Cyclic curiosity

[extrapilot]

X

ETL is a complex phenomenon with a couple a main components. The big one for us regards blade drag. For the blade, there is induced drag (that part of the total drag resulting from the generation of lift), and profile drag (the remainder). Because we run high headspeed and low blade loading, profile drag accounts for about 75% total rotor drag in hover. Full scale, for a machine like the 47 with some payload), that number is closer to 20%

ETL exists partly because the lateral motion of the rotor reduces induced drag. So just as an example, if ETL drops induced drag 10%, that has a much larger impact on total drag for the full scale machine here than it does for the model.

I think this is a general problem for people here who look at models vs full scale and believe the laws of the universe don’t apply to models because the results are different. They apply- but ratios/magnitudes change- and other things are going on (as always with helicopters) that can mask things further.

Kind regards-

[Xrayted]

[R_Lefebvre]

These guys figured out how to make a tandem fly. Two Trex800's bolted together. Controlled via a hack to Ardcopter running on a Pixhawk. Sounds pretty cool.

SPH Engineering T-Rex Tandem Rotor Helicopter (3 min 2 sec)

[MariaFan]

That was excellent.

[Block137]

Originally Posted by Xrayted

A tandem heli yaws by one rotor tilting one direction while the mixing tilts the other rotor the opposite way.

This opposing aileron force of the rotors keeps the heli from banking either direction, but instead causes the heli to spin around on its axis, but it can lose a little lift at the same time when this is occurring.

My buddy had a very nice Hirobo tandem RC model that works the exact same way, but he would adjust the collective during yaw himself. I'm sure he could have created some mixing in the TX to do this for him.

I'm not sure if there is any collective mixing involved on the full scale, or if the pilot takes care of this.

If both rotors are very rigid (no flapping etc,
will it still be able to yaw?

Not trolling... really wanted to know.

[Xrayted]

There is an element of flap in all helis, even rigid heads.The blades themselves will flap. Flapping is a required physics phenomena that allow a heli to fly properly.

Even so, flapping is not a factor of anything in this discussion. This is a cyclic function we are talking about here.

Its no different that any single rotor RC heli when you apply R or L aileron. The swash tilts the rotor and the heli will move that direction because you have only one rotor. In the tandems case, one rotor tilts one direction, and the other tilts the opposite, so the heli simply spins in a circle.

Don't confuse blade "flap" while in flight with "cyclic" swash inputs on the rotor. They are two completely different things

[extrapilot]

Originally Posted by Xrayted

There is an element of flap in all helis, even rigid heads.The blades themselves will flap. Flapping is a required physics phenomena that allow a heli to fly properly.

Even so, flapping is not a factor of anything in this discussion. This is a cyclic function we are talking about here.

Its no different that any single rotor RC heli when you apply R or L aileron. The swash tilts the rotor and the heli will move that direction because you have only one rotor. In the tandems case, one rotor tilts one direction, and the other tilts the opposite, so the heli simply spins in a circle.

Don't confuse blade "flap" while in flight with "cyclic" swash inputs on the rotor. They are two completely different things

No- they are not.

Cyclic excites flap- which is why the tip path plane changes with cyclic input. Each degree of cyclic input yields that same number of degrees of flap. It is a basic law of rotors.

And, with the tandems, it is exactly cyclic flap which causes this tip path plane change- which yields the yaw torque, for a pedal turn at low airspeed (at any speed- but point being- you dont need other factors involved here to confuse why the blades are bouncing up and down).

You can also see flap that results from dissymmetry of lift- where the advancing side of the rotor sees higher airspeed than the retreating side. But this flap is countered by the pilot with opposing cyclic. If it weren’t, you would get the rotor leaning back, which would slow the machine.

[Xrayted]

Yes, I'm fully aware that cyclic causes blade flap, but that wasn't what I was talking about or meant in my reply.

I was operating under the assumption that the OP was confusing the terms cylic and flap based on how the question was asked. Yes they go hand in hand one driven by the other, but I wasn't trying to go any deeper than simply distinguishing the two terms.

We don't refer to aileron cyclic commands as applying "left or right flap" any more than we refer to making right or left turn in a car anything else either despite there being a multitude of other physics actions and reactions occurring down stream to cause the car to turn.

My point was simply that there are cyclic commands being made on both rotors in opposing directions which cause the heli to yaw. I'll admit I could have worded things better, but the first paragraph of my reply answered his specific question correctly one way or the other.

[Block137]

From your picture above^^^
Does the rotor discs actually tilt like that?

If so, what I'm asking is that when everything is "ideally" rigid (rotor discs are always parallel) what will happen?

[Xrayted]

And this is what I assumed you were asking in my initial reply but wasn't exactly sure.

You can also see your RC helis rotor tilt when you give cyclic commands and the swash adds cyclic pitch to the blades while on the ground . Our helis have a rigid head design, DFC for example where the blade spindle is practically solid within very hard plastic dampers.

It could be forced to roll the heli and blades right over into the ground if you worked hard enough at it. As EP stated, the cyclic triggers blade flap and tip path change. The image may be exaggerated for example somewhat (not my drawing).

A heli with a "rigid" head design head does not mean the rotor remains parallel at all times. RC helis are a great example of this.

[kramrle]

For details about ETL, cyclic, head designs and much more, check out this: FAA rotorcraft flying handbook for helis & gyros

https://www.faa.gov/regulations_poli...-h-8083-21.pdf

[Vladlen]

Retreating Blade Stall VNE in Helicopters (8 min 40 sec)

The greater the cyclik of the swash plate the greater the tilt of the rotor the lower the relative angle of attack "pitch" on the advancing blade and on the retreating blade more.

How does a Helicopter fly ? (8 min 29 sec)

Helicopter Aerodynamics - Retreating Blade Stall (1 min 16 sec)