Allied tests of captured Bf-109's

[drgondog]

Ok fair enough Bill, I apologize for the sarcasm then. And let's be objective about this.

About the slats first;

My thesis is not and has never been that the slats deploy fully in conditions close to straight flight, and I honestly can't really understand how you interpret it that way either. Also I don't bring forth any thesis on this subject only the facts.

You need to understand that the slat deployment process is gradual, the slats starting to deploy at a very low AoA's, not fully extending ofcourse, but extending out slightly. And so in climbs, landing approaches and slow turns a pilot wont even notice the slats popping out unless he looks at them as the deployment process is so slow and the slats themselves not fully extended. However if the pilot banks hard where the Critical AoA of the original airfoil is reached nearly instantly, then he will feel a very slight notch on the stick as the slats pop out to their fully deployed position almost instantly.

Furtermore the slats aren't linked together, they're completely independant of each other, and thus so is the deployment process. So if one wing is starting to stall before the other then the slat on that wing is also further extended.

As Mark Hanna puts it:
"As the stall is reached, the leading-edge slats deploy-together, if the ball is in the middle and slightly asymmetrically, if you have any slip on."


Anyway got get back to work now, will address the rest later.

PS: Glad we can discuss this in a calm objective manner Bill.

Soren - this is the statement which triggered my comments

Oh when it comes to the issue of pressure distribution and boundary layer seperation I see things quite clearly Bill, and nothing of what I explained is wrong, nothing.

The slats start to deploy at very low AoA's as the pressure on the top of the wing becomes lower than the pressure under the wing, making the slats extend. Quite simple.

Typically leading edge slats deploy at near stall conditions. Low angle of attack typically is not near stall for any aircraft until low speeds. Typically at medium to high speeds in normal flight regimes the stagnation pressure on the zero lift/flow diversion point..

from a theoretical point the flow is brought to a specific point on the nose of the airfoil and changes its momentum at that point - then travels over the top and bottom surface of the airfoil.

So, the slat at that point of the wing for free stream impingement, is experiencing 'positive pressure (relative to freestream) then as the flow travels normally back and over the top surface, the pressure distribution in comparison to the free stream (and the stagnation point on the slat) becomes rapidly 'negative' over the surface of the airfoil for the maximum lift region, then drops rapidly to freestream pressure as separation begins and finally to freestream pressure in the region of the boundary layer wake.

So, from my perspective the only way a slat should deploy is when the pressure behind the slat is at same or slightly higher dynamic pressure behind the slat as the dynamic pressure on the nose of the slat - which is a typical stall condition.... otherwise the slat is conceptially 'pressed' against the wing surface behind it.

If the slat deployment occurs in level flight at low AoA versus either level flight at high AoA at low speed or medium AoA in a normal turn, then I would not happily fly that a/c because it implies that indicial gusts in normal flight or even in a relatively slow turn could cause the slat to deploy.

The F-86 slat deploys at high AoA. I had read from Mustang Designer that it was a close design approach to the Me 262 slat... so I am confused by your statement that the Me 109 slat deploys at low AoA for all the reasons I just relayed above.

If you were to draw a free body diafram mappring out the forces on the leading edge slat at low AoA, how would you describe it..

 

[Soren]

You misunderstand me abit Bill.

The slats don't start to extend at 0.1 degrees AoA, but they don't start first at 15 or 16 degrees either (Assuming the critical AoA is 17 degrees). Infact there's a MTT document mentioning the AoA at which the slats start to extend, and it's low (Compared to the critical AoA when they're deployed), around 10 to 11 degree's IIRC.

Holtzauge has the data as he posted it months ago somewhere on this forum.

As for the F-86's slats, they're exactly the same as the Me-262's, no difference, except they drop down abit on deployment, but they operate just the same.

Moving on to the drag debate and the bubble canopy,

Looking at Lednicer's figures I do find ONE thing strange, and that is the smaller wetted area of the P-51B, AFAIK the P-51B has a larger wetted area than the P-51D which hasn't got that big aft fuselage anymore. Ofcourse the D series has a slightly larger wing as I have already mentioned (enlarged root chord), but that doesn't make up for the loss of a huge chunk of the aft fuselage area. Don't you find that strange ?

Furthermore just from experience bubble canopies are known to cause higher drag than the razor back configuration, the sudden drop of the rear canopy causing boundray layer seperation and thus a turbulent flow to the rear, the reason behind the directional instability - a problem which also plagued the P-47 when it first got the bubble canopy, and even with the added dorsal fins the problem was never fully solved.

 

[Hunter368]

Good debate guys

 

[drgondog]

You misunderstand me abit Bill.

The slats don't start to extend at 0.1 degrees AoA, but they don't start first at 15 or 16 degrees either (Assuming the critical AoA is 17 degrees). Infact there's a MTT document mentioning the AoA at which the slats start to extend, and it's low (Compared to the critical AoA when they're deployed), around 10 to 11 degree's IIRC.

You might see my confusion as 10 to 11 degrees is way above my own standards for 'low AoA - at least not for a high performance fighter . So when you said low AoA I kept asking myself 'why would anyone design that way.

Having said that.. it is perfectly sensible to have mechanical slats and fowler flaps for STOL a/c as the should be deployed at takeoff.

Holtzauge has the data as he posted it months ago somewhere on this forum.

As for the F-86's slats, they're exactly the same as the Me-262's, no difference, except they drop down abit on deployment, but they operate just the same.

No doubt about operation mode - but they (86 slats) would operate near local stall at whatever the AoA

Moving on to the drag debate and the bubble canopy,

Looking at Lednicer's figures I do find ONE thing strange, and that is the smaller wetted area of the P-51B, AFAIK the P-51B has a larger wetted area than the P-51D which hasn't got that big aft fuselage anymore. Ofcourse the D series has a slightly larger wing as I have already mentioned (enlarged root chord), but that doesn't make up for the loss of a huge chunk of the aft fuselage area. Don't you find that strange ?

I found it somewhat strange.. because I am sure the only external difference between the two a/c externally was the slight increase in the LE Stake on the wing (two places for the D - minus the 'triangular' patch of sheet metal representing the removal of the turtle deck. In all the P-51B would seem to have slightly more surface than the D

Having said that, Lednicer's model, if incorrect on the fuselage wetted area and modelling the 51B with LESS area, would make the surface friction component very slightly lower than it should be.. and consequently the model should predict a slightly higher CDwet for the B than the D if the area was added in.

Furthermore just from experience bubble canopies are known to cause higher drag than the razor back configuration, the sudden drop of the rear canopy causing boundray layer seperation and thus a turbulent flow to the rear, the reason behind the directional instability - a problem which also plagued the P-47 when it first got the bubble canopy, and even with the added dorsal fins the problem was never fully solved.

Actually that is what modelling is all about.

'Known and Well Known' are terms not particularly useful in this discussion. You are the first person that has described the problem -as 'a sudden drop of the canopy causing boundary layer separation and thus turbulent flow to the rear' to me. That doesn't make your statement untrue. On the other hand I was in the modelling business for awhile and have yet to see that occurance in either a wind tunnel or design calcs or model results.

As an example, only a few operational fighters in the USAF or any other modern program from the 1970's forward, in which computer modelling to the sophistication of VSAERO has been available, have ever had anything BUT a bubble canopy. If turbulent flow was aroused then all fighters would have canopies like an F-102 or F-106

Nothing is certain to that extent. I imagine if the Brits had seen Lednicer's model they would have looked at sloping the windscreen more to look at the next stage past it to see whether the Malcolm Hood design was optimal.

The stated design problem for NAA in trying to reduce or eliminate the increased yaw at .7-.8 mach for the D from the B wasn't separation, it was the elimination of the 'long' rudder strake surface as represented by the turtledeck.. had nothing to do with increase to turbulent flow according to their perspective.

Those comments are anecdotally referenced in Both "Mustang" by Gruenhagen and "Mustang Designer" about Edgar Schmeud and the Mustang through F-100 era at NAA.

I suspect, but do not know that the removal of the P-47 turtledeck had a similar consequence.

Thinking it through, if the issue was increase in turbulent flow, the entire rudder and horizontal stabilizer would be affected and why would a small ventral fin help much there. Turbulent flow would not be 'fixed' by a ventral fin.. but the ventral fin area, added well behind the cg at the tail, would be more effective that larger vertical surfaces at or closer to the cg.

As late as 1973 I was involved as a consultant from GE, in various studies using Ansys and Nastran as well as working with GD engineers to look at various F-16 canopy models. The problem to be solved was called in the trade, "The MIL SPEC _Chicken Test".

The theoretical analysis - pre computer finite model analysis - was having a hard time defining the 'certain' design specs for the canopy which would satisfy the wind tunnel drag targets but also satisfy resistance to failure of a 3 pound have frozen chicken 'projectile' head on - to similaute bird strikes at low altitude while in a landing pattern. The problem was both failure and also an associated travelling 'wave' deflection interferring with the space the pilot's head was in.

We solved it by changing the thickness of the canopy at the forward region, then tapered back to constant thickness of the Acrylic Shell - it was an expensive solution... but I saw all the aerodynamics from both a model and wind tunnel test because we also had to consider changing the lines and see what the associated 'aero' effect was to increasing heighth of canopy top.

If you have a reference discussing turbulent flow issues as a result of the bubble canopy I would like to see it and would like to understand the background of both the tests and the resultant design approach to solve.

 

[kool kitty89]

Maybe he should have said 'realitively low AoA'

 

[claidemore]

This is a little off the 'off the topic' topic, lol, but...

I believe it's been mentioned that during the RAE trials of 109E that the British pilots didn't use 'combat flaps' in the 109. I was reading one of the reports (Wing Commander G.H. Stainforth) and noticed this:

The rate of turn obtained was the maximum possible in every case. The effect of putting the flaps down about 10 degrees was tried but this had little, if any, effect.

Claidemore

 

[drgondog]

This is a little off the 'off the topic' topic, lol, but...

I believe it's been mentioned that during the RAE trials of 109E that the British pilots didn't use 'combat flaps' in the 109. I was reading one of the reports (Wing Commander G.H. Stainforth) and noticed this:



Claidemore

The use of flaps in a Mustang did not help in the turn comparisons of the 51 vesus the Spit IX or XIV either for those tests in 1944. There was no mention in what I saw that flaps were used in the 109G vs 51B turn comparisons.

I have seen anecdotal reports expressing some positive results in a turning fight with a 109 but an equal number saying the 51 did not gain an advantage by dropping 10-20 degrees.

 

[drgondog]

The suction issue was braught over from "Best Piston Engined Fighter Ever
"...

I'm not sure that was intentional, but oh well.


I think some of the confusion is coming from interpretaion of terminology. (though most of this, particularly the specifics, is over my head)



Maybe this will help to bridge the canopy issue: How does the Malcolm hood P-51B/C compare to the "birdcage" or teardrop/bubble canopy?

I re-read the report. There is an obscure reference to an experiment in which a 'more rounded and sloped windscreen' tried in 1943, resulting in 12 mph increase in speed at .79 mach for the Spit IX. The comments are on page 88.

A more interesting point is that the 190D (fig 11) with blown hood has a better region of suction/lift on the canopy behind the windscreen than the 190A-8 (fig 10) model. The Table 1 Cdwet also shows a distinct advantage of the 190D over the 190A-8.

The Spit w/malcolm hood shows better suction than 51B but much larger region of positive pressure forward and on the the windscreen.

Speculatively, the Malcolm Hood should be a beneficial addition to the 51B.

It would be interesting to see a 109G with the basic square angle canopy in comparison. I suspect it would be the worst of all the models compared.

Having said all of this, the primary advantage in drag for the Mustang vs the Spitfire and Me 109 was a.) the wing, and b.) the radiator design.

 

[Soren]

I'm abit busy at work so I only have 5 min, so this will be a very short reply..

Having said all of this, the primary advantage in drag for the Mustang vs the Spitfire and Me 109 was a.) the wing, and b.) the radiator design.

Versus the 109 it was only the wing really, since the 109 benefitted from a similar radiator design generating very little drag and a little thrust (Meredith effect).

However I do believe that the Mustangs radiator produced more thrust than that on any other a/c of WW2 except for the Do-335. IIRC it was the same has having an extra 300 HP, not bad..

 

[drgondog]

I'm abit busy at work so I only have 5 min, so this will be a very short reply..



Versus the 109 it was only the wing really, since the 109 benefitted from a similar radiator design generating very little drag and a little thrust (Meredith effect).

However I do believe that the Mustangs radiator produced more thrust than that on any other a/c of WW2 except for the Do-335. IIRC it was the same has having an extra 300 HP, not bad..

Whether Lednicer was correct or not in his interpretation of the difference between the Me 109F and all previous models, he states the different design for better boundary layer control as reported by Brown and Smelt "Aerodynamic Features of German Aircraft", Journal of Royal Aeronautical Society, August 1944. He states from this source that Messerschmidt redesigned the intake specifically to address this drag component, and the new design was incorporated in F and subsequent models.

Your source to the contrary would be?

The actual thrust of the radiator design of the Mustang was far below the calculated value.

I have seen various reference from 18 to 75 pounds, but never higher than 75.. Lednicer discusses some of the reasons why, as discovered in the modelling of Strega in attempts to improve flow characteristics in that area and below/aft the inboard wing/body interface.

What is your source for the Do335 'Thrust" values?

 

[Soren]

Long time no see! Been very busy at work, but now I've got a two week holiday, so nice

Bill,

The DO-335 utilized the exact same radiator design as the P-51, so the gain in thrust would've been similar for both.

 

[Soren]

Whether Lednicer was correct or not in his interpretation of the difference between the Me 109F and all previous models, he states the different design for better boundary layer control as reported by Brown and Smelt "Aerodynamic Features of German Aircraft", Journal of Royal Aeronautical Society, August 1944. He states from this source that Messerschmidt redesigned the intake specifically to address this drag component, and the new design was incorporated in F and subsequent models.

Your source to the contrary would be?

Contrary ?? Bill you've only confirmed what I said.

The Emil's radiator design is completely different from the F series and beyond, the F series and beyonds radiators benefitting from the meredith effect and actually providing a little thrust.

 

[drgondog]

Soren sez -Huh ?

And what's with the sudden paranoia Bill? You seriously think I've been away from the forum because of a discussion we had ? Bill I could care less, besides the discussion was over in my eyes.

And as to suction, well I thought we had settled this already, and yes suction equals drag. A razorback design has less drag than a bubble canopy one, the simple reason being that there's not the turbulent area right behind the canopy creating extra drag. I thought you understood this.

In the Lednicer Model there are three basic values of Pressure assigned to colors.

Red is 'suction', is lower than Freestream pressure, to laymen it is called Lift as it is a force PERPENDICULAR to freestream. In a freebody diagram it is opposite direction to Gravity

Blue - at the base of all the canopies and the intersection of horizontal stabilizer and horizontal stabilizer, is Stagnation Pressure, resulting in a force PARALLEL to Freestream and opposing Thrust.

Lednicer spends some time talking about this (Blue) as a flaw in Spitfire Canopy/windscreen design as well as the benefits of 'suction' (Red) to the 51D canopy

The sudden drop over the top of the canopy is what causes the boundary layer to seperate, causing turbulence to the rear(Hence the stability issue), and therefore extra drag. It's the same with bullets Bill, if you say cut way the boattail you'll get sooner seperation and more turbulence which means more drag, hence why spitzer bullets aren't as drag efficient as boattailed ones.

You are 100% incorrect in both statements. First, there is essentially zero difference in the calculated Pressure distribution between the two (P-51B and D models) aft of the canopy/cockpit area. This is a FLOW model Soren not a STABILITY AND CONTROL MODEL. There is a difference, and one you frequently do not seem to grasp in this discussion

If you read and comprehend the entire reports - you will note that the entire region of Red includes the top surface of the Wings and Canopy top for the P-51D.

The Red includes the Wings of the P-51B (exactly same distribution as P-51D with same wind) and a small portion on the top of the forward Canopy.

The Red includes the Wings (smaller region due to non-laminar airfoil) and no Red on the Top of the Spitfire Canopy and a LOT more BLUE on the windscreen due to 'steeper' angles which Lednicer discusses in detail.

Correspondingly, the P-51B does NOT have a 'low pressure distribution' over the top of the canopy. Why? you should ask? Because the flow over the P-51B (non Malcolm Hood) windscreen separates (as does the Spitfire but further back) and the pressure distribution from that point aft approaches freestream pressures.

Lednicer goes on to illustrate the separation caused by the Stagnation Pressure Buildup on the Spitfire and the subsequent 're-attaching' the Boundary layer on the top of the Canopy to give it better suction than the P-51B.

NET of Lednicers models. P-51D most aerodynamic canopy, P-51B had less lift over top surface but also less Pressure Drag than the Spitfire windscreen.

Fundamentals for you Soren.

Pressure Drag is in fact a function of separated flow and the resultant force is a.) opposite of thrust, and b.) absent Thrust, in the same direction of Free Air stream.

Induced Drag is a function of lift, wing geometry and is a resultant force in opposite direction to Thrust and 'nearly' same direction as freestream flow.

Friction Drag is a function of surface roughness and is a force in parallel to freestream.

All of these DRAG forces will be aligned in a free body diagram to oppose Thrust axis of the body analyzed.

Lift forces in Lednicer's model are ORTHOGONAL to both induced drag and Pressure Drag (and friction drag).. Suction is the Red 'thingy' area represented on Lednicers Wings and Canopy of the 51D.

Repeat - He didn't have a model that had a force (pressure) distribution in orthogonal directions for same values. He didn't illustrate the Red region over the top of the model wings as "PRESSURE DRAG".. any more than the Red region over the canopies

Repeat - RED is LOWER (attached) PRESSURE DISTRIBUTION region than FREESTREAM PRESSURE. Those that are knowledgeable about Aerodynamics will usually call those forces "LIFT"

BLUE is HIGHER PRESSURE DISTRIBUTION region than FREESTREAM PRESSURE. Those that are knowledgeable about Aerodynamics will usually describe those forces as PRESSURE DRAG..

The Model is a Potential Flow singularity distribution model with subroutines and Iterative calculation solution methods to intruduce boundary layer separation. By definition Potential Flow is a perfect inviscous flow so the other modelling capabilities have to be introduced to approach realistic/wind tunnel results.

The areas where there are little diiferences in freestream pressure and the boundary layer pressures are represented by the collage of color different from RED and BLUE.



Hope this clears up your confusion a little.

 

[Soren]

You are 100% incorrect in both statements.

No I'm not Bill. The sudden drop WILL and DOES create turbulence to the rear which means extra drag, and it's EXACTLY the same with bullets, hence the transition from flat based spitzers to boattailed ones. So I'm 100% correct.

The problem is you're relying on data from computer generated models of the -51 in this discussion, and obviously something isn't entirely right about these seeing the -51D is shown to have a higher wetted area than the -51B which wetted area should be larger because that huge hunk of extra fuselage.

It is interesting to note the slightly lower pressure on the -51D's aft fuselage though, again confirming the reason to the stability issues.

What I did notice just now though, from looking closely at the two a/c's profiles, and this DOES alter the argument, is the -51D's higher windscreen slope compared to the -51B's which is much more straight, something Lednicer oddly doesn't mentioned. This increased slope will help maintain the boundary layer while the -51B's windscreen will cause seperation right away, which kinda offsets the advantage of the razorback design. This difference in windscreen design will have a very direct effect on how the pressure distribution is over the rest of the canopy, and this explains Lednicers illustration. In short had the front windscreen been the same (Which I thought it was) Lednicer's results would've been very different.

So like I said, a razorback design is less draggy than a bubble canopy one IF (and this is normally the case) the front windscreen remains atleast similar.

 

[drgondog]

No I'm not Bill. The sudden drop WILL and DOES create turbulence to the rear which means extra drag, and it's EXACTLY the same with bullets, hence the transition from flat based spitzers to boattailed ones. So I'm 100% correct.

His model shows exactly the opposite conclusion from yours, namely the flow remains attached and is less pressure for the P-51D all the way to the aft fuselage deck - than the freestream around it. The 51B separates almost immediately off the top of the canopy

The problem is you're relying on data from computer generated models of the -51 in this discussion, and obviously something isn't entirely right about these seeing the -51D is shown to have a higher wetted area than the -51B which wetted area should be larger because that huge hunk of extra fuselage.

Er, this ISN'T my PROBLEM. This DISCUSSION is ABOUT the results of the computer generated Model and the data extracted from it and the conclusions drawn about the results.

Independent of what it should be for Wetted area, if the wetted area in the model is more for the P-51D than the P-51B despite losing the turtledeck, then the comparisons between the P-51D wetted drag in real life will be to the advantage of the P-51D. Less wetted are in real life would mean less total friction drag

It is interesting to note the slightly lower pressure on the -51D's aft fuselage though, again confirming the reason to the stability issues.

The Lednicer Model has nothing to do stability, nor does it show 'slightly less' pressure on the 51D's aft fuselage. In fact the pressure distribution at near freestream pressures are the same aft of the canopy for the D as aft of the windscreen for the P-51B.

Further, if you knew what you were talking about the only time the 'pressure distribution' on the side of the turtleback would show up asymetrically (i.e Rudder Effect) would be in a YAW condition - this model is Symetrical Soren.

What I did notice just now though, from looking closely at the two a/c's profiles, and this DOES alter the argument, is the -51D's higher windscreen slope compared to the -51B's which is much more straight, something Lednicer oddly doesn't mentioned.

He doesn't mention it because it isn't so. Perhaps you are comparing the Fw 190 to the P-51B/D.. The 190 has the least angle, the Spitfire the greatest and the 51B/C/D exactly the same

This increased slope will help maintain the boundary layer while the -51B's windscreen will cause seperation right away, which kinda offsets the advantage of the razorback design.

You are dabbling in a.) faulty conclusions and b.) a subject you haven't demonstrated much grasp of. The 51B flat windscreen to forward rounded top of windscreen shows an initial attachment then immediate separation. The Spitfire shows more stagnation pressure on the (flat plate like windscreen in comparison with other 3 models) frontal area but it re-attaches and then maintains attachment about 2/3 of the way back and on both sides of the Malcolm Hood... despite the B having more slope than the Spitfire.

This difference in windscreen design will have a very direct effect on how the pressure distribution is over the rest of the canopy, and this explains Lednicers illustration. In short had the front windscreen been the same (Which I thought it was) Lednicer's results would've been very different.

Lednicer a.) said that, b.) illustrated it in the Spifire/Malcolm Hood discussion and c.) contrasted it with the less effective transition for a top surface that was not a.) a Malcolm Hood or b.) a bubble canopy. You may have missed it the first couple of times through the article but I didn't.

The Primary difference is Not the slope of the windscreen between A/B/C an D/K models - it is the top surface of the windscreen in cross section. All of the birdcage and Malcolm Hoods were 'curved surface' when viewed from front, whereas the D was flat where the top of the canopy interfaced with the top of the windscreen.

The slope of the H (and J and G) was 'steeper - in terms of less angle between WL reference and slope of windscreen... more like the 190D

Where the D/K became superior to the A/B/C was exactly in that transition. In a profile for the B you went from slope (Windscreen) to flat (top surface of birdcage canopy) instead of continued slope of forward part of P-51D canopy transitioning to an airfoil like cross section on the D versus 'flat plate' for the B. He showed how the Malcolm Hood nicely enabled flow to re-attach on the tops and sides of the Spitfire - but NOT the P-51B. The 51D did not separate at all on the canopy top.

Your argument about boundary layer on the windscreen is interesting since for all of his models the windscreen piles up stagnation pressure with the Spitfire being the worst - coming closer to 'flat plate angle relative to 51 and the Fw 190 had the steepest angel - even more than the H.

What you miss is that there is NO Boundary Layer attachment on the windscreen in that high stagnation pressure area. The airflow bypasses it entirely. The Fw 190 will have the lowest stag pressure component and Spifire the highest.. This will manifest as Pressure or Form Drag )or equivalent Flat Plate) - use your preferred term

So like I said, a razorback design is less draggy than a bubble canopy one IF (and this is normally the case) the front windscreen remains atleast similar.

Like you said - you are flat wrong. The angle of the flat windscreen between the A-K model Mustangs is same. The top surfaces differ for the Malcolm Hood and D/K in that there is a continued angle at the top of the windscreen transitioning gradually to the top of the canopy about 18 inches behind windscreen rail, then on aft and downward very much like a fat airfoil.

The Malcolm hood on the Spitfire loses the nice lower pressure distribution it regained as it nears the aft part of the malcolm Hood to the (parallel) transition of the fuselage.. On the P-51D it loses the lower pressure transition when it reaches aft fuselage deck behind the canopy... same reason but the low pressure laminar flow region is greater on the P-51D than the Spitfire (and the Fw 190D) and far greater than the P-51B.

The P-51B never really has reattachment except for the very small portion as it leaves flat windscreen top.

Your conclusions are exactly opposite Lednicer's and exactly opposite the grahically presented data from the VS Aero Model, and exactly wrong relative to Razorback vesrus Bubbltop drag.

And your definition of what Lednicer meant by Suction is?? You still think it is Drag or the equivalent to wake drag on a bullet?

 

[Soren]

So you don't see the difference in windscreen slope ?

More ??

Is it not VERY apparent to you ???

Er, this ISN'T my PROBLEM. This DISCUSSION is ABOUT the results of the computer generated Model and the data extracted from it and the conclusions drawn about the results.

NO, it isn't! It's about the difference between a razorback and bubble canopy design!

And as to the lower pressure area I observed, what's a matter with it ? Did I not read it correctly ? Perhaps I got it the opposite way around ?

 

[kool kitty89]

Soren, I think the slope difference might be an optical illusion, look at these:

 

[Soren]

Hehe, those aren't accurate KK, you can clearly see that by comparing to the real thing, the cockpits on the B C look completly wrong, but it is what it would've looked like if they had used similar front windscreen.

In reality the P-51D's front windscreen is clearly more sloped than the P-51B C's, there's no doubt about it at all.

 

[Soren]

There's clearly a difference in slope, somehitng which will have a big difference on the pressure distribution over and behind the canopy.

 

[Graeme]

those aren't accurate

These aren't either, but I am leaning towards your assertion that the P-51D had a more acute angle for its front windscreen. Problem is resolution on such a small aspect of an aircrafts frame. Soren, the photos don't illustrate the angle, to my eyes anyway. Clave would be the man to illustrate the differences better.