Theory: Density learner question

[dj Mcrae]

I was wondering if someone could help answer this and explain how it was determined as in ISA comparison


You are taking off from an elevation of 200 feet. Density height is 3,250 feet. Which one of the following statements is correct?

a)The take-off roll will be shorter than normal, with an improved rate of climb after take-off

b)The take-off roll will be longer than normal with a greatly reduced climb performance

thanks
Dj

[Alex Whittingham]

Density altitude is your altitude corrected for the effect of temperature. In this case the figures indicate that, even though you are near sea level, the air is hotter and thinner than normal and would be the equivalent of an altitude of 3250ft in an ISA atmosphere. Thin air means less thrust is available and higher groundspeeds are required to attain the same IAS. This means, in turn, that the take-off roll would be longer and climb gradients would be less than you would achieve at 200ft in standard temperatures.

[dj Mcrae]

Thanks Alex... I was fairly convinced it was b. It was the Low elevation that made me query it... Would there be a way to transpose it back to find a temp? ... i would imagine that the day must have to be extremely hot or/with a very large pressure difference from ISA.

[Wee Weasley Welshman]

There must be something in the air.. This is the third thread in three days that would better be made in TechLog.

Whilst I appreciate such theory questions are of great interest to Wannabe and anyone under training we can't allow them here.

To do so would see a flood and the purpose of this forum would be lost.


So sorry, padlocks out,

WWW