Another Dumb Australian question

According to Murphey's Rocket Calculator. The answer is always the nearest Tree, Pond/Creek or Rooftop.

But seriously I guess Rocsim does that but I never check accuracy on drift distance.

Layne

guesstimating

Or in my case the nearest paddock containing the most irritable Red Angus Bull on the face of the Earth!

But thanks for that mate.

Or as I saw recently in a list of "Funny Signs From Around The World"...

The farmer will gladly let anyone cross the field for free... but the bull charges!

-dave w

It's actually a couple simple calculations.

Altitude / descent rate = duration

duration * wind speed = drift

Example: a rocket ejects at 5000', has a descent rate of 20 f/s, and the wind speed is 15mph.

5000f / 20fps = 250 seconds or .06944 hours 15 * .06944 = 1.04 miles

Have a nice walk.

Thermals change the descent rate!

Bob Kaplow NAR # 18L TRA # "Impeach the TRA BoD" >>> To reply, remove the TRABoD!

Thermals may make the descent rate negative!!!

So do differing wind speeds -- often the wind at altitude is much faster than the wind at ground level.

Unless the wind is moving vertical, how would that change the descent rate?

It generates lift.

Jam replied:

D'oh! You're right. What I meant to say was that it changes distance the rocket will travel. You could calculate the distance based on the wind at ground level, yet have the rocket go much farther than that due to faster winds at altitude.

Been there. Done that.

Bob Kaplow NAR # 18L TRA # "Impeach the TRA BoD" >>> To reply, remove the TRABoD!

Also true. BTW, for those that don't know, when you call the FAA at

1-800-WX-BRIEF to get the pilot weather briefing, they give you the winds aloft numbers as well. They are often in a different direction than surface winds.

Bob Kaplow NAR # 18L TRA # "Impeach the TRA BoD" >>> To reply, remove the TRABoD!

That would be a thermal. Or a tornado...

Bob Kaplow NAR # 18L TRA # "Impeach the TRA BoD" >>> To reply, remove the TRABoD!

Either you have a rather low descent rate, or you are flying in winds over

20mph.

9000/20=450 seconds or .125 hrs .125 * 20 = 2.5 miles

Bob Kaplow NAR # 18L TRA # "Impeach the TRA BoD" >>> To reply, remove the TRABoD!

component of the

Yes, I admit I wasn't following the conversation closely enough. But, are you saying that a cross wind won't help generate lift?

Likewise...

When you have an A PD model thermal away it is fun. When you have a G powered 4"x84" Mega-Roc thermal away that is just COOL.

Jerry

Or Turbulence..

the

parachute,

Yep, that's what I'm saying. An object in free fall cannot "sense" any crosswind at all. It is has no ability to resist the crosswind, so therefore it travels at the same speed and direction as the wind. Jump in a river and swim across... as soon as you hit the water you'll be traveling down stream, and you wont feel the current at all.

Likewise, if you threw an airfoil (hydrofoil) in the river, it would float downstream, generating absolutely no lift what-so-ever.

steve