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  Shuttle Carrier Aircraft mid-air refueling (Page 2)

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Author Topic:   Shuttle Carrier Aircraft mid-air refueling
mmcmurrey
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posted 09-16-2021 09:21 AM     Click Here to See the Profile for mmcmurrey   Click Here to Email mmcmurrey     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by LM-12:
What was the purpose of the dot patterns seen on the 747?
My guess about the dot pattern were sensing devices to measure the air disturbance generated by the tanker.

Jim Behling
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posted 09-16-2021 09:25 AM     Click Here to See the Profile for Jim Behling   Click Here to Email Jim Behling     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by mmcmurrey:
This is coming from a pilot with thousands of hours refueling behind KC-10 KC-135...
Being an airplane driver and experience in being behind a tanker doesn't give knowledge of plans and needs of higher headquarters. Or knowledge of what the contractors can do.

I was in what was the USAF shuttle program office and reverse refueling of the SCA was in the works.

mmcmurrey
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posted 09-16-2021 09:38 AM     Click Here to See the Profile for mmcmurrey   Click Here to Email mmcmurrey     Edit/Delete Message   Reply w/Quote
Best laid plans of mice and men. You speak in theoretical. I'm only knowledgeable in the practical.

Jim Behling
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posted 09-16-2021 10:03 AM     Click Here to See the Profile for Jim Behling   Click Here to Email Jim Behling     Edit/Delete Message   Reply w/Quote
Only knowledgeable in the existing state of the art, not what is practical or possible.

LM-12
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posted 09-16-2021 10:21 AM     Click Here to See the Profile for LM-12     Edit/Delete Message   Reply w/Quote
On NASA 905 at the rear orbiter support struts, there are dots/tufts on the left side of the fuselage only.

mmcmurrey
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posted 09-16-2021 10:57 AM     Click Here to See the Profile for mmcmurrey   Click Here to Email mmcmurrey     Edit/Delete Message   Reply w/Quote
I can't really see what they are but are you talking about the same pattern on forward orbiter struts and on the vertical tail elevators?

LM-12
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posted 09-16-2021 11:00 AM     Click Here to See the Profile for LM-12     Edit/Delete Message   Reply w/Quote
Yes, looks like the same pattern. Hang on, and I will post photo links showing both sides of the fuselage... (I think I got that right)

mmcmurrey
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posted 09-16-2021 12:06 PM     Click Here to See the Profile for mmcmurrey   Click Here to Email mmcmurrey     Edit/Delete Message   Reply w/Quote
I still think those are some kind of wind sensors checking the disruption of air flow in or on the orbiter area. If you notice the tankers position to the SCA, that's called the "pre-contact" the receiver calls the position with "ready". The boom operator then gives the receiver light signals from the bottom of the tanker.

Also of note is the unusual 135. That aircraft is usually used to monitor atmospheric anomalies. I don't have a clue why it is used here other than looks like someone is peering out the portals?

mmcmurrey
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posted 09-16-2021 12:20 PM     Click Here to See the Profile for mmcmurrey   Click Here to Email mmcmurrey     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by Jim Behling:
I was in what was the USAF shuttle program office and reverse refueling of the SCA was in the works.
I never said I was an expert in planning and acquisitions. So in the mid 70's and with 20/20 hindsight why didn't NASA jump on the two Boeing 747 tankers?

mmcmurrey
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posted 09-16-2021 01:24 PM     Click Here to See the Profile for mmcmurrey   Click Here to Email mmcmurrey     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by mmcmurrey:
Also of note is the unusual 135.
Sorry about referring to the 135. I initially couldn't open your pics of the KC-10 so I was referring to your first pics.

LM-12
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posted 09-16-2021 01:39 PM     Click Here to See the Profile for LM-12     Edit/Delete Message   Reply w/Quote
On that KC-135 (#53127) tanker, those portal windows were on the left side of the fuselage only. There were no portal windows on the right side.

mmcmurrey
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posted 09-16-2021 03:51 PM     Click Here to See the Profile for mmcmurrey   Click Here to Email mmcmurrey     Edit/Delete Message   Reply w/Quote
I looked that a/c up and it is not a WC-135. It's just listed as KC-135 with portals?

The WC-135 is receiver capable with no boom.

LM-12
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posted 09-17-2021 09:34 AM     Click Here to See the Profile for LM-12     Edit/Delete Message   Reply w/Quote
The very first Boeing 747 rolled off the assembly line in September 1968.

In April 1972, a KC-135 refueling boom was installed on that very same 747 for flight testing at Edwards AFB in July.

That 747 is also seen on the cover of Aviation Week and Space Technology (October 2, 1972 issue) with this caption:

Modified Boeing 747 in refueling tests with USAF/Lockheed SR-71

Jim Behling
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posted 09-17-2021 09:52 AM     Click Here to See the Profile for Jim Behling   Click Here to Email Jim Behling     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by mmcmurrey:
So in the mid 70's and with 20/20 hindsight why didn't NASA jump on the two Boeing 747 tankers?
In the mid 70's, there wasn't the concept of Trans-oceanic Aborts Landings (TAL). There was only Return to Launch Site and Abort Once Around. TAL didn't appear until STS-2/3 in 1982.

TAL allowed for a performance increase due to change in the trajectory. The DOD didn't like it because of the chance of the orbiter landing in a foreign country with DOD payload. To retrieve an orbiter from Easter Island would have required removal of engines and payload so that the SCA could have made the longest leg on the return. The DOD didn't want that so SCA refueling was looked at.

mmcmurrey
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posted 09-17-2021 10:59 AM     Click Here to See the Profile for mmcmurrey   Click Here to Email mmcmurrey     Edit/Delete Message   Reply w/Quote
And that was a good contingency plan. But until the refueling test flights ended in 1984, I'm willing to bet you or anyone else had never heard of reverse refueling.
quote:
Originally posted by LM-12:
In April 1972, a KC-135 refueling boom was installed on that very same 747 for flight testing at Edwards AFB in July.
Thanks. When Boeing didn't win the contract for next generation tankers (McDonnell Douglas DC-10 won) I believe this B-747 and 1 other one were sold to Iran in a 10 B-747 bundle.

Jim Behling
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posted 09-17-2021 12:07 PM     Click Here to See the Profile for Jim Behling   Click Here to Email Jim Behling     Edit/Delete Message   Reply w/Quote
In 83/84 is when the USAF wanted a second SCA and refueling capability.

mmcmurrey
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posted 09-17-2021 12:31 PM     Click Here to See the Profile for mmcmurrey   Click Here to Email mmcmurrey     Edit/Delete Message   Reply w/Quote
I don't doubt that what so ever. What "refueling capability"? Being able to receive in flight refueling or operating as a "tanker"?

Jim Behling
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posted 09-17-2021 04:43 PM     Click Here to See the Profile for Jim Behling   Click Here to Email Jim Behling     Edit/Delete Message   Reply w/Quote
Receive by reverse refueling. The boom would be on the SCA.

mmcmurrey
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posted 09-17-2021 07:54 PM     Click Here to See the Profile for mmcmurrey   Click Here to Email mmcmurrey     Edit/Delete Message   Reply w/Quote
Okay guys, this is my final response to this antiquated argument of procedure from 40 to 50 years ago. The terminology "reverse fueling" is not what you perceive it to be. Reversing the pumping of fuel from the receptacle into a boom is not happening.

The references to reverse refueling demos in KC-10 to KC-10 is in regards to the receiver and boom operations of each A/C. NATO stated some KC-135 are fitted with receptacles to receive from the boom: all have the capability to reverse fuel pumping capability.

When I was flying with RSAF, their KE-3 tankers had receiver capability plus a center rear boom and a drogue on the l/r wing. During training we would fly with two tankers, one acting as tanker, the other as receiver. After practicing being a receiver and offloading 10,000 to 20,000 pounds of gas, we would swap positions and the other set of students practiced receiving and taking on 10,000 to 20,000 pounds, thus reverse refueling.

So all my contacts from the past I'm still in contact with have never heard of reverse refueling. The supervisor of flight test at Tinker AFB, Oklahoma said there was no way to pump fuel forward out of a receptacle.

I hope maybe this explains my position to you, but I'm finished arguing over 50 year old possibilities.

oly
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posted 09-17-2021 10:11 PM     Click Here to See the Profile for oly   Click Here to Email oly     Edit/Delete Message   Reply w/Quote
KC-135 R/T Facts:
KC-135 R/T Facts:- A KC-135 R/T tanker not only can refuel other planes, but also has the capability to siphon fuel back in to the tanker from certain receivers. This process is called reverse air refueling.
To quote a former KC-135 boom operator:
The procedure is pretty simple:

Normal RZ procedures;

  1. Determine how much fuel can be on-loaded into the aft body tank (the only tank you can fill), based on the desired CG.

  2. Establish a normal contact with a large receiver, like a B-52.

  3. Once the receiver is stabilized, the Boom Operator will slightly pull back on the extend/retract lever to open the Boom by-pass valve that dumps fuel into the aft body tank.

  4. The receiver will pressurize his fuel system and begin pumping fuel to the tanker.

  5. Once fuel is observed being on-loaded in the aft body tank the Pilot will configure the fuel panel to feed fuel to all 4 engines from the aft body tank, then turn on one aft body fuel pump.

  6. The Pilot will notify the Boom Operator when the desired amount of fuel has been on-loaded to prevent exceeding the aft CG limit.

  7. The Boom Operator and Receiver Pilot will initiate a normal disconnect.

  8. The Receiver will stay with the tanker for further fuel transfers if needed.
From Air Force Manual 11-2KC-135, Volume 3, 10 September 2019, Flying Operations, KC-135 Operations Procedures:
15.2.6. Reverse AAR will be accomplished only in an emergency or for operational necessity, or IAW FTU or USAFWS syllabus training (T-2).

mmcmurrey
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posted 09-18-2021 03:23 PM     Click Here to See the Profile for mmcmurrey   Click Here to Email mmcmurrey     Edit/Delete Message   Reply w/Quote
Very interesting. I'm surprised they wrote out something that can only be used in emergencies and can only be used to put gas back into the KC-135's upper aux tank.

My only question to your boom operator would be what pumps would a receiver turn on to siphon gas back into the tanker? I'm not familiar with fuel system on any aircraft other than the E3, KC-135, DC-10 and B747.

Jim Behling
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posted 09-19-2021 08:49 AM     Click Here to See the Profile for Jim Behling   Click Here to Email Jim Behling     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by mmcmurrey:
Reversing the pumping of fuel from the receptacle into a boom is not happening.

Don't you understand this would not be using stock aircraft or be a fleet wide mod? The USAF would have modified only those KC-10s or KC-135s necessary for this role. They would have added the required systems to make it possible. Just as they modified a two C-5s or the KC-135Qs. At the time, it was that important for this to happen.

Again, you were only knowledgeable on what was done and not what could be done.

mmcmurrey
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posted 09-19-2021 10:37 AM     Click Here to See the Profile for mmcmurrey   Click Here to Email mmcmurrey     Edit/Delete Message   Reply w/Quote
Okay! This is my final stab at explaining the problem you don't understand.
  1. Tanker aircraft are/were designed as flying gas stations. They have a special fuel bladder with special fuel pumps in them that pump fuel out the boom under high pressure.

  2. Receiver aircraft have an additional refueling port mounted usually on top that makes that port accessible to the boom of the tanker.

  3. Ground operations at airports/bases have fueling pits, fueling trucks that are capable of connecting to and pumping(high pressure) into planes fuel through ground accessible ports. During fueling operations someone is in charge near the fuel panel to insure the right loads are distributed to the correct tanks.

  4. In flight this fueling process is accomplished the same way EXCEPT it uses the a/r receptacle. Flight engineers are the ones that make sure tanks are filled in correct sequence or limits.

  5. Aircraft operate their fuel system to their own engine under positive pressure from their fuel pumps (I'm guessing in the 3-4 psi).
So in conclusion there is no way for a receiver aircraft to pressurize fuel out of their inflight refueling port. However if you can show me how maybe a KC-135 (we called these ac/dc tankers) can pump gas up to their receptacle under their two special more powerful pumps.

So oly, if your boomer bud that says he can trick the system design by way of his description have you asked him about the pumps to turn on?

mmcmurrey
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posted 09-19-2021 01:04 PM     Click Here to See the Profile for mmcmurrey   Click Here to Email mmcmurrey     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by oly:
To quote a former KC-135 boom operator..
Thanks for getting my curiosity tweaked on your post. I've made some connections with old buddies from my AF days. One of which was a instructor boom operator that confirmed your boomer friend's explanation of reverse refueling.

He said it was only discussed at his instructor boom training classes at Castle AFB, Ca.

He went on further to add that it was only possible with B-52's and he didn't know what type of pumps they had to pressurize the refueling manifold, but whatever it was, was very slow. He didn't remember or ever know what circuit breakers had to be pulled in order to pressurize their manifold to open their receptacle valve. He also stated he never heard of anyone trying this other than training at Castle.

oly
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posted 09-20-2021 02:32 AM     Click Here to See the Profile for oly   Click Here to Email oly     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by Jim Behling:
In the mid 70's, there wasn't the concept of Trans-oceanic Aborts Landings (TAL). TAL didn't appear until STS-2/3 in 1982.
The logistics that were planned following a TAL were incredible.
NASA estimates it would take about 19 C-17/C-5 aircraft sorties, a significant Navy sealift operation, and 450 NASA and contractor personnel to complete the turnaround. Not all of these personnel would be on site at any one time. In addition to these personnel, another 150 to 200 DOD personnel may be required to put in place a “bare-base” operation consisting of portable general-purpose shelters, latrines, a kitchen, aircraft hangars and other support equipment if the TAL site does not have adequate facilities to support such a large team.Payloads and/or airborne support equipment will remain onboard the orbiter for the flight back to Kennedy Space Center unless the capability of the shuttle carrier aircraft, landing site location or other requirements dictate otherwise.

Jim Behling
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posted 09-20-2021 07:47 AM     Click Here to See the Profile for Jim Behling   Click Here to Email Jim Behling     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by mmcmurrey:
...there is no way for a receiver aircraft to pressurize fuel out of their inflight refueling port.
The SCA and a few tankers would be modified specifically so that reverse refueling could be done. What the current fleet could or could not do had no bearing on the matter.

mmcmurrey
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posted 09-20-2021 11:20 AM     Click Here to See the Profile for mmcmurrey   Click Here to Email mmcmurrey     Edit/Delete Message   Reply w/Quote
I'll make this very simple: Imagine a flying gas station with 100,000 to 200,000 pounds of fuel available designed to pump out of its boom 1,200 to 2,000 pounds per minute into a receiver.

Now reverse it and you have ac/dc tanker with that same 100,000 pounds available to off load from its bladder tanks. Tell me how they could get the pressure and fuel to pump gas up the 6" to 7" diameter boom of a forward flying aircraft.

oly
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posted 09-20-2021 07:01 PM     Click Here to See the Profile for oly   Click Here to Email oly     Edit/Delete Message   Reply w/Quote
By engineering a system capable of doing the required task.

How do the fire fighting helicopters lift water up a giant hose into their hopper so fast while hovering?

mmcmurrey
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posted 09-21-2021 11:19 AM     Click Here to See the Profile for mmcmurrey   Click Here to Email mmcmurrey     Edit/Delete Message   Reply w/Quote
By sucking it up the large hose. Much like a sewer servicing truck sucking out sewer tanks when they get to capacity.
quote:
Originally posted by oly:
The logistics that were planned following a TAL were incredible.
Nice information and an interesting read. I'm in complete agreement on your assessment of a colossal undertaking. Not having the knowledge of the "big picture" I'll throw my two cents worth of opinion on.

Just looking at the air assets 17 KC-10/C-5's. I'm speculating the planners were already thinking they would have to disassemble the shuttle to get it into the modified C-5 that Jim informed us about. This is based on the abort bases not being able to support putting the shuttle on the back of the SCA or support a loaded SCA/shuttle on their runways. Also the limited amount of fuel for the SCA to fly out to the next point to get fuel.

Now with the modified C-5 loaded with bulk of the shuttle and take off accomplished with probably a lighter fuel load, They could air refuel all the way back to the US using the KC-10 (witch also operates as a cargo a/c).

Jim Behling
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posted 09-21-2021 11:50 AM     Click Here to See the Profile for Jim Behling   Click Here to Email Jim Behling     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by mmcmurrey:
By sucking it up the large hose.
And instead of just "sucking" which can only provide a max 14.7 pressure differential, the supply aircraft can pressurize its tanks or use pumps.

Again, these won't be stock aircraft but a few modified for the role.

quote:
I'm speculating the planners were already thinking they would have to disassemble the shuttle to get it into the modified C-5.
I never said the shuttle was going in the C-5. Those C-5s were modified for hauling shuttle payloads around the country.

The SCA would still have been used for an overseas landing. Part of the reason for the number of C-5s/C-17s support is to haul over the derrick and crane to lift the Shuttle onto the SCA.

The part about "disassembling" the orbiter was to make it light enough so that the SCA could make the longest leg of the return flight. The issue is that it was unknown that it could be made light enough and hence inflight refueling of the SCA was pursued and that is want led to reverse refueling.

I used the modified C-5s has an example where the USAF would modified a small portion of a fleet for a specific task. Meaning that it could and would do the same to the KC-135/KC-10 for SCA reverse refueling if needed.

quote:
...abort bases not being able to support
Abort bases were specifically selected because they could support both items or they were modified so that they could support both.

mmcmurrey
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posted 09-21-2021 12:08 PM     Click Here to See the Profile for mmcmurrey   Click Here to Email mmcmurrey     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by oly:
Yet it has been demonstrated that the tanker types have transfer pumps capable of providing fuel pressure...
Just wondering where you received your information that tanker a/c have shown capability to provide pressure out of their receiver receptacle?

Jim Behling
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posted 09-21-2021 12:13 PM     Click Here to See the Profile for Jim Behling   Click Here to Email Jim Behling     Edit/Delete Message   Reply w/Quote
Does really matter?

Like he said, you seem fixated on using an stock aircraft. If it couldn't, they would engineer a new specific additional receptacle and add it to a few aircraft for this purpose.

mmcmurrey
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posted 09-21-2021 04:05 PM     Click Here to See the Profile for mmcmurrey   Click Here to Email mmcmurrey     Edit/Delete Message   Reply w/Quote
No it doesn't matter one iota. But maybe in closing our argument would you expound on the reason the TAL recovery was nixed. You keep referencing Challenger disaster as the end of pursuing reverse refueling as you stated in one of your first post.

"The AF wanted additional SCA aircraft air refuelable, and if needed they would make it happen." When was the "need" no longer there? The missions resumed some years later.

Jim Behling
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posted 09-21-2021 10:41 PM     Click Here to See the Profile for Jim Behling   Click Here to Email Jim Behling     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by mmcmurrey:
When was the "need" no longer there?
I stated it earlier.

TAL sites for the east coast were in Europe and Africa, and there were short enough legs within the range of the basic SCA to get back to the USA. East Coast TAL sites were in place and manned until the end of the program.

It wasn't the same in the south Pacific for west coast (Vandenberg) launches. There was just Easter Island and it is too far for the basic SCA to make to any other island or South America. After Challenger, the west coast launch capability was canceled and hence so was the need for SCA inflight refueling.

oly
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posted 09-21-2021 11:06 PM     Click Here to See the Profile for oly   Click Here to Email oly     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by mmcmurrey:
Just wondering where you received your information that tanker a/c have shown capability to provide pressure out of their receiver receptacle?
Several links and articles have previously been offered to support the original topic of this forum, that mid-air refueling of the SCA was seriously considered by NASA as a means of extending the range of shuttle ferry flights. The scheme had some initial test flights done to determine potential issues, which identified some issues that required engineering solutions. Air-to-air refueling of the SCA never eventuated, but the procedure is possible and is done elsewhere.

We could have an entire discussion on the pro's and con's of fuel pump designs including reversible pumps, motive flow pumps, pressure differential systems of transfer, and the myriad of other available ways of achieving fluid transfer between containers, however, it would all be speculative because we are not on the specific design or engineering panels.

Some of the information provided that identified that reverse air-to-air refueling was a capability that already existed also identified that doing so was unique to specific model variants and installed equipment and that the procedure was not a run-of-the-mill event, but restricted to operational requirements, training, and approval.

During my time within the aviation/aerospace industry, I have seen first hand how aircraft of a common type can have design variations between individual aircraft, that commonality between types can vary between consecutive serial numbers (I know of nine aircraft, consecutive serial numbers, three different equipment fit-outs, same type certificate datasheet, same pilots and maintenance manuals, and not one pilot could identify any differences between them. As long as the thing turns on when you push the button, everything is good). Aircrew have never been the highest authority regarding the capability of an aircraft.

If modifying the SCA were to be done using existing and available equipment or using program-specific one-off equipment is moot because the program never reached fruition. Having never been involved in that specific program, I offered a theoretical method based upon existing equipment and data that minimizes the additional weight of an already weight-restricted system. The addition of a refueling boom to the SCA may require some of the bags of gravel ballast to be offloaded, I gladly yield to those who were involved in the space shuttle program and would openly consider other ideas of what could have been from such.

I see no benefit in flogging the proverbial dead horse by demanding to know what button to press to get something to work, that's why we use technical manuals.

mmcmurrey
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posted 09-22-2021 10:37 AM     Click Here to See the Profile for mmcmurrey   Click Here to Email mmcmurrey     Edit/Delete Message   Reply w/Quote
I'm with you. No more flogging. I enjoy reading your theoretical solutions and you present a sound argument of your theories. My only critique would be you don't understand the fuel system plumbing.

Tankers are built with extra fuel bladders for offloading fuel through their system at rates of 1,200 to 2000 lbs per minute. I think Jim stated it as 14.5 psi. Aircraft burn their own fuel through a manifold system under positive pressure 3 to 4psi. I'm not sure about the KC-10 but the 135 refueling bladders are non-burnable fuel to their own operating engines. So my thinking in theory, it would take some major re-engineering to get the 3 or 4 times psi pressure to the receptacle.

quote:
Originally posted by Jim Behling:
After Challenger, the west coast launch capability was canceled and hence so was the need for SCA inflight refueling.
Thanks for the clarification.

Jim Behling
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posted 09-22-2021 01:08 PM     Click Here to See the Profile for Jim Behling   Click Here to Email Jim Behling     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by mmcmurrey:
My only critique would be you don't understand the fuel system plumbing.
I made not such claim. I just know that the USAF and NASA were working a solution that involved reverse refueling through a boom on the SCA. I had no idea how the actual details were to work.
quote:
I think Jim stated it as 14.5 psi.
That had nothing to do with an actual system. That was related to the comment where a helicopter was sucking water up through a hose. 14.7 psi is highest pressure differential you can get by "sucking" (Atmospheric minus Vacuum) vs using pumps.

mmcmurrey
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posted 09-22-2021 01:28 PM     Click Here to See the Profile for mmcmurrey   Click Here to Email mmcmurrey     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by Jim Behling:
That was related to the comment where a helicopter was sucking water up through a hose.
Those questions were to oly.

oly
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posted 09-22-2021 08:46 PM     Click Here to See the Profile for oly   Click Here to Email oly     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by mmcmurrey:
Tankers are built with extra fuel bladders for offloading fuel through their system at rates of 1,200 to 2000 lbs per minute.
Perhaps I don't understand the fuel system plumbing.

Some of my previous experience was a part of the engineering maintenance team for a modification program to convert Boeing 707 aircraft with in-flight aerial refueling equipment, including two underwing fuel pods driven by "hydraulically" powered fuel pumps.

Four submerged fuel pumps were installed in the center section fuel tank which fed fuel into 3inch pipes via a crossfeed valve arrangement, designed to allow any pump to feed either pod, creating the required redundancy, designed to minimise the likelihood of fuel pump failure interrupting an air-to-air hookup.

The 3-inch fuel pipes were installed through the wing main spar box, then to mounting flanges in the wingtip pylons, which were structurally attached to the forward and aft wing main spars. The fuel management strategy used during air-to-air refueling operations differed from for regular B-707 operation, as fuel from the inboard and outboard wing tanks was pumped into the center section tank from where it is offloaded to receiver aircraft. This design was adopted because it allowed the aircraft to retain its VIP transport role as well, as the aircraft still had the cabin interior and seats installed.

The Mk.32B underwing pods used a combined fueldraulic and mechanical system that was fully self-contained and derived its fuel working pressure from a variable pitch ram air turbine, controlled by the pod computer. Fuel supplied from the aircraft at pressures as low as 6 psi was amplified to a working pressure of about 50 psi using a centrifugal pump, which fed fuel into a multiport rotary valve, which directs the fuel either back into the parent aircraft fuel system or a vane pump/motor. The valve position and fuel flow are determined by pod operating mode.

The high-pressure fuel flow produced by the centrifugal pump was fed into the receiver fuel system, with a nominal flow rate of 2800 lb/min.

It is perhaps prudent to also mention that the Airbus A330 tanker variant also operates without a specialised fuel bladder, and feeds its Air-to-Air Refueling system from the aircraft fuel tanks.

As a side note, I also have about 6,000 hours in my pilot's log book.

mmcmurrey
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From: Austin, TX, USA
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posted 09-23-2021 02:18 PM     Click Here to See the Profile for mmcmurrey   Click Here to Email mmcmurrey     Edit/Delete Message   Reply w/Quote
Very nice reading. Boeing provided Royal Saudia AF with two or three B707-320 KE3 that were built exactly as you described above. This was a program sold to SA in a package E3 (AWACS) and KE3 tankers with both equipped with CFM-56 engines.

I'm not knowledgeable of current refueling capabilities or newer designed a/c, but in the period we are talking over 80'-90's the notion that we could pump fuel back up into a boom was not possible. I don't know the exact diameter of the boom nozzle and hose (5"-7") but as you stated the pumps in the bladder tanks provided the needed pressure to pump gas out to receivers with enough pressure to fill their tanks. Just like ground refueling large aircraft from fuel pits or fuel trucks. Those pumps (ground) have no way of reversing their flow so would be unable to suck out fuel. That is why refueling large a/c is monitored carefully as to overloading because that process of defueling is an extremely slow process as it basically requires draining the system via gravity back into a truck.

I'm guessing if you watched LM's video on the KC-10 capabilities near the end at 22:56 they showed mid air refueling between two KC-10. Their comment was "capable of reverse refueling." What you see is the ability to receive fuel and pump it to a receiver. They are not pumping fuel back up the boom from the receiver a/c. I think this terminology "reverse refueling" is the culprit. What I see is the duel capability of receiving and pumping gas.

I understand the fill pipes and transfer of fuel from tank to tank. As you know some of the wing tanks are designed to auto fill into inner tanks at a designed quantity level as the inner tanks burn fuel. Also the fuel panel on the 135 and KE3 are managed from the cockpit in order to move fuel around to get fuel into the center bladder tank that has the ar pumps that provide the pressure to pump out the boom.

So now I'll ask you when you were working theories and testing systems to enhance air refueling, was there any discussion on how you would get the fuel from the refueling bladder back through the fuel system and too the upper receptacle? It's just a question and I'm not trying to diminish your work or any others. You've just piqued my curiosity about something I was familiar with 50 years ago.


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