Name: The Insane Engineering of the X-15
Uploaded: 2021-06-09T05:35:46.000Z
Duration: 31 min 30 s
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

Throughout the battle of the space race between the United States and Soviet Union, both unions

experimented with remarkable and experimental technologies in the pursuit of the data and

wisdom required to conquer this new frontier. The task of gathering this data itself was

a tremendous challenge that required new aircraft, capable of reaching the edge of space and

pushing the boundaries of human understanding. One plane that stands out during the ascent

of the space race was the X-15. A plane designed to be the first to break into the hypersonic

regime and climb past the Kármán line, 100 kilometres above the earth's surface, and

break into space. The plane would help NASA develop the materials needed to survive the

intense heat of re-entry, the structures need to ensure stability and control in the hypersonic

flight regime and the development of control mechanisms for the vacuum of space, while

providing the impetus to develop several new technologies required to allow humans to survive

the vacuum of space, like the first of its kind fully pressurised space suit. This was

The plane laid the groundwork for both the Apollo Program, the Space Shuttle and the

To this day the plane holds the record for the fastest ever crewed flight with a top

speed of 6.7 mach. Leaving even the SR-71 in the dust as this rocket powered plane powered

through into the edge of space. This is the insane engineering of the X-15.

When the X-15 was first proposed in the 1950s, no other aircraft came even close to its proposed

capabilities in both max altitude and max speed.

The closest any previous plane came, was the X-2, which topped out at a max speed of Mach

3.2. Less than half of the eventual record the X-15 would achieve.

The X-15 wasn't just a step forward in capabilities, it was a tremendous leap that would require

the best minds in NASA, or the NACA as it was called then. The first step on this road

to the record 6.7 mach, was developing an engine capable of powering such an aircraft,

and for this, the designers had to turn to rocket propulsion.

Even the advanced hybrid engines of the yet to be developed SR-71 couldn't push into

the hypersonic regime, and no air-breathing engine would be able to function at the altitudes

The engineers knew the engine they required would need to produce around 240 kilonewtons

of thrust at sea level with an ability to vary thrust output, while fitting into the

narrow body of the plane. This powerful engine did not exist, and developing it would prove

to be one of the greatest challenges facing the X-15.

The first problem to solve was this variable thrust output, which was desired to give pilots

more control over the aircraft and allow for testing at various speeds. Blasting straight

into the hypersonic regime without extensive testing at lower speeds would have proved

disastrous as the difficulties of frictional heating were solved.

Older engines, like those of the Bell X-1, the first plane to break the sound barrier,

achieved variable power output by simply selectively igniting 4 separate combustion chambers. This

provided stepped power output, but not true throttle.

The X-15 needed finer control than this, and needed to achieve it without adding significant

weight and complexity to the engine. Added complexity would decrease the safety, putting

any pilot in danger, while any added weight would significantly reduce the maximum altitude

The X-15 achieved this control by varying the speed of it's turbopump, which is the

pump which forces the oxidiser and fuel from their respective storage tanks into the combustion

Pumping fluid at the rate a rocket consumes it is actually a tremendously difficult challenge.

The X-15 carried 8,165 kilograms of fuel and oxidiser, which the plane burned through in

just 85 seconds. That's 5897 kilograms per minute.

That task would require a powerful pump, and that pump would need a powerful energy source.

Now, it may seem like an obvious choice to simply use a portion of that rocket fuel to

power the pump, and indeed this is how modern rockets, like the Space-X Merlin engine power

Turbopumps operate by spinning a turbine using hot fast flowing gas, but using the products

of rocket fuel combustion in a spinning turbine would quickly lead to severely melted and

The combustion products of rocket fuel are simply too hot for this application.

The Merlin engine gets around this by using a very fuel rich mixture for the turbopump

pre-burner, which leads to incomplete combustion and lower exhaust temperatures. That exhaust

has a large portion of useful fuel contained within it, but the sooty exhaust is not suitable

So, that fuel is simply dumped overboard. You can see that fuel rich sooty gas coming

out of this exhaust here on the Merlin engine.

The X-15 used an entirely separate fuel to power it's turbopump. A monopropellant in

the form of hydrogen peroxide. A monopropellant, like hydrogen peroxide, decomposes in an exothermic

reaction when in the presence of a catalyst. In this case hydrogen peroxide was passed

through a silver screen catalyst which caused the hydrogen peroxide to decompose into oxygen

and superheated 737 degree steam. It was this superheated steam that drove the turbine,

and the speed of the turbine could be controlled by simply adjusting the amount of hydrogen

peroxide passing over the silver catalyst with the use of control valves.

The exhaust of this system was then simply dumped overboard through this exhaust port.

This was not the only use for hydrogen peroxide on the X-15.

A similar system powered the auxiliary power system, or APU, which powered the plane's

The pilot would also need some form of control when outside of earth's atmosphere, where

the plane's aerodynamic control surfaces would no longer work, so the plane was fitted

with thrusters on the wing tips and nose to provide control while in space, these thrusters

Using hydrogen peroxide to power the turbopump came with some challenges. This turbine operated

two separate impellors, one for the liquid oxygen storage tank, which operated at 13,000

RPM, and one for the anhydrous ammonia tank, which operated at 20,790 RPM. These different

pumping speeds ran on the same drive shaft, which necessitated gearing to achieve the

appropriate fuel mixtures, but also incorporated serious safety concerns over accidentally

fuel leakage from the respective hydrogen peroxide, liquid oxygen and anhydrous ammonia

lines, as a spinning shaft is more difficult to ensure adequate sealing. Double seals were

placed between each section in an effort to prevent mixing, while a system of pressurised

The choice of liquid oxygen and anhydrous ammonia was an interesting one. This engine

needed to be powerful, extremely powerful, and getting it to the required thrust levels

was going to need the right fuel and oxidizer combination. [Page 95 of Ignition]

When speaking of rocket power capabilities, one of the first stops is specific impulse.

Specific impulse describes how efficiently a fuel can convert its mass into thrust. To

understand this let's first look at total impulse, which describes the thrust force

generated over the entire burn period of the engine. We can graph this rather easily, by

plotting the thrust the engine is providing in each second of its flight, that may look

The total impulse is found by finding the area under this graph, which gives us the

This is a useful metric in itself, but specific impulse is better, because not all propellants

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The Insane Engineering of the X-15

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