Jump to content

Supersonic flight for civilians?


Errol

Recommended Posts

I'm going to put a resounding "maybe" to this concept. Engineering will not doom this plane, economics will; they would be catering to relatively niche markets who've developed habits to work around subsonic travel, such as sleeping on the plane for long flights.

That said, I wish them the best of luck; it would be something for us to once more have supersonic civilian flight.

No Mr. President, you hitching a ride on an F-22 doesn't count.

Link to comment
Share on other sites

There are half a dozen outfits right now trying to finance and sell supersonic bizjets. Whether any of them ever get made is a debatable question.

Larger supersonic transports keep getting worked on too, but they keep running into the same problems: airport noise, speed restrictions over land, and ticket cost.

Link to comment
Share on other sites

I remember once upon a time, being told (in print by a rocket scientist who had some reason to know: G. Harry Stine) that the full size Delta Clipper could operate globally for similar cost per passenger to what the Concorde (then in its heyday, with daily flights from London and Paris to New York) could within its operating range.  This would be suborbital, with less than an hour transit time (ignoring time zone and date line changes, of course) to anywhere on Earth, it was claimed.  There was even a semi-serious suggestion of using it to set up a hyper-express package delivery network -- for certain heavily used business transfer routes (Far East to Europe and especially America), it would live up to an even older SNL gag about "Temporal Express -- for when it absolutely, positively, has to be there yesterday."  Launch from Tokyo early in the day, you'll either outrun midnight, or beat it by going the other way.

I think most if not all of us here are convinced that SSTO without air-breathing engines, on the real Earth, is a non-starter from an economic standpoint (though it's surely possible with modern materials, if you won't mind payload fractions in the single digit percentage level) -- but a suborbital to anywhere is significantly less dV than orbit (though if it is, it's going to take a lot longer than 45 minutes to travel to the antipodes).  This might have been the civilian "supersonic" travel of the mid-21st century -- 45 minutes from New York to London or LA, seat belt light on the whole trip.  Flight attendants would issue Dramamine at boarding...

Link to comment
Share on other sites

8 minutes ago, Zeiss Ikon said:

I remember once upon a time, being told (in print by a rocket scientist who had some reason to know: G. Harry Stine) that the full size Delta Clipper could operate globally for similar cost per passenger to what the Concorde (then in its heyday, with daily flights from London and Paris to New York) could within its operating range.

Leaving aside that he was clearly wrong, this highlights a mistake that supersonic transport fans have been making for 50 years. They pick the wrong targets. Concorde, for instance, was designed to meet the noise levels and fuel efficiency of the worst subsonic jets of its day, not the best of them. So by the time it left service it was a huge outlier.

You want a supersonic transport to be successful? Make it as quiet and efficient as a 787.

Link to comment
Share on other sites

Are there any limitation to usage of high-bypass ratio turbofan in supersonic aircrafts ? Or is it purely an area one, so that it complicate the fuselage, maintenance and structure ?

Because yeah, if you want to justify supersonic flights, at least they have to only be just rationally more expensive than the subsonic ones. If it's a few times I doubt people would even consider it. And if anything, fuel cost makes the bulk of the fares...

Edited by YNM
Link to comment
Share on other sites

On 5/16/2017 at 11:17 PM, YNM said:

Are there any limitation to usage of high-bypass ratio turbofan in supersonic aircrafts ?

According to a quick wiki-read HBR Turbofans offer efficient performance up to mach 1.6. Further for supersonic transport flight a bypass ratio of .45 is considered "proper". To put into perspective, military LBR Turbofans like the F119; a pair of which powers the F-22, operate with bypass ratio of .30.

Now I am aware that the Air Force is presently developing technologies under the ADVENT program; Adaptive Versatile Engine Technology, It would allow for a jet engine to be able to operate over a wide range of airspeeds and altitudes. In other words an engine derived from ADVENT could allow an aircraft to operate efficiency at low speed and low altitude much like a HBP turbofan and when at high speeds and high altitudes operate efficiently as a pure turbojet. ADVENT could find it's way into civilian powerplant systems. Which would allow a future SST to surmount that technological hurdle.

Edited by Exploro
Link to comment
Share on other sites

22 hours ago, Exploro said:

According to a quick wiki-read HBR Turbofans offer efficient performance up to mach 1.6. Further for supersonic transport flight a bypass ratio of .45 is considered "proper". To put into perspective, military LBR Turbofans like the F119; a pair of which powers the F-22, operate with bypass ratio of .30.

Now I am aware that the Air Force is presently developing technologies under the ADVENT program; Adaptive Versatile Engine Technology, It would allow for a jet engine to be able to operate over a wide range of airspeeds and altitudes. In other words an engine derived from ADVENT could allow an aircraft to operate efficiency at low speed and low altitude much like a HBP turbofan and when at high speeds and high altitudes operate efficiently as a pure turbojet. ADVENT could find it's way into civilian powerplant systems. Which would allow a future SST to surmount that technological hurdle.

A bypass ratio of less than 1:1 ? Sounds pathetic for the point of my question. I was asking something like the engines on B787 and A350 and GE90 and such. Now those are efficient at subsonic speeds. I do understand that traditionally they become "obsolete" at supersonic speeds, but how far can we afford to lose ? I mean, if we just end up with a sliver more or less fuel than a specifically designed engine, that's one more RnD to cut...

Boeing did at one time considered a Mach 1 SST using "usual modern low" bypass ratio turbofan (the sort of ratios you get at fuselage-mounted engines near tails and things like B737 and A320 family); but ofc you need to fly long routes that way to ensure that passengers enjoy the travel time cut wrt ticket price !

DISCLAIMER : I am NOT in any way an aerodynamic engineer ! So I have no idea at all how far things are.

offtopic : seems like firefox mobile is extremely horrible !

Edited by YNM
Link to comment
Share on other sites

On 2017-5-17 at 4:17 AM, YNM said:

Are there any limitation to usage of high-bypass ratio turbofan in supersonic aircrafts ? Or is it purely an area one, so that it complicate the fuselage, maintenance and structure ?

Because yeah, if you want to justify supersonic flights, at least they have to only be just rationally more expensive than the subsonic ones. If it's a few times I doubt people would even consider it. And if anything, fuel cost makes the bulk of the fares...

 

17 minutes ago, YNM said:

A bypass ratio of less than 1:1 ? Sounds pathetic for the point of my question. I was asking something like the engines on B787 and A350 and GE90 and such. Now those are efficient at subsonic speeds. I do understand that traditionally they become "obsolete" at supersonic speeds, but how far can we afford to lose ? I mean, if we just end up with a sliver more or less fuel than a specifically designed engine, that's one more RnD to cut...

Boeing did at one time considered a Mach 1 SST using "usual modern low" bypass ratio turbofan (the sort of ratios you get at fuselage-mounted engines near tails and things like B737 and A320 family); but ofc you need to fly long routes that way to ensure that passengers enjoy the travel time cut wrt ticket price !

DISCLAIMER : I am NOT in any way an aerodynamic engineer ! So I have no idea at all how far things are.

My (slightly educated) guess is that the limit is a thermal one, rather than anything inherently limiting with the concept of HB turbofans. The turbine blades on a commercial airliner are already a marvel of materials science, aerodynamic development and structural engineering, and can (and often do) operate above the melting point of the material they're made out of; and that's at airline speeds. I imagine that if you tried to push one further than slightly supersonic (for the sake of argument let's say higher than about Mach 1.2) you'd just end up with a casing full of molten metal. There's nothing to say you couldn't design a HB engine to work at higher speeds, but if you're going to go through all the trouble of doing that, why not just design a LB engine instead, which will have a far greater specific thrust (i.e thrust per unit mass), far less complex internal and only a marginal decrease in efficiency (not to mention significantly less R&D than trying to design a HB Mach 2 engine)

Link to comment
Share on other sites

14 hours ago, Steel said:

My (slightly educated) guess is that the limit is a thermal one, rather than anything inherently limiting with the concept of HB turbofans. The turbine blades on a commercial airliner are already a marvel of materials science, aerodynamic development and structural engineering, and can (and often do) operate above the melting point of the material they're made out of; and that's at airline speeds. I imagine that if you tried to push one further than slightly supersonic (for the sake of argument let's say higher than about Mach 1.2) you'd just end up with a casing full of molten metal.

Hmm... interesting... but why ? Is it because of the more confined space of HB engine's turbine at a specific overall diameter (compared to LB engines) ? I mean, say on a B737, CFM LEAP vs the predecessor CFM56 (or the even older JT8D), I know LEAP's combustion turbines are really, really small, yet they produce around the same thrust (even without the fan, say), but it's interesting. I do believe that the way forward would be to actually use some higher bypass ratios, because otherwise it seems that economical supersonic flights will never be in the game.

Edited by YNM
Link to comment
Share on other sites

15 hours ago, Steel said:

 

My (slightly educated) guess is that the limit is a thermal one, rather than anything inherently limiting with the concept of HB turbofans. The turbine blades on a commercial airliner are already a marvel of materials science, aerodynamic development and structural engineering, and can (and often do) operate above the melting point of the material they're made out of; and that's at airline speeds. I imagine that if you tried to push one further than slightly supersonic (for the sake of argument let's say higher than about Mach 1.2) you'd just end up with a casing full of molten metal. There's nothing to say you couldn't design a HB engine to work at higher speeds, but if you're going to go through all the trouble of doing that, why not just design a LB engine instead, which will have a far greater specific thrust (i.e thrust per unit mass), far less complex internal and only a marginal decrease in efficiency (not to mention significantly less R&D than trying to design a HB Mach 2 engine)

The thermal issue is the turbine blades behind the burn chamber, they use air cooling to cool them, air passes into the blades from the hub and out on the back or front of blade. 
This is done on all advanced jet engines. 
An issue with turbofans at high speed is probably that you don't want the tip of the fan blades to break the sound barrier. This limit speed of turboprop and imagine it will restrict fans at high speed even if you reduce airspeed inside the engine you loose lots of the benefit. 
Not sure how multiple smaller fans would work out, you would probably have to run them electrical and use the engine to generate power. 

Link to comment
Share on other sites

Sadly the tread is for maximum fuel economy. Business class is simply too expensive for the vast majority of us (my dad flew Concorde once, back when he was commuting to work in the UK from our home in Connecticut, and some airline strike or another delayed him, so "he" (his company, lol) ponied up the cash for Concorde to get home for the weekend).

What's worse is that flights are longer now than when I was a kid for this reason. Trends are really all going the wrong way, as composite aircraft can be pressurized to lower altitude and greater humidity, allowing more comfort for the now slower, more economical flights. I'm not saying that SSTs won't be a thing again, but for most of us it will be farther away than walking past the elite in the front of the plane now, with their glasses of champagne and dancing girls (they have dancing girls up front, right?).

Link to comment
Share on other sites

9 minutes ago, tater said:

Sadly the tread is for maximum fuel economy. Business class is simply too expensive for the vast majority of us (my dad flew Concorde once, back when he was commuting to work in the UK from our home in Connecticut, and some airline strike or another delayed him, so "he" (his company, lol) ponied up the cash for Concorde to get home for the weekend).

What's worse is that flights are longer now than when I was a kid for this reason. Trends are really all going the wrong way, as composite aircraft can be pressurized to lower altitude and greater humidity, allowing more comfort for the now slower, more economical flights. I'm not saying that SSTs won't be a thing again, but for most of us it will be farther away than walking past the elite in the front of the plane now, with their glasses of champagne and dancing girls (they have dancing girls up front, right?).

Checked the prices some time ago, business class tend to be 3x more expensive than coach on intercontinental, it make sense as you take up far more space. This is just for the seat, an common feature with business tickets is flexibility in that you can cancel the flight right up to departure and this add an huge overhead on the already expensive ticket. 

However for the majority its too much money, you rater sit uncomfortable for some hours and save the money. The slower travel speed is also an effect of the price focus. 
Its also an increased focus on direct flights who tend to save a lot of time, also issues for airliners, who get the multiple jump logistic. 
This is also an issue for an supersonic flight who would be all first class, Say you want to go from Berlin to Miami, you can either take an direct flight or jump to pairs or London, supersonic to new York then new flight to Miami as the supersonic only cover the most popular routes. I guess the direct would be just as fast and far less stressful.    

And the best thing who has happened with air flight is the on demand video, just zoning out and watch cartoons for most of the trip :)

Link to comment
Share on other sites

Yeah, my daughter did a Marvel movie fest last summer from the US to Milano. I watched a series of different things. I should have just gotten wifi and posted nonstop here, lol.

Link to comment
Share on other sites

3 hours ago, magnemoe said:

An issue with turbofans at high speed is probably that you don't want the tip of the fan blades to break the sound barrier. This limit speed of turboprop and imagine it will restrict fans at high speed even if you reduce airspeed inside the engine you loose lots of the benefit. 
Not sure how multiple smaller fans would work out, you would probably have to run them electrical and use the engine to generate power. 

Surprisingly the fan blade tips on a typical commercial HB engine are supersonic in standard cruise conditions, so that's not a hard limit. The faster you go the less efficient the engine will become, but its less of a problem than you'd imagine. The fact that they are shrouded (unlike a prop) means that a lot of the problems that traditional propellers run into (shockwaves diverting airflow around the prop, excessive noise e.t.c) are largely avoided.

Edited by Steel
Link to comment
Share on other sites

4 hours ago, tater said:

What's worse is that flights are longer now than when I was a kid for this reason. Trends are really all going the wrong way, as composite aircraft can be pressurized to lower altitude and greater humidity, allowing more comfort for the now slower, more economical flights. I'm not saying that SSTs won't be a thing again, but for most of us it will be farther away than walking past the elite in the front of the plane now, with their glasses of champagne and dancing girls (they have dancing girls up front, right?).

It is all a matter of perspective... I once sailed a sailboat from Maine to Barcelona via the Azores. We were 17 days underway from Maine to Horta and another 14 days from there to Barcelona. I flew home, crossing not just the Atlantic but also the entire North American continent in a little over 20 hours, door to door. Trust me, that flight felt immensely fast.

Link to comment
Share on other sites

11 hours ago, magnemoe said:

However for the majority its too much money, you rater sit uncomfortable for some hours and save the money.

If you actually have business where you are going, business class is well worth it. You arrive feeling rested and ready to go.

Are there any limitation to usage of high-bypass ratio turbofan in supersonic aircrafts ?

The answer to this is propulsive efficiency.

Propellers have their highest propulsive efficiency when the airplane is moving slowly. Jets have their highest propulsive efficiency when the airplane is moving at nearly the same speed as the exhaust jet velocity. Turbofans work something like a blend between a propeller and a jet.

So the faster you are going, the more you want a pure jet rather than a turbofan.

Here's a picture from wikipedia that shows this idea.

Gas_turbine_efficiency.png

Edited by mikegarrison
Link to comment
Share on other sites

13 hours ago, magnemoe said:

An issue with turbofans at high speed is probably that you don't want the tip of the fan blades to break the sound barrier. This limit speed of turboprop and imagine it will restrict fans at high speed even if you reduce airspeed inside the engine you loose lots of the benefit. 
Not sure how multiple smaller fans would work out, you would probably have to run them electrical and use the engine to generate power. 

Geared fans ? Now the highest bypass ratio engines (the PW1100G I found so far) uses those to achieve a bypass ratio of 12.5 : 1 .

1 hour ago, mikegarrison said:

Propellers have their highest propulsive efficiency when the airplane is moving slowly. Jets have their highest propulsive efficiency when the airplane is moving at nearly the same speed as the exhaust jet velocity. Turbofans work something like a blend between a propeller and a jet.

So the faster you are going, the more you want a pure jet rather than a turbofan.

Here's a picture from wikipedia that shows this idea.

Gas_turbine_efficiency.png

Ah...

Well, in that case, it'll be a hard job then...

Yeah, better go back sleeping the flight in some flat-folding seat.

Edited by YNM
Link to comment
Share on other sites

1 hour ago, mikegarrison said:

If you actually have business where you are going, business class is well worth it. You arrive feeling rested and ready to go.

The answer to this is propulsive efficiency.

Propellers have their highest propulsive efficiency when the airplane is moving slowly. Jets have their highest propulsive efficiency when the airplane is moving at nearly the same speed as the exhaust jet velocity. Turbofans work something like a blend between a propeller and a jet.

So the faster you are going, the more you want a pure jet rather than a turbofan.

Here's a picture from wikipedia that shows this idea.

Gas_turbine_efficiency.png

Ok so supersonic you want an pure turbojet. 

And yes, you don't want to show up as an zombie, only done regional flights for business here the main issue is how early you have to show up. 
Fun in that many seasoned business traveler on that route take an sleeper train, you sleep while traveling and is ready to go, travel to airport and airport actions take longer time as the flight. 
For me I can not sleep sitting, that is unless I'm dead tired as in has not sleep for 40 hours, think very drunk. Laying down and its no issue. 

Link to comment
Share on other sites

6 hours ago, YNM said:

Well, in that case, it'll be a hard job then...

Now keep in mind, propulsive efficiency isn't everything. It's only one of many parts of the overall efficiency.

But yeah, it's very hard to make supersonic flight fuel efficient. And it's extremely hard to make the same airplane and engine efficient in landing and takeoff as well as supersonic cruise. Variable engine cycles would help. The SR-71 has a famously complicated variable engine cycle, but even so it wasn't especially fuel efficient. Very fast, though.

I think most of the supersonic proposals floating around now use low-bypass turbofans.

6 hours ago, magnemoe said:

And yes, you don't want to show up as an zombie, only done regional flights for business here the main issue is how early you have to show up. 
Fun in that many seasoned business traveler on that route take an sleeper train, you sleep while traveling and is ready to go, travel to airport and airport actions take longer time as the flight. 
For me I can not sleep sitting, that is unless I'm dead tired as in has not sleep for 40 hours, think very drunk. Laying down and its no issue. 

I have flown from Seattle to Europe in business class "lie flat" pods, deeply reclining seats, and regular coach seats. Being able to lie down and sleep on the trip to Europe makes a huge amount of difference for at least a day or two after. I also flew first class one time, and while it was more comfortable than business class, it wasn't otherwise much different.

Coming home from Europe, I tend to stay awake for the flight. (It's a time zone issue.) So there it's more of just a general comfort question than an ability to sleep question.

And some of the other business class perks are nice too, like using the airline lounges and fast-pass lines for customs, security, check-in, etc.

Link to comment
Share on other sites

I wonder if something like a propfan would work for this. LB turbojet core, variable-pitch geared pusher prop in the back of the engine cowling. The propfan would give it good takeoff and landing efficiency at low speeds, but would be windmilled or simply fixed at high speeds. Or folded back completely.

Link to comment
Share on other sites

2 hours ago, sevenperforce said:

I wonder if something like a propfan would work for this. LB turbojet core, variable-pitch geared pusher prop in the back of the engine cowling. The propfan would give it good takeoff and landing efficiency at low speeds, but would be windmilled or simply fixed at high speeds. Or folded back completely.

That's a variable cycle, like I mentioned before. But it's hard to see how it would work. Feathered props certainly aren't dragless, and now they would be stuck out in a supersonic airflow as well.

Link to comment
Share on other sites

42 minutes ago, mikegarrison said:

That's a variable cycle, like I mentioned before. But it's hard to see how it would work. Feathered props certainly aren't dragless, and now they would be stuck out in a supersonic airflow as well.

Hence folding back. Maybe all the way into a cowling.

Link to comment
Share on other sites

This thread is quite old. Please consider starting a new thread rather than reviving this one.

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...