Longer Blades or Wider Blades

[CompleteDestruction]

What one will give you more "bite" and bog less?

For example 600mm blades...

Going to 620mm x 55mm
or
600mm x 60mm

The wide cords have much more surface area, but because of the length I would assume that they would loose speed faster than the longer blades. But i would also think that the wide cord would recover faster.

Does that sound right?

I have no science to back this up..

[Snakebite]

Instinctively, I would say that thinner chords would bog less because they're trying to bite less air...

[jared_of_atlanta]

You may not notice that kind of difference unless you are really hammering it or carefully monitoring efficiency.

[Colin Broughton]

In my experience it really depends on the brand of blade the most. I've flown some blades that are mushy and slow off center where another brand of same length and cord would be extremely quick off center and snappy. I usually tend to try and use blades that are popular amongst pilots of a similar flying style. This cuts down on spending a ton on trying them all

[Wrencher62]

The question you're asking has no simple answer.
In the fixed wing concept a long tapered wing with less chord results in less overall drag giving you a much improved glide ratio.
A shorter wing with more chord will give the same lift at the cost of increased drag.

This also means more power is needed to achieve the same result.

Although our rotor blades are governed by the same aerodynamic principles it becomes much more complicated when you have to account for disc loading and efficiency. Add to that the complexity of the various tapers that different blade manufacturers use in their designs and it becomes an even more difficult equation.

If we were comparing airfoils of straight rectangular planform then the longer blade with less chord would produce more lift with less power required which would then would give a "floatier" feel.

The chord isn't constant with taper designs and is usually measured at it's widest point. Too much chord near the blade root will produce good lift in hover but will cause a nose down tendancy in fast forward flight. The designers know this so they juggle the trade off between lift and efficiency.

At best I'd have to think a longer blade with less chord would give more lift at less power while a shorter blade with more chord would need more power which would make it more likely to bog.

I'm digging really deep into what I learned about rotor effiency in A&P school and I may not be completely right but it's the best I could do to try to answer your question.

[extrapilot]

CD

I think you are asking a couple of different questions. Recovery has a lot to do with the mass distribution in the blades, and longer blades with mass near the tips tend to have more energy (angular momentum). So, you have to define the CG and the blade mass to figure that out.

But the bog happens because of what happens at the rotor (drag related to lift and just skin friction). Larger, narrower blades tend to be more efficient. In your example, at 2000RPM and 8deg pitch at a pitch pump, the longer rotor produces about 4% more thrust, at a cost of about 4% more power. But if you correct for thrust (reduce the pitch on the loner blades), for the same thrust, the longer blades eat about 1-2% less power.

All this can change once you get into high speed flight, high Z axis (collective punch) speed, etc. The general rule is that if you want efficiency in normal flight, you want a larger rotor with minimal chord. If you want maneuverability, you want more chord (or more blades). Bogging is all related to how much power your are pulling, and blade mass/CG, vs your powerplant capability. No simple rules here- just general guidance.

Regards

[CompleteDestruction]

Thank you!

This helps alot. I think I am interested in trying wider at the moment.

They say autos are insane with a nice wide cord blade.. Im not too concerned with efficiency and understand that the energy will probably wear off a little quicker with the wider blades.

[learnedthehardway]

From the little bit of testing I've done wider/heavier blades are smooth and stable and narrow/liter blades are more agile.

I would say wide for sport flying or smooth 3d and narrow for more of a smack style.

Although with one being short and wide and the others narrow but longer it will probably equal out for the most part.

[Relisys190]

My largest helicopter ( goblin 630) has been known to be on the heavy side for its blade size. I tried some longer and wider blades at 660mm and 64mm wide

For my flying style is was just what I needed. I did reduce my overall positive and neg pitch and lowered headspeed a wee bit also to use approx the same mah per flight.

Good luck with your tuning.
Markus

[K2Freak]

Too wide a chord, and you can find your bird pitch sensitive at hover. Had that once with Align 800 blades, but the 780mm took it all away. Quite a bit narrower...