Fun, Learning, Friendship and Mutual Respect START  HERE


Unregistered
Go Back   HeliFreak > R/C Helicopters > Main Forum - Helicopter Talk


Main Forum - Helicopter Talk R/C Helicopters and the people who fly them. VENDOR TOPICS DO NOT GO HERE. Full Scale Heli threads go in OT please


Like Tree35Likes
Reply
 
LinkBack Thread Tools Display Modes
Old 09-22-2021, 06:28 PM   #1 (permalink)
Registered Users
 

Join Date: Jun 2006
Default 3 blade head vs 2

Hi guys , what is the main difference between the 2 ?
Never flown a 3 blade head and although it looks interesting, are there any advantages to it? How different are the flying characteristics ?
Or is it simply a cool thing to have or look at ? (Besides cost of crash ,lol
Thanks.
Elgreco is offline        Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
Old 09-22-2021, 08:34 PM   #2 (permalink)
Registered Users
 
Posts: 8,946
 

Join Date: Apr 2016
Location: Michigan
Default

Main difference is an extra blade.

Sent from my moto g power using Tapatalk
jhamel, Rabid121, blarks and 4 others like this.
Thickfog is online now        Reply With Quote Quick reply to this message
Old 09-22-2021, 08:37 PM   #3 (permalink)
Registered Users
 
Posts: 65
 

Join Date: May 2021
Location: Arkansas
Default

I've got a 3 blade I swap to every now and again on my 230s. I've noticed it does have more lift than the 2 blade, with the 2 blade it gets light on the skids just a hair above midstick, the 3 blade it gets light a little under midstick, it seems quicker with it also in flight, and maybe a little more floaty but not much.
jshultz is offline        Reply With Quote Quick reply to this message
Old 09-22-2021, 08:42 PM   #4 (permalink)
Registered Users
 
Posts: 4,937
 

Join Date: Feb 2015
Default

More parts to break in a crash. It was the cool kid thing a few years ago.
yakky is offline        Reply With Quote Quick reply to this message
Old 09-22-2021, 09:03 PM   #5 (permalink)
Registered Users
 

Join Date: Mar 2020
Location: Central WA
Default

Can be more efficient and smoother with a smaller rotor disk. With the cost of added complexity & cost.
Av8hi is offline        Reply With Quote Quick reply to this message
Old 09-22-2021, 10:58 PM   #6 (permalink)
Registered Users
 
Posts: 13,907
 

Join Date: Dec 2011
Default

Quote:
Originally Posted by Thickfog View Post
Main difference is an extra blade.

Sent from my moto g power using Tapatalk
And less vibrations.
zurgxd likes this.
Atomic Skull is offline        Reply With Quote Quick reply to this message
Old 09-23-2021, 01:31 AM   #7 (permalink)
Registered Users
 

Join Date: Mar 2021
Location: usa
Default

Did a quick search seems 3 blade quicker off center for cyclic and a bit more lift. Roll and flip rates and transitions are slower due to simple physics more rotating mass = gyroscopic force. For the cost and complexity, its no wonder it died
CrackSmacklePop is online now        Reply With Quote Quick reply to this message
Old 09-23-2021, 01:55 AM   #8 (permalink)
Registered Users
 
Posts: 2,727
 

Join Date: Nov 2017
Location: Lincolnshire, United Kingdom.
Default

Nice to have multi-blade options for scale projects - that for me is their real benefit.
Cyclone7 is online now        Reply With Quote Quick reply to this message
Old 09-23-2021, 02:59 AM   #9 (permalink)
Registered Users
 
Posts: 3,458
 

Join Date: Apr 2007
Location: UK, Kent coast
Default

With three blades you have more thrust, but a bit less efficiency. You have more spinning mass which equates to some added stability but with the weight penalty of the extra blade.

Three blades has a smoother feel, to me anyway, it's hard to describe.

You can have a totally rigid head with no damping and yet you won't get any nodding in a hover. The rigid head gives a very 'connected' feel. You can have very high agility with light blades (check out some of Nick Maxwell's flying with the three blade Raptor E700).

There are both pros and cons basically, so it's a subjective choice.
__________________
2009 TDR, TDSF, Kasama Dune and Faifa, Minicopter Triabolo 700, RMJ Raptor gasser, Beam E4 and Avantgarde, JR E8 leggero, Suzi Laos, Shape S8, 'TDRex' 800, Rave 450, Trex 500.
trillian is offline        Reply With Quote Quick reply to this message
Old 09-23-2021, 03:13 AM   #10 (permalink)
Registered Users
 
Posts: 13,907
 

Join Date: Dec 2011
Default

Quote:
Originally Posted by CrackSmacklePop View Post
Did a quick search seems 3 blade quicker off center for cyclic and a bit more lift. Roll and flip rates and transitions are slower due to simple physics more rotating mass = gyroscopic force. For the cost and complexity, its no wonder it died

Gyroscopic precession is not a significant factor in helicopter rotors, the phase offset has basically nothing to do with that which is why the Robinson R22 can have a phase lag of 72 degrees.
Atomic Skull is offline        Reply With Quote Quick reply to this message
Old 09-23-2021, 05:26 AM   #11 (permalink)
Registered Users
 
Posts: 165
 

Join Date: Jul 2012
Default

Quote:
Originally Posted by Atomic Skull View Post
And less vibrations.
Why???
tolerance of 3 blades must be greater than 2 blades
Laos_pilot is offline        Reply With Quote Quick reply to this message
Old 09-23-2021, 05:45 AM   #12 (permalink)
Registered Users
 
Posts: 4,331
 

Join Date: Feb 2019
Location: USA::Ohio
Default

Quote:
Originally Posted by Atomic Skull View Post
Gyroscopic precession is not a significant factor in helicopter rotors, the phase offset has basically nothing to do with that which is why the Robinson R22 can have a phase lag of 72 degrees.
https://www.rchelicopterfun.com/gyro...recession.html
__________________
Vcontrol Touch, AccuRC & Heli-X Simulators
Oxy 5 MEG, 4 MAX, 2 (215)
SAB Goblin 500 Sport
XL Power Specter 700
fiddle is offline        Reply With Quote Quick reply to this message
Old 09-23-2021, 10:20 AM   #13 (permalink)
Registered Users
 

Join Date: Aug 2010
Default

When you are looking to get to the truth of some question, don’t go looking for an article which confirms your belief. Look for one that contradicts it, with proof. There are all kinds of examples which address some of the core/repeating errors people make on this site for example, and instead of going out and looking for contrary evidence, people actually end up linking to invalid posts which themselves are based on invalid videos/posts etc.

There are a bunch of these core questions:
1 vs 2 vs 3+ blades
Raised Tails
Telemetry
Transmission technologies (belts, gears, TT etc)
Coax
Chassis lean in still-wind hover
CG
Core materials/engineering stuff
Etc.

That ‘Smarter Every Day’ moron used as ‘proof’ in the linked article knows nothing about rotor dynamics, and he is dead wrong about phase lag = precession. If he had to pay $0.10 for every hit to that video, Id bet he would fix his error in an hour. I wrote to him when he posted that, and explained his error- and that when he is off explaining to the world how everything works, where there are a slew of rotary wing machines flying then (and now) with phase lag in the 57-75deg range- you have to be intentionally ignorant to leave a video like his up. And this doesn’t help his cause- where when he is so obviously/provably wrong about his ‘Helis are gyroscopes!’ nonsense, how can anyone have any confidence that his other content is correct/valid? He doesn’t care about being correct. He cares about making more content to make more money. Heck, if he doesn’t have time to correct his ‘precession’ video, at least just pull it down. The fact he hasn’t, some years after it was explained to him why he is wrong and which systems disprove his theory etc tells you what motivates him.
__________________
"The problem with quotes found on the internet is you have no way of confirming their authenticity." - Abraham Lincoln
extrapilot is offline        Reply With Quote Quick reply to this message
Old 09-23-2021, 02:40 PM   #14 (permalink)
Registered Users
 
Posts: 651
 

Join Date: Nov 2011
Location: Silver Spring MD
Default

Quote:
Originally Posted by Thickfog View Post
Main difference is an extra blade.

Sent from my moto g power using Tapatalk
That’s helpful
__________________
goblin 380 bk servos brain2 xnova
blade 230 S, DX7 GEN 2
junior10 is offline        Reply With Quote Quick reply to this message
Old 09-23-2021, 09:55 PM   #15 (permalink)
Registered Users
 
Posts: 1,197
 

Join Date: Oct 2014
Default

My Urukay had a triple head in the beginning. Had a "cool and wow " factor and sounded different. Flew very stabil in smooth low speed maneuvers but never could get it to perform like my 2 bladed 770 sport. Converted the Urukay to 2 blade and never looked back. Triple tails are fantastic for me as I like flying lower headspeeds.
3 blade head is not worth it IMHO

Sent from my SM-G960U using Tapatalk
FlatCrank is offline        Reply With Quote Quick reply to this message
Old 09-24-2021, 04:16 AM   #16 (permalink)
Registered Users
 
Posts: 3,458
 

Join Date: Apr 2007
Location: UK, Kent coast
Default playing devil's advocate for a sec

Quote:
Originally Posted by extrapilot View Post
That ‘Smarter Every Day’ moron used as ‘proof’ in the linked article knows nothing about rotor dynamics, and he is dead wrong about phase lag = precession.
Out of curiousity, I watched that video and I note that he does not ever use the term 'phase lag'.

So before you go around calling people a moron, you might want to make sure they are actually making the claim you are condemning them for :-)
spork and cyclo like this.
__________________
2009 TDR, TDSF, Kasama Dune and Faifa, Minicopter Triabolo 700, RMJ Raptor gasser, Beam E4 and Avantgarde, JR E8 leggero, Suzi Laos, Shape S8, 'TDRex' 800, Rave 450, Trex 500.
trillian is offline        Reply With Quote Quick reply to this message
Old 09-24-2021, 10:16 AM   #17 (permalink)
Registered Users
 

Join Date: Aug 2010
Default

Id suggest you look up Phase Lag as an official term. Wikipedia is a typical hit, and they summarize it as: “the angular difference between the point at which a control input to a rotor blade occurs and the point of maximum displacement of the blade in response to that control input.’

In the video, the entire discussion is focused on why it is that the control inputs are out of phase with the behavior of the rotor. In multiple instances, he discusses precession as a physics principle, and then nearer the, end, asserts ‘That’s it. That’s why helicopter blades operate 90deg out of phase.’ He titled the video- ‘Are helicopeters gyroscopes?’

The phenomenon he is talking about has nothing to do with precession- and it is fair to say his ignorance of this is why he doesn’t refer to it as phase lag. Im not going to refer to phase lag as precession- any more than I would call addition ‘multiplication.’ In that world, you can say, OK, well, 2+2=4, and 2*2=4, so, the analogy for that video title becomes ‘Is addition multiplication?’ and concluding after testing 2+2 and 2*2 that yes indeed, they are equivalent. When I tell him- the S76 has a phase lag of 57deg, and the BO105 is something like 78deg (from memory), and all gyros precess at 90deg by a core law of the universe, how can he not see a problem with his assertions? If he types 3*3 on a calculator, and he believes it will output ‘6’- but it outputs ‘9’, you would think a guy who named his channel ‘Smarter Every Day’ might want to revise his errors.

Phase lag isnt some esoteric concept that makes no practical difference to you as an RC pilot. So while Id hope that anyone interested in learning about how things work would care about the error for that reason alone- there is a practical reason to understand the error. Rigid-head machines- 3-bladed heads etc will have significantly less than 90deg phase lag. Not 1-2 deg less. Some of you are flying with 10deg error or more. And that is literally analogous to rigging a head with the swash drivers rotated 10deg off for a teetering head. You put in pure forward cyclic, you get some roll with that. Pure roll, you get some pitch with that. That is a ‘couple.’ And nothing good comes from it. The FBL sees a pitch command, and the machine rolls a bit with the pitch output. So, it puts in opposite roll, and that takes out some of the pitch. So it adds more pitch, and that reverses the roll error etc. On hard stops, you will see the rotor wobble hard. This is easy to fix- adjust the phase lag in the FBL. But if you believe lag is precession, and lag by law is ALWAYS 90deg, there is no reason to alter lag unless you are compensating for a rigging problem on a 5-blade head etc where maybe the links can only permit 45deg offset. So you think you need 45deg more lag to be good- to get to 90. And now your 80deg rotor is setup with 90deg lag, and you have problems again…
MariaFan and baba_yaga like this.
__________________
"The problem with quotes found on the internet is you have no way of confirming their authenticity." - Abraham Lincoln
extrapilot is offline        Reply With Quote Quick reply to this message
Old 09-24-2021, 10:49 AM   #18 (permalink)
Registered Users
 
Posts: 3,458
 

Join Date: Apr 2007
Location: UK, Kent coast
Default

Quote:
Originally Posted by extrapilot View Post

In the video, the entire discussion is focused on why it is that the control inputs are out of phase with the behavior of the rotor. In multiple instances, he discusses precession as a physics principle, and then nearer the, end, asserts ‘That’s it. That’s why helicopter blades operate 90deg out of phase.’ He titled the video- ‘Are helicopeters gyroscopes?’
Well, where the error exists here, is when that video is used in a context that is beyond the purview in which it was intended. The beginning bit with the children and tinkertoys should be the giveaway...

Quote:
Originally Posted by extrapilot View Post

Rigid-head machines- 3-bladed heads etc will have significantly less than 90deg phase lag. Not 1-2 deg less. Some of you are flying with 10deg error or more. And that is literally analogous to rigging a head with the swash drivers rotated 10deg off for a teetering head. You put in pure forward cyclic, you get some roll with that. Pure roll, you get some pitch with that. That is a ‘couple.’ And nothing good comes from it. The FBL sees a pitch command, and the machine rolls a bit with the pitch output. So, it puts in opposite roll, and that takes out some of the pitch. So it adds more pitch, and that reverses the roll error etc. On hard stops, you will see the rotor wobble hard. This is easy to fix- adjust the phase lag in the FBL.
This is interesting. Is there a good way to determine what the actual lag should be?
spork likes this.
__________________
2009 TDR, TDSF, Kasama Dune and Faifa, Minicopter Triabolo 700, RMJ Raptor gasser, Beam E4 and Avantgarde, JR E8 leggero, Suzi Laos, Shape S8, 'TDRex' 800, Rave 450, Trex 500.

Last edited by trillian; 09-24-2021 at 11:08 AM..
trillian is offline        Reply With Quote Quick reply to this message
Old 09-24-2021, 12:20 PM   #19 (permalink)
Registered Users
 
Posts: 6,134
 

Join Date: Jul 2012
Default

Quote:
Originally Posted by trillian View Post
Out of curiousity, I watched that video and I note that he does not ever use the term 'phase lag'.

So before you go around calling people a moron, you might want to make sure they are actually making the claim you are condemning them for :-)

Yep... I wouldn't call the guy a moron, probably an ambassador. He might have actually enticed more people to the hobby before with his previous video about CP helis.. This one has over a million views on YouTube:


Helicopter Physics Series Intro - #1 Smarter Every Day 45 (3 min 54 sec)
trillian likes this.
__________________
Compass Chronos | 7HVU | 550U | Atom 500 | Oxy 5 HF 560 | Oxy 5 HF 625 | Gaui X3 #1 | X3 #2
cyclo is offline        Reply With Quote Quick reply to this message
Old 09-24-2021, 04:38 PM   #20 (permalink)
Registered Users
 
Posts: 13,907
 

Join Date: Dec 2011
Default

(wrong thread deleted)
Atomic Skull is offline        Reply With Quote Quick reply to this message
Reply




Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the HeliFreak forums, you must first register.
Please enter your desired user name, your REAL and WORKING email address and other required details in the form below.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself. Use a real email address or you will not be granted access to the site. Thank you.
Email Address:
Location
Where do you live? ie: Country, State, City or General Geographic Location please.
Name and Lastname
Enter name and last name here. (This information is not shown to the general public. Optional)
Helicopter #1
Enter Helicopter #1 type and equipment.
Helicopter #2
Enter Helicopter #2 type and equipment.
Helicopter #3
Enter Helicopter #3 type and equipment.
Helicopter #4
Enter Helicopter #4 type and equipment.

Log-in


Thread Tools
Display Modes

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On




Copyright © Website Acquisitions Inc. All rights reserved.
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2021 DragonByte Technologies Ltd.

SEO by vBSEO 3.6.1