Collective Pitch explained

[markarch]

Ok, I have been into planes for quite a while and am getting more and more hooked on helis. I have a honeybee FP that I am playing with right now. I can hover it really well and will definitely be stepping up into the cp world.

That brings me to my question(s) Can anyone either explain or point me in the direction of the basic principles of cp helis? I am confused about throttle hold, pitch curves, idle on/off and all of that stuff. I don't really know what they are used for and what affect they have on the heli. Will my DX6 work for my next cp heli or should I get an RTF version that has a better tx? Ugh so many questions. I'm just gathering information before I make the step up. I just need a little better understanding of the principals so I can make good decisions and understand a little better what I am reading.

I know this is probably second nature to you all but this is the beginners section after all. I look forward to advancing in the world of helis. Thanks in advance!

Mark

[Hellraser]

Hi Mark As I am sure you know a helicorter rotor is basically a rotating wing faster it travels the better lift it generates at a set pitch - and that is your fixed pitch helicopter.

with a collective pitch the Pitch or angle of incidence is kept low until a good headspeed is reached and then increased to generate lift. also has the advantage that it can be reversed for aerobatic flight and negative pitch is also helpful in getting the heli down in a breeze.

Throttle and pitch curve's are used to give the best throttle / Pitch combination for the smoothest flight - it changes from model to model depending on size and setup - some of the big boys hover at 1800 rpm the little T-Rex 250 has 4500 rpm - best to seek advice on the particular model.

Throttle hold tends to be used for one of two things a/ to set a low throttle for a autorotation landing - b/ as the motor cut off - at zero throttle for safety.

DX6 is a good radio main weakness is the 3 point pitch and throttle curve's and its only DSM1.

Hope this Helps....David

[racin06]

Mark,

Welcome to the world of helis!

Throttle Hold – A switch that sets the throttle to zero irrespective of the left stick position. Throttle hold also does not affect the pitch curve, unless you have programmed a specific pitch curve for throttle hold. Throttle hold is used as a safety feature and is used to practice autorotation landings.

Pitch Curve – A curve that is setup in the radio that sets the main blades pitch angle based upon the position of the left stick. Most pilots set a pitch curve for idle up and normal modes. In idle up mode, I usually set my CP helis where the blades are -10 degrees at full bottom left stick, 0 degrees pitch at mid-left stick and +10 degrees at full up left stick (-10, 0, +10). I also set this curve to be linear. So, for example, if my left stick position is half-way between mid-stick and the full up stick position, my blades are pitched at +5 degrees.

In normal mode, I set up my pitch curve to be -2, 0, +10.

Idle Up Mode – The mode in which the heli is at a fairly high throttle speed regardless of the left stick position. The throttle speed is established by setting up a throttle curve in the radio. In order to fly inverted and to perform most 3D maneuvers, the heli must be in idle up mode.

By the way, check out this thread for a good heli glossary of terms: http://www.swift-tuning.com/glossary.php.

Regarding your radio, your DX6 will do just fine for your next CP heli. I use the DX7.

You say you are hovering well…have you mastered hovering in all orientations? The reason I ask is because I also began with the HBFP, as well. I didn’t move up to CP helis until I could hover in all orientations and could fly figure 8s and circuits in both directions. Believe me, your wallet will thank you ;). As you know, the HBFP is a durable little heli. Also, if you can fly the HBFP, you’ll be able to fly any CP heli. I’m proof of that. To be honest, in many ways, the HBFP is more difficult to fly versus a CP heli. The CP helis are way more stable versus an FP heli; HOWEVER, the CP helis are also MUCH faster and more sensitive to stick inputs versus the FP helis. Therefore, there is a learning curve moving up to CP helis…though I found the learning curve to be rather short. Another difference that takes a little time to be accustomed to is variable pitch of the CP heli main blades. It doesn’t take you long to learn that suddenly cutting the throttle on a CP heli creates an immediate lead balloon :eek:.

Anyway, we are all here to help. By the way, I’m doing the opposite of you. I’ve flown helis for a while (26 months) and now I’m just starting to fly airplanes. I maidened (http://www.rcgroups.com/forums/showpost.php?p=11427546&postcount=198) my first airplane a week ago. What a blast!

[jasmine2501]

That is a really great explanation!

I put collective pitch into Google and found some interesting links.

http://en.wikipedia.org/wiki/Helicopter_flight_controls
http://www.helihobby.com/html/collective_pitch_and_ccpm.html
http://www.helifever.com/fixed-pitch-vs-collective-pitch.php
http://www.centennialofflight.gov/essay/Dictionary/pitch/DI39.htm
http://www.helis.com/howflies/ontheair.php

Some of this is for full-scale helis, but it's pretty much the same.

[markarch]

Thanks everyone! You really gave me some good info and I'm going to check out your links. After reading your explainations it doesn't seem quite as intimidating. I just love the challenge that the helis give me right now.

Racin,
What a great explaination. The pitch curve makes perfect sense to me now. I am not quite at all orientations in the infamous hover. I actually was just in the basement and did some repairs and when I got it back together it seemed like I was starting all over again. It took a little adjusting and now it is back to my old HPFP as far as feel goes. Good luck with the airplanes. I am totally adicted to them with all of the scratch built designs out there it seems like there are endless models to try. I have four new ones to maiden in the spring that I built this winter. Let me know if I can ever help with your flying.

Jasmine,
I'll be checking out your links. I watch quite a bit of your vids, including the CCPM set up. That was a bit over my head or at least it didn't translate to my DX6 for me. But none the less, a great vid.

I'll stay tuned for any more info you folks have for me. You can never have too much info.

Thanks, Mark

[jasmine2501]

I think I might do a video about how CCPM actually works, but I'll admit that while I understand the mechanics of it, I don't fully understand the physics of it. Precession has me really confused, because I don't see it on my helicopters. I'm also not clear on flybar-cyclic interaction, but I'll figure it out eventually. Just haven't bothered to do the research yet.

[osterizer]

Jasmine- don't spend too much time on precession. It's often cited as the explanation for the rotor's behavior, but it doesn't have that much to do with cyclic pitch operation- precession is a phenomenon in gyroscopic physics, but it doesn't account for the fact that the forces on the rotor from cyclic are constantly changing.

A very good source of information is Colin Mills' articles at http://www.w3mh.co.uk/articles/articles.htm. Scroll down to the bottom for the links to his articles. If you want to jump to the discussion of the control interaction, it's the last link (parts 9, 10, and 11), starting at part 10, but the whole series is worth reading. The info on gyros and other systems is dated, but it can give insight into modern ones because the problems they're solving are still out there.

I've thought off and on about making a simplified description of the control behavior, also. Mr. Mills' articles are excellent, but detailed. If that would be interesting to people I can write something up.

[markarch]

I have another question for all you pros.....
I could ask this somewhere else on the forums but I thought I'd start here since it sorta relates to my original question regarding the transmitters. I have been using my stock HPFP transmitter with my clearview sim to practice on. I must add that it is easier to hover my real heli than it is on the simulator for some reason. I don't think that is the norm but I'm happy to get real stick time over the sim......Anyways my question is since the transmitter is just a 4 channel model is it able to give me good training for the cp helis? It doesn' have all of the bells and whistles that the cp txs have so should I look for another option to fully practice my cp skills.

Thanks folks.
Mark

[osterizer]

Another FAQ! "Is the FP a good trainer for CP, or am I wasting my time?" :)

Sorry, Mark, it's a very good question-- FP is a lot simpler, so does it really work to practice? The answer is yes, though there will be differences between them. The commonalities, are, of course, that the controls are the same. You use the same motions to increase altitude or decrease it, to bank or pitch fore and aft, and to turn the tail. You'll develop control skills that translate directly.

On the other hand, the FPs have more pitch response in the tail, i.e., when you raise the "collective" to increase altitude, the tail will slew a lot more with a feep. Since to increase or decrease rotor thrust, the rotor has to speed up or slow down, a feep is a lot slower on collective, too. Cyclic is slower to respond (a good thing), but the tail typically doesn't stay put anywhere near as well. All this adds up to the FP being both gentler on the controls, and a bit harder to fly in some ways than a CP helicopter. With practice, you can fly it smoothly, though, and some even do basic aerobatics with them.

In the end, you'll learn a lot from an FP, and when you switch to a CP, you'll find it revelatory in the more precise control, but a new challenge in learning new things it can do.

[jasmine2501]

I never did FP, but I agree it is a super common question, and no I don't think it matters. You are still flying with "4 sticks" that basically do the same things, and that is really what you are learning from either FP or simulator practice. The rest is just a performance difference between helicopters, and it's a good thing to be able to handle those differences because you'll eventually have more than one helicopter, and even a single helicopter can perform differently from day to day.

With your simulator, as long as you can flip into idle-up somehow, the 4-channel transmitter should be fine for practicing, even for simulating aerobatic helicopters.

[markarch]

Alright. I have a commercial on right now watching the Steelers. I am really enjoying the FP experience for what it is. The stick control is really tough to get used to at first. I have heard it compared to balancing a marble on a dinner plate. That translates pretty well for me. But with all of this talk of comparisons between the control of fp vs cp I am really curious about the stability of the cp. I have to fight the urge to get a cp to fire up every once in a while between flying the HBFP.

Clearview does have the idle up mode so I could use that to try out the cp models. I am really interested in the Blade 400 perhaps for my step up eventually. The HBFP just meets the budget and time constraints right now and it is a blast.

Mark

[osterizer]

Watching it, too- love that 83 yard, 9 play drive by the Cards! :)

I enjoy flying my FP, too (bone stock HB FP3). The CP helis are more precise and more direct- it makes them more predictable, but quicker to get out of hand when you're learning. I wouldn't be in any rush.

[jasmine2501]

CPs can be more stable because of the higher head speed and belt-driven tails with higher-quality gyros. Also, when flying in idle-up modes, they often have a fairly constant head speed which makes the tail work better. However, it's a trade-off because they also are less "forgiving" of mistakes and can get out of hand pretty quickly and they have no self-stabilizing characteristics like a CX does.

[Hellraser]

CPs can be more stable because of the higher head speed and belt-driven tails with higher-quality gyros. Also, when flying in idle-up modes, they often have a fairly constant head speed which makes the tail work better. However, it's a trade-off because they also are less "forgiving" of mistakes and can get out of hand pretty quickly and they have no self-stabilizing characteristics like a CX does.

Yes I agree -also dont forget the learning to fly is on part of the learning curve - the learning how to keep the heli in the air is the other half - the more complex the setup - the more complex is the re-setup after your first crash - and that is where many find the greatist difficulty - if you go fixed pitch first you will learn a fair amount about the mechanics - without the really complex stuf that comes with the more complex heli's - Dual rate gyro, pitch and thottle curves, CCPM - I have seen a number of cases over the years where somebody has baught a complex heli and tried to go it alone because they had no expert help on hand - and never actually got the heli flying corectly - crashed it paid out $$$ for parts to repair and crash it again and eventually given up.

Regards David

[markarch]

Oh yeah lets get the game back on. What an interception. Pretty good game so far.

Anyways I am not in a hurry to get another heli. It is just so tempting, you know we all want what we really don't need or aren't ready for. I can't wait to get outside in the spring and do some circuits. I really haven't even started to wring out what the fp can do as far as fff and circuits.

This has been a good discussion. I'm usually over in the electric plane area. You folks are equally as awesome as the ones over there. Back to watching the game........I may get my mCx out and buzz around.

[jasmine2501]

Equally? :eek:

Actually I fly some electric planes too...

[markarch]

LOL.
Yeah...... you actually helped me out with some questions I had with my Art Tech Pitts a while back.

[Hellraser]

:D LOL :D Markarch - you will find many of us started off with planes - I did 30+ years ago - I think I still have my old Sanwa kicking around someware - you might say from planker's to plonkers ;)

Regards David

[jasmine2501]

LOL.
Yeah...... you actually helped me out with some questions I had with my Art Tech Pitts a while back.

Yeah that plane is fun... I wish I could get some better video of it...

http://www.vimeo.com/1837877

Why can't we just post a freekin link to those?

[Hellraser]

Yeah that plane is fun... I wish I could get some better video of it...

http://www.vimeo.com/1837877

Why can't we just post a freekin link to those?

Christ that landing was slow for a pitts :eek: my old pitts would have stalled at that - is this a very light electric version

Regards David

[jasmine2501]

Christ that landing was slow for a pitts :eek: my old pitts would have stalled at that - is this a very light electric version

Regards David

Yeah it's a foamy.

I wonder if it could be possible to make a foamy helicopter?

[osterizer]

Picoo Z :).

Bigger? Of course. You'd need a shaft or motor tail, since a foam boom wouldn't be able to maintain belt tension, and a lot of clearance from mains to boom since the blades would flex more. Certainly possible, though.

[Cpt Marvel]

So whats a "CP" and "FP'?

[jasmine2501]

Fixed pitch and Collective Pitch.

With fixed pitch, the blades have a fixed angle of attack into the wind as they spin around (sort of). With collective pitch, the blades are usually symmetrical vertically with no 'twist' to them, and they rotate up and down together.

Coaxial helicopters are a type of fixed-pitch helicopter. The reason I say "sort of" is because the blades do change a little bit up and down with cyclic control input.

I really need to make that video...

Look at the end of this video - there is a simple explanation of collective pitch. The video shows a Blade 400 which is a fairly popular type of RTF(ready-to-fly) CP helicopter. The one in the video is extensively upgraded.
http://www.vimeo.com/2666191

[Balr14]

Yeah that plane is fun...

I remember discussions about that plane! I had the Cox Christen Eagle version of it. I sold mine to buy a heli.

[TMorita]

This is an old but good thread:

http://www.rcgroups.com/forums/showthread.php?t=323392&highlight=ccmp

I posted a bunch of picture in it to demonstrate how CCPM works.

Toshi

[Mike_Then]

Mark,

Welcome to the world of helis!

Throttle Hold – A switch that sets the throttle to zero irrespective of the left stick position. Throttle hold also does not affect the pitch curve, unless you have programmed a specific pitch curve for throttle hold. Throttle hold is used as a safety feature and is used to practice autorotation landings.

Pitch Curve – A curve that is setup in the radio that sets the main blades pitch angle based upon the position of the left stick. Most pilots set a pitch curve for idle up and normal modes. In idle up mode, I usually set my CP helis where the blades are -10 degrees at full bottom left stick, 0 degrees pitch at mid-left stick and +10 degrees at full up left stick (-10, 0, +10). I also set this curve to be linear. So, for example, if my left stick position is half-way between mid-stick and the full up stick position, my blades are pitched at +5 degrees.

In normal mode, I set up my pitch curve to be -2, 0, +10.

Idle Up Mode – The mode in which the heli is at a fairly high throttle speed regardless of the left stick position. The throttle speed is established by setting up a throttle curve in the radio. In order to fly inverted and to perform most 3D maneuvers, the heli must be in idle up mode.

By the way, check out this thread for a good heli glossary of terms: http://www.swift-tuning.com/glossary.php.

Regarding your radio, your DX6 will do just fine for your next CP heli. I use the DX7.

You say you are hovering well…have you mastered hovering in all orientations? The reason I ask is because I also began with the HBFP, as well. I didn’t move up to CP helis until I could hover in all orientations and could fly figure 8s and circuits in both directions. Believe me, your wallet will thank you ;). As you know, the HBFP is a durable little heli. Also, if you can fly the HBFP, you’ll be able to fly any CP heli. I’m proof of that. To be honest, in many ways, the HBFP is more difficult to fly versus a CP heli. The CP helis are way more stable versus an FP heli; HOWEVER, the CP helis are also MUCH faster and more sensitive to stick inputs versus the FP helis. Therefore, there is a learning curve moving up to CP helis…though I found the learning curve to be rather short. Another difference that takes a little time to be accustomed to is variable pitch of the CP heli main blades. It doesn’t take you long to learn that suddenly cutting the throttle on a CP heli creates an immediate lead balloon :eek:.

Anyway, we are all here to help. By the way, I’m doing the opposite of you. I’ve flown helis for a while (26 months) and now I’m just starting to fly airplanes. I maidened (http://www.rcgroups.com/forums/showpost.php?p=11427546&postcount=198) my first airplane a week ago. What a blast!

Great explanation! Thanks!