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#11
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Wooden Prop Drive Methodology - was: Pills & Propellers
On Nov 23, 9:35*am, " wrote:
On Nov 23, 3:32*am, Stealth Pilot wrote: something for Veedubber to explore is whether epoxy saturation of the hub area could increase the crush strength of readily available softer woods. laminating hard faces wont do it because they just transfer the pressure unabated to the soft core and crush it. -------------------------------------------------------------------------------------------------------------------------------------- I don't know if just saturation would work. *As Richard points out, on healthy wood epoxy hardly soaks in at all. *But if your hub has an accurately made center-bore and if you make or buy drive lugs, you can auger out the area where the drive lugs would seat and fill that area with JB WELD or other filled epoxy. *You have to wax the drive-lugs and the bolts, and you need to get the filled epoxy deep into the holes you've made (you don't want any of it to squeeze-out between the prop and the hub), you'll end up with a softwood prop capable of being torqued to hardwood specs. *This is usually done as a repair procedure. *Just look at the clamping ring. *If it has been drawn into the wood by any amount you'll probably find charring between the prop and the hub. *Soaking the charred portion with epoxy will harden it but the real problem is that the softwood prop simply lacks the required compressive strength. *That's where the filled epoxy comes in. *This also works for the valley created by the clamping ring. *You can use a WIRE BRUSH on a drill-motor to get down to clean, bare wood then brush on a thinned coat of epoxy to act as a primer. *Let it get tacky then FILL the valley with a filled epoxy... such as JB WELD. *It will take a couple of tubes to fill a serious 'valley.' *After it cures you can sand it flush. *Just make sure you keep it flat. *If it has been varnished (as opposed to epoxied) you may have to do the wire- brush trick over the entire surface so you can apply a finish-coat of epoxy once you've returned the surface to truth. *(Tracking will tell you if you've got it right.) There's a lot of elderly VP's and other basic designs that, despite their age, have accumulated relatively few hours, such as fifty hours in fifteen years -- stuff like that. (And most of that will have been accumulated during the first year or two.) * The sale of such airplanes is often tied to an estate sale -- the builder has died and there's no one who can give you accurate information about the condition of such things as the prop, engine and landing gear. *And they may not want you to go digging into it. *But if you're allowed to dig (or just remove the prop, for that matter) you'll often find charring, especially if they've glued on a spacer to allow the prop to clear the #3 exhaust stack. At a real auto-parts store (as opposed to a franchise, such as Pep Boys, et al) in the 'Dorman' trays, you will find 'drive lugs' for about six bits as opposed to the $18 or $20 wanted for an 'aircraft' drive lug. *They don't call it a drive-lug of course -- it is a brake part, I think for early Chrysler products. -R.S.Hoover I don't think epoxy saturation of a soft prop would safely, even if we could get the whole hub saturated to its full depth. The hub would get hard enough, certainly, but the blade roots would still be soft and the flexing of soft wood is therefore concentrated at that point instead of tapering off into the hub as it should. Saturating the whole prop would stiffen it without increasing its tensile strength. Brittleness would result, along with much more weight and cost. Better to use a hardwood in the first place. Pine is soft. It doesn't have the tensile strength of hardwoods. Concentrating stresses is asking for trouble. We've seen this in several older strut-braced high-wing aircraft designs where the wooden spars are plated with birch or mahogany ply at the strut attach points, and the spruce spars suffer compression failures at the ends of the plates on the top of the spar. There are so many ways of introducing "unintended consequences" when we "fix" something. If I was to build a prop (and I plan to) I'll be using a wood that's worked for many people for many years. Something like hard Canadian Maple. Dan |
#12
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Pills & Propellers
There is a method I have done thought experiments on, in which a wood
part could be soaked through with methyl methacrylate monomer, which will penetrate to the deepest cell structure, and then activated chemically to cross link. Something of this nature could possibly be of use. Methyl methacrylate monomer will cross link under UV such as direct sunlight, which I have used (taking several days to start the reaction). You would need to maintain the saturation in a closed container since the monomer is quite volatale. A.L. Phoenix |
#13
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Pills & Propellers
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#14
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Pills & Propellers
"cavelamb himself" wrote in message ... wrote: There is a method I have done thought experiments on, in which a wood part could be soaked through with methyl methacrylate monomer, which will penetrate to the deepest cell structure, and then activated chemically to cross link. Something of this nature could possibly be of use. Methyl methacrylate monomer will cross link under UV such as direct sunlight, which I have used (taking several days to start the reaction). You would need to maintain the saturation in a closed container since the monomer is quite volatale. A.L. Phoenix I think I'd rather just buy a good prop from Tennessee Props and go fly... OK I can find the definition and properties of: Methyl methacrylate monomer , but what is that word: "FLY"? Is the other word Fishing? My helicopter has been down for sometime now waiting for me to quit "Digging Dirt" and finish a small "Put Back" job. Stu |
#16
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Pills & Propellers
On Nov 23, 2:19*pm, cavelamb himself wrote:
The democracy will cease to exist when youtake away from those who are willing to workand give to those who would not. * * * * * * * * * * * * * * Thomas Jefferson Falsely attributed to Thomas Jefferson http://tinyurl.com/6gmvmz |
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