THE BEST WORLD WAR II FIGHTER (1941/Eastern Front)

The higher up the airplane flies, the slower it seems to move because angular speed is reduced. Flying against light flak is more hazardous at the higher end of the gun’s ceiling. So, the attack airplane either flies higher than 1000 meters (3500 feet) ! (which reduces bombing accuracy compared with very low altitude attacks) or else flies at the lowest possible altitude (which makes things more difficult for the gun and increases bombing accuracy).

Both were liquid-cooled V-12 powerplants with single-stage superchargers to compensate for their lower power delivery at higher altitudes !. The AM-35A displaced 46.7 liters while the DB-601N was more compact at 33.9 L. Although the more powerful AM-35A appears to have an edge, its inferior power-to-weight ratio and larger size negated this advantage !.

German and Soviet refineries processed crude oil to obtain gasoline of about 70-octanes and then further refined it and added additives (like Tetra-ethyl lead @ 1.15 cc/L) to obtain gasoline of around 90-octanes. To get C-3 fuel it was necessary to blend 15% of synthetic isoparaffins with 85% of supplementary refined B-4 gasoline to increase its aromatic content (isoparaffins and aromatic hydrocarbons increase octane rating). The higher difficulty to obtain C-3 fuel meant that its supply was never abundant !. The Soviets used B-95 on their fighters throughout the war !.

It is not an overstatement to say that there is nothing like too much power. Drag increases with the square of the velocity and any speed increase require enormous additional power. For instance, the 1175 hp Daimler-Benz DB-601N engine propelled the Messerschmitt Bf 109F-2’s to 495 km/h at sea level !. If a speed of 700 km/h at sea level was desired (40% increase), a new engine with over triple power would have been necessary !!

Three months after the invasion onset, the Luftwaffe introduced the Bf-109F-4 with the even more powerful DB-601E. This engine operated at 2700 rpm (100 rpm increase), boasted a larger supercharger and incorporated the GM-1 system which injected nitrous oxide to the intake manifold, increasing oxygen supply at high altitudes !. With these improvements, the power increased to 1350 hp at sea level and 1300 at 5500m. The Bf 109F-4 maximum speed improved to 523 km/h at sea level and 606 km/h at 6500m !.

The DB-601E continued in production until March 1942 when the Germans decided to discontinue further development in favor of the newer, larger displacement DB-605 !.

Engineers in all combatant nations strived to extract the last ounce of power from their engines, but metallurgical limitations set an ultimate limit to their efforts. An aviation engine converts at most 34% of the fuel’s energy into power, 32% is lost through the coolant systems, and 34% through the exhaust gases. And this is under economic cruise conditions (lean mixture), under combat power, thermal efficiency decreased to 26%, and during take-off to 20% (the last two conditions require rich mixture) !. If alloys could be found that permitted the engines to operate hotter, more power could be extracted, but during WW II, that level was state-of-the-art.

Engine selection, although indispensable, represented only the beginning of the design process. Knowing the available power, the next step consisted of establishing an adequate power-to-weight ratio since this factor alone decided much of the theoretical performance of the aircraft !. The higher the ratio the better, but since power was now fixed, the only alternative to improve this ratio entailed the reduction of the aircraft’s weight, specifically take-off weight, to the smallest possible value !.

Take-off weight is the sum of empty weight plus payload. For our purposes, we will define payload as the weight of the pilot and parachute, fuel, oil, and ammunition, that is, the variable weight. Empty weight is the fixed weight and includes the complete aircraft fully equipped to carry out its mission, comprising the engine, airframe, radios, weapons, armor protection, self-sealing fuel tanks, and other equipment (i.e. gunsights, etc.).

For the designers, the decision over what should be included and how much, remained a dilemma. To save on weight, the airframe was made as small as possible and the structure stressed to withstand the projected flight loads, but not much more. Since a pilot could endure a maximum of +6g without blacking out, the structural limit applied to fighters was somewhat higher (+7g or more). A structure built without enough sturdiness implied risks. The wings of the Bf 109 remained its weakest point reaching their load limit at 750 km/h ! and instructions were broadcasted not to exceed this speed because instances of wings breaking off occurred.

Other alternatives to reduce weight included the installation of less powerful (lighter) weapons, reduced armor protection, and less ammunition or fuel. All of this meant better performance at the cost of a reduction of other fighter capabilities. Finding the optimum configuration required practical experience and inspiration.

Professor Messerschmitt designed its Bf 109s within narrow weight margins (2700 to 2900 kg) to achieve a PWR/Weight ratio of at least 0.40 hp/kg, while the newer VVS fighters were heavier (2900 to 3300 kg) because of bulkier engines or wooden airframes.

The more modern LaGG-3, Yak-1, and even the MiG-3 started the war with a disadvantage in PWR/Weight ratio (between 2 to 27% depending on the model). When months later the Germans introduced the F-4 the disadvantage grew even more.

It should be mentioned that the diminutive I-16, considered by many historians obsolete had the best power-to-weight ratio of all the contenders, including the not yet deployed Bf 109F-4.

Having specified the power (by selecting the most powerful engine available), and weight (to keep the PWR/Weight within parameters) the next step consisted of deciding the area of the wing. This was done by calculating the wing loading and using the known weight of the aircraft (wing loading is aircraft weight/wing area) !.

Wing loading affects maneuverability and speed. A large wing area produces more lift so climb and turn performance improve, everything else being equal. Also, the low-speed regime, so important for landing, improves since stall speeds are lowered. However, a larger wing also produces more drag, so maximum speed is reduced.

The philosophy of the use of the fighter affected greatly the wing-loading selection. The Luftwaffe and RAF had differing visions for what a good fighter was. The former preferred high speeds with its associated relatively high wing loadings and war experience only reaffirmed this trend. Every new model of the Bf 109 had a higher wing loading than its predecessor and the introduction of the Fw 190 within months of the Barbarossa initial assault, made this proclivity even more evident.

The comparison between the different models of Luftwaffe fighters and the newer VVS fighters is on the first analysis relatively straightforward. Both had similar wing loadings, but the Germans achieved superior power to weight ratios, and this gave the Jagdwaffe and edge !. The assessment with the British is more difficult. The power to weight ratio was similar but wing-loadings markedly different. The advantage would fall with the side that set the conditions of the fighting to favor its selected characteristics.

The Devil is in the Details: Revealing the best fighter in the summer of 1941

Power to weight and wing loading ratios embody the major decisions made by designers to meet the air force specifications but based on these, many more detailed choices follow until an effective prototype is ready: One of the most critical is the type and shape of the wing because the wing produces almost all the lift and most of the drag in an airplane. The selection of the optimum lift/drag ratio of the wing is paramount. Other crucial choices are the aerodynamics of the plane to minimize drag, the altitude at which the supercharger speed is fastest, weapon selection, aircraft controls and degree of stability !, structural strength and construction type, all-around visibility !, communications equipment, and others.

These decisions are further complicated because the fighter needs to fly under different flight regimes. Low-speed, low-altitude for landing and high-speed, higher-altitude for combat operations at a minimum. Other operational regimes may be involved, like very-high altitude interceptions for instance.

Decisions made for one regime sometimes negatively affect performance on another (an example is a short wingspan to attain high maximum airspeed, but which also increases stall speed, making landings more difficult, and increasing accident rates).

To complicate matters further, the technological state of the country, availability of raw materials, skilled labor, and machine tools, all become part of the overall equation. Fighter designs is not an easy task.

How can we assess fighters and select the one that surpasses all the others?

Fighter comparisons are intricate because air combat is a fluid action where numerous important factors intervene, many of them interconnected. We can approach this with more objectivity by selecting and contrasting the performance attributes that are most relevant for the mission, although as will be seen, this still leaves some important gaps.

The fighter’s mission is to destroy other airplanes and to accomplish this the aircraft must maneuver in the airspace to attain the same plane where the enemy is moving until the weapons are in range. Then it must fire with sufficient lead (firing ahead of the target) to achieve hits and keep firing until the target is wrecked.

Against an unsuspecting target achieving a firing solution requires minimum steering while attacking a rival that is fully aware and flying an agile aircraft requires time-consuming, hard maneuvering to attain a firing opportunity that lasts only a few seconds. Because hard maneuvering reduces situational awareness and this endangers the attacker, the most fundamental tactic is to achieve surprise. The best aces applied ambush tactics and shunned dogfighting as a low-payoff activity. However, some pilots embraced dogfighting, and these differing styles required divergent attributes in their planes.

Pilots that preferred surprise chose boom and zoom tactics, where they launched a swift attack from a superior position (usually from a higher altitude and behind) and then converted speed into altitude to avoid exposing themselves. Airmen that selected dogfighting, flew forcefully to position their airplane in the rear quarter of the enemy and then tightened their turns until they achieved sufficient lead.

With this introduction it is possible to outline the main attributes that a fighter needs to be effective:

• Good visibility on every quarter to detect the enemy first and avoid being surprised.

• Superior communication equipment to broadcast sightings quickly by any pilot in the unit and for the leaders to direct the action of the formation.

• High speed to catch up with the enemy rapidly or to escape from him.

• High climb rate to attain an advantageous position for attack or to reduce exposure after it.

• Fast dive speed to overtake the enemy or to break off the action.

• Heavy firepower to maximize the short-lived openings during combat.

• Exceptional maneuverability to attain a good firing position or to negate one to the enemy (this can be subdivided into tight turn radius, fast roll rate, rapid acceleration, and as much power as feasible to maneuver horizontally or vertically).

• A high ceiling that furnishes altitude advantage.

• A respectable range to penetrate the enemy airspace .

• Capability to absorb damage and return to the base

To make a good comparison it is necessary to have accurate and complete data. Erik Pilawskii !, the author of a book about WW II fighter performance, did extensive research to properly quantify many relevant attributes and corrected many errors found in the historical literature. For the comparisons that follow I have used his data for the most part although I have used other reliable sources to fill up some gaps (i.e. max speeds at different altitudes). It has to be said that unfortunately, some relevant information is not available (rate-of-roll, dive speeds, and durability to damage is non-existent except as anecdotal information, while visibility is somewhat subjective).

Maximum speed is without a doubt the parameter that more readily comes to mind when comparing fighters. From WW I to the end of WW II (and thereafter) the different manufacturers embarked on an endeavor to increase the maximum speed at almost any cost since this factor, more than any other, conferred the initiative in combat.

When Hitler launched Barbarossa the latest Luftwaffe fighter, the Bf 109F-2, equipped 70% of the Jagdgruppen while almost a third kept the older Bf 109E-7, at least until the German factories provided replacements.

This plot corroborated that the Bf 109F-1 ! flew faster than any Soviet fighter at every altitude except over the almost empty skies above 6000 meters where the MiG-3 reigned alone. The LaGG-3, Yak-1, and MiG-3 surpassed the Bf-109E-3, but the Germans did not deploy this type for Barbarossa. The Bf 109E-7, which was 21 km/h slower than the F-1, was slightly faster than the Soviet fighters at all altitudes. It used the same engine as the F-1 but it was not as clean aerodynamically) .

The next important virtue of a fighter is a good climb rate. The greater PWR/Weight ratio of the German fighters helped them achieve a higher climb rate !. The I-16 excelled in PWR/Weight ratio, but its climb rate was mediocre due to a draggy airframe as revealed by its high Drag Coefficient (0.055 vs 0.30 to 0.040 of the other fighters making it the least aerodynamic efficient of them all). While the rest of the fighters utilized relatively small liquid-cooled engines, the I-16 was the only one equipped with a radial engine which gave it the largest frontal area while its power was no greater. This, along with its relatively large wing (low wing loading) negatively impacted its speeds, climb, and acceleration.

Several factors have a bearing on a fighters’ maneuverability. Acceleration is a nifty quality because air combat is not fought at a constant speed. Often, the fighter is trying to avoid an excessive closing speed against a slower moving target to improve aiming and to increase the time the opponent will be in the gun’s sight. Once the kill is achieved, the fighter wants to regain a high energy condition to reduce vulnerability and to chase after the next target. The Bf 109 held the cards against its opposition as seen in the previous chart while the heavy LaGG-3 possessed the lowest performance. Turn radius or the ability to turn in the smallest possible circle is considered by many the quintessential mark of maneuverability. Some authors even go as far as considering it a more important trait than maximum speed. Turn radius is effective when defending to prevent the enemy from obtaining a good firing position and when dogfighting on the horizontal plane. Combat flight simulators enthusiasts usually fight on the horizontal plane and thus tend to stick to tight turns as the means to win a dogfight. However, when battling trained pilots in energy tactics turn radius loses much of it allure. The unmistakable trend in air combat from World War I to World War II to contemporary fighter jets reveals the increase of maximum speed at the expense of turn radius. This evidence should be a powerful argument on why speed is more important.

Compared with the previous three attributes, turn radius is a more subjective parameter, partly since it is difficult to measure accurately ! but mainly because it depends on the pilot’s skill !. The same aircraft will also have widely different turn radii depending on how fast it is flying at the moment of starting the turn !. The data in the next chart was calculated by Pilawskii at the same altitude for each airplane and compared with actual observations, so it is the best comparison available !.

Given the similar wing-loadings, it is not surprising that the calculated turn radii of all of the Eastern Front fighters were comparable. The much lower wing loaded I-16 as expected, enjoyed a significant advantage over all the monoplanes fighters on 22 June 1941. The Bf 109s had to avoid turning battles and stick to vertical plane fighting to overcome their adversaries.

The capacity to change direction quickly is arguably more important for a fighter than turn radius, but sadly, quantitative information of roll rate is lacking, and it will not be considered in the comparison. An interesting point, however, is that the soon to be deployed Fw 190A, would excel in this category, as evaluated subjectively. In general, the roll rate tends to suffer near maximum-air speed because of strong stick forces caused by intense dynamic pressure.

Power/weight ratio affects all the aircraft attributes, not only maneuverability, but it is included as a factor in this category because the execution of any maneuver from a straight and level flight (turns, climbs, aerobatics) demands plenty of excess power (that is, power above that required to keep the aircraft flying straight and level). This excess power is proportional to the power/weight ratio and the Polikarpov I-16 shined in this category. This partially explains its extraordinary agility.

The human eye remained the only inboard sensor available to detect enemy aircraft in World War II during the daytime. The cockpit design helped or hindered the ability of the pilot to see outside and until the Fw 190A introduction, the cockpits of the fighters that faced each other off were very similar, allowing good visibility to the front and the sides and poor visibility rearwards because of turtle-decking to improve aerodynamics !. The bubble canopy of Kurt Tank’s fighter commanded better visibility to the all-important rearward sector and was deemed superior. Eventually, most new fighters would feature it.

When detected, it is critical to convey the information to the leader quickly for him to take immediate action. The lack of transceivers in most Soviet aircraft (except the leader) placed the Russian pilots at a grave disadvantage because the German pilots received the information of the enemy presence and position immediately upon detection, while several seconds elapsed before the Soviet leader became aware.

An aircraft that can absorb punishment and continue fighting (or at least escape) could live to fight another day instead of being permanently lost. This durability-to-damage quality is of great consequence in a protracted attrition campaign.

A study carried out by the US Navy between 1944 and 1945 on the causes of lost and damaged single-engine aircraft during air combat provides enlightening information. For every five stricken aircraft, two did not return, and three returned damaged (2:3 ratio of loss vs damaged).

The aircraft structure exhibited the highest probability of sustaining hits since it is the largest part of the aircraft. 43% of the airplanes suffered damage on it (only) but of them, 89% returned reflecting its toughness.

The second area with the highest probability of receiving hits was the pilot and cockpit controls. 19% of the airplanes suffered damage in this area. Despite the small size of the pilot and cockpit, this appears logical because most of the attacks come from the rear quarter, and from this sector, there is a high likelihood of hitting this exposed part. When hit there, 76% of the aircraft were lost, despite the armor protecting the pilot and cockpit. The penetration power of armor-piercing ammunition at the average distance of attack shows that it was more than a match to the armor plates defending this sector.

Smaller areas like the powerplant, the oil system, fuel system, and hydraulic system were proportionally less likely to be shot (between 5 and 7% of the time) but when struck the likelihood of receiving a fatal blow stood high (between 62% and 85% of the planes failed to return) demonstrating their extreme vulnerability despite self-sealing tanks, and the use of radial engines without coolant system. Had the Americans used liquid-cooled engines in the Pacific Theater, the proportion of aircraft destroyed when struck in the engine would have been much higher. The I-16, the only aircraft equipped with a radial engine during Barbarossa had higher durability to damage as compared with the rest.

The performance of the Soviet fighters stood remarkably close. We can classify them from best to worse in the following order: Yak-1 (score 92), MiG-3 (90), I-16 (90), and LaGG-3 (88).

The Yak-1 rated highest, despite its low power-to-weight ratio (0.35 hp/kg) due to outstanding aerodynamics (the lowest drag coefficient of VVS aircraft at 0.030 and equal to the Bf 109F-4) that permitted acceptable all-out speed (561 km/h), adequate climb (918 m/min), and acceptable firepower. On the other hand, the LaGG-3 rated the worst because of the lowest power-to-weight ratio: it was too heavy for the available power. Even though it was a clean aircraft (drag coefficient of 0.033) its heavy weight worsened its speed (535km/h), climb (828 m/min), and maneuverability. The two light machine guns were removed early to reduce weight. Losses in combat were high and the morale in the IAPs equipped with this fighter became very low by the end of the year. So much so, that Lavochkin himself had to tour the units to hear the complaints of the pilots. The VVS High Command terminated the production of this fighter in favor of the Yak-1 by the summer of 1942 !.