N.K.A.W.T.G – Nobody Kicks Ass Without Tanker Gas

Air-to-air refueling

Find out what’s behind the cryptic title and come on a visit to the 100th Air Refuelling Wing at RAF Mildenhall.
N.K.A.W.T.G – Nobody Kicks Ass Without Tanker Gas
The mysterious headline of this article needs no Latin translation skills as it is the unofficial tanker pilot motto: Nobody Kicks Ass Without Tanker Gas. In this article, we will take a look at the history of air refuelling, a closer look at the dominant tanker aircraft of the USAF and we will take to the skies on an air refuelling mission with the 351st Air Refuelling Squadron which is part of the 100th Air Refuelling Wing at RAF Mildenhall, England.

The history of air-to-air refuelling
The first attempts to refuel one aircraft in the air from another took place back in the early 1920s. The first successful air refuelling was finally conducted on 27 June 1923, between two Airco DH-4B bi-planes from the US Army Air Service. The refuelling was carried out by lowering a hose from the top aircraft to the receiving aircraft which was flying below and behind. One of the crew members on the receiving aircraft had to catch the hose and then manually insert it into the normal filling point.

Just one month later three DH-4B aircraft, two tankers and one receiver aircraft, set a world record by keeping the receiver aircraft in the air for over thirty seven hours. This was made possible by nine air refuelling’s during which 2600L of fuel and 140L of engine oil were transferred.

During the 1920s and ‘30s, the techniques and the equipment used for air refuelling were refined and in 1935, the record for the longest time in the air had been raised to twenty seven days. Air refuelling was still a complex and dangerous task and it was not until the late 1930s that Richard Atcherley from the RAF developed the first practical air-refuelling system called the “looped-hose”.

Even with a more convenient and safe method to perform air-refuelling, it was still seen as something that was most useful for long-haul commercial aircraft. It was only during the very last months of WWII that the USAAF began to consider using air-refuelling to extend the range of their bombers during the expected battle for the Japanese mainland. However, the war ended before these plans could be implemented.

After the war, the USAF rebuilt a small number of B-29 Superfortress aircraft so they could act as air-refuelling aircraft and refuel other B-29’s and the later B-50 bombers.

A F-15E Strike Eagle is being refueled while both the KC-135 and the F-15E carries out a soft and steady left turn.

“The advantages of the probe-and-drogue system are that it is relatively simple and can be retrofitted to many different types of aircraft”
An example of the “probe-and-drogue” tanking method. A USMC KC-130 tanker aircraft, is “tanking” two CH-53 Super Stallion helicopters.
After WWII, the company behind the looped-hose method, Flight Refuelling Ltd, realised that this system was not an optimal way to conduct air-to-air fuelling so they began developing a newer and better idea. What they came up with was the “probe-and-drogue” system, which is one of the two methods still used today for air-to-air refuelling.

A probe-and-drogue system was installed in a Lancaster from the RAF and to test the system, a modified Gloster Meteor F.3 was used for the refuelling trials. In short, the probe-and-drogue system works by the tanker aircraft unreeling a fuel hose out into the slipstream behind itself. At the end of the hose is a basket shaped like a badminton shuttlecock. The receiver aircraft must connect to the inside of the basket using an external probe that is connected to the aircraft fuel tanks.

Some of the advantages of the probe-and-drogue system are that it is relatively simple and can be retrofitted to many different types of aircraft, from large transport aircraft such as the C-130 Hercules to smaller fighter aircraft like the F/A-18 Hornet. On larger aircraft, multiple probe-and-drogue systems can be installed, for instance one under each wing making it possible to refuel two aircraft at the same time.

However, there are also some drawbacks to the design including a slow fuel flow (between 680 to 2040 kg per minute). This is due to the relatively small diameter fuel hose which in turn means it takes longer to refuel the receiving aircraft. It can also be difficult for the receiving plane to insert the probe into the basket due to turbulence behind the tanker aircraft.

Today, most US Navy aircraft and helicopters as well as some of the USAF and US Army’s helicopters use the probe-and-drogue method. In addition, all non-US aircraft manufacturers use the probe-and-drogue system in their designs if in-flight refuelling is needed.res jagerfly.

Flying boom
In the late 1940s, Boeing was given the task of developing a system that was able to transfer fuel faster than the probe-and-drogue method. This resulted in the “flying boom” system. The rigid, larger diameter fuel pipe, or boom, is guided into a mating receptacle on the receiving aircraft by the operator, called the “boomer”, on board the tanker aircraft.

The system was first installed on a B-29 aircraft in 1950 and a total of 116 B-29s were converted to KB-29P models by Boeing. Subsequently, Boeing developed the KC-97 tanker aircraft. However, as the KC-97 had both propeller engines and jet engines, it meant that it had to carry two types of fuel, which proved to be less than ideal. Despite this, the flying boom concept had proven its worth as it offered a number of advantages over probe-and-drogue method amongst which were a much high fuel flow rate (up to 2900 kg per minute).

Having the boom controlled by the boomer on board the tanker also made it easier to refuel in bad weather. Planes with a flying boom installed, could typically also be retrofitted with probe-and-drogue system under their wings to overcome the main disadvantages of the flying boom, that is to say that it can only refuel one aircraft at a time.

After building the KC-97, Boeing received orders from the USAF to develop a new tanker aircraft based on their 367-80 (Dash-80) concept. This resulted in the KC-135 Stratotanker.The flying boom system is now standard on all USAF fixed wing aircraft that need aerial refuelling.

The mighty flying gas station, KC-135 is ready for the next sortie.
The WSO on this F-15E Strike Eagle keeps a sharp eye on the boom while the pilot keeps the plane in the correct formation with the tanker aircraft.

Boeing KC-135 Stratotanker
The first KC-135A tanker aircraft were delivered to the USAF on 24 January 1957. A total of 808 C-135 aircraft were delivered to the USAF, in various models and configurations:
  • 729 KC-135A – Standard tanker configuration
  • 17 KC-135B – Temporary designation for EC-135 type
  • 18 C-135A – Standard transport aircraft
  • 30 C-135B – Standard transport aircraft
  • 4 RC-135A – Special edition used for mapping
  • 10 RC-135B – Temporary designation for special surveillance

All aircraft were delivered with either the Pratt & Whitney J57-P-59W turbojet engines (A models) or the Pratt & Whitney TF-33-PW-102 turbofan engines (B models). Of the total of 808 aircraft delivered to the USAF, approximately 454 are still in use today. These aircraft have undergone many updates over the years and they have evolved to cope with many tasks other than just air refuelling.

The turbojet engines used in the A-models were very inefficient as they had high fuel consumption and required long runways for take-off. As a temporary solution, the USAF began to replace turbojet engines with TF-33-PW-102 turbofan engines in 1982. These engines were taken from retired airliners and in total, over 150 KC-135A models had their engines replaced. Their designations were changed to KC-135E.

The latest upgrades
As the first E-models were put into service by the USAF, Boeing came up with a proposal for a more radical plan to extend the service life of the KC-135 family. One of the major changes was to install the high-bypass turbofan CFM International CFM56 engines. These received the military designation F-108-CF-100.

This engine gave significant improvements in terms of both more power and lower fuel consumption. Boeing completed the first upgrade with this type of engine in June 1984 and this aircraft model was designated the KC-135R. Besides the new engines, the upgrade also included an auxiliary power unit (APU), which is located in the rear of the aircraft’s cargo compartment. The APU meant that the aircraft was now able to start the engines without help from equipment on the ground.

R-models were also given the so-called Pacer CRAG update, which replaced the old analogue style cockpit with a new digital version. These and a number of other upgrades, transformed KC-135 aircraft into the modern planes that will be in service for many years to come.

Today’s KC-135 models
There are five types of KC-135 tanker aircraft currently in the USAF inventory:
  • KKC-135R: Standard tankers, a total of 313 in service
  • KC-135T: Originally KC-135Q used to refuel SR-71 Blackbirds, a total of 54 in service
  • KC-135R AAR: KC-135R tanker aircraft which can receive air refuelling via a receptacle above the cockpit, a total of 8 in service
  • KC-135R MPR: KC-135R with probe-and-drogue refuelling system under the wings, a total of 20 in service

A total of 22 KC-135R tanker aircraft are upgraded to perform tasks with US Special Forces, but the detail of the upgrades is classified.
“The upgrade also included an auxiliary power unit (APU), which is located in the rear of the aircraft’s cargo compartment. The APU meant that the aircraft was now able to start the engines without help from equipment on the ground”
After the start of the four engines, the KC-135R aircraft taxis
out to RAF Mildenhall runway 11.

As if it’s not hard enough to get a large aircraft in close formation with the tanker aircraft,
it must be done while both aircrafts are flying in an oval track.
Tanker for strategic bombers
Initially the plan was to primarily use the KC-135’s to refuel Strategic Air Command’s (SAC) B-52 bombers and as such the KC-135 units were often placed on SAC bases with B-52 aircraft. However during the Vietnam War, the KC-135 aircraft were heavily involved in refuelling fighters, attack aircraft and bombers during the attacks on North Vietnam. Since then, air refuelling has become an integral part of virtually all combat missions flown.

Nowadays with the global war on terror which the US began after the attacks on September 11 2001, the KC-135 units have been very busy. The many fighter jets, transport planes and bombers participating in operations over Afghanistan and Iraq rotate regularly with new units from bases in the United States and they all require air fuelling on the trips back and forth. In addition to this, many combat missions also require air fuelling.

KC-135 outside USAF
Despite the KC-135 aircraft’s success as tanker aircraft in the USAF, only France has bought brand new KC-135 aircraft. Between 1963 and 1964, the French Air Force received twelve KC-135F Stratotanker aircraft.

They were primarily used to refuel the Mirage IV aircraft. One of planes crashed in 1972 and the remainder have all been upgraded to KC-135R standard now.

Between 1997 and 1998, Turkey purchased seven ex-USAF KC-135A aircraft, all of which were upgraded to KC-135R standard. Singapore Air Force bought four KC-135A aircraft in 1998 and these were all upgraded to KC-135R MPR standard. The only KC-135E models to have been exported, three examples, were sold to Chile in 2008, where they replaced old Boeing 707’s.

Five KC-135 aircraft are currently in AMARG in Arizona where they are ready to be sold to an as yet un-named buyer. In April 2013, the United States approved the sale of a unpublished number of KC-135 tanker aircraft to Israel as part of a major arms deal. Israel today uses eight old Boeing 707 aircraft and it is these that KC-135s will replace.

Although the exact numbers of aircraft is not known, it is expected that it will be the five KC-135 aircraft currently located on AMARG. These aircraft will require a major upgrade before delivery.

The future of the KC-135 Stratotanker
The replacement for the KC-135 aircraft is to be the Boeing KC-46, which, after “extra time and a penalty shoot-out” with the Airbus A330, was declared the winner of the USAF’s KC-X competition. The cost of producing the 179 aircraft that the USAF has ordered is so high that production will have to be spread out over many years.

Currently, the last example is not expected to be delivered until 2030. Logically, this means that there will still be KC-135 aircraft in service until then and by that time, the aircraft will have been in service for over seventy years.

351st ARS, 100th ARW – RAF Mildenhall
The KC-135 tanker aircraft have long been associated with RAF Mildenhall. The first unit on the base was Detachment 1, 98th Strategic Wing (SW), which in January 1970, moved from RAF Upper Heyford to RAF Mildenhall.

The unit’s primary task was to support RC-135 missions over Europe. For many years there were approximately sixteen KC-135’s temporarily stationed at RAF Mildenhall from units in the United States. Although the aircraft were dedicated to supporting the US Air Force Europe (USAFE), the aircraft were still under SAC command.

This was however changed on 1 February 1992, when the 100th Air Refuelling Wing (ARW) was activated at RAF Mildenhall, with fifteen KC-135R tankers attached to the 351st Air Refuelling Squadron (ARS). These tankers operate around the clock every day of the year.

The large reduction of USAF aircraft in Europe in the last few years has meant that the unit can concentrate more on refuelling the American transport, bomber and patrol aircraft flying to and from the US to combat zones, especially in the Middle East. In addition, the squadron is also responsible for a large part of the air refuelling training that many European air forces undertake as they do not have their own tankers.

The 351st ARS have a number of KC-135R MPR aircraft and can thus also train with air force’s using the probe-and-drogue method as well as the flying boom system, among them the Royal Danish Air Force, which regularly practice air refuelling with Mildenhall tankers.

At the beginning of 2015, the USAF announced that RAF Mildenhall was to be closed down. The MC-130H Hercules and CV-22B Osprey used by the 352nd Special Operations Group will move to the nearby RAF Lakenheath base while the 100th ARW and their KC-135R Stratotankers will most likely move to Ramstein in Germany.

The creew carries out the papers, and equipment they have had on the trip, after ending the mission, and KC-135 will then be handed over to ground personnel.
The pilots ensures that the KC-135 is in a constant soft left turn.

On February 6 2015, FLYMAG fortunate enough to fly on board a KC-135R from RAF Mildenhall – call sign QUID 76 – on an air refuelling mission.

BAt 06:00, the crew met to brief the mission. The briefing took place at a table in the squadron’s recreation area next to the pool table. Present were the pilot, co-pilot, two boomer’s and an instructor pilot. The briefing took place in a relaxed but professional atmosphere with the pilot starting by reviewing the day’s mission.

The original plan for the mission was to refuel six F-15E Strike Eagles from the nearby RAF Lakenheath base, but shortly before the briefing, the pilot was told that when the six F-15E had been refuelled, the remaining fuel should be given to an RC-135 Rivet Joint aircraft which was on its way back to the United States.

After briefly explaining who we were refuelling, the pilot went through the mission profile, which area we would be refuelling over, what bases were available in emergency situations, the weather and a myriad of other smaller details about the mission.

After this, the co-pilot went through the refuelling in more detail and finally the boomer reviewed the refuelling operations from his point of view.

Lastly, at the end of the briefing, the boomer covered the safety procedures for the passengers who were along for the flight (FLYMAG and two press officers). When the briefing was over, all the necessary equipment was loaded on board a bus that took us to the aircraft waiting in the morning darkness.

By the aircraft, we were met by the crew chief responsible for the aircraft. He and the pilot went over the things that have been updated since the aircraft’s last flight and once the plane had been handed over to the flight crew, we boarded the aircraft through a hatch on the left side, below the cockpit. Once inside the aircraft, the two pilots started to go through the many pre-flight checks, which needed to be completed before the engines could be started.

While the pilots were busy in the cockpit, one of boomers went over the safety procedures once again and also showed where the aircraft’s emergency exits were located and how to use them. As the sun slowly rose over England, the pilots got far enough into their pre-flight checks as to allow the APU inside the aircraft to be started.

Shortly after that, over the noise of the APU, a low “bang” was heard as the first engine started up. This was quickly followed by a further three as the remaining engines were started in sequence. With all four engines up and running, the APU was turned off again and the noise level inside the cargo compartment fell to a level which was comparable to that of a conventional passenger aircraft.

The first customers
At just past 08:00 local time, approximately one hour after we arrived at the aircraft, we were ready to taxi out to the runway. After getting permission from the tower, we taxied all the way out to runway 11. As soon as the aircraft was lined up on the runway and the tower had given take off clearance, the pilots applied full power to the engines and the plane accelerated swiftly down the runway. Once airborne, the pilot’s headed towards a refuelling area called “Track 8” over the North Sea.

This was where we were to refuel the F-15E’s and the RC-135 Rivet Joint aircraft. The Boomer was now busy getting ready for the first F-15E to be refuelled and he had his own checklist to go through to make sure everything worked the way it should. The short flight from Mildenhall to the refuelling area was a clear benefit to both the tanker and the aircraft to be refuelled as it cut down on time and fuel wasted going to and from the refuelling track.

At about 09:20, the first two F-15E to be refuelled arrived at the tanker. Standard procedure when refuelling aircraft arriving in formation is that they approach the tanker from below on the tanker’s left side. Once they have visual contact with the tanker, they get in formation on the tanker’s left wing.

The lead aircraft then asks the boomer for permission to move in behind the tanker. When the boomer is ready to refuel, permission is given. The receiving aircraft then slowly moves into a position behind and slightly below the tanker. Lights on the underside of the tanker guide the pilot of the receiving aircraft into the correct position.

Once the receiving aircraft is in a stable position within the correct area behind the tanker, the boomer guides the boom to the receiving aircraft refuelling receptacle. On the F-15E, this is located on the wing root on the aircraft’s left side. When the boom is in the correct position the boomer extends the fuel pipe rearwards until it locks into the receiving receptacle with an audible “klonk”. The job of actually pumping the fuel and ensuring that tanker aircraft remains in balance is the co-pilots task.

Since this was a training mission and it was not necessary to give the F-15E’s a full load of gas, the aircraft were only connected to the tanker for approximately two minutes. The boomer then released the boom and the receiver aircraft dropped slightly down and back to create a little distance with the tanker aircraft.

It then slowly moved over to the tankers right hand side and took up formation on the right wing. Here the aircraft waited until the second aircraft in the formation had been refuelled. Once both had completed their task and were sitting behind the right wing, they were cleared to leave the tanker; the two F-15E gently climbed away from the tanker.

The Weapon System Officer (WSO) ensures that the boomer hits air-refuelinghole on the first try.

The big delivery
Less than ten minutes later the next F-15E arrived for refuelling. This time the aircraft arrived alone and made a direct approach from behind and below the tanker. The boom made it hard to see anything rearwards from the observers position beside the boomer and the dark grey fighter suddenly popped up out of nowhere.

It slowly slid into position behind the tanker and the boomer guided the boom safely into the receiver aircraft’s refuelling receptacle. Again, the two aircraft were only connected for a few minutes before the boomer broke contact and the F-15E fell back and turned right to disappear, continuing on its mission.

This was followed by another lone F-15E and finally two more Strike Eagles arriving in formation. We had now refuelled the six F-15E Strike Eagles that the initial briefing called for, but there were two more aircraft in the area and they asked for permission to come up and be refuelled. This was approved and they duly arrived in formation about five minutes later to receive their fuel.

Now we only needed to refuel the RC-135 Rivet Joint. The RC-135 is one of the many variants of the C-135 aircraft family that are in service with the USAF. The plane arrived at the tanker around fifteen minutes after the last two F-15E had departed, coming in from behind and well below. The RC-135 approached slowly whilst it climbed into the correct position behind the tanker.

The connection
After several minutes of careful manoeuvring the RC-135 aircraft was in close formation behind the KC-135R aircraft and the boomer guided the boom down into the refuelling receptacle located just above the cockpit.

The plan was to give the RC-135 aircraft all the fuel we could spare without leaving the tanker short, but even with the high fuel transfer speed, it took about ten minutes to complete the full refuelling.

In these ten minutes, the pilot on board the RC-135 Rivet Joint aircraft kept it in tight formation with tanker aircraft and made sure that it did not go outside the boom’s range of motion, a very difficult task for such a large aircraft.

When the refuelling was over and the boom detached from the RC-135, it slowly fell back and downwards before flying away, the procedure being that the fighter jets leave the tanker upwards and large aircraft leave it downwards.

With the last refuelling over, we turned back towards RAF Mildenhall and around 11:30, we landed back on runway 11 approximately 3.5 hours after take off. The pilot taxied the aircraft back to the stand and the engines were powered down. Once the ground crew had secured the aircraft, the crew hatch was opened and the boomer lowered the ladder down so that we could climb out into the cold clear winter air.

After the crew signed the aircraft over to the ground crew chief again, we drove back to the squadron building where the crew then de-briefed the full mission.

FLYMAG would like to thank A1C Kyla M Gifford from Mildenhall Public Affairs Office for having made the flight with QUID 76 possible and the crew aboard QUID 76, Captain Dan Ouper, 1st Lt. Adan Lubin, SRA Kyle Cleis and SRA Amy Lizauckas for all of their help and support in producing this article.
“In these ten minutes, the pilot on board the
RC-135 aircraft kept it in tight formation with tanker aircraft and made sure that it did not go outside the boom’s range of motion”
The large RC-135 Rivet Joint has contact with the tanker aircraft.
The aircraft has started to get the very last jet fuel, which QUID 76 has available.