When a car on the ground measures its own speed, it measures the speed of the wheels, and when you know the speed of the wheels, you can multiply it by the circumference.

But planes in the sky can't.

Therefore, since the aircraft began to fly, there have been various means to measure the speed of the aircraft, and this measurement method, after continuous development, has become the most effective way of airspeed management.

The nose of the fighter has a long stick-like device with a sharp point, which is the airspeed tube.

To be on the safe side, the fighter has more than one airspeed tube, and there are spare airspeed tubes on the side of the nose, which together form the main speed measuring device of the aircraft.

As the aircraft flies forward, the airflow rushes into the airspeed tube, and the sensor at the end of the tube feels the impact force of the airflow, i.e. the dynamic pressure. The faster the aircraft flies, the greater the dynamic pressure. If you compare the pressure of the air when it is stationary, i.e., the static pressure with the dynamic pressure, you can know how fast the air rushing in, that is, how fast the plane flies.

In this case, the speed measured by the airspeed tube is not the actual speed of the aircraft relative to the ground, but only the speed relative to the atmosphere, so it is called airspeed.

If there is wind, the speed of the aircraft relative to the ground should also be added or subtracted.

Moreover, the principle of airspeed tube velocity measurement uses dynamic pressure, which is related to atmospheric density. With the same relative air velocity, if the density of the atmosphere is low, the dynamic pressure will be small, and the deformation of the diaphragm box in the airspeed meter will be small, so that the measurement of the airspeed meter will always be incorrect.

In modern aviation flight, only the speed measured by the ground is the most accurate, so many flights require the ground to report the ground speed every time they fly to a console, so as to guide their flight more accurately.

Now, because Qin Feng is flying at an ultra-low altitude, and it is at high speed, there is a gap between the airspeed meter and the actual value at this time, although it has just pointed to one thousand two, in fact, the fighter has reached supersonic speed!

You can't go wrong with that feeling of getting into hypersound. Moreover, when entering supersonic speed, the airspeed tube will be affected by shock waves, and errors will also be generated.

Mr. Gu analyzed, Qin Feng nodded again and again, yes, I don't have to fly anymore, I have completed this test flight perfectly!

After the completion of this test flight, Qin Feng rested for a few days, because all the muscles of his body were strained due to the change in the dive, and he rested for a week, and after the doctor's examination was normal, he continued to start the test flight.

For the J-8, the test flight work has come to an end, and the various indicators of the fuselage design have met the requirements.

"We originally planned to use the 30-2 30mm single-barreled rifled gun imitated by Factory 847 in 1962, with a rate of fire of up to 1600 rounds per minute, which is an ideal high-speed aerial gun. However, in the actual development, there were frequent failures, and there were many major failures such as blowing up the bore and bending the barrel. ”

Lao Zhang, who is in charge of the J-8's weapon system, began to explain to everyone.

How weak is the domestic scientific research force? A simple cannon cannon, you can't imitate it!

Once on the second-generation aircraft, many designers thought that the cannon was useless, and the future war was the era of missiles, but unfortunately, the Vietnam War taught the Americans to be human again, and their F-4 fighters were forced to add a cannon pod in the later stage, otherwise the Sparrow missile, which is not very reliable, is almost useless with uncontrolled rockets.

The later F-4 fighters learned to be obedient and were equipped with cannons at the factory.

Up to now, there are many models of fighter cannons, and their core performance is high rate of fire and low weight.

Air combat is changing rapidly, the high rate of fire can catch the fighter, and the low weight can reduce the burden on the fighter.

If we talk about the United States, the standard equipment of their fighters is the M61 Vulcan cannon.

Vulcan uses a Gatling structure, and the most obvious advantage is the extremely high rate of fire. The weight of the M61A1 was 112 kg with a rate of fire of 6000 rounds per minute, the weight of the A2 was reduced to 92 kg and the rate of fire was increased to 6600 rounds per minute.

In this way, it seems that the M61 is the perfect fighter cannon, but unfortunately it is used as a transfer machine gun, from idle to full speed, that takes time, taking the M61 as an example, this thing takes a second to reach the maximum rate of fire, and a second in air combat is not a second on the ground, and it is easy to miss the fighter.

So, Soviet fighters did not adopt this way.

For example, the GSh-30-1 cannon on a Soviet fighter weighed only 46 kilograms. It features a short-stroke recoiled bolt that significantly reduces external size and overall weight. The GSh-30-1 has a rate of fire of up to 1,800 rounds per minute, although it cannot be compared with the M61's 6,000 rounds per minute, but don't forget that the M61 needs a second to have such a high rate of fire, the GSh-30-1 can instantly fire a large number of 30mm high-power ammunition at the highest rate of fire, and the air combat performance is not inferior to the M61.

After many researches, the country wants to imitate this Soviet cannon, but unfortunately, the technology is not good, and a cannon cannot be imitated.

"Now, seeing that our J-8 fighter is about to be finalized, our superiors have decided not to wait, let's directly install the J-7's 30mm gun."

The J-7 has used different types of machine guns at different times. The early J-7A/B and J-7G/MG used 30 mm caliber single-barreled guns with a reserve of 50 rounds, and the current model of the 30-1 is installed in the lower right of the cockpit and the right rear of the front landing gear.

The J-7 prototype and J-7C/D/E/FS are all 23 mm caliber double-barreled cannons with a reserve of 150 rounds, and the current model uses the 23-2/3 model, which is installed directly under the cockpit and directly behind the front landing gear.

Now, the early model of J-8 still intends to use J-7A's 30mm cannon, a total of two, which are installed side by side on the left and right sides of the cockpit close to the fuselage, after all, this caliber is large enough, the power is good, J-8's main task is to intercept the bomber, if the power of the cannon is not enough, there may be a situation where the opponent's bomber cannot be destroyed.

Even if it is this aircraft artillery, there have been some twists and turns in China, and the 30-1 aircraft gun ammunition supply and disposal system is also a design difficulty, which can be solved after a period of time. The Soviet Union has always kept the system of feeding and discharging ammunition for aircraft guns a secret, and finally domestic designers and workers modified an aircraft gun that could simulate shooting and fired 10,000 rounds of fake ammunition before achieving the success of the design.

"This cannon, the amount of ammunition is too small." Qin Feng frowned.

A large caliber will inevitably lead to less ammunition in reserve, what is 50 rounds enough for? Not even three short shots could not support it.

"Also, our aiming system is very backward." Qin Feng said: "If there is a hot line aiming, it can also greatly improve the accuracy. ”

With that backward optical aiming system, and with such a cannon with so little ammunition, it would be just a showcase, Qin Feng asked two questions in a row.