Motor Designation says a lot... or not?

[strudleman]

Hey guys, I'm just getting into HPR (got lvl 1 this past weekend) and I've noticed a talent a lot of the old timers had.

By looking at a motor, they know it's style of performance. They know if it's a short burn, long burn, etc. For instance, I asked the vendor for a large I motor with a short burn time and he handed me the AT I-357T.

Is this just experience talking? He's seen enough motors to just 'know' how they perform? Or is there something in the designation, where he can look at a motor he's never seen fly, and know this sort of thing?

 

[r1dermon]

you can sortof tell by the letter, which gives the impulse range, and the average impulse. like if i have an E30, a 100% E motor is something like 40Ns of total impulse. therefore an E30 is going to be one powerful E motor, it will burn a little more than 1 second because its average is 30Ns, so every second it burns 30Ns of thrust, therefore it will burn for another 1/3 second more than the first second so that it can reach 40Ns of TOTAL thrust. like, if you wanted a LOOOONG burn J motor, you wouldnt go with a J1200, you'd go with a J150 or something like that. because that means for every second of burn time, it burns 150Ns of thrust, and so to reach its PEAK total impulse for a J motor, it would have to burn for something like 11 seconds, in that range. if i had an E60 however, that would tell me that it doesnt burn for a full second, because an E only has 40Ns of TOTAL impulse. thats 40newtons per second of burn time. so to have 60 newtons, it would have to burn for less than a second. and if it burned for a full second, then it would be an F motor. if you know the impulse range of the letter designations, its not that hard to figure out how long the motor will burn for.

 

[strudleman]

Wow, that's interesting. I don't think I fully understood everything you said, but I got enough out of it to start doing some research and learning.

Thank you!

 

[r1dermon]

dont look at it as how much power the motor has, look at it as time elapsed. so say i light off an E motor, that E motor burns for 4 seconds and is a 100% E motor, that means the E motor has 40newtons of total thrust. and if it burns for 4 seconds, then we know its an E10. now take an E40. its got 40 Ns of TOTAL impulse, JUST like the 1st motor. that means it does the SAME amount of work as the E10, just in 1/4 the time. however we can tell that since its an E40, it only burns for 1 second. because if it burned for more, then it would be more than 40 Ns of total impulse and it would be an F motor. once you understand, its really easy to apply.
i'd go online and check out some numbers, like the power ratings of each letter, then check out some popular reloads and try to guess what the burn time is by looking at the letter and the average thrust.

 

[strudleman]

Okay, I'll take the AT I-211W

Here's the info from Aerotech's site:
RMS-38/480 I211W 460 N-sec

Burning 211N per second, the I211W should burn for 2.2 seconds.


Another example would be the I357T that I just launched this weekend.
Info from AT's site:
RMS-38/360 I357T 350 N-sec

Burning 357N per second, this motor should burn for .9 seconds.

So if all of my math is correct, I guess a good rule of thumb would be:

Burn Time = Total Impule / Impulse per second

How'd I do?

 

[r1dermon]

good. thats all that there is to it. congradulations, you're now a certified rocket scientist. the certificate will be mailed.

 

[strudleman]

Haha

Thanks for the help. I can't wait to get back to the range and show off my new found knowledge to my fellow rocketeers

 

[r1dermon]

i've heard awesome things about the I357, im going to go for my lvl 1 cert next season, since this season is over on saturday for CMASS. probably going to use an H128 in a PML sport rocket of some sort. i WAS going to use the I357 on a LOC warlock, but i decided to go with a smaller rocket. and the I would put the rocket i have in mind well over 4500ft. so thats not an option. but i will definately be burning that I357 in another guys rocket on saturday. i love that 38mm set. got a deal on it, can't wait to stretch its legs. hopefully i can use the 480 casing, I300 maybe, next season. something with some POWER!!!

 

[rstaff3]

The I357 is a cool motor and its high average impulse will get a rocket moving...but in actuality it is a SMALL I motor.

 

[strudleman]

I launched my Amraam 3 on the I357T this weekend. It was an a mazing launch! Superfast takeoff, plenty of altitude. I had planned on using the I211W on my next flight, but now that I can read these motors a little better, I think I'll use either the I284W(2 sec burn time, 590 total impulse) or the I195J (2 1/2 second burn time!)

Ahh, motors just got 100 times more interesting

 

[r1dermon]

yeah man, its really exciting when you can read the motors and decide based on the motors numbers wether you want that motor for a high speed super fast flight, or you want the lower average thrust motor for the slow high flights. like apogee's motors. they make an E6, very low average impulse, however, it burns for 6 seconds!!! and the F10, which burns for 8 SECONDS!!!! sends their little aspire mpr bird to over 1 mile.

 

[DynaSoar]

Originally posted by strudleman
Hey guys, I'm just getting into HPR (got lvl 1 this past weekend) and I've noticed a talent a lot of the old timers had.

By looking at a motor, they know it's style of performance. They know if it's a short burn, long burn, etc. For instance, I asked the vendor for a large I motor with a short burn time and he handed me the AT I-357T.

Is this just experience talking? He's seen enough motors to just 'know' how they perform? Or is there something in the designation, where he can look at a motor he's never seen fly, and know this sort of thing?

Some of both.

Within a given engine class, there's a range of numbers. Knowing at least approximately what that range is is a matter of experience. There is overlap in the numbers across classes (there's an F50 and a G35, for example).

But with those numbers, the bigger the number in a particular motor class (as compared to the other numbers within that same class) the faster burner it is. The more precise answer involves the area under the curve on a thrust-curve graph, but that's not necessary to rule of thumb figuring.

 

[Chuck Rudy]

Originally posted by strudleman
Hey guys, I'm just getting into HPR (got lvl 1 this past weekend) and I've noticed a talent a lot of the old timers had.

Was gonna chime in earlier, but you were asking for old timers and it left me out. So I let all the old heads do the talkin'.

 

[r1dermon]

lol, im 19 years old BTW. just to get that info out there.

 

[wwattles]

Now that you've gotten familiar with the basic mathematics of it, there are some other nuance-level things to be aware of.

First of all, in your research you probably saw some things called "thrust curves." Those are sometimes useful for picking out motors because they can tell you what kind of performance you'll be getting from a particular motor. For example, if you have a motor that has a sharp peak at the left side, you know it's going to give a good strong kick off the pad at the start - good for those heavy rockets that you need to jump-start to get them aerodynamically stable before they leave the rod/rail. More gradual curves will give you nice slow, graceful takeoffs, a very pretty effect for some models.

Second, you'll see a lot of stuff with different letters after the numbers. Things like "W" and "T". Those have to do with the propellant chemistry itself, and each refers to a "name" for the composition (White Lightning, Blue Thunder, Smoky Sam, etc.). Different compositions will give different performance characteristics, in addition to different visual effects. Smoky motors tend to be a bit slower, White Lightnings are have a bit more zip. Go hang out at the LCO/RSO table some time and just watch what each rocketeer brings out, and watch and listen to the different types. Eventually you'll be able to pick out compositions just by the sound/appearance.

Third, and perhaps most importantly, ask your L2 and L3 compadres. They'll give you more info than you can ever imagine, based upon their experience.

WW

 

[r1dermon]

absolutely. talk to as many people as possible. hang out with them at the high power pads as they set up. ask them whats a good motor to send your lvl 1 bird up on. you'll get so many answers your mind will warp. lol. you'll also learn a ton about other motors, not just aerotech. ellis mountain, hypertek. hybrid motors are the new thing.
oh, its also a determining factor in picking your delay. if you have an E30 which is a high thrust E motor, and you put it in a small dink rocket, you're going to want a really long delay. BUT, there's another factor, if you put that E motor in a large rocket which perhaps thats the SMALLEST recommended motor, then you'd want a really short delay. but you'd want that high thrust E because it will get it off the pad and stable and perhaps a lower E wouldnt be able to provide the thrust required to get that baby moving.

 

[strudleman]

You guys are awesome. This has been one of the most practical and informational thread I've read here on TRF. Thank you all!

 

[rstaff3]

OK now that you are fully trained we expect lots of contributions...including PICS

 

[strudleman]

Oh you want pics? How about Video?

Fox 11 news was at our launch this weekend, and aired this video:
https://strudleman.com/ROCStock_XX_FOX11.mpg.mpeg (~13 Megs)

Despite my son and I both being on TV at the end of the clip, the true highlight was seeing my Level 1 CERT flight on TV!

Yup, in the first half of the clip, there are three rocket launches featured. A huge Hawk, a Red/White Amraam3, and a grey full-scale Amraam. My cert flight is the Red/White Amraam3, flying on a Pro38 H153. Yea, that's right. My rocket and I are famous! Oh yea, and my son too

 

[BlueNinja]

Wow, r1dermon, I never got that much into it. I just thought E30=fast, E9=slow.


Now I know, thanks alot for making me think

 

[r1dermon]

lol, until about 5 months ago, i wasnt really even aware of MPR and HPR rocketry. so i decided to get into it. bought an E kit from estes, best kit i ever bought. the eliminator. that was the gateway. i read the whole info section of the estes catalog, then i did some research on the aerotech website. decided to apply it a little bit deeper, and here i am. 5 months ago i didnt even know i could buy an F motor. lol. now im getting my CERT next season and i just purchased a 38mm set. its really interesting stuff. and its really cool how you can tell pretty much how a motor will perform just by checking out its numberings. I LOVE ROCKETRY!!!!!

 

[rstaff3]

Originally posted by strudleman
Oh you want pics? How about Video?

Fox 11 news was at our launch this weekend, and aired this video:
https://strudleman.com/ROCStock_XX_FOX11.mpg.mpeg (~13 Megs)

Despite my son and I both being on TV at the end of the clip, the true highlight was seeing my Level 1 CERT flight on TV!

Yup, in the first half of the clip, there are three rocket launches featured. A huge Hawk, a Red/White Amraam3, and a grey full-scale Amraam. My cert flight is the Red/White Amraam3, flying on a Pro38 H153. Yea, that's right. My rocket and I are famous! Oh yea, and my son too

Sweet, a celeb

 

[edwardw]

When your choosing a motor for a rocket be sure to check the thrust curve. I have a motor (EX) that is a J850. Now the common 5:1 rule would say that the rocket could weigh 38 lbs and safely lift off (850 N = 191 lbs /5 =~38 lbs). Now if you look at the thrust curve in the first 1/2 second the motor doesn't go above 400 N in thrust. So in reality you need a vehicle less than 18 lbs if you want it to lift off quickly and not burn on the pad for a couple seconds. The thrust profile is highly progressive - meaning that ending thrust is greater than initial thrust. The max thrust peaks out at over 1900 N so that skews the average thrust (J 850).

Edward

 

[North Star]

Originally posted by r1dermon
i WAS going to use the I357 on a LOC warlock

The Warlock is a good example to show the differences in performance for - say - the I357T and the J350W.

I357T ....350Ns lifts my 11lb Warlock to 512ft with burnout at 130ft
J350W ....700Ns lifts my 11lb warlock to 1181ft with burnout at 465ft

Average thrust is about the same but the J (at twice the power/burntime) gets over 3 times the height before the fire goes out. For interest the I211W fits about halfway between the 2 ... not as easy as it first sounds izzit?

I have only flown one I357T and I was surprised (even after running a flight sim) that the power cut off very quickly after a very fast launch to leave the rocket (5.6" scratchbuilt - Magnum sized) hanging in the air at quite a low altitude. End result was fine but a bit of an Ooooh moment

Calculations courtesy Alticalc

 

[North Star]

Warlock on a J350W

 

[r1dermon]

god, thats a sweet rocket. i WAS going to use it for my lvl1 but i've decided to go for a smaller rocket. maybe for my lvl2, i'd rather have the flexibility to launch it on a bunch of different motors when i get it, instead of being restricted to high impulse I's.

 

[North Star]

I just love the shape and size of the Warlock. My only regret was building it stock (more or less). I've since cloned it using a 54mm mmt and G10 fins, but it was the ill fated Wizz-Ard and was destroyed following a Pro 54 K570 cato.

Not to be downhearted I've started a PML parts - based clone and this will have a 75mm mmt ... might as well be prepared to expand the flight envelope

 

[r1dermon]

lol, a warlock breaking mach is truly a beautiful thing.