2 or 4 rotor? - RCCanada - Canada Radio Controlled Hobby Forum
RCCanada - Canada's Radio Control Hobby Forum
General RC Heli Discussion Discuss general topics on rotary wing aircraft, including construction, Servo's, Gryo's and Stabilizer discussions. Heli Pro Shop

Closed Thread
Thread Tools Display Modes
Old 04-14-2009, 07:14 PM   #1
RCC Apprentice
oni's Avatar
I am: mael i
Join Date: Mar 2009
Location: Toronto

Feedback: 1 / 100%
Posts: 95
Total Props: 0
2 or 4 rotor?

       Remove this ad - become a site supporter!
it would make sense to me that a 3 or 4 rotor head would provide more lift then a 2 rotor head but i figured id ask
i plan to run the Spartan RC AP2000i so i think it will provide the stability
anyway please let me know what you think

also an one stretch a jr voyager e if so what parts did you use?
thank you Mael
oni is offline   Quick reply to this message.

Sponsored Links - Subscribe to remove this ad.
Old 04-15-2009, 09:26 AM   #2
Level 3 Supporter
★ Site Supporter ★
Cougar429's Avatar
I am: Gary L
Join Date: Aug 2008
Location: Tecumseh, Ontario

Feedback: 72 / 100%
Posts: 5,255
Total Props: 30
Re: 2 or 4 rotor?

There is a lot of nice theory involved, but you will SHARE the lift, (carrying the weight) between any number of blades. Disc loading would be identical if the aircraft weight is the same, but the blade loading goes down.

Unfortunately, in our case that does not mean we also increase stability.

Our original 2 bladed designs use a Bell/Hiller setup with a flybar for two reasons: First is to reduce the load on the servos. You basically "Fly the Flybar", ie. your cyclic control inputs go there. The paddles out on the end of the flybar act as aerodynamic levers to increase your inputs up to the main rotor blades. This is an internal input.

Second, the flybar acts as a damper against short-duration inputs, such as wind gusts, coming from outside the heli. It will try and return the heli to whatever state it was in before that force acted on it.

Now, let's say you go with 3 or more main blades. Naturally, you cannot use a flybar for this type of rotor system, so you have not only removed the device that gives you that natural stability, but since the servos now have to control the pitch of the main blades directly, their loads have increased dramatically. In your case you would seriously need to look at the capability of the servos.

Sure, any spinning mass will have inertia and some form of natural resistance to change, but in this case that also means you have to add your own control inputs to counter excursions from your desired state.

p.s., here's the really fun part:

Due to the fact each blade does not carry so much of the weight its Angle of Attack can go down. Therefore the Induced Drag from producing lift decreases, partially offsetting the increase in profile drag from the extra blades.

However, this system is what is called a "Rigid Rotor" and other means to adapt for Lead/Lag and other forces have to be made. In our little ones this is done with the O-Ring dampers in the center holder. Simple when the one feathering shaft attaches both blades, but this can get interesting when you try and adapt that capability to multiple rotor designs.

In earlier designs there were hinges and oil-filled damper systems, (go look at a 50's era Sikorsky. There were more grease fittings than I can remember). Now, along with rubber isolators at the blade root, composite blades have the rigidity AND flexibility to compensate for those forces.

Hope I didn't get too complex. My mother told me there's be no more math when I got out of school!

Last edited by Cougar429; 04-15-2009 at 09:30 AM.
Cougar429 is offline   Quick reply to this message.
Closed Thread

Quick Reply

Register Now

In order to be able to post messages on the RCCanada - Canada Radio Controlled Hobby Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

Member names may only be composed of alpha-numeric characters. (A-Z and 0-9)

!!ATTENTION ADVERTISERS!! If you intend on advertising anything on this forum, whatsoever, you are required to first contact us here . Additionally, we do NOT allow BUSINESS NAMES unless you are an Authorized Vendor. If you own a business, and want to do sales on this site via posting or private message, you will need to follow the rules. Shops, Stores, Distributors, Group Buys without being authorized will see your account terminated.
User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:
Your Name
Your first name and last initial is required if you plan on using the forum.
Which city & province you live in. This is mandatory for classified listings.
Radio of choice?
Which radio is your current favorite to use?
Number of RC Vehicles?
How many boats, cars, planes do you own?


Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
vBulletin Message

Thread Tools
Display Modes

Forum Jump

All times are GMT -5. The time now is 11:58 PM.

vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2016 DragonByte Technologies Ltd.