The most fascinating section in the article for me is the one on sink rate and drag. In order to understand that section, you must know that parasite drag is drag caused by moving a solid object through a fluid. Induced drag is drag due to lift. Here is an interesting chart from Wikipedia:
Here are some gems from that section: "What aerodynamicists discovered is that there are some interesting performance relationships between parasitic and induced drag. The first is that the airspeed for minimum sink rate occurs when an airplane's induced drag is exactly three times its parasitic drag. Any other speed, whether slower or faster, will require more power to fly."
Veerrrrryyyy interesting. You can see that in the chart.
"The second relationship occurs when the parasite drag is equal to the induced drag. At this speed, the airplane is flying at its best lift to drag (L/D), or glide, ratio. This occurs at an airspeed that's 32% greater than the minimum sink airspeed. The max L/D speed is what you would want to fly at if maximum range or fuel economy is your goal."
I did that in a Piper Cherokee 160 after reading this article. Its best L/D speed is 82 mph. I flew around for an hour to see what it was like. First, I noticed that it was quieter in the cockpit. The engine was not laboring very much. I found it to be quite serene. And consider this - when people want to know how much experience you have as a pilot, what do they ask? They ask how many HOURS you have. They don't ask how fast or far you fly. They don't ask how big a hurry you are always in. So if you fly at max L/D, you are gaining more hours of experience AND you are saving fuel AND you are being easier on your engine simply by flying a little slower.
But back to the article...
"The last relationship occurs at the airspeed when the parasitic drag is three times greater than the induced drag. This condition is sometimes referred to as Carson's speed, and is 32 percent greater than the max L/D speed, or 73 percent higher than the minimum sink speed... ...While flying at maximum speed will get you to your destination the quickest, it requires the most power and fuel burned. Flying at maximum L/D gives you the best fuel economy, but it is slower than most people want to fly. ... there is a speed where you get the most increase in speed for the least amount of excess power (and fuel) burned... This is the Carson speed mentioned earlier."
Okay, so the Carson speed for that Cherokee 160 would be 1.32 times 82 miles per hour, or 108 miles per hour. I have not gone up to see what engine rpm that correlates to, but I think it would be an interesting experiment.
For me, the point of this article was to remind me that I can fly at any speed I want to, and there are benefits and consequences to any speed I select. I think I should become familiar with the relationship between speed and fuel consumption in any plane I fly.
One more comment. If you rent a plane wet (that means the fuel is included in the rental rate, for you non-pilots), you get charged the hourly rate regardless of whether you are saving fuel or not. If you slow down and save fuel, it takes you longer to get to your destination, so you end up paying more for the trip. You pay MORE for conserving! The economics of aircraft rental are such that you minimize your rental cost if you fly as fast and fuel-inefficiently as possible. That is harder on the plane and wastes fuel, but it costs the renter less.
If you own your own airplane, however, I think there are true benefits to slowing down a little. Your fuel costs will be lower. Your engine will last longer. It will take a little longer to get where you are going, but that means you get to fly for a longer period of time! It's win-win-win-win!
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