Okay. Please quote any recollections of a Soviet front-line pilot who complained about insufficient altitude for attacking bombers. I can quote Soviet pilots who claimed that most escort flights were at an altitude below 3,000 meters, and that flying 500 meters above the bomber formation was quite sufficient. Escort fighters cannot fly too high above the bomber formation, or they will not be able to fulfill their mission. It is not always possible to spot a formation of bombers if they are flying 3-4 km lower producing no contrail. In general, high altitude did not provide any tactical advantage on the Eastern Front. The Soviets sent all aircraft with good altitude characteristics to the air defense forces. In addition, fighters with good altitude performance did not always demonstrate high efficiency at the front - for example, the Spitfire IX did not cause any enthusiasm at all.
How did the I-16 Really Perform in WWII?
- Thread starter Airborne2001
- Start date
Shortround6
Lieutenant General
Is exhaust thrust being modeled in these calculations?
It fairly easy to estimate exhaust thrust based on the mass of the exhaust gases and using an estimate of the gas velocity.
What is a lot harder to figure out is the actual practical thrust due to problems in the exhaust pipes, the direction of the exhaust flow, the altitude being used (back pressure on exhaust affects the exhaust gas velocity) and speed of the aircraft. Exhaust thrust works better for high speed than for climbing due to the miss match between aircraft speed and exhaust gas speed/velocity.
massimotessitori.altervista.org
Actual thrust from this set up is hard to figure out. Actual path of the exhaust gasses in relation to the path of the airplane is a little hard to figure. Velocity of the gases depends on the size of the opening in the pipe and pipes cut on slants have a larger opening than a 90 degree cut across the pipe.
This is better than British exhaust systems of the 1930s with long convoluted exhaust systems and better than the exhaust systems used on the American P-35 and P-36. It was better than the V-12 engines that just used flush ports in the side of the cowl. It is not as good as the exhausts used on the 109E.
The potential for around 10% additional power due to exhaust thrust is there on most engines. Actually getting it is a lot harder.
It fairly easy to estimate exhaust thrust based on the mass of the exhaust gases and using an estimate of the gas velocity.
What is a lot harder to figure out is the actual practical thrust due to problems in the exhaust pipes, the direction of the exhaust flow, the altitude being used (back pressure on exhaust affects the exhaust gas velocity) and speed of the aircraft. Exhaust thrust works better for high speed than for climbing due to the miss match between aircraft speed and exhaust gas speed/velocity.
massimotessitori.altervista.org
Actual thrust from this set up is hard to figure out. Actual path of the exhaust gasses in relation to the path of the airplane is a little hard to figure. Velocity of the gases depends on the size of the opening in the pipe and pipes cut on slants have a larger opening than a 90 degree cut across the pipe.
This is better than British exhaust systems of the 1930s with long convoluted exhaust systems and better than the exhaust systems used on the American P-35 and P-36. It was better than the V-12 engines that just used flush ports in the side of the cowl. It is not as good as the exhausts used on the 109E.
The potential for around 10% additional power due to exhaust thrust is there on most engines. Actually getting it is a lot harder.
Modifications of the I-16 with M-62/-63 engines were only tested in the summer and fall of 1939, so they could not participate in the war in Spain. But I didn't write that they were there - the "doras" could only encounter I-16s with M-25 engines.
The short answer is YES, but ...
To start with, I am using a simple model based on indicated power. This gives an estimate of maximum obtainable exhaust thrust for a particular case. The uncertain part is how much of the exhaust thrust is actually available. There are few hard data so my best estimate is usually somewhere between 1/3 and 1/4 of the theoretical maximum. The I-16 is at lower end, IMHO.
An I-16 field modification in Spain was reported using Wright R-1820 F53 engine procured from USA. I need to find the source document.
F54. This is a well-known fact mentioned in many sources, for example, in the book by Mikhail Maslov. Flight performance was significantly improved.
Sorry! I can not remember even a single report about coordinated attack of an enemy bomber formation from a member of the Red Army Air Force. I can remember description of a few encounters from which I got an impression the action was performed as a "zveno" of three in a best case - "go ahead and do something" style.
Then I recommend you take a look at the following sources (Tactics in combat examples: squadron-[single]crew / regiment):
They contain examples of coordinated attacks of bombers by fighter squadrons and regiments (well, rather, "reinforced" squadrons).
И-16 М-25В true air speed
И-16 М-25В rate of climb
An И-16 М-25В (I-16 M-25V) variant of about 1938, my best estimate. One source states 1394 examples of I-16 M-25 were on strength of the Red Army Air Force (ВВС РККА) as of July 1, 1938.
Fast forward to the second half of 1940, with uprated versions of the I-16 M-62/63.
И-16 М-62 АВ-1 true air speed
И-16 М-62 АВ-1 rate of climb
The final production variant И-16 тип 29 [I-16 type 29, M-63, AV-1] was equipped with R-2 automatic propeller speed control, automatic boost control, automatic mixture altitude compensation, ability to carry underwing auxiliary fuel tanks and zero-length rocket launchers, and the voice radio receiver / transmitter was supposed to became a standard equipment.
И-16 М-63 АВ-1 (тип 29) true air speed
И-16 М-63 АВ-1 (тип 29) rate of climb
The propeller diameter was 2.9 m fixed pitch for M-25 engine variants. Constant speed propellers were 2.8 m diameter (M-62) and 2.7 m diameter (M-63). Engine cowl cross-section was about 1.6 square meters.
All the figures show aircraft performance model results without flaps and without external stores (e.g. bombs, fuel tanks, or rocket launch rails).
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German bombers — no fewer than a hundred aircraft — were moving toward Bataysk. Above them, barely discernible in the gaps between the clouds, at altitudes of 6,000 to 7,000 meters, flew Messerschmitt fighters. This time they employed a new method: operating at an altitude that could not be sustained without oxygen equipment. We had no oxygen cylinders. p 119
At that time (March 1943), Lavrinenkov's regiment was flying the Yak-1.
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Lipfert Н. Das Tagebuch des Hauptmann Lipfert
I wasn't going to let the Russians catch us so easily the second time, so we quickly climbed 4,500 meters. But even at this altitude, several "Aircobras" attacked us from above and gave us such a beating that I came to my senses only on the way home. During the third flight, we climbed to 6,000 meters; I had never encountered Russian aircraft at such a high altitude before. But this time we couldn't even reach the front line. All I could see were the Aerocobras above us. They forced us to flee once more. Now I really had enough, and after a steep half-ride, I went home with my wingman at top speed. Until that day, there had never been a case where the Russians had not even allowed me to take up an attack position.
May 1944 Romania
I wasn't going to let the Russians catch us so easily the second time, so we quickly climbed 4,500 meters. But even at this altitude, several "Aircobras" attacked us from above and gave us such a beating that I came to my senses only on the way home. During the third flight, we climbed to 6,000 meters; I had never encountered Russian aircraft at such a high altitude before. But this time we couldn't even reach the front line. All I could see were the Aerocobras above us. They forced us to flee once more. Now I really had enough, and after a steep half-ride, I went home with my wingman at top speed. Until that day, there had never been a case where the Russians had not even allowed me to take up an attack position.
May 1944 Romania
This was apparently a fairly rare occurrence - several group sorties at high altitude. From the same source just a few paragraphs above:
Two separate examples from memoirs are not statistics. In almost all interviews with Soviet front-line pilots, there are mentions of the rarity of battles at high altitudes, although Lavrinenko himself considers the altitude performance of the La-7 to be quite sufficient up to 7–8 km - according to him, the La significantly outperformed the Yak-3 at this altitude.
Again, a special case. Battles at high altitude did occur, but RARELY.
No. As soon as experienced pilots received an aircraft capable of operating at altitude, they immediately took the fight there. Pokryshkin's first combat sortie on the Airacobra was a ground-attack cover mission, but with a completely different tactical approach — no low-altitude patrolling at all. The first pair flew at 4,000 meters, the second pair 200–300 meters higher, and a third pair higher still. Attacks were made with a descent followed by a climb back to altitude. Subsequent engagements followed a similar pattern. Altitudes of around 5,000 meters were used, and when encountering Messerschmitt "hunters," the fight went upward after them. The point is that only Airacobras or La-7s were really capable of fighting this way.
Medium altitudes. No combat at 7-8 km. From the same source:
Furthermore, there is no need to cite the 16th GIAP as an example - it was a rather unique air regiment, while most Soviet fighter regiments escorted Pe-2 and Il-2 aircraft at altitudes of up to 3,000 meters. German bombers flew at altitudes of 4.5-5 km and continued to do so, but only at night.
An И-16 М-25В (I-16 M-25V) were produced in significant numbers since 1937, e.g. I-16 type 10 and type 17, but it is not easy to find a reliable set of performance data.
The full throttle height for the M-25V is 2900 meters standard atmosphere (for comparison: M-25 2000 m at 1950 rev/min; M-25A 2500 m at 2100 rev/min), rated horsepower (metric) is 750 hp at 2100 rev/min, supercharger gear ratio 8.31 : 1. Take-off rating is 775 hp at 2200 rev/min, 700 hp at 2100 rev/min normal. In flight at a speed of more than 400 km/h the full-throttle altitude is estimated to be about 3500 metres if the engine induction system and mixture control are functioning properly, and the propeller pitch is set for best performance at the rated engine conditions. For some reason many sources list maximum level speed of I-16 M-25V variants in excess of 400 km/h at altitudes between 2500 and 3150 metres.
Let take a look at the propulsion system parameters from the model : engine speed, manifold absolute pressure, and propeller tip speed.
There is a direct drive engine of 750 hp at 2100 rev/min driving a two blade propeller of 2.9 m diameter. Propeller tip speed at 3645 m, 435 km/h is 1.045 Mach. There is a significant reduction of the effective trust of the propeller due to supersonic tip speed.
When diving, the I-16 M-25V could easily reach and even exceed a speed of 500 km/h. According to the pilot's manual, it was forbidden to exceed a speed of 500 km/h when diving, as this caused the propeller overspeeding (>2,500 rpm). The loss of thrust during a dive was of no significance.
During a dive the engine overspeed can be a problem. On late model machines, the slow response of the "AV-1" propeller pitch control really caused overspeed in excess of 2600 rpm.
Propeller efficiency is important for maximum level speed. The penalty on propeller efficiency is significant, ever at speed of about 450 km/h. In order to better 500 km/h in level flight with a reasonably good take-off and climb performance a reduction gear and a variable pitch propeller are necessary.
Really? I cited the pilot's manual for the I-16M-25 from 1937.
The I-16 equipped with the turbocharged M-62 exceeded a speed of 500 km/h in level flight.
