Overspeed Question

[ALPHA320]

I think it depends on how the auto-pilot was designed. Mechanically, it is certainly that a consistent TOGA power setting will allow the aircraft to go over the safe speed. But electronically whether a limit is imposed would be another question. Also, the safe speed would be different at different altitude under different weather, so it's not as "set-in-stone" as cars. Without access to the technical manuals and the design specification, I would think Airbus' automation philosophy would put such speed limit on the computer and Boeing would probably allow the pilots to manipulate the aircraft beyond its design limit. But that's pure speculation. Boeing would tell you that the incident of CI006 would show you the benefit of allowing such flexibility to the pilots and Airbus would tell you that the US Airways Hudson River incident would show you the benefit of a fixing a flight envelope, so there's no right-or-wrong answer here.

Actually are you sure there are electronic speed limiters on cars? I know they
generally put them on trucks and buses, but I am not sure about cars.

Airbus FBW aircraft have overspeed protection.

[Gabriel]

I meant when you have a sudden loss of tailwind the aircraft can go in overspeed for a short moment......

Ah, ok. The same than an increase in headwind.

[brianw999]

.......Actually are you sure there are electronic speed limiters on cars? I know they generally put them on trucks and buses, but I am not sure about cars.

Yes...and motorcycles. As an example....I believe it's Germany that has a maximum 155mph speed capability and vehicles manufactured in Germany, or manufactured for the German market, that are capable of exceeding that are electronically restricted to 155 mph.

For the UK market only, Mercedes-Benz has launched a special edition of the C63 AMG dubbed C-Class DR 520. Available in both saloon and estate configuration, the DR520 adds the AMG Performance Pack Plus to the C63, and then, gets a 60 hp increase over the standard AMG for a healthy 520 hp and 650 Nm (479 ft-lb) of torque. That launches the saloon to 60 mph in 4.1 seconds and the estate in 4.2. That acceleration continues until an electronically-limited top speed of 301 km/h (187 mph). Only 20 will be made and will only be available in Matte Black or Matte White. All will be sold through Mercedes-Benz World in Brooklands, Surrey, England at a dear cost of £62,430 for the saloon and £63,680 for the estate, including taxes and fees.

....bit of a bummer if you're German, wanting to buy a German made rocketship, and you find that the Brits get a max 187mph version but yours will only (only !!!!) do 155mph.
The Brit versions come in Matte Black and Matte White only.....I wonder if the seats come in Matte Brown to hide the stains ?

[TeeVee]

Yes, in normal law it has an overspeed protection as part of its envelope protection. What it does is to climb to prevent an overspeed.

climbs to prevent overspeed? though im not a pilot, that doesn't seem to make sense. why not have the system retard throttles?

[TeeVee]

Yes...and motorcycles. As an example....I believe it's Germany that has a maximum 155mph speed capability and vehicles manufactured in Germany, or manufactured for the German market, that are capable of exceeding that are electronically restricted to 155 mph.

....bit of a bummer if you're German, wanting to buy a German made rocketship, and you find that the Brits get a max 187mph version but yours will only (only !!!!) do 155mph.
The Brit versions come in Matte Black and Matte White only.....I wonder if the seats come in Matte Brown to hide the stains ?

good thing not all cars have this or the lads at top gear would be quite unhappy and bored!

[ALPHA320]

Yes...and motorcycles. As an example....I believe it's Germany that has a maximum 155mph speed capability and vehicles manufactured in Germany, or manufactured for the German market, that are capable of exceeding that are electronically restricted to 155 mph.

....bit of a bummer if you're German, wanting to buy a German made rocketship, and you find that the Brits get a max 187mph version but yours will only (only !!!!) do 155mph.
The Brit versions come in Matte Black and Matte White only.....I wonder if the seats come in Matte Brown to hide the stains ?

Never heard of that before... I have seen many driving faster on our unrestricted motorways...

[Gabriel]

climbs to prevent overspeed? though im not a pilot, that doesn't seem to make sense. why not have the system retard throttles?

The "normal law" refers to what the "stick" does.

The "autothrottles" would normally prevent the plane to accelerate to overspeed.

If it accelerated to overspeed, it's because something prevented the autothrottles to avoid it in the first place.
Maybe the human pilot manually set max thrust (which was your hypothesis).
Or maybe the plane was descending at such a rate that even with the engines idled the plane exceeded the speed limit (in this case "climb" must be taken more liberally, as in "reduce descent")

(Note: I'm not fully correct with the explanation here, but the technically correct explanation would have been longer and more complicated and I think that the above is enough to understand the concept)

[TeeVee]

yes, i understand that autothrottle would normally prevent overspeed. but if for some stupid reason the pilot disconnected AT operation, selected max thrust in level flight, i still don't understand why airbus logic dictates "climb" to correct overspeed. theoretically, if the plane were lightly loaded, climbing alone may not solve the problem until it passed its max operating altitude.

yes i know my scenario is a weird one. i'm just trying to understand why airbus chose climb over retard. it's not as if the system can't and doesn't completely ignore other "stupid" pilot inputs...

[Gabriel]

yes, i understand that autothrottle would normally prevent overspeed. but if for some stupid reason the pilot disconnected AT operation, selected max thrust in level flight, i still don't understand why airbus logic dictates "climb" to correct overspeed. theoretically, if the plane were lightly loaded, climbing alone may not solve the problem until it passed its max operating altitude.

yes i know my scenario is a weird one. i'm just trying to understand why airbus chose climb over retard. it's not as if the system can't and doesn't completely ignore other "stupid" pilot inputs...

First, rest assured that the plane won't climb past it's climbing ability. It seems tautological, but not so because there is a way to climb past the ceiling, like Air France did.

The thing is that to do it, you'll have to trade speed for altitude, and that's not what this protection does. What it will do is, upon reaching Vne/Mme establish whatever climb it takes to convert all the excess power to altitude (excess power is the power that the engines are producing minus the power needed to keep the plane flying straight and level, excess power WILL make the plane increase it's mechanical energy, be it in the form or kinetic energy -speed- or potential gravitational energy -altitude-, or a combination of both. You use the stick to govern where that energy goes). So it will keep keep climbing at Vne/Mme as the engines loose power (due to altitude) until it reaches the point where all the power the engines are producing is exactly what is needed to keep the plane flying straight and level at that speed.

As why doesn't the plane just say "screw the pilot, even if he disconnected the autopilot and wants full thrust I won't allow it", well, it's a sort of philosophical question. Who has the last word? The pilot or the computer? Do we allow the pilot to disconnect HALL? He already overrode the autothrottle but not the flight control computers which can prevent the overspeed in this way. If the pilots go further to override the FCCs (what he can do), then nothing at all will prevent the pilot from overspeeding (we can almost say that you are not in an Airbus any longer).

Other than letting the pilot judge that the computer is crazy (for example, that the overspeed is not such), I can think of only one scenario where it would be good do it as it is now, that I concede is too crazy: the plane approaching high terrain and the pilot applying TOGA but not immediately climbing for whatever reason. Let the plane accumulate energy in whatever form that the pilot can then use to trade for latitude. When the "speed" energy tank is full, start filling the "altitude" energy tank but please don't stop accumulating energy.

On the other hand, I don't see anything wrong with letting the plane climb except the "little" problem of traffic separation.

[TeeVee]

thanks for taking the time Gabriel.

what i still can't comprehend is this: in a bus, if the pilot commands a bank that HAL thinks is too steep, HAL simply ignores the continued sidestick pressure at a point which HAL determines the bank angle to be within operational limits. in other words, HAL countermands the pilots inputs directly. however, when it comes to level flight overspeed due to excessive throttle, HAL says, climb, to reduce the effect of the throttle "input."

of course the sum total my knowledge of aircraft operation and aerodynamics can be written on a 2" x 2" piece of paper. but is still think that HAL would be better off retarding the throttles as opposed to climbing.

[snydersnapshots]

thanks for taking the time Gabriel.

what i still can't comprehend is this: in a bus, if the pilot commands a bank that HAL thinks is too steep, HAL simply ignores the continued sidestick pressure at a point which HAL determines the bank angel to be within operational limits. in other words, HAL countermands the pilots inputs directly.

Which is why, in my opinion, "If it's not Boeing, I'm not going." If, for some reason, I need to roll into a 60 degree bank (traffic avoidance perhaps?), I don't want the damn computer telling me I can't. Sure--squawk "Bank Angle, Bank Angle" all you want (my Boeing already does), but let me fly the airplane and do what I need to do.

OK...off my soapbox now...

[Gabriel]

thanks for taking the time Gabriel.

what i still can't comprehend is this: in a bus, if the pilot commands a bank that HAL thinks is too steep, HAL simply ignores the continued sidestick pressure at a point which HAL determines the bank angle to be within operational limits. in other words, HAL countermands the pilots inputs directly. however, when it comes to level flight overspeed due to excessive throttle, HAL says, climb, to reduce the effect of the throttle "input."

of course the sum total my knowledge of aircraft operation and aerodynamics can be written on a 2" x 2" piece of paper. but is still think that HAL would be better off retarding the throttles as opposed to climbing.

I think you are making a too close link between "speed" and "throttle".

With no data to support this, I'll bet 1 cent that, when related with "pilot technique", there are much more cases of overspeed due to wrong pitch than wrong throttle. Examples: When descending from cruise, even with the speed at idle the plane cannot descend with a great rate without increasing speed. Exceed that rate and you will depart from your target speed and risk an overspeed. During climb, don't point the nose high enough and you'll overspeed (especially before the airplane is clean).

Not for nothing there is a saying in aviation that goes "stick controls speed, throttle controls altitude" (no, I don't want to start a discussion on the truth of this saying)

An other thing to consider is Airbus philosophy toward throttle management (which is nearly "don't touch this lever"). Very shortly after take-off you reduce the throttle levers from the "take-off" setting to the "climb" setting and let it there for the remainder of the flight until you are 20ft above the runway, when HAL must remind you of your mental condition for you to pull the levers back to idle ("Retard, retard!"). The "climb" setting is nearly the "one-for-all" setting: Climb, cruise, descent, approach. Obviously the engines themselves don't stay at climb all the time. Just the thrust levers do and HAL takes care of the engines. If you move them to TOGA (or any setting past climb) you are effectively telling the plane "I have the throttles", so the plane has no choice but to think that you have compelling reasons to do whatever you are doing with them. You are already overriding HAL, at least the "thrust" aspect of it. If HAL still wants to prevent the overspeed, then it must work with whatever it has left.

Also, maybe you are overjudging the "power" of the Airbus version of HAL.
It will still let pilot screw it up big time. Especially with the thrust levers.
Example: Fail to completely idle one of the thrust levers during the landing (it should happen at 20ft). The spoilers won't deploy upon landing, the autobrake won't engage, the autothrust won't disengage, and when you start to brake manually while asking "what is it doing now", the still engaged autothrust will increase thrust to try to hold the speed selected for the approach.

With the stick HAL is a bit harder to beat. It takes a few clicks or some failures (like Air France).

And finally, again, I see no compelling reason to declare one of the two choices the "best" one.

[TeeVee]

ok, i'm beginning to see. thanks again for the time!

[3WE]

...there is a saying in aviation that goes "stick controls speed, throttle controls altitude" (no, I don't want to start a discussion on the truth of this saying)...

Oh, you'll always start a discussion on stalls (your favorite thing) but you use my rule without a courtesy PM?



There are those who say it's not really true because there are several flight modes where it does not work well.

[snydersnapshots]

Oh, you'll always start a discussion on stalls (your favorite thing) but you use my rule without a courtesy PM?

Seems to me I saw "your" rule in Wolfgang Langeweische's book STICK AND RUDDER a few years back. OK, it was when I had hair, so it was a LOT of years back. Of course, if you're actually Wolfgang Langewiesche, would you autograph my book???