DeltaWings
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What Is This For (On The Bae 146)

Sun Aug 15, 2004 10:47 pm

Hello together.

Can anyone explane the purpose of this opened part of the Bae 146, and is this usual?




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isitsafenow
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What Is This For (On The Bae 146)

Sun Aug 15, 2004 10:49 pm

speed brake to slow the puppy down...
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wedgetail737
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What Is This For (On The Bae 146)

Sun Aug 15, 2004 10:50 pm

That is the air brake on the 146. It used on a normal basis.
 
A3204eva
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What Is This For (On The Bae 146)

Sun Aug 15, 2004 10:59 pm

This is deployed before the wing speed brakes.

A320
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L-188
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What Is This For (On The Bae 146)

Sun Aug 15, 2004 11:09 pm

Vents the cabin in the case of a stinky passenger.
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OV735
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What Is This For (On The Bae 146)

Sun Aug 15, 2004 11:20 pm

Not many jetliners have such devices. I know that the Fokker F.28 had it, whether the F70 and F100 did also, I'm not sure.
 
DeltaWings
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What Is This For (On The Bae 146)

Mon Aug 16, 2004 4:03 am

Oh thanks . I just couldnt figure it out

DeltaWings
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Starlionblue
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RE: What Is This For (On The Bae 146)

Mon Aug 16, 2004 8:37 am

The advantage of this type of airbrake is that it can be deployed in flight regardless of flap position. Most wing mounted spoilers have restrictions in this regard.

Many Avro/BAe-146s fly into airports with steep glideslopes and short runways. You often see it deployed all the way down.


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QantasA332
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RE: What Is This For (On The Bae 146)

Mon Aug 16, 2004 9:25 am

Also keep in mind that when deployed, normal wing-mounted spoilers increase the stall speed of aircraft by reducing the wing's maximum coefficient of lift Clmax -- something you don't really want just prior to landing. Being mounted on the aft fuselage rather than the wings, the BAe 146's style of speedbrake slows the plane effectively and without stall speed side-effects.

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Starlionblue
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RE: What Is This For (On The Bae 146)

Mon Aug 16, 2004 10:08 am

And that's why wing mounted spoilers are sometimes referred to as "lift dumpers".

This is also the reason they are immediately deployed on touchdown, in order to ensure that the plane "sticks". The (wing mounted) spoilers deploy (in general automatically) when the shocks are compressed with a certain force, and the wings lose much of their lift, "letting go" of the plane.


EDIT: OV735, the F70/100 is also equipped with an ass mounted airbrake.

[Edited 2004-08-16 03:10:51]

[Edited 2004-08-16 03:12:09]
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learpilot
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RE: What Is This For (On The Bae 146)

Mon Aug 16, 2004 11:50 am

Hopefully there's an AVRO driver around here to answer this. I've always wondered why you guys fly final with this open. Is it because you would really have to unspool the engines to come down if it wasn't open?
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Starlionblue
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RE: What Is This For (On The Bae 146)

Mon Aug 16, 2004 11:52 am

They like to wear out the seatbelts  Big grin
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FredT
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RE: What Is This For (On The Bae 146)

Mon Aug 16, 2004 6:04 pm

Hopefully there's an AVRO driver around here to answer this. I've always wondered why you guys fly final with this open. Is it because you would really have to unspool the engines to come down if it wasn't open?

Or perhaps rather since you’d have to wait for the engines to spool up from a lower RPM in case you decide that you really want to go around the airport once more before landing... compare with how they’re often used in jet fighters with engines which are slow to accelerate from low RPMs.

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musang
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RE: What Is This For (On The Bae 146)

Sat Oct 03, 2009 9:32 am

Good Day All.

Fred T's explanation is valid, but more of a fringe benefit than standard policy, because being such low mass engines, they spool up from idle very quickly.

If I remember correctly (manuals in the attic now) the manufacturer's SOP was to deploy the tail brake at 100 feet on approach. This procedure was designed to wash off 8 knots by the time touchdown arrived. Without the brake (e.g. when the auto-deploy was u/s [very rare] and I forgot) it was quite slippery and didn't want to land.

Procedure was to pull the speed brake lever (to the left of the thrust levers) to the flight detent at 100 feet. The brake had a maximum rate of extention/retraction so even if you whipped the lever back, the brake moved at a civilised rate. This also armed the spoilers, which deployed on touchdown. As a back-up, we pulled the lever through to the ground detent on landing, in case the auto spoiler deploy failed.

On a steep approach (London City for example) I seem to recall the speed brake was out all the way down, and Fred T's comment becomes more relevant as the idle RPM necessary to keep the speed down would cause a slight delay to spool up in the Go Around.

Regards - musang

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