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Pills & Propellers
To All:
Some time ago I mentioned having to take something like sixty pills every day. That generated quite a bit of traffic, some of which was loud in its disbelief, based on the author's direct, personal experience as a corpsman, pharmacist or whatever. And they were right... if they read my message to mean sixty DIFFERENT pills. What they had overlooked or failed to comprehend was the fact I was taking pills several times per day. Some pills were taken at three hour intervals, meaning I took them eight times across a 24 hour day. Others were taken every six hours (ie, 4 times) some only once, and so on. Then there was the fact I had to take two, three or four pills to make up the required dosage. And finally, there were the pain- killers, some of which were to be 'Taken As Required' up to a certain maximum per 24hr period. Just keeping them all straight was a hell of a chore, something I'm sure I never could have handled on my own. But my wife tackled the problem with grim determination and not only memorized the names & dosages, she would track me down whenever I was due for a pill-session and stand over me until I'd gagged the things down. (Some of the pills make you want to throw up. I got no sympathy.) In many cases the local pharmacies did not carry a particular pill in the dosage called out by the physician. For example, a certain steroid commonly used by body-builders was only available in 4 milligram tablets. But that same steroid, in 20Mg doses, has proven to be an effective anti-tumor medication when taken with certain other drugs. Bottom line is that I was taking the things five at a time and hitting the local pharmacies for a hundred tablets a week. Turns out, taking 60 OR MORE pills a day is not uncommon for CANCER patients. Ditto for the blood tests; the so-called 'lab work.' Using the team approach, I've got four physicians (plus a shrink!) not only prescribing for me (but only one writing the 'scripts so as not to create conflicts), at least three of the four want to see the results of period 'lab work.' Sometimes the lab work for one includes data needed by another but often times it would call for a different frequency, such as a weekly report versus monthly, or a different series of tests. This really isn't much of a problem. You can expect to visit the blood lab at least once a week, the only thing that changes is how much blood they need to draw. Some weeks it's only a single sample but sometimes they collect four or even five samples. But as I said, it isn't a problem since they only need to stick you once, even if they need to draw five samples. Then comes the IV's: drugs that are given intravenously. That's where they plug you into a plastic baggy holding a quart or more of some medication. You get to sit there and listen to elevator music while the stuff drips into your vein. A busy day is when things happen to coincide, typically around the start -- or the end -- of a month, when you may be scheduled for xrays, an IV and a five-sample blood-work session. Followed by hitting the various pharmacies. These are the logistic realities of trying to deal with a cancerous tumor and it provides a neat insight into the professional foundation upon which America's medical system is based. But it also reveals the role played by the PATIENT. There is no ombudsman to oversee your treatment; there is no one to protect you from clerical errors. Indeed, often times the ONLY complete record of a patient's treatment is the one maintained by the patient themselves... including casual remarks such as taking sixty pills per day :-) ---------------------------------------------------------------------------------------------- Yeah... well, gee whiz an' gosh darn; waytago Bigfella... but what's that got to do with PROPELLERS? I'm glad you asked :-) Kid pops up on the internet and asks what kind of a propeller he needs for his airplane. And gets five different answers, all of which are CORRECT, in that they reflect props presently mounted on the nose (or tail) of successful flying machines. The truth is, unless EVERYTHING is idential to the kid's airplane, all of those answers are liable to INCORRECT. So follow me through here. What defines a prop? Think about it for a bit and you'll probably come up with diameter and pitch, such as 54x31. But that barely scratches the surface. You also need to know if it's a left-hand or a right-hand prop; you need to know which direction it ROTATES. Then you need to know the BLADE AREA, as well as the AREA DISTRIBUTION. and finally you'll need to know how that area is distributed relative to the blade. Wanna guess what happens when you DON'T KNOW all that stuff? Not knowing that stuff causes a huge hairy hand to rip your wallet outta your jeans an' run off with a handful of MONEY. And not just once; you're liable to have to buy two OR MORE props before you find one that hits the 'sweet spot;' that lets your airplane perform the way it should. that's because props are expensive. Which is why it's a good idea to roll your own. In fact, it works something like this: You mount a prop on your engine and go fly. In some cases you don't even have to fly it to know its not the right prop, just getting the thing up to take-off speed can tell you it's the wrong choice. In doing so, the prop tells you it needs to be shorter. Or longer. Or needs more pitch.. Or less. Did you get that? You haven't even flown the plane and you know the trial prop is wrong for your particular application; that you need more (or less) pitch, for example. Or mebbe less diameter; something shorter... or perhaps the same length but with less 'bite'... something with less pitch. If you're wealthy selecting the correct prop may be a trivial chore.. You simply haul out your wallet and order another prop. But wht about guys like you & me? A well-made prop is worth a well- made price. And lots of times you can say EXACTLY what is needed, less diameter or less pitch? And if you've put the prop on the PROPER end of the crankshaft you can forget about the possibility of selling it to someone else. The handy solution to your problem is to learn to make your own propellers! Which is a lot easier than most folks think. In fact, the hardest part of making a prop is convincing YOU that you should give it a try. Which is what this series of Cancerous Propeller messages will try to do, beginning with what I've always considered to be the hardest part of the job: making a good blank. That means gluing and stacking and clamping a stack of boards into a fence-post sized pile of lumber. Because once you have a good blank, the remain steps of the procedure are fairly simple. And why did I start with pine or whatever is being sold for shelving in your neck of the neighborhood? Because the first two or three 'propellers' are going to be the gawdd-ugliest things you've ever seen. To learn how to do something RIGHT you've got to do it wrong to begin with. That's what these props are for; they're going to show you how NOT to carve a propeller. And if you think that's a wacky way to carve a prop, you're wrong, pard. So let's get busy and make a good blank. You want a good squeeze-out all the way around. But get that frown off your face. Every one of those dud props is worth at least $100... just as soon as you install a clock in the middle. Seriously! It's a real propeller... you can even type a little vitae to go along with the prop, saying how its diameter and pitch indicate it was carved for the Continental A40 engine but that the prop is no longer suitable for service. And to prevent someone from trying to use it on an E-2 Cub, you've installed that spiffy clock in the hub. You can even include a picture of an E2 with an A40 on its nose... and a close copy of YOUR prop, ready to go flying. For a hundred bucks. No swap meets in your area? No Craig's list? Then use it as a gift. Learning to make the blank, then learning to cut the basic angles to the top & bottom surfaces, is the Basic Lesson here -- those chores are sucking all the good out of it. After that we get into SMOOTHING the UPPER surface; making a nice streamlined shape. Then making both blades IDENTICAL. (That's where grown men have been known to cry.) But none of it is being wasted; it's all 'good' in the sense that you have to know it in order to do it. Once you know how to carve a good prop you simply go looking for better wood. Birch is okay. Maple is better but the Borg carries birch and for a lot of you, the box stores are going to be your only source of wood. There's better glues; real props use different stuff. But Plastic Resin will work for 'low-power' props, meaning anything under 100hp. But a prop is a life-time sort of thing; a good prop will last as long as the airframe, assuming you don't taxi into a rock. Line anything made of wood, a good prop can be freshened-up by sanding it down and giving it a new finishing... and then balancing it to within an inch of its life. Don't worry about checks or dings -- there's lots of ways to deal with such things. And if you decide the prop has finally had its day, it's still worth a hundred dollar bill as a clock. So think about your new career as a Prop Carver. And believe me when I say there have been days when I had to take sixty or more pills :-) -R.S.Hoover |
#2
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Pills & Propellers
On Sat, 22 Nov 2008 00:22:49 -0800 (PST), "
wrote: To All: selecting goood propeller wood... almost any wood has the tensile strength to keep a prop's blades on. wooden props are bolted to the front of the aircraft with , typically, 6 bolts. those bolts hold the prop on to the prop driver by compression and it is the friction generated between the prop and driver that makes it do its stuff. what I have found is that the arbitrating factor in whether a wood is suitable as a prop wood is the compression strength of the hub. on my O-200 powered Tailwind the wood prop is held on by a crush plate and bolts torqued up to 120 inch pounds. the wood needs to be able to withstand that compression without deforming or crushing. also wood, no matter how well finsihed, will absorb some moisture in wet weather and swell slightly, and conversely in dry weather it will lose some moisture and shrink slightly. the way to maintain the compression without having to continually retorque the bolts is to use a sufficient stack of the conical tempered spring washers called Belleville Washers. these have a known compressive force and you stack them together to get the compression needed. my prop uses 8 washers each bolt with 4 washers facing cone up and 4 washers facing cone down toward each other to generate the compression needed. with these I need retorque my bolts only annually. ol' snake unda the verandah. (the belleville's are stacked like this... ^ ^ ^ ^ V V V V with a bolt through the middle) |
#3
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Pills & Propellers
Stealth Pilot wrote:
On Sat, 22 Nov 2008 00:22:49 -0800 (PST), " wrote: To All: selecting goood propeller wood... almost any wood has the tensile strength to keep a prop's blades on. wooden props are bolted to the front of the aircraft with , typically, 6 bolts. those bolts hold the prop on to the prop driver by compression and it is the friction generated between the prop and driver that makes it do its stuff. what I have found is that the arbitrating factor in whether a wood is suitable as a prop wood is the compression strength of the hub. on my O-200 powered Tailwind the wood prop is held on by a crush plate and bolts torqued up to 120 inch pounds. the wood needs to be able to withstand that compression without deforming or crushing. also wood, no matter how well finsihed, will absorb some moisture in wet weather and swell slightly, and conversely in dry weather it will lose some moisture and shrink slightly. the way to maintain the compression without having to continually retorque the bolts is to use a sufficient stack of the conical tempered spring washers called Belleville Washers. these have a known compressive force and you stack them together to get the compression needed. my prop uses 8 washers each bolt with 4 washers facing cone up and 4 washers facing cone down toward each other to generate the compression needed. with these I need retorque my bolts only annually. ol' snake unda the verandah. (the belleville's are stacked like this... ^ ^ ^ ^ V V V V with a bolt through the middle) I know that this is going to inspire more controversy than a political statement, but here goes: All that stuff above is absolutely correct, *except* the opening premise. Notice those big cylinders that all the bolts go through in the flange? The ones that extend into enlarged holes in the wood hub of the prop? They are called 'drive lugs'. They are called drive lugs because they are what drives the prop. If the prop bolts get loose, the same thing happens to a prop that happens to the wheels on your car if you let the nuts get loose. It starts wobbling, which wallows out the holes the drive lugs run in, which allows the prop face to move against the face of the flange, creating the hangar tales about charred wood caused by inadequate clamping force. To analyze this, you can approach it from multiple directions. Shear strength of wood fiber just isn't enough to handle the kinds of loads we are talking about. Or, look at those drive lugs. If it's friction preventing prop rotation on the flange, why do they bother to do the extra machining on the flange, make 6 extra parts (and weight), and counter-bore the prop bolt holes to accept these extra parts? Centering could be accomplished with a raised center ring on the flange. The reason for the drive lugs is to provide a machined precision fit to the counter-bores in the prop, and to provide a larger 'working surface' in the wood to take the load. You can see the same thing in the spar attach points of highly stressed wood wings, where there are metal bushings for the attach bolts. Charlie |
#4
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Pills & Propellers
On Nov 22, 7:58*am, Charlie wrote:
Stealth Pilot wrote: On Sat, 22 Nov 2008 00:22:49 -0800 (PST), " wrote: To All: selecting goood propeller wood... almost any wood has the tensile strength to keep a prop's blades on. wooden props are bolted to the front of the aircraft with , typically, 6 bolts. those bolts hold the prop on to the prop driver by compression and it is the friction generated between the prop and driver that makes it do its stuff. what I have found is that the arbitrating factor in whether a wood is suitable as a prop wood is the compression strength of the hub. on my O-200 powered Tailwind the wood prop is held on by a crush plate and bolts torqued up to 120 inch pounds. the wood needs to be able to withstand that compression without deforming or crushing. also wood, no matter how well finsihed, will absorb some moisture in wet weather and swell slightly, and conversely in dry weather it will lose some moisture and shrink slightly. the way to maintain the compression without having to continually retorque the bolts is to use a sufficient stack of the conical tempered spring washers called Belleville Washers. these have a known compressive force and you stack them together to get the compression needed. my prop uses 8 washers each bolt with *4 washers facing cone up and 4 washers facing cone down toward each other to generate the compression needed. with these I need retorque my bolts only annually. ol' snake unda the verandah. (the belleville's are stacked like this... ^ ^ ^ ^ V V V V * with a bolt through the middle) I know that this is going to inspire more controversy than a political statement, but here goes: All that stuff above is absolutely correct, *except* the opening premise. Notice those big cylinders that all the bolts go through in the flange? The ones that extend into enlarged holes in the wood hub of the prop? They are called 'drive lugs'. They are called drive lugs because they are what drives the prop. If the prop bolts get loose, the same thing happens to a prop that happens to the wheels on your car if you let the nuts get loose. It starts wobbling, which wallows out the holes the drive lugs run in, which allows the prop face to move against the face of the flange, creating the hangar tales about charred wood caused by inadequate clamping force. To analyze this, you can approach it from multiple directions. Shear strength of wood fiber just isn't enough to handle the kinds of loads we are talking about. Or, look at those drive lugs. If it's friction preventing prop rotation on the flange, why do they bother to do the extra machining on the flange, make 6 extra parts (and weight), and counter-bore the prop bolt holes to accept these extra parts? Centering could be accomplished with a raised center ring on the flange. The reason for the drive lugs is to provide a machined precision fit to the counter-bores in the prop, and to provide a larger 'working surface' in the wood to take the load. You can see the same thing in the spar attach points of highly stressed wood wings, where there are metal bushings for the attach bolts. Charlie Not all wooden props had the bushings. Many had more, larger bolts instead, some didn't even have that. The earlier Continental A65 had a tapered crankshaft with a separate hub, and that hub had no bushings. Bolts went through it from behind (before the hub was put on the crank) and the prop went over the bolts, a clamping plate was put over that, the plate splined to the hub so the prop was driven from front and back both, and castellated nuts finished the job. It looked like this: http://farm1.static.flickr.com/4/597...8088ae.jpg?v=0 Biggest hazard was overtightening the bolts. Only 175 inch-pounds for that one. Too much crushes the wood and it loses its elasticity and won't maintain the pressure against the flange. Dan |
#5
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Wooden Prop Drive Methodology - was: Pills & Propellers
Charlie wrote:
... They are called 'drive lugs'. They are called drive lugs because they are what drives the prop. With metal props, you're absolutely correct. However, with wooden props, it is in fact the friction of the face of the prop hub on the mounting flange that drives the propeller. The wood is not strong enough to withstand the torque pulses (especially in the larger engines) if only the small area in the drive lug holes was taking the force. Sensenich, Catto, Hertzler, and all wooden prop manufacturers are clear on this point, and talk about just how much compressive pressure is required to assure safe operation. Sensenich claims (in a paper downloadable on their website) that it's about 600 psi. If the drive lugs were doing the torque transmission, then the pressure would be meaningless, and all you'd need is a good fit on the lugs and some safety wire so the bolts didn't come off. It starts wobbling, which wallows out the holes the drive lugs run in, which allows the prop face to move against the face of the flange, creating the hangar tales about charred wood caused by inadequate clamping force. Not hangar tales at all. If the pressure is too low, then a small amount of relative motion can occur, which will then wallow out the holes - not from wobbling, but from relative rotational motion. You can read about my experience with this issue at: http://www.cozybuilders.org/Desert_Center/ and: http://www.cozybuilders.org/Oshkosh_Presentations/ I'm currrently using bellevilles (as the other poster mentioned, although I disagree with some of his setup) on my prop, and have a number of other canard flyers that are using my general setup on 1/2" and 3/8" bolt installations. To analyze this, you can approach it from multiple directions. Shear strength of wood fiber just isn't enough to handle the kinds of loads we are talking about. This is just incorrect, as I've pointed out before - the wooden prop manufacturers themselves state clearly that it's the friction of the hub on the mounting flange that drives the prop - NOT the drive lugs. Again, with a metal prop, you're absolutely correct that it's the drive lugs. ... Or, look at those drive lugs. If it's friction preventing prop rotation on the flange, why do they bother to do the extra machining on the flange, make 6 extra parts (and weight), and counter-bore the prop bolt holes to accept these extra parts? Because the engine flange manufacturer has no idea whether you're going to use a metal or wooden prop - this way, you can use either one. If the lugs weren't there, you could ONLY use a wood prop. The reason for the drive lugs is to provide a machined precision fit to the counter-bores in the prop, and to provide a larger 'working surface' in the wood to take the load. Nope. For metal, you're correct. But for wood, it's the friction. On the wooden props, the conterbores are there because the drive lugs are there, but not to take the loads. ... You can see the same thing in the spar attach points of highly stressed wood wings, where there are metal bushings for the attach bolts. Wing attach points tend not to take huge torque/force pulses that are substantially larger than the average load that the bearing surface needs to withstand. It's not an appropriate analogy. -- Marc J. Zeitlin http://www.cozybuilders.org/ Copyright (c) 2008 http://www.mdzeitlin.com/Marc/ |
#6
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Wooden Prop Drive Methodology - was: Pills & Propellers
On Nov 22, 2:08*pm, "Marc J. Zeitlin"
wrote: ... for wood, it's the friction. On the wooden props, the conterbores are there because the drive lugs are there, but not to take the loads. ---------------------------------------------------------------------------------------------------- The late John Thorpe said much the same with regard to using wooden props on the GPU that powered one of his last designs (the 'Tiger'?) Even more surprising was the torque specs for wooden props. As I recall it was on the order of 14 lb-ft. Of course, the best joke is the claims made by 'experts' selling prop hubs with drive lugs :-) -R.S.Hoover |
#8
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Wooden Prop Drive Methodology - was: Pills & Propellers
On Sat, 22 Nov 2008 14:08:15 -0800, "Marc J. Zeitlin"
wrote: Charlie wrote: ... They are called 'drive lugs'. They are called drive lugs because they are what drives the prop. With metal props, you're absolutely correct. However, with wooden props, it is in fact the friction of the face of the prop hub on the mounting flange that drives the propeller. The wood is not strong enough to withstand the torque pulses (especially in the larger engines) if only the small area in the drive lug holes was taking the force. a few years ago a friend just out of the shakedown flight for his quickie Q200 flew from Orange to a flyin that I attended. when he landed he was quizzing the other fliers from his area about the bushfires. what bushfires the other guys asked? I could smell bushfires all the way down here but we couldnt see where the hell any of them were. one of the wags asked "y' gotta wooden prop?" "yeah" "y' betta check y' prop mate" so we all went over, found a screwdriver, and removed spinner, pulled off the lockwire and took the prop off. the back of the bearing surface of the prop was charred to a depth of about an eighth of an inch. the bushfire was quietly developing in the spinner. my mate was horrified because he had retorqued the prop nuts the night before making the flight. the prop was one made for a certain manufacturer in bundaberg and was from Queensland Hoop Pine. QHP imho doesnt have the crush strength needed at the hub. I'm told that none of their props ever succeeds in service much longer than 300 hours.they all lack the crush strength. 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. btw bob your specialists are schmiked up guys. they have long beaten the survival estimates given in my old medical texts. looks like they are going to succeed. Stealth Pilot |
#9
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Wooden Prop Drive Methodology - was: Pills & Propellers
Epoxy "saturation" is a very misleading term.
Even water thin viscosities like GetRot don't penetrate more than a couple of millimeters into healthy wood. Where is will penetrate is rotted out pulpy wood. Or end grain balsa. |
#10
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Wooden Prop Drive Methodology - was: Pills & Propellers
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 |
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