Aerotech Reload?

I just built a 24/40 with an E28-4T load.

Per the instructions I centered the grain in the casing, but this just feels wrong. The grain is free to move 1/4" to 1/8" in either direction. It seems there should be a spacer but one is not included.

I finally decided to seat the grain against the delay charge and leave all the space at the aft end.

Am I missing something? Why the extra space and no spacer? Does it matter if I push the grain fore or aft?




So many rockets, so little time, and money.

Lowpuller said:

I just built a 24/40 with an 18-4 load.

Per the instructions I centered the grain in the casing, but this just feels wrong. The grain is free to move 1/4" to 1/8" in either direction. It seems there should be a spacer but one is not included.

I finally decided to seat the grain against the delay charge and leave all the space at the aft end.

Am I missing something? Why the extra space and no spacer? Does it matter if I push the grain fore or aft?




So many rockets, so little time, and money.

Click to expand...

E18-4, I take it?

https://www.aerotech-rocketry.com/c...s_assy_dwgs/24mm_mr_rms/24-40_e18-4w_assy.pdf

It probably doesn't matter if there is no spacer, but the drawing above seems to indicate that there should be a spacer.

All that matters is you need to make sure the igniter makes it into the top of the slot.

If you're worried about it, call Aerotech's customer service.

I printed out the pictures from the Hobbyline sticky and keep them in my ammo can. The picture is much easier to folllow. Your 24/40 reload should look like page 3 of the pdf file found here:

https://www.rocketryforum.com/showt...-Assembly-Diagrams-Videos&p=365100#post365100

There is also a picture for 18/20 and 29/40-120 that is worth printing out.

CarVac,

Thanks for reminding me of the drawings. It is actually an E28-4T. I revised my original post. I also looked up the drawing for the 28, it also shows a spacer as Item 17.

I have already shot one load this way and it worked, it just bothered me.

The instructions say center, drawing shows it aft with spacer.

I would call AT but I'm gonna shoot this thing in the morning!!

Thanks for the help, I will call on Monday.


So many rockets, so little time, and money.

So, You're gonna fire a reload, knowing it's missing a part? You must not like the rocket, the motor case or warranties. Good luck.

Tony

Tfish

Per the instructions and parts list on hand no spacer is included. My instructions are different from those online but even the online instructions do not list a spacer or show one installed.

In other words I do not believe I am missing apart rather I am concerned how the instructions describe putting the reload together.

I plan to fly Saturday and call AT on Monday.



So many rockets, so little time, and money.

I would go with your gut instincts.

I had a reload (my first for the 29/40-120 RMS) and when I put it together it just didn't feel right. After assembly the propellant grain was moving around. I figured out that I was missing an "O" ring and a grain adapter. I contacted AeroTech they sent the missing part. They just needed my address and the lot number of the reload. The communication was done via email.

Greg

It should have a spacer. The typical assembly is the spacer is at the fore end of the liner, with a piece of cellophane tape over the end of the grain to properly locate the igniter at the top. I can't guess what will happen if fired without it, but I'm certainly curious to find out.

Well it worked great, 2nd load I have fired that way with no problem. But I did see 2 Estes BPs Cato see my other thread for details.


So many rockets, so little time, and money.

A little bit of play or slop in the grains is not usually a problem. With many of the HPR motors, you can shake the motor after assembly and hear the grains sliding back and forth. Larger motors use O-rings between grains to maintain the gap. This gap is needed so the faces of the grains lite. That is the way Bates grains maintain a flat thrust curve, the grain get shorter as the center core gets larger so it maintain and even burn area.

The Hobbyline motors with shorter grains usually use a spacer at the forward end. I think this does two things. One, it adds insulation to the liner since the part of the liner exposed to flame with a short grain would be exposed much longer then the area in contact with the grain tube. The second thing is that it positions the grain where it will be when thrust starts, which is aft. This keeps the grain from moving during flight and causing problems.

I would read and reread the instructions and follow them. The manufacturer that designs the motors know what they are doing and write the instructions to enhance and support the design.

It's been 8-10 years since I've flown a hobbyline motor that required an internal spacer, but IIRC, the very very old ones (15+ years old) used to instruct you to put the spacers aft of the grain. This reduced the flame size significantly in the smaller motors and also made proper igniter installation very difficult. I've flown ones that instructed you to put the spacer forward (but it's been a while). Sounds like Aerotech decided the spacers weren't needed anyway, which seems pretty reasonable.

xenon said:

It's been 8-10 years since I've flown a hobbyline motor that required an internal spacer, but IIRC, the very very old ones (15+ years old) used to instruct you to put the spacers aft of the grain. This reduced the flame size significantly in the smaller motors and also made proper igniter installation very difficult. I've flown ones that instructed you to put the spacer forward (but it's been a while). Sounds like Aerotech decided the spacers weren't needed anyway, which seems pretty reasonable.

Click to expand...

The aft placement of the spacer probably improves performance a bit, since it allows for slightly more complete burning.

That would explain the smaller flame, certainly.

Curious. Your instructions are different than these: https://www.aerotech-rocketry.com/customersite/resource_library/Instructions/MR-RMS_Instructions/RMS-24_40/rms_24_d9-e28_4-04.pdf ? The "grain adapter" has always been in the E28 packs I've flown.