Ok let’s take a look on some easy techniques for
simplifying problems with multiple equations involved such as in the time,
speed, and distance problem.
First remember that there will be only four variables
in the formula, and the interviewer will need to give you three of them.
The four variables are wind, distance, time, and true
airspeed.
The basic time-speed-distance formula is this.
(GS) X (Time) = (Distance)
Remember every 30 knots equals 5 miles/minute or 60
knots equals 1mile/minute.
So if you have a speed of 480 knots, you travel 8
miles/minute.
Ground
Speed Knots
|
Miles
per minute
|
60
|
1
|
90
|
1.5
|
120
|
2
|
150
|
2.5
|
180
|
3
|
210
|
3.5
|
240
|
4
|
270
|
4.5
|
300
|
5
|
330
|
5.5
|
360
|
6
|
390
|
6.5
|
420
|
7
|
450
|
7.5
|
480
|
8
|
510
|
8.5
|
540
|
9
|
No wind factor
involved, if it’s not given to you, you can assume it to be zero.
If you are given TAS, and want to find the Ground
speed, you use this formula.
TAS plus/minus Wind = GS
Ok let’s practice this with some examples.
KTAS
|
WIND
|
TIME
|
DISTANCE
|
240
|
60
TW
|
?
|
200
NM
|
280
|
70
HW
|
10
MIN
|
?
|
150
|
0
|
?
|
5
NM
|
?
|
0
|
4
MIN
|
20
NM
|
420
|
60
TW
|
?
|
400
NM
|
?
|
0
|
2
MIN
|
14
NM
|
?
|
0
|
1.5
hr
|
600
NM
|
500
|
0
|
45
MIN
|
?
|
?
|
0
|
40
MIN
|
340
NM
|
Calculate the examples and fill in the blanks.
Here it is good to use the technique of converting the
ground speed to miles per minute to make the problem solving easier during the
interview.
It is important to keep it as simple as possible since
you probably not are allowed to use calculator or, pen and paper.
When you are given the ground speed or can figure it
out from the true airspeeds and winds, convert it to nautical miles per minute.
Example 350 knots GS= 360 divided by 60 = 6 miles per
minute
You can then more easily multiply these nautical miles
per minute by the number of minutes to get the distance traveled. 10 @ 6 nmpm = 60 miles
Or you can divide the distance by the nautical miles
per minute to figure the number of minutes
90 miles @ 6nmpm = 15 minutes
Here are the answers from the previous task.
KTAS
|
WIND
|
TIME
|
DISTANCE
|
240
|
60
TW
|
40
MIN
|
200
NM
|
280
|
70
HW
|
10
MIN
|
35
NM
|
150
|
0
|
2
MIN
|
5
NM
|
300
|
0
|
4
MIN
|
20
NM
|
420
|
60
TW
|
50
MIN
|
400
NM
|
420
|
0
|
2
MIN
|
14
NM
|
400
|
0
|
1.5
HR
|
600
NM
|
500
|
0
|
45
MIN
|
375
NM
|
510
|
0
|
40
MIN
|
340
NM
|
Notice that the last three problems are easier to
solve using an approach of proportions.
1,5 hour is three segments of 0,5 hour, and that 600
NM is three segments of 200 NM, then you realize that you travel 200 NM per
half hour or 400 NM per hour = 400 knots ground speed.