Dear Rod:
I’m having difficulty understanding how density altitude affects my airplane’s climb attitude. Do I climb at the same attitude at a higher density altitude airport as compared to a sea-level airport?
Wayne
Greetings Wayne:
OK, here’s how to think about this. Higher density altitudes (thinner air) result in an increase in your true airspeed and a reduction in engine power. How does this affect the airplane’s climb angle? Well, thinner air means you need a higher true airspeed (resulting in a higher groundspeed) on takeoff to produce the same indicated climb speed. Combine this faster speed across the ground with a smaller climb rate and you get a shallower climb angle at higher density altitudes.
Do you use the same climb attitude that you used for takeoff at a sea-level airport when departing a high density altitude airport (don’t confuse the terms attitude and angle here). The answer is a big no! Your attitude in the climb is lower when departing high density altitude airports.
Let’s say that when departing a sea-level airport, your climb angle is 8 degrees. At VY (your climb airspeed), your angle of attack is approximately 10 degrees. Add these two together and you get 18 degrees. Is this the climb attitude you’d fly on takeoff? Not quite. Remember that in level flight the wings have a built-in angle to the horizontal (known as your angle of incidence) of about 4 degrees. So subtract 4 degrees from 18 degrees and you get your approximate climb attitude above the horizontal (14 degrees) when departing a sea-level airport.
At higher density altitude airports, the wings must still fly at nearly the same angle of attack (or 10 degrees) to produce VY. Your climb angle at higher density altitudes will be less than 8 degrees. If we assume that the airplane’s climb angle is now 2 degrees and the angle of attack is 10 degrees, this adds up to 12 degrees. By subtracting the angle of incidence (four degrees), you obtain a climb attitude of approximately 8 degrees.
When taking off from a high density altitude airport you’ll want to rotate to 8 degrees instead of 14 degrees above the horizontal for the climb. Of course, these values are for a fictitious airplane and would vary based on wind, airplane performance, and so on. The important thing to understand is that you’ll need to use a much lower attitude for the climb to maintain the desired airspeed when departing airports with higher density altitudes.
Dear Rod:
I have an instrument rating but do not feel proficient, even though I’m current. My instructor always does the radio work, and I fly the airplane under the hood. I really feel deficient in my radio work. I’ve asked him to let me do more radio work, but I think he really enjoys hearing his voice on the radio.
Kip
Greetings Kip:
Your instructor is doing you a great disservice by working the radios for you. Being able to talk and fly at the same time is an essential IFR skill. If your instructor wants to work a radio, he should get a job as a radio announcer or buy an iPhone and talk to Siri. If he enjoys hearing his voice that much he should consider a career testing recording devices. Give him one more chance. If he won’t let you talk and fly at the same time, fire him and find yourself a more capable, less self-centered flight instructor.
Dear Rod:
What is your recommendation for using full flaps (40 degrees in our Cessna 172) when landing in very strong crosswinds?
Ryan
Greetings Ryan:
I’m not a big fan of using 40 degrees of Cessna flaps in a strong crosswind. Strong winds often mean strong gusts. The slower speeds associated with 40 degrees of Cessna flaps means less control response. It also means less rudder authority when using a sideslip for crosswind correction. I prefer no more than 20 degrees of flap extension when landing in strong crosswinds.
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