[Stock 0.17] TurboPROP (fully functional propellers)

[VincentLaw]

This is a 100% stock parts, fully functional turboprop. The two propellers are counter rotating to eliminate torque. This does not exploit the magic turbine bug to generate thrust because there are no control surfaces on the propellers. If it did, you would know because it would go faster. It is big, slow, and ugly, has terrible maneuvrability and range, but it works and is adequately stable.

Thrust on the propellers increases with speed. This is because they are fixed pitch, so they start out beyond the stall angle. As forward speed increases the blade angle of attack decreases. Regardless of this, due to the slow rpms of the propellers, the cruise speed is around 40 m/s. The propellers will windmill if you cut power during flight, but this does not provide any forward thrust. If you are not convinced that the props are generating thrust, then you can try putting a strut between a prop blade and the wings and it will not reach takeoff speed.

Despite any resemblance to the osprey, this is not a tilt rotor and the TWR is much less than 1. The rotor diameter required for a TWR > 1 at the available RPMs prohibits taking off or landing with forward facing props. Having large props mounted on the wing tips was simply a design constraint due to the laser beam of doom effect that jet engines have.

Do not ever time warp to any degree while the props are spinning unless you want to explode. Also don't touch the props in the SPH or you will break symmetry from the VAB.

Takeoff

Here is the most aerobatics this thing does.

Level Flight

Vortexy smoke trails.

Mountainy

Prop closeup.

A nice comparison for scale.

Trees Not Recommended.

Edited September 25, 2012 by VincentLaw

[Neurosys]

thats insane dude.

Very cool

[m5o5]

mother of god...

[TalonX273]

H-How does it spin with out breaking off? What dark sorcery is this?! O_O

[VincentLaw]

The hub of the entire propeller assembly is held together by a single structural pylon with no struts between the propeller and the main structure of the airplane. Using symmetry in the VAB causes the attached blades to be distributed evenly around the center of rotation of the structural pylon. This means only one of the blades physically touches the pylon and the rest float around it at the same radius. The structural pylon provides some resistance to making full rotations, but if you force it all the way it will continue to rotate without breaking, so there is a minimum power required to get the propellers to spin. The small radial decoupler also works, but its not possible to center the rotation around what you mount it to, so that's why I prefer the structural pylon.

This construction technique had a bug in 0.16 that would cause the hub to spontaneously explode after about 6 km of travel (someone called it the aerokraken), but that bug was fixed in 0.17, which is why I waited until now to try this design out. I was able to successfully cruise this airplane until my fuel ran out without encountering any bugs.

Also I want to emphasize the importance of the counter rotation of the propellers. The friction on the structural pylon is high enough that if you only use one propeller it will spin the entire airplane. A coaxial contra-rotating design can be used to compress the propeller layout, but this results in higher vibration on the mounting point.

Edited September 25, 2012 by VincentLaw

[Clouds]

I don't even...

(Actually, the MOST mystifying part to me is how the engines aren't being flung off, as has happened with any of my past Kerbocopter attempts...)

[oneredpanther]

Orville and Wilbur Kerbal have been up all night in grandpa's shed again!

[anersis]

Good Job, it work.

[RedDwarfIV]

That's awesome Vincent.

And what's nearly as awesome on a personal level is that I had some hand in its design! You made the contra-rotating helicopter because I was unimpressed by all the magic turbines in the stock copter challenge thread, and this uses the same principles as that.

Well, I'm happy.