Tangowhisky From United States of America, joined Jun 2006, 862 posts, RR: 8 Posted (6 years 7 months 3 weeks 2 days 9 hours ago) and read 9538 times:
Boeing uses conventional column on the 777, with full fly by wire primary flight controls. Airbus does the same with a sidestick. Both provide full envelope protection. Who has the better system?
Over the weekend, I got together with old friends, one is a pilot, and two are aerospace engineers. We got into an interesting discussion: which fly by wire has more value in terms of operating costs?
Boeing 777/787 Philosophy
Full fly by wire using conventional control column and yoke. Artificial forces and electromechanical systems are added to retain the traditional feel of flying and airplane.
Flying philosophy is vastly different. Pilot no longer applies a force on the controls to achieve maneuvering, but the sidestick displacement is a rate command. There is no need to provide the pilot with a feedback force or stick shaker as the plane will always fly within its structural and aerodynamic limits.
The engineers went on to say that the Airbus philosophy is lighter and requires less maintenance as there is no artificial feel systems, the sidestick is lighter, etc. They also said that it is easier to tune the software that makes the A320/330/340 to fly the same with a "no artificial feel force" flying philosophy and less simulator time is required for pilots to get acquainted to the handling qualities. I even read somewhere (can't remember where) that the Boeing system requires about 8 inches of increased cockpit length to make space for the column displacement.
KBFIspotter From United States of America, joined May 2005, 729 posts, RR: 1 Reply 1, posted (6 years 7 months 3 weeks 2 days 8 hours ago) and read 9490 times:
While having never flown either type (accept for an hour of T7 sim time), I would have to say that the Boeing method would make training easier, as the pilot still can "feel" the airplane. I think that the Airbus method, without any feel, would require more initial training, and more sim time. Once the flight crew is trained, though, I feel that it would not make much of a difference. It would be easier to over control the Airbus, however, IMO.
Aviator27 From , joined Dec 1969, posts, RR: Reply 3, posted (6 years 7 months 3 weeks 2 days 8 hours ago) and read 9459 times:
As a pilot, who has flown A320's I can add this. I transitioned from Boeings, albeit not fly by wire. Getting used to the Airbus sidestick took me 15 mins in the simulator. After that, everything was intuitive. The Airbus is really easy to fly. That is the Airbus philosophy. Everything that TangoWhiskey says about both manufacturers philosophy is completely true. Given that, I think the Airbus way is safer and better.
You'll have to qualify that, as in objective terms it is not true of the Boeing Philosophy.
Quoting Tangowhisky (Thread starter): There is no need to provide the pilot with a feedback force or stick shaker as the plane will always fly within its structural and aerodynamic limits
That's certainly not the main reason :what people, especially on this forum, have failed to realize is that airbus has drastically changed the piloting way : moving the sidestick is in reality flying a trajectory, regardless of speed or altitude.
Quoting KBFIspotter (Reply 1): I would have to say that the Boeing method would make training easier, as the pilot still can "feel" the airplane.
We've stopped feeling airplanes since the Connie, my friend.
Quoting KBFIspotter (Reply 1): It would be easier to over control the Airbus, however, IMO.
And you're dead wrong.
Quoting KBFIspotter (Reply 1): I think that the Airbus method, without any feel, would require more initial training, and more sim time.
You're this time a wrong cadaver !
Quoting Aviator27 (Reply 3): I transitioned from Boeings, albeit not fly by wire
It wouldn't have made a difference anyway.The Boeing philosophy was to make the FBW transparent to the pilot... But things change...he he he he !
Quoting Aviator27 (Reply 3): Given that, I think the Airbus way is safer and better.
I'll bring flowers to your grave after they shoot you for high treason
Actually, I think the same way you do, but,Hey! I'm the enemy !
PS : for what it is worth, I'll add to you to my RU list for insane courage of opinion .
Rick767 From United Kingdom, joined Jan 2000, 2662 posts, RR: 52 Reply 5, posted (6 years 7 months 3 weeks 2 days 7 hours ago) and read 9371 times:
Quoting KBFIspotter (Reply 1): I would have to say that the Boeing method would make training easier, as the pilot still can "feel" the airplane. I think that the Airbus method, without any feel, would require more initial training, and more sim time.
Sorry, but that is nonsense. I transitioned from flying Boeings for several years (757/767 then 737) onto the Airbus and like Aviator27 was comfortable with flying using the sidestick in 10-15 minutes during the first simulator session.
The Airbus has many advantages from a pilot perspective. I am now flying the Boeing again (744) but do miss the Airbus - by far it was the best aircraft I ever flew and I look forward to hopefully flying it again one day.
I used to love the smell of Jet-A in the morning...
Stratofortress From United States of America, joined Dec 2005, 178 posts, RR: 1 Reply 6, posted (6 years 7 months 3 weeks 2 days 6 hours ago) and read 9321 times:
Most pilots I have talked to like the comfort (no yoke) of Airbus' cockpit and the ease of learning how to fly it and transitioning between models. However, most of them like Boeing for its "real" airplane feel. Some of them even poked fun at Airbus drivers about being Flight Sim drivers.
IMO, it's hard to say which one is "better," but the opinions are cerainly strong on both sides of the fence.
Tangowhisky From United States of America, joined Jun 2006, 862 posts, RR: 8 Reply 7, posted (6 years 7 months 3 weeks 2 days 6 hours ago) and read 9281 times:
Quoting Pihero (Reply 4): That's certainly not the main reason :what people, especially on this forum, have failed to realize is that airbus has drastically changed the piloting way : moving the sidestick is in reality flying a trajectory, regardless of speed or altitude.
Pihero, that is very interesting - perhaps the true thinking or philosophy of the Airbus system is simply flying a trajectory, it makes sense. Perhaps feeling the airplane is less important these days as pilots are managing a flights more and flying less.
I wonder why Boeing chose the stick and yoke when they went full FBW on the 777? safety reasons? both pilots know what the other is doing perhaps? Is that an issue on the Airbus types? Can anyone explain?
It is also interesting to read how many pilots like the Airbus FBW system. I remember back in the late 80's when the A320 hit the market, and so many pilots initially did not like the FBW philosophy of the A320.
It would also be interestng to know from pilots who have flown the 777 and the Airbus types of their views of the different FBW philosophies.
Tangowhisky From United States of America, joined Jun 2006, 862 posts, RR: 8 Reply 8, posted (6 years 7 months 3 weeks 1 day 16 hours ago) and read 9103 times:
Quoting Pihero (Reply 4): Quoting Tangowhisky (Thread starter):
Both provide full envelope protection
You'll have to qualify that, as in objective terms it is not true of the Boeing Philosophy.
My understanding is that the 777 provides envelope protection. But if the pilot applies extreme force on the controls, he/she can then override envelope protection. I could be wrong, but I read this on an old thread some few years back. Would you have any clarifications?
Zeke From Hong Kong, joined Dec 2006, 7726 posts, RR: 73 Reply 9, posted (6 years 7 months 3 weeks 1 day 15 hours ago) and read 9045 times:
I have posted this before in CivAv, sorry I have not got time to add to it today.
Quote: As far as Flight Surface Control, CG Control, Trajectory Control, Navigation Control between FBW and "conventional" aircraft is the Flight Surface Control in a FBW aircraft is done via automation (electronically via a computer), whereas a conventional aircraft its a either via a human or autopilot.
Basically all new aircraft coming out now are FBW, eg A318/19/20/21/30/40/50/80, 777, 787, 748 (my understanding), Embraer ERJ-170/190, C-17 all all examples of modern transport aircraft with FBW.
Airbus chose to introduce a flight control law know as C* (pronounced C-star) on the A320/330/340 and A380 family of aircraft. This particular FCS (flight control software) is a blend of G command at higher speeds (above around 200 knots), and pitch rate command at lower speeds. This FCS is basically a flight path command in which the pilot commands a particular flight path, and the FCS manages the flying surfaces through speed, configuration, and thrust changes to achieve the commanded flight path. This gave the A320/330/340 excellent control of flight path during all flight phases and especially during landing, however the down side is that has poor-average speed control.
McDonell Douglas on the F/A-18 aircraft chose both speed and flight path FCS systems at different phases of flight. With the landing gear retracted, the F/A-18 operates on a flight path control system like the Airbus FCS. With the landing gear extended, the aircraft uses a conventional speed referenced FCS. Both 'flight path hold' and 'speed hold' have their advantages and disadvantages. The F/A-18 has both systems, with gear down has accurate speed control to land on carrier at exact speeds. F/A-18 with gear up has accurate control of flight path to employ weaponry (guns, missile, bombs)
Boeing chose to introduce an FCS based on airspeed on the 777 like the F/A-18 gear down mode. By using an FCS that mimics conventional aircraft, the 777 has similar handling characteristics to other Boeing aircraft and all other conventional aircraft. B777 pilots must 'trim' the aircraft longitudinally, The advantage for the 777 is during all flight phases especially during landing it has good speed control, but poor-average flight path control.
Airbus FBW aircraft autotrim, which as you can see from the posts above causes many strange misinterpretation of what the aircraft does when you flare for landing, or are below 100/50 ft rad alt. The landing is conventional, however behind the scenes unknown to the pilot a bias is added to the flight control system so when the pilot comes into land, the tactile feel on the stick mimics a conventional aircraft.
The reasons for switching to FBW include :
Flight test savings. FBW offers the prospect of using software changes to solve otherwise difficult and expensive handling problems uncovered during flight test.
Uniform handling characteristics. One of the advantages offered by Airbus and Embraer with their family of aircraft concept is uniform cockpit layouts and uniform flying characteristics. This is achievable only through FBW and offers reduced flightcrew training costs as well as increased crew scheduling flexibility.
Weight and complexity savings. FBW along with FADEC technology reduces the requirement for direct cable linkages between the flight deck and engines and control surfaces.
Avoiding structural resonance. Large slender aircraft such as the A340-500/600 can encounter pilot control induced structural resonance. In this particular instance, Airbus have introduced a special version of FCS to prevent pilots from exciting the natural resonance modes of the aircraft.
Avoiding tailstrike. The FCS can be programmed to indicate the limit of nose up attitude during take off and landing ensuring that the tail does not strike the runway - A340-600
Flight envelope protections. FBW allows designers to introduce flight envelope protection features covering low speed flight (stall), over-speed, bank angle, aircraft G factor and engine out handling.
Improved fuel efficiency. Airbus are designing the A380 to operate at a greater aft centre of gravity position than is safely possible on conventional aircraft. This reduces the tail down force requirement with a reduction in drag and fuel consumption.
Lift Augmentation. Here both ailerons are symmetrically 'drooped' to provide additional lift when flaps are extended. Airbus FBW.
Manoeuvre Load Alleviation. The ailerons are deflected upward (11°max) in order to create a downward force on the wing, which in turn reduces the overall load on the wing. This is used in a high 'g' manoeuvre where wing loading is at a maximum. Airbus FBW
Speed brake. Spoilers are deflected upward at high angles (max 30°) in order to generate increased aerodynamic drag, slowing the aircraft down, Alto automatically retracting in certain circumstances e.g. TOGA for a GPWS recovery. Airbus FBW.
When looking at a FBW system a design trade off is made by the manufacturers to work out what sort of flight envelope protections they want with their aircraft. The difference between Boeing and Airbus is black and white. Airbus has adopted hard limits, and Boeing soft limits.
The subject of hard versus soft limits has been an emotional battlefield for Airbus and Boeing pilots wedded to the particular merits of their designs. In the heat of the argument some of the rational elements of the debate are lost with statements like "...soft limits allow the pilot to retain authority over the aircraft..." or "...hard limit prevent pilots from breaking aircraft."
Transport aircraft are constructed with a very narrow purpose in mind, that being long range wings level flight at 1G. Structural safety margins are built around this requirement such that the structure needs to be able to handle 2.5G during line operations and survive a 3.75G load (1.5 x 2.5G) for 3 seconds once in the aircrafts life.
As an aircraft with low drag characteristics and high weights, transport aircraft gain airspeed rapidly with mild nose low attitudes (i.e. below 10 degrees nose down), and lose airspeed rapidly with high nose attitudes (i.e. above 30 nose up). If maneuvered aggressively in pitch, a transport aircraft will find itself rapidly approaching the stall, or quickly exceeding limiting structural speeds. Transport aircraft are not designed for even the mildest forms of aerobatics.
The Airbus design solution makes it simple for flightcrews to achieve the aircraft's limit performance of 2.5G across the flight envelop, the cost of such simplicity being that no more than 2.5G can be achieved. The conventional design solution (Boeing and all other designs without hard limits) makes it possible for the pilot to achieve any G loading, however the onus is on the pilot to do just that.
As with everything in aircraft design its all about compromise, swings and roundabouts.
To enable the Airbus to have hard limits in roll it needed it "commands a roll rate" while on a 777 the pilot "commands control surface deflection". The basic difference, Airbus you cannot roll the aircraft (with the computers turned on), once you achieve the bank limit the rate will go to zero and you achieve your 2.5G limit, on a 777 you could continue your roll and exceed the 2.5G design limit.
Obviously the cockpit arrangement differs further between Boeing and Airbus, moving throttle vs fixed, yoke vs stick, connected vs independent controls, mix that up with the FBW differences above you can see why some people will prefer one or the other.
If you have not had a chance to read it already, I think you would find the article "Unlike Airbus, Boeing lets aviator override fly-by-wire technology"
from the Seattle Post interesting. I dont agree with everything said in the article, it does a fairly balanced job.
If you have further questions on that I would be more than happy to answer them.
We are addicted to our thoughts. We cannot change anything if we cannot change our thinking – Santosh Kalwar
Tangowhisky From United States of America, joined Jun 2006, 862 posts, RR: 8 Reply 12, posted (6 years 7 months 3 weeks 1 day 8 hours ago) and read 8824 times:
NAV20 thanks for the link and Zeke thanks for the great contribution you have made.
In an industry where we see more and more standardization and airplanes looking the same, system architecture similarities, it is remarkable to see that when it comes to fly by wire flight controls of the primary systems, how the two manufacturers have such different philosophies.
After reading all the great information, I must say that the Airbus system has more advantages with less disadvantages than the Boeing system. Here is why:
* Easier to program handling characteristics of vastly different family types with the sidestick concept versus the force feel concept
* Lower overall components and parts weight with the sidestick, while the column also requires a few more inches of cockpit length for column displacement.
*Less parts, and less wear and tear with the sidestick concept
* Flying a flight path trajectory with auto trim reduces pilot workload more than the 777 philosophy
* The Airbus system can deliver all it can out of the airplane in emergency situations by more automation with less workload to the pilots: emergency descent, traffic collision avoidance, windshear escape, etc.
* The 777 philosophy on the other hand seems to make the pilot more connected to the flying automation
* The 777 controls give a better idea to both crews on what the other guy is doing
* I am not sure that having the pilot the capability to override has any benefit in the 777. For example, if the pilot want maximum lift, he gets maximum attainable lift on the Airbus, if the pilot wants to avoid a potential collision, the Airbus system still provides huge bank and g limits.
IMO the Airbus system is better and that Boeing is stuck with a control column and yoke to mimic old way of flying that is good, but could be much better. I would say this is the only drawback of the B787 as they seem like they got the rest of this plane and th 777 right. Imagine if the Space Shuttle kept a column and yoke.
Charliejag1 From United States of America, joined Aug 2006, 238 posts, RR: 0 Reply 15, posted (6 years 7 months 3 weeks 1 day 7 hours ago) and read 8731 times:
As a commercial pilot that has not flown anything larger than a Super King Air (changed my mind about my career), I have a somewhat unqualified yet educated opinion. To that end, the only thing I worry about in this topic is the fact that the Airbus' computers 'vote' on your control input, deciding if they agree with you. To a degree, that means that the pilot does not have full, direct control of the aircraft at all times. It reminds me of the a320 crash at the airshow with all the kids on board (who survived). The airplane was not in the correct mode, so the pilot was unable to convince the computers that they should climb. Instead, they flew into a forest and crashed.
I know Airbus has fixed these 'software problems', but it still is an odd concept to me. I will not hesitate to fly or ride an Airbus, but I have to stick with Boeing on this one.
Zeke From Hong Kong, joined Dec 2006, 7726 posts, RR: 73 Reply 18, posted (6 years 7 months 3 weeks 1 day 6 hours ago) and read 8674 times:
Quoting Charliejag1 (Reply 15): I know Airbus has fixed these 'software problems', but it still is an odd concept to me.
I had a fairly good understanding of this accident. As far as I am aware if you were to do the same procedure in any aircraft the result would have been the same. The accident in my view did not highlight any problems with FBW per say, it did highlight some problems with the man-manchine interface.
I am not aware that the aircraft did anything wrong, it did what the pilots commanded it to do. What the pilots commanded it to do, and what they thought they wanted it to do are not the same. To that extent, I am not aware of any 'software problems' that were fixed as a result of this accident.
If I understand the accident correctly, the same thing could happen today. We are not in the habit of flying passenger jets level at very low altitude below Vref with engines at idle, autothrust disconnected, towards obstacles. The DGAC set a hard deck for the flypast, the pilots went way under that hard deck.
We are addicted to our thoughts. We cannot change anything if we cannot change our thinking – Santosh Kalwar