AWACS Refueling Question

[BenThere]

Another aspect is the time from pre-contact to boom engaged versus approach to and latching with the probe.

An experienced fighter pilot can park in pre-contact and move to boom engaged in ten seconds or so, having the advantage of receiver director lights, aircraft markings, and assistance from the flying moveable boom and its operator. Empirically speaking, I think the drogue takes quite a bit longer on average, often after comical contortions.

A wise pilot once told me (in a commercial environment): "The only thing we have to sell in aviation is time." In a military refueling variation of the same concept, the only things we have to sell are range, reach, and time on target." In that sense, very marginal optimizations pay large dividends. I still have to go with using the boom as a preference.

The risk of leaving the probe in the basket, while inconvenient in training scenarios, can be mission critical when it counts, if there is no good 'no AAR' option.

If I had a small air force with only probe receivers, I'm sure I would look at it another way. The only advantage of having a boom would be in multinational ops with boom equipped receivers.

To all, I'm enjoying this good discussion.

[D-IFF_ident]

I don't think the PDIs work until the receiver is in contact - unless the ARO flashes them manually. Time from visual the tanker to fuel flowing depends largely on the receiver pilot, but also on joining techniques. ATP 56/A/B has the receiver join echelon, then move astern - so an substantial overtake can work, the energy being bled in the join. Some nations with Boom refuelling equipment join straight to astern the equipment, demanding a longer, more drawn out 'reverse PAR' from a mile or more. SO I would say getting on a hose is probably quicker. However, once in contact the argument is one of flow rates and simultaneous top-offs. If I flew fighters then I'd look for 2 hoses on one tanker - have us both filled to full at the same time and not taking a great deal of fuel. But, if I was a heavy aircraft pilot I'd look for a boom. Were I to be taking-on 80 tons, I'd rather do it in 10 minutes than 40 minutes.

That's why the boom was developed isn't it? To refuel bombers for 'force extensions', whereas the probe and drogue came about more for small aircraft?

My dear old Dad was an AEO on Nimrods. Believe me, I know nothing about maritime aviation.

[Art Field]

D-IFF_ident. Your dear old dad spent too much time eating pies rather than teaching you maths. If a Tristar transfers 80 tonnes in 40 min by P and D then a KC10 will take 25 min not 10 using its boom. Yes a difference but not that great.

On the joining issue. The echelon join has proved significantly faster every time because of the freedom to manoeuvre right up to the move astern at the last minute.

My dear old dad was an accountant. As a mess sec I soon found out I knew nothing about accountancy.

[sonicstomp]

Art - the reality for heavy receivers is that there is little time saving from an echelon join vs straight-in astern (used for boom)......On the E3 we teach the same closure speeds for both...the echelon join is inherently safer as more of the window is available as an escape exit!

[D-IFF_ident]

Art,

My apologies; I've got used to thinking in Lbs. Therefore, to clarify:

Tri* offloading 80KKg of fuel at 2200Kg/min - (ATP56(A) - http://www.raf.mod.uk/downloads/docu...tedKingdom.pdf)

Time to offload = 37 mins (including a few seconds to push the hose in)

KC-10 offloading 80KKg of fuel at 3630Kg/min - (ATP56(A) - http://www.raf.mod.uk/downloads/docu...sofAmerica.pdf)

Time to offload = 22 mins (including half a second for the BO to put his playboy down).

That difference seems substantial to me.

Maybe more important though, is the receiver's ability to take fuel at a decent rate - microbore pipes and a P and D, or a big fat tube and all 6 pumps? Fnnarr fnnarr...

It's even quicker if you're download Lbs, isn't it?

[Art Field]

D-IFF_ident. My figures agree, I rounded off to allow for slowdown as tanks fill, as you say receiver plumbing is always relevant. I would have been very grateful for any lessening of on-load times. I still think the flexibility of the P and D system in a mixed fleet like ours is the best solution.

Being now some time removed from the action and never having prodded with the E3 I am wary of jumping in but feel I am a little surprised they do not believe they can join in echelon and get behind the hose any faster than a line astern join. The echelon join worked best for all the other multis I flew.

[Brain Potter]

In recent ops the refuelling slot time required by SPINS to deal with a 4-ship was significantly longer than was routinely achieved by 2 point P&D tankers. I don't know if this is because it takes longer to cycle a 4-ship through a boom or if the slot times were too conservative. I think the higher onload rates achievable by US fighters reduce the disadvantage of only being able to fill one at a time. The lower onload rates of European fighters increases the value of multipoint refuelling. However, it would be an interesting comparison to see if a 4-ship of F-18s cycling through a 2-point tanker would be done quicker than a 4-ship of F-15s taking the same fuel from a boom. Also, I bet that the first F-18 to plug would leave the tanker with an equivalently better fuel state than the lead F-15 - hence the formation as a whole is better placed. If TAC had been the dominant force in the USAF in the 1950s and 1960s would they have retained P&D? As it was, SAC owned the tankers, which were primarily for the bomber force, and the boom was adopted.

TCAS will not cause RAs and breakaways as it should be set to "TA only".

My dad knows nothing about tankers. But would he have agreed to a new tanker that cannot receive fuel itself?

[sonicstomp]

Art - Any speed advantage from the join to echelon is then lost waiting for a clearance and the move to astern....Indeed our SOPs have our overtake on the tanker the same irrespective of whether it is an echelon join or straight to astern...(+30kts at 2nm, +20kts at 1nm, +10kts at 0.5nm - At night we generally will go for +20 at 2, +10 at 1 etc....)

Brain - TCAS will be off as M3 will be strangled on the "Judy/Visual" call at the end of the RV phase and the start of the "join-up" phase.

[BenThere]

The tanker will set TA only, but conflicting traffic will be in TA/RA. The tanker's TA only alert will still display the conflict. If the tanker formation chooses the same judgmental resolution as the conflicting traffic's RA computer demands, there is increased chance for collision. Is the best procedural option to ignore TCAS assuming the bogey will resolve any conflict?

[D-IFF_ident]

Brain, I'll time it and let you know.

I've found that a keen eng with post AAR checks really wakes you up when he switches to TA/RA before the rcvr departs...

[Brain Potter]

Not all receivers switch of their Mode3/C at the Judy/Visual call. In fact leaving it on as long as possible provides good SA for a TCAS equipped tanker, particularly during autonomous joins. The tanker's TCAS must be in TA or an RA could well be generated by the receivers transponder. A large receiver being particularly careful to strangle parrot whilst closing may not cause an RA, but fast movers with high rates of climb certainly would. Departing aircraft would probably also trigger an RA when they switch their transponder back on - as related by D_IFF . Leaving the TCAS in TA/RA would put too far much onus on the receiver to fly a very mild join, switch the transponder off early and be very careful where it was switched back on. Most receivers are not TCAS equipped and so do not really know the parameters that would cause the various alerts. As AAR usually takes place in fairly well protected airspace and an RA with receivers in contact could not be actioned safely within the timescale that the system demands, it is much safer to set TA only. At least a TCAS equipped intruder would not expect a co-ordinated RA. It is exactly the same principle that calls for the TCAS to be set to TA when engine-out etc.

SS - I would expect a large receiver to reduce to a max 30 kts overtake at 2nm, whilst maintaining a 1000' split and then to kill the overtake with a climb to wide echelon commencing at 0.5 nm. It is easy then to slide into close-ish echelon, before being cleared astern. The tanker does not expect to see a perfect close echelon before clearing the receiver astern - just a safe enough postion with no overtake from which the receiver will drop back to go astern. If you make your "Echelon Right" call when you are ready to start moving astern there should be no delay in receiving clearance to move - even if it is from quite a wide echelon and still with some vertical spilt. The tanker just doesn't want you to go behind whilst still moving forward with no escpe route. I guess the pre-contact postion on the boom must have more vertical seperation than that of the centreline hose - allowing an escape route downwards as you join astern.

D_IFF. If the F-15s win then I'll swap the hose jets to F-14s

I think the Indian IL-78s can refuel 3 jets simutaneously

[Art Field]

Brain Potter. many are with your old dads thoughts about a receiver capability for FSTA [should it ever arrive] but in the real world you get what you ask for or more certainly you do not get what you do not ask for. One more example of the "we will never need to do that again" mentality.
I know the Tri motor guys hated the probe, the airflow noise kept them awake.

[BEagle]

A330MRTT for the OzAF will have a receptacle, but as for the Fictional Strategic Tanker Aircraft, I don't think so.

Unfortunately the USAF is still very boom-obsessed and the boom operator mafia have too great a stranglehold, for my money. If only, as has been said earlier, TAC and the USN had held the upper hand rather than SAC, then perhaps things would be different today....

Even the OzAF were surprised to hear that the RAF operated large aircraft in echelon with no problems; the boom mafia had tried to convince them that the slow join to astern was the only way.

[bounce'em all]

BDA is a truly dreadful device.

Originally Posted by BEagle

The RAF E-3D has both probe and receptacle. As far as I'm aware, it is the only bisexual receiver in RAF service; every other reciver uses the 'male' probe-and-drogue technique rather than the 'female' boom-and-receptacle method.

The BDA is a truly dreadful device.I had to prod against it with a Q-fit Phantom (8 missiles, 3 tanks) once without ever having had any dual instruction.... You are supposed to make contact very slowly, then push until valves at both ends of the adaptor open; the hose ends up in a sort of S-bend shape and is highly likely to snap the probe off as allowable positional tolerance is much less than with a proper hose - and if you miss on the approach to contact the boom person is likely to move the damn thing. It doesn't have any hose response system and seems to rely purely on hose flex to compensate for receiver movement. It truly sucks!

I don't think that any large aircraft are cleared to use the BDA - and detcos in Incirlik certainly weren't happy to let some UK aircraft prod against it.

BEagle, first of all, my utmost respect to a Phantom driver.
I couldn't have described it better. I guarantee, it's still a b**** on a lighter but fully loaded fighter. No dual instruction as well: first time I had to do it, the colourful brief received wasn't much help really....

[BEagle]

Perhaps I should have added, this was on a live QRA(I) scramble.....

No proper brief, no dual instruction.......it wasn't easy! But having the genial E**c H**p in the back was a great help, he gave me some very good guidance when I was trying to work out what to do...

But what really annoyed me was that the miserable Flt Cdr criticised me for the time I'd taken to get the gas against the infernal donkey cock. Yet a few months later, he had the temerity to signal Gp (after the rest of the Sqn had being doing some dual trips in Charlie fit against the BDA) to say that it was so difficult that dual continuation training was essential. Pricks like that you just don't want to work for - so glad I was off to the pre-VC10K MER a week or so later!

[bounce'em all]

Originally Posted by BEagle

Perhaps I should have added, this was on a live QRA(I) scramble.....

No proper brief, no dual instruction.......it wasn't easy! But having the genial E**c H**p in the back was a great help, he gave me some very good guidance when I was trying to work out what to do...

But what really annoyed me was that the miserable Flt Cdr criticised me for the time I'd taken to get the gas against the infernal donkey cock. Yet a few months later, he had the temerity to signal Gp (after the rest of the Sqn had being doing some dual trips in Charlie fit against the BDA) to say that it was so difficult that dual continuation training was essential. Pricks like that you just don't want to work for - so glad I was off to the pre-VC10K MER a week or so later!

Well, while we're at it: how about a Sqn Ops Chief who keeps debriefing you on how much better your hook-up could have been done and who comes back for rejoin, about a week later, sporting a brand new basket on the tip of his probe?
Needless to say, that was a delight to all the junior officers in the Sqn...