Subject:  C.16.  Why do the USAF/USN use incompatible refuelling systems?

By far the most common method for in-flight refuelling is the
"probe-and-drogue" system, in which the tanker unreels a hose behind it with a
drogue on the end (a meshwork cone whose drag keeps the end of the hose in a
stable position).  The receiving aircraft has a probe attached to it, which is
inserted into the drogue to link the fuel systems.  Some receiving aircraft
have probes permanently mounted, some have bolt-on probes that can be attached
if a mission requires them, and some have retractable probes.  This method is
used by the US Navy, modern Russian aircraft, and every other country that
uses in-flight refuelling.

The US Air Force alone uses the "flying-boom" system.  In this system, a rigid
boom, with control surfaces on the end, is extended from the tanker and
inserted into a socket on the receiving aircraft.  This method has two major
disadvantages over the probe-and-drogue method.  First, the boom has to be
attached directly to the tanker's fuselage, which prevents refuelling from
detachable pods attached to a tanker's wings (allowing more than one receiver
to link up at a time) or to the centreline hardpoint on a fighter or strike
aircraft (allowing such aircraft to refuel each other without a dedicated
tanker), both of which are commonly done with probe-and-drogue refuelling.
Second, the equipment on the receiving aircraft is incompatible with the
probe-and-drogue system, which means that USAF aircraft can neither refuel nor
receive fuel from any other aircraft, including the US Navy's.

The reason why the USAF puts up with this is that the flying-boom system can
achieve much greater fuel flow rates than the probe-and-drogue system (mainly
because the rigid boom is shorter and wider than the flexible hose).  This is
mainly for the benefit of large bombers such as the B-52 and B-1; refuelling
such large aircraft by probe-and-drogue would take much longer, enough (in the
USAF's judgement) to cause significant tactical problems.  Few other air
forces operate aircraft of similar size; the handful that do are prepared to
live with the refuelling delays in the interests of compatibility.

The third refuelling system used is the "wingtip-to-wingtip" system, used only
by older Russian bombers.  In this system, a hose is unreeled from one wingtip
of the tanker, and caught by a socket in the opposite wingtip of the receiver;
the two aircraft then fly side by side, with the hose joining their wingtips
(the length of the hose is comparable to the wingspan of the aircraft).  The
tankers are all converted bombers themselves, mainly the Myasishchyev M-3MS-2
"Bison-B". This system is very tricky to link up, occasionally dangerous, only
usable with bombers (smaller aircraft can't carry the necessary receiving
equipment on their wingtips), and gives flow rates even worse than
probe-and-drogue; not surprisingly, the Russians have largely replaced it with
the probe-and-drogue system, and it will probably become extinct with the
retirement of the last M-3 tankers in 1994 or 1995.

Please E-Mail me at johansson@ctrl-c.liu.se