#1
So... a friend of mine is having a pirate themed weekend for his birthday soon and being the utter loser that I am I want to mod my car to look like a pirate ship for this particular event. I've got just about everything sorted apart from the mast.

I did Physics to A Level Standard but calculus was never my strong point so... those who are of mathematical/physics persuasion can you give me the formulas to calculate the forces that would be acting on a mast attached to the roof of the car. I need to be able to work out how fast I'll be able to go (I'll be going down a motorway but not stupidly quickly) and to help work out how thick the mast should be etc to reduce the liklihood of it snapping. Whilst sails maybe attached they definitely WON'T be unfurled. The mast/sail is purely for visual purposes, hence why it won't have to be that tall.

FYI I am NOT able to drill a hole through the roof to drop the mast down. That was my first idea but I then realised that I'd like to be able to use the car afterwards!

The car is a Ford Ka (no flaming!)

Many thanks
Quote:
Originally Posted by ihavnofingrprnt
well there are only three true people alive today who are actually possesed by satan

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#2
Put holes in the flag to reduce the force from the wind, either that or attach it to the car a block up from the house instead of driving down the motorway with it, it'll save you a lot of hassle.
Last edited by HEXAGRAM66 at Jul 1, 2009,
#3
we'd have to take into account air resistance and turbulence and stuff, which as far as i know can't be done :O
#4
25 miles?

Just a rough estimate, but it seems about right. If not then 15.

Edit: Wait, you mean a full mast don't you?
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Last edited by Jesstaa at Jul 1, 2009,
#6
Why not create a folding, or detachable, mast?

Or assemble the mast a few blocks away from the party?
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#7
Quote by frankibo
we'd have to take into account air resistance and turbulence and stuff, which as far as i know can't be done :O


Umm..it can. But will you want to put in soo much work ?

You could ignore turbulance and put in a safety factor. It's not like it has to be a perfect answer...but i say attach the mast after you get to his house or go overboard with the tube thickness.
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#8
Hmmmm... Pie.

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#9
this is a bad idea.

just buy a parrot or something.
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#10
Quote by X-Boy
Umm..it can. But will you want to put in soo much work ?

You could ignore turbulance and put in a safety factor. It's not like it has to be a perfect answer...but i say attach the mast after you get to his house or go overboard with the tube thickness.


ahh fair enough, i just didnt want him to get some estimated answer which resulted in a wrecked car D:

i'm all for putting it up when you get there
#11
The force that acts on the mast is friction with the air if the car moves at constant speed, and when the car accelerates or decelerates inertia is added.
#12
Quote by Mad Marius
The force that acts on the mast is friction with the air if the car moves at constant speed, and when the car accelerates or decelerates inertia is added.


Then you'll need to figure out all the moments acting at the point of fasting, find out how much his mounting method can actually handle...and then see if it'll snap...

I'm pretty sure your tube won't snap, but it'll be more of your mounting failing.
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#13
The mast doesn't need to be able to propel the car at all it's just for show. I think attaching it close to the party is probably the way forward.

My initial thought was to build a "crow's nest" and put in a false bottom. That way the pivot would be moved further up the mast so the moment forces would be less (in my head) I know the "physics" of what's going on but I can't/don't know how to do the necessary calculations. The nest would be attached to the roof of the car by way of an old style roof rack.

The sail was going to be one the old style forward facing one's not the one's such as the pic above. And for just about all purposes it would be furled, because it would play hell if it wasn't with the wind resistance and increased surface area... guaranteed snappage! If I was even slightly nautically minded I'd probably be making alot more sense...

Also what about holes through the flagpole to decrease wind resistance? Or would that compromise the structural integrity too much? I'm thinking the mast will have a diameter of 10cm max. Maximum height of 150cm. But all that depends on whether or not it's doable.
Quote:
Originally Posted by ihavnofingrprnt
well there are only three true people alive today who are actually possesed by satan

Dakota Fanning, the kfc general dude, and my neighbor and all of them dont have much musical ability
#14
Quote by frankibo
we'd have to take into account air resistance and turbulence and stuff, which as far as i know can't be done :O

Are you kidding?
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#15
we could calculate it and everything,.
but why not just make something so solid that it will hold...?
shouldn't be too hard

and WHY THE HELL DO YOU WANT TO DO IT?
seems like a waist

edit: F=1/2 * rho * cw * A * v^2
or something, don't have my binas here
the problem is that the wind has a speed and direction too, which are not constant.
so actually... this formula won't help you
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Last edited by Neo Evil11 at Jul 1, 2009,
#16
There is no simple way to do this, unless you know the Drag Coefficient of the mast,

using:

0.5*rho*S*Cd*V^2

Where rho is 1.225, S is the profile area of the mast, Cd is the drag coefficient and V is your speed (ms^-1). But that's an extremely simplified model, and probably wouldn't work anyway.


But unless you have a spare wind tunnel, I'm not seeing it. The force directly down on the roof of your car is just the mas multiplied by 9.81.

But these numbers are meaningless - You're not going to be able to use them in any way, are you?

If you want to do this, make the mast REALLY short, and attach it to a wide base. Strap that on the roof of your car to distribute the pressure caused by the weight. But I'm not even sure that's going to be legal, plus Ka's have sloping roofs so there's an excellent chance that your cables/lashings will snap and it'll fall off, causing serious damage to your roof and anyone behind you.

Seriously, buy an eyepatch and a fake parrot. Don't try this stunt, because not only is it hard to pull off, it's also a major safety hazard.
Last edited by LordBishek at Jul 1, 2009,
#17
Quote by LordBishek
There is no simple way to do this, unless you know the Drag Coefficient of the mast. But unless you have a spare wind tunnel, I'm not seeing it. The force directly down on the roof of your car is just the mas multiplied by 9.81.

But these numbers are meaningless - You're not going to be able to use them in any way, are you?

If you want to do this, make the mast REALLY short, and attach it to a wide base. Strap that on the roof of your car to distribute the pressure caused by the weight. But I'm not even sure that's going to be legal, plus Ka's have sloping roofs so there's an excellent chance that your cables/lashings will snap and it'll fall off, causing serious damage to your roof and anyone behind you.

Seriously, buy an eyepatch and a fake parrot. Don't try this stunt, because not only is it hard to pull off, it's also a major safety hazard.


I think he is talking about the sails catching winds and bend the mast
you can calculate that actually
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Last edited by Neo Evil11 at Jul 1, 2009,
#18
Quote by Neo Evil11
I think he is talking about the sails catching winds and bend the mast
you can calculate that actually


He said they were furled.
#19
Quote by LordBishek
He said they were furled.


then what the hell is the problem?
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#21
Quote by LordBishek
Drag from the mast.


I think he will get a problem attaching the mast to the roof without drilling hole
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#22
Quote by Neo Evil11
I think he will get a problem attaching the mast to the roof without drilling hole


That's why I told him he could do it by attaching the mast to a wide base that he could secure through the windows instead of drilling holes. I then pointed out the flaws in THAT plan.
#23
Quote by LordBishek
That's why I told him he could do it by attaching the mast to a wide base that he could secure through the windows instead of drilling holes. I then pointed out the flaws in THAT plan.

psst, I would rather calculate if the mast would bend
this is just silly
to TS just use glue
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#24
Quote by Neo Evil11
psst, I would rather calculate if the mast would bend
this is just silly
to TS just use glue


The mast will bend, but not by much if he's using thick enough wood.

Wait, actually



Use bamboo cane! you can get it from your local garden centre.
#25
Quote by frankibo
we'd have to take into account air resistance and turbulence and stuff, which as far as i know can't be done :O



meh meh meh. youre wrong. to properly solve this problem you have to write a differential equation since air resistane is a function of speed. i dont wanna do this, but as long as its secured down well id say 20 mph.
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#26
Thanks for the help!

20mph sounds sensible... I was hoping to be able to do more to be able to go on A roads at a decent speed.

I like the idea of Bamboo Cane, as that would be flexible and would bend appropriately and hopefully not snap off. Are there any other flexible but sturdy woods out there? I think it would be theoretically quite easy to resolve the problem of the sloping roof by securing the mast to a roof rack and keeping the roof rack flat and secure.

With greater thought, I've decided that travelling a long distance with it raised probably isn't ideal based on the fact that yeh it is a safety hazard if anything goes wrong... Health and Safety... it's ruining everything!! So i'll probably knock the back seats down and carry it with me till I'm about a mile away and then mount it there.
Quote:
Originally Posted by ihavnofingrprnt
well there are only three true people alive today who are actually possesed by satan

Dakota Fanning, the kfc general dude, and my neighbor and all of them dont have much musical ability
#27
Quote by Joycey
Thanks for the help!

20mph sounds sensible... I was hoping to be able to do more to be able to go on A roads at a decent speed.

I like the idea of Bamboo Cane, as that would be flexible and would bend appropriately and hopefully not snap off. Are there any other flexible but sturdy woods out there? I think it would be theoretically quite easy to resolve the problem of the sloping roof by securing the mast to a roof rack and keeping the roof rack flat and secure.

With greater thought, I've decided that travelling a long distance with it raised probably isn't ideal based on the fact that yeh it is a safety hazard if anything goes wrong... Health and Safety... it's ruining everything!! So i'll probably knock the back seats down and carry it with me till I'm about a mile away and then mount it there.


Right, compromise. Go for thickish sort of dowel - 8mm to 10mm from a place like B and Q or summat. Shouldn't bend much under air resistance and should be strong enough to support the weight of a sheet, plus it's more likely to be strong enough to safely attach it to the base. If you can, make it as SMALL as possible, certainly small enough to fit in the car. Then, drive over to a place near where you need to go, and then strap it to the roof and drive SLOWLY there. That way, it's safe and you don't run the risk of it falling off while you're tear-arsing round a corner on an A road. It'll still have the same impact, you just won't be able to attach it at home.

EDIT:^ Spot on, son.
#28
i would use straps to secure the mast, that way its sturdy and you can raise/lower it fairly easily
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#29
I'll draw up some plans and post them on here tonight to see what you think. It's got to be done somehow anyway!!
Quote:
Originally Posted by ihavnofingrprnt
well there are only three true people alive today who are actually possesed by satan

Dakota Fanning, the kfc general dude, and my neighbor and all of them dont have much musical ability
#31
Quote by McTodd
this is a bad idea.

just buy a parrot or something.


a sensible answer.


no one is going to like you anymore than they do now TS, so don't waste your time trying to 'impress' everyone with your very dangerous and tedious boatcar
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