Great discussion, Don.
Quick question: the wingrod in this Windfree needs to be bent to the
dihedral angle of 16 degrees. The wingrod material I have is from
DreamCatcher and is listed as "high strength steel". It's polished, with a
precise diameter, so it's not "piano wire": Iknow nothing of the metallurgy
of this material. Is there any reason why it can't be bent to this angle?
Thanks,
--Bill
>From: "Don Stackhouse @ DJ Aerotech" <[EMAIL PROTECTED]>
>To: [EMAIL PROTECTED]
>Subject: Re: [RCSE] spar-sizing calculations
>Date: Thu, 09 Aug 2001 14:46:47 -0400
>
>Skye Malcolm writes:
>
>>It seems to me that you're on the right track with the steel rods. You =
>>might see if you can find one tempered. ...
>
>There are several different ways to harden different types if steels. One
>is by heat treating. The typical process is to heat it above the
>temperature where all the alloying elements go back into a solid solution
>("dissolve") in the iron (typically around 1500 degrees F for
>garden-variety hardenable steel alloys), then quench (rapidly cool) the
>part so that some of the alloying elements get caught in harder types of
>microstructures (such as martensite), since they don't have time to revert
>back to their fully-annealed types of microstructures (typically ferrite
>for plain-carbon alloys). The resulting fully hardened part is extremely
>hard but very brittle. Even dropping it on the floor could result in
>shattering (that's also why they have a warning on hammers to not hit the
>hardened face against another piece of hardened steel, it could shatter and
>send splinters of itself into various soft and fragile things, such as your
>eyes). Fully hardened alloys also often have very high internal stresses.
>In some cases, just letting it sit around for a while in that state could
>result in microcracking.
>
>For this reason, it is normal practice to "temper" a part after quenching.
>The part is re-heated to something less than the quench-hardening
>temperature (typically around 700 to 900 deg. F for common steel alloys,
>with the higher temperature resulting in a softer final part), then slowly
>cooling back to room temperature. The alloy loses some of its hardenss but
>gains back enough ductility to eliminate the brittleness.
>
>Another type of hardening is work hardening. The alloy is mashed,
>stretched, or otherwise physically abused, which causes the buildup of
>physical stresses and microstructure changes in the material that have
>essentially the same effect as heat treating. In the case of music wire,
>the alloy is AISI 1060 steel (that means it's an iron-carbon, or "plain
>carbon" alloy, with a carbon content of 0.60%). It is drawn through a
>series of dies to work it down from the initial ingot diameter to the final
>desired wire size. Each time it gets pulled through a die, it gets work
>hardened. After a few steps it's been cold-worked so much that it's just
>about fully hard and has lost almost all its ductility. It is then annealed
>(slowly heated and then SLOWLY cooled) to make it soft again, and then the
>drawing process is continued.
>
>They use the minimum number of annealing steps, so that the wire at its
>final diameter is nearly fully hard, about the same hardness as the best
>you could get from it by heat treating. It's quite brittle at that point,
>which is why music wire can crack and snap if you bend it and then try to
>straighten it. It's already been subjected to about all the work hardening
>it can stand, and if your bending back and forth imposes more on it, it
>says ENOUGH!!
>
>At that hardness it's also close to about the same hardness and strength as
>most tool steels, which is why it will leave nice semi-circular dents in
>the jaws of your diagonal cutters if you try to use them to cut it. This
>also means that going to a heat-treated version of some other alloy (with a
>few very exotic exceptions) is not likely to get you any significant
>improvement in bending strength. You might get some improvements in
>toughness, but the hardness and strength (and therefore the bending load at
>which it gets bent) is not likely to see much improvement.
>
>The stiffness of all steel alloys is nearly identical, so the tip
>deflection due to elastic bending (i.e.: bending from which it can still
>spring back to its original shape) will not be changed in any case.
>
>About the only thing you can do that will significantly improve the bending
>strength of the rod is a diameter change.
>
>>Also you might try shortening the rod instead of lengthing it. At some =
>>shorter length this will theoretically put more stress into the wing rod =
>>sleeves...
>
>This will increase the stresses in the connections between the joiner rod
>and the wing spars, but it will not change the stresses in the joiner rod
>itself in the middle. There are a certain number of inch-pounds bending
>moment created by the lift forces and the length of the wing panels, and
>the center of the joiner rod has to absorb that amount of bending moment,
>irregardless of how long the joiner is. The only thing that matters at that
>center point in the rod is the amount of bending moment, the size and shape
>of the joiner's cross-section, and the properties of the joiner's material.
>If your joiner is tearing up its sockets in the wing roots, a longer joiner
>could help. If your joiner is bending in the middle, the best fix is to get
>a fatter joiner.
>
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