35
Stand on its rotor head? yes, maybe. Spin? not for long.
The rotor hub and blades are quite strong and can take the helicopter weight at-least temporarily (leaving aside the balancing issue). The blades are designed to overcome stresses in flapping and can take the load. The rotor hub however, is not designed to take loads in this attitude (it is designed ...
30
This looks like a model that was carefully set up to spin.
First the facts: FAR part 27 regulates the design criteria for rotorcraft. Specifically, FAR 27.337 states:
The rotorcraft must be designed for—
(a) A limit maneuvering load
factor ranging from a positive limit of 3.5 to a negative limit of
−1.0 [snip]
So yes, contrary to the unsubstantiated claims ...
24
Scaling laws are your enemy here.
Model helicopters can be controlled with changes in rotational speed, but for full-sized helicopters the energy needed to quickly change the speed of their rotors relative to the energy needed for lift creation is far too high. In detail:
The moment of inertia of a scaled-up rotor changes with the fifth power of length. ...
23
Nope, they cannot. There is a hinge in the rotor head that will make the helicopter want to topple over, it won't be spinning like in the video: it is not supported by the blades laying on the ground. Picture the blades not being there and you'll see how impossible it is to balance the whole construction on top of the rotor mast. And functionally (for this ...
17
In the Mars Helicopter Technology Demonstrator paper these are refered as "Chinese weights" and the purpose stated is
Chinese weights provide a restoring force on the blade moments when
under centrifugal loads thereby reducing the torque requirements on
the swashplate actuators.
Searching for the term leads mostly to RC sites, for example this ...
17
that can not flap or pitch or adjust otherwise?
Yes, you can design one like that, but you won't get many people to fly it.
In the early days of helicopter flying, any number of crashes occurred before the designers began to account for the problem of differing airflow over the retreating and advancing bladed in forward flight. If you don't change the ...
11
An interesting thought. Control the aeroplane through its propeller(s), like a helicopter does.
Propeller torque differential would control roll
Propeller cyclic would control both pitch and yaw
Propeller collective would control engine thrust, like already done in constant speed propellers.
The thing that immediately comes to mind is moment arm for pitch ...
9
There are pipes inside the blades which connect the engines to a rotary seal inside the main rotor head assembly. That seal allows fuel to be pumped into the blades from a port outside the main rotor head. Such seals are used in a variety of mechanical engineering applications where a fluid, usually lubricating oil, has to be provided to a rotating piece of ...
8
All rotor heads need to deal with multiple forces but two in particular have a big influence on the design and complexity of the rotor head.
As a blade moves forward (the advancing blade), it experiences an airflow equal to the speed of the blade plus the air speed. As the blade moves backwards (the retreating blade), it experiences an airflow equal to the ...
7
Yes, controllability can even be accomplished with only one (rigid) rotor.
Degrees of freedom
In a three-dimensional space there's generally six degrees of freedom (DoF):
forward/backward
left/right
up/down
roll
pitch
yaw
Most aircraft allow engine rpm and velocity to be controlled separately (variable pitch propeller/rotor) as a seventh DoF.
rpm
Multi-...
7
This will work as long as the propellers produce enough thrust and blade pitch can be adjusted fast enough to outrun all eigenmodes.
As soon as you need to throttle back (and eventually you must, to come down again), the control effectivity of the propellers will be greatly reduced. Granted, you can float down in autorotation like an autogyro, but the ...
7
The engine mount is an important component that transfers the prop thrust to the airframe. It's clearly visible in this photograph of a fast and powerful plane, a Bf109. Of course, bearings transfer thrust between the rotating and static parts. That is common to all engine-propelled vehicles, ships, cars, planes... The main thrust load, in the picture ...
6
It's because the blade's span-wise axis is "swept" relative to its flapping hinge line, so when it flaps, the sweep angle results in the blade's effective AOA changing somewhat (for the advancing blade, reducing; that's what the feathering part means).
To picture it, imaging you are standing directly in front of the tail rotor disc watching the advancing ...
4
You couldn't do it to control reentry, but you certainly could do it for a vertical landing system that might be a bit less technically demanding than a rocket that can descend under control with its engine running as SpaceX does.
You are limited by the mach# of the tips of the rotor, which have to be subsonic while spinning. You would want a rotor that ...
4
According to the Web site, http://www.rotaryaction.com/e.html, the helicopter was a real Hughes 500 with extended landing skids.
I would assume that even if the frame was real, they would use a touch of movie magic to pull off the effect. To get the spin-rate right for a movie, I would assume they pulled the engine, used a rotary electric motor to control ...
3
It's basically the teetering Bell/Robinson 2 blade rotor concept applied to a 4 blade rotor. Like a teetering system, the gimballed rotor head accounts for most of the lead/lag/flapping, with whatever isn't accounted for absorbed by flexing of the long skinny root shafts.
With a 2 blade teetering system you have the weight of the machine hanging from a ...
2
Theoretically yes, you could build a full-size quadcopter with four fixed pitch rotors, and control it through independent variation of the rpm of each rotor. The power density now achievable in permanent magnet electric motors (eg, 25 hp in a 85mm diameter motor) makes it seem possible to build a small, one man quadcopter with a single motor/generator, but ...
2
It is indeed possible. One of the first helicopters was the Petróczy-Kármán-Žurovec PKZ 2 Helicopter, fitted with two contrarotating, coaxial rotors that had fixed blades, with no provisions for flapping or pitch change:
https://oldmachinepress.com/2012/09/24/petroczy-karman-zurovec-pkz-2-helicopter/
2
I worked medium and heavy transport helos in the Marines, and I never heard of an incident caused by a rotor head failure. Blades, transmissions, all kinds of other things, sure, but not main rotor heads.
2
No. You have neglected to account for how drive systems work.
When the engines engage with the transmission, the blades begin to turn. The sprag clutch/freewheeling unit is only oriented in one rotational direction and to catch. If the load comes from the other direction of rotation, it disengages. (See page 4-6 of the link).
In this particular case -...
2
Picture above is from Helicopter Performance, Stability, and Control by Ray Prouty, and shows the fully articulated rotor such as installed in the Apache. The Fully Articulated term means that the blades can rotate in three Degrees of Freedom: fwd/aft, up/down, and nose up/down. The rotation axes are single points of failure: when they break the blade is ...
1
The strap pack is the structural member which transmits loads between the blades and the pitch housing assembly. Not shown in the drawing above is the shear pin that goes down through the hole in the pitch housing and through the holes in the strap pack members. The pitch housing ends at that junction and there is no other connection between the blades and ...
1
There is no need to attach the wing to the rotor head - simply attach it to the top of the fuselage. You could run the rotor through a hollow tube and attach the wings to that - the inner uncovered section of the wing is an interesting idea.
If you are looking for VTOL, a tilt rotor with two electric motors driven by the gas turbine may be a better option.
1
This type of rotor is not common because flapping blades make the helicopter fly better. Flapping vertically allows the blades to reduce angle of attack as they advance/rise and increase angle of attack as they retreat/fall, evening out lift in concert with cyclic feathering. Flapping horizontally damps vibration and eases acceleration/deceleration.
1
Can it...? Yes. But... practically No.
The points below explain why the answer is, strictly speaking, yes. But then, they explain why it,s not actually helpful in practice. Note how each case fails so fast that the technical properties of the helicopter are mostly irrelevant.
Can it stand on the rotor head?
Yes. The helicopter is in a nice equilibrium.
It's ...
1
Yes and no.
I've never seen such a design for a large helicopter but there are plenty of micro sized RC helicopters which utilize such a scheme using a pair of contra rotating main rotors and a smaller tail rotor to control pitch.
This kind of design works fine, albeit difficult to control for Palm sized toys but does not scale well for larger vehicles.
...
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