This might sound like an odd kind of comparison, but as pilots we are constantly amazed by flying machines and know that their structure and function are everything. Our own structure and function are pretty awesome too, it’s just that sometimes we take it all a bit for granted. Maybe just to boost my own morale, I decided to get some engineering details of the airplane and compare that to our own capabilities and see just how we might fare.
So I hit up a friend of mine, Keith Otsuka, who is the chief pilot at Boeing’s Commercial Airplanes Test and Evaluation Center, with the challenge: Who (or what) is the better engineered machine – his airplane or we humans? The folks at Boeing were all great at working on this little project with me. Here’s a quick shout out and thanks to Keith and the others at Boeing, particularly Shaniqua Manning-Muhammad, communications specialist at Boeing Flight Testing and Flight Ops, and Boeing’s first 777 chief pilot, John Cashman.
First, to make comparisons we need a couple of definitions that we can use as standards to apply to both machines. The basic measures of energy are watts and joules. We all have a sense of the power in a watt; the average tabletop lamp bulb is a 100-watt bulb so one watt is a pretty dim bulb. The joule is a measure of energy transfer over time and it’s pretty simple in that 1 watt equals 1 joule of energy used per second. For reference, one joule is about the amount of energy transferred from your arm to lift up a medium-size apple (100 g) 1 meter vertically off the table to your mouth.
We’re also familiar with calories since we wrestle with them every day. Calories (actually kilocalories) are the amount of energy contained in various fuels (foods, AvGas, JetA, etc.) and that energy is measured in watts and joules. We’ll get to the energy content of airplane fuel later on but for now, just keep in mind that each Kcal from the food we eat is equal to about 4200 Joules of energy.
Let’s start out our contest from right there by comparing our energy efficiencies. Humans are incredibly energy efficient and we do not produce nor require much power. The average daily caloric intake for a reasonable diet is about 2000 to 2500 Kcal. Assuming we are not dipping into energy reserves over the course of a day, the 24-hour power requirement for basic biochemical and metabolic activity (not figuring anything strenuous) is only about 100 watts. That’s about equal to the energy of that 100-watt light bulb in your living room or 4 watts per hour. Compare that to the 777LR that carries 53,500 gallons of Jet A fuel and burns about 2200 gallons per hour. One gallon of Jet A equals about 40 watts of energy so the 777 clocks in at 88,000 watts per hour of energy. The average 777LR usually has about 275 passengers on board so to fly through the skies a 777 is burning about 325 watts per person per hour. About 80 times more energy than the human machine requires. By the way – that’s pretty pricey too. Although fuel prices fluctuate, the fuel bill for a 777LR costs about $11,550 per hour or approximately $40 per person per hour. That buys a lot of cheeseburgers if that’s what you want to fuel your own engine!
What does all that energy get? It gets people around the world pretty fast so let’s check out the energy it takes to get from here to there for us and for the airplane. First, an average weight 155lb person walking at a pace of 2.5 mph expends about 4 Kcal per minute and one mile will take 24 minutes at this speed. That means that the average person needs about 100 Kcal of energy to cover a mile. If we were burning Jet A for this workout, someone out for a stroll would get about 260 miles on the equivalent of a gallon of gas (MPG). Just be careful; that stuff tastes terrible! (Tom Murphy has a really extensive dive into this math for those who want to see more.) Even Prius drivers don’t get close to that kind of mileage. But how does the 777 stack up against a fuel-efficient machine like us? Using the numbers in the last paragraph, it’s around 0.2 MPG, or 73 MPG per passenger. Humans are about 4 times more fuel-efficient. But then again it takes us 25 minutes to walk a mile and the 777 can take us halfway around the world in a few hours. I guess I’d rather be on the airplane.
Airplanes are all about lifting heavy loads off the ground but we can do that too. With all that power and energy, which machine is the more capable of getting things off the ground and fighting gravity? The world power lift record in the 75 kg weight category is only a year old and held by Russian behemoth Dmitriy Nasonov who set the record with a clean jerk of 760lbs. So assuming that he stands on two feet each of which is about a square foot of area, the human power lifting record in an average weight class is 380lbs per square foot. Not too shabby. The beast of the sky 777 has 4,606 square feet of wing area and with that the MTOW is in the range of 775,000 lbs. That works out to 168 lbs per square foot of lifting capability. Once again, this awesome human machine is pretty well put together.
On the same topic of power, exactly how fast can the huge airplane accelerate down the runway in order to generate all that lift it needs to get up in the air? Let’s start with human acceleration and again go to some world records. The “fastest human” in the last few years is Usain Bolt with an average acceleration 10.2 feet per second but he only gets to a maximum speed of 28 mph at best. Now a 777 has an almost unbelievable 230,000lbs of thrust from those two huge GE engines so it’s going to be hard to beat. At average MTOW the 777 accelerates down the runway at a rate almost the same, about 10 feet per second. But for the airplane that’s just the start since it keeps accelerating to VR, the average takeoff speed of around 170 mph. Pretty close acceleration for each machine to start, but this one really isn’t much of a contest with that incredible size and all that weight, so these points also go to the airplane.
Keep all this in mind and in the next post we will compare some of the actual machinery that does all these miraculous things for these two unbelievable machines. Then we’ll add up the points and see who wins!