Speed distance time

[slow_bird1]

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

[Alex Whittingham]

You'd need a groundspeed to get anything useful. What's the TAS and wind component?

[buster172]

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.

[eoincarey]

yep, i got the same as buster, 1166fpm. Anyone got any better?

ETC

[sicky]

so simple when you break it down like that!

[mckrll]

I get 1166.7ft/min with a Slp of 4.4deg.

Mind you that's electronically, which I suppose doesn't count?!

Andrew

[High Wing Drifter]

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.