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watermelonman

watermelonman

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Sorry if this is a silly question, but why do forward seal discs even exist?

Would it not be reasonable to simply build that functionality into the forward closure? Or do the thermal properties make that infeasible?
 
The Aerotech seal discs cam about because of problems with the longer case sizes. Motors like the J350 and K700 had problems with gas flow that blistered cases.


I can't locate anything about the J350 but this Aerotech news item from 1997 talks about changes to the I211 and friends.
 
Most of my Dr Rocket hardware is dated 1996-2000.

Up until the new motors were certified There was no 38 mm x 720 or 1080 cases.
The 29 mm x 360 case and it's only load at the time; the I 200 also required a seal disc.
With the introduction of the J 350 and newer BT loads for the 480 and 600 cases... They added a seal disc and the larger opening aft closure to allow the new nozzles for these loads.

They did a demo of a longer than the 1080 case and was dubbed the J 520 circa 1998.

JD

UhClem said:
The Aerotech seal discs cam about because of problems with the longer case sizes. Motors like the J350 and K700 had problems with gas flow that blistered cases.


I can't locate anything about the J350 but this Aerotech news item from 1997 talks about changes to the I211 and friends.
Click to expand...
 
It is possible to build a fwd closure with the functionality of a seal disc (see Loki's current 76 mm bulkheads and 54 mm extended bulkheads). For AT, that would have had a significant impact on those who were already invested in the original closure, plus it would require either modification to reload kits that don't need the functionality or different fwd bulkheads for different motors. A separate seal disc is a relatively inexpensive retrofit that allows the use of a single fwd closure.

David
 
Wizard said:
It is possible to build a fwd closure with the functionality of a seal disc (see Loki's current 76 mm bulkheads and 54 mm extended bulkheads). For AT, that would have had a significant impact on those who were already invested in the original closure, plus it would require either modification to reload kits that don't need the functionality or different fwd bulkheads for different motors. A separate seal disc is a relatively inexpensive retrofit that allows the use of a single fwd closure.

David
Click to expand...

I think, retrofit for existing customers, is exactly the answer I was looking for. Thanks!
 
In this vein, what is the purpose of insulators in AT motors? There are these washers, fiber, neoprene or phenolic, that go above the nozzle and below the forward closure when the motot has no seal disk.

What is the purpose of these washers?

This, too, may sound silly coming from an L3, but I really am unclear on their purpose.

Ari.
 
Ari, I too have wondered that. I get the purpose of the seal disk with an o-ring. Maybe to give a bit of protection to the forward closure? There's not much left of them after use.
 
If it wasnt for all the insulators around the propellant as it burns the case would develop hot spots and fail while under pressure. The cardboard and or fiber parts are a sacrificial "casing" during the short period of the burn they get mostly consumed while transmitting minimal heat to the motor casing. The fiber washers are the same and keep the closures from being permanently welded to the casing.
 
One thing the fiber washers do, is act as a sealing surface for the O-rings. Without them there is nothing but the liner for them to compress against. Now the forward seal disks are the sealing surface for the o-ring. IIRC the 38mm AT motors have a fiber washer with the nozzle and o-ring and maybe the one grain 54mm motors does too.

Tony
 
tfish said:
One thing the fiber washers do, is act as a sealing surface for the O-rings. Without them there is nothing but the liner for them to compress against. Now the forward seal disks are the sealing surface for the o-ring. IIRC the 38mm AT motors have a fiber washer with the nozzle and o-ring and maybe the one grain 54mm motors does too.

Tony
Click to expand...

I see, this makes sense. So in AT single use HP motors, they omit these, right, along with the o-rings? They just pot top and bottom with epoxy.

Ari.
 
iter said:
I see, this makes sense. So in AT single use HP motors, they omit these, right, along with the o-rings? They just pot top and bottom with epoxy.

Ari.
Click to expand...
I seriously doubt it. Liners, seal disks and O-rings prevent thermal energy and hot gas from overheating the casing while the motor is burning. When a plastic or aluminum casings gets too hot, it will soften, expand and burst resulting in a CATO. Doesn't matter if it's single use or a reloadable.

Bob
 
You could just make the disposable case thicker. Is there any particular advantage in making in in multiple layers? With a reusable case, you want to erode the liner and preserve the aluminum, so you make the case in two separate layers. Or is it about different materials providing different functions, like the fiberglass is good a shear strength and containing pressure but poor at thermal stability, so you insulate the fiberglass with paper?

Ari.
 

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