Vfrpilotpb,
Your thought of using an electro-mechanical means to twist the blade is probably what we will see in the not too distant future. They are coming up with neat products such as piezoelectric actuators etc. If interested,
this provides some information on piezoceramics.
slowrotor,
I'm open to participating in the 'simple', the 'complex', or both. However, the latter one really "turns my crank".
IFMU,
"That torque tube has a lot of potential windup over the span of a blade. And, even those rigid rotors generally aren't all that rigid. So, it's not like the torque tube is going to have a nice straight tunnel to ride in as the blade whirls around. This will induce bending, chafing, and honest to God fatigue cycles."
Thanks for the very valid concerns. The following is the 'theoretical' attempt to overcome them and any comments will be appreciated.
The torque tube will only have layers of biased filament wound carbon tow. The odd numbered layers will have a +45º bias and the even numbered layers will have a -45º bias. The innermost layers will extend out to the tip of the spar. The overwrapping layers will have progressively shorter lengths, in the spanwise direction. The final result will be a torque tube that has an extremely strong resistance to twisting and very little resistance to bending. Ref.
Picture
The spar used in the Sikorsky XH-59A ABC was fairly rigid , however, it was only made of titanium because back then they were not willing to trust composites and pultrusion was probably not yet known of. It appears that even the rigid Bo105 spar Ref.
Pictures was not pultruded. My belief (hope) is that the final spar will be very rigid inplane and out-of-plane, but very soft in torsion.
The torque tube is to fit inside the spar. It will be anchored to the spar at the tip end and rotate within the spar at the root end.
A long elastomeric bearing is intended to bridge the gap between the OD of the torque tube and the ID of the spar, all the way along the span. It is intended that the elastomeric bearing will off-load an ever-increasing portion of the twist from the torque tube to the spar on its way from the root to the tip. The tip is the final and firm transfer of twist. It is also intended that this elastomeric bearing will negate the possibility of chafing.
The skin of the blade will be made from fiberglass cloth, for flexibility. The leading and trailing edges will contain pultruded carbon, for rigidity.
"You already have a strong piece of structure absolutely required that can serve duty as a torque tube. It's called the spar. Why wouldn't you use that as your torque tube, secure the airfoil to the tip, and have seperate pitch horns inboard, one for the spar and one for the airfoil. That reduces the parts count by one. Of course, the same problems with chafing and bending will still be present."
The
Independent Root & Tip Control by Floating Root Method will certainly be easier to manufacture. However, it will result in a smaller diameter spar for a comparable airfoil size since the 'bearings' must fit between the spar and the skin. It will also mean that the start of the twist must be a fair way inboard from the tip of the blade. In addition, it places the majority of the blade's forces on the tip control and tip bearing.
The desire is to use the
Independent Root & Tip Control by Torque Tube Method since the major blade forces will be handled by the spar and therefor by the root control and root bearing. The root pitch angle will be set primarily by the collective and the airspeed. For a Very-Light helicopter, this might allow the tip control to be connected to the cyclic stick without servo assist.
Bug
Thanks.
Lu,
"I'm ...... just a fat kid from Cleveland."
Was the hospital food really that good?
Scathing or polite rebuttals accepted; begrudgingly.
Dave