Flight Planning range question

[Jinkster]

Can somebody please advise me where I am going wrong with this question.

Refer to CAP 697 SEP fig 2.4

Give:

A/c mass at start up = 3663lbs
fuel load (density 6lbs/gal) = 74gal
take-off alt = sea level
headwind = 40kt
crusi altitude = 8000ft
power setting full throttle = 2300rpm 20C klean of peak.

Question:

Calculate the range

a) 633nm <---------- answer
b) 844nm
c) 730nm
d) 547.5nm

This may seem an easy question to some but why do i keep getting 840nm when the answer is 633nm (none of the line will fit into 633nm)

Hmm maybe someone knows or is it just a funny question.

Jinkster

[Send Clowns]

844 nm is the still-air range, in nautical air miles. You have not considered the headwind. Note that at this altitude and power setting the TAS is 160 kts, groundspeed with a 40-kt headwind is therefore 120 kts. Use the equation on page 40 of the CAP, in effect

nautical ground miles = nautical air miles x G/S ÷ TAS

in this case ngm = 844 x 120 ÷ 160 = 633 ngm, the range over the ground.

Hope this helps

Send Clowns
Flight planning instructor, BCFT