Mustang canopies.

[packardpursuit]

Well, technically, the B/C retrofit of Dorsal Fin Fillet, and early D retrofit with up locks were not factory included items, although they were to become so, to one extent or another. B/C dorsal retrofit was covered by same opriginal combat TO which required them on P-51D's and only last block P-51C's had them factory installed. It's pretty clear now the D's canopy and" loss of side area" had nothing to do with the official reason for the DFF (and other related tail fixes).

 

[drgondog]

Well, technically, the B/C retrofit of Dorsal Fin Fillet, and early D retrofit with up locks were not factory included items, although they were to become so, to one extent or another. B/C dorsal retrofit was covered by same opriginal combat TO which required them on P-51D's and only last block P-51C's had them factory installed. It's pretty clear now the D's canopy and" loss of side area" had nothing to do with the official reason for the DFF (and other related tail fixes).

Agreed on all points - and to the latter only the H really solved the problem with redesign including length of Fuse and wing location.

Charlie, wasn't a redesigned vert stab spar attach fitting also added?

 

[packardpursuit]

I've not head anything abouta beefed up vertical attach fitting, but seems plausible.

I would respectfully question your ascertion "H solved the problem" What problem exactly are we talking about? The B/C/D/K's apparent penchant for high speed yaw instablilty and resultant structural failure? And the need for a few aerodynamic, structural, and mechanical fixes? Or the H's apparent need for more and more vertical area?

One would think adequate P-51H tail strength and sufficient vertical area factors would have been addressed while in design, especially given the problems believed associated with immediate earlier types. Tail strength seems to have not been a problem . However the H's Vertical stab got added to at least once and its rather miniscule DFF was never altered.

It has been my observation nearly ALL high speed aircraft developed during WWII got progressivly larger vertical surfaces, as combat speeds rose. IMHO, Mustangs, including H, fall into that general category, while the apples vs oranges specifics between the two can be harder to quantify.

NACA tested additional fin area first on P-51B and then a D. British appear to have also tested larger fin and rudder on a Mustang III (p-51B) Niether types were adopted during WWII. The NACA fin cap WAS included on some late Cavalier Mustangs, becoming standard in the 60's. Interesting thse often mistaken as having an H fin and rudder.

 

[drgondog]

I've not head anything abouta beefed up vertical attach fitting, but seems plausible.

I would respectfully question your ascertion "H solved the problem" What problem exactly are we talking about? The B/C/D/K's apparent penchant for high speed yaw instablilty and resultant structural failure? And the need for a few aerodynamic, structural, and mechanical fixes? Or the H's apparent need for more and more vertical area?

Improved yaw stability was achieved in combination with tail redesign and lengthening the fuselage. The resultant yaw stability improvement at high speed also apparently led to better take off characteristics vis a vis rudder pedal forces as well as less vertical stab trim required.

The primary problem with the B/C/D/K was inadequate rudder surface area as well as inadequate structural integrity to compensate for the increase in torque due to the Merlin.

One would think adequate P-51H tail strength and sufficient vertical area factors would have been addressed while in design, especially given the problems believed associated with immediate earlier types. Tail strength seems to have not been a problem . However the H's Vertical stab got added to at least once and its rather miniscule DFF was never altered.

Charlie - The H tail increase to both height and area was specifically to provide for better yaw control with less rudder input at high speed (IIRC). NAA finally figured out that the ventral fin did not improve yaw stability to the degree expected, and experimented with higher Vertical stab, with inconclusive results, which never was put in production. But that higher, 'skinny' tail was the fore runner for the H.

Increasing the static margin by 'extending' the fuselage some 13" was the key to providing good design response to the increasing torque output of the Merlin 1650-9.

The key to reducing the asymetric structural load due to increased rudder deflection and engine torque was to focus on a design which contributed most to reducing rudder input from pilot to control the yaw - both in high speed dive as well as rolling manuevers. The increase in fuse length was probably more important than the slight increase in Vertical Stab height and area. The change in moment arm from cg to AC of the Stab/Rudder automatically provided more lateral stability with even a D tail and the increase for the H contributed more positve benefits.

It has been my observation nearly ALL high speed aircraft developed during WWII got progressivly larger vertical surfaces, as combat speeds rose. IMHO, Mustangs, including H, fall into that general category, while the apples vs oranges specifics between the two can be harder to quantify.

Yes. increasing tail area easier than extending fuselage.. but sooner or later you have to redesign when you make a dramatic mod like either a much more powerful engine - or moving the Cg around - Fw 190D is a good example of both, and the P-51B/C/D was another example.

The 109K tail grew for the same reason but in each case some new limits must be placed on manuevers because the Fuselage/Tail structure aft was not designed for the increased aero loads imposed with a delta in rudder deflection/load due to the increased torque.

NACA tested additional fin area first on P-51B and then a D. British appear to have also tested larger fin and rudder on a Mustang III (p-51B) Niether types were adopted during WWII. The NACA fin cap WAS included on some late Cavalier Mustangs, becoming standard in the 60's. Interesting thse often mistaken as having an H fin and rudder.

I made that mistake when I first saw a Cavalier mod TF-51D but quickly corrected when I got close enough to look at the radiator cowling and leading edge of the wing - then the size of the tires became more noticable.

 

[packardpursuit]

Having a bit of a problem following your logic. It could be me.

I decided to check the distance differences between aircraft under discussion. So far very surprising. Will have to triple check, but I'm finding some interesting figures that may color our understanding of supposed"givens".

Since both B/C/D and F share almost same lengths (32'-2.9" vs 32'-3") I've included the later. P-51H is 33'-3.25". So right off we can appreciate that total fuselage length is 12-1/4" longer than earlier types.

How about distance over spinners to 25% chord line? According NAA dimensioned 3-views: F is 130.25" while H is 139.25" and BD is133.437"

Distance from 25% line to rudder hinge line is most revealing: 231.063" for F. 235.500" for H and 228.11" for B/C/D.

Please double check my math. front of B/C spinner is approx 34.436" infront of Fuse. Sta. 0. 25% wing datum is located Fus.Sta.99, and rudder hinge line is at Fus. Sta.327.11 (34.436+ 99=133.436") (327.11"- 99"= 228.11" )

I arrived at distances between 25% and Rudder hinge lines of P-51's F&H by subtracting the over spinner to 25%, plus rudder width dimensions from the overall lengths, in inches.

By my calculations the moment arm from respective 25% chord lines (which is also 25% of all M.A.C.'s and not an unreasonable common CG for calculation purposses) of the H is 7.39" farther aft than B/D. That 12.25" inches longer is not looking that effective to me. BTW- comparative lengths for P-51A is about 1/8" less than for B/C/D but all fore'aft surface locations identical.

I checked Gruenhagen's area charts and find them a bit confusing.Will have to sort that one out, as well. Initial production P-51H's had 75.5" tall fin. Later, added cap to 82-9/16".

Again, I see nothing in the design of the P-51H that specifically addressed the problems of the P-51B/D. It was a different design entirely athough laid out in a similar general premis. General dynamic fixes were incorporated and yet the un-anticipated directional issues of the H were addressed by a fix tried out on B/D, but not deemed important enough to fit or even retrofit, during WWII, and some 11 years later.

 

[drgondog]

Having a bit of a problem following your logic. It could be me.

Specifically what, the benefits to extending the fuselage so that the wing and cg could also move slightly aft and still derive an extended moment arm to the tail MAC's? Or?

I decided to check the distance differences between aircraft under discussion. So far very surprising. Will have to triple check, but I'm finding some interesting figures that may color our understanding of supposed"givens".

Since both B/C/D and F share almost same lengths (32'-2.9" vs 32'-3") I've included the later. P-51H is 33'-3.25". So right off we can appreciate that total fuselage length is 12-1/4" longer than earlier types.

Sounds right on the H, although my recollection was "~13" with no precision

How about distance over spinners to 25% chord line? According NAA dimensioned 3-views: F is 130.25" while H is 139.25" and BD is133.437"

For stability comments, knowing the location of the cg relative to the MAC of the wing (and horizontal/vertical Stab mac's) is critical but we can assume for the moment that NAA engineers would keep the 25% chord/c relationship the same - assuming the new wing Moment Coefficient was the same as the D.

Distance from 25% line to rudder hinge line is most revealing: 231.063" for F. 235.500" for H and 228.11" for B/C/D.

Please double check my math. front of B/C spinner is approx 34.436" infront of Fuse. Sta. 0. 25% wing datum is located Fus.Sta.99, and rudder hinge line is at Fus. Sta.327.11 (34.436+ 99=133.436") (327.11"- 99"= 228.11" )

I get the same results

I arrived at distances between 25% and Rudder hinge lines of P-51's F&H by subtracting the over spinner to 25%, plus rudder width dimensions from the overall lengths, in inches.

I don't recall what design specific design changes were incorporated in the H tail. If the plan view of the horizontal stab/elevator is essentially the same then we can conclude that measuring to the respective hinge lines will maintain a similar relationship with 25% chord of the wing.

By my calculations the moment arm from respective 25% chord lines (which is also 25% of all M.A.C.'s and not an unreasonable common CG for calculation purposses) of the H is 7.39" farther aft than B/D. That 12.25" inches longer is not looking that effective to me. BTW- comparative lengths for P-51A is about 1/8" less than for B/C/D but all fore'aft surface locations identical.

The combination of moving the H cg aft, along with reducing fuel from 85 gallons to 50 would be very significant in removing the aft cg issue of the B/C/D for full fuel load out.

I don't know whether the Elevator mac of the H was the same as the D nut, if so, Seven + inch movement aft of the tail mac from the cg is important for pitch stability. Ditto for the H Vertical Stab/Rudder in context of improving yaw stability

I checked Gruenhagen's area charts and find them a bit confusing.Will have to sort that one out, as well. Initial production P-51H's had 75.5" tall fin. Later, added cap to 82-9/16".

Again, I see nothing in the design of the P-51H that specifically addressed the problems of the P-51B/D. It was a different design entirely athough laid out in a similar general premis. General dynamic fixes were incorporated and yet the un-anticipated directional issues of the H were addressed by a fix tried out on B/D, but not deemed important enough to fit or even retrofit, during WWII, and some 11 years later.

Charlie, the combination of moving the cg aft assists in decoupling the added fuel tank from creating an aft cg problem, and the extra moment arm between the new cg and the tail mac's improves yaw and pitch stability.

As to why a 'fix' (what fix?) was not deemed important enough to retrofit? First - we don't know what the modification cost issues were for the D/K to retrofit them to improve either the yaw issues at very high speeds, or the pitch/roll coupling of the aft cg issue with 85 gallons... so hard to comment. One thing was clear however, the P-82 was taking on the role of long range escort and the D was assigne Fighter Bomber roll, while the H was the Bridge Interceptor. I suspect cost/benefit for the D/K mods was not there in very tight USAF post WWII budgets?

Charile - I see two changes - namely the implied extension of the cg/MAC (assuming NAA chose to design to the same margin between cg and MAC) to the horizontal stab mac, and the movement of the cg/MC of wing aft toward the fuel tank should have positive stability implications for both yaw and pich.

 

[drgondog]

Charlie - I have a couple of questions that occurred to me after the last post.

Since both B/C/D and F share almost same lengths (32'-2.9" vs 32'-3") I've included the later. P-51H is 33'-3.25". So right off we can appreciate that total fuselage length is 12-1/4" longer than earlier types.

How about distance over spinners to 25% chord line? According NAA dimensioned 3-views: F is 130.25" while H is 139.25" and BD is133.437"


Distance from 25% line to rudder hinge line is most revealing: 231.063" for F. 235.500" for H and 228.11" for B/C/D.

By my calculations the moment arm from respective 25% chord lines (which is also 25% of all M.A.C.'s and not an unreasonable common CG for calculation purposses) of the H is 7.39" farther aft than B/D. That 12.25" inches longer is not looking that effective to me. BTW- comparative lengths for P-51A is about 1/8" less than for B/C/D but all fore'aft surface locations identical.

Questions -
1. are you measuring to 25% chord point at CL Root chord? Or 25% Chord point at the WS of the MAC? Or 25% of the wing chord as WS where the fuselage intersects the wing?

If the latter, then the comparisons between the Cg should be close between the models.

If the second condition I would assume that the MAC would be close between D and H wings relative to WS and the respective chord at MAC.

If the former, then I have to ponder the significance of the much larger length of the CL Root chord of the D/K to that of the H.

I checked Gruenhagen's area charts and find them a bit confusing.Will have to sort that one out, as well. Initial production P-51H's had 75.5" tall fin. Later, added cap to 82-9/16".

Again, I see nothing in the design of the P-51H that specifically addressed the problems of the P-51B/D. .

The design parameters for the H were, improve performance by reducing weight, improve stability problems encountered as result of initial P-51A to P-41B mod to incorporate Merlin, improve stability while keeping the aft fuselage fuel tank, anticipate greater horsepower and weight increases due to future engine upgrades - while retaining armament and range capability.

For stability improvements to yaw conditions at high speed - the primary approach would include
1. Bigger rudder/Same relationship between cg and MAC of Rudder (Vert Stab/Rudder combo) - tried, didn't work, couldn't increase vertical tail surface area without REALLY rebuilding aft tail/fuse structure to resist the lateraL load increase due to larger surface. It was already failing when large asymmetric loads were applied in high speed skids and rolls.

2. Extend moment arm from cg to Vert Stab/Rudder mac - better approach given structural capability after check to longerons and aft fuselage structure. Consider change to design for potential aerodynamic improvements. Design envelope focus on a.) take off, b) asymmetric laod conditions (rolls in particular), c. High Q loads in max power dives. This type change could only occur with major airframe mod or redesign.

For stability improvements to pitch/roll coupling due to aft cg
1. Remove or reduce fuel capacity of aft tank. (Partial P-51H approach)
2. Increase moment arm between cg and horizontal stabilizer/elevator mac so that enough pitch down control may be maintained for extreme aft cg state (P-51H approach)
3. Increase surface area of Horizontal Stab/Elevator consistent with structural capability of airframe. (P-51H approach)

The P-51H did all three key design changes, plus increased rudder deflection to assist in take off for the bigger engine/lighter weight H.

You know most or all of this - I was outlining to keep my own thoughts in focus.

 

[packardpursuit]

My perception of our conversation thus far, is that we both tend to see-saw a bit, first one of us is speaking in generaliiies and then switching over to specifics. The other reciprocating in turn. Quite a dance. LOL

I believe you tend to see the H as a natural evolution and extention of the earlier variants. It is only natural to compare the the newer to the earlier D variant, as it is a most obvious one to make. USAAF did same early on.

I tend to see the H as a totally new airframe with no direct physical connection whatsoever with earlier production types (which clearly have a direct evolved developement),except for basic configuration similarities, and more advanced thinking incorporated (to which I humbly, now, stipulate did in fact address some issues that plaued B/C/D. And yet, as a new design, had problematic issues with stablity of its own).

 

[drgondog]

My perception of our conversation thus far, is that we both tend to see-saw a bit, first one of us is speaking in generaliiies and then switching over to specifics. The other reciprocating in turn. Quite a dance. LOL

Only by you providing the specific details regarding STA locations was it possible for me to be specific regarding the effect of different design changes on the H as far as weights and balances and moment arms to help me explain why the changes to the H geometry help solve the stability issues inherent in B/D due to the Merlin upgrade.

Nobody I know (other than you) has the full set of aircraft specific lines/WS/Fuse STA details to flesh out this discussion or any other regarding 51 configurations.


I believe you tend to see the H as a natural evolution and extention of the earlier variants. It is only natural to compare the the newer to the earlier D variant, as it is a most obvious one to make. USAAF did same early on.

Charlie - from my perspective the H was, as you state below, a near totally different aircraft if one defines 'nearly the same' as having much in common - per my comment below.

I tend to see the H as a totally new airframe with no direct physical connection whatsoever with earlier production types (which clearly have a direct evolved developement),except for basic configuration similarities, and more advanced thinking incorporated (to which I humbly, now, stipulate did in fact address some issues that plaued B/C/D. And yet, as a new design, had problematic issues with stablity of its own).

I agree.

Further, I see the H as a different airplane as far as commonality of parts, but very similar in lines and airfoil and powerplant. The major changes to the H from the D include:

New radiator cowl lines, new upper front cowl line, redesigned horizontal and vertical stabilaizer, moved wing position and cg position and static margin to address stability issues, leading edge of wing planform and smallr/lighter tires to accomodate the new changes, different canopy, longer fuselage and VERY few common airframe parts to get the weight out of the airframe.

 

[packardpursuit]

I guess what I'm chaffing at is how we tend to think in absalutes, aided by our 20/20 hindsight. For all the problems we pecieve tody, about the stablitiy issues of the Merlin being adapted to the basic Allison type airframe, the fact is, the manufacturer, in concert with official tech oversight and THOUSANDS of flight test hours, did not feel an immediate change to the Fin/rudder area was warranted.

 

[drgondog]

I guess what I'm chaffing at is how we tend to think in absalutes, aided by our 20/20 hindsight. For all the problems we pecieve tody, about the stablitiy issues of the Merlin being adapted to the basic Allison type airframe, the fact is, the manufacturer, in concert with official tech oversight and THOUSANDS of flight test hours, did not feel an immediate change to the Fin/rudder area was warranted.

Good observation.. I also imagine expediency of solving the looming defeat of 8th AF over Germany probably drove a conclusion that a few sacrifices to structural failure was worth defeating the LW?

Having said that, NAA did invest a lot of energy tinkering with partial solutions including reverse rudder boost, wheel uplocks, etc to put a bandaid on the problem. The "Go Light' initiative for the P-51F and H gave the engineers a chance to do what they probably recommended back in 1943... I imagine the production board said NFW to ANY disruption to the prodction lines on the B/D models.

 

[packardpursuit]

"I also imagine expediency of solving the looming defeat of 8th AF over Germany probably drove a conclusion that a few sacrifices to structural failure was worth defeating the LW?"

Not at all. A general perception that a problem existed is not the same thing as saying there was, infact, a problem. The fixes for percieved structural failures, believed caused by high speed yaw occuring in certain flight regimins, is not the same as saying in absalute terms, "faulures were occuring because of a known deficiency and were cured by a specific fix".

It has been reported such failures were reduced but not eliminated entirely. If I had to guess, I say the two biggest factors in that reduction was 1. the implimentation of the anti-servo rudder tab, which greatly reduced rudder sensitivity and increased input forces 2. education of the pilots flying Mustangs. Warning of possible dangers that may be encountered in certain prolonged flight regimens, would dampent the desire to play closer to the edge with abandon.

It is known some British based P-51D-5-NA's were on ops without bennifit of DFF (can't comment about possible less obvious mods) as late as Feb '45. Possibly overlooked and forgotten in the general rush of combat operations? Or as has also been reported, inplimentaion of mods mentined in the TO were sometimes left to discretion of squadron C.O.s? Or did such aircraft survive because of knowledgable pilotage? Could have been a bit of all three.

 

[drgondog]

Charlie - first of all I do not know what communication filtered back to NAA, or the context, regarding structural failures on the new P-51B. IIRC Tommy Hitchcock was killed pulling out of a high speed dive and the preliminary guess was perception of landing gear sagging under high G popping the gear door - and subsequent wing failure.. but IIRC they had no definitive smoking gun. His death was one of the very first symptoms of the problem

The issues encountered in March, 1944 with increasing frequency, included similar failures as well as losing the aft in in slow roll manuevers, then the 85 gallon 'snap roll' events while the tank was still causing an aft cg problem.

I suspect the inputs to NAA Engineering came in rapid fire about the time the P-51D-5 was rolling off the line and headed for ETO/MTO.

So, I really don't know what the conclusions were and when an ECO was created to experiment with different fixes, but we know the Dorsal was standard with the D-10 so that 'guess'/fix was approved quickly as was the reverse boost tab for the rudder...

I also agree that the Dorsal was not the answer to a mother's prayer relative to yaw stability and in any case should not have provided that much benefit anyway.

I do agree your two thoughts regarding reducing structural failures while the design on the H and flight testing of the F was progressing.

Having said that, I doubt that NAA ever explored or recommended any fix which would have caused a stop to re-tool, and what we did see were fixes that could be applied with ECO and effectivity changes, with mod kits for the field - while the P-51F was in full blown test. The F model was built with the D tail and experienced the same yaw issues as the D, despite the slightly longer Fuselage.

 

[drgondog]

Charlie - it is intersting that this conversation started witj 'mustang canopies'

 

[packardpursuit]

I was thinking that too. It could go in any number of directions.

One question that has bothered me is the implimentation of the boundry layer air gap, as developed for P-51B radiator air inlet. According to Gruenhagen and others, this was instituted when the XP-51B's were being tested and entailed considerable effort before arriving at a fianlized successful design. There is a glaring problem with the accounts that has not, IMHO, been addressed satisfactorily. As I see it, it concerns NAA engineers in a case of "what did they know and when did they know it?"

If we recall, the first Mustangs had a rather short carb intake situated on top of the cowl, about a foot aft of the spinner. I n rather short order this was modified by moving the intake to actually overhang the spinner rear by approx.1" Anothe feature of new configuration was a raised lip boundry layer by-pass that allowed dirtier air to escape injestion,below the intake itself.

Somehow I find it a bit difficult to understand how they developed a succesful fix for a boundry layer issue in the spring of 1941, but seemed to have (if the accounts are to be believed at face value) entirely forgotten the lesson for a year and a half, while deciding on a similar fix for the radiator intake.

While it is possible that they really didn't understand what was happening with those early Xp-51B radiator intakes, I find it a bit far fetched that no one, apparently, appreciated the great similarity of issues, earlier on. There HAs to be more to the story or it wasn't the earth shaking discovery purported.

 

[drgondog]

I was thinking that too. It could go in any number of directions.

One question that has bothered me is the implimentation of the boundry layer air gap, as developed for P-51B radiator air inlet. According to Gruenhagen and others, this was instituted when the XP-51B's were being tested and entailed considerable effort before arriving at a fianlized successful design. There is a glaring problem with the accounts that has not, IMHO, been addressed satisfactorily. As I see it, it concerns NAA engineers in a case of "what did they know and when did they know it?"

If we recall, the first Mustangs had a rather short carb intake situated on top of the cowl, about a foot aft of the spinner. I n rather short order this was modified by moving the intake to actually overhang the spinner rear by approx.1" Anothe feature of new configuration was a raised lip boundry layer by-pass that allowed dirtier air to escape injestion,below the intake itself.

Somehow I find it a bit difficult to understand how they developed a succesful fix for a boundry layer issue in the spring of 1941, but seemed to have (if the accounts are to be believed at face value) entirely forgotten the lesson for a year and a half, while deciding on a similar fix for the radiator intake.

I suspect that both adjustments to the carb intake design (Pre-Merlin) were more trial and error than analytical approach. Practical analytical prediction of boundary layer characteristice when immersed in a turbulent prop stream tube was not really possible in those days

While it is possible that they really didn't understand what was happening with those early Xp-51B radiator intakes, I find it a bit far fetched that no one, apparently, appreciated the great similarity of issues, earlier on. There HAs to be more to the story or it wasn't the earth shaking discovery purported.

IIRC Charlie - both the intake of the XP-51 and the future XP-51B were refined more by trial and error method for the radiator cowl config than analytics. I don't have an opinion on the carburetor but would tend to believe the same approach - absent some other documentation.

When the 'rumbling problem' indicative of turbulent flow cropped up in the XP-51B they (NAA) had to do a lot of testing to reconfigure the cowl intake to reduce the drag and the turbulence.. Remember the X-P51B also had a fairing from the lower aft part of the cowl into the wing as the X-P51B wing was still at the P-51A WL...

I wonder whether any wind tunnel tests were repeated after the wing was dropped and lower cowling redesigned for the production P-51B and/or the XP-51F and P-51H?

 

[packardpursuit]

Weather by anylitical or emperical means the solutions to both problems resulted in near identical configurations. It's the apparent year and a half difference that doesn't make sense to me.

It's quite possible there is a plausible explaination, however, that's the apparent mystery. In another forum, it was suggested that other firms had found similar solutions to the carb intake ingestion problems with near identical (in principle) configurations , at near the same time. P-38's for example, with a complet ly faired intake standing off the contours of the boom's side. IIRC P-39 got similar, though less pronounced carb scoop treatment, on spine aft of canopy.

The principle was known and used inthe industry. NAA used it sucessfully quite early on in Mustang production Hoever it took them quite a while to apply it to the radiator intake. It strikes me that P-38 also went to by-pass configuration for radiator intakes. Perhaps there was some general bias against using it there?

 

[Shortround6]

A wild guess and maybe totally wrong but extending the carb intake doesn't increase the frontal area of the aircraft by much if any. It may increase drag a bit but changes in power/intake pressure are going to be measurable fairly quickly.

Increasing the size (depth ) of the radiator scoop to allow for the boundary layer by pass will increase the frontal area and theoretical drag. Practical drag and or changes in cooling ability might take longer to measure.

 

[packardpursuit]

Shortround,

Good to hear from another interested party!

 

[drgondog]

Weather by anylitical or emperical means the solutions to both problems resulted in near identical configurations. It's the apparent year and a half difference that doesn't make sense to me.

?

Charlie - I still don't get the question regarding 'year and a half to fix the problem'?

Are you talking about the XP-51 through P-51A/Mustang I mods in UK? That radiator scoop design worked pretty well until the lower cowl config changes. So, if this is the timetable it seems the issue was a non issue for the first period of production.

When the XP-51B prototype was built following Brit initial mod to the MkI, it had a better looking lower cowl fairing but the pilots reported the 'rumbling' and NAA engineers started looking at the 'old' P-51A radiator cowl geometry and sent it to Ames to develop a solution... IIRC that took about two months in spring 1943 and again IIRC that was when the wing WL was dropped about 6-7", the lower radiator cowl was re-designed, problem with noise eliminated and the P-51B tooling was altered to accomodate these (and other changes)

If this isn't the problem or concern you are talking about, what is it?