Please explain the rear cargo door of the C-5 Galaxy

[Monkeyfume]

I am just curious as to how it works. Thanks.

 

[DerAdlerIstGelandet]

I am just curious as to how it works. Thanks.

Hydraulics...

 

[GrauGeist]

Well..there's a bigass hinge...and a bigass latch...

Undo the latch and "voila!"

 

[Koopernic]

I am just curious as to how it works. Thanks.

The C5 has both a nose loading hatch and a tail loading hatch. At the end of its life it can therefore be purchased from the bone yard and used as a drive through liquor shop. Obviously the aerodynamic costs of making the rear loading hatch large enough to handle a full width load was considered greater than the cost of nose loading. I imagine it might be difficult to get paratroopers to jump out of the front, unless positive ejection could be used.

I am however now curious. Why wouldn't it be possible to parachute a complete 71 ton M1 Abrams from a C17. Surely its just a matter of a big enough parachute.

I figure the parachute would be 185 meters in diameter on the basis that a M1 would weigh 700 times more than a Paratrooper and so would need to be square root of 700 times bigger.

 

[davebender]

How large is the rear cargo door vs tank size? You will need a bit of clearance. Otherwise if the tank wobbles a bit while being yanked out by cargo chute it's likely to damage the C-17.

 

[GrauGeist]

In all seriousness, the rear cargo door of a C-5 has a series of hydraulic cylinders that raise or lower the ramp/hatch.

While the C-5 can carry two M1 tanks easily, there is no way the tank could be air-dropped. Besides the logistics of slowing the tank's descent, the rear hatch could not support the weight of the tank by the hydraulic rams alone if it were "pushed" out the back during a drop. The rams can support the weight of palletized cargo and/or vehicles being dropped by LVADS or LAPES. Pretty sure the max-weight for a drop is 60,000 pounds (30 tons) per unit. An M1 Abrams is 62 tons - twice the limit.

 

[Koopernic]

How large is the rear cargo door vs tank size? You will need a bit of clearance. Otherwise if the tank wobbles a bit while being yanked out by cargo chute it's likely to damage the C-17.

I would think that would be the least of many issues; perhaps rails?

The circular parachute is 150ft in diameter, about 1/4rd the size that would give the same area per unit weight as a human, if it were dropping a M1A2. It was designed to return ARES booster to earth. The Elliptical Parachute has a span of 175ft and is designed to deliver 26000lbs (12 tons) by GPS navigation over 20km flight to troops.
The Abrams is there for scale.

 

[DerAdlerIstGelandet]

I think someone just watched the A-Team...

 

[Donivanp]

The doors on the C-5A work much the same as a C-130 or C-141 it's little brothers. There are a series of hydrolic latches that engage to lock the doors. They also unlock them the same goes for the visor. The aft doors have on either side doors that move to the sides and the center door then splits in half, top fold up and in and the lower folds down to make the ramp. The ramp can be dropped to level position for a K loader or all the way to the ground for a drive in. The main gear is positionable up and down to assist in this process. The Nose visor raises up and the ramps are lowered in from in front to the needed position, again the nose gear is also capable of being raised and lowered. If you want to know my credentials I worked Avionics on the C-5A at the 436 AMS, 436 MAW form 1978-1980. I dealt heavily with the visor as the multi-mode radar and Doppler nave radar were in the nose and we had to get through the forward ramps to get to the the radar RT's. when it is in the up postion the ramp and two doors that allow access to the visor where the RT's are mounted.

 

[tyrodtom]

Even if the aft ramp could support the weight, could any aircraft have enough control authority to allow shifting 130,000 lbs. the 25 feet or so to the rear to get that M1 off that rear ramp.
That would have to be a big shift in the CG even for a C5.

And then think what the aircraft would do when that giant aft CG suddenly goes away when the tank left the ramp.

 

[Donivanp]

If you will note, there are stands that support the ramp and the aircraft when the ramps go down and the C-5 can and does fly up to two M-1A1's. I've seen up to 7 F-5's loaded and flown. Loaded 18ton aircraft tugs, Fire trucks. The C-5 is capable just as the AN-124 is.

 

[pbehn]

Surely 62 tons moving inside an aircraft even a galaxy would make it unstable?

 

[GrauGeist]

When the C-5 (or C-17) is in transit, the M1 tank(s) are secured and definitely not going anywhere.

 

[Donivanp]

Everything going into a cargo aircraft is secure and not moving. Surly if you follow the weight and balance charts and the load master does his job, it all works. That's what weight and balance is all about. You find the lubber line and do you calculations. It's freken magic.

 

[pbehn]

Everything going into a cargo aircraft is secure and not moving. Surly if you follow the weight and balance charts and the load master does his job, it all works. That's what weight and balance is all about. You find the lubber line and do you calculations. It's freken magic.

I thought people were discussing dropping an M1 while in flight?

 

[Koopernic]

Even if the aft ramp could support the weight, could any aircraft have enough control authority to allow shifting 130,000 lbs. the 25 feet or so to the rear to get that M1 off that rear ramp.
That would have to be a big shift in the CG even for a C5.

And then think what the aircraft would do when that giant aft CG suddenly goes away when the tank left the ramp.

Those are good points.

I'm just asking the question to see what the limits might be.

If an 70 ton M1 was extracted from a C5 or C17 several times that weight it might be gone before the C5 or C17 pitched up. A fly by wire controller might be developed to stabilise the aircraft during extraction and the transient C of G changes and the sudden 'lift' as the aircraft is suddenly lighter.

I'm also curious about a parachute large enough: how thick would the material have to be for instance or is it simply a matter of the ribbons and sheets being thick enough while the panels remain standard 'silk'.

It's obvious that a parachute that handles 26,000lbs exists; why not 130,000lbs.

 

[tyrodtom]

In the middle 70s they dropped a Minuteman II ICBM from a C-5 by parachute, and fired while hanging by that parachute.

But a Minuteman is 60 feet long and around 80,000lbs, that would be a lot less CG change than a 25 ft. Abrams weighing 130,000lbs.

What I'm asking is even though a C5 might be able to carry 2 M1s at the same time, and the ramp couldn't support the weight of a M1 in flight. Does it have control surfaces with enough control authority, or power to take care of the CG change that would result if the back M1 was slide off the back ramp while the C5 was inflight ?

 

[DerAdlerIstGelandet]

Everything going into a cargo aircraft is secure and not moving. Surly if you follow the weight and balance charts and the load master does his job, it all works. That's what weight and balance is all about. You find the lubber line and do you calculations. It's freken magic.

They are talking about the notion of dropping an M-1 Abrams out the back with a parachute.

 

[GregP]

All you'd have to do is cut the M-1 free, open the door, pull into an almost vertical climb, and push it out. But when its gone, the center of gravity will be WAY forward and pulling out of the subsequent dive might be problematic.

Of course you could just push BOTH tanks out ... I believe you could do it if you were only hauling ONE tank, but my question would be ... why?

MUCH easier and less dangerous to land and drive it off.

I'd rather air-drop pigs so the guys on the ground can at least B-B-Q when they come down. Might have to air drop grills, smokers, charcoal, paper plates, and napkins, too ..., not to mention cole slaw and B-B-Q beans ... and spoons. Oh, and ... B-B-Q sauce.

 

[Shortround6]

They are talking about the notion of dropping an M-1 Abrams out the back with a parachute.

Well, it worked so well with the M551 Sheriden......................................................not.

According to legend none of the vehicles that were parachuted were ever operational again and if things go wrong??

and with that many chutes the chances of something gong wrong are...............

and
View: https://www.youtube.com/watch?v=pRhFRGzh0s0