Grain Bonding on Aerotech Motors?

SilicdyneTRF
shop deals on amazon
the model rocket show
The Rocketry Forum

Help Support The Rocketry Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
AlnessW

AlnessW

Well-Known Member
Joined
Oct 6, 2013
Messages
1,221
Reaction score
3
I am wondering if people have any thoughts on gluing grains in Aerotech 75mm motors. As far as I know, the 75/6400 M650W and 75/7680 M685W are the only 75mm motors that require grain bonding.
The reason I ask is because many 75mm CTI motors require grain bonding, but it seems less common with Aerotech. Is this just because of motor design?

Has anyone ever had a need to glue grains with motors like the M1550R or M1850W? The instructions state not to...
 
AlnessW said:
I am wondering if people have any thoughts on gluing grains in Aerotech 75mm motors. As far as I know, the 75/6400 M650W and 75/7680 M685W are the only 75mm motors that require grain bonding.
The reason I ask is because many 75mm CTI motors require grain bonding, but it seems less common with Aerotech. Is this just because of motor design?

Has anyone ever had a need to glue grains with motors like the M1550R or M1850W? The instructions state not to...
Click to expand...
Do you know what you're asking?

Why would you assemble a commercial motor from any manufacturer differently than the instructions state? The only reason I can think of is that you want to live on the edge and void the warranty.

Am I missing something?

--Lance.
 
Last edited:
llickteig1 said:
Do you know what you're asking?

Why would you assemble a commercial motor from any manufacturer differently than the instructions state? The only reason I can think of is that you want to live on the edge and void the warranty.

Am I missing something?

--Lance.
Click to expand...

+1 on what he said.
When it comes to assembling rocket motors I have always deferred to the manufacturer of record for correct assembly instructions. :2:
 
The Aerotech 75 and 98 mm moonburners require grain bonding because they are intended to burn from the core outward. If the grain faces were not epoxied together, they would burn also and the motor would burn more quickly. I assume the larger moonburners would probably be cast as one piece if it weren't for shipping restrictions. I'm not a hazmat shipping expert but I think a grain over a certain size would put the motor into a different class other than 1.4C, or whatever most motors are shipped as.

The 54 mm K270 moonburner is essentially a 6 grain motor but is cast as one peice and not sliced into multiple grains.
 
AlnessW said:
I am wondering if people have any thoughts on gluing grains in Aerotech 75mm motors. As far as I know, the 75/6400 M650W and 75/7680 M685W are the only 75mm motors that require grain bonding.
The reason I ask is because many 75mm CTI motors require grain bonding, but it seems less common with Aerotech. Is this just because of motor design?

Has anyone ever had a need to glue grains with motors like the M1550R or M1850W? The instructions state not to...
Click to expand...

There are two different reasons for bonding grains. One the one hand, grains are sometimes cut into individually packed smaller pieces to comply with less restrictive shipping regulations (e.g. ADR 1.4C instead of 1.3C). This is was happens with the M+ moon burners. To bring it back to the intended geometry, the grains have to be bonded together. You'll note that in this case, glue gets directly applied to some propellant surfaces, inhibiting them from burning. If these motors were not bonded, the would likely cato because of the increased propellant surface.
The other reason for bonding propellants is for structural reasons. In this case, the glue gets applied to the casting tube, where offers mechanical support but doesn't affect the burning surface. This is more relevant for bigger motors and for faster propellants. CTI offers more big motors that fall a bit on the wild side (Vmax, White Thunder, C-Star) or are otherwise higher stressed (full M in 75mm, full N / baby O in 98mm), therefore you see more CTI motors requiring grain bonding. AT has also produced a motor with similar characteristics in the past, the N4800 (nearly full N with a comparably short burn time), but this motor was only reloaded at the factory (customers had to send the casing back). I have no idea if bonding was a reason for this, because it also had a rather special geometry.

Reinhard
 
I epoxied the grains into an I1299 in advance of a 220G flight just in case. I can't say that it wouldn't have survived without the glue, though the glue did no harm.
 
Pretty sure there is confusion between gluing grains into a liner and grain bonding. They aren't the same thing.
 
Talked to Karl at AT about the J510W in a MD rocket with a high-G launch a couple of years ago, and he recommended 'bonding the grains' with a laminating style epoxy (easy flow). This apparently prevents the upper grains from crushing the lower ones, collapsing and causing a CATO on under high acceleration. He also said a little goes a long way, so I just lightly wet the liner with a brush or painting sponge before putting a grain in. As someone already pointed out, the grains were still uninhibited afterwards; the grains were not bonded to each other, just the liner.

I am sure one of our motor experts could add more to this.
 
I understand now, thanks Viper. Still, most 75mm CTI loads require NO glue for either reason.
 
MarkH said:
The Aerotech 75 and 98 mm moonburners require grain bonding because they are intended to burn from the core outward. If the grain faces were not epoxied together, they would burn also and the motor would burn more quickly. I assume the larger moonburners would probably be cast as one piece if it weren't for shipping restrictions. I'm not a hazmat shipping expert but I think a grain over a certain size would put the motor into a different class other than 1.4C, or whatever most motors are shipped as.

The 54 mm K270 moonburner is essentially a 6 grain motor but is cast as one peice and not sliced into multiple grains.
Click to expand...
That is my understanding of the reasoning behind that, as well. And yes, all the Aerotech 54mm moonburners are a monograin and shipped that way - everything from the J90W all the way up to the K270W and K250W.

Reinhard said:
There are two different reasons for bonding grains. One the one hand, grains are sometimes cut into individually packed smaller pieces to comply with less restrictive shipping regulations (e.g. ADR 1.4C instead of 1.3C). This is was happens with the M+ moon burners. To bring it back to the intended geometry, the grains have to be bonded together. You'll note that in this case, glue gets directly applied to some propellant surfaces, inhibiting them from burning. If these motors were not bonded, the would likely cato because of the increased propellant surface.
The other reason for bonding propellants is for structural reasons. In this case, the glue gets applied to the casting tube, where offers mechanical support but doesn't affect the burning surface. This is more relevant for bigger motors and for faster propellants. CTI offers more big motors that fall a bit on the wild side (Vmax, White Thunder, C-Star) or are otherwise higher stressed (full M in 75mm, full N / baby O in 98mm), therefore you see more CTI motors requiring grain bonding. AT has also produced a motor with similar characteristics in the past, the N4800 (nearly full N with a comparably short burn time), but this motor was only reloaded at the factory (customers had to send the casing back). I have no idea if bonding was a reason for this, because it also had a rather special geometry.

Reinhard
Click to expand...
This was kind of more the explanation I was looking for. Thanks! I guess CTI just has more "wild" motors than Aerotech does.

CarVac said:
I epoxied the grains into an I1299 in advance of a 220G flight just in case. I can't say that it wouldn't have survived without the glue, though the glue did no harm.
Click to expand...
Good to know!

GRIFFIN said:
Pretty sure there is confusion between gluing grains into a liner and grain bonding. They aren't the same thing.
Click to expand...
If I am correct, "gluing grains into the liner" means just what it sounds, whereas "grain bonding" means gluing grains end-to end (that of a moonburner M).
 

Similar threads

mhanna
Question on Grain Bonding to the liner tube
Replies
4
Views
316
mrwalsh85
M
Richardx
AeroTech 75/2560 liner length
Replies
16
Views
496
rfjustin
rfjustin
davidshewitt
Grain Bonding an M1550R
Replies
19
Views
2K
Steve Shannon
Steve Shannon
M
Aerotech RMS J275W - Loose Grains Forward to Aft - This is not good right?
Replies
28
Views
1K
3stoogesrocketry
3stoogesrocketry
P
Sold CTI CTI 75mm cases and 75mm Monster Motors case
Replies
10
Views
2K
cwbullet
cwbullet

Latest posts

Back
Top