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Old May 21, 2014, 08:04 PM
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United States, WI, Fond du Lac
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Build Log
P-61 Black Widow (or RF-15 Reporter) 1/12 scale

Time for another P-61! I've done 2 smaller P-61s in the past and they were great flyers. The P-61 has a lot going for it; a large broad wing and elevator plus twin rudders in great proportions for a model. It's also a trike with large wheels which makes it a good candidate for grass runways. Unlike a P-38 and many other twins, it has a long nose which makes it easy to get the CG right without adding lead. Like most twin boom aircraft, it makes sense to build the wing center and twin booms as one unit. This will be 1/12 scale or 66" wingspan so I'll make the outer wing panels removable.

The P-61 has a big downside and that is all that glass! I spent more time making the vacuform plugs than I did on the rest of the model for my smaller one. There is however, the last P-61 variant: The RF-15 Reporter which was an unarmed photographic reconnaissance aircraft. The prototype was modified from the last fighter version, the P-61e. The Reporter had a single tandem cockpit with a bubble canopy.

I've tried to interest some other members of the club to also build one and share some of the cost of getting all the plugs made and the canopies pulled by offering copies of the fuselage shells. If I can get a couple takers, I'll go ahead and do the fighter version. If not, I'll buy a canopy from Parkflyerplastics.com and do the Reporter version.

WS 66"
Length 50"
Motors: 3536 1000KV
Battery (2) 2200mAh 3S
Target wt. 75 Oz.
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Old May 21, 2014, 08:11 PM
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United States, WI, Fond du Lac
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Getting started.

The first thing I do is find a good 3-view and import it into CorelDraw. I use an old version that runs on Windows XP but it does everything I need. I resized the 3 view to 1/12 scale. On a new layer, I trace the outlines of the nacelle. I'll trace a second outline 1/4" inside the first to account for the FFF skin and build the forms to that line. On a another new layer I start drawing in structure. In this case, I'll need some support for the retracts. This is where I work out the geometry and the support structures. For the nacelles, I'll use a simple 3 former unit for the firewall and retract supports. Finally, I derive the shapes of the formers using the top and side views along with cross sections from the 3-view. That will usually get me close. I'll tweek the shapes if needed when I make the forms.
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Old May 21, 2014, 08:35 PM
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The nacelles, tail, and wings are the same on the Black Widow and the Reporter. So I can build those before I decide on which version to build.

I'm working on the nacelle molds here. I printed out the mold outline and glued it to two 1/2 plywood backer boards. After cutting them out and sanding to the lines with a disk sander, I rough cut foam blocks with a hotwire and glued them to the backer boards. I left a gap between the blocks so I could slide in cardboard templates to check my progress while I shaped the forms. Once the forms are close to the final shape, I'll worry more about getting the right and left halves the same than matching my drawing. I never know if the 3-view is correct or if my drawings are accurate.

I'll be using the heat formed FFF technique I've used for the last few years. (See here for links to various builds using the technique.)

Shaping the rudder/fuselage junction was tricky but photographs and a 1/48 plastic model helped get that area at least close to the scale shape. You have to compensate for the thickness the FFF skin will add.

Drywall sanding screen is my weapon of choice for shaping the forms.

The FFF is covered with PVC packing tape (over the film) and then taped to the form. The covered form is then baked at 100 degrees C for 15-20 minutes. The FFF will now hold the shape of the form. It's light and the shaped shells are quite stiff when glued together so there is very little internal structure needed.
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Old May 21, 2014, 09:08 PM
Now in TN!
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Chapel Hill, TN USA
Joined Apr 2001
24,350 Posts
This will be another nice pmullen build.

J
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Old May 21, 2014, 09:48 PM
The "pro" in procrastination
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Canada, ON, Kingston
Joined Mar 2004
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Hey Pat,

This is going to be cool!

Steve
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Old May 22, 2014, 06:45 AM
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Liverpool, England
Joined Jan 2005
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Looking forward to this one Pat, the widow is one of my favourite all time planes, I built one a couple of years ago and the profile of it in the sky looked great

The technique you are using is really interesting, what does FFF actually stand for? Do you have a really big oven to bake the parts in or have you made something?

Dependent on how scale you are going you might find the MAAM restoration project a good reference for photographs and its a great story of how they recovered the P-61 for the jungle and the work they are doing to make it airworthy - http://www.maam.org/p61.html

Cheers, Ken
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Old May 22, 2014, 07:39 AM
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USA, PA, Westmoreland Co.
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The F-15 reporter is a sleek design and mostly unknown. It will be a unique model for sure.
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Old May 22, 2014, 08:33 AM
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Blacksburg, VA 24060 USA
Joined Feb 2000
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pmullen,

Are your GA drawingsm from this site? http://napoleon130.tripod.com/p61blackwidow/id26.html

I saw an F-15 fuselage outside a hangar in Dallas-Fort Worth, 1960. Hadn't known about the F-15 prior to then. P-61C-1NO c/n 1376 AF Ser. No. 43-8330, formerly NASA's, is part of the NASM at the Udvar-Hazy center near Dulles Airport. Another P-61 is at the National Museum of the USAF, Dayton, OH.

Jim R.
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Old May 22, 2014, 12:00 PM
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United States, WI, Fond du Lac
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Quote:
Originally Posted by J Morgan View Post
This will be another nice pmullen build.

J
Quote:
Originally Posted by Steve85 View Post
Hey Pat,

This is going to be cool!

Steve
Thanks guys.
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Old May 22, 2014, 12:18 PM
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United States, WI, Fond du Lac
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Quote:
Originally Posted by heli_madken View Post
Looking forward to this one Pat, the widow is one of my favourite all time planes, I built one a couple of years ago and the profile of it in the sky looked great

The technique you are using is really interesting, what does FFF actually stand for? Do you have a really big oven to bake the parts in or have you made something?

Dependent on how scale you are going you might find the MAAM restoration project a good reference for photographs and its a great story of how they recovered the P-61 for the jungle and the work they are doing to make it airworthy - http://www.maam.org/p61.html

Cheers, Ken
The FFF stands for fan fold foam. The technique can also be used with depron or $Tree foam. The oven is just foil faced polyisocyanurate foam. I had some 1.25" thick stuff from a building project and made a box 16 x 16 x 48". The sides are just taped together so it stores flat when not in use. The heat comes from a ceramic space heater with the overtemp cutoff bypassed I now use a PID controller and a thermocouple temp probe to control it but I used to just watch a thermometer and flip the switch on and off. There's a more detailed explanation in some of my earlier build logs.

I'm aware of the MAAM restoration. There are many, many good photos that show more details than I'll put in. It's probably the best source for P-61 scale documentation photos all in one place.
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Old May 22, 2014, 12:26 PM
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Quote:
Originally Posted by JRuggiero View Post
pmullen,

Are your GA drawingsm from this site? http://napoleon130.tripod.com/p61blackwidow/id26.html

I saw an F-15 fuselage outside a hangar in Dallas-Fort Worth, 1960. Hadn't known about the F-15 prior to then. P-61C-1NO c/n 1376 AF Ser. No. 43-8330, formerly NASA's, is part of the NASM at the Udvar-Hazy center near Dulles Airport. Another P-61 is at the National Museum of the USAF, Dayton, OH.

Jim R.
I've had several 3-views for years but that looks like the ones I'm using.

I've seen and photographed both the P-61s at Udvar-Hazy and at NMUSAF. You really appreciate just how big this "fighter" is when you stand next to one.
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Old May 22, 2014, 05:05 PM
Parkcityflier
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Park City, UT, USA
Joined Aug 2001
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A good friend of mine, Ralph Ponte, flew the last flyable F15 years ago as a fire fighting air tanker. Unfortunately, he had a crash with it and destroyed the aircraft. We were both pilots in the business and flew many aircraft that have now been saved as vintage warbirds.
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Old May 23, 2014, 06:18 AM
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Originally Posted by parkcityskier View Post
A good friend of mine, Ralph Ponte, flew the last flyable F15 years ago as a fire fighting air tanker. Unfortunately, he had a crash with it and destroyed the aircraft. We were both pilots in the business and flew many aircraft that have now been saved as vintage warbirds.
Wow, that's cool. I am familiar with the story. I've thought about doing the tanker version of the Reporter.
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Old May 23, 2014, 06:56 AM
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Here's a shot of the rudder setup. The P-61 has a distinctive curved LE on the rudder and I wanted to reproduce that. I took 2 layers of 1/16" balsa, wet them, and pre-bent them by rolling them over a can. Then I glued them together and taped them to a foam mold cut to the proper curve and let them dry. I made the balsa wide enough to get both sides from the one lamination.

After the piece was dry, I cut it in half and used it to trace the cutout on the foam. The balsa was then glued to the foam. The balsa will give a nice strong surface to glue the hinges to and acts as a vertical rib to strengthen the rudders.

I built up a pair of new rudders from balsa. I found out on the Tigercat that it's easier to build new rudders than to try to use the foam cut offs. The full scale P-61 has fabric covered control surfaces and that's easier to reproduce in balsa.

I'll use a pair of micro servos to operate the rudders. They'll be partially hidden by the elevator and that's much simpler (and probably lighter) than linkage to tie the rudders together and 1 servo. I'll use pin hinges for the rudders in more or less scale locations. I'll need to use a long, 3/16" pin hinge at the center to reach!

The LE of the fin was reinforced with two layers of 1/16" balsa. The balsa LE will add a lot of dent resistance. The balsa was wet and pre-bent with heat to the approximate shape and glued onto a flat sanded into the foam. The fins were sanded to shape and given a coat of WBPU to harden the foam a bit. That way, any filler can be sanded flush with the foam without removing more foam.
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Old May 25, 2014, 08:05 PM
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I'll make the wing center section so I can trace it for the templates to hot wire cut the wing saddles in the nacelles.

I'm using the so called "laser method'. Rib blanks are glued between two boards and the ribs are cut with a hot wire. It combines the best attributes of a solid foam wing and a built up wing. The two boards ensure a straight wing every time. It looks complicated, but each step is easy and fast.

Structurally, I'll use a pair of blade spars in the center section. The formers that carry the main gear mounts will bear on the spars as well. The outer sections will be removable and I'll use carbon arrow shafts and epoxy soaked paper wing tubes. I'm going to attempt to make the entire center section straight, in one piece, and then cut it two and sand in the dihedral angles. The spars will be one piece so I'll build in balsa boxes to receive the spars.

Steps:
1. Cut out the rib blanks and hot melt glue them to a board. The layout was transferred from the plan and drawn directly on the board. Either FFF or 3/4" foam depending on their location.
2. Glue on the top board with dots of Gorilla glue. (Takes too much time to use hot glue.)
3. Affix the hot wire templates.
4. Make the first cut.
5. Make the slots for the spar boxes.
6. Make the holes for the wing tubes. Each side has to be done separately to get the angles right.

Still more to do before I add the top skin but that's enough for tonight.
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