A funny looking experiment!!!

[Professor Brensec]

You're absolutely correct, mate.





........................................you are wasting you're time!!  ;D

I understand all this, but still, the fact remains that the NA blokes had the drawings which Curtiss were 'forced' to handover. But NA refuse to confirm the obvious 'temptation' was given into, to look at what the Curtiss people had come up with. Even in the face of their 'famous' 102 day feat (or however many days it was), they still mantain that they simply "tossed" such a valuable asset aside and went about designing their 'unique' fighter.      Ha!!!!!!!!

It means much to me that Curtiss, who were approached first for the 'much needed' high performance, high altitude fighter (shortly to have 'long range' added to the requirement), were unable to entertain the idea of such a project because they were busy stocking ALL the allied Air Forces with the fighter that held the lines for 3 years (bar the Spit), in every theatre of the war.  :D

Seriously, I know what you say is true, but we all have our favourite plane and we defend it, even when the odds are stacked high........like the P40.  

[Hagar]

LOL You're as bad as Ozzy & his Spitfires, if not worse.

Whatever the truth of the matter I don't think anyone would disagree with my opinion that the P-51D is a beautiful aeroplane. This gives me the excuse to post a couple more of my photos of a fine example, probably the most immaculate warbird I've ever seen. I don't need much encouragement.

If a designer were to sit down now & design a Merlin-engined fighter it would probably turn out looking something like this.

[C]

LOL You're as bad as Ozzy & his Spitfires, if not worse.

Getting there...

This gives me the excuse to post a couple more of my photos of a fine example, probably the most immaculate warbird I've ever seen. I don't need much encouragement.

If you ever need an excuse Doug, just ask...

Charlie

[Rifleman]

Hi Prof. I know I'm wasting my time but I couldn't resist it. .........
.........However, from what "Lee" Atwood explains in the article the Heston would not have benefitted from the Meredith Effect. This is caused by the design & shape of the radiator scoop itself. The important thing seems to be that the front part of the scoop is clear of the fuselage as it is on the P-51D & not directly bolted on or faired into the fuselage itself ............................. The full extent of the air scoop's effect on perfomance was not fully appreciated until after WWII was over.
............PS. It didn't strike me until recently how similar the air intake on the F-16 is to the Mustang air scoop. This might explain its remarkable performance.

This is not unlike the design of the intake on the F-4 Phantom .........if you are not aware, check out this frontal shot of the splitter-plate/engine intake on one.............this gap seems a necessity for performance and somehow must help avoid a boundary layer which may prevent "clean flow" into the intakes ?

[Professor Brensec]

Certainly lovely photos Hagar.  And a beautiful plane. As far as WWII birds go, I've only ever seen them up close in Museums and the Australina War Memorial (except when I flew in the Spit...... But I was too young to be that thrilled about the plane itself. Just a mixture of scared and exhilarated, is all I recall from my flight in "The Kangaroo Plane").

I do love the P51, although I prefer the B/C version (a bit faster and still looking like your 'classic' - 'framed canopy'/ridge back - WWII fighter). I know these things actually impeded the pilots ability to see, but I just like it. I also think the 'ridge back' arrangement contributed to some more 'longitudinal stability', which I feel may be lacking in your 'bubble canopy' types.

Most Australian pliots I have read accounts by, preferred their B/C's to the D, citing some sort of "lack of stability, especially in a tight turn against torque"

It (the P51) would be my next 'sentimental' choice after the P40, between which there is no comparison, because of the part it played in the RAAF after the P40 was finally discontinued as the 'frontline fighter' (although this was very late in the peice, and many pilots flew the P40 later variants up till the end of the war).

By the way. The ammo in the wing of that P51 is obviously 'empty' and harmless, but are there 'complete' guns in there (maybe with firing mechanisms missing)? Or are there just 'barrel ends' projecting out the front of the wing, with no 'body' inside?  ;D

[Hagar]

This is not unlike the design of the intake on the F-4 Phantom .........if you are not aware, check out this frontal shot of the splitter-plate/engine intake on one.............this gap seems a necessity for performance and somehow must help avoid a boundary layer which may prevent "clean flow" into the intakes ?

You're probably correct Ken. I've seen these plates many times but assumed they were some sort of deflector. Until now I never associated them with an improvement in performance. Going back to "Lee" Atwood's article.

... the first Mustang design had a similar entry opening [to the Spitfire Mk IX]. It was later apparent that the thin boundary layer of air flowing along the lower surface of the wing was progressively thickening in front of the duct opening, and that the flow would break away at a point on the upward curve of the duct wall. While the resulting turbulent unsteady airflow apparently did not cause a serious vibration [on the Spitfire], it certainly reduced the efficiency of the radiator & prevented complete closure of the exit opening, which is necessary to develop the jet thrust.

In the case of the Mustang, the duct opening was larger and the flow instability more violent, creating an unacceptable vibration & rumble. Resourceful engineers at NA, working with wind-tunnel models, overcame the problem by lowering the intake a couple of inches to provide a gutter or scupper via which this layer of turbulent air could bypass the intake. This has been common practice for such ducts ever since.

Atwood reckoned, with the benefit of hindsight, that a similar modification to the Spitfire radiator intakes would have increased its speed by more than 20 mph.

By the way. The ammo in the wing of that P51 is obviously 'empty' and harmless, but are there 'complete' guns in there (maybe with firing mechanisms missing)? Or are there just 'barrel ends' projecting out the front of the wing, with no 'body' inside?

To be honest I'm not sure Prof. I was so impressed with the darned thing I didn't know where to look next. I never expected to see any warbirds that day, never mind anything like this beauty. Like many others I was most surprised when it turned up at a vintage light aircraft fly-in.

Going by the accuracy of the superb restoration I imagine it still has the guns fitted although these would have to be permanently deactivated to fly in UK airspace. I think it's now based at North Weald but I'm not sure of its history. It could possibly have been restored in France, in which case the regulations might have been different. I know a French "large-scale" R/C modeller who has a scale Stuka & Fw 190 that can drop real bombs. These are used mainly for film work.

PS. The "Lee" Atwood article I'm quoting from is in the May 1999 "Mustang Special" edition of Aeroplane (Monthly) magazine.

PPS. Brief history & more pics of Jumpin' Jacques. http://www.mustangsmustangs.net/p-51/survivors/pages/44-72035.shtml

[Rifleman]

[quote]Certainly lovely photos Hagar.

[Hagar]

Very interesting set of profiles there Ken. It shows the continuous development of the radiator scoop over the different models quite well. The gap between the nose of the scoop & the fuselage is not clear in the drawings unless you're aware of it. I think this is the cause of much of the confusion as to how the principle works. According to "Lee" Atwood, the much-vaunted "laminar flow" wing is a fallacy & had no noticeable effect on performance. I suspect this belief that the wing was responsible was encouraged to prevent Willy Messerschmitt & other Axis aircraft designers discovering the real reason. It was also believed by people who worked on & flew the aircraft & is still referred to today by many veterans & even test pilots. As with other similar examples, what started out as wartime propaganda turned into a legend. I've also heard many well-known & otherwise well-informed air display commentators stating that the distinctive "Mustang moan" (caused by the radiator scoop) is the sound of the airflow over the open gun ports - even when the particular aircraft has no guns & the ports are covered over. It's quite possible this was another wartime legend.

I think this is borne out by the additions on some models of the dorsal fin in front of the main vertical stab

This problem was not unusual when fitting more powerful engines or converting "razorback" fighters to "bubbletops". The later P-47 bubbletops had a similar dorsal fin to the P-51D. It was overcome on the Spitfire by first enlarging the rudder & later the complete vertical tail surfaces on the bubbletop versions.

As this topic started off with the P-40 I got to wondering what happenened to the Curtiss company. This once-famous name does not crop up much after the end of WWII. I found this interesting history of the Curtiss-Wright Corporation. http://www.curtisswright.com/history/Default.asp

[Professor Brensec]

Thanks for that set of profiles, Ken. I have seen it a few times in my travels, but to be honest, didn't notice the fin having been added on later D models.

Obviously, the Australian pilots that I mention, were not alone in their having criticisms of the D model in terms of this 'longitudinal stability'. I'm sure, for the manufacturer to make such additions, it would have to have been an obvious and commonly acknowledged problem for them to have engineered a modification.

I'm certainly no 'aerodynamics' expert. In fact, I understand little. But it seems to me that this 'instability' could well have had something to do with the abnormal speed 'bleed-off' in tight turns experienced by the D model (but not the B - another reason I prefer the B).

(Let me see if I can explain my idea without a knowledge of the aerodynamic terms).
It seems to me, if you are directing the plane to turn sharply (while using the elevator pivoting upwards, when the plane is 'banked'), the plane is going to want to tend to go in the original direction, belly first. Without a good degree of 'directional' guidance (for want of the correct term), like that which would be given by the 'razorback' or the added fin, the plane, when it eventually began to move in the direction required, will have spent much of it's speed being 'forced' by inertia belly-first in the original direction.  ::)

I can picture it, but I don't know if I've been able to explain it  clearly. But anyway, in my head, it would seem to account for the 'bleed-off' of speed that the D experienced in tight turns. (Like I siad,  in my head, anyway  ;D .

I always found it disappointing that the P51D, being such a wonderful plane, in most ways, could literally 'turn on a sixpence, but after having done so, you look at the ASI and find you've lost 100 knots somewhere in the process.

[Rifleman]

Actually Bren, the reason that planes bleed off speed in turns is that effectively, in a turn you are going "up hill".....first you roll into the turn and with the reduced wingspan presented to gravity due to the bank and hence increased wing loading (weight/wing area - also due to the bank) you will need to add elevator to fly through the turn with a higher angle of attack on the wing to make up for these deficiencies.....this is the same effect as trying to climb, as opposed to flying straight and level.........once you are banked into the turn and have the elevator input increased, you will add in some rudder to balance the turn and make the tail follow the nose through the turn......in a very steep turn you may need less rudder and more elevator along with added power to overcome the drag of the higher angle of attack required to maintain altitude through the turn......

........more confusion added now ?

[Professor Brensec]

........more confusion added now ?  

This would appear to be the case......

Thanks mate.

[Rifleman]

Sorry but it seemed to make sense to me at the time.... ........

..........only trying to be helpful, but sometimes I go on a bit........

[Hagar]

I've forgotten more about aerodynamics than I ever knew which wasn't a great deal to start with.

Ken will know from his experience with R/C models that it's possible to fly an aircraft perfectly well on ailerons & elevator alone with no rudder at all, even doing basic aerobatics. Many popular sport models have a fixed fin with no rudder. On conventional piston-engined aircraft & gliders the rudder is used to help initiate turns but "opposite rudder" is often required to hold the nose up once the turn is established. In a real aircraft this tends to be instinctive & you might not even notice what you're doing with the rudder or what position it's in relative to neutral.

From what I do remember about aerodynamic theory, the problem with the bubble canopies is that modifying an existing design by cutting down the rear fuselage decking to fit them reduces the surface area of the fuselage profile. When the aircraft is banked in a steep turn the fuselage acts as a wing & creates its own lift. The deeper the fuselage, the more surface area & hence more lift available when banked. This also helps to maintain stability in the yaw axis in all normal flight conditions. Reducing the surface area of part of the basic airframe without compensating for it will upset the delicate balance of the original design & make it twitchy & less controllable.

Many WWII fighters had a short tail moment arm* & were by no means perfect in this respect to start with, suffering from instabilty problems throughout their time in service. The canopy itself might also disturb the airflow over the vertical tail surfaces, further reducing stability & control - especially at low airspeeds. Fitting a dorsal fin or using other methods for increasing the area of the fin & rudder will often but not always correct this problem. Fighter aircraft are flown to the limits in combat situations & the usual rules go out of the window. An aircraft with predictable flying characteristics & responsive controls throughout the speed range must be a great bonus to a fighter pilot.

I discovered to my surprise when I had a flight in one many years ago that the rudder is very rarely used in normal flight on jet fighters like the Hunter. It's only required for advanced aerobatic manoeuvres & steering on the ground.

*PS. The XP-37 in Prof's original topic is a perfect example. I suspect it suffered from longitudinal instability in the pitch & yaw axes. Lengthening the rear fuselage by even a couple of feet would improve it considerably, both in looks & performance. Leaving aside all aerodynamic theory, the old adage, "If it looks right, it will fly right" proves true more often than not.