Helicopter Performance

Question 1

Your altimeter is set to the prevailing sea level pressure (QNH) of 1017 hPa when you land at a site of 2500’ elevation. Your altimeter will read ——- feet after landing.

Answer 1

2500’
Remember that if the QNH is true you get a true altitude at elevation.

Question 2

When you fly at 4500’ indicated on your altimeter with the prevailing sea level pressure of 30.03 in.Hg set on the kolsman window, the pressure altitude is ——- feet.

Answer 2

4390’
30.03- 29.92 = 0.11 x 1000 = 110 deduct from 4500’

Question 3

When you wish to establish what the pressure altitude is without calculating it, you can find the answer by turning the Kollsman dial to ——- or ——- but you must remember to ——- it to the prevailing QNH afterwards

Answer 3

29.92 Hg

1013.25 hPa

Question 4

The outside air temperature gauge in your helicopter shows +21deg while you cruise at 2500’ and the sea level pressure is 29.92 inHg or 1013.25 hPa which you have set in the Kollsman window.
The density altitude is ——- feet.

Answer 4

Remember 2 degree loss per 1000’
2.5 x 2 = 5 deg
We should have 15deg - 5 = 10 deg
We have 21 deg so - 10 = 11deg higher than usual and we allow 120 ‘ per deg
11 x 120 = 1320’
2500’ + 1320’ = 3820’
High temp is bad so we add to give a higher altitude value

Question 5

When you do your pre-start checks in your light piston engined helicopter, you turn the Kollsman window setting to 29.92 in Hg (1013.25 hPa) and the altimeter reads 1200’. When you set the known elevation of 1500’ in the window you expect the reading to be ——- inHg or ——- hPa

Additional question.
The outside air temp is 28 degrees. You calculate the density altitude to be —— feet

Answer 5

Pressure altitude = 1200’which is 300 feet lower than elevation of 1500’, thus sea level pressure is greater than 29.92 inHg. 300’ = 0.3 inHg. Thus Kollsman will read 29.92 = 0.3 = 30.22 inHg or 1023 hPa

Additional question.
Pressure altitude is 1200’, we round that down to 1000 x 2 deg = 2 deg
We should have 15 deg - 2 deg = 13 deg
We have 28 deg so take away 13 deg and we are 15 deg high
15 deg x 120’ = 1800’
1200’ + 1800’ = 3000’

Question 6

When you do your pre-start checks in your light piston engined helicopter, you turn the Kollsman window setting to 29.92 in Hg (1013.25 hPa) and the altimeter reads 1200’. When you set the known elevation of 1500’ in the window you expect the reading to be ——- inHg or ——- hPa

Answer 6

Pressure altitude = 1200’which is 300 feet lower than elevation of 1500’, thus sea level pressure is greater than 29.92 inHg. 300’ = 0.3 inHg. Thus Kollsman will read 29.92 = 0.3 = 30.22 inHg or 1023 hPa

Question 7

Go to waypoints Principals of Helicopter Flight, page 265 and do review questions 7 and 8 as a graph is required.