Build Log - Giant ~120" P-61 Black Widow

[Liam B]

With FliteFestWest being anounced, I figure that it will be here before I can snap my fingers. So, I started cookin'. And, as the title suggests, my project is a Giant Swappable P-61. I can only fit so much in a car, so I'm doing a 3 piece slot-in wing to save space. I also am not bothering with spoilerons. I tried a few concepts, only to find that they do absolutely nothing on a foam board model(I challenge you to make operating spoilerons). That brings me to saying that this model is 100% foam board construction. Two wood spars, waterproof foam board, some aluminum bar stock and rods and cardstock. Landing gear is some aluminum wires bent to make rear gear, and the front is a combination of wood and aluminum stock using a Lego wheel. I was thinking of using these: http://www.emaxmotor.com/emax-gt-3520-power-40-brushless-motor.html#.WHwLVrQ77YV for motors coupled with some 70a ESCs. But then I decided to use C Packs because i already had them and they were cheap. Im going to run it of 4s because I firstly want it to get off the ground and maybe also have a bit of oomph. Servos are a ton of coupled 9g's (2 on each aileron, 1 17g on elevator, 1 on each rudder).


Three Ways and Schematics:





So, I'll get to the build. Please share what you think!

 

[Liam B]

I glued all the foam sheets together for the center wing. Wonder what my mom will say about me cutting on the kitchen table!

 

[Liam B]

Just got the first bevel done. I've also included a picture of my 60" P-61's center wing compared to this one's.

 

[Liam B]

With the bevels finished, I'm now working on cutting the spars.


I think the wing looks really good.

 

[Liam B]

Spar is on and glued in! Making slots for the wing joiners...

 

[Liam B]

The wing is done! Came out very well, and only a little warped in some places. The wing yardsticks slot in to the spar. And now it's ready for installing booms, motors and the fuselage. I probably won't get to those until next weekend because of school, but I'll try to inch along on it through the week.

 

[Liam B]

By the way, anybody have any ideas on what motors to use?

 

[Tench745]

I have a couple notes on this build.
1) I'm quite impressed with the size and the decision to build this big. My 92" Spirit of St Louis build is intimidating enough for me. Keep it up!
2) I would recommend installing your yardstick vertically rather than horizontally; you'll get a lot more strength in the wings from it that way.
3) The thickest part of your wing looks too far forward. The camber of most airfoils is about 30% back from the leading edge. I'd suggest making your first panel from the leading edge fold about twice as wide as it is and moving the spar back the appropriate amount to accommodate it. It will fly the way it is, but it will need more airspeed for the same lift as an improved airfoil, stall at a much lower angle of attack, and probably stall pretty sharply.

Something a little more like this might perform better.

 

[Liam B]

I have a couple notes on this build.
1) I'm quite impressed with the size and the decision to build this big. My 92" Spirit of St Louis build is intimidating enough for me. Keep it up!
2) I would recommend installing your yardstick vertically rather than horizontally; you'll get a lot more strength in the wings from it that way.
3) The thickest part of your wing looks too far forward. The camber of most airfoils is about 30% back from the leading edge. I'd suggest making your first panel from the leading edge fold about twice as wide as it is and moving the spar back the appropriate amount to accommodate it. It will fly the way it is, but it will need more airspeed for the same lift as an improved airfoil, stall at a much lower angle of attack, and probably stall pretty sharply.

Something a little more like this might perform better.
View attachment 80951

I think I might just do that. The yardstick was a concern of mine.

As far as the wing shape goes, I think that I'm too far in to change it or start over, so I'll just cross my fingers!

 

[Liam B]

Guess who got a snow day? Me! So I'm spending all day on the plane.

 

[CaptBill]

Wish you would move off Mom's table. I Just looking at it causes me to expect to get chastised.

 

[Liam B]

Wish you would move off Mom's table. I Just looking at it causes me to expect to get chastised.

Yeah. Luckily I'm past the big part, so I'm moving it up stairs now.

 

[Liam B]

Took a break to go skip the Sea Duck around in the snow. Very fun, even more with frozen thumbs. I'm back in the indoors and am cutting out the fuselage.

 

[Tench745]

Good to hear, don't let this stagnate like so many of my builds!

 

[Liam B]

Alright. Back at it. I just got the fuse done, and I'm in the process of cutting the slots for the wing. The first slot is butter smooth, hopefully so will the second one.


So, I'm thinking these motors: https://hobbyking.com/en_us/turnigy-aerodrive-sk3-4240-740kv-brushless-outrunner-motor.html

About right?

 

[Liam B]

Fuselage is on! Reinforcing the fuse a bit but also trying to keep the weight down. I'm thinking about using 12 inch props on a 4s, so I'm really looking to keep it light.

 

[Liam B]

Right motor pod/boom installed!

 

[Liam B]

I've installed the motor and ESC, along with the twin engine wire harness. The turret servo is on a Y Harness with the motors, so it's controlled by the rudders and throttle. I did this because I ran out of channels. I also partly covered the center fuselage with foam ribs and cardstock that was leftover posters from our school musical. I covered the motor pods as well.




The firewalls are interesting. They are impact resistant, and they're directly mounted, but I braced them with foam that I got from the box of my FPV camera. I call them adaptive firewalls. Snazzy name, right?

 

[Liam B]

Adaptive Firewall

 

[DamoRC]

Nice! Are you planning on transporting this as a single unit or will it be in a couple of parts?

DamoRC