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Ash Small

Fri Jul 18 2014, 05:14PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Looks like you do want a naca profile (or something similar) after all, apparently symmetrical blades were only used due to the difficulty of making assymetrical blades strong enough

"The types of aerofoils used with a rotorblade differ (figure below). For a long time, most of them were symmetrical. However, a higher L/D ratio is possible with non-symmetrical versions. Due to the greater internal forces occurring in these types of blades, they only came into existence when the appropriate composite materials were developed. These can cope with the high internal strain, while their weight is kept low.

"

I'm still reading this, but it looks like it's got a lot of good theory in it.

EDIT: There is a rather humorous typo in it, namely when it refers to the 'sound of speed'

EDIT: The comment at the bottom looks interesting too:

"As an alternative approach, engineers may wish to consider trying the VABS software for modeling very complex composite rotor blades. Developed at Georgia Tech and Utah State University, VABS is capable of quickly and rigorously decoupling an original 3D slender solid with complex microstructure (sophisticated cross-section with or without spanwise heterogeneity) into a simple engineering beam model. VABS (Variational Asymptotical Beam Sectional Analysis), is a unique tool capable of realistic modeling of initially curved and twisted anisotropic beams with arbitrary sectional topology and materials. Evaluation licenses of VABS are available through AnalySwift."

Maybe you can obtain an evaluation license through your college, Patrick?

EDIT: This is just one page of a series that starts here:

and seems to cover pretty much the whole 'helicopter design' thing, albeit fairly concisely.

EDIT: I forgot to answer this question above:

Patrick wrote ...

Ash, do you have access to and knowledge of the CAD, and its ways?

I do have a twenty year old version of TurboCad Pro V3, which I bought when I was running my own company, and I also picked up a copy of TurboCad V16 Deluxe, which is not a pro version, but does have some features that V3 doesn't have, although it doesn't have all the 'Pro' features.

I can do most things with them, and they are compatible with AutoCad .dwg and .dxf files. I believe the V16 deluxe version also produces Adobe .pdf files, etc.

Patrick

Fri Jul 18 2014, 09:12PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

ill go you one better, i have it in with Georgia tech, ive even been at the IARC Mission 6 compettion with them for 3 years in a row (Grand Forks, North Dakota) let me contact my Professor Robert Michelson at Georgia Tech. He might vouch for me since we've met and talk often.

EDIT: im trying through their website too.

Patrick

Mon Jul 21 2014, 07:58PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

i got all the props, about 10 mnutes ago. Ill run the loading tests in a few hours.

Patrick

Sun Jul 27 2014, 08:19AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

Ok had some delays due to family health issues, but got it done. It appears the 12x4.5 is best? the 14x5.5 i think has to be due to the steeper pitch and seperation flow ?

Ash Small

Mon Jul 28 2014, 10:25AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

Patrick wrote ...

Ok had some delays due to family health issues, but got it done. It appears the 12x4.5 is best? the 14x5.5 i think has to be due to the steeper pitch and seperation flow ?

That makes sense.

Any news on the VABS software yet?

Any more thoughts regarding producing some low pitch, low drag, low disc loading blades?

(I think we all agree that this is the way forward)

Patrick

Mon Jul 28 2014, 08:01PM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

yep, it looks like heli blades are the solution, endless tinkering with heavy disc loaded props wont lead any where useful.

BigBad

Mon Jul 28 2014, 11:48PM

Registered Member #2529 Joined: Thu Dec 10 2009, 02:43AM
Location:
Posts: 600

Makes sense.

That's why heli blades are built like that; for maximum hang-time.

Patrick

Tue Jul 29 2014, 01:23AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

BigBad wrote ...

Makes sense.

That's why heli blades are built like that; for maximum hang-time.

but im not sure they should be symetric, they may need to be more chord width at the root too.

ive put in a request for a academic demo, i didnt see where to download a trial copy though.

Ash Small

Tue Jul 29 2014, 04:57PM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

I agree that assymetric blade design should be well within your capability, Patrick.

Lift/drag ratio, as I believe Udo pointed out earlier in the thread, will be the dominant factor once disc loading has been finalized.

Increasing chord at the root, in my opinion, should only be done if extra strength at the root is required, as there is less lift here anyway. (Tapering the blade towards the tip 'should' improve lift/drag ratio if done correctly, I think).

It all depends how complicated you wish to make it. A 'D' shaped blade of constant section would be easiest to produce, and may be useful for some initial disc loading modelling (make some long blades, then cut them shorter in order to plot a graph, maybe?)

Maybe others have some suggestions here as well?

Patrick

Wed Jul 30 2014, 12:54AM

Registered Member #2431 Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639

ok lets try a conventional constant chord and large diameter, with a D crossection.

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