workhorse
Topic Author
Posts: 683
Joined: Sun Jul 10, 2005 11:35 pm

Pressurization of transport/cargo aircraft with ramps

Mon Jan 20, 2020 1:14 pm

Rear pressure bulkhead is one of the most sensitive pieces of an aircraft subjected to some of the biggest wear forces.In a rear loaded cargo/transport aircraft, these forces are applied to the ramp which bears the additional complexity of being movable.

So, how are aircraft with ramps pressurized? Can they have the same cabin altitude as an airliner when flying, for example, at FL350? And if not, how do they transport people (e.g., troops)?
 
GalaxyFlyer
Posts: 4674
Joined: Fri Jan 01, 2016 4:44 am

Re: Pressurization of transport/cargo aircraft with ramps

Mon Jan 20, 2020 3:05 pm

The C-5 was fully pressurized, just like an airliner. In the front the visor and the ramp were the pressure doors, both with multiple locks. Aft, the ramp, ramp extension and aft pressure door we’re pressure doors with dozens of locks. The aft pressure door could either extend to the ground in drive-in mode or retract into the overhead in truck bed mode, think loading dock. As I understand it, the aft potions of 141 and 130 were similar.

GF
 
User avatar
fr8mech
Posts: 7884
Joined: Mon Sep 26, 2005 9:00 am

Re: Pressurization of transport/cargo aircraft with ramps

Mon Jan 20, 2020 3:15 pm

It’s no different then a B747 freighter with a nose door, or the lower cargo doors on any transport category aircraft. I would assume that the door/ramp forms the rear pressure “bulkhead”.
When seconds count...the police are minutes away.
Unless it's expressly prohibited, it's allowed.
You are not entitled to a public safe space.
Ego Bibere Capulus, Ut Aliis Sit Vivere
 
GalaxyFlyer
Posts: 4674
Joined: Fri Jan 01, 2016 4:44 am

Re: Pressurization of transport/cargo aircraft with ramps

Mon Jan 20, 2020 3:22 pm

Exactly, the aft pressure door on the C-5 could have been a bridge, 17’x17’ and probably a truss a foot thick. The forward ramp could hold a tank or bulldozer (seen both).
 
workhorse
Topic Author
Posts: 683
Joined: Sun Jul 10, 2005 11:35 pm

Re: Pressurization of transport/cargo aircraft with ramps

Mon Jan 20, 2020 9:20 pm

GalaxyFlyer wrote:
The C-5 was fully pressurized, just like an airliner. In the front the visor and the ramp were the pressure doors, both with multiple locks. Aft, the ramp, ramp extension and aft pressure door we’re pressure doors with dozens of locks. The aft pressure door could either extend to the ground in drive-in mode or retract into the overhead in truck bed mode, think loading dock. As I understand it, the aft potions of 141 and 130 were similar.

GF


fr8mech wrote:
It’s no different then a B747 freighter with a nose door, or the lower cargo doors on any transport category aircraft. I would assume that the door/ramp forms the rear pressure “bulkhead”.


OK, got it, thank you very much to both of you.

I was asking because living in Europe and being a FlightRadar24 addict I sometimes see over my head planes such as C17s flying quite long missions (for example, Sweden to somewhere in Africa) at quite low altitude (for example 17,000 feet or 19,000 feet). I was wondering if it wasn't because of pressurization.
 
GalaxyFlyer
Posts: 4674
Joined: Fri Jan 01, 2016 4:44 am

Re: Pressurization of transport/cargo aircraft with ramps

Mon Jan 20, 2020 9:27 pm

Can’t say why so low—RVSM MEL problem, weight for mission, max gross weight take-off headed for an AAR, etc.
 
BravoOne
Posts: 3863
Joined: Fri Apr 12, 2013 2:27 pm

Re: Pressurization of transport/cargo aircraft with ramps

Mon Jan 20, 2020 9:31 pm

Here is another example albeit no ramp. Flying Tigers, Seaboard and Slick all operated this aircraft with pretty good sucess

https://en.wikipedia.org/wiki/Canadair_CL-44
 
JayinKitsap
Posts: 1820
Joined: Sat Nov 26, 2005 9:55 am

Re: Pressurization of transport/cargo aircraft with ramps

Tue Jan 21, 2020 7:00 pm

There is a recent thread on a.net on cargo planes, but I can't find it with a quick look.

The rear ramp has gaskets including some air filled ones that perform the seal, however the size of the doors is huge. The leakage at the seals limited the altitude difference between the cabin and outside to like 20k feet difference, (8K interior elev, 28K flight elev).
 
User avatar
SheikhDjibouti
Posts: 1931
Joined: Sat Sep 30, 2017 4:59 pm

Re: Pressurization of transport/cargo aircraft with ramps

Thu Jan 23, 2020 1:44 am

workhorse wrote:
I was asking because living in Europe and being a FlightRadar24 addict I sometimes see over my head planes such as C17s flying quite long missions (for example, Sweden to somewhere in Africa) at quite low altitude (for example 17,000 feet or 19,000 feet).

I have never seen a C17 displayed on FR24; is this something that comes with a paid subscription?
Can you describe a typical routing?
You mention Sweden to Africa as an example, but Sweden doesn't have any C17s, so..... who is providing the hardware?

(If you were to tell me you were watching Volga-Dnepr Il-76s and An-124s, then I could understand that better, but I would still find FL190 unusual for them)
Nothing to see here; move along please.
 
workhorse
Topic Author
Posts: 683
Joined: Sun Jul 10, 2005 11:35 pm

Re: Pressurization of transport/cargo aircraft with ramps

Thu Jan 23, 2020 10:50 am

The last one was 4 days ago, in the late evening, in the middle of French Alps. I first heard the noise, raised my eyes and saw a large low flying 4 engine jet aircraft right over my head. We sometimes see A380s or cargo 747s over here but they always fly much higher, look much smaller and are hardly audible. I looked it up on FR24, it was identified as a C-17, no reg, no flight number, no information about the operator. There was no information about origin and destination neither but looking at the flight path I could see it took off from Örebro in Sweden, climbed to 17,000 then 19,000 feet and then stayed at that altitude heading towards Algeria. I lost it when it was approaching the Mediterranean.

I also remember having seen Il-76s over Paris region, quite lower than other traffic as well (something like 20-22,000 feet), heading from the UK to the Southeast.

P.S. Yes, I have a paid subscription but I don't think it's related.
 
workhorse
Topic Author
Posts: 683
Joined: Sun Jul 10, 2005 11:35 pm

Re: Pressurization of transport/cargo aircraft with ramps

Thu Jan 23, 2020 11:39 am

JayinKitsap wrote:
There is a recent thread on a.net on cargo planes, but I can't find it with a quick look.

The rear ramp has gaskets including some air filled ones that perform the seal, however the size of the doors is huge. The leakage at the seals limited the altitude difference between the cabin and outside to like 20k feet difference, (8K interior elev, 28K flight elev).


OK, I see, thank you. I was wondering how it works with flights to/from Antarctica, for example. They are always done by aircraft with ramps (C-17s, C-5s, Il-76s), carry people and the distance to fly is quite big. What is the typical cruising altitude of a flight to McMurdo, for example?
 
SAAFNAV
Posts: 589
Joined: Wed Mar 17, 2010 5:41 pm

Re: Pressurization of transport/cargo aircraft with ramps

Thu Jan 23, 2020 12:59 pm

workhorse wrote:
JayinKitsap wrote:
There is a recent thread on a.net on cargo planes, but I can't find it with a quick look.

The rear ramp has gaskets including some air filled ones that perform the seal, however the size of the doors is huge. The leakage at the seals limited the altitude difference between the cabin and outside to like 20k feet difference, (8K interior elev, 28K flight elev).


OK, I see, thank you. I was wondering how it works with flights to/from Antarctica, for example. They are always done by aircraft with ramps (C-17s, C-5s, Il-76s), carry people and the distance to fly is quite big. What is the typical cruising altitude of a flight to McMurdo, for example?



Only picture I can easily find on Google of a C-130 ramp: http://tiny.cc/krc3iz

You'll see the 2 of the 5 locks/latches. When you raise the ramp, those locks go over a steel protrusion of the aircraft structure, then it basically hangs off the airframe. The pressurization acting upon the ramp also assists in creating the down-force to keep it it solidly connected, and it forms one solid structure.
There isn't really much difference from an engineering point of view to create an entrance door that can withstand pressurization vs a cargo ramp - you employ much of the same principles.

Of course, the integrity of the locks, and ensuring that all have engaged correctly is critical to the safety of the pressure vessel, and part of the loadmaster checks. Also one of the emergency actions should the light come on/visually see the locks coming off.

On the C-130 at least, the seal is made by making an outline of Petroleum resistant compound (or 2 lines, not sure now), and while it is wet closing the door. Pretty much like bathroom caulking.
L-382 Loadmaster; ex C-130B Navigator
 
User avatar
SheikhDjibouti
Posts: 1931
Joined: Sat Sep 30, 2017 4:59 pm

Re: Pressurization of transport/cargo aircraft with ramps

Thu Jan 23, 2020 3:27 pm

workhorse wrote:
]The last one was 4 days ago, in the late evening, in the middle of French Alps. I first heard the noise, raised my eyes and saw a large low flying 4 engine jet aircraft right over my head. I looked it up on FR24, it was identified as a C-17, no reg, no flight number, no information about the operator. There was no information about origin and destination neither but looking at the flight path I could see it took off from Örebro in Sweden, climbed to 17,000 then 19,000 feet and then stayed at that altitude heading towards Algeria. I lost it when it was approaching the Mediterranean.


I love a challenge, and filtering out one rogue C17 from a host of Cessna C172s that were also airborne at that time was all of that. (i.e. Aircraft type = "C17" comes with a lot of background noise...)

This aircraft in fact climbed to FL280 and picked up a really impressive ground speed whilst over Germany & Luxembourg, but then started slowing & descending to FL190 as it approached Grenoble (~17:15 UTC)
After some intermittent data drop-outs (aka funny business) it displayed a steady track over Marseille, allegedly climbing back to FL290, eventually reaching FL320 before disappearing into the black hole that is Algerian airspace (i.e. very limited FR24 coverage). But I also have my doubts....

If one was into conspiracy theories, I would suggest it slowed down & descended in order to deploy some HALO paratroops.
Note also that the flight was scheduled to take advantage of darkness. :stirthepot:

You want more?
Before Orebro, this aircraft was at Pápa Air Base (Hungary), which probably makes it one of these guys.
i.e one of three Hungarian Air Force C-17s - who knew?

And all of a sudden, the HALO paratroop drop doesn't seem so totally impossible. :o

Could it have been related to Trump's arrival in Zurich? Air Force One never travels alone, and support staff and equipment (cough...guns) usually comes in 24-48 hrs ahead. They would also hide the true identity of these aircraft, and indeed the flightplan. Anything flying direct from Edwards AFB to ZRH would be too obvious, hence route it via Orebro (just an idea!)

This doesn't explain other examples that you may have seen at other times.

I also remember having seen Il-76s over Paris region, quite lower than other traffic as well (something like 20-22,000 feet), heading from the UK to the Southeast.
Before it was closed in 2014, Manston (MSE) in Kent was a favorite holding point for Il-76s. Manston to Paris is a relatively short distance and maybe a heavily laden il-76 was still gaining altitude?
Nothing to see here; move along please.
 
VSMUT
Posts: 3591
Joined: Mon Aug 08, 2016 11:40 am

Re: Pressurization of transport/cargo aircraft with ramps

Thu Jan 23, 2020 4:09 pm

GalaxyFlyer wrote:
The C-5 was fully pressurized, just like an airliner. In the front the visor and the ramp were the pressure doors, both with multiple locks. Aft, the ramp, ramp extension and aft pressure door we’re pressure doors with dozens of locks. The aft pressure door could either extend to the ground in drive-in mode or retract into the overhead in truck bed mode, think loading dock. As I understand it, the aft potions of 141 and 130 were similar.

GF


You seem to know them pretty well. Did the doors ever get bent out of shape causing minor gaps where air squeaks out? Because we get that on smaller planes where the cargo door doesn't even bear any load, let alone several ton military vehicles.


SheikhDjibouti wrote:
Could it have been related to Trump's arrival in Zurich? Air Force One never travels alone, and support staff and equipment (cough...guns) usually comes in 24-48 hrs ahead. They would also hide the true identity of these aircraft, and indeed the flightplan. Anything flying direct from Edwards AFB to ZRH would be too obvious, hence route it via Orebro (just an idea!)


There are a ton of US military transports over Europe at night, typically flying under Reach callsign. We would hear them every night flying night cargo out of CGN, where there is barely any traffic over Europe apart from freighters. I've seen a fair few in the early morning light too.
 
SAAFNAV
Posts: 589
Joined: Wed Mar 17, 2010 5:41 pm

Re: Pressurization of transport/cargo aircraft with ramps

Thu Jan 23, 2020 8:08 pm

SheikhDjibouti wrote:
workhorse wrote:
]
After some intermittent data drop-outs (aka funny business) it displayed a steady track over Marseille, allegedly climbing back to FL290, eventually reaching FL320 before disappearing into the black hole that is Algerian airspace (i.e. very limited FR24 coverage). But I also have my doubts....

If one was into conspiracy theories, I would suggest it slowed down & descended in order to deploy some HALO paratroops.
Note also that the flight was scheduled to take advantage of darkness. :stirthepot:



When you state Algeria, might I suggest that they went into Mali? Quite a hot zone with a lot of military ops.. You see all kinds of aircraft working there.
I once even saw an IL62 there, and not long ago either.

Having dispatched HALO/HAHO troops before, it is a risky operation, and more so at night. It would make sense to do it into a combat zone, but into Europe... Not since Normandy I guess.
L-382 Loadmaster; ex C-130B Navigator
 
GalaxyFlyer
Posts: 4674
Joined: Fri Jan 01, 2016 4:44 am

Re: Pressurization of transport/cargo aircraft with ramps

Thu Jan 23, 2020 8:57 pm

VSMUT wrote:
GalaxyFlyer wrote:
The C-5 was fully pressurized, just like an airliner. In the front the visor and the ramp were the pressure doors, both with multiple locks. Aft, the ramp, ramp extension and aft pressure door we’re pressure doors with dozens of locks. The aft pressure door could either extend to the ground in drive-in mode or retract into the overhead in truck bed mode, think loading dock. As I understand it, the aft potions of 141 and 130 were similar.

GF


You seem to know them pretty well. Did the doors ever get bent out of shape causing minor gaps where air squeaks out? Because we get that on smaller planes where the cargo door doesn't even bear any load, let alone several ton military vehicles.


SheikhDjibouti wrote:
Could it have been related to Trump's arrival in Zurich? Air Force One never travels alone, and support staff and equipment (cough...guns) usually comes in 24-48 hrs ahead. They would also hide the true identity of these aircraft, and indeed the flightplan. Anything flying direct from Edwards AFB to ZRH would be too obvious, hence route it via Orebro (just an idea!)


There are a ton of US military transports over Europe at night, typically flying under Reach callsign. We would hear them every night flying night cargo out of CGN, where there is barely any traffic over Europe apart from freighters. I've seen a fair few in the early morning light too.


Not in my experience, but seals were common cause of air leaks. The aft pressure had something like 26 locks, all of which were pinned after closing. The rumor was the Saigon Baby Lift crash wasn’t rooted in a loading exercise a week before where a heavy load was off center on the aft ramp causing hidden damage that, in turn, caused a zipper failure of the locks. The floor and ramps were built like a bridge, heavy trussing and could load 36,000# every 40”.
 
chimborazo
Posts: 299
Joined: Sun Sep 25, 2011 7:51 pm

Re: Pressurization of transport/cargo aircraft with ramps

Fri Jan 24, 2020 6:29 am

Hey Galaxy Flyer.... you seem to know the C5 (Galaxy) pretty well :-) :-) :-)

That’s the best thing I’ve read in months.
 
workhorse
Topic Author
Posts: 683
Joined: Sun Jul 10, 2005 11:35 pm

Re: Pressurization of transport/cargo aircraft with ramps

Fri Jan 24, 2020 10:13 am

SheikhDjibouti wrote:
I love a challenge, and filtering out one rogue C17 from a host of Cessna C172s that were also airborne at that time was all of that. (i.e. Aircraft type = "C17" comes with a lot of background noise...)


Very impressive investigation, thank you very much! So, basically you're saying I'd better watch out for Hungarian Special Ops troopers in the woods around me. :mrgreen:
 
workhorse
Topic Author
Posts: 683
Joined: Sun Jul 10, 2005 11:35 pm

Re: Pressurization of transport/cargo aircraft with ramps

Fri Jan 24, 2020 10:18 am

SAAFNAV wrote:
When you state Algeria, might I suggest that they went into Mali? Quite a hot zone with a lot of military ops..


True, but there's also quite a bit of transport flights into Algeria as well. Usually they are Ukrainian registered An-12s flying between Germany/Benelux and various ports in Algeria.

SAAFNAV wrote:
Having dispatched HALO/HAHO troops before, it is a risky operation, and more so at night. It would make sense to do it into a combat zone, but into Europe... Not since Normandy I guess.


Covert Hungarian operation in France? :scratchchin: :mrgreen:
 
User avatar
SheikhDjibouti
Posts: 1931
Joined: Sat Sep 30, 2017 4:59 pm

Re: Pressurization of transport/cargo aircraft with ramps

Fri Jan 24, 2020 1:13 pm

workhorse wrote:
SheikhDjibouti wrote:
I love a challenge, .( Aircraft type = "C17" comes with a lot of background noise...)


Very impressive investigation, thank you very much! So, basically you're saying I'd better watch out for Hungarian Special Ops troopers in the woods around me. :mrgreen:

Probably not Hungarian; but if we are taking this idea seriously then it is one of two genuine possibilities.

1) US Special Forces (Rangers, Marines, whatever) airlifted firstly from US to Sweden, and then transfered to a "local" (Hungarian) C-17, operating as part of the multinational (12 nations) Heavy Airlift Wing at Pápa Air Base, Hungary.
or
2) Swedish Special Forces (Ski/Winter troops) perfectly adapted to operations at this time of year in the Alps.
FWIW the Vice-Commander of the Heavy Airlift Wing unit is Colonel Peder Söderström of the Swedish Air Force

https://en.wikipedia.org/wiki/Heavy_Airlift_Wing

Most likely it was just a practise exercise just in case they suddenly needed to put some men on the ground to save President Trump from a kidnap attempt. (Even though more than half of America would pay the kidnappers to keep him hostage.... :duck: )

American paranoia is such that they don't necessarily trust even their closest allies to do a good enough job in terms of protecting POTUS. And Switzerland is such a dangerous place. :roll: The fact that every US President who has ever been attacked, was attacked on US soil... ...by US citizens, doesn't appear to count.

But enough of politics and talk of paranoia, and btw if the CIA are monitoring this conversation, please believe I am only joking... honest. :white:

p.s. Galaxy Flyer does indeed have all the answers to your questions; he is absolutely "the man" (and probably a good deal more on top, that he probably daren't talk about.)
He should write a book; I'd buy it. :yes:
Nothing to see here; move along please.
 
User avatar
SheikhDjibouti
Posts: 1931
Joined: Sat Sep 30, 2017 4:59 pm

Re: Pressurization of transport/cargo aircraft with ramps

Fri Jan 24, 2020 1:28 pm

p.s. there is another C-17 airborne right now (this time out of Ramstein) that has just performed the same flight (but without the reduction in altitude).
It flew down the France / Swiss border, then past Marseille and then did a 180 turn a few miles over the Med.

In daylight fully visible, just letting everybody know that they've got the President covered.
Nothing to see here; move along please.
 
GalaxyFlyer
Posts: 4674
Joined: Fri Jan 01, 2016 4:44 am

Re: Pressurization of transport/cargo aircraft with ramps

Fri Jan 24, 2020 3:15 pm

SheikhDjibouti wrote:
workhorse wrote:
SheikhDjibouti wrote:
I love a challenge, .( Aircraft type = "C17" comes with a lot of background noise...)


Very impressive investigation, thank you very much! So, basically you're saying I'd better watch out for Hungarian Special Ops troopers in the woods around me. :mrgreen:

Probably not Hungarian; but if we are taking this idea seriously then it is one of two genuine possibilities.

1) US Special Forces (Rangers, Marines, whatever) airlifted firstly from US to Sweden, and then transfered to a "local" (Hungarian) C-17, operating as part of the multinational (12 nations) Heavy Airlift Wing at Pápa Air Base, Hungary.
or
2) Swedish Special Forces (Ski/Winter troops) perfectly adapted to operations at this time of year in the Alps.
FWIW the Vice-Commander of the Heavy Airlift Wing unit is Colonel Peder Söderström of the Swedish Air Force

https://en.wikipedia.org/wiki/Heavy_Airlift_Wing

Most likely it was just a practise exercise just in case they suddenly needed to put some men on the ground to save President Trump from a kidnap attempt. (Even though more than half of America would pay the kidnappers to keep him hostage.... :duck: )

American paranoia is such that they don't necessarily trust even their closest allies to do a good enough job in terms of protecting POTUS. And Switzerland is such a dangerous place. :roll: The fact that every US President who has ever been attacked, was attacked on US soil... ...by US citizens, doesn't appear to count.

But enough of politics and talk of paranoia, and btw if the CIA are monitoring this conversation, please believe I am only joking... honest. :white:

p.s. Galaxy Flyer does indeed have all the answers to your questions; he is absolutely "the man" (and probably a good deal more on top, that he probably daren't talk about.)
He should write a book; I'd buy it. :yes:


Thanks! One cloudy morning on arrival at RAF Alconbury, the loads were configuring to unload a group of SF going to training with the SAS, IIRC. Out of Base Ops walks two bobbies and ask to speak with the captain. I go down the ladder to be informed that John Major will soon be arriving by helo and could I please delay unloading until he left. Sure, no problem, the delay might have been 10 minutes. I’ve landed at KTEB behind CANFORCE 1, like it was just another arrival. The Secret Service, the FBI and whole security theatre in the States is out of control.

GF
 
workhorse
Topic Author
Posts: 683
Joined: Sun Jul 10, 2005 11:35 pm

Re: Pressurization of transport/cargo aircraft with ramps

Mon Jan 27, 2020 12:22 pm

Thanks to SheikhDjibouti, GalaxyFlyer and other participants for their great contibutions.

To enrich this thread with more info (and to use it later as reference), let me add this.

After spending some time playing with search engines, I have found a source (unfortunately, in Russian only) that gives the pressurization specs for the Il-76:

https://tvzvezda.ru/news/forces/content ... 4-qmok.htm

It says that:
- up to 6700 meters (22,000 feet) normal ground pressure can be maintained in the cockpit AND the cargo hold
- at 11 000 meters (36,000 feet), pressure equivalent to 2400 meters altitude (7,900 feet) can be maintained

However this source:

https://www.arms-expo.ru/articles/armed ... lok-il-76/

says that apparently only some versions of Il-76 built to carry troops maintain pressure in the cargo hold, and that there are other versions where it is not pressurized.

Who is online

Users browsing this forum: boacvc10, VC10DC10 and 24 guests

Popular Searches On Airliners.net

Top Photos of Last:   24 Hours  •  48 Hours  •  7 Days  •  30 Days  •  180 Days  •  365 Days  •  All Time

Military Aircraft Every type from fighters to helicopters from air forces around the globe

Classic Airliners Props and jets from the good old days

Flight Decks Views from inside the cockpit

Aircraft Cabins Passenger cabin shots showing seat arrangements as well as cargo aircraft interior

Cargo Aircraft Pictures of great freighter aircraft

Government Aircraft Aircraft flying government officials

Helicopters Our large helicopter section. Both military and civil versions

Blimps / Airships Everything from the Goodyear blimp to the Zeppelin

Night Photos Beautiful shots taken while the sun is below the horizon

Accidents Accident, incident and crash related photos

Air to Air Photos taken by airborne photographers of airborne aircraft

Special Paint Schemes Aircraft painted in beautiful and original liveries

Airport Overviews Airport overviews from the air or ground

Tails and Winglets Tail and Winglet closeups with beautiful airline logos