No, IIRC it's the integral of the solid cross section area distance from
the axis. That's why triangular sections have the greatest rigidty for
their cross section area, and square sections are more rigid than oval
or round.


gonefishiing wrote:
MEANING TO THE EXTREME OUTER FIBERS IN BOTH AXIS?

No, all fibers along the tension/compression axis. That's why it's an
integral.


but this is for rectangular sections right?
how do you calculate this for an oval section?

Personally, I don't. I look it up! But this is also not foolproof, you'd
be amazed how many mfg'rs fudge their specs (or maybe they can't do math).


YEAH BEEN THERE RECENTLY: IT IS ALSO CALLED EXPENSIVE WHEN YOU DISCOVERED
THEIR PUBLISHED ERRORS.

I hope nobody got hurt. This is called "letting your customers do your
failure mode testing." It's very popular with software firms, too

Regards
Doug King

"Lady Pilot" wrote in message

| Forget the ice pick...I've invested in a sturdy axe! ;-D

Heh... that's for cutting woody things...

OUCH!

CM

I'm wondering what you are talking about.

Cheers

Scout wrote:

And I'm wondering what the formulation time has to do with how long you've
been waiting to work it into a conversation.
Scout

"Nav" wrote in message
...

I wonder what "formuilating a problem" has to do with typing?

Cheers



Capt. Mooron wrote:

Heh... who cares... she gets paid.. she types.

CM

"Scout" wrote in message
...
| I'll bet she just loves being forced into asa ****ing contests.
| Scout
|
| "Capt. Mooron" wrote in message
| ...
| He uses a secretary ... she types about 120 wpm.
|
| CM
|
|
|
| "Scout" wrote in message
| ...
| | I don't believe you can type that fast.
| | Scout
|
|
|
|

DSK wrote:

Nav wrote:


Are you sure? The geometry _is_ defined.



You're right. Lesson 1- always look the problem over thoroughly.


Actually, on 2nd look, you're wrong. It isn't, unless you *assume* the
mast is perfectly vertical and the boom perfectly horizontal.


Assume nothing. If it were not vertical or horizontal the angle would be
given. One wonders if you ever took any engineering courses...
Introducing "perfectly" shows a clear lack of engineering expertise and
an attempt to smoke screen. It's pretty clear you can't do it can you?


Are you saying it is not 118 lbs in the topping lift case?


Probably not. With the ratios you give (assuming vertical mast & level
boom, since you don't seem capable of defining the problem correctly)
the compression is going to be somewhat less than 1/2 the weight.

And, if you look closely, you'll see that the tension on the topping
lift is *more* than the weight! Hello! How did that happen?

Wait there's more... a mysterious force has appeared on the mast!
Apparently the pulling of the topping lift and the pushing of the boom
has run amok! HELP HELP!


Yes, you need help -the diagram is pretty much worthless and you've not
shown your incorrect "cosine" anyway . I'd say you just failed freshman
engineering.


I gather that you have never heard of a "Free Body Diagram"?
Freshman engineering stuff. That is the way to solve such problems.
If you don't believe me, ask Scout.



But I'm not asking Scout. I'm asking _you_ to solve this freshman
problem -if you can.



Actually it took the longest to convert the file and upload it. What a
PITA. All to prove a stupid point.


The point being you can't draw a proper free body diagram or solve the
problem?

... The question was one of seamanship and appropriate use of
equipment, spars and rigging. Do you deny that a given weight that
will fold a boom in the vang lift will be easily lifted by the boom if
a topping lift is used?


So, I take that you've folded up a boom trying to lift something? Can we
assume that you learned nothing from it, other than "don't"?


Such vivid imagination. Assume what you like but it's obvious from this
thread to any engineer that you don't even begin to understand basic
engineering.

Cheers

DSK wrote:

gonefishiing wrote:

refresh my memory:
i'm looking for the section modulus for a boom section to understand
allowable bending stress.
sx= bd(squared) ?


No, IIRC it's the integral of the solid cross section area distance from
the axis.

Perhaps term you are groping for is "section moment"? You can look it up
on the web.

That's why triangular sections have the greatest rigidty for
their cross section area, and square sections are more rigid than oval
or round.

I think you may be confusing a truss with a section. For bending in
plane, the most rigid section per unit weight is close to a T
section with the top under compression and the bulb (or smaller bottom
plate) at the bottom in tension. If the direction can be up and down
this becomes the familiar I beam. For compression, a circle (tube) is
generally best as again, it places most material away from the axis for
all planes containing the axis. This important as the failure mode is
almost always buckling and not material compression. For a combination
of compression and bending the best solution lies between these cases so
we see egg shapes and ovals but the object is always to place as much
material from the axis as needed to contain the stress well below a
yield stress.

Hope this helps.

Cheers

gonefishiing wrote:

refresh my memory:
i'm looking for the section modulus for a boom section to understand
allowable bending stress.
sx= bd(squared) ?
but this is for rectangular sections right?
how do you calculate this for an oval section?
gf.


The shape of the section is taken care of by it's moment of inertia.
The bending stress is the bending moment times the distance from the
neutral axis divided by the moment of inertia of the section.

Stress = M Y /I

This is known as the flexure formula.

Cheers

nav
thanks--got it.
its been awhile but yes all that is understood
i can make the calculations, figure the loads, determine the max moment,
check the deflection, shear at the bolts etc.
all i need is the moment of interia and the section modulus (it is the
correct term) for an oval section
i don't generally deal with oval sections and none are listed in any manuals
i have here.
probably just need to search an alum. association reference. as i have alla
the dimensions of the section involved ( both axis, wall thickness)

i am looking for the section properties to understand max loading in a given
situation..
(working backwards)

as in S sub x (required) = M/f(alum.)
S sub x (actual) of a section = ??

whe
I = moment of interia (inches 4th)
S sub x = section modulus (inches 3rd)
M = moment (#-inches)
F sub b = bending stress. (psi)

simple statics really--i'll just pull a couple of books off the shelf and
dust em off.
actually i'll just call one of my engineers in the morning.
in the meantime.........i'm outta here to find a glass of wine and a blonde
thanks
gf.







"Nav" wrote in message
...


gonefishiing wrote:

refresh my memory:
i'm looking for the section modulus for a boom section to understand
allowable bending stress.
sx= bd(squared) ?
but this is for rectangular sections right?
how do you calculate this for an oval section?
gf.


The shape of the section is taken care of by it's moment of inertia.
The bending stress is the bending moment times the distance from the
neutral axis divided by the moment of inertia of the section.

Stress = M Y /I

This is known as the flexure formula.

Cheers

You can use a simple rule of thumb. If you know the moment of intertia
for a box section of the same wall thickness and outside dimensions the
moment of inertial of the tube or ellipse that has the same dimension is
about 14% less.

Hope this gives you what you want.

Cheers

as the tune
gonefishiing wrote:
nav
thanks--got it.
its been awhile but yes all that is understood
i can make the calculations, figure the loads, determine the max moment,
check the deflection, shear at the bolts etc.
all i need is the moment of interia and the section modulus (it is the
correct term) for an oval section
i don't generally deal with oval sections and none are listed in any manuals
i have here.
probably just need to search an alum. association reference. as i have alla
the dimensions of the section involved ( both axis, wall thickness)

i am looking for the section properties to understand max loading in a given
situation..
(working backwards)

as in S sub x (required) = M/f(alum.)
S sub x (actual) of a section = ??

whe
I = moment of interia (inches 4th)
S sub x = section modulus (inches 3rd)
M = moment (#-inches)
F sub b = bending stress. (psi)

simple statics really--i'll just pull a couple of books off the shelf and
dust em off.
actually i'll just call one of my engineers in the morning.
in the meantime.........i'm outta here to find a glass of wine and a blonde
thanks
gf.







"Nav" wrote in message
...


gonefishiing wrote:


refresh my memory:
i'm looking for the section modulus for a boom section to understand
allowable bending stress.
sx= bd(squared) ?
but this is for rectangular sections right?
how do you calculate this for an oval section?
gf.


The shape of the section is taken care of by it's moment of inertia.
The bending stress is the bending moment times the distance from the
neutral axis divided by the moment of inertia of the section.

Stress = M Y /I

This is known as the flexure formula.

Cheers

So, I take that you've folded up a boom trying to lift something? Can
we assume that you learned nothing from it, other than "don't"?


Nav wrote:
Such vivid imagination.

Well, I have seen booms supported by rigid vangs that didn't fold up, so
obviously it can be done... if you do it right.

You think it can't be done, why? Conclusion: you did it wrong, and
decided it was impossible.


.... it's obvious from this
thread to any engineer that you don't even begin to understand basic
engineering.

Funny you should say that, since you show no comprehension of how to
read the diagram, yet you pass judgement on my competence. The
resolution of forces is not obvious but it's also not rocket science.

If OTOH you *do* have some clue what you're talking about, tell us what
the mysterious symbol next to the mast represents.

DSK