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#1 Windbreaker

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Posted 21 March 2012 - 09:55 AM

I just saw this on another forum.

http://www.foxtechfp...ller-c-112.html

The Foxtech rep mentioned they'll be making 14" and 15" props, too. No specifics yet on the pitch or design.

#2 astronutski

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Posted 21 March 2012 - 12:39 PM

SSCCCHHHWING!!!

What is the impact rating on those puppies? I'll bet I could break them with my ironwood trees.

Currently flying: QAV500 Quadcopter, OpenPilot Revolution, 4S setup with 10x4.5 props

 

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#3 jbkappirossi

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Posted 21 March 2012 - 01:02 PM

nice.. but you still need 2 for a quad making it stil 80,- :wacko: .
And one other thing i see is that those ceaper CF props are replica's of normal Slowfly props.
Why not the same shape as the ones from microdrones or flyduino for extended efficientcy.

Isn't ther a way to rapid prototype some kick as props?

#4 John888

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Posted 21 March 2012 - 04:38 PM

nice.. but you still need 2 for a quad making it stil 80,- :wacko: .
And one other thing i see is that those ceaper CF props are replica's of normal Slowfly props.
Why not the same shape as the ones from microdrones or flyduino for extended efficientcy.

Isn't ther a way to rapid prototype some kick as props?


Maybe you need to get some low KV motors so we can try and hit the 45 min mark <_< ?

I tried shaving half the wood off this: http://www.hobbyking...?idProduct=9360 to get the weight and momentum down.

My craftmanship skills are nowhere near yours though and I ruined the amount of lift it gives.

PS: if you use your tricopter, don't need CW props <_< .
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#5 Windbreaker

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Posted 21 March 2012 - 07:54 PM

I'm guessing there's a lot of hand work that goes into making these things, thus the higher cost. Other props can be injection molded for a lot less.

This company is also making carbon fiber-reinforced nylon props that cost less.

Interesting that they say the blades are sharp. If they're referring to the leading edge, I thought the leading edge of props were supposed to be slightly rounded with the trailing edges sharp.

Someone told me the if the tail blades of a helicopter are too sharp they tend to increase vibration levels.

#6 SeismicCWave

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Posted 22 March 2012 - 03:34 AM

I just saw this on another forum.

http://www.foxtechfp...ller-c-112.html

The Foxtech rep mentioned they'll be making 14" and 15" props, too. No specifics yet on the pitch or design.


I am going to get some to play.

#7 jbkappirossi

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Posted 22 March 2012 - 06:23 AM

Maybe you need to get some low KV motors so we can try and hit the 45 min mark <_< ?

I tried shaving half the wood off this: http://www.hobbyking...?idProduct=9360 to get the weight and momentum down.

My craftmanship skills are nowhere near yours though and I ruined the amount of lift it gives.

PS: if you use your tricopter, don't need CW props <_< .


haha, yeah i know. You can go ahead. I'm first building a frame for my dad.
Maybe after that i'll make a mini hexaand beat youre time.

Thanks, but i dont think it has that much to do with building skils.
if i had the money 1hour or more should be any problem.
Just buy the bigest, strongest motors and basicly make a frame thats no more than a battery carrier.

Nope, i not using the Tri, its to heavy, more motors means more maximum power.
And you can create a higher weight to trust ratio.

Well, i was thinking a lot lately of making a handmade CF prop.
I think it can be don with the limitation of highend machines.
I just need a good design. I thought i have seen a program some where, a few weaks back, that could basicly output a 3d model based on the input you give.
I thought it was a dark brown looking ap and i think it was german. can't fing it, yet.
But it puts out this type of prop.
Posted Image

edit;

found it :D
http://www.mh-aeroto...s/jp_applet.htm

Edited by jbkappirossi, 22 March 2012 - 06:35 AM.


#8 jes1111

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Posted 22 March 2012 - 01:20 PM

The problem I've found with all the prop design software is that they are aimed at fixed wing applications, i.e. there is always a "forward airspeed" parameter against which the prop design is optimised. You can't enter "zero" (i.e. hover) so you put in the lowest forward airspeed it will accept and it gives you a ridiculously exaggerated root chord. Optimising for hover seems to be beyond the scope of such apps. We don't see these exaggerated profiles on helicopter blades (although I agree that variable pitch changes the whole game).

I've asked many times on many forums for an aeronautical engineer's opinion/advice but have never had any useful responses.
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#9 Windbreaker

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Posted 22 March 2012 - 06:34 PM

In due time prop manufacturers are going to begin developing props for multi-rotor use.

There's a good business incentive to do that: Every new customer means selling at least three or four props! :-)

And the first ones to provide an optimized design that helps extend flight times are sure to build a good customer base. If the props are reasonably priced I'd sure be interested in getting two sets (one as a spare).

#10 SeismicCWave

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Posted 22 March 2012 - 08:09 PM

The problem I've found with all the prop design software is that they are aimed at fixed wing applications, i.e. there is always a "forward airspeed" parameter against which the prop design is optimised. You can't enter "zero" (i.e. hover) so you put in the lowest forward airspeed it will accept and it gives you a ridiculously exaggerated root chord. Optimising for hover seems to be beyond the scope of such apps. We don't see these exaggerated profiles on helicopter blades (although I agree that variable pitch changes the whole game).

I've asked many times on many forums for an aeronautical engineer's opinion/advice but have never had any useful responses.


From the perspective of the propeller blade it is always seeing an airspeed. The difference is the angle of attack of the air flow in relations to the air foil. So we are not talking about some magical formula in designing airfoil for multi rotor.

As far as a single main rotor helicopter is concern it is not so much the collective pitch that dictate the shape of the airfoil. It has to do with the compromise that a lot of users flip their helicopter upside. So the airfoils are mostly designed for aerobatics and structure. The original helicopter blades are oblong shape because they were made out of wood. Composite made it easier to create different shape but they are still aiming at the aerobatic pilots. Besides our models are so over powered that there is no incentive to design any efficiency in helicopter rotors.

Even the multi rotor are so over powered that efficiency is really not something in the minds of the designer.

So far the slow flyer props are really not a bad design. I just wish they can make them better so the hubs are not so far off. It is also amazing that some props are just made from the TLAR method. Then again we do want cheap props.

#11 jes1111

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Posted 22 March 2012 - 09:33 PM

:D I had to look up TLAR! I agree - too much of that attitude about.

You've highlighted an important point. The word "pitch" should really only be applied to fixed-wing propellers - it being the measure of how far forwards the aircraft will move for each revolution of the blade. Obviously, at hover our aircraft isn't moving at all! IMO "Angle of attack" is a much better description. More AoA equals more "bite" but more "drag". Too much AoA at low forward airspeed and your blade will literally stall, just like an aircraft's wings if the nose is too high and the airspeed too low.

We don't need high AoA for a multirotor, for sure. Those 18x16 carbon fibre props you see in shops are strictly for high speed pylon racers and the like. Low pitch gives less drag and therefore faster acceleration/deceleration.

I've thought of trying symmetrical (3D) heli blades cut down - CW/CCW just by turning it over - but, as you say, very poor efficiency.
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#12 SeismicCWave

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Posted 22 March 2012 - 10:05 PM

>> More AoA equals more "bite" but more "drag".<<

Exactly, each airfoil shape as a lift/drag coefficient curve at different angle of attack.

>>Too much AoA at low forward airspeed and your blade will literally stall, just like an aircraft's wings if the nose is too high and the airspeed too low.<<

Right, the stall characteristics will depend on the shape of the foil. A thin semi-symmetrical foil have a narrow margin of angle of attack because it stall but more lift and less drag when operating within the narrow angle of attack. A fat symmetrical foil is not a efficient but has a wider range of angle of attack it can operate and the stall characteristic is more gentle. That's why the aerobatic planes use the fat symmetrical foil as does our helicopter main rotor blades.

>>We don't need high AoA for a multirotor, for sure.<<

That's why the slow flyer type of propellers are so ideal. We also get into the smaller Reynolds number area in our multi rotor. That's why sometimes a flat piece of carbon with some camber can work so well.

>>Those 18x16 carbon fibre props you see in shops are strictly for high speed pylon racers and the like.<<

We call those "square" props. That's when pitch and diameter are the same number.

>>Low pitch gives less drag and therefore faster acceleration/deceleration.<<

Low pitch and light weight props will give us better stability in multi rotor for sure.

>>I've thought of trying symmetrical (3D) heli blades cut down - CW/CCW just by turning it over - but, as you say, very poor efficiency.<<

Some one has tried the tail rotor blades from helicopters. I think it will work but I am not sure about the efficiency.