FW 190A critical mach?

[FLS]

Do you know where I can get that data?  Is it in a book or reference somewhere?

That's in Brown's book Wings of the Weird and Wonderful.

Brown doesn't use the term "critical mach". He uses "tactical mach" the highest speed where you can still fight with the aircraft, and "limiting mach" where you can't fight and will lose control if you go faster.

My bad, I wrote critical mach then realized Brown hadn't said that, hence the quick edit.

[Brooke]

That's in Brown's book Wings of the Weird and Wonderful.

Thanks! 

[icepac]

Remember that the wing isn't the only surface affected by "critical mach" and not all planes "tuck" when approaching that speed.

Also.....controls don't simply "lock up" in all instances since some simply become ineffective depending on where the shock wave is in regards to the control surfaces and their hinge points.

[Brooke]

Yep, good points.

[PR3D4TOR]

Icepac, could you give us an example of a WWII plane that does not experience Mach tuck?

[Zimme83]

While not having data for every single aircraft from WW2 i would claim that all planes were subject to mach tuck, OK that some planes in reality where unable to reach that speed and others, such as the spitfire, suffered from other aerodynamic related problems before they experienced mach tuck (it the case of Spitfire, aileron reversal)

Thick and straight wings are always subject to mach tuck and all planes during WW2 had such wing. that's why the first generation of jet fighter (F-86, MiG-15) had swept wings to be able to handle transsonic speeds.

[icepac]

Icepac, could you give us an example of a WWII plane that does not experience Mach tuck?

All the planes that start losing parts long before mach tuch becomes an issue.

[PR3D4TOR]

What a silly answer. You were implying that some aircraft are not affected my Mach tuck when "approaching that speed".

Remember that the wing isn't the only surface affected by "critical mach" and not all planes "tuck" when approaching that speed.

You are clearly not quite sure what Mach tuck is. Mach tuck will not occur "when approaching" critical Mach. It will occur when you have gone beyond critical Mach. And all WWII aircraft that are capable of reaching their critical Mach speeds will experience Mach tuck.

[Brooke]

Critical Mach is just at the point that shock waves appear.  That is not when the plane has big problems.  Tactical Mach, which is greater than critical Mach, is when there is enough trouble to cause the plane to no longer be maneuverable.  Limiting Mach could be higher than that -- not just lacking maneuverability, but completely uncontrollable.

[icepac]

What a silly answer. You were implying that some aircraft are not affected my Mach tuck when "approaching that speed".

You are clearly not quite sure what Mach tuck is. Mach tuck will not occur "when approaching" critical Mach. It will occur when you have gone beyond critical Mach. And all WWII aircraft that are capable of reaching their critical Mach speeds will experience Mach tuck.

Yeah man........and my time in a lear 25 has no bearing whatsoever.

There's a lot more going on than just the wing losing lift when the air going over the top of it goes supersonic.

It's not something you can simplify as much as you are attempting to do.

Haven't you got some more rule #4s to reap.

[PR3D4TOR]

Critical Mach is just at the point that shock waves appear.  That is not when the plane has big problems.  Tactical Mach, which is greater than critical Mach, is when there is enough trouble to cause the plane to no longer be maneuverable.  Limiting Mach could be higher than that -- not just lacking maneuverability, but completely uncontrollable.

When the shock waves are formed the wing loses lift and the pressure differential of a conventional wing profile typical of WWII aircraft will make the plane tuck under. The altered down wash can also affect the tailplane. It is not immediate and in most rides the pilot can compensate for a while by pulling the stick. In some planes it was abrupt like in the P-38 at about Mach .72 if I recall correctly, but the 38 is a special case.

Yeah man........and my time in a lear 25 has no bearing whatsoever.

You're right. None what so ever.

[PR3D4TOR]

And no Brooke. Tactical Mach is not above critical Mach. You can't fight in the plane when its bucking like a bronco and the stick is flailing about beating up the pilot. The tactical Mach speed of the 109 according to Brown is .75. That's 508 mph at 30k, or a mere 60 mph over the 109K's top level speed and is a result of the 109's heavy controls, not any compressibility effects. The Germans test dove a 109F to more than 900 kmh (560 mph) and Mach .805 before compressibility started to noticeably affect the aircraft.

http://www.wwiiaircraftperformance.org/me109/Diving_Test_109F_W.Nr.9228_ger_eng.pdf

[Brooke]

And no Brooke. Tactical Mach is not above critical Mach.

Yes, it is.

At critical Mach, there is just barely a shock wave or just barely none at all.  It is the point when airflow anywhere (even the tiniest area) is just up to Mach 1.0.  See the first image in this picture where there is no flow separation yet and no large shockwave yet:



Then, as your airspeed increases, there are larger and larger areas where airflow is above Mach 1.0, there begin to be shock waves, and there can begin to be flow separation.  At some point, this impacts things enough so that the plane is no longer maneuverable.  This is what Eric Brown terms "tactical Mach".   That is the second image in the picture above.

Then, as your speed increases, eventually the shock waves are large enough that there is definite large-scale flow separation (a full stall aft of the shock wave, which is spanning all or a substantial span of the wing).  That is the third image in the picture.

Another way to look at it is this:



Note that "critical Mach" is where the drag coefficient is starting its large increase -- not where it already has its large increase.  That large increase happens as you go faster than critical Mach.

[Brooke]

Another way to look at it.



In these graphs from NASA (from http://history.nasa.gov/SP-4219/Chapter3.html ), we can see that critical Mach (where drag starts to increase) at 2 deg. angle of attack is at about 0.5 M.  Coefficient of lift, however, for 2 deg. angle of attack doesn't plummet until more than 0.7 M.  At 0.7 M, C_L is still higher than at 0.5 M.

[FLS]

Brooke I notice one graph is labeled "One definition of critical mach number."   

My USN Aerodynamics book defines critical mach as the "free stream Mach number which produces first evidence of sonic flow."
This is what your first illustration shows. Supersonic flow occurs after the critical mach number.