Chuck Yeager once said (1), "The pilot with the most
experience is going to whip your ass, no matter what you
were flying- it's that simple". Yeager had just proven his
point by beating a Lieutenant Colonel in two dogfights. In
the first Yeager had the MiG 15 and the Colonel had the
Sabre. In the second the pilots swapped aircraft. The
result though was the same: Yeager stuck to the tail of the
Colonel as if he was attached by glue.
This article is about the two key aircraft in Rowan's
Korean War Flight Sim entitled: MiG Alley. The MiG15 and
the F86 Sabre fought for air dominance in the skies over
MiG Alley during the world's first jet vs. jet air war. It
is true that the first jet v jet combat did not feature the
F86 but it was soon realised that the Sabre was the only UN
aircraft that had a chance against the MiG. In this note
the strengths and weaknesses of the two aircraft are
explored in as much depth as possible. The aim is to
produce a set of data that can be used to tune the MiG
Alley flight model so that a thoroughly realistic
experience of flight and combat can be enjoyed.
Most written accounts are necessarily qualitative in
nature. For flight sim work we must adopt a much more
quantitative approach. It takes time to dig out this data
and we are sure that more exists. If you come across any,
please pass it on: a flight sim is never finished and we
can always improve it.
As Yeager said, it is experience that
counts. Part of that experience is knowing the strengths
and weaknesses of yours and your opponent's aircraft. The
data in the appendices of this note should certainly help
you fly smarter.
2 Background
The first jet v jet combat took place over Korea on the 8th
November 1950. Lieutenant Russell J. Brown(2) flying an
F80C "Shooting Star" shot down a MiG15, which was one of a
flight of four that had dashed across the Yalu. Despite
this first success, it was soon apparent that the "Shooting
Star" was no match for the MiG. With a speed advantage of
over 100mph, the MiG was able to evade the F80C with ease
and attack the B29 bombers tasked with bombing missions on
the Chinese Border.
The two straight winged USAF fighters: the F80C and the
F84E, were relegated to strike missions. Along with the
F51D, a veteran from the Second World War, these aircraft
took on the ground attack missions: the grunt work of the
war.
It was left to the swept wing F86 Sabre to
face up to the MiG and grab the glory. The MiG15 and the
F86 are very similar in design. They are both all-metal,
single seater monoplanes powered by a single turbojet with
the wing swept back at 35 degrees and swept tail
surfaces(3). However there are differences that the flight
model must address and the pilot can use to his advantage.
MiG Alley F86 Cockpit
3 Variants
MiG15s were available to the communist
forces very early in the Korean War. In 1951, a more
powerful version, the MiG15bis appeared in Korea.
The first F86A Sabre mission over Korea took place on the
17th December 1950. One MiG out of a flight of four was
shot down. On December 22nd 1950, the MiGs shot down a
Sabre, but later that day six MiGs out of a flight of 15
were destroyed.
The E was the next variant to enter active
service in Korea. The only difference from the A was the
"all-flying" tail. In this modification, the horizontal
stabiliser pivoted on its rear spar so that the leading
edge moved up and down with the normal action of the
elevator controls. The "all-flying" tail eliminated the
undesirable compressibility effects of the F86A (2).
Recovery from supersonic dives was much easier.
The F86E first saw action in Korea with the 4th Wing in
September 1951. The F86F reached Korea in June and July
1952. Essentially the F86F was an F86E with a more powerful
engine. In September 1952, the "6-3" wing modifications
were fitted to F86Fs in the field. The "6-3" wing
modification consisted of adding 6 inches to the leading
edge of the wing root. The extension tapered to 3 inches at
the tip. In addition the leading edge slats were removed.
The F86F could out-turn and outrun the
MiG15bis. However, for most of the war, it was the MiG that
enjoyed the performance advantage. In fact the action in
the MiG Alley flight sim is centred on the Spring Offensive
and so we concentrate on the F86A v the MiG15 and MiG15bis.
4 Energy Fight
The two aircraft were capable of delivering similar thrust
(Appendix A), but because the
MiG was much lighter it had a significantly higher thrust
to weight ratio.
The MiG could out-climb and out-accelerate the Sabre.
Curiously though, the Sabre had the higher top speed up to
an altitude of 30,000ft. The MiG had a higher wing
thickness to chord ratio compared with the Sabre. Higher
drag resulted in a lower top speed in level flight and more
importantly in the dive. In fact the MiG could not go
supersonic in the dive whereas the Sabre could.
The MiG service ceiling was much higher than that enjoyed
by the Sabre. The MiGs were able to bypass fighter screens
by flying high. MiGs chose when to fight.
5 Angles Fight
With the higher thrust to weight ratio and lower wing
loading, the MiG should have demonstrated the better turn
performance. In fact performance was compromised by the
MiG's poor stalling characteristics. During combat, the
aircraft would suddenly stall and the inexperienced pilot
could not avoid the aircraft going into an uncontrollable
spin.
The result of the MiG's poor stall characteristics was that
pilots were uneasy about pushing the aircraft to the limit
and hence the Sabre pilot had the edge in a turning
contest.
The MiG armament only exacerbated the situation. As the MiG
was fitted with large bore slow firing canons, the MiG
pilot had to pull far more lead in a turning fight compared
with the Sabre pilot. As a result the Sabre pilot found it
easier to get a gun solution than did the MiG pilot.
The Sabre wing had a torsion box type structure which
prevented wing flexing. The MiG's wing construction was not
as stiff and the MiG suffered badly from wing flexing. In
addition, the variation in MiG wing manufacturing quality
was wide. These factors are likely to have contributed to
the poor stalling characteristics of the MiG.
Poor roll rate on the MiG could also have been caused, in
part at least, by the MiG's wing design and construction. A
roll-rate of 180 degrees/sec at all speed ranges has been
reported for the Sabre(4) whereas the MiG could only
produce a performance that was half to two-thirds as good.
In fact the Sabre was generally more refined and
controllable with no tendency to yaw. Overall, the Sabre
was the better aircraft for a turning fight.
The differences between the two aircraft determined the
tactics during combat. MiGs tended to fight in the
vertical. They would choose the moment of engagement and
then swoop down in a slashing attack and then zoom back to
a safe altitude. MiG pilots could control the separation by
use of the vertical, better climb and acceleration rates.
Sabres preferred to engage in turning and diving fights.
The lower the altitude, the less the performance advantage
enjoyed by the MiG. However an aggressive and skilful MiG
pilot could take on the Sabre. There are many reports of
MiGs forcing the combat and ending with a duel at ground
level.
7 Other Considerations
No Kum Sok was in no doubt about which was the better the
fighter(1):
"Some of the advantages were the efficient General Electric
J47 axial flow engine for long range, extra large external
fuel tanks, the capability of supersonic fight, fast firing
machine guns for dogfights, a radar gun-sight, better
environment in the cockpit, the cockpit's large dimensions,
orderly placement of gauges and controls, crystal clear
canopy, an advanced hydraulic control system with a
controllable horizontal stabiliser for superior
manoeuvrability, stall warning system, advanced radio, rear
view mirror and a better view for the pilot. It was like a
Cadillac compared to the family Chevrolet."
The range advantage enjoyed by the Sabre is of interest to
the strategist of the ground war. It meant that combat
occurred on the MiG's doorstep rather than over the front
line. The MiG did nothing to support communist ground
troops. However when combat was joined over the Yalu, range
advantages were largely irrelevant.
Yeager(1) added his weight to the argument:
"Flying the MiG15 is the most demanding situation I have
ever faced. It's a quirky airplane that's killed a lot of
its pilots." In his book he writes, "Man that thing was a
flying booby trap, and nobody would be surprised if I got
killed."
But as General Albert Boyd said about the MiG 15, "A light
plane with a big engine." In the final analysis, the MiG
had the edge and for the pilot willing and capable of
flying that edge, the MiG gave him the advantage.
4 Notes on discussions with Mark Hannah of the Old
Flying Machine Company.
5 F86 Sabre, MiG 15 "Fagot", Hawker Hunter (Legends of
the Air 1), S. Wilson, Aerospace Publications Ltd., Weston
Creek (Australia)
6 Communications with Anton Maree
7 MiG15 (Warbird History), Y. Gordon and V.Rigmant,
Motorbooks, Osceola, USA, 1993
8 Check 6, F. C. Blesse, 1987
9 Central Fighter Establishment report
10 USAF Museum Web Site
11 Rowan Software Flight Model
12 Sabre MkIV Flight Manual
13 MiG15 Design, Development and Korean War Combat
History, Rigmant and Gordon, Motorbooks Int 1993
14 OKB MiG: A History of the Design Bureau and its
Aircraft, Midlands Counties Publications 1991
APPENDICES
Data
Data is quoted in SI units in preference. However, for the
sake of familiarity, imperial measurements have been
retained for altitude, rate of climb and speed.
Mass
The mass used in flight model calculations is critical. The
terms empty, gross, combat and clean can have different
meanings. The following assumptions have been made:
empty as manufactured
prepared empty plus oil, internal gun, residual fuel,
camera, oxygen, pilot, parachute which is taken as standard
to amount to 326kg
gross prepared plus ammo and internal fuel
clean50 prepared plus ammo and 50% internal fuel
mission gross plus external stores
The gross figure is the clean gross take-off weight.
Clean50 is used to produce the flight model performance
data.
Some authors use the term combat. This does not appear
to have a clear definition.
Conversions
1 US gallon = 3.785 litres = 0.003785 m3 1 lb thrust =
4.449 N All miles quoted are assumed to be statute miles
unless otherwise stated. 1 mile = 1.59km
Summary
The following figures have been obtained from the MiG Alley
flight model.
The following summary has been obtained from ref (9). The
information is based on combat experience in Feb to May
1952 and so it is assumed that the comparison is between
the F86E and the MiG15bis:
The MiG can outclimb and accelerate away from the F86
at any altitude.
· Above 30,000ft the top speed of the MiG is
greater.
· The MiG15 ceiling is estimated to be at least
5,000ft higher.
· Below 30,000ft, the F86 can out-turn the MiG15
in level and diving turns.
· In a sustained dive the F86 has the edge.
· At altitudes below 20,000ft, the level top
speed is about equal.
Performance Tables
For raw performance numbers click HERE to download figures for
the MiG 15 and F86 variants.
Specific Power Curves
The specific power curves presented here have been produced
by interrogating the MiG Alley flight model. As well as
being used to check on the accuracy of the flight model,
the curves can also be used to make comparisons between the
aircraft involved in MiG Alley. It should be possible to
develop a tactical plan before entering the cockpit.
Specific power is defined as the rate of change of specific
energy and it is used to measure the ability of an aircraft
to change its state. The idea of specific power was
developed during the sixties as part of the famous Top Gun
programme. In the early stages of the Vietnam War, USAF
pilots were not doing as well as they did during the Korean
War. Pilots were sent to the Top Gun School and results
improved significantly.
Pilots were introduced to the concept of energy
manoeuvrability. They learnt how to measure and manage
energy during air combat. As these theories were not
developed until the sixties, specific power curves do not
exist for the Classic Jets of the fifties. The curves
presented here are generated from the MiG Alley Flight
Model.
The Equation
Specific Power (Ps) = v. (T - D) / W Where: T is thrust D
is drag W is weight V is velocity
T, D, and W should all be in same units of force.
Velocity is usually defined in feet per second. This means
that Ps is also in units of feet per second.
When the Ps = 0, the thrust balances the drag exactly and
it is possible for the aircraft to sustain its conditions.
A positive Ps can be used to either change the height or
the speed of an aircraft, e.g.:
If Ps = 100ft/s and v = 600ft/s:
It can climb at 100 x 60 = 600 feet per minute
Or have an instantaneous accel. = Ps.g / v = 100 x 32.2
/600 = 5.4 ft/s/s
It is very important to realise that the Ps calculated is
for a point condition. As soon as the altitude, weight or
velocity changes, then a new Ps must be calculated.
A negative PS cannot be sustained. Either the velocity will
drop or the aircraft will have to lose altitude.
The Lift Line
It is usual for the specific power curves to be bounded by
the physical limitations imposed on the aircraft:
The left side is bounded by the lift limit line. The
aircraft cannot generate sufficient lift to sustain a
position on the left of this line. The top boundary is set
by the maximum g that the aircraft can tolerate. The right
boundary is set by the maximum speed that the aircraft can
tolerate. For the classic jets the airframe was rated at
7g.
In fact there were reports of 10g being reached without
serious consequences. This seems reasonable because a 50%
tolerance is usually built into the figures. Inspection of
the following curves shows that the aircraft are very much
under powered and so the g limit is largely irrelevant when
considering performance.
The classic jets were not capable of exceeding mach during
level flight. There is then an invisible barrier to the
right! The MiG was not capable of exceeding mach 1 even in
a dive. However the Sabre could and so it is likely that at
some very large negative Ps the curve will exceed the speed
of sound.
For the Classic Jets, only the lift limit
line has any practical significance and so it is the only
one drawn in the following diagrams.
General
Interpretation
Specific Power curves have been produced for the two MiG
variants and the three Sabre variants for an altitude of
20,000ft. Additional curves for the MiG15 and F86a have
also been produced for 10,000ft and 30,000ft. For each
curve it is possible to extract the following information:
Maximum Instantaneous Turn Rate
This occurs at the intersection of the lift limit line and
the maximum g line. So for instance, on the F86a at
20,000ft this occurs at 20 deg/sec and a speed of 0.62M. In
practice this condition is very difficult to achieve. If a
break turn is initiated at high speed, then the speed
bleeds off quickly and will be below 0.6M before the
maximum turn has been achieved. Turn rates of about 16
degrees/ sec have been achieved on the model.
The Maximum Instantaneous Turn Rate is lift limited and
cannot be sustained.
Sustained Turn Rate
The sustained turn rate, which depends on available thrust
and the drag on the airframe, is obtained by finding the
maximum on the Ps = 0 curve. On the F86a at 20,000ft this
occurs at about 6.5 degrees/sec at a speed of 0.42M.
It is important to realise that a pilot does
not fly his aircraft at this condition by pulling back hard
on his stick and flying the lift line. Inspection of the
diagram shows that the pilot flying in this way will only
achieve a turn rate of 5 degrees/ sec and he will have
slowed down to about 0.25M. He will be flying at the point
where the Ps=0 line intersects the lift limit.
It is easier for the MiG pilot to fly the sustained turn
rate at 20,000ft because the maximum turn rate coincides
with the lift limit line.
Minimum Turn Radius
Turn radius lines are displayed on the diagrams. On the
F86a at 20,000ft, it can be seen that the minimum radius is
between 1500-2000ft. Generally the minimum turn radius is
obtained by drawing a line from the origin which produces a
tangent to the lift limit line.
Maximum Climb Speed
This is a difficult quantity to determine from the curves
and so, at some point, we will present the data in a table.
However for the MiG15bis at 20,000ft the Ps=100ft/s line is
available. From this it is possible to estimate the maximum
Ps position on the x axis. For the MiG15bis it will be just
over 0.7M.
F86f performance at 20,000 feet
MiG 15bis at 20,000 feet.
To download the set of energy charts for MiG and F86
variants click HERE
750K.
As Yeager said, it is experience that
counts. Part of that experience is knowing the strengths
and weaknesses of yours and your opponent's aircraft. The
data in the appendices of this note should certainly help
you fly smarter.
