MiG Alley: MiG 15 vs. F86 Sabre
By: Author Unknown
Article Courtesy of Rowan Software.
Performance characteristics of the Classic Jets
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.
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
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.
MiG Alley Campaign GUI
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.
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.
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.
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:
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
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:
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.
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
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.
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