FLYBOYJ
"THE GREAT GAZOO"
If you watch the video I posted you'll see the uneven airflow off the wing at higher Mack number eliminates elevator control. The start of the shock wave at speeds approaching Mach 1 starts at the wing (leading edge).
P-47N/M vs P-51H
- Thread starter mig-31bm
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swampyankee
Chief Master Sergeant
- 3,954
- Jun 25, 2013
Never exceed speeds and never exceed Mach numbers can be set by a number of different criteria, including loss of control (the P-38). aileron reversal (I believe that a later airplane, the B-47, was limited by this), pieces coming off (I've been told that it was set by the windshield collapsing in the Cessna 172), or flutter. Some later jet aircraft had this limit set by engine heating (the F-4K/M in British service).
SaparotRob
Unter Gemeine Geschwader Murmeltier XIII
Did airflow over the wing section between the boom and the pilot go faster than outboard of the booms?
fubar57
General
Any mail?
SaparotRob
Unter Gemeine Geschwader Murmeltier XIII
Paying bills.
Thumpalumpacus
Captain
Didja remember your coat?
SaparotRob
Unter Gemeine Geschwader Murmeltier XIII
D'OH!
- Thread starter
- #128
I mean this, in the red square:
from sea level to 10,000 ft,
P-47D-30 IAS limit is 500 mph
P-47N IAS limit is 482 mph at 10,000 ft, 522 mph at 5,000 ft and 564 mph at sea level
P-51H IAS limit is 495 mph at 8,000 ft, 505 mph at 4,000 ft and 505 mph at sea level
So dive limit
P-47N > P-51H > P-47D-30
That what very confusing for me, if go to wing design then it shouldn't it be: P-51H >P-47N > P-47D-30
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drgondog
Major
You are mis-interpreting the P-51 chart on the right. The Max Permissible (not the same as Possible) Dive (Speed) Limit from 40000 feet to SL is 0.75M. Period. The red vertical line is just that but NAA in its infinite wisdom did not extend the Dive Limit curve from 8,000 feet AGL to SL, as the chart presented is to show the pilot how much altitude he has remaining before he becomes a smokey hole in the ground.
564mph IAS = 564mph TAS = 0.75 M at SL. Only Voodoo has EVER approached 0.75M in level flight, but All stock P-51s have the same ability to dive and all (B, C. D. K, H) to enter supersonic shock wave regime in a dive and not stress parts of the airframe beyond Limit Load conditions per the Vne Diagrams published in the P-51 Operating Manuals (and P-47D/N Operating manuals). The P-51D attained 0.84M, survived and was scrapped. The 'actual' Dive Limits for both 47 and 51 were in 0.80M without damage - but the P-51 did not experience 'pitch down' effect due to the wing design maximum thickness location further aft of P-47 (and F-6 and P-38 and F4U and Fw 190 and Bf 109).
1. The P-47D and N Operating Limitations of M=0.75 are the same as P-51B/D and H.. The difference between the two is that the P-47 when exceeding the Dive Limit experienced 'pitch down' moment as transonic to supersonic transition on the top of the wing moved the Center of Pressure (lift) to the rear (same of all fighters except P-63 and P-51). That experience of pressure movement was extremely serious for P-38 which occurred ~ 0.65-69M and required installation of dive flaps for both the P-47D-30 and P-38J-15 (kit), -25 (production.
Your interpretation of a lower limit for the P-51 was incorrect as you assumed that the Mach limit curve going pure vertical at 8000 feet somehow meant the Limit Dive Speed IAS changed. No, NAA assumed the reader would assume he better start pulling out at 8K or, else.
2. Both the P-47 and P-51 attained 0.80M frequently in dives without experiencing actual structural damage. The 0.75M limit translated to IAS for different temps and density altitudes was for easy reference for pilot.
Hopefully, you will research Vne diagrams from both Operating Manuals (or all Operating Manuals), you will learn to calculate Mach Number as f(altitude), you will learn the difference between IAS and TAS. You will research and understand the concepts of non-compressible, compressible, mach transition, drag rise and local Mach number flow over an airfoil with respect to free stream flow. You will hopefully inderstand the mechanics of effects of a local shock wave on the airfoil airflow and center of pressure movement as well as the turbulent wake behind the shock wave and its effects on the downwash of the H.Stab/elevator and why elevator trim is important in dive recovery. Hopefully you will comprehend why CP movement aft influences pitch down Moment about the aerodynamic center.
Absent understanding of the above you are just flinging 'stuff' up for others to explain this to you. There are more than a couple on this forum that can help you.
Now, I am pretty much done with this discussion with you. Go forth rich in your assumptions.
wuzak
Captain
I thought it may be difficult to pull out of a 500mph+ dive at 0ft!
- Thread starter
- #131
I still don't get it, how can they have the same dive capability?
For example: in the green box.
At 30,000 ft, P-47D-30 is limited to 250 mph IAS / P-47N is limited to 318 mph IAS / P-51D is limited to 330 mph IAS
At 25,000 ft, P-47D-30 is limited to 300 mph IAS / P-47N is limited to 360 mph IAS / P-51D is limited to 360 mph IAS
At 20,000 ft, P-47D-30 is limited to 350 mph IAS / P-47N is limited to 400 mph IAS / P-51D is limited to 400 mph IAS
At 15,000 ft, P-47D-30 is limited to 400 mph IAS / P-47N is limited to 442 mph IAS / P-51D is limited to 440 mph IAS
At 10,000 ft, P-47D-30 is limited to 450 mph IAS / P-47N is limited to 482 mph IAS / P-51D is limited to 480 mph IAS
At 5,000 ft, P-47N is limited to 522 mph IAS/ P-51D is limited to 505 mph IAS
So it look like at high altitude
P-51D > P-47N > P-47D-30
At medium altitude
P-51D = P-47N > P-47D-30
At low altitude
P-47N > P-51D > P-47D-30
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swampyankee
Chief Master Sergeant
- 3,954
- Jun 25, 2013
I fail to understand why you find this surprising or counterintuitive, as dive limits have nothing to do with perceived cleanness of an airframe. Also, to put things in perspective, the P-47 was a lower-drag airframe than several V-12 powered, single-engine fighters, e.g., the Bf109. If one bothers to look up the data, the zero-lift drag coefficient, the only sensible measure of relative "dragginess" of an airframe, does not show a statistically different mean between radial-engine and V-12 engine fighters. The P-51's zero-lift drag coefficient was massively lower than any other WW2 piston fighter; the P-47 was somewhere in the middle of the soup of all the single-engine fighters.
Never-exceed airspeed is not determined by perceived aerodynamic cleanliness. Maximum attainable speed in a dive would be somewhat correlated to weight divided by (wing area times zero-lift drag coefficient), but that's a different parameter and one which doesn't tend to be put in things like operating manuals because Vne will almost always be lower, which means that achieving the maximum possible dive speed is, at best, highly inadvisable and, at worst, is likely to be fatal.
- Thread starter
- #133
Hmm, but the zero lift drag coefficient is still just a coefficient, you can have lower coefficient yet higher total drag though.
Like for example: a Mig-31 likely has lower zero lift drag coefficient than a Fokker Dr.I but the total drag of Mig-31 is still bigger since it is much more massive
So, while P-47 drag coefficient probably lower than BF-109, i actually doubt that the actual drag is also lower
I guess the issue here is with how I phrase my question/opinion since English isn't my mother tongue so might be something is loss with translation.
When I asked about dive limit, I don't mean the absolute maximum speed that the aircraft can't excess.
I mean the maximum speed which it can achieve at certain altitude in a dive (may be there is a word for this?)
So, for example:
Let say a P-47D and a P-51D both flying at 30,000 ft.
Then let say the P-47D somehow able to get behind the P-51D, so the Mustang pilot dive down to 10,000 ft and the P-47D pilot follow him.
Since, P-51D speed limit at 10,000 ft is 480 mph IAS while P-47D limit is 450 mph IAS, that mean P-51D can potentially out dive the P-47D and run away?
That the sort of question i'm trying to answer
You are getting lost in numbers. 5,000ft is slightly less than a mile/1.6KM. In a 45 degree dive at 505mph IAS calculate the time taken to hit the sea. In many places in the world an altitude of 5,000ft is below ground level. Reno races are at a ground level of 4,500 ft this is less than the average altitude of Nevada which is 5,500ft.
drgondog
Major
True. Drag Coeffient(s) for Parasite Drag are functions of Wing Area. In most examples of WWII aircraft the Wing dominates, followed by Fuselage.
Good as such is Unknown with precision during Design. Failure in dives is most often due to dynamic Pressure loading - which is a function of Velocity and local density of air - for which a 'wall' is shown on the Vne diagram, representing the airframe manufacturer's Limit Loading. If the airframe in question has been analyzed part by part for Stress on each part for the limit before Yield point (or established stress/strain curve for the material), then the collective values forlevel flight, dive, manuever are presented in graphic form as a "Vne Diagram". Vne Diagrams are calculated for a specific Gross Weight and 'allowable' or 'limit' G load at THAT Gross Weight. The outer 'Envelope' on a Vne Diagram - composed on Ultimate G load in which an airframe/or components of the airframe exceed elastic stress and enter into 'Fracture/fail/crush/break' zone.
In my airframe world, all airworthy critical parts (spars, longerons, etc) were designed for a tensile or shear stress allowable/stress applied due to the Ultimate Load >1.01 Different factors other than 1% were used.
You need to craft a very sophisticated model in which a.) ALL your drag components for Parasite drag are known and you have the 'near correct' equation derived in wind tunnels to expresss CD total as a function of RN. RN will change as the modeled aircraft pitches over, accelerates, increases velocity, changes density due to loss of altitude, changes kinetic viscosity.
Fortunately you are only comparing say, 90 degree dives at 1G and dealing with zero lift.
You also need to build in total CD as a f(Mach Number) as both the P-51 and P-47 have different drag rise characteristics - only the Spitfire with the thinner wing had nearly the same small increase in CDt through M=0.65 as the Mustang. I have not seen Performance calculations for P-47 so can not comment on the wind tunnel recorded, then Calculated and Plotted CDp as a f(RN).
ALL Parasite/pressure Drag components must be corrected for Mach - but not Induced Drag. That said at zero lift in dive you don't have to calculate Induced drag.
BTW in performance calculations Projecting/Predicting ROC, top Velocity, Take Off and Landing limits, there are so many references you have to find and bring into your stack of parameters - that are simply not available without direct access to the manufacturers legacy data and reports. For example, given modeling P-51. Beyond what I explained above about RN and Mach corrections, the following are needed"
1. Hamilton Standard propeller model data to extract efficiencies as a function of RPM and altitude. Crucial for THP calcs.
2. Packard Merlin engine fuel properties data as funtion of Manifold Pressure, RPM and altitude, to be able to calculate Exhaust Gas thrust as a f(MP, altitude, ambient static pressure, engine charge consumption, total stack area) - and convert to THP.
3. Increased Drag due to prop tip drag rise ~ 0.98 M (or what ever you aircraft prop diameter/RPM shows you)
THP losses due to pressure drag of carburator and radiator/oil cooler plenum.
THP losses due to Prop vortex for the drag items within the vortex.
And so on...
Sounds like you are in the Gaming world. Good luck.
swampyankee
Chief Master Sergeant
- 3,954
- Jun 25, 2013
Dimensionless coefficients are the only sensible way of comparing aircraft of different sizes.
SaparotRob
Unter Gemeine Geschwader Murmeltier XIII
Is that like rigidly defined boundaries of uncertainty?
GregP
Major
The elevator is connected to the stabilator which, in turn, is connected to the fuselage which, in turn, is connected to the wing. If the elevator is going 505 mph, so is the wing and hte rest of the airplane except for the prop, which is likely going faster as it spins.
If shock waves form on the tail, you can bet pretty good money they'll form on te wings and maybe the cockpit, too, not to mention the prop tip.
Barrett
Senior Airman
I cannot find the source (of course) but reputedly the elliptical wing was optimized for high altitude performance, which explains the Spit and P-47 configurations.
First I heard of it was from a Canadian ace who knew A LOT about A LOT. The late Rod Smith.
First I heard of it was from a Canadian ace who knew A LOT about A LOT. The late Rod Smith.
Howard Gibson
Senior Airman
The Thunderbolts were fast at high altitudes because of their turbochargers. They were replaced with Mustangs partially because their wings suffered more from compressibility. The Spitfires had very high critical Mach numbers because they had thin wings.
