Fun, Learning, Friendship and Mutual Respect START  HERE


Unregistered
Go Back   HeliFreak > R/C Helicopter Support > Scale Helicopters > Heads and Rotor Blades


Heads and Rotor Blades Heads and Rotor Blades Discussion


Reply
 
LinkBack Thread Tools Display Modes
Old 10-21-2016, 08:44 AM   #1 (permalink)
Registered Users
 

Join Date: Nov 2007
Default Blade length to blade count ratio for multi-blade heads?

Hi guys,

I have a Logo 500 in a Fun-Key A109 fuselage. It started with 2 blades at 620mm running ~1800rpm. I put a 4-blade head on it, but figured that 4 of the 620mm blades would probably be too much. I currently have 4 550mm blades that seem to be ok, but that was a random selection based on availability. I think 570's will look better, but don't feel like spending $100 just to see.

Basically, is anyone aware of a formula on adding blades vs. reducing blade length?

For example:
2 blades = 100% of manufacturer's recommended length
3 = 95%
4 = 90%
5 = 85%

How are all you multi-blade guys figuring this out?
gfyss is offline        Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
Old 10-21-2016, 09:26 AM   #2 (permalink)
Registered Users
 

Join Date: Nov 2013
Location: Aberdeen, UK
Default

Allowing for the fact that efficiency is proportional to rotor diameter squared I get:

2 = 100%
3 = 90%
4 = 84%
5 = 80%

The higher blade counts should produce the same lift at the same RPM but will require more power (i.e. they are less efficient).
__________________
Gob Kraken |Gob 700 BT 'T' | Gob 770 Comp | SoXos Strike 7 | Henseleit TDR, TDSF & TDR2 | Kasama Dune | OMP M1&M2 | UK stockist for OMPHobby M1/M2 ScotiaRC.co.uk
Smoggie is online now        Reply With Quote Quick reply to this message
Old 10-21-2016, 10:47 AM   #3 (permalink)
Registered Users
 
Posts: 20,239
 

Join Date: Jan 2006
Default

I about that too.

The length of the blades on the Three-Bladed set I am using on my Chronos is 690mm, the same as the Two-Bladed set.

I put a larger motor (800 size O.S.) and ESC (200 Amp HobbyWing) in it to accommodate the additional load of the third blade.

So far, it is unbogable (there's a word spell check can't deal with).



I do get less flight time on the same size batteries as before (3.5 minutes vs. 5 minutes).
__________________
KBDD-Team Captain, JR DFA Team Pilot. Forza 450, Forza 600N, Forza 700,
Compass 6HV-U, Warp, 7HV,Knight Pro,Knight 3D, Atom, Odin II, 6HV, 3D Plus, Knight 50, Chronos, Velos, Steam 550 and 600, OMP M2 (and anything else I can get my hands on...).
Ah Clem is offline        Reply With Quote Quick reply to this message
Old 10-21-2016, 12:50 PM   #4 (permalink)
Registered Users
Thread Starter Thread Starter
 

Join Date: Nov 2007
Default

By that logic, the 2x620mm blades equates to 4x520mm blades? Basically I should be happy with the 4x550 blades (motor & ESC being equal across all configurations) and fly it like a real scale ship.
gfyss is offline        Reply With Quote Quick reply to this message
Old 10-21-2016, 02:55 PM   #5 (permalink)
Registered Users
 

Join Date: Nov 2013
Location: Aberdeen, UK
Default

Yes, alternatively you may be able to gear it down for lower headspeed and keep the same blade size.
__________________
Gob Kraken |Gob 700 BT 'T' | Gob 770 Comp | SoXos Strike 7 | Henseleit TDR, TDSF & TDR2 | Kasama Dune | OMP M1&M2 | UK stockist for OMPHobby M1/M2 ScotiaRC.co.uk
Smoggie is online now        Reply With Quote Quick reply to this message
Old 10-21-2016, 03:22 PM   #6 (permalink)
Registered Users
 
Posts: 20,239
 

Join Date: Jan 2006
Default

"Yes, alternatively you may be able to gear it down for lower headspeed and keep the same blade size."

And/or use a lower KV motor.
__________________
KBDD-Team Captain, JR DFA Team Pilot. Forza 450, Forza 600N, Forza 700,
Compass 6HV-U, Warp, 7HV,Knight Pro,Knight 3D, Atom, Odin II, 6HV, 3D Plus, Knight 50, Chronos, Velos, Steam 550 and 600, OMP M2 (and anything else I can get my hands on...).
Ah Clem is offline        Reply With Quote Quick reply to this message
Old 10-21-2016, 10:10 PM   #7 (permalink)
Registered Users
Thread Starter Thread Starter
 

Join Date: Nov 2007
Default

I'm currently at a 12.75 gear ratio (153/12) with the smallest pinion available. The motor is a Savox rated for 1200kv. The governor is now set down to 1650. That puts the throttle around 79%. I have a Hacker 1100kv motor waiting in the wings, which would bring the throttle up to 86% for the same rpm.

Obviously this is only going to do scale aerobatics. Is it worth it to swap motors, or just leave the 1200kv installed?
gfyss is offline        Reply With Quote Quick reply to this message
Old 10-22-2016, 03:24 AM   #8 (permalink)
Registered Users
 
Posts: 4,228
 

Join Date: Apr 2008
Default

I am not sure why you would reduce blade length at all. Same blades slower.

What is the scaled length from a full size A109 ?

IMO a 600mm bladed 4 blade heli should run around 1300-1350rpm for gentle scale-like flying. This may not be enough for "scale aerobatics" (whatever that is ) To my knowledge I have never heard of A109 helis doing any aerobatics, so technically there is no such thing as scale aerobatics for that model (that I am aware of). If it was a 4 blade MD500 or BO-105 then scale aerobatics would equate to light sport flying flying (gentle loops & rolls).

Depending on your ESC, 79% may be slow enough to generate heat, but if it is a active freewheeling ESC it is probably OK.

For the record I run;

Seahawk 600 - 4x 600mm at 1350rpm
EC-145 - 4x 820mm at 1050rpm

Both run around 55W/lb of weight, so only marginally more power-hungry than a 2 blade.

Colin
__________________
Vario Long Ranger 700e
Seahawk 600
UH-1N 500
Baumann EC-145 800+ (coming soon )
Andy01 is offline        Reply With Quote Quick reply to this message
Old 10-22-2016, 10:41 AM   #9 (permalink)
Registered Users
Thread Starter Thread Starter
 

Join Date: Nov 2007
Default

The ESC is a YGE90LV that supports active freewheeling, which is enabled. If I do end up switching motors, it sounds like a 900-1000kv one would make more sense for the 1500-1600rpm range. The only 910kv motor I see is the Gaui GM-601. There are a number of 890kv motors though. I'm running 6S batteries. Thoughts?

I had to reduce blade length to deal with tail authority issues. 2 620's were too much for the stock tail blades (85mm) and the longest I can fit without hitting the horizontal stabilizer is 95mm, which were able to hold the tail fairly well at 1800rpm.

Even with shorter main blades, I tried reducing the rpms but ran into tail authority problems below 1400rpm. I haven't found any way to speed up the tail on a Logo, or an "easy" way to get a 4-blade tail. I'm currently running 1600rpm because the tail holds very well and I'm breaking in a new tail assembly. I'll re-try 1500rpm once I have some more flights on the bird.

I define scale aerobatics as the stall turns, high bank turns, and other maneuvers you don't do with passengers on-board the real thing. I'm not going to loop it.

The fuselage is listed as semi-scale. Here's a link to the size info:
http://www.centuryheli.com/products/...?currentid=181

I'd love to put 4 620's on it and run a sub 1300 head speed, but the current 2-bladed tail definitely won' t hold on that setup. I have a Vario Benzin going into a Gaupner Long Ranger III fuselage this winter that flies fine in the 1000-1200rpm range. I'll probably have to wait for that build to get to that range of lower rpms.
gfyss is offline        Reply With Quote Quick reply to this message
Old 10-23-2016, 03:59 AM   #10 (permalink)
Registered Users
 
Posts: 4,228
 

Join Date: Apr 2008
Default

The tail authority (or lack of) seems to be a common complaint with the A109 models because the stab limits blade length. On most scale helis, it is usually a case of fitting longer, wider, asymmetrical or sometimes more-off tail blades if the mains to tail ratio cannot be sped up - the easiest is usually to go longer, but that option is not available to you - perhaps the other 2 before trying a multi-blade tail.

Colin
__________________
Vario Long Ranger 700e
Seahawk 600
UH-1N 500
Baumann EC-145 800+ (coming soon )
Andy01 is offline        Reply With Quote Quick reply to this message
Old 10-23-2016, 09:55 AM   #11 (permalink)
Registered Users
Thread Starter Thread Starter
 

Join Date: Nov 2007
Default

semi-symmetrical tail blades, I hadn't thought of those . . . It looks like Spinblades makes a pair 95mm long. That will just clear the horizontal stab, but extends a bit below the vertical stab. I can probably attach something to the bottom of the v-stab to keep the blades out of the ground. Looks like I have a new minor project, and a bit of a wait until those blades are back in stock.

If that solves the tail authority issue and gets me down to the 12-1300rpm range and/or lets me use the 620 main blades, I'll consider changing the motor/pinion to match.

Honey! . . . I need to order some more parts!
gfyss is offline        Reply With Quote Quick reply to this message
Old 10-24-2016, 03:32 AM   #12 (permalink)
Registered Users
 
Posts: 4,228
 

Join Date: Apr 2008
Default

Just make sure you get asymmetrical blades that are the correct rotation. I think Spin only has one type (which might be OK, but HeliTec has different options I think (you can select the setup based on diagrams).

Both Spin & Helitec appear to be 30mm chord although the Helitec blades are a bit squarer, so they might have slightly more power ?

http://derblattschmied.com/epages/5b...oducts/HD-95-W

Colin
__________________
Vario Long Ranger 700e
Seahawk 600
UH-1N 500
Baumann EC-145 800+ (coming soon )
Andy01 is offline        Reply With Quote Quick reply to this message
Old 10-24-2016, 08:09 PM   #13 (permalink)
Registered Users
Thread Starter Thread Starter
 

Join Date: Nov 2007
Default

I haven't had to read that much German in a while! Menus are a lot more fun to read. I finally settled on a pair of Spin Blades, and found a set in stock at Fast Lad in the UK. They are out of stock just about everywhere else. With luck they may arrive before Thanksgiving!

Thanks for the suggestion!
gfyss is offline        Reply With Quote Quick reply to this message
Old 11-14-2016, 11:36 AM   #14 (permalink)
Registered Users
Thread Starter Thread Starter
 

Join Date: Nov 2007
Default

Wow, what a difference! The semi-symmetrical tail blades hold so much better. With 4 of the 620mm blades it held a solid tail at 1170 rpm with a barely noticeable wiggle at the start of a climb out. I'll probably set it to 1250 while I get comfortable with the new setup.

Thanks again!
gfyss is offline        Reply With Quote Quick reply to this message
Old 11-16-2016, 02:41 AM   #15 (permalink)
Registered Users
 
Posts: 4,228
 

Join Date: Apr 2008
Default

Great news. Glad it worked.

Colin
__________________
Vario Long Ranger 700e
Seahawk 600
UH-1N 500
Baumann EC-145 800+ (coming soon )
Andy01 is offline        Reply With Quote Quick reply to this message
Reply

Tags
multi blade, scale




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