Maths Question

[Doofus]

I want to make a tank dipstick for the petrol tank of an old jalopy, mainly because I don't trust the fuel gauge.

I know the dimensions of the tank, and I know the angle at which the dipstick goes in. I also know how much of the dipstick gets wet.

So I have a right angled triangle. I know the three angles, and I know the length of the hypotenuse. How do I find the length of the vertical side? I don't care about the other side.

Once I have the vertical, I know the depth of the petrol, and multiplying that by the width and length will give me the volume.

I've Goolged the solution, but there are many, and none seem to be exactly what I want. I suspect it involves sin or somesuch, so I'm way out of my depth (ha ha. 'Depth'. Geddit?)

[RicharDC5]

cos theta = adj/hyp

hypotenoose cos bottom angle = vertical

[RicharDC5]

I assume theta is at the bottom of the tank as he is looking at it

rotate the triangle above 90 anti-clockwise

eta - i suppose it doesn't make a difference which way you look at it

Edited by RicharDC5 on Saturday 4th February 16:46

[Doofus]

DELETED: Comment made by a member who's account has been deleted.

Thank you. So if the dipstick goes in at 35deg, then the third angle (the one the hyp makes with the vertical) must be 55deg.

So if hyp is 10, then vertical is 10 x Cos 55. Yes?

[RicharDC5]

Deleted my reply as I'm getting confused now lol

If the dipstick is 35deg to the horizontal that is correct

Edited by RicharDC5 on Saturday 4th February 16:56

[Doofus]

DELETED: Comment made by a member who's account has been deleted.

I might have it back to front...

I used a spirit level, and an app on my phone. I think it's 55 deg to the vertical, not 35.

[Greenmantle]

looks to me like its 55 degrees to the horizontal not vertical.

john

[Doofus]

Yeah, I suspected I'd got it arse about face.

So the vertical side is hyp x Cos 35 then?

[Doofus]

Brilliant, thanks.

So now I can mark up my dipstick in litres

[Sir Lord Poopie]

At the risk of coming across as bit thick - you'll find the tank volume by filling the tank with fuel whilst it is empty. If you want to find the volume of fuel between set points on the stick, similarly measure it at the fuel pump.

[Doofus]

Sir Lord Poopie said:

At the risk of coming across as bit thick - you'll find the tank volume by filling the tank with fuel whilst it is empty. If you want to find the volume of fuel between set points on the stick, similarly measure it at the fuel pump.

How am I supposed to get it to the petrol station if the tank is empty? Are you proposing that I drive there, and sit idling on the forecourt until the tank runs dry, and then fill it?

I know how big my tank is; I want to know my range, and knowing how much i put in it last time doesn't tell me that, if I don't know what was in it to start with.

[4Q]

Dip it now, add a known amount of fuel 1,5,10 litres or whatever and dip it again. That will give you the scale along the length of your dipstick.

[Sir Lord Poopie]

Doofus said:

I know how big my tank is; I want to know my range, and knowing how much i put in it last time doesn't tell me that, if I don't know what was in it to start with.

Now I am most confused. But as long as you're satisfied with the solution that's the main thing.

[anonymous-user]

Wait until empty at home,

Add 5x2L of fuel, everytime you do this, mark it, (that mark will be 10L of fuel) until full... Much easier then all that math mumbo jumbo

Sorry..I'm not very good at maths thats all

[williamp]

4Q said:

Dip it now, add a known amount of fuel 1,5,10 litres or whatever and dip it again. That will give you the scale along the length of your dipstick.

this would be my way. Tanks are rarely uniform size, so the maths might not be relevent

[Doofus]

williamp said:

this would be my way. Tanks are rarely uniform size, so the maths might not be relevent

This one is. I've had it out before, and I know that it is exactly rectangular.

[Doofus]

Sir Lord Poopie said:

Now I am most confused. But as long as you're satisfied with the solution that's the main thing.

I want to know, at any point in time, how much fuel I have in the tank. I don't want to rely on the fuel gauge, so I need to dip the tank.