supersonic no more

[peekay4]

How is Aerion overcoming this problem which is inherent to that configuration?

A few years before the X-3 even flew, a NACA engineer by the name of William Phillips had theorized the possibly of inertial roll coupling, provided precise mathematical equations of the phenomenon, and even devised solutions to the problem if it were ever to occur in practice (which of course it did).

I believe part of the solution is to increase pitch and yaw stability by having a larger tail. Stability augmentation (similar to a yaw damper) can also be used.

[tdracer]

Originally Posted by n5296s

The Aerion is real enough - a friend of mine, one of my instructors, is a senior engineer on the project. Lots of interesting stories... (not to be repeated here I'm afraid).

Don't misunderstand my skepticism. I have no doubt that Aerion is working on this project. What I question is if it will ultimately result in a certified commercial product.
There have been a lot of new aircraft projects that failed to make it past the prototype phase (many didn't even make it that far - including the Boeing SST). The cost and regulatory challenges to a supersonic commercial aircraft are massive. As I've noted the changes to the FAR and JAR/CS since the 1970s will make it incredibly difficult to certify a supersonic capable bis jet.

[G-CPTN]

The company claims 50 letters-of-intent from customers, each with a $250,000 deposit.

[KenV]

We've had unstable aircraft with computer-controlled control surfaces for over 40 years, the inherent inertia coupling tendencies will be controlled by that same philosophy.

This is not the same as aerodynamic instability. This is an inertial instability. It is caused by forces of a rotating mass overpowering the forces of an aerodynamic surface. No amount of computer sophistication can overcome this instability. The aerodynamic control surfaces must be enlarged. Further, look at any relaxed stability aircraft and you will see large control surfaces. Software alone cannot generate the large forces required to maintain control. The software needs powerful control surfaces to work with. Those do not appear to be present on the Aerion AS2.

[KenV]

Then there was the Lockheed Starfighter.

Indeed. The Starfighter's wing is (roughly) based on the X-3's wing. Lockheed learned much from the X-3 so that the Starfighter had MUCH larger tail surfaces than the X-3 AND it had a ventral strake for additional aero authority. All this appears to be absent on the Aerion AS2.

[megan]

It is generally recognised that coupling can be ameliorated by,

1. increased directional stability
2. reducing dihedral effect
3. minimising the inclination of the inertia axis at normal flight conditions
4. reducing undesirable aerodynamic coupling
5. limiting roll rate, roll duration, and angle of attack or load factor for performing roll manoeuvres

The typical high speed aircraft has some sort of roll performance limitation by flight restrictions or automatic control device to prevent reaching some critical condition from which recovery is impossible.

I can't think of any manoeuvre on an aircraft such as this where coupling could be an issue, and assume modern flight control computer systems would look after point (5). They won't be doing twinkle rolls. With Airbus part of the team, whatever is the product produced I'm sure you could take it to the bank.

[underfire]

[pax britanica]

Well if cost is no object and these people are so incredible important they won't have any problem with a 100% VAT paid at the location of manufacture (not some rinky dinky modern day pirate haven place of registration) will they?

No one is that important, although some people might think they are; if Putin and Obama can make do with subsonics and telecoms links so can they.

On a less bitter note, it looks like it might be a bit of a hot ship to handle at low speed, would it be able to get into Citation sized airfields.

[dcoded]

The future will tell what will become of this project.
Seem interesting though and I wish all the luck for those involved.
But I couldn't help myself posting this little picture. I Think that some of you will get it and maybe laugh a little!





Edit: Type-o

[llondel]

On a less bitter note, it looks like it might be a bit of a hot ship to handle at low speed, would it be able to get into Citation sized airfields.

You can always get an aircraft onto a landing field. Whether it's in a condition to fly out again is another matter.

What sort of altitude are they planning to fly this thing? Concorde was pretty much on its own up at FL600 where it didn't have to worry about other traffic, I'm guessing this will be flying lower

[peekay4]

Yes the faster you go, the higher you need to fly.

Since the AS2 won't fly as fast as the Concorde, its optimal altitude should be closer to FL450, with service ceiling around FL510.

[KenV]

Well if cost is no object and these people are so incredible important they won't have any problem with a 100% VAT paid at the location of manufacture

Predatory taxation is usually counter productive. When they raised the excise (luxury) tax on yachts here in the US, they stopped producing them here and many thousands of jobs were lost. When they raised taxes on and demonized those who flew in biz jets, many thousands of jobs were lost. The politics of envy are not only ugly, they are self defeating.

[space-shuttle-driver]

Originally Posted by peekay4

Yes the faster you go, the higher you need to fly.

.

What you say does not hold for supersonic flight.
i) The speed of sound is a function of air temperature ONLY.
ii) Temperature remains constant from the beginning of the stratosphere up to 65000 feet, after which the temperature increases again.

[Genghis the Engineer]

Being higher, at fixed IMN, will reduce sigma, which will increase the difference between TAS and EAS. In the fixed temperature region of the stratosphere then, the higher you are, whilst TAS will stay fixed, EAS will go down, reducing aerodynamic loads on the aircraft, and potentially drag and thus fuel burn required.

So the higher the better, so long as it stays within the lower stratosphere, and there may be some value in creeping into the middle stratosphere a bit.

I think, it's late, might come back and check my maths in the morning.

G

[con-pilot]

Well if cost is no object and these people are so incredible important they won't have any problem with a 100% VAT paid at the location of manufacture

Then the manufacturer will move the location to a country that does not have such crippling taxes.

It's a big world.

[peekay4]

What you say does not hold for supersonic flight.

In supersonic flight, lift-dependent wave drag increases rapidly with Mach speed (by M^2), while some other drag components decrease with altitude. So the faster you go, the higher you need to fly to minimize drag.

[megan]

Aerion make no mention that I can see of planned altitude capability, though they mention approach speeds will be less than 135 Knots.

An interesting paper on inertia coupling, X-2, X-15 and Space Shuttle

http://www.nasa.gov/centers/dryden/p...ain_H-2106.pdf

[poorjohn]

This is not the same as aerodynamic instability. This is an inertial instability. It is caused by forces of a rotating mass overpowering the forces of an aerodynamic surface. No amount of computer sophistication can overcome this instability. The aerodynamic control surfaces must be enlarged. Further, look at any relaxed stability aircraft and you will see large control surfaces. Software alone cannot generate the large forces required to maintain control. The software needs powerful control surfaces to work with. Those do not appear to be present on the Aerion AS2.

I suppose great minds have considered thrusters of some kind to augment aerodynamic controls, and that doesn't work?

[MG23]

Originally Posted by poorjohn

I suppose great minds have considered thrusters of some kind to augment aerodynamic controls, and that doesn't work?

The fuel would probably weigh more than bigger control surfaces, and would require more maintenance to keep the thrusters working.

If I remember correctly, one of the first warnings the Columbia crew had of impending doom was the low fuel level in the thrusters that were compensating for a molten wing.

[megan]

For those questioning the economics, not what you would call overwhelming though.

Supersonic Bizjet Math Makes Sense Now, Says Analyst | Business Aviation News: Aviation International News

No amount of computer sophistication can overcome this instability

You can by not allowing the aircraft to encroach the areas where the instability will manifest itself. Think envelope protection, as used in the Airbus. As I previously posted,

coupling can be ameliorated by limiting roll rate, roll duration, and angle of attack or load factor for performing roll manoeuvres

The typical high speed aircraft has some sort of roll performance limitation by flight restrictions or automatic control device to prevent reaching some critical condition from which recovery is impossible.

In essence, it's not a lot different to the relaxed stability aircraft we have now. A less stable aircraft requires smaller control surfaces, and deflections, to initiate maneuvering; consequently drag and control surface imposed stresses will be reduced and aircraft responsiveness will be enhanced. Since these characteristics will typically make control by the pilot difficult or impossible, an artificial stability will typically be imposed using computers, servos, and sensors as parts of a fly by wire control system.