What is it like climbing into an aircraft that weighs 150 tons and then flying it around the sky?
I am in a very, very good position to answer that question, as a matter of fact.
In a way, I am a very rare commodity. In a country of 330,000,000, the USAF has around 60,000 officers. That’s about 0.02% of the general population. About one quarter of those are pilots.
If you want to be thorough, and include all pilots of all types of aircraft (fixed wing, rotary wing, balloons, propeller, jet, gliders, etc, etc) in all the US military, private pilots, and commercial pilots, there are about 700,000 or about 0.2% of the population.
Let’s multiply that by 8 to account for the many ex-pilots living among us and say that maybe one in one hundred people in America have, at one time or another, piloted an aerial vehicle of some type.
Whichever way you count it, there are very, very, very few of any of those pilots that have had the opportunity to fly, in the same tour of duty or job, both heavy jet aircraft and small, supersonic jet aircraft.
I have. Oftentimes in the same day.
What is a heavy jet aircraft and what is a small, supersonic jet aircraft?
A ton is 2,000 pounds and is a lot of weight. I flew a jet aircraft that weighed 150 tons, fully loaded, at the same time I was flying a jet aircraft that weighed 3 tons.
Wait! Why are even the “lighter aircraft” so heavy? 3 tons!
Once you are committed to designing a military jet aircraft with a pilot and a mission, it takes a few tons to just fit in all the life-support, mission-essential equipment, fuel, and other important pieces and parts. Heck, a light jet engine could weigh a half ton and you probably want two. At max thrust, you are consuming more than 5 tons of fuel per hour. So you need a few thousand pounds of fuel on board for an aircraft to be useful. (And you need to not being flying around at max all the time.)
It all adds up to a few tons for even a small, supersonic jet aircraft.
Eliminate the man or woman, use a small electric engine, and you might have a very simple flying camera that weighs a few pounds. But, there are larger, mission-ladened, unmanned jet aircraft that can weigh 15 tons.
So, what’s it like flying a jet aircraft, heavy or “light”?
Jet aircraft can supply lots of power to move you forward and get enough air past your structure to fly controllably — just like a propeller aircraft. With propeller aircraft, however, there are limits to speed (due to drag) and you tend to feel a tail sway as you increase the gas to the engine. This is because of the gyroscopic effects of the power plant and propeller. It is not a big deal. The pilot pushes a bit on the rudder pedals to have the tail rudder take care of it. But a light prop aircraft (about 1/2 ton) can be the very closest you can get to that feeling of flying. Whereas piloting a heavy sometimes feels like managing a weapon system, rather than flying.
The early jet aircraft engines were prone to flaming out and sometimes were very slow to wind up to full thrust. But these problems are pretty much gone now.
The lead aircraft in the photo above is a KC-135A Stratotanker. From 1977 to 1982, I was a pilot on KC-135A and Q-model tankers. They weighed 50 tons dry and 150 tons when fully loaded with fuel. They used the old J57 engines which could sometimes blow up on you, but overall worked pretty well.
During in-flight refueling, we could off-load most of that fuel within just a few minutes.
So what did that feel like? Moving all that weight around in the sky? Dropping all that weight so quickly?
First, it is really important to keep that weight balanced. Aircraft fuel is held in tanks distributed along the body and in the wings.
The B-1 in this photo was incorrectly filled with fuel, most of it going to the rear tanks. If you try this in the air, by mismanaging the burning of your fuel… well, the aircraft will simply not fly anymore.
If you are offloading two thirds of your total weight in fuel to another aircraft, in the span of a few minutes, just make sure you take it from the right tanks and you will be fine.
Second, there certainly is a different feel to the aircraft when fully loaded or almost empty. A fully loaded KC-135 has a lot of inertia. Cutting the engines back, for instance, will not result in the aircraft slowing down as fast as it would have when the aircraft is very low on fuel and very much lighter. If this seems counter-intuitive, you are thinking of drag, not weight, or more correctly, mass.
Third, landing a heavy aircraft, being as it is bigger, is a lot like landing a building while looking out the third floor window. You need to pull back on the yoke sooner (higher up in the sky) and make sure you are not directing all that weight downward at too great a speed because all that inertia is hard to re-direct at the last minute. Poor inertia management will result in the aircraft bouncing off the runway and back into the air. Very poor inertia management will result in the same thing with all the tires blown.
I do not wish to discuss very, very poor inertia management since that is known by another name — a crash.
The T-38, on the other hand, gives you the feeling that you are about to drag your butt along the runway as you tip the nose up at the last second to land on the rear wheels. It is a lot more forgiving in terms of quick changes near the runway.
As you might expect, the large aircraft has a very short, but noticeable lag in the reaction of the aircraft to the pilot’s control inputs. In the small aircraft, thinking about a roll and turn is almost enough to find yourself in a roll and turn.
“Going faster than the speed of sound” is an odd physical phenomena. It really isn’t as much about your speed as it is about the various speeds-of-sound around your aircraft.
Taking the T-38 past the “sound barrier” is simply a continued excursion at a higher speed. Being that the aircraft is designed for it, the pilot may have to look at the mach meter to tell if it is occurring. On a mach meter, “1” is the speed of sound. So as you see the needle approach and go past the “1”, the aircraft transitions to supersonic pretty much all together at the same time. That is, the shock waves appear at about the same time and are well-behaved across the entire aircraft.
The larger aircraft, on the other hand, with a lot more sticky-out parts, have speed limits imposed on the pilot such as “0.77 Mach”. This is the mach number, about three quarters the speed of sound, as measured at the fuselage skin surface ports and at the cockpit gauges. In actuality, the engine cowlings are approaching the speed of sound. A shock wave will begin to form at the engine inlets at speeds slightly above the 0.77 indicated in the cockpit. When this happens structures are strained, but more importantly, engines can flame out. As you are probably already in an uncontrolled, high-speed dive for you to get into this situation, things are already pretty bad and getting worse.
There are a few other items to discuss: the cockpit deck freezing your feet, noise, and the feel of g’s pressing against your body are a few. But I’ve gone on too long already. We’ll just have to revisit this in the future.
A much better photo and article about seeing shock waves. Vapor cones can be controversial since they are a transonic phenomena.