Blackbird
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Laminar Flow Control Question

Wed Feb 14, 2007 1:11 am

Have they ever figured out a way to clear out the tiny holes effectively?

Andrea K
 
oly720man
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RE: Laminar Flow Control Question

Thu Feb 15, 2007 8:31 am

Quoting Blackbird (Thread starter):
Have they ever figured out a way to clear out the tiny holes effectively?

Not that I'm aware of. There are many issues including what's blocking the holes (e.g. dust or water or dead insects.) Because of surface tension the pressure to remove water can be enormous. Also the holes are conical, because of the nature of laser drilling and if the cone points outwards (inner diameter > outer diameter) then it can be hard to blow stuff out.

We did a lot of research at our lab with our previous prof looking at boundary layer transition on the leading edge, as well as on surfaces representative of engine nacelles. It all worked in the wind tunnel, including the situations with dead insects on the leading edge to create turbulence and increased suction removed it.

The main problem was that the savings on a conventional aircraft were too small to justify the effort when all the operational issues were taken into account. It would only come into its own on flying wings, but there are the inevitable maintenance issues as well as safety.... what happens if the suction stopped mid flight and the drag went up?
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Blackbird
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RE: Laminar Flow Control Question

Thu Feb 15, 2007 11:51 am

For an SST/HSCT type design would it be worth the effort?
 
oly720man
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RE: Laminar Flow Control Question

Thu Feb 15, 2007 11:15 pm

I don't know of any numbers showing the drag saving that could be produced so it's difficult (for me) to judge. In this report

http://ntrs.nasa.gov/archive/nasa/ca...asa.gov/20000004183_1999207938.pdf

it suggests an improvement in cruise L/D of nearly 10% (figure 131 right at the end) so there are clear benefits.

However there are plenty of design issues relating to the suction rate, the hole size and separation (to name a few) which if wrong could make things worse rather than better.


The problems with the civilian market are always going to be reliability and maintenance (maintenance to keep the holes clear.) If cleaning is something that has to be done at the end of every flight I'm not sure any airline would go for it. If the system was only used during cruise, i.e. above the weather in clean air then that should reduce the chances of contamination/blockage, but it's still something that would have to be checked on the ground and you couldn't do that on a rainy day, for example, unless there was the added infrastructure - a covered gate, maybe - to stop the leading edge getting wet.

To be pessimistic, I'm not sure there's a market for another SST, even if it did have reduced drag. The world market would have to be, what, 100, 150 aircraft to break even? Are there that many operators and routes, and people willing to pay for the premium service??
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Blackbird
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RE: Laminar Flow Control Question

Fri Feb 16, 2007 4:23 am

Could you use a powerful vibration to break up the crud and stuff that gets into the holes?

Andrea K
 
oly720man
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RE: Laminar Flow Control Question

Fri Feb 16, 2007 9:21 am

Quoting Blackbird (Reply 4):
Could you use a powerful vibration to break up the crud and stuff that gets into the holes?

The trouble is that the holes are very small, you're talking less than 0.1mm, and the inner surface is not smooth. I don't think that vibration will work at that scale. Also vibration = fatigue.

Cleaning the holes during flight is probably going to be impractical. I don't think the levels of suction (vacuum) could be generated on the aircraft to clear holes and there would be the matter of how the leading edge would be subdivided into separate suction areas and how these would be individually monitored and controlled.

It would probably be best to find out what sort of crud gets into the holes before attempting to remove it and I'd imagine this being a ground based activity. Water, if any remained, could conceivably be evaporated with a heated leading edge and this may possibly be used in flight. Biological substances (dead insects) could be dissolved by some sort of digestive substance and the leading edge washed. Dust and other muck will be the difficult ones.
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Blackbird
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RE: Laminar Flow Control Question

Sat Feb 17, 2007 6:12 am

Oly720man,

So your idea is essentially to clean the crud on the ground, and simply use a type of solvent to dissolve the materials?

Could some kind of pulsed laser be used to blow up the stuff that gets into the tube? I know the holes are small, but you could use one laser beam, and then divide the beam up into thousands of little beams with some kind of fiber-optic type mechansim or something like that and simply burn up the tiny amount of crud in the holes?

Andrea K
 
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RE: Laminar Flow Control Question

Sat Feb 17, 2007 7:09 am

Fokker conducted test flights with laminar flow in the early nineties.

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Photo © Andries Waardenburg

The truth lives in one’s mind, it doesn’t really exist
 
oly720man
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RE: Laminar Flow Control Question

Sat Feb 17, 2007 7:37 am

Quoting Blackbird (Reply 6):
So your idea is essentially to clean the crud on the ground, and simply use a type of solvent to dissolve the materials?

Well appropriate materials could be dissolved. Dust or other airborne particulates will be insoluble and unlikely to be easily cleaned from blocked holes in flight, hence the need to clean on the ground. It's really going to depend on how quickly the holes get blocked, when and by what. It's possible that with suction the holes will be kept clear, but air is not absolutely clean, especially at lower levels, and inevitably small/microscopic particles will attach to the surface and be drawn into the holes when suction is applied.
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Blackbird
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RE: Laminar Flow Control Question

Sat Feb 17, 2007 8:47 am

Does using a type of laser to burn up crud sound like a feasable idea or not? Like taking one powerful laser and dividing it into millions of tiny little beams and fired into the holes from the inside out.
 
oly720man
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RE: Laminar Flow Control Question

Sat Feb 17, 2007 9:15 am

Quoting Blackbird (Reply 9):
Does using a type of laser to burn up crud sound like a feasable idea or not? Like taking one powerful laser and dividing it into millions of tiny little beams and fired into the holes from the inside out.

The complexity of the optics to split up the beam like that would make it near impossible and there would be a loss of power to the individual minibeams, such that they would have little or no effect. Having such a laser on the inside of an aircraft wing/fuselage is probably a complication airline operators would happily live without. A high power laser on some form of traverse would probably be more effective, if it worked. Possible scenarios are the high energy would cause any crud to burn and block the hole, or the crud would vaporize. You would probably want to use such a system pointing inwards, not outwards because the shape of the hole - increasing area inwards - would probably help to dislodge the crud as it superheated.

The health and safety implications of such a device near an active aircraft would probably make it too risky to operate in an airport environment.
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Blackbird
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RE: Laminar Flow Control Question

Sat Feb 17, 2007 9:54 am

What's a traverse? I know what it means TO traverse a large distance, but I'm not sure what a traverse is.

Andrea K
 
oly720man
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RE: Laminar Flow Control Question

Sun Feb 18, 2007 1:12 am

Quoting Blackbird (Reply 11):
What's a traverse?

Ah, sorry. Talking shop there. A traverse is essentially a linear motion system that holds a piece of equipment so it can be moved to, or be directed towards, a particular location.

You can have 1 axis to 6 axis traversing systems - 3 linear motion x,y,z and 3 rotations about the axes, as in CNC milling machines..

A simple traverse is what moves the ink cartridge in a printer, for example, though it's not usually known as that.
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Blackbird
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RE: Laminar Flow Control Question

Sun Feb 18, 2007 1:17 am

So you mean a laser equipped traverse located UNDER the holes in the wings?

Andrea K
 
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RE: Laminar Flow Control Question

Sun Feb 18, 2007 5:35 am

Interesting, but what about weather . . .on the ground a bit of snow or ice means De-icing / Anti-cing and then what? How will you ever get all that anti-icing fluid out of the holes in order allow laminar flow to take effect during flight? Or are all these "laminar flow birds" kept in the hangar until the weather clears? Maybe a good idea for summer weather flying but not for everyday airline operation.

Unless a safe and efficient solution is found to heat the entire upper wing surface (currently only on ground leading-edge heating is available on some aircraft types), preventing a contaminated wing in the first place, adverse winter weather operations would come to a halt using the laminar flow concept. If there was a simple solution for this, it would probably have already been incorporated in the present generation of aircraft, laminar flow system or not. As long as it is not available, i'll be doing tactile inspections on wings after an anti-icing fluid treatment (for aircraft without laminar flow wings of course).


Starglider

[Edited 2007-02-17 21:58:24]
 
oly720man
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RE: Laminar Flow Control Question

Tue Feb 20, 2007 1:56 am

Quoting Blackbird (Reply 13):
So you mean a laser equipped traverse located UNDER the holes in the wings?

I was thinking more of something that could be done on the ground. I'm not sure it would be possible to have such a system in a wing leading edge because of space requirements.
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Blackbird
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RE: Laminar Flow Control Question

Tue Feb 20, 2007 3:53 am

It sounds like a start... icing and de-icing issues would still allow the system to be workable, right?

Andrea K
 
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RE: Laminar Flow Control Question

Tue Feb 20, 2007 5:21 am

Quoting Blackbird (Reply 16):
It sounds like a start... icing and de-icing issues would still allow the system to be workable, right?

Andrea K

De- / anti-icing is the last operation on the aircraft just before takeoff. After that no more tampering with the aircraft because the moment you start spraying anti-icing fluids on the aircraft surfaces, the hold over time kicks in and the anti-icing fluid is not to be touched or it loses its protective function during the takeoff roll. Not that it matters much trying to clean the holes, anti-icing fluid a thick, oily goo.

There may however be a solution. Flight tests have been performed with a Hybrid Laminar Flow Control (HLFC) system. A suction system design, installed on a Boeing 757.

The system was designed to provide a suction flow of 11.5 lb/min at Mach 0.80 and 39,000 ft altitude, with exterior surface pressures corresponding to an airplane lift coefficient of 0.50. The overall flow was controlled by varying the speed of the turbocompressor that served as its suction source.

Purging and thermal anti-icing capabilities were provided by valving engine bleed-air into the system and blocking the turbocompressor inlet. The bleedflow then pressurized the ducts and flutes, providing transpiration heating of the leading edge.

This is anti-icing by a reverse flow of hot air through the suction ducting. This scheme has the potential for greatly increased efficiency compared to the conventional approach of blowing hot air against the inside of the leading edge.

These tests were based on an airborne system with airflow over the wing, perhaps it could be made to work on the ground at lower temperature settings but the problem of an unheated wing remains, meaning that as long as there is no change in that approach, de- / anti-icing fluids would still have to be applied to protect the wing surfaces against contamination and potential run-back ice from the heated leading edges.



Starglider
 
Blackbird
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RE: Laminar Flow Control Question

Tue Feb 20, 2007 5:51 am

The Hybrid Laminar Flow Control system does sound like a good idea.

Andrea K
 
Starglider
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RE: Laminar Flow Control Question

Tue Feb 20, 2007 9:24 am

Quoting Blackbird (Reply 18):
The Hybrid Laminar Flow Control system does sound like a good idea.

Here is the link to the report, very interesting "food for thought":

http://ntrs.nasa.gov/archive/nasa/ca...asa.gov/19990052585_1999066365.pdf




Starglider
 
Blackbird
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RE: Laminar Flow Control Question

Wed Feb 21, 2007 2:25 am

I know this is slightly off topic...

But when Lockheed recently stated that the maximum theoretical L/D ratio for a Mach 3 double-delta is 10:1. Was that the maximum with boundary layer control or not?

Andrea K
 
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RE: Laminar Flow Control Question

Sat Feb 24, 2007 6:48 pm

Quoting Blackbird (Reply 20):
But when Lockheed recently stated that the maximum theoretical L/D ratio for a Mach 3 double-delta is 10:1. Was that the maximum with boundary layer control or not?

How recently was that? Lockheed-Martin has been out of the civil aviation industry since the L1011.

Recently Lockheed-Martin's "Skunk Works" has been contracted to SAI's QSST, a joined wing (inverted stabilizer) Mach 1.6/1.8 (quiet) supersonic business jet. But it does not have a double delta wing and does not use exotic materials or manufacturing technologies as far as i know.


Starglider
 
Blackbird
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RE: Laminar Flow Control Question

Sun Feb 25, 2007 2:56 am

I'm not sure Starglider,

I think it was either Mach 2.7 or Mach 3.0, and IIRC they said the maximum theoretical L/D ratio was 10:1. I am not sure as to that meaning with or without laminar flow-control, and I'm not sure when they arrived at this figure.

The QSST is an interesting looking plane. But it isn't even able to equal the Concorde in speed, and the design does not look like one that would scale up well.

Andrea K
 
Starglider
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RE: Laminar Flow Control Question

Sun Feb 25, 2007 8:49 pm

Quoting Blackbird (Reply 22):
I think it was either Mach 2.7 or Mach 3.0, and IIRC they said the maximum theoretical L/D ratio was 10:1. I am not sure as to that meaning with or without laminar flow-control, and I'm not sure when they arrived at this figure.

In other recent threads B2707SST showed a figure about potential designs for a successor to Concorde, the ASTF3 which had an L/D ratio of 10.1. But this was a cranked arrow wing, not a double-delta.

Furthermore, the Japanese with their JAXA-NEXST program have done tests on cranked arrow wing (CAW) designs. They used Computational Fluid Dynamics (CFD) where area rule and warp concepts were integrated with the adoption of natural laminar flow (NLF) technology. They modified their initial CAW design into one having a thicker (perhaps super-critical) cross section and higher incidence angle (Cp), e.g. less negative, at 30% of the wing span and a less cambered cross section with less negative Cp at 70% span relative to the initial design (the initial design had an obvious down wash, more negative Cp).

Recently the Japanese have teamed up with ONERA of France and DLR of Germany and in cooperation with them have conducted further supersonic boundary layer optimization tests.

On October 10, 2005 an unmanned test model was flown at the Woomera test range in Australia. Results from these tests show that the boundary layer transition locations on the wing measured from the flight test were more delayed at the design point than those at off-design points. See figure below:

Big version: Width: 500 Height: 562 File size: 32kb
JAXA NEXST-1 - Natural Laminar Flow.



From the Cp distributions on the upper surface of the wing and transition measurement results, the validity of the NLF wing design concept has been confirmed with the above-mentioned flight test.

Quoting Blackbird (Reply 22):
The QSST is an interesting looking plane. But it isn't even able to equal the Concorde in speed, and the design does not look like one that would scale up well.

It's cruise speed may be lower but it may be the first civil aircraft allowed to fly supersonically over land. I agree that up-scaling the concept to airliner size is not very likely. It's fuselage reminds me of the B-70 design which was not designed with hundreds of passengers in mind. A larger version, at multiple times the size and weight, would certainly also affect its sonic boom signature, probably prohibiting it from flying supersonically overland.


Starglider
 
Blackbird
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RE: Laminar Flow Control Question

Mon Feb 26, 2007 11:18 am

That's what I was talking about. The XB-70 like character of the fuselage makes it difficult to carry a significant amount of passengers in the event that such a plane was scaled up.

Andrea K
 
Starglider
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RE: Laminar Flow Control Question

Tue Feb 27, 2007 8:23 am

For a business jet it is quite large at 132 ft in length, 63 ft wing span, 153,000 lb max. weight. All that frame for 12 to 14 passengers (possibly 20 to 25 pax in a future stretched version). Looking at the landing gear configuration it may have the same characteristics as the XB-70 with it's cockpit so far ahead of the nose gear.

It's shape would be something different for a change. This bird will probably fly as good as it looks.


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