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Old Nov 01, 2005, 03:53 PM
SoarScale
United States, WI, Wind Lake
Joined Nov 2004
814 Posts
P61C Black Widow series - Additional fuse notes

I forgot to mention a few points.

1). The Ziroli instructions call for balsa stringers for the fuse. If you intend to install a detailed front cockpit area, I would change this strategy. When you remove the internal crutch from the fuse between formers F2 and F5 for the "sunken" pilots floor, the sides of the fuse become very flexible and in my opinion, too weak. To strengthen this area, since this is where the front nose gear is mounted, I would suggest using basswood or spruce stringers from F1 through F6. I did not do this and when I finally hollowed out the cockpit area for the interior details, I found it nessecary to laminate 1/32 marine ply between each former (F2 to F6) from the canopy lip to as low as I could within the cockpit area. Using basswood stringers MAY eliminate the added weight of the ply laminates on the inside (or it may not!).

2). If you choose to create "scale" retract doors, then the method drawn by Ziroli won't easily convert to a scale "internal" look. BEFORE you cut the front doors out of the fuse, you need to make the decision to either stick with the doors as produced by the kit construction, or to go with thinner doors with internal vacuum formed inner surfaces to the doors to look scale. If you choose the later, NOW is the time to create the Fiberglass laminates OVER the contours of the front door area. This is not a difficult process and if you need more info in this area, I can share!

3). Front fiberglass nose cone mounting. The construction of the fuse basically brings the sheeting to the "front" of former F1. There are two ways I could think of to mount the nose cone. Either lay it over the nose sheeting - creating yet one more step, or create a slightly smaller version of F1, smaller by the thickness of the fiberglass of the nose cone and attach it ahead of F1. I chose to create the additional, smaller F1 from 1/4" lite ply. The nose cone then simply fit over this former and four countersunk screws were used to hold the nose cone on. If you choose to do this, cut the additional F1 former BEFORE you start the fuse assembly using the existing F1 as a reference so that it is ready for use later. Cutting it out after the fuse is made is not simple.
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Old Nov 01, 2005, 07:12 PM
the-plumber
Joined Feb 2003
1,094 Posts
Interesting techniques.

A couple of notes, in the FWIW column . . .

I admire Nick Ziroli and his designs, that I have three of his plans/plastic sets to be built when work doesn't intrude, and I know very well that Nick's designs have been built, flown, and admired by who knows how many modelers over the years (and will continue to be built, flown, and admired).

Would that I had the ability to design feasible plan sets for difficult models the way Nick does it.

Even so, Nick's designs omit details on occaision, mostly for good reason, and the P-61 is a good example.

I dunno how many folks know it, but the ailerons (spoilerons if you must) in a P-61 are not at all simple sailplane fence structures, they are cylindrical sections which extended above >and below< the wing over their full travel arc.

Secondly, and less important, the P-61C had fighter brakes very similar to the dive brakes on the North American A-36 Apache. The P-61 had two panels in each wing surface, top and bottom (8 panels total).

Nick chose not to implement these features (probably because of the degree of difficulty in so doing), and to date I have yet to see a scale P-61 which had either fighter brakes or ailerons which functioned and looked as did the 1:1.

Not finding fault in your effort here, and a fine effort it is. It's just that if you'd ever stood under the wing of a P-61 as I (and countless thousands of others) have, you'd have noted right off that the P-61 ailerons (and fighter brakes in the "C" model) were a whole different breed of cat from what is generally implemented in scale models of the last version of the Black Widow.

Photos show the fighter brakes and aileron location in the bottom of the P-61 wing.

The bottom opening for the aileron has been covered by the restoration folks at WrightPat to prevent the structure drooping over time (to prevent gawkers whacking their heads as they walk under the wing), as have all the flight control surfaces on all the 1:1 aircraft on display at WP - the elevators, ailerons, and flaps are all locked in place with straps or covers of some flavor or other.

The actual aileron has a flat plate on the top and bottom edge which, when the aileron is in the neutral position, helps seal the whopping great slot running clear through the wing top to bottom.

I have the actual figures somewhere in my archives, but IIRC the ailerons extended half as far below the wing as they did in the full up position, or thereabouts. I can go find those numbers if anyone is actually interested.

In the end, I doubt that there are more than a handfull of modelers who would realize that sailplane spoilers on a P-61 are just plain wrong, but even those few of us wouldn't care one little bit if the thing looks 'stand-pretty-close-scale'.

Again, FWIW.
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Old Nov 01, 2005, 07:44 PM
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Augusta, GA
Joined Nov 2003
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I'm ...speachless!!

I assembled a VQ P-61 ARC this year and it took me 9 months to work everything out to my satisfaction and get it in the air. Its a great flyer and I've taken the top award at the two local events that I entered it in this past month. But my plane is NOTHING compared to what Tony is doing with his Ziroli...

...WOW!!!
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Old Nov 01, 2005, 10:16 PM
SoarScale
United States, WI, Wind Lake
Joined Nov 2004
814 Posts
P61 details from the documentation

Thanks for the input the-plumber. I must admit to having very different data than you obviously do. I too have been to Dayton and collected my fair share of digitals of Moonlight Seranade. An impressive aircraft to say the least.

The data I have in the documentation says different to your statements.

The ailerons or spoilerons WERE originally used both in the up and down direction, but, during operational flights of the P61, it was reported that some blades shattered due to excessive vibration caused by air flow between top and bottom surfaces of the wing. At the time, the magnesium material used was fairly brittle. The data I have states that the cap over the bottom of the spoileron was added sometime in the flight history of the P61B to eliminate the issue. Pilots reported that handling charactistic changes were minimal and the majority of P61's were flown this way. Due to the complexities of the mechanism in the wing, Northrop decided not to mess with it but simply to cover it up to eliminate the vibration issue. The specific aircraft I am modeling from 1947 is the P61C's, nine of them, used for project Thunderstorm. The specific aircraft photograph I have already shows the lower spoileron cover in place - back in 1947. I can only assume that when Dayton got their P61 it was minus the cover and they consequently added it for the reasons you state.

On the subject of dive brakes, similar documentation depicts that the initial installation and operation of the dive brakes ended up in a near fatal crash where the pilot, Northrop Pilot Max Stanley, at the behest of the Air force, deployed the airbrakes to demonstrate structural integrity, and I quote: "this test required the pilot to apply maximum Gs at the maximum permissable air speed at the critical Mach number. This dictated perfoming the maneuver at 17,000 feet".It is at this time, Pilot Stanely noted, that I activated the brakes. When I applied back pressure on the stick to produce the desired G's, I found the stick force had reduced to zero. The stick ended up in my lap and the last thing I recall is noting the accellerometer pegged at 10Gs. The aircraft was greatly overstressed; both wings and empanage failed, structurally, and separated from the airplane. This produced negative Gs to the extent that I was pitched forward with such a force that the pilots seat pulled free from its attach points on the floor. etc etc etc. The Northrop test pilot Stanley did survive the incident and bailed from the aircraft. The cause was defined as compressibility. "No effort was made into finding a solution to the problem", and here is the major point, "All P61's coming off the line consequent to this had fighter brakes installed. However, they had been rendered inoperative and bolted closed. P61 fighter brakes were never used in combat."

As such, the fighter brakes on my P61 will, in fact, be there - purely as surface details only because like the later P61's, the C version I am modeling, one of nine P61C's used for project Thunderstorm, also had the fighter brakes made inoperative and were bolted down. You'll definately be able to see them on bottom and top surfaces of my model, but, they will not be operative - per the 1:1.

Anyway, on with the series.
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Old Nov 01, 2005, 10:38 PM
SoarScale
United States, WI, Wind Lake
Joined Nov 2004
814 Posts
P61C Black Widow series (#19)

Stabilizer/Elevator Construction.

Not much to be said here – I followed the plans and instructions for the stabilizer itself. I deviated from the plans a little when it came to actuating the elevator. I am not a fond proponent of nyrods or similar from the front of a fuse to a control horn on the rear elevator or rudder surfaces. I prefer to mount the servo in the flying surface and chose to go this route for the P61. Now, with the advent of the ultra-slim digital servos from most of the servo manufacturers, this really becomes feasible without adding significant weight in the tail.

Now, initially, I was going to outfit this aircraft with two receivers, split the elevator and control each half of the elevator via separate receivers/servos. During the overall construction of the P61, I changed my mind on this but not until after I had built the split elevators!! So, the first pictures attached here show the elevators split. My current stab/elevator assembly in the other pictures now has one complete elevator driven at both ends by separate servos mounted in the stab itself. Elevator servo’s are driven through a JR matchbox and via one channel on the now, single receiver installation.

Another item you may notice in the pictures is the addition of the RDS (Rotary Drive System) pockets in the elevator halves and slots pre-cut into the LE of the elevator halves. This too was going to be my approach to completely hide the elevator control linkages from the exterior view. Again, with my desire to make the elevator completely removable using a 1/16” hinge pin, use of the RDS became difficult as the RDS drive shaft crossed directly in the path of the 1/16” hinge pin. In the final version of the elevator/stab assembly, I abandoned the RDS in favor of an external control horn and linkage. What I did do however, was add servo arm fairings on the bottom of the stab to “minimize” or cover up the control linkages. Not exactly true scale, but acceptable for me on my very first scale modeling experience with a powered aircraft

Now the servo’s I decided to use were the Hitec digital wing servo’s – HS5125. These deliver about 50 inoz of torque at the 6V I intend to distribute around the aircraft. Two of these give me 100 inoz on the elevator. With the control horn, ball link actuation point being about ¾” from the elevator hinge line, this translates to about 120inoz of torque total on the elevator. I used the available tools on the web, several of them, to calculate the torque on the elevator at the flying speeds I anticipate and for the elevator deflections reasonable at those speeds and 120 inoz is plenty for the job. The bigger question is whether the gear train of this ultra-slim servo will hold up under vibration.

Now, this is where the engine choice comes in. The Laser 300 V-Twin has SIGNIFICANTLY lower vibration than a single cylinder gas or glow engine. This therefore reduces the vibration on the tail surfaces and therefore on the servo’s themselves. I won’t know if this is truly going to be the case until the engines are run at all speeds and vibration monitored on the ground. If I find the servo’s are exposed to excessive vibration, I can remove them and put other slim digitals in their place with thicker gear trains.

I feel pretty confident that I have sufficient torque for the elevator but decided to create two additional servo bays (not currently populated however) in the stab for them if needed. I think these would be overkill but are there if I need them. During construction was the time to insert them so I did. Control horn blocks are also installed in the elevator where required for these additional horns should I need them later.

In my installation of servos in the stab, I had to drill holes in the ribs to route servo wires. I actually chose to clean that up even further with the addition of rocket tubes in the stab for routing – very clean

An additional point about my construction. The same TE considerations was given to the top and bottom TE’s of the stabilizer AND the TE of the elevator. I laminated glass ply where it was needed on both to make the TE’s stiff and sharp!

At the beginning of this series, Don Bailey posted pictures of my P61 as it is today. It is fully built, engines installed, spinners, props, radio gear (which I will show later), wires, gear, servo’s, fully glassed and ready for painting. The weight as shown in the pics is 46lb. Add the ignition units and the LiPo’s, and the weight would be around 48lb and it has a balance point very near the position stated in Ziroli’s plans. To me, the servo’s in the rear for the elevator, and later you’ll also see for the rudders, was a solid decision – at least from my point of view!

One last note about the open structure build process for the elevator and rudder shown on the plans. Over the course of building this aircraft I have taken advice from a few folks including Dave Platt (Mr Scale) in Florida. Dave’s personal experience is that open structures, when covered in your favorite fabric, don’t look like they are open structures covered in fabric! The surface is too small and the rib spacing too short to create an effective open structure look. His recommendation to create a better open structure look is to sheet the surface, mask and paint the details on via multiple coats of paint over the ribs, and then wire wool the painted ribs down to round them off. This is the method I chose for the elevator and rudders. They were consequently built somewhat differently than the kit parts allowed and plans suggested.
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Old Nov 01, 2005, 10:53 PM
SoarScale
United States, WI, Wind Lake
Joined Nov 2004
814 Posts
P61C Black Widow series (#11)

Note the last post title should have been #10, not #19 - oops!

Anyway, nacalles:

Nacelles (part 1).

Again, I followed the general instructions from Ziroli in his instructions and didn’t deviate a whole bunch. Where I did deviate, I have added notes below.

Deviations from plan!

Again, the rudder servos were mounted directly in the vertical fin, below the elevator/stab and on the inside for minimal external viewing. Custom vacuum formed fairings were created to cover the servo and control linkages and inset into the fin sheeting for flush mounting. Next to the rudder servo was an access panel so that you can connect and disconnect the servo connectors if needed. Additionally, a servo wire rocket tube was added from the fin to the rear of the servo well for the servo extensions.

If you look at a good three view of the P61 you will also notice four access hatches on the outer surface of the fin about half way up for stabilizer attachment bolts. The two shown on the Ziroli plans are for the bolts only. I also added the third large one in the middle between the bolt access hatches so I could feed the elevator servo wires down into the fin to the inner servo connector access hatch. This also meant that a hole had to be drilled in fin rib R2 to allow the connector to pass through to the inside access hatch and consequently through to the rocket tube location.

Unfortunately, the only photos I have of the hatches are attached below. I did not take any during construction and the ones I just took are of these features WITH the aircraft masked for priming – but I think you get the idea.

All of the actual hatches were made from a 0.006” layup of fiberglass over the finish sanded fin surface and each one cut out. The internal structure does not allow you to create cut-outs in the fin sheeting the size of each hatch so the balsa hatches were cut out smaller and internal mounting rails added to the hatch opening. The resultant, cut out, balsa hatches were then glued to the “inside” of each fiberglass hatch and will be screwed to the outer surface of the fin and detailed later. The fourth hatch, a smaller one between the LE hatch and the middle one shown on the photo will be glued directly to the fin surface later completing the line of hatches on each outside surface of the fin. The remaining hatches on the fin will be cut from adhesive sheet aluminum and will become surface details below the paint.

What else. Ah yes, the P61C version. The P61C version has a superturbocharger air intake situated below the cowl as shown in the pictures of the original posting. The plans do not cater for mounting these two air intakes because they were not drawn for the C version, so mounting locations need to be added before you sheet the nacelle.

I will cover the air intakes in a later post as these deserve a post of their own.

I have added a few pictures of the fins, hatches and fairings. I'll put the nacelle build pictures in the following post (part 2).

The vertical fin build actually occurred at a later stage AFTER the nacelle was sheeted so the comments above about fin hatches actually occurred later in the build process.

The final picture in this post is of the nose cone mount that I talked of in an earlier post. It was cut out slightly smaller than F1 of the fuse and screwed to F1 instead of glue to it. Creates a nice fitting nose cone.
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Old Nov 01, 2005, 11:07 PM
SoarScale
United States, WI, Wind Lake
Joined Nov 2004
814 Posts
P61C Black Widow series (#12)

Nacelles (part 2).

Here are a few pics of the nacelle build. Not much to show here since the majority of the build was via the Ziroli instructions.

Once the nacelles (minus fins) were sheeted, the next challenge was getting them attached to the wings with the wing saddles as designed and built from kit parts and to build the fins accurately. I pondered this situation for a couple days and decided on my third “jig” of the project.

What I felt was needed was a simple, quick to build jig that put the two nacelles in the exact position they would be in on the assembled aircraft. I therefore created a front alignment jig and a rear alignment jig. Placed the two nacelles between the two jigs and then bolted the wings to the nacelles to keep the saddles aligned and therefore the nacelles aligned. The pictures below show the idea. I used some 90 degree angled aluminium as location devices which located in the rear fin rib post and on the engine boxes. Once these were in place, the nacelles located and the wing in place, the fin build started.
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Old Nov 01, 2005, 11:09 PM
SoarScale
United States, WI, Wind Lake
Joined Nov 2004
814 Posts
P61C Black Widow series (#13)

Nacelle jig continued - some more pics of the jig
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Old Nov 01, 2005, 11:33 PM
SoarScale
United States, WI, Wind Lake
Joined Nov 2004
814 Posts
P61C Black Widow series (#14)

Vertical fin build using the nacelle jig

The nacelle jig, once everything was in place gave a relatively good platform for building the fins. The first three pictures shows several stages of building each fin. Not a complicated thing to do nor did it take very long. The key note here is that the fins were built using a "good eye" for alignment. Note 2 below shows how I took the "align by eye during the build" to the "final locked alignment"

I eventually removed the nacelles from the jig without the full sheeting on the fin in place. This was done to allow me to do two things:

1). Get into the fin for servo mounting and any adjustments to existing pieces for servo wiring
2). With the aircraft assembled as shown in the final picture, I was able to do a final check of the fin alignment in a fairly assembled state. The final locked alignment only occurs when the final piece of sheeting is applied. It is for this reason the final peice was left off and added when the aircraft was together.

The final picture in this post is of the first realy assembly of teh aircraft with all the bits I had built so far - motivation to continue perhaps!!

Now, unfortunately, this is where my digital camera crapped out and I had to send it away for repair. At the time I didn't think of the disposable kind so I do not have any further pictures of the assembly process - bummer!!!

In reality, from an assembly perspective, only the rudders were left to do and they are farily simply. I used the 1/16" hinge pin method again and built them fully sheeted for later paint detailing of ribs.

However, there are still some pictures I can take now of some of the components and molds I made to convert this A/B version plan into the C version P61 I chose to model. As I take them, I will add them with details of what I did.

I was however, asked to bring my P61, in the state it was in at the time, to a scale masters qualifier event in northern California in September I think, which I did. The next post shows some of the progrees I had made between completing the fins and what you see in the next post.
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Old Nov 01, 2005, 11:55 PM
SoarScale
United States, WI, Wind Lake
Joined Nov 2004
814 Posts
P61C Black Widow series (#15)

P61 state in the September timeframe.

As I stated in the last post, I was invited to bring the P61 as it was around September to a scale masters qualifier in Woodland, CA. The aircraft had gone through a number of additional build stages:

1). doors were removed for gear and hinged using minature piano hinges
2). Robart gears were added
3). Semi-scale wheels that I acquired from a fellow modeller were added. The final wheels as seen in the initial posts were from Glennis Aircraft and included brakes.
4). The rudders were built but had not yet had their sheeting applied
5) The cockpit areas had been hollowed out and the Dynamic Balsa cockpit kit had been partially painted and installed
6). The front retract servo had been installed
7). The door air sequencer valves had been installed (2 of them for the P61C) along with servo
8). The electronics deck had been installed with some of the components. Note here the two receiver installation I had originally planned. This is no longer the case for this aircraft.
9). The air service panel was installed for air fill and routing of lines to each side of the main gear and doors
10). Engines had been installed along with on-board starter rings
11). main gear and brake air tanks had been installed - main tank beneath wing, brake tanks beneath gunners floor
12). Stock Ziroli cowls had been installed before their conversion to the C version cowls.

There was still quite a bit to do at that time.

I will add more pictures as I take them and add details. The updates will be a little slower from this point forward as the major assembly stuff has been covered and I don't have any more pictures of later stages!!!
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Old Nov 02, 2005, 12:03 AM
SoarScale
United States, WI, Wind Lake
Joined Nov 2004
814 Posts
Further notes

I wanted to add a few more notes on the response from "the-plumber".

I just want to make sure you know that I too admire the work done by Nick Ziroli senior. In fact, I have called him a few times for further advise on building to his plans and possible modifications for the C version. My comments in the previous posts were simply to highlight where I deviated from his plans in order to make the P61C version and to better replicate the available three-views and photographs for a scale outline judge at a scale competition.

In NO WAY, were any of my comments meant to belittle Nicks skills in the design and drawing of his plans - they are outstanding and without them, I would have no chance to build this aircraft.

If you're out there Nick - thanks.
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Old Nov 02, 2005, 01:06 AM
SoarScale
United States, WI, Wind Lake
Joined Nov 2004
814 Posts
P61C Black Widow series (#16)

OK, I lied. Since it is late here and my next phase is painting, I decided it was too late to start setting up the spray gun and mixing paint, so I took a few pictures instead.

P61C Superturbocharger air scoops.

As you probably noticed in the initial post from Don, there are two air scoops below the two cowls. These were built using a foam plug, glassed and painted. A two part mold was made of it and the two scoops layed up in the mold. The plug was made oversize, depth wise to allow me plenty of adjustment material for a good fit on the aircraft.

The pictures show the plug, the two halves of the mold and the parts that were pulled from the mold. Note that the rear segment of the part was actually not part of the mold since there is a left and right side required and they are differently shaped. These were made using the lost foam technique rather from a mold and attached to the main intake part when cured. These are identified by their different color.

I chose not to go to the extent of building in the intake LE "lip" and instead molded the front intake portion as a simple flat surface, cut out the hole and sanded to shape. The intake lip is actually a resin/microballoons mixture with the glass layed up behind it. It realy simplified the mold and part and didn't take very long to shape.
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Old Nov 02, 2005, 01:29 AM
SoarScale
United States, WI, Wind Lake
Joined Nov 2004
814 Posts
P61C Black Widow series (#17)

The mount for the intake was made by covering the front, bottom of the nacelle with monokote as a parting film and laying up several layers of 6oz glass and polyester laminating resin over the monokote. This allowed the glass to follow exactly the contours of the bottom of the nacelle.

Once cured, it was pulled off, monokote striped, and the part cut to shape. Note that the actual shape of the intake was drawn on the bottom of the nacelle in the correct position using the intake as a guide beforehand. Since clear monokote was used as the parting film, the lines drawn on the bottom of the nacelle showed through the cured glass. This line was traced onto the glass laminate itself BEFORE the part was removed. It was then cut to that shape, a line was then drawn all the way around the periphery of the part the thickness of the air intake side wall and sanded to a final fit into the intake.

The mounting braces were carved to shape using basswood and glued to the mounting plate, drilled and screwed to the previously installed mounts beneath the nacelle sheeting in this area.

Four screw hole plates were then glued in appropriate locations inside the intake, around the edge of the part to allow mounting screw holes to be drilled and countersunk for final mounting. Additional blocks were created and carved/sanded to shape, pre-drilled and fitted with blind nuts. These would be the blocks that would be glued to the main mounting plate just made.

The blocks with the blind nuts installed were then screwed to the intake part and test fitted against the glass mounting plate. Once the fit was satisfactory, wax paper was added anywhere there was a possibility of any parts sticking together (between nacelle and glass mounting plate, between mounting blocks and screw hole plates on the inside of the intake etc). Once adequately "separated" by wax paper and with the mounting blocks screwed in place on the intake, glue was applied to the bottom of each block and the assembly placed over the mounting plate and taped in place to cure.

When cured, the four screws were removed, intake lifted away and fillets added around the blocks now glued to the mounting plate for extra strength.

The photos only show the mounts rather than the process to make them but they are fairly simple to make and with Polyester resin, cure fairly quickly for shaping and final installation.
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Old Nov 02, 2005, 01:54 AM
SoarScale
United States, WI, Wind Lake
Joined Nov 2004
814 Posts
P61C Black Widow series (#18)

OK, P61C cowl air intakes.

Now, there were two ways to approach this part of the build, all new cowls or modify the existing ones I had already ordered and received from Ziroli. Obviously, I chose the later!!

I set about by carving a solid scoop from blue foam - fairly easy and quick. In then had to carve a mounting block for the carved scoop to sit on prior to molding. The mounting block needed to match the curvature of the cowl around its circumference. I used a curve guage to create a form of the outer curvature of the cowl and used that to sand the top surface of the mounting block. The two were then glued together, glassed and painted.

Once dry, PVA was sprayed over the part - 3 to 4 coats and the glass layup for the mold commenced. Since I was only going to pull a few parts from this mold for my own use, the mold was not made very thick - probably about 8 layers of 6 oz glass. Once that part cured, it was pulled from the mold and trimmed.

Again, I chose not to add the intake lip to the mold but rather build up the lip area with resin/microballoons and cut/sand to shape later.

Once I had all four scoops for both cowls, the attachment method was prepared. For this I cut a rectangular hole in the correct locations in the Ziroli cowl. The parts were trimmed so that there was a "tab" left on either side of the scoop in the exact location of the hole in the cowl. The front and back edges of the scoops were trimmed so they were flush against the cowl outside surface. The cowl scoop was "squeezed" together on each side where the "tab" was and the tabs inserted into the rectangular holes in the cowl and released. Once in position, final adjustment was necessary and when I was happy with the fit, the parts were glued in place.

The major part of the glue was applied to the tab that was now inside the actual cowl. If you look closely at the interior picture of the cowl, you may be able to see this.

The last stage was adding a small fillet along the length of each side of the scoop to finish the installation.

One major gotcha for this installation is that the two lower cowl mounting screws as designed by Nick Z are now covered by the scoop!!! The only two mounting points you have left are the two top ones. I do have a solution to this problem but have not yet implemented it. When I do, and it works, I will add an additional post.
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Old Nov 02, 2005, 02:07 AM
SoarScale
United States, WI, Wind Lake
Joined Nov 2004
814 Posts
P61C Black Widow series (#20)

Since I already used #19, I'll go to #20.

The final parts of the cowl/intake system are the end caps that attach to the nacelle and cover the end of the cowl scoop. There are obviously four of these also, one for each cowl scoop but since they are all the same, a plug and mold was the obvious choice.

This plug was not made until the cowl scoops were added to the cowl and the cowl fitted to the nacelle and aligned accurately. A block of blue foam was then placed at the necelle end of the cowl air scoop. The air scoop outline was then traced onto the foam. Each scoop was checked to make sure they were all fairly close to this resulting line on the foam. A second line was then added outside this reference line by about 1/8 to 3/16" for clearance per the real aircraft.

When happy, I set about carving the part from the foam block. The same nacelle-based curvature mounting block was required for this part. The curve guage was used for this also. Once the two foam parts were done, they were glued together, glassed and painted. The mold created, pulled from the part when cured and trimmed.

The parts themselves are features only and are simply glued to the sides of the nacelles. As such, I chose to make them very light with minimal glass in the layup.

Once these were done, the outlines was sanded to shape and were then ready for nacelle attachement after the priming was complete.
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Black widow from KTEH sci-am show! Great tech cramp!! jas_Qfix Electric Plane Talk 5 Apr 27, 2001 06:05 PM