High Density Altitude Takeoff Tip


Flaps… more flaps does not equal more lift.

The other day I was at an FBO and I overheard a conversation between two pilots talking about flying to Denver in the summer.  The one pilot who had flew to Denver last summer was relaying his experience.  He was flying a 182 into Front Range Airport and said he had a heck of a time departing, because he couldn’t get the plane off the ground.  Finally, after using over 6,000 feet of runway he lifted off was able to just barely get a climb going.

This pilot had stated that he couldn’t understand how any aircraft could ever fly in or out of an airport like Leadville since he had so much trouble going to Denver.

I was intrigued by this conversation and decided to introduce myself as a pilot from Colorado and ask some questions.  It turns out the plane was loaded properly, well below gross, the pilot, his wife, and maybe 75-100 pounds of bags.  He had taken off into the wind of 7 kts.  The temp was 95, and that was a factor to the performance, but as I asked more questions the real problem became evident.  This pilot had used 20 degrees of flaps.  His thinking was that more was better, and a short field procedure of 10 degrees should be adapted to high altitude procedure of 20 degrees of flaps.  WRONG!

The reality of the situation is just the opposite.  Generally speaking, the first flap setting usually adds more lift than drag, the second, third or even forth flap settings on most aircraft add more drag than lift.  The better procedure would have been to use no flaps, or at the most use the 10 degree setting.

I explained that the 182 is a very capable machine, he just needed a different procedure.  I also explained that I had flown 150hp 172’s to and from Leadville (not in 95 degree temps though).

So what is a good procedure for takeoff from a high altitude airport?  First we’ll assume you have evaluated the wind, temp, aircraft performance, weight and balance and have concluded that the attempted takeoff is within the capabilities of the aircraft.

If that’s the case then the procedure I like to use is to taxi into position using every available foot of runway, lock the brakes, engine to full power, and flaps in the up position (i’ll get to using flaps in a second).  When you’re ready for the takeoff run, release the brakes.  Once you get the aircraft in the air keep it close to the ground to use ground effect to accelerate (Ground effect is a reduction in drag caused by being close to the ground in flight).  Once airborne in the ground effect you may want to retract flaps if you had used them as well as landing gear.  As the plane accelerates past Vy then it will handle and climb better than if it were at or below Vy.

As you were doing the takeoff run, if you got to the 1/2 way point of the runway and you’re not airborne or close to airborne then you can extend the first setting of flaps.  The benefit of doing this during the takeoff run is that the aircraft will initially accelerate faster without flaps.

Every aircraft is different, this procedure may not be corect for some aircraft, but this will work well for many small single and multi-engine aircraft.