Castle of Black Iron

2 hours later, Iron-Dragon Airboat flew across a thick cloud which looked like a huge marshmallow. When Iron-Dragon Airboat left this cloud in less than 1 minute, Zhang Tie had already left Iron-Dragon Airboat and appeared in the cloud tens of thousands of meters above the ground.

The airboat had already left the border of Longxi Prefecture in Zhongzhou Province.

At this moment, Pingsha Valley might still be cloudy and rainy; however, this place had been sunny with white clouds. Airships would fly below the cloud now and then. There was a faintly prosperous city on the horizon in the distance.

There were secret tunnels in some rooms of Iron-Dragon Airboat which could help knights access to Iron-Dragon Airboat rapidly for the sake of escape and executing special tasks. These secret tunnels could only be opened from inside. After a few seconds, they would close up automatically. One secret tunnel was in Zhang Tie's cultivation room. Besides Bai Suxian, nobody else knew that Zhang Tie had left.

Zhang Tie was flying in the white clouds, where the visibility was less than 100 m. The others could not see what was inside the white clouds at all. Riding the wind in the white clouds, Zhang Tie really looked like an immortal.

After leaving Iron-Dragon Airboat, Zhang Tie became alone once again. He could do whatever he wanted. Zhang Tie felt being free once again. He did not have such a relaxing experience for a long time.

Over these years, Zhang Tie was escaping and thinking about how to reverse his case or fight demons and Three-eye Association constantly. When he could move alone, Zhang Tie felt pretty good.

Zhang Tie had been floating in the white clouds for over 10 minutes. When Iron-Dragon Airboat completely disappeared in the skyline, Zhang Tie had changed into an average middle-aged tough man in a blue long gown with rich eyebrows, a swarthy face and closely cropped hair. Given his qi, his battle strength became unidentified.

After changing his look, Zhang Tie flew out of the cloud when he was sure that there was no knight or airboat within dozens of square miles. Closely after that, he flew towards the north as he gradually ascended and turned into a small point.

Zhang Tie sensed that the thunder hawk was pretty excited when it was flying towards him. Additionally, its flight speed increased by almost 30% once again, which startled Zhang Tie a lot. Closely after that, Zhang Tie was moved.

It was similar to the feeling when you saw a dog that you fed many years darting towards you desperately while swaying its tail.

Zhang Tie was flying fast too. In only a few seconds, his flight speed had reached 600 miles per hour and was still increasing. In the blink of an eye, he had entered the stratosphere over 13 miles above the ground. A knight flying rapidly in the stratosphere could barely be discovered by others on the ground.

After entering the stratosphere, Zhang Tie continued to ascend while his speed had reached 650 miles per hour.

His two chakras of King Roc Sutra were rotating forcefully and slowly as firm as mountains. It was like an effective engine entering the velocity range for stable operation. The rotating chakras could offset the gravity from the earth and provide Zhang Tie with a greater speed. As a result, he had the impulsion to fly higher and faster.

After sensing this impulsion carefully, Zhang Tie discovered that 1/3 of this impulsion came from his curiosity, 2/3 of this impulsion came from the instinct that drove his chakras of King Roc Sutra to rotate.

As for the human aircraft in this age, airships and gliders could only fly in the troposphere 15 miles above the ground; however, airboats and knights could fly in the stratosphere between 15 miles and 80 miles above the ground. If he was higher than 80 miles, he would enter another atmosphere. Zhang Tie wondered about the feeling in the strange atmosphere. Neither had he heard about it from other earth knights. Therefore, he was curious about that.

Zhang Tie felt a bit strange about the instinct of King Roc Sutra. He started to admire about the terrifying flight speed of the thunder hawk. After that, he sensed that the virtual image of King Roc Sutra in his shrine became a bit restless. What a weird feeling!

Driven by this curiosity and the instinct of the emperor-level secret method, plus the proper time and location, Zhang Tie had a heroic feeling inside as he wanted to test how high he could reach.

Since he promoted to an earth knight, Zhang Tie had not got a chance to try this ability yet.

When he thought about this, Zhang Tie constantly ascended at an increasingly higher speed and broke the upper limit of 700 miles per hour for the first time. At this high speed, Zhang Tie soon entered the top region of the stratosphere which was over 80 miles above the earth.

At this height, the air became thinner. He was actually standing on white clouds. He felt like watching cotton fields on the top of a skyscraper. At this height, commoners could only see the outlines of very huge individuals such as cities, mountain ranges, lakes, long railways in the cotton fields.

However, with lotus-flower eyes, the higher Zhang Tie reached, the better visual field he would gain. Even at such a height, as long as he would like to concentrate, he could see clearly each grass and wood on the ground.

When he recalled the item called reconnaissance satellite before the Catastrophe, a hilarious whim suddenly occurred to his mind, 'Compared to those metal instruments, I'm a real "artificial satellite"'.

Zhang Tie didn't know why few earth knights mentioned the atmosphere above the stratosphere. At least he didn't feel it difficult to break through the stratosphere. His feeling and chakras which were still normally rotating granted him a very great confidence.

Zhang Tie entered the atmosphere above 80 miles high smoothly. He felt cold at once. Additionally, the convective motion that he met in the troposphere reappeared. After his flight speed reached 750 miles per hour, an invisible barrier appeared in front of him for the first time...

'Sonic barrier', a term occurred to Zhang Tie's mind.