Page 1 of 1

L188 Electra

Posted: Fri Mar 30, 2018 8:41 am
by Bat_Hog
Now I have my Anet A8 3D printer, I thought I needed a new project. I've been on a couple of turbo prop airplanes and always liked the idea of a multi engine airliner model. IC engines can be a problem, but modern electric motors are powerful and cheap. So I decided to do an L188 Electra, the commercial version of the P3 Orion.
l188 elecra2.jpg
l188 elecra2.jpg (150.38 KiB) Viewed 1711 times
Design principles: Needs to be big enough so that the wheels are suitable for our grass fields. Not too big that I can't get it in the car!
there are several examples on the web, but I will probably go with the one featured in Air Crash Investigation. A propeller came off and struck the underside of the fuselage, severing engine control and trapping control cables. The crew fought for hours to fly the crippled airplane and finally landed successfully against all odds. So for size I am basing it on my Avios Bush Mule, which is twin engine. From plans (not brilliant 3 views) I ended up with a scale 1:19. This gives a wingspan of 1600mm and fuselage diameter of 190mm. I am designing the parts in Blender 2.79 (it's awesome and free!)
Progress: designed and printed the propellers and spinners. Tested them on the Bush Mule. printed the rudder. prototype for the gear doors, prototype for the cockpit and nosecone. prototype for the front gear oleo. also printed some fuselage bulkheads. I have the servoless retracts (set of 3 from Hobby king for £20 !). I have the 4 motors and escs, same as on the Bush Mule. The wiring for 4 motors is interesting. you have the outer two on a separate battery and channel, and all but one positive is cut to the receiver.
on with designing the engine nacelles.

Re: L188 Electra

Posted: Mon Jun 04, 2018 4:10 pm
by Bat_Hog
Had a bit of a setback. My main PC threw a wobbly and wiped out a memory stick, with all my 3D files, in the process.

But these things are always better when you redo them. Found some better reference pictures for the actual example I am building.
Reeve Aleutian Electra
N1968R.jpg (391.72 KiB) Viewed 1557 times
I have 3D printed the Rudder. It came out really well, picture to follow. It is the first real production part.

Now I am designing the Engine Nacelles. They are the hardest things I have ever designed. See the picture.
nacelle closeup.jpg
This is hard to model
nacelle closeup.jpg (10.6 KiB) Viewed 1557 times
On the outside they are a combination of 3 curved surfaces plus the intersection with the wing. When I get the outside shape right, I have to hollow the shape and design the internal structure. There has to be a slot through for the main spar, room for the main wheels and retracts, cooling vents, fire wall to bolt the engine to. Then the thing has to be split into separate pats for printing, the gear doors split off and removable access panels created. And at the end of that it has to be strong and light.
Blender pictures to follow.

Re: L188 Electra

Posted: Tue Nov 26, 2019 11:43 pm
by Bat_Hog
I'm back on the forum now (thanks Colin).
Thought I'd post a progress update.
The design of the parts is harder than the actual 3D printing. For the cockpit I did about 60 file saves, until I was happy with the design.
Actually have quite a few parts ready to go:
Cockpit, nosecone, front landing gear, front lights, gear doors.
4 off propellers and spinners, with motors and ESCs.
The 2 inner engine nacelles, front part anyway. main landing gear.
port leading edge wing root (Random!)

Still doing the design in Blender which is now up to version 2.81. As you can see from the picture, it is modelled in flat surfaces (Quads) and then just before exporting as an STL I apply a Subsurface Modifier. If I've done it right and retained all the edges that have to remain "Sharp" then I get a beautiful smooth finish.