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 correct for some aircraft, but this will work well for many small single and multi-engine aircraft.
Density Altitude and Mountain Flight Training Courses and Mountain Checkout
Alpine Flight Training in Eagle Colorado provides year-round mountain flying instruction and mountain checkout. We have options for a 1 or two day course. No matter what time of year you come, we'll always we talking about density altitude, even though, the influences of density altitude are most significant in the summer. If you're interested in learning mountain flying and getting a mountain checkout then come to the heart of the Colorado Rockies and fly with Alpine Flight Training.
There are more factors than just Altitude and Temperature
Most people commonly believe there are only two factors related to determining density altitude: field elevation and temperature. The belief that these are the only factors stems from the age-old use of the “density altitude chart” that every pilot encounters in textbooks, on tests, and in aircraft performance manuals.
This chart doesn’t tell the whole story, a pilot also needs to determine the effect on density altitude of humidity and atmospheric pressure.
In reality, humidity and air pressure also impact density altitude, however not to the extent of temperature and field elevation. Combined however the impact of these two factors can be significant.
Today, many of the electronic flight calculators include functions for calculating the actual density altitude. Additionally, there are several web sites with complete density altitude calculators such as the one created by Richard Shelquist that can be found at:
http://wahiduddin.net/calc/calc_da.htm
See Also
- Richard Shelquist Density Altitude Calculator
Density Altitude
How close to the edge of the performance envelope are you?
The importance of closely examining aircraft performance in the summer and at higher elevations.
We frequently hear about complacency with relation to flying. The tendency of course is that as pilots get more and more time under their belts, they tend to become complacent with regards to the operation of their aircraft. We see this in all aspects, from planning, to preflight, and right on into flight operations.
This last weekend I was at the Glenwood Springs airport where I witnessed a takeoff that could have easily ended in tragedy. This particular incident made me think back to another incident several years earlier that was very tragic indeed where lack of flight planning resulted in a child burned to death on the side of a mountain in the wreckage of a small plane crash. This particular crash actually killed 2 of the four passengers, one being a child and the other being his father. The irony of this wreak was that it was an airplane in perfect working order, had plenty of fuel, and was being flown on a perfect sunny cloudless day here in Colorado.
I see it everyday, pilots becoming lazy… not flying with precision of altitude and heading, not scanning for traffic as intently as they had when they first got licensed. What used to be a thorough preflight becomes a brief walk around. Of course no single aspect seems to fade more than the flight planning process. What was once a well prepared flight plan seems to go away entirely.
During our mountain flight training I often fly with pilots that have been flying for years if not decades. I usually begin each flight with what did flight service say? It’s amazing how many pilots will not hesitate to hop in the plane without even so much as a weather check. This is problem for a variety of reasons, which I will get into. But even if you think you know and understand the weather in your local area and you’re only staying in the pattern it’s still smart to see what’s happening with temporary flight restrictions.
Lack of flight planning is an even larger issue when flying in the mountains. Thinner air means operating much closer to the airplane performance limit. With both the incident that nearly occurred this weekend as well as the wreak I referred to, the issue was the same. The pilot’s failure to do any type of planning and subsequent failure to understand the performance limitations of their aircraft.
In the case of the wreak, the pilot departed Eagle Airport with full fuel and 4 passengers and tried to fly direct to Salt Lake. The only problem, it was high density altitude and the aircraft simply could not deliver the climb performance needed to fly direct. The missing ingredient… planning. A thorough planning would have revealed the aircraft’s inability to fly direct over a 13,000 foot mountain, and the result of the planning would have been either a lighter fuel load or a different route.
The incident I watched nearly unfold was all too similar. Without thinking (or ranther any planning), a pilot of a normally aspirated ’74 Arrow topped off the tanks, and him and his passenger took off. They got in the air with only a couple feet remaining of runway and cleared the trees at the end with only a couple feet of clearance. Had they consulted the POH and some some basic performance calcs they would have known they were on the very edge of their aircraft performance.
