Author Topic: Cryogenic swing arms  (Read 2544 times)

Offline Liryc

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Cryogenic swing arms
« on: 06/25/2012 04:11 PM »
Hi all,

I'm trying to understand how the Delta IV swing arms are triggered off at launch..

On the shuttle, the plates are pulled with wires (simmilar to many other launchers in the world) but in the Delta case, the movement is horizontal, making the cable system more tricky..

Is it triggered by the rocket on board computer using pyrobolts (on pre-constrained arms ?) or is it a pure mechanical/gravity system ?


P.S : the indian GSLV has a similar kinematics



Offline Jim

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Re: Cryogenic swing arms
« Reply #1 on: 06/25/2012 04:33 PM »
Hi all,

I'm trying to understand how the Delta IV swing arms are triggered off at launch..

On the shuttle, the plates are pulled with wires (simmilar to many other launchers in the world) but in the Delta case, the movement is horizontal, making the cable system more tricky..

Is it triggered by the rocket on board computer using pyrobolts (on pre-constrained arms ?) or is it a pure mechanical/gravity system ?



No, cables are used in the same way on Delta.

There are actuators on the tower that pull the arms away

Offline Liryc

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Re: Cryogenic swing arms
« Reply #2 on: 06/26/2012 12:10 PM »
Ok, I see.

but how do they prevent the launcher from lifting off with the arms attached ? (in case of an actuator failure) ?

What I mean is that on wire-type systems, they seem to always have a back-up wire system that pulls off the plate even if the main system does not (without breaking the launcher of course ;))

It seems so much easier, I can't really figure out how it could be done on an "horizontal-displacement"arm.

Offline Jim

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Re: Cryogenic swing arms
« Reply #3 on: 06/26/2012 12:15 PM »
Ok, I see.

but how do they prevent the launcher from lifting off with the arms attached ? (in case of an actuator failure) ?

What I mean is that on wire-type systems, they seem to always have a back-up wire system that pulls off the plate even if the main system does not (without breaking the launcher of course ;))

It seems so much easier, I can't really figure out how it could be done on an "horizontal-displacement"arm.

Redundant actuators
But the arms are not attached, there is a plate just like the wire system

Offline Liryc

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Re: Cryogenic swing arms
« Reply #4 on: 06/27/2012 07:14 AM »
Yep, that's what I guessed for the plates. But still, even if the arms are not attached, the plates are.
Must need quite some efforts to pull them off the launcher, moreover as they are not using the luncher motion to help this (like the wire systems)

Offline Jim

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Re: Cryogenic swing arms
« Reply #5 on: 06/27/2012 11:12 AM »
Yep, that's what I guessed for the plates. But still, even if the arms are not attached, the plates are.
Must need quite some efforts to pull them off the launcher, moreover as they are not using the luncher motion to help this (like the wire systems)

No, it does not take much force to remove the plates in either case

Offline Liryc

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Re: Cryogenic swing arms
« Reply #6 on: 08/20/2012 07:49 AM »
I still don't get how it works, and how they make sure the arms swing away at lift off (in case they don't, I guess that would lead to a major failure)

Offline Jim

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Re: Cryogenic swing arms
« Reply #7 on: 08/20/2012 08:32 AM »
I still don't get how it works, and how they make sure the arms swing away at lift off (in case they don't, I guess that would lead to a major failure)

like I said redundant actuators.  How is it so hard to see that?
« Last Edit: 08/20/2012 08:34 AM by Jim »

Offline JohnFornaro

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Re: Cryogenic swing arms
« Reply #8 on: 08/21/2012 12:25 PM »
Is he suggesting two sequential failures?  The swing arm and the redundant one?
Sometimes I just flat out don't get it.

Offline Liryc

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Re: Cryogenic swing arms
« Reply #9 on: 08/21/2012 12:33 PM »
I just have some doubts on the kinematics itself.
Triger an actuator to open the arms so quickly, and after the motors are ignited seems very risky (even with a redundant set of actuators).

I would have thought of prestressed mechanical device, with some sort of pin that is removed to release the arms.

It's not hard to see the redundant actuators, just difficult for me to imagine
1/ an actuator is efficient enough
2/that this would be a FS-FS system..

Offline Jim

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Re: Cryogenic swing arms
« Reply #10 on: 08/21/2012 12:54 PM »
Not with hydraulic/pneumatic actuators

Offline Liryc

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Re: Cryogenic swing arms
« Reply #11 on: 08/21/2012 01:03 PM »
Ok thanks.

Any references ?
I'm writing a short paper for school and they don't like when we don't quote (no offence to you guys ;))

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