Chapter 975: So Ugly

In fact, Gao Zhendong only knew about the MiG-21. In his previous life, there were many improvements to the old Zhan-7, and the wing fuel tank happened to be one that he remembered.

Mr. Huang roughly calculated in his mind: "Well, we can add some fuel here, but not too much."

Gao Zhendong suddenly laughed. Mr. Huang didn't know what he was laughing at. When he was about to ask, Gao Zhendong drew a silhouette of the MiG-21 on a piece of paper, and then with a big stroke of the brush, he drew a line from the rear edge of the canopy to the vertical tail.

Then he drew a top-down view and also outlined the side view.

"Here, add another dorsal fuel tank! I just estimated that it can increase the fuel capacity by at least 600 liters. And at the same time, raise the cockpit cover by a few centimeters. One is to accommodate the dorsal fuel tank, and the other is that the cockpit of this aircraft is too low."

The height of the aircraft cockpit is a very counterintuitive thing. In fact, no matter whether it is a tank, infantry fighting vehicle or an airplane, at least the pilots are not very tall. They are not as big and strong as imagined. Our pilots felt uncomfortable when they went in.

As for increasing the fuel tank, this is what the Russians have been doing from F-PF-S-MF all the way to BIS, they have been adding more!
In the beginning, they were a bit shy, and only enlarged a part of it, leaving a little wasp waist to maintain its appearance. Later on, they let go completely, and did whatever was practical. The spine fuel tank became bigger and bigger, and uglier and uglier.

Mr. Huang almost vomited blood. No wonder he was laughing. Looking at it this way, the plane looked even uglier!
Originally, the MiG-21 did have a dorsal ridge, but it was not obvious and very coordinated. After Gao Zhendong added this, the plane suddenly changed from having a waist to a flying can, with the front and back aligned!
And... with that big mouth it's really ugly!
Mr. Huang was complaining in his mind, but after calming down, he had to admit that this modification was the most economical and direct.

It will not change the maximum forward cross-sectional area of ​​the aircraft. At the same time, the increased wet area and cross-sectional area of ​​each section are not much. It is easy to handle according to the area ratio. The increased weight is distributed more evenly on the middle fuselage, and the impact on the change of the aircraft's center of gravity is not too great.

In other words, without performing any major surgery on the entire aircraft, more internal fuel is obtained, which greatly improves the range. The fuel carrying efficiency of internal fuel is much higher than that of auxiliary fuel tanks.

Although this would further increase the weight of the fuselage and might affect the flight performance of the clean configuration, Gao Zhendong did not care much about it. The thrust of the R-21F11-2 engine used in the Russians' earliest interceptor MiG-300PF was increased by less than 10%, and it worked well all the way to the M model. The R13-300 engine used in the subsequent SM/MF only increased the thrust by about 21% compared to the MiG-15F.

In any case, loading more fuel into the fuselage when possible is actually more beneficial for actual combat mounting configuration.

After weighing the pros and cons, Mr. Huang accepted it with a pinch of his nose. This thing is ugly, but ugly in a cute way.

"Okay, let's go back and calculate carefully to see how big it can be." The schematic diagram provided by Gao Zhendong was basically done in one step, directly following the diagram given by the MF's spine fuel tank. It looked like a giant pig worm crawling on the back of the MiG-21.

For later comrades, this is one of the few times in Comrade Gao Zhendong's career that he became uglier as time went by, and it can also be regarded as adding an interesting anecdote.

"By the way, I think this place can be modified. Move the parachute up and put it at the root of the vertical tail." Gao Zhendong pointed to the tail of the aircraft on the line drawing before Mr. Huang asked the next question.

The MiG-21F's parachute compartment is below the engine nozzle and behind the ventral fin, but later both the Russians and we placed it in the position Gao Zhendong mentioned.

"Put this up? It doesn't seem to make much difference. Is there any point?" This thing was too detailed and Mr. Huang didn't know what it was for a moment.

"No, this will improve the landing performance..." Gao Zhendong explained: "In the original position, the connection between the parachute and the fuselage is lower than the center of gravity of the aircraft. Once the parachute is opened, the aircraft will tend to bury its head, which is not conducive to landing. If it is placed on top, there will be no such problem." Gao Zhendong simply drew a force analysis on the side view just now.

"Well, from the perspective of mechanical theory, it is true! Details, too many details. The landing performance has been improved, so is it possible for the take-off performance to..." Mr. Huang was very happy, and when he returned, several model managers were so happy.

Gao Zhendong thought about it and felt that it was not fair to do things halfway. "It's not impossible, but it's a bit complicated."

“It doesn’t matter if it’s complicated, as long as it can be improved. If it’s really too complicated, just change it back.” Mr. Huang was very calm.

"Then let's do this..." Gao Zhendong pointed to a certain position of the engine on the line diagram, and the next words almost made Mr. Huang and the others jump up: "Drill a hole here to draw out the high-pressure air in the engine, and blow it out from this position above the flap. Pay attention, in this case, the gap between the flap and the main wing should be small."

Drilling holes in the engine? That's a bit troublesome indeed. And why blow the flaps upwards instead of downwards? Wouldn't blowing downwards generate more upward force on the curved flaps?

After hearing their questions, Gao Zhendong smiled and said, "The main thing here is to use the airflow to eliminate the separation turbulence above the flap when the flap is opened, and form a stable airflow on the back of the flap, further improving the efficiency of the flap and providing greater lift." Looking at the airflow diagram drawn by Gao Zhendong on the flap profile diagram, the two finally understood what the comrades from the Cifei Factory meant when they said that Chief Engineer Gao had profound attainments in aerodynamics.

What else is there to say? Write it down quickly. This matter is troublesome, but it is also relatively simple. It is easier to extract air from the compressor section than to extract gas from the rear section of the combustion chamber, right?

Moreover, it seems that this can indeed further improve the aircraft's takeoff performance based on the flap system, which is very important for aircraft that may gain weight due to radar, fuel, etc. after modification. In addition, the takeoff performance of the MiG-21F is already quite average, so it should be modified if possible.

Speaking of wings, he remembered another important matter during his visit. This aspect was also initiated by Chief Engineer Gao, so it would be a good idea to ask him.

"Mr. Gao, it was you who proposed the wing strip, and we would like to ask you for advice on this aspect as well." After all, the benefits of the new Zhan-7 using the wing strip are visible to the naked eye, and whether the MiG-21 can use this wing strip and how to use it are unknown.
The wings! Gao Zhendong is even more excited than Mr. Huang. Apart from the nose, the biggest change he wants to make is the wings!

Looking at Gao Zhendong's excited eyes, Mr. Huang felt a little panicked for some unknown reason. Was he going to do anything big?
Sure enough, Gao Zhendong rejected his idea with his first sentence.

"This plane doesn't need slats!"

There is no reason. If there is a reason, it is that no matter we or the Russians have made so many changes, none of them use wing strips, so Gao Zhendong naturally would not think about it.

"No wing strips?"

"The wing strips are not a panacea. This is a high-speed aircraft. Let's think of other ways." After saying that, Gao Zhendong drew a wing on paper, which looked a bit strange.

"Let's use a double delta wing! I've calculated that the sweep angle of the inner wing remains unchanged at 57 degrees, while the sweep angle of the outer wing is changed to 42 degrees, and the trailing edge of the wing is swept forward. In this way, the inner wing is used to ensure high-speed performance as much as possible, while the outer wing takes into account low-speed performance in medium and low altitudes. This way, both ends can be taken into account relatively well. In addition, the space inside the wing is larger, and fuel, lift characteristics, wing loading, and range can also be improved to a greater extent."

The maximum flight speed of the previous 7th generation double delta wing model is still Mach 2. Gao Zhendong is not too worried that this wing shape will significantly reduce the high-speed performance of the aircraft.

How can this be possible? Genius!
Although we have only seen this concept and there is no specific design, calculation, or experimental data, most of the benefits are visible at a glance. Even the most suspenseful one that takes into account both high and low speeds does not seem outrageous.

To put it in an analogy, after the large swept section splits the air, the small swept section can follow up more easily.

The most important thing is that this design does not actually cause much change to the aircraft and there is no manufacturing difficulty. Instead, it is more troublesome to determine the sweep angles and sweep angle change points of the two sections.

Even Chief Engineer Gao has calculated the sweep angle. As for why the changing point of the sweep angle is not given, it is probably because there are still some unclear points about the aircraft and it needs to be adjusted according to the specific situation.

But Mr. Huang is very confident about the double delta wing. There are not many unknown factors left. The rest is easy to deal with. Blow it up in the wind tunnel! Even if it is not used in the imitation and improvement of the MiG-21, this airfoil is still a very useful one.

"57 degrees... 42 degrees... Hey, Mr. Huang, is this the number?" Another comrade wrote down the temperature while confirming with Mr. Huang, fearing that he had made a mistake.

"Yes, yes, that's the number."

Huang was answering him while taking notes, muttering to himself: "In this way, the original hardpoints are too few. Hmm, add two more full-function wet hardpoints on the outside of the wing to hang auxiliary fuel tanks, missiles... oh yes! And rocket pods!"

There is a situation that most people would not think of. The MiG-21F and our basic model, the old 7, have only two wing attachment points, and they are not wet attachment points, so auxiliary fuel tanks cannot be hung. They both have only one belly attachment point to hang auxiliary fuel tanks, and the combat radius is even more pitiful.

As for why you generally don’t see photos of Old Master 7 with only two hanging points, it’s because the Old Master 2 with two hanging points produces less and retires early.

Premier Huang sorted out the suggestions he had received from Gao Zhendong and found that although the changes seemed to be major, in fact only very few parts of the structure needed to be changed, mainly concentrated in the nose and outer wings.

(End of this chapter)