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Ash Small

Sat Jul 05 2014, 06:23PM

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

I think the conclusion I'm coming to is that we need more data to plot before we can perform any 'reliable' extrapolation.

It may even be worth designing and constructing some larger props, and plotting the data obtained from them, but this is quite a large undertaking.

Patrick

Sat Jul 05 2014, 08:17PM

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

Let me get you some other sizes...

9x4.5 mr

10x4.5mr

11x4.5mr

12x4.5mr

14x5.5mr
There is no 13 inch MR prop...

Ash Small

Sat Jul 05 2014, 09:04PM

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

We need data that I can convert into Lbs/Foot^2 and Lbs/Hp. Data we've measured ourselves.

Unless anyone wants to try predicting from manufacturer's data sheets? I wouldn't know where to start, and certainly wouldn't rely on their info.

We know we get 8 minutes from what we measured. We should stick to this procedure for the figures to be meaningful, I think.

Patrick

Sat Jul 05 2014, 09:12PM

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

Ash Small wrote ...

We know we get 8 minutes from what we measured. We should stick to this procedure for the figures to be meaningful, I think.

OK we'll have to wait for the mailman then... I have props coming.

EDIT 1: So if we were to design heli like blades, what would they look like? Would we make the the root crossection different than the Tip?

EDIT 2: link

this is important, as he claims to push the thrust more inboard, even if we dont copy the 'ellipse" prop, we should consider the implications on a constant chord heli blade.

EDIT 3: im going to cut 0.5 inche diamters off the 10x5.5mr props tomarrow, to see where the thrust-power is located.

Ash Small

Sun Jul 06 2014, 04:24PM

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

It's usual to have a different section for root and tip as the tip is travelling faster than the root. I'm not that familiar with heli blades, but I think we should find some examples.

I don't think we need to copy the LIPPS prop. My opinion is that it may be advantageous in a 'tilt wing' or 'lift fan' aircraft, but we wan't low disc loading and low drag.

It may be advantageous to increase material at the root if we decide we need it for reasons of strength/rigidity, but I don't think I'd consider it for any other reasons for this application.

We want low disc loading and low drag. The LIPPS design looks like it's more suited for high disc loading applications.

Patrick

Sun Jul 06 2014, 06:44PM

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

should we be looking at NACA profiles then?

Ash Small

Mon Jul 07 2014, 02:55PM

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

Patrick wrote ...

should we be looking at NACA profiles then?

Well, Wikipedia says they are 'airfoils'

"The blades of a helicopter are long, narrow airfoils with a high aspect ratio, a shape that minimizes drag from tip vortices (see the wings of a glider for comparison). They generally contain a degree of washout that reduces the lift generated at the tips, where the airflow is fastest and vortex generation would be a significant problem. Rotor blades are made out of various materials, including aluminium, composite structure, and steel or titanium, with abrasion shields along the leading edge."

EDIT: I also found this:

Which includes a "Rotor Blade Case Study", which I'm reading now, and which includes this:

I imagine you're experienced enough now with composites to attemp a prototype, Patrick

EDIT: Also found this:

Patrick

Mon Jul 07 2014, 07:23PM

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

the shape along its lenght, airfoil cross section, and hub are the parts i worry about most, i can layup the CF and GF easilly enough.

Ash Small

Mon Jul 07 2014, 07:29PM

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

Patrick wrote ...

the shape along its lenght, airfoil cross section, and hub are the parts i worry about most,

Well, I'm sure we can help with the design. Udo seems quite eager to get stuck into the prop design

I wanted to get some idea of what size prop the 'disc loading' thing says we require before moving on to prop design.

Patrick

Mon Jul 07 2014, 09:09PM

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

Im thinking 14, 16, and 18 inch props 2-blade. Since those are the best sizes too given shipping and disc loading.

But,

Ash Small wrote ...

I wanted to get some idea of what size prop the 'disc loading' thing says we require before moving on to prop design.

are you meaning your graph? or my 14 inch prop?

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