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All air-to-air refuelling systems appear to use either a hose or a boom that extends below and behind the tanker aircraft. This poses many problems due to wash from the wings and engines/props. I notice that they have said that the A400M will never be able to refuel helicopters inflight (one, if not
the most important, of its designed roles) because helicopters find it too difficult to maintain stable flight in the turbulent air behind and below the tanker.
There’s much cleaner air above the wing of the tanker – engines and propellers are predominantly below the wing, and I have a feeling (very technical I know) that lift induced turbulence is probably worse below the wing. Why not have small wings (computer and gyroscopically stabilized) on the trailing drogue that lift the hose and drogue like a kite into the cleaner air above the tanker? As helicopters have their rotors on top, the rotor would be even further away from the turbulence.
I know the Americans use a rigid flying boom but this also unimaginatively extends below the tanker.
In the A400M’s case, the enormous T- tail might pose a problem but it would just need a longer hose and more lift from the drogue's wings to give a bit more vertical separation.
Here's a problem
http://aviationweek...ow-research-project
Airbus Defense and Space’s military aircraft division says that the aerial refueling of helicopters by the company’s A400M airlifter is now the subject of a research project after admitting it will be impossible to achieve in the aircraft’s current configuration. [Gordon Comstock, Dec 17 2015]
Warthogs don't go fast.
https://www.youtube...watch?v=DCVmPffxDkU
[Voice, Dec 18 2015]
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Pretty sure the booms extend well below any
turbulance caused by the tanker. |
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Structurally speaking, hanging a lightweight hose is
much easier than extending a rigid support member
upwards. |
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//Structurally speaking, hanging a lightweight hose is much easier than extending a rigid support member upwards// - said the actress to the bishop |
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////Structurally speaking, hanging a lightweight hose is much easier than extending a rigid support member upwards// - said the actress to the bishop// Thank you Finbarr. |
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But this would not be extending a rigid support member upwards. The bell-shaped end of the hose would have wings and would be flying and would support the weight itself like a kite does its string. |
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Not a free ride. The wing would lift the hose using
angle of attack which would cause drag. The heavier
the member, the more drag. Not a factor with a
gravity positioned hose. |
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I would guess the additional "weight" of that drag,
that is, workload imposed on the tanker aircraft
would be much more than just having a lightweight
aluminum crane arm hold the hose upwards. |
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Additionally, the stability imparted to the hanging
hose from its weight is gone in the one that you're
flying like a kite. |
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That being said, your idea might be worth the
additional load if it's the only way to clear the rotors.
I know they currently refuel helicopters with
extended fuel booms at the front of the helicopter.
Do you know whey they can't
do that in this case? Just extending the hose as low as
you have to go to avoid the turbulence? |
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//Pretty sure the booms extend well below any
turbulance caused by the tanker.// |
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Actually no, according to an airman friend of mine, this is
a scary harrowing pain in the ass. |
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It seems to me that having the hose try and 'fly' would
make it terribly difficult to connect due to lack of
controllability. Try hooking up to a kite which is dancing
in the wind. |
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I suppose you could make the hose an extension of the
copter, but the weight of it might not be ideal. |
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It seems to me that whichever aircraft is on top also has
to be out in front. This makes it the aircraft in the back's
responsibility to try and hook up, simply for vision's sake.
But that's far too impractical to expect the tanker to bob
and weave to connect to the smaller craft. |
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Perhaps a vision system aid for the aircraft in front might
make it workable with enough training. But it still would
be tricky as the connection point would essentially
become at the tanker, and not at the aircraft. |
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//It seems to me that having the hose try and 'fly'
would make it terribly difficult to connect due to
lack of controllability. Try hooking up to a kite which
is dancing in the wind.// |
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And try flying that kite in the downwash of a
helicopter. |
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I think this is a good idea. Not all kites are unstable, and
if you had an over-sized kite with computer controlled
surfaces it could be made to be very stable. Seems to me
it should be the responsibility of the hose to hook up with
the helicopter. Neither the tanker nor helicopter should
weave around to catch the hose. Both should fly straight
and level. The house should adjust length altitude and
side-to-side position to catch the inlet on the helicopter. |
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One problem could be the weight of the hose full of fuel. |
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Or maybe the helicopter or jet should just land on top of
the tanker. Imagine the 747 carrying the space shuttle,
but with mid-air docking. That way you can change out
the pilots as well if needed. |
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//How about a system that simply dumps fuel in
mid- air? The aircraft requiring the fuel has the
responsibility to grow the necessary techniques and
apparatus to scoot around and catch all the falling
fuel before it goes too far. A big sponge, for
example.// |
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I had actually started to post that then erased it. |
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My idea was a funnel on the trailing aircraft with a
vacuum to suck it into the fuel tank. Problem is, you
miss and get that fuel trail into the turbines of the
trailing aircraft, you've got issues. Plus a spark turns
that well aerated fuel stream into a flame thrower. |
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There's a couple of different turbulences (turbuli?) in play
here. The wingtip vortices, and that from the engines.
Normally the receiving aircraft is below these, not by
much. Big receiving aircraft can get their empennage
involved easily. I was talking to a hog driver (A10 pilot)
last Christmas who said one of the only legitimate
criticisms of the A10 is that it's a pig to refuel... when
loaded, it's only just able to keep up with faster tankers.
So the tanker obliges and slows down, they have to put
out some flaps to stay in the air, now there are wake
vortices trailing behind the flaps and the A10 is right on
the limit. Anyhow, from turboprops I'd imagine the prop
wash is a major concern, maybe some added flap vortices
from the heavy plane having to slow down to helicopter
speeds. Anyhow, I think the principle here is workable,
maybe have the probe extending back from the top of the
vertical stabilizer? oh this gives me an idea. |
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I think the "kite" idea is potentially excellent.
Note also that the idea suggests a "stabilized"
drogue, which ought to be doable. Depending on
the length of the fuel line, the drogue could be
dynamically stable against deflections of at least a
few metres (including downwash from the
helicopter). Then the helicopter pilot only has to
compensate for his own aircraft's movement. |
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In fact, why not make the drogue smarter? Given
some sort of communication between tanker and
helicopter, the flyable drogue should be able to
compensate for small movements of both aircraft -
in effect flying itself to the nozzle of the
helicopter. The drogue should be much more
maneuverable, over small distances, than either of
the aircraft. |
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// But this would not be extending a rigid support member upwards. The bell-shaped end of the hose would have wings and would be flying and would support the weight itself // |
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Hur, hur, hur, wink wink, nudge nudge, say no more, say no more ! |
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Oh ... that's not a double-entendre, then ... ? |
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Why not use an upward boom with a trailing hose and drogue? Then you can bin the computer and fancy auto-magic fins. |
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//In fact, why not make the drogue smarter? Given some
sort of communication between tanker and helicopter,
the flyable drogue should be able to compensate for
small movements of both aircraft - in effect flying itself
to the nozzle of the helicopter. The drogue should be
much more maneuverable, over small distances, than
either of the aircraft.// |
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I have just written that up.... |
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//Why not use an upward boom with a trailing hose and
drogue?// They put drogues on the end of probes for
reasons of versatility, slow, and they have to land to
change them back. |
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// Then you can bin the computer and fancy auto-magic
fins.// |
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How does it deal with the getting the bugs off
the windscreen? |
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