Question about the F4 barricade blade?

[Ebphoto]

Hello All,

I was listening to a interview of a female pilot, forgive me please for I cannot remember her name or the podcast I heard her on, but she mentioned a design on the F4 that was strictly made for the US Navy that allowed the F4 to cut through some of the emergency barricade. They kept this design for the Air Force as well because it was easier than re-designing it. She mentioned this because the Russians copied it in the Mig 23 or might have been the Mig 27,  thinking it had something to do with aerodynamics which she said it didn’t. Does anyone know what she was referring to? I thought it was the blades before the engine air intakes, but I’m not sure because I thought those were to assist airflow at supersonic speeds to slow the air down to assist the engine. I might be 100% wrong on that though since I don’t know very much about the F4 Phantom. I would be very interested if anyone can explain what she is talking about! I’ve looked at the F4 and the Mig23 and those blades on the side right before the air intakes are the only thing I can think of. Appreciate any help on this.

Thank you,

B

[Sacarino111]

27 minutes ago, Ebphoto said:

I thought those were to assist airflow at supersonic speeds to slow the air down to assist the engine.

True, you are right. Indeed, they have a lot of little holes on them to help the intake.

Saludos.

Saca111

[Zpigman]

She is talking about blades that are technically under the air intake. This was done, because the air intake wasn't attached to the skin of the aircraft to correct bounded (I believe that is the term) air from entering the engine. The problem is when taking a barricade, the thin straps would go between the two parts of the aircraft ripping the intake off and 100% destroying the aircraft. The solution is the blades that you find meant to cut the barricade and maintain the structure of the aircraft.  

[Ebphoto]

So it’s in between the body of the aircraft and the air intake! So I guess that would be on the backside of those blades? Is that right or actually on the bottom of the planes intake? That sounds like what she was referring to. She mentioned them because the Soviets copied it over to the Mig which didn’t make any sense since they were all AF jets and not on a carrier. I’ll have to look and see if I can find a picture of it. Thank you for the reply. I just thought it was interesting and couldn’t figure out what exactly she was talking about.

[Snappy]

On 8/10/2022 at 7:45 PM, Ebphoto said:

Hello All,

I was listening to a interview of a female pilot, forgive me please for I cannot remember her name or the podcast I heard her on, but she mentioned a design on the F4 that was strictly made for the US Navy that allowed the F4 to cut through some of the emergency barricade. They kept this design for the Air Force as well because it was easier than re-designing it. She mentioned this because the Russians copied it in the Mig 23 or might have been the Mig 27,  thinking it had something to do with aerodynamics which she said it didn’t. Does anyone know what she was referring to? I thought it was the blades before the engine air intakes, but I’m not sure because I thought those were to assist airflow at supersonic speeds to slow the air down to assist the engine. I might be 100% wrong on that though since I don’t know very much about the F4 Phantom. I would be very interested if anyone can explain what she is talking about! I’ve looked at the F4 and the Mig23 and those blades on the side right before the air intakes are the only thing I can think of. Appreciate any help on this.

Thank you,

B

If you remember the name of the podcast again or find it again by chance.could you link it here?sounds interesting!

Kind regards ,

 Snappy 

[Bulldog_1]

 

@ 5:50 he talks about the "blades"

 

 

[Ebphoto]

Oh that’s great, thank you! It’s something that I heard on the interview & for some crazy reason it just stuck in my head & I couldn’t figure out exactly what she was referring to. I had an idea but didn’t know if it was the actual fin that’s before the air intake or in between the blade and the fuselage. Anyway thank you for all the replies and the video! Great stuff! It’s kinda funny how the USSR copied it over onto their Mig thinking it had something to do with aerodynamics at high speed. I’m sure we, the US, has made similar moves! As I was watching the video, I never realized how pointy the nose is with that big pitot tube! Also I wanted to ask if you knew how the blade, not the cutting blade, moved? Does it slide out at an angle and those holes in it slow down the airflow to the engine? Or do they move differently than that. Sorry for the question I’ve never really looked at them before. I saw them and knew it slowed air at super sonic speeds to the engine but never thought much of it. It’s very interesting. 
 

Thank you again I appreciate it,

B

Edited August 14, 2022 by Ebphoto

[G.J.S]

7 hours ago, Ebphoto said:

. . . Also I wanted to ask if you knew how the blade, not the cutting blade, moved? Does it slide out at an angle and those holes in it slow down the airflow to the engine? Or do they move differently than that. Sorry for the question I’ve never really looked at them before. I saw them and knew it slowed air at super sonic speeds to the engine but never thought much of it. It’s very interesting. 
 

Thank you again I appreciate it,

B

 

The “Splitter plates” don’t move forward or backward. The rearmost half (immediately before the intake) will move, in increasing angle relative to the airflow (think constriction of the inlet). At higher air speeds, the angle increases.

The “small holes” on the plates, are to remove the sluggish boundary layer airflow before it enters the inlet.

Edited August 14, 2022 by G.J.S

[WarthogOsl]

I watched this video when it originally came out. I recall there was a bunch of criticism, in that some of the stuff he pointed out was just wrong. I'm not an expert so I don't know.

[Ebphoto]

Hey Snappy I think this is the interview. Not 100% positive this is it but it’s the only one I could find in my YT history so it might be it. Either way it’s still a great interview and she sounds like a solid pilot. Here’s the link…

 

[r4y30n]

The “Splitter plates” don’t move forward or backward. The rearmost half (immediately before the intake) will move, in increasing angle relative to the airflow (think constriction of the inlet). At higher air speeds, the angle increases.
The “small holes” on the plates, are to remove the sluggish boundary layer airflow before it enters the inlet.

To further elaborate, the reason for the holes and the reason the inlet is separated from the fuselage is to keep the air speed as even as possible across the face of the engine. Without those features the air would be slower on the inboard side and that asymmetry in flow would increase the risk of stalls. In this case, you’re trying to keep air speed high in the duct.

The engines can’t handle supersonic flow, however, so the ramps change angle to create and maintain shockwaves across the inlets that slow supersonic air to subsonic speeds in the duct by compressing it. This process is much more efficient than compressing air in the engine itself and is pretty much mandatory on aircraft going Mach 2+. In this case you’re trying to keep air speed low (subsonic) in the duct.

The reason you don’t see moving ramps on newer aircraft is because they’re either not designed to go that fast anymore (F/A-18) or they use brute force with very high static thrust engines (F16, F-22).

[Ebphoto]

That’s wild, you’d think compressing the air would speed it up. Much like moving water from a larger pipe to a smaller pipe builds the pressure. Unless I’m not thinking correctly. Either way it’s amazing how all this came to be & the technology changed as advancements made. Really interesting stuff.

[SgtPappy]

1 hour ago, Ebphoto said:

That’s wild, you’d think compressing the air would speed it up. Much like moving water from a larger pipe to a smaller pipe builds the pressure. Unless I’m not thinking correctly.

No, increasing the speed of the flow decreases its static pressure. When we say compressed here, it means "increase static pressure", not necessarily "squeeze the flow geometry in the duct (i.e. decrease duct cross section)". In any case, for subsonic flow, decreasing the cross section of the pipe will increase velocity and the static pressure decreases; it does not build. The same geometry will slow down supersonic flow. That's why we use diverging nozzles when the flow is supersonic to speed up that flow more but that's another topic.

For compression, think of the problem backwards. Say you have a tank of compressed air. There is no velocity and the static pressure of the air inside is at its highest.

If you open it up to the atmosphere, or a pipe/duct with lower pressure, the air will escape due to the pressure gradient and will attain velocity at the opening to the duct and onward. The static pressure drops across the place where flow accelerates and is "converted" to dynamic pressure (q = 0.5*density*v^2). The total pressure (ignoring friction and viscosity) is the same as what the static pressure was in the tank when it was closed because total pressure is the sum of static and dynamic pressure.

Now when you have supersonic flow across the Phantom's intake ramps, for example, the ramps deflect the air away, creating shocks which slow down the flow. Some of that dynamic pressure is being recovered back to static pressure, hence the air is being compressed.

Edited August 16, 2022 by SgtPappy

[Phantom711]

vor 8 Stunden schrieb SgtPappy:

No, increasing the speed of the flow decreases its static pressure. When we say compressed here, it means "increase static pressure", not necessarily "squeeze the flow geometry in the duct (i.e. decrease duct cross section)". In any case, for subsonic flow, decreasing the cross section of the pipe will increase velocity and the static pressure decreases; it does not build. The same geometry will slow down supersonic flow. That's why we use diverging nozzles when the flow is supersonic to speed up that flow more but that's another topic.

For compression, think of the problem backwards. Say you have a tank of compressed air. There is no velocity and the static pressure of the air inside is at its highest.

If you open it up to the atmosphere, or a pipe/duct with lower pressure, the air will escape due to the pressure gradient and will attain velocity at the opening to the duct and onward. The static pressure drops across the place where flow accelerates and is "converted" to dynamic pressure (q = 0.5*density*v^2). The total pressure (ignoring friction and viscosity) is the same as what the static pressure was in the tank when it was closed because total pressure is the sum of static and dynamic pressure.

Now when you have supersonic flow across the Phantom's intake ramps, for example, the ramps deflect the air away, creating shocks which slow down the flow. Some of that dynamic pressure is being recovered back to static pressure, hence the air is being compressed.

 

Well however, @Ebphoto is still right here. The idea of the extending ramps is to decrease the crossection of the intake, whereas the crossection of the intake duct behind it stays the same and thus increases in relation to the intake, hence slowing down the supersonic airflow down to subsonic speed. All in accordance with the Bernoulli‘s Law…

[Dragon1-1]

It works in a weird way because supersonic flow behaves very differently from subsonic flow, and the transition between them is not a reversible (in thermodynamic sense) process. The point here is to generate a shockwave to change the flow from supersonic to subsonic, and then expand it in the duct, slowing the air down.

[SgtPappy]

9 hours ago, Phantom711 said:

Well however, @Ebphoto is still right here. The idea of the extending ramps is to decrease the crossection of the intake, whereas the crossection of the intake duct behind it stays the same and thus increases in relation to the intake, hence slowing down the supersonic airflow down to subsonic speed. All in accordance with the Bernoulli‘s Law…

I see what you're getting at, but the original statement is not quite right: that moving water from a larger pipe to a smaller one builds pressure and that compressing it speeds it up. These two things cannot happen at the same time.

Either flow is supersonic and it slows down through a restriction and builds pressure (usually nonisentropically across shocks) or flow is subsonic and speeds up and lowers pressure through a restriction.

Edited August 17, 2022 by SgtPappy

[Ebphoto]

Very complicated stuff! I need my coffee this morning to even understand it!