Phenomenal P61 Black Widow project!
Tony Elliott, (old flying buddy o' mine and famed in sailplane circles for his enormous 35-foot span ETA-- seen on Paul Naton's Pro Aerotow video), is building an incredibly sophisticated 114" P61 Black Widow, from the Ziroli plan.
Modeled after the post-war P61C for the Thunderstorm project, this version has the turrent removed, the radar placed up front, and a black/red/yellow color scheme, for investigating thunderstorms (and eventually hurricanes).
Two Lazer 300 vee-twins converted to spark, with dual electronic ignition systems on each engine, on-board FEMA starters, Ziroli air retracts with three air sequencers and wheel brakes, SEVENTEEN servos (yup, count 'em, 17), three gyros, two opto-isolators to prevent glitches, four Matchboxes to sychronize ganged servos, one Equalizer II (for spoilers), 6 lipo batteries and one (absolutely bulletproof and ultra-reliable) receiver. Man!
In addition to the complete cockpit detail kit, Tony plans to add all panel lines and simulated flush riveting, with weathering. I look at stuff like this and it makes me cry for envy. Having the time to do a project like this is one hurdle, having the skill and stamina is another!
Go, Tony, go!
P61C Black Widow build
Anyone interested in construction pictures? I have a ton of them - general construction plus some custom methods developed from my large scale sailplane experiences, special jigs for setup, special considerations not included in Ziroli plans, custom molded parts for the "C" version, hints on canopy fitting, glassing, electronic setup etc
I have an Aeroplane Works wood kit and Nick's plans n' plastic package sitting on the shelf waiting for a shot at the building bench.
I plan to bash it into "C", and I'd like to add the fighter brakes.
Lemme know how to snag the photos . . .
Well, I decided to post some pics here and describe my building process as I believe, at least for the wings, it's a little different that normal - so here goes!
Why a P61? Actually, I had decided to build a scale, engine based aircraft about mid last year. I wanted something that looked nice, a twin specifically and something that handled relatively well (as well as twins can handle!). I searched for plans and found Ziroli. Since I have traditionally been a large scale sailplane builder, Ziroli and his plans were new to me. I ordered the B-25, P-38 and P61 plans and finally selected the P61.
Prior to actually selecting a twin aircraft to model, I had already decided on the engines. The laser 300 V-Twin has a reputation of excellent reliability – especially when converted to electronic, spark-based ignition from glow. C&H ignitions were consequently selected and through further publication research, so was the P61C.
Since the 300 V-Twin was a marginal fit inside the cowls of the Ziroli P61 (made for the A and B versions) – especially with a spark plug and cap on each head, the P61C/D versions really lent themselves to this engine setup due to the air intake “scoops” on each cowl. This meant a custom set of cowls or custom parts to add to the existing Ziroli cowls. The later was chosen as you’ll see later.
Additionally, since I am a fan of the “true scale look”, the lower supercharger scoops below each cowl with their deisgned exhaust outlets at the rear really leant themselves to a muffler system that would be internal to the aircraft and would exit where the real one has the exhaust exit. A perfect solution – no holes in the cowl for cylinder heads or mufflers, great cylinder head cooling (through the side scoops and internal baffles) as well as muffler cooling (through the opening in the lower scoop)!
This was also my very first, scratch bulit “stick and sheet – built up model”. My sailplanes have always been foam winged aircraft with fiberglass shell fuses. So, this model was essentially a test bed for me to learn new building techniques.
Since I now had the engines and the specific model I wanted to replicate, what was next? The research from widely available P61 Black Widow documentation showed me that, while the Ziroli plan, was capable of producing a “relatively” accurate scale representation of the P61, it was not complete in its representation. The three-views of the P61 showed many “subtleties” that were simply not on the plans. I therefore proceeded to add these items to the plans BEFORE starting the build and ensuring that all the supporting features for these additions, if any, were added prior to starting the build. Once I was happy with the additions to the plans, I started the construction process.
The construction order was as follows:
1). Center wing section
2). Wing tip panels
3). Center Fuselage
I will cover each section in separate posts with pictures.
Note also that my initial plan was to cut very part out by hand. After reviewing how many parts there were (lots!!) and actually starting the hand cut parts process, I decided on a different approach and purchased a laser cut kit of the Ziroli P61 from Precision Cut Kits. The kit was complete and really sped up the build process. I believe that this kit is created directly from the plan so any inaccuracies in the plan led to inaccuracies in the parts. There were a few that had to be corrected during the build.
I started this build in March of this year – it is now ready for priming, surface details and final painting
P61C Black Widow series (#2)
Wing Center section.
I have built many sailplanes in my modeling history, both small (10ft span) to large (38ft span) and have used foam exclusively for the core material. I have gained a significant amount of experience with foam cutting and wanted to use that experience for the P61. I did choose however, not to build the flying surfaces with foam as a core material and sheet them. What I did choose to do is use the foam “beds” from pre-cut foam wings as the “building boards/jigs” for each wing section. You’ll see this in the pictures. Essentially, the wing structure was built ON the foam beds providing a stable, consistent surface for each wing. There were some other benefits from this approach also.
1). The foam beds AND cores were used to pre-form the airfoil contours into the sheeting PRIOR to rib application therefore removing any wood bending stresses (read warping) from the skins
2). the foam beds became very useful when applying the final sheeting panels to lock the wing in shape.
3). The dihedral was already built into the foam beds making the complete center section a breeze to build
4). The washout on the wing tips was pre-cut into the foam cores using templates with washout built in. This created a wing building jig again, with all the necessary top and bottom surface requirements and provided an excellent building surface for the relatively complex spoilerons present on the P61. In the case of the tip panels, these were cut upside-down so that the ribs and spars were applied to the top surface sheeting first.
So, to construction:
Two cores were cut from white foam. It was important to create the center section foam beds to the exact height on both top and bottom surfaces for center section building AND for later alignment and building of the tip panels – specifically the joiners (see later). Due to the dihedral of the center section and then anhedral (with respect to the center section) of the tip section, careful calculations were made to get the template heights perfect for the resultant foam beds. The center section of the wing was to be built “top-surface up” and the tips were to be built “top-surface down” due to the spoileron assembly requirements. If you choose to use a method like this don’t forget to keep the cores themselves. They become a wonderful form in association with the beds to pre-form the skin sheeting prior to their assembly using alcohol/water.
Bottom line, when all the foam beds for the three wing sections were laid out, upside down, on my building bench, the resultant “building” surface was an exact form for the top surface of the wing from tip to tip – almost like making a mold of the top surface of the wing in one piece and building the structure within it. Great for setup, alignment of joiners etc – see later
The first piture shows a “dry run” of the first half of the wing center section – checking to see if the parts are accurately cut and fit well. Note the two separately cut foam cores as the building base. One other requirement of this method is that the spar locations and rib spacing must be marked on the sheeting prior to construction – maybe a drawback, but I didn’t find it so!
If you have a real keen eye, you may notice a “black” layer laminated between wood in the spar caps. That’s carbon – or, specifically, Graphlite. Graphlite is a pultruded carbon that can be purchased in differing rectangular cross sections in very long spools. I typically special order my spools in 500ft+ lengths and have used it extensively in my sailplanes for spar caps. Don Bailey, the guy who decided to post my original P61C pictures in this forum, mentioned the 35ft ETA I built a while back. This is a sailplane that weighs approx. 45lbs, has a 10 ½” wing cord at the root and a 35 foot wingspan. Graphlite and end-grain balsa were used exclusively for this wing spar structure. This aircraft looped under high speeds with wing flexing at the tip in excess of 3 feet. The graphlite spar caps were the primary reason for both the flexibility and strength of this spar system and consequently the sailplanes’ wing. Anyway, I digress!
The second and third picture shows both sides of the center section internal structure – Ribs and bottom spars are glued in place, the remaining items are dry fit – this includes top spars, the wing joiners, servo wire routing tubes, spar braces and all servo hatch mounting rails. Note that the servo hatches and the general shape of the bottom surface sheeting is already precut prior to gluing the ribs in place. As long as you are accurate and mark the sheeting well, this assembly method works very well.
The forth picture shows the main structure gluing complete, servo mounts added for the small flaps, flap structure in place, wing mounts in place (note lightening holes to reduce weight)
P61C Black Widow series (#3)
The picture here shows the top surface sheeting added. Since I only have a picture of the end result, it is probably worth explaining how I got to this stage.
Again, the 3” wide balsa sheets were pre-joined on a flat surface with wood glue and sanded for finish. The outline was then cut for the flaps and nacelle fitting at the TE. The center join curve was pre-cut prior to gluing to ensure an excellent fit between the two top surface sheeting halves. When happy with the fit, the sheeting was glued. Now, a point here about the glue and the method of gluing.
Firstly, you’ll remember that not only do I have the foam bed for the bottom surface (the surface the wing was constructed on), but I also have a foam bed that follows the top surface airfoil contour almost exactly. This is where the benefit, in my mind, of the foam bed technique really comes in handy.
The glue used to attach the top sheeting was Polyurethane. One version is guerilla glue, another is Elmers Probond Polyurethane Ultimate Glue. I used the later. The glue was applied to the tops of the ribs and spars of both center section halves. The sheeting was misted with water (the curing agent) and the top sheeting placed and taped in position. Then, a few sheets of wax paper were laid over the sheeting (just in case of glue seepage) and the foam cores laid on top of that and weighted down evenly. The structure was then left overnight to cure.
In my personal opinion this has a few advantages.
1). The sheeting can be applied in one piece giving an excellent final finish
2). The foam provides even pressure over the complete top surface and to some extent, allows the sheeting to conform directly to the smooth, accurate, airfoil contoured surface of the foam core. The polyurethane glue will fill any voids between sheeting and ribs also.
3). Since the sheeting is applied over slow curing glue, once the sheeting is applied, foam cores added over the top and weighted, the whole structure then cures to the exact dihedral and geometry you need (no warps, twists etc).
Now, this result can only be achieved by having accurate, no warp, no twist cores so core template design and cutting as well as core cutting itself needs to be accurate.
The only items left to do on the center section after sheeting was to cut out the small flaps, wrap some 1/16 balsa around the leading edges, check out the hinging mechanism I chose, hook up the control rods to the servo’s and flaps. And create the servo covers. All pretty simple stuff.
P61C Black Widow series (#4)
Wing Tip Panels
The wing tip panels were built in a similar way to the wing center section except this time, they were built upside down. The reason for this was the need to have access to the bottom of the wing to install the spoileron mechanism. This can only be effectively done from the bottom surface. Again, foam cores were cut at the correct heights, correct anhedral and correct washout at the tips. The goal of these cores was to mate each side up to the center section, TOP surface cores, place the center section onto the center section cores and use these to align the tip panels to during construction.
The first picture shows one of the tip panel foam beds, pre-shaped top sheeting and the parts needed for the structure. Of particular note should be the assembly that is pre-built – the left most spar looking object laying on the sheeting. This is the hinge pin assembly for the spoileron. It was made with differing thickness ply laminates and the yellow internal component of a Sullivan Nyrod. The internal diameter of the yellow core is almost exactly 1/16” diameter which allows for a 1/16” piano wire hinge pin to pass through it. The slots that are precut are for the spoileron arms and allow them to pivot the required amount. Note also that some of the larger ribs have some reinforcement laminations where the spoiler blade recesses into the wing. Balsa alone at this point would make the rib very prone to damage. You’ll also note on the right hand side of the picture the beginnings of the internal structure layout and gluing of the other wing tip panel. Again, careful marking of the sheeting for spar, spoileron and ribs is important.
The second picture is of the wing assembly in the top right of the first picture photo. You’ll see the basic structure in place as well as the internal framing structure for the spoileron glued to the top surface. On this wing, I have already cut out the slots in the top surface for the spoileron arms and blade. I simply used a dressmaker pin to mark the corners of the slots while the wing was resting in the core as you see it. Flip it over, cut them out and your done.
The third picture shows a mid-stage shot in one wing tip panel construction. The foam cores are now all temporarily joined together on my flat working surface and aligned along the LE which is straight. The center section is positioned in place on the cores and weighted in position. The root rib, joiner and locator pins on the root rib are placed in position against the end rib of the center section therefore ensuring good alignment. Spars and ribs are added and when satisfied with the fit of the joiner tube, it too is glued into place.
Servo hatch rails are added between ribs where servo’s will be installed, wire tubes, LE etc.
Now, with only the top surface sheeted and the structure in place, the wing was still fairly “flimsy”. I needed to have the wing a little more rigid to support the building of the spoileron. I therefore decided to sheet the LE section to the center of the spar and accomplished the sheeting task of the bottom surface of the main wing in two parts. The forth picture shows the addition of the LE sheeting to the center of the spar. It really made a difference and provided a good base to install the spoileron. This would not have been my chosen method of applying sheeting to the bottom surface of the wing but due to the spoileron requirement, it needed to be split into two pieces – LE to spar, spar to TE.
Servo mounts and servo’s were also added at this point.
P61C Black Widow series (#5)
The first and second pictures show the spoilerons. They were actually assembled and tack glued in the wing itself. Shims were used on either side of each arm, the hinge pin was inserted capturing each arm and the blade inserted for best fit, clearance in the spoileron blade slot etc. The arms were then tack glued to the blade. The wing was lifted from the foam bed (BTW, there was wax paper between the sheeting and the foam at the spoileron location to avoid glue contacting the foam), and the general operation of the spoileron checked. The spoileron balde was then removed and final glued.
A note here!! The spoiler blade, if not cut accurately from the blade pre-laminated blank (see Zirloi instructions) can easily end up warping in the spoileron slot – my first one did. It is very difficult to describe or show via pictures the right process for cutting the blade from the blade blank. The only advise I can give is, make several blanks on your 3 ¼ to 3 ½” tube, cut one out per the plan, see how it fits with the curvature on the end of each spoileron arm, lightly tack glue and check operation. If you are not happy with the way the blade seats in the slot, carefully identify what needs to change, identify how that change can be accomplished from the blade blank and re-cut the blade. The final result is as you see in the third picture. This was the second blade I made for this first wing. The angles of cut described in the Ziroli plans are “rough” estimates only in my opinion and with careful consideration of what changes need to be made to the blade, my second one was almost perfect.
P61C Black Widow series (#6)
Wing Tip panel flaps (or Flaperons)
I am personally not a fan of gluing control surfaces permanently to any flying surface. I always make them removable. The first picture shows the layout and design of the flap (in my case, the flaperon as the outer flaps will also be used as augmenting ailerons if needed) hinging I chose for the P61. I designed these through careful consideration of what I needed the flap to do and were laser cut from marine ply using a friends laser cutter. A total of four per flaperon were used. The hinge line on the P61 flap is very close to the bottom surface of the wing and therefore this type of hinging solution was the best I could come up with at the time. The “single” part of the hinge is to be attached to the TE of the wing, the double part in the flap itself.
In order to make sure the hinge pin was aligned and in a straight line, I decided to make a hinge alignment jig from material in the workshop. This proved to be simple to make and very affective at achieving the result I wanted and is shown in the second picture. Fundamentally it was a jig to align both the horizontal and vertical positioning of each hinge plus a hinge pin guide. Both a left and right jig was made – the left on one side of the jig, the right on the opposite side of the same jig! Remember, this is a jig only and not part of the aircraft. It is used for alignment only them removed. Here the picture shows the hinge pin and hinges in place just prior to alignment on the TE of the wing.
The third picture shows the hinge jig in place over the TE of the wing with the hinges “captured” by the hinge pin in the jig. Careful alignment is needed here obviously.
The forth picture shows how the sheer webs were then cut and slotted for the hinge. The sheer webs were glued into place between the top and bottom TE stringers and the locking bars inserted through the back of each hinge and glued to the sheer web. This was done for all four hinges and when cured, the hinge pin was removed from the jig and the jig removed – Viola! Four perfectly aligned flaperon hinges (picture 5)
P61C Black Widow series (#7)
Final flaperon hinging and sheeting
Once the wing TE hinges were in place, the double sided hinges and cross bars were threaded onto the hinge pin ready for applying half the flaperon bottom surface skin. These are shown in the first picture.
Picture two shows the half TE width sheet in place, drilled for glue access to the cross bars. The hinges and sheeting were tested and trimmed as required for fit prior to the sheeting being glued to the ribs and leading edge of flaperon. With the flaperon sheeting in place, holes predrilled for hinge cross bar glue access, each hinge block could be lifted into place and glued in position.
Allthough the third picture is not very informative, it does show one of the flaperon hinge blocks glued in position.
The forth picture shows the addition of the final piece of flaperon bottom surface sheeting and the remaining sheeting on the bottom of the wing and aileron using Ultimate Glue and the foam cores. This completed the main structure of the irst wing panelwing panel. The other wing panel was a repeat of this one.
The last picture is all three panels together with tip blocks added.
Throughout this construction process, the structure was never placed over the plans. Everything was built on the foam cores. After checking the incidences in a static position on my bench, moving only the incidence meter, all root chord locations/angles on the wing were identical. Each tip was measured and the difference between root and tip calculated – both tips were identical. For me, a testament to the method I used. I'm happy!!
P61 - Pause!
Want me to continue or was this too much already?
P61C Black Widow series (#8)
OK, so, the wings were almost done - would I have done anything differently?
Well, yes. The primary thing I would have done differently was to use fiberglass laminate for the trailing edges of the small flaps and flaperons. There are a couple of fiberglass laminates out there - G10 and Glass Ply from ACP. I had never used balsa as a sheeting material for my sailplanes - I have always used Obechi. Between the obechi and foam has always been a wet-layup of either fiberglass cloth or carbon cloth, depending on the aircraft. This created a very stiff TE that could be sanded to knife edge and preped accordingly for the finish. I didn't consider it for the P61 wings.
As it turned out, the small flaps were a non-issue and with the addition of the vellum coves in the flap area, the TE was stiff enough (see later pics). The flaperon however, was a different story. Predominantly caused by the tapering of the TE grain of the balsa at the flaperon TE, the result was fragile. I therefore decided to laminate some 0.020 Glass ply from ACP to the top surface of the TE's of both flaperons. This was done AFTER the wing was constructed. I used a dremel as a router and routed a 0.020 recess, about an inch back from the TE to the actual TE and then glued in a piece of glass ply. Not the easiest taks and you only have one chance to get it right - fortunately, I did - on both wing tips! If I had it to do again, I would laminate the glass ply into the balsa sheeting BEFORE applying it to the wing. Lesson learned!
Another item I did not mention was the hinge system for the small flaps in the center section. As I noted before, I am a big fan of removable surfaces. The Ziroli plans do not show a removable flap. Also, the flap itself is "captured" both ends by wing structure making it almost impossible to slide in a 1/16" piano hinge pin from either end. So, I made a call to go a little non-scale and drop the hinge line down below the bottom surface of the wing by about 1/8" and built two hinge systems similar to the flaperon above and used 2-56 socket head bolts and brass hinge bearings to attach. Not truely scale, but not permenantly attached to the wing either - see pics below. I have also vacuum formed a few small fairings to cover the hinges - the result is much better than just the hinges themselves.
Last item: The later versions of the P61 were fitted with four pylons for drop tanks. There are no mounting plates in the Ziroli plans for these so they need to be added. Unfortunately, I completely forgot to add them to the center wing section during construction but DID add them to the wing tip panels. Where they are located on the aircraft means that for the center section, there is nothing but the sheeting to attach them to for me. I think I will vacuum form them from a plug making them very light ang glue directly to the sheeting with perhaps some CA hardened screw holes in the sheeting. The tips are now no issue with the braces I installed between the ribs.
P61C Black Widow series (#9)
The P61 Fuselage.
The P61 fuse is almost a direct following of the Ziroli instructions including the building jigs noted. There are no real special deviations from this EXCEPT for the canopy mounting and cockpit area.
There is no special consideration in the Ziroli instructions for mounting the canopy. I have seen other pictures of P61’s built from the Ziroli plans and most of the canopies are simply screwed to the outside of the fuse. This can be done but leaves three areas where you have “steps” equal to the thickness of the canopy plastic – for the front canopy these are the front over the nose, the sides, and all the way around the rear of the canopy. This is almost the same for the rear canopy – sides and around the “front” edge of the rear canopy. The rear edge of the rear canopy is a little different in that it sits on top of the rear most former which is where it should be.
So, what to do. If you take a close look at the first two photos, you will see what appears to be a different material inset into the fuse sides below the canopy area. This again is glass ply. What I decided to do was to live with a 0.010 step along the sides of the two canopies and eliminate the front and rear step on the front canopy and the “front” step on the rear canopy where it butts to the center removable gun-turret section of the fuse.
To do this, the former where the rear of the front canopy sits was sanded down to allow the canopy to butt join to the gun-turret section (center) of the fuse – this was done after fuse construction. Same for the former at the “front” of the rear canopy.
On the front canopy at the nose, I recessed the balsa sheeting so the canopy was flush to the nose. Good so far
Now, there were two ways to approach the sides of the canopy that I could think of at the time. One resulted in a step, the other did not.
1). NO STEP: Create a recess on the outside surface of the balsa around the canopy line with a “final” depth equal to the thickness of the canopy plastic in the right position so that the canopy could be screwed directly to the fuse sides. The canopy would be cut to fit that recess and screwed to the sides of the fuse – this would result in a flush mounting of the canopy. There are a couple of problems I found with this method however.
i). Drilling holes in the plastic canopy is easy – countersinking them HAS to be done over a hard wood surface otherwise the plastic simply “indents” but does not cut. This leads to mounting problems on a balsa sided fuse!
ii). Once the screw holes ARE countersunk, the recess cut in the balsa MUST be deeper than the thickness of the canopy plastic alone and MUST have at least a 1/16” ply laminate glued to it. This is because when you screw the canopy directly to balsa, the balsa indents and the canopy does not stay straight along its length. The surface beneath the canopy must be hard to prevent bowing of the canopy plastic.
Since I didn’t think of the hard surface beneath the canopy before I thought of option 2 below, I did not use this method but probably would on the next one. A lesson learned!
2). STEPPED: Create a “pocket” along the edge of the fuse for the canopy to slip into. This is the method I used. The fuse was actually made before I even though about canopy mounting and so this technique required some modification to the existing fuse.
I essentially made two assemblies via lamination. I also apologise that I do not have photos of this assembly but the old digital camera crapped out on me. I will take pictures of the final result and add below.
If you look at the first photo below of the finished structure, you will note the fiberglass laminate on the sides of the fuse just below the canopy. This was essentially a lamination of different materials to create a 0.020” “slot” along both sides of the fuse for the canopy plastic to slip into. The “inside” laminate was 1/16” marine ply for the screws to screw into (remember a hard surface from option 1 above). Then another laminate of 0.020 glass ply, smaller in size (vertically smaller), to create the pocket area, then a final exterior laminate, as you see in the picture, of 0.010 glass ply. Since I used 3/32 sheeting for the fuse, the resultant 1/16” + 0.020 + 0.010 was very close to that thickness.
The canopy itself was under 0.020” in thickness and would have created a “sloppy” fit in the resultant slot in the fuse. To fix this, I laminated small strips of glass ply along the inside, bottom edges of the canopy to “tighten” the fit of the canopy in the slot.
The final result is as seen on the two first two photos. With the addition of the flightmetal framing on the canopy and along the top of the fuse side laminate, I feel it is a “good-enough” solution and looks fairly realistic. One of the primary reasons I chose to add the outer 0.010 glass ply laminate was because of the countersinking issues I faced with the plastic of the canopy. With the glass ply on the outer surface, I was able to successfully countersink this with a clean cut, drill the holes in the canopy slightly larger to clear the countersunk head of the screw and everything laid flat, screw heads were flush and the result was pleasing!
Now, I am sure there are alternate and probably better ways to do this but as I said earlier in this series, this is the first time I have attempted this type of model building so what I came up with was the best I could think of at the time.
I have added three additional pics of the fuse construction. The first is general framing per the instructions. The second one is where the above comments about canopy mounting apply. This first panel of sheeting per the Ziroli instructions does NOT cater for any other canopy mounting method other that screwing it to the sides. I would recommend that you consider laminations, slots, whatever you feel works best for the canopy BEFORE you apply this first sheeting. Doing it afterwards is a pain in the rear!
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