AeroTech Open Thread

Advertise with us
shop deals on amazon
Wildman Rocketry
The Rocketry Forum

Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
SolarYellow said:
Not sure if this has been answered before, but figured this is the thread to ask.
I'm looking at using 24mm RMS motors in a minimum diameter 24mm rocket with a carbon fiber tube. I assume the motor case gets hot and will thus expand during flight. How much room does it need? If I mount it in a carbon fiber tube that is a true 24mm ID, is that enough clearance for thermal expansion? Or does it need to be 24.1mm? I'm assuming straightness of the tube and motor case will be adequate over the relevant 40-60mm.

I'm asking because I've found a supplier of off the shelf nominal 24 ID / 25 OD carbon tube. There's a build thread here (probably a few) for a successful 29mm rocket >1.5 Mach with a 0.013 carbon sleeve over 0.013 cardboard tube, so I'm figuring 0.020 solid carbon with some bulkheads and couplers reinforcing it should be enough structure to get into the transonic range and knock on the door of Mach 1 safely. Don't want to add too much weight; 1mm wall thickness is available, but obviously weighs twice as much and that eats into performance.

Basically, I'm looking to build an MD rocket to mess around with the bigger MPR 24mm motor ranges. Not having to deal with the material, tooling and labor costs of sleeving cardboard is attractive. Until today, I hadn't found anyone selling appropriate solid c.f. tubes in 24mm sizes. And they are all much thicker in the larger sizes, so I'd discounted solid carbon as an option.
Click to expand...

Very minimal expansion . If your supplier is Amazon , they are not entirely carbon weave. Only the outside layer is , with two layers of uni on the inside.
 
Yesterday, I was using a skeleton of a 75mm DMS casing (no fuel grains, forward closure taped on) to block the motor mount in an ejection charge test. The charge was a little over enthusiastic and used the nozzle about a inch into the casing. I was able to push it back from the forward side and there’s no visible damage to the nozzle, liner, or closure. Is there anything else I should check before gluing everything up?
 
Howdy all.

In preparation for Airfest, I opened up my M4500ST tonight to go over the parts, grains, liner, etc. I like to do a dry fit before I commit to a glue-up.

I have a small question on this liner and grain stack-up. It would seem that either my liner is a weeeee bit short, or my grain and o-ring stack is a little too long. The liner to FSD gap is .070" which exposes a decent portion of the o-ring land in the FSD; the glue-up is done nozzle down so the gap will be at the FSD. The picture I have taken is the stack, upside down, so I am measuring the gap in relation to the nozzle as it's easier to photograph.

Liner is 18 23/32" long

Now something to also bare in mind is that once the liner/grain assembly is glued up, nozzle down. That leaves the FSD o-ring land exposed. And since it is glued, no matter how hard you try and crank down the closures, I don't think they will close the FSD gap since you are trying to compress a glued grain against a liner that is bottomed out against the nozzle shoulder. The glue will not budge and if it did, something will give and it won't be the metal parts.

I don't plan on doing the glue-up till tomorrow or Wednesday, so I have time; leaving for Airfest early Thursday morning. I would prefer not to glue the motor at the launch but if I have to, I will.

I have put many motors together over the years and I have not seen a gap this large. If it did not expose the ring land, or was on a more tame propellant, I would just assemble it. Since ST is hot and the lad is exposed, I would rather wait for verification and not just go 'full send' on it.

Tim might have another 98mm 3-grain liner with him that I could swap out but he's either already on the road or is leaving early AM tomorrow. Plus, I've already bugged him enough the past week. 🙃

Input from those with experience is encouraged. @AeroTech is preferred. :)

Ok, off to bed. Engineering Dept is in a shambles and tomorrow is my last day before a nearly 2 week vacation. I give me till 1pm for the IDGAF to set in and I mentally check out. 🤣🤣




20220829_224059[1].jpg







20220829_224149[1].jpg







20220829_224504[1].jpg
 
Last edited:
I could glue it upside down or gap the FSD till I just cover the ring land and then grease up the nozzle shoulder to liner intersection like crazy to inhibit flame tracking.

Could also chuck the nozzle up in the lathe and face off the convergent section a tad to allow the FSD to seat fully. Could also trim a grain down....

Hmmmm.....
 
Have you tried test fitting all of the parts into your case? Aerotech motors are dependent on having the correct liner length in order to compress the o-rings.
 
I had the same issue with a M2500 (also going to Airfest). I had already glued the grains in place. Karl from AT told me NOT to fly with the FSD not fully seated against the liner.

I fabricated a sanding disc from a plywood centering ring and 1/4" bolt into a drill and very very slowly removed about the same amount of propellant you're talking about from the front grain in the liner. After several tries the FSD did fully seat in the liner

Long story short the motor performed nominally with no issues. Hope this helps.
 
agree with the above.

would very carefully remove a 1/16" of propellant from one gain. this will address the gap and allow for the adhesive to "foam" sufficiently securing the entier assembly in place.

kudos for the dry fit. no doubt this is a very important step!
 
Sent an email last night to Karl and also just sent a PM as well.

I can make several modifications, I would just prefer the MFG to have the first swing at it. Rocket, motor, hardware, etc. is around $2000 not to mention the time investment. While a 98mm ST CATO likely would be impressive, I would rather not pay the bar tab that I would incur from drowning my sorrows afterwards.
 
3stoogesrocketry said:
Are you using grain spacer O-rings ? Have you tried to assemble without the two grain spacer O-rings?

Eric
Click to expand...

would advise against this

these motors are designed to function with the grain spacer o-rings as they ensure consistent combustion on all surfaces as the motor is placed under G load during liftoff.
 
They usually give you the same number of grain spacer O-rings as grains. Leave out the O-ring between the top grain and the seal disk. The main O-rings (nozzle and forward closure are radial seals and will work just fine even if the liner is slightly short. I show the liner as 18.750" long. Seat the seal disk all the way in and let the nozzle have the gap. Tighten the closures before the glue dries and the O-rings will compress some, reducing the gaps. You can leave the motor assembled for at least a year. You don't need to loosen the closures if you do not fly it.
 
Hey Tom

I have (2) spacer o-rings (1/16") and (3) grains, the bottom and top grains sit flush against the nozzle and the FSD. No o-ring between the FSD and the top grain. The 3/32" o-ring is for the FSD radial land that seals the FSD to the liner. Then obviously (2) 1/4" o-rings for the closure sealing work.

The liner I have is about 1/32" short and that leaves the balance of the .070" being likely in a single grain that might be long. I will measure when I get home. If there is a single grain that is a smidge long that equates to about .040, then that's where the other .040 came from.

I am leery about doing a glue-up and then installing it in the case as if there is squeeze out (there always is), that it will be a bear to get out post firing.

I also don't have spare closures and a spare SS FSD; Adrian is bringing me some spares of his to use but I wanted to get the glue-up done in advance. That way I can just pop my std FSD out, replace it with his SS FSD, stuff it into the case with his closures and we're off to the races. I have the L2500ST already loaded up so my SS FSD and closures are used on that motor right now, hence why I need to borrow his. I was hoping to fly these motors back to back and was trying to avoid tear down and cleaning till I got home......lazy lol.

Adrian and I were yacking on the phone during lunch and he mentioned (coincides with Stooges and Justin) of just leaving one spacer out and clamping it during the glue-up to close the slight gap that will likely result. He mentioned that he has burned lots of CTI crossloads with no rings. Though with the speed of ST being similar to Vmax, we both have concern about the flame front NOT getting between two stacked and glued grains, thus causing a progressive start and overpressure. Since I don't have the pressure response curve for that motor, its hard to even guess. AT propellant is really safe, but ST is new and not sure how twitchy it is. Recall, the M6000 had some issues and needed revision.


Any thoughts on what I wrote?

I called AT a few times today and left a VM. Have not heard anything yet via PM, email, or call. I am sure they are all quite busy so I will wait. Leaving the office in a few so I will tinker a bit when I get home to see what I can come up with.
 
StreuB1 said:
Hey Tom

I have (2) spacer o-rings (1/16") and (3) grains, the bottom and top grains sit flush against the nozzle and the FSD. No o-ring between the FSD and the top grain. The 3/32" o-ring is for the FSD radial land that seals the FSD to the liner. Then obviously (2) 1/4" o-rings for the closure sealing work.

The liner I have is about 1/32" short and that leaves the balance of the .070" being likely in a single grain that might be long. I will measure when I get home. If there is a single grain that is a smidge long that equates to about .040, then that's where the other .040 came from.

I am leery about doing a glue-up and then installing it in the case as if there is squeeze out (there always is), that it will be a bear to get out post firing.

I also don't have spare closures and a spare SS FSD; Adrian is bringing me some spares of his to use but I wanted to get the glue-up done in advance. That way I can just pop my std FSD out, replace it with his SS FSD, stuff it into the case with his closures and we're off to the races. I have the L2500ST already loaded up so my SS FSD and closures are used on that motor right now, hence why I need to borrow his. I was hoping to fly these motors back to back and was trying to avoid tear down and cleaning till I got home......lazy lol.

Adrian and I were yacking on the phone during lunch and he mentioned (coincides with Stooges and Justin) of just leaving one spacer out and clamping it during the glue-up to close the slight gap that will likely result. He mentioned that he has burned lots of CTI crossloads with no rings. Though with the speed of ST being similar to Vmax, we both have concern about the flame front NOT getting between two stacked and glued grains, thus causing a progressive start and overpressure. Since I don't have the pressure response curve for that motor, its hard to even guess. AT propellant is really safe, but ST is new and not sure how twitchy it is. Recall, the M6000 had some issues and needed revision.


Any thoughts on what I wrote?

I called AT a few times today and left a VM. Have not heard anything yet via PM, email, or call. I am sure they are all quite busy so I will wait. Leaving the office in a few so I will tinker a bit when I get home to see what I can come up with.
Click to expand...

Your progressive burn rate will be offset by the nozzle erosion . How hard ( many g's ) are you expecting to see ? It takes a incredibly large amount of force to slump a grain. If you have any concerns of the grain faces not lighting , carefully give the grain core to face a slight ( .125 ) radius . Have a great flight
 
Spent 10min on the phone with Karl.

DON'T FLY IT

Gary is coming to the launch and is going to hand carry a new liner that's on the longer side, which is preferred.

The ST is too hot to chance it and while he said modifying a grain to shorten it up could work, he preferred I waited and got the new longer liner. Even with the shorter grain allowing the stack to assemble, the shorter length would potentially affect the FSD seating and the compression afforded by the main o-rings. Hence why a liner that is a touch long, with a nozzle closure that has a gap, will help assure hard compression on the stack and keep the FSD seated and sealed.

Aerotech = A++++ :)
 
Last edited:
Sooner Boomer said:
Something I thought of while getting things layed out for Airfest; it would be nice to have a motor martix that breaks out motors/loads by propellant type in each diameter/case. Sometimes I want a particular "flavor" to fly a specific rocket with.
Click to expand...
Buyrocketmotors.com has that sorting option.
 
StreuB1 said:
Spent 10min on the phone with Karl.

DON'T FLY IT

Gary is coming to the launch and is going to hand carry a new liner that's on the longer side, which is preferred.

The ST is too hot to chance it and while he said modifying a grain to shorten it up could work, he preferred I waited and got the new longer liner. Even with the shorter gain allowing the stack to assemble, the shorter length would potentially affect the FSD seating and the compression afforded by the main o-rings. Hence why a liner that is a touch long, with a nozzle closure that has a gap, will help assure hard compression on the stack and keep the FSD seated and sealed.

Aerotech = A++++ :)
Click to expand...
This is exactly how the j615 assembles. Aft closure not quite fully seated so it really gets the liner tight to the nozzle and fsd.
 

Attachments

  • 20220829_190047.jpg
    20220829_190047.jpg
    1.6 MB · Views: 0
I just assembled my first 75mm motor, a L1390, and I am using a 75/5120 case with the adapter kit since I don’t have a 3840 case yet. When I screwed the fwd closure ring on, I get about a 1/8 gap between the case and the closure. Is this normal? Is it ok to fly as is?418DEBEA-1BDE-459A-BA24-F04EB1FDC0F8.jpeg
 
LMS motors. You needed to assemble them and epoxy the forward closure into the casing provided. I ordered two by mistake once. Easy enough to assemble. G77s, G78s, G79s. You can still buy them. I am guessing they were designed that way so they could be shipped non-hazmat.
 
If the forward end is flush and rear as tight as possible, it will be fine. Did you use 1 too many grain spacer rings? None goes next to the seal disk.
 
jimzcatz said:
If the forward end is flush and rear as tight as possible, it will be fine. Did you use 1 too many grain spacer rings? None goes next to the seal disk.
Click to expand...
Correct. Three grains, 2 spacer Orings. I shifted the gap to the aft closure, and pulled the calipers out this morning, and the gap is tighter than I thought last night… it measures out to be .072, so just over 1/16. I will probably be fine.
 

Similar threads

Valkyrie Recovery Systems
Valkyrie will be going to NSL 2024!
Replies
2
Views
279
Valkyrie Recovery Systems
Valkyrie Recovery Systems
overklock
Aerotech G-force Build Thread - WIP
Replies
12
Views
2K
gldknght
gldknght
Dane Ronnow
Build thread: Aerotech HV Arcas
2
Replies
43
Views
5K
Dane Ronnow
Dane Ronnow
Bruiser
RIP IQSY Tomahawk
Replies
3
Views
1K
waltr
W
fyrwrxz
  • Locked
The end of the Never Ending Story
2
Replies
46
Views
4K
OzHybrid
OzHybrid

Latest posts

Back
Top