A question about speedbrakes?
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A question about speedbrakes?
Can anyone tell me why some speedbrakes, such as those used on the Cessna Citation have holes in them?
Are they purely for creating interference drag, or do they have some other purpose? Wouldn't a flat panel have more aerodynamic effect?
Are they purely for creating interference drag, or do they have some other purpose? Wouldn't a flat panel have more aerodynamic effect?
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Ready to be corrected but that doesn't look like a speed brake to me and the wing doesn't look like a Citation wing to me, isn't that the rear end of a piston or tubo prop engine on the left of picture?
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It's fitted to a Baron, it was the only picture I could find...
If you look closely here, you can see the lower speedbrake just foward of the flap. It's very similar to the one above.
So why the holes?
If you look closely here, you can see the lower speedbrake just foward of the flap. It's very similar to the one above.
So why the holes?
Last edited by TotalBeginner; 23rd Aug 2008 at 09:24.
Nemo Me Impune Lacessit
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Look again TB, there is no way the speed brake shown in the Citation picture, below and forward of the flap, could eventually stow above the flap as in your original picture! Mechanically impossible I would say!
(Not to mention the four screws that seem to attach the well holed piece of metal to the wing in your original picture, with no hinge or extend mechanism visible).
(Not to mention the four screws that seem to attach the well holed piece of metal to the wing in your original picture, with no hinge or extend mechanism visible).
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I have absolutely no idea what you're talking about! I posted the original picture because it shows the kind of speedbrake that my question referes to. Look at the citation picture again (closely). You can just see the top of the upper speedbrake above the wing. No, it doesn't stow above the wing because there are two. One on the surface and one on the underside! 
Back to the original question...
Back to the original question...
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Sorry TB, I have obviously not fully understood your original question, I thought you were suggesting that the holed piece of metal in Pic 1 was an actual speed brake.
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The holed piece of metal in pic 1 IS a speedbrake. It's a modification fitted to a Beech Baron!!! I posted it because it looks very similar to the speedbrakes used on the Cessna Citation, for which I could not find a picture! Maybe this question is more suited to "Biz Jets, Ag FLying, GA etc." Mods?
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The holed piece of metal in pic 1 IS a speedbrake.
As parabellum mentioned, there are four screws attaching that piece to the wing, with no hinge or other mechanism to extend that piece visible. Looks more like some kind of step to me.
Anyway, waiting to be corrected...
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The upper picture seems to be some sort of vortex generator that comes in to play when the flaps are lowered, probably to compensate for the engine.
I must agree with the other posters in that it doesnt apear to be a speed brake, which is a device that is presented to the ariflow, in a manner which causes drag thus slowing the aircraft.
As to Speed brakes them selves, a speed brake the is flatish (Like a board) can cause an aircracft to pitch up or down, depending on its position. By placing a regular system of holes in the surface, this pitching effect is reduced, but also has the effect of creating greater turbulance behind the brake causing more drag therefore greater slowing performance.
I must agree with the other posters in that it doesnt apear to be a speed brake, which is a device that is presented to the ariflow, in a manner which causes drag thus slowing the aircraft.
As to Speed brakes them selves, a speed brake the is flatish (Like a board) can cause an aircracft to pitch up or down, depending on its position. By placing a regular system of holes in the surface, this pitching effect is reduced, but also has the effect of creating greater turbulance behind the brake causing more drag therefore greater slowing performance.
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Why on earth would they bolt a piece of metal to a wing that looks just like a speedbrake? I know, because it's a speedbrake!
I think avtrician has answered my question. The holes reduce the speedbrake's spoiler effect, while maintaining efficiency as a speedbrake?
I think avtrician has answered my question. The holes reduce the speedbrake's spoiler effect, while maintaining efficiency as a speedbrake?
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I have no idea what the answer is but at least I do understand the question; why are some speed brakes perforated? Come on, someone must have a theory, or shall we all just keep debating which picture shows what? 
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OK TB, I'll save you further head banging! Now that you show the picture of the extended speed brake it is very obvious that the four screws attach to the operating mechanism and yes, it really is a speed brake!!!
Sorry about that, I'll stick to aircraft I know in future!
Sorry about that, I'll stick to aircraft I know in future!
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Lightening holes
I suspect that the holes in the speedbrakes are a way of reducing weight, in which the overall plate effect (due to the size of the holes and the turbulence introduced) is as good as a solid panel, but with only half the weight.
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I was thinking that maybe the holes reduce the force required to extend the panel into the airflow, and hence the size and weight of the actuator required to operate them?
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Sorry!
Why on earth would they bolt a piece of metal to a wing that looks just like a speedbrake? I know, because it's a speedbrake!
Regards,
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Clever Wikipedia (Spoilers vs Speed brakes)
TotalBeginner,
Found this on Wikipedia, and it explains the difference between spoilers and speed brakes very nicely. Personally I still do not understand the use of speed brakes on on pistons (except the slick Mooneys maybe)...
Here goes (curousy of Wikipedia)....
In aeronautics a spoiler (sometimes called a lift dumper) is a device intended to reduce lift in an aircraft. Spoilers are plates on the top surface of a wing which can be extended upward into the airflow and spoil it. By doing so, the spoiler creates a carefully controlled stall over the portion of the wing behind it, greatly reducing the lift of that wing section. Spoilers differ from airbrakes in that airbrakes are designed to increase drag while making little change to lift, while spoilers greatly reduce lift while making only a moderate increase in drag.
Spoilers are used by gliders to control their rate of descent and thus achieve a controlled landing at a desired spot. An increased rate of descent could also be achieved by lowering the nose of an aircraft, but this would result in an excessive landing speed. However spoilers enable the approach to be made at a safe speed for landing.
Airliners too are usually fitted with spoilers. Spoilers are sometimes used when descending from cruise altitudes to assist the aircraft in descending to lower altitudes without picking up speed. Their use is often limited, however, as turbulent airflow which develops behind them causes noticeable noise and vibration, which may cause discomfort to extra-sensitive passengers.
The spoilers may also be differentially operated to provide roll control. On landing, however, the spoilers are nearly always used at full effect to assist in slowing the aircraft. The increase in form drag created by the spoilers directly assists the braking effect. However, the real gain comes as the spoilers cause a dramatic loss of lift and hence the weight of the aircraft is transferred from the wings to the undercarriage, allowing the wheels to be mechanically braked with much less chance of skidding.
Found this on Wikipedia, and it explains the difference between spoilers and speed brakes very nicely. Personally I still do not understand the use of speed brakes on on pistons (except the slick Mooneys maybe)...
Here goes (curousy of Wikipedia)....
In aeronautics a spoiler (sometimes called a lift dumper) is a device intended to reduce lift in an aircraft. Spoilers are plates on the top surface of a wing which can be extended upward into the airflow and spoil it. By doing so, the spoiler creates a carefully controlled stall over the portion of the wing behind it, greatly reducing the lift of that wing section. Spoilers differ from airbrakes in that airbrakes are designed to increase drag while making little change to lift, while spoilers greatly reduce lift while making only a moderate increase in drag.
Spoilers are used by gliders to control their rate of descent and thus achieve a controlled landing at a desired spot. An increased rate of descent could also be achieved by lowering the nose of an aircraft, but this would result in an excessive landing speed. However spoilers enable the approach to be made at a safe speed for landing.
Airliners too are usually fitted with spoilers. Spoilers are sometimes used when descending from cruise altitudes to assist the aircraft in descending to lower altitudes without picking up speed. Their use is often limited, however, as turbulent airflow which develops behind them causes noticeable noise and vibration, which may cause discomfort to extra-sensitive passengers.
The spoilers may also be differentially operated to provide roll control. On landing, however, the spoilers are nearly always used at full effect to assist in slowing the aircraft. The increase in form drag created by the spoilers directly assists the braking effect. However, the real gain comes as the spoilers cause a dramatic loss of lift and hence the weight of the aircraft is transferred from the wings to the undercarriage, allowing the wheels to be mechanically braked with much less chance of skidding.
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During the dacades there have been quite a few Airplanes using drag devices with holes in them.
My best guess would be that it has to do with flutter.
You can try this at home. Make a small parachute from cloth or similar material.
Then drop it. You will see it starts to oscilate as it descends.
Now cut a hole in the center and repeat. The swinging should have stopped. If not hole propably too small.
I would suspect a similar phenomenon here with the "boards"
My best guess would be that it has to do with flutter.
You can try this at home. Make a small parachute from cloth or similar material.
Then drop it. You will see it starts to oscilate as it descends.
Now cut a hole in the center and repeat. The swinging should have stopped. If not hole propably too small.
I would suspect a similar phenomenon here with the "boards"
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Personally I still do not understand the use of speed brakes on on pistons (except the slick Mooneys maybe)...
As another user pointed out, the main use of a speed brake on a Baron, or similar piston-powered aircraft, is to permit a rapid descent while still carrying a reasonable amount of power - to prevent over-cooling the engine(s).
The Mooney is a bit of a different beast, in that the aircraft is so "slick" that it can approach or exceed VNE very easily in a descent if the pilot isn't paying close attention. The speed brake helps to prevent that.
In any case, I belive that the main reason for the holes is to reduce the aerodynamic forces on the speed brake panel when it is extended - which allows for the use of a small, lightweight electrically-driven actuator and less need for heavy-duty supporting structure for the panel and actuator.
On large turbojet aircraft, where the spoiler panels serve the dual purpose of dumping lift AND augmenting the ailerons in controlling roll, the panels have to be solid - and that requires a very powerful, hydraulically-driven actuator, as the aerodynamic forces on a solid panel can be quite high.
Jim Barrett
The Mooney is a bit of a different beast, in that the aircraft is so "slick" that it can approach or exceed VNE very easily in a descent if the pilot isn't paying close attention. The speed brake helps to prevent that.
In any case, I belive that the main reason for the holes is to reduce the aerodynamic forces on the speed brake panel when it is extended - which allows for the use of a small, lightweight electrically-driven actuator and less need for heavy-duty supporting structure for the panel and actuator.
On large turbojet aircraft, where the spoiler panels serve the dual purpose of dumping lift AND augmenting the ailerons in controlling roll, the panels have to be solid - and that requires a very powerful, hydraulically-driven actuator, as the aerodynamic forces on a solid panel can be quite high.
Jim Barrett
Last edited by JRBarrett; 24th Aug 2008 at 15:25.