P-47N/M vs P-51H

[SaparotRob]

It is a brave man who states "wings are not important" in anything to do with an aircrafts speed, I can sense Drgondog warming up his keyboard as we speak.

Or perhaps, the keyboard of our dreaded intellectual overlord?

 

[fubar57]

It is a brave man who states "wings are not important" in anything to do with an aircrafts speed, I can sense Drgondog warming up his keyboard as we speak.

 

[Metrallaroja]

Have you ever heard of compressibility?

Yes but we are talking about a ww2 era fighter manual. The speeds that says there are at what the airplane is safe to fly. I fail to see how wing compressibility has a role here.
If im wrong please explain it to me.

 

[Metrallaroja]

It is a brave man who states "wings are not important" in anything to do with an aircrafts speed, I can sense Drgondog warming up his keyboard as we speak.

What?

 

[fubar57]

What?

Drgondog slept at a Holiday Inn once and knows a little bit about airplane stuff

 

[pbehn]

Yes but we are talking about a ww2 era fighter manual. The speeds that says there are at what the airplane is safe to fly. I fail to see how wing compressibility has a role here.
If im wrong please explain it to me.

When an aircraft, even a WW2 aircraft goes into a dive it gets to a speed where the airflow over is at the speed of sound even if the aircraft isnt. The P-38 with its twin engine twin boom design suffered with this. The P-51 was faster with the same engine than the Spitfire in all regimes except high speed dives because the Spitfires thin wings went "critical" at a higher speed, as I understand it on the Spitfire the fist shock waves come from the windscreen. Maintaining control and aeroelasticity (stiffness) of wings is another factor. I am just an interested observer some have studied and practiced this in their professional lives, it is slightly complicated.

 

[FLYBOYJ]

Yes but we are talking about a ww2 era fighter manual. The speeds that says there are at what the airplane is safe to fly. I fail to see how wing compressibility has a role here.
If im wrong please explain it to me.

The post about this one says it well. Earlier P-38s were limited in diving away from attacking aircraft because of their critical Mach number. We have a whole thread on this - WWII A/C: Maximum Mach Number & Airspeed in Dives

 

[FLYBOYJ]

 

[drgondog]

I have a question though, how come P-47N dive so much faster than p-51D? How come P-51H dive limit is similar to P-51D eventhough their wing are different?
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I don't know what you think you are discerning from the table above. Calculate value for M as function of altitude = 33.42*Sqrt (R) where R= degrees Rankin for each Altitude (on right). Divide the TAS (i.e. 495mph TAS @40,000 feet) by the calculated local Speed of Sound(M). R=390.0 at 40K. M= 1.0 at 659mph at 40K.
IAS limit at 495mph IAS = 495/659 = .751 Mach.

ALL the TAS values from 40,000 to SL are 0.74-.75M Limit Dives - same as P-51, P-51A, P-51B, P-51C, P-51D, P-51K and about the same as the P-51H which very slightly higher.

The Dive limits of P-47C, P-47D, P-47M, P-47N same as P-51s

 

[Metrallaroja]

The P-51 was faster with the same engine than the Spitfire in all regimes except high speed dives because the Spitfires thin wings went "critical" at a higher speed, as I understand it on the Spitfire the fist shock waves come from the windscreen.

I thought we werent talking about max speed in a dive but about safe dive speeds where the pilot can pull out safely in normal operations.

The post about this one says it well. Earlier P-38s were limited in diving away from attacking aircraft because of their critical Mach number. We have a whole thread on this

Isnt the P38 a bit unique to use it as an example?

 

[Metrallaroja]

I don't know what you think you are discerning from the table above. Calculate value for M as function of altitude = 33.42*Sqrt (R) where R= degrees Rankin for each Altitude (on right). Divide the TAS (i.e. 495mph TAS @40,000 feet) by the calculated local Speed of Sound(M). R=390.0 at 40K. M= 1.0 at 659mph at 40K.
IAS limit at 495mph IAS = 495/659 = .751 Mach.

ALL the TAS values from 40,000 to SL are 0.74-.75M Limit Dives - same as P-51, P-51A, P-51B, P-51C, P-51D, P-51K and about the same as the P-51H which very slightly higher.

The Dive limits of P-47C, P-47D, P-47M, P-47N same as P-51s

I think he is talking about higher IAS at lower alts (5000feet) for the N (505mph vs 522mph)

 

[fubar57]

I think he is talking about higher IAS at lower alts (5000feet) for the N (505mph vs 522mph)

You are quoting this guy....

"James Marshall holds both a Bachelor's and Master's degree in Aerospace Engineering from the University of Texas and currently resides in Texas. His hobbies include breeding Irish Wolfhounds, researching and writing aviation history, shooting sports and building gunstocks. He was president of the 355th Fighter Group Association from 2008 through 2012."

 

[Metrallaroja]

I think he is talking about higher IAS at lower alts (5000feet) for the N (505mph vs 522mph)

anyways this seems to be a estructural limit

 

[FLYBOYJ]

I thought we werent talking about max speed in a dive but about safe dive speeds where the pilot can pull out safely in normal operations.

Yes, and this will ultimately be affected by the critical Mach number of the wing.

Isnt the P38 a bit unique to use it as an example?

Not really since all higher performing WW2 fighters experienced this. The P-38's issues were the most publicized

 

[pbehn]

I thought we werent talking about max speed in a dive but about safe dive speeds where the pilot can pull out safely in normal operations.

Isnt the P38 a bit unique to use it as an example?

They are quite obviously linked. All are unique, I just chose the worst case as an illustration. Read the link and drgondogs post above for more informed opinion.

 

[pbehn]

Yes, and this will ultimately be affected by the critical Mach number of the wing.

Not really since all higher performing WW2 fighters experienced this. The P-38's issues were the most publicized

Try finding any history of the P-38 that doesnt contain the word "compressibility", how can anyone think it didnt affect ww2 aircraft?

 

[Metrallaroja]

Try finding any history of the P-38 that doesnt contain the word "compressibility", how can anyone think it didnt affect ww2 aircraft?

I thought elevator compressibility was more important at the lower speeds of ww2 aircraft, even more at low alts where M mig-31bm made his question.

 

[SaparotRob]

You are quoting this guy....

"James Marshall holds both a Bachelor's and Master's degree in Aerospace Engineering from the University of Texas and currently resides in Texas. His hobbies include breeding Irish Wolfhounds, researching and writing aviation history, shooting sports and building gunstocks. He was president of the 355th Fighter Group Association from 2008 through 2012."

But did he read the manual?

 

[SaparotRob]

Leaving. I have to go to the post office anyway.

 

[pbehn]

I thought elevator compressibility was more important at the lower speeds of ww2 aircraft, even more at low alts where M mig-31bm made his question.

I have seen these discussions many times. You cannot learn by firing off unrelated binary questions about a subject that is huge and complicated. Best to read up on the types concerned and the issues they had, then google all the aerodynamic terms used and get it straight in your own mind how they interact.