Control Uses

[slick1537]

Well I am just starting to learn about how helicopters work. Not going to school or anything (yet) but I just figured I would try to figure out how things worked by myself because I like understanding how mechanical things work. Anyway, I am having a tough time trying to gather how everything work but from what I picked up, you have two pedals which control the tail rotor and allow you to spin to the left or right. Then my biggest problem is trying to understand the difference between teh collective and the cyclic. I think when you lower or raise the collective it adjust the angle of all the rotor blades, causing the helicopter to go up or down. The thing that doesnt make any sence to me is how the cyclic works. Does it adjust each blade indepentendly? So basically if you have the cyclic moved to the right, as the blades adjust as they reach the right side of the helicopter, causing it to pitch right, and then as they move toward the front of the helicopter they straiten out back to normal again? I think my idea on this might be wrong, but again, thats why I am here asking about it. Also, what role does the throttle play in all this. Are you always at full throttle or is adjusted for different moves? Thanks for the help in advance. BTW, I have my first demo flight on the 17th which I am very excited about. I know they will explain some of this stuff, but I really want to have a type of understandign of how stuff is working, instead of just which control will cause the helicopter to do what.

[Snowball-in-hell]

Hehe.....try this, I think you'll like it:

 

http://www.faa.gov/library/manuals/aircraf...a-h-8083-21.pdf

 

[flyby_heli]

Pedals: Increas or decrease thrust from tail rotor (antitorque), used to neutralize the torque from the main rotor in the different phases of flight. If you produce more antitorque than torque (left pedal in US made helicopters) you will turn left. If you produce less antitorque than torque, you will turn right.

 

Collective: Changes the pitch of all the blades collectively (hence the name). Pulling collective will increase the pitch angle, thereby increasing the angle of attack and thereby increasing the lift. Makes you ascend if you are in a hover to start with. Lowering the collective will do the opposite and makes you descend.

 

Cyclic: Changes the pitch of each blade individually depending on where the blade is in the cycle of rotation (hence the name again). This causes the rotor disc to tilt in one direction or the other and produce thrust in that direction, which again makes the helicopter move in that direction (you will learn about gyroscopic precession later, so i won't go into that for now). Remember you are really flying the rotor disc, the bubble that you sit in is just attached to the disc.

 

Throttle: Just like in a car, the throttle is used to control RPM. However we have two types of RPM. Engine and rotor RPM. In normal flight these two needles on the tach should be "joined". And the RPM should stay fairly constant. However, when you increase pitch of the blades you increase the drag they create (along with the increase in lift) this causes the blades to want to slow down and you have to increase the throttle (read: increase the power from the engine) to keep the blades from slowing down.

Most helicopters have some sort of electrical or mechanical system, like a governor or correlator, to help you keep RPM constant, but on some you still have to fine tune with manual inputs to the throttle.

 

 

Hope this helps

Flyby

[slick1537]

Snowball, thanks, I took a quick look at that yesteray, but I was having trouble understanding the way they explained certain things. Flyby, thanks for your definitions, but perhaps you could define rotor disk as I kind of understand how things work but I am still have trouble making the connection to the cyclic. Thanks again.

[flyby_heli]

slick-

 

The rotor disc is the circular surface made up by the spinning blades. Just imagine a ceiling fan. As it speeds up you can no longer count how many blades it has, you can only see the whole disc area of the fan.

 

The cyclic inputs you make goes through a mixer bellcrank, into the control rods and then make their changes to the stationary swashplate. The stationary swashplate in turn changes the rotating swashplate which again makes the changes to the blades via the pitch links as the blades are spinning, depending on where the blade is in the cycle of rotation. The cyclic will only change the direction of the thrust produced, it will not change the thrust!!

 

Try http://www.howstuffworks.com and search for helicopters. Might be explained in a different way that allows you to understand it.

 

 

Flyby

[slick1537]

I think I understand, it was as I orginally proposed? Say you are moving the cyclic to the left. This will cause the helicopter to increase thrust on the rightside of the aircraft, decrease thrust on the left side, and thus, cause the helicopter to pitch to the left, and move to the left. What is actaully causing the change in thrust is that when a blade approaches the right side of its rotation it is angled in a position that creates additional thrust, wheras it approaches the leftside, it is angled at a position that creates less thrust.

[Gomer Pylot]

The cyclic controls the swashplate, which tilts as the cyclic is moved, and thus tilts the rotor disk. If you move the cyclic to the left, the swashplate tilts to the left, and thus each blade tilts as it goes around, moving higher on the right and lower on the left. At least that's the simple explanation, ignoring gyroscopic precession and other complicated issues.

[flyby_heli]

Cyclic control does not increase or decrease thrust.....it tilts the thrust in any required direction.

 

In a two bladed rotor system, moving the cyclic forward will decrease the blade angle on the right side blade (on a counterclockwise rotor system) and increase the blade angle on the left side blade. Due to gyroscopic precession the maximum displacement happens 90 degrees later in the direction of rotation, which means the blades reaches their lowest point over the nose of the aircraft and highest point over the tail. The result of this is that the disc, and also the total thrust produced by the disc, is tilted forward and the helicopter moves forward.

 

Flyby

[Guest pokey]

the cyclic stick ( the one inbetween yer legs--unless yer flying a robinson)( the one in yer right hand even if ya are) is connected to the swash plate which works much like a camshaft----it "times" the blade pitch for each blade for a certain "clock angle" depending which way ya move the stick.

 

Gomer? ever see a Hiller? they call it a "wobble plate" & if ya push stick forward? the stupid "wobble plate" tilts backwards ! ----ALL you "wanna-be" Hiller mechanics out there? DO NOT attempt to remedy this "problem" will confuse the sh@* outtah the pilot !

[West Coaster]

It's best not to try and figure out how a helicopter flys, just accept the fact that it does fly.

 

Decide not to follow this advice and you will go cross-eyed in a hurry.

[Bristol]

Pedals: Increas or decrease thrust from tail rotor (SNIP SNIP

 

slick1537

 

Ditto all that AND try drinking out of a fire hydrant at the same time...

Yep, it's a lot to manage and think about. I would suggest taking a test flight or something along those lines

[Witch]

I'm not even going to attempt to explain it. I'm confused as it is.

 

Oops, gotta go...there's sewage coming in through the bathtub and toilet.

 

Later

[slick1537]

The 17th I am taking a demo flight at northeast helicopters. I am quite excited. I am pretty sure I understand the basics of what makes the aircraft move and change directions. I havent really put much thought into the swashplate or how that does its job, but I am sure it will be covered in the future if I go to flight school.

[Gomer Pylot]

Don't worry about it, and don't try to think about it. Push the cyclic in the direction you want to turn, and you'll go that way. In a hover, the whole helicopter will tilt and move in that direction. In cruise fllight, it will bank in that direction, or the nose will rise or sink. You don't have to think about what the swashplate or anything else is doing, just move the controls in the direction you want to go. Just like riding a bicycle or driving a car, you soon don't think about controlling it, you just do it.

[Witch]

Try thinking of the rotor as a giant dinner plate. In a hover, the plate is level. When pushing the control around, the plate tilts in that direction and thrust from that plate is offset causing the plate to go in the opposite direction. Kinda like a frisbee?

 

If you can find youreself a Vertibird, play with that and you can see that the rotor blades are in one position and don't change angle in reference to each other, but rather merely tilt forward and backward.

 

I had that same problem because of looking at those pictures of the relative wind and angle of attack seen in figure 3-15 of the Rotorcraft Flying Handbook, FAA-H-8083-21. It sucks, these pictures. Hard to decypher. Well, what do you expect from the Gubmint?

 

Later,

[Goldy]

Don't worry about it, and don't try to think about it. Push the cyclic in the direction you want to turn

 

 

 

 

 

 

Hey Slick- When Gomer says to "push" the cyclic what he really means is using slight pressure, move the cyclic about a quarter of an inch in the direction you want to go...much more than that in a hover you will find yourself standing on your head. ( kinda like my photo )

 

 

Goldy

[slick1537]

Gomer, I prefer to have a deeper understanding of the way things work. Obviously when I go to fly I am not going to be making caculations in my head of what is happening mechanically when I push cyclic right, rather, I am going to be learning about how each control affects movements, and how they all work with each other. I find I like to know how all components work, because later down the road, when something isnt working for me, and I just can't figure out why, it helps me to have an understanding of how the aircraft works and the limitations of the mechanics. I usually learn the behind the scene stuff of everything I do. Whethere it be fixing computers, or riding motorcycles. Take my example for instance: Knowing little things like how the height between the bars and the seat on a motorcycle will allow you to anticipate how it will handle. I know for a fact that because I have a better understand of my motorcycle, I am a much better rider than say my friend, who just jumps on it and rides, yet his bike has twice the horsepower of mine.

 

EDIT: I just relized you guys think I am thinking to far into this. You are misunderstanding me, I do relize what each control does now, but I was trying to get a understand of how they worked. I know if you get into a car, and turn the wheel to the right, the car goes right. I just wanted a understanding of all the different mechanical systems (IE. powersteering) that makes you turning the steering wheel right, make the car tires turn right.

[500E]

Dont forget movements of one control will have an efect on the others, as the rotor consumes power, (more colective) the torque will be transmitted to the hull and this will start to rotate, so a pedal input will be required, on small helios this may require a further input to colective to stay at a constant hover hight due to the tail rotor consuming horsepower, the faster you go the pedals will not be as important.

GOMER P is correct go fly thinking to hard to start with will fry your brain!

when you do the ground Checks you will soon pick up how the basics work.

A quarter of an inch is a long way.

[Gomer Pylot]

Slick, I understand your wanting to understand the systems, but I don't think it's possible to do a decent explanation of how the controls work in text. You have to look at it. Plus, each manufacturer does things differently, so you need to learn the way each model does things. Everyone uses a swashplate, which works the same way in general terms, but it's still better to look at one, and see with your own eyes what happens through the system when the controls are moved. Text just won't do the job.

[FauxZ]

Everyone uses a swashplate, which works the same way in general terms, but it's still better to look at one, and see with your own eyes what happens through the system when the controls are moved.

 

To fully complicate the issue, I don't think Kaman's use swashplates do they? I'm still at work and could only skim through this, but it might help with the original question posed as well.

 

http://www.helis.com/howflies/servo.php

[niftyben]

I found this article a while back and ended up turning it into my home page. All my friends got a kick out of it. I did too, come to think about it...

 

http://www.verticalreference.com/articles/...rticle_63.shtml

 

My HTML isn't working. Anyone know why?