Windrunner

[Sparweb]

Check out this behemoth.

WindRunner | Radia

Delivering the largest, most efficient wind turbines directly to the wind farm.

radia.com

It's a "point design" with one clearly stated purpose: to transport wind turbine blades wherever needed.
Has about 7x the enclosed volume of an Antonov 124.
This one ambitious.

Won't it be cheaper to design WT blades to be assembled from 2 or 3 sections in the field?
The only problem this aircraft is meant to solve is delivering long (>100m) WT blades to remote sites.
If trucking is such a problem, then use the solution that's already in use for cranes: split-em in two.
I thought of this immediately as I looked at the marketing photo that shows such a crane in the background.

 

[rb1957]

? what has a $2 plastic toy got to do with this ? Who mocked this toy idea ? I suspect the people selling googles loved it !?

The idea of a huge plane to transport large turbine blades IMHO deserves mocking as it at best partially solves the problem it is addressing.
The obvious solution is transportation joints (with the hassles they bring with them) or dirigible airship.
Why are extra long blades the way to go ? Yes, I know about aerodynamic efficiency, but extra length brings extra cost (like designing a system to deliver the blades to the site). Why are all turbine 3 bladed ? I suspect someone did a design study and concluded that 3 is the right number, but it is right only within the parameters of the study.

 

[GregLocock]

"Why are all turbine 3 bladed ?" Worth googling to see a lot of bad physics and hand waving!

 

[Lou Scannon]

I read something about a compromise between disk solidity and harmonics with the tower (e.g. vs 4 blades).

 

[verymadmac]

Why are all turbine 3 bladed ? I suspect someone did a design study and concluded that 3 is the right number, but it is right only within the parameters of the study.

Last time I discussed this with a wind turbine manufactures Chief Engineer, the comment was that the biggest appeal of 3 blades is that they were visually more appealing than 2 blades (he was in the process of building the first article of a 2 bladed wind turbine program).

 

[rb1957]

wow ! nothing about blade efficiency or dynamic stability ... huh ! I've only seen 2 blades on very small turbines.

more blades would make an alternative to longer blades ... with some advantages and some disadvantages.

 

[verymadmac]

wow ! nothing about blade efficiency or dynamic stability ... huh ! I've only seen 2 blades on very small turbines.

more blades would make an alternative to longer blades ... with some advantages and some disadvantages.

It was a 33m diameter windturbine (timber laminate blades), the blades where more like a 2 bladed helicopter rotor than a normal propeller. They had a bit of a learning curve with the first unit when a gust / controller configuration issue cause the whole thing to be almost pulled off the top of the tower (I seem to recall it being described as a stopped with the blades horizontal and feathered).

 

[LittleInch]

The three blades thing is partly due to smoothing out the energy input. Wind increases as you get higher off the ground so the top half of the sweep generates something like 75% of the power compared to a full rotation. So two blades have a higher fluctuation in power compare to three. Four blades cost more in terms of blades and also the blade attachment on the hub. So three is better.

I think.

 

[rb1957]

and 4 better than 3 (at smoothing the energy input), or 6 ?? more blades would allow shorter blades and a shorter tower for some (small?) cost in aerodynamic efficiency.

 

[LittleInch]

More blades though is more cost and complexity for a limited additional power.

Like everything, it's s balance and three seems to be the sweet spot.

 

[verymadmac]

I would guess the non dynamic structure is largely cheaper than dynamic structure i.e more tower is cheaper to build than building more blades.

With respect to the number of blades, the power output isn't constant even before one considers the effects of the blades as the wind isn't constant (remembering power output is a V cubed relationship). The wind velocity's are low (~3 m/s in europe) so a mild gust could cause quite a change in possible power output.

 

[WKTaylor]

From my 'prop-Acft' and helo days...

More blades can make the rotor quieter. Remember the distinctive sound of a UH-1 Huey 'whop---whop---whop---whop---whop---'? Most 3-or-more-blade props tend to produce a softer 'overlapping' whaa--whaa--whaa--whaa--whaa--' sound. Each rotor blade system produces aero-pulsing sound and 'feelings' thru sound/vibration pulse-frequencies, which are huge environmental factors. As I understand-it windturbine blade noise-dynamics can drive some 'sensitive' people crazy... others 'not-so'.

Why?... As the blade-count increases the noise decreases further, as more blades accept the same amount of power. The 'power-per blade' is lower, since the chord-width tends to narrow for the same span ['aspect ratio thing'] to extract the engine or wind energy of a given 'disk-are'. BUT, Never forget that practical structural and mechanical issues with the pylon/mountings/hubs for blades are all major design issues. The bigger-the-blade the bigger/beefier, everything else is for that blade.

Also... multi-blades tend to be easier to dynamically 'track and balance'. More places to adjust track/mass around the disk. Odd numbers of blades 3-5-7-9 etc tend to balance easier than even numbers of blades.

Ahhh this explanation is missing something. I'm tired.

There are several good books/documents on this subject.

My 'smart just hit a wall'...

 

[rb1957]

that's what I was thinking. as for cost ... not the first thing to be mentioned when asked. sure probably is a thing, but then adding blades is a more manageable option for longer blades (than building an entire delivery system).