Single Use Aerotech Motors Question

[Wm Reid]

Hi, I am starting to explore mid-power rockets with the hope of moving on to get my level 1 certification. I have a newbie question...

As I’m building my kit from North Coast Rocketry, there is no engine block or retaining hook...does one just friction fit the SU in place or does one apply epoxy to the little cardboard ring that comes with the motor and use that with the retaining ring?

A silly question, I know but, still learning.

Thanks!

 

[rcktnut]

The Aerotech motors have thrust rings, no engine block needed, and you can fly on larger motors without the engine block. I did this for retaining on my NC Big Brute. The red retaining ring does not work with some of the motors.

Don't know which NC model you have or what year check MMT make sure it is a 29mm tube. You might have to replace the included MMT tube with a different one that is 29mm., the included one is less than that on some/{ all.??} No problem with the reloadable cases, but for single use ones they are Tight with a capital T.

 

[Wm Reid]

The Aerotech motors have thrust rings, no engine block needed, and you can fly on larger motors without the engine block. I did this for retaining on my NC Big Brute. The red retaining ring does not work with some of the motors.

Don't know which NC model you have or what year check MMT make sure it is a 29mm tube. You might have to replace the included MMT tube with a different one that is 29mm., the included one is less than that on some/{ all.??} No problem with the reloadable cases, but for single use ones they are Tight with a capital T.

View attachment 446209

Thanks, I see where the reloadable ones have the thrust ring...but on the single use, the econojet motors, there is no physical thrust ring built onto the unit...but it does come with a little cardboard ring that could act as such if you epoxied it on.

I know on my low powered stuff I have friction fit smaller motors before but I’m not sure how that works with the mid-powered stuff. Last night I did a test fit of a 29mm single use and it just slid through the motor mount tube...I’m just curious about the details of using single use aerotechs without an engine block.
Thanks,
Reid

(I can post a photo tonight when I get home from work)

 

[neil_w]

Thanks, I see where the reloadable ones have the thrust ring...but on the single use, the econojet motors, there is no physical thrust ring built onto the unit...but it does come with a little cardboard ring that could act as such if you epoxied it on.

The single use Aerotechs I’ve flown (24 mm Es and if I recall correctly 39mm Fs) certainly have integrated thrust rings.

 

[rcktnut]

Thanks, I see where the reloadable ones have the thrust ring...but on the single use, the econojet motors, there is no physical thrust ring built onto the unit...but it does come with a little cardboard ring that could act as such if you epoxied it on.

I know on my low powered stuff I have friction fit smaller motors before but I’m not sure how that works with the mid-powered stuff. Last night I did a test fit of a 29mm single use and it just slid through the motor mount tube...I’m just curious about the details of using single use aerotechs without an engine block.
Thanks,
Reid

(I can post a photo tonight when I get home from work)

Understood with the motors you are talking about. They are the older Econojets, and do not have a thrust ring. You could epoxy the ring on or just use masking tape for a thrust ring.

 

[hball55]

Understood with the motors you are talking about. They are the older Econojets, and do not have a thrust ring. You could epoxy the ring on or just use masking tape for a thrust ring.

That cardboard ring that is supplied with the motor is for use with rockets that HAVE an engine block. The econojets are shorter and that ring goes in the motor mount before you insert the econojet motor. That way, you don’t need a thrust ring, IF THE ROCKET HAS A MOTOR BLOCK INSTALLED. I do not recommend glueing the ring to the motor. What I have done, is wrap some tape around the aft/nozzle end of the motor, enough so that the motor doesn’t go all the way in the rocket. Be sure not to obstruct the nozzle.

 

[Arsenal78]

Is it a newer North Coast kit? The original kits (pre-2000) had a few things that wouldn't work with today's standards. On the new era kits, leave 1/4" of the motor tube sticking out from the aft centering ring so you can glue on an Aeropack retainer, you need Aeropack 29L. I know friction fit is ancient technology and a lot of old rocketeers trust it but I don't unless it's low power. All Aerotech motors these days should have a thrust ring built into them so you don't need a motor block. If the rocket is for Level 1, you cannot use a motor block because the motors are a lot longer in high power. If the rocket will fly on F and G motors as well, invest in an Aerotech 29/40-120 casing.

 

[Wm Reid]

Thanks everyone, I appreciate the input!

 

[David Schwantz]

I just went and checked, all of mine have thrust rings. Post a pic of yours.

 

[Antares JS]

Just going to add, ALWAYS have some kind of positive retention. NEVER rely on friction fit for anything bigger than a D.

 

[Walter Longburn]

NEVER rely on friction fit for anything bigger than a D.

I've done it on L motors... the ejection charges aren't putting any force on the motor though in my scenario.

 

[rcktnut]

That cardboard ring that is supplied with the motor is for use with rockets that HAVE an engine block. The econojets are shorter and that ring goes in the motor mount before you insert the econojet motor. That way, you don’t need a thrust ring, IF THE ROCKET HAS A MOTOR BLOCK INSTALLED. I do not recommend glueing the ring to the motor. What I have done, is wrap some tape around the aft/nozzle end of the motor, enough so that the motor doesn’t go all the way in the rocket. Be sure not to obstruct the nozzle.

You are correct I call them spacers. When OP said that he had a little cardboard ring that came with the motors, thought maybe Aerotech was supplying thrust rings with them in between transition. I still have a bunch of the spacers here, some are around an inch long some around 1/2 in. long. They are/were exclusively made to fit Aerotech kits built stock for use when they manufactured the motors without the thrust rings.

 

[Rocketjunkie]

The ring that comes with the Econojet motors should fit over the motor, not inside the motor mount tube. Epoxy it on the nozzle end of the motor for a thrust ring. Back in the day, we used masking tape thrust rings even on L motors. Build your rocket with the motor tube sticking out 1/2" past the rear centering ring. Slide motor in then tape around the joint between the motor thrust ring and motor tube.

 

[ThirstyBarbarian]

If you have Econojet motors with cardboard rings, those are old motors. Econojet motors have had molded thrust rings for at least 6 or 7 years, probably more. That doesn’t necessarily mean there’s anything wrong with them, but sometimes (not always) older motors can be harder to light or have other issues. If I were just starting out with midpower and flying my very first composite motors, I’d buy some fresh ones and save the older ones for when I had more experience troubleshooting. Make your first flight a little easier and straightforward.

Do you actually have the motors already, or are you going by pictures and descriptions on a vendor site? Because some vendors just never bothered to update their pictures when the molded thrust rings came out. If you buy from an active vendor, it’s very unlikely they have the old ones with the cardboard rings still in stock.

 

[ThirstyBarbarian]

This website still has the old pictures. If you buy this motor, that’s not what you will get. It’s going to have a molded thrust ring and no cardboard rings. http://www.hobbylinc.com/aerotech-f...motor-2-f-composite-model-rocket-engine-62007

 

[CoachSteve]

Friction fit (tape wrapped around the motor case until a tight fit in the motor tube) - has beed used since the beginning of rocketry and is regularly used well above D power motors.

 

[Antares JS]

Friction fit (tape wrapped around the motor case until a tight fit in the motor tube) - has beed used since the beginning of rocketry and is regularly used well above D power motors.

I've seen too many expensive motor cases (not mine) get spit out in the air and lost to seriously consider friction fit a good idea. Even if it's a single use motor, littering your landowner's field with those plastic single-use cases composite motors use is not a great idea. At least an Estes motor case is biodegradable.

 

[prfesser]

Friction fit (tape wrapped around the motor case until a tight fit in the motor tube) - has beed used since the beginning of rocketry and is regularly used well above D power motors.

And people like me, who don't take enough care when friction fitting an I motor, end up losing a motor case and destroying a rocket.

My own fault. But it taught me a lesson. I just avoid taking even the slightest chance of having a prang and a lost motor. Positive retention is essentially foolproof. I shouldn't say that; fools (like me) can be ingenious...

Best -- Terry

 

[neil_w]

I have nothing against other people using friction fit... but for myself, I hate it. Will always choose positive retention if I have any choice.

 

[Walter Longburn]

I mostly save friction fit for minimum diameter rockets. It's a lot easier to get the motor in and back out with positive retention. So if you can easily do positive retention then I would say do positive retention.

 

[ThirstyBarbarian]

Good news is, the Econojet motors with a molded thrust ring don’t require friction fit, because there is a thrust ring. Put a positive retainer on that rocket. Put one of these on it: https://www.acsupplyco.com/estes-9750-29mm-motor-retainer-set?search=29 mm retainer