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Author
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Topic: Shuttle Carrier Aircraft mid-air refueling
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LM-12
Member Posts: 3602
From: Ontario, Canada
Registered: Oct 2010
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posted 08-04-2021 01:32 PM
  
Mid-air refueling of the Shuttle Carrier Aircraft (SCA) is mentioned in "The Spoken Word III: Recollections of Dryden History: The Shuttle Years" (NASA SP-2011-4552). Photo EC83-24285 on page 109 has this caption: In preparation for taking the shuttle Enterprise to the Paris Air Show in 1983, NASA put a type of anti-missile device on each engine pylon of the Boeing 747 SCA. When asked about the devices at the show, aircraft personnel offered different answers, including that they were used to aid in-flight refueling. NASA 905 was the only SCA that NASA had at the time, so there was some concern about the risk of sending it overseas to Europe. |
LM-12
Member Posts: 3602
From: Ontario, Canada
Registered: Oct 2010
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posted 09-03-2021 12:31 AM
Although the two NASA 747s were not equipped for mid-air refueling, there were test flights in 1984 with NASA 905 and USAF KC-135 and KC-10 tankers.What was the purpose of the dot patterns seen on the 747? |
PeterO
Member Posts: 434
From: North Carolina
Registered: Mar 2002
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posted 09-03-2021 07:39 AM
By 1984 the 747 (as the E-4) was already cleared for aerial refueling. Purely speculation, but the dots may be tufts, to visually show how the orbiter attach fittings interact with the airflow behind the tanker. I doubt that refueling with the orbiter attached was ever seriously considered, since the orbiter would have been directly in the tanker's wake, resulting in high stresses to the orbiter/SCA combination. |
oly
Member Posts: 1280
From: Perth, Western Australia
Registered: Apr 2015
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posted 09-03-2021 10:11 AM
It appears that the refueling probe is being used to upset the airflow to disturb the boundary layer flow of the region being tufted and the tanker is probably also observing the airflow from above while the T-38 is observing from the side. |
mmcmurrey
Member Posts: 179
From: Austin, TX, USA
Registered: Jun 2012
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posted 09-03-2021 12:05 PM
I'm not sure what you guys are referring to about "tuffs and dot" but I am quite familiar with air-to-air refueling in USAF. On the E4 the refueling is accomplished by plugging into a receptacle below the windshield in nose of aircraft. Doors open and the boom is flown into the receptacle. You can see the red spaced stripes in the photo that allow the boom operator to judge the distance he has to go to make contact. The receiving aircraft must maintain his aircraft in a boxed area that the boom can maneuver in to make contact to receive fuel. |
LM-12
Member Posts: 3602
From: Ontario, Canada
Registered: Oct 2010
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posted 09-03-2021 02:43 PM
Here is a closer shot of NASA 905 and a KC-10 tanker that shows a bit more detail. |
oly
Member Posts: 1280
From: Perth, Western Australia
Registered: Apr 2015
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posted 09-03-2021 06:33 PM
quote:
Originally posted by mmcmurrey:
You can see the red spaced stripes in the photo that allow the boom operator to judge the distance...
The markings may have been applied to the nose of the 747 for the boom operator's reference. |
LM-12
Member Posts: 3602
From: Ontario, Canada
Registered: Oct 2010
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posted 09-04-2021 03:26 AM
From the February 10, 1984 issue of JSC Space News Roundup, on page 2: SCA Inflight refueling tests begin
Initial flight tests began last week at the Dryden Flight Research Facility to see if inflight refueling during Shuttle ferry flights is feasible. Nine flight tests are scheduled with the Shuttle Carrier Aircraft (SCA), NASA 905, six of them with the prototype Orbiter Enterprise aboard. The first three flights will use just the SCA and test refueling procedures with KC-135 and KC-10 tankers. The other six flights, with the Enterprise aboard, will also test both types of tanker aircraft. Each flight will be about two and a half hours at speeds and altitudes simulating actual ferry missions... A major motivation for inflight refueling is to improve SCA capabilities should an overseas Shuttle landing occur. Fitzhugh Fulton and Thomas McMurtry of the Ames Research Center and Gordon Fullerton and A. J. Roy of JSC are flying aboard the SCA during the tests. The next issue of Roundup (Feb 24) had this article:
NASA 905 refueling tests suspendedIn-flight refueling tests on NASA 905, the Shuttle Carrier Aircraft, were suspended earlier this month when buffeting from tanker aircraft produced cracks in the tail of the 747. The cracks are considered minor and the 747 is classified as ready to support any necessary transport of Shuttle Orbiters. Preliminary tests of the refueling technique were conducted at Edwards Air Force Base in early February using a KC-135 and a KC-10, the two types of tankers in the U.S. Air Force inventory. Heavy turbulence encountered in the vortices of the tankers produced the cracks, and NASA officials are now studying another approach. The alternate technique would allow the 747 to fly in front of the tankers during the refueling. |
mmcmurrey
Member Posts: 179
From: Austin, TX, USA
Registered: Jun 2012
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posted 09-04-2021 01:02 PM
The only reason I can come up with the canceled test flight for minor cracks would be the modification made to SCA's tail elevators. USAF E4 routinely air refuel in air by KC135 and KC10 refuelers. As for as an alternate refueling with the SCA in the lead is pure fantasy! |
LM-12
Member Posts: 3602
From: Ontario, Canada
Registered: Oct 2010
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posted 09-04-2021 08:08 PM
That does sound odd, but there is a photo of NASA 905 flying ahead and above the KC-10 tanker. |
oly
Member Posts: 1280
From: Perth, Western Australia
Registered: Apr 2015
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posted 09-04-2021 09:17 PM
quote:
Originally posted by mmcmurrey:
As for as an alternate refueling with the SCA in the lead is pure fantasy!
The SCA structural modifications of the forward and aft pylons introduced reinforcement plates and structural reinforcements that changed the way stress and flex interacted through the fuselage structure, making the fatigue strain map different to a standard airframe.Theoretically, using the probe and drogue system, fuel could be pumped from the trailing aircraft to the leading. |
mmcmurrey
Member Posts: 179
From: Austin, TX, USA
Registered: Jun 2012
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posted 09-05-2021 10:41 AM
Theoretically picture a drogue (fuel hose with circular basket cone at the end) extended from wing, streaming aft, being able to turn into the slipstream 180 degrees and pump gas into the ass end of a plane with no receptacle.  quote:
Originally posted by LM-12:
...there is a photo of NASA 905 flying ahead and above the KC-10 tanker.
Probably a photo op for unknown reason? |
PeterO
Member Posts: 434
From: North Carolina
Registered: Mar 2002
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posted 09-05-2021 01:40 PM
quote:
Originally posted by oly:
Theoretically, using the probe and drogue system, fuel could be pumped from the trailing aircraft to the leading.
Royal Air Force tankers are configured to both offload and receive fuel via the drogue, with the receiver aircraft in front of the refueler. There's no reason the USAF's flying boom system couldn't do the same, as long as the refueling system is set up to be bidirectional. The KC-135 did not have that capability when I worked on them in the 1970s, but the KC-10 and KC-46 might. |
mmcmurrey
Member Posts: 179
From: Austin, TX, USA
Registered: Jun 2012
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posted 09-05-2021 03:45 PM
There's one giant reason it would never be feasible: $$$. Can you grasp the amount of money it would cost to retro fit one airplane to accomplish this feat? |
oly
Member Posts: 1280
From: Perth, Western Australia
Registered: Apr 2015
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posted 09-05-2021 08:20 PM
Probe and drogue systems already exist and are in use, with some refueling aircraft capable of handling three aircraft requiring fuel at a time, one from each wing and a centreline position. It is a system used to refuel helicopters in flight because there is no feasible receptacle mounting position on a helicopter that would enable the use of a flying boom within the proximity of a spinning rotor.Mounting a refueling probe to the SCA and using US Navy A/A assets would not be a cost limiting factor for a program like the space shuttle.
No case existed that required the maturation of the A/A refueling concept, although the SCA was required to plan routes using military runways of sufficient length because it was fuel range limited due to the low altitude/high power settings required when carrying the shuttle. Should a shuttle landing have occurred overseas I suspect that the retrieval may have included the incorporation of A/A refueling to the SCA. Not all launch abort alternative runways were positioned near a seaport where a shipping recovery was possible, and these tests show what additional problems needed attention. |
mmcmurrey
Member Posts: 179
From: Austin, TX, USA
Registered: Jun 2012
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posted 09-06-2021 11:04 AM
Ok guys, this is probably my last post on this subject.Helos use a drogue because they can't fly forward speed fast enough to A/A behind a boom. C-130 equipped with drogue fly near stall speed to accomplish A/A with helos RSAF KE3 have configuration of wing drogue 2 and a tail boom 1. This idea didn't happen in the 80's. It's not needed now. Won't and didn't happen in future. My last statement: Designated tanker aircraft "KC" 135, 10 and whatever the new one is called are designed and equipped with special plumbing in their fuel tanks. There are two pumps in the center bladder (not your normal fuel pumps) that are specifically designed to pump the offloading fuel to the receiving aircraft. This fuel panel is monitored in the cockpit so as to offload the required amount or transfer from the wing fuel bladder into the belly bladder. Once the boom operator gets a signal light that contact with the receiver is made, the cockpit turns on one or two of the more powerful fuel pumps. Higher pressure opens up a butterfly valve that allows passing gas. Now if you want to waste your time to try to convince me that that any country has spent an unnecessary expense to all their probe-equipped aircraft to be able to reverse refueling I'm all ears. |
LM-12
Member Posts: 3602
From: Ontario, Canada
Registered: Oct 2010
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posted 09-06-2021 07:24 PM
Here is a 1979 photo of tufts on the winglet of a KC-135A tanker in flight. |
oly
Member Posts: 1280
From: Perth, Western Australia
Registered: Apr 2015
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posted 09-06-2021 11:42 PM
Many Boeing 707 derivatives have been converted into in flight refueling aircraft by using bladder tanks for additional fuel, and the incorporation of hose and drogue pylons on each wing. The aircraft are still used for troop or executive transport as well.It is feasible that such pylons could be mounted to the wing of the SCA. It is also feasible that an existing inflight refueling tanker could be modified with a probe, either fixed or retractable or extendable, that can be connected to the existing in-flight refueling pump system. Using such modifications can be used to couple the two aircraft, in flight, in a reverse configuration. The existing airborne tanker still acts as a tanker, pumping fuel through an attached hose to the recipient aircraft, in this case positioned in front. This removes the SCA from the wake turbulence created by the tanker, as identified by the test program. When you consider the engineering behind this, none of it is complicated, and existing equipment can be modified to suit in what would be a low cost modification relative to the budget assigned to the shuttle program. In the end, this requirement was considered but never acted upon. A single SCA was used until the post accident review identified a capacity issue with the SCA and a second aircraft was commissioned, and no shuttle ever required retrieval from distances beyond the range of the SCA withing the continental US. Given some of the other in flight refueling systems that have been used throughout aviation history, this scheme is not so inconceivable. As a side note, one of the most impressive flying displays I have seen was the New Zealand Air Force A4 Skyhawks flying an airshow routine while coupled. |
LM-12
Member Posts: 3602
From: Ontario, Canada
Registered: Oct 2010
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posted 09-09-2021 08:32 AM
The KC-10 (#91951) in the above photo was later painted all-gray. It is seen landing in a 2018 photo, and may still be flying today. |
Jim Behling
Member Posts: 1678
From: Cape Canaveral, FL
Registered: Mar 2010
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posted 09-13-2021 09:06 AM
quote:
Originally posted by mmcmurrey:
As for as an alternate refueling with the SCA in the lead is pure fantasy!
Not true, it was seriously considered. It would have been needed for Easter Island TALs. The Air Force wanted it and a second SCA before the Challenger accident. |
LM-12
Member Posts: 3602
From: Ontario, Canada
Registered: Oct 2010
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posted 09-13-2021 11:48 AM
Interestingly, reverse refueling (from receiver to tanker) was tested with two USAF KC-10 tankers. |
LM-12
Member Posts: 3602
From: Ontario, Canada
Registered: Oct 2010
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posted 09-13-2021 09:05 PM
Here is a great USAF film about the KC-10A Extender tanker aircraft. |
mmcmurrey
Member Posts: 179
From: Austin, TX, USA
Registered: Jun 2012
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posted 09-14-2021 11:05 AM
quote:
Originally posted by LM-12:
Here is a great USAF film about the KC-10A Extender tanker aircraft.
Nice video and informative. At 22:56 they talked about reverse refueling between two KC-10 aircraft. That is significant. Both aircraft are designed and capable of pumping fuel from a designated fuel bladder. In minutes before 22:56 they described the refueling with the SR-71 which requires special fuel. Explaining the need to be able to offload a different fuel from the a/r bladder tank without interfering with the normal engine fuel burn from its other fuel tanks. So my whole point in saying reverse refueling with the SCA was a fantasy was that to retrofit a non-configured tanker aircraft without the offloading capability was and would have been cost prohibitive. |
oly
Member Posts: 1280
From: Perth, Western Australia
Registered: Apr 2015
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posted 09-14-2021 07:53 PM
I don’t see it as requiring the capability in isolating/quarantining different fuel types as the 747 SCA aircraft's Pratt & Whitney JT9D-7J engines burn the same fuel as the KC-10 tankers CF6-50C2 engines. The donor aircraft could offload the same fuel from main, aux, or bladder tanks to the recipient.NASA considered using existing equipment that would require minimal modification. They did not consider purchasing, modifying, and maintaining an entire fleet of airborne tankers for shuttle exclusive use. There is a long list of aircraft types that have air-to-air refueling probes that are hard mounted and removable when not required. Developing a modification to install an existing system would neither be difficult or expensive in the big scheme of things and cost does not appear to be the prohibitive factor that led to the cancellation of the idea. It appears that the aircraft hardware and capability already existed at the time and that the stress cracks found in the empennage were the cause to pause further development. The US DOD has supported NASA many times. Providing logistical support for air-to-air refueling for the Space Shuttle program would be something I imaging they could take within their stride and considered critical to recovering a national asset. The maintenance cost for the additional hardware would be negligible and the crew training would be along the same lines as existing training. For the SCA, the modifications would be the installation of wing-mounted hose and drogue systems adapted from other four engine Boeing types, and the crew training would be to fly the aircraft straight and level. |
LM-12
Member Posts: 3602
From: Ontario, Canada
Registered: Oct 2010
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posted 09-14-2021 09:00 PM
Some nice aerial footage in that film. Regarding the boom refueling, the larger aircraft (C-5, B-52, SR-71, KC-10) seen in the film all have the receiving receptacle aft of the cockpit windows. The 747 (E-4 in the film) has the receiving receptacle in front of the cockpit windows. |
oly
Member Posts: 1280
From: Perth, Western Australia
Registered: Apr 2015
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posted 09-15-2021 12:18 AM
The location of the receptacle has several design considerations including airflow. The location is best positioned in a region of stagnant or low energy laminar flow where there is the least amount of low air pressure so that if a receptacle were to fail to close fully, the low air pressure does not draw fuel out of the valve. It is also nice to have the receptacle somewhere spilt fuel does not contaminate the windscreen or canopy, and somewhere that is already a structurally sound area to avoid the requirement to add weight to reinforce the structure. And if given the choice is is nice for the crew to be able to see what is happening as reassurance that there are no leaks etc. That said, there is generally a shortage of outside real estate and inside space to position the valve in the most convenient location, on the top of the aircraft. For the SCA, the drawings and data already existed for the 747 air-to-air refueling with the receptacle in the nose, but this brings with it the problem of turbulence from the tanker and the risk of a boom damaging the Shuttle if things go awry. Fuel spill contaminating the shuttle tiles and debris from a boom strike are some additional risks. |
Jim Behling
Member Posts: 1678
From: Cape Canaveral, FL
Registered: Mar 2010
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posted 09-15-2021 07:42 AM
The actively worked concepts were all reverse refueling. quote:
Originally posted by mmcmurrey:
...was and would have been cost prohibitive.
That is wrong. It was actively in work until the Challenger accident. |
mmcmurrey
Member Posts: 179
From: Austin, TX, USA
Registered: Jun 2012
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posted 09-15-2021 10:20 AM
Okay! You guys are not grasping the fact that tanker aircraft have different fuel plumbing. They have fuel pumps in tanks for their own use during flight. Then during refueling they use these two more powerful pumps that through the extra pressure pump out the fuel from the refueling bladder. Receiver a/c DO NOT HAVE that capabilities. The KC-10's both have that capability so in theory the may have the ability to perform reverse refueling. In my 21 years of flying USAF planes I never heard of reverse refueling. |
oly
Member Posts: 1280
From: Perth, Western Australia
Registered: Apr 2015
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posted 09-15-2021 12:03 PM
quote:
Originally posted by oly:
NASA considered using existing equipment that would require minimal modification.
From NATO publication ATP-56(A) Air to Air Refuelling (2000) KC-135. The USAF has a large fleet of KC-135s with several variants in service; the main differences are in fuel capacity and engines. Some KC-135s are fitted with a receptacle to receive fuel from boom equipped tankers; all of these have the capability to reverse pump fuel from their receptacle into a tanker. KC-10. The USAF has a 59 KC-10s in service. The aircraft has a receptacle for receiving fuel from boom-equipped tankers, and has a reverse fuel pumping capability. |
mmcmurrey
Member Posts: 179
From: Austin, TX, USA
Registered: Jun 2012
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posted 09-15-2021 12:54 PM
And once again I'll point out this is capable between tanker designed a/c. Majority of KC-135 are not receiver equipped. KC-10 were designed and built with receiver capability. |
Jim Behling
Member Posts: 1678
From: Cape Canaveral, FL
Registered: Mar 2010
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posted 09-15-2021 04:19 PM
And that doesn't matter. If NASA and the Air Force deemed that this was necessary to support Vandenberg launches, a portion of the the KC-135 and/or KC-10 would modified be to support reverse refueling of the SCAs.After all, the Air Force did modify two C-5s to carry a special spacecraft container (see C-5C). |
mmcmurrey
Member Posts: 179
From: Austin, TX, USA
Registered: Jun 2012
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posted 09-15-2021 06:33 PM
Well I'm not going to bang my head against the wall. But could you answer one question? How were they going to attach a boom to the ass end of the SCA in order to reverse fuel from whatever had a receptacle.
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mmcmurrey
Member Posts: 179
From: Austin, TX, USA
Registered: Jun 2012
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posted 09-15-2021 06:42 PM
quote:
Originally posted by LM-12:
The 747 (E-4 in the film) has the receiving receptacle in front of the cockpit windows.
Yes almost all large AF A/C have their receptacles on top and behind the cockpit. Doors open up and expose the receptacle under the doors. Kinda like playing corn-hole. 
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PeterO
Member Posts: 434
From: North Carolina
Registered: Mar 2002
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posted 09-15-2021 08:23 PM
quote:
Originally posted by mmcmurrey:
How were they going to attach a boom to the ass end of the SCA in order to reverse fuel from whatever had a receptacle.
The design studies for a 747 tanker were done by Boeing back in the 1970s. |
mmcmurrey
Member Posts: 179
From: Austin, TX, USA
Registered: Jun 2012
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posted 09-15-2021 09:00 PM
Concepts/ideas/proposals. Nothing came to fruition. Did you see any designs for mods to make this 747 tanker a SCA aircraft? |
oly
Member Posts: 1280
From: Perth, Western Australia
Registered: Apr 2015
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posted 09-16-2021 01:03 AM
You seem fixated upon the fact that NASA had to use an existing tanker as is, without modification, and that there is no conceivable way that a KC-10 or KC-135 could be used to refuel a leading aircraft from behind. Yet it has been demonstrated that the tanker types have transfer pumps capable of providing fuel pressure and flow rates to the upper connection point, that the tanker would require some type of modification to enable it to couple to the SCA from behind, That such a connection would be easily achievable with existing US air-to-air refueling hardware, and that modifying the SCA to receive fuel during air-to-air operations could be achieved using a wing-mounted hose and drogue system.What type of modification the air-to-air tanker would undergo has not yet been determined within this forum, but several off the shelf options are easily conceivable including the helicopter air-to-air extendable probe, an F-18 style retractable probe, or a hard-mounted rigid metal pipe style similar to the A4 Skyhawk, plumbed into the existing upper connect point to provide the required fuel flow rates and pressures needed. There is also the possibility of sourcing used hardware from retired aircraft types to reduce cost. For the SCA, an off the shelf wing-mounted retractable hose and drogue provides the lowest drag profile and weight penalty for the already weight compromised gravel hauler and a crew station could be installed to observe the air-to-air refueling process and operate the hose and drogue system within the SCA fuselage without disrupting the SCA center of gravity significantly. A fuel bladder may have been installed to allow a more rapid transfer of fuel and protect the aircraft fuel tanks from an overpressure, as free space was abundant within the SCA fuselage, but this would also require additional plumbing and weight and could be avoided. It is highly likely that a squadron of air-to-air tankers would have required modification and be assigned shuttle support operations so that trans-Atlantic or trans-American non stop ferry flights could be achieved, which would require a staging of tankers along the route. The SCA, which was altitude restricted when carrying the orbiter, would maintain S&L flight, extend the hose and drogue so that a tanker could couple from behind using the new refueling probe (mounted on the front of the tanker) which would be plumbed into the existing air-to-air refueling system. Without knowing what NASA contractors had planned, the above system is feasible using existing equipment and known engineering practices. If previous engineering designs existed to install a boom station and equipment to the 747 design, it may have been considered, however, such a system has a higher weight and drag penalty and it is highly probable that additional structural modification would be required that would further change the SCA fuselage fatigue stress model, whereas the wing-mounted hose and drogue introduces turbulence outside the empennage aerodynamic footprint which avoids the tail crack issue. It is also probable that the KC-33A design could not be incorporated into the SCA modified structure because the SCA fuselage was reinforced where the KC-33A boom station and hardware are located. Perhaps the two biggest issues are would NASA consider the cost of modifying the SCA and a fleet of tankers acceptable? Would the military be prepared to provide the additional support the SLS? As the program was never adopted, it seems that a convincing argument for this idea never came to fruition. Somewhere out there may be the original concept plans that may make interesting reading. |
mmcmurrey
Member Posts: 179
From: Austin, TX, USA
Registered: Jun 2012
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posted 09-16-2021 09:09 AM
You have quite the imagination but obviously no experience in air to air refueling. All of your first paragraph refers to easy add on of probes and a drouge for the wing of the SCA. Fighter type aircraft use probe/drouge. Large/heavy aircraft use center booms. Go back and read your NATO document you posted in a previous post about the different procedures and types of refueling.This is coming from a pilot with thousands of hours refueling behind KC-10, KC-135 and KE-3s. There is no way two heavy a/c are flying under the wing tip to try and engage a drouge. Wing tip vortices are like horizontal tornadoes. |
Jim Behling
Member Posts: 1678
From: Cape Canaveral, FL
Registered: Mar 2010
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posted 09-16-2021 09:13 AM
quote:
Originally posted by mmcmurrey:
How were they going to attach a boom to the ass end of the SCA in order to reverse fuel from whatever had a receptacle.
The 747 was a competitor to the DC-10 for the Advanced Tanker Cargo Aircraft Program. Boeing did all the design work for attaching a boom to an 747 and tested it. quote:
Concepts/ideas/proposals. Nothing came to fruition.
Because the DC-10 won and Challenger happened. quote:
Did you see any designs for mods to make this 747 tanker a SCA aircraft?
The other way around. A boom would have been added to existing SCAs. |
mmcmurrey
Member Posts: 179
From: Austin, TX, USA
Registered: Jun 2012
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posted 09-16-2021 09:14 AM
quote:
Originally posted by PeterO:
The design studies for a 747 tanker were done by Boeing back in the 1970s.
Do you know if Boeing made a prototype of the 747 tanker or was this just a design concept? |
Jim Behling
Member Posts: 1678
From: Cape Canaveral, FL
Registered: Mar 2010
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posted 09-16-2021 09:20 AM
See: The World's Only KC-747 Tanker Is Flown By The Iranian Air Force ...the largest aerial refueler of them all is based on the iconic Boeing 747, a symbol of American might and ingenuity. Ironically, it flies for none other than the Islamic Republic of Iran Air Force. |
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