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Old Aug 13, 2012, 06:04 PM
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carbondale il
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I pretty much have the plan drafted. Need to do the drive train detail and chose prop size. I'm seriously considering 8" props with a small 1" indentation built into the fuse on both sides to accommodate the inside nacelle props. The stab and fin/rudder are built up and I added 2" to the stab span. I've ordered the 8 sprockets and plastic chain I'll need for the drive train. They should arrive in a day or two or three. The sprockets are approximately 3/4" in diameter with a 1/8" hub. If I put in an opposing gear in the fuse I can make counter rotating props. I've been drawing on a roll of tracing paper, much cheaper than the pads and I just roll out what I need and cut. They come on differing widths, I'm using 12"

Kev
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Old Aug 13, 2012, 09:30 PM
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carbondale il
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Been working on the drive train now that I know the sprockets will be 3/4" in diameter. I'm planning on 3 degrees down thrust. The thing is I won't be able to change the down thrust once built in. The bottom run of the chain will run just under the bottom of the wing, there is no other way. I'm wondering about a lot of things. Would it help to make a small wind deflector in front of the chain? I discovered a company: Flying Hobby, which carries both 7" and 8" three bladed plastic props. I don't know if they have the right design in regards to pitch, camber and blade width. For the canopy and other clear openings I ordered from Guillow's. They offer a Liberator with a wing-span at 48" and you can buy replacement parts.

Kev
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Old Aug 14, 2012, 12:26 PM
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carbondale il
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Just checked the FAC rules. They state that the outline of the plane, if scale, may not be altered. I guess the indentation in the fuse to accommodate 7" or 8" propellers is out of the question. I did find the best 6" two bladed props at Shorty's Basement, online. They also carry 6" tri-blade balsa props but are currently out of stock. It appears adding polyhedral is okay.

Kev
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Old Aug 14, 2012, 03:38 PM
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Ajax, Ontario, Canada
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> "They state that the outline of the plane, if scale, may not be altered."
> " It appears adding polyhedral is okay."

Are not those statements contradictory?
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Old Aug 14, 2012, 08:23 PM
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carbondale il
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Applehoney, I don't know. Adding dihedral is stated as okay. Polyhedral isn't mentioned either way. Enlarging the stab is mentioned as okay.

Kev
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Old Aug 14, 2012, 08:35 PM
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carbondale il
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I'm having trouble designing a way to wind the motor from the rear. Securing the drive train at the nose is no problem - If I add a hook to the drive axle in front of the nose gear which lines up with the motor, I can use an aluminum tube which runs through the hook and into holes in the fuse sides, like a rear motor anchor. I want to use a bobbin and aluminum tube for the rear motor anchor. I can make slots at the fuse rear and slip the rear anchor into them from the rear. What's the technique for transferring a wound motor onto the anchor tube? I'm picturing myself trying to get the wound motor from the winder onto the anchor and having it slip out of my hand. I've got a picture now of how to incorporate a blast tube, winding and removing it, but I need help with this.

Kev
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Old Aug 14, 2012, 09:38 PM
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carbondale il
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I'm considering putting the drive sprockets in the more front part of the nacelles, rather than having the top chain inside the wing. With the sprockets placed where the bottom chain runs just under the front area of the wing on bottom, I'm thinking it will disturb the airflow under the wing in a bad way. Placed in the nacelle front area, both top and bottom chains will be exposed, but away from the wing. Maybe more drag this way but I'm bothered by placing them so close to the bottom of the LE area. I'm also thinking of running the chain, top and bottom, in a tube, some kind of small, light weight tube.

Kev
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Old Aug 15, 2012, 12:01 PM
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carbondale il
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It looks like the FAC rules are silent about using different propeller sizes. A dummy engine is allowed with a dummy prop. If I made the inside props dummy, with a three bladed scale look, and use 9 1/2" or 11" props on the outside my problem will be solved.

Kev
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Old Aug 15, 2012, 12:17 PM
B for Bruce
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The 'Wack, BC, Canada
Joined Oct 2002
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On the drive train;

Stick with the original plan of the upper side in the wing and lower return side of the chain under it. Don't worry about drag. It's a slow flying rubber model. Adding anything in an attempt to fair it in would be clunky, add needless weight and likely to produce more drag than it saves.

The other reason for keeping the drive back where you can hide one run in the wing is that the lower side won't be all that noticable except from below. But if you run the drive chains or cables external and in front of the wing it'll look like hell out there. So use the wing to hide the one run inside and the other by being quite close to the lower surface.

Adding dihedral is OK. But you want to keep any added dihedral in character with the original. The B24 did not have any outboard dihedral breaks in the wings. So the last thing you want to do is put any in. Instead just add a couple of extra degrees of dihedral at the root and call it good. Otherwise you'll totally change the look and feel of the model and your scale points will plummet. It is a "scale" event you're building for after all.

You didn't like or didn't understand my idea for how to wind the motor? Plug in nose and tail ends. The motor anchors in the removeable tail "turret" plug that fits into the fuselage just like a removable nose block. The anchor tube holds the rear motor bobbin in the tail plug. The nose plug comes off along with the transfer gearing. So winding would go like this;
  1. Anchor model in stooge with rod through rear plug motor tube.
  2. Remove nose plug/gear box and let front motor "Crockett hook" or similar front fitting hang out. This "Crockett hook" is something used by many high performance rubber models where the props are removed to allow using blast tubes or some other motor winding arrangement needed to avoid model damage in the event of a blown motor.
  3. Hook up winder and winding rod. The winding rod is a long rod or small diameter tube that is longer than the fuselage by about 6 to 8 inches.
  4. Slide the fuselage with wings and all forward onto the winding rod. The motor stays behind and is now fully exposed and out in the open. The model is resting on the extension rod.
  5. Go ahead and wind the motor. The model simply hangs on the extension rod and the motor is being wound safely out of the model.
  6. When fully wound you, or a helper, slides the model back over the motor and onto the tail plug.
  7. Transfer the front end of the motor from the winding rod to the nose plug/gearbox and seat the nose block which engages the coupling joint for the drive at the same time.

To lock the motor against spinning out you don't want to have to hold the props. Instead a locking pin that locks the gearing in the nose block would be the better option. Something with a big "Remove Before Flight" ribbon on it for proper effect....

The benefit of this method is that you don't need to work with a blast tube. Instead the motor is out where it can't do any damage to the model. A nice bit of insurace would even be a round blast sheild that you snap onto the winding rod as well so if the motor does break the lashing ends are prevented from whipping forward and slapping the tail of the model.
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Old Aug 15, 2012, 12:58 PM
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carbondale il
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I like your winding method, It's just that I"m having trouble with the removable gear's in front. Another question is would I get more thrust from four 6" 3 Bladed Superior balsa props, or two 9 1/2" Czech props? Shorty's Basement carries both.

Kev
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Old Aug 15, 2012, 01:43 PM
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carbondale il
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According to my calculations: prop diameter x pi x number of props - the combined swept area of 4, 6" props is 75.36 sq. in. The combined swept area of 2, 9 1/2" props is 59.66 sq. in.

Kev
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Old Aug 15, 2012, 06:38 PM
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carbondale il
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Been working on the plan. I still need to buy the nose transfer gears. I'm thinking of 1" x 1/4" with 1/4" hubs so I can use the large nylon white thrust buttons to hold the axle wire. I'm going with small wire just like the small prop shafts which are common, for everything except the transfer gear axle which will have the rubber hook at one end. The motor stick length is 22 1/4". The sprockets and chain length arrived today. They are plastic. The chain lengths are snap together. The small white nylon thrust buttons fit in the sprockets nicely. I'm going to make the sprocket units and glue in the axle which will ride in two small buttons with the wire prop shaft inserted.

Kev
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Old Aug 15, 2012, 08:59 PM
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carbondale il
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Sorry, I did my math wrong. The area of a circle is calculated pi x radius squared. The swept area of 4 x 6" props is 113.04. For 2x 9 1/2" it's 141.69.

Kev
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Old Aug 15, 2012, 09:19 PM
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carbondale il
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I can get two Superior 10" 3 bladed balsa props from Shorty's Basement when they are back in stock. I can use these with two dummy 6" 3 bladed balsa props. This way is closest to a scale look.

Kev
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Old Aug 16, 2012, 01:34 AM
B for Bruce
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The 'Wack, BC, Canada
Joined Oct 2002
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A lot of the results also depends on the pitch of the props. Not having seen any of the options you are mentioning it's impossible to say which option would be best.

I do know that my own carved props have always worked better for me than the commercially available items.
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