I'll chip in with a piece on simulating a high density altitude takeoff by reducing power to simulate the effects of less dense air associated with high temperatures and/or altitudes. If you use this simulation, make sure to carefully explain what you're doing. Don't reduce power on takeoff and say to your student, "OK, Bob, this is a density altitude takeoff." Why? Because your student may return from a trip to a high altitude airport on a hot day and say, "I'm sure glad you showed me that procedure because I'da been tempted to use full power on takeoff." Ouch!
From The Right Seat
Density Altitude Simulation: Teaching Performance Parameters
Anyone who has made a takeoff at high density altitude knows what it's like to climb at a marginal rate. Most pilots have heard about high density altitude takeoffs. Few have had the chance to appreciate how the airplane's performance deteriorates under these conditions. Here's where you can help as a CFI.
It's possible to simulate a high density altitude takeoff under low density altitude conditions. First, explain to your student that you're going to simulate taking off from a high-elevation airport (or a medium-elevation airport on a warm day). You can simulate this by making a reduced power takeoff.
For instance, if you're flying the typical four-place, fixed-gear Cessna or Piper, you might begin the takeoff at 2,300 rpm instead of at full power. Of course, you want to do this with full consideration for all relevant safety issues such as runway length, obstructions in the departure path, current density altitude conditions, and the airplane's present performance capabilities.
Your students will first notice an increase in ground roll. Be sure to point out how the airplane's climb performance is also substantially reduced. This is especially noticeable once the airplane climbs out of ground effect. Carefully show how steeper turns after takeoff under these conditions usually result in a further decrease in the rate of climb. Demonstrate how difficult it is to accelerate to the proper climb speed when a gust of wind or an inappropriate attitude change temporarily increases the angle of attack.
You can modify this simulation by further reducing the takeoff power with the intent of aborting the takeoff. Your intent here is to simulate the point where the student realizes that he or she won't be able to continue the takeoff without excessive risk. Of course this takes a little bit of experience to know just how much to reduce the power. The aborted takeoff simulation will make quite an impression on your student. You'll want a runway with sufficient length on which to do this demonstration safely.
As long as you're on that long runway, you might also want to demonstrate an airplane's inability to climb out of ground effect. This requires taking off with power sufficient to become airborne but not quite enough to climb. Once again, you'll probably need to experiment a little on your own to determine the typical power settings necessary to demonstrate these maneuvers. Above all, remember that your objective is to educate your students, not scare them or expose them to excessive risk. So make sure you have sufficient runway length for this simulation.
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