4 ms·

Can anyone tell me what is more expensive about hypersonic jet travel? Fuel costs, I would imagine, are higher- wind resistance is a function of speed squared

by mabbo 8y ago

Can anyone tell me what is more expensive about hypersonic jet travel? Fuel costs, I would imagine, are higher- wind resistance is a function of speed squared after all. But where else does the higher price come from? Are the jets just that much more expensive to build? If so, why?

Something1234 8y ago
If you remember 1/2 mv^2 = KE from high school physics, then you'll realize just how bad it is. It an N^2 relationship, and that's really expensive. Faster you go the more it costs.
nfg 8y ago
I’m no expert by any means but one major factor is that the airframe is subjected to a lot of heat due to friction which can require exotic or expensive construction materials.
rayiner 8y ago
Fuel costs are a lot higher. Concorde used four times as much fuel per passanger as a 747. Plane costs are higher—you need exotic materials and building techniques in the aircraft and engines to deal with the high temperatures. But what really gets you is the economics of building niche products. Even if the long run incremental cost diffefence isn’t that much (say double), only a tiny fraction of people will be willing to pay the premium. That means you might amortize your fixed development costs, which will be much higher of that of a conventional jet, over 1/100 as many planes. 1,500 747s were ever built, but just 20 concordes. The 787 cost $32 billion to develop. Amortizing that over just dozens instead of hundreds or thousands causes per-unit costs to explode.
- dx034 8y ago
  To add to this, many of the most popular airports with business travellers (LHR, JFK, HKG) have restricted capacity. They'd have to use the same number of slots for a small supersonic plane as for a widebody flying that route otherwise. That can significantly increase cost per seat.
7952 8y ago
The engines are likely to be more elaborate than the turbofan you find on a jet liner. To get to Mach 5 you need to accelerate through different speeds and need an engine that works and is efficient enough at each speed. A turbojet works well at lower speeds but cannot go much above Mach 3 in its traditional form. A ramjet is efficient at high mach numbers but does not work at low speeds. One solution is to reconfigure the engine at different speeds, such as a variable cycle engine. Alternatively, some designs include precooling of intake air (sabre), or even a hybrid rocket/jet engine. But all these options are more complex and expensive.

by mabbo 8y ago

Something1234 8y ago

If you remember 1/2 mv^2 = KE from high school physics, then you'll realize just how bad it is. It an N^2 relationship, and that's really expensive. Faster you go the more it costs.

nfg 8y ago

I’m no expert by any means but one major factor is that the airframe is subjected to a lot of heat due to friction which can require exotic or expensive construction materials.

rayiner 8y ago

Fuel costs are a lot higher. Concorde used four times as much fuel per passanger as a 747. Plane costs are higher—you need exotic materials and building techniques in the aircraft and engines to deal with the high temperatures. But what really gets you is the economics of building niche products. Even if the long run incremental cost diffefence isn’t that much (say double), only a tiny fraction of people will be willing to pay the premium. That means you might amortize your fixed development costs, which will be much higher of that of a conventional jet, over 1/100 as many planes. 1,500 747s were ever built, but just 20 concordes. The 787 cost $32 billion to develop. Amortizing that over just dozens instead of hundreds or thousands causes per-unit costs to explode.

dx034 8y ago
To add to this, many of the most popular airports with business travellers (LHR, JFK, HKG) have restricted capacity. They'd have to use the same number of slots for a small supersonic plane as for a widebody flying that route otherwise. That can significantly increase cost per seat.

7952 8y ago

The engines are likely to be more elaborate than the turbofan you find on a jet liner. To get to Mach 5 you need to accelerate through different speeds and need an engine that works and is efficient enough at each speed. A turbojet works well at lower speeds but cannot go much above Mach 3 in its traditional form. A ramjet is efficient at high mach numbers but does not work at low speeds. One solution is to reconfigure the engine at different speeds, such as a variable cycle engine. Alternatively, some designs include precooling of intake air (sabre), or even a hybrid rocket/jet engine. But all these options are more complex and expensive.