Rubber Band Power

[southwestforests]

Originally Posted by mbauer

That sub is totally awesome. Great photos of it diving. Really like the prop wash when near the surface.
Just watched the video. It really moves out fast!

Thanks!

Cavitation shows inefficiency but that's only when it is close to surface and seems to draw in a bit of air. Reduces and becomes zero as it gains depth.

What did you rig up for the prop?

Took some pics just now to answer that and probable other questions.
Prop was from a Traxxis twin motor speedboat of some sort.
2 different props were available in both left and right rotation.
This is, I think, the greater pitch prop.

Prop shaft and hook is music wire with telescoping brass and/or copper tube over it to fit shaft tunnel in prop.
Tubes were notched at far en and an L in wire soldered in to notch, so as to ensure torque transmission, i.e. non-slippage of wire inside tube "sandwich".

Because prop is pushing versus pulling, thrust bearing from some Horizon Hobby mini-truck is used. It's never been oiled that I can recall.

Fitting in stern and propellor thrust button come from some full-body styrofoam airplanes by MRC that I'd acquired who knows when.

Bow and stern planes are sheet brass soldered to brass rod and tube.
Go through brass tube across hull.
Made use of that annoying barcode sticker K&S started putting on its individual tubes in the counter display of its tubes and rods by using its adhesive residue to allow friction setting of the planes.

Shaft is solid.
One plane was soldered to shaft.
Shaft was inserted through tube in hull, then sub wrapped in wet washcloths and far side plane quickly soldered with butane torch.

Stern planes were eventually "filled out" with balsa underneath because a little additional flotation was needed aft for trim to look right to me.

Bow planes were left 'unfilled' on bottom because they sometimes get bent when sub impacts pool side if I've misjudged pool current or circle radius when running in circle.

Rudders definitely have "Rudder Authority" They are styrene sheets super glued to brass shaft, one sheet each side of shaft.
Prior to gluing each sheet was bent a bit to give shape.
Gap between sheets was gradually filled with that baking soda then super thin super glue thing to give solidity.

Bellcranks for rudderes were supposed to eventually be cut from brass sheet and soldered to Carl Goldberg model plane wheel collars but I made some temporary sheet styrene bellcranks for ballasting tests and superglued them to wheel collars with cheap super glue figuring they'd be easy to pop off when I got ready to solder on the final brass cranks.
... that was in 2005 ...
styrene cranks are still there, because why not, they're working!

Book directions showed strip of solder bolted on for sub keel; I cut slot in bottom plan and used K&S brass strip inset. It might or might not have a couple retaining tabs soldered to its top edge, I don't remember.

Handrails are Athearn 'blue box' HO scale locomotive stanchions and beading wire.

Periscopes are K&S tubing, don't remember if brass or copper, they are open and go through to hull interior, which is free flooding.
They bubble as sub goes under

Ballasting of hull:

There is a LOT of steel shot glued in to recesses cut in hull bottom and in to box block.

After hull was assembled entire exterior of hull was soaked with super thin super glue to harden the balsa.

Hull interior is open and free flooding, it was treated same way.

It seems pool chlorine has seriously negative effects on rubber motor longevity, be prepared to get only 2 or 3 runs sometimes from motor loops.
Yes, I do use glycerin lube while prepping rubber for installation.

2 loops of FAI 3/16 tan sport rubber is enough to get that speed and power seen in video. Puts out plenty of torque to get that prop to get a solid bite of the water. Enough to cause hull to torque roll a bit at beginning of run.





Shoelace in photo below is to keep prop from falling out and becoming lost/damaged while sub is on display.
And it winds and turns prop just like rubberband! :D

[southwestforests]

Oh, and a 1980s project for which I have no pictures.
A 3 foot cardboard rubberband sub.

It had a U shaped cross section with top of U squeezed a bit.
Construction material was brown cardboard dividers between layers of candy bar counter display boxes at the F.W. Woolworth store where I worked.

It was free-flooding like model in book.

Sub had an inner skin and an outer skin, I forget what width of U frames was.
3/8 inch, maybe?
All cardboard was soaked with varnish as sub was constructed.
Space between inner and outer skins was sealed to not flood.

Middle of hull could be described as modular U-channels which were the assembled.
Bow and stern each tapered, were similarly based on U-channels. Exact shapes are not remembered but bow shape was inspired by typical USN and Kriegsmarine 1940s subs.

Took almost 5 pounds of BBs poured between skins to ballast the boat to float deck awash.

Don't remember how I made dive planes, rudder, or what was used for prop.
Pretty sure a test prop was made form sheet metal, but not used for actual running as my friends had an above ground vinyl-lined backyard pool and it would have been rude to cut their pool liner.
Prop was much bigger than above, was several inches.

[mbauer]

Plenty of time for glue to completely dry. Did weight and balance finally.

Tonight installing 1.49oz of lead fishing weight to balance.

Looking at options to install:
1) Lead is 1/4" Dia. tube. Scored every 2" so able to snap off a short length.
2) Drill holes in front engine inlet area and super glue or
3) Drill hole in side just behind the balsa wood bulkhead for the engine intake/prop mount. Can stack on top of each other (3-short sections) and superglue, small patch will hide opening. Plan is to make a small weight "Bay" on the next build to hold the lead. Have an order heading this way with stick on tire weights.
4) Probably going to move the wings back a little to move CG rear ward. This should decrease the balance weight needed.

Model will be near 6-oz for flight conditions. Hoping to use warehouse at work tomorrow morning for first flight.

Already starting on next project: WWII models. Been collecting 3-views.

I do have a plan for a rubber band power DF (like an EDF but uses rubber for power) EDF= Electric Duct Fan. RDF will be jet fighter power hopefully.

Tracing paper order is not happening. Cost $15 more for shipping than 100ft long roll of tracing paper!

Mike

[mbauer]

Finished adding the weights for the weight & Balance.

Model weighs: 5.8oz ready to fly

Some photos of how I added the weight:


Lead package of fishing weights. I have a big order of lead tire weights that have stick back; are on the way:


Used tape to close the little door created to add the weights. Used super glue to stick them to the cardstock/balsa mount.

After a 9-hour run at a new design, first print is complete, now to build the latest Rubber Band Power Model:

P51-D
22" Wing Span


However won't be able to do any modeling until late Mon or Tuesday.

Flying to Fairbanks in a few to go watch the start of the 2020 Iron Dog snow machine race.

Son-in-law is racing this year! Temple/Spain Team.

Dressing for the outside in Fairbanks means lots of layers.

Mike

[Gil]

Stay warm Mike and enjoy the race....,

-Gil

[mbauer]

Originally Posted by Gil

Stay warm Mike and enjoy the race....,

-Gil

Thanks Gil!

Was warm, actually day of start went from -33deg f day before, to a balmy -17 day of race. Serious layers.

Then walked on the Chena River to the first bend that was full of fog. Racers started at 4-minute intervals. Team 19 Temple-Spain is my son-in-law's team.

Went to the banquet the day before. Incredible! First part of everything was Inductees to the Irondog Hall of Fame. Racers First, then just as many volunteers in the villages that actually make this race do-able. Very impressive group.

Son-in-law crashed going 80mph on the Nenana river just outside town. Villagers saw him crash opened up their shops and home, certain rules apply to repairs, only certain people can help or get parts. Took 4-hours to get back on trail. Those 4-hours get added. They caught back up with pack and approaching Nome at this time.

White out blizzard conditions, 11-teams have quit due to crashes. Serious injuries and a support plane wreck, everyone ok, on take off. Bad conditions all over state. Climbed on an airplane for 5-minutes in Anchorage this morning at 545am, by 555am after de-ice attempt, heavy wet snow coming down faster than de-ice could remove.

Rented Suburban with couple of others and drove home. Blizzard most of way.

Yesterday drove from Fairbanks to Willow, Alaska towing an enclosed car hauler trailer. White out blizzard conditions, was down to 30-35mph for 250+miles.

2409-Mile Race this year.

Back to model building tomorrow.

Mike

[Gil]

Thanks for the first person report. Made me remember how individualistic and self sufficient Alaskans are by the necessity of their environment.

Got me to checking the condition of my -45 dF boots - kinda weird for somebody who lives most of the time in sunny California...,

-Gil

[mbauer]

Originally Posted by Gil

Thanks for the first person report. Made me remember how individualistic and self sufficient Alaskans are by the necessity of their environment.

Got me to checking the condition of my -45 dF boots - kinda weird for somebody who lives most of the time in sunny California...,

-Gil

Gave my bunny boots away years ago.

For this trip used my new canvas mukluks with some lacross iceman felt liners. Some old socks bought while stationed at Ft Richardson, made with poly and wool blend. Poly to wick moisture and wool to keep warm. Didn't have a problem outside taking photos in -28 drg wx total time outside before and after start was 3+ hours.

Team 19 is at half way point: Nome, Alaska, daughter is there got good video of first team to arrive, and when Travis got in late last night.

Doing good: was in 10th place for a short while, now standing at 13th as everyone is having forced layover. Lost 4-hours on repairs and is in front of quite a few teams. Avg dist each day is 522 miles.

The 2020 Irondog has GPS Tracking available. https://track.irondograce.org/



Has the leaderboard available on-line, and you can check all the racer's specs on-line as well.


Shows their speed levels and time sustained, and elevation




One racer with a collar bone broke in 4-places rode 50-miles to get to Kotzebue.

Next Saturday, flying to Anchorage, getting in rental car and driving to Big Lake for the Finish.

More shoveling to do outside, got 3-more inches of snow last night. Then will start building P51 Model.


Mike

[mbauer]

Bought some lead weights to use for weight and balance. Thinking purchased a few to many...


Perfect for these models. 1/4 oz and 1/2 oz size stick right on balsa wood mount prop mount bulkhead.

Mike.

[mbauer]

Good start yesterday on the P51D model. Three sides complete for fuselage, including the balsa support box. Once the rubber band tube is in place, will install rubber band and then close up top of fuselage.

Still haven't decided on landing gear wire mount yet. Balsa support glued to wing or full width wire to each leg across bottom of fuselage.

Parts fit is good so far, couple of graphic changes have been done.

Gluing side to bottom pieces:




Fuselage Bottom Done:


3-Sides Complete:


Balsa Support Box Complete:


Closeup:


Fuselage Sideview:


Couple of thoughts on the rubber band going to use. Used the full width of the 11x17 paper when it was rolled into the tube. Now going to cut it short to fit in place. So far this tube has held up to two 3/16" rubber bands. Thinking since this is a shorter length, might try 2 each 1/4" rubber bands for power before using them in longer versions of the tube.

Hopefully finish today.

Mike