Help on a new project

[Handeman]

Ok, did you mean that all those prices just listed are ONLY the reloads. I still have to purchase the casing and all other requirements? If so, what is the estimated price range for the same motors(only casing and hardware)? As for the certification, I will purchase the Black Brant and go for my Jr.cert, instead of the 4 G motor project. Just out of curiousity, what is the price for an m motor. Also what is the biggest motor out there... Z?

Yes, those prices are for the reloads only. You still need to buy/borrow the casing. Of course if you borrow a casing and CATO, you bought it anyway.

The largest commercial motor is an O8000 by Cesaroni for their Pro150 casing. If you make your own motors, they sky's the limit.

 

[4G's]

Ok, so it will be a little pricy for me, but nothing that bad...One thing I found out real quickly about model rocketry is: Things add up...fast. Oh, and speaking of "the sky's the limit" here is something I thought was the coolest thing ever: ( Many of you might have already heard or seen this video) https://www.youtube.com/watch?v=bj4lj6YSwzg&feature=channel_page .
I will beat that record someday...
Steve's: 36ft tall, 8 N and 1 P motor, 3000-5000 ft.
Me: 40 ft tall, enough propellant to lift it, destination...Space!:shock:
Im thinking big haha

 

[4G's]

Oh, in regard to red arrow hobbies, I actually have a lot of interest in that site since they seem to have everything I need. For the Black Brant it recommends motors: g64, h128, h180, h220,h238,h123...what type of "I" motor should I put in that? (Can you use an I for level 1 cert?) I am interested in the aerotech engines: https://www.redarrowhobbies.com/aerotech_38mm.htm . Thanks for all the help guys..you're getting me started and on my feet here...I cant thank you enough.

 

[cjl]

For that size rocket, you could easily fly an I211, probably an I284 as well if you built it well. In fact, most of the AT motors up through a 38/600 casing would probably work, with the exception of the warp 9s.

 

[4G's]

Ok, I looked at Red Arrow, and found a 38/600 MOTOR W/CLOSURES AND RING. Is this the correct size? Here's the link to all the sizes: https://www.redarrowhobbies.com/aerotech_rms_hardware.htm . Also what size reloads can the 38/600 hold, H and I maybe? And also, what do the numbers mean like 38/600, ect.? This is a whole other realm for me, going into HPR.

 

[hardinlw]

While there are J reloads in 38mm, this particular rocket may not be able to handle them. The Aerotech J-350 is pretty long and there may not be enough room for it in this kit. You should check that out. Also, the J impulse may push the rocket to speeds that it will not survive. I've built a lot of Public Missiles kits (including the 2" and 4" BBXs) and some of them require additional strengthening (fiberglassing) to take some of the larger engines that will physically fit in the mount. Another consideration with the larger engines is whether you will need nose weight to keep it stable with the big engine installed. At first, I loaded the NC with sufficient lead to make the rockets stable with the biggest engine that would fit and then almost never flew it on that engine because the fields I flew from were not big enough. Now, I build to the normal engine I would use and if I want to fly a big one that requires nose weight, I'll buy another nose cone and ballast it appropriately.

 

[Handeman]

The 38/600 casing uses all I reloads.

Here's a link to the Aerotech RMS External Dimension drawings.

Here's a link to the Aerotech 2009-2010 Catalog in pdf format. I highly recommend downloading a copy and printing at least the SU and RMS motor pages, 4 - 12, as a quick reference. There's a huge amount of very useful info including weights and thrust curves.

 

[MarkM]

Ok, I looked at Red Arrow, and found a 38/600 MOTOR W/CLOSURES AND RING. Is this the correct size? Here's the link to all the sizes: https://www.redarrowhobbies.com/aerotech_rms_hardware.htm . Also what size reloads can the 38/600 hold, H and I maybe? And also, what do the numbers mean like 38/600, ect.? This is a whole other realm for me, going into HPR.

I would go with either 38/360 (small I loads) or the 38/480 (mid-I loads). The 600 accomodates motors that are near full I. I suggest you start with something smaller for your first HPR loads (maybe even the 38/240 which uses H motors). Once you have the closures all you need is right size casing so its reasonably inexpensive to add larger motors to arsenal with minimal investment in hardware. Check the Aerotech website & their catalog. Only certain reloads fit in certain casings. You CANNOT put a smaller motor into a larger/different casing than it was designed for.

The case numbers, such as 600, present the approximate total impulse (in Ns) that motors which fit that casing have. The total impulse will vary depending on propellant type; some types give more impulse than others (due to differences in Isp).

 

[4G's]

Ok, thanks for the pdf catalog handeman. I have another question. What is the difference between a jr level one and normal level one? they can both use H and I motors right? Anyway, back to the motor. I think I should go with a lower impulse and longer burn since this rocket is quite tall(82") and slim(3") along with the fact that it recommends G and H motors and I am going to use a small "I". I will go with the 38/360(like Markm recommended) since I need a smaller impulse for this rocket. (If there is to much impulse, wont the rocket do a 180 in midair and fall apart?) Also, Markm, I didnt quite get what you were explaning about the different sizes of casings. (If I buy a 38/360, will I have to put down another $100 for a 38/600, or can I buy a seperate piece(s) to accomidate the change? if so what is the piece(s) called? Iam going to purchase the aerotech 38/360 MOTOR W/CLOSURES from redarrow...does that come with everything I need to get going? besides the propellant. Correct me if I am wrong with anything here.

 

[MarkM]

Ok, thanks for the pdf catalog handeman. I have another question. What is the difference between a jr level one and normal level one? they can both use H and I motors right?

A jr L1 needs basically a sponsor who is the flier of record. A jr L1 cannot purchase the motor, cannot handle the motor, cannot assemble the motor and cannot install the motor in the rocket. You can observe/supervise, but anything having to do with motor handling must be done by a standard L1 or higher. In terms of which motors are allowed, there are no differences.

Anyway, back to the motor. I think I should go with a lower impulse and longer burn since this rocket is quite tall(82") and slim(3") along with the fact that it recommends G and H motors and I am going to use a small "I" <SNIP>
(If there is to much impulse, wont the rocket do a 180 in midair and fall apart?)

You're confusing impulse with thrust again. Just because a motor has a longer burn does not mean it will have lower impulse. It depends on the design. A high impulse motor will not necessarily damage a rocket. However, a high THRUST motor can depending on materials used and construction quality. You need to get impulse, thrust, burn time and their relationships clear and what the motor designation means. The Aerotech catalog does a good job explaining this.

Also, Markm, I didnt quite get what you were explaning about the different sizes of casings. (If I buy a 38/360, will I have to put down another $100 for a 38/600, or can I buy a seperate piece(s) to accomidate the change? if so what is the piece(s) called?

You only need the additional casing...the tube (~$40 depending on size). The tube is called the casing; the tube plus closures is called the motor or complete motor. The propellant that fits into the motor is referred to as a reload.

I am going to purchase the aerotech 38/360 MOTOR W/CLOSURES from redarrow...does that come with everything I need to get going? besides the propellant.

Yes...except you may still need a seal disk. Some reloads require an aluminum seal disk. I can't remember if a seal disk comes with the 360 motor as I bought my AT hardware as a set with several casings and it included the seal disk. Make sure the 360 motor comes with the seal disk; if not, I suggest getting one ($10) to be sure you have it in case you need it.

 

[4G's]

Ok thanks for all the input Markm. Yes! I definately need to learn the difference between thrust and impulse, as well as many other terms. Its just like not knowing the difference between speed and velocity..forward and straight, etc. And I wouldnt mind someone else assembling the motor. I would rather have if "professionally" done anyways. In regards to the "complete motor" I will make sure it comes with a seal disk; if not, I will make sure to get one. Also, I am trying to shoot for an ROC launch in late July, since I got the OK from my dad. I might actually get to meet one of you there personally.

 

[cjl]

I'm pretty sure the 360 doesn't have (or need) a seal disk. I believe it is only needed for the longer motors (I can't remember if the 480 needs it, I know the 600 needs it).

 

[MarkM]

I'm pretty sure the 360 doesn't have (or need) a seal disk. I believe it is only needed for the longer motors (I can't remember if the 480 needs it, I know the 600 needs it).

Yeah..you're right the 360 doesn't require the seal disk (checked the AT site). I just couldn't remember...it's been a few years since I've flown an AT load and wasn't certain if the new Warp 9 loads might've needed it. I knew the 480 case needed the seal disk as I've flown a few I211's which required it. It never hurts to have the seal disk. Besides, once you go to the motors requiring the 480 case (or above) you'll need the disk anyway.

 

[powderburner]

4Gs,

Way back in your first post in this thread you asked about fin design. There are a couple ways you can go on this, ranging from copying someone else's fin design (if you see one you like) and adding nose ballast (as required) to move the center of gravity forward far enough, all the way up to doing everything scientifically/computationally by using an analysis tool like rocsim.

(And if you do want to use rocsim, there is a free trial version on the Apogee website at: https://www.apogeerockets.com/RockSim.asp)
You can use their free trial version, or you can spend $100 and buy the software, or you can use other methods...as in the following.

Fin size needs to be big enough (individual fin size & number of fins) and far enough aft on the rocket to result in an overall center of pressure (c.p.) that is one to two "diameters" behind the overall center of gravity (c.g.). The basic diameter or "caliber" of the rocket body is used as a reference, and the one to two calibers of stability margin is sort of a rule of thumb. When making this comparison, the c.g. needs to be determined with the loaded motor in place, as well as all other components that will be onboard during launch. A short stubby rocket design might get by with a bit less stability margin, but an excessive margin (three or four calibers, or even more) can turn into the wind on windy days, reducing altitude and potentially leading to an early descent and crash if the recovery system is not deployed in time.

You can estimate the overall c.g. on paper, knowing the weights of all components and their locations. (If you want help with that, PM me.) Or you can build the rocket, load it as though you are about to launch, and find the actual longitudinal c.g. by balancing the rocket on your finger.

You can estimate the overall c.p. by several methods. Don't be afraid of them, they might look scary but they are really pretty simple. Check out the Barrowman c.p. equations at a website like: https://my.execpc.com/~culp/rockets/Barrowman.html
(Again, if you want help with this stuff, PM me.) You can also use free online methods like VCP at: https://v-serv.com/vcp/
When you are done locating both c.g. and c.p. you can compare how far apart they are to see if you have the proper stability margin for your design.

At this point, if your design has too much stability, you can play with selecting fewer or smaller fins, or moving them forward (slightly), and re-run the numbers. Or if your design does not have enough stability, you can play with larger fins, or more fins (there is nothing wrong with using five, or six, or 34 fins). This design process is usually one that requires a few cycles of iteration before an "optimised" design comes out.

If you have one design "look" that you are locked in on (in other words, maybe you don't want to change the fin design) and you still need to adjust the stability margin, then you may just have to use some ballast. It usually doesn't take much ballast weight to adjust the c.g. position if you locate the ballast near the nose or tail, so it will not impair the rocket's performance too badly. Many rockets use ballast to adjust stability. (If you want some help with ballast calculations, PM me.)

Bottom line: there is no single fin design that is "best" and you have a wide range of choices for the size, shape, and location of fins that you design. But you have to check that the overall design will indeed work properly.

I hope some part of all that is useful to you-

 

[jadebox]

Originally Posted by hardinlw

The FAA has a total propellent weight of 125g as one of their limitations. That would be two G engines. The impulse of the typical G engine is 100 N-s impulse which means that two would be on the order of 200 N-s which is above the 160 N-s limit for the G impulse class. There are three limits that you must stay under :

125g total propellent weight
160 N-s total impulse
80 N average thrust

Going over any of those puts you out of the model rocket category. With black powder engines, 125g of propellent would still be under the limit.

And 4) 3.3lb total rocket weight - including motors

And, just to be complete ...

5) Including any airframe parts of ductile metal.

-- Roger

 

[shreadvector]

And, just to be complete ...

5) Including any airframe parts of ductile metal.

-- Roger

The above post quoted an incorrect limit for a Model Rocket (in the portion quoted from a previous post and dropped by the software when I made this posting, but you can see it directly above here). A Model Rocket can have up to 2 G motors of total impulse installed in any combination of motors as long as ALL of the motors are Model Rocket Motors and the the total propellant limit is observed.

I always suggest that rather than retype this information and risk the possibility of making mistakes and propagating errors, simply refer people to the pre-existing and complete info. I prefer to not exerpt and quote only small parts of the NAR MRSC. I provide a link to the entire code on the site where it resides at the NAR.

Here are those links again:

https://www.nar.org/NARmrsc.html

https://www.doug79.com/stuff/HPR_metric9c.pdf

 

[jadebox]

The above post quoted an incorrect limit for a Model Rocket (in the portion quoted from a previous post and dropped by the software when I made this posting, but you can see it directly above here). A Model Rocket can have up to 2 G motors of total impulse installed in any combination of motors as long as ALL of the motors are Model Rocket Motors and the the total propellant limit is observed.

That was what I was looking for when I came across the statement that the use of metal can define a rocket as a High-Power Rocket. I was sure that you're allowed higher total impulse when clustering so I searched the NAR site and couldn't find any mention of it. But didn't think to look in the Safety Code.

-- Roger

 

[mkadams001]

I think that handeman stated this first and it bears repeating; that 4g should spend some time flying mid power before jumping directly into high power. I love the enthusiasm but, it is kinda like going from a go kart into Formula 1 in one step. Spend a little time flying a few rockets using F and G reloads, visit with the high power guys and watch them set up and fly. Then you will get a clearer idea of what your personal goals are for the sport and the experience you need to move up to the next level.

 

[4G's]

I agree with you there. I should maybe try a a few F and G engines, but this is is just one of those hobbies that I want to get good at fast..in this case, flying HPR. I will still go with the Black Brant..since it can be flown on G, H and I, as some of you have stated. This will allow me to use midpower reloads, get acquanted with them, then possibly move up to HPR.

 

[4G's]

I just finished my AMRAAM..I think its 1/3 scale(54in tall, 2 3/4 in dia). I attached a picture. I didn't really feel like following the paint scheme so I made up my own.

 

[cjl]

That's a bit over 1/3 scale, yes (full scale is 7 inch). That paint job looks nice btw - I like it .

 

[4G's]

Ok cool. Thanks. Theres actually a dark blue strip half way down the rocket..the picture just didnt show it.

 

[bobkrech]

Any 4 motor cluster will make a lot of noise and flame. To get back to your original question, why don't you look at a LOC Precision Viper IV kit https://shop.rocketsbymelissa.com/product.sc?categoryId=13&productId=101 It's available from many on-line suppliers for $40-$45 and is all set for 4 motor clusters and has an unloaded weight of only 17 ounces.

You can fly it on (4) D12s for about $12 a launch which won't break the bank by give you clustering experience. After you get the hang of it you can use 24 mm AT motors.

Provided you keep the total propellant weight below 125 grams or 31 grams per motor, you don't need certification, or anything else.

Bob

 

[4G's]

Hey thanks Bob..I like the rocket a lot, Ill keep it it mind.

 

[MarkII]

I apologize for jumping into this conversation late - I only just now found it.

4G's - you asked a little while ago about the difference between thrust and impulse. One way to think of it is this:

1. impulse is how much "push" the motor has in total (the total amount of power that the motor puts out over the course of its burn). The measure of impulse is always in terms of the total amount of power in the motor. In solid propellant motors, there is no such thing as "peak impulse," for instance - impulse is always about the total amount of power that the motor puts out.
2. thrust is a measure of how "hard" the motor is pushing. This can vary over the course of the burn. You can talk about the motor's "initial thrust," its "peak thrust," its "sustained thrust" and its "average thrust," among others. These are all measures of how hard the motor is pushing at certain times. The "average thrust" is how hard the motor pushes, on average, over the course of its entire burn.

If you look at one of those performance graphs that accompany most motor certification documents, the vertical axis is the amount of thrust, and the horizontal axis is time. The line that is plotted is the amount of thrust that the motor is putting out at any moment during its burn, starting with ignition at the left end and burn-out at the right. Different motors have different "performance curves" based on such things as the specific mix of chemicals in the propellant, the shape of the motor's nozzle, and where in the grain the propellant is ignited, among many other factors. The thrust that the motor is putting out is a point on that line corresponding to a particular moment in time. Now if you were to calculate the total area underneath that line, you would come up with the total impulse of the motor, which is the total amount of power that the motor puts out over the course of the burn.

Does this make it any more clear? (Also, stay tuned for any corrections to what I just wrote above by other people participating in this conversation... )

MarkII

 

[MarkII]

Regarding designations like "38/240," "38/360," etc.

The first number is the motor's outside diameter (OD) in millimeters. The second number is the total amount of impulse that the motor is designed to put out. This second number requires some explanation:

With solid propellant motors, whether they use black powder or ammonium perchlorate composite propellant, the total impulse of the motor has much to do with the amount of propellant it contains. (There are other factors, too, but this is the main one.) Aerotech and other companies mold their propellant in standard sized slugs, or "grains." The particular sizes of the grains vary with the diameter of the motor. Using Aerotech as an example, they designed their 38mm diameter line of RMS motors to take between 1 and 9 grains of propellant. The size and number of grains in their line of RMS motors varies a little bit from one diameter to the next. (Other makers of reloadable motors do essentially the same thing.) The variation in impulse of the different motors in a given diameter that a company makes basically comes down to how long the motor is.

Take a look at this diagram of a 38mm diameter motor. The wide, cross-hatched area in the middle of the side view of the motor represents the propellant grain. (The horizontal white area on the middle of it is the propellant core, a channel cut through the middle of the grain.) The casing of the RMS 38/120 is 3.25" long, and is designed to take one propellant grain. Now, all other factors being equal, there is only so much impulse that can be packed into one grain of APCP. That amount maxes out at about 120 Newton-seconds for a 38mm diameter grain, so Aerotch calls their one-grain RMS motor that is 38mm in diameter the RMS 38/120 motor.

Now take a look at a diagram of a longer motor. Look at the cross-hatched section again. Remember that this represents the propellant. Notice that instead of just one cross-hatched section, there are three of them, all in a line. That shows that this motor, whose casing is 7.0" long, is designed to hold three grains of propellant. If one 38mm diameter grain of propellant maxes out at about 120 N-s, then three of them maxes out at about 360 N-s. Therefore Aerotech calls this motor their RMS 38/360 motor.

You can continue to see the relationship by counting the grains in the 38/240, the 38/480, the 38/600, the 38/720 and the 38/1080 RMS motors. The total amount of power that the motor is designed to put out (its total impulse, remember?) is basically determined by how many propellant grains it can hold, which is a function of how long it is. So if you see a 38/600 and a 38/720 for sale on a vendor's website, you will know that the 720 motor will be the longer of the two, and will also be the more powerful one.

MarkII

 

[cjl]

Yes, although the amount of impulse the case holds isn't exact. Due to differences in pressure, propellant efficiency, and grain dimensions (among other things), the loads for a given case will vary in total impulse (though they will all be somewhat near the case's rated value). For an example of this, the 38/360 holds loads varying from 280Ns total (the H112J) all the way up to 383Ns (the I49N).

 

[MarkII]

Yes, although the amount of impulse the case holds isn't exact. Due to differences in pressure, propellant efficiency, and grain dimensions, the loads for a given case will vary in total impulse (though they will all be somewhat near the case's rated value). For an example of this, the 38/360 holds loads varying from 280Ns total (the H112J) all the way up to 383Ns (the I49N).

Yes, I agree. Those numbers (120, 240, 360, etc.) are essentially just ballpark approximations, rounded off to make easy to follow multiples of each other. The precise value in the number isn't as important as is the relationship of each case's number to that of its siblings in the same diameter "family." Aerotech's numbers for its line of RMS motors simply represent a naming system, and are not absolute limits. (I did throw in the "all other things being equal" qualifier, didn't I? )

Cesaroni Technology, Inc. (CTI), on the other hand, makes their reloadable motor casing sizes much more obvious. Instead of naming them by impulse levels, they simply name them by the number of grains that they hold. So, for example, they offer a Pro38 1-grain motor, a Pro38 2-grain motor, a Pro38 3-grain motor, etc. But this system isn't as meaningful as it once was, because with the addition of multiple types of reloads and propellant mixtures that CTI has added to their line in the past couple of years, knowing the grain number of the case doesn't tell you all that much anymore.

MarkII