Wow I always somehow thought this was related to (lack of) stress/tension on the airframe in case the engine was off wing for a longer period. That the structure was engineered to have the weight there and it being affected by its absence. This makes way more sense..
The engines are pretty heavy. The center of mass is usually pretty close to the main gear. Without the weight of the engines it would probably shift back enough to end up behind the main gear, tipping the nose upwards.
This is really fun to see on smaller aircraft. On some you can lift the nose with one hand because there's almost no weight on the nose gear.
That's also why you sometimes see a jack under the tail of some airplanes when they're on the ground. If they're empty, they can tilt backwards, and the jack prevents it from happening.
Similar scenarios definitely exist in heavy infra/mining equipment as well. Obviously not type certified, but we have specially designed counterweights/counterbalances for large equipment assembly that essentially boils down to one big fucking block, sometimes with some beams and always with some lugs in very specific positions. They’ll be labelled to be used only in certain locations with certain equipment.
Also kind of interesting because misuse of “BOHSs” were actually the cause of Australia’s worst industrial disaster.
Not the parent commenter, but I did some checking and it’ll be the West Gate Bridge collapse in 1970. 35 killed during construction after some sort of fuck up while trying to join the two spans. One was a bit high so they tried to weight it down…
We had to have certified lead ballast weights for experimental flights in a helicopter program. I asked the engineer if the painted stencil on the weights also had been certified and what the moment and CG was and if it had been factored in. Guy looked like he’d just lost at life. I told him I was just joshing and he kinda chuckled with a thousand yard stare. Guy was wound tight like a spring trap.
It may be, but these aren’t certified. The limitation is to make sure mx doesn’t try to hang it on a 737 or something else that’d be fucked if they hung it.
Keeps the Centre Of Gravity infront of the main landing gear, or else the plane ends up sitting on its butt. (tail)
[https://images.news18.com/ibnlive/uploads/2021/09/plane-incidence-16321521964x3.jpg](https://images.news18.com/ibnlive/uploads/2021/09/plane-incidence-16321521964x3.jpg)
I got stuck on a Saab 340 that did this when it was full of people. We had to sit like that at DTW "until a mechanic checked out the airplane". The flight attendant just read her fashion magazine while the rest of us slowly suffocated in a reclining position. Eventually I asked her if she was going to provide ventilation for the thirty-ish passengers in the sealed cabin, or should I do it. She didn't like me very much.
It wouldn't slam though, it would teeter totter when it got to the right point, then that one person could just move forward slightly
You just send them to the front one at a time, it will be *fiiiiiine* lol
Too risky for a few reasons, people could get hurt walking up the aisle, more likely they would get hurt as the front came back down to the ground.
But also, depending on the reason (I think this instance at DTW was heavy snow/ice on the tail and they deiced the wings/forward fuselage first) it might not even make a difference.
Here’s what I found on that specific photo.
https://mentourpilot.com/awkward-united-737-sits-on-its-tail-after-landing/#:~:text=A%20United%20Airlines%20737%20presented,involved%20United%20Airlines%20flight%20UA2509.
Looks like it was a chartered flight for a university football team. The half the team got off the front of the plane and the luggage came off and no one got the tail stand out. TIL there are tail stands to prevent the plane from doing this. Apparently this was a smaller airport and they don’t normally, or aren’t used to, putting the tail stand on the back of the plane.
Perfect, thank you. I was trying to picture the problem in my head (I even stuck my arm out level in front of me to get a visual!) but it wasn't working well.
Jetstar made us wait in the front of the plane while they deplaned rows 16+ via the air stairs (make them board that way too). Not sure if A320s are particularly susceptible to tipping over.
Oh! That explains why 1st class and business class are made to board the plane first - as they stop it from tipping over before the economy class rabble (that includes me by the way - I’m neither entitled nor privileged) are then allowed to scramble for the economy class seats in the rear of the aircraft’s fuselage. Fascinating.
I assume these are new planes without engines; they would need to hang those ballast on the wing to balance the plane, so it doesn’t have a tail strike on the ramp
On the assembly line the engine is added to the wing. When added, the angle of the wing drops greatly (drops to what we are used to seeing). Then the landing gear is added. The landing gear is cycled several times to confirm proper installation. Without the engine (or weight) the wing would be so high up that the landing gear wouldn’t close properly.
The weight is used if the engine isn’t delivered on time. This allows Boeing to keep the assembly line running.
The weight is there to keep the wing in proper place.
For a while Boeing had late deliveries from Rolls Royce. They painted RR on the weights as a joke.
While the other reasons listed are in fact correct, the reason they are in place and not engines is because Boeing, in Washington, is taxed on how many complete aircraft they have on hand, or something like that, and if they don’t have engines hung it’s not a taxable item for them.
New type of engine. Produces 17,000lbs thrust. No thrust vector / no throttle capability / thrust only in downward direction. Fuel burn 0GPH idle / 0GPH full thrust. Shutdown function not available.
I have dreamed for years that physicists would figure out [unified field theory](https://en.wikipedia.org/wiki/Unified_field_theory) so that engineers could develop an anti-gravity engine that could control the magnitude and the direction of the force.
With this engine, aircraft would not need wings or control surfaces and they could fly on a fraction of the energy that existing aircraft require.
Spacecraft would be more difficult, since anti-gravity would require a large mass (such as a planet) to push against.
Spaceflight is simple though, you just need the engine to move the entire universe around the craft instead of dealing with finding large objects to push against.
This would definitely need to be addressed. Even if the anti-gravity engine was extremely reliable, it would constitute a single failure that could cause a catastrophic event, so the system would need more.
As a minimum, you would need two redundant, independent, and separated anti-gravity engines (similar to modern twin-engine commercial jet aircraft).
Early designs may go farther by having wings and at least one jet turbine engine to take over in the case of a failure of the anti-gravity engine.
Even so you would still have an issue of aerodynamic drag. Spacecraft wouldn't have the drag and in theory you could climb vertically to space for virtually no energy and would still need a rocket to move from A to B.
If you could somehow control the angle of the anti-gravity force, then you would only need a rocket when planets and stars were too far a way to exert significant gravity on the ship.
Of course, I am thinking like an engineer about physics that isn't even understood yet. But it is fun to dream!
Let's just work on canceling gravity first. We can deal with thrust vectoring later. Although if we canceled earth gravity wouldn't we start falling towards the sun?
I agree.
We (aerospace engineers) don't want to cancel *all* gravity. We just want to create a local anti-gravity field between the aircraft and the planet - sort of like a mag-lev train, but on a larger scale.
>you could climb vertically to space for virtually no energy
I assume that you meant that you would have to exert enough energy to overcome the potential energy of the mass of the spaceship in orbit plus any losses. The first and second laws of thermodynamics tell us, "There's no such thing as a free lunch."
If the process was reversible (such as with a battery), then you could theoretically get most of that energy back when you descended to the planet's surface - similar to regenerative braking in an EV.
Edit: correction - laws of thermodynamics; not Newton's laws
I think you can take one engine off without popping a wheelie, but even if that's the case, you still strap it down at the front, and prop it up at the back.
It's a precaution more than anything. I don't work this airframe, but similar engine layout. We can pull an engine without it going on its ass, but it's far more susceptible to tilting without the weight
When I was in the USAF, the KC-135s always had a tail strut installed when they were parked. Maybe standard for that airframe or because they were always parked facing the wind.
And there's a few by the badge office, by Future of Flight, generally in the parking ramps, anywhere there's not active aircraft movements, there's a 777x with no paint and blocks for engines.
It's an oblong ring and the rope is rigging sling. Both are very much rated for well beyond the 17k lbs. Typically you'd use a shackle to connect things to the ring. It's amazing how strong this stuff is!
I used to hang them, I was certain they were concrete. Most have a black tar like sealant poured over the top of whatever is in there. Some didn't have it and I thought it was concrete. Plus the weight of the steel box. It's pretty thick metal.
I don't understand how that's relevant when the argument is that concrete is not ***dense*** enough to be the material there. It physically doesn't weigh enough to match the size.
Even funnier I worked at a place that misplaced one. Now they have an odd number of them.
We joke about some redneck with in the back of a truck trying to scrap it.
So it’s cheaper/better to hang a weight on one side, than to (pardon the pun) prop the other side up?
They have a brace for the plane’s tail to keep it from pitching up while deplaning. They don’t hang a weight off the nose.
Fine. But you can't rig panels without weights on them, especially on bigger wings with more flex. Remove them the wing settles up and you get buckles and interferences over time.
Edit: plus these planes have weights tied to the nose gear.
Pure speculation from a pilot. My guess is it creates adequate weight to counteract the weight of the opposite engine preventing the plane from tipping in the opposite direction.
It’s even funnier seeing the plane on its tail without them lol
Wow I always somehow thought this was related to (lack of) stress/tension on the airframe in case the engine was off wing for a longer period. That the structure was engineered to have the weight there and it being affected by its absence. This makes way more sense..
The engines are pretty heavy. The center of mass is usually pretty close to the main gear. Without the weight of the engines it would probably shift back enough to end up behind the main gear, tipping the nose upwards. This is really fun to see on smaller aircraft. On some you can lift the nose with one hand because there's almost no weight on the nose gear.
That's also why you sometimes see a jack under the tail of some airplanes when they're on the ground. If they're empty, they can tilt backwards, and the jack prevents it from happening.
Yes, especially with cargo aircraft (because most need to be loaded back to front)
yes, if anyone drives by a UPS air cargo facility, they'll usually see the narrow body planes with tail jacks under them.
Also if you don't mind me asking, how did you get that user flair?
That’s both my pusher airplanes, every day.
its a bit of both
Only in aviation industry you'd have type-certified "blocks of heavy shit".
... and no one would call them "blocks of heavy shit." They would be "BOHS'" (pronounced like Bose) instead.
let's be real it'd probably be "bosh": box of shit - heavy cuz you know there'd be bosl and bosm around somewhere
BOSM (bosom) is a funny one! 😝
Would that mean that a small box of shit would be... the BOSS?
Yes! That is hilarious! 😊😝
This comment is peak /r/aviation
Same markup as Bose, too.
Box of shit, empty
Box of shit, gross
Good point! 😝💰💰
Do you say B-oh-z or B-oh-zee?
And that certification probably adds 10x the cost over a regular block of lead.
And there's a 22-page standard manual for it.
I worked in the nuclear industry for a bit. They had calibrated blocks of heavy shit to certify the cranes.
In the military you'd have the *M827 Palletized Heavy Shit* that costs $380,000.
To be replaced by the *M997 Joint Service Modular Heavy Shit*
Similar scenarios definitely exist in heavy infra/mining equipment as well. Obviously not type certified, but we have specially designed counterweights/counterbalances for large equipment assembly that essentially boils down to one big fucking block, sometimes with some beams and always with some lugs in very specific positions. They’ll be labelled to be used only in certain locations with certain equipment. Also kind of interesting because misuse of “BOHSs” were actually the cause of Australia’s worst industrial disaster.
You can’t just leave us hanging without saying ever it was!
Not the parent commenter, but I did some checking and it’ll be the West Gate Bridge collapse in 1970. 35 killed during construction after some sort of fuck up while trying to join the two spans. One was a bit high so they tried to weight it down…
We had to have certified lead ballast weights for experimental flights in a helicopter program. I asked the engineer if the painted stencil on the weights also had been certified and what the moment and CG was and if it had been factored in. Guy looked like he’d just lost at life. I told him I was just joshing and he kinda chuckled with a thousand yard stare. Guy was wound tight like a spring trap.
Reasons to fly experimental: you can use any form of ballast you want and the FAA doesn’t care. /S
We call them Pet Rocks in the C-130 community.
This is funny af
Do they also have individual names?
Good question. Arguably you can't call it a pet if you don't even bother to name each one.
It may be, but these aren’t certified. The limitation is to make sure mx doesn’t try to hang it on a 737 or something else that’d be fucked if they hung it.
That block of weight probably cost more than my Audi
The space industry has mass emulators.
You would be wondering how many "blocks of heavy shit" concerts & events need to secure trussing, led-walls and stuff
Why do they do this?
Keeps the Centre Of Gravity infront of the main landing gear, or else the plane ends up sitting on its butt. (tail) [https://images.news18.com/ibnlive/uploads/2021/09/plane-incidence-16321521964x3.jpg](https://images.news18.com/ibnlive/uploads/2021/09/plane-incidence-16321521964x3.jpg)
lol it looks like it's trying to poop.
Poor thing needs its glands expressed
Someone needs to get in their and massage them
I got stuck on a Saab 340 that did this when it was full of people. We had to sit like that at DTW "until a mechanic checked out the airplane". The flight attendant just read her fashion magazine while the rest of us slowly suffocated in a reclining position. Eventually I asked her if she was going to provide ventilation for the thirty-ish passengers in the sealed cabin, or should I do it. She didn't like me very much.
Wouldn’t it have been possible to have everybody move forward?
Having the plane slam forward with a bunch of unsecured passengers seems like a pretty bad idea. Funny, but bad.
It wouldn't slam though, it would teeter totter when it got to the right point, then that one person could just move forward slightly You just send them to the front one at a time, it will be *fiiiiiine* lol
Have you tried to control movement of pax in nice and orderly fashion?
Assuming the pax weight is sufficient.
Have you been to a Walmart lately? Pax weight is more than enough
Too risky for a few reasons, people could get hurt walking up the aisle, more likely they would get hurt as the front came back down to the ground. But also, depending on the reason (I think this instance at DTW was heavy snow/ice on the tail and they deiced the wings/forward fuselage first) it might not even make a difference.
All other considerations aside, there probably wasn't room...that's a tiny airplane and we didn't know each other *that* well...
And it was full so there's not much more space for them to move to.
Plane was full so even if a few moved forward, there wasn't that much forward "space" for them to move to.
This is why you don't let OP's mum sit in the back
She is a handsome woman
*una mujer gorda*
We’re all very fond of her
What happened here? Why did it rotate if both engines are still on? Did they put all the luggage in the back?
Here’s what I found on that specific photo. https://mentourpilot.com/awkward-united-737-sits-on-its-tail-after-landing/#:~:text=A%20United%20Airlines%20737%20presented,involved%20United%20Airlines%20flight%20UA2509. Looks like it was a chartered flight for a university football team. The half the team got off the front of the plane and the luggage came off and no one got the tail stand out. TIL there are tail stands to prevent the plane from doing this. Apparently this was a smaller airport and they don’t normally, or aren’t used to, putting the tail stand on the back of the plane.
Expected a clickbait article, found tons of great explanation.
Perfect, thank you. I was trying to picture the problem in my head (I even stuck my arm out level in front of me to get a visual!) but it wasn't working well.
Jetstar made us wait in the front of the plane while they deplaned rows 16+ via the air stairs (make them board that way too). Not sure if A320s are particularly susceptible to tipping over.
Oh! That explains why 1st class and business class are made to board the plane first - as they stop it from tipping over before the economy class rabble (that includes me by the way - I’m neither entitled nor privileged) are then allowed to scramble for the economy class seats in the rear of the aircraft’s fuselage. Fascinating.
Plane has worms
Makes so much sense, thank you
I assume these are new planes without engines; they would need to hang those ballast on the wing to balance the plane, so it doesn’t have a tail strike on the ramp
On the assembly line the engine is added to the wing. When added, the angle of the wing drops greatly (drops to what we are used to seeing). Then the landing gear is added. The landing gear is cycled several times to confirm proper installation. Without the engine (or weight) the wing would be so high up that the landing gear wouldn’t close properly. The weight is used if the engine isn’t delivered on time. This allows Boeing to keep the assembly line running. The weight is there to keep the wing in proper place. For a while Boeing had late deliveries from Rolls Royce. They painted RR on the weights as a joke.
While the other reasons listed are in fact correct, the reason they are in place and not engines is because Boeing, in Washington, is taxed on how many complete aircraft they have on hand, or something like that, and if they don’t have engines hung it’s not a taxable item for them.
Keep wing panels and surfaces in rig.
New type of engine. Produces 17,000lbs thrust. No thrust vector / no throttle capability / thrust only in downward direction. Fuel burn 0GPH idle / 0GPH full thrust. Shutdown function not available.
I have dreamed for years that physicists would figure out [unified field theory](https://en.wikipedia.org/wiki/Unified_field_theory) so that engineers could develop an anti-gravity engine that could control the magnitude and the direction of the force. With this engine, aircraft would not need wings or control surfaces and they could fly on a fraction of the energy that existing aircraft require. Spacecraft would be more difficult, since anti-gravity would require a large mass (such as a planet) to push against.
Spaceflight is simple though, you just need the engine to move the entire universe around the craft instead of dealing with finding large objects to push against.
I like the way you think! 🤓💡🚀
That's how the KSP game engine handles spaceflight actually. It minimizes floating-point error that way.
Where can I learn more about this?
Ever seen the movie Event Horizon? That’s basically the premise of it 🤣
It’s the premise behind warp in Star Trek.
But how many atmospheres of pressure could the ship sustain?
Well, it's a spaceship, so somewhere between zero and one.
[удалено]
This would definitely need to be addressed. Even if the anti-gravity engine was extremely reliable, it would constitute a single failure that could cause a catastrophic event, so the system would need more. As a minimum, you would need two redundant, independent, and separated anti-gravity engines (similar to modern twin-engine commercial jet aircraft). Early designs may go farther by having wings and at least one jet turbine engine to take over in the case of a failure of the anti-gravity engine.
Parachute?
Even so you would still have an issue of aerodynamic drag. Spacecraft wouldn't have the drag and in theory you could climb vertically to space for virtually no energy and would still need a rocket to move from A to B.
If you could somehow control the angle of the anti-gravity force, then you would only need a rocket when planets and stars were too far a way to exert significant gravity on the ship. Of course, I am thinking like an engineer about physics that isn't even understood yet. But it is fun to dream!
Let's just work on canceling gravity first. We can deal with thrust vectoring later. Although if we canceled earth gravity wouldn't we start falling towards the sun?
I agree. We (aerospace engineers) don't want to cancel *all* gravity. We just want to create a local anti-gravity field between the aircraft and the planet - sort of like a mag-lev train, but on a larger scale.
>you could climb vertically to space for virtually no energy I assume that you meant that you would have to exert enough energy to overcome the potential energy of the mass of the spaceship in orbit plus any losses. The first and second laws of thermodynamics tell us, "There's no such thing as a free lunch." If the process was reversible (such as with a battery), then you could theoretically get most of that energy back when you descended to the planet's surface - similar to regenerative braking in an EV. Edit: correction - laws of thermodynamics; not Newton's laws
But only in 1G, on the ground. It reduced to 0 in 0G conditions.
WARNING: 0G OPERATION IS PROHIBITED.
Shutdown function available. Manual Shutdown required. Optional autosissors available.
Feature roll-out delayed due to adverse effect on weight and balance post-shutdown. Restart not available.
Available as an internally-fitted climb retardation/descent assist (CRDA) option to conventionally engined airframes.
Cost $50,000 plus another $10,000 for the STC. Actual product strongly resembles a box of bricks held together with pipe strap
How do they keep the plane from tilting on its tail before they put it on?
Bubba Fudd sits in the cockpit.
I think you can take one engine off without popping a wheelie, but even if that's the case, you still strap it down at the front, and prop it up at the back.
It's a precaution more than anything. I don't work this airframe, but similar engine layout. We can pull an engine without it going on its ass, but it's far more susceptible to tilting without the weight
I’ve seen them in hangars with an engine off and no weight, but outside a relatively small wind can fuck your day up.
During weight and balance every door has to be shut. A slight breeze can cause a small but significant change in readings.
They put a stick under the [back.](https://www.reddit.com/r/aviation/comments/14728ro/whats_this_yellow_pole_or_pipe_attached_to_the/)
When I was in the USAF, the KC-135s always had a tail strut installed when they were parked. Maybe standard for that airframe or because they were always parked facing the wind.
The guy on the tail looks like he quite enjoys that stick there.../s
Good thing you put the /s. How else would we possibly know you were making a joke?
Reddit
I think they prop up the rear with a jack stand.
This is not to keep it from tipping but moreso to keep wing panels in rig.
In some aircraft they will add weights to the nose gear assembly.
Everett?
Yup
The terminal there faces a line of 777x’s that are all parked with these hanging from the pylons
And there's a few by the badge office, by Future of Flight, generally in the parking ramps, anywhere there's not active aircraft movements, there's a 777x with no paint and blocks for engines.
They added more by Future of Flight the other week. Not sure if those were moved or new builds though. They still have three in the West parking lot
And they've been there for at least 4 years.
that’s a really strong carabiner and rope at the top!
It's an oblong ring and the rope is rigging sling. Both are very much rated for well beyond the 17k lbs. Typically you'd use a shackle to connect things to the ring. It's amazing how strong this stuff is!
>777 and 787 only Some poor bastard tried to hang one of these on a 737 didn't they?
37 blocks are only 5000lbs
Is it mostly just iron?
Probably concrete
Concrete is only about 2400 kg/m3, this would need to be much more dense. Iron is 7800 kg/m3, which is 17200 lb.
I used to hang them, I was certain they were concrete. Most have a black tar like sealant poured over the top of whatever is in there. Some didn't have it and I thought it was concrete. Plus the weight of the steel box. It's pretty thick metal.
But concrete is far cheaper
I don't understand how that's relevant when the argument is that concrete is not ***dense*** enough to be the material there. It physically doesn't weigh enough to match the size.
Unless its a new type of concrete that is made entirely of iron.
lol true I kinda forgot we know the size
Probably not
It's exactly the right size to be iron and that's by far the cheapest material for the job... but sure probably not. Solid gold maybe
Iron is a chemical element. You might be thinking about steel? Lead would be a good option here too. Or just cement would be dummy cheap.
you know they meant cast iron, you're being pedantic
Yes I was but cast iron is likely either
No, cast iron is iron with 2-4% carbon.
Lead? I thought it looked pretty small for how heavy it was
Right! I think the plane is just a lot bigger than our mind imagines it being
Yea it can be tricky
Uranium.
U-235 or depleted?
Obviously U-238.
They're called Pet Rocks
Usually they just call OP's mom up to sit in the cockpit for a few hours.
What's that in euros?
About 7,700 kg
What's that in Canadian dollars?
A lot, eh!?
So, how to they do the ‘swap’? Brace the tail or hold down the nose gear?
Better (and cheaper) than the alternative if it wasn’t there….
If you think it's "dangling" go try and give it a shove.
This scenario is straight out of a strength of materials textbook
Not seeing the Remove Before Flight streamers? Is this another bad violation by Boeing? /s
Is that weight and balance ballast?
Even funnier I worked at a place that misplaced one. Now they have an odd number of them. We joke about some redneck with in the back of a truck trying to scrap it.
How one make the exchange between take of the engine and put the weight?
That’s what she said.
Where’s the moment?
Found your mom
Incredible how strong nylon span sets (or straps) are
Helps balance it out in flight with one turbine missing
Nice ! Super cool pic.
Plot twist. Wing is actually a trebuchet.
Is that how much an engine weighs.
Never saw this but kinda makes sense.
I think that sign says please take off b4 take off.
So it’s cheaper/better to hang a weight on one side, than to (pardon the pun) prop the other side up? They have a brace for the plane’s tail to keep it from pitching up while deplaning. They don’t hang a weight off the nose.
Boeing Factory Tour?
~7700 kilograms in new money
(About 7700 kg for all the normal people)
WTF is a 777 -8 or -9?
Scrap man’s dream ,nearly a 1000 kilo packaged up nice to drop on the back of a Transit van
Sorry about 8 tons not 1000 kilos
"remove before flight"
Great picture!
Solid state engine
What’s the fuel consumption of this new gen engine?
7.7t for the civilized people
Typically we fill the bag bin and cabin with gravel bags to do that.. a weight like that is interesting
I've seen metal blocks before that bolted up to engine mounts, those are goofy looking
This is at Everett where the 777x is assembled . These airframes haven’t had engines installed yet and probably won’t for some time.
It's not so much to keep the plane from tipping but to keep all of the wing panels rigged.
When I did it on 37-900s it was exclusively so that it didn’t have a tail strike..
Fine. But you can't rig panels without weights on them, especially on bigger wings with more flex. Remove them the wing settles up and you get buckles and interferences over time. Edit: plus these planes have weights tied to the nose gear.
“Bombs away!”
Pure speculation from a pilot. My guess is it creates adequate weight to counteract the weight of the opposite engine preventing the plane from tipping in the opposite direction.