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I looked at them today and there are no springs it appears to me they work on airpressure from the airflow they can be pushed in and out with one finger , but it was once stated that they got jammed up by dirt ,sounds like poor maintainence to me as there as there is very little airborne dirtThanks Soren, we needed an expert opinion on this.
I stand corrected.
There's quite a few sources that mention springs, but heres a hobby site with some good diagrams.
basepage
I looked at them today and there are no springs it appears to me they work on airpressure from the airflow they can be pushed in and out with one finger , but it was once stated that they got jammed up by dirt ,sounds like poor maintainence to me as there as there is very little airborne dirt
A little off topic, but did the F-86's LE slats use the same mechanism? (It would make sence since the Me 262, and HG variants, had alot of influence on the Sabre iirc)
Call it suction or seperation, it's the same and it creates drag and this is the prime reason for the P-51B being faster than the P-51D, as-well as the dive speed issues.
No, Soren - and no.
In the model 'suction' is a lower pressure than the freestream dynamic pressure.
The nature of a singularity distribution across finite element 'surfaces' in the model generate 'increased' flow across the top surface in accordance to wind tunnel flow results obtained chord wise on the airfoil at that wing station..until the 'iterative modelled' increase in boundary layer results in a local 'positive' pressure gradient from one model element upstream from the next one considered.
Isn't that your understanding?
Others tend to call it 'lift' in the real world. Separated areas are the 'non red' areas in the model. It should be intuituve Soren? Are you suggesting that the 'red' regions in Lednicer's model is 'separated' flow and that the rest is 'lift??
And yes, Lift creates drag but that drag manifests itself as induced drag due to the energy loss due to the tip vortex... not across the top of the wing where laminar flow/small boundary layer exists (or in the case of the 51D canopy - where flow has not yet gone 'positive' relative to freestream. Those drag elements are described as Profile or Wake drag and are represented in his tables. I don't recall seeing a friction drag component, but neither 51 would have much and both should be less than the Spit IX and Fw 190D if the distribution of flush rivets, and surface finish of a 51 is any indication.
From Lednicer's comparisons between the 51D and the 51B, it seem intuitive to me that one of the factors that kept the 51D at the same total drag coefficient was the improved (delayed) separation over the canopy..
what is your interpretation?
and if you don't like the Lednicer Comparison and tables - the same model results that you used to demonstrate your knowledge of 'flat plate' drag a month back in our Fw 190D vs Fw 190A 'disappointment' debate - why did you use it?
Dive speed issues? The 51D added a strake to the rudder to compensate for the loss of turtleback 'stabilizer', and added uplock kits to the landing gear doors and thickened/stiffened the ammo doors to improve some issues experienced in the B.
IIRC there is a pretty good report on the visible effects of the ammo doors Beginning to locally distort at near .85 mach in Mike Williams Website - but that was past recommended Max dive speed by some 40 mph TAS. I admit I was suprised that a dive was ever made at .85 for sanity reasons but apparently it was done under controlled conditions.
The wetted drag is the same for both 51B and 51A ships... so make your case that weight was or was not the key factor when a.) drag same, b. P-51D weighed approximately 600 pounds more, and the P-51D had a more powerful engine (at lower altitudes than 25,000 feet)
The reason the P-51H is so much faster than the P-51 is not only because of the much more power available (It ran at 90" Hg) but also the different wing.
And your proof that the 51H wing was more efficient is to be found where?There IS a slight difference in both the plan form and the airfoil itself, but I assume you have wind tunnel results or model results to justify your statement? I don't so would love to see them
Yes exactly the same, but the F-86 pilot was also given the option of locking them in place incase of a jam or other mechanical issues, otherwise they operated just the same.
Guys as already explained the LE edge slats operate by means of airpressure alone (There are no springs what'so'ever), extending as the pressure on the top of the wing decreases while the AoA increases. Thus the speed of the deployment is completely dependant on how quick the increase in AoA is, so if it's slow and gradual than so is the deployment, and if it's fast and gradual then so is the deployment.
It is therefore that automatic LE slats are AoA dependant devices.
Oh when it comes to the issue of pressure distribution and boundary layer seperation I see things quite clearly Bill.
And I trust Lednicer very much on this as-well, no doubt about it, and here's his words exactly:
Stronger suction = more drag. Very simple Bill, no need to complicate it.
Not complicated at all.
It is clear that you may not understand either the model or the results. It is more clear that you may not fully have the principles of Fluid Mechanics, and extended further, the theoretical tools of Aerodynamics..
Can you explain the theory behind the use of 'singularities' as he has used them to model the pressure distribution? and why that is a valid model approach?
You should also attempt to put that paragraph in context as other may see by looking at the entire article. For those that care - look to the comments Lednicer makes regarding the poor canopy design of the Spitfire and contrasts it with the P-51D and look at the relative 'suction' distribution over both canopies
And furthermore from the very same article:
Again like I said, the P-51B features less drag than the P-51D, and primarily because of the bubble canopy. A bubble canopy creates more drag than the razor back configuration, that's a common known fact Bill, deal with it.
Words like 'commonly known facts', 'far superior' etc are what occasionally cause issues with us Soren.
If you refer to Gene's Lednicer's models and report your interpretation as 'the commonly known facts', then you have mis interpreted the both analysis and the conclusions - he draws exactly the opposite conculsion in Table II/Section VII of the P-51B vs P-51D report.. and explains that the results do not include the 'scoop'..In other words the Table II results include canopy difference, etc but not the oil cooler and radiator intake fairing. As I will repeat below his model resulted in .0033 for P-51B and .0031 for P-51D as the respected wetted Drag Coefficients.
The Table you chose to show was the roll up including friction drag, induced drag and profile drag. The numbers on the left of your table are the SUM of the flat plate equivalents of Friction/Wake/Induced streamwise components of force.
If the 51D has greater area and same wing can we conclude that the factual flat plate equivalent of friction drag is greater and the induced drag is the same? But the wetted drag coefficient is exactly the same for all drag components? would you conclude that the profile drag (including canopy, boundary layer/wake drag) is Slightly Higher for the P-51B than the D?
I would. An that is what Lednicer was showing with 'suction' on the canopy as boundary layer attached region.. i.e Not Separated creating additional wake drag.
Is there another source that would better serve the 'phrase 'commonly known fact'?
Do you care to present the rest of the tables showing the wind tunnel comparisons, and the past theoretical calculations between the two ships, and his words Soren, and note that the Total Coefficient of Wetted Drag is the same in that table which is extracted from his model? When you have presented your past 'models' using drag - did you use 'flat plate drag' or Total Drag Coefficient.
And as for the P-51H's wing, it's slightly smaller = less drag (Decreased Root chord) and there's plenty more power available to the a/c, hence the higher speed.
So far I find 235 sq ft for all variants even though the leading edge 'strake' was completely removed. Your source for less wing area is?
As for the dive issues, well because of the bubble canopy and cut down aft fuselage the D series suffered from directional instability, something which was shared by the P-47's featuring bubble canopy's as-well. This is the cause for adding the dorsal fins.
This is ridiculous Bill,
Are you claiming that bubble canopies don't increase drag over the razor back configuration or not ? I need you to answer that question specifically.
Yes.
I am claiming that in Lednicer's reports, the Model, and cases to compare the bubble canopy of the P-51D,to the birdcage canopy version P-51B, the malcolm hood Spitfire IX and the blown hood Fw 190D - in the common report you and I both have and for which I have posted in their entirety (and you have not) he CLEARLY demonstrates the greater Suction (normal force), and hence LOWER pressure drag (horizontal force in streamwise direction.
Lednicer's graphs does indeed show a similar CDwet for both a/c, but that doesn't mean that the bubble canopy doesn't provide any additional drag over the razorback configuration, esp. seeing there were other design changes between both a/c. In short a stronger suction means more drag Bill, it's that simple really.
Specifically Suction is a Normal Force (i.e Perpendicular to the modelled surface) and Drag is a Streamwise Force (or Parallel force to the modelled surface in the stream/flow direction. To go any further you have to understand the difference. Do you?
If you understand Vectors you should understand. Where are we on that? In Vector terminology these two forces are Orthogonal (perpendicular) to each other and most specifically are Not the same in either direction or magnitude
Specifically Soren, he shows a LOWER CDwet for the 51D sans lower faired radiator/oil cooler structure - and EXACTLY the same CDwet for the TOTAL components of Friction, Pressure/Form/Wake (whatever term you want), and Induced Drag for the two airplanes. You seem to be equivocating and obscuring what he wrote when you say 'similar'
And as for the British tests, well why use them and not the US ones ?? If I wanted to compare the P-51B D I'd use data from its country of origin, i.e. the same place, leaves out many possible discrepancies.
I used it only to show the only reported and controlled test that measured a velocity of .85Mach for ANY version of a Mustang - to help you understand visual observations during the course of the controlled tests. I have the results of the terminal tests performed by NAA on the P-51B in which it reached .75 Mach without prop (and prop drag) in controlled tests. That is not the limit speed of a 51B but I haven't yet seen a similar test to ultimate in a controlled test - have you
But since you don't want to realize any of the above I guess it'll take a vet P-51 pilot to convince you;
Why introduce a component of sarcasm - I will keep my comments objective and relevant. I was under the impression that we were debating the Lednicer models, reports and conclusions relative to drag.
Robert C. Curtis, American P-51 pilot:
"The P 51 was redlined at 505 mph, meaning that this speed should not be exceeded. But when chasing 109s or 190s in a dive from 25-26,000 it often was exceeded, if you wanted to keep up with those enemy planes. The P 51b, and c, could stay with those planes in a dive. The P 51d had a thicker wing and a bubble canopy which changed the airflow and brought on compressibility at lower speeds."
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.
It would be interesting to see Soren actually respond to all the questions u've put in ur posts Bill....
I too feel that he is not interpreting some of the issues brought up in the report correctly, and would really like to see him, in his words, answer some of the insights u have about the Lednicer Report...
I cant really understand how one extremely intelligent person can interpet a set of facts completely different from another extremely intelligent person...
This is a very interesting discussion, way beyond my grasp on several levels, but learning new stuff is always a treat... But honestly, Im confused at the discrepancies between u two guys...
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...
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?