Bf-109K (1 Viewer)

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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!:x-mas:

All the best,

Crumpp


You still have refuse to answer my inquiry on the following examples

Crumpp, you have taken a specific altitude and a specific airspeed for a Bf-109K4 and compared that with a specific altitude and specific airspeed for a P-47M an stated that the K is faster than the M. I have shown that you can take other specific airspeed and altitudes and, using your logic, come up with a completely different conclusions. You have ignored commenting about that. Instead of addressing these descripancies, you have become abusive.

Two more examples I would like you to explain:

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.

SR-71 flying at Mach 3 at 100,000 ft. Using all the appropiate formulas for calculating TAS and EAS for supersonic flow we get a TAS of 2048 mph and a EAS of 238 mph. You may say that both the P-47M and Bf-109K4 is going faster than the SR-71 because their EAS is higher but I bet you a bottom dollar that the SR-71 would make it from LA to NY in a whole lot less time than the other two aircraft.


So here is a list of the plane discussed in descending EAS values , and according to you, the fastest one is at the top and the slowest one is at the bottom.

Bf-109K4, at 24k ft, TAS = 440mph, EAS = 299 mph

P-47M, at 32.5k ft, TAS = 467mph, EAS = 272 mph

SR-71, at Mach 3, 100k ft, TAS = 2048 mph, EAS = 238 mph

F-15, at 55k ft, TAS = 600 mph, EAS = 209 mph

It seems intuitively obvious to me that EAS is not an accurate way to compare aircraft airspeed.

Crumpp please address these items:

1. 440mph / 1.4678<SMOE FL24> = 299 mph EAS
467mph / 1.71295<SMOE FL325 = 272mph EAS

440mph / 1.4678<SMOE FL24> = 299 mph EAS
451mph / 1.4678<SMOE FL24> = 307mph EAS

430mph / 1.71295<SMOE FL325> = 249 mph EAS
467mph / 1.71295<SMOE FL325> = 272mph EAS


Why does the first equations make the Bf-109K4 faster than the P-47M ("The Bf-109K4 is the faster of the two aircraft according to this data") and the other two do not make the P-47M faster than the Bf-109?

2. If EAS represent the true (verses true airspeed) airspeed of an aircraft, would you say that the two piston power planes are faster than the F-15 and SR-71?
 
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.

I think this statement is self evident and a good indicator.

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.

There is no need for me to be insulting.
 
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! :x-mas:

Soren, because of mutliple discussion we have had, I have gained a high regard for your aerodyamic expertise. I know it would be a pain, but could you review my comments and discuss with me any errors I could have made or if they are confusing?
 
I think this statement is self evident and a good indicator.



There is no need for me to be insulting.

I am not asking you to be insulting, I am asking you to exlain an apparent descreptancy. I will make it simpler. Just tell me why you have determined that the Bf-109K4 is faster because of this comparison

440mph / 1.4678<SMOE FL24> = 299 mph EAS
467mph / 1.71295<SMOE FL325 = 272mph EAS

and yet this comparison is disregarded. The calculations are the same, only the conclusion is different. If your statement was true, wouldn't the Bf-109K4 still have a higher EAS?

440mph / 1.4678<SMOE FL24> = 299 mph EAS
451mph / 1.4678<SMOE FL24> = 307mph EAS
 
You think like you're in a car.

Aircraft are machines of the air.


Crumpp

Okay, lets talk about this at the molecular level. You're in a car at sea level traveling 50 mph. Up ahead is a sign and a single air molecule is hanging around in the air beside it. You stick out your hand and hit the air molecule. You and your hand are going 50 mph and the molecule is moving zero. The collision make a minute impact on your hand. You are now a 10000 ft and ahead of you is a sign and beside the sign is an air molecule not moving. You stick out your hand and strike that air molecule. You hand is going 50 mph realtive to the air molecule (the same closure speed as to the sign), the same speed as it was at sea level. Since the weight is the same for molecule, and the impact speed of your hand on the molecule is the same, the impact pressure of that one molecule is the same as the one at sea level. Lets see, two molecules, same mass struck by a hand going the same speed, 50 mph, therefore, same impact force. The difference in real life, and why the force is different, is because your hand strikes many more molecules at that instant at sea level than it does at 10,000. The speed hasn't changed, only the amount of air molecules struck. It doesn't matter if you are in car or an aircraft, the aerodynamics is the same.
 
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.

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.

I am asking you to exlain an apparent descreptancy.

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.


All the best,

Crumpp
 
So.........can anyone add further thought on how maneuverable a 109K is at high altitude in comparison to the P-47? :|

oh and Merry X-mas everyone. :)
 
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.........
 
I'm still confused.

You should be confused. A wonderful job of muddying up the waters has been done in this thread to the benefit of one.

Now instead of folks learning something, everyone reading this is confused.

Why? A supersonic flow problem such as the one below is well beyond the scope of this thread. That fact it was even used as an example speaks volumes.

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.

The forces the aircraft traveling in the supersonic realm are not on the same scale as what the P47 and Bf-109 are experiencing. We can make no comparison between supersonic and subsonic flight.

It is a nonsensical comparison.

There are some methods of estimating transonic drag rise but none of the work in the supersonic realm. We could SWAG the RAM rise too but that would be useless exercise since our drag rise does not work for supersonic flow. It only works for from the transonic realm up to Mach .95.



All the best,

Crumpp
 
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.........

Not usually. I always prefer acredited book sources over Google, or what others are telling (or yelling in some cases) However I did just recently spend close to $1000.00 purchasing most of Christopher Shores' series detailing day to day air operations as part of my reserach project. (Including his out of print "Fighters over x" series.) Apologies for the name dropping but as one might imagine, my budget for new book purchases is up for the time being. :p I'm not above taking advice or listening to someone who knows what they are talking about or happens to know something I don't.

As I mentioned in the beginning of the thread, my library purchases also tend to focus on air history and campaigns vs. books dedicated to individual aircraft types. I'd need a whole new bookcase if I did that. Worse....even if i purchased the recommended books, i'm not sure that they would have the info I was curious about as not all do. (for example, the old title I have devoted to USN naval fighters of WWII....it has the expected stats.....ceiling, powerplant specs....max speed etc...but nothing regarding roll and turn rates etc) Should I ever win Lotto however, concerns over the size and cost of my library would go out the window along with my crap job. :twisted:

Having come across this site recently, and having read one poster in the Best Fighter III thread give one of the better P-51 breakdowns i've seen recently, I thought maybe someone might have some info on the 109K and how it stacks up.

I didn't expect the responses to be so complicated or etherial however! :oops:
 
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.

I won't disagree with you on this on the SR-71. I only wanted to show that no matter how fast your aircraft is going, EAS will drop off with altitude. By the way, I did see that you verified my data for the SR-71. But in general, supersonic comparisons with non supersonic performance is not a safe place to be.

Same goes with your F-15 comparison. It's nonsensical comparison as the P47 and Bf-109 are both subsonic designs.

I don't agree with you on this. I selected 600 mph TAS because I thought it was subsonic and indeed it is .91. Except for limiting Mach on the prop jobs, if they could produce the same thrust at 55k as they did at the points noted, it is reasonable to assume they could achieve a similar TAS, in other words, maintain the same EAS. 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.

However we will put on our pretend caps and pretend that there is validity to your argument simply to illustrate the value of EAS.

No doubt about it. But when estimating airspeed performance for an aircraft at various altitudes, thrust available must be considered.

Neither the P47 or the Bf-109 can achieve 0 mph EAS at 100K. They are unable to produce any power at that altitude.

Exactly! The reason the Bf-109K cannot meet the airspeed of the P-47M at 32k ft is that it is unable to generate the necessary thrust to make the EAS.

However aerodynamically, the P47 and Bf-109K are traveling faster through the air.

This is where we continue to disagree. In reality, there is only one airspeed for airplane. That speed is the rate at which that aircraft passes a molecule of air, or a mass of molecules of air. When an SR-71 at Mach 3 passes a non-moving (no wind) molecule of air, the speed differential between the molecule and the SR-71 is approximately 2000 mph. or TAS. Now, how those molecules affects the aircraft maneuvering and flight characteristics is another thing. In addition to TAS, that depends mostly on how many molecules are impacting, causing drag, lift, etc. For this kind of performance, TAS is modified by density (no. of molecules in a given volume) and EAS is generated that gives equivalent performance over a constant EAS value. 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.

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.

Yeah, the supersonic flight tends break down the thrust vs. EAS curve.



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 will agree with this on supersonic airflow

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?

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.

"The Bf-109K4 is the faster of the two aircraft according to this data."

I am not sure I am the only one who read it that way

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.

Well, it was confusing, especially when I calculated that the EAS of the P-47M was higher at the same altitude where the Bf-109k was calculated.


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.
 
I selected 600 mph TAS because I thought it was subsonic and indeed it is .91.

You are correct.


I was looking at Knots at a quick glance to an altitude table. Since the basic concepts are not correct, I did not bother to calculate anything out.

However that does not change the fact Mach .91 is well into the transonic realm and compressible theory applies. The drag forces it must over come are nothing on the scale of the P47 or Bf-109 experience in level flight.

It remains a very poor example.

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.

It is definitely generating an order of magnitude more thrust than the P47 or Bf-109. This statement indicates you have no idea of the basics concepts of power producers and how they develop thrust.

The F-15 is a thrust producer and follows typical thrust producer characteristics. It has considerably more drag to overcome and needs all of that excess thrust to counter transonic drag rise.

Basic stuff, once again.

In reality, there is only one airspeed for airplane.

Baloney.

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.

Name one TAS speed where aircraft performance occurs?

You cannot other than Vy. Vy only because of the density relationship with CAS. There is a reason we use EAS for performance comparison. It has been proven mathmatically and by the laws of physics.

What is Vs1 at sea level in TAS? What is Vs1 at 20,000 ft?

For the reader,

L/D ratio and angle of attack is fixed by design. The same L/D ratio occurs at the exact same Angle of Attack every time. Only a design change or a configuration change will alter this relationship.

There are very good reasons why EAS is used for comparing aircraft performance by engineers.


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.

That is completely different from your original claim that EAS was not used for aircraft performance comparison. Now you are changing your tune.

I don't really care what you claim to have done or worked on. Your grasp of the basics is rickety at best.

All the best,

Crumpp
 
You gloss over this:


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.


In fact you regurgitate the very reasons we use EAS to compare performance. Using EAS eliminates the density effects of our altitude!

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.

Read questions 1 and 2. Notice what they want the answer's in when comparing aircraft performance!

http://www.aer.bris.ac.uk/course_material/1st_year/papers/05aeng11301q.pdf

it would show TAS and not EAS.

That's because we cannot navigate without TAS speeds.

All the best,

Crumpp
 
I don't see any credible way that anyone who attended an aerodynamics class on any level could forget having to deliver the vast majority of answers in EAS.

All the best,

Crumpp
 
Let's get this discussion back on track.

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.

What altitude Nik?

All the best,

Crumpp
 
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