# Questions tagged [density-altitude]

Density altitude is a measure of air density. It is the altitude where the air density under ICAO Standard Atmosphere conditions is equal to the actual density. On hot days, the density altitude is above the pressure altitude, on cold days it is below. Density altitude is an important factor for aircraft performance modelling.

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### Why does air density increase with temperature? [closed]

Why air density increases with increase in temperature , but this is opposite in case of liquid.
86 views

### How does density altitude affect performance, temperature, and pressure; and how is it calculated?

I'm trying to better understand density altitude. If the density altitude at Rand Airport (for example) is 8300 ft: What does the 8300 ft mean? Does it mean that at that altitude, aircraft ...
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### How does the less dense air affect the reciprocating aircraft engine performance? [closed]

How does the less dense air can affect the reciprocating engine performance ? For an example " rotax engine "
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### How does humidity's effects on density altitude get factored into Takeoff Distance Performance Charts?

Given that density altitude is a function of Pressure, Temperature, and Humidity, and most takeoff performance charts adjust takeoff distance as a function of pressure altitude and temperature, how is ...
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### What ISA temperature to use in the density altitude calculation?

In the density altitude formula: DA = PA + [120 x (OAT - ISA Temp.)], should one use the ISA temperature at the field elevation or the ISA temperature at the pressure altitude?
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### Propeller Characteristics at Different Altitudes

Assuming I have a propeller with a given diameter (D), pitch, blade twist, and number of blades, I can theoretically analyze discrete airfoil sections in XFOIL and come up with lift and drag polars ...
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### Why is the relation of height and temperature different when calculating altitude?

I'm trying to grasp the essence of altitude calculations. One thing I can't figure out in my head is this: In the International Standard Atmosphere (ISA) the temperature of the air decreases with the ...
855 views

### Does airspeed affect the critical angle of attack on an airfoil?

I understand that the critical angle of attack is mostly affected by the shape of the airfoil. However does the airspeed of the airfoil or the density of the air affect the critical angle of attack? ...
117 views

### What is the background of the maximum altitude formula?

This question What determines the maximum altitude a plane can reach? has a formula at Peter Kämpf's answer : $$\rho_{min} = \frac{2\cdot m\cdot g}{(Mach^2 \cdot c_L)_{max}\cdot a^2\cdot S}$$ Does ...
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### How do I calculate density altitude by hand?

I've seen the following equation for calculating density altitude on a dozen websites: [ (OAT - ISA) * 120 ] + Pressure Altitude. But it was never very clear ...
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### Am I correctly calculating the density altitude?

I came across the following question while studying for the FAA PPL written test: Determine the density altitude for these conditions: Altimeter setting: 30.35 Runway temperature: +25°F ...
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### Why are oxygen requirements based on pressure altitude?

The FAA's oxygen rules in §91.211 are based on pressure altitude. Assuming our lungs are like our engines and wings and dependent on density altitude, why are the oxygen requirements not based on ...
2k views

### Does density altitude affect actual altitude?

Student pilot here, working on my first rating. A lot has been drilled into my head about density altitude as we approach the hot summer months here in the northern hemisphere, and how it causes the ...
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### When calculating takeoff performance why include airport elevation in pressure altitude?

When calculating the pressure altitude for aircraft performance I learned to calculate it the following way: Pressure Altitude = (29.92" - altimeter setting) * 1000' + elevation So at an airport at ...
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### Why is Cessna 172 POH performance chart based on Pressure Altitude and Temperature instead of Density Altitude?

While calculating takeoff distance for Cessna 172, POH need to be used. POH charts has pressure altitude and temperature and then distance for those two known parameters. Does this mean if we have ...
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### Is there a maximum airfield elevation in which a Cessna 172P can operate?

The title says it all: is there a maximum airfield elevation in which a Cessna 172P can operate? Or a maximum density altitude at which take off shouldn't be considered?
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### How is the Density Altitude performance penalty split between propeller and engine?

Let's say we have a Cessna 150 with a Continental O-240. How is the density altitude performance hit split between the engine air intake and the propeller ability to "grab" the air. Let's say I was ...
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### Why not use flaps in take off from High Density Altitude airport?

Why can we use flaps in short field take off but not in high density altitude airports? Why can't they be used in high density altitude to shorten the take off distance as in short field take off? ...
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### How is non-standard OAT accounted for?

This pdf from Airbus has a chart from ICAO showing the amount of correction to be applied to altimeter readings for temperatures below 0°C. Do aircraft with flight data computers automatically ...
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### How can you find the best altitude for range or speed?

How can you select best cruise altitude (altitude for best range velocity) and maximum speed altitude? The specific case is a turboprop aircraft of gross weight 8000 lb.
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### How is pressure related to air density?

This is confusing to me: Since pressure increases with temperature (I don't know why), how can air density decrease with temperature. In a hot day then pressure would increase and air density ...
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### Do instrument approach procedures sometimes have a minimum temperature?

Non-precision instrument approaches generally have altitude restrictions which get lower when you get closer to the airport. I always figured these restrictions were AMSL using the current altimeter ...
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### How do I determine the best altitude to fly for fuel economy?

If you fly low, air is dense so you can get more thrust from your engines, but you get more drag. On the other hand if you fly higher you have less drag but the output of engine decreases as well. So ...