Forward flight - control explanation for a fixed wing pilot?

[Steve St.Laurent]

Somewhere along the lines I read an article that explained how the disc acts like a wing in forward flight - in terms that a fixed wing pilot could understand. I've been searching and searching and can't find it now. I'm an instrument rated private pilot with ~500 hours and am learning CP heli's. I've gone through the flight school videos at rchelicopterfun.com and am doing decent with forward flight - flying in circles in front of me as well as figure 8's. But I'm doing it by feel and haven't wrapped my head around the theory yet. As a fixed wing pilot I know the aerodynamics inside and out and that has certainly helped me over the years. On the helicopter side though I'm having trouble with knowing exactly the differences in controls between the hover and forward flight portions of flight. Anyone know of a good article that would explain this?

Thanks in advance.

[ARM_Coder]

I found this article on helicopter flight theory. Didn't read it in depth, but I skimmed it a bit and it looks quite good. It's sort of an article "for dummies" (no fancy math), but illustrates the basic concepts very well.

For you that have a solid background on fixed wing, it should be a piece of cake.

I hope that it helps!

[ARM_Coder]

That said, the article above is about "true" (full-sized) helis. For RC 3D helis some things change dramatically:

- Rigid main rotor
- Much bigger power/weight ratio
- Much bigger (proportionally speaking) main and tail blades
- Much lighter disc loading
- Much higher G loads allowable, and they can be negative
- Main blades are very stiff and almost don't flap
- Gyro-stabilized tail, most often including heading hold

In a sense, flying a 3D heli without doing any stunts is easier than the real thing due to the characteristics above(*). You don't need to correct the tail thrust to compensate changes in the main rotor torque. Conditions like retreating blade stall, or vortex-ring, are a non-issue, as the models are very powerful to their sizes.

Scale models are somewhat closer in behavior to the real helis, however.

* Of course, the pilot needs to learn to cope with the changes in orientation, that's a big deal in itself.

[Jmann841]

Originally Posted by ARM_Coder

That said, the article above is about "true" (full-sized) helis. For RC 3D helis some things change dramatically:

- Rigid main rotor
- Much bigger power/weight ratio
- Much bigger (proportionally speaking) main and tail blades
- Much lighter disc loading
- Much higher G loads allowable, and they can be negative
- Main blades are very stiff and almost don't flap
- Gyro-stabilized tail, most often including heading hold

In a sense, flying a 3D heli without doing any stunts is easier than the real thing due to the characteristics above(*). You don't need to correct the tail thrust to compensate changes in the main rotor torque. Conditions like retreating blade stall, or vortex-ring, are a non-issue, as the models are very powerful to their sizes.

Scale models are somewhat closer in behavior to the real helis, however.

* Of course, the pilot needs to learn to cope with the changes in orientation, that's a big deal in itself.

Our Helis are real heli's.

We do not have rigid heads, it is a hybrid semi-articulated/fully articulated (Because we have 1 screw holding the blade on it allows for lead and lag, most FBL heads allow for rotational forces as well, the only thing not allowed for is flapping although the dampeners allow for it to an extent,however, that is done naturally through blade flex) head all the forces of a real helicopter are applied to our helis as well. There are some full scale heli's that have fully rigid heads and some that have semi articulated.
Many real heli's have heading hold and fly-by wire systems similar to our gyros (Again, M Model blackhawk). It is true, our disk loading tends to be much lower.

In terms of the disk acting like a wing in forward flight think of it in two fold. You have the blades which are individual wings, however, in forward flight it acts as one large disk like a wing. I think this is what you referring to.

If you understand aerodynamic theory, understanding a helicopter is not a huge leap, the details get crazy but the basics are basic.

Essentially it is just a rotating wing that we use a swash plate to control the angle of attack. For collective movements it is controlled at all angles, for cyclic movements it is controlled only in that direction of the movement. This has to account for phase lag as well (In our heli's we typically see around 90 degree's of phase lag, however, it is not always 90 degree's contrary to popular belief)

Just understand our Heli's are the Ferrari's of the heli world. They are designed to do 3d and crazy stunts in all directions. They are terribly inefficient and typically not too much thought goes into the aerodynamic design of them. Typically a generic symmetrical blade foil is used and I doubt they use an Aerospace Engineer to design the airfoils.