Step Climb

[Lunar Landing]

Hi, just wondering what a step climb exactly is and anything technical about it.
Also, being a flight simmer,(and PPL-in reality that is!) i have noticed that the IAS is different to the GS (ground speed) displayed on the GPS, and when i select MACH. hold instead of IAS hold, the mach number remains the same, but checking up on the speed hold button, the speed changes, even tho the MACH is the same? I will add, that this is happening as i climb. Is it that thing called 'compression'or something like that, which ive heard of?

Smooth skies,

Dan <img src="smile.gif" border="0">

[whats_it_doing_now?]

OK, i'm going to be as brief as i can be with this answer, so i appologise in advance if i slightly miss-explain!
Step climb is used because your ceiling height increases as you burn fuel and lose weight. Also, because we fly at certain levels depending on the direction we fly in, the 'step' to the next available level may be 4000', and it can take some time before you are light enough to make the step. The FMC computes when it thinks you can make this climb, but due to a reluctance to fly in coffin corner, most people wait a bit longer, essentially ignoring the FMC and going up when you are happy! You can select the size of step to make on the perf init page, if your flt sim has this.
VERY briefly, ground speed is true air speed (speed through the air) taking in account for the wind, and TAS is a rectified speed taking into account outside air temp and pressure then factoring this to your indicated airspeed. IAS is basically measured using differances in airpressure as you speed up and is whats displayed on the dial. It is important for aerodynamic purposes.
SO... TAS increases for a constant IAS as you climb (due to drop in air temp) and continues to do so. Meanwhile the speed of sound is slowing with altitude because of the reduced density of the air, so eventually, you start to become limited in speed because you are approaching your climb/cruise mach no. (about .80 on the 757). From this point you climb at a fixed mach, and the IAS and TAS will reduce to maintain this constant mach no.
Once in the cruise, if you fly through areas of different air temp, the IAS/TAS will change, even though you are at a constant mach number.
RAM compression is caused by friction heating of the air striking the the aeroplane as you move through it. This is called total air temp and can be 40 degrees c above the outside air temp at normal cruise speeds in an airliner. TAT is the limiting factor for concordes speed, they cant let the nose get hotter than 100 degrees c, i think. Hope this answers your questions!

Your lucky i'm on an uneventful airport standby or i would never have got round to writing this much!

[Lunar Landing]

Many thanks member! I have printed it out to re-read. I appreciate the time you took to answer.

Just to save another new topic, i'll extend this one...(to anyone of course)...
What is the complete course for taking off, including speeds, flap extention altitudes, and how are these worked out? Why cant flaps just be retracted whenever the pilot wishes?
And, as i see the planes on the dover departures, can anyone tell me what the actual departure structure is...like from 09R, a common is climb LON2DME and turn right HDG 230, climb 6000.

1 more thing while im here...what is a radar heading? I thought that mag heading was used. why do controllers sometimes change between giving a heading and a radar heading? Or is it the same thing they just have two ways of saying it?

Smooth skies,

Dan <img src="smile.gif" border="0">
(and many thanks in advance!)

[whats_it_doing_now?]

You'd think i had something better to do wouldn't you?

Again, as brief as i can be...

Flaps are used to give more lift at lower speeds, and you extend them with referance to speed and not altitude. For the 757/767 (and i think this is true for most airliners, but can't be sure. It should work on the 737 on flight sim), we base the flap speeds on the minimum speed for land flap (flap 30). This speed changes with weight, is computed in the FMC and is called Vref30, or just Vref for short. To find the rest of the minimum speeds for various configurations you just add increments. So minimum clean (no flap) is vref+80, min speed for flap1 = vref+60, flap5 = vref+40, and flap15/20/25 = vref+20 - or there abouts!
For take off, use flap 15 and you rotate at vr, and climb to a thousand feet at v2+15. These are speeds calculated for the weight and have implications if you have an engine failure on take off, but if you use vref+10 for vr, and +15 for v2, you wont be far wrong. At a thousand feet, half whatever pitch you have to maintain v2+15, you will start to accelerate as you climb, so take the flaps up as you approach each min speed. You don't fly slower than the min speed for each flap setting as you risk stalling the aircraft.
Radar heading is a heading to steer onto that the atc ask you to do, they mean the same whether they drop the radar bit or not.

Someone else can answer the other bit!