Formulae or Rule of thumb?

[rbr919]

Hello.

Please could you give me the following formulae or a rule of thumb for the following.

1. When to start the decent (ie calc distance)
2. when to level out at a specific altitude (calc feet before)
3. When to start the turn(distance before)
4. Calc crosswind
5. any others that may be useful

I start my CPL & IR soon and your help would be useful.

[Farmer 1]

I suspect you might be looking for problems that don't exist - 2 and 3, for instance.

4, I think you'll learn soon enough on the course, or use your Dalton computer.

For 1, use time, not distance. i.e. No. of feet to descend divided by the time in which to do it, and you have the answer directly.

As with most of these calculations, you will find there is more than one way of swinging a cat.

[Ropey Pilot]

As farmer said time is far easier (2000 feet to lose in 2 mins = 1000fpm!)

However,

For start of descent by distance you can use height in hundreds of feet' / 3

eg to lose 9000' you need 30 miles
to lose 6000' you need 20 miles
to lose 3000' you need 10 miles
to lose 1000' you need 3.3 miles

That gives you a 3 degree glide In still air which is what you will need on most approaches and is also comfortable. Can't say I ever used that till my first job - on the IR I started a climb/descent when told pretty much!

The opposite also works (obviously) if you have 15 miles to run how much height can you lose = 4500' (15 x 3 = 45 hundred feet)

To work out your RoD on a 3 degree glide half your groundspeed and add a zero (the easy way to multiply by 5)

eg 240 knots = 1200 fpm RoD

That one is useful: If you are at 180 knots (groundspeed) on an ILS with a 3 degree glide and your RoD is not 900 fpm you are going to leave that glideslope in the near future!

Seem to remember a rate 1 turn is airspeed/ 10 plus 7

ie at 100 knots a rate 1 turn is 17 degrees. At 150 knots it is 22 degrees. (Could be wrong with that one I stand to be corrected)

[rigpiggy]

1. 1/2 your g/s add a zero, 3 time alt to lose=3degree slope. Use your rnav and depending upon wind/g/s use a higher rate of descent in a tailwind

2. 20% of your climb/descent ie 1000fpm 200' before level off, start your push pull. keep it smooth

3. 10% of your g/s ie 220ktas start turn 2.2 miles out from waypoint.


These are all relative and work on small to medium turboprops. bigger a/c have more inertia and may require some fine tuning

[Farmer 1]

An addendum to my previous post.

Two rules of thumb:

1. Always do a gross error check at the end of any calculation. Or perhaps ask your colleague to do it in his own way, and compare results.

2. Keep things simple. For instance, if a calculation seems complicated, you might not be doing it right. Try ignoring the numbers and look at the units.

Speed, for instance (and this is really keeping things simple), is measured in knots, i.e. nautical miles per hour. So, on the top line you put the miles (distance) and divide it by the hours (time). It often helps you find a mistake - using minutes instead of hours, for example. Then you replace the units with your figures.

[Ropey Pilot]

Also rbr:

How do you find you work best?

Some people find that they like to have things like these imprinted into their minds for months and they become second nature. If this is you go ahead and get familiar with them!

If you are like a lot of people who struggle for capacity when the IQ fan at the front is switched on make sure you are not overloading yourself by thinking about more thanyou have to!

Your instructor (should) be able to tell you these tricks of the trade - and more importantly which ones are important. As I mentioned before the 3 x distance = height for 3 degree was something I had never even heard of till I worked commercially. it is v useful now but during my IR it would just have been something elde that was melting my brain whilst I was trying to fly!

Finally: some of these 'rules of thumb' require mental gymnastics that not everyone is capable of whilst maintaining a decent instrument scan. If you find some of theses taking too much capacity away from your flying - din't fret it may not be important or there may be another way!

ps a trick for VFR diversions - measure the parts of your hand on the charts you are going to use! You may prefer getting your protrator and rulers out whilst flying solo but in the military we were taught (as solo pilot - rotary):

1: draw a line from a to b
2: estimate heading (with a bit of practice you can get this to within 10 degrees
3: estimate distance:Where the hand comes in. e.g. I know my open span is 32nm, the width of my palm is 13nm the top joint of my thumb is 5nm (on a 1:25 000 chart) etc. mark the line in 1/5/10nm increments if it helps (50000/ 250 000/ 500 000 chart)
4: estimate time
5: estimate fuel

Don't know if this is accurate enough for CPL in general, but the ac I flew had no trims so this was done with 1 hand (usually the left) so the niceties of spreading the chart and getting the dividers out weren't available! All i can say is that it worked for me on test day! (obviously the approximation errors increase with distance so make sure you pick a couple of time and track markers thatyou pass enroute to make sure all is going to plan. If it isn't revise heading/time estimate as appropriate

[Henry VIII]

rbr, take a look here...

http://www.flightinfo.com/rulesofthumb.asp

...enjoy...