User avatar
Faro
Posts: 1494
Joined: Sun Aug 12, 2007 1:08 am

Spoilers Systems: Holes Instead Of Panels

Thu May 31, 2012 9:08 am

Following on the contributions in another recent thread All Wing Lift = Net Downward Airflow? (by faro May 4 2012 in Tech Ops) how about the following alternative implementation of a spoiler system.

Instead of panels on the upper wing surface that deploy about a front hinge point to destroy lift and create drag, how about having a series of holes punched into the airfoil and linking the upper and lower wing surfaces in a spanwise, linear arrangement. In normal flight these holes would be closed by small, sliding panel doors. With the holes ‘deployed’, the panel doors would open up and let the higher pressure air on the underside of the wing gush up to the upper wing surface thereby destroying lift and creating drag. The conduits linking the holes may also be angled forward (direction: going from the lower wing surface to the upper one) so that the air streaming out on top would have a forward velocity component, compounding the lift destruction/drag creation effect.

Advantages IMO would include:

- A lighter spoiler system: one is using the force of the airstream itself to get the spoiler effect and not a heavy actuation system to forcibly push back against the airstream as with a classic panel arrangement. The actuation mechanism needed for a series of small panel doors sealing the holes would be simpler and lighter than present panel actuation systems; hydraulic and/or electric actuation may be envisaged;

- The reversal of direction of the air entering the lower hole is contributing to the drag effect with a net negative momentum change imparted to the airframe;

- The holes/doors may be heated to preclude failure due to icing or other environment factors;

- For punctual, very high drag or roll requirements, a small semi-circular scoop may be implemented just behind the lower wing surface hole to divert greater quantities of air to the upper wing surface;

- The size of the holes can be scaled in order to have bigger holes closer to the wing root so as to have a graded spoiler effect; and

- Structurally, the holes/conduits may be integrated within –or affixed to– the rear wing spars so as to lessen the impact of the extra structural weight of implementation (though I should imagine this would still be far less than that of classic panel-spoiler systems).

The only disadvantages I can think of (though I imagine there are more) are:

- How to address the need for ground spoilers: I don’t know just how effective such an arrangement may be at very low airspeeds; and

- The need for regular inspection of the conduits to ensure that the passages are clean and unobstructed (especially in desert climate regions).

Any thoughts?


Faro

[Edited 2012-05-31 02:32:49]
The chalice not my son
 
tdscanuck
Posts: 8572
Joined: Wed Jan 11, 2006 7:25 am

RE: Spoilers Systems: Holes Instead Of Panels

Thu May 31, 2012 12:56 pm

Quoting faro (Thread starter):
Instead of panels on the upper wing surface that deploy about a front hinge point to destroy lift and create drag, how about having a series of holes punched into the airfoil and linking the upper and lower wing surfaces in a spanwise, linear arrangement.

My first thought is that you just gave the structural engineers a heart attack by drilling large unfilled holes (3x stress riser) into their upper and lower wing skins.

Quoting faro (Thread starter):
With the holes ‘deployed’, the panel doors would open up and let the higher pressure air on the underside of the wing gush up to the upper wing surface thereby destroying lift and creating drag.

I see how it kills lift, I don't see how you get much drag.

Quoting faro (Thread starter):
- A lighter spoiler system: one is using the force of the airstream itself to get the spoiler effect and not a heavy actuation system to forcibly push back against the airstream as with a classic panel arrangement.

Unless the holes are way more effective at lift destruction, you're going to need more of them, which means the actuaton system may be more complex (and maybe heavier) due to number of actuators.

Quoting faro (Thread starter):
The actuation mechanism needed for a series of small panel doors sealing the holes would be simpler and lighter than present panel actuation systems; hydraulic and/or electric actuation may be envisaged;

Current spoilers are simple hydraulic/electric actuators today, so I'm not really sure where the gain is here.

Quoting faro (Thread starter):
- The holes/doors may be heated to preclude failure due to icing or other environment factors;

This is a big issue; spoilers don't need deice at all. On a pneumatic plane, how will you deice the holes? No way that the flammability regulations will let you run hot bleed air into a fuel tank. On an electric plane, now you're running high power wires inside the fuel tank.

Quoting faro (Thread starter):
- Structurally, the holes/conduits may be integrated within –or affixed to– the rear wing spars so as to lessen the impact of the extra structural weight of implementation (though I should imagine this would still be far less than that of classic panel-spoiler systems).

This would help with the structural engineers freaking out, but for the idea to work your holes have to connect the highest pressure area of the lower surface to the lowest pressure area of the upper surface; that's farther forward than the rear spar.

Quoting faro (Thread starter):
- How to address the need for ground spoilers: I don’t know just how effective such an arrangement may be at very low airspeeds; and

It wouldn't work at low speed for drag...it might work at killing lift.

Tom.
 
roseflyer
Posts: 9606
Joined: Fri Feb 13, 2004 9:34 am

RE: Spoilers Systems: Holes Instead Of Panels

Thu May 31, 2012 4:01 pm

There are two conditions that determine size of spoilers. First is landing distance due to increased drag. This is for ground spoilers. Lift reduction and drag increases are important. Lift reduction puts more weight on wheels and improves braking performance. Drag directly slows the airplane down. Holes don’t increase drag. It would require all stopping distance to be accounted for with the brakes (reverse thrust is typically not calculated in landing performance, but spoiler deployment is).

The second condition determining size is emergency descent, which is flight spoilers. Emergency decent. In this case drag is more important than lift reduction. That airplane has no problem getting the nose down, but the flight spoilers are needed to keep the airplane from an overspeed condition.

Spoiler panels accomplish lift reduction and drag. Just lift reduction is not enough.

And then of course, where would the fuel go if there were holes in the wing?
If you have never designed an airplane part before, let the real designers do the work!
 
tdscanuck
Posts: 8572
Joined: Wed Jan 11, 2006 7:25 am

RE: Spoilers Systems: Holes Instead Of Panels

Thu May 31, 2012 6:48 pm

Quoting Roseflyer (Reply 2):
And then of course, where would the fuel go if there were holes in the wing?

I'm pretty sure faro is envisioning tubes connecting the upper and lower holes.

Which does bring up one point that negates some of my initial negatives...put the lower surface holes in the fuel tank access doors. That way you don't put extra holes in the lower wing skin. You still have an issue on the upper wing skin though...

Tom.
 
User avatar
Faro
Posts: 1494
Joined: Sun Aug 12, 2007 1:08 am

RE: Spoilers Systems: Holes Instead Of Panels

Thu May 31, 2012 8:57 pm

Quoting tdscanuck (Reply 1):
Quoting faro (Thread starter):
With the holes ‘deployed’, the panel doors would open up and let the higher pressure air on the underside of the wing gush up to the upper wing surface thereby destroying lift and creating drag.

I see how it kills lift, I don't see how you get much drag.

From this passage in the opening thread: "The conduits linking the holes may also be angled forward (direction: going from the lower wing surface to the upper one) so that the air streaming out on top would have a forward velocity component, compounding the lift destruction/drag creation effect".

Quoting tdscanuck (Reply 1):
Quoting faro (Thread starter):
- A lighter spoiler system: one is using the force of the airstream itself to get the spoiler effect and not a heavy actuation system to forcibly push back against the airstream as with a classic panel arrangement.

Unless the holes are way more effective at lift destruction, you're going to need more of them, which means the actuaton system may be more complex (and maybe heavier) due to number of actuators.

Good point: I am now considering chucking out the holes and replacing them by a long, slit-like aperture that would broaden towards the wing root. An incidental advantage of such a slit is that one can use one actuation servo for the whole thingie.

Quoting tdscanuck (Reply 1):
Quoting faro (Thread starter):
The actuation mechanism needed for a series of small panel doors sealing the holes would be simpler and lighter than present panel actuation systems; hydraulic and/or electric actuation may be envisaged;

Current spoilers are simple hydraulic/electric actuators today, so I'm not really sure where the gain is here.

The point is that one is obturating or opening apertures, not working to raise a control surface against the dynamic pressure of the airstream. The force required should therefore be less.

Quoting tdscanuck (Reply 1):
Quoting faro (Thread starter):
- The holes/doors may be heated to preclude failure due to icing or other environment factors;

This is a big issue; spoilers don't need deice at all. On a pneumatic plane, how will you deice the holes? No way that the flammability regulations will let you run hot bleed air into a fuel tank. On an electric plane, now you're running high power wires inside the fuel tank.

This a tougher one to address...need some creativity here...

Quoting tdscanuck (Reply 1):
Quoting faro (Thread starter):
- How to address the need for ground spoilers: I don’t know just how effective such an arrangement may be at very low airspeeds; and

It wouldn't work at low speed for drag...it might work at killing lift.

This is the big problem item and the reason that one will still need ground spoilers...perhaps in combination with the aforementioned slit-spoiler on the outboard wing sections. At least save some weight out there.

Quoting tdscanuck (Reply 3):
Quoting Roseflyer (Reply 2):
And then of course, where would the fuel go if there were holes in the wing?

I'm pretty sure faro is envisioning tubes connecting the upper and lower holes.

Yes, that is the idea. With a slit arrangement the tube would gradually morph into a thin, planar duct of sorts as it approaches the upper wing surface aperture.


Faro
The chalice not my son
 
N353SK
Posts: 826
Joined: Thu Jun 08, 2006 5:08 am

RE: Spoilers Systems: Holes Instead Of Panels

Thu May 31, 2012 11:07 pm

If my spoilers fail, they're more than likely going to fail down. How will you ensure that these "holes" don't fail open in the event of a malfunction?
 
User avatar
larshjort
Posts: 1427
Joined: Wed Dec 19, 2007 6:54 pm

RE: Spoilers Systems: Holes Instead Of Panels

Thu May 31, 2012 11:47 pm

Quoting faro (Reply 4):

This a tougher one to address...need some creativity here...

Prohibit flight into known icing  
Quoting faro (Reply 4):
The point is that one is obturating or opening apertures, not working to raise a control surface against the dynamic pressure of the airstream. The force required should therefore be less.

The spoiler actuators on a CRJ 200 weigh about ~3 kg a piece. you have 2 on each of the flight and roll spoilers and one on each of the ground spoilers. That is 12 actuators total. Regarding the force required, you already have a hydraulic system dimensioned for retracting the main gear that is doing almost nothing when you need to extend the spoilers.

/Lars
139, 306, 319, 320, 321, 332, 34A, AN2, AT4, AT5, AT7, 733, 735, 73G, 738, 739, 146, AR1, BH2, CN1, CR2, DH1, DH3, DH4,
 
tdscanuck
Posts: 8572
Joined: Wed Jan 11, 2006 7:25 am

RE: Spoilers Systems: Holes Instead Of Panels

Fri Jun 01, 2012 1:27 am

Quoting faro (Reply 4):
From this passage in the opening thread: "The conduits linking the holes may also be angled forward (direction: going from the lower wing surface to the upper one) so that the air streaming out on top would have a forward velocity component, compounding the lift destruction/drag creation effect".

I'm not sure you can move enough air this way to get appreciable thrust; your flow area is going to be necessarily small, relative to the wing area, and you have a finite and fixed pressure differential to work with. It would be interesting to analyze it in depth though.

Quoting faro (Reply 4):
Good point: I am now considering chucking out the holes and replacing them by a long, slit-like aperture that would broaden towards the wing root. An incidental advantage of such a slit is that one can use one actuation servo for the whole thingie.

This would help with actuation (and flow area) but now you've got a torsion problem in the wing...open shapes have a tiny fraction (less than 1%) of the torsional rigidity of the same closed shape.

Tom.
 
User avatar
jetmech
Posts: 2316
Joined: Wed Mar 29, 2006 2:14 am

RE: Spoilers Systems: Holes Instead Of Panels

Fri Jun 01, 2012 1:50 am

Quoting faro (Thread starter):

As others have mentioned, you may need to be careful with the details of such a design. I'm not sure if you can access the following paper, but it would make for interesting reading.

Krzysiak, A., “Control of Flow Separation Using Self-Supplying Air-Jet Vortex Generators,” AIAA Journal, Vol. 46, No. 9

The problem with jets of air issuing from small holes at appreciable velocity is that you may actually prevent flow separation occurring over the top surface of the wing. This in turn may limit the drop in lift and increase in drag that is desired. I could certainly see that a reduction in lift may occur due to the loss of some positive pressure on the bottom surface of the wing however.

Regards, JetMech
JetMech split the back of his pants. He can feel the wind in his hair :shock: .
 
User avatar
Faro
Posts: 1494
Joined: Sun Aug 12, 2007 1:08 am

RE: Spoilers Systems: Holes Instead Of Panels

Fri Jun 01, 2012 8:32 am

Quoting N353SK (Reply 5):

If my spoilers fail, they're more than likely going to fail down. How will you ensure that these "holes" don't fail open in the event of a malfunction?

Good point; have to think about that one.

Quoting larshjort (Reply 6):
The spoiler actuators on a CRJ 200 weigh about ~3 kg a piece. you have 2 on each of the flight and roll spoilers and one on each of the ground spoilers. That is 12 actuators total. Regarding the force required, you already have a hydraulic system dimensioned for retracting the main gear that is doing almost nothing when you need to extend the spoilers.

If on the other hand we forget about holes and go for the linear slit-spoilers arrangement, then we only need one actuator per wing, not 6.

Quoting larshjort (Reply 6):
Quoting faro (Reply 4):

This a tougher one to address...need some creativity here...

Prohibit flight into known icing  

Now that I think about it, if the whole spoiler system is placed near or at the rear spar (cf. the 6th advantage in the thread opener), then we can avoid the fuel tank altogether and route hot air/electricity from a proximate fuselage source (if applicable) or up the rear of the engine pylon (if it reaches that far back) to the spoiler aperture system.

Quoting tdscanuck (Reply 7):
Quoting faro (Reply 4):
From this passage in the opening thread: "The conduits linking the holes may also be angled forward (direction: going from the lower wing surface to the upper one) so that the air streaming out on top would have a forward velocity component, compounding the lift destruction/drag creation effect".

I'm not sure you can move enough air this way to get appreciable thrust; your flow area is going to be necessarily small, relative to the wing area, and you have a finite and fixed pressure differential to work with. It would be interesting to analyze it in depth though.

It may or may not be workable. As you mentioned Tom, a key success factor would be sourcing the highest possible pressure air off the wing lower surface. The fact that i) the system would be ideally placed near the rear wing spar on the upper surface for structural reasons and that ii) the highest pressure air on the lower surface is more towards the front portion of the wing presents another challenge...

Quoting tdscanuck (Reply 7):
Quoting faro (Reply 4):
Good point: I am now considering chucking out the holes and replacing them by a long, slit-like aperture that would broaden towards the wing root. An incidental advantage of such a slit is that one can use one actuation servo for the whole thingie.

This would help with actuation (and flow area) but now you've got a torsion problem in the wing...open shapes have a tiny fraction (less than 1%) of the torsional rigidity of the same closed shape.

Is this easily handled via CFRP's? Can one tailor CFRP's to a desired degree of torsion tolerance when fashioning thin, open shapes?


Faro

[Edited 2012-06-01 01:39:34]

[Edited 2012-06-01 01:41:00]
The chalice not my son
 
User avatar
Faro
Posts: 1494
Joined: Sun Aug 12, 2007 1:08 am

RE: Spoilers Systems: Holes Instead Of Panels

Fri Jun 01, 2012 8:59 am

Quoting faro (Reply 9):
Quoting tdscanuck (Reply 7):
Quoting faro (Reply 4):
From this passage in the opening thread: "The conduits linking the holes may also be angled forward (direction: going from the lower wing surface to the upper one) so that the air streaming out on top would have a forward velocity component, compounding the lift destruction/drag creation effect".

I'm not sure you can move enough air this way to get appreciable thrust; your flow area is going to be necessarily small, relative to the wing area, and you have a finite and fixed pressure differential to work with. It would be interesting to analyze it in depth though.

It may or may not be workable. As you mentioned Tom, a key success factor would be sourcing the highest possible pressure air off the wing lower surface. The fact that i) the system would be ideally placed near the rear wing spar on the upper surface for structural reasons and that ii) the highest pressure air on the lower surface is more towards the front portion of the wing presents another challenge...

Another little brainwave: how about placing the whole contraption at the *front* wing spar. At that location you get both the highest air pressure off the underside and the lowest air pressure on the upper wing surface. The lift destruction/drag reduction effects would be at their maximum potential. One may even be able to reduce the size/weight/complexity of the aperture system given the high duct flow rate acheivable at this location.

One would have to have a super-slick aperture on the upper wing though, I imagine the upper front wing surface is critical in terms of surface smoothness. With CFRP spars, you may even be able to integrate the planar duct *into* the spar structure though that would certainly present interesting engineering challenges...

Quoting jetmech (Reply 8):
As others have mentioned, you may need to be careful with the details of such a design. I'm not sure if you can access the following paper, but it would make for interesting reading.

Krzysiak, A., “Control of Flow Separation Using Self-Supplying Air-Jet Vortex Generators,” AIAA Journal, Vol. 46, No. 9

The problem with jets of air issuing from small holes at appreciable velocity is that you may actually prevent flow separation occurring over the top surface of the wing. This in turn may limit the drop in lift and increase in drag that is desired. I could certainly see that a reduction in lift may occur due to the loss of some positive pressure on the bottom surface of the wing however.

Didn't have this in mind at all. Would the placement of the whole system towards the front of the wing change anything in this respect? One for the expert aerodynamicists I'm afraid...


Faro
The chalice not my son
 
tdscanuck
Posts: 8572
Joined: Wed Jan 11, 2006 7:25 am

RE: Spoilers Systems: Holes Instead Of Panels

Fri Jun 01, 2012 12:52 pm

Quoting faro (Reply 9):
If on the other hand we forget about holes and go for the linear slit-spoilers arrangement, then we only need one actuator per wing, not 6.

I'd stick with two per wing...you want redundancy.

Quoting faro (Reply 9):
Is this easily handled via CFRP's? Can one tailor CFRP's to a desired degree of torsion tolerance when fashioning thin, open shapes?

CFRP can do better because of the directionality, but the huge drop in torsional stiffness when you open up a closed section is a physics thing, not a material thing, so the CFRP will still see a huge drop off. The weight penalty will be severe, even in CFRP, unless you can close the wing box back up (i.e. put it ahead of the front spar or behind the rear, or use holes instead of slots, or some other fix like altering the configuration to reduce the torsional stiffness requirements).

Quoting faro (Reply 10):
Another little brainwave: how about placing the whole contraption at the *front* wing spar. At that location you get both the highest air pressure off the underside and the lowest air pressure on the upper wing surface.

A linear slot connecting the lower surface to the upper surface along the leading edge just ahead of the front spar...I think you've just described a slat. Sorry, couldn't resist.

I think the front is probably a better location but integrating with the slats could be very tricky, especially when they're using the same technique to accomplish opposite goals.

Tom.
 
rwessel
Posts: 2448
Joined: Tue Jan 16, 2007 3:47 pm

RE: Spoilers Systems: Holes Instead Of Panels

Fri Jun 01, 2012 2:42 pm

Quoting faro (Reply 4):
The point is that one is obturating or opening apertures, not working to raise a control surface against the dynamic pressure of the airstream. The force required should therefore be less.

As others have pointed out, the force required isn't really an issue. But if it were, you could always build a spoiler as is used on some gliders, with a surface on both the upper and lower side of the wind, and have the lower surface hinged at the back. With the appropriate interconnect, the airloads mostly cancel out (you want to the load to always be slightly positive, so that the spoilers need a bit of force to open). You can see that on this 1-36 photo, with the upper surface spoiler on the other wing visible through the canopy:


View Large View Medium
Click here for bigger photo!

Photo © Mark Carlisle



But I think the biggest problem with this idea is that your taking up a bunch of space inside the wing, compared to basically a flat bit of metal and a hinge that rests on top of the wing. With a simpler mechanism to boot.

Who is online

Users browsing this forum: No registered users and 12 guests