Mach 0.95 Boeings...
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Mach 0.95 Boeings...
Questions, questions, questions...
Ok, so I'm sceptical about the strategic direction that Boeing is taking, but I have to admit they must have great engineers on the case, so the project must be feasible. I'm basing all these questions on the artists impression of the delta-winged wonder, issued by Boeing:
i. How is Boeing going to stop the airflow going supersonic around critical areas such as the engine nacelles, etc, etc?
ii. If they can't, would limited areas of supersonic airflow still create a sonic boom?
iii. I've always understood that delta-winged aircraft require higher take-off speeds (i.e. after-burner augmented take-offs for Concorde). Does Boeing have the same issue to resolve?
iv. Ditto for landing speeds?
v. Is such a design stretchable? Contractable?
vi. Why the SR71-style engine nacelles?
Any ideas?
TW
Ok, so I'm sceptical about the strategic direction that Boeing is taking, but I have to admit they must have great engineers on the case, so the project must be feasible. I'm basing all these questions on the artists impression of the delta-winged wonder, issued by Boeing:
i. How is Boeing going to stop the airflow going supersonic around critical areas such as the engine nacelles, etc, etc?
ii. If they can't, would limited areas of supersonic airflow still create a sonic boom?
iii. I've always understood that delta-winged aircraft require higher take-off speeds (i.e. after-burner augmented take-offs for Concorde). Does Boeing have the same issue to resolve?
iv. Ditto for landing speeds?
v. Is such a design stretchable? Contractable?
vi. Why the SR71-style engine nacelles?
Any ideas?
TW
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Don't have the answers TW but the initial pictures remind me of the work that both NASA & Boeing were doing on the TU-144. Especially the Canard designed shown in the pictures.
http://www.lerc.nasa.gov/WWW/HSR/9608.htm
http://www.lerc.nasa.gov/WWW/HSR/9608.htm
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Tricky Woo,
Aircraft with delta shaped wings do have higher V speeds, Boeing will have to overcome this with leading and trailing edge devices.
Engine inlet design is a bit of a black art, but the main idea is to present the airflow in a predictable and uniform manor to the engine at subsonic speed. It is necessary to slow the airflow down going into a turbofan/turbojet engine so that the flame stays in the combustion chamber.
The cone of the SR-71 engine intake sets up a shockwave at the right location and presents the engine with downstream axial flow in a controlled direction and subsonic airspeed.
The shockwave that is deliberately induced forms what is known as a choked nozzle and delivers a set about of air mass in a consistent direction through the shockwave regardless what supersonic airspeed the airframe is doing.
Aircraft with delta shaped wings do have higher V speeds, Boeing will have to overcome this with leading and trailing edge devices.
Engine inlet design is a bit of a black art, but the main idea is to present the airflow in a predictable and uniform manor to the engine at subsonic speed. It is necessary to slow the airflow down going into a turbofan/turbojet engine so that the flame stays in the combustion chamber.
The cone of the SR-71 engine intake sets up a shockwave at the right location and presents the engine with downstream axial flow in a controlled direction and subsonic airspeed.
The shockwave that is deliberately induced forms what is known as a choked nozzle and delivers a set about of air mass in a consistent direction through the shockwave regardless what supersonic airspeed the airframe is doing.
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From the pictures, one can notice the twin tail-fin design, presumably for a twin rudder system; so should a set of rudder PCUs go berserk, the other side would at least be able to counteract the failure in some way.
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lazybones,
Exactly my thoughts when I first saw the picture. That's why I think this is really going to happen.
Zeke,
Thanks for all that.
I guess that the fancy lift devices are going to add plenty of weight.
I've read before that the air flowing into a turbojet (or turbofan) must be slowed to subsonic speeds. I never knew why, until now.
I seem to remember that the cone-shaped nozzle on the SR71 is adjustable, fore and aft, to allow the position of the shockwave to be matched against the airspeed. True?
Seeing as the SR71 was designed to accelerate to, and cruise at, Mach 3, why has Boeing shoved similar intakes onto their 'almost sonic' design? Something pretty that the artist thought up? Or an important part of the design?
Exactly my thoughts when I first saw the picture. That's why I think this is really going to happen.
Zeke,
Thanks for all that.
I guess that the fancy lift devices are going to add plenty of weight.
I've read before that the air flowing into a turbojet (or turbofan) must be slowed to subsonic speeds. I never knew why, until now.
I seem to remember that the cone-shaped nozzle on the SR71 is adjustable, fore and aft, to allow the position of the shockwave to be matched against the airspeed. True?
Seeing as the SR71 was designed to accelerate to, and cruise at, Mach 3, why has Boeing shoved similar intakes onto their 'almost sonic' design? Something pretty that the artist thought up? Or an important part of the design?
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Tricky Woo,
Yes, true.
To quote the Aviation Week & Space Technology interview with Michael B. Bair, Boeing Commercial Airplanes vice president for business strategy and development, he said
From an aerodynamics point of view if the airflow has been accelerated in some way via duct or over the wing it may be supersonic flow and require some form of shock to be created to limit the air into the engine.
Seems like a marketing think to me, little efficiency gained for a whole lot of work.
<font face="Verdana, Arial, Helvetica" size="2">I seem to remember that the cone-shaped nozzle on the SR71 is adjustable, fore and aft, to allow the position of the shockwave to be matched against the airspeed. True?</font>
<font face="Verdana, Arial, Helvetica" size="2">Seeing as the SR71 was designed to accelerate to, and cruise at, Mach 3, why has Boeing shoved similar intakes onto their 'almost sonic' design? Something pretty that the artist thought up? Or an important part of the design?</font>
<font face="Verdana, Arial, Helvetica" size="2"> To keep noise down, the fan and core exhaust will be mixed before exiting, and the inlet has a long duct to suppress fan noise. "The fan face can't be seen," Bair said, making the sonic cruiser appear as if it has taken stealth lessons from military aircraft (AW&STMar. 19, p. 92). Indeed, Boeing claims the design draws from military aircraft such as the F-22.</font>
Seems like a marketing think to me, little efficiency gained for a whole lot of work.
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So it all seems possible Tricky BUT:-
Will Joe Public really be interested?? Given the high development cost of this project. Operators will expect to pay more for this aircraft, and the operational cost will probably be higher. And at the end of the day you'll be getting a 10% speed increase for a probably higher than 10% ticket price. Will the average flyer really go for this??
Will Joe Public really be interested?? Given the high development cost of this project. Operators will expect to pay more for this aircraft, and the operational cost will probably be higher. And at the end of the day you'll be getting a 10% speed increase for a probably higher than 10% ticket price. Will the average flyer really go for this??
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lazybones,
I am indeed extremely cynical as to the commercial viability of this aircraft. (I think that Boeing has rather lost the plot). However, the reason I created this thread was to question the technical viability. It's an interesting concept, in itself.
The answer so far is that the aircraft may well be technically viable... although there's an awful lot of lose ends.
Can anyone answer my earlier question as to whether localised hotspots of supersonic flow, here and there, would create sonic booms?
I am indeed extremely cynical as to the commercial viability of this aircraft. (I think that Boeing has rather lost the plot). However, the reason I created this thread was to question the technical viability. It's an interesting concept, in itself.
The answer so far is that the aircraft may well be technically viable... although there's an awful lot of lose ends.
Can anyone answer my earlier question as to whether localised hotspots of supersonic flow, here and there, would create sonic booms?
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All said about sonic boom, shock waves, and higher v speeds (therby requirement for longer runways) are correct. But to make the project Technically feasible boeing has to count on new fuel technologies as wingtanks fuel capacity does not seem to be sufficient for longrange based on todays engine fuel consumption especially at high compressability effects. Also I reckon that the canards may be helpful in slightly reducing v speeds but are going to give them heck of a problem while Taxing in to the gate and the jetty operation. One solution could be a retractable canard at the cost of higher empty weight. As far as Economic feasibility is concerened, I am no specialist but I have serious doubts. I hope Boeing or the Americans in general dont try to envisage it as a national pride like the concorde people did ( I am sure they still don't admit its economic inviability).
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Why go with a canard?
I seem to remember that one advantage of a canard configuration is that both surfaces generate upward lift components, whereas in a conventionally winged aircraft the wing and the tail are generating lift components against each other. Presumably, there's some reduction in drag available from this?
Enough to justify all other complexities the canard configuration introduces?
Are there any other advantages to the canard configuration that I'm missing?
I seem to remember that one advantage of a canard configuration is that both surfaces generate upward lift components, whereas in a conventionally winged aircraft the wing and the tail are generating lift components against each other. Presumably, there's some reduction in drag available from this?
Enough to justify all other complexities the canard configuration introduces?
Are there any other advantages to the canard configuration that I'm missing?
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Couple of points here.
First, with regard to "sections going supersonic so creating a shockwave", it might surprise you to learn that the supercritical airfoils used on the newer Airbus and the B-777 do just that, intentionally creating supersonic flow over the entire wing to "just move past" the high drag rise in the transonic region. Bit more complex than that, but I think that gives you the idea.
On the canard issue, I am a bit surprised that they are going that direction as well. I am curious to the advantages they found. The CG issues are fairly great for starters. It appears that the canard and wing in their design is not close-coupled, so the adverse effect of the canard creating downwash inboard and upwash outboard on the main wing would be minimized, but another aspect is that for high speed aircraft the thin aerfoils required on the canard could lead to a nasty leading edge stall. If this were to happen it could result in a rapid pitch rate change -- even possible to get an aircraft to tumble end over end as a result. Passengers take a dim view of this sort of antic.
The other advantages of canards would be positive lift from the horizontal stab, but this is really a non-issue in augmented stability aircraft, where we can have that situation in conventional design anyhow. The other operational advantage is eliminating pitch transients, but I don't think Boeing envisions the need for rapid pitch changes to avoid enemy fire in this aircraft!
So, I am curious about the choice of canards also.
[This message has been edited by Prof2MDA (edited 04 April 2001).]
First, with regard to "sections going supersonic so creating a shockwave", it might surprise you to learn that the supercritical airfoils used on the newer Airbus and the B-777 do just that, intentionally creating supersonic flow over the entire wing to "just move past" the high drag rise in the transonic region. Bit more complex than that, but I think that gives you the idea.
On the canard issue, I am a bit surprised that they are going that direction as well. I am curious to the advantages they found. The CG issues are fairly great for starters. It appears that the canard and wing in their design is not close-coupled, so the adverse effect of the canard creating downwash inboard and upwash outboard on the main wing would be minimized, but another aspect is that for high speed aircraft the thin aerfoils required on the canard could lead to a nasty leading edge stall. If this were to happen it could result in a rapid pitch rate change -- even possible to get an aircraft to tumble end over end as a result. Passengers take a dim view of this sort of antic.
The other advantages of canards would be positive lift from the horizontal stab, but this is really a non-issue in augmented stability aircraft, where we can have that situation in conventional design anyhow. The other operational advantage is eliminating pitch transients, but I don't think Boeing envisions the need for rapid pitch changes to avoid enemy fire in this aircraft!
So, I am curious about the choice of canards also.
[This message has been edited by Prof2MDA (edited 04 April 2001).]
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The inner wing portion of the sonic cruiser appears to be a slender delta. At high AoA on the approach, vortices shed from the canard will have a beneficial effect on Cl over this portion. Ask Sven-the-Viggen!!
And anyway, it looks just the business!!
And anyway, it looks just the business!!
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I must admit that I have a very limeted knowlede of Aeronautical engineering, bbut many years of plying around with flight simulator have led me to wonder:
i) If the plane is supposed to fly 9,000 miles, where are they going to get the fuel from? the design i've seen doesnt seem to have the space for fuel when you take baggage/cargo hold and PAX into account
ii)Without being too cynical, this looks a lot like a scaled down version of the boeing SST of the 60's. does anyone else think it will be the same?
iii) I thought the 747 and (really old) coronados could do this speed?
i) If the plane is supposed to fly 9,000 miles, where are they going to get the fuel from? the design i've seen doesnt seem to have the space for fuel when you take baggage/cargo hold and PAX into account
ii)Without being too cynical, this looks a lot like a scaled down version of the boeing SST of the 60's. does anyone else think it will be the same?
iii) I thought the 747 and (really old) coronados could do this speed?
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I stand by my original statement on the vorticies negative effects, however I think the coupling is long enough for it not to be a big issue.
Since my earlier post I got a chance to look again at the concept picture. I think now that the canard design is to take maximum advantage of the Area Rule.
Since my earlier post I got a chance to look again at the concept picture. I think now that the canard design is to take maximum advantage of the Area Rule.
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Tricky Woo,
There are some aspects of canards that that have already been mentioned by Prof2MDA, but I have to disagree with Beagle with his comments.
There are several attractive features of a canard surface. The canard, if properly positioned, is free from interference from the wing or the engines (unlike a conventional tail plane). Canard control is more attractive for trimming the large nose-down moment produced by high-lift devices. To counteract the nose-down pitching moment, the canard must produce lift which will add to the lift being developed by the wing, a conventional tail plane produces a down load to counteract the pitching moment, or as many aircraft do they pump fuel to the tail plane to change the CG location to minimize the amount of down load required.
They must be designed so they stall before the wing. This is normally done by the selection of aerofoil section (this effects Clmax), and the angle of incidence. When the canard stalls it produces a nose down pitching moment, and the downwash at the wing also disappears so the lift on the wing increases, the wing center of pressure moves forward and this also gives a nose down pitching moment. The hard bit is making sure this occurs at all airspeeds, control deflections, cg locations, and flap configurations.
Normally the flow over the canard has to be made turbulent as it has a short chord a laminar flow canard would uncontrollably go turbulent when it encountered ice or rain, so it is better do design it to be turbulent from the scratch.
To quote the AW&ST article again
it would seem Boeing are going for the variable incidence canard.
If Boeing decides to employ a variable incidence canard with elevator on it, the stall (i.e. exceeding the critical angle of attack) will be a function of the trim (cg location) which is undesirable but controllable with a fly by wire system. The variable incidence canard used primarily for longitudinal control and the aircrafts flight control system is able to predict the impending stall scenario and prevent the pilot from entering this regime. This may require Boeing to come up with a new flight control law called “canard alpha protection”, if I was in the aircraft when one of the flight control computers or hydraulic systems controlling the canard developed the fault I would be very worried (if it employed variable incidence canard). There is no doubt that this aircraft would need a full fly by wire system with little chance any direct mechanical backup as found on previous Boeings.
The disadvantages of a canard is that it produces a destabilizing contribution to the aircrafts static stability. The canard also interferes with the span wise lift distribution on the main wing, which has its most dramatic effect on wing stall, which can induce wing tip stall in an extreme case.
The canard downwash and trailing tip vortices cause in increase in induced drag as the it causes a deviation from the elliptical span wise loading of the lift distribution. For those who remember Cd=Cdo+k*Cl^2, where k=1/(pi*e*AR), where AR is the wing aspect ratio, and e is Oswald’s efficiency factor (also know as span efficiency factor), the efficiency of the lift distribution compared to the theoretically efficient elliptical span wise loading, and also effects the efficiency of the wing structure to get a gradual and constant increase in bending moment.
The Beech Starship overcame these issues with inefficiencies caused by the downward of the canard by adding and removing camber to the wing. Camber was added where the trailing vortex had a negative effect on the wing lift (this was done for a small distance parallel to the tip of the canard on the wing towards the wing root), and camber was removed from the wing for a small distance from distance of the tip of the canard outboard along the wing (to visualize this looking from behind the aircraft, the vortices off the canard are in a clockwise direction on the port side, and anti-clockwise direction on the starboard side).
As you can imagine this lead to a number of inefficiencies in the structural design of the wing, how Boeing is going to overcome these problems as well as the transonic drag rise is unknown.
Prof2MDA I would have thought it be prudent to reduce the fuselage cross section at the canard to minimize drag using the area rule ?
There are some aspects of canards that that have already been mentioned by Prof2MDA, but I have to disagree with Beagle with his comments.
There are several attractive features of a canard surface. The canard, if properly positioned, is free from interference from the wing or the engines (unlike a conventional tail plane). Canard control is more attractive for trimming the large nose-down moment produced by high-lift devices. To counteract the nose-down pitching moment, the canard must produce lift which will add to the lift being developed by the wing, a conventional tail plane produces a down load to counteract the pitching moment, or as many aircraft do they pump fuel to the tail plane to change the CG location to minimize the amount of down load required.
They must be designed so they stall before the wing. This is normally done by the selection of aerofoil section (this effects Clmax), and the angle of incidence. When the canard stalls it produces a nose down pitching moment, and the downwash at the wing also disappears so the lift on the wing increases, the wing center of pressure moves forward and this also gives a nose down pitching moment. The hard bit is making sure this occurs at all airspeeds, control deflections, cg locations, and flap configurations.
Normally the flow over the canard has to be made turbulent as it has a short chord a laminar flow canard would uncontrollably go turbulent when it encountered ice or rain, so it is better do design it to be turbulent from the scratch.
To quote the AW&ST article again
<font face="Verdana, Arial, Helvetica" size="2"> A classic difficulty with canards is that the wing fuel is so far aft, causing a large center-of-gravity (CG) shift as it burns off. This is at least partly compensated by placing fuel farther forward in the glove. There is no fuel in the canard or fuselage, Bair said. "It requires different CG management than a conventional airplane but computers are wonderful," he said. As the flight progresses, the canard will carry a greater fraction of a lesser load, causing handling shifts that should be manageable with a fly-by-wire system.</font>
If Boeing decides to employ a variable incidence canard with elevator on it, the stall (i.e. exceeding the critical angle of attack) will be a function of the trim (cg location) which is undesirable but controllable with a fly by wire system. The variable incidence canard used primarily for longitudinal control and the aircrafts flight control system is able to predict the impending stall scenario and prevent the pilot from entering this regime. This may require Boeing to come up with a new flight control law called “canard alpha protection”, if I was in the aircraft when one of the flight control computers or hydraulic systems controlling the canard developed the fault I would be very worried (if it employed variable incidence canard). There is no doubt that this aircraft would need a full fly by wire system with little chance any direct mechanical backup as found on previous Boeings.
The disadvantages of a canard is that it produces a destabilizing contribution to the aircrafts static stability. The canard also interferes with the span wise lift distribution on the main wing, which has its most dramatic effect on wing stall, which can induce wing tip stall in an extreme case.
The canard downwash and trailing tip vortices cause in increase in induced drag as the it causes a deviation from the elliptical span wise loading of the lift distribution. For those who remember Cd=Cdo+k*Cl^2, where k=1/(pi*e*AR), where AR is the wing aspect ratio, and e is Oswald’s efficiency factor (also know as span efficiency factor), the efficiency of the lift distribution compared to the theoretically efficient elliptical span wise loading, and also effects the efficiency of the wing structure to get a gradual and constant increase in bending moment.
The Beech Starship overcame these issues with inefficiencies caused by the downward of the canard by adding and removing camber to the wing. Camber was added where the trailing vortex had a negative effect on the wing lift (this was done for a small distance parallel to the tip of the canard on the wing towards the wing root), and camber was removed from the wing for a small distance from distance of the tip of the canard outboard along the wing (to visualize this looking from behind the aircraft, the vortices off the canard are in a clockwise direction on the port side, and anti-clockwise direction on the starboard side).
As you can imagine this lead to a number of inefficiencies in the structural design of the wing, how Boeing is going to overcome these problems as well as the transonic drag rise is unknown.
Prof2MDA I would have thought it be prudent to reduce the fuselage cross section at the canard to minimize drag using the area rule ?
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Just to add my few cents worth here, to the hypothetical scenario.
The piccie is somewhat an artist's impression and is, I will agree, very pretty. But it is more "Star Wars" than practicality. Those canards are really in the way - but it doesn't really look right without them. However more on that later.
The biggest single objection to a canard config in a civil airliner is practical rather than aerodynamic. That LH canard is going to have to be an articulated unit (retract or fold) to have any chance of a normal airbridge engagement. What price a "folding wing"?
The area ruling is totally stuffed with the proposed fuselage format. If Mr B is looking for a 0.95 cruiser then most of the local airflow is going to be transonic at best and with a huge great lump in the "area" just abaft the nose section life in the cruise end of the pond is going to be very draggy.
I agree on all the points about the downflow interference and I can see that the canard wings will probably have little work in the cruise segment and will probably be "feathered" - leaving conventional aft surfaces to do the work. The inference about trim changes are mute, since there is a lot of wing there for fuel and any canny design should be able to effectively reduce time/ burn trim variations to zero.
So we are left with a single wing - probably reflexed (in good delta tradition) doing all of the work in the climb / cruise / descent portions. However the sheer scale (and inertia) of the (proposed) beast suggests that some form of pitch enhancement may well be needed at the lower IAS end to provide pitch authority.
All the newer B aircraft utilise (in some form or other) the concept of fuselage lift at the higher alphas. This is powerfull stuff - draggy, but stable (see flat plate).
As an aside, I have done a little work on this (at the flying modelling end to be sure), but I can attest to the fact that a little bit of turbulence, well forward, at the right time, can modulate the pitch wonderfully on a flat bottomed fuselage.
My take on this is that the canards may well be there, but they will be in the expanding area nose portion and very small. Little prehensile thingies really. We shall see.
I personally doubt that this baby will ever see the light at end of any tunnel. Pity really - she is soooo pretty.
MG
The piccie is somewhat an artist's impression and is, I will agree, very pretty. But it is more "Star Wars" than practicality. Those canards are really in the way - but it doesn't really look right without them. However more on that later.
The biggest single objection to a canard config in a civil airliner is practical rather than aerodynamic. That LH canard is going to have to be an articulated unit (retract or fold) to have any chance of a normal airbridge engagement. What price a "folding wing"?
The area ruling is totally stuffed with the proposed fuselage format. If Mr B is looking for a 0.95 cruiser then most of the local airflow is going to be transonic at best and with a huge great lump in the "area" just abaft the nose section life in the cruise end of the pond is going to be very draggy.
I agree on all the points about the downflow interference and I can see that the canard wings will probably have little work in the cruise segment and will probably be "feathered" - leaving conventional aft surfaces to do the work. The inference about trim changes are mute, since there is a lot of wing there for fuel and any canny design should be able to effectively reduce time/ burn trim variations to zero.
So we are left with a single wing - probably reflexed (in good delta tradition) doing all of the work in the climb / cruise / descent portions. However the sheer scale (and inertia) of the (proposed) beast suggests that some form of pitch enhancement may well be needed at the lower IAS end to provide pitch authority.
All the newer B aircraft utilise (in some form or other) the concept of fuselage lift at the higher alphas. This is powerfull stuff - draggy, but stable (see flat plate).
As an aside, I have done a little work on this (at the flying modelling end to be sure), but I can attest to the fact that a little bit of turbulence, well forward, at the right time, can modulate the pitch wonderfully on a flat bottomed fuselage.
My take on this is that the canards may well be there, but they will be in the expanding area nose portion and very small. Little prehensile thingies really. We shall see.
I personally doubt that this baby will ever see the light at end of any tunnel. Pity really - she is soooo pretty.
MG
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MasterGreen,
Maybe Boeing learnt something from the Russians when Boeing and NASA borrowed a TU-144 from the Tupolev design bureau.
The TU-144 had retractable canards, with a maximum speed with canards deployed of 250 knots.
But the ones on the Boeing look a little big to retract.
Maybe Boeing learnt something from the Russians when Boeing and NASA borrowed a TU-144 from the Tupolev design bureau.
The TU-144 had retractable canards, with a maximum speed with canards deployed of 250 knots.
But the ones on the Boeing look a little big to retract.
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Zeke,
If you look at the pictures, the fuselage has some taper in the area of the wings, and is just beginning to taper in the area of the canard, so there you get some coke-bottling at those points. I read the AWST article last night and noticed it pointed out that facet as well, although the author did not seem to think that the area in the canard was smaller at all. From looking at the drawing it appears to me that it is, but hard to say for sure.
If you look at the pictures, the fuselage has some taper in the area of the wings, and is just beginning to taper in the area of the canard, so there you get some coke-bottling at those points. I read the AWST article last night and noticed it pointed out that facet as well, although the author did not seem to think that the area in the canard was smaller at all. From looking at the drawing it appears to me that it is, but hard to say for sure.