Temperature increase from amperage loss in wire

scott_alexsk

Yes Nitinol has already been used as the control surface as opposed to the piston. Several groups have already tested nitinol applications including Nasa which concluded that a curved wing surface from nitinol 'trained' to transform into that shape is about 10% more effecient at moving air, whatever that means. Mech Engineer, Nitinol does not just pull, it simply returns to its predeformed shape. So if I squish it, when heated it will exert force to push back out, to its trained shape. On the issue of temperature control, with the literature I have read suggests using insulators. Also using a heating element of some sort, like Tungsten filaments, has been shown to be more efficient than electrical heating.

Thanks,
-scott

Gokul43201

Nitinol can be engineered to have a transformation temperature anywhere from -100C to +100C. I've got a piece of wire in one of my desk drawers with a trans. temp. of about 0C (32F).

scott_alexsk

Also by subsituting titaninium with platnium, the transformation temperatures have be shown to go up to 1000 C (ie for high speed applications).

-scott

Mech_Engineer

A Tungsten filament would still be resistive heating, unless you are planning on inductive applications... I fail to see how a Tungsten filament would be more efficient at heating a piece of Nitiniol, compared to just passing an current through the piece itself, since heating the Nitinol directly could allow more uniform heat generation if the current density is carefully managed. You would also need far more current to pass through the Tungsten given it's excellent electrical resistivity (or lack thereof comapred to Nitinol).

It would be quite a feat to design a system that would be able to heat something quick enough to allow for control of an aircraft, especially in adverse weather conditions where reaction times are needed to be far less than one second... This system would also have to be very efficient since the whole point is to come up with a more efficient method of controlling an aircraft. Of course, it might be possible to use such a method for something that does not need to react very quickly, such as flaps.

Hmm, I didn't realize they were considering making an entire control surface out of the material. I worry about the time constant for heating an entire surface in order to make it return to its memory shape; and then to bend it back again you would need to heat an opposite side or opposing surface...

Just mentioning problems that I am seeing... by all means you should give it your best shot.

scott_alexsk

According to what I have seen from information on just heating small wires, depending on the methods you use, you can get transformations in the millisecond range.

Perhaps unevenness in heating could be dealt with by putting a grid of some sort of a heating element over the surface of the material. Also from what I have read uneveness in heating is fairly minimal, even with heating from just one corner of a sheet is at most 1 degrees C difference, within several seconds. The heat also spreads very quickly, so it will not be an uneven warping, or atleast, nothing noticable to the human eye, (which may be a problem with higher speeds) However I am only going to deal with, at least this year, low speed applications.

I will have to find flexible, thin, and light insulators which can minimize the heat loss that will form the actual surface of the aircraft. I think that is one of my biggest problems, along with constructing the wing to measure the 'effeciency' of the nitinol wing agaisnt.

Thanks,
-scott