07-06-2014, 02:01 PM

For fun I hammered out a density altitude app in Java and decided to change things up so it works on the HP 35s. I used the NOAA calculators and associated formulas from here: http://www.srh.noaa.gov/epz/?n=wxcalc

Here is the EQN formula for the HP 35s...

D = 145442.16 * (1 - ((17.326 * B * ((288 - 0.0065 * (A / 3.2808)) / 288) ^ 5.2561 / ((9 / 5 * ((5 / 9 * (T - 32)) + 273.15 / (1 - 0.379 * ((6.11 * 10 ^ ((7.5 * (5 / 9 * (W - 32))) / (237 + (5 / 9 * (W - 32))))) / (33.8638816 * B))) - 273.15) + 32) + 459.69)) ^ 0.235))

D = Density Altitude

B = Barometer(inHg)

A = Station Altitude

W = DewPoint(F)

T = Temp(F)

Example…

Solve for D (Density Altitude)...

B = 30.11

A = 5130

W = 39

T = 89

Result for D = 8040.64

In the formula I’m calculating Vapor Pressure, Virtual Temperature, and Station Pressure to get the Density Altitude.

I seem to get a very slight variance on the 35s vs the NOAA online Density Alt calculator but still its very accurate.

Cheers!

Here is the EQN formula for the HP 35s...

D = 145442.16 * (1 - ((17.326 * B * ((288 - 0.0065 * (A / 3.2808)) / 288) ^ 5.2561 / ((9 / 5 * ((5 / 9 * (T - 32)) + 273.15 / (1 - 0.379 * ((6.11 * 10 ^ ((7.5 * (5 / 9 * (W - 32))) / (237 + (5 / 9 * (W - 32))))) / (33.8638816 * B))) - 273.15) + 32) + 459.69)) ^ 0.235))

D = Density Altitude

B = Barometer(inHg)

A = Station Altitude

W = DewPoint(F)

T = Temp(F)

Example…

Solve for D (Density Altitude)...

B = 30.11

A = 5130

W = 39

T = 89

Result for D = 8040.64

In the formula I’m calculating Vapor Pressure, Virtual Temperature, and Station Pressure to get the Density Altitude.

I seem to get a very slight variance on the 35s vs the NOAA online Density Alt calculator but still its very accurate.

Cheers!