Moore’s Law of Aircraft Technology

I attended the Thunder Over Michigan airshow last weekend. What a great time seeing old warbirds, newer warbirds plus current aiforce inventory by way of The USAF Thunderbirds. Here are a few pictures:

P-38 -- RUff Stuff

P-38 –Lightning —  “RUff Stuff”

P-51 Mustang

P-51 Mustang — “Petie 2nd”

P-73 King Cobra

P-63 Kingcobra

PT13 Stearman, primary trainer

PT13 Stearman, primary trainer

F86 Sabre

F86 Sabre

USAF Thunderbirds

USAF Thunderbirds


Watching these time machines in action in Ypsilanti, MI got me thinking about the evolution of technology, in general, and how a mature technology, like aircraft technology compares to semiconductor technology. I’m sure you’ve heard comments like, if the technology of a car was like semiconductor technology, a car would cost $x (where x is a relatively small number, like $200) and go y MPH (where y is a relatively large speed, like 600 MPH). So, I was curious what the Moore’s law curve might look like if you looked back at aircraft technology.

Moore’s Law states that the number of transistors that can be put on a chip doubles about every 2 years. Since the dimensions in the chip are going down, the corollary to that is that the speed of the chip goes up on a similar exponential curve. Using speed as an analog for the improvement resulting from Moore’s Law, I thought it would be interesting to compare the evolution of chip speed versus the evolution of aircraft speed. I decided to use Intel processors, generally referred to as X86 processors, as a simple example of the speed-up of Moore’s Law. I found a table of all the Intel chips on Wikipedia at http://en.wikipedia.org/wiki/List_of_Intel_microprocessors, and a list of air speed records at http://en.wikipedia.org/wiki/Flight_airspeed_record

Interestingly, the first airplane, the Wright Flyer, made a whopping 6.82 MPH, barely faster than a walking pace.

I graphed out the aircraft speeds and processor speeds to see how similar they were:

AIrcraft speed records

AIrcraft speed records

X86 Clock Speeds

X86 Clock Speeds


The airspeed looks fairly linear early in its curve and then has a late sharp swing up. The x86 curve seems flat at the beginning with a sharp upward curve towards the end. In both cases, it looks like it flattens out in the last few samples. In the case of airspeed, there has not been a new airspeed record since 1976. A better view would be to look at the data with the speed as the logarithm of speed. That will allow us to see the low-end better and a straight line will show us an exponential (i.e. doubling every x years) relationship.

logarithmic Aircraft speed records

Logrithmic Aircraft speed records

logarithmic X86 clock speed

Logrithimic X86 clock speed


On the log scales, the x86 curve looks like a straight line would fit well, but the last few have flattened out. The aircraft speed record flattens out in the 1930s, then jumps again when jets came into being. It’s not a great linear fit on the log scale.

If you look at the doubling time, for x86, between 1971, when the 4004 came out at 710 KHz, and 2010 when 3.6 GHz Clarkbridge came out, the clock speed grew 4096 times, or doubled 12 times over 39 years. That works out to doubling every 3.3 years or so. The aircraft didn’t do so well, they went from 6.82 MPH to 469.22 MPH at the best piston engined result in 1939, for a 68.8 times greater speed  over a similar 36 years. So, aircraft doubled speed 6 times in 36 years, or doubled every 6 years. There was a short relative jump when jets came out, but it flattened out by the early 60s.

Interestingly, if you look at the data, you can see both curves having some flat spots when they ran up against technical problems that needed to be solved. In the case of aircraft, the first aircraft were bi-planes or even tri-planes. The planes needed 2 or more wings in order to get enough lift to get in the air. But, two wings create a lot of drag and limit the maximum speed. In the 1920s, single wing planes became practical and the speeds jumped. Then, piston engines became the bottleneck, and speeds didn’t change much until the jet era. In reality, no propeller driven plane would be able to get close to the speed of sound because the tips of the propellers reached the speed of sound well before the aircraft did.As the propeller tips approach the speed of sound it creates turbulence. The turbulence robs the propeller of the ability to push the plane through the air. Even slower planes like trainers, especially the AT-6 Texan, can get their propellers near the sound barrier. Pilots jokingly call this a “great way to turn av-gas into noise.” Jets solved that problem, but then friction with the air and drag become the limiting factor. The fastest airplane ever was the SR71 Blackbird, whose skin was made of titanium that was light, but also heat-resistant. The fuel was stored just under the skin to dissipate the heat from the friction. Even in the thin air at 70,000 feet, the friction caused tremendous heat in the skin of the plane as it flew around Mach 3 and 2000 MPH.

Similarly, in semiconductors, it seems that x86s had a relatively flat spot in the late-90s when major speed gains weren’t made until 2000. Now, they are facing the limits of physics. The gate dimension is approaching the size of a single atom. This drives up electrical the resistance, especially at high clock speeds. Higher resistances causes greater heat generation in the chip. And that is reaching the maximum ability to remove the heat from the chip. You can even see the peak clock speeds decreasing slightly from it peak.

While aircraft technology was relatively new, from 1903 until the early 30s, aircraft speed went up very quickly, and given the technical challenges of engine technology, material science, and understanding of aerodynamics, it is pretty amazing how quickly they improved. Semi-conductors have seen even faster leaps in performance due to Moore’s Law and have to overcome technical challenges as the dimensions have shrunk. Now, as semiconductor technology is starting to approach the limitations of physics, it will be interesting to see how electronic systems evolve with a smaller level of increase in speed.

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