4 or 5 blade head for ap?

[Sugarbaker]

so, I've seen the pros and cons of using the virtual flybar setups, but I haven't read much on whether there is a benefit to using multi-blade heads for stability and efficiency. (perhaps I haven't searched hard enough). I'm curious to know, if you can get it set up with the proper equipment, would a 4 or 5 blade head be more efficient than a 2 blade head (on a trex 600e)? I'm wondering if I could increase the effective payload and flight times with fewer modifications to my drive train... could I use the stock motor and 6s batteries to drive a multi-blade head? Or would the mass of more blades be detrimental even at a slower head speed? Curious to hear your thoughts. Hope everyone had a wonderful thanksgiving weekend!

Stephen

[j_kookboy]

so, I've seen the pros and cons of using the virtual flybar setups, but I haven't read much on whether there is a benefit to using multi-blade heads for stability and efficiency. (perhaps I haven't searched hard enough).

Yes/No. You will have more lift and more drag. You'll need a heavy powerplant to take the extra load.


I'm curious to know, if you can get it set up with the proper equipment, would a 4 or 5 blade head be more efficient than a 2 blade head (on a trex 600e)? I'm wondering if I could increase the effective payload and flight times with fewer modifications to my drive train... could I use the stock motor and 6s batteries to drive a multi-blade head?

UAVVision are the only guys I can think of that may still be using a 3-bladed head but that's running a massive turbine powerplant.

There's no way a stock Trex600 would be able to take the load of the extra weight/mass rotating while carrying a payload.

IMO it would be very dangerous. You would need to upgrade the head from top to bottom, and have I'm guessing at least a 10S-12S setup with a large motor/esc like the skycrane at the very least.

The reason to go with a 3-4 blade head is to put more power to what the heli is working against, air.

To get more lift, put more power into your system. That's why you see many people running a 10S powerplant Trex600 setup with AUW of around 11-12 lbs.

Try and successfully autorotate (intentional) an 11lb stock Trex600 AP ship. Let me know how you make out.

There's only so much power that can be put into a two bladed rotor head with any given diameter before you run into other problems. That's when you add more blades to absorb that power and transfer it to move the air for lift.

Jesse

[Sugarbaker]

thanks for the advice. With that being said, I may still look into a flybar-less set up, but just run the 2 blades... seems to me that this would be a more efficient use of the stock motor setup.

[Sugarbaker]

oh, and no thank you for autorotating the 11lb Trex... I'm not very good at autorotating my stock setup let alone adding weight to it.

[crewchief]

According to aerodynamic theory, the most efficient means of getting mechanical energy converted to airflow (and vice versa) is to have a minimum number of blades turning at the maximum speed (Betz's theorem, 1939). However, other factors come into play, which is why the leading-edge wind turbines have 3 blades instead of 2 (or 1 counterbalanced). This is due to vibration, tower wind shadow and other nasty things they discovered the hard way through experience.

On helicopters the two-bladed head is called a semi-rigid teetering rotor, and is subject to mast bumping and other kinds of instability when the head is unloaded. These problems have been addressed in the RC world, and are not a factor, because the materials can handle greater stresses on a small scale. On "real" helicopters, it requires a fully-articulated (3+ blade) rotor system to be able to perform zero-G and other maneuvers that would be disasterous in something like a Robinson.

Remember in WWII the Spitfires and Mustangs started going to 4- and 5-bladed props as the engines improved. This was because, as Jesse said, you can reach a point where you have a hard time transferring a massive amount of engine power (e.g. Merlin or turbine engine) into the airstream. Look at it like a step in the direction of a ducted fan.

Bottom line - can't beat a two-blade head with mechanical paddles for simplicity and efficiency.

[Sugarbaker]

I'm glad I'm not responsible for designing helicopters... too much to take into consideration. I'm sure you've made the subject seem more simple than it really is, but I appreciate your explanations.

[j_kookboy]

oh, and no thank you for autorotating the 11lb Trex... I'm not very good at autorotating my stock setup let alone adding weight to it.

Flaming hat on. :)

Do it. Auto your Trex loaded with dummy weight to simulate your AP gear.

Why ?

Because when (it's not 'if', it's a matter of when) you do have an unplanned/forced auto, you will be prepared and know what will happen.

If you load up your stock Trex and never even attempt a planned auto, I can tell you from experience on 5 different 10-13lb ships, that you will be in for a big surprise when it happens.

Especially if you have an unplanned auto with an audience (client/people) and flying outside of your normal flying field.

Jesse

[Sugarbaker]

I'll work my way up... maybe by new years (weather permitting) I'll be up to 11 pounds. (and hopefully my bird will still be in tact.)

I agree that I don't want it to be too much of a surprise when it happens unexpectedly.

[bullaculla]

I gotta practise mine too, I did one straight down from about 20 feet last week. I'm running 620s so I still had lots of energy. Most cases for us wont have much forward speed.

[RWC]

Sugerbaker check this out. http://www.deeteeenterprises.com/NS.DeeTee.Hughes.500E.php

RWC

[bullaculla]

If you read this page, there is a lot of custom work and headache involved.
http://www.deeteeenterprises.com/NS.DeeTee.Hughes.500E.5.Blade%20Head.php
Too much for AP work imo. 4 blade would be alot easier. Some of the high end turbine AP helis use a 3 and 4 blade head like the UAV vision helis http://uavvision.com/slides/T21%204BLADE.html