Speed distance time
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Speed distance time
Hi
How would you guys work out the below or simular problems?
you want to be at 1000' 5 miles from the beacon. You are currently at 8000' and 20 miles from the beacon and your airspeed is 150kts. What descent rate do you need?"
thanks
Sb1
How would you guys work out the below or simular problems?
you want to be at 1000' 5 miles from the beacon. You are currently at 8000' and 20 miles from the beacon and your airspeed is 150kts. What descent rate do you need?"
thanks
Sb1
Join Date: Jun 2001
Location: UK
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Hi Speedbird,
Its been a while since I did one of these but, perhaps something like this?
Your at 8000ft at 20miles and you need to be at 1000ft at 5 miles.
This means we need to lose 7000ft in 15 miles.
At 150kts, it will take you 6 minutes to fly those 15 miles 15/150 x60 =6 mins
So, we have 7000ft to lose in 6 minutes, 7000/6 = 1166ft, or about 1200ft/min if I was flying :-)
It often helped me to draw a diagram out and look at the problem side on.
Hope that helps,
Regards,
Buster
Re Alex, I had assumed (never do that! ) that airspeed and groundspeed were the same given no wind information. That makes it a little more straightforward.
Its been a while since I did one of these but, perhaps something like this?
Your at 8000ft at 20miles and you need to be at 1000ft at 5 miles.
This means we need to lose 7000ft in 15 miles.
At 150kts, it will take you 6 minutes to fly those 15 miles 15/150 x60 =6 mins
So, we have 7000ft to lose in 6 minutes, 7000/6 = 1166ft, or about 1200ft/min if I was flying :-)
It often helped me to draw a diagram out and look at the problem side on.
Hope that helps,
Regards,
Buster
Re Alex, I had assumed (never do that! ) that airspeed and groundspeed were the same given no wind information. That makes it a little more straightforward.
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I prefer to think in nm/min. You can just plug nm/min into any speed based rule of thumb, I find it much easier to juggle 1.5,2,2.5,3 etc in my head than thinking in longhand (15/150*60).
That 150 kts. Is that TAS or IAS? If it is TAS then it should be the the average TAS from 8000' to 1000', who would fly a constant TAS when descending? Assuming it is IAS it doesn't change it much, rule of thumb answer using the rule of squares for TAS still pops the answer out at ~1200fpm. However, will make a big difference if descending from hypoxic altitudes though.
That 150 kts. Is that TAS or IAS? If it is TAS then it should be the the average TAS from 8000' to 1000', who would fly a constant TAS when descending? Assuming it is IAS it doesn't change it much, rule of thumb answer using the rule of squares for TAS still pops the answer out at ~1200fpm. However, will make a big difference if descending from hypoxic altitudes though.
