Windplayer et al, in the real world descent profiles are generally standard at a 3 degree profile to get you nicely onto the ILS or IAP fix, as indicated above the way to work it out is simple, some people use a 4 X profile but the outcome is the same.

Here is what we (I) used to do and what I taught as an instructor and check and training captain for years on a variety of real aeroplanes. Once you understand it, it is actually simple math then it become simple and all the tools you need are in the cockpit- Airspeed indicator, Altimeter, Distance readout (DME or GPS) and an approach chart.

ALT x 3 is distance to commence descent minus the altitude of the aerodrome and or IAF (instrument approach fix) commencement altitude:

EG. Your at F330 the ILS starts at 3000ft and airport elevation is say 100ft. 3x33 =99 nautical miles TOD to go all the way down at that profile, speed is generally irrelevant so you can barber pole or max or stay at a speed profile depends on the aircraft. Slowing down is the issue and you need to slow the descent and go level now and then to reduce speed and then keep descending (in a big and heavy aeroplane that may require a minute or two at level speed to deaccelerate or slow down, then away down you go again,

If the aerodrome your goind to land at is say at a high elevation then you take that off for example, aerodrome is 5000 ft then you actual height to lose from F330 is 28,000 feet, so F280 multiplied by 3 gives you - 84 nautical miles. For all intents and purposes ignore the last 0 on the FL. Remember you need to be ready to go and prepared by looking at the approach etc way before the descent point and then waiting for it to arrive and away you go.

So how do you stay on profile all the way down and as you slow the aeroplane to different speed profiles for the approach and landing?

The answer is quite simply you match your ROD to the IAS - How?

You divide IAS speed by 2 to give you the required rate of descent to stay on profile, hence:

If you descending at 300 kts then your ROD is 1500 fpm
if your descending at 225 kts then your ROD is 1100 fpm
if your descending at 200 kts then your ROD is 1000 fpm
if your descending at 180 kts then your ROD is 900 fpm
if your descending at 150 kts then your ROD is 750 fpm and,
if your at 120 kts your ROD is 600 fpm.

And so it goes.

So all you have to do is change the pitch attitude up or down to keep to or obtain the desired rate of descent.

You can check your profile if you have GPS or DME as you will go through 1000 ft of altitude every 3 nm. So if your a little ahead because of wind then you increase your ROD to stay on profile, or if your getting behind because of a headwind you decrease the ROD.

So you can easily check how your going by taking the distance and dividing it by 3 to find the altitude you should be at with a 3x profile, e.g. at 21 DME or NM you should be at ? 7000 ft. AT top of descent or 99 nm divided by 3 gives? guess what F330.

See how it works, the trick of using ROD to keep on profile means as you reduce speed by the time you arrive at you FAF or commencement of the ILS for example, your on profile and this works for all aeroplanes no matter what type. The great thing about this technique is that you also fly the Instrument Approach the same way by managing your ROD and you will also find that this matches very nicely the ROD or descent rate required for the speed to fly an ILS or other instrument approach.

Hope this helps, happy to put together a quick downloadable tutorial if people really would like this.  8-)

It only becomes a bit of an art form when you want to fly say an non precision approach (NDB) or DME Arc arrival then you need to work back on all the distances including the arc distance to work out your descent point - but that as they say is for another time.