P38 Performance

[GScholz]

Yeah, that would be Pyro's department if I'm not mistaken. What surprises me is that it wasn't done when the flaps was added in the first place.

[Randy1]

Flight Tests of Dive Recovery Flaps on a Twin Engine Fighter Aircraft (Lightning). A.R.C.9251.
1945.

I tried to find this document.

There is one on the tempest and P47

[GScholz]

What do the Tempest and Thunderbolt tests say about drag?

[Randy1]

What do the Tempest and Thunderbolt tests say about drag?

I have not found the documents for any of the dive flap testing.

here is the document that references these test.

http://naca.central.cranfield.ac.uk/reports/arc/rm/2622.pdf

I have been digging to try to find the technical reason for placing the flap where they do on the P38.  The only conclusion I can reach at this time is the flap creates a shockwave of its own on the bottom of the wing and flow separation on the back-bottom of the wing to match the top wing  more of less.  I want argue with anyone who has this pinned down better than me.

All of this does create a lot of additional mach drag when in the transonic region but not in the laminar flow of level flight.

As a side note, the flap could have been considerably smaller if it could have been placed on the inside of the engine nacelles.   I can only guess the attachment points prevented that.

[GScholz]

What boggles my mind is that anyone can rationally conclude that it is physically possible to have an airflow with an object in it that doesn't create drag. It must be magic... No wonder the Allies won the war!  

[BuckShot]

The Borg cube had no drag either, so maybe its possible.

[LCADolby]

The Borg cube had no drag either, so maybe its possible.

Space doesn't have an atmosphere.

[GScholz]

Actually even in space a moving object would generate some drag from the minute amounts of particles that are there. The solar wind must also be accounted for. So yes, a Borg cube does produce some drag when it moves on impulse power, but not at warp speed of course... Because then it isn't actually moving at all. 

[LCADolby]

Warp is an impossibility 

[BuckShot]

Space doesn't have an atmosphere.

We are Borg. It was a joke, corrections are futile.

[GScholz]

 

[earl1937]

I have not found the documents for any of the dive flap testing.

here is the document that references these test.

http://naca.central.cranfield.ac.uk/reports/arc/rm/2622.pdf

I have been digging to try to find the technical reason for placing the flap where they do on the P38.  The only conclusion I can reach at this time is the flap creates a shockwave of its own on the bottom of the wing and flow separation on the back-bottom of the wing to match the top wing  more of less.  I want argue with anyone who has this pinned down better than me.

All of this does create a lot of additional mach drag when in the transonic region but not in the laminar flow of level flight.

As a side note, the flap could have been considerably smaller if it could have been placed on the inside of the engine nacelles.   I can only guess the attachment points prevented that.

Randy, I cannot place my finger on any document or tell you where to look, but Johnson and company of the skunk works at Lockeed tried the dive flaps both inboard of the engines and outboard. I recall reading that the problem with the dive flaps outboard of the engines created, under turning conditions, a aileron buffett and that is why they are place where they are. One thing I don't understand is why the DF's doesn't interfere with the air flow around and over the elevator. Our in game 38 doesn't seem to recognize where or not they are extended, and I think that is why all this discussion about them. I would think that the nose should pitch up some when you deploy them, but it doesn't and that is why I make that statement. (I know I am going to get an argument about pitch up or down, so have at it guys)

[FLS]

Here's a document. It mentions drag and pitching up.

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20030066111.pdf

[Ack-Ack]

One thing I don't understand is why the DF's doesn't interfere with the air flow around and over the elevator. Our in game 38 doesn't seem to recognize where or not they are extended, and I think that is why all this discussion about them. I would think that the nose should pitch up some when you deploy them, but it doesn't and that is why I make that statement. (I know I am going to get an argument about pitch up or down, so have at it guys)

You are incorrect, the dive flaps do work as intended in AH and do provide a positive pitch when deployed.

ack-ack

[Brooke]

I have been digging to try to find the technical reason for placing the flap where they do on the P38.

When compressibility hits, shockwaves are formed initially on the top surface of the wing, and there is flow separation after the shock wave, which is why the wing loses lift just as if it were stalled while not in compressibility.  This is known at "mach stall" of the wing, and is like this:



There is no flow separation in front of the shock wave.  So, if you want a flap to increase lift of the wing (to make up for the fact that everything behind the shock wave is producing no lift), you need to put it in the forward portion of the wing rather than the stalled-out rear of the wing.

Putting it outboard of the nacelles means it will generate less potential turbulence or other effects to airflow for the elevator.

With regard to whether or not the "dive recovery flap" increases lift or drag, it does both, because generally anything that adds lift is also going to create at least some (not zero) drag.  The main purpose of the flap is to increase lift, though.  It helps avoid or at least reduce "mach tuck," which is the nosing down of the aircraft as a result of the mach stall, and helps give the wing some lift instead of none.  Adding drag is also helpful for obvious reasons, so even though it is a side effect, it is not a harmful one.