Diabolo maiden flight today - Page 2 - RCCanada - Canada Radio Controlled Hobby Forum
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Old 12-28-2012, 03:21 PM   #11
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Re: Diabolo maiden flight today

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I'm not much into scale to be truthful, that said many of the same principals apply. You may want / need a slightly higher headspeed to generate the additional lift required to compensate for the added weight.
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Old 12-28-2012, 05:28 PM   #12
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Re: Diabolo maiden flight today

There are four things that are related to the development of lift by a rotor blade;

1 - blade airfoil (including tip design) - can NOT be changed in flight
2 - length - can NOT be changed in flight
3 - rotor speed - can be changed in flight
4 - angle of attack (pitch) - can be changed in flight

1 & 2 infer the same blade, so without changing blade, you can increase or decrease lift by either increasing or decreasing rotor speed (you see that in fixed pitched helis and multi-rotors) or changing pitch (angle of attack).

We all know that when our heli is set for a constant rotor speed, we climb or descend by increasing or decreasing the collective.

The difference you will find, for setting it to hover at a lower head speed, will be that it will require more pitch, and at a higher head speed, it will require less pitch. So if you would set your governor for a lower head speed, then you would have to increase the pitch at all the points on your pitch curve.

How much power you have on tap from your power system will determione the max collective pitch you can pull at your chosen rotor speed. When set up for a high rotor speed, you may not loose rotor speed when fully opened, and pulling 11 degrees in a climb, but it may do so if you try to pull 12 degrees in that same climb at that same rotor speed.

On the other hand, at a lower rotor speed, you may increase the top end pitch to 14 and you may find that your power system may well be able to pull that much pitch without loosing rotor speed..

You will also find that at the same rotor speed, you would need more pitch with shorter blades to hover the same weight, or less pitch with longer blades. If you do not change pitch settings with shorter blades, then you will need higher head speeds and with longer blades, lower head speeds.

You will also find that some blades, of the same length, are more efficient at developing lift as they may take 10% or 15% less power to hover and maneuver your heli at the same rotor speeds.

As you can see, the science of rotor blade lift is a truly interesting one.
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Last edited by Phil Noel; 12-28-2012 at 05:38 PM.
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Old 12-28-2012, 05:32 PM   #13
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Re: Diabolo maiden flight today

Thanks Phil looks like I have some research to do.
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Old 12-29-2012, 04:07 AM   #14
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Re: Diabolo maiden flight today

Originally Posted by RCcanuck View Post
Sure head speed plays a big role since the lower it is the less lift you generate. So sure there is a spot where you simply do not get enough lift to take off.
However even at the top end there is a spot where increasing head speed further would not give you much improvements any longer because you simply generate dirty air in the waive of the spinning blades.

A guy mentioned that he did some testing to find out that on a 90 size heli head speed above 1900 will only give you minor improvements but takes way more juice off the batteries. You simply loose efficiency.
In addition at speed cups where they do run these machines at about 2200 - 2300 rpm they tried even more and learned that only very minor improvements while drawing lots of power. Turned out better for the winner of the speed cup at IRCHA to get a aerodynamic fuselage and ... improved way more than higher head speed.

Every heli has a sweet spot and with the proper blades on the Diabolo its somewhere around 1700 - 1800 rpm while going higher is cool for noise and speed passes. 3d flying is awesome at that head speed. Ingolf (owner of the Diabolo) tried different brands of blades during the last couple of days. So far the ZigSaw 700 mm proven best for 3d flying and SAB doing good on speed passes. It is fun playing with that stuff. but as I like to point out - increase of head speed by itself will not make the heli more efficient. Actually at a certain level its the opposite. In addition its a combination of setup, blades and head speed. FBL systems help a lot because you can do different setups. Thats where like v-bar and ikon FBL systems are cool because you can run different setups while flipping the switch.

Agree to most of this, but 1900 is hardly enough for fast 3D transitions on a 90 - (700) class. With Nitro sure you are limited to that, but on a 700 Electric heli, 2050-2100 is a HUGE difference over 1900 when it comes to piro manuevers and transitions, even on a lighter heli in this size. You CAN do everything at 1900 but it is slow and not near as reactive. It is surely about each pilots needs.
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