Descent to a beacon?
 

Hi All,
I am preparing for g/nav exam and have come across a type of question that i dont seem to have a formula for.It is the type where u need to lose a certain amount of height by a certain range,using a certain groundspeed but with no glide slope angle.I have tried fiddling with every type of glideslope formula i have but all seem to need the angle! Any ideas? Im sure it's a doddle to anyone with half a mind for maths which unfortunately excludes me!

Cheers

Yorky

Here goes with my 2p's worth.

If I've got it correct you need to lose a certain amount of height by a certain distance with an associated groundspeed.

Q. At 20,000 ft and 100 miles from a beacon. You need to be at 10,000 and 40 miles from the beacon. Your groundspeed it 360 kts.

A.10,000 ft to lose. Travelling at 6 miles a minute. And 60 miles to lose the height. Which is 10 mins. So RoD 1000ft / min.

Is that what you are looking for ?

There is no formula! The glide slope formulas are not the best way of answering the question, so no angle is needed. This is one you have to work out from your knowledge of navigation. You will not be handed everything in navigation on a plate, as a formula, as the information you learn is too broad in application. The mathematics are not difficult for the question, you simply need the speed / time / distance equation, applied twice.

The common factor is TIME. You must descend and cover the ground in the same time, so that is the first thing to calculate.

If you are given descent and space available and asked for the RoD required, then work out the time from the distance to be covered and the groundspeed. Use this time, and the descent needed, to calculate the rate of descent.

If on the other hand you are given descent and RoD and asked for the distance required to descend then work out the time for descent from the amount of descent and RoD. Use the time and groundspeed to work out how far you will travel in this time.

Send Clowns
Gen Nav
BCFT

Thanks very much guys,i think i was trying too hard to complicate it.It's amazing how staring at the same subject for hours on end seems to limit the use of common logic!

cheers again

YD

I'll say to you this
 

Don't stick on the same question if it requires more than 5 minutes of your time. Mark the question and write down what page it's on. Proceed on doing the next question.
When you have time, go to your school, show them the question and write down how it's done.
Doing this will maximize your use of time to prepare for the exams.


Of course you can post the q's here or just PM some of the G-nav experts here. Think it was Alex or Keith.

One in 60,

That sounds like a plan! Unfortunately my school has closed it's doors since i left (this is a re-sit),so my back up is limited.I'm therefore really grateful for the answers i've had from "pruners" willing to help with the odd question that i've had.Any questions that i can remember from exams will be posted for anyone who is interested.

Cheers again (no doubt i'll have a new query or three sometime before next week)

YD

Well that's a bit of a weeeee
 

tiny tiny problem isn't it?

Curious I am, what and how many exams are you sitting this time round?

Cheers
1/60

1in60,
Just the 2,g/nav and instruments.I think it was u that answered an instrument query for me the other day so cheers again.(I am piper pervert but working from mates house for a few days to get peace and quiet,he set up account today so sorry to confuse!)

PP/YD

No problem, Yorky, any further questions you're welcome to try me with a PM. Not your fault your school closes (I was working for SFT just before they did!), we all try to help in circumstances.

SC,
Thats really good of u and i will probably take u up on that offer in next day or two.

Cheers Again

YD

Ah yes
 

I in fact did reply to one of your posts.
I'm on line most of the time during the day so I might be able to help with some G nav questions you may have.