h a l f b a k e r yA few slices short of a loaf.
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Yes, it would be completely stupid to try this without a comfortable handle ... |
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The idea title should support an after-market kit of brackets
and/or prepositions, so that keen hobbyists can retro-fit meaning. |
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The flutering leaps between meaning fragments are too far. Doesn't stay airborne, in my mind at least. |
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This is basically a D'agneaux-Brise device, is it not? |
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It's more like an early Flettner design, built on the original work by Whitehead and Brotherhood. Given its derivation, it should really be classified as a Jus d'Escargot-volant mechanism. |
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I think you'll find he dropped the acute accent when he moved to the US. |
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Yes, but that was much later. In the citation for the Jakobsen
Medal that they won for their original published paper, it's spelt
with an acute e, as it is in the paper itself. |
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It was probably just a matter of accepting the inevitable,
because most American typewriters can't imprint accented
vowels. |
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But back to the point. What really worries me about [JHC]'s proposal is the Q coefficient. I think that, as designed, this thing is going to suffer from a wicked ballistic shimmy, or else just go into cyclic inversion. |
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Modern electronics and software could probably overcome the tendency to cyclic inversion by the same sort of fast closed-loop feedback used on negatively-stable fighter aircraft designs. Simple directly-linked 4-axis controls would never be able to do that. |
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But the Q value is the problem. You need high Q to get the thing to work, but then there will be a whole range of harmonic resonance points and if it dwells at a resonance point, the reflected power into the drive system will cause it to blow up ... but if the Q is low enough (or the system is damped to prevent resonance) then you have to feed in extraordinary amounts of energy to get it to work, which means a much bigger drive system, forced cooling, which means more weight ... |
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It's an attractive idea on paper, but it won't make it off the lab bench in the near future. |
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Program the thing to not dwell at the resonance points.
Include some gear ratios that keep the motor below resonance
and the output of the transmission above it. |
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GM did something like this in the 60's, but then they scrapped
it because the controls back then weren't quick or fine enough
to prevent it from going bang. |
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He could always use a Spandrell arm. If it's the right mass and length, it would suppress the major modes without overdamping. It's not ideal, but it would be almost as good as having a decent Q, at least in level flight. Lots of people pooh-pooh Spandrell arms, but they were an effective low-tech solution to a high-tech problem. |
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// Include some gear ratios that keep the motor below resonance and the output of the transmission above it. // |
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Ideally yes, but the loss of drive during gearshifts (even with an electronically-controlled clutch) would be a real problem. The answer is a CVT, but finding one that isn't too bulky and heavy, and can handle the power and (especially) the huge starting torque, is the obstacle to that approach. You could use a conventional torque converter with daisy-chained epicyclics, but cooling is still going to be a massive issue. |
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// He could always use a Spandrell arm. // |
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Using titanium, or carbon-fibre composites, you could certainly make a long-moment Spandrell arm light enough while being both strong and stiff: but the bearings would be a problem. The inboard end is easy, but how do you get the lubrication to the outboard end ? You need flow and return lines, remember. |
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If you had a dynamic damper pivoted at a point halfway along and attached to the main chassis, you could probably get round the flutter problem, but wouldn't that tend to limit the free travel too much ? And then there'd be an extra bearing to lubricate ... |
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You're overthinking, [8th]. Just make the outboard bearing a service component and skip the lubrication. And I'm pretty sure dynamic dampers are impractical for smaller craft - just remember the Little Bee. |
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That was a specialised racer, very nearly a one-off ... not a mainstream design. True, it's difficult to implement at a small scale. |
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As to the lubrication, yes, if you're happy with short service intervals, it would work. But that limits it to specialised applications, like the Wankel engine - high power, compact, but maintenance-heavy. |
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Why not just do away with the outboard bearing altogether then, and make the joint rigid, like the Lippisch design ? If you've got fast closed-loop control, then the compression limit that scuppered the pre-war Volkswagen add-on would be completely avoidable, for a very small weight penalty. |
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Well, the arc-cage bearings and the Wyvell cam (I assume he's using one) will need overhauling every 60-80 hours anyway, and the Spandrell arm bearings should be good for that, so it can all be done at the same time. |
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You'd need a system for service-exchanging and remanufactuing components, otherwise the cost would be exorbitant. |
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No no no. The Spandrell arms are only operating in one plane, so you can use cheap-n-cheerful bearings. You're probably thinking of 2-axis Spandrells (which, technically speaking, are Griffiths arms anyway). Do try to keep up. |
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Yes, but doesn't that mean that you'll need double cone needle-roller thrust bearings ? |
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Would you specify an E-section or an H-section ? The H-section would give better torsional resistance, but the E-section would give superior lateral stiffness ... |
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With light enough materials, you could actually go back to the original C-section of the Lutterworth design, but that would tend to limit clearance at the lower end of the travel, which is where you need it most. |
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Given the other limitations of the design, I'd probably go for a 3ft length of bamboo with a brick tied to one end and be done with it. |
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That would work nicely ... but remember the R101 ... |
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R101: wrong type of bamboo. |
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<backs slowly out of the room> |
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With a CVT there's no avoiding the resonance points,
unfortunately. A conventional step-transmission is the only
way around them. I recommend the Getrag 238, but easy
on the synchronizers--they were cheapened out in the early
2000's, so an early model is better. |
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Personally I wish that whatever butterfly keeps beating its
wings and sending storms this direction would kindly stop
for awhile. |
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Dragonflies. Swarms of captive-bred hungry predatory giant dragonflies is what you need.
Has it occured to you that the butterflies might be in the pay of some secret organization that's bribing them with nectar to make bigger hurricanes, for their own sinister ends ? |
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// With a CVT there's no avoiding the resonance points, unfortunately. A conventional step-transmission is the only way around them. // |
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A "dumb" CVT would have that problem, certainly. But if both the powerplant and the CVT ratio are managed by a common control system, then the drive can be "hopped" past the nodes. |
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// I recommend the Getrag 238, but easy on the synchronizers--they were cheapened out in the early 2000's, so an early model is better. // |
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It's a nice unit, certainly, and handling the load wouldn't be a problem. The mountings could be difficult - unless you adopt BMW's solution of an aluminium torque tube ? That would allow a lighter frame, but would't stop the quarter-shafts winding up. |
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Going back to the R-101, they used a tensioned cable fixed to the prop spinner to transmit the thrust back to the frame. Rather than a fixed support, if the out board end of the torque tube was attached by tensioned cables attached to the bamboo cross-members (using Bouch's gib-and-cotter tensioning slides, as on the Tay Bridge) then you wouldn't need the whalebone bracing struts. |
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//A "dumb" CVT would have that problem, certainly. But if
both the powerplant and the CVT ratio are managed by a
common control system, then the drive can be "hopped" past
the nodes.// |
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But not without a critical temporary dropout in power. In a
flying machine, that's probably important. |
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What was the goal weight again? |
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//a tensioned cable fixed to the prop spinner to transmit the thrust back to the frame// |
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Yes, that was just one of many engineering idiocys. It's what happens when you let a government design an airship. The privately-built, competing R100 was more or less perfect from day 1. |
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Well, of course - they had Neville Shute Norway, and Barnes Wallis - how could they fail ? The concept of putting half a brick at each end of the bamboo was pure genius. |
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That whole coal bag experience seems to have done the two of
you a power of good; kudos to [xenzag] for suggesting it.
Perhaps you could market it as a sort of exclusive executive
retreat. I'm picturing a broad expanse of movers and shakers, all
neatly bagged up, doing a lot of muffled networking. Come
Monday morning, the knowing looks and a faint smell of Marmite
betray them. |
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Sturton will be coming for you, [pert], as soon as he's finished with [xen]. |
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Will he be bringing the requisite petroleum jelly? |
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Oh yes. For his birthday, he got a 20 litre backpack tank with a 2-
stroke
motor and a long-reach nozzle on a flexible hose. |
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Be afraid. Be very afraid ... |
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Akshully, I'll have you know, he only uses Rentishams. |
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Nonsense. Nobody actually uses Rentisham's, at
least nowadays. Those that tell you that they've
used it are simply peddling fake news. People have
been rumored to use it, but when pressed for proof
they dance around like water-dowsing, fluoride-free
sasquatches. |
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No, he really does. He steals it by the case from the warehouse, on his "quality inspection" visits. We've seen him do it. How many people do you know who who carry a fold-out sack truck in their attaché case ? The trip to the hydraulic fluid plant was unbelievably embarrassing. |
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You won't catch the Buchanan family paying for anything, when they can get it by any other means whatsoever. The way [Max]'s niece pays her taxi fares is, quite frankly, nauseating. |
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There are some who appreciate yodelling, [8th]. |
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That is absolutely true (link). |
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And my dad did, as well. Those who say that was the cause of his demise do not know the full story. |
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More people have yodelled in the course of dying than have died in the course of yodelling. |
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//Sturton will be coming// |
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I shall be sure to dust off the second-best tea things and
straighten the garden path. |
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