48 votes
Accepted

Why Didn't the USSR Build An X-15?

I like the X-15, it was certainly an amazing airplane, but the truth is there were few benefits to the space program from the X-15. It was far from a critical or necessary step: The Mercury space ...
  • 51.7k
29 votes

Why Didn't the USSR Build An X-15?

I'll complement GdD's answer from a slightly different perspective. In the history of aerospace engineering... Wait, there is a problem right there. Due to various historical reasons, there was ...
  • 8,815
22 votes

Won't sonic booms prevent Space X's BFR intercity transport plan from being acceptable?

The only way to get anything that far that quickly is to send it into space, and that's exactly what Musk is suggesting. The BFR will launch a passenger carrying spacecraft out of the atmosphere and ...
  • 51.7k
11 votes
Accepted

Is there currently any heat shielding and paint for speeds of up to Mach 6?

I'm reasonably certain the speed limit (so to speak) on the SR-71 wasn't to prevent its skin from melting. The hottest the skin got during flight was less than 600 C. That's definitely hot--but it's ...
  • 2,937
11 votes
Accepted

Can a plane with air-breathing engines in level flight achieve enough velocity to make a single orbit?

No. Currently the altitude record for a jet is 37,650m (This is a zoom and climb record, not sustained flight). Ralph J sum up the issue pretty well, but let me add some data: Ramjets are the kind ...
  • 4,103
10 votes

Why Didn't the USSR Build An X-15?

Great question, but no, the X-15 was not a "critical and necessary step on the path to manned space flight" at all, it was used to test the feasibility of sustained and controlled hypersonic flight ...
9 votes
Accepted

Why does linear airfoil theory break down at hypersonic speeds?

The linear theory makes certain assumptions in its formulation: The flow is irrotational and isentropic. The perturbations are small; i.e. the bodies are small at small angles of attack. However, ...
  • 99.2k
9 votes

Can electroaerodynamic propulsion be used to circumvent sonic booms?

No. Sonic booms are caused by shockwaves which form on the aircraft structure as it moves through the air, not by the engines. Completely unpowered craft can create sonic booms, for instance the Space ...
  • 51.7k
8 votes

Spinning wing heat dispersion dynamics for Mach 24 and beyond?

This is the heat distribution during reentry for the Orion capsule: So the leading edge is hotter than the trailing edge, even for very large angles of attack (almost perpendicular). I assume a ...
  • 10.2k
8 votes
Accepted

What is the maximum speed for regulation of sonic boom noise?

Business jets are developed to different rules than airliners. The biggest difference is that, indeed, fuel price and fuel efficiency are not an issue when what counts are bragging rights for the ...
8 votes

Why is a blunt trailing edge a better stabilizer at hypersonic speeds?

A converging shape at hypersonic speed in a low-pressure medium will produce close to vacuum pressure on its surfaces (hypersonic shielding). A small sideslip angle will only result in a very small ...
7 votes
Accepted

Would a rotating skin design mitigate the heating problem limiting hypersonic flight?

TL;DR Probably not. Assuming we would have a very good mechanical solution/design we would still need a way to get rid of the heat, i.e. a heat-sink. Imagine the panel (or what ever we will call a ...
  • 1,547
7 votes
Accepted

Are there any planes that have ramjet or scramjet engines?

Scramjets There's only a couple flying examples. The early Soviet-born Kholod, the HyShot series, and the recent ISRO ATV all flew small scramjet engines, although none were designed for net thrust. ...
7 votes

Does waverider have much lower drag than Sears Haack body?

A waverider will prevent the compressed air under the airframe from escaping sideways. An equivalent view is that the sideways component of the air displaced by the body is used for lift creation by ...
7 votes
Accepted

What are maximum G forces humans can survive?

I read that very high g forces could kill a pilot, brain pushing into the skull. High G-Forces cause blood flow to the brain to be impeded due to blood pooling low in the body under high ...
  • 97.6k
6 votes

What are maximum G forces humans can survive?

I read that very high g forces could kill a pilot, brain pushing into the skull. Not really. Humans who have been killed by very high accelerations (in the order of tens to hundreds of gs for a ...
5 votes
Accepted

Would pressurised air holes on supersonic aircraft mitigate the heat problem?

The idea of using small air holes to cool a surface is not completely 'out there'. In turbine engines, the turbine blades are cooled by blowing bleed air from a compressor stage over the blades. ...
  • 12.6k
5 votes

What technical problems stopped scramjets from being used on hypersonic aircraft?

I'm don't research hypersonic flight, but I bet the primary barriers of hypersonic flight are less technological and more political/economical. After all, we pay money and conduct research in order to ...
  • 1,048
5 votes

Could hydrazine be used as a scramjet propellant?

Technically yes, you could use hydrazine in a scramjet. But there's no reason to do so. The singular purpose of building a scramjet is to get air into the combustion chamber, so that you don't have ...
  • 17.9k
5 votes

Could liquid alkali metal fuels be used for ramjet/scramjet propulsion?

How long does the lithium take to evaporate and then to react with oxygen? Air in a scramjet is moving extremely fast (supersonic by definition!), so there is very little time left for mixing and ...
5 votes

Hypersonic Boost Glide Range

Gliding implies that lift equals weight. This is not the case for hypersonic boost glide vehicles. They ascend like rockets during the burn phase (or are carried aloft by a rocket) and then fly mostly,...
4 votes

Are there any planes that have ramjet or scramjet engines?

René Lorin invented the ramjet in 1908, and his ideas were tried in flight for the first time from 1941 onwards. Different sizes were tried; below are two pictures, one of a Do-17 Z with a small Lorin ...
4 votes

Are there any planes that have ramjet or scramjet engines?

Are you asking about current production or through out time? The SR-71 was powered by a Pratt & Whitney J-58 engine which operated as a partial ram jet at high speeds. At lower speeds it ...
  • 97.6k
4 votes

What is the theoretical maximum speed of a rocket-powered aircraft in the atmosphere?

The upper limit is given by the L/D of the rocket-powered vehicle and its thrust. In order to follow the curvature of the Earth so it will stay within the atmosphere, the vehicle must create enough ...
4 votes

Can hypersonic aircraft be agile without the G forces harming the pilot?

Well, 2 G's is 2 G's, regardless of what speed you're flying. A level (coordinated) turn with 60 degrees of bank is 2 G's, regardless of your airspeed. What changes is your turn rate and turn radius;...
  • 44.1k
4 votes
Accepted

Is hypersonic flight possible with a Busemann's Biplane?

Why Mach 10? Would Mach 3 or 4 not be enough? See here and here and here for the complications which arise at higher speeds. The linked article is full of misrepresentations - of course will the ...
4 votes

What mechanism or design aspect prevents jet blast from escaping the front of a Ramjet or scram jet?

Pressure is the greatest just before the combustor in both jet and ramjet engines - therefore air would have against the pressure differential for this to happen (turbine only has therefore an ...
  • 2,312
4 votes
Accepted

What rotors would be best for atmospheric reentry?

You couldn't do it to control reentry, but you certainly could do it for a vertical landing system that might be a bit less technically demanding than a rocket that can descend under control with its ...
  • 114k
4 votes

Why Didn't the USSR Build An X-15?

There were three competing ways to space pursued in the US while in the USSR everything was centrally managed, so they followed only the way that Konstantin Tsiolkovsky had first proposed. What were ...
4 votes
Accepted

Below what altitudes do shock waves form?

Shock waves form any time the speed of the airflow over or around a vehicle exceeds the speed of sound. The local speed of sound varies with ambient temperature in a well-defined way; in general it ...

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