“Once the fight begins, the outcome is determined by a pilot’s experience in the air, his tactics and the airplane itself.”

By Marc Liebman

MOST comparisons of aircraft focus on a numerical evaluation, i.e. which plane has a better rate of climb or flies faster. Yet to make a judgement of two airplanes using basic performance numbers doesn’t do either airplane justice because the evaluation fails to take into account the physics and aerodynamics of aerial combat. Dogfight tactics really haven’t changed since World War II. What has changed are sensors, weapons, thrust-to-weight ratios, aircraft speed and maneuvering capability. 

Prior to the advent of air-to-air radar and missiles, victory in air combat was dependent on spotting the enemy before he spotted you. This was certainly the case in World War Two.

From there, the pilot could maneuver to gain tactical advantage, preferably by climbing and turning to get above and behind or below and behind his enemy.

How the fight begins has become known as “the merge.” Control the merge and the chances of shooting down the other airplane go up exponentially. During the Battle of Britain, for the most part, radar direction enabled Royal Air Force squadrons to determine when and where they would engage the German formations.

Similarly, in the skies around Guadalcanal, Marine aviators flying the F4F Wildcat had two major advantages over the Imperial Japanese Navy A6M Zeros. The first was radar keyed by coastwatchers in the Solomon Islands. These look outs (and the information they provided) enabled the Wildcats to climb and position themselves to control the merge. As such, Marines could dive, shoot, dive away, then climb and re-engage. Secondly, the Japanese pilots didn’t have radios so coordinating a defense was limited to what each pilot in a Japanese formation saw with his own eyes.

Once the fight begins, the outcome is determined by a pilot’s experience in the air, his tactics and the airplane itself. Training and confidence can do wonders even if the pilot is flying an airplane that is roughly equal or even inferior to the enemy’s fighter. Pilots who control the merge generally get off the first shots before the enemy has time to react.

Interestingly, in the 1930s and during the ramp-up to World War II, the U.S. Navy taught aerobatics as “confidence maneuvers.” Why? The Navy wanted fliers to be able to instinctively point the nose of the airplane where they wanted it to go from any attitude. Aerobatics taught the basics but engaging with other airplanes in mock dogfights in which the movements are not scripted taught pilots how to fly in a three-dimensional environment. Deflection shooting, i.e. shooting at an enemy aircraft from an angle, from any position — be it diving, climbing, level flight, or some combination of these — was a key component of the training given to U.S. Naval aviators.

With this in mind, let’s explore the specific factors that are relative in a fight with airplanes only armed with machine guns and cannon. There are additional variables that can be decisive in air combat beyond the commonly cited factors: speed and rate-of-climb.

Thrust-to-weight ratio

This is simply the amount of power or thrust the plane has versus its weight at the time of the dogfight. Normally, it is measured in pounds of airplane being pulled through the air by each horsepower. Or in a jet, pounds of thrust per pound of airplane. You hear the term “combat weight,” which measures an airplane’s heaviness after it has burned some of its fuel. Put another way, combat weight is pilot, airframe, ammunition, and roughly 60 per cent of its fuel. 

Until the advent of the afterburner, most fighters had a thrust or power-to-weight ratio of less than one. This means that in a 90-degree angle of bank, the plane will slow and/or descend. With a ratio of more than 1:1, the fighter can accelerate and/or maintain altitude in a 90-degree angle of bank. 

As an airplane banks, it loses lift. The steeper the turn, the more lift is lost and the more power is required to maintain altitude and speed.

Consider the following example. For a P-51D at maximum takeoff weight, the ratio of horsepower (thrust) to weight meant that each unit of horsepower was pulling 6.48 pounds of airframe, fuel, ammo and pilot. For the F4U-4 Corsair, it was 6.97 pounds at takeoff. The much smaller Spitfire Mk. IX’s Merlin-61 engine dragged 4.39 pounds per horsepower through the sky.

At its maximum takeoff weight of 10,000-pounds, each of the FW-190A-8’s 1,700 horses produced by its BMW 801D-2 twin row radial engine was dragging 5.88 lbs. through the air.

Yet, the airplane was slower than the Spitfire, Corsair or the P-51. So, the point is, horsepower isn’t everything in a dogfight, but it helps.

Another example is the ME-109K, the last mass-produced version of the standard Luftwaffe fighter at the outbreak of the war. It weighed only 7,438 lbs. at takeoff and had an engine that generated 2,000 horsepower at takeoff giving it a very low 3.7 lbs per horsepower power-to-weight ratio. Yet, the Me-109K couldn’t compete with the later generation fighters that had aerodynamically boosted controls that made them easier to maneuver at higher airspeeds. Its controls, like the Japanese Zero’s, got very heavy above 300 m.p.h. limiting what maneuvers the pilot could make.

This power-to-weight ratio also varied based on the external stores being carried as well as the internal fuel. It does not account for drag from external tanks, rockets or bombs. External stores increase drag along with adding weight, which increases the rate of deceleration in a turn. The steeper the turn, the faster the airplane slows.

As good as these three airplanes — the F4U, P-51D and Spitfire Mk IX — were in their day, none could maintain altitude in a steep level turn for very long. This is why most World War II (and World War I and later Korean War) turning dogfights were in fact, descending, decreasing radius spirals.

Manifold Pressure

Closely related to power-to-weight is, for a piston engine airplane, manifold pressure or MAP. This metric is nothing more than an indication of the amount of power the engine is using to turn the propeller. At sea level, unless the airplane’s engine has either a supercharger or a turbocharger, the maximum manifold pressure available is 29.92 inches of atmospheric pressure. In aviation, the U.S. Federal Aviation Administration defines a standard day as 59 degrees Fahrenheit or 15 degrees Celsius at sea level and 29.92 inches. 

As an airplane with a normally aspirated, i.e. not turbo or supercharged, engine climbs, manifold pressure decreases by one inch per thousand feet. So, at 5,000 feet, the maximum power a normally aspirated engine can generate is 25 inches. At 10,000 feet, manifold pressure is 19 inches, which tells the pilot that the engine is generating about one third of its sea-level rated power.

This explains why the early war Bell P-39 Airacobras, Curtiss P-40s and Mk. I Mustangs delivered to the Royal Air Force powered by normally aspirated engines were considered dogs when compared to the Spitfire, Hurricane, A6M Zero and Me-109. Down low, they performed well; above 10,000 feet, they couldn’t compete (or in many cases survive) in a dogfight against Me-109s or A6M Zeros with supercharged engines.

A turbocharger or supercharger transforms the engine and the airplane. All of the top World War II fighters either had a gear driven supercharger or an exhaust driven turbocharger. The R-1830 and R-1820 powerplants installed on the F4F Wildcat along with the R-2800 engines fitted to the Corsair and the P-47 had two stage superchargers.

The air-cooled R-2800 in the F4U Corsair and P-47 Thunderbolt and the liquid cooled V1750-61 in the P-51D Mustang and Spitfires were capable of 60+ inches of manifold pressure at sea level. This level of manifold pressure (and power) could be maintained up past 20,000 feet.

Later in the war, several airplanes had either water or methanol or a combination injection to further boost their power for short periods in what was known as War Emergency Power. Several airplane engines, e.g. the P-51D, could sustain manifold pressures north of 70 inches.

Turn Radius

This is the distance from an imaginary point around which a plane would turn when flying in a circle at a constant angle of bank and airspeed. It is usually measured in feet  (but don’t try to use a tape measure). 

The turn radius is dependent on the angle of bank and the speed of the airplane. The slower the airplane flies, the shorter the radius or the smaller the diameter of the turn. Increase the angle of bank and the turn radius decreases along with the diameter.

However, as an airplane turns, it loses lift; to maintain airspeed and altitude, the pilot must add power. The steeper the angle of bank, the more power is needed because the wings are generating less lift. Beyond about 70 degrees angle of bank, the only lifting surface is the vertical stabilizer. And, as noted earlier, unless the airplane has a thrust or power-to-weight ratio greater than one to one, the airplane will slow and descend.

Turn Rate

This is how fast an airplane goes around a circle, not in terms of airspeed, but in terms of arcs of the circle. It is measured in degrees per second or radians per second. From an air-to-air tactics perspective, as the speed of the turning dogfight drops, any advantage of turn rate begins to dissipate because the diameter of the circle is shrinking and the arcs that are used to measure turn rate are smaller.

Roll rate

How fast an airplane rotates around its longitudinal axis is called the roll rate. In a dogfight, rolling the airplane, especially when coupled with movements of the rudder and elevators, makes the plane harder to hit, particularly when the enemy is firing from the six o’clock position. A high roll rate also enables the pilot to execute other maneuvers such as displacement rolls, wingovers to fly his plane in position to fire at his enemy.

If you were flying an F4U-4 Corsair level at 200 knots indicated airspeed and decided to do an aileron roll. Without going through all the rudder and stick movements needed to keep the fighter on the same heading, the airplane’s maximum roll rate was 84 degrees /second. In other words, it would take 4.28 seconds to roll 360 degrees.

In an Me-109, the control forces at high speeds are very heavy. Neither it or the Japanese Zero had servo tabs on the ailerons, elevators or rudders. These tabs operate in the opposite direction the control surface is being moved to enable the pilot to move the control surfaces against the aerodynamic pressure. The faster the airplane is flying, the higher the pressure and the greater the need for these servo tabs. 

For example, if you were sitting in the cockpit trying to engage P-47 and were flying above 300 mph, you could only apply about one fifth of the total deflection available due to the pressure on the rudder and aileron. As a result, your plane needs about four seconds to roll 45 degrees. The P-47 can roll 360 degrees  in about 4.2 seconds, so its pilot needs a fraction of the time needed by the Me-109 pilot.

Rate of Climb

In flight testing, rate of climb is measured at sea level, then every thousand feet. Rates of climb of piston engine aircraft decline with altitude. Add super or turbocharging, and the reduction in the rate of climb diminishes. Note that unless the difference in rate of climb between two piston engine fighters that is not greater than 500 feet per minute is not tactically significant.

According to the Navy’s pilot operating handbook for the F4U-4 Corsair, published in 1944, if the pilot maintains climb power at the best rate of climb airspeed, using water injection and maximum power, the Corsair at maximum takeoff weight will climb from sea level to 10,000 feet in 3.6 minutes, averaging ~2,800 feet per minute. Reaching 20,000 feet at the same power setting should take only 7.7 minutes or an average of ~2,600 feet per minute.

Use only military power (no water injection, but “normal” climb power) in the Corsair, 10,000 feet is reached in 5.2 minutes (averaging ~1,900 feet per minute) and 20,000 in 10.8 minutes (an average of ~1,850 feet per minute).

True Airspeed

At sea level, true and indicated airspeed (IAS) are the same, assuming that the airspeed indicator is properly calibrated. True airspeed (TAS) is simply the speed of the airplane compensated for altitude and temperature. Unless an airplane is significantly faster, i.e. 20 to 30 m.p.h., at any given altitude, the difference is not significant because the faster airplane cannot fly out of gun range quickly enough to avoid being shot down.

Tactics, Training and Skill Usually Win

Given two airplanes that are roughly equal, in some or all of these variables, which one comes out on top is dependent on tactics and the skill of the pilot. Early in Pacific War, the Japanese pilots at the controls of A6M Zeros had the advantage over their American counterparts in the Grumman Wildcat, because most of the former had already flown in combat. Many had 600+ hours in the Zero.

By the end of the Guadalcanal campaign, the tables were turned. The U.S. Navy and Marine Corps aviators were better trained, employed tactics that offset the advantages of the Zero and could, through radar direction, control the merge.

On the other hand, many of the top Japanese pilots were killed or disabled. The Japanese did not rotate pilots back to the home islands to help train new pilots and give them a break from the stress of combat flying. New Japanese pilots in 1944, thanks to fuel and airplane shortages, were lucky to have 150 hours of flying time when they took off on their first combat mission.

By the end of the war, when U.S. Naval aviators finished flight training and earned their wings, they had about 250 hours. By the time they launched on their first combat mission, Naval and Marine Corps aviators often had 350 plus hours with the last hundred in the airplane they were flying. And, many of the training sorties were against experienced pilots under near combat conditions. For more details on why the Wildcat pilots earned a 5.9:1 kill ratio over the Japanese fighter, see my earlier article.

In the skies over Europe, the P-38J, P-51D and P-47D were faster and, in the hands of a skilled pilot, could defeat Me-109s, FW-190s, even TA-152s flown by the Luftwaffe. Although German pilots had the advantage of radar direction, attrition had killed off or disabled many of the Third Reich’s more experienced pilots. By 1944, the Luftwaffe was dangerously overextended. Faced with fuel shortages and an ever-diminishing amount of “safe” airspace in which to train new pilots, newly minted German aircrews were being sent into battle with 150 flight hours, or less.

The U.S. fighters in the VIII Fighter Command and Ninth Air Force were flown, on average, by better trained pilots who, like their Navy counterparts, had 350 hours or more before they flew their first combat mission. They too were trained and led by combat veterans. Give these pilots the advantage of greater numbers and better airplanes in the P-38, P-47 and P-51 and the results were predictable.

Conclusion

First, beware of any comparison of an airplane unless the criteria are well defined and appropriate. To be accurate, any evaluation that matches one airplane against the other must take into consideration the mission requirements, how the airplane is flown and look at the dynamics of the fight. This is why the military tests fighters in mock, free for all dogfights to learn the ins and outs of an airplane. How the airplane is flown in a dogfight is more important than the airplane itself.

Second, tactics and piloting skills can overcome an airplane’s technical disadvantages. Ask all the Luftwaffe pilots shot down by Hurricanes during the Battle of Britain or the Japanese pilots in their Zeros who had to face F4F-4 Wildcats over Guadalcanal.

By any statistical/numerical comparison, the Luftwaffe and Japanese pilots should have won every dogfight. But they didn’t. In fact, the kill ratios of the Allied fighters was enough to turn the tide. The Japanese never regained the initiative and Britain became the base that supported the campaign to free Nazi-occupied Europe.

 

Marc Liebman is a retired U.S. Navy Captain and Naval Aviator and the award-winning author of 14 novels, five of which were Amazon #1 Best Sellers. His latest is the counterterrorism thriller The Red Star of Death. Some of his best-known books are Big Mother 40, Forgotten, Moscow Airlift, Flight of the Pawnee, Insidious Dragon and Raider of the Scottish Coast. All are available on Amazon here.

A Vietnam and Desert Shield/Storm combat veteran, Liebman is a military historian and speaks on military history and current events.

Visit his website, marcliebman.com, for: past interviews, articles about helicopters, general aviation, weekly blog posts about the Revolutionary War era, as well as signed copies of his books.

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