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Landing Charts

  • Rolf
  • Topic Author

Rolf created the topic: Landing Charts

Why is the landing climb weight limit only a function of pressure height and not the density height? Neither the 'runaround' or the linear landing charts take temperature into consideration for this calculation. This is in contrast to the takeoff charts which use both pressure height and temperature (i.e. density height) to determine the maximum takeoff weight. I don't understand why temperature is omitted when calculating the landing climb weight limit. I'm missing something here.
#1

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  • Richard

Richard replied the topic: Re: Landing Charts

Hi Cetinski,

No, you're not missing anything. They do indeed use PH for the landing climb weight limit. You are right in thinking the DH would be a better value to use here. After all, those are the conditions we are in while attempting to reach that magical 3.2% climb gradient after a baulked landing.

One argument I read was that sufficient "fudge-factor" is already built into the charts to compensate for non-standard temperature. There is also the argument that the aircraft will be much lighter at arrival than at departure. However that says nothing about its ability to climb out at 3.2% in the landing configuration :huh: These arguments are good but I don't think they get to the bottom of it.

If you look at CAO 20.7.4, an aircraft must be able to climb out at 6% after take-off in the take-off configuration with gear down, outside of ground effect and with take-off power set. There is no reference to ISA conditions. In other words the aircraft must be able to achieve at least this 6% in any conditions. Therefore, the manufacturer has to make sure the aircraft can achieve that 6% at all times under any temperature and pressure combination. Hence the climb weight limit line being affected by temperature and pressure.

If you now look at the landing climb performance, CAO 20.7.4 says the an aircraft must be able to climb at 3.2% in ISA in the landing configuration, at take-off power and not exceeding 1.3 Vs. The manufacturer therefore only needs to ensure that 3.2% can be met in ISA conditions and so the landing climb weight limit graph is designed to represent ISA conditions only. That's why you don't have the temperature scale since in ISA for any pressure height, the standard temperature can be assumed.

Cheers,

Rich
#2

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  • Rolf
  • Topic Author

Rolf replied the topic: Re: Landing Charts

Thanks Richard, it's great to be able to get a quick response to some of those anoying little questions.
Many thanks, Rolf.
Now to work out how to change my user name from my surname to my first name.
#3

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  • Richard

Richard replied the topic: Re: Landing Charts

I can do that for you. I've changed your user name to "Rolf" and you can keep the same password.

Cheers,

Rich
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