Boundary layer bleed on the Scimitar

[Max89]

Does anyone know if the boundary layer bleed "vents" on the Supermarine Scimitar (if that is the correct term) could be opened and closed from the cockpit? I have these circled in red in the diagram below.

 

 

And a slightly more complicated question... what benefit do these provide? And why were they positioned above the engine intakes in this manner?

Edited November 21, 2021 by Max89

[ClaudioN]

38 minutes ago, Max89 said:

And a slightly more complicated question... what benefit do these provide? And why were they positioned above the engine intakes in this manner?

Put it simply, the boundary layer is a thin layer of air that gets slowed down through contact with the airframe when an aircraft is flying. Letting it enter a jet engine air intake does no good to it, since air flow in the boundary layer is turbulent. In the cutaway drawing you posted, you can see a large arrow pointing into the air intake, showing the main air flow, and many smaller arrows closer to the fuselage, getting into the boundary layer intakes and out of the vents on top. That's the path boundary layer air is supposed to follow.

 

As to the first part of your question, I should think there is no reason to let a pilot change the position of the vents, but somebody else may know better.

[KevinK]

32 minutes ago, ClaudioN said:

Letting it enter a jet engine air intake does no good to it, since air flow in the boundary layer is turbulent.

 

It's not so much that it's turbulent, it's more that it is slow-moving, compared with the free-stream velocity. If the intake were to ingest the boundary layer, this momentum deficit would manifest itself as a loss in thrust/increase in intake drag, however the designer accounts for it.

 

Related, but slighty off-topic, boundary layer control became a big research area in the '50s, both for intakes and airframes. Dedicated prototype aircraft were built for this  - e.g. the Hunting 126.

[Scimitar F1]

Most designs now move the intake away from the fuselage and have a splitter plate. The Scimitar has an internal splitter plate (similar in concept to the Hunter.

 

Boundary layer bleed over flaps and ailerons is to re-energise the boundary layer on the upper surface so that it remains attached to the wing. This allows a higher angle of attack to be flown than would otherwise be possible so a lower airspeed. it is fed in typically at the leading edge of the flaps. It has a similar effect to the slotted flaps that you see on airliners today. HTH

 

Will
 

 

[Dave Swindell]

To answer the original question, there's no control over the boundary layer ducts, they're an open duct from the inboard side of the intake splitter plate to the fuselage top and bottom outlet vents.