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Old 15th March 2019, 10:21 PM   #41
PRR is offline PRR  United States
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Quote:
Originally Posted by traderbam View Post
What is a jackscrew?
When something has to move, not real far, not real fast, but must STAY when not being moved, a screw is a favorite device.

When you park your camper-trailer, the leg on the tongue has a jacking screw so you can level the camper for better cooking and sleeping.

To raise a house and hold it there, use a jack-screw.

Race-cars need to trim their wheel springs for height, also side-side and front-back for track force balance. Look in the rear window of a NASCAR 'stocker' and you can see the jack-screws.

Hydraulic cylinders are an alternate device. They can be made to move faster. They get awkward if you need HIGH force in small weight. And they don't "hold" well. The valves leak. A JCB/backhoe parked arm-up, the arm will drop in days. And the hoses burst, allowing sudden falls.

When aircraft got too big to man-handle the large control surfaces, some kind of boost was needed. Spruce Goose advanced this art, though I don't know if it was cylinders or screws. Jack-screws are an obvious choice for "trims" which are set rarely and must hold huge force. I believe aircraft flaps (extra wing area slid out for low speed) are routinely jack-screwed, it makes a neat simple and mostly reliable action. I'd bet that elevators etc are also jack-screwed.

A further after-the-crash feature of jackscrews is that they tend to hold their last setting even after great violence. Sometimes it is found that the screw was in the right position but the end-link had not been fastened properly so the flap was not where it was supposed to be; this suggests talking to the last few mechanics who worked in this area.
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Old 15th March 2019, 10:25 PM   #42
Cal Weldon is offline Cal Weldon  Canada
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Let's not head down the wrong road here.
PRR, this comment is not sent your direction.
We wish this issue to remain civil.
Uninformed comments and retaliation have no place in such a thread.
We appreciate your understanding and cooperation.

Last edited by Cal Weldon; 15th March 2019 at 10:31 PM. Reason: corrections
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Old 15th March 2019, 10:38 PM   #43
gpauk is offline gpauk  Scotland
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Quote:
Originally Posted by chrisb View Post
I think its been said that a modern jetliner is 40,000 (or more) parts flying in close formation.
I always heard that about Helicopters - definitely appropriate. That and the "jesus bolt" -- or jesus nut to some.... Jesus nut - Wikipedia
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Old 15th March 2019, 11:08 PM   #44
stvnharr is offline stvnharr  Australia
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Originally Posted by gpauk View Post
I always heard that about Helicopters - definitely appropriate. That and the "jesus bolt" -- or jesus nut to some.... Jesus nut - Wikipedia
If you have ever flown in helicopters regularly, as I once did, you know everything there is to know about the Jesus Nut.
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Old 15th March 2019, 11:19 PM   #45
traderbam is offline traderbam  Canada
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Wikipedia:
Quote:
If the Jesus pin were to fail in flight, the helicopter would detach from the rotor and the only thing left for the crew to do would be to "pray to Jesus."
Brilliant.
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Old 15th March 2019, 11:24 PM   #46
traderbam is offline traderbam  Canada
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Quote:
Originally Posted by PRR View Post
When something has to move, not real far, not real fast, but must STAY when not being moved, a screw is a favorite device.
Thanks for this and the very interesting application examples. I thought that was what it was. Being in Europe I am familiar with the term "worm drive" rather than "jackscrew". Archimedes drive is also very clear.
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Old 16th March 2019, 07:32 AM   #47
traderbam is offline traderbam  Canada
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Automated control system caused Ethiopia crash, flight data suggests
Quote:
Therefore, it appears that the various automatic control systems conspired to prevent the pilots from asserting direct control over the ailerons, elevators and rudder that keep the aircraft aloft and on course.
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Old 16th March 2019, 01:10 PM   #48
DF96 is offline DF96  England
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I always thought the Jesus bolt got its name from Colossians 1:17 'in him all things hold together' (NIV).
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Old 16th March 2019, 03:49 PM   #49
6L6 is online now 6L6  United States
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traderbam - With the exception of very rudimentary radar data, that article is 100% conjecture. Please read it again with a more critical eye, and you will see language use that shows it to all be guesswork, assumptions, hypothesizing, simulation, theory, presumption, and speculation -- with no factual data at all.


DF96 - Lol!! Being that a helicopter is "1000 moving parts loosely organized around an oil leak," I think that is precisely where that term is from!!

Last edited by 6L6; 16th March 2019 at 03:56 PM.
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Old 16th March 2019, 04:08 PM   #50
Mark Johnson is offline Mark Johnson  United States
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I often grab a window seat around the trailing edge of the wing. This lets me watch the jackscrews in action, which lower and raise the flaps for high-lift, high-drag, low speed flight. (Takeoff and landing). They're right there in the wing, undisguised, visible as plain as day. When you see them in action you'll suddenly notice the relatively loud and extremely distinctive noise the screw-motor makes when twisting the jackscrew. See it and hear it just a couple of times, and the sound becomes embedded in your memory forever after. Now even when you're way up front, in an aisle seat in First Class, swilling down Roederer champagne, and you hear that sound you'll immediately know the flaps are being lowered or raised.
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