How do they do it? - Growth Rotor Blade

[Phoinix]

A lot has been said over the GRB these days.

So, how do you gain hover efficiency and cruise speed? Is it something completely new or just new geometry design?

Thanks for any answers, google didn't tell much :rolleyes:

[Dave_Jackson]

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http://static.howstuffworks.com/gif/viagra-2.jpg

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[Phoinix]

I can't belive it, the answer was in my spam mail all the time... Thanks Dave.

I guess they are selling top secret...

[Graviman]

Phoinix,

The secret seems to be in the design process to determine number of blades for a given MAUW. It is not uncommon to chose an aspect ratio outside of the flapping hinge of 12, to keep blade 3/4 wave mode below 3P. The fewer the blades the less the vortex interaction, so the number of blades is a compromise between high solidity ratio and blade tip vortex interaction. BugDevHeli's rotor ring development may well change all this.

My guess is that Sikorsky are keen to push up the solidity ratio for higher figure of merit, without increasing vortex interaction. A great deal of development will have gone into the blade to control it's aeroflexural eigenmodes, at say 3P 5P etc. This means that the number of blades stays the same for a given rotor radius, hence the aspect ratio goes down.

So GRB is a package which gives you better rotor dynamics, and both higher hover and cruise efficiency. This last part is accomplished because Nr is beeped down for hover, and beeped up to counter cruise retreating blade stall. Again better rotor dynamics improves the Nr range.

Mart

[NickLappos]

The Sikorsky 4th gen blade has an advanced airfoil that is quite efficient, and a modified anhedral tip that is a bit better than that on the S92. These were designed with very advanced CFD design tools. The combination makes the 4th gen work. Certainly the solidity is chosen to get close to peak figure of merit at the normal takeoff hover condition, but with enough extra solidity (which reduces hover efficiency) to push off stall at normal cruise speed.

As I described a long time ago, the BERP blade on the EH-101 costs it not quite 2,000 lbs of lift relative to the 3rd gen blades on the S92. I do not know how efficient the R&D BERP blade is, but the regular BERP blade is about 1987 technology, perhaps 3.5% less efficient that the S-92 and about 2% less efficient than the blades on the EC-225.

[Graviman]

The Sikorsky 4th gen blade has an advanced airfoil that is quite efficient, and a modified anhedral tip that is a bit better than that on the S92. These were designed with very advanced CFD design tools.


Ah, so one of the 4th gen tricks is to optimise for spanwise flow normally resulting from the downwash inflow near the tips. That's the great thing about CFD you can study 3D affects, and nowadays even couple them to structural models. Worked with a guy who did his pHd on heli aerodynamics, and it taught him a thing or two that has probably benefitted Peugeot.

Mart

[Phoinix]

Thank you for all the information, now i'll have to refresh my theory knowledge to understand it all...

[zigandzag]

Ok girls,

Here's the answer. The Reynolds number is the same, whether you model a flying Ant or or Flying Duck.

Ducks have the characteristic of eating from the bottom of rivers or ponds, or whichever low level water feture they happen to be around.

However, Ants live in Nests, and are little barstads if they bite you and inject you with a lump of nasty acid stuff!

So, to conclude, when you have a finite aspect ratio for a rotating blade, you need enough monkeys to write Hamlet for you.

Lots of love xxx