Martin 262C - Vaporware

[Inq]

I like challenges. Now... my goals are pretty mundane, like just flying my Storch for 10 flights without damage. Right now... I'm kind of home bound... it reached -2F here last night. Didn't get above 10 F yesterday or today. I don't even open the door for that stuff. Anyway... I have lots of planes on the queue to build someday.

This plane caught my eye... a mechanical engineering marvel...

At 1/12 scale, it'd be roughly 50" long and 32" wingspan. It would have two, 3-bladed counter rotating propellers of 16" in diameter and a 4" diameter body. VTOL with a pilot who had lot's of skill. (read... someday)

However, the challenge of the major feature is more of a mechanical engineering challenge that I want to take a stab. I've been working it out in my head off-and-on for a while. I finally decided the first hurdle was a light-weight bearings of a large diameter that has a large inner diameter to pass the main structural loads between the tail and forward fuselage. I've also integrated the reduction gear into the bearing race. This first one is simply printed in ABS, but for the real-thing, I'll probably try both an CF/PC that would be stronger, or a Nylon that might be quieter.

 

[Piotrsko]

Arrow shaft to handle the flight loads, or at least historically for me. Large gear reduction to use smaller motors or very large props?

 

[quorneng]

I am sure it is all technically possible but like all the prop 'tail sitters' hovering accurately enough to land effectively is almost impossible without a positive and independent roll, yaw and pitch control system. In this case it would likely mean stabilised cyclic pitch control on both props as in a superimposed twin rotor helicopter.
A VTO is possible if you have sufficient excess thrust (2:1?) as the model's inertia keeps it pointing roughly in the right direction until its velocity has built up sufficiently for its conventional aero dynamic controls to take effect but the configuration does not make for a good belly landing.

 

[Inq]

At the moment, this is merely a mental, engineering and 3D printing exercise. Actually wrapping a plane around the drive-train is not really planned. If I can put it on a load-cell and determine that it outputs 2x of the drive-train, the plane, electronics and battery weight, I might finish off the plane. But I'm sure I wouldn't be able to fly it.

Arrow shaft to handle the flight loads, or at least historically for me. Large gear reduction to use smaller motors or very large props?

The large gear reduction is required:

1. to have tail surfaces behind the propellers, unless you know of motors with hollow shafts that can put your suggested carbon arrow shaft down the center. The larger it is, the easier to make structure passing through the center.
2. smaller motors and larger props. The scale prop will be 16" diameter. Haven't spec'd out motor(s) yet, but I can't imagine the size motor required to drive 6 blades at 16" directly. I still imagine it being a rather beefy motor even with the gear reduction. The gear ratio above is 53:11.
3. Using 3D printed bearing races, its easier to reduce the stresses with larger diameter / more balls.
4. I'm also toying with making variable pitch blades, (constant velocity or maybe constant current) and need the room in there to activate the prop blades.

but the configuration does not make for a good belly landing.

The video shows it with landing gear, although it looks like a secondary attachment and it doesn't clear the blades. I was mulling over (if it got in airplane form) thinking I'd have some spring-loaded, extendable skids if/when I realize I can't land it on its tail or... maybe a parachute. Take off should be pretty easy... pour the coal to the motor and spin up the blades and pull the collective... it should nearly launch.

 

[Piotrsko]

Had a copter with those blades, ran on a 22kv 18? Dia recommended inrunner motor. Did fry the motor after a while but not the Design fault.

Um, no, your illustration showed the drive gear offset to the ring gear circumference so I interpreted the motor being mounted there. The arrow shaft was a tie point for mounting the surfaces much like a pod and boom plane from the '60s with essentially spinners used as a fairing. Pushrods went through the shaft. Think horizontal orientation helicopter with stuff mounted on top of the shaft like current blackhawks. However, now thinking about it, just use a cyclic system for control and fixed surfaces.

 

[Inq]

Um, no, your illustration showed the drive gear offset to the ring gear circumference so I interpreted the motor being mounted there.

Yes, that is where the motor goes at the offset drive gear position. Can you think of a way to make this work, without a ring gear? I can't. The structure holding the empennage goes next to the drive gear/motor, but still inside the ring gear. the propeller blades are connected to the outside of the ring gear. The ring gear outer diameter is the same 4" diameter of the fuselage.

About the only helicopters that have this problem are ones like...

... with the pod above the rotors. There must be some structure going up inside the drive shafts that is not turning to hold that pod. Same problem as this plane. I think you are right a carbon arrow shaft should be strong/stiff enough to hold the empennage.