Launcher Load Factor

Question

Launcher Load Factor

sarclee (Mechanical)

(OP)

13 Apr 22 13:11

Hi, may I ask the load factors given in the launcher user manual are used for static analysis only?

Say, axial 5G,lateral 9G and we run the static acceleration.

What about vibration analysis? Are we also take these 5G as a multiplier in vibration axial direction?

Thanks!

rb1957 (Aerospace) · Answer 1 · 2022-04-13 14:17:12

there should be a vibration spec.

"5G" ... is limit, but static design to ultimate ?

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sarclee (Mechanical) · Answer 2 · 2022-04-13 15:33:41

Hi rb1957, there is vib profile. Some of colleagues talking to use the 5G as multiplier to multiply with the G force given for vibration profile as the axial 5G is given under design load factor which might confuse them?

rb1957 (Aerospace) · Answer 3 · 2022-04-13 15:43:39

oh boy !

no, I would definitely not multiply their vibration loads spec by their static load factor.

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SWComposites (Aerospace) · Answer 4 · 2022-04-13 23:59:47

RE: Launcher Load Factor

SWComposites (Aerospace) 13 Apr 22 23:59

Concur with rb.

sarclee (Mechanical) · Answer 5 · 2022-04-18 00:17:21

Thanks everyone!

Another concern is if combined load factors shall be considered? Either to apply the G force in three axis at the same load step or calculating the combined margin based on the result from each axis load condition?

GregLocock (Automotive) · Answer 6 · 2022-04-18 01:02:03

That's a mistake I often see. Typically the force in the 3 directions are uncorrelated in the time domain, hence you should test with 1, 0 and -1 scaling in each direction, which in a linear system gives you 13 tests
x y z
1 1 1
1 1 0
1 1 -1
1 0 1
1 0 0
1 0 -1
1 -1 1
1 -1 0
1 -1 -1
0 1 1
0 1 0
0 1 -1
0 0 1

Cheers

Greg Locock

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sarclee (Mechanical) · Answer 7 · 2022-04-18 01:24:05

Hi Greg Locock,

Thanks for your sharing. Is the below what you are pointing?

GregLocock (Automotive) · Answer 8 · 2022-04-18 03:32:36

That looks right. If the system is linear the superposition of load cases can be done at any stage in the analysis. If the system is non linear then you need to do each run separately.

Cheers

Greg Locock

New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

rb1957 (Aerospace) · Answer 9 · 2022-04-18 20:03:33

sorry , but is it ?

particularly if az is between 1.8 and 3.2 ?

but if you number unit cases in each direction, wouldn't you run 5 unit cases (assuming X only +ve), then factor these together ...
case1 is 1 m/s +X
case2 is 1 m/s +Y
case3 is 1 m/s +Z

then 2.5 m/s X 0.3 m/s in Y and Z is 2.5*case1 + 0.3*case2 + 0.3*case3 ?

unless that's what people meant, or unless I'm wrong (again) ...

I can see that you may want to run the full gamut of cases (+veY and +veZ, +veY and -veZ, -veY and +ve Z, -ve Y and -ve Z, +veY only, +veZ only, -ve Y only, -ve Z only)
and combine these unit results to achieve what you want.

is +veY only = (+ve Y and +ve Z) + (-ve Z only) ?

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