performance

[aaaabbbbcccc1111]

I hope these questions have not been asked before, I have looked briefly at the Forum and cannot find them.


ok here goes..

1. What is the effect of altitude upon aircrafts speeds and rate of climb/descent.

2. What is the effect of climb and descent upon aircrafts ground speed.

3. Can anyone recommend a website, where I can study a/c performance, esp ROC/ROD also rate of turns. I have searched lots but cannot find anything really. Is there a general rule of thumb between sizes, engines etc..


Thanks in advanced

[max nightstop]

You question makes me a little nervous....smacks of "i don't want to learn how to take off or land, just how to turn and go up and down" (M Atta, 9/11)

In short, if you are turning, your rate of climb will decrease for a given power setting, you rate of descent will increase, for a given speed.

The higher you go the lower your rate of climb, until eventually you stop going up. The angles involved are relatively shallow and so have little effect on groundspeed.

Coming down is rather easier, gravity is helping. You can go as fast as you like without tearing off the wings. If you get your dive steep enough you can reduce your groundspeed to zero, but your airspeed will increase very quickly!!! Furthermore, all the passengers will join you in the flight deck!
In airline terms, ROD is shallow enough to have negligible effect on groundspeed.

most airliners will be stressed to around about 2.5g. You can work out turn performance from that and a top speed of say 340Kts/M.84 call it 500Kts TAS as a max for ball park figures. If you are any good at maths you can work out the theoretical turn rates and radii from that. These may not be sustainable in level flight though.

Are you thinking of doing some widebody air combat?

[aaaabbbbcccc1111]

no not at all.

I am a trainee air traffic controller, very early into my career.

I find sometimes that figures quoted are quite unrealistic, and I wanted a pilots perspective about what there aircraft can do when at higher altitudes and what they will realistically set as their climb and descend rate, not when expediting. I recently heard of the expression "coffin corner", which somewhat surprised me.

[batty]

Coffin corner , very basically go faster and you stall due to the high mach number fly slower and you stall due to low TAS. Basically your buggered....

[Old Smokey]

aaaabbbbcccc1111,

Aha! You're a trainee Air Traffic Controller. You should have said so earlier so that the question could have been answered in that context.

1. What is the effect of altitude upon aircrafts speeds and rate of climb/descent. - Aircraft climb at a fairly constant IAS, and then transition to Mach Number at a Pressure Height in accordance with the Climb IAS/Mach schedule. When climbing at an IAS, TAS increases with increasing Pressure Height, thus the angle of climb decreases due to the longer horizontal vector. Simultaneously, thrust declines with increasing Pressure Height, reducing Rate of Climb, and, allied with increasing TAS, further reduces the Climb Angle. As the TAS increases, some of the thrust which would have been available for climb is required for acceleration, further reducing Rate and Angle of climb.

Thus, both Rate and Angle of climb decrease as climb continues.

When the aircraft transitions to climb at a constant Mach Number, TAS now decreases due to decreasing temperature with increasing Pressure Height, until the Tropopause is reached (36089 ft in ISA). Both Rate and Angle of climb now improve again, as no thrust is wasted due to acceleration, and in fact, some kinetic energy given back due to deceleration. Also, because IAS is decreasing, overall drag is decreasing. With further Pressure Height increase, Rate and Angle decrease again due to reducing thrust.

Thus, when changing over to Mach Number, both Rate and Angle of climb improve, but decrease as climb continues.

After the Tropopause has been passed, TAS remains constant, but Rate and Angle of Climb decrease much more rapidly.

During descent, basically the reverse process takes place, i.e. the aircraft descends initially at a Mach Number, and changes over to IAS at a lower level. Thrust is relatively constant, being at idle. At the Mach Number phase, IAS, TAS, and thus, drag, are increasing, so the Rate and Angle of descent increase as descent continues. When transition to IAS takes place, TAS decreases with further descent at a fairly constant Rate of Descent, thus, whilst Rate is FAIRLY constant, Angle increases due to the shortening horizontal speed vector. Drag increases to a small degree due to increasing EAS, and this adds to both the Rate and Angle of descent.

2. What is the effect of climb and descent upon aircrafts ground speed. - If you're implying here "what is the effect compared to Cruise speed", then, at the Mach Number phase of climb or descent, very little different to cruise. For the climb and descent phase at IAS, on average it will be much less than at cruise. The aircraft that I fly has an initial climb TAS of 320 knots, but cruises at a nominal 500 knots - a very large difference. A similar situation exists on descent. Wind, of course, has an effect upon Ground Speed at every phase of flight.

3. Coffin corner - (Your late question) An aircraft is speed limited at the lower end by a minimum IAS before pre-stall buffet is encountered. It is speed limited at the upper end by Mach Number, where excessive Mach leads to extremely undesirable control problems. Too low, or too high on the speed, and as Batty said, "Basically your buggered." As mentioned earlier, as we climb to higher levels at a constant Mach Number (which is all too often close to Mmo, the limit), IAS decreases. If I go too high then I am sitting close to the Upper AND Lower speed limits simultaneously, my "playground" has shrunk enormously. And then along comes a bit of turbulence, 1.2 to 1.3 G can be enough, and........refer to Batty. Please, please, pass this on one to your buddies at ATC.

4.Rate of turns - Rate and Radius of turn depend upon speed, that is TAS, squared. As speed increases, for a given bank angle, turn Radius Increases, and Turn Rate Decreases.....exponentially. So, for a given IAS, the radius of turn will increase, and the rate of turn will decrease with increasing altitude. Now, let's throw in Coffin Corner (been there, didn't like it). At lower more 'normal' levels, bank angle is usually of the order of 25 to 28°. Because of the 'G' in the turn, the effective weight of the aircraft increases, thus increasing the low speed limit at which pre-stall buffet will occur, so, at high levels, angle of bank is reduced to something like 15° to reduce the 'G', almost doubling the turn radius, and halving the turn rate.

That's the short answer.

Regards,

Old Smokey

[aaaabbbbcccc1111]

Thank very much. It is much appreciated.

[Inverted81]

No avoiding action basically at high level then :) oh aaaabbbbcccccc1111 we got our work cut out for us in the coming weeks !

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