It is often written that the MiG-25 Foxbat was built to counter the B-70 Valkyrie, and was put into production out of some kind of inertia after the bomber was cancelled. I think the continued existance of the RA-5C had a lot to do with it.

The RA-5 was never a threat. It was a reconaissance aircraft. What should it have to do with the MiG-25?
As I said that are only rumours and nobody can say if they are true.

Hm, that is strange. The ICAO recommended wake separations are 4 miles for a Heavy behind Heavy on approach/take-off, 5 miles for cruise – only 25 % bigger. For a Heavy behind Ai-380, it is 10 miles for approach/take-off, 15 miles for cruise – only 50 % bigger. Whereas the cruise speed, at about 0,85 Mach or 500 knots TAS, is at least 200 % greater than the speeds on approach/take-off (around 150 knots…). So a plane at a minimum safe distance behind a craft cruising ahead is leaving at most a half, and likely one-third, the time for wake decay that is allowed on approach/take-off.

How do the separation requirements change from 4 miles takeoff limit to 5 miles cruise limit over the course of the climb?

And that is reasonable, because wake intensity is not constant. It decreases with airspeed and configuration, so that the wake of a cruising aircraft is considerably lower amplitude than that of a approaching aircraft with similar weight. Same with sensitivity: At cruise speed a wake would induce lower forces than at approach or take-off speed (same vortex strength, same aircraft, same configuration). Additionally, any turbulence or even upset is far less dangerous in cruise as ground clearance is suffcient to counteract and small deviations from planned flight-path is less of concern.

Bmused, you’re right. I took a cheap hit. Mostly because I was annoyed by the simple attitude of the posted article. I am working for Airbus, so please apologize that I am biased. I however agree with you in two important points:

1
Boeing may and in my perception will deliver more airplanes than Airbus at least from 2008 on (if 787 goes as planned). That is a fact and I don’t consider it a “defeat” (I don’t even see a battle).

2
Airbus is doing similar business strategies as Boeing, in my perception with lower amplitude. Airbus is not outsourcing its production as Boeing does. Once again, the article was somehow ‘cheap’, hence my reply also ‘cheap’.

I think that this A vs B thing will become different in some years. We will see both companies going shoping around the world to get their aircrafts together. The opinion that Boeing is American and Airbus is European is outdated. The American workshare on an A380 can be similar to that of an B787 if the according variants are chosen.

So, to make it short: I try to be rational. Articles like the posted one let me get ‘irrational’.

US Agent,
you seem very focussed in determing a ‘winner’ of a ‘battle’. Fact is, that the A380 is flying. It is experiencing problems, which are all solvable in reasonable time and cost (believe, I’m working on it). True is, it was planned different by cost-concerned Airbus managers.

And here comes the lesson: Do not celebrate victory before your plane is flying. The 787 is sure a good design, but hasn’t even lifted off not speaking of certification or revenue service.

My advice: Just be happy, be excited, but do not predict something on the limited facts you have. Only do it if you want to emberasse yourself due to wrong predictions. Building an airplane is such a difficult task, Boeing promised the final marvel to the airlines and, at the same time, re-invented the Boeing Company to a organization that does not reflect its employees wishes (no enginees likes to divert activities to Russia and lay off his buddies). I wish best luck to Boeing. The will need some of it.

Your 4 points in the end are BS. And, please believe me, if Airbus would have won all 4 I would call it BS, too.

Airbus say the pilot acted wildly, American say he did what he was trained to do.

So there is no way you or I can sayfor sure who is to blame. Personaly I say both parties have responsibility. Although to Airbus’ credit, the tail didn’t snap till around 130% designed max load.

I would orientate myself on the official report of the NTSB that clearly states that
– the co-pilot was responsibly due to “excessive and unnecessary” rudder inputs
– the training of AA contributed to the accident
– the rudder control system contributed to the accident

The tail withstood 1.9 times the limit load, that is the maximum allowed load on vertical tail. The structure behaved exactly as Airbus predicted and NTSB stated that in the report. The rudder travel limiter was object heavy criticism by authorities and the reason why AA blamed Airbus as responsible. However, the limiter is not well designed and tricky to handle, but was certified.

Hence we can clearly conclude who is responsible.

Large aircraft are still sensitive to wakes. I remember seeing a few pictures of 707’s and DC-8’s who had engines removed by the wakes of similar aircraft they were following. Sure, the dangers for a 747 are different than a C152 but there are still risks.

Isn’t only the 753 considered a Heavy aircraft? I believe I have also heard the Heavy callsign for 739’s as well but I could be mistaken. I know there was an attempt to get the 737NG’s recategorized as the wakes off their new wings packed quite a punch when compared to the previous 737’s. I know the few times I’ve gotten rocked rather hard by a previous airplanes wake it was reported as a 738 or 739.

I actually concentrated more on the aircraft as rigid-body system. But you are right: A high-energy vortex may cause structural damage at large aircraft. Especially parts like vertical tail plane.

The impact of a Wake Vortex Encounter is dependend on:
– aircraft’s span
– inertia
– airspeed
– mass
The higher inertia will reduce the effects of rolling. The size will maybe result in encountering both vortices at the same time. Generally I think the effect is neglitible.

@Bmused55: Be aware about the preliminary status of the ICAO-recommendation. The seperation categories by ICAO are outdated and not appropriate at all. The understanding of wake vortex generation is limited. We will see a totally new approach developing over the next years. After being threatened by ICAO with the increased seperation, Airbus is doing research in order to prove that A380 will have only slightly increased vortex. Additionally, the A380’s climb performance will enable it to clear the airspace faster than a B747.
This research was not conducted before because nobody was really interested. The (sorry to say it this hard) propaganda of Boeing, that A380 will nullify its slot-advantage, is embarassing for such an old company. I actually believe that they have no idea what kind of vortices their own aircraft produce.

Just to add: Category heavy starts at 136 tons (including everything from a A310 to a B747-400). A B757 is actually rated as “heavy”, too, because it produces such strong vortices. Taking the ICAO-seperation as proven fact is scientificly not valid.

Would they be able to increase the speeds without affecting the fuel efficiency in future for the replacement aircrafts like 320/737 etc..

Is there a technically availaible viable solution for this?

No, I doubt that. The way to go is more the other way round: reduce speed and gain weight-saving and reduced fuel consumption. A speed reduction to M0.7 or M0.65 would cost you some minutes but most time you spend in taxiing, take-off and landing. All those are restricted in temrs of speed.

As I tried to explain to Bmused it is this not just as it is with previous porgrams. The manufacturers will have to go very deep inside the topic and evaluate the costs of all aspects of operation. Ths will maybe cause a diversification of the market with Bombardier, the Russians, Embrear or even the Chinese entering the market.
Definetly the market for single-aisle will be completly different than that for B787 or even A380. The single-aisle airliner will stay less sophisticated and development of a competitive design is achievable by other companies than A&B.
That is actually what I read out of the quote from the Boeing guy, just filter out the US-typical adjectives and you can find my statements in it.