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More KC-46A woes....

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More KC-46A woes....

Old 5th Feb 2019, 13:35
  #881 (permalink)  
 
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Originally Posted by PDR1 View Post
I'm still waiting for Ken to explain why the required fuel pressure for a mid-span fuel hose increases when an aeroplane banks.PDR
Two comments:
1. I never made such a claim. But nice try anyway.
2. If you're referencing the discussion of fuel having to move "uphill" due to dihedral and/or anhedral, the fuel system is not only designed to accommodate such features, but is designed to accommodate the worst possible unbalanced/uncoordinated bank condition (be it a slip or a skid) within the aircraft's performance envelope. Clu4U: aircraft are equipped with turn and slip/turn coordinator instruments for a reason. And if it has escaped you, the "uphill" condition created by a slip/skid far exceeds the "uphill" condition created by an/dihedral. And for the KC-10, the "uphill" condition of the tail engine far exceeds the "uphill" condition created by dihedral. Clear enough?
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Old 5th Feb 2019, 13:41
  #882 (permalink)  
 
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Originally Posted by Just This Once... View Post
ARBS reduces the maximum pitch angle available.
So Airbus's solution to reduced ground pitch angle is to reduce MTOGW, thus preserving critical field length? Interesting. But this means that anytime the MRTT is operating from long runways where critical field length is not a factor, the airplane remains weight restricted. Seems like an odd trade to me. But hey, there's a number of things about Airbus design approaches I find odd, but are perfectly acceptable in normal service.

But wait. Voyager does not have ARBS. So if ARBS is why MTOGW is reduced, why is Voyager's MTOGW reduced? Something does not add up.

Last edited by KenV; 5th Feb 2019 at 17:22.
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Old 5th Feb 2019, 13:50
  #883 (permalink)  
 
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Originally Posted by Tengah Type View Post
BEagle

The problems at Scampton were not caused by the wing mounted AAR pods but by the ground clearance below the Underwing Fuel Tanks on the K2. The pods were head high, whereas the clearance below the tanks was only about 18 inches. So low that they were likely to hit any snow depth warning indicators next to taxiways. At Paine Field (Washinton State,USA) my Nav Rad and Crew Chief had to navigate us about 2 miles, on foot, over these as we taxied in to the parking area for an airshow. One other snag at Scampton was the "lumpy" nature of the runway construction which would have had severe consequences for the Victor fatigue life. This together with the need to remove concrete kerbs and refuelling pipes at all the dispersals was too expensive to rectify for the, then, proposed life of the Victor K2.

The choice of using the wing pods or centre line HDU was also a function of the flow rate of the various receiver types. The Mk 20 pod on the Victor, which had an integral 1000lbs fuel tank, had a flow rate of 1500lbs/min whereas the HDU was 4000lbs /min. With aircraft such as the Lightning and Jaguar, which took fuel at 1100 lbs/min, it was quicker to refuel a pair on the pods rather than sequentially on the HDU. The F4 took fuel at 4000lbs/min, so would empty the pod fuel tank fairly quickly, which would not pass any more fuel until it had filled to half fuel again. Hence it was quicker to refuel a pair of F4s one at a time, with continuous fuel flow, on the HDU.

The VC10 had the Mk 32 pod, which did not have an internal tank, and gave a fuel flow of 2800lbs/min, however the VC10 fuel system only allowed 2200lbs/min if both pods were in use together. The HDU was the same on both types. So, again it could be quicker to use the HDU for a pair of F4s than to use the wing pods.

All of the above figures are from memory of 30+ years ago, so anybody with the reference books can challenge me without me getting upset or descending to personal abuse.
Thank you Tengah, I was not aware of all of the differences in flow rates between the types, very informative. Curious about keeping the Mk 20 pod "topped off" when it was actively dispensing fuel. Sounds like it could be drained pretty quickly (especially by the Phantom), so did you have the pumps going to the pod tank continuously? Gravity? Automatic shut off when the pod tank is full?
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Old 5th Feb 2019, 14:13
  #884 (permalink)  
 
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Originally Posted by KenV View Post
Two comments:
1. I never made such a claim. But nice try anyway.
In #864 you said:

Originally Posted by KenV View Post
KC-10 has a significant dihedral. Lotsa "uphill" flow there. And besides, the plumbing and pumping is sized to provide good flow even when the tanker is flying in a bank where the "uphill" may be much more pronounced than the "uphill" provided by dihedral.
Can you show how have I misinterpretted that?

but is designed to accommodate the worst possible unbalanced/uncoordinated bank condition (be it a slip or a skid) within the aircraft's performance envelope. Clu4U: aircraft are equipped with turn and slip/turn coordinator instruments for a reason. And if it has escaped you, the "uphill" condition created by a slip/skid far exceeds the "uphill" condition created by an/dihedral. And for the KC-10, the "uphill" condition of the tail engine far exceeds the "uphill" condition created by dihedral. Clear enough?
You said nothing about "unbalanced" - you just said "banked". Stop wriggling - you made a yet another schoolboy error and exposed your ignorance. At least have the intergrity to admit it. Sorry, but I still recon you're probably a Walt.

PDR
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Old 5th Feb 2019, 14:27
  #885 (permalink)  
 
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Ken

As for your claim about being the first to say anything here about the F-35's strike-dominated design: maybe you are right but in order to know that, you would have had to read the 200+ pages in the F-35 thread that were there before you joined this forum. If that is so, there are places to get help:


On the HMD, you made the specific claim in 2015 that a Block IV version existed and that it had eyeball tracking. This was false, and I am aware of the source you claimed. I have met the person myself and I suspect that you misunderstood him.
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Old 5th Feb 2019, 15:05
  #886 (permalink)  
 
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Originally Posted by BEagle View Post
Pressure drop and the need for higher volumetric flow rates to provide the required pod pressure for the TriStar pod programme led to the need for larger pipe bores than initially specified - getting the fuel all that way to the pod pylon wasn't very easy. Whereas the A330MRTT has the huge benefit of taking advantage of the redundant outboard engine locations of the A340 and the existing fuel feed pipework.
May I offer two comments:

1. Sounds like someone screwed up twice if they had to enlarge the fuel tubes. First in under specifying the tube size to begin with, and second in not adding a jet pump down the line to up the flow and increase the head pressure to the pod. On the other hand, upsizing the tube by one standard size may be easier than adding a jet pump.

2. Consider that the A340 uses CFM56 engines. The highest thrust version used is the CFM56-5C4 @ 34,000 lbf. Fuel flow at max static thrust is about 187lb/min. (see here) For simplicity let's call it 200lb/min. Will a pipe sized to deliver 200lb/min satisfy a fuel pod that is supposed to deliver as much as 4500lb/min? I think not. So yes, having existing piping in the area of the pod is an advantage, but no, that existing piping is woefully undersized and would make the undersized Tristar pod piping problem you described above seem like child's play. The localized wing strengthening of the A330 wing to accommodate the outboard engine pylons is an advantage, but serious overkill for the much much lighter WARP that also, unlike an engine installation, generates almost no torque loads.

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Old 5th Feb 2019, 17:42
  #887 (permalink)  
 
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Originally Posted by PDR1 View Post
Can you show how have I misinterpretted that?
I don't know why I even bother. Your personal attacks are irrational and will continue anyway, but here goes. Read what I wrote, not what you wish I wrote. Since you missed it, allow me to add emphasis: flying in a bank where the "uphill" may be much more pronounced than the "uphill" provided by dihedral. Banking may create an "uphill" if the bank is not flown coordinated. Because the airplane may be flown that way, (indeed the aircraft design specifically enables it, the flight manual specifically calls for it under certain conditions like crosswind landings, and flight instrumentation provides means to measure it and display it to the pilots) the fuel system is designed to cope with that flight condition. And that flight condition creates a far greater "uphill" effect than dihedral. Therefore dihedral is moot. And that was my point, one you apparently missed.. On the subject of schoolboy, your "schoolboy" reading skills coupled with your schoolboy mind conjuring up schoolboy personal attacks failed to take any of this into account.

Sorry, but I still recon you're probably a Walt.
Sorry? No you're not. That's a transparent lie. Recon all you want. Schoolboy reconning often goes amiss. As for being a Walt, I'll stack up my technical knowledge displayed in just this one thread against yours any day. You're a PM? For both Dod and MoD programs? Sure you are!

Last edited by KenV; 5th Feb 2019 at 18:17.
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Old 5th Feb 2019, 18:07
  #888 (permalink)  
 
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Originally Posted by LowObservable View Post
Ken
As for your claim about being the first to say anything here about the F-35's strike-dominated design: maybe you are right but in order to know that, you would have had to read the 200+ pages in the F-35 thread that were there before you joined this forum.
Another one taking personal potshots. Probably an effort in futility, but OK, here goes.

Really? Reading every word is the only way? Fascinating claim. Are you asserting that this forum does not provide a word search for key words such as "bomber", "air to ground", "tactical strike", etc? Clu4U, with the search function one can research a subject quite thoroughly without reading every word in a thread. Further, if (a damnably big if) the subject of the F-35's air-to-ground dominated design had been previously asserted and confirmed, why would dozens of folks take such extreme umbrage with the assertion being made again? I assert that it is reasonable to assume that if a particular claim draws such deep and wide spread ire, that the claim is a new one, and not an old one. So mayhaps you should take your own advice and watch that cartoon yourself.

On the HMD, you made the specific claim in 2015 that a Block IV version existed and that it had eyeball tracking. This was false, and I am aware of the source you claimed. I have met the person myself and I suspect that you misunderstood him.
I said that a class mate of mine was president of the company that made the helmet and that he had shown me their development lab where I had seen and worn a lab version that had eyeball tracking. I misspoke when I indicated that was part of the Gen IV (not "Block IV") design. That was an assumption on my part and it was incorrect, an error I admitted to and conceded years ago.

On the subject of Walts: you just claimed to "have met the person" yourself. If so, what is his name and how do you know him?

And on the subject of schoolboy (not your subject): dredging up stuff from four years ago and then getting it wrong....yeah, pretty schoolboy. Using that four year old stuff you got wrong to justify the unjustifiable? Well below schoolboy.

Try to have a nice day. Mine is wonderful, thank you.
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Old 5th Feb 2019, 18:21
  #889 (permalink)  
 
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I just made my last reply in this thread to the various folks who made and are making personal attacks. I suspect they're attempting to get this thread shut down, and that would be a genuine shame.
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Old 5th Feb 2019, 18:52
  #890 (permalink)  
 
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Originally Posted by KenV View Post
You're a PM? For both Dod and MoD programs? Sure you are!
I never said I was a PM - I'm an engineer (C.Eng, if you want to be precise - because that's something you can look up against my name). I'm in the UK defence industry and over the last 37 years have worked at levels up to lead engineer, TA/TS, lead integrator, ops consultant etc on a range of programmes and platforms from initial concept through to in-service partnered support. My employer has programmes with UKMoD, USDoD and at least a dozen other nations. I've been the engineering report into the quarterly reviews more often than I care to remember, and standard agenda items in all those reviews (for all customers) is invariably proposed contract amendments. The standard forms of contract include specific terms that provide for either customer or contractor to propose amendments, how they would be reviewed, priced, negotiated and implemented. If you are the person you like to portray you would know that such things are routine day-job stuff.

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Old 5th Feb 2019, 19:09
  #891 (permalink)  
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The TriStar fuel pipe issue came about due to someone's clever idea to have an operational reason to refuel from both pods and the centreline hose simultaneously. Under such circumstances, the original pipe size would have been inadequate... Then those with a little more operational knowledge than some of the MoD advised that 3-point simultaneous prodding would be highly risky anyway and would also require the pod hoses to be extended so that all 3 receivers could keep an eye on each other. By then the whole TriStar pod issue was getting increasingly late and doubtful, plus the VC10K4 and VC10C1K would soon be entering service...

A pity that the TriStar never had pods - it would have been extremely useful with multi-hose capability and a massive fuel offload potential.

All history now though.

As for the F-35, I thought that it was originally seen as an F-16 / F-18 replacement, low cost (hah!) and stealthy? Which meant that it would cover all the roles of the F-16 / F-18 (and Harrier), so was never conceived as a single role fighter. That's the job of the superb F-22 - a great pity that the USAF order was curtailed.

Anyway, back to tankers. How's the KC-46A going down with the end users now that they've finally got their hands on it?
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Old 5th Feb 2019, 20:00
  #892 (permalink)  
 
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Sandiego89 # 883

The Flight Refuelling Mk 20 AAR pod was designed as an underwing store to be carried by Royal Navy aircraft such as Buccaneer, Sea Vixen and Scimitar for Buddy-Buddy refuelling. To this end it was mainly a self-contained unit, carried on a drop tank pylon, and requiring minimal input from the host aircraft. 28v DC, Air Pressure and of course a fuel supply. The Air Pressure was to pass the fuel back to the host aircraft for its own use.

On the Victor the pod was filled from the main aircraft fuel system at normal Booster Pump pressure and could be isolated from the main system. The pod was normally kept full in flight to assist with wing relief (empty for Take Off and Landing). It was possible to jettison fuel (used to "Mark" to give a visible vapour trail to assist with visual RVs) or in emergency. The fuel in the pod was usually recycled with the main supply to reduce cold-soak which could be harmful to some receivers.

The main motive power to the pod was provided by a Ram Air Turbine on the front of the pod. This drove the Hydraulic system which held a "Balanced Hose" during refuelling or to wind the hose in after use. The RAT also ran the internal fuel pump when passing fuel. This was controlled by the electrical system and was activated automatically by microswitches after the receiver aircraft had made contact and pushed the hose in 6-7 feet, and also switched on the Green Light.

The fuel tank contained 3 Float Switches, The High Level float switch shut off the fuel supply into the pod. If the pod fuel tank emptied the Low Level float switch cut the fuel pump. When the fuel tank was half full the Mid Level float switch put the pump on again .

I will add the caveat that this is all from memory. I have not operated the pod since 1971, or flown with it since 1982. My Sex and Drugs and Rock and Roll lifestyle may have impaired my memory. Mind you these days the drugs are Viagra to assist with the first part of the lifestyle, and the Rock and Roll is my gait after the obligatory nightly litre (liter) of Rose.

If any ex-Victor Nav Rad has any corrections to make, feel free, I will not be upset or insult you.
I will now end and let the kiddies squabble amongst themselves
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Old 5th Feb 2019, 20:28
  #893 (permalink)  
 
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Thank you Tengah for taking the time to write up that on the MK 20 pod in #892, I do appreciate it. Good stuff to satisfy my curiosity. Did not know the F-4 could receive so much fuel that quickly- thirsty beast.

I will avoid the squabble as well.
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Old 5th Feb 2019, 20:58
  #894 (permalink)  
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Tengah Type , I need to query one of your facts.

You stated that your nightly rose consumption is a litre. One litre? Surely that's an underestimate??

Hope all's well - TBs again in the Spring?
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Old 5th Feb 2019, 22:33
  #895 (permalink)  
 
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Ken, Ken - When I start being personal you will know about it. Have I called you a poxed-up Bedlamite? A thrice-unlaundered molly-boy's codpiece? A grits-for-brains Simonist? I have not.

As for search engines: sorry, no. They are good for phrases. Lousy for meanings and intent. In a few years you'll be able to go site PPRuNe.org "poxed-up Bedlamite" and hit this post right on the nose. Look for posts with people being mean to Ken and the results will be incomplete. Also, as I know all too well, posts commenting on the F-35 draw exactly the same response time after time. Mention its delays and someone will go "what about Typhoon and Rafale?"

Drew Brugal, VSI boss for four years. Talked to him a few times. I believe, however, you may be mis-speaking or mis-remembering the sequence of events. First you said that the F-35 helmet used eyeball tracking. Then you said it was in the "Gen IV" helmet, being prepared for Block 3F. Then you admitted that you were thinking at best of a technology demonstrator. Retreating from one misleading statement to the next, like the Wehrmacht retreating from one bombed-out wreck to the next in Stalingrad.
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Old 6th Feb 2019, 07:56
  #896 (permalink)  
 
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BEagle

More than a litre? Maybe! Sometimes it is of a darker hue. The local Bordeaux is quite palatable also.

I got an email from Nic to say he is handing over the TB reins. Hope somebody else will take over, as I enjoy them when I am in country. Hope to see you there.
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Old 6th Feb 2019, 12:03
  #897 (permalink)  
 
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Originally Posted by BEagle View Post
The TriStar fuel pipe issue came about due to someone's clever idea to have an operational reason to refuel from both pods and the centreline hose simultaneously. Under such circumstances, the original pipe size would have been inadequate...
Interesting. So the undersized pipe is not the pipe in the wing feeding the pod, it is a main feed pipe (fuel manifold) that feeds all three hose drogue systems. Interesting.

A pity that the TriStar never had pods - it would have been extremely useful with multi-hose capability and a massive fuel offload potential.
Agreed. Same applies to KC-10. For whatever reason only a few KC-10s have been equipped with wing pods.

All history now though.

As for the F-35, I thought that it was originally seen as an F-16 / F-18 replacement, low cost (hah!) and stealthy?
I don't think it was seen as an F-16/F-18 "replacement" so much as an airplane in those aircraft's size class. As opposed to the size class of the F-14/F-15.. In other words, the "low" of the "high/low" mix with F-22 being the "high". And to ensure it stayed "small", "light", and "cheap" it was required to be single engine. And by being able to service all three US services (USAF, USN, USMC) it could be mass produced at high build rates, further driving down costs. And because it's small and light, it would have simple systems. Basically they were trying to force the JSF down the development path followed by F-16. Small, light, simple, & mass produced. But by growing the engine they were able to grow the airplane so it was neither small nor light. And they stuffed it full of bleeding edge systems never before used on any aircraft, so simple was gone. And while yes, it does service all three US services, there is really little structural commonality. Lack of commonality, size, weight, and extreme complexity ensured it could not possibly be cheap.

And it was always supposed to be optimized for air-to-ground while preserving air-to-air capability. It was never supposed to be the 9G turning fighter the F-16 was. F-22 was to cover the really critical air to air missions. USN took a decidedly different approach and always viewed F-35 and stealth in general as but one piece of their air power puzzle. Looks like USAF is now going down that path also They want to not only preserve their legacy non stealth F-15 fleet, they want to recapitalize them with new-build F-15Xs. Round and round we go.

Anyway, back to tankers. How's the KC-46A going down with the end users now that they've finally got their hands on it?
The folks at McConnell AFB are loving it. Large numbers of blue suiters have been in Everett for some time learning the airplane and its systems and assisting Boeing in writing the maintenance and tech documents. Now that they've got their own toys to play with, they're ecstatic.
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Old 6th Feb 2019, 14:17
  #898 (permalink)  
 
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KevV: I don't think it [F-35] was seen a F-16/F-18 "replacement" so much as a replacement in those aircrafts size class....
I believe the JSF program was absolutely touted and understood as a "replacement" in the original JSF program specifications, program of record, and literature without any qualifiers about size class.

The JSF program was touted as a replacement for the F-16, A-10, F/A-18 A-D for USN (and perhaps USMC), AV8B and UK Sea Harrier/GR7/GR9 and Tornado GR4. Also specified to complement F-22 and F/A-18 E/F.

https://apps.dtic.mil/dtic/tr/fulltext/u2/a472773.pdf
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Old 6th Feb 2019, 15:41
  #899 (permalink)  
 
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Not only that, many of the specifications and requirements were drawn specifically against a baseline of an F-16C, with some F/A-18C numbers mixed in for certain requirements. This gave a 'no worse than' backstop on various metrics, some of which were waived down the line when things got difficult.
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Old 6th Feb 2019, 16:06
  #900 (permalink)  
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KenV wrote:
Interesting. So the undersized pipe is not the pipe in the wing feeding the pod, it is a main feed pipe (fuel manifold) that feeds all three hose drogue systems. Interesting.
No, the feed to the wing pods would have been adequate using the originally specified wing fuel pipe. But with the HDU supplied simultaneously (not using some 'main feed pipe' - the systems were not interconnected), the pressure drop at the pod using the original pipe would have been unacceptable. Hence a larger bore pipe would have been needed to cater for the situation. Which was a bolleaux idea anyway!
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