Surgery on a fixed-pitch flybar...

[buffo]

I guess the FP flyers also have a certain amount of yaw/rudder mix in to the throttle stick, to counteract the increased/decreased yawing motion of the different rotor speed?

If you have a good gyro, it will take care of that for you. On smaller birds (and especially ones with motors on the tail rotor), the tail can "blow out" during hard maneuvers, but on larger birds with strong motors and a good gyro it's not a problem. Of course, the best setup is a constant-speed tail rotor with variable-pitch blades, but that's usually only available on larger birds. (Like the X3V I was talking about above.)

I thought the 'elevator' on a single rotor FP heli was via the back/forth tilt to the swash plate

It is, and this changes the pitch as the blades rotate, which ends up pitching the rotor head (and eventually the entire bird) forward. Randy just got his wires crossed. Maybe he hasn't had his morning coffee yet!

Adam

[norty303]

It is, and this changes the pitch as the blades rotate, which ends up pitching the rotor head

This is what I thought. So in actual fact, the term 'fixed pitch' is a bit of a misnomer, in as much as they are not fixed (otherwise you'd never have any cyclic control) - they're just not user controllable?

P.S. getting a transmitter in the wrong mode is not too much of a deal breaker usually. Its normally as simple as swapping a spring plate over or swapping a whole gimbal.

[buffo]

the term 'fixed pitch' is a bit of a misnomer, in as much as they are not fixed (otherwise you'd never have any cyclic control) - they're just not user controllable?

No, not quite. All standard helicopters (quads and some hybrids excepted) have cyclic pitch control. That's how you fly them. (Cyclic pitch control = elevator and aileron.) But not all helicopters have collective pitch. That's the difference.

A "Fixed Pitch" bird still has a swash plate and cyclic pitch control. But there is no way to increase or decrease the average pitch of all the blades at once - all you can do is vary the pitch as they rotate around the mast, and then only in opposition to one another. Thus, in order to control your altitude, you have to speed up or slow down the speed of the rotor head to generate more or less lift.

This causes a delay in the throttle response, because the rotor head has a considerable mass and it takes time to spin it up and slow it down. That's why fixed-pitch helicopters don't perform as well as a true collective-pitch bird does.

In a collective-pitch bird, the rotor is running at maximum RPM all the time. The servo that controls the collective pitch will simultaneously change the pitch of all the rotor blades at once. (Actually, it's not a single servo, but a common signal that is applied to 3 servos at the same time.) Since this happens almost instantly (limited only by the speed of the servos), you can make the helicopter "jump" into the air. You can make it pogo up and down rapidly. And there are lots of other cool tricks you can do.

All of this is possible because on a collective pitch heli, the rotor head is already running at maximum speed, so as soon as you begin to make a pitch change to the blades, the results are instantly felt. Where as on a fixed-pitch bird, you have to wait for the rotor head to spin up and slow down.

Does that help?

getting a transmitter in the wrong mode is not too much of a deal breaker usually. Its normally as simple as swapping a spring plate over or swapping a whole gimbal.

If you don't mind doing surgery on your radio, yes. But it's easier to order a Mode-2 unit from the start. (Also, some of the cheaper radios are monolithic, so you may be able to swap the gimbals for the sticks, but the underlying pots may be mounted solid to the TX board.) Also, some radios do allow you to switch modes. (Two of mine have this feature.)

Adam

[Stuka]

Umm... I think you've got your wires crossed, Randy. Elevator control on a helicopter is accomplished with cyclic pitch control, just like roll control is. Neither one is really affected by rotor RPM, provided you have enough RPM to remain airborne of course. I think you're confusing the airplane term "elevator" with "lift" on a helicopter, as lift is definitely a factor of RPM on a fixed-pitch bird, but the elevator on an airplane is a control surface on the tail that causes the airframe to pitch up or down.

Dude - really?
I'm pretty sure I know what I was referring to ... talking about copters or airplanes is not my first rodeo with the models OR the real ones

"Elevator", in quotes, is referring to the similarity, or lack thereof, between altitude pitch control of airplanes - the elevator - and the equivalent control combination on helicopters. Intentionally simplified the comparison for someone who doesn't have much experience with collective-pitch helicopters.

I'm very aware that helicopter pitch & altitude control is a combination of both cyclic & collective pitch.
(And surprisingly, some helicopters do have actual functioning elevators - the AH-1 uses them as an aid primarily for high-speed / diving flight)

Without collective pitch, the only way you can maintain a climb setting - "up elevator" - on a fixed-pitch helicopter is to increase the rotor RPM, which increases the lift of the entire main rotor system. Yes, cyclic pitch is a factor with any helicopter, but without an increase in RPM of a fixed-pitch rotor system, the copter can't maintain a climb.

Collective pitch does it by increasing the blade pitch of all blades simultaneously, with a relatively constant RPM setting that is maintained "behind the scenes" with fuel controls on the real aircraft, or throttle / pitch curve mixing on CP models using a programmable computer radio.

Also, keep in mind that a true helicopter - model or real - does NOT need cylic input to climb vertically.
True vertical takeoff is all about the vertical lift generated by the rotor system, whether by collective pitch or rotor RPM increase.
For this mode of flight, cyclic control is merely being used to stabilize the copter horizontally.

Mostly everything you just said in the post prior to this one, I just started out with a more simplified approach to make make my initial comparison.

Kind of a leftover trait from being an instructor / test pilot when flying for Uncle Sam ~
Start out simple, but pile on the details when it's time for a check ride...

[norty303]

Well, all that aside, I've just ordered a V912 (well 2 actually, and a spares kit... and a water cannon and camera, and 3 upgraded 1000mah LiPo...)

Oh, and an 1/32 RC car for my 4 yr old daughter (she'll want to play with the heli so its distracting tactics)

Lets see how long it takes to get bored/broken

[Stuka]

Those might have a better tendency to fly off, since it would be just a set screw holding them in place.

Actually, they work quite well for the smaller copters -
I have an old E-Sky coxial Comanche that uses them (with a fancier name other than "wheel collars" to make them more expensive...), and they were "options" on the early Blade CP micros.

You'll need a retainer / clip in the end of the flybar as a backup, but with a little loctite on the setscrew they actually hold quite well.

[Stuka]

Well, all that aside, I've just ordered a V912 (well 2 actually, and a spares kit... and a water cannon and camera, and 3 upgraded 1000mah LiPo...)

Oh, and an 1/32 RC car for my 4 yr old daughter (she'll want to play with the heli so its distracting tactics)

Lets see how long it takes to get bored/broken

Awesome!

Can you haul the camera & water cannon at the same time?
Would make for some awesome first-person footage while chasing the dog / cat / kid!!

[Bradfo69]

I'm blissfully happy with my ignorance after reading the last 10-12 posts.

April 8, 2014 3:12pm EST... "I am not getting into flying RC helicopters."
























(I don't think.)

[buffo]

"Elevator", in quotes, is referring to the similarity, or lack thereof, between altitude pitch control of airplanes - the elevator - and the equivalent control combination on helicopters.

Strictly speaking, the elevator on a plane is not for climbing, but for pitch control. You add power to climb, just as you do in a helicopter. So there is a 1-1 correlation between the Elevator/Aileron combination on a plane and the cyclic control on a helicopter.

And in both cases, if you pitch up, you will lose airspeed unless you also add power. So you always have to add power to climb. But you can climb in both a helicopter and an airplane by simply adding power. You don't need the elevator (or the cyclic) to climb, assuming you are already in level flight. They're both for pitch control. You CAN use them to increase your climb rate, but when you get right down to it, it's still the POWER that is making you climb, not the pitch. (Adding pitch without power causes you to slow down, and eventually stall.)

Intentionally simplified the comparison for someone who doesn't have much experience with collective-pitch helicopters.

Given that Norty (Adam) is an experienced RC airplane pilot, I think your simplification was only confusing him. He's already got the idea of the cyclic down pat, which is arguably the biggest hurdle. More to the point though, it leads people to believe that you can't directly swap the controls from a plane to a heli, when in fact the stick configuration is essentially the same. (CP helis not withstanding, due to the extra switches and the differences encountered when transitioning from throttle-pitch mix to max throttle.)

And surprisingly, some helicopters do have actual functioning elevators - the AH-1 uses them as an aid primarily for high-speed / diving flight

Exceptional case that does not apply to RC, but I agree. And I left them out purposefully to avoid confusion. (I'm pretty sure both the super stallion and the sea king birds have functioning elevators as well.)

Without collective pitch, the only way you can maintain a climb setting - "up elevator" - on a fixed-pitch helicopter is to increase the rotor RPM, which increases the lift of the entire main rotor system.

I don't disagree. But remember that in a properly trimmed airplane you do not need the elevator to climb either. You can climb solely by adding power. (More power = more speed. More speed = more lift. More lift = climb) You can climb FASTER if you pitch the nose up (and also add power), but it's not required. (And yes, you can also climb by only pitching up without adding power, which will cause your airspeed to drop, but you risk a stall if you continue this.)

Collective pitch does it by increasing the blade pitch of all blades simultaneously, with a relatively constant RPM setting that is maintained "behind the scenes" with fuel controls on the real aircraft, or throttle / pitch curve mixing on CP models using a programmable computer radio.

I've played around with 4 different collective pitch birds so far, plus the Wasp Nano that I own, and all of them are set to run the main rotor motor at maximum RPM all the time once the throttle-up switch is thrown. Everyone I've seen fly only uses the throttle-pitch curve mixing to get the bird off the ground. Then they switch to full speed. The electronic speed control for the main motor that drives the rotor head is only working when the throttle-up switch is off. Otherwise it's wide-ass-open all the time.

Why would you want to throttle the rotor speed up and down anyway? The whole advantage of a CP bird is that you have maximum RPM (and thus potentially maximum lift from the rotor) available at any time, instantly. If you take that away, you've just introduced the same lag that a fixed-pitch bird suffers from. (True, it would make it easier to fly, but my theory is that you should be an advanced flyer before you try CP anyway.)

Also, keep in mind that a true helicopter - model or real - does NOT need cylic input to climb vertically.

And an airplane doesn't need elevator control to climb either. (Of course, you can't climb vertically!)

I just started out with a more simplified approach to make make my initial comparison.

Like I said - Norty gets it. He sounds like an advanced RC plane pilot to me. I think he's more than ready for a fixed-pitch bird.

Hell, I was flying mine 5 minutes after I unboxed it, and there's no way I was an advanced pilot! I hadn't touched an RC transmitter in almost 35 years... (And had never flown rotary-wing before in my life.) I had only been flying for about 5 weeks when I brought that bird to SELEM last year, which was when Chris told me I should step up to a CP bird, because he felt I was ready.

With modern gyros, it's a lot easier than it used to be...

You'll need a retainer / clip in the end of the flybar as a backup, but with a little loctite on the setscrew they actually hold quite well.

It would be nice to have them adjustable, and with a retaining clip it would be safer than just a set-screw, but the JB-Weld epoxy is about as solid as you can get short of welding them in place. It's pretty much a permanent fix; there's no way it's coming apart now. (Though I might play around with the spare flybar I have.) Truthfully though, this V912 is always going to fly like a truck (as Mark said), so I don't know that I want to spend too much time fiddling with it.

Can you haul the camera & water cannon at the same time?
Would make for some awesome first-person footage while chasing the dog / cat / kid!!

The mount is only designed to hold one at a time, but the bird definitely has the lift capacity to hoist both of them (plenty of excess lift available). So if you rigged up your own mount (duct tape to the rescue!) it would probably work. Only problem is that if you plugged them both into the control board, when you triggered the video to start, the water cannon would start shooting too. And since it doesn't hold much water, your video would be rather short. (Well, you could continue to shoot video once the cannon ran dry, but that sort of defeats the purpose.)

Adam

[norty303]

OMG Adam, what have you done!!!!????!!

The stuff they sell on that Banggood site!!!!!

Temp controllers, tecs, DC-DC adjustable converters... all very cheap too. The missus is looking at clothes and strangely, a rubber unicorn head mask thing. :-/


Aside from that, yes, I get how Helis work, I'd just never really thought about how the awash plate actually moves the pitch of the blade. I thought long and hard about how I might just go straight for the CP bird but ultimately my budget wouldn't stretch to a large enough one for my liking.