Delta II SRB

[Spaced Out]

Why is it that the Delta II SRB nozzles are pointed outwards? It would make sense that it is to prevent the exhaust from the SRB's hurting the main engines, but is that really the case?

[DDE]

Apparently that, and structural loads, yes.

[GoSlash27]

Also so that their thrust is directed through the CoM instead of parallel.

Best,
-Slashy

[Spaced Out]

1 hour ago, GoSlash27 said:

Also so that their thrust is directed through the CoM instead of parallel.

What would happen if it wasn't directed through the CoM or was paralell?

[GoSlash27]

30 minutes ago, Spaced Out said:

What would happen if it wasn't directed through the CoM or was paralell?

Spaced Out,

 If you notice, the Delta II-500 has 9 structural hardpoints, and many configurations wind up in an asymmetrical arrangement.

*EDIT* Wrong rocket! (Thanks Bill Phil)

If the boosters thrusted parallel to the stack, the asymmetry would result in a torque moment, trying to rotate the stack. This also sidesteps control problems that might result from variations in burn time or cross-sectional "throttling". Having the SRBs thrusting through the CoM eliminates a lot of potential headaches.

Best,
-Slashy

Edited November 26, 2017 by GoSlash27

[Bill Phil]

13 minutes ago, GoSlash27 said:

Spaced Out,

 If you notice, the Delta II-500 has 9 structural hardpoints, and many configurations wind up in an asymmetrical arrangement.

If the boosters thrusted parallel to the stack, the asymmetry would result in a torque moment, trying to rotate the stack. This also sidesteps control problems that might result from variations in burn time or cross-sectional "throttling". Having the SRBs thrusting through the CoM eliminates a lot of potential headaches.

Best,
-Slashy

That image is an Atlas V, not Delta II. Delta II has the 6000 and 7000 series.

[GoSlash27]

*DERP!*

 

Same deal with the asymmetrical arrangements.
Thanks for the catch,
-Slashy

[GoSlash27]

 

A really good example of how keeping the thrust pointed through the CoM really helps with stability.

Best,
-Slashy

[PB666]

46 minutes ago, GoSlash27 said:

 

A really good example of how keeping the thrust pointed through the CoM really helps with stability.

Best,
-Slashy

Too bad they could not find a parachute.

[Nibb31]

12 hours ago, Spaced Out said:

Why is it that the Delta II SRB nozzles are pointed outwards? It would make sense that it is to prevent the exhaust from the SRB's hurting the main engines, but is that really the case?

The same is true for pretty much all SRBs. Even the Shuttle SRBs were pointed outwards.

[Zeiss Ikon]

15 hours ago, Nibb31 said:

The same is true for pretty much all SRBs. Even the Shuttle SRBs were pointed outwards.

Not enough to matter for thrust asymmetry.  I once read that if one SRB ignited and the other failed, the entire stack would (if it could hold together) rotate through 90 degrees in less than a second.  Challenger's destruction was completed when the leaking SRB tore completely loose from the tank, and the still-attached SRB turned the stack 90 degrees to the Mach 2 windstream -- which no portion of the Shuttle was built to withstand.

Edited November 28, 2017 by Zeiss Ikon

[DerekL1963]

4 hours ago, Zeiss Ikon said:

Not enough to matter for thrust asymmetry.  I once read that if one SRB ignited and the other failed, the entire stack would (if it could hold together) rotate through 90 degrees in less than a second.  Challenger's destruction was completed when the leaking SRB tore completely loose from the tank, and the still-attached SRB turned the stack 90 degrees to the Mach 2 windstream -- which no portion of the Shuttle was built to withstand.

Challenger was destroyed when the ET broke up due (essentially) to the aft end falling off, throwing the Orbiter into the airstream.  The stack had no time to turn before it was completely shredded due to these forces.  (That's why the pictures show the trails of the SRB continuing more-or-less on trajectory.)