# Why isn't tungsten used in supersonic aircraft?

Why isn't Tungsten used in supersonic jets or flights even though it has a High Melting and Boiling point?

• It is a very dense metal which would make the aircraft heavier at the same size. There might be some tungsten alloys used in aircraft though. – SMS von der Tann Oct 22 '16 at 14:28
• Tungsten is used on aircraft, for counterweights, in replacement of uranium that was a bit more touchy to recycle. See a list here (while trying to close popups...) Tungsten and uranium are more dense than lead, which is a problem for aerospace for other uses. – mins Oct 22 '16 at 15:35
• We have a 40lb chunk of tungsten that lives in a little tight-fitting Pelican case. It's fun to hand it to someone and see people do a double take when they misjudge how heavy it is- tungsten is almost twice the density of lead. – Spehro Pefhany Oct 22 '16 at 20:10
• @SpehroPefhany: I've the same problem when carrying my gold ingots to Grand Cayman, it's not like in movies. – mins Oct 22 '16 at 22:57

While tungsten does have a high melting point (I'm not sure what's the relevance of boiling point here), it has little else to offer for aircraft construction. The main issue of course is weight. One of the main goals of aircraft design is to reduce weight while achieving all the required performance parameters and tungsten is among the heaviest elements around, even beating Uranium.

When you factor in its density, it appears less than ordinary- its specific strength is less than 100 KNm/kg, less than half of Aluminum. Another thing is that tungsten is not exactly an easy material when it comes manufacturability. Even its saving grace, the high melting point (over 3000$^{\circ}$ C) is not very relevant as far as supersonic aircraft are concerned. The temperatures experienced in aircraft anywhere other than engines is well within that limit. For example, the surface temperature of Concorde wouldn't even get to a tenth of it.

Concorde surface temperature; image from erau.edu

Surprisingly, tungsten is indeed used in aerospace industry- at exactly the other end of the speed spectrum. it is used as a counterweight for controls in small aircraft and also as balancing masses in rotorcraft blades.

• Does tungsten form alloys with lighter metals that might take advantage of the properties of both? – TomMcW Oct 22 '16 at 16:35
• @TomMcW Tungsten Carbide Cobalt coatings are used in a number of applications, as a thin flame sprayed coating, to increase hardness in selected areas of aircraft components. (I have seen this application on a bearing journal for the main shaft in a helicopter transmission). The virtue of that coating is its hardness, which leads to reduced or no wear on that area in the base metal. A similar virtue is found in tungsten carbide coatings for cutting tools used by machinists to shape steel parts. – KorvinStarmast Oct 22 '16 at 17:30
• " the surface temperature of Concorde wouldn't even get to a tenth of [that temperature]" It doesn't make sense to talk about a tenth of a temperature, unless you're using kelvin (and, even then, I'm not convinced it's meaningful). The temperature of Concorde's nose (127C, according to the diagram) is 3.7% of the melting point of Tungsten in celsius, but 4.2% in fahrenheit and 10.8% in kelvin. – David Richerby Oct 22 '16 at 18:24
• @Nived Why do you need armour that can cope with 3000C when your plane only heats up to 127C? Your frying pan gets hotter than that but you don't go hunting for tungsten cookware. – David Richerby Oct 22 '16 at 18:26
• @Nived The horse is dead. Stop flogging the horse. – David Richerby Oct 22 '16 at 19:22

While having one of the highest melting points, Tungsten is very heavy (very dense). Excess weight is detrimental in aircraft design.

Some of the parts that would need to be the most heat resistant, such as turbine blades are subjected to rotational forces that increase directly with the mass of the part. Thus a high mass material such as tungsten would increase the forces the part would have to withstand. These forces are already measured in tons per blade. Tungsten is also brittle. If a turbine blade failed, as does happen, it would be very difficult to contain. Tungsten is used in armor piercing projectiles; the results of a tungsten turbine blade failure would not be good.

Most other heat critical uses do not require high melting points, making other materials quite suitable.

Tungsten could have applications in ballast or balance weight applications, but lead usually works quite well here. On heat sensitive supersonic aircraft, tungsten could possibly be a suitable choice for this application, as lead does have a very low melting point of 327.5°C. On some of the fastest supersonic aircraft, skin temperatures could reach 200-500+°C, making lead unsuitable for these applications.

• Fun fact: the name tungsten comes from Swedish tung sten, meaning heavy stone. – Peter LeFanu Lumsdaine Oct 22 '16 at 17:32

In extreme flight conditions (i.e., hypersonic flight), it is; the nosecap of the X-51A was tungsten (PDF). Its density just isn't worth it at mere supersonic speeds.

Being at the extreme end of a scale (see: melting point) isn't necessary to cross the threshold of being the most useful. For example, the B-2s carbon-graphite frame is stronger than steel, less dense than aliminum, and has a melting point of 3,500 degrees C, whereas tungsten would melt at about 3,400 degrees C. Both of these are far higher than necessary even if you account for gas-turbine compressor combustion, but reducing weight reduces work and increases speed.

• Worth noting that, at terran atmospheric pressures, carbon doesn't melt at all - that 3500C figure is its sublimation point. – Sean Dec 9 '18 at 4:24