Ad: This forum contains affiliate links to products on Amazon and eBay. More information in Terms and rules
Certainly that could be the case. He has forgotten a considerable amount of information.
Look. I am really trying not to insult anyone in this or make any personal attacks.
We are having some stumbling blocks over some very basic concepts. I will try not to put it in terms of credibility.
I know some folks on these boards who have worked in the aerospace industry some time ago and have forgotten things. However the conversations are still on an entirely different level. Every case is different.
Absolutely! Power available to Power required IS the fundamental relationship that determines aircraft performance.
Over the same altitude, there is no need to convert to TAS. The relative performance remains the same as TAS is soley a function of the properties of the atmosphere.
Merry Christmas All!
All the best,
Crumpp
Actually, I don't think I have ever disagreed with any of this except the last statement for comparing airspeed at different altitudes with different aircraft using EAS.
SR-71, at Mach 3, 100k ft, TAS = 2048 mph, EAS = 238 mph
F-15, at 55k ft, TAS = 600 mph, EAS = 209 mph
Therefore, the Bf-109K4 and the P-47M are both faster than the SR-71 and F-15 because they have a higher EAS.
You're right Crumpp but perhaps Davparlr has forgotten some of this. I haven't experienced Davparlr ever being dishonest, just so you know.
Merry Christmas all!
I think this statement is self evident and a good indicator.
There is no need for me to be insulting.
You think like you're in a car.
Aircraft are machines of the air.
Crumpp
F-15 flying at 600 mph TAS at 55,000 ft. Using your calculations the F-15 EAS is 209 mph. Using your logic, the F-15 is flying at 70% of the speed of the Bf-109K4. This is not logical nor aerodynamically true.
I am asking you to exlain an apparent descreptancy.
I'm still confused.
SR-71, at Mach 3, 100k ft, TAS = 2048 mph, EAS = 238 mph
F-15, at 55k ft, TAS = 600 mph, EAS = 209 mph
Therefore, the Bf-109K4 and the P-47M are both faster than the SR-71 and F-15 because they have a higher EAS.
so Nik did you get any books on the Bf 109K from Klaus ? you need to instead of dependence on what others are telling you and the net.........
Nik, after reading this thread, I'm still confused.
It is logical and it is aerodynamically true.
That is really a crappy comparison too if you know anything about supersonic aerodynamics. The P47 and the Bf-109K are not contending with the same level of drag rise. The rules have changed.
Same goes with your F-15 comparison. It's nonsensical comparison as the P47 and Bf-109 are both subsonic designs.
However we will put on our pretend caps and pretend that there is validity to your argument simply to illustrate the value of EAS.
Neither the P47 or the Bf-109 can achieve 0 mph EAS at 100K. They are unable to produce any power at that altitude.
However aerodynamically, the P47 and Bf-109K are traveling faster through the air.
The SR-71 requires a large amount of thrust in comparison to either of the WWII fighters. It has much higher drag forces acting on it.
There is no discrepancy. Your taking 1/2 the picture and trying make it the whole picture.
It's a nonsensical argument as explained.
I think I see where your erroneous thinking has come into this. You think I made a case that the Bf-109K is faster than the P47M, right?
You do think like a gamer. You are not well versed in the basics of aerodynamics. Those are not meant to be insults, just the facts of your behavior.
Assuming the altitude listed for the P47M data represents FTH of the turbocharger system.
It is very easy to gauge general performance trends when we use EAS. That quick SWAG tells me that in general anything below FTH for the Bf-109K it will be faster than the P47M. However, this trend will change as we pass FTH as the Bf-109 does not have as high a ceiling as the P47M.
That is what my SWAG showed. Not some asinine blanket statement.
I selected 600 mph TAS because I thought it was subsonic and indeed it is .91.
In fact, of course the F-15 is considerable larger than these planes, proportionally, it is probably not generating a whole lot more thrust than the piston powered planes at there optimum.
In reality, there is only one airspeed for airplane.
There is nothing in the air that passes the aircraft at the EAS velocity. TAS is real speed, EAS is calculated. You claim all airspeed is calculated. That is usually true because of errors in measureing. However if we could measure the air molecules passing the aircraft directly, say with a laser, which I know they were working on once (I was the responsible engineer for the air data computers for the TACIT BLUE aircraft which is now in the AF museum), it would show TAS and not EAS.
My argument was (and is) that EAS alone, without the understanding of the thrust available to maintain EAS, is not a valid way to predict aircraft performance at other altitudes.
Originally Posted by Crumpp
It is the faster of the two aircraft. Your whole argument is nonsensical.
Do you understand about the important of dynamic pressure and its relationship to aircraft performance? I really don't think you have a clue about it.
This is lack of understanding of the basic fundamentals.
I will give it my best shot to help you out.
For example:
It is a fact that the coefficients of Drag represents the ratio of drag pressure to dynamic pressure and equals DRAG PRESSURE / DYNAMIC PRESSURE.
If we want to compare our Bf-109 and our P47 using TAS, any idiot can see that the P47 is the much faster aircraft, right!
Well if we compare our DYNAMIC PRESSURE between these two aircraft using TAS:
P47 at FL325 467mph * 1.47 = 686fps
q=.5rV^2 = .5*.000840785 slugs * 686fps^2 = 197.8 psf
Bf-109 at FL24 440mph * 1.47 = 6478fps
q=.5rV^2 = .5*.00110327 slugs * 647fps^2 = 230.9 psf
Wow! Check that out. The slower aircraft has higher dynamic pressure! That can't be if our planes are under the same conditions.
Dynamic pressure is a function of speed:
q=.5rV^2
If our planes are under the same conditions, then the faster one MUST have the higher dynamic pressure. It's our frame of reference and I am sure you know how important that is in physics.
Of course we can ignore the science and just go ahead with a silly comparison of airplanes under very different conditions using TAS.
davparlr says:
Of course the pressure is higher in the second equation because the medium in which it is traveling is denser (more slugs)! The value of the force has increased because it requires more effort to go through a denser medium. You can ride in a boat at 10 mph with your hand out and feel a slight pressure from the air. If you put your hand in the water, it would feel it could be snatched off. That is not because you are going faster through the water than through the air, you are not; it is because the water has many times the density of air causing a lot more drag. This also occurs, to a lesser extent, in the air as we go from a higher altitude to a lower altitude. The increasing density of the air causes the force to increase without any change in airspeed.
The equivalent airspeed is a direct measure of the incompressible free stream dynamic pressure. It is defined as the true airspeed multiplied by the square root of the density ratio (air density at some flight altitude over density at sea level). Physically the equivalent airspeed is the speed which the aircraft must fly at some altitude other than sea level to produce a dynamic pressure equal to a dynamic pressure at sea level.
it would show TAS and not EAS.
Looking for some more in-depth info on this last varient of the venerable 109 series. Also would like some opinions on how it stacks up in high alt combat vs. the P-47D. Done some self research online but so far havn't found enough to satisfy.