Why is it so difficult to design and manufacture jet engines used in fighter aircraft?

Since +30 years of our lives have been spent in dealing with aircraft and aircraft systems including engines, the above question is one of the questions and topics that I am frequently asked for my opinion in peer-friend assemblies, industrial consultations, scientific events, etc. We try to answer as much as our knowledge and experience allow. I wanted to address the subject in this article as a statement of opinion.

All jet engines, not only those used in jet fighter aircraft, are very difficult to design and manufacture. However, we have to accept that the design and manufacturing of jet engines used in jet fighter aircraft, which are expected to provide high output at low volume, are even more difficult than those used in civil aircraft.

A. What are the reasons that make jet engine design and manufacturing so difficult?

Although there are several important reasons, which I will try to explain below, I should immediately state that the most important reason for not being able to design and manufacture jet engines is the lack of a sufficient level of materials science, engineering and industry. 

Failure to have an adequate materials industry results in the inability to design and manufacture not only jet engines, but also many other necessary and useful materials, components and systems (For our detailed opinion statement, please see Ref.-1 and Ref.-2).

Countries that have been able to reach these levels through years of effort, perseverance, knowledge and experience (in fact, only the USA, Russia, the UK and France) are making special efforts to take all possible measures in order to preserve this advantage they have gained and not to share their knowledge, skills and experience with any country and dry mile.

Let us now try to elaborate on these issues to the extent permitted by this article.

1. The Secret Structures of the Materials Used in Manufacturing within the Scope of Commercial and National Secrets:

All materials used in the manufacture of jet engines, without exception, have their own secret formulas in accordance with the purpose of the region in which they are used, and even the raw materials of some of them are secret. 

Do you know how many countries there are in the world, and how many of them produce any jet engine?

Jet engine manufacturing is a very rare industrial capability.

Even building a low-efficiency jet engine with old materials is impossible for most countries.

Every undeveloped country has neglected research in metallurgy and materials science, and every such country will continue to pay the price in the coming decades. (For detailed explanation please see Ref.-1 & Ref-2)

All of the materials used in jet engines (steel, titanium, metal composites, etc.) are "non-standard materials with special alloy formulations, manufactured only for the performance of the specified function". The formulae of these material alloys are kept top secret. You can only buy the material if it is approved to be sold to you by the producing company and the government of that company. Most probably, this material will not be sold to you within the scope of "national secrecy".

To give an example; you cannot buy the formula of Coca Cola, you cannot buy Coca Cola itself! In this case; you have to create Pepsi-Cola. Pepsi-Cola may not be Coca Cola, but it can fulfil the same function. 

The leading materials used in the Jet Engine are;

a. Single Crystal Turbine Blades:

They are located in the turbine section behind the combustion chamber where temperatures are above the melting point of steel. The material used is titanium, which is a single crystal from top to bottom. From the tip to the connection point on the axle, this track is machined from a single unidirectional crystal. This is necessary because if there were more than one crystal/amorphous, it would weaken significantly under heat. The metallurgical techniques and formulation used to do this are closely guarded trade (or even national) secrets.

b. Combustion Chamber Lining:

This section faces the fires of hell and does not even have a built-in cooling system. It needs a lining that can withstand the heat and radiate it away from most of the combustion chamber. The composition of this lining is a closely guarded military secret.

2. Sensitive, rare, difficult-to-machine minerals:

Almost all jet engine components are manufactured from non-standard, specially formulated alloys.

The most basic characteristics of these materials are that they are extremely heat resistant, extremely strong and lightweight. Because jet engines create excessive heat and thus create power, they must be heat resistant, strong and as light as possible.

For example, let's take cobalt, which is a very necessary and strategic mineral mineral, which is widely used in the alloying of materials, especially in the manufacture of parts that require extreme heat resistance.

Cobalt is an indispensable element for the production of strategic technologies such as advanced batteries, jet engines, rare earth permanent magnets, petroleum catalysts and tool parts for construction, manufacturing and mining. 

Cobalt is a very important and essential mineral used in the alloying of materials that must maintain their durability at high temperatures. Due to this feature, it is one of the most important components in many aerospace, defence and medical applications. 

Seventy per cent of the world's cobalt reserves are in the Democratic Republic of the Congo, and for this reason alone, this country has not been at peace for 100 years. The mining lords of the exploiting world roam this country and instability and unrest are necessary for their continued exploitation. In other words, this mine, which should bring prosperity and happiness to the Congolese people, has been the main source of poverty and unhappiness of this people for a century. Figure 1 below visualises this situation very well.

Figure-1: 100 Years of Cobalt Production of Democratic Congo.

3. Precision and Complex Machining Techniques: 

Any inconsistency in the metals in the engine or asymmetry in machining can have devastating consequences. For example, there are cooling ducts drilled into the blades, if more material is removed from one blade than the others in the manufacture of these cooling ducts, this will cause eccentricity, then vibrations, and eventually disintegrate the entire engine.

4. Financing: 

Financing is one of the leading reasons which is very difficult and tiring. Companies cannot undertake the financing of jet engine design and manufacturing on their own. Even if they do, a customer must have a purchase guarantee for this product and must have ordered and paid for it in sufficient quantities. If this jet engine is to be used in a jet fighter aircraft, the approval of the government will be required, and if an air force from another country is to purchase it, the approval of your own government and the approval of the government of the air force will be required. Getting governments to invest money in such projects, which will almost certainly exceed time and budget constraints, will require a lot of negotiation.

Countries that can design and manufacture jet engines have also built jet aircraft, but not vice versa!

As of today, there are only four countries and one consortium (EU) building fighter jets.

1. USA 

2. Russia

3. France 

4. England 

5. EU consortium (joint efforts of EU countries)

There are quite a few other main and sub-components that "unite" the fighter aircraft platform. We know that a fighter aircraft consists of four basic components", these are:

1. Aircraft Engine(s) (aero-engine/s)

2. Body 

3. Flight control systems 

4. Avionics

5. Weapon systems

Unless you do all or most of these things yourself, you are designing and even manufacturing a fighter aircraft, but unfortunately you cannot claim that the entire control and lifelong maintenance of that whole system belongs to you. In a real operational environment, you cannot rely one hundred per cent on a jet fighter aircraft that you cannot ensure the control and maintenance of all its systems.

Let me try to explain with a few examples: 

China. They have come a long way in the design and manufacture of indigenous jet fighter aircraft, but most of their engines and weapons, or their technologies and materials come from Russia.

Sweden. It has already designed and built some very important jet fighters (Hansen was able to design and build the Saab JAS 39 Gripen), but the engine comes from the USA (GEF404) and the weapons from the USA and Europe. Some avionics are also sourced from abroad.

Japan has a significant indigenous industry and financing, but is dependent, or rather is being made dependent, on the USA for engines and some other key technologies and weapons. 

South Korea. Historically dependent on the US for its indigenous fighter aircraft programme. It first designed and built the KAI T-50 with the US LMA. Subsequently, in co-operation with the US LMA, it designed and started manufacturing the KAI KF-21 Boramae, and the engine is the US GEF414. In this system, South Korea is cooperating with EADS technologically and Indonesia financially. In addition, most of the weapons to be used by this platform will be supplied from Europe and the USA.

Pakistan (JF 17). There is a serious national effort and success in the production of its national aircraft JF-17. However, almost everything in the aircraft, except the fuselage, is from China or Russia. Some of the avionics are also supplied from Europe.

India. Designed and manufactured HAL Tejas, but the engine is from the USA (GEF404) and the weapons are from almost everywhere. Some major advances have been made in the airframe and flight control elements. Some of the avionics are also indigenous, but key materials still come from abroad.

Turkey. HÜRKUŞ, HÜRJET, MMU TF-X. A similar situation to the KAI KF-21 Boramae is particularly true of the MMU TF-X.

Conclusion:

In order to be able to design and manufacture jet engines, especially jet engines to be used in jet fighter aircraft, you must attach importance to and develop materials science, engineering and technology. Of course, you must also have sufficient knowledge, skills and experience in the design of jet aircraft and engines. And you must also have the financial strength to undertake all these studies. Otherwise, it is unlikely that you will be able to build a jet engine. 

Bibliography:

1. Why Turkey Should Focus on Materials Technology in Industry (Part-1)

https://strasam.org/analiz-ve-raporlar/analiz/turkiye-sanayide-neden-malzeme-teknolojisine-odaklanmali-bolum-1-1255

2. Why Turkey Should Focus on Materials Technology in Industry (Part-2)

https://strasam.org/analiz-ve-raporlar/analiz/turkiye-sanayide-neden-malzeme-teknolojisine-odaklanmali-bolum-2-1256