JonathanRP
Topic Author
Posts: 47
Joined: Tue Sep 20, 2016 7:38 pm

Air-to-air refuelling; what about wake turbulence?

Sun Apr 09, 2017 8:02 pm

Hi all,

just a quick question about something that's been bothering me for a while! When aircraft are being refuelled mid-air do they not encounter wake turbulence? The separations required on approaches are well documented, but when aircraft are flying much closer together, doesn't this cause issues?
 
greg85
Posts: 73
Joined: Tue Jun 26, 2007 9:45 am

Re: Air-to-air refuelling; what about wake turbulence?

Mon Apr 10, 2017 2:48 pm

I've never been a military pilot. But I've spoken with several of my colleagues, who flew jets such as the f-4 Phantom, Tornado, Jaguar and Mirage 2000. And yes, wake turbulence is an issue. Procedures are designed accordingly to approach and leave the tanker safely. I remember an ex Tornado guy telling me that the "basket" would move up and right just as they are about to put the probe in. It was predictable, so the guys knew to fly up and right at the correct point to capture it. He said it got harder if you refuelled from an American tanker, with the basket coming out of the end of the "flying boom". It was harder because the boom operator would try to "help", and they'd move the basket down and left, just as the pilot moved up and right. Several radio conversations later, the boom driver "kept it f£&@!'g still!".
 
26point2
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Joined: Wed Mar 03, 2010 6:01 am

Re: Air-to-air refuelling; what about wake turbulence?

Mon Apr 10, 2017 3:07 pm

In day-to-day flight operations we are concerned about wake turbulence but really what we are trying to avoid is the wing tip vortices. I suppose air-to-air refueling is at such close tange and between tanker wingtips that wingtip vortices are perhaps not a concern but the actual tubulence left behind by the mass of the aircraft? Is there even a name for this or do we just call anything associated with turbulent air folloiwing an aircraft "wake turbulence"?. An honest question.

It has always puzzled me why ground controllers say "caution, wake turbulence" when instructed to taxi behind a large jet when what they really should say is "caution, jet blast".
 
mmo
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Re: Air-to-air refuelling; what about wake turbulence?

Mon Apr 10, 2017 6:36 pm

After spending countless times behind a 135 and -10, with the typical plug boom, there is very little turbulence. I flew the B-52 on active duty and then the F-4 and F-15 in the Guard and each was fairly easy to refuel. I would say the B-52 was the most difficult. I will date myself but I flew D and G models, and the D was old fashioned cables and pullies. It was a handful in the best of times and a real pig most other times. However, if you refueled at a slightly faster speed, 280 KIAS, it was much easier. It was not uncommon to have an onload of 60,000lbs from one tanker or 100,000lbs from 2. If you couldn't refuel you were in the wrong business.

In all aircraft as you went from the pre-contact to contact position, you did experience a slight amount of aerodynamic interference. It was nothing you couldn't handle and most times you got so used to it you didn't even notice it.
If we weren't all crazy we'd all go insane!
 
tupperjets
Posts: 12
Joined: Mon Oct 31, 2016 11:41 pm

Re: Air-to-air refuelling; what about wake turbulence?

Tue Apr 11, 2017 6:57 am

I found this article interesting.

The first thing in our "Dash 1" technical orders states: "Because of the magnitude of interrelated aerodynamic effects flying two aircraft at close vertical proximity is unsafe." So basically the USAF tells us that our job is not safe right off the bat. But I've hit turbulence during refueling where we had to initiate an emergency separation or "breakaway" several times. The boom operator disconnects, the tanker hits full throttle and the receiver plane drops a thousand feet in a couple seconds just to get separation. We also practice this all the time. Almost every flight since we have to separate and give up MARSA (Military Assumes Responsibility of the Separation of Aircraft) anyway.
lessonslearned.faa.gov
 
JonathanRP
Topic Author
Posts: 47
Joined: Tue Sep 20, 2016 7:38 pm

Re: Air-to-air refuelling; what about wake turbulence?

Thu Apr 13, 2017 10:28 pm

Thanks a lot for all your responses!
 
GlobalMoose
Posts: 42
Joined: Sun Aug 19, 2012 10:44 pm

Re: Air-to-air refuelling; what about wake turbulence?

Thu Apr 13, 2017 10:46 pm

After just refueling today, wake turbulence isn't really that bad at all, in fact, i'm more worried about atmospheric turbulence than any 'turbies' produced from my tanker. The -135 and -10 each present their own challenges, advantages, and 'turbulence.' Approaching the -135, you'll often feel a 'burble' (rumbling in the aircraft, much like driving fast on a roughly paved road) passing up to the astern position (50 feet in trail). Also, the -135 has many more visual references on the aircraft (antennas, convenient locations of the engines in my window, etc) to help maintain position in both astern and in contact (in addition to the pilot director lights). A downside of the -135 is the relatively small refueling envelope.

The KC-10 is much, much larger. They have a burble that you feel in the aircraft all the way up to contact. Once there, you have a much larger refueling envelope than the -135, however, there are substantially fewer references to maintain your position. Also, while you are supposed to maintain centerline, if you get too far left or too far right, the exhaust from the number 1 & 3 engines tends to bump you back toward centerline, however, never do you have a jolt that one would expect from traditional atmospheric turbulence.
When it absolutely positively has to be there ... at some point.
 
RetiredWeasel
Posts: 376
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Re: Air-to-air refuelling; what about wake turbulence?

Thu Apr 13, 2017 10:57 pm

The only turbulence I worried about during refueling was the atmospheric turbulence, CAT and convective type as Moose mentioned. Tanker crews were pretty good at requesting altitudes to avoid it and also to try and stay out of the clouds. Flying the F-4 for 8 years with scores of hookups I cant remember encountering any thing that really shook me up. You knew where the wingtip turbulence was and disturbed air from the tankers engines, and you just avoided it.
 
GalaxyFlyer
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Joined: Fri Jan 01, 2016 4:44 am

Re: Air-to-air refuelling; what about wake turbulence?

Fri Apr 14, 2017 2:07 am

While refueling the C-5 behind the KC-10, the center engine would push the C-5 to a bit of skid off go one side. If you tried to stay perfectly centered on the lights you would pushed either way. Usually, you just state to one side and accepted the yaw.

GF
 
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tjwgrr
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Re: Air-to-air refuelling; what about wake turbulence?

Fri Apr 21, 2017 2:59 pm

GalaxyFlyer wrote:
While refueling the C-5 behind the KC-10, the center engine would push the C-5 to a bit of skid off go one side. If you tried to stay perfectly centered on the lights you would pushed either way. Usually, you just state to one side and accepted the yaw.

GF


Conversely, I've heard the C-5 generates a bow wake. Can that be felt by, or affect, the tanker?
Direct KNOBS, maintain 2700' until established on the localizer, cleared ILS runway 26 left approach.

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