Can we achieve practical personal flight with current options?

[Ryan_m_b]

Here's my proposal:

Lets first understand and mimic what nature did because nature solves problem oh so well.

The biggest reason why this won't work: the square cube law. You can't scale an object up and expect it's characteristics to be the same as the volume increases faster than the area. In the case of birds this means that if you double the size you have double the wing area but four times the mass to lift.

lets not get into the non-technical issues, if this can be build today, the world would bend around making this commercially available.

Saying "let's not talk about this because I'm right" is a bit of a poor thing to do. Regardless the non-technical issues are probably more important than the technical ones in this case. We can build things like jetpacks and whilst they aren't very good they could feasibly be made. But the issues of safety and economics massively favour not doing this.

 

[Ryan_m_b]

Is teleporting too far off the subject? My brain can go off on a tangent sometimes.

Yes it is very off topic. Can members please remember that this thread is under the same site rules as any other. Keep all proposals to technologies that have been demonstrated to be possible, if not economical.

 

[meloettakawaii]

<< Comments deleted by Moderator >>[/color]

 

[timthereaper]

<< Comments deleted by Moderator >>[/color]

Good luck with getting that kind of contraption commercial. There might be someone like a Chuck Yeager willing to follow you up into the sky on a wing and a prayer, but no one in their right mind will pay you for that.

lets not get into the non-technical issues, if this can be build today, the world would bend around making this commercially available.

So again, what's your use case for this exoskeleton/wing vehicle? I agree that personal flight may have good military applications, but so does a tank and we don't see those riding down the street every day (unless you're in Crimea/Syria/Afghanistan/a military base). A strong commercial use case is a very non-trivial thing. Even if you could somehow build this thing tomorrow, for the world to bend around to make this commercial you have to show the world it needs this.

 

[berkeman]

This thread is closed for Moderation...

Thread re-opened. Let's all keep in mind Ryan's comments. We discuss mainstream science here on the PF.

 

[NTW]

Since a gyro has no tail rotor to counter the torque, that coupling is only possible during initial "spin-up" on the ground.

If ram jets at the tips of an autogyro's blades are used then you have a helicopter and the airfoil angle of attack must be reversed. A helicopter requires a swash-plate to control pitch. An autogyro flies forwards with nose up so air flows up through the blades causing them to "auto-rotate". The autogyro blades are then effectively gliders providing lift. A helicopter flies forwards with nose down as the blades push air down and backwards. The transition between those distinct modes is quite dangerous as the vehicle must fall through the low airspeed period without lift while the blade angle of attack is reversed.

I agree with everything you're saying here, and just wish to make a small comment: at the transition between 'helicopter mode' and 'autogyro mode', the blade angle of attack is not reversed, but just reduced, as autorotation takes place with positive angles of attack at any station of the blade.

Both helicopters and autogyros fly with positive angles of attack, as the relative wind is 'seen' from any station of the blade. If a helicopter has engine trouble, the pilot usually resorts to autorotation to glide safely to the ground, and in order to keep the rotor in autorotation he reduces the pitch to the optimal autorotation value, but the AoA is kept positive...

For the same reason that the wing of a glider has always a positive AoA, the autorotating rotor blade has to keep a positive AoA...

 

[Baluncore]

Thanks for the incisive analysis. I agree that “angle of attack is reversed” should be replaced with “angle of attack is reduced”.

So, if angle of attack is only reduced, then what is reversed to flip between the two distinctive modes?
Consider the airfoil lift and drag forces on a blade relative to the plane of the rotor disk. The vector sum of those forces on a driven airfoil is a backward leaning upward vector. On a glider, or during auto-rotation, it must become a slightly forward leaning upward vector. That requires a reduction in AoA. It seems that some lift is being sacrificed to overcome drag and so provide auto-rotation.

 

[NTW]

For every helicopter, there's probably a pitch setting that gives the best autorotation. That pitch is lower than the 'cruise pitch', and I'm sure that the manufacturer provides that vital information in the pilot's manual...

The 'helicopter mode' is not radically different from the 'autogyro mode'. In the latter, the rotor does also provide the lift, the rotor being indirectly powered (one can think in a 'pneumatic transmission' from the engine driving the propeller) by the relative wind produced by the movement of the aircraft.

In the very simple, present-day gyros, during the 'spin-up', the weight of the aircraft is slightly reduced, because the rotor is producing lift... The revs don't reach the critical value (the one usual in level flight), both for mechanical reasons (the pre-rotators, as they are called, are not built to transfer so much power, and a gyro rotor is not built, either, to withstand a very high torque) and because that could cause an unintended take-off and an accident.

 

[Baluncore]

For every helicopter, there's probably a pitch setting that gives the best autorotation. That pitch is lower than the 'cruise pitch', and I'm sure that the manufacturer provides that vital information in the pilot's manual...

It all gets a bit debatable. Unlike common propellers, the typical rotor blades of helicopters and autogyros have no twist along the blade. At any point in time, part of the blade is auto-rotating and part is driven. Those parts and the section between the two is producing lift. It is the sum of all the effects that decides performance. The active region may be centred at different radii at different points of the rotation cycle.

If you cannot get rotation in an autogyro without a pre-rotator, then it is probably unsafe to lift off. I have designed and evaluated autogyro pre-rotators and now believe them to be an unnecessary complexity.

Having just examined the discarded blades from an autogyro and a helicopter I notice the helicopter blade has a symmetric airfoil while the autogyro has an asymmetric profile. I assume that is because the helicopter blade must operate in both modes while the autogyro blade is always auto-rotating.

 

[NTW]

Present-day gyros use simple blades, without taper or twist. Helicopter blades are sometimes more complex, and that may mean a difference in the distribution of the driven/driving regions of helicopter and simple gyro rotors while in autorotation. Concerning the airfoil, an important consideration in helicopters is the movement of the center of pressure with pitch variation, so that feathering forces may be kept kept within limits, and that favors the symmetrical profile, where pressure center travel is short. In gyros, the choice of airfoil is directed to optimize autorotation.

But nothing of the above affects the main point; namely, that the rotor in autorotation is essentially similar to the engine-powered rotor. Hence, only a pitch reduction adjustment is necessary to pass from the 'engine-powered rotor' condition to the 'wind-powered' auto-rotating condition. They are different, but not 'reverse' conditions, and share a positive (if also different) angle of attack. Both are, after all, rotating-wing lifting devices.

The two gyros that I have flown had mechanical pre-rotators fitted. I have seen people spinning the rotor of their (lighter) gyros first by hand, and then taxiing 'to get revs' till they reached enough rotor speed to take off. But that's primitive and may cause blade sailing and much hammering of the stops...