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Nov 24, 2016, 10:52 AM
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Found a good shot of the "flat spot " on the spinner. Dark access hole for the propeller dome wrench is 7/8" dia., so I'm estimating a 3/4" outside of that, making overall diameter approx. 2-3/8". The hole is normally covered with a hard rubber plug/cap that continues the spinner curve, but has a mall raised, area dead center. However, on WWII ops ( and to this day), the plug was often left off.
Last edited by packardpursuit; Nov 24, 2016 at 11:00 AM.
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Nov 24, 2016, 12:03 PM
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A real good vista of the "flat spot" on the rudder outline appears here:

https://www.rcgroups.com/forums/show...1&postcount=27

there's a vertical segment above the tail light. I have often wondered why they built it that way?

Imagine... one of the most streamlined aircraft ever,... shows blunt at both ends!
Nov 24, 2016, 01:21 PM
Terrain! Terrain!
Twelveblades's Avatar
Quote:
Originally Posted by packardpursuit
A real good vista of the "flat spot" on the rudder outline appears here:

https://www.rcgroups.com/forums/show...1&postcount=27

there's a vertical segment above the tail light. I have often wondered why they built it that way?

Imagine... one of the most streamlined aircraft ever,... shows blunt at both ends!
I got the flat spot on the spinner (shows up well on the 1/48 Tamiya P-51 models), but I can't locate the one on the rudder. Do you have a close-up photo of it? Probably just my old eyes...
Nov 24, 2016, 04:27 PM
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Twelveblades asked:" ... I can't locate the one on the rudder. Do you have a close-up photo of it?

Photo in the link is pretty large and quite clear. Find the light fairing on rudder TE. flat spot emerges vertical, directly from the light. I'd guess its about 4" -5" high.

Here's another Mustang anomaly although not quite as clear, and DEFINITELY not on any current P-51B kit . What is gong on in this photo? There is definite lump in cowl profile, about a foot infront of the windscreen (Hey! Another flat spot!). It is a regular feature of P-51B/C, but top cowl will not interchange with D's. Once appreciated, this will be easily seen in all sorts of B/C photos. Current "P-51C Princess Elizebeth", flying in GB is actually a D cowl on a modified D fuselage.
Make sure to enlarge to max .
Nov 24, 2016, 08:30 PM
Terrain! Terrain!
Twelveblades's Avatar
packardpursuit said, "Photo in the link is pretty large and quite clear. Find the light fairing on rudder TE. flat spot emerges vertical, directly from the light. I'd guess its about 4" -5" high."

OK, I think I see what you mean, as I've indicated in these two photos. The break in the TE curvature occurs between the tail beacon fairing and the next rib, which isn't really noticeable from a distance. Maybe it was just faster and more cost-effective to manufacture it this way, rather than form the TE of the rib to continue the curvature? I can't imagine it having any negative aerodynamic value.
Last edited by Twelveblades; Nov 24, 2016 at 09:08 PM. Reason: oops
Nov 27, 2016, 01:13 AM
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I've been searching my stuff for a decent photo and remembered this shot from the old AirCam P-51B/C booklet. It is only one I've ever seen where a D is flying behind. Kind of small, but it does give an idea of the differences, if you look REAL close(??).

I've put an arrow on call sign, MC-L, indicating bump. No bump on D, beyond. The D's firewall is about 7/16" lower than B/C's firewall.
Nov 29, 2016, 12:48 AM
Terrain! Terrain!
Twelveblades's Avatar
packardpursuit said, "Here's another Mustang anomaly although not quite as clear, and DEFINITELY not on any current P-51B kit . What is gong on in this photo? There is definite lump in cowl profile, about a foot infront of the windscreen (Hey! Another flat spot!). It is a regular feature of P-51B/C, but top cowl will not interchange with D's. Once appreciated, this will be easily seen in all sorts of B/C photos. Current "P-51C Princess Elizebeth", flying in GB is actually a D cowl on a modified D fuselage.
Make sure to enlarge to max."

That's a puzzler, but there has to be a good reason for the "bump". It appears to be in the area above the oil tank, but I haven't been able to find any B and D cutaways to the same scale to see if the oil tank was lowered on the D model. Can't imagine why it would be, and since the vast majority of P-51Bs and all P-51Ds used the same V-1650-7 engine, that wouldn't explain it either.

Could the absence of the bump on the D model be due to aerodynamics? Because the B had a much more upright windscreen than the D, maybe the bump on the B was to improve airflow over its windscreen, while the more raked windscreen on the D, with its lower drag coefficient, obviated the need for that bump. That's a possibility, because I do know that all models of the P-51 underwent extensive wind tunnel testing to squeeze every possible drop of performance from the airframe.

Just guessing.
Last edited by Twelveblades; Nov 29, 2016 at 01:43 PM. Reason: Typo
Nov 29, 2016, 02:50 PM
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B/C's were actually a couple mph faster than D's, probably because of being OVERALL aerodynamically cleaner than the D's etc. Oil tank not lowered that I can tell, however the firewall appears to have been re-faired to better flow into new windscreen. The new profile goes from cowl Sta. 47-1/8 (former right behind engine cylinder banks) thru top of firewall, to wind screen. It would be interesting to find out if the top of the firewall (and armour!) was trimed (most likely) or if the firewall was moved down the canted angle, trimed to fit top of wing and all the bolt holes were re-located higher?

I believe B/C have a "bump" in the cowling because priority was getting Merlin Mustangs into production and operations as quickly as possible. B/C are a compromise utilizing earlier design elements (A-36/P-51A wing , guns and landing gear, etc.). BTW- guns were mounted at angle because of the A-36 gun mounting. There is NO TRUTH that B/C wings are thinner than a D's.

AFAIK ,any existing photos of P-51D wind tunnel models show a considerably different canopy arrangement, than what finally appeared. There are no factory drawings that I'm aware of, that show the new profile. IIRC, D cowl drawings show a hump, exactly as per B/C but give a different ht dimension at rear of cowl(where it meets/lands on firewall). Conversly, due to the larger wing root of D, it could be argued that latter is actually" thinner" than B/C!
Nov 29, 2016, 04:25 PM
Terrain! Terrain!
Twelveblades's Avatar
Veery interesting. There are a lot of myths about the P-51, perpetuated by writers who just repeat previously published inaccurate information rather than doing original research. And the internet certainly hasn't helped.

True, the B/C was marginally faster than the D. And...the Allison model was certainly no slouch below about FL150.

Now for a question: who was actually responsible for mating the RR Merlin to the P-51 airframe, the British or the Americans?

There is some evidence to suggest that is was the doing of 1st Lt Benjamin S. Kelsey, who was an aeronautical engineer with a degree from M.I.T., and the head of the Army Air Corps Pursuit Projects Office at Wright Field. It seems that even before the XP-51 first flew, two of the P-51 airframes were set aside for testing with the Packard-built Merlin.

But other sources state the Merlin Mustang was suggested by the British in 1942.

Who is right?
Nov 30, 2016, 08:39 AM
Registered User
History is a funny thing. It SHOULD be based upon established dates and facts, HOWEVER, it is rife with personal bias and outright lies. Aviation history, especially seems to suffer inordinately, in this regard... but then... I'm biased!

Don't know exactly who suggested mating Merlin 61 to Mustang I airframe. Could have been RAF, Roll Royce, an enthusiastic test pilot or two, etc.. Once suggested however it seems to have gotten a lot of support from several different influencial people. There was a US AAF pilot stationed in Britain named Tommy Hitchcock, who championed the cause, both there and stateside. Can't imagine forward thinking NAA engineers not salivating over prospect of their advanced airframe fitted with the best aero engine in the world. They would also have been aware of Curtiss' use of a lower rated Merlin in P-40F.

Early indicator of NAA interest saw introduction of a projected design known cryptically as... wait for it... "Packard Pursuit". A detailed plan for wind tunnel test model was made. IIRC, the plan is dated about the time the British started looking into such a union.

Speaking of myth, on of the Great ones is the 100 day wonder story. Central to that particular story is the notion that the Mustang was built to a" British specification" and that the British also stipulated that a prototype must be completed in so many days, etc., etc.

While there was a" british specification/contract", the aircraft details were dictated by NAA . The british put the time stipulation in the contract, but was in fact suggested by NAA. They were selling airplanes!

History seems to like glossing over mundane details to make the story more exciting. People often forget that NAA as an industry leader had a very astute PR dept., always ready to shine the best light on NAA accomplishments and products. This provided much of the later division between the engineering and the "front office". The former feeling the latter kept loudly espousing the official PR, long afterward.
Dec 01, 2016, 12:03 PM
Registered User
This just in! Additional data on spinner front detail here:
https://www.rcgroups.com/forums/show...0&postcount=88
GOOD STUFF!
Dec 04, 2017, 06:11 PM
I think I go fly
pyrobus's Avatar
Thread OP

Another


51.
Dec 05, 2017, 08:51 AM
Registered User
Nice try.

appears to be a homebuilt, probably a Stewart 51. The give away is miss-shaped cowl and prop bladescanopy too big for the scale. While one can generally reduce the overall scale to 70%, successfully, one still has to fit in a full size pilot. Thunder Mustang seems a more realistic effort, but again, canopy too large.

Several years back, Scott Hanchet ( Viper Jet) was very interested in developing a full size Mustang project for homebuilt market. He felt, if carefully built to same weight and power of 70% versions, would only lose 20 mph from top speed and gain in rate of climb, due to larger wing area. It would also carry second seat better , too.
Dec 11, 2017, 07:10 AM
I think I go fly
pyrobus's Avatar
Thread OP

My Bad


Thought so you got me
Mar 20, 2018, 09:38 AM
Suspended Account
Quote:
Originally Posted by pyrobus
This one was spotted at Reno today
It's a D model modified by NACA
P-51D-25NT
NACA mod.
44-84900
N51YZ

http://www.mustangsmustangs.com/p-51...erial/44-84900


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