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Old May 19, 2012, 09:32 AM
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United States, MD, Elkton
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Originally Posted by AndyKunz View Post
You know, I giant rubber-style prop spinning at 300 RPM would have been a neat touch on this.

Andy
It has crossed my mind to put a windmilling 30" prop on her,mounted on bearings with the drive prop through the center.At least ,when she's inactive.

As a joke I asked for 75'of 1/2" tan rubber....I would have flown it once with a hand carved prop.

I've also considered a dummy folded prop fastened to the fuse,full time.
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Old May 20, 2012, 06:07 PM
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United States, MD, Elkton
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No shaft center bearing?

Well it was certainly enlightening,was my trip to the marine store.The world has changed.
While we were living in the past,racing engineers have discovered"European cable shafts"....What a concept! There is an adjustable collet on the engine and prop,with a flexible 1/4" dia.Stainless steel cable(shaft)connecting the two.Any alignment woes are moot,now,with only an anti-whip support,which can be a simple lubricated tube.
Bazinga!
It's the same style shaft used in countless string trimmers world wide.All curved-shaft weed whackers utilise the same technology.,with gas engines up to around 25cc.
If I put that on my .91 4 cyc.,it'll be overkill.Let's overkill it.Alignment now consists of bolting the engine and prop drive in place,in boats, and airplane,(in my case )
The cable collet is threaded to screw onto existing crankshafts,which solves one end of the system.The opposite end will need to be custom made for my requirements as originally thought..
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Old May 21, 2012, 09:02 AM
AndyKunz's Avatar
Illinois
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That's funny, we've been using cables for decades for boat racing. A big step up (lower drag, lower cost, lower maintenance) is flexible piano wire drives, which we've been using for probably 15 years. They don't allow as much curve as a cable, but that's a minor trade-off considering all the benefits.

Andy
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Old May 21, 2012, 09:55 AM
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Originally Posted by AndyKunz View Post
That's funny, we've been using cables for decades for boat racing. A big step up (lower drag, lower cost, lower maintenance) is flexible piano wire drives, which we've been using for probably 15 years. They don't allow as much curve as a cable, but that's a minor trade-off considering all the benefits.

Andy
That's great-I meant it was new to me-my last boat was powered by a K&B .40 outboard,many,many years ago.
My main concern on the mid engine Sparky was side loading the bearings....the cable all but eliminates that.
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Old May 21, 2012, 01:05 PM
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Illinois
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Your K&B had a cable in it.

The best sources for cable and couplers would be from Octura. They likely have a collet that is already threaded to fit your engine. Their couplers are really good. You don't want one with a set-screw to lock the cable in, if you can at all avoid it. It's really hard to get one that stays centered that way.

Cable comes in different sizes, too. Make sure you get the correct lay - it comes in both left and right. Since you're spinning the engine in the standard direction this shouldn't be an issue, but if you buy from somebody other than a boat vendor you might run into issues.

Starting will become an issue, unless you have something like a marine flywheel on the engine. You don't want to try starting by flipping the prop (or with a starter) because that will unwind the cable, which will kill it in short order. I suggest you run the cable in a tubing (brass is good, it lubricates well). If it should fail without a tube, it will flail inside the model and destroy things.

Andy
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Old May 21, 2012, 01:21 PM
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You're a wealth of valuable information,and you answer my questions before I ask them.....I had thought a pulley on the engine and a boat belt hanging out the bottom of the fuse would be satisfactory....There's going to be a cooling air outlet near the engine anyway.I could tuck the belt in there till I needed it.
The bolt on collet and a lock nut seem advisable for the engine.
Checking Octura now.Thanks.
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Old May 21, 2012, 05:18 PM
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Illinois
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The belts are often found in heli departments, too. I'm pretty sure you can get one from Octura.

Octura can be rather interesting to buy from. They sell direct, but don't have a website. You have to have a brick-and-mortar hobby shop to stock their products, but several of these guys sell online too. If you need help hooking up, let me know, I have friends that retail and some that even stock Octura products.

Andy
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Old May 21, 2012, 06:53 PM
Fly fast, turn left
Joined May 2012
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First question is, how are you going to lubricate the forward bearing? In the engine, it lubed by the fuel.

Then, for those that don't remember,(No, ii ain't that old either) Sparky was designed by Ed Lidgard as an entry into the Wakefield competition, was a winner, and Comet picked it up some time later, probably after WWII. Lidgard had, either a single wheel retracting landing gear or no gear, not sure what the rules called for then, it might have required ROG. Nice work though, craftsman.

Cheers.
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Old May 21, 2012, 08:40 PM
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lube

The front crankcase is surrounded by two schools of thought...My idea is to just make a plate to cover the severed cylinder,and a couple of plugs in various other holes.Filling the front case partially with light oil will do the trick.
The second school of thought is to just squirt the bearings before we fly,and they'll be adequately lubed for the day,most likely.
New ideas keep my head spinning,but man I like the flex shaft better.
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Old May 31, 2012, 02:43 PM
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Wood 'n wheels

RCRobby alerted me today,he has the scaled up wheels turned for me..He'll ship them soon,and they'll be a welcome addition to the Sparky.
5-1/2" wheels,scaled from the original Comet ones...How cool !
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Old Jun 03, 2012, 08:54 PM
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Suddenly,there's a plethora of builds, constructed of open frame work! The Sparky is designed from a scaled up rubber powered free flight,brought to life in the 40's.
Most of the smaller models didn't need the myriad of diagonals I'm using,but I fly in windy conditions at times,and I want the extra safety margin.

I delivered a contract airplane today,so I'll get back to the stabilizer building soon

The laminations are finished,for the elevators,so it's on to finishing the stab.

The machined wooden wheels will be here in a couple of days-anticipating that part of the assembly..
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Old Jun 04, 2012, 07:53 AM
Laser Cutter Guy
United States, PA, Greensburg
Joined Oct 2009
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Quote:
Originally Posted by epoxyearl View Post
Suddenly,there's a plethora of builds, constructed of open frame work! The Sparky is designed from a scaled up rubber powered free flight,brought to life in the 40's.
Most of the smaller models didn't need the myriad of diagonals I'm using,but I fly in windy conditions at times,and I want the extra safety margin.

I delivered a contract airplane today,so I'll get back to the stabilizer building soon

The laminations are finished,for the elevators,so it's on to finishing the stab.

The machined wooden wheels will be here in a couple of days-anticipating that part of the assembly..
Here is a link to my stick build. I hope to finish it within the next 5 years, lol. It's a long read but some good pics are in there.
http://www.flyinggiants.com/forums/s...ad.php?t=56968
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Old Jun 04, 2012, 04:46 PM
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Wooden wonders

The wheels RCROBBY turned for me are here. We are blessed with some fine craftsmen in or hobby,and he's one of them.
My attempt to have someone locally manufacture them was dashed when he wanted $80 to make two 5-1/2 " wheels.!

RcRobby stepped up and offered to make them for 1/3 that! "I'm playing around with a CNC cutter- let me try".,it's my new toy."

If I had given him written instructions,he couldn't have do a more satisfactory job.

Remember,I'm doing this as if it were 1940,and most all parts were handmade then.(I know-no CNC then),but that "feel" is there! airplane,prop,wheels-all homemade.
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Old Jun 04, 2012, 08:38 PM
Laser Cutter Guy
United States, PA, Greensburg
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Thanks for the kind words Earl. I am glad you are happy with them.

A little background/plug about me..
I have had my CNC router for about 4 years now and wanted to try 3D toolpaths with it. This was a perfect subject for the task. I also have had my 36"x48" laser cutter for almost 2 years now. They are my favorite tools in the shop and help me support my hobby. I do CAD work for a living so it makes the hobby more fun. I also make parts for other kit Mfg.s and my own kits as well. I can do one off parts (like Earls wheels) or thousands of parts for production run.

http://kustomaerodesign.weebly.com/index.html

Shameless plug end..
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Old Jun 11, 2012, 09:40 AM
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United States, VA, Petersburg
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sub'd. Where do you go to get the old wood from restored planes.
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