Rebuild of BBI P-51...

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Rebuild of BBI P-51...

Post by Geo » Tue May 20, 2014 5:09 am

Greetings All,

I was directed here by a fellow member on Large Scale Planes (LSP). Ive long been an aerophile and an unabashed admirer of the Mustang. After building in various scales upon my recent return to modelling, I discovered 1/18nth scale, thanks to a friend, and was instantly hooked.

I watched JW (a friend on the P-51 SIG) rebuild a C-21 Mustang and was just bowled over by the possibilities 1/18nth provided. Hence, I looked through available airframes on ebay and found two for a total of $100.00 USD. One would be rebuilt, the other would be used as a parts bird should it be needed as such. Armed with a set of NAA Engineering Drawings, the EMM, the IPL and a set of drawings done by Charles Neely, long accepted as the best drawings of the Mustang available, the process of correcting and rebuilding began.

This project began months ago and progress has been made, but its slow going. Research, and making parts consumes a tremendous amount of time, effort and material. Never the less, the fuselage exterior is nearly complete. The empennage was a monumental task as it is mostly all new and has been converted to the earliest version of the Mustang. The spinner and prop blades are new, as is the entire front end. My goal in this effort is to produce a scale replica to the Mustangs engineering specs or as close as can I could get it.

PROP BLADES and SPINNER ASSEMBLY

While waiting for the air frame drawings to arrive from Charles Neely, work was begun on the prop blades and spinner assembly. Understandably, the BBI offering wasnt intended to be a scale representation. However, as such, it does provide a good set of bones upon which to add what is need to make it true to scale.

The spinner assembly was disassembled and checked for dimensional accuracy. The diameter was spot on, but the spinner cone was too short, and the backing assembly too long. This causes the split between the two to be misplaced. It was also slightly out of geometrical form and the prop shank apertures of incorrect shape.

To remedy the deficiencies, square ABS stock was added to the back end of the spinner cone and the back plate was reduced in height.

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New prop shank apertures were installed on the backing plate and the shank apertures were reshaped to match the "peanut" openings found on spinners when the Hamilton Standard Prop was used.

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Re: Rebuild of BBI P-51...

Post by Geo » Tue May 20, 2014 5:35 am

Next, the prop blades would need considerable rework to bring them into spec. In terms of length, they were perfect, but the cuff segment was not shaped properly. This cuff error seems to be a common mistake made by many. Understandably, if looking at photos of the Mustang prop, one could be fooled into thinking that the cuff flairs out at the bottom. It doesnt. Its one of the many illusions presented by the camera angle.

I really had no idea the trouble the prop blades would present. Whatever the material is that theyre made from, maybe some kind of vinyl, they are almost impervious to sand paper and files.

After hours of filing, one blade was reshaped. It was at this point the decision was made to cast the blades in resin both to insure uniformity and so hours more wouldnt need to be spend trying to modify the awful things.

On the left is the kit original next to the reshaped blade ready for casting.

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I called upon my dear friend Jerry Rutman to pour the blades for me. His expertise with resin, having produced full kits and conversions for years, would make short work of it.
I wasnt at all disappointed in the outcome.

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Re: Rebuild of BBI P-51...

Post by Geo » Tue May 20, 2014 5:50 am

Upon arrival of the Neely drawings, and after having then them adjusted from 1/16nth to 1/18nth, the nose diameter was checked and found to be a line on line match.

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Check of the spinner assembly for fit. Note that the curve of the spinner is tangent with the upper curve of the cowling and forms a continuous line. Looking at the line of the drawing, youll note that the cowling lacks sufficient height. This would be corrected during the nose rework.

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Re: Rebuild of BBI P-51...

Post by Geo » Tue May 20, 2014 6:33 am

COWLING REWORK

Before beginning this segment, it should be pointed out that this is a protracted rework. The cowling on the Mustang is a rather complex set of compound curves that, depending on viewing angle, appear and disappear. The most commonly missed aspects of the forward cowling are the bulges atop the cowling which clear the rocker covers of the Packard built V-1650. While Merlin has become the accepted way of referring to the Mustangs power plant, It was not refered to as such in the states. The Brits called it Merlin, here in the U.S. it was the Packard V1650.

To begin the rework, The fuselage was disassembled and sectioned into three pieces; cowling, center section, and empennage. The cowling halves were then chemically welded together.

It was decided to rework the exhaust fairing aperture first since it was badly positioned and shaped incorrectly.

The true position of the opening should run parallel with the thrust line with the bottom of the opening right on it.

A new opening was cut into the fuselage for the new aperture insert. A template was made directly from the drawing to insure accuracy of the opening. The insert was then welding into place.

Note the up angle of the front of the opening on the original. The new opening is actually two (2) degrees nose down but its not readily apparent.

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Re: Rebuild of BBI P-51...

Post by Geo » Tue May 20, 2014 6:42 am

SUPER CHARGER INTAKE OPENING and TUNNEL

Now that the exhaust stack fairing aperture has been replaced, attention turned to the super charger chin intake.

Since the outside dimension needed to be preserved, all rework was done on the inside. Heres the starting point.

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Re: Rebuild of BBI P-51...

Post by YT » Tue May 20, 2014 6:59 am

Excellent work!
"There are some people who disagree with me, they are wrong." --Gen George S. Patton

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Re: Rebuild of BBI P-51...

Post by Geo » Tue May 20, 2014 7:08 am

To effect the modification, several layers of .020 sheet stock were laminated into the opening, such that the opening became undersized. Once the welds were fully cured, the opening was slowly reopened and reshaped with files.

This is the form used to rework the intake and the resultant new intake shape. The balsa form would also double as the plug used to vac form the super charger intake tunnel.

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Last edited by Geo on Tue May 20, 2014 7:45 am, edited 1 time in total.

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Re: Rebuild of BBI P-51...

Post by Geo » Tue May 20, 2014 7:10 am

YT wrote:Excellent work!

Thanks YT! Hang in there, theres much more to come.

Geoff

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Re: Rebuild of BBI P-51...

Post by Geo » Tue May 20, 2014 7:24 am

The intake tunnel for the super charger is a vac form duplicate of the balsa plug you see in the mouth of the intake.

The intake tunnel runs from the intake opening and down along the bottom of the cowl, back to the super charger. I didnt run it back that far but I wanted to put enough of it in, in case someone looked in it. As it is, its about 4.5 in. long and consists of an upper and lower half.

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The completed tunnel installed in the nose...

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Re: Rebuild of BBI P-51...

Post by Geo » Tue May 20, 2014 7:43 am

COWLING RESHAPE


The shape of the cowling, especially at the very front, is remarkably elusive, and has escaped model manufacturers with the exception of the 1/32 Tamiya and perhaps ZM in the same scale, but Ive not seen that offering.

Most notably, the bulges atop the forward cowling are almost imperceptable when viewed from the ground and all but disappear in photos while at the same time being remarkably prominent.

Using the Neely drawings, Station locations were marked out on the cowl. These locations would supply locations for the templates. I should note that there are no factory drawings of the full fuselage. There might at one time been sectional drawings used by NAA model makers for wind tunnel models, but if there were, theyve long since disappeared.

Once the station locations were identified and transferred to the nose section, templates were made directly from the drawings. The thrust line was marked on each template for alignment to the thrust line on the nose for accuracy and symmetry.

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Re: Rebuild of BBI P-51...

Post by Geo » Tue May 20, 2014 7:43 am

COWLING RESHAPE


The shape of the cowling, especially at the very front, is remarkably elusive, and has escaped model manufacturers with the exception of the 1/32 Tamiya and perhaps ZM in the same scale, but Ive not seen that offering.

Most notably, the bulges atop the forward cowling are almost imperceptable when viewed from the ground and all but disappear in photos while at the same time being remarkably prominent.

Using the Neely drawings, Station locations were marked out on the cowl. These locations would supply locations for the templates. I should note that there are no factory drawings of the full fuselage. There might at one time been sectional drawings used by NAA model makers for wind tunnel models, but if there were, theyve long since disappeared.

Once the station locations were identified and transferred to the nose section, templates were made directly from the drawings. The thrust line was marked on each template for alignment to the thrust line on the nose for accuracy and symmetry.

You can see the areas that would need to be built up to add the rocker bulges at the eleven (11) and two (2) oclock positions at fuselage station -0- (STA 0) and cowl station .406 (CS .406).

Templates were also made for STA 20 and STA 50.5. Surprisingly, from STA 20 and aft, the cowling was remarkably accurate in both X and Y planes.

From this point, a generous coat of white Miliput Sculpting Epoxy was added to the nose and rough shaped while it remained uncured and wet. It was then left over night to cure.
Once cured, its remarkably hard and becomes a permanent part of the underlying surface.

This was a multi step interative process of sanding, checking contours with the templates and again sanding. Admittedly, on more than one occassion I oversanded and had to go back and add more Milliput to correct my error.

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Not quite there yet but well within guns range...

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Sanded out and primed to make sure it had proper geometry and fit the back end of the spinner. Like i said, the rocker bulges are near invisible but theyre there. If you look right behind the spinner at the top of the cowl youll see a glare spot. Thats where the cowl bends down into the spinner. The rocker bulges are right behind it. See it? :D

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That pretty much raps up the reshaping of the nose. Mind you this took a couple of weeks to complete and it was far from done. Next, the cowl fasteners and panel splits would need to be added and the card air intake breather plates would need to be installed.

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Re: Rebuild of BBI P-51...

Post by Geo » Tue May 20, 2014 8:52 am

The panel splits were next penciled onto the nose along with the fastener locations. In scale, the Dzus fasteners come out to be .047" in diameter. Care and a lite touch needs to be used when applying the panel splits. They shouldnt be wide, deep troughs like the original. Its time consuming and difficult to do; especially where they bend around the bottom curvature of the nose.

Once the panel splits were done, the fastener locations were marked out in pencil and then hand drilled using a .047 bit. Fortunately, Evergreen sells .047 rod stock. This would be used to form the fastener heads. The fastener holes are purposely drilled the same size as the rod stock to be used to insure a press fit. Once all the holes were in place, each was bevelled/chamfered to form the dimple or oil can effect so common on aluminum aircraft skin.

Note also that the carb air breather plates have been installed at this point. These were CNC'd for me by a friend to the NAA print.

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Ill stop here. The exhaust stack fairings still need to be added but Ill save that for the next update.

Hope everyone is well...

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Re: Rebuild of BBI P-51...

Post by Jay » Tue May 20, 2014 2:25 pm

Beautiful workmanship there Geo.
"you get in a steep dive in this thing and you've got almost no maneuvarabilty at all. You couldn't hit the broad side of a barn with the broad side of another barn"

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Re: Rebuild of BBI P-51...

Post by Geo » Tue May 20, 2014 7:43 pm

Jay wrote:Beautiful workmanship there Geo.
Jay

Thanks for looking in and your generous compliment. I hope you'll continue to look in.

Best

Geoff

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Re: Rebuild of BBI P-51...

Post by supersonicfifi » Thu May 22, 2014 1:41 am

fantastic ! keep us updated ! i can't wait to see the result !

here is something i found intersting for you :

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http://www.kingscale.eu/kat119.html
1/18 mirage 2000 & RAFALE should i say more ?

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Re: Rebuild of BBI P-51...

Post by supersonicfifi » Thu May 22, 2014 1:44 am

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if you needs some more details !
1/18 mirage 2000 & RAFALE should i say more ?

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Re: Rebuild of BBI P-51...

Post by normandy » Thu May 22, 2014 5:36 pm

Wonderful work!! and Welcome to the site Geo!!

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Re: Rebuild of BBI P-51...

Post by Geo » Fri May 23, 2014 10:23 am

normandy wrote:Wonderful work!! and Welcome to the site Geo!!
Normandy,

Many thanks for the welcome and your kind compliment. I hope youll continue to look in. Lots more to come.


Best

Geoff

I see your in LI...Im at the Jersey Shore.

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Re: Rebuild of BBI P-51...

Post by Geo » Fri May 23, 2014 11:00 am

Now that the nose rework is complete, something needed to be done about the exhaust stack shroud. Their purpose was to prevent hot exhaust gas from getting into the engine compartment. Often times however, they were removed so it can be modeled either way.

I chose to go with the shrouded exhaust stacks. A friend suggested a way to make the shrouds which was excellent. Unfortunately, I wasnt able to pull it off. I didnt want to discard his idea so rather than trying to hold machine tolerances bare handed, a way to end up in the same place was incorporated.

To begin, .180" was used as a starting point. The nice thing about the bar stock from Plastruck that was used, is that its center drilled. The center hole was too small but it was opened to .156". The original center hole served as a nice guide for the .156 bit.

Twelve pieces were cut. One end was left square and the other was cut on an angle of 55 degrees. In doing this, it naturally formed the required eliptical opening for the the exhaust stack opening.

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Six (6) pieces are glued side by side to create two stacks of six (6) each. A .020" ABS spacer is placed between each piece for proper spacing between each aperture.

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Each stack was then sanded to shape.

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Dummy stacks were then made up to check form and fit.

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The carb air breather plates were CNC'd by a friend to the NAA drawing.

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If anyone would likemore information, please feel free to ask.

Next on the very long list of things to do is the Empennage.

Hope everyone is well...

Geoff

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Re: Rebuild of BBI P-51...

Post by Axis Nightmare » Fri May 23, 2014 4:36 pm

WoW :!:

I considered the BBI P-51 to be pretty good. Coming from someone who spends a lot of time around P-51D "Cincinnati Miss" at the Tri-State Warbird Museum, I can say you are doing a magnificent job of reproducing an exacting scale replica of the Mustang. The 1/18 toys from the various companies were made as a close representation of the different aircraft allowing clumsy moving parts like retracting landing gear and sliding canopies which cause overly thick wings, too narrow of wheels, no dihedral and non accurate sliding canopy tracks or slots. I kind of think of them like an artist painting that's not always quite right in shape yet with the proper colors and markings makes an impressive example if taking in the entire effect. The problem in our case is that you can't have it both ways. It can either be a toy or a scale model. The paint and markings, however detailed, are in some cases just lipstick on the pig. Look close and it is still a pig. The overall effect is impressive non the less.
We tinker with making improvements from time to time. That's always the fun and challenge to me.

Your efforts are truely amazing :!:
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What makes the P-51 Mustang so special?

"It would do for 8 hours what a Spitfire would do for 45 minutes."

Brig. Gen. Chuck Yeager

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Re: Rebuild of BBI P-51...

Post by Geo » Sun May 25, 2014 7:58 am

Axis,

Thanks for looking in and your kind compliment. Its always rewarding to know other enjoy my work. Thank you.

I understand what you're saying about these large representations of classic aircraft. It would seem that there has been a good deal of cross talk between manufacturers. Comparing notes with a friend about his C21 Mustang and my BBI, they are dimensionally the same and share the same deficiencies. The BBI was also compared to the 1/24th scale Trumpeter kit. They are mechanically an exact match. Based on this, I have to believe there's been a lot of pyanky danky going on out in the hen house.

Your assessment of the BBI item is understandable. It looks the part save for the gimmicks. The fuselage is remarkably close in plan form. Its good (with minor variations)back to STA 248. From 248 aft, its a smoking hole. There is a scale .270" missing in length and all of the empennage is just overblown. Its bad enough, such that, it requires the empennage to be replaced almost in total. Its a heavy lift job that makes or breaks the rebuild. Converting it to an
NAA P-51 D-5 NA adds another aspect of difficulty in that the dorsal fin fillet must come off and all new tail fairings need to be made.

I've looked briefly at the wing. Its close in shape, but is short in span .5" in total, the root cord dimension is short, and the extended leading edge is is too small. Cord depths at 50% are pretty good. As you stated, there is zero diheral. There's also an awful warp/material irregularity span wise. With some car full bending And a belt sander I was able to correct it, but the span still needs stretching along with other corrections.

I'm fortunate, in that I have a copy of the NAA Engineering Drawings, the EMM, IPL, and MaintainanceManual, plus the guys on the P-51 SIG. They are a tremendous bunch of guys and an even greater resource. You're fortunate that you can bet up close and personal with Cincinatti Miss. Getting close to a Mustang is something I don't have the ability to do.

I do thank you for looking in and hope you'll continue to do so. Thanks for commenting.

Regards

Geo

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Re: Rebuild of BBI P-51...

Post by Geo » Mon May 26, 2014 4:30 am

Greetings All,

The preceding finishes up the easy part. This next segment will deal with the fuselage and the make or break aspect of this effort...the empennage.

The initial layout revealed a very large discreprncy in LOA. The exact same discrepency exists in the Trumpeter 24th scale kit. Otherwise, the alignments in profile were pretty much line on line with the exception of the cockpit sill which was also out quite a bit.

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Re: Rebuild of BBI P-51...

Post by Geo » Mon May 26, 2014 4:56 am

As noted earlier, all is fairly good back to STA 248. The tail plane geometry matches up fairly well but its too far forward. Meaning, there is a considerable section of fuselage missing.

Note, on the drawing, the note states not to remove the bottom pan. Initially the plan was cut aut along the bottom pan line, slide the upper fuselage section back, and then add material to the bottom pan to increase length. The bottom pan was removed based on geometry issues found later. Mainly the flat nature of the aft tail section.

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It was decided to make a cut at at STA 248 and move the entire tail back the required amount. In doing so, the elevator hinge line and the rudder tail post come into proper placement.

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In shifting the tail section aft .270, the required distance to correct the LOA, the cross sectional dimensions of the front of the tail section are now slightly larger than the drawing. This oversize condition would allow for the tail section to be pivoted in order to bring the rudder hinge line and the elevator center line into proper plane.

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Last edited by Geo on Mon May 26, 2014 5:10 am, edited 1 time in total.

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Re: Rebuild of BBI P-51...

Post by pickelhaube » Mon May 26, 2014 5:08 am

Geo your doing a great job . It seems the more you do , the more that has got to be done.

My hat is off to you :D :D :D
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Re: Rebuild of BBI P-51...

Post by Geo » Mon May 26, 2014 5:13 am

pickelhaube wrote:Geo your doing a great job .It seems the more you do the more that got to be done.

My hat is off to you :D :D :D
Hi pickle,

Thanks very much or youre kind compliment. Your certainly correct in your observation. This thing is like an old house...the more you fix, the more you find wrong.

Many thanks for looking in.

Cheers

Geo

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