Allied tests of captured Bf-109's

[lesofprimus]

I would just start a new thread and start adding the pics Bill... Make a disclaimer in the Thread Title **56k NO WAY** or something like that... Its gonna take awhile to upload em that way, but damn they'll be pretty for anyone willing to wait for them to load....

Or......

U could try and email me a few at a time due to mailbox size, I'll shrink em down to a more manageable size, and email u for more.... In a few days, we could get em all done...

[drgondog]

Originally Posted by lesofprimus

I would just start a new thread and start adding the pics Bill... Make a disclaimer in the Thread Title **56k NO WAY** or something like that... Its gonna take awhile to upload em that way, but damn they'll be pretty for anyone willing to wait for them to load....

Or......

U could try and email me a few at a time due to mailbox size, I'll shrink em down to a more manageable size, and email u for more.... In a few days, we could get em all done...

just sent you a PM

[kool kitty89]

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?

[drgondog]

Originally Posted by kool kitty89

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?

Good question. It didn't seem to help per se in the lednicer model but he made a specific comment that the Spit IX wind screen had a larger angle from the P-51 D and suspected that was more of a problem than the geometry aft of that.. in other words separation high on thr windscreen in his model. Go back and look at the reports I posted and see if he amplifies

[Soren]

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.

[drgondog]

Originally Posted by Soren

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]

Originally Posted by 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.

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]

Originally Posted by 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:



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]

Originally Posted by kool kitty89

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]

Originally Posted by Soren

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?