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Propeller Physics and VABs Program.

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Ash Small

Fri Apr 24 2015, 02:28AM

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

Sorry to double post, but has any progress been made with this recently? Where are we at the moment?

We need some figures.

Patrick

Fri Apr 24 2015, 07:23AM

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

i havent forgotten about this. the profile and loading are still undecided at the moment, but ive made and will show some 3d printed parts to alter the pitch of the span in a clever way.

Also, as a practical and safety matter, ive come up with a way to continuously stretch fiberglass or carbon fiber from tip to hub to tip.

Next, ive captured some shredded rotors for a 700 size helicopter. the guy really augured it in, its internal are surprising.

ill post more tomorrow its mid-night here.

Patrick

Sun Apr 26 2015, 04:23PM

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

heli blades, ill explain more later.

theres some unique features ill mention after work.

Ash Small

Mon Apr 27 2015, 10:14PM

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

Fascinating

By the way, I think I may have made an error in the maths somewhere regading RPM, Tip Speed, and Mach1.

I'm not sure how feasible it is to achieve near Mach tipspeed. You don't want to get too close anyway, even when tip speed is nearing Mach 1, if you have any turbulence, some of it can go supersonic. It's about finding a balance

Patrick

Tue Apr 28 2015, 06:28AM

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

In depth examination of 700mm helicopter blades.

Ill have more to post but im super tired.

I was given these blades from a fellow hobbyist who had is machine go in full-force and explode to pieces. These blades are being examined here for what can be learned for multirotor use. There are significant differences between constant head speed and multirotor props, but this is still a useful persuit.

i was told there would be a lead whiegt in the tip of each blade, held in place with a fiberglass tow for safety. And that i may not find it since the tips were gone.

this surviving blade will be sectioned off at 4, 9 and 15 inches.

from the original crash damage, the plies can be seen.

there is a odd placed section of fiberglass but a void too. The top thin surface was carefully removed to reveal more of the interior. Seen here is a foam that wont dissolve in acetone. Im thinking its polyurethane.

there is mysterious void and beefy fiberglass thats broken and loose.

SURPRISE! those voids were missing lead rods running through the leading edge, not the tip! they must have been stripped out from cracking and deceleration forces!

BigBad

Tue Apr 28 2015, 02:34PM

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

Interesting, so presumably the lead weights are in the right place that will stop the blades fluttering because it keeps the CofM ahead of the CofL.

Ash Small

Tue Apr 28 2015, 03:35PM

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

Are these blades designed for constant RPM, and variable angle of attack (ie swashplate)?

The reason I ask is that, if you have constant A of A, and vary the RPM to control lift, you will be constantly accelerating and deceleration the lead weight, which sounds inefficient.

Also, I'd expect the chord length to be shorter that this. The profile does correspond to a NACA 0012 profile quite well, from first glance, though.

I realise there are practical problems and limitations, and compromises need to be made, but it's certainly worth seeing how others have addressed the issues here.

EDIT: The lead adds inertia to the blade which, when spun up, resists any fluttering, etc., but response will be slower, as you have more mass to accelerate/decelerate, unless you use a swashplate, if my assumptions are correct.

Patrick

Tue Apr 28 2015, 06:13PM

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

BigBad wrote ...

Interesting, so presumably the lead weights are in the right place that will stop the blades fluttering because it keeps the CofM ahead of the CofL.

I never would have realized this.

Ash Small wrote ...

Are these blades designed for constant RPM, and variable angle of attack (ie swashplate)?

Yes.

Ash Small wrote ...

The reason I ask is that, if you have constant A of A, and vary the RPM to control lift, you will be constantly accelerating and deceleration the lead weight, which sounds inefficient.

EDIT: The lead adds inertia to the blade which, when spun up, resists any fluttering, etc., but response will be slower, as you have more mass to accelerate/decelerate, unless you use a swashplate, if my assumptions are correct.

yes for our purpose totally inefficient. we need the tip to be light weight, but well supported and stiff.

The chord width is 2.4 inches. The 1k plain weave carbon, is at +45 and -45 degrees, while the 6k harness is at 0 and 90 degrees. This gives torsion and flexural strength.

My in progress Kickstarter, i just wish i knew how to get links to appear as clickable text.

Patrick

Sat May 02 2015, 05:52AM

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

New pics with important info. Id like to here from BigBad on this new info.

The lead was not the shape or in the place i thought. At its full - undestroyed length, the lead would wheigh 47grams

This Blade has been enormously helpful, as has been seeing it in flight, doing +/- 5 g changes. It squeels and whines when they go high alpha at high G.

Only some of this is valuable to our task at hand. But the thickness ad weave has been one such lesson.

BigBad

Sun May 03 2015, 12:37AM

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

Yeah, so the lead will help with the aerodynamic stability. If it was in the rear edge it would massively destabilise it, it would flutter like crazy. Adding weight to the tip would probably help with flutter a bit too, but leading edge is much more important, and most of it can be further inboard. Angular momentum goes as the square of the distance from the axis, so you want as much of the lead inboard as possible for responsiveness.

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