Mustang canopies.

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I'm wondering why it took NAA a year and a half (if the dates cited are true) to apply a benifit from a by -pass configuration at the nose , to a very simlar situation to the radiator intake???

Do the "rumble"accounts given by Gruenhage and others make sense? Do photos of the Xp-51B prototypes bolster the accounts as stated??

In my opinion, we are looking at too many instances where the dots cannot be logically and chronologically connected.
 

They make sense to me if the turbulence was close to a natural frequency of 'something' (like the exit shutter door/hinge structure).. I haven't read anything but the Gruenhagen account but resonance would be the first thing I would suspect due to the increased turbulence experienced in the new airframe geometry.

You could be right but I have been digging into the other books to see if any early test pilot reports mentioned 'rumble/annoying noise' at high speed but have been unsuccessful so far.

I had a conversation with Bill Cullerton, last surviving 357FS ace, this morning. His recollection of Malcom Hood vs D canopy was same as my father - namely the Hood was an improvement over birdcage but inferior to D tear drop - all models. Cullerton flew a P-51C, P-51D-5 and a P-51D-25 in combat, getting air to air scores in all of them.

He also remarked that the P-51B/C was slightly superior in performance but the D canopy and six .50's made it his favorite. Bill is not only an ace but also the top ground scorer in the 355th FG..Technically Clay Kinnard was tops but he had 2.5 credits when he led the 4th FG after Blakeslee before returning to command the 355th.

Having said all this re: slight superiority of the B/Hood combo, it is also interesting that despite the rank (my father was a Lt Col at the time) none (kinnard, Cullerton, Marshall) reverted Back to a B from the D..
 
Let's try a different tack.

1. When did by-pass configuration become a production feature on Mustangs?

2. When was fixed intake incorporated and did it have by-pass feature?

3.Was the boundry layer by-pass configuration the answer to the rumble issue of 1st XP-51B?


(1) It would appear Mustang I had a radiator intake with by-pass configuration from the very beginning.

(2) Ist production production mustang to feature fix intake appears to be A-36 and P-51A. Boundry layer by-pass more pronounced (bigger gap or "gutter").

(3)Yes, because it appears that the first XP-51B, in its originoal configuration, appears to have reverted to a large, very plain open front scoop , with no by pass feature.

If one looks at the NAA comparative chart provided by Gruenhagen, ALL are of the by-pass type. Photos would suggest the open front reversion was not tested at Ames.
 
Wouldn't you know it? This AM I noted a photo of an early Mk I that has than extended carb intake but it's not to rear of spinner. It stops short by some 4". What is evident is a slight crease at the front lower edges/sides indicating a possible beginning of a boundry layer by-pass configuration.

My perceptions are constantly changing, being re-evaluated, honed. Please feel free to question any statement you do not agree with. Correction and comments welcomed.
 

I'm confused by 'Open Front'. The version (figure 5) appears to be depicted in the lower right hand pic on page 79 - and labeled "wind tunnel tests during scoop development".. what distinction are you referring to as 'open front'?

An additional reference in Gruenhagen is that the results of the tests (NAA and RAF) were incorporated by NAA for the subsequent production proposal for the P-51B - and completed January 19, 1943. Presumably this includes the lowered wing, the modified scoop, etc changes that resulted in the ship one of the new P-51B at Inglewood.

Edit - Charlie there is a reference in Gruenhagen that ties both the change to both the carburetor air scoop and lower cowl radiator intake to be caused after RAF acceptance flight tests of first Mk I in April 1941 - by which time four production ships had been completed. They were retrofitted with incorporated design changes. The narrative on the changes were clarified on pages 48-49.
 
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Well, there you go, drgndog. Who knows their Gruenhagen? You apparently!

However it proves my point (instead of re-reading Gruenhagen, I arrived at similar conclusions as you found on pages 48-49 by looking at photos of early aircraft ), from a rather interesting egg vs chicken thrust, the early Mustangs had by-pass configuration at both carb intakes and the radiator.

In my understanding the gutter itself provides the by-pass feature. The lip (as eventually seen on XP-51B) has nothing to do with it, except as a refinement. You may recall that all aircraft developed beyond B/D saw a return to a lipless, yet still definitely a by-pass feature.

Now the earliest configurations of XP-51B, in my estimations, appear to have a large open ended, rather simple scoop with no apparent or readily observable gutter. We need a good front view close up, but one hasn't appeared, as far as I know.

As far as I cn tell the variable radiator intake was deleted fromA-36 onward, only the rear scoop (air exit scoop) . being movable.
 
Gruenhagen has a lot of gems but he has also intersting takes on items that simply are not verifiable, such as mentioning booster tab ailerons for those early Mustang I's (pages 48-49). IIRC production MkI's had like all the later evolved variants had a fixed tab on the port aileron and had an adjustable or trimable tab on the starboard aileron.
 

I am unclear on the variable radiator intake deletion date but see no eveidence that there was any change to the lower cowl geometry from the 4th Production P-51 (MkI) including A-36, until the aforementione Merlin mod and Ames Tests were concluded and changes made resulting in P-51B.

We may draw our independent conclusions but I am of strong opinion that the redesign modified interna dividedl duct was the primary change resulting in better flow properties and eliminated rumble.

If you found evidence that the gutter was also changed I could believe that was also a key factor. What is not shown is a subsequent test series at Ames for either the production B/C/D to validate the combined effect of dropping the wing/radiator cowl WL as well as the production lower cowl. Each should influence flow upstream of the radiator cowl intake..
 
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drgndog,

My problem is the context ofpopular Mustang history as oft repeated by Gruenhagen and others (including some by Horkey and Atwood), that the solution to the rumble was to introduce the by-pass feature. IIRC both Atweood and Horkey attribute the enlargement of the gap or by-pass and of th extended upper lip to a fellow engineer Irv Ashkensas (sp??). It all comes across as if introductioon of the by-pass in fall of 42 was a brand new developement, which is the thrust of my original question "what did they know and when did they know it". I think it's pretty clear that one cannot discover somethng if one has known about it and used prior to it's being announced. Idon't suppose I'd have a problem withi it if it was offered in the context of "we took this concept and developed it for uset here" , but that is not how the story is told and re-told.

I meant to comment on your getting to ask the WWII pilot about the Malcolm Hood.Thank you for doing that. Perchance , did you ask him about the term "razorback"? I'd have liked his thoughts on that.
 
Have re-visited chart page 79 and see two things I'd not noticed befor. "original" designation for 1st configuration shown.Thanks for making me look again.

IIRC by-pass within the duct itself is not a feature of production duct interiors or has it been offered as the solution to the rumble.. All by-pass of turbulet boundry layer air flow occurs outside of the intakeand duct work infront of the radiator.
AFAIK, the lip prevented dirty outside air from spilling into the open intake.

If i had to guess, and given poor photo quality and the lack of clear identication of th e various ducts, the top rt image on page 79 may be the first radiator intake of XP-51B #1 see page 108 "Mustang Designer". Never the less a gutter is visble in all the images.
 

I did ask the question and he never heard the term Razorback applied to the B/C.
 

I continue to see the divided duct and the extension forward as a major contibutor to solve both the increased drag and necessary mass flow rate issues along with the rumble noise - as the more important design change.

In boundary layer control most of the successful design changes occur Downstream of an original (problematical) separation to change the upstream flow properties. The name of the game in BL control is to reduce the pressure gradient downstream of the problem
 
drgndog,

Youve given me a lot to think about and will try to assimilate. I'm eaning toward the the idea that what hppens inside is not a contributing factor to th eboundry layer question. IIRC, other accounts attribute the rumble to the ingestion of turbulent boundry layer into the intake itself.All of the designs present on chart published by Gruenhagen show a devided duct of one type or another.
 
What is your take on the the "paddle blade" prop meaning the "square tipped" Hamilton Standard prop which became production standard on both Inglewood and Dallas built P-51D's?
 

Charlie - as an Aero by education I can say with conviction that devices, artifacts, etc downstream of flow separation are installed to a.) channel the flow chordwise, b.) reduce the pressure gradient/alter stagnation properties. You see such artifacts in vortex generators, suction slots, fowler flaps, etc.

Having said this I have zero data on actual flow improvements made when the divided duct was extended forward to the intake mouth. It seems reasonable to infer from the charts and the associated geometry presented with the data that the extension of the divided duct actually improved the flow characteristic inside the plenum over the original geometry.

Further, absent data on any changes that may have been made to the gutter, the 'new' divided duct configuration showed demonstrable improvement (was it the only factor? - I don't know) of the noise in either extended lip or no change to lip - over the original duct/plenum design.

Looking at the Gruenhagen photos on 79 it does look like the spacing from the top of the cowl inlet with the extended lip geometry is farther apart from the bottom of the wing than the top two photos of the XP-51B.

This designe change if correctly assumed from the photo would have the tendency to 'drop' the intake geometry into a boundary layer build up upstream of the cowl inlet. Candidly, before looking in detail at Gruenhagens data, this was my original assumption.

Now I lean to the extended divided duct reaching to the inlet as a more important change - simply based on holding the airframe constant for the XP-51B while altering the internal divided duct length to achieve the initial elimination of the rumble.

Call it educated speculation.
 
packardpursuit said:
What is your take on the the "paddle blade" prop meaning the "square tipped" Hamilton Standard prop which became production standard on both Inglewood and Dallas built P-51D's?
Click to expand...

Charlie - I don't really have an opinion. The design of props is an arcane art which is tested and refined over time - and always represents a compromise between best speed, best climb, lowest drag choices.

My conclusion? - NAA liked this configuration and went with it after considering original design, Brit experiments, etc. I had one chapter in a designe course as a senior which dealt solely with prop design and selection - enough to make me dangerous but not really knowledgable...

Regards,

Bill
 
I could have been clearer. This question wa soffered in a way similar to the propriety of term "razorback". Over the years most have equated "paddle blade" as interchangable or equal to, the "square tipped" blade. it is a pervasive notion among enthusiasts and operators of Mustangs, down to this day.

However, later versions of P-51D maintenance manuals('44 [?] thru '56) mention exact opposite, using the term "paddle blade" in connection with the cuffed types of blade and makes distinction between the two HS types.

BTW, according to a1946 article in Aerodigest magazine, HS engineers explain why the "square tipped" was adopted in favor over the cuffed types was due to the cuff assuming too much destabalizing side area forward of the C of G when in high pitch. Specifically, spiral instability, at high speed.
 

I had heard this was the reason. Notably as velocities (and prop rpm increased) the blade designs tended towar square tips and lower aspect ratios on the props throughout the industry.
 
Good find Charlie - you ought to put that file in the "P-51 Performance' section here.

Question a.) was there a P-51C-11 designation for last 400 ships under contract NA-111 and b.) if so was it the engine change from 1650-3 to 1650-?
 
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