How true is it that you shouldn't top off C-130's with fuel and leave them parked overnight because the weight of the fuel stresses the wings? Any other planes that this is true for?
Posted by PeteyMcPetey@reddit | aviation | View on Reddit | 89 comments
This is the second or third time I've heard this from the U.S. Navy C-130 crews, but the USAF or USMC crews have never said anything about it.
Was just curious if anyone knew more about this.
B1BLancer6225@reddit
I never worked C-130's but we'd leave 280,000 on the C-5 for ages, full fuel was 332,500... I've never heard of aircraft stress overnight, but one would think a few hours at MG fuel weight wouldn't hurt an aircraft when the dynamic load of flight is worse.
epicenter69@reddit
It’s been awhile, but isn’t the fuel tanks’ liquid nitrogen system still active while the C-5 is parked?
B1BLancer6225@reddit
Yes, there are 2 ea 750L dewars, one in each wing aft root, you can see them from the #1 flap well, they are for tank pressure and inerting. There's also the climb and dive valve, in the last flap well, it's basically the vent valve.
pilot62@reddit
412s stress out the skids if they are left full, but yeah I agree it’s the fuel venting that is the issue here
Shadowrend01@reddit
I’m was a C-130 tech and it’s not about the weight stressing the wings, it’s about the fuel venting
I’ve left C-130’s at max gas overnight before with no issues, but once the sun hits the wings and the fuel warms and expands, it’ll start venting out of the dump vents
PerformerPossible204@reddit
The Japanese LOVE it when you leave a hundred gallons on their ramp!
xampl9@reddit
Story time: I was stationed in Germany and we didn’t have fancy piping to carry fuel to the ramp or shelters. We had trucks to carry it, as God and Chuck Yeager intended.
Well, the fuels guy hooked up at the tank farm, started the pump to fill the tank, then got in the cab of the truck and took a nap. Meanwhile….
The fuel delivery (spill) to the ground only stopped when his supervisor came by to see what the holdup was. I was told it was over 30,000 gallons spilled.
Fly4Vino@reddit
Today's world it would be potentially a million dollar cleanup.
My friends in the environmental world tell me there is a virtual sea of jetfuel under LAX from decades of leaking fuel lines.
MapleMapleHockeyStk@reddit
That guy is about to get his ass chewed.....!
kytulu@reddit
So, basically, a C-130 is just a C172 with a thyroid issue...
Killentyme55@reddit
"I can't help it, it's my glands!"
kytulu@reddit
Salivary glands working overtime?
jeroen-79@reddit
A fat C172
Carlito_2112@reddit
It's not fat, it's big ~~boned~~ fuselaged/winged
EmbarrassedTruth1337@reddit
This is true for most aircraft. We'll get a king air fueled for a winter medevac that gets cancelled and if they don't tell us there'll be puddles on the floor a few hours after they push it back inside.
reduhl@reddit
So your saying you should not smoke in the shade of the C-130.
jacoob_15@reddit
How else are you supposed to fuel supe while deployed?
ttystikk@reddit
Or any plane.
ArcticBiologist@reddit
Did the same with my snowmobile once. I was told to fill it to the brim when parking up for summer to reduce the formation of moisture in the fuel tank. So I did that at the end of winter (with a temperature around 2-3°C).
It was gushing out when it was standing in the sun at 20°C a few months later...
fotowork3@reddit
Why would you not empty out the tank for that period of time?
Spaceinpigs@reddit
Corrosion in the fuel tank is usually the reason. Moisture can condense on the walls of an empty tank and lead to water buildup which then rusts out the tank or leads to fuel line blockage
fotowork3@reddit
Maybe it depends on the part of the country but here on the north northwest every time there’s a power outage my son has to go and fix every generator because all of the gas and everybody’s generator has turned to garbage. And ours starts right up because it’s empty and we just put fuel in it, but I’m not a mechanic myself.
Spaceinpigs@reddit
Depends how long the fuel sits. Fresh fuel is obviously the best but regular gas can go bad within months unless treated with a stabilizer or if you use a special fuel. Fuel usually has ethanol in it now and if moisture gets in the tank, the ethanol can separate out into a sludge in the bottom of your tank. The best thing to do is empty the tank IF you can keep the vehicle or tank in a warm place that doesn’t have temperature variations
ArcticBiologist@reddit
Never had any trouble with fuel going bad, we had no ethanol added to it
Spaceinpigs@reddit
Aviation fuel won’t have it. Aviation fuel also doesn’t generally go bad. Regular gas will start to deteriorate within 3-6 months of production and is usually completely expired within 3 years
ArcticBiologist@reddit
I wasn't putting aviation fuel in my snowmobile. It was regular petrol from the fuel station down the road.
FNGforlife@reddit
As another 8 year C-130 knuckle dragger I can confirm.
CarminSanDiego@reddit
Apes together strong
Hlcptrgod@reddit
Hahahahaha
GolfArgh@reddit
Spent 28 years as an AF crash firefighter, can confirm the fuel spill.
Fatherbiff@reddit
This is true for any aircraft. Unless i know they are departing shortly, I always leave room for expansion. Obviously weather dependent as well.
badcrass@reddit
Why is the plane peeing?
besidethewoods@reddit
I mean we all need to take a leak first thing in the morning. Why should we expect our C-130s to be any different?
PeteyMcPetey@reddit (OP)
So each time, these guys take about 15-20k of fuel after landing, and then want another 25-30k in the morning.
That light initial load seems like there'd be plenty of room for expansion.
Maybe they just want to shove off and get to the bar 20 minutes quicker after landing.
Signal_Examination70@reddit
Ramp load vs mission requirements.
Drenlin@reddit
A LOT of planes do this, too. It's not at all limited to the 130.
Taptrick@reddit
Same on the P-3 for fuel venting. Once the sun goes up and heats up the wings it starts pissing fuel all over the ramp.
Moroz_Enderas@reddit
The worst part of the P3 leaking fuel onto the ramp is that it makes it harder to see the leaking hyd fluid which is the best way to know that there is still hyd fluid in the system 😅
Killentyme55@reddit
Yep. With the Orion, leak-checks good means "is it leaking? Then it checks good".
MapleMapleHockeyStk@reddit
The Chinook and oil.....
BearPaws0103@reddit
Yep, had this happen more than a few times
That70sShop@reddit
It reminds me of when there was a worldwide shortage of mining tires and a tremendous demand for copper. We ended up having to get some Russian Belshina tires. We weren't allowed to tie them down loaded for risk that they would blow which seems awfully silly because if it's that much of a risk it's a risk every time there's anyone on the ground near the tires. We also weren't allowed to hit 6th gear. I guess you'd have to measure the heat, but I would think a long run in fifth would heat up the tires a lot more than a short run and sixth. I think somebody had a mishap somewhere sometime and then that resulted in overabundance of caution. From time to time you get a nice Bridgestone blow at 250 psi, and you don't bring production to a halt just because you got one bad tire once.
It doesn't make any sense at all. Either the structure is designed to support that weight, or it's not. If it can support the weight for 5 minutes, it'll be fine for 5 hours, 5 days, or 5 years. Engineered structures don't get tired or need a nap
discombobulated38x@reddit
Yeah they do. Corrosion, creep, and cyclical loading all make structures tired.
That70sShop@reddit
"Cyclical loading." Of course. But once it's fueled the cyclical nature of that load cycle is complete. While it sits, the forces exerted are in stasis.
discombobulated38x@reddit
Except they clearly aren't, given the person in the know in this thread saying that when the sun hits the aircraft in the morning it starts leaking fuel everywhere, because thankfully the breather vents in the tanks mean that they don't burst.
phedders@reddit
Ahh cyclical is the key there. But this is a plane. It is designed to do cycles... of take of and landing, and handle turbelence etc. And those are shock loads.
Static loads within limit are not going to be a problem. Time or no time.
Corrosion is going to happen loaded or not.
That70sShop@reddit
Exactly.
discombobulated38x@reddit
Yes, it's not necessarily designed to handle having fully topped off fuel tanks overnight sat static though, as evidenced by this very issue. We know from elsewhere in the thread that this is a fuel wastage issue not a mechanical issue, but there are similar issues with a mechanical impact on engines and airframes of a similar vintage, so you can't just discount something that wasn't explicitly designed for not causing a problem.
Indeed, provided all possible loading scenarios have been assessed as I've said above.
Some forms of corrosion only occur at high strains and or temperatures, acoss airframes and engines.
Hidden_Bomb@reddit
Thanks for the cool story, but that really isn’t how material science works.
SubarcticFarmer@reddit
You obviously don't understand tires or engineering.
juanmlm@reddit
Engineered structures do get tired though. It’s literally called metal fatigue.
Visual_Confidence460@reddit
But metal fatigue is cyclical not static so the point still stands.
That70sShop@reddit
. .and it literally doesn't happen while it's sitting still. It literally happens when it's under varying stress. The process of refueling puts far more stress on it than sitting there fueled.
galvanized_steelies@reddit
Yeah it turns out leaving 80k lbs of fuel on a 60ft lever arm puts a fair amount of stress on the attaching points, and also on the PRC inside and outside the wing that’s keeping all the fuel in.
Also fuel expands and contracts, so if you go to full bags and then don’t take off before it warms up you’ll get the golden shower of doom, and some enviro tech somewhere is going to have an aneurysm
Galf2@reddit
I don't think that amount of fuel creates any danger for the wing structure, they're supposed to flex taking the full weight of a loaded plane, some fuel in the wings shouldn't be a problem and if it is you probably shouldn't fly the plane... But as others have said the venting issue is a big deal so that's why.
Probably in the scope of decades of service leaving it ALWAYS fully loaded is going to add some stress in specific spots but that's surely such a minimal issue you just factor it in the maintenance checks assuming always for the worst
galvanized_steelies@reddit
I mean there’s a reason the maintenance manual has a maximum fuel uplift on the pre-flight, and it’s nowhere near the full fuel amount, and it’s not just for venting purposes because that’s a different number that is also mentioned.
It is genuinely bad for the wing and aircraft structure, it’s one thing when the wing is suspending itself and the load of the aircraft in the centre, but to leave a massive amount of weight bending in a non-flight direction for 24+ hours is not good
Also, not all airports are built the same, so there’s a max weight you can leave on the ramp for any given period of time. Not an issue at most bases, but you don’t always deploy to a base
justhereforthesalty@reddit
Not exactly what you're referring to but there's a limit for how little fuel you can have in the wings with a heavy cargo load.
Essentially if you've got a heavy cargo bag, you need to have some extra fuel left in the wings so it doesn't put too much stress pulling down the middle.
psillyhobby@reddit
I know this is true but I feel like a diagram would help it make more sense.
Searching4Health@reddit
Very simplified.
If you think that in flight the wings literally want to fly up and all that stops them is being attached to the big fat fuselage that wants to drop back to earth.
Put some weight in those wings and they’re less flighty.
A side story I heard - Special Forces Herc in Africa moving lots of gold from one country to another. They had to add tip tanks to the wings to keep them happy.
Took them over certified max takeoff weight but they managed - apparently never went over 250ft on the flight anyway.
mig82au@reddit
Adding fuel never reduces wing bending moment, only changing its distribution from inboard to outboard does that. So, if you have some centre tank fuel you can move it outboard, or choose to fill outboard instead of centre. Alternatively you can reduce the time spent at high bending moment by feeding from the centre first.
jememcak@reddit
That's not true, as evidenced by the fact that C-130 wing relieving fuel absolutely is a thing, and there is no requirement for us to put it in outboard main tanks except to maintain fuel balance.
It seems that you're assuming the inboard and outboard fuel tanks are perfectly symmetrical around each wing's center of lift, but that's not the case. We generate much more lift from the inboard section of the wing, and increasing total fuel weight does indeed reduce the bending moment of the wing by increasing the overall wing-down moment.
If what you're saying is true, we wouldn't use wing relieving fuel in the C-130 at all.
gijose41@reddit
a moment is the weight of the object times the distance from the fulcrum.
Adding fuel can reduce the wing bending moment, as the extra lift required for that fuel is concentrated inboard (producing less moment) then the weight of the fuel outboard (more moment)
JPaq84@reddit
Huh. So this is probably why SOP on the 737 is to feed from center tanks first?
psillyhobby@reddit
So distributing the weight across the entire wing with more fuel or outboard tanks means there’s less of a hinging type of force being applied at the center of the wingspan.
mig82au@reddit
I believe you've misunderstood what Minimum Zero Fuel Weight is. It's the maximum amount of weight that can be put in the fuselage, for wing bending reasons. Adding fuel does not relieve this, the limit is simply to stop an operator from almost filling a fuselage to MTOW because there's little fuel required. i.e, the MZFW limits how centered MTOW can be.
ABoutDeSouffle@reddit
Sounds like nonsense. If the couple tons of fuel at rest would stress the wing attachment points too much, flying with full tanks would just shear them off.
Killentyme55@reddit
While it's true that the OP's claim is a myth, keep in mind the way wings are designed as far as stress loading. Especially in the case of cargo aircraft, the wing structure is built to handle much higher positive G loads than negative, for pretty obvious reasons. A heavy fuel load on a parked aircraft would put considerable downward force on the wings, which is essentially the same effect as negative G loading. Once in flight and lift takes over, we're back to positive wing loading where the spars and fittings are much happier.
Again, the venting issue is the actual reason for limited fuel loading overnight on the Herc. The wings are built strong enough to handle the weight, but from a structural point of view it's not beyond the realm of possibility.
AtomR@reddit
Couple of C130 techs in thread have confirmed that it's due to fuel venting
martinjh99@reddit
Is this the same for SR71's and their dripping fuel ??
The only way they stop leaking fuel is get topped up after launch and go as fast as they can to get the thermal expansion to stop up the holes...
Nimhface@reddit
When I was a lineman we could not fill the tanks of the MU-2 fully on one side but had to alternate wings a little at a time. I was told that if you toped off one side with the other empty then you could crack the windows under the wings.
Conscious-Fact6392@reddit
I believe it was because it would tip over
Nimhface@reddit
Very possible. Those were some hefty tip tanks. I just gave the reason I was told.
Ginagreen9@reddit
It's true. If the wing tanks are filled when cool, they will vent as the ambient temperature expands the fuel. So when refueling I would stop filling 500 lbs before the automatic shut off. On the 130 models with external tanks there was no reason to top the mains off unless fuel would be that critical. As far as wing stress. Lockheed dictated that the outboard fuel tanks have a minimum of 715 lbs more fuel in them than the inboard. Just kept 1000 more to make it easier. This kept the center wing stress minimal by keeping the wing flatter in flight.
sierrahotel74@reddit
There was an incident involving a C-141 several years ago, can’t remember the whole story, just bits here and there. I believe they had done maintenance on its fuel system and were testing if the repairs held. It failed and the, I think left wing, broke.
KazakhstanPotassium@reddit
I’m on mobile so I can’t do the fancy auto scroll hyperlink, but scroll down to “Memphis Int'l Airport TN/2001”.
https://c141heaven.info/dotcom/mishap_paul_hansen.htm
23_Red@reddit
This happened to a E-8 JSTARS out in Qatar. Plane went through heavy maintenance prior to deployment and the plugs were left in fuel vents. One of the tanks blew during AR and damaged the wing structure beyond repair.
Fabulous_Pitch9350@reddit
u/sierrahotel74 may be remembering this. I remember being just able to see this from the street that runs in front of the FedEx hub (KMEM).
sierrahotel74@reddit
That’s the one.
DeathlyBro@reddit
When I was working with KC-135s, we had to roll the alert jets (topped off with fuel always) back and forth every few days so the tires wouldn’t get deformed due to the amount of weight on them. I don’t know if its the same with the C-130’s cause they don’t hold nearly as much fuel (200,000lbs) but just a cool little fact
bobbygamer121@reddit
When I was working with KC-135s, we had to roll the alert jets (topped off with fuel always) back and forth every few days so the tires wouldn’t get deformed due to the amount of weight on them. I don’t know if its the same with the C-130’s cause they don’t hold nearly as much fuel (200,000lbs) but just a cool little fact
TheMightyPushmataha@reddit
DC9’s had a spot on the top of the wings that would ice up overnight under standard conditions if the tanks were topped off. Something about the tanks being too close to the wing surface and the fuel cooling faster than the aluminum.
Silly_Primary_3393@reddit
This true for every aircraft than has vented fuel tanks, and it‘s also true for just about all liquids. All jet fuels fall into the category of kerosene type and have an expansion ratio of 0.00055 per F degree change. This means if you fill up a 32F but they the tank warm up to 100F, the fuel will expand by about 4%. If you max out the tanks when filling with fuel, the expansion has to go somewhere and the one way is via the vent system that dumps the fuel on the ground. The gas you pump in your car has an expansion rate of about 0.069 per F change but you usually won’t encounter this for as soon as you fill up you drive away consuming the fuel and leaving a void. Note cars nowadays have a vapor recovery system that stores the expansive fuel vapors for later use so the odds of you encountering fuel spillage are slim as long as you don’t overfill the tank.
rinfodiv@reddit
It literally depends on which crusty old FE trained that particular crew. I’ve had FEs that don’t care how much gas we have (other than too little), and FEs that won’t let me fuel under any circumstance overnight…
The S in NATOPS doesn’t stand for anything in this community…
BigJellyfish1906@reddit
Think about it like this. The airplane is rated to 2+ Gs in flight. That means the wings can easily take twice the weight of the plane. So how could fuel on the ground cause a problem?
cman528@reddit
If not accounted for, fuel expansion can make a mess regarding anything…..not just the C130
SnarfsParf@reddit
GA line tech here. If I get an order to top someone off in the morning I make sure to leave extra room (don’t fill it all the way up to the tippy top) if I know it’s going to sit into the afternoon. A coworker did just that to a baron once in July and by the time 1500 rolled around the fuel had expanded and siphoned out of the vents onto the ramp.
RightRudderz@reddit
Ex c130j pilot/ip, never worried about fuel weight overnight but slope of a ramp/temp changes/slight tire pressure differences could cause fuel to overflow/vent in minimal amounts if absolutely filled to max.
We were more worried about big AF coming after us for an “accident” and the months of paperwork/followup afterwords.
phedders@reddit
IF that was true... you better not take off.. or land... or hit turbulence.
I would suspect its more about pressure issues (from change in temp) and fuel loss through evaporation. Maybe even leaks - Some planes (the high flyers) are famous for not being "able to hold their drink" on the ground and at static temperatures. (U2? and/or blackbird?) due to the fuel tank design.
BrewCityChaserV2@reddit
I'm sure the people who designed the airplane at Lockheed Martin never heard of this problem. Maybe you should contact them via a time traveling system from the 1950s.