http://johnsalvatier.org/blog/2017/reality-has-a-surprising-...
A reverser only redirects thrust, and only generates about 60% of max thrust pushing backwards.
It's only on for a limited time on the ground because under a certain speed, you run the risk of blowing FOD into the intake path, putting the engine at risk.
I'm not aware of any reason to outright lockout a reverser in flight other than to hedge your bets against a very, very poor set of configuration choices by the pilot (reversing near stall speed too low to recover). I could foresee scenarios where being able to use reversers in the air could save the aircraft with the right combination of subsystem casualties.
Not a pilot or engineer, but absolutely LOVE aviation.
[EDIT remove "roughly speaking an order of magnitude"]
No. No it is not. 787 approach speed is 145-153 knots. It does not cruise at 1400+ knots.
What would you like to call the factor? 3? Call me a weasel, but I was hoping "roughly speaking an order of magnitude" would go down to 3. I suspected it was comfortably above 2. Am I right about that?
I'd call that half a order of magnitude, considering log₁₀(3) is around 0.477. So you're off by more than a factor of two.
0: Uniform, linear and logarithmic are obvious candidates, but depending on the domain you can end up with some really wierd scales (eg floating-point ULPs, which can look logarithmic or linear, but aren't either).
1: hence > So you're off by more than a factor of two.
roughly 10x going down to 3x would also mean it would go up to 17x. That's a pretty wide range, so I don't think that order of magnitude is going to ever really be similar to 3x of something on the basis of what it means.
In fact, the reversed kicking in would decrease the loading on the aircraft by decreasing it's airspeed.
This isn't a case of acceleration being able to break the mount from the frame. If it ever could, one wouldn't want it on the plane in the first place.
Doesn't mean you couldn't ruin your day with it, but it isn't an instant catastrophic failure either.
Read the accident report and follow up on Lauda Air Flight 004. Boeing specifically was forced to issue a statement that it was virtually impossible to overcome a catastrophic failure outcome from a thrust reverser deploying at cruising speed.
That counts as a pretty serious thing to avoid :-).
Ideally, yes. I submitted a recent incident where the RAT deployed on a 777 because it's so unusual (and was also not due to lack of fuel):
"For every complex problem there is an answer that is clear, simple, and wrong." -- H.L. Mencken
One of the things I have experienced in my career is the mind boggling complexity of the software in systems that are capable of killing people. The more people it can kill the more complex the software.
As a result when I read articles like the one posted I find it tantalizing to speculate about the requirements behind the story. Taking the story at face value that Boeing has thought a lot about it and that is how the software has to be, what prevents the other solution of disabling the reverser? My guess is that you want the reverser to work in the event of software failure so it has to always work, but if the pilots pull it while you are flying that would probably rip the engines off the plane. Perhaps the compromise is to take the reverser off during flight and relight the engines using aerial pressure to spin up the engines. (which has me wondering if airlines still have a turbine they can drop down to start an APU which can then be used to start the engines). Which leads me to wondering if the pilots turn off the reverser right away do they have enough residual engine power to relight? Versus when they got to the end of the runway and had nothing? Clearly the 777 doesn't have an APU running when it lands since they would have used that to do an engine start at the end of the runway or if it does, it isn't running.
It is one of those things that my like minded systems friends could sit around lunch and make a good hour and a half discussion out of.