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I'm not so sure. I once made my 9th grade Algebra teacher throw up her hands in despair.
I sense a PM coming your way pleading for mercy.
Bf-109K
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I'm not so sure. I once made my 9th grade Algebra teacher throw up her hands in despair.
I sense a PM coming your way pleading for mercy.
davparlr
Senior Master Sergeant
Perhaps the following will explain my confusion.
You wrote earlier-
This statement is entirely incorrect. More in detail.
Let's look at TAS. It is defined like this-
True airspeed (TAS) is the speed of an aircraft relative to the airmass in which it flies, i.e. the magnitude of the vector difference of the velocity of the aircraft and the velocity of the air. Under zero wind conditions and in horizontal flight, this is equal to the speed over the ground.
So, in your example, assuming no wind, the first aircraft at sea level is going 200KEAS which equals 200KTAS. According to the definition above, the aircaft has a ground speed of 200 kts (also, a speed through the air mass of 200kts). Now the second aircraft at 35,000 ft is going 200KEAS or 326KTAS. Now, according to the TAS definition, this aircraft has a ground speed of 326 kts (and a speed through the air mass of 326kts). This is why high altitude aircraft can get such good milage.
Both aircraft are indeed going the same EAS but the aircraft at 35000 ft. is going much faster, through the air and over the ground, than the one at sea level by everyone's definition.
You claim that the aircraft with the highest EAS is the faster of the two. We just showed that, in reality, the one with the TAS advantage is the faster (through the air and over the ground). Now, to show the uselessness of EAS without some other supporting data lets look at this set of data.
At 24000 ft the P-47M has a TAS of 451 mph. Now according to your formula, We have.
440mph / 1.4678<SMOE FL24> = 299 mph EAS
451mph / 1.4678<SMOE FL24> = 307mph EAS
Now you would say, that the P-47M was faster of the two aircraft. This is different from your initial conclusion.
Now, let's do the reverse. The Bf109K4 at 32500 ft has a TAS of 430 mph. Now we have
430mph / 1.71295<SMOE FL325> = 249 mph EAS
467mph / 1.71295<SMOE FL325> = 272mph EAS
Again the P-47M has a higher EAS (much higher), thus higher speed (according to you), but again, you originally said that the Bf-109K4 was the faster of the aircraft. There is a problem with your theory. It does not take into account the HP curves of the two aircraft. I think you will find that the Bf109K4 (and all aircraft, since EAS roughly represent F or drag on the aircarft) requires a certain fixed hp to maintain a constant EAS. However, as the aircraft climbs, the hp is not constant and starts to drop off and it cannot maintain EAS (supercharger operaion also affect hp curve). In this case it drops off quite a bit faster than the P-47M (they start out a roughly an equal EAS at 24k ft but the Bf-109K4 EAS drops quite a bit lower than that of the P-47M by 32.5k ft.
EAS is useless in comparing aircraft at different alitudes without some idea how hp is behaving. It is accurate at the same altitude but then TAS is by far a better estimate.
I was able to find a couple of charts that showed EAS in all the flight test reports and contractor reports. This was on the F4U and showed EAS as a function of hp. A light went on and I realized that this was very useful in calculating aircraft airspeed performance if you did not have a test. By knowing the hp required for an EAS (maybe by a test at sea level or computer), and by knowing the hp output of an engine at an altitude, the EAS can be found and one can calculate TAS of the aircaft at that altitude. I suspect this is one of the major uses for EAS. Apparently it is also used in other performance items other than speed.
For this site use, TAS at a specific altitude, which is data that is typically readily available, is the best method for comparing aircraft performance. And since air combat between two aircraft usually occur at roughly the same altitude (pre-AA missile environment), this is plainly satisfactory. EAS, which is not readily available, is not worth calculating and just confuses the issue. Again, without horsepower behavior over altitude, comparing aircraft airspeed of aircraft at different altitudes, whether using EAS or TAS, is not a valuable effort.
I would bounce this off one of your aero friends. I am always willing to know when I am wrong.
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.
Only because of the density effects of altitude, because our air is less dense, our dynamic pressure is less at a given velocity. Hence we have a much larger difference in our TAS and our EAS.
It is useful for all aspects of aircraft performance, see above.
Don't add any silly uninformed leaps of logic to it. Just leave it at that.
From an old college textbook:
It's my opinion that you have never worked on any aeronautical science field or related to aeronautical engineering. I think your posturing was complete baloney.
You would at least have a grasp of the basic fundamentals.
Airspeed is a step by step process. You cannot skip one airspeed type and directly convert to another.
Your "discovery" is a simple basic fact of aerodynamics. If you want to know the TAS, you first have to know the EAS. If you want to know the EAS, you first have to know the CAS. In order to find the CAS, you have to have the IAS.
So the big mystery of finding EAS before finding TAS is solved!
On your other observation, you don't need EAS to get the effects of power. Power effects maintain the same ratios over any given velocity measurement. The effect is relative. Just keep track of your units!
Some airspeed's are more useful for certain things. IAS is very useful for flying the plane. TAS is useful for finding our Ground Speed and flight planning.
EAS is useful for performance comparisons.
Neither EAS nor TAS is very useful for comparing aircraft data recorded over different atmospheric models with different standards for the application of compressibility affects. Comparing data recorded in Germany by Mtt directly with data recorded by North American is silly and meaningless unless the data is converted to the others standards.
Obviously you do not realize that if we have TAS we do not need power data to figure EAS. All we are doing is accounting for the density effects of the atmosphere on our airspeed. Eliminate the effects of altitude and we have our EAS.
Since you felt so compelled to brag about your being an engineer and working in the aerospace industry, what part of it did you work in, again?
Honestly, this about as basic as you can get and all of this would be covered in a 100 level Aerodynamics course. It is readily apparent you have had absolutely no formal education whatsoever in this field.
All the best,
Crumpp
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- #84
Sure!
As long as the data is all converted using the same standards.
See, despite some uninformed speculation, all of this data is calculated.
The "flight test data" still has to be converted from actual to standard conditions, the PEC, CEC, and density effects still have to be applied.
When you get right down to it, all the data calculated!
All the Best,
Crumpp
- Thread starter
- #86
all-right. That clears up some confusion. 8)
Now in regards to the chart I posted in post#51 on page 4 showing estimated roll and turning rates at x speeds for several major airframes. Is that useful for a basic comparison and if so, does any similar info exist for the Bf-109K and P-47D/M?
Now in regards to the chart I posted in post#51 on page 4 showing estimated roll and turning rates at x speeds for several major airframes. Is that useful for a basic comparison and if so, does any similar info exist for the Bf-109K and P-47D/M?
You cannot use same altitude TAS when comparing a report written in Germany by Mtt on an airplane flown in March and make any meaningful comparison with a report written in Britian on a Plane flown in August by the Boscume Down.
I would say it is not useful.
Some very large unknowns:
1. Condition of the aircraft?
2. Is all the data collected and processed using the same formulation and methodology?
3. Was the onset of CEC applied to a universal standard?
4. Was the atmospheric model the same?
I have some reports I can share. IIRC it has both the P47 and Bf-109 series roll rates. The data is not useful for specific comparison. You cannot say, plane X out rolls plane Y by a specific rate. Frise ailerons have a very wide swath of normal range.
All you can do is get a general idea of most probable trends in performance. The term for it is "in the realm of significant digits it is correct".
All the best,
Crumpp
Hi Crumpp,
>It is the faster of the two aircraft. Your whole argument is nonsensical.
Hm, I think Davprlr actually has a point. Equivalent Air Speed is a useful tool, but it works best when we can assume that the available propulsive power is proportional to the density of the ambient air, which is a commonly used approximation - but only an approximation.
Non-linear supercharger curves, the effect of exhaust thrust, Mach-dependend propeller efficiency etc. can affect the EAS comparison - Davprlr points out that top speed EAS varies with altitude even for one aircraft, which demonstrates that we can't simply pick one certain top speed EAS and consider it representative for the type.
EAS undisputedly is very useful to compare relative performance if only one data point for each aircraft is given ... as often the case with lesser known types.
Merry Christmas,
Henning (HoHun)
>It is the faster of the two aircraft. Your whole argument is nonsensical.
Hm, I think Davprlr actually has a point. Equivalent Air Speed is a useful tool, but it works best when we can assume that the available propulsive power is proportional to the density of the ambient air, which is a commonly used approximation - but only an approximation.
Non-linear supercharger curves, the effect of exhaust thrust, Mach-dependend propeller efficiency etc. can affect the EAS comparison - Davprlr points out that top speed EAS varies with altitude even for one aircraft, which demonstrates that we can't simply pick one certain top speed EAS and consider it representative for the type.
EAS undisputedly is very useful to compare relative performance if only one data point for each aircraft is given ... as often the case with lesser known types.
Merry Christmas,
Henning (HoHun)
Hello Crumpp
"A design that, like its contemporaries the Ta-152 or Tempest II, represented the pinnacle of propeller driven technology that just was not quite ready for service during the war in Europe."
to my understanding Tempest II missed the war altogether so I'd say that it 's service entry was later than that P-47M.
If we look 56 FG missions from 10th March 45 onwards when the P-47M pilots got their second kill according to Frank Olynyk, 56 FG last P-47D kill had been very early in Feb 45 according him,
10.3.45 23 Jugs up no mentions on aborts
11.3.45 49 Jugs up, one Jug crashed in England, pilot killed
12.3.45 51 Jugs up, six aborts and one landed in France on way home
14.3.45 "A" Group 36 Jugs and "B" Group ? Jugs, 3 Jugs landed on continent because of mechanical problems and one crashed into Channel, pilot killed.
15.3.45 again "A" and "B" Groups, no numbers, 6 hours mission, one take-off crash, pilot killed.
24.3.45 first mission, 24 Jugs up, no mention of aborts
24.3.45 second mission 36 Jugs up, no mention of aborts
Source McLaren's Beware the Thunderbolt!
Clearly problems on some missions in the first half of March, but nothing near your 50% abort rate, may I ask Your source(s)?
Juha
"A design that, like its contemporaries the Ta-152 or Tempest II, represented the pinnacle of propeller driven technology that just was not quite ready for service during the war in Europe."
to my understanding Tempest II missed the war altogether so I'd say that it 's service entry was later than that P-47M.
If we look 56 FG missions from 10th March 45 onwards when the P-47M pilots got their second kill according to Frank Olynyk, 56 FG last P-47D kill had been very early in Feb 45 according him,
10.3.45 23 Jugs up no mentions on aborts
11.3.45 49 Jugs up, one Jug crashed in England, pilot killed
12.3.45 51 Jugs up, six aborts and one landed in France on way home
14.3.45 "A" Group 36 Jugs and "B" Group ? Jugs, 3 Jugs landed on continent because of mechanical problems and one crashed into Channel, pilot killed.
15.3.45 again "A" and "B" Groups, no numbers, 6 hours mission, one take-off crash, pilot killed.
24.3.45 first mission, 24 Jugs up, no mention of aborts
24.3.45 second mission 36 Jugs up, no mention of aborts
Source McLaren's Beware the Thunderbolt!
Clearly problems on some missions in the first half of March, but nothing near your 50% abort rate, may I ask Your source(s)?
Juha
davparlr
Senior Master Sergeant
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.
You found me out. I am really a thirteen year old gamer.
Huh? Let's see, we have TAS, EAS, and hp. Not many units to keep track of.
This, I agree.
This is true for some aircraft performance parameters, just not for airspeed comparison at different altitudes
I did assume that Germany has the same atmosphere as the US. I wasn't aware that compressibibity calculation were different in Germany. Soren, can you educate me on this? I guess you mean we must convert metrics to english or vice versa? I guess I should have thought of that.
All I was saying is that in order to maintain an EAS as you climb, hp must be constaint. Since hp is never constant in climb, predicting EAS at a different altitude, without the hp generated at that altitude cannot be done. If an aircraft is making 350 mph EAS at sea level generating 1000 hp and it climbs to 10000 ft. the EAS cannot be predicted because the engine may only be generating 800 hp therefore the plane is going to be going slower and having a lower EAS. If the engine was still generating 1000 hp, the EAS would still be 350 mph.
Only because you called me a gamer.
And now I am an uneducated idiot gamer?
Using your quotation, here is a simpler example of the difference between EAS and actual speed. If you drive at 50 mph at sea level and stick you hand out, you will feel a certain amount of pressure, this represent EAS which would also represent TAS. If you go to the mountains at 10000 ft., and 50 mph, and stick you hand out, the pressure on your hand would be less. It is not less because you are going slower through the air, you are not, but rather because the density of the air is less (the air is thinner). You are now going at a lower EAS (< 50mph) but your actual speed through the air is the same (50mph). In order to calculate your actual speed from measuring the pressure on you hand (assuming there is no wind) you would have to correct the pressure felt by some factor to correct for the density change in the air (in other words calculate TAS). This is an accurate representation of what is required in finding your true speed in an airplane. First you measure dynamic and static airpressue (indicated airspeed), correct for any installation error (calibrated airspeed), correct for compressability (air is compressable and therefore generates error) (equivalent airspeed), and then you must correct for atmospheric density changes (air pressure and temperature) (true airspeed), which would then show your actual speed through the air mass.
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.
Boy, I hope I kept track of my units!
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 appears intuitively obvious to me that EAS is not an accurate way to compare aircraft airspeed, but what do I know, I'm an idiot.
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?
True airspeed is called true because it represents the actual speed of an aircraft through an air mass. EAS does not.
If my question above confuse you, take them to one of your aero buddies which I really think you should do anyway.
There are many young airplane enthusist on this site that are seeking to understand the froces that affect aircraft and I feel that are you are misleading them in relation to EAS and airspeed comparison.
Sorry guys for writing so much but I think that it is important for everyone to understand accurately the relationships of the various airspeeds.
davparlr
Senior Master Sergeant
MERRY CHRISTMAS everyone. I hope you all have a great holiday time.
evangilder
"Shooter"
While you give good information in your posts, the above examples are the kind of statements that I will again ask you to stop. You have information to share, great, please do. Keep the insults and personal attacks out of it.
Merry Christmas, Henning. I hope things are going well for you!
He does not have a point. He does not understand the basics and that is obvious.
Power effects are irrelevant to the type of airspeed as long as you maintain the same airspeed classification and the ratio relationship.
Using EAS makes "altitude changes much easier to do this in fact. Only difference in using EAS and "changing altitude" is that we only have ONE parameter to change in our analysis, the power!
You understand what I am saying right? If you want to change altitude, all we have to do if our analysis uses EAS is change the power available to the value at that altitude.
That is why it is industry standard.
TAS assumes density effects at altitude. Any values calculated using the TAS velocity are only appropriate for that specific altitude.
Using EAS eliminates this as a step and there is no need to recalculate all of our values for density effects.
It is then much easier to convert EAS to TAS if we want to account for density effects. The differences in EAS to TAS velocity are solely based on atmospheric properties alone. Two aircraft at the same EAS will have the same TAS if they are at the same altitude.
However if we want to compare aircraft performance, then using EAS puts the aircraft under the same conditions which is essential for a good comparison.
All the best,
Crumpp
EAS is the only acceptable way to compare aircraft speeds at dissimilar altitudes. Otherwise it is impossible to tell if the plane is really faster or if it is just receiving the benefits of being higher in altitude.
Any basic or entry level aerodynamics class will teach you this!
Climbing is a different condition of flight and uses different formulation. If you had some formal education in aerodynamics, you would know this. You would also know that using some basic calculus to derive the change in one value based of the relationship of another value is very much in the realm of possibility.
There are different techniques and formulation out there in the community but most are based on this simple principle.
Here is where you are making your errors in logic.
You think like you're in a car.
Aircraft are machines of the air.
On the units, you have completely misunderstood what I wrote to you.
We have to maintain the same ratio relationship and units.
In other words, if we wanted to figure our power required at a new velocity, we could use the ratios:
We could use IAS, CAS, TAS, or EAS for our Velocity as long as we are consistent.
These boards do not accept MathType fonts so it makes it very hard to display equations.
All the best,
Crumpp
Hi Crumpp,
>If you want to change altitude, all we have to do if our analysis uses EAS is change the power available to the value at that altitude.
I believe that's what Davprlr meant to point out too when he contrasted speed data points of the Me 109 and the P-47 for identical altitudes
It's my impression that at the core of the issue, there isn't actually that much of a disagreement after all.
In any case, this looks like a good example for my personal hobbyhorse - the overriding influence power plants have on aircraft performance!
Regards,
Henning (HoHun)
>If you want to change altitude, all we have to do if our analysis uses EAS is change the power available to the value at that altitude.
I believe that's what Davprlr meant to point out too when he contrasted speed data points of the Me 109 and the P-47 for identical altitudes
It's my impression that at the core of the issue, there isn't actually that much of a disagreement after all.
In any case, this looks like a good example for my personal hobbyhorse - the overriding influence power plants have on aircraft performance!
Regards,
Henning (HoHun)
davparlr
Senior Master Sergeant
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.
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
davparlr
Senior Master Sergeant
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!
So, you agree with this statement.
"440mph / 1.4678<SMOE FL24> = 299 mph EAS
467mph / 1.71295<SMOE FL325 = 272mph EAS
The Bf-109K4 is the faster of the two aircraft according to this data"
If so, you must agree with this-
So here is a list of the plane discussed in descending EAS values , and according to Crumpp, 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
Therefore, the Bf-109K4 and the P-47M are both faster than the SR-71 and F-15 because they have a higher EAS.
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