Resultant wind speed/direction .

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    Resultant Wind
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Discussion Overview

The discussion centers around calculating the average or resultant wind speed and direction from multiple wind measurements, specifically for a parachutist dropped from 12,000 feet. Participants explore methods for quickly calculating these values using mathematical approaches, particularly focusing on vector resolution and averaging techniques.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant seeks a quick method to calculate resultant wind speed and direction from multiple wind measurements taken at different altitudes.
  • Another participant suggests using vector addition in Cartesian coordinates to resolve individual wind vectors into components.
  • There is a discussion about the format of wind data, with one participant noting that winds are recorded in degrees magnetic and knots, and questioning whether they need to be converted into Cartesian vectors.
  • Participants mention that while the winds are not recorded simultaneously, they are treated as such for the calculations.
  • One participant shares their experience using a PDA with an Excel spreadsheet to calculate average wind, indicating a reliance on technology for these calculations.
  • There is a playful acknowledgment of the potential consequences of miscalculating wind for parachutists, emphasizing the personal interest in the problem rather than a real-life application.

Areas of Agreement / Disagreement

Participants generally agree on the need to resolve wind measurements into Cartesian components for calculation purposes. However, there is no consensus on the best method for quickly calculating the resultant wind speed and direction, and multiple approaches are discussed without resolution.

Contextual Notes

Participants note the importance of understanding how wind speed is specified and the implications of treating non-simultaneous wind measurements as simultaneous for the purpose of calculations. There is also uncertainty about the specific mathematical steps required for accurate calculations.

BT80
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Resultant wind speed/direction...

Hi, new here and am hoping this is in the correct forum and if so that someone can help with this little problem.

Basically I would like to know if there is a "quick" way of calculating an average or resultant wind speed and direction given a selection of 5 or so winds. My aim is to establish the mean wind that acts on a parachutist dropped from, say, 12000ft. If I take off in my plane and note the wind speeds and directions at 2000ft intervals as I climb up I can then manually plot them on paper, draw the resultant and measure the necessary angle; the length of the resultant divided by the number of samples gives me a wind strength. This average wind speed and direction can then be used to calculate the release point for the parachutist so that he lands on the drop zone.

What I was wondering was if there was a way of calculating it accurately and, importantly, quickly using a calculator, rather than drawing it out on graph paper. I can obviously calculate a resultant from 2 winds by dredging up some schoolboy math but anymore than 2 and I'm stumped (other than repeatedly resolving winds in pairs until left with one resultant!)

I'm no math/physics genius so please be gentle!
 
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BT80 said:
Hi, new here and am hoping this is in the correct forum and if so that someone can help with this little problem.

Basically I would like to know if there is a "quick" way of calculating an average or resultant wind speed and direction given a selection of 5 or so winds. My aim is to establish the mean wind that acts on a parachutist dropped from, say, 12000ft. If I take off in my plane and note the wind speeds and directions at 2000ft intervals as I climb up I can then manually plot them on paper, draw the resultant and measure the necessary angle; the length of the resultant divided by the number of samples gives me a wind strength. This average wind speed and direction can then be used to calculate the release point for the parachutist so that he lands on the drop zone.

What I was wondering was if there was a way of calculating it accurately and, importantly, quickly using a calculator, rather than drawing it out on graph paper. I can obviously calculate a resultant from 2 winds by dredging up some schoolboy math but anymore than 2 and I'm stumped (other than repeatedly resolving winds in pairs until left with one resultant!)

I'm no math/physics genius so please be gentle!

Real problem or homework problem (I won't give my guesses on a real problem, since I don't want to kill a real parachutist). Do you mean 5 simultaneous winds?

LHS of this formula adds the individual vectors, RHS is the resultant (only works with cartesian coordinates):
(v1x,v1y,v1z)+(v2x,v2y,v2z)+...(v5x,v5y,v5z)=(v1x+v2x+v3x+v4x+v5x, v1y+v2y+...v5y, v1z+v2z+ ...v5z).

Again, just my guess.

Edit: I just re-read your post and understand the winds are not simultaneous, so the resultant gets divided by 5 as you said. Also, I realized I don't know how the windspeed is specified, ie. is it already in cartesian form, or is it specified by speed and angle?
 
Last edited:


Hi and thanks for the reply. This is based on a "real" problem; I'm a pilot and we normally calculate this using a pda with an excel spreadsheet on it. I've "reverse engineered" a lot of the formulae in the spreadsheet (I'm nosy like that) but was a little stumped with the wind vector thing. If the pda goes the way of most things electronic when they're needed most (!) then we revert to the manually plotted vector diagram to resolve an average wind, which works fine.

The winds are recorded every thousand feet as we climb up to drop altitude. They are recorded in degrees magnetic and nautical miles per hour (kts). Thus a wind out of the north east at 10kts would be recorded in pilot-speak as "045 at 10". I guess I would need to resolve that into cartesian vectors then?

Whilst the winds are not recorded simultaneously they are treated as being such for the purpose of the exercise. Put them all into the spreadsheet and it miraculously spits out an average wind for us. :smile:

Don't worry though - this is purely a personal interest/idle curiosity thing by the way - I shan't be scattering parachutists across the countryside if I can't work this out! :eek:
 


BT80 said:
Hi and thanks for the reply. This is based on a "real" problem; I'm a pilot
BT80 said:
Don't worry though - this is purely a personal interest/idle curiosity thing by the way - I shan't be scattering parachutists across the countryside if I can't work this out! :eek:

Whew! :smile: I shall continue with my guessing then. :smile:

BT80 said:
The winds are recorded every thousand feet as we climb up to drop altitude. They are recorded in degrees magnetic and nautical miles per hour (kts). Thus a wind out of the north east at 10kts would be recorded in pilot-speak as "045 at 10". I guess I would need to resolve that into cartesian vectors then?

Yes, I would try resolving into cartesian components.

For a given speed v, and direction θ:
vx=vsinθ, vy=vcosθ

Then adding:
(v1x,v2y)+(v2x,v2y)+...(v5x,v5y)=(v1x+v2x+v3x+v4x+v5x, v1y+v2y+...v5y)=(vRx,vRy)

From the resultant (vRx,vRy),
get the magnitude: vR=sqrt(vRx2+vRy2)
and direction: θR=arctan(vRy/vRx)
 

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