That’s why I added the “for the most part” bit. Structural breakup is very, very, rare. The times it DOES happen are probably too unique to make training for it in a simulator practical. Seems that there are too many possibilities to train for all of them, or even enough to be useful.
Now, to correct myself on something earlier, I should have said G-Loading is relatively easy to calculate. Other things such as dynamic loading and flutter would be hard to incorperate into the sim.
BTW- I hope this post doesn’t read like I am disagreeing with you. I do agree with you, it would be nice to train for every possible situation. It’s just there are too many possible situations that are each too rare to worry about.
Anecdotal: A friend of mine’s old man claims that he sat as copilot while someone flew a proper loop in a B-25 somewhere over the Himalayas while screwing around with some free time in the CBI theater in WWII. Hearing him tell it, I gathered he was not pleased.
A perfectly executed loop would NOT over-stress an airliner’s airframe. A perfectly executed loop can be done at a constant G force of 2 or 3 g’s, well under the rated load of the wing. Bob Hoover used to do loops in a business twin all the time, and he used to put a glass of water on the glareshield before entering the loop. It would just stay in place all the way around. I’ve done loops - you don’t feel yourself going around. From your perpective (and the airframe’s), the horizon just drops away, and then re-appears over the top after a minute. There’s absolutely no sensation of being upside-down or rotating if the loop is performed properly. It’s not a stressful manoever at all.
On the other hand, if you tried to loop a jet you’d probably get the nose up 70 or 80 degrees or so, and then thing would flop over into a hard stall. What that would do to the airframe, I don’t know.
Worse case scenario is probably that it manages to just roll over on its back and plummet straight down, in which case you’d probably over-stress the thing trying to pull out of the manoever.
I imagine a tail slide would result in the loss of the plane. Hell, tail slides have broken the tails off of aerobatic planes. THe wings and tail are not meant to be loaded backwards.
I know what you’re trying to say, but I am not as sure as you. An unladen, commercial airliner is a powerful beasty. A 747 with a minimal load of fuel and no/minimal passengers will climb like a rocket. It isn’t much of a stretch in my mind to loop it… unloaded of course.
Interesting thought though. If I have time, I think I will get some engine ratings and weights today.
I believe this was an incident involving the ‘uncommanded’ deployment of the leading edge slats at cruise. When the pilots tried to retract them, one retracted and one didn’t. The airplane did a complete barrel roll before the pilots recovered.
The ‘unofficial’ version of that I heard was the pilots were idiots, and were talking about a claimed ‘fact’ that the jet would be more fuel efficient at cruise with the slats slightly deployed. They tried it, and got themselves into big trouble.
I believe any modern airliner could roll without too much problem. That is one of the least stressful aerobatic maneuvers you could do. In a properly executed roll, you could sit in the plane with your eyes closed and never know it was happening.
The loop would be a problem. Just like Sam Stone said, it takes a lot of energy to get that airliner over the top. If you did pull it off, it would probably be very ugly. You would probably be able to get the nose pitched up beyond vertical, and then the thing would pretty much fall the rest of the way through the loop. In other words, the loop would be kinda egg shaped, instead of a nice round circle.
A guy I worked with many years back was on that plane. He was being served a drink when he noticed that the glass he was holding was now upside down. IIRC the engines flamed out and they lost lots of altitude before restarting the engines and landing the plane, somewhere in the upper midwest.
To slow the plane down from its rapid dive they deployed the landing gear, which was bent backwards by the force. They still had enough structural integrity to survive the landing.
This is all from many years old memory, anyone find a cite on Google?
This is probably the most common misconception about an aerobatic manoeuvre.
A barrel roll is not a 1g manoeuvre, it can’t be. It requires the aircraft to pitch and roll, while an aircraft is right way up (ie for half of the manoeuvre) pitching of the nose upwards must induce more than 1g as the aircraft is undergoing an acceleration against gravity. Once inverted the nose is now pitching back towards the ground, with gravity, and the g loading can be anything from slightly more than -1 to positive 2 or more, depending on the airspeed and smoothness of the pilot.
A good barrel roll that looks nice from the ground will have very similar g loadings to a loop, about 3-4g at the entry and exit, and between 0-1g at the top.
A barrel roll intended to feel gentle and pleasant for any passengers would maybe have 2.5g at the entry and exit and somewhere around 1g over the top.
If you were really concerned about the aircraft structure and you had lots of airspeed to play with you might be able to use less g for the entry and exit, but always it must be more than 1.
Just previewed and thought I’d add that I’m not saying the barrel roll is stressful, just that it involves more than 1g and commonly up to 3 or 4g
I remember an interview with Tex Johnson about that roll, on the History Channel I think. IIRC, he said he did it after calculating that the engines would be subject to a steady +1g acceleration throughout the maneuver. Apparently the risk he was most concerned about was a constant fuel flow. Too few or many gs could kill the engines by flooding or starving them.
So, given that Concorde is made to withstand more force (sound barrier, G’s), and that it has better power to weight ratios, could it do a loop? I tried finding info on it, but failed miserably.
My experience is with Pitts Specials rather than airliners but my WAG would be that the Concorde’s wing is designed specifically for high speed flight and it may be difficult to prevent the wing from stalling going over the top of the loop where airspeed is lowest. The other consideration would be that if the manoeuvre wasn’t done perfectly, the engines may experience disruption of airflow which could cause a flame out.
I guess the main consideration with aerobating non-approved aircraft is that there is no margin for error. In the Pitts you can make a complete and utter balls up of something and you won’t come close to damaging the airframe. Pull a little too many gs in something non-aerobatic and you’d better have the engineers check it over, fall out of a manoeuvre and you could have serious structural problems.
In regards to the Tex Johnston incident, not only did he not have permission from the Boeing brass to do it (he only told his copilot right before the flight), but after he rolled it the first time he circled around and rolled it AGAIN!
After landing, when he explained to the pres of Boeing how the plane was never in any danger (being a 1g maneuver the jet never knew it was upside down) the Boeing CEO said, “You know that, and I know that, but just don’t do it again.”
He’s a really neat guy. He has that Chuck Yeager-like, totally casual, absolute confidence in himself.
Well, this might not add much to the discussion, but I just did a quick test of a 747-400 in my flight simulator (X-Plane 6.10–A pretty realistic program) with no cargo and 50% fuel, I WAS able to do a barrel roll after a little practice (Note to self: Keep UNDER redline speed when doing manuevers in an airliner), but I WASN’T able to do a loop…Pulling up sharply with engines at full throttle STILL wouldn’t allow me to climb fast enough, and an attempted “Upside-down” loop (i.e. Diving down, then rolling over and climbing back up to complete the loop) quickly caused the wings to rip off after I built up too much speed and/or G-Forces.
I imagine the problem would not be structural integrity, but fuel pumps. High-power fuel pumps are needed for any sort of serious +/- g manuevers. Passenger planes are made very tough, but I don’t think the designers throw in the needed fuel pumps for maneuvering
