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Comment: Re:Copter data (Score 1) 91

by wagnerrp (#48018413) Attached to: DHL Goes Live With 'Parcelcopter' Drone Delivery Service

Now you have a quad engine rocket propelled _brick_ flying by thrust only, no aero dynamics involved at all.

Technically, aerodynamic principles govern the conversion of temperature and pressure in the combustion chamber into exhaust velocity as the propellant travels through the nozzle.

Now to the helicopter: it does not fly by thrust at all, with "thrust" it it only gets its "directions", its lift it is getting from the profile of its "moving wings" in the rotor. Thrust it gets from the tilting of the rotor as the rotor creates a minimal amount of thrust in addiction to its lift.

Actually, helicopter rotors are typically symmetric, meaning they produce zero lift/thrust at zero angle of attack. The amount of lift/thrust they get is directly dependent on the pitch of the rotor blades, and the "profile" or camber of the blades is only to prevent flow separation on the suction side of the blade at higher angles of attack.

You mention the "tilting of the rotor", which I suspect is a serious misunderstanding of how a helicopter works. Helicopter rotor blades pitch up and down to produce more or less lift/thrust, but the rotor disk itself does not move in relation to the attitude of the helicopter The disk is fixed. If the helicopter wants to move forward, the entire craft, rotor disk, fuselage and all must pitch forward to change the direction of thrust.

It pitches the swashplate such that the rotor blades currently at the front of the disk have a low or negative angle of attack, while those at the back have a high angle of attack. This shifts the center of lift/thrust rearward with respect to the center of mass, causing the helicopter to pitch forward. Now that the whole craft, including the rotor disk, is pitched forward, the lift/thrust vector tilts rearward, and the rotor now produces forward thrust.

A quadcopter uses _only_ the thrust of its engines/propellors ... it has nothing to aero dynamically generate _lift_.

Just how does a propeller work, if not aerodynamically?

Comment: Re:Copter data (Score 1) 91

by wagnerrp (#48006827) Attached to: DHL Goes Live With 'Parcelcopter' Drone Delivery Service

A our dates car engine is below 20% ... not in the 30% range.

The average system efficiency may be that low, when you account for transmission losses and off-design operation.

Thise videos show unloaded helicopters versus unloaded quad copters.

Yes. The point was this "fantastic maneuverability" of quadrotors as seen on youtube videos is nothing special. It's merely a function of the squared-cubed law allowing for very high thrust to weight ratios, and traditional helicopter designs offer a no less impressive display.

A helicopter and any quad, hexa, octo or what ever copter fly on complete different physical principles.

Eh, what? The aerodynamic principles governing subsonic flight have been known for a century and a half, and they're the same regardless of whether you have fixed or rotating wings, and fixed or variable pitch.

If that would be the case: we had plenty of news about drone helicopteers flying on ethanol or other burning fluids.

People have been developing drone helicopters since the 90s, and they have seen active military use for several years.

But what we actually have is plenty of news about 'strange' copters flying on batteries. Next try?

That's because any asshat with $300 can go buy an AR Drone and make a nuisance of themselves. As I've explained, fixed propellers, electric motors and batteries have lowered the barrier for entry to rotorcraft and opened it up to a much larger audience. Just because they're widely available does not mean they're efficient or performant.

Comment: Re:Copter data (Score 1) 91

by wagnerrp (#48005747) Attached to: DHL Goes Live With 'Parcelcopter' Drone Delivery Service

Further your claim about fuel efficiency is simply wrong. A emgine big enough for a car is below 20% efficiency.

Excluding transmission losses, modern automotive gasoline engines are typically in the low 30s.

Engines small enough for a 'drone' are in the range of ten percent.

Engines small enough for RC aircraft are typically 2-stroke, which significantly increases your power-to-weight ratio, but roughly halves your energy efficiency. They also typically run on alcohol and nitromethane blends, which have low energy density but high power outputs. Four stroke gasoline engines on the order of a couple cubic inches are used on large scale models, and some rough power and fuel consumption estimates from manufacturers puts them around 0.45-0.5 lb/hp*hr, which is on the high side of what you see in automotive engines.

a combustion engine mini helicopter is heavier than a plastic quad copter, so the inertia is on its draw backs

Just how light do you think enough battery for an hour long flight is? Hint, it's going to weigh more than the IC engine and a comparable amount of fuel.

Contradicting to your ideas: all quad copters react like a quick insect while the helicopters fly around very sluggish. I suggest you watch some youtube videos about it :)

Those videos show the performance of an unloaded quadcopter. If you try to put any significant payload on one, you will see something very different. I suggest you watch some youtube videos about 3D aero helicopters.

Comment: Re:Copter data (Score 2) 91

by wagnerrp (#48004275) Attached to: DHL Goes Live With 'Parcelcopter' Drone Delivery Service

A single rotor is certainly not more efficient

In terms of thrust per unit power, larger disk area is always better than smaller. That's why turbofans use less fuel than turbojets. That's why props use less fuel than turbofans. That's why helicopters can lift so much weight, but propeller aircraft can very rarely accelerate vertically.

especially if powered by a combustion engine.

Electric motors typically operate at around 90% efficiency, while combustion engines are closer to 30%. On the other hand, that combustion engine will use fuel with an energy density some 40x better than the best batteries we have. If you expect to have any significant loiter or range, you're going to need a lot of energy storage, and that very quickly means your battery powered aircraft simply won't cut it. This is why we don't have battery powered aircraft.

Also every crash landing completely destroys the 'drive section' of a helicopter. A quad copter (made 90%) from plastics likely only needs a battery charge after a crash

Who cares? First, the whole purpose of drones is supposed to be that they're disposable. They're cheap enough to source and operate that you're not supposed to care too much if you lose one. Besides, in this application, carrying medical supplies, the payload is going to be valued at far far more than the aircraft itself.

Also, you're fooling yourself if you think a several kg object made of plastic and impacting at 30m/s is going to survive. This is real hardware, not your RC toy.

Automating a helicopter, especially to fly in narrow areas or under strong, quickly changing wind, is much much harder than automating a quad copter, or octo copter.

You're going to have to explain your logic on this one to me. On a quad copter, you vary the RPM of your independent motors to shift the center of thrust. On a traditional helicopter, you change the pitch of your swashplate to vary the angle of attack of your rotor and shift the center of thrust. The only difference I can see between the two different control systems is that the quad copter requires an additional matrix mixer on its outputs, and reacts more slowly since it has to fight inertia.

Comment: Re:Meh (Score 1) 131

by wagnerrp (#47995433) Attached to: Euclideon Teases Photorealistic Voxel-Based Game Engine

What they needed to do to make the demo a "wow" demo is put the camera inside the physics engine, and give it the mass and movement of a real camera. The results would have been much better.

That's why head tracking demos that allow you to shift your head to get a slightly different viewpoint on screen are so effective.

It's been a business doing pleasure with you.

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