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Slower headspeed with more pitch or faster headspeed with less pitch???

Justin Stuart

rrMaster

Plano, Texas

There are lot of difference choices these days for motor kV. Is it better to run a slower headspeed and more pitch with a lower kV motor, or a higher headspeed and less pitch with a higher kV motor? I really like the "pop", but I think at too high a headspeed you're just wasting energy beating the air.

Any comments?

Avant RC
Scorpion Power Systems
Thunder Power RC
Kontronik Drives

03-22-2011 Over year old.
Wingman77

rrProfessor

Pulaski Tennessee

I personally like lower head speeds, a lot less wasted energy.

03-22-2011 Over year old.
HOMEPAGE  
Justin Stuart

rrMaster

Plano, Texas

It seems to me that you can vary headspeed and pitch to give the exact same performance. Like for example, a 2500rpm headspeed with 11 degrees of pitch give essentialy the same "pop" as 2000rpm headspeed with 14 degrees of pitch.

Avant RC
Scorpion Power Systems
Thunder Power RC
Kontronik Drives

03-22-2011 Over year old.
helicraze

Elite Veteran

Victoria - Australia

From the TDR manual:
Thanks to light models with flybarless main rotors it is not necessary any more to race with a rotor head speed exceeding the limit of 2000. The properties when flying straight on are even fantastic at 1300 rpm at the main rotor. Every flybar head helicopter would pitch up hopelessly at these manoeuvres.
Most of the 3D figures can be flown because of a lower rotor disc load also using a more moderate head speed. So more than 1800 rpm at the main rotor are unnecessary when flying this helicopter.
The logger data show that the efficiency of the blades decreases rapidly with increasing head speed, so that most of the energy is wasted.
For the same flight condition „Hovering at one position“ 570W is required at 1300 rpm at the rotor and at 1850 rpm you already need 1000W. At more than 2100 rpm 1500W are required, i. e. nearly the triple amount, although you do nothing more than hovering.
This result shows clearly that the flight time can be increased considerably, if the rotor does not constantly rotate at full speed. All these results have contributed to and influenced the choice of the speed reduction and the recommended drive of the Rigid.

03-22-2011 Over year old.
hornet dave

Key Veteran

Cedar Rapids, IA USA

This should be juicy. Whos got the popcorn?

The tradeoff is how much you prefer flight time versus noise. Some like a lot of noise, some like the attention that noise brings, etc. Others like quiet and or longer flight times.

I myself like the lowest headspeed that is still fun for me. 1850ish on my FB 6hv suits me well. Much lower and piros at speed start to suffer and pitch pumps make the tail bark.

I got a fever! The only prescription is MORE 6HV

03-22-2011 Over year old.
oldfart

Elite Veteran

Vancouver, Canada

Without writing a book to explain it all (here are books that do already), the main reason for high head speed is to increase the cyclic rate in ANY helicopter.

cyclic pitch - a pitch change that occurs once per revolution (per cycle) of the rotor

The faster the rotor turns, the more cycles of cyclic pitch, the faster the response rate.

Phil Noel

03-22-2011 Over year old.
MrMel

rrProfessor

Lidingo, Sweden (GMT+1)

Each 100RPM costs quite a lot of flight time, don't remember exact formula but I think I calculated it to be 8-12% per 100 rpm if memory serves me correctly.

But high RPM has it's purpose for crowd pleaser, much more "fun", but for normal flying I rather fly with moderate RPM.

Then there is times where really low head speed serves you well, when you are doing training (you get more time to react) or for sample when I compete in F3N to do precision 3D, much easier with low head speed.

I actually (in my own opinion) think it's crazy those running 2300RPM on a 700mm heli, not only danger wise but there is no real point except getting the "pop", I rather take minutes more of flighttime per flight.
In comparsion I think 2250 on a 600 is "high"

With FBL there is no need for headspeed to get higher cyclic rate or stability.

Gone fishing..or hunting..or something
My site: http://heli.dacsa.net - VBar videos and more

03-22-2011 Over year old.
mustang67ford

Key Veteran

Central Pennsylvania

High headspeed=better chance at unwanted auto.

03-23-2011 Over year old.
Zaaaguy72

Elite Veteran

MN

I used to fly higher head-speeds but recently dropped the head-speeds down a few hundred RPM's and am loving it. My heli's still have tons of power but are very smooth and precise. Not to mention the longer flight times.

Team HeliProz

03-23-2011 Over year old.
HOMEPAGE  
Supercoolheli

Key Veteran

Stillwater, Oklahoma

i was flying my ENV at 2050 RPM but for a little longer flights i think i'll start at 1900 when i instal my Jive 120 . I don't have a logger but i'm sure that'll be nice and easy on it. i bet it will still be plenty powerful at lower rpm, i just might need to raise pitch a bit. IMO, lower headspeed is a good idea for practicing and just normal flying. From now on i probably won't raise headspeed unless i'm competing, or at a funfly or something

Eric Olson:
Team SAB USA
Team Pulse Ultra

03-23-2011 Over year old.
permagrin2010

Senior Heliman

Surrey

Without writing a book to explain it all (here are books that do already), the main reason for high head speed is to increase the cyclic rate in ANY helicopter.

cyclic pitch - a pitch change that occurs once per revolution (per cycle) of the rotor

The faster the rotor turns, the more cycles of cyclic pitch, the faster the response rate.
I agree 100%. And I would bet, that for 95% of the flyers out there, they do not need anywhere near the cyclic response that the rotor speeds they turn deliver. Specially when you see how much expo they tune into their cyclic.

So for longer flights, and longer component life, most would be much better served by setting for lower rotor speeds.

03-23-2011 Over year old.
SamurAchzar

Heliman

Israel

You don't want to go too low with the headspeed or you will lose tail authority. Basically as you go lower headspeed and higher pitch, you are generating a lot more work for the tail.

Now if you reduce headspeed by going with a lower gearing, you also benefit by increasing the motor torque, which means less tendency to bog (that has a positive effect on the tail and most everything else if you're talking FBL. Control systems like constant RPM).

On my 700N, I started flying in idle1 instead of idle2, that's about 1850rpm vs 1950rpm, and I like it much better - calmer and I stress the engine less. But nitros are of course different, you have the thing with the engine powerband, you'd want the RPM high enough for the governer to place the engine in it's peak HP figure most of the time. That's not an issue with electrics.

On my 12S Furion 6, I just swapped the pinion to 12 (with 470Kv Xera 4030 motor) so that I'll get about 2100-2200 rpm on the head at 80% throttle curve. It was around 2400rpm with the 13 pinion.

I'd say around 1800-1900 rpm for 700mm and 2100 rpm for a 600mm is what I personally like.

03-23-2011 Over year old.
hornet dave

Key Veteran

Cedar Rapids, IA USA

Yep, lower headspeeds need longer tail blades. But its the loss of tail rotor pitchspeed that finally gets you, piros during fff start to suffer.

I got a fever! The only prescription is MORE 6HV

03-23-2011 Over year old.
Rogman88

Elite Veteran

West Monroe, LA

Basically as you go lower headspeed and higher pitch, you are generating a lot more work for the tail.
Couldn't have said it better myself. Higher head speed with low pitch sends more thrust vertical through the main shaft. Higher pitch with lower head speed sends more rotational force through the frame thus tougher on the tail rotor blades to compensate. That combined with lower tail rotor speeds equals poor 3D performance. Now if you like to hover and FFF, may not be an issue. For me, it sucks...

High Voltage just works better

03-23-2011 Over year old.
HOMEPAGE  
Jeff polisena

Elite Veteran

westpalmbeachflorida usa

On all my setups I run 1910 headspeed max , this seems to be where I feel I have effeciency and pop .

I stole it ,flew it and gave it back ;)

03-23-2011 Over year old.
Supercoolheli

Key Veteran

Stillwater, Oklahoma

might i point out that Nick was flying 1890 on his Rave at the 3DM, and he took 1st place. And i'm not even going to begin to argue that he's not a master of piroetting manuvers, so it's obvious that each setup has it's pros and cons based on the pilot

Eric Olson:
Team SAB USA
Team Pulse Ultra

03-23-2011 Over year old.
sharam

Elite Veteran

Northern California - Fly at Morgan Hill Field

For my style of flying, I am a fan of lower headspeed. It may not provide the pop but it sure puts less stress on the system. It also forces you to use more finesse in your maneuvers rather than relying on sheer power to get you out of a fix.

This is just my personal preference - others have different and valid views for their style of flying.

Verba volant, scripta manet

03-23-2011 Over year old.
oldfart

Elite Veteran

Vancouver, Canada

Relating tail rotor to head speeds, yes, as a general rule, the lower the mainrotor speed the more pitch the mainblades need to generate the same lift so the more torque compensation they will need from the slower turning tail rotor.

But that will be at a relatively very low rotor speed compared to what we can comfortably fly at. And as some had mentioned, using longer tail blades is a way to compensate. You can also change the tail gear ratio, moving it upwards so that it turns faster relative to the mainrotor.

This also relates directly to the disc loading of your heli. Generally, the smaller the heli, the higher the disc loading, so the higher will be the rotor speed required to keep everything working properly.

As an example, s big heavy scale heli with 800mm blades will happily fly around at a rotor speed as low as 900.

You can even do some reasonable sports aerobatics with a 550 sized heli using 550mm blades with a 1400 head speed, but it would not even lift off at 900.

On the other hand, a small electric 450 with 325mm blades will still be relatively maneuverable with a 2000 rotor speed, but would be hard pressed to lift off at a 1400 rotor speed.

All in all, we must be careful of over generalizing here.

Most (other then the hard core 3Ders) will find that for flying some fairly good 3D aerobatics at a low rotor speed of 1900 would be fine on a 550mm blades heli, 1800 on those using 600mm blades and 1700 on 700mm blades. Of course there would not be the rapid pop type of cyclic or collective at these speeds as you would have at higher speeds, but the energy required from your power systems would be substantially reduced...and you would probably also find that you are a lot more relaxed during the flight.

Phil Noel

03-23-2011 Over year old.
Supercoolheli

Key Veteran

Stillwater, Oklahoma

Watch at YouTube

1890 headepeed for 1st place flight, and check out the power! Tail doesn't look like it's suffering to me

Sorry this is the recording with the fence and other things in the way but i think it gets the message across

Eric Olson:
Team SAB USA
Team Pulse Ultra

03-23-2011 Over year old.
BladeStrikes

Elite Veteran

Shelby TWP,Mi

Supercoolheli,
When he does the fast moving stuff,you'll hear the tail going "zing,zing,zing" and half way around (each full spin) you see it go a little faster (watch the video real good and turn the sound up) .That's called tail whipping.He's also a pro pilot and has awesome collective management which help's ALOT at keeping the tail from blowing out with a low headspeed.A pro pilot or one close to their level can make a GY 401 look good..

03-25-2011 Over year old.
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Slower headspeed with more pitch or faster headspeed with less pitch???

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