How do you tell when your casing is bad?

[firemanup]

My brother launched an AT J420R at whitakers last weekend for his cert flight.

When he took the casing apart to clean it post flight he noticed the plastic liner that the fuel grains go into had split lengthwise the full length of the liner.

When cleaning the case he noticed that it had pitted along where the liner had split...

So is the case no longer trustworthy? Are there any signs that cases have about had it..?

I'm liking the redline motors and find myself launching many of them with many more in reserve, they seem to burn hotter and i'm already noticing a little discoloration on the inside of my hardware at the ends of the casings from them..

Any opinions..?

 

[BlueNinja]

I'd contact AT and ask them.

 

[Donaldsrockets]

Well Jason I think the discoloration is the anodize wearing off I just finished reading your post and looked at my 29/240 that I fired an H210R in and I noticed a little discoloring myself.

My 38/240 case has a little discoloring also but from an H242T reload. Maybe it has something to do with the lubricant but I'm not exactly 100% sure.

As for the pitting, I think you could probably use the case again but you might want to contact Aerotech or Dr. Rocket to be sure.

Hope this helps

 

[n3tjm]

Aerotech Redline is their hottest fuel... that is why they make them burn fast. Send the case back to Aerotech.

 

[Ryan S.]

that pitting would be bad, I have never heard of this happening, but if the case is thinner in any place I wouldnt uyse it agian

 

[AlexNUMB]

Originally posted by n3tjm
Aerotech Redline is their hottest fuel... that is why they make them burn fast. Send the case back to Aerotech.

Uhh.... no, it isn't.

Blue Thunder is way hotter than redline.

 

[AlexNUMB]

oh yeah and to answer the original poster's question...

In many of my EX casings are pitted form the inside out and I use them with no problems. I run my chamber pressures between 500 and 700 psi w/o problems.

Terchnically, there is no reason it wouldn't work again. However, since it's a commercial motor, you might want to send it back anyway.

--Alex

 

[rocwizard]

In EX motors, blue is typically one of the hotter propellants because of the aluminum/magnesium people put in. However, in AT's blue thunder, they use very little if any aluminum, hence the very small amount of smoke produced (which is mostly from the binder) Aluminum and magnesium are thermic agents, meaning they make the propellant burn hotter, and increase chamber pressure, among other things. Redline however, produces much more smoke in relation to BT. It is not the stronium doing this, it is serving as additional oxidizer/ color agent. the smoke comes from added Mg. or Al. to intensify the redness of the flame (ever notice in pics, that when a red motor, or any color has very little smoke, the flame is not very bright or intense. that means there is very little thermic metal in the mix. If it is bright, then it most likely has more exhaust particulate from the said thermic agents. blue is an exception as far as intensity and brightness because it does not use the same salt types as the other color agents. A final example in commercial propellants is Green Gorilla from AMW. it has a very bright green flame, as well as a substantial amount of smoke as compared to BT. This follows the same things mentioned before.

There's today's chemistry lesson for you. I hope i didn't make all they Mods. angry, i didn't list formulas or anything, just explaining what makes all the pretty colors we all love!

HTH

 

[rocwizard]

and about the case, how bad is the pitting? can you feel it with your finger, or is it just visible? You might try showing it to a vendor to get his opinion. Or you could take a pic and let us analyze it the best we can.

 

[solrules]

I had a similar problem with my H268R.....when disassembled, the liner was cracked lengthwise. Although the casing was not marred as in your situation. I would agree the BT burn much hotter than the Redlines of AT.

 

[MarkABrown]

Originally posted by rocwizard
...There's today's chemistry lesson for you. I hope i didn't make all they Mods. angry, i didn't list formulas or anything, just explaining what makes all the pretty colors we all love! ...

This is exactly the kind of thing that I like to see in here. Explanations of why motors work the way they do is one of the primary purposes of the Propulsion forum. Good Job Eric.

 

[Ryan S.]

Originally posted by rocwizard
blue is typically one of the hotter propellants

AMWs blue is very hot, it needs a phenolic liner or the casing will be exposed to too much heat

 

[rocwizard]

yeah, it is very hot, and notice the increased amount of smoke it produces. Most likely from some Al. It would tear up an AT case real quick.


Don't get me wrong, Blue Thunder burns hot, but with the absence of metals, it is likely cooler than Redline. since blue doesn't need a thermic agent to produce a good looking flame, they probably favored to not use any to keep it low solids and pourable, a good thing in commercial manufacturing.

 

[n3tjm]

Originally posted by solrules
I had a similar problem with my H268R.....when disassembled, the liner was cracked lengthwise. Although the casing was not marred as in your situation. I would agree the BT burn much hotter than the Redlines of AT.

A lot of times, the liner is OK during motor operation, but cracks as the motor cools.

 

[AlexNUMB]

So In relation to the discussion on blue being hot....

I went out this weekend to static fire a 3 grain 75mm L1500 and a 5 grain 75mm M2200.

The 3 grain burned fine. 2 second burn time, brilliant blue... thing of beauty.

The 5 grain M burned fine, but after the case had cooled enough to examine, revealed a bubble in the side of the case.

Grumble grumble grumble... there goes another $15 worth of casing....

--Alex

 

[kgholloway]

It doesn't take an "M" class motor with a blue reload to bulge a casing. I have a Dr. Rocket 29/180 casing with a real nice bulge just aft of the forward closure. It was discovered after I fired a H238T "Blue Thunder" reload in it.

Ken