in the summer of 1948 a very unique
aircraft took to the sky
or rather was dropped into the sky
this was the mcdonnell xf-85 goblin it
was one of america's attempts at
creating a so-called parasite fighter
and as far as designs go it's one of the
weirdest planes to be flown by any us
pilot
during world war ii the huge formations
of american bombers were protected by
long-range escort fighters
as bomber technology developed and their
effective range increased the fighters
could roughly keep up thanks to the
addition of drop tanks
however with the emergence of the first
generation of jet fighters there came a
problem
they lacked the range to keep up with
any of the heavy bombers
for reasons that usually involved
explosions aerial refuelling wasn't
quite far enough along in its
development to facilitate that line of
thinking and so the us army air force
considered reviving the idea of the
parasite fighter
these aircraft had seen some use in the
1930s and during the earlier parts of
the second world war mostly by the
soviet union the united states had also
dabbled with the idea of parasite
fighters but development work had been
discontinued before their entry into the
war owing to the improved range of
conventional planes
but as the aforementioned new generation
of jet fighters now had considerably
shorter range the concept was once again
appealing enough to consider
and so in early 1944 the army air force
directed the air technical service
command to undertake studies on the idea
and invited industry manufacturers to
submit concept proposals
unfortunately they didn't get many
responses
most manufacturers were busy producing
conventional aircraft or working on what
they considered more promising projects
and many believed that the parasite
fighter was a dead end road in terms of
development
this proved to be fortuitous for the
relatively young mcdonnell aircraft
corporation who were keen to expand
their portfolio as they were the only
aircraft manufacturer to respond with
enthusiasm
that being said their initial proposal
the model 27 was not well received
unfortunately no drawings of this
aircraft seem to exist so here's a
pretty photo of a b-29 for the time
being
designed by a team led by hermann d
barclay the model 27 was a small but
rather conventional fighter that was
meant to be carried partially within the
belly of set b-29 or the newer and
upcoming b-35 or b-36
however the model 27 was rejected in
1945 as the army air force concluded
that such a design would cause too much
drag and it was decided that any
parasite fighter must be contained
completely within the b35 or the b-36
the b-29 at this point was removed from
consideration as it was deemed
hilariously too small
undaunted mcdonnell completely revised
its parasite fighter design and on the
19th of march 1945 submitted a proposal
for the model 27d
it was a diminutive aircraft with an
egg-shaped fuselage triple vertical tail
surfaces a tail plane with a pronounced
anhedral and vertically folding wings
with 37 degrees of leading edge sweep
it was to be powered by a westinghouse
j-34 turbojet and it was to be armed
with four 50 caliber machine guns
mounted in the fuselage
also as a quick side note here the wing
sweep of this design was pretty
adventurous for the time as it both
predated to the acquisition of german
engineering data post-war and north
american's recommendation for
redesigning the original straight-wing
xp-86
the only other major developer of
sweatwing aircraft at the time had been
northrup with their xp-56 and the xp-59
mcdonald's proposal for their new
parasite fighter was received favorably
and in spite of the post-war gutting of
military aircraft orders they received
an order for a static test model and two
prototypes tailored for use with the b36
on the 9th of october 1945.
a wooden mock-up of the prototype was
built in 1946
this included both a mock-up of the
model 27 and a modified version of the
b-36 bombay that would house it
the army air force conducted an
inspection in june after which the
mock-up was accepted with only minor
modifications recommended to the oxygen
stations in the bombay and mcdonald
began construction on the two prototypes
in the latter half of 1947.
initially the model 27d was redesignated
as the xp-85
but in 1948 this was changed to xf-85
and the aircraft was given the name
goblin by the air force
though some mcdonald personnel gave it
the more affectionate nickname of
bumblebee in parallel with the
development of the xf-85 the army air
force which in september 1947 became the
us air force planned that the 24th and
subsequent b-36s would be capable of
carrying one f-85 plus a bomb load while
some of the bombers would be modified to
carry three fighters with no bomb load
at all as a sort of floating aircraft
carrier providing the test results of
the two prototypes proved favorable the
us air force were prepared to place an
initial order for 30 of the f-85
parasite fighters
as far as designs go and as a direct
result of its unusual requirements the
xf-85 was almost as far away from a
traditional fighter design as it was
possible to be in the late 1940s
indeed almost everything about this
plane could be considered weird in one
form or another
in terms of operation the xf-85 was
designed to be launched and recovered
from a retractable trapeze that would
extend beneath the parent bomber as a
result the xf-85 was not fitted with an
undercarriage but had a retractable hook
in the fuselage set forward of the
cockpit and for emergency landings it
had a retractable steel skid beneath the
fuselage and its wingtips were protected
by small steel runners
for moving the goblin on the ground a
special four-wheel transport dolly was
built that allowed it to be transported
from the hangar to the mothership or
other testing facilities
as it would spend most of its time
nestled in the steel bosom of a
strategic bomber the xf-85 only needed a
combat endurance of 30 to 40 minutes
this meant that only a small 420 liter
fuel tank was required though compared
to the total size of the airframe this
would still take up a considerable
amount of space
in fact the arrangement was so compact
that the center of gravity would move
several inches during the course of a
flight as the fuel tank was drained
there are also some sources that give
the fuel capacity as 720 liters
but for the moment i'm more inclined to
go with the lower figure as that seems
to be the more dominant amongst various
source materials that i could find
in terms of aerodynamics the short
length of the xf-85s fuselage reduced
the effectiveness of the tail surfaces
and so mcdonald grew inventive with the
flight control layout
to keep the xf-85 stable more tail
surface was needed but having one or two
very large tail sections would a present
all kinds of terrifying drag problems
and b prevent the aircraft from fitting
in the bombay of a b-36
in the end five stabilizing surfaces
were mounted around the rear of the
plane
four were arranged in an pattern with
the fifth as a vertical stabilizer
continuing with the trend of weirdness
there was no traditional rudder on said
vertical tail section
instead four so-called rudovators were
mounted on the other four stabilizers
which combined the functions of
conventional rudders and elevators
these operated in pairs with the upper
right and the lower left working
together and vice versa
though in an unusual departure to
normality there was nothing special
about the control surfaces of the main
wings which had conventional ailerons
for roll control
the trapeze system was equally unique as
the fight it was designed to carry
it had three sections the upper two
sections were hinged to hold the xf-85
level as the mechanism was extended and
a pincer-like stabilizing arm was
mounted at the forward end of the lower
portion to restrain the movements of the
fighter whilst it was still attached the
trapeze mechanism was removable and
mcdonald was directed to ensure that it
would take no more than 12 hours to
remove the system and allow normal use
of the b-36's bombay the whole system
was designed to launch the xf-85 from
the parent bomber in less than two
minutes once the bombay doors were open
to launch the fighter the trapeze would
fully extend the pilot of the xf-85
would lower the wings and lock them in
position and start his engine
the trapeze operator aboard the bomber
would then release the pincer arms that
kept the fighter in place
and finally the pilot of the xf-85 would
flick a switch that unlocked the head of
the skyhook and the fighter would drop
free
by the summer of 1948 the first
prototype was almost ready for flight
trials unfortunately some butterfingers
resulted in it being dropped in one of
naca's wind tunnels damaging the nose
intake and lower fuselage and after a
relatively short delay the second
prototype was hastily readied for use
instead initial flight trials began on
the 23rd of august however as no b-36s
could yet be spared for testing the
xf-85 would be carried aloft by a
specially modified b-29 superfortress
this had a cutaway bombay complete with
the trapeze installation that was
intended for the larger b-36
the first three test flights were simply
captive flights with the xf-85
performing the parasite part of its role
to admiration and clinging onto the
trapeze of the b-29 without incident
it was also lowered down into the
airstream with its engine turned off to
give the test pilot a feel for how it
handled in the air piloting the goblin
was mcdonnell test pilot edwin shark he
would be the only person to fly the
xf-85
partly because he was one of mcdonald's
best and most prolific test pilots
and partly because the aircraft's size
meant that it couldn't be flown by
anyone over five foot eight
after the first three captive flights
were completed without incident shock
was ready for the first free flight of
the goblin
this was made on the 28th of august when
at an altitude of 20 000 feet and flying
above the murak dry lake the modified
b-29 evicted its parasite and shock took
the xf-85 for a 15-minute flight to
evaluate its handling characteristics
despite looking like a squashed melon
with fins stuck on the side the xf-85
was reported to be surprisingly stable
and it responded quickly but not
dangerously to the controls
indeed it handled so well that it could
almost come as a surprise that the
project was cancelled
but then came the moment of reattachment
hooking onto the mothership was perhaps
one of the most terrifying things that
any pilot could experience in 1948 on
its own lining up the sky hook with the
trapeze was difficult enough as
mentioned before the controls were
somewhat sensitive but then there was
the added problem of the incredibly
turbulent air beneath the parent b-29
in the process of reattaching the xf-85
was caught in this violent turbulence
and struck the trapeze with such force
that it shattered the canopy and ripped
off shock's helmet and breathing mask
thankfully he managed to regain control
of the aircraft and safely performed an
emergency landing on the dry lake bed
below but it was a worrying start
following its repairs the prototype made
three more flights on the 14th and 15th
of october 1948 with successful
recoveries using the hook and trapeze
however each of these attempts required
the full concentration and effort of an
experienced test pilot to avoid disaster
and on the fourth flight shark had to
again make another emergency landing
courtesy of the severe turbulence
notwithstanding the addition of
auxiliary vertical surfaces at the wing
tips to improve directional stability
whilst flying through the turbulent air
the sixth flight also ended with the
landing on a dry lake after another
heavy impact with the trapeze
the same fate also awaited the first
prototype when on its first and only
flight it also headbutted the mothership
and had to commence an emergency landing
in spite of this the favorable comments
regarding its stability control and spin
recovery prompted mcdonald to remain
confident about the xf-85
and it was hoped that a redesigned
trapeze system might make the docking
process easier
to air force personnel however it was
obvious that even with major
improvements the goblin was still going
to be quite the handful for the average
pilot as even the best will in the world
couldn't magically make the prop wash of
a b-29 let alone a b-36 simply disappear
this combined with the waves of funding
reductions that began in the autumn of
1949
made it increasingly difficult to
justify further development work on the
xf-85
the final nail in the coffin was the
realization that foreign interception
fighters were now in development with
performance figures that far out class
to the xf-85
and so after accruing just two hours and
19 minutes of flight time mcdonnell
received a termination notice for the
xf-85 program
thankfully for aviation enthusiasts
everywhere these aircraft did not go to
the scrap heap the first prototype is on
display at the national museum of the
united states air force in ohio and the
second is on display at the strategic
air and space museum in nebraska
their survival can partially be owed to
their extreme uniqueness
but also to the fact that lessons
learned from their development were
applied to the development of the
republic rf-84k thunderflash which
itself saw limited use as a parasite
reconnaissance aircraft as part of the
ficon program
but that is a story for another day as
always thank you all very much for
watching and i'll catch you all next
time goodbye
[Music]
you