When I stop at a grade crossing for a passing train, I notice some tank cars that are “sway backed” and others that are straight. Is the sway back caused by fatigue or was it designed that way?
You are probably seeing funnel flo cars.
The sway back is probably by design to get the liquid to the middle of the bottom where there should be a unloading cap under the car.
Tank cars dont get tired, they simply fail.
Some tank cars have a 'sway" built in them to facilitate unloading by gravity. That way everything drains to the center.
Safety Valve: "Fatigued"could have been a correct term. It means when metal fails due to an excessive number of stress cycles. For example you can “cut” steel piano wire by holding it in a pair of pliers and bending it back and forth several times in a row. You can actually hear it cracking. Fatigue cracks are a common cause of aircraft failure which is why they have to be inspected so frequently.
Dave H.
I understand your posting. Metal fails quite rapidly in trucking, Ive seen flatbeds break clean in half… probably not without some advance warning.
Tanks is not my area of expertise (Is anything? LOL) but back in the milk tank days they drummed one Commandment into my head:
Thou shalt open thine hatch or thee wilt see tank collapse under the vacumn placed on the line during unloading or sanitizing.
Aircraft is pressurized, you dont want stressed metal to fail while people is on board.
The one issue I have in my head is that these are gravity tanks and assuming they are built stout enough to carry the weight of the liquids within, how then could they possibly rupture due to fatique? Just a question I am tossing out.
Have a GREAT weekend!
The fatigue comes from cyclical loading. Over time it weakens the metal. Also, the parts of aircraft that are most prone to fatigue are the wings.
It is actually the pressurized fuselage from pressurization cycles. Aircraft airframes are tracked for hours of use as well as number of cycles for this reason.
Mike in Tulsa
BNSF Cherokee Sub
That surprises me. It seem more common to hear of problems with the wings than with the fuselage. I guess it would be that way with military aircraft since most of them do not have the fuselage pressurized. Civilian aircraft never interested me as much as military aircraft.
I am an aircraft mechanic, and am very familiar with metal fatigue.
As N737AA stated commercial aircraft fuselages are the weak part, due to the pressurization cycles.
Military fighters are more prone to wing cracks due to “over G” imagine going around a curve to fast in
a car. You will squeal the tires and go off the road because you made too sharp a turn at too great a
speed. The same in an airplane only there is no road to go off, but you are still attempting to sharp
of a turn and are overstressing the wings and other parts of the airframe. Mostly this is attributed
to pilots watching Top Gun to many times.
Anyway back to trains, metal fatigue occurs over time in the form of hairline cracks very hard to
detect until it is to late. Try bending a paperclip back and forth after 10 -15 times it will break.
But on the 14th bend it looks normal. The last one will result in a spontaneous failure.
But not so familiar with air combat manoeuvres?
Nought to do with watching Top Gun. Over stressing was just as common before Tom Cruise as after TG hit the big screens. It has everything to do with attempting to get the most out of the aircraft. The more G you pull the faster the rate of turn and the greater probability of getting inside the turn of the other guy, or pulling enough lead to get a shot. There is a limit, and the pilot tries to sit on that limit. He hits a bit of turbulence (jet wash) while sitting on the limit and, OOPS. If you don’t fly to the limit you are dead meat. If you bust the limit you are on the mat. Can’t win.[xx(]
Sorry [#offtopic] Forgive the nostalgic reminiscences.
I worked F-15 line maintenance , for 9 years.
Sure there are times when you need max performance from the aircraft.
But in most cases 6-7 Gs is what I see on a day to day sorties.
The F-15 is an air superiority fighter. The radar has a range of over 100 miles.
The AIM 7 missile 6-9 miles.
AMRAAM 120 missile 40 miles.
With that said most shots are BVR, beyond visual range. If you can get the first shot
chances are the other guy never knew you were there until its to late.
As for the Top Gun reference that is more of a joke about competitive nature of
fighter jocks. He did this, I have to do that, to show I’m better.
Sometimes this has little to do with flying the mission and more about bragging rights.
None of this has anything to do with trains, but I just wanted to clarify.
Sounds like the Combat pilots have to deal with weak aircraft.
Gotta turn out stronger and more powerful (As in energy) aircraft for them to fly.
This topic sure went into the tank (Pun intended) quickly!
You would think that the Airline industry will use better materials to contain a life supporting atmosphere in a tube 7 miles above the earth. Are we certain that we are dealing with just metal fatique and not temperature differences?
I flew a Fs2004 747 on the computer from Heathrow to Baltimore earlier this week and noted that the air temperature outside was a nice balmy -28c at about 45,000 feet using Jeppersen’s (Spelling?) weather data.
Hello Tiger,
Yeah I knew you were just joking about Top Gun. I am a bit older than you. Used to be a GIB (guy in back) on F-4E Phantom. In those days 6 - 7 G would have been an overstress. Depended on what you had hanging underneath what the limit was. I forget the clean aircraft limit.
Getting a BVR shot depends on the politicians. Probably better now days with advanced technology AWACS and so on, but in the old days in most cases you had to identify the target to make sure he was a bad guy, so the luxury of a long range Fox 1 was something to dream of.
Safety Valve,
The aircraft are strong enough. If you are much over the sort of G that Tiger mentioned you need stronger people not stronger airframes. And you are right about it being a balmy day when you were bringing your 747 to Baltimore. Should be colder than -28deg C at 45 grand.
How can we go from tank cars to this stuf??? [#offtopic] Sorry to the rest of you who only want to read about trains.
Back to the original subject, tank cars.
Since most modern tank cars are “frameless” designs, the tank takes the stress that is normal to the underframes of house and other cars. This adds a whole new set of possible fatigue points where the buffing forces from the draft gear are transmitted to, and concentrated in, the tank itself. Checking those welds, and the tank body, thus becomes just as critical as checking the stress points on any pressure vessel, with or without wings.
As for what fails on aircraft and why, consider that commercial airliners do NOT “pull G.” Therefore, the wings aren’t very heavily loaded and fatigue is usually more concentrated at places where pressurization applies stress. G forces which are routine in aerobatic and combat maneuvers would scatter a people box all over the sky (not to mention the effect on passengers, most of whom are NOT in the prime of life and supurb physical condition, even if the aircraft somehow managed to hold together.)
Chuck (ex crew chief, ex quality control inspector, who models tank cars with frames)
Meanwhile… back at the question…
Those cars are not sway backed , they are built in a shallow V. they are funnelflow cars and designed as stated.
Something you will see on both tank cars and covered hoppers is an instruction / warning sign for workers to open hatches before commencing unloading. I have seen pics of tankcars where this hasn’t been done… they look like soft drinks cans that have been scrunched and twisted. getting this wrong is not a career enhancing move.