Making rotor blades 2

[qmechanics]

Hi all,
I'm in the process of building composite rotor blades for an existing helicopter. I know all the aircraft particulars (gross weight, engine hp etc) and know about the existing metal rotor blades but I'm in need of assistance and insight into the conversion from metal to composite. Obviously, the
composite blades will weigh much less and I'm at a loss as to how I can get the weight right, center of gravity, center of pressure etc. to work out. Any help would be appreciated.

 

[MikeHalloran]

It's not obvious >to me< that composite blades will weigh much less than metal blades.




Mike Halloran
Pembroke Pines, FL, USA

 

[qmechanics]

They do weigh much less Mike. One can compensate for this by
various weighting schemes but that's why I post this thread. I'm unsure what the best way to do this is. There are other issues as well such as flapping moments, twisting moments, movement of the centers that need to be addressed.
Ultimatley, what I would like to be able to do is replace the existing (metal) blades with these "new and improved" composite blades. That may not be possible because of the difference in aerodynamic and dynamic properties of the new blade. Any help would be appreciated.

 

[GregLocock]

So, you are going to make some composite rotor blades, but you don't know much about composites, or rotor blades?





Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[Intermesher]

You have an interesting project.

I too intend to build composite blades.

The following information may be of help;
Blade - VR-7b - Composite:

http://www.unicopter.com/BladeVR-7b.html

Composite:

http://www.unicopter.com/A029.html

... and information related to the construction of a blade with 'Active Blade Twist'

http://www.unicopter.com/UniCopter_Rotor.html

Dave J.

 

[qmechanics]

Thanks Dave this is helpful. Perhaps it would help if I was more specific. My plan is to replace and existing metal rotor blade with a composite without having to reconfigure the rotor head or anything else if possible. If I make the composite versions identical to the exist metal blade (that is in size, shape, weight, center of balance) I do not think that will work very well. Sure the moments work out but this blade is different material and will bend, flap, twist differently so how do I compensate? Greg, I am new to both areas but have some experience with composites (build an 4 seat fixed wing aircraft). For instance I plan to put the spar 18mm behind the leading edge. On the current blade the D spar is the leading edge and is made of steel. If my new blades leading edge is composite won't it be damaged rather quickly? Cause delamination? What can I put on the leading edge to prevent this? Some sort of tape?

 

[Intermesher]

qmechanics;

Perhaps your first consideration (of many) is that of using the existing profile, or using a 'hopefully' better one(s).

Dave J

 

[qmechanics]

The existing profile is NACA0012...an old proven profile.
The existing ship has GW or 1360 pounds. Currently running
a two blade system each blade weighing 26 pounds including grip. Very light.

 

[Intermesher]

If you are going to a composite construction you may want to consider the advantage of the VR-7 & VR-7b

http://www.unicopter.com/0733.html

over the NACA 0012

http://www.unicopter.com/0428.html.

Just a thought.
Dave

 

[PEW]

As professional helicopter pilot, this worries me, to say the least. I sincerely hope that you are talking about a model helicopter, not a full sized one.

Any failure of a rotor blade has the strong likelihood of killing someone, either in or around the helicopter.

 

[PEW]

Having just re-read your recent post, unfortunately I see that you are talking about a light helicopter. The stresses involved are huge in comparison to the wings of an aeroplane. Please be extremely careful with this project!

 

[klyde]

gmechanics: The Safari Kit Helicopter was initially issued with all aluminum blades. The current version utilizes composite blades weighing about 37# each. I don't remember the weight of the aluminum blades but I'm pretty sure they were lighter. The reason the manufacturer changed was that the aluminum blades were more labor intensive. This is on a helicopter of max gross wt of 1500# and the blades are redlined at 500rpm. I have flown both blades and currently am flying the composites. The autorotation characteristics are an improvement over the aluminum blades. Both the aluminum and the composite use the 0012 airfoil.
It would seem a good idea to have a whirl tower if you are going to develop from scratch a composite blade. Some problems don't show up in the first 100 hrs.

 

[qmechanics]

Klyde: Are you currently flying a Safari? If so what is your opinion of it? I heard they were having problems with the new blades. Also heard there's very little tail rotor authority.
Any truth to these rumors? Thanks.