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Old 10-19-2011, 03:19 PM   #81
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RE: Windlass, not a clue!!!

A jackshaft, also called a countershaft, is a common mechanical design component used to transfer or synchronize rotational force in a machine. A jackshaft is often just a short stub with supporting bearings on the ends and two pulleys, gears, or cranks attached to it.
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Old 10-19-2011, 03:43 PM   #82
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RE: Windlass, not a clue!!!

Wow!! More information than I needed. But now I know.

Thanks mark.

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Old 10-19-2011, 03:51 PM   #83
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RE: Windlass, not a clue!!!

Quote:
Willy wrote:
I have seen the use of jack shaft systems on some of Bill Gardens boats. There is one of them vessels here for sale.
*The use of cardan shaft drives has become a common solution for a lot of engine placement and drive "problems." They offer a lot of versatility and provide for soft mounting of engines to reduce vibration and noise as well as providing relatively simple alignment.

Tractor tugs (Z-drives) use them and more large yachts use them to allow better use of the mid body space that would otherwise be filled with machinery. Some of them are based on carbon fiber shafts and save a lot of weight in addition to their other benefits.

There are no additional gears associated with a cardan shaft drive, all it does is allow the gearbox to be mounted someplace away from the engine. A ten or twenty foot section of carbon fiber tube is far less weight than an equal length of propeller shaft, it absorbs torsional vibrations and it doesn't have transmit the same torque.

In the P-39 all it did was separate the reduction gear from the engine, there were no additional gears or complications. It was done that way because it allowed the engine to fill the fat part of the fuselage and provided room for the gearbox and cannon while reducing form drag.
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Old 10-19-2011, 06:28 PM   #84
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RE: Windlass, not a clue!!!

Quote:
RickB wrote:
In the P-39 all it did was separate the reduction gear from the engine, there were no additional gears or complications. It was done that way because it allowed the engine to fill the fat part of the fuselage and provided room for the gearbox and cannon while reducing form drag.
*The drive shaft of the P-39's engine (located behind the cockpit) was connected to a lower shaft running below the cockpit which in turn connected to a higher shaft connected to the propeller.** Gears were used to transfer power among the shafts.* *The engine's location*made room in the nose for heavy armanent (heavy machine guns and cannon) and provided for*a tricycle landing gear,*and made the plane highly maneuverable, but the rear engine required the pilot to work harder because the plane wasn't very stable, and the engine was exposed to enemy fire from the rear.
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Old 10-19-2011, 06:58 PM   #85
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Windlass, not a clue!!!

I've been in a P-39 a number of years ago that was being restored at the Planes of Fame Museum in Chino, CA. The driveshaft of the P-39 came straight out of the engine, ran forward under the pilot's seat to the nose where the power was stepped up via a simple gearbox to the short, hollow driveshaft of the propeller. There was no step-down gear train from the engine to the driveshaft The driveshaft from the engine to the propeller gearbox was in two sections with a coupler midway along to allow the driveline to accomdate the flexing of the fuselage.

The Oldsmobile T9 37mm cannon and two .50 machine guns occupied the entire nose of the plane. The cannon barrel projected through the hollow propeller driveshaft and hub. If additional machine guns were needed, they were mounted in pods carried underneath the plane's very thin wings.

The P-39 suffered from the lack of a good engine at altitude. The supercharger on the Allison V-12 was not all that great so the perormance of the plane fell off greatly with altitude. On the other hand, the driveshaft from the engine forced a higher placement of the pilot which gave him terrific visibilty. The Russians used the P-39 with great success as a ground attack plane.

The P-39 was so pitch and CG sensitive due to the engine placement that the 37mm cannon could not eject its shells overboard as it fired--- this would gradually shift the CG too far aft.* So the shell casings were retained in the magazine after firing. One of Bell's test pilots during the war was Tex Johnson, the man who famously rolled the Boeing Dash-80 over Seafair in Seattle.* I got to know Tex quite well in the early 1990s as I was contemplating writing a book in which a P-39 would play a major role and he agreed to tell me anything I wanted to know about the plane.* Tex told me a lot of great stories about the P-39 and flying it, including the fact that if you wanted to go fly one without live ammunition in the cannon magazine you had to load special dummy rounds that weighed the same as live ones.* If you didn't, the plane could kill you because the CG would be so much out of limits aft.

The Germans did something somewhat similar with their Bf-109. The design specification called for a cannon to carried in the nose firing through the propeller hub. In order to accomodate this, Daimler-Benz developed an inverted V-12 engine which mounted low in the nose. This is why the exhausts come out near the bottom of the cowl. A simple gearbox on the front of the engine carried the engine crankshaft rotation up to the hollow propeller shaft and hub, similar to what was done in the P-39. The cannon "lay" on top of the flat bottom of the engine and occupied the upper portion of the nose. The cannon barrel, like the P-39's, extended out through the hollow prop shaft and hub.


-- Edited by Marin on Wednesday 19th of October 2011 07:08:02 PM
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Old 10-19-2011, 07:08 PM   #86
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RE: Windlass, not a clue!!!

You're right, Marin, there were only two shafts.

"... The solution adopted was to mount the cannon in the forward fuselage and the engine in the center fuselage, directly behind the pilot's seat. The tractor propeller was driven via a 10-foot-long (3.0 m) drive shaft which was made in two sections, incorporating a self-aligning bearing to accommodate fuselage deflection during violent maneuvers. This shaft ran through a tunnel in the cockpit floor and was connected to a gearbox in the nose of the fuselage which, in turn, drove the three- or (later) four-bladed propeller via a short central shaft. The gearbox was provided with its own lubrication system, separate from the engine; in later versions of the Airacobra the gearbox was provided with some armor protection. ..."
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Old 10-19-2011, 07:22 PM   #87
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RE: Windlass, not a clue!!!

Eric, I have the 8-plait brait spliced to my anchor chain. It flows through my lesser windlass (Lewmar) with ease. I ordered mine already spliced to the chain from Defender.

Here's a link showing how to splice it.
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Old 10-19-2011, 07:24 PM   #88
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RE: Windlass, not a clue!!!

"In the P-39 all it did was separate the reduction gear from the engine, there were no additional gears or complications."

What part of that is so difficult to understand? Instead of mounting the red gear to the engine it was mounted separately and connected by an extended shaft. There were no additional gears. Allison (now RR) used the same technique on the T-56 turboprop used on the P-3 and on C-130s with a shorter shaft to connect the engine to the gearbox.

"the rear engine required the pilot to work harder because the plane wasn't very stable"

Stability and maneuverability are two opposing values. The latest in fighter designs are impossible for a human to fly without a computer interface because they are so unstable ... and that is what makes them so incredibly effective. Boeing likes stability (to a point) but General Dynamics and Sukhoi happily trade that for maneuverability.
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Old 10-19-2011, 07:41 PM   #89
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RE: Windlass, not a clue!!!

Quote:
markpierce wrote:
You're right, Marin, there were only two shafts.
It seems that you need a drawing or a picture. P-39 did not use an additional shaft or gearing. The 10 foot long shaft simply replaced Item #4 in the drawing. It allowed the designer to separate the engine and the reduction gear.

There were no extra shafts or gears used. The propeller shaft that you see is the same one that is used in the close coupled versions.
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Old 10-19-2011, 07:51 PM   #90
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RE: Windlass, not a clue!!!

I used the wrong term in describing the propeller end of the P-39's drive train. I said "short, hollow propeller driveshaft" or something like that. But as Rick's illustration shows there isn't a "driveshaft" turning the prop, it's attached to the output shaft of the reduction gearbox. I had the right layout, but used the wrong term.
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Old 10-19-2011, 07:54 PM   #91
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RE: Windlass, not a clue!!!

My memory failed me.

*

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Old 10-19-2011, 08:24 PM   #92
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RE: Windlass, not a clue!!!

Quote:
Marin wrote:
I used the wrong term in describing the propeller end of the P-39's drive train. I said "short, hollow propeller driveshaft" or something like that.
*No, you had it right, the prop shaft was hollow to accomodate the cannon barrel.

The picture below shows the prop hub as it mounts to the hollow prop drive shaft. If you look closely at the reard of the reduction gear box in the other photos you can see where the barrel fits through the aft end of the shaft.

I always had a soft spot for the P-39, the CAF had one in San Marco Texas way back when and I used to fly up there from Houston to hang out while the guys worked on restoring it.

*
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Old 10-19-2011, 08:51 PM   #93
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Windlass, not a clue!!!

Looking at these illustrations it continues to amaze me that people can not only design, but build things like this. I've been at Boeing for a long, long time. I've shot in our fabrication plants where huge slabs of aluminum come in on special freight cars and are machined down into wing skins. The mill beds are a hundred feet long and the aluminum slabs weigh Lord knows how many tons. Yet they still require vacuum to hold the aluminum flat and keep it from shifting. And on and on and on.

When you go to an airport there will almost always be someone who looks at the 747 or 777 or Airbus out the window and says, "I can't believe something that big can fly." I have no problem with that whatsoever. They fly for the same reason the little Cessna or Beaver that I fly flies. What I can't believe, even after decades in the business and watching us do it, is that anyone can build one.

I find it amazing that people not only designed but could fabricate out of raw metal something as "simple" as the Ford diesels in our boat. Wood I can sort of understand. But metal? Amazing to me.


-- Edited by Marin on Wednesday 19th of October 2011 08:53:42 PM
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Old 10-20-2011, 04:30 AM   #94
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RE: Windlass, not a clue!!!

IF you have ever anchored in tight places such as Block Island you will see the advantage of all chain

Visiting Block, we simply use a Bahimian moore , two anchors fore and aft , lead to the bow , and stay in place and watch the crowd .

This way we can anchor in the shallower water , where the locals have grabbed all the space to charge for moorings .

Much easier to avoid a moored boat than an imbecile with 300 ft of line out.
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Old 10-20-2011, 01:48 PM   #95
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RE: Windlass, not a clue!!!

Quote:
Marin wrote:
Looking at these illustrations it continues to amaze me that people can not only design, but build things like this.

I have the same feeling about 17th/18th century sailing ships.* The amount of organization and coordination that went into building, sailing and fighting these incredibly complex machines is mind boggling.* And they pulled this off hundreds of times, 250 - 400 years ago.

And we can't seem to even get a damn road resurfaced around here without it being a 10 year project!
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Old 10-20-2011, 11:44 PM   #96
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RE: Windlass, not a clue!!!

Thanks for the link Fly Right. The "imbecile" you speak of Fred is probably just trying to do a good job of anchoring. I anchored once in 85' of water just to get away form too many boats anchored in too small of a place. But you're right. Chain rodes do help a lot in places where there is too many boats and not enough room. But when the wind starts blow'in hard big heavy anchors drag w the best of them especially on short scope. But if it's good weather you can pack a lot of chain rode boats into a small anchorage. And the heavy chain will have lots of catenary (lightly loaded) and tend to help a low performance anchor perform fairly well. I anchored last night in a strange place and my XYZ didn't set right away as it has been doing so I was disappointed but this morning when I pulled it up I was a bit shocked as I could'nt see the anchor for all the weed. The stuff was like Scotch Bright. No wonder the anchor was having trouble setting. I backed down at 2000rpm and finally got it set and what I probably should have done was to pull it up to see if I could determine why it was'nt setting. Did'nt think of mass weed. As to using two anchors (I've been tempted) how does one do that without launching a dinghy? Looks to me like it would take 3 people.*

As to the sensitive CG on airplanes on my first ultralight (a flying wing biplane) the CG was so sensitive I could gain at least 5mph trim speed (probably more) by changing from sneakers to hiking boots while flying. But by saying a vehicle is sensitive to control is also saying that it is more controllable, IF indeed you have the means to control it. I flew ultralights that were like barges compared to the Biplane and I could do things w the biplane that just could'nt be done w the more stable machine so it was actually safer in many ways. By the way this may have nothing to do w the fact that my ultra controllable ultralight was a biplane. I'd say sensitive to control is more desirable than slow to respond but a good balance of sensitivity and controllability is no doubt best.
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Old 10-21-2011, 12:12 AM   #97
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RE: Windlass, not a clue!!!

Quote:
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As to using two anchors (I've been tempted) how does one do that without launching a dinghy?
*Well, you can do it but it might be*almost as much trouble as launching a dinghy.* We've never done but I've watched a boat do it.* What they did was deploy the stern anchor, pull forward and set it and continue moving forward until they were over where they wanted the bow anchor to be.* (So you need plenty of rode for the stern anchor.).*

They then deployed the bow anchor and drifted back paying out rode while at the same time a person on the stern took in the stern anchor rode as the boat drifted down on it.* When they got to where they wanted to be they set the bow anchor with a shot of reverse and once the boat had moved forward after setting the anchor (all-chain rode so the catenary pulled the boat back forward a bit), they tightened up the stern rode and that was that.

And you're correct, it took three people to do this, helm, bow, and stern.

We use a Fortress sized to be the main anchor for the boat as our stern anchor.* We carry it in a mount on the swim step and the rode is kept in a large plastic*milk crate on the aft deck that my wife made a Sunbrella*cover for.**The dinghy is easy to deploy*(Weaver davits and the boom fall make this a real quick task) and since the Fortress is so light it's easy to lift off its mount, put in the dinghy, and then put it over the side of the dinghy where we want it.* We have some*35 feet of chain on the Fortress and about 250' of nylon line.* The chain and line are sized to be the main rode for the boat as well.
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Old 10-21-2011, 12:44 AM   #98
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Windlass, not a clue!!!

Are we talking about two anchors forward of the bow, or an anchor off the bow and another off the stern?* If we're talkin' bow and stern, without a dinghy, at least one rode should be substantially longer than the other if one wants to limit the maximum combined lengths.* (Drop an anchor, move away and set anchor, drop the other anchor, move away and set that anchor ending up with both rodes will adequate scope.)


-- Edited by markpierce on Friday 21st of October 2011 12:52:52 AM
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Old 10-21-2011, 10:33 AM   #99
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RE: Windlass, not a clue!!!

Mark.

Marin said about his stern anchor "we carry it in a mount on the swim step" and "(so you'd need plenty of rode for the stern anchor". Bout covers it as I see it. You must be one of those speed and crash readers.

Marin,

That's exactly as I see it. So being by myself night before last I was quite sure I'd get the stern rode around my prop shaft and have a devil of a time w my propwalk. Here is another place where twin engines would be better. The only fairly good anchorage was plenty long enough but very narrow. Recommended to me by a fisherman*. Anchoring fore and aft has a terrible downside in a cross wind as tension on the rodes would become strong enough to drag most any anchor, especially one full of weeds. And the boat would not only become part of the rode it would be broadside to cross winds. I anchored in another narrow anchorage (Lyman Anchorage) and even with a slight change in wind direction we were 50' from the beach half the night. Don't ask me how I know. So I'm not a fan of fore and aft anchoring. That leaves me w few options all including a considerable amount of chain. It's beginning to look like I may need lots of chain whether I like it or not. And I don't. Using a combination rode w a splice, all chain or a heavy combination rode and a reel winch seem to be my only options. I'm resistant to using all chain for reasons talked about at length in the past. I do like the simplicity and convenience of all chain so I'm thinking the weight penalty may be worth the extra weight on the bow. But the reel winch would be better performing (especially at short scope) and I could keep my rode on deck where I want it and nobody could say it may be a problem pulling the boat up to the anchor. Still a bit iffy on the splice. Convenient like all chain but w the chain weight where it belongs and perhaps the option of using the next size up rode w the chain weight savings. Right now I think I'll look into the weight of a new reel winch and see if it could be worth it to buy a new one v/s rebuilding my old monster reel. Here is a pic of one of the other Willard's on the island w a reel winch.*
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Old 10-21-2011, 12:25 PM   #100
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Windlass, not a clue!!!

Quote:
nomadwilly wrote:
*As to using two anchors (I've been tempted) how does one do that without launching a dinghy? Looks to me like it would take 3 people.*
*
<h3>When simple's not enough</h3>


In more challenging situations, it is good to understand how your boat can move when Bahamian moored; it is also important to understand the direction and magnitude of the loads on the anchor system.

You can see in the illustration that in a single anchor mooring the boat is free to move within a circle with a radius roughly equal to the length of rode that is out (ignoring scope and three-dimensional considerations for simplicity).

With a single anchor, it is necessary to make sure that, if your boat swings toward shore, you will have enough depth. This requires anchoring farther off to allow for the swing. Even so, there is always some guesswork in making this allowance, and sometimes it would be nice to go closer to shore.
<h3>Closer to the shore</h3>
Note in the illustration that with a Bahamian moor, the boat is only free to move within the common zone of the intersection of the two circles. With this arrangement, when you drop the first anchor up against the windward shore, you are as close to shore as you are going to get. The anchor to leeward will not allow you to get any closer. Knowing this allows you the option of going in closer to shore when there is an advantage to doing so. Considering the example above of anchoring in 14 to 16 feet of water and letting out 100 feet of rode, if you choose, you could anchor in 7 feet of water and let out 50 feet of rode (vessel draft and tide permitting).

*Chapmans has a better view of a Bahamian moor.

Drop your first anchor and drive to where you want the second anchor paying out rode as you go. Let it go then back off to give scope. You can sit in the middle of two anchors or let it Y. The Y will give you more swing.

SD

*


-- Edited by skipperdude on Friday 21st of October 2011 12:30:03 PM
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