Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: Brooke on January 16, 2015, 01:50:47 AM
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Does anyone have reference for critical mach for the FW 190A?
The FW 190A-5 in AH has a critical mach of about 0.80 by testing.
Looking around, all I can find is reference to it being 0.75 (from testing done by Eric Brown) for the FW 190:
https://en.wikipedia.org/wiki/Eric_Brown_%28pilot%29#Wartime_service
The P-38 according to Brown has a critical mach of 0.68, which is what it is in AH by testing.
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It could also differ some version vs version, A6-A8, F8 had a different wing vs the A5, 30mm version had bulges all over the wings :)
Currently it is its only advantage it still has against some late allied fighters, it is even faster diver than a full set of diving and shooting B17s, that can do close to 600mph :rolleyes:
It can easily be out turned by any allied fighter and many fully loaded bombers at slow speed :confused:.
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It could also differ some version vs version, A6-A8, F8 had a different wing vs the A5, 30mm version had bulges all over the wings :)
Currently it is its only advantage it still has against some late allied fighters, it is even faster diver than a full set of diving and shooting B17s, that can do close to 600mph :rolleyes:
It can easily be out turned by any allied fighter and many fully loaded bombers at slow speed :confused:.
Regardless Save, and I do sympathize, but if it is modeled incorrectly, consideration should be given to updating its FM :salute
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here is an older thread about the p47 vs 190A critical mach
http://bbs.hitechcreations.com/smf/index.php?topic=204256.0
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Brooke, check:
Einfluss hoher Mach' Zahl auf Fw 190 (http://www.wwiiaircraftperformance.org/fw190/Fw_190_Dive.pdf) Translation - Influence of high Mach number on Fw 190 (http://www.wwiiaircraftperformance.org/fw190/fw190-0022-dive.html)
Betriebsdatentafel Fw 190 A-3 bis A-6 (http://www.wwiiaircraftperformance.org/fw190/Fw_190_A-3-6_Data.jpg)
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According to Eric Brown the Fw 190 and Bf 109 both had tactical Mach numbers at or near .75. Tactical Mach being the speed at which the aircraft is still capable of useful maneuvering. Critical or limiting Mach would be higher than the tactical and is the speed at which you lose control.
A very interesting video of a lecture by Eric Brown was posted here some time ago. I'll see if I can find it.
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Can't find it. Search really suxxors on this site.
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According to Eric Brown the Fw 190 and Bf 109 both had tactical Mach numbers at or near .75. Tactical Mach being the speed at which the aircraft is still capable of useful maneuvering. Critical or limiting Mach would be higher than the tactical and is the speed at which you lose control.
A very interesting video of a lecture by Eric Brown was posted here some time ago. I'll see if I can find it.
This is a good point. The reference I gave says "tactical Mach" not "critical Mach". It's the tactical Mach of the 190 that is 0.75. However, it is also tactical Mach of the P-38 that is 0.68 according to that reference.
In AH, the tactical Mach of the P-38 is about 0.64, and critical Mach of 0.68.
EDIT: No, I have the nomenclature wrong -- see post below.
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It tucks under at .68?
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"Mach tuck would occur when the aircraft attained Mach 0.68; the air flow over the wing roots would become transonic, and the wing therefore would lose lift..."
http://en.wikipedia.org/wiki/Mach_tuck
It's wiki, but still.
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Looking more carefully at nomenclature, "critical Mach" should be where shock waves just start. Critical Mach is not where the controls lock up -- that would be past critical Mach. The Brown reference uses "tactical Mach" to mean the speed at which you can still maneuver the aircraft but faster than that you can't. In that case, tactical Mach should be greater than critical Mach.
Here is a diagram:
(http://upload.wikimedia.org/wikipedia/commons/6/6d/Transonic_flow_patterns.svg)
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The tests Brown mentioned were a P-51B and a P-38H. Brown defined tactical Mach as the max safe handling speed.
Capt Brown also tested an F5E with dive flaps and was able to pull out from Mach .71 without the dive flaps and Mach .75 with dive flaps.
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It tucks under at .68?
There is a net full of sloppy nomenclature and references on this, a result of the difference between the start of stock waves and when you can't control the aircraft anymore. It might be that some references are using Mcritical as Mtactical for the P-38, as it is the most-studied WWII fighter for compressibility, and so there is more potential for references to get the details all messed up.
If they are all judged on when they can't be maneuvered well anymore, supposedly Brown did that, and found the P-38 to be Mtactical = 0.68 and FW 190 Mtactical to be 0.75.
In AH, Mtactical for the P-38 is 0.68 at most (it gets nearly impossible to maneuver it lower than that -- more like 0.65), and Mtactical for the FW 190 is 0.80 (or a little bit less, like 0.79).
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The tests Brown mentioned were a P-51B and a P-38H. Brown defined tactical Mach as the max safe handling speed.
Capt Brown also tested an F5E with dive flaps and was able to pull out from Mach .71 without the dive flaps and Mach .75 with dive flaps.
Do you know where I can get that data? Is it in a book or reference somewhere?
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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.
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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.
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That's in Brown's book Wings of the Weird and Wonderful.
Thanks! :aok
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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.
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Yep, good points.
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Icepac, could you give us an example of a WWII plane that does not experience Mach tuck?
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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.
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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.
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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.
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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.
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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.
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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.
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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
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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:
(http://upload.wikimedia.org/wikipedia/commons/6/6d/Transonic_flow_patterns.svg)
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:
(http://i146.photobucket.com/albums/r279/sampaix/Critical-Mach.jpg)
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.
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Another way to look at it.
(http://history.nasa.gov/SP-4219/4219-074.jpg)
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.
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Brooke I notice one graph is labeled "One definition of critical mach number." :lol
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. :aok
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Brooke, it varies with different aircraft, but as a general rule both the tactical and limiting Mach speeds are below critical Mach. This was certainly true with the 109 because of the heavy stick forces at high speed. The P-38 was a special bird because of all the interference drag and Bernoulli effects created by the central pod and nacelles interacting with the airflow. Brown defines tactical Mach as the speed at which you can fight the aircraft and limiting Mach as the speed where you no longer can, and if you go past the limiting Mach speed you'll get into serious trouble.
The RAE extensively tested both the Typhoon and Tempest and they too had both tactical and limiting Mach speeds well below critical Mach. I quote from Brown's book Testing for Combat:
"Our other great interest in the Tempest V at the RAE was in its high Mach number characteristics, and these proved to be very similar to those of the Typhoon, except that it had limiting Mach number of 0.81 true and a critical Mach number of 0.83 true. At the latter speed the nose-down trim change was very strong, and a full-blooded pull was required to keep the dive angle constant until the altitude had fallen to about 15,000 ft, when recovery could be affected."
"We had found out that the Bf 109 and the Fw 190 could fight up to a Mach of 0.75, three-quarters the speed of sound. We checked the Lightning and it couldn't fly in combat faster than 0.68. So it was useless. We told Doolittle that all it was good for was photo-reconnaissance and had to be withdrawn from escort duties. And the funny thing is that the Americans had great difficulty understanding this because the Lightning had the two top aces in the Far East."
There, from the man himself.
The difference between the 109 and P-38 is that in the case of the 38 the tactical Mach speed is limited by compressibility effects, while for the 109 it is the heavy controls that limit its ability to fight above Mach .75. It doesn't get into compressibility until .80 or thereabouts.
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In "Wings on My Sleeve" Brown defines critical mach as loss of control. I had posted that earlier but couldn't find it in "Wings of the Weird and Wonderful" so I edited it. Helps if I look in the right book. :bhead For the F5E or P-38L that would be .72 mach without using the dive flaps and .75 with dive flaps.
All the other references I've seen to critical mach refer to the minimum speed where some airflow becomes supersonic.
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Brooke,
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There, from the man himself.
I stand corrected on Brown's terminology. :aok
Also, thank you for another reference (the book "Testing for Combat").
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Brooke I notice one graph is labeled "One definition of critical mach number." :lol
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. :aok
Yes, the two definitions in my view are the same: the critical point at which any part of the wing goes from no supersonic flow to any supersonic flow, such that at speed Mcr-epsilon there is no sonic flow and at Mcr+epsilon there is. That is where drag will start to diverge.
However, it is (at least for most wings) not yet the point where there are large shock waves, drastic drag divergence, loss of lift, etc.
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I'm having no luck finding any definitive data on these things anywhere but in Brown's book (or books).
Other than Brown's books, I can't find any online references except ones that say something like "critical Mach of the P-38 was 0.68" without any backup of where that comes from or what *they* specifically mean by "critical mach" (i.e., the transition from subsonic to some sonic, or where maneuverability is starting to be lost, or where there is absolutely no control, or anything in between). Or references that say "we dove this airplane to such and such a speed", which means almost nothing in this context.
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Have you seen this Brooke? It's wind tunnel model testing of dive flaps but it shows some mach numbers.
P-38 Dive Tests (https://www.amazon.com/clouddrive/share/1y_FKr8f1xOTB2BGKa_kZ3nrrYirXNXjRkCKvAxZg0s)
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Have you seen this Brooke? It's wind tunnel model testing of dive flaps but it shows some mach numbers.
P-38 Dive Tests (https://www.amazon.com/clouddrive/share/1y_FKr8f1xOTB2BGKa_kZ3nrrYirXNXjRkCKvAxZg0s)
No -- thanks for the link.