Wake Turbulence

[Lister Noble]

I hope this is the right placed to post this.
I am a student pilot learning to fly in East Anglia.
Often when near Lakenheath/Mildenhall we are warned of a "heavy" which is usually an air re-fuel tanker.
How is it that they can re-fuel a much smaller aircraft such as an F15 which flies quite close and below without it being torn apart?
Lister:)

[charliegolf]

I suspect that it's to do with the way the turbs 'fall off' the heavy, and the way the smaller aircraft joins and positions itself outside the predictable pattern.

Formation flying teams like the Red Arrows always look like they're very closely behind the aircraft in front, but they are always a bit above or more likely below it.

Someone will explain the physics I'm sure.

CG

[Sideshow Bob]

It's all explained in Aeronautical Information Circular AIC17/1999 (Pink 188) 25 February. They are available on line at the NATS web page, you'll have to register, but on the bright side, it's free!!

http://www.ais.org.uk/aes/pubs/aip/pdf/aic/4P188.PDF

[16 blades]

Wake turbulence is generated by wingtip vortices, which themselves are generated by the pressure difference between the top & bottom surfaces of a wing. When refuelling, you stay out of the way of the vortices. Immediately behind an aircraft, the vortices are separate and distinct. They tend to join and form a 'wake' much further behind the aircraft, which in the case of a heavy aircraft, can persist for up to 4 minutes.

16B

[Lister Noble]

Thank everyones,16 Blades,yes thank you I did know that from my studies,but what about the tanker tailpane,would there not be some minor vortices from that but still enough to be some trouble?
Also I imagine the small one must be very careful to remain within the wingtip vortix areas when he comes in on the big one.
I will ask my CFI tomorrow as he has done a lot of this from the small end.
Lister:)

[mbga9pgf]

Wake vorticies are strongest when the alpha is large, ie takeoff and landing, as thay are a result of, as stated above, induced drag.

The speeds at which AAR occurs, Alpha is small, this induced drag is small, and thus the main turbulence is caused by the disturbed air. Note also, that the control effectiveness at AAR speeds is far greater than that at takeoff/landing speeds, and thus why wake vorticies are far less of an issue.

My take on it, may not be the authoratative answer of course!:8 (I Knoooow!!!)

[effortless]

You approach from one side and below. You the break down and to the opposite side from your approach. The boom flies lower than the vortices.

[Tarnished]

The receivers, be they large or small, never put themselve in a position where they have to penetrate the wake turbulence (be that wing tip vortex, jet exhaust or any other disturbance).

Training and procedures have most receivers come along side the tanker before dropping down and under into the pre-contact and contact positions. Larger receivers tend to come up from behind and below(typical truckie behaviour!).

As has been said the strength of the vortex varies (strongest during high speed high g manoeuvres). It is unlikely to damage another aircraft but it will affect its flightpath. I saw a fighter refuelling off the wing hose of a VC10 that got a little high, got caught up in the vortex and spat out over the tail of the the "Fun Bus" (as Beagle call it). Scary for all concerned.

Hope that helps Lister

Tarnished

[Lister Noble]

Thank you everyone and it is a lot clearer for me now,but very brave boys these fighter pilots,especially if someone is trying to shoot you down at the same time!
I will stay to refuelling from the bowser at our local strip!
Lister:) :)

[Time Flies]

very brave boys these fighter pilots

You bet your sweet ass! :ok:

[4Greens]

Lister, forget flight refuelling! As a pilot never get behind a heavy jet on approach,after take off or a go around. I was on approach, a mile behind a DC10 which did a late go around and had my work cut out controlling a 707.

Also while you are at it avoid flying through thunderstorms; ever!

Good flying

[mbga9pgf]

You bet your sweet ass! :ok:


Try flying in a threat environment, getting shot at on a regular basis, without a bang seat Jet-Jockey!

[Time Flies]

Try flying in a threat environment, getting shot at on a regular basis, without a bang seat Jet-Jockey!

Why? That just sounds plain silly old boy. :confused:

[Widger]

Been in a VC10 behind a Tristar. The high tail on the VC10 penetrates the airflow from the Tristar and it does get a bit bumpy.

[Lister Noble]

I've been flying today and asked the CFI who has flown most UK fighters.
He said he has air re-fuelled Harriers and other aircraft from VC 10 tankers ,not too much problem but there is severe turbulence if you get it wrong.
He then explained the different methods the UK and US use.
The UK pilots aim for the basket on a hose,the US have a boom with small wings which the tanker crew use to guide the connector hose onto the recipient, when in place.
It all sounds quite demanding!
Lister:)

[OFBSLF]

The UK pilots aim for the basket on a hose,the US have a boom with small wings which the tanker crew use to guide the connector hose onto the recipient, when in place.The US airforce uses the boom. The US Navy and Marine Corp use probe and drogue like the UK. US helicopters equipped to refuel use probe and droque as well.

[Safety_Helmut]

The UK pilots aim for the basket on a hose,the US have a boom with small wings which the tanker crew use to guide the connector hose onto the recipient, when in place.
So that's how they do it ! :rolleyes:

[Onan the Clumsy]

I suppose it's a lot like being towed in a glider. The glider stays a little below the tow plane just above the burble. They train a maneuver called "boxing the wake" where they fly off to one side and then down, back across, up and over. This keeps 'em in still air and avoids the burble. They also train to descend into the burble to see wot it's like. It's a little bumpy that's all, the wings stay on and everything, but then again, it's just a Pawnee you're behind.

[16 blades]

Getting caught in a VC10's wake is considerably more than 'a little burble' I can assure you.....even in something the size of Albert.

16B

[Safeware]

The UK pilots aim for the basket on a hose

I thought that 'chasing the basket' was a bad idea and that it is done by reference points which end up with contact?

sw

[Art Field]

Indeed, basket chasing will usually end up in overcontrolling and unpleasantness. To precis the whole probe and drogue procedure, the join will be to echelon, avoiding any wake turbulence, then a downward movement before moving astern the cleared hose, a forward move up the line of the hose to a hold about 8-10 feet behind the droque, trim and relax and then move forward up the line using the appropriate references at 3-5kts. Departure is the reverse. There is of course much more to it than that but you will need to do the conversion for that. High tail aircraft can get some pitch effect if a bit above the line, tall fin aircraft can be prone to dutch roll.