Many fighter planes have the capability to refuel in air. When a plane moves in air, turbulence is generated at its back. To refuel, the fighter plane must come near to the parent plane (which has fuel in it).
When fighter plane reaches the back of parent plane, it is actually in the turbulent zone of the parent plane. How does fighter plane manage to fly and precisely adjust its position even in the zone of turbulence?
Ex US Navy pilot here. I flew the S-3 Viking, which refueled via the probe/drogue method, as opposed to the USAF flying boom method. I can confirm that the receiving plane is below the wake turbulence of the tanker, maybe by 8–10 feet. Although, even if you should ride up into the wake, the sensation is perhaps not as violent as you might think.
The technique they teach is that you just fly formation. You do NOT fixate on the basket (this is the 'drogue' part of the apparatus, which resembles a big badminton birdie).
Instead, you must position the tip of your probe about 4 feet aft of the basket, stabilize, then smoothly add throttle until contact is made. You may need to hit the basket at a couple of feet per second relative velocity in order for it to latch.
Then you have to maintain position. It's just formation flying, really. The hose apparatus on the tanker measures your position fore and aft – when you are within limits for fuel transfer, a light goes on. So, as the receiving pilot, you fly formation and maintain your position fore and aft so that the light stays lit. When you've taken on your gas, you need to exit straight back. Too much vertical offset can cause the basket to 'whip' as it disconnects. You can smash a canopy this way – I've seen it happen, and it's pretty colorful. You won't soon live it down.
Former B-52 crewdog here...The receiver aircraft flies below the wake turbulence of the tanker. In the case of the typical USAF method, using the boom, the receiver aircraft flies into a "contact" position and holds there. The boom operator (boomer) then "flies" to boom to the correct final position, then extends the nozzle into the refueling receptacle, the receiver aircraft just has to stay in the correct position relative to the tanker.
Whereas, as with "probe and drogue", the shuttlecock basket is trailing behind and below the tanker, the receiver pilot flies their aircraft such that the refueling nozzle goes into the basket. I'm not sure if the tanker has any directional control over where the basket goes other than just extending the hose.
Although the USAF primarily uses the rigid boom method, there were some number of KC-135R's that had the drogue on the end of the boom, so they could refuel Navy and some NATO aircraft. I don't know about the KC-10, but I would imagine there a few of them also with this capability.
Like to see the fleet and crews talking here. I am a US Navy A7E pilot who flew in the Med aboard the USS Nimitz in the mid-1980's. I served as tanker pilot, and had my share of plugging behind an A6 or A7 at night. Hit a KC-135 once with a flyable boom and that was sweet.
If you are tanking off of something like an A6, which I believe was designed with a refueling mission in mind, it isn't to bad. There isn't too much turbulence behind them. The store is internal to the fuselage and the drogue extends directly behind. Now the A7E is a different matter. Sitting behind it, with its "short" hose length, your vertical stabilizer stuck right up into the tankers jet wash. It was a rough session getting bounced around, but it is random and so doesn't affect you too much, i.e. it doesn't move the probe around much. I remember in particular random yaw inputs here and there, but one was much more susceptible to pilot induced oscillations than this sort of nuisance.
I had one of those nights where my first approach wasn't, let's say, the best, and I boltered off the end of the deck. As I entered the blackness in front of the ship I was praying that the controller turned me down wind. I could imagine my skipper in Ops saying, "Give him another chance at the deck ..." Instead I heard, "Alpha Juliet 4-2-7 what is your fuel state?" I replied that I was at 2,000 pounds. 1,200 pounds was emergency fuel for us and in the pattern you were at 3,000 to 5,000 pounds per hour consumption. With 800 pounds you have around 12 minutes flight time until things get really serious. Next was the call, "4-2-7 your signal is tank, tanker 9 o'clock, 5,000 feet."
I joined on the tanker, an A7E flown by my squadron mate "Boris". I was stationed alongside when he told me the drogue was extending. He carried a buddy store (tank) under his wing with 2,000 pounds of gas to give away. He had been directed to give me a 1,000 pounds. When the hose had successfully extended he cleared me in to tank. I moved back and got in position feeling the familiar jet wash hitting my tail. It was a very black night. The drogues at the end of the hose are not that big, kind of like the size of a basket used to carry apples in the orchard. It had lights all around the circumference to help you locate it and give you some depth perception. Of course in operation the lights seldom worked. You relied on the probe light on your aircraft that came on when you extended your probe and it is like a headlight on your car, but not that bright.
The A7E was a bit peculiar when it came to refueling, in that the probe extended out of the right side of the fuselage alongside you in the cockpit. The probe wasn't much in front of you. So you were steering the probe in to the basket while it was off-center. Not a big deal, but it did get time to get used to. I was behind him and stabilized and working my way up to the basket. You fly the tanker, keeping the basket in your peripheral. The minute you focused too much attention on the drogue probe closure, and this would usually happen for me when I was close to plugging in, the pilot induced oscillation would start. Trying to correct for a small difference leads to a bigger, leading to a bigger, and so on. You get the picture. Ugly.
As I came in to plug I was nervous and gripping the stick tightly, never a good sign, I was barely holding it together when I got the probe deep in the basket, but hit off center with too much closure, bowing the hose. Then the oscillations started and that was that. I was trying to recover and eventually slammed the throttle to idle to get out the drogue as quick as possible. This situation can lead to ripping the hose out of the buddy store, which then can lead to a fire on the tanker. There was this big bow in the hose, and I watched the tip of the probe slip off the basket. The basket, now in the tankers wind stream, whipped around, coming back, slamming into the canopy. Oh, yeah that is the other thing that can happen. In my case the canopy did not break and I was relieved. I still had to get my fuel and it took a few more attempts, all better than the last. At some point Boris asked me if I was alright back there. "Oh yeah, no problems back here. There finished." When I left the tanker I was asked my fuel state, and when I looked down I saw it was at 1,900 pounds. I had spent all the fuel he gave me trying to get fuel. "Ah ... right-o ... 2,500 pounds."
Here was the other thing that they didn't tell you about getting your canopy slapped by the drogue. It sprays the fuel all over your canopy, which in close to the deck, turns into the most beautiful rainbow streaks making it nearly impossible to see the ball.
Practice. Lots of practice.
Smaller planes like fighters usually refuel from a hose trailing behind the wing, far enough from (and below) the main body to avoid the worst turbulence. The tanker is completely passive here - the receiving pilot does everything. If it's too turbulent he just backs off and tries again
Larger planes use the flying boom method - they're the ones who have to come in right behind the tanker and hold position while the boom gets slotted into place. These planes are a lot heavier than a single-seat fighter and can handle the turbulence better. That doesn't mean it's easy - there are plenty of near-miss videos on YouTube.
The problem is less turbulence than downwash. Flying behind and below the tanker means that both vertical and horizontal position will change the downwash in a way that makes holding the position difficult. Flying behind a tanker is flying in an unstable equilibrium.
Both falling back and climbing up will position the receiving aircraft in stronger downwash. If the receiving aircraft moves forward relative to the tanker, it flies into reduced downwash angles which let it accelerate further, because with less downwash less power is required for the same flight speed. The opposite happens when it falls back, now the pilot needs to advance the throttle to keep his position.
