New CTI J145 Long Burn Skidmark

Very impressive flight of my Madcow Frenzy on Saturday to 2716ft. Rocket was 8.5lbs on the pad. The initial kick got it off the rail quick then settled into that nice long Loud 5 second burn. Very cool motor, the heat generated for that length of time singed the paint off the tail around the retainer. That will get some engine enamel. Otherwise, a cool motor! Definitely a regular for this rocket! Hopefully I will get the link to the video in the next couple days from the club videographer.

Can't wait to see the video!

Sounds like a very cool motor

This was my favorite flight of the day

Wow. Jim Scarpine showed it to us at the launch on Saturday, and I was drooling.

I absolutely need to fly one of these. Long, loud crackly burn!


Later!

--Coop

It was/is a kick a$$ motor! Actually thinking of mixing up some JB-Weld and smearing it around the inside of the tail to protect it from the heat. the paint literally peeled off! My Frenzy has about 2" of space between the aft CR and the end of the airframe, if you have a rocket thats got the retainer and aft CR even with the end of the airframe you'll be good.

Wayco said:

Can't find the CTI data on this load, 54mm but how many grains?

Click to expand...

2 grain case.

It's right there on the CTI website.

what a GREAT L2 motor ! Originally thought it was going to be an I ..but its is a J !

https://pro38.com/products/pro54/motor/MotorData.php?prodid=699J145-19A

Paging Exactimator and Fyrwrxz . . time to arrange a cert special !

Kenny

One thing that bothers me about the description of the motor is the peak thrust. Yes, it has a peak of over 500n, but it only lasts for a few milliseconds, probably when the ignitor is being ejected out of the motor. The true peak is closer to 250n. I don't think this is CTI's fault, it's just the way the powers that be have decided to report the results.

I would LOVE to fly one of these J145 long burn Skids in my Polecat Skeeter 5.5.

ChrisAttebery said:

One thing that bothers me about the description of the motor is the peak thrust. Yes, it has a peak of over 500n, but it only lasts for a few milliseconds, probably when the ignitor is being ejected out of the motor. The true peak is closer to 250n. I don't think this is CTI's fault, it's just the way the powers that be have decided to report the results.

Click to expand...

Well, rest assured as long as you don't exceed 9-10lbs you will be fine. I flew one in my Jimbo Jart 4in 9.2lbs on the pad....it jumped off the rail and cruised nicely to 2800ft.

What ever they did.... it does have quite a nice "kick" off the rail. More than enough to get above specs moving safely.

It's really a full I, barely a J.... 1% if I remember correctly.

ChrisAttebery said:

One thing that bothers me about the description of the motor is the peak thrust. Yes, it has a peak of over 500n, but it only lasts for a few milliseconds, probably when the ignitor is being ejected out of the motor. The true peak is closer to 250n. I don't think this is CTI's fault, it's just the way the powers that be have decided to report the results.

Click to expand...

That's definitely an ignition spike that should have been edited out of the thrust curve.......

Bob

blackjack2564 said:

Well, rest assured as long as you don't exceed 9-10lbs you will be fine. I flew one in my Jimbo Jart 4in 9.2lbs on the pad....it jumped off the rail and cruised nicely to 2800ft.

What ever they did.... it does have quite a nice "kick" off the rail. More than enough to get above specs moving safely.

It's really a full I, barely a J.... 1% if I remember correctly.

Click to expand...

Jim is right, it definitely had a good kick, my Frenzy was 8.5lbs on the pad and it got up and out quite nicely.
At 699Ns it's at 9.2% of a J

The motor averages about 225N for the first 1.5 seconds...I figure it would boost most rockets up to about 9-10 lbs just fine.


Sent from my iPhone using Rocketry Forum

I'd love to fly one but I'll have to wait until they are CSFM approved. :^(


Sent from my iPhone using Rocketry Forum

ChrisAttebery said:

One thing that bothers me about the description of the motor is the peak thrust. Yes, it has a peak of over 500n, but it only lasts for a few milliseconds, probably when the ignitor is being ejected out of the motor. The true peak is closer to 250n. I don't think this is CTI's fault, it's just the way the powers that be have decided to report the results.

Click to expand...

I'm not sure there are really any "powers that be". The raw pressure cell readings from the test stand can be smoothed or not before graphing. I'm not sure about Canada, but the NFPA only mentions consistency of total impulse, average thrust and delay time (see this excerpt).

In theory there are supposed to be 2 firings of HPR motors (10 of MR motors), so ideally we'd get an average curve of multiple firings, but AFAIK none of the certification organizations do this.

JohnCoker said:

In theory there are supposed to be 2 firings of HPR motors (10 of MR motors), so ideally we'd get an average curve of multiple firings, but AFAIK none of the certification organizations do this.

Click to expand...

The CAR/MC2 curves are averages of the firings. - A lot of work for the volunteers.

Jeroen

I know I'm being picky. It's a niggle, nit, or whatever you'd like to call it. Take all of this with a grain of salt.

You're right John, it's looks like the raw data from the sensor. I tend to look at the peak thrust on the web site as a starting point to pick out a motor. My current project weighs about 8.5lbs empty so I'm looking for motors with around 225n of thrust for the first second. Most of the Peak Thrust numbers quoted on CTI's website look pretty reasonable to me, but because of that spike this one is roughly 2x what I would consider to be the "reasonable" peak. That was my only point.

Any way about it. I ran Open Rocket with this motor in my rocket and it will definitely work. Like I said, I'd love to fly one as soon as they are CSFM approved.

Jeroen_at_CTI said:

The CAR/MC2 curves are averages of the firings. - A lot of work for the volunteers.

Click to expand...

If that's the case, then this spike may not be an anomaly.

I used RockSim, Thrustcurve, And the data from CTI when I picked this motor, I also waited until the winds had died (they were around 10mph on the ground in the morning then subsided to about 5 later when I launched) just to make sure. Of course everyones rockets are different. (weight, height, diameter etc) All of these factors play a part in choosing a motor along with weather. I cant wait to fly this one again!

JohnCoker said:

I'm not sure there are really any "powers that be". The raw pressure cell readings from the test stand can be smoothed or not before graphing. I'm not sure about Canada, but the NFPA only mentions consistency of total impulse, average thrust and delay time (see this excerpt).

In theory there are supposed to be 2 firings of HPR motors (10 of MR motors), so ideally we'd get an average curve of multiple firings, but AFAIK none of the certification organizations do this.

Click to expand...

NAR S&T will remove the ignition spikes if they are deemed anomalous. CTI motors have a BP pellet at the head end so they ignite quickly. Load cells have a non-linear response near their resonant frequency and so can the test stand. The rapid onset of thrust generated on ignition can have high frequency components that excite a resonant frequency on some test stands producing an anomalous spike response. This can be filtered out of the data with a FFT/ inverse FFT filter routine.

S&T does indeed fire at least the minimum number of motors required for certification. We have published thrust curves both ways. If all the thrust curves are similar, we usually publish a typical thrust curve. In reality it makes little difference in a simulation. Certification data is taken at >400 Hz and reduced to a 16 to 32 point curve fit known as the engine file. This is done intentionally to average out individual motor nonuniformities. The NFPA requirements for motor performance are not overly tight so that the motors can be made affordable.

Bob

JohnCoker said:

In theory there are supposed to be 2 firings of HPR motors (10 of MR motors), so ideally we'd get an average curve of multiple firings, but AFAIK none of the certification organizations do this.

Click to expand...

For anyone interested: below are the individual firings from the certification session. We fired 5 motors to bracket the adjustable delay. 2 firings is only sufficient in case of a non-adjustable delay or a plugged motor.

All motors have a very reproducible spike caused by the igniter pellet. This effect is always larger in a moonburner geometry like these motors are.

Jeroen

View attachment 06061476.pdf

View attachment 06061477.pdf

View attachment 06061478.pdf

View attachment 06061479.pdf

View attachment 06061480.pdf

Donaldsrockets said:

I would LOVE to fly one of these J145 long burn Skids in my Polecat Skeeter 5.5.

Click to expand...

if you do this make sure your fins are something more than stock..

I flew mine on j90's over and over.. switched up to the J135 and the fins started flapping near the end of the burn.. tore a fin off... but WOW cool flight!

I completely forgot about the igniter pellet. Any way about it I'm sorry for derailing this thread.

ChrisAttebery said:

I completely forgot about the igniter pellet. Any way about it I'm sorry for derailing this thread.

Click to expand...

No derailing, this turned out to be quite informative. I learned a bit more about the curves than I knew.
Thanks to everyone for the responses and questions and to Jeroen for the direct input!

dgreger said:

No derailing, this turned out to be quite informative. I learned a bit more about the curves than I knew.
Thanks to everyone for the responses and questions and to Jeroen for the direct input!

Click to expand...

+1 this was one of the better thread-morphs.

Thread-morph: I like it.

wfcook said:

+1 this was one of the better thread-morphs.

Click to expand...

Jeroen_at_CTI said:

For anyone interested: below are the individual firings from the certification session. We fired 5 motors to bracket the adjustable delay. 2 firings is only sufficient in case of a non-adjustable delay or a plugged motor.

All motors have a very reproducible spike caused by the igniter pellet. This effect is always larger in a moonburner geometry like these motors are.

Jeroen

Click to expand...

The ignition spike in a CTI motor is part of the thrust curve as the BP pellet is part of the motor and not the igniter. On the other hand, the impulse of BP is only ~0.5 Ns per gram so the small amount of BP in the starter pellet doesn't significantly contribute to the thrust curve. So it really doesn''t matter whether or not you include it in a motor file will not significantly alter the results of a hobby rocket simulation. For example, if a starter pellet of BP weighs 5 grams, the total impulse from it would be ~2.5 Ns or equivalent to an A impulse BP motor. If the BP burned out in ~0.01 seconds, the propellant rating would be ~2.5 Ns / ~0.01 = ~250 N with a peak thrust of about ~500 N or ~112 pounds which is pretty close to the valve on the thrust curve.

Bob

This one cries out to be used in a night launch rocket! Does anyone have an eng file for it?