Axial Loading on a missile structure 1

[Dralos]

Hello,
I attached a part out of a book which is explaining how to assume stresses in a missile body in the pre-concept phase.
the theory behind is to assume a simple beam with a circular cross-section.
but what i dont quite understand is how they derive the second diagrams?
as far as i understand if you apply a 10G acceleration on the missile every weight increment of the missile reacts with an opposite force of 10G*m
so what does one need to do to end up with the second diagram?

Thanks!

http://i55.tinypic.com/54buds.png

 

[desertfox]

Hi Dralos

If I understand it correctly then the second diagram is the combination of bending stresses and axial stresses, however without the earlier pages I can't tell what they are.

desertfox

 

[Dralos]

thats the problem, the previous pages dont really explain anything related to that diagram.
i think the second diagram is supposed to be only the axial load P (see y-axis) over the missile length.

 

[desertfox]

Hi Dralos

Can you share the earlier pages?

desertfox

 

[paddingtongreen]

I think I understand, the missile is not vertical when it is fired, some are almost level at firing although they are not usually supported at the nose.

I disagree with the axial load as shown, it indicates a push from the tail end; in fact, the pressure is in the interior of the body except at the tail; the body is in tension. Think of blowing up a balloon and releasing it without closing the neck, it takes off like an out of control rocket, but the push is inside, not outside.

Most of those big rockets that are vertical when fired can only stand when full of fuel, the shell buckles unless held in place by the fuel, mostly solid fuel.

I picked up most of this information when I designed part of a rocket fuel mixing and loading facility.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[Dralos]

the missile is a tactical missile and its fixed horizontally from an aircraft. i understand T=10W as the acceleration caused at the end of it by the rocket motor (as paddingtongreen said, the push).

i uploaded the previous pages.

http://hotfile.com/dl/104365272/070df90/MISSILE_CONFIGURATION_DESIG.PDF.html

 

[BAretired]

The left diagram is 10*dead weight in #/". It looks as if the right hand diagram is the integral of the left hand diagram over the length. There should be three branches to the diagram with the middle branch the steepest and the end branches slightly curved.

BA

 

[JStephen]

It looks like the right chart is just all the weight to the left of point x times the 10g. The change in shape at the left end represents the cone shape.

On where the pressure is applied- I would assume a good bit of the force is from the nozzle, at least on a liquid-fueled rocket.

 

[paddingtongreen]

@JStephen, You are correct the liquid fueled jobs, below is a diagram of the WW2, V2, I picked it because I remember it well, it was the only weapon against which, we had no defense.

http://en.wikipedia.org/wiki/File:V-2_rocket_diagram_(with_English_labels).svg

I was thinking of the solid fuel rocket where the fuel burns all the way up to the nose

http://ffden-2.phys.uaf.edu/102spring2004_web_projects/andrew_allen/rocket_engine.html

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[desertfox]

Hi Dralos

Still can't see the other pages, can you load them as pdf's and upload them through eng-tips as an attachment.

desertfox

 

[IRstuff]

Just be careful that you do not broach into classified subjects. Structural loading is a potential weakness, and weaknesses of weapons systems are generally classified.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[Dralos]

@IRstuff, no worries i am just asking about things i found in a book. i want to know how to create an axial loading diagram if you assume that the missile structure is a circular tube.

and by the way. i am new here. could anyone tell me how to edit my posts after posting and how to send private messages?

thanks

 

[rb1957]

i think the 2nd diagram is showing the axial load in a stringer, refer eqn 14.15, and they're showing you what the axial load in a strgr where the bending load adds to the thrust load.

as much as weight (and maneouvre) loads there'll also be lateral aerodynamic loads

 

[IRstuff]

a> there is no edit feature. if the typo is egregious, you can Red flag the posting and ask the moderators to fix the errors.

b> private messaging is discouraged, since any such discussions would not be available to, and serve, the larger population here.

c> next time, use the Engineering.com file download; it's free, there are no delays or captchas to futz with

d> please refrain from posting copyrighted materials, particularly in their entirety, as this site does not condone nor permit copyright violations.

TTFN

FAQ731-376
Chinese prisoner wins Nobel Peace Prize

 

[paddingtongreen]

The second diagram shows the internal force needed to accelerate the portion in front of any particular point. It assumes that the push is from the back of the rocket. It is simply ten times the weight forward of any plane of reference. When you get to the back, it is the total weight by ten.

There are no bending stresses involved. The first diagram is a listing of the masses for the second diagram.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[rb1957]

yeah, i'd buy that, michael ... the fuel mass being distributed along the length of the body

 

[Dralos]

@IRstuff: thanks. i deleted the link.

@paddingtongreen: i guess that makes sense. so the reaction force inside the structure is just going into the opposite direction of T?