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  #91  
Old 07-19-2020, 10:41 AM
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Are you going to try and have the two props spin together at close to the same speed?
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  #92  
Old 07-19-2020, 10:44 AM
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AirDave says:
I always wonder about the rounded wing tip ends on most aircraft.
Why do wings always end that way.? Different ways to reduce drag
Why not end flat, with the last rib?Massive drag vortices from the wing tips, notice on airlines the winglets? They are designed to reduce these vortices at a certain airspeed the airliner is most efficient flying at-conserves fuel
Whats beyond that point, isnt wing shape...doesn't do much as a wing surface.
Its just extra material, extra construction, extra weight.Yes, extra weight but the shape is designed for each particular airfoil shape to transition the airflow to the still air beyond the wing
Spitfires and Mustangs look cool with their clipped wings. As does the P47. The P47 and Spitfire have elliptical shaped wings which are more efficeint to reduce drag, have read that Swallow shaped wings are even better, and if you've ever seen a Swallow fly, they can turn less then their body length
Air Racers clip the ends of the wings.They don't care about fuel burned/mileage during a race, they need quick handling racers, the wingtips slow roll rates

Mike

Last edited by mbauer; 07-19-2020 at 11:03 AM.
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  #93  
Old 07-19-2020, 10:57 AM
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U-Joints and Drive Shaft

Quote:
Originally Posted by SCEtoAUX View Post
Are you going to try and have the two props spin together at close to the same speed?
Hi Doug,

They each will have their own rubber band, yes, they should spin at the same speed if I make all the u-joints the same, that is one of the tech challenges, knowing full well the drag won't be the same for each joint.

Basically the vision I see has the u-joints going from the prop shaft (wire) through the wing to the inside of the fuselage where it will attached to a balsa support. The u-joint "drive-line", inside the wing, will either be carbon fiber, aluminum tube, or plastic. A plastic bearing will be glued to the balsa support, with the drive shaft rotating inside of this mount.

I do have really small brass ball bearings 1/16", 2mm diameter to use if needed for these mounts. Once each of the u-joints are now located inside the fuselage, the rubber bands will be mounted like a normal straight run one would be.

Mike
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  #94  
Old 07-19-2020, 10:59 AM
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Quote:
Originally Posted by southwestforests View Post
It is as interesting watching the design process happen as watching the model come together.
Really hoping this one won't disappoint!

It will be a learning experience for sure.

Thank you for the kind words!

Mike
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  #95  
Old 07-19-2020, 12:16 PM
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Some ideas from bygone times perhaps
https://outerzone.co.uk/plan_details.asp?ID=9352
https://outerzone.co.uk/plan_details.asp?ID=41
https://outerzone.co.uk/plan_details.asp?ID=3710
https://outerzone.co.uk/plan_details.asp?ID=1098
The drive on the Short Scion puts more of the weight forward.
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  #96  
Old 07-19-2020, 12:34 PM
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Quote:
Originally Posted by maurice View Post
Hi Maurice,

Saved the links and photos, it is hard to see their drives, but will investigate further.

The final one looks like it might be as simple as wire with loops at either end, this is something I had been thinking about before looking at u-joints.

Thank you for the info!!!

Found a youtube video of the wire with loops on the end, the main drive uses a geared setup that spins the two wire connects to each of the props, maybe been over thinking the u-joint issue. It does look like the wire and loop method works.

Then I found a patent from 1986 that uses shafts and belt drive to spin both props from a central rubber band. This is going to get real interesting!

Mike

Last edited by mbauer; 07-19-2020 at 12:45 PM.
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  #97  
Old 07-19-2020, 12:36 PM
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Scan down the pages for links to the plans.
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  #98  
Old 07-19-2020, 01:06 PM
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Geared Twin Engine Airplane Rubber Band Power

While doing a search after maurice added the links above, here is probably the best bet yet. Might try to do away with the gearing.

Here is a link to the youtube video, shows how to construct as well as model in flight: https://www.youtube.com/watch?v=3TKl0TJSYgo

Now for some screen shots:
Here is the connection of the two wires; Rubber Band Power-twin-drive.jpg

Here is photo of wire connection in relation to wing mounts: Rubber Band Power-twin-drive2.jpg

Here is the gearbox: Rubber Band Power-twin-drive3.jpg

Now thinking the gearbox might be the reason why this works: No tension on the wires so they can flex and rotate without wearing through a bearing/guide surface.

If I hook rubber band directly to the wire shafts, it will tend to pull it with force. and cut through a guide tube like what this designer used to angle it towards the engine mount once leaving the fuselage.

Boy this is going to take some studying. I've messed around with gear drives when I did the wind turbines several years ago. Made mine out of cardstock pulleys using o-ring rubber to create drive belts. Still have several plastic gear cogs that I could use as well.

Now thinking a 3D printer could help with a gear box...

Mike
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  #99  
Old 07-19-2020, 02:37 PM
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Thank You! Did Not Scroll Far Enough

Quote:
Originally Posted by maurice View Post
Scan down the pages for links to the plans.
Hi Maurice,

Man, you've got my brain all twisted up now. I scrolled down as you suggested.

I've looked at each drive system, found a patented system, and the patented system on the Short Scion.

Here are some screen shots:
Airspeed Envoy uses a simple angled approach, until you have to modify the prop shaft using a flexible piece of rubber tubing or some kind of spring glued to allow bending as shown in this screen shot. The Beaufighter uses a similar approach:Rubber Band Power-airspeed-envoy.jpg

Now for the Beaufighter, two screen shots showing the similar connection, but has photo screen shot of flexible plastic/rubber tubing used:
Rubber Band Power-beau-fighter-rubber-band.jpg

Rubber Band Power-beau-fighter-rubber-band2.jpg

The B-17 model screen shot:
Rubber Band Power-b-17.jpg

Now for the patented shaft drive, boy this is complicated, it looks like the rubber band is inside the wing and not towards the tail for weight and balance: Rubber Band Power-shaft-type.jpg

Ok, the final model uses another patented system, talk about complicated, uses gears, and has an extension shaft to help with winding. The extension shaft is the "tin" tube part going towards the front of the model after the plywood gear mount. Here are several screen shots showing the system parts in detail:
This is the load bearing mount inside the wing
Rubber Band Power-short-scion4.jpg

Here is the front mount, the brass extension with tin to wind it all with:
Rubber Band Power-short-scion6.jpg

Rubber Band Power-short-scion7.jpg

Rubber Band Power-short-scion8.jpg

Rubber Band Power-short-scion9.jpg

Plenty of options to think about!


Mike

Last edited by mbauer; 07-19-2020 at 02:58 PM.
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  #100  
Old 07-19-2020, 11:40 PM
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Help: Need Reference Photos

Hi,

Been working on my NAA B25 B Mitchell Bomber.

Have a screen shot of progress today:
Rubber Band Power-b25b-screen-shot.jpg

Now need help identifying the following photos for reference. I decided to do the Ruptured Duck, as it is one of the very first books I read from a school library last century. However searching found a couple of different nose art renditions on the right side. Does anybody know what was actually flown off of the Hornet?

I'm in panic mode, can't find my 30-Seconds Over Tokyo book..., I do have the movie, but Holly Wood can never get it right when dealing with history.

Here are the ones I've found:
Rubber Band Power-unnamed.jpg

Rubber Band Power-unnamed-2-.jpg

Rubber Band Power-unnamed-1-.jpg

Rubber Band Power-img_20200116_135311.jpg

Rubber Band Power-1ec52396-b647-431f-9f5f-e6a9b53265a7._sl300__.jpg

Rubber Band Power-img_20200116_135135.jpg

Mike
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