid off by cheaper propellants.
• Larger variety of options, particularly in more powerful motors
• When using AeroTech brand, you most likely won't have to pay for HAZMAT shipping (see the note about propellant segment length above)
• Assembly required, with AeroTech having more steps than Cesaroni
• Precise control over delay times (except if it's plugged).
• More difficult to find at hobby shops, often require a special order or online purchase.
• Age of 18+ verification required (due to access to propellant itself)

Apogee carries several different brands of motors: Estes, Quest, Apogee, AeroTech, and Cesaroni.

Estes

Estes motors are the most common, especially for beginners.  You can find these in nearly every hobby shop across the country, and even overseas.  Although readily in stock on our website, if you need a motor and cannot wait for ground shipping, you can very likely pick them up locally.    Most Estes motor are made with black powder propellant, though they do manufacture a few composite propellants in their "Pro Series II" line.  They range in size from 1/4A to G.

Quest

Quest motors are all black powder motors.  They are very similar to the Estes motors as far as performance goes.  People often prefer Quest motors to Estes due to the starters having longer tails and thus increased ease of use and reliability.   The starters by themselves may be difficult to locate due to low stocks, but Apogee almost always has the motors (which come with starters) in stock.

Apogee Medalist

Apogee has commissioned AeroTech to manufacture two specialty motors to meet demands in getting lightweight rockets to extreme altitudes.  They are identical to AeroTech in construction and quality.

AeroTech

AeroTech is one of the most versatile brands out there.  They are all composite style motors, but are available 3 different styles (Single Use, Loadable, and Reload) in 18mm D size and up.  When people are getting into High Power rocketry, they often want to know the difference between the two major dealers of high power motors, Aerotech and Cesaroni.  Pros and Cons are as follows:

• Readily available. Typically takes less than two weeks to order and receive out of stock items.
• While all 38mm and larger motors require HAZMAT shipping, there are options for certifying on 29mm motors that don't require that shipping method. Since we cannot ship HAZMAT motors to Hawaii, Alaska, Puerto Rico or other protectorates, these motors are your only options for getting your Level 1 Certification in those locations.
• You can use up to 3 casing spacers (one more than Cesaroni) to reduce the number of casings you need for a full arsenal.
• Getting the casing and closures can be more expensive than Cesaroni, but you have a number of options for forward and aft closures depending on your needs. If you need the basic set up of a casing, open forward closure and standard aft closure, be sure to get them all at once to take advantage of the combo discount.
• Assembly and cleaning of the motors are more time consuming. Since AeroTech motors ship piecemeal, it can help with shipping costs in some cases, but requires careful assembly before use. Since there is only a simple open-ended sheath around the propellant slugs, the inside of the casing collects more residue and must be cleaned thoroughly to prevent buildup and keep you able to slide the propellant kits in.
• AeroTech offers a few high power single-use motors. This means that there is no expensive casing to purchase and potentially lose. While they are currently only available in 38mm diameter, they can be a great option for nervous flyers or ones who aren't sure they want to dedicate themselves to a specific brand quite yet. Another great thing about the single-use motors is you don't have to clean out casings after every flight.

Cesaroni

Cesaroni is a Canadian company, and a prolific dealer stateside in high power motors.  All their motors are composite reload style

• Since Cesaroni propellant kits come mostly pre-assembled, you just need to the adjust delay, then slide the propellant into the Cesaroni casing. Easy peasy.
• There are fewer closures required for the Cesaroni system. No forward closure is required for any casing, and for 38mm motors, the aft closure is built into the propellant kit. Just slide in and twist into place. All other diameter Cesaroni motors require the purchase of a separate aft closure.
• Since the propellant kits are contained in an enclosed plastic sheath, you just need to slide that out, take a quick paper towel wipe to the casing and you're ready to load up for your next launch.
• You can often get fantastic deals from Cesaroni. If their Certification Special is inactive, you can buy the motor and the coordinating starter set, which includes casing(s), spacers, the delay adjustment tool at quite the discount from what it would cost individually.
• Cesaroni motors are imported from Canada, and if we run out, we might be out of that motor/casing/accessory for a while. We place bulk orders with them to save on shipping and import fees, so we only place orders ever few months.
• All Cesaroni motors are required to ship via HAZMAT (average $50 shipping cost), so it's best to order as many as you can at once since the fee is per shipped box, not per motor. Ordering with fellow club members is a great idea.
• There are often 7, 8, 9, or more motors that will work in each casing, depending on what you like.
• You can use up to two spacers in each casing so you really only need the 3-grain and 6-grain casings to get the most out of your Cesaroni collection.

Please remember that theCesaroni and AeroTech systems are not cross compatible. While you can use them interchangeably in the same kit, you cannot use, for example, a Cesaroni casing with an AeroTech propellant kit.