Tanker-configured A-7E Corsair with Buddy Store.

If you woke up yesterday wondering about Aerial Refueling and why military pilots do it, or if you were in a bar and someone suddenly mentioned that same question but you thought they were talking about the sans-serif font Arial, well this post is for you!

Jet engines are thirsty. In aircraft with relatively short ranges, fuel quantity roughly determines the time remaining before the engine flames out so the fuel gauge is one of the most closely monitored in the cockpit. (Yes, altitude and airspeed are actually more important, but only until you run out of “go” juice.)

Buddy Store, inflight refueling package.

At high altitude (30,000 feet) and cruising speed, the A-7E’s TF-41 engine consumed about 3,000-lbs of fuel per hour. That’s 50-lbs/minute. At low altitude and full throttle, it burned closer to 7.5K lbs/hr, which is 125-lbs/minute. (18.4 gal/minute!) Big difference.

There’s a lot to keep you busy in a single-pilot jet like the A-7 because there’s nobody else to help with the housekeeping. When flying off the carrier you are constantly doing mental “what-if” calculations to ensure that the current remaining fuel and expected consumption don’t take you below your required minimum fuel for landing.

The time required between launch and recovery is fixed – either 75 minutes (first and last launches of the day) or 105 minutes for the others. Your jet’s fuel load is fixed unless you can get extra fuel from one of the airborne jets with a “Buddy Store”,  (the tank with the retracting hose – see above) assuming they haven’t already unloaded their extra fuel. (If you haven’t already seen it, this great video shows the difference between Navy and Air Force refueling equipment.)

A-7E Corsair with 300-gallon drop tank.

Between startup, taxi, launch and climb to altitude, an A-7 would convert about 2,000-lbs of fuel into noise, altitude, and airspeed. The Corsair held 10,000-lbs of fuel internally. When flying off the carrier it usually carried a single 300-gallon drop tank on the inboard wing pylon with 2,000 lbs of fuel to increase its range and loiter time. So, assuming a typical take-off and rendezvous with your wingman, you would have about 9-10,000 lbs of fuel remaining. On the longer launch cycle (105 minutes), you could have 90 minutes remaining before the recovery. One of the requirements is that you land with as close to your maximum landing weight as possible and your “fuel remaining” is the only variable you control.

Fun With Numbers

So let’s do the numbers for a typical carrier-deployed A-7 with a drop tank (200 lbs empty), a Sidewinder missile (180 lbs), and a six-station MER** (300 lbs).

**(MER: multiple ejector rack – a device that attaches to a wing pylon that carries up to 6 general-purpose (unguided) bombs like the MK81 (250 lbs), MK82 (500 lbs), MK83 (1K lbs) and MK84 (2K lbs). Total capacity is only 5K lbs so you could only carry (5) MK83s.).

The aircraft weighs a little under 20K without ammo but with full ammo, (1,000 rounds = approx. 200 lbs) we could use 20K for our empty dry (unfueled) weight. After adding 700 lbs for the external racks, missile and fuel tank, I would use 21K as my flameout (no fuel) weight.

The Corsair’s maximum carrier landing weight was 25.3K lbs. That leaves 4,300 lbs of fuel remaining when you rolled into the groove and called the ball. During daytime operations “folks” became concerned if you called your fuel-remaining below 2.5K because that meant less than a half hour to flame out. The A-7 Low Fuel Light came on with 1,500 lbs of fuel remaining (about 20 minutes maximum if a climb to higher altitude wasn’t needed). And that’s where the aerial refueling comes in and why it’s so important to be able to do it day or night and in all weather conditions.

Most of the time, the aircraft carrier operates out of range of land airfields – at least farther than a typical jet could comfortably divert under low fuel conditions. The nearest land airfield might be in a hostile country and thus inaccessible. Therefore the only response for a low-fuel state is to join the tanker aircraft orbiting over the carrier and get more gas, assuming the fighters haven’t already drained it! (We had very thirsty F-4 Phantoms on my first couple deployments!)

When you’re low on fuel, you need to perform the rendezvous and refueling quickly to avoid the flameout and subsequent ejection and loss of aircraft. Another factor is that the ship can’t complete the recovery and begin moving planes around for the next launch, until the last aircraft (you) has landed. No pressure! Surprisingly the Corsair could actually land with one of the larger fuel buffers, compared to the F-4 Phantom, the EA-6B Prowler, and some of the other planes in the Air Wing.

E-2D Hawkeye refueling from MQ25 drone.

In my time, the E-2C Hawkeye (airborne radar plane) didn’t have a refueling probe and wasn’t able to refuel airborne. Today, the new E-2D Hawkeye does have that capability. In fact, here’s a picture of one refueling from an MQ-25 drone.

I recall the Prowler pilots talking about their limited maximum landing weight fuel due to the weight of all the external electronic jamming pods they carried. It meant they might only get two landing attempts during the day before having to refuel.

These consumption numbers seem astronomical in comparison to other vehicles you’re accustomed to. An A-7 burned up to 7,500-lbs/hr of JP5 fuel (weight per gallon: 6.8 lbs) and that’s 1,137 gallons per hour! That can generate an impressive 500 knots (nautical miles per hour) airspeed (= 575 mph); which equates to an economical 0.5 nm/gallon! That sounds crazy but only if you don’t consider even larger aircraft. A large Air Force cargo aircraft (C‑17 Globemaster III) at high altitude cruise, burns around 5,000-lbs/hr for each of the four engines – 20,000 lbs/hr. total! (That’s 50 gallons/minute total; or 333 lbs/minute.) Care to guess its fuel economy? (For fellow numbers nerds, I’m using JP5; the jet fuel used on ships due to its low flammability.  Calculation: 20,000 lbs/6.8 lbs/gal = 2,941.2 gallons/hr. At its customary 450 nm/hr that yields just 0.15 nm/gallon! That’s comparable to a commercial airliner and justified by the number of pounds of cargo it can carry.

Back to the process of inflight refueling…

It is not a risk-free process. That’s one reason that practice and proficiency are so important. The riskiest refueling operations are those performed by those still learning or in bad weather with significant turbulence.

Imagine the damage that the heavy all-metal receiver basket on the end of the hose could do to a receiving aircraft. The basket is flexible in order to collapse as the hose fully retracts back into the tanker package. But that means it has many parts and in a collision, those parts can dislodge or break off and be swallowed by nearby jet intakes, damaging the engines.

One memorable incident involved an A-7 approaching too fast and overshooting and missing the basket while going slightly high. The basket disappeared down the intake! This immediately disrupted the engine airflow which in turn caused loud and flight-suit-soiling compressor stalls which reduced the available thrust dramatically and produced the fortunate result that the A-7 lost some airspeed and backed away from the tanker, causing the hose to be pulled back out of the intake, thus restoring normal power to the engine.

F/A-18 Hornet getting gas.

The hose-swallowing A-7 didn’t appear damaged but as required the shaken pilot declared an Emergency and immediately returned to the ship in case there was undetected damage that could cause imminent engine failure. In this particular incident, the inexperienced pilot and his jet escaped harm. His story quickly circulated through the other squadrons and many young pilots learned again why “Not” to approach the tanker too fast.

You must approach the basket as smoothly as possible. The most common new-guy mistake is over-controlling; chasing the basket as it bounces around. But your much-heavier jet isn’t as nimble so your corrections get ever larger until you either back out to try again (the right response) or you chase it with increasing frustration until something bad happens – a basket or hose slap. The harder you try the worse it gets. The expression for the action you’re trying to avoid is “Killing snakes in the cockpit”. In other words, you’re moving the stick way too much. You have to back away, let the basket settle down, and try again. At night in bad weather with your low fuel light ON, you can imagine that it’s even harder.

The Navy was smart in how it handled safety incidents. It didn’t discourage pilots from reporting problems and mistakes. Everyone reported their mistakes and accepted the consequences knowing that they might be saving someone else’s life by teaching them a second-hand lesson rather than them repeating the same mistake themselves. In an imperfect world, this attitude and process worked remarkably well most of the time.

A “basket slap” was what occurred if the receiving aircraft was out of position or not flying smoothly. The basket could smack the nose or canopy and potentially damage both depending on the severity of the slap. The pitot-static tubes that drive the airspeed and altimeter gauges are usually on the outside of the aircraft’s nose and if damaged, you have a big problem, especially if you need to fly through instrument conditions (without a functioning altimeter or airspeed gauge). Canopy damage was fortunately rare.

Another rare occurrence is the failure of the hose take-up reel on the tanker. A small propeller on the front of the “buddy store” is driven by the slipstream and powers the hydraulics used to take up slack during refueling and retract the hose upon completion. If the hydraulics fail you have two problems. First, when the next aircraft plugs in with the normal slight closure rate (which ensures the proper coupling of the probe and basket), instead of the hose retracting slightly and remaining straight, a sine wave (“s” curve) develops, starting at the receiving aircraft, going up to the tanker store and reflecting back down the hose. When the reflected wave hits the probe on the receiving aircraft it can damage the probe – in severe (though rare) cases actually breaking it off.

The second problem is that the tanker hose can’t be retracted. That’s why the buddy store has an internal hose guillotine that can be activated by the pilot, severing the hose and allowing it to fall free (hopefully not into someone’s backyard).

I did hear of a case where the guillotine failed and the tanker had to land with the hose dangling behind. This creates a significant FOD and flying debris hazard when the basket and hose hit the flight deck. So that was a critical item for the refueling aircraft to notice when plugging in. If the hose reel didn’t take up the slack, you immediately aborted the plug and backed out before the sine wave made it back down the hose. This phenomenon was often the first indication of the buddy store failure.

When your probe engaged the basket, you needed to push the hose back into the buddy store to the “refueling range”, marked by tape on the hose. The hose had to be under compression and retracted to this point to enable the fuel pump that transferred the gas to the receiver.

If a tanker had to land with an extended hose, they were landed last. As they rolled into the groove and called the ball, everyone working on the deck was warned over the loudspeakers and radios so they could duck behind something. The reason you landed the tanker last was because afterward flight operations had to be halted until the flight deck had been walked from bow to stern (all flight deck personnel formed a line abreast at arms’ length) so any debris could be picked up and removed to avoid FOD damage to the jet engines. For the tanker aircraft itself, the pilot would be ready to pull his engines back to idle and then to OFF as soon as the arrestment was confirmed by the deceleration and flight deck crewman using the hand signal to “secure his engines”. This was to avoid the tanker ingesting any debris from the hose and basket. The flight deck crew would be ready with a tow tractor to hook up and move the aircraft out of the landing area. (This is another reason he was landed last.)

Hornet wearing a refueling basket.

The last refueling mishap I remember involved a jet having to land with a basket and about 10 feet of hose still stuck on his probe. Somehow the hose had failed or the buddy store guillotine had activated while the hose was still attached to the jet’s probe.

Most of the time it’s just the basket at the end of the hose that breaks off and remains on the receiver jet’s refueling probe. And based on my Google search of aviation refueling accidents, that has happened more than a few times. If that happens, the jet with the new “basket accessory” would likely fly a straight-in approach, more like an instrument approach than the standard daytime landing pattern.

CH-53 Sea Stallion refueling from KC135.

My final aerial-refueling item has to do with helos. This picture shows a CH53 Sea Stallion doing inflight refueling. Notice how the helo is tilted forward? That’s because it’s going fast (for a helo). Anything I said before about how dangerous aerial refueling is for fixed-wing jets, pales in comparison to the challenges for a helicopter.

The photo is from this short video in which a CH53 refueling from a KC135 suddenly pitches up in turbulence and the helo blades actually cut off the end of its own refueling boom. It must have damaged the blades but apparently insufficiently to cause a crash because according to everything I could find, the helo landed safely (the probe-end landed in a farmer’s yard!).

Finally, if you’re a glutton for punishment, this longer video shows 15 minutes of additional aerial refueling mishaps from the earliest days (in the 60s) up to the present.

(Please send any suggested corrections to my mailbox. Thanks!)