Max Q
Topic Author
Posts: 6917
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In flight refueling to over MGTOW

Thu Nov 08, 2018 6:12 am

I was just reading an article by an
Air Force boom operator on a KC135


He stated they offloaded so much
fuel to a C5 that the Galaxy’s ‘in flight
weight’ exceeded one million pounds


This was to allow it to fly non stop from
Afghanistan to the west coast of the US


Couple of things, I think it’s possible that
certain military aircraft are permitted a higher in flight weight than MGTOW after
in flight refueling ?



But I would think over a million pounds on a C5 seems excessive and overstress the airframe ?
The best contribution to safety is a competent Pilot.
 
WIederling
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Re: In flight refueling to over MGTOW

Thu Nov 08, 2018 9:52 am

I've seen a couple of "overrefuel" stories mentioned here over time.
( though not C5 more related to B-52 )

i.e. get the plane off the ground and then fill up to full tanks.
( MTOW stands for Max Take Off Weight :-)
Murphy is an optimist
 
GalaxyFlyer
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Re: In flight refueling to over MGTOW

Thu Nov 08, 2018 2:57 pm

The C-5A/B emergency war in-flight gross weight was 840,000 pounds. It was occasionally waivered for peace time missions that couldn’t be accomplished otherwise. When they hauled the DSRV out to HI when the USN sub struck and sank the tour boat, I think they were waivers. I planned a trip carrying the Mark V SOC boat ex-Townsville that required an EWO waiver. The problem leg was Andersen to Hickam, not getting the waiver would have required a tech stop for both tanker and C-5. Took some persuading but granted.

Considering the city-pairs and M models can make the East Coast non-stop, depending on load, without AR, I suspect, it was not anything like that. OEW is about 396,000, max fuel is about 325,00, so full fuel TOW is about 721,000 leaving a 119,000 pound payload, about right for 36 pallets. An AR coming off the NATs or over Canada would work.

A million pounds is a little hard to believe as 903,000 I think was the record and you’d be refueling in the low to mid-teens. The M has 840,000 as the standard MTOW.


GF
 
mmo
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Re: In flight refueling to over MGTOW

Thu Nov 08, 2018 7:50 pm

Back in the early 80s, The B-52D was tested for a max inflight weight. MTOW was 450,000 (G/H 488,000) but on the D with a full load internally and both pylons full you were not even close to full tanks. IIRC the capacity was around 250,000 lbs and I think we ended up at about 550,000 inflight. We also upped the refuelling airspeed from 255 to 280 which put the aircraft on the good side of the power curve, but it was a real pig. Could barely hold on with 7 engines.
If we weren't all crazy we'd all go insane!
 
GalaxyFlyer
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Joined: Fri Jan 01, 2016 4:44 am

Re: In flight refueling to over MGTOW

Thu Nov 08, 2018 8:20 pm

The dreaded 7-engine refueling.

While C-5 performance was dreadful at EWO, we practiced take-off and emergency OEI returns in the sim. At standard day, I think the MTOW achievable was about 809,000. The OEI approach was similar to a two-engine approach, gear first, flaps 40% at G/S capture, speeds were high.

GF
 
Max Q
Topic Author
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Re: In flight refueling to over MGTOW

Thu Nov 08, 2018 11:57 pm

Thanks for the replies

Just to be clear, do any military aircraft have a permitted inflight weight above normal MGTOW after inflight refueling


If so is this often done ?
The best contribution to safety is a competent Pilot.
 
GalaxyFlyer
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Joined: Fri Jan 01, 2016 4:44 am

Re: In flight refueling to over MGTOW

Fri Nov 09, 2018 12:03 am

Yes, the C-5A/B did, by HQ waiver for mission accomplishment. With the waiver, one could go from normal T/O weight of 769,000 to 840,000 inflight only. Not frequently, AR is often too expensive unless high priority mission. The M just operates to 840,000.

GF
 
Max Q
Topic Author
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Re: In flight refueling to over MGTOW

Fri Nov 09, 2018 12:14 am

GalaxyFlyer wrote:
Yes, the C-5A/B did, by HQ waiver for mission accomplishment. With the waiver, one could go from normal T/O weight of 769,000 to 840,000 inflight only. Not frequently, AR is often too expensive unless high priority mission. The M just operates to 840,000.

GF




Thanks, interesting, that’s a significant increase in weight once airborne
The best contribution to safety is a competent Pilot.
 
GalaxyFlyer
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Joined: Fri Jan 01, 2016 4:44 am

Re: In flight refueling to over MGTOW

Fri Nov 09, 2018 1:08 am

Lots of military planes have EWO weights for wartime missions, but they involve more damage cycles and performance restrictions. As I said, a C-5 couldn’t met take-off perf at EWO weights. Formatting behind the tanker was also a performance limit, 800,000 pounds would probably have a max altitude of F200.

In my example, the C-5 and the tanker would have had to tech stop at Wake Island and possibly Midway, if the waiver wasn’t granted. Often, we could work around it by careful planning of the tracks or ALTREVs, but Guam-Hawaii with a 250,000 payload and only about 4 hours of fuel made it hard.

GF
 
JohnM
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Joined: Sat Feb 24, 2001 12:35 pm

Re: In flight refueling to over MGTOW

Fri Nov 09, 2018 7:49 pm

Another issue is when FRED has a high fuel load, expect fuel leaks from the extended range tanks. The ER tanks don't see high fuel levels very often, so expect leaks. I don't think it would be a huge issue in flight, but sitting on the ground like that, be prepared to see some puddles around the airplane, and the hassles with that.
 
GalaxyFlyer
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Re: In flight refueling to over MGTOW

Fri Nov 09, 2018 8:39 pm

True enough!
 
Gyrfalcon
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Re: In flight refueling to over MGTOW

Thu Nov 15, 2018 1:58 am

I know of a couple instances where a KC-10 was A/R to over 600,000lbs on accident. Tanks full would always exceed the MTOGW of 590,000lbs so if the engineer/boom/pilots were late to cut off the fuel it could happen. This was very much not standard however.
 
GalaxyFlyer
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Re: In flight refueling to over MGTOW

Thu Nov 15, 2018 3:56 pm

Relatedly, sort of, when JP-8 was introduced, it was recognized to be denser than JP-4. I heard from a Kelly C-5 F/E they were fueling for some ridiculously long empty flight back to Kelly from Asia, the pilots sent out the fuel order of 320,000#, so they just told the fueler to “top it off”. Well, they a far piece past the book number of 332,000#, something like 345,000. When they returned, they asked about the fuel weight limits—volume or structural. Lockheed said structural and suddenly, by the -1, the tank volume got smaller

GF
 
bhill
Posts: 1575
Joined: Thu Sep 13, 2001 8:28 am

Re: In flight refueling to over MGTOW

Mon Nov 19, 2018 8:00 pm

Interesting..so when one of these waivers are granted, does the airplane "require" special inspections when it returns? Or is the airplane still within manufacturer specs and all is good to go?
Carpe Pices
 
GalaxyFlyer
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Joined: Fri Jan 01, 2016 4:44 am

Re: In flight refueling to over MGTOW

Mon Nov 19, 2018 10:17 pm

It’s recorded in the maintenance records, EWO weights were already in the design so not exceptional. Unpressurized flights are similar—HQ and Lockheed waiver. That’s more stressful than EWO weights as unpressurized flight waivers were more difficult to get.

GF
 
A350
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Joined: Tue Nov 30, 2004 6:40 am

Re: In flight refueling to over MGTOW

Fri Nov 23, 2018 12:02 am

Wasn't it a standard procedure for the SR-71 to start with nearly empty tanks and then "re"-fuel directly after take-off?
 
Ozair
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Re: In flight refueling to over MGTOW

Fri Nov 23, 2018 12:39 am

A350 wrote:
Wasn't it a standard procedure for the SR-71 to start with nearly empty tanks and then "re"-fuel directly after take-off?

I believe that was related to metal contraction and expansion with temperature and that the aircraft leaked like a sieve on the ground without the expansion.
 
Max Q
Topic Author
Posts: 6917
Joined: Wed May 09, 2001 12:40 pm

Re: In flight refueling to over MGTOW

Fri Nov 23, 2018 6:25 am

Ozair wrote:
A350 wrote:
Wasn't it a standard procedure for the SR-71 to start with nearly empty tanks and then "re"-fuel directly after take-off?

I believe that was related to metal contraction and expansion with temperature and that the aircraft leaked like a sieve on the ground without the expansion.



Richard Graham flew the SR71 extensively
and has a very interesting interview easily found on you tube


He states the accounts of the Blackbird ‘leaking fuel like a sieve’ on the ground are untrue and vastly exaggerated


There was a maximum certified leak rate
that was carefully monitored, If it exceeded this rate the aircraft was taken out of service and its fuel tanks resealed which was not an easy job


They did not take off with full tanks but this was to improve performance in the event of an engine failure not because the tanks were ‘leaking so fast’


And it did burn a lot of fuel on take off and climb so inflight refueling after departure was the optimal solution to those issues


It’s a great recording, well narrated and worth a listen
The best contribution to safety is a competent Pilot.
 
Ozair
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Joined: Mon Jan 31, 2005 8:38 am

Re: In flight refueling to over MGTOW

Fri Nov 23, 2018 6:55 am

Max Q wrote:
Ozair wrote:
A350 wrote:
Wasn't it a standard procedure for the SR-71 to start with nearly empty tanks and then "re"-fuel directly after take-off?

I believe that was related to metal contraction and expansion with temperature and that the aircraft leaked like a sieve on the ground without the expansion.



Richard Graham flew the SR71 extensively
and has a very interesting interview easily found on you tube


He states the accounts of the Blackbird ‘leaking fuel like a sieve’ on the ground are untrue and vastly exaggerated


There was a maximum certified leak rate
that was carefully monitored, If it exceeded this rate the aircraft was taken out of service and its fuel tanks resealed which was not an easy job


They did not take off with full tanks but this was to improve performance in the event of an engine failure not because the tanks were ‘leaking so fast’


And it did burn a lot of fuel on take off and climb so inflight refueling after departure was the optimal solution to those issues


It’s a great recording, well narrated and worth a listen

Thanks, good info and will not propogate that further.
 
GalaxyFlyer
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Re: In flight refueling to over MGTOW

Fri Nov 23, 2018 2:55 pm

We did post-departure AR rarely in the C-5 for performance reasons. I planned a trip out of Townsville, QLD with a heavy load that required the ARIP 100 miles off the runway due to take-off perf.

Speaking of leaks, on a fuel stop in the F-100 we’d would jokingly say to the crew chief, “top it off and put in two quarts of whatever’s on the ramp when you’re done”.

GF
 
strfyr51
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Re: In flight refueling to over MGTOW

Wed Nov 28, 2018 11:36 am

When I was in the Navy? We Used the Max Gross Weight as an "Advisory" Number. We loaded what we needed to load to do what we needed to do. Once we loaded 3 Mk46 Torpedos in the Bomb-bay and 2 Depth Charges on the outer wings, with a full loadout of Sono-bouys and Max fuel we were at 142.5K with a published max Gross of 135K. But? We were sent to find and Localize a soviet Nuke off the West coast. We found it in 6 hours down to "Kill" criteria and Came home in 8 hrs to unload all the Crap we had installed., We tracked the sub another 4 days before Laying off of it. There probably are still Subs the Russians send down to lay off the West coast. I know our Attack Subs Probably keep an eye on them.
 
Max Q
Topic Author
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Re: In flight refueling to over MGTOW

Thu Nov 29, 2018 11:31 am

strfyr51 wrote:
When I was in the Navy? We Used the Max Gross Weight as an "Advisory" Number. We loaded what we needed to load to do what we needed to do. Once we loaded 3 Mk46 Torpedos in the Bomb-bay and 2 Depth Charges on the outer wings, with a full loadout of Sono-bouys and Max fuel we were at 142.5K with a published max Gross of 135K. But? We were sent to find and Localize a soviet Nuke off the West coast. We found it in 6 hours down to "Kill" criteria and Came home in 8 hrs to unload all the Crap we had installed., We tracked the sub another 4 days before Laying off of it. There probably are still Subs the Russians send down to lay off the West coast. I know our Attack Subs Probably keep an eye on them.



Very interesting, this was a P3 ?
The best contribution to safety is a competent Pilot.
 
User avatar
kc135topboom
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Re: In flight refueling to over MGTOW

Sat Dec 01, 2018 5:14 pm

When you air refuel above MTOW, you are limited to a lower maneuvering load factor in "Gs". IIRC we could air refuel a EWO loaded B-52G to something like 512,000 lbs, well above the 488,000 lbs MTOW. But the bomber was limited to something like 1.5G maneuver load factor until he burned back down to 488K.
 
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Runway28L
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Re: In flight refueling to over MGTOW

Sun Dec 02, 2018 3:58 am

Max Q wrote:
Ozair wrote:
A350 wrote:
Wasn't it a standard procedure for the SR-71 to start with nearly empty tanks and then "re"-fuel directly after take-off?

I believe that was related to metal contraction and expansion with temperature and that the aircraft leaked like a sieve on the ground without the expansion.



Richard Graham flew the SR71 extensively
and has a very interesting interview easily found on you tube


He states the accounts of the Blackbird ‘leaking fuel like a sieve’ on the ground are untrue and vastly exaggerated


There was a maximum certified leak rate
that was carefully monitored, If it exceeded this rate the aircraft was taken out of service and its fuel tanks resealed which was not an easy job


They did not take off with full tanks but this was to improve performance in the event of an engine failure not because the tanks were ‘leaking so fast’


And it did burn a lot of fuel on take off and climb so inflight refueling after departure was the optimal solution to those issues


It’s a great recording, well narrated and worth a listen

Another reason why they didn't fully fuel the SR-71 on the ground was to save on maintenance of the landing gear and tires. IIRC, the tires were special-made and the landing gear was made out of titanium, a resource that was very hard to come by. Leaving a light fuel load reduced the stress on the landing gear/tires less and extended the intervals between maintenance for each.
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Max Q
Topic Author
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Re: In flight refueling to over MGTOW

Mon Dec 03, 2018 12:31 am

Runway28L wrote:
Max Q wrote:
Ozair wrote:
I believe that was related to metal contraction and expansion with temperature and that the aircraft leaked like a sieve on the ground without the expansion.



Richard Graham flew the SR71 extensively
and has a very interesting interview easily found on you tube


He states the accounts of the Blackbird ‘leaking fuel like a sieve’ on the ground are untrue and vastly exaggerated


There was a maximum certified leak rate
that was carefully monitored, If it exceeded this rate the aircraft was taken out of service and its fuel tanks resealed which was not an easy job


They did not take off with full tanks but this was to improve performance in the event of an engine failure not because the tanks were ‘leaking so fast’


And it did burn a lot of fuel on take off and climb so inflight refueling after departure was the optimal solution to those issues


It’s a great recording, well narrated and worth a listen

Another reason why they didn't fully fuel the SR-71 on the ground was to save on maintenance of the landing gear and tires. IIRC, the tires were special-made and the landing gear was made out of titanium, a resource that was very hard to come by. Leaving a light fuel load reduced the stress on the landing gear/tires less and extended the intervals between maintenance for each.



Interesting, makes sense, thanks for that
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