You may have heard about “flying in High DA” or “High Density Altitude”, but does that really mean anything to the aspiring helicopter pilot looking for the right training program?
I can tell you that it didn’t mean anything to me when I first started looking into flight schools.
Back then, I had seen it mentioned here and there, and roughly understood that it was supposed to make you a better pilot, but I didn’t understand why, or what high density altitude actually meant. Honestly, I didn’t really think about DA when I chose a school.
It turned out that I just happened to pick a school where all my flying would be in high density altitude, and looking back on it I am so happy that I did.
So if you’re like I was, let me explain why learning in a high DA training environment is something you should take into serious consideration.
The ultimate training helicopter
Over 90% of the schools in the U.S. train in Robinson Helicopters. Most if not all of the training is done in the two-seat, R22 helicopter. This is a great little helicopter, but it’s not exactly what you’d call a “powerhouse” at any altitude.
The R22 was designed in the 1970’s by Frank Robinson for the upper class earner to own a personal helicopter. It was not originally intended for flight training, but it’s been widely adopted for exactly that purpose. Due to its great design and low cost of operation, it’s become the go-to aircraft for helicopter flight training. Many flight schools around the world use the R22, and it has been the most popular helicopter in flight training for more than 30 years.
Most of the time, the little R22 helicopter is what we call “power limited.” The seat weight limit in the R22 is 240 lbs. That means if we had a 240 lb person in the pilot’s seat and our fuel tanks were full, then the person in our passenger seat would have to weigh 94 lbs or less. Any more than that and we would exceed the legal limitations. And that’s with no baggage.
Simply put, the R22 is a great single person helicopter, but not necessarily the best for hauling around two full grown adults.
An important point to note is that these numbers don’t change with altitude: If you are within weight and balance limitations at sea level, then you are within limitations at all altitudes.
So what is high density altitude?
Now with this in mind, let’s talk about high density altitude. I’ll keep it simple here, but know that there is a lot more to DA than what follows.
The engine in the R22 works very much like the engine in your car. It’s a combustion engine. It takes in oxygen and liquid fuel and compresses and ignites them to produce power. Those are the two ingredients—air and fuel—and when the engine doesn’t get enough of either, then the amount of power that it’s able to produce diminishes.
Normally, the amount of fuel that flows into the engine doesn’t change, but what can and does change is the amount of available oxygen. (There are different techniques for getting more oxygen into the engine but we won’t get into those right now).
The engine of our little R22 performs optimally and low altitude, and is less performant at high altitudes. Why is this? Because of differences in air density.
A brief physics refresher
The density of air varies
In a gas like air, molecules are loosely packed and randomly arranged. They’re free to move as forces are applied and fill volume as it’s available.
In dense air, the molecules—mostly oxygen and nitrogen—are tightly packed and there are more of them in a given volume of air. In less dense air, the molecules are further apart and in the same volume, there are fewer molecules.
The two primary factors that affect density are temperature and pressure. As pressure increases so does density. With temperature, it’s the opposite: increased temperature results in decreased density.
Air pressure changes with altitude
The earth’s atmosphere is like a sea of gas, and the air at the top weighs down on the air at the bottom, creating pressure. At sea level, the atmospheric pressure is at its highest, and as you ascend in altitude you’ll experience lower and lower pressure. As a consequence, air at lower altitudes is more dense and at higher altitudes, less dense.
Altitude impacts engine performance
Atmospheric pressure at sea level on average is about 14.7 pounds per square inch (psi), and this pressure is optimum for the engine. It has all of the oxygen it needs to perform as intended.
As we go up in elevation atmospheric pressure decreases. As pressure decreases the air flowing into the engine is less dense, and less dense air has less oxygen by volume available to be burned by our engine. With less oxygen to burn, the amount of power that the engine can produce is diminished.
So, simply ascending in altitude means a decrease in power available from the engine.
Temperature also impacts performance
Just as high altitude produces less dense air, so do high temperatures.
As air is heated, it expands becoming less dense, and as we have stated before, less dense air will produce less power.
This also affects our aircraft performance in terms of lift. We use air molecules to generate lift. The further they are spaced out the harder the aircraft has to work in order to fly.
So at high temperatures, the aircraft is hit with a double whammy: hot, thin air equates to less power from the engine and a diminished ability to produce lift.
So what’s the benefit of training at high density altitude?
What’s it all mean and why should you care?
Everything we’ve talked about so far means that the R22 is significantly harder to fly at a higher altitude then it is at sea level.
At high altitudes a pilot’s inputs must be much more calculated and precise. Knowing exactly how the aircraft is going to react and what to do is essential. If you get yourself into a tough situation, you most likely won’t have the power to bail yourself out of it, while at sea level or a lower altitude in a similar situation you very well may have the power.
Here in Prescott, Arizona the elevation is 5045 feet above sea level. That’s pretty high.
And on a hot day in the middle of summer the helicopter acts more like you’re flying at 8000 feet. Speaking from experience, it’s tough.
When I flew the R22 at the Robinson safety course in Torrance California at near sea level, even in the middle of summer it felt like a totally different and significantly more powerful helicopter than what I was used to up in Prescott, Arizona where I did my training.
So you might be thinking to yourself:
“Why would I want to train where there is high DA when I can go to a school at sea level and have some power?”
The simple answer is, it makes you a better pilot, and it prepares you better for a career in the industry. If you train in a high DA environment then you’ll find it significantly easier to fly at lower altitudes, and the habits you’ll have learn will make you a safer pilot.
Flying tours in the Grand Canyon with a load of excited passengers in the heat of summer at max weight, or fighting fires, or spraying chemicals: when you get into the industry as a pilot you will most likely experience the difficulties of being “power limited” even if you are in a much more powerful machine.
My opinion is, if you’re going to train, train in the toughest situation you can, and you’ll be better prepared for any situation.
Here at Guidance Aviation that is exactly what we do. We make safer pilots.
We were the first FAA-approved high altitude training program in Robinsons and we fly in it every day.