Rubber Band Power

[mbauer]

Lots of drag issues when sticking this model engine on a flying model. The cooling fins will for sure affect how it flies.

The main reason for the museum photo version of the front engine area. It is less drag than the model engine will be.

Then again, drag can be overcome with power....

Geez, I like to hotrod paper airplanes!

Okay, this is going to get really interesting before I'm done.

Safety steps needed: Will be using more rubber band than there is data on. Initial web search shows over 25lbs of energy available in a 6-strand 1/4" model.

I will be testing 10-strands to verify energy, measured with two different fish style 50lb weighing scales, purchased an expensive heavy duty rubber band winder with wind counter.

Will be wearing a motorcycle leather jacket and helmet for eye head protection.

Not sure how much my paper tube rubber band design can handle. Since this project has a removable front engine, now tests must be done on new tube design.

Want to know exactly when the design fails, will then add design over protection to model for safety.

Will be testing revolutions at different stages to verify unwind time. Basic need for this info. Goal is motor to be able to handle 2000-winds or 1-minute of unwind time. How long does a 500 count at this length and strand count take to freewheel? 1000-total winds? 1500? 2000?2500? Ka-blooey?

Ka-Blooey = which failed? The paper tube? The rubber bands broke? The o-rings used to attach the rubber bands to the prop hook/rear motor mount? If the paper tube failed, can more wrappings work to fix it? How did it fail-slow rip or all at once? Does the paper tube contain the damage if the rubber band breaks or the tube fails?


Photo of Arch hole punch completed. Please note that most holes are not centered. Shown 81 of 90 total, cut top row off and process of cutting them out for prototype cylinder build. 81 total square inches as each fin is 1" diameter on the outside:


Photo of Alpha cylinder build. Note that edge and backside coloring looks better than the lightly colored edges only look -can see difference in lower fins, last three rows have under the back side coloring using a Silver Sharpie marker, also shown are both the 1" outer hole punch and the inside 3/4" on the right:


Closeup of first cylinder:


To the rescue Mayhew Pro 66002 Hole punch kit.

In this photo please note: sheet of photo paper does not have circle outlines. Paper has been inked, but new punch allows to stamp anywhere and get perfect washers to use as fins. You can see margin edge where ink stops. Yes, it looks better with ink than without for the fins. Photo soon of all cylinders on engine case fit test... Total of 261 fins took 3-hours of "slug" cutting instead of time to do with knife or scissors:


New punch with both hole punches installed ready to be slugged with my hard wood, hand crafted hammer:


$360 total dollars spent for the Mayhew, have other uses for it. This project demanded it's purchase. Bought the $2 plastic cutting board from W-mart for the hole punch backing block. Worked great-some blows buried the punch, didn't seem to effect the cutters edge.

Plastic zip-loc baggies for the size rings needed.

Mike

[Texman]

Looks like I'm saving my pennies for one of those Mayhew toys!

[mbauer]

A couple of photos of the cylinders and how they look.

Lots of edge coloring and then on the back side coloring to get the look correct. White color on the back side of the fins didn't look good, Silver sharpie took care of that.

Once again gluing became an issue. Stopped using both styles of the super glue (liquid/gel). The Beacon ZIP DRY is the best glue tested so far for this project.

To finish the engine model, will be using aluminum wire and tubing, some lead fishing weights will be added as needed for weight and balance.

Pushrods are cut and painted ready to install, however; need to get the rest of the model ready/built.

These photos are where the engine is at this morning. Having issues with the electronic wiring harness, parts didn't fit, looking at options. Need to get the wiring harness done so that the cylinders can be glued and the pushrods installed.

The wiring harness is a ring that has been used in different locations throughout the history of the engine. Some models have the wiring harness in the back, some have it in front, some have both. This one was originally drawn up to be installed in the front, behind the pushrods. Some models have it in front of the pushrods. Since the parts didn't fit, thinking on options, print new? Use what I've got but modify for the back-where I can hide the flaws of the part fit? If I use it in the back, will the model still fit the firewall?

Then it is wait until the weight and balance stage to decide what weight still needs added for balancing. Have two sizes of lead fishing weights, 3/16" diameter tube and 1/4" tube. These will be used for exhaust/intake plumbing.

Plan is to paint the intake pipes a gold color, the exhaust pipes will have some chrome paint on them. Using the lead tubing gives the open look to the pipes. I do have some aluminum tubing that can work as well, if the weight of everything works without the need for adding lead.

Engine Case + Cylinders + Pushrods weighs in at 59.7gm.

Note the aluminum look to the cylinders, can see the "metal" shine the paper gives to the gray ink:






Mike

[mbauer]

Hello,

I miss-read the rubber band power calculator.

Finally went to the webpage that talks about rubber band free flight, the author covers many areas, one is the rubber band power that can safely wound into the system.

The calculator I found does the results in inch/ounces not foot pounds.

Also of note is how they figure the amount of rubber band. I've been counting 1-loop as a strand. This is also wrong.

Actual way to count is this ratio: 1 Loop = 2 Strands. Makes sense.

Looks like my 50lb fishing scale is way to large. Now going to make the preferred style listed in the PDF file I found on rubber band power/free flight.

It goes into detail about how much the rubber band looses in power each time you wind it up. Each time you wind it, to get the same torque you must add more winds to it.

Not just a revolution counter (windings) but actual torque value that can be measured with a strain gauge.

Okay, the PDF just downloaded is a big source of help, all kinds of formulas and tips on rubber band power.

Two assumptions, two mistakes.

6-loops of rubber does not equal 25.5 lbs of force, but 86.6 inch/ounce or 5.4125 inch/pounds.

Still need to test my system to verify it is safe to continue with these rubber band models.

Mike

[southwestforests]

Hmm, interesting. I was never in to rubber power deep enough to start getting concerned about the power math.

[mbauer]

Originally Posted by southwestforests

Hmm, interesting. I was never in to rubber power deep enough to start getting concerned about the power math.

Today, found a new area to read. Learned about the strands and loop terminology, the math has to do with safety.

Main reason for my use is how heavy the P26A is going to be. The photo paper is 270gsm coated with a spray gloss sealant. Once complete with the draggy engine in place, this model is going to need super rubber power to get it in the air. This new knowledge now lets me know approx. how many loops to use, once the model is weighed for flight.

How many turns/windings can you get into the model safely? They used to use windings, then found that each time you wound it up, you lost about 10% of the Torque, each time!

By using the torque values to wind with, you can safely add the 10% back into the motors windings. Yes, more windings will be added to the original amount, but the torque reading shows you can do so staying within the 75% safety rule.

Eventually the rubber band will need to be replaced. Each time it is wound, it tears and the elongation happens, each and every time. Eventually the rubber band starts to develop nicks from the breaking/tearing action. Once the nicks show up, time to replace or risk a total break failure.

BIG FIND for today's searching: A really cool working/looking "Wobbly Peg" motor mount.

What does it do? Allows the model to handle longer rubber motors than the length of the space. Read about a small model with 4.5" of space that was using a 20" long rubber band!

4-5 times the length is the standard way to use the mount. A modeler, Dave Stott invented it, several others have modified it. Designed for multiengine aircraft using rubber bands for the power.

The modeler who I read about wanted to save weight, so he used this motor peg in a single engine Sopwith Camel fighter. He was able to move the rear motor mount forward to save weight during the balance phase.

Plan to use the "Peavey Rotating Motor Peg" for the B25B Bomber project.

Keeps the weight forward, and yet allows longer motors to be used.

A simple idea that works: Two tubes, one inside the other. The outer tube is cut into three pieces. The center piece is left to rotate, the two outside end pieces are superglued to the ends of the inner shaft.

Here is a quick screenshot drawing:


Lot simpler than the Moore system, or the others that I've looked at. Weighs almost nothing to make.

The length available inside the B25 Nacelle is 8.9" long x 4 = 35.6" long strands should work

Once the P26A Peashooter is done-back to the B25 project!

Made some table charts today for safety torque values. Then went online looking for torque Screwdrivers. Found what I needed, two analog ones that measure .02 thru 5nm (newton-meters). Translating those numbers into 1/4" wide rubber band: range from 3-strands through 17-loops (34 strands).

Took a major break today from model building, had some questions needing answered so, went online to find answers. Besides began feeling like a tank modeler after all those cooling fins...

Did you know that 1lb of rubber band is 2000ft-lbs/1lb of energy? If you lube the rubber band the numbers change: 3000ft-lbs/1lb.

Mike

[southwestforests]

Originally Posted by mbauer

Besides began feeling like a tank modeler after all those cooling fins...

Hehehe!
Hmm, now that tanks are mentioned, I wonder if the all metal P-26 felt like a bit of a tank to pilots previously flying fabric covered aircraft.

Did you know that 1lb of rubber band is 2000ft-lbs/1lb of energy? If you lube the rubber band the numbers change: 3000ft-lbs/1lb.

Nope, I was clueless as to the energy numbers.
So, that 1/4 lb box of 3/16 tan sport rubber I got from FAI Model Supply fall of 2019 to use in my rubber band submarine summer of 2020, which didn't happen due to worldwide crises beyond my control (bummer) and still sits here under this desk, would have within its fiberboard cubicness ...
500ft/lbs of energy?
And I did buy lube. Still unopened.

[mbauer]

Originally Posted by southwestforests

Hehehe!
Hmm, now that tanks are mentioned, I wonder if the all metal P-26 felt like a bit of a tank to pilots previously flying fabric covered aircraft.


Nope, I was clueless as to the energy numbers.
So, that 1/4 lb box of 3/16 tan sport rubber I got from FAI Model Supply fall of 2019 to use in my rubber band submarine summer of 2020, which didn't happen due to worldwide crises beyond my control (bummer) and still sits here under this desk, would have within its fiberboard cubicness ...
500ft/lbs of energy?
And I did buy lube. Still unopened.

P26A-that would be a real good question, now that you've brought it up.

Now I want/need to know. Wonder how long that will take. Might be faster to see what most Squadrons moved up from and compare wing loading/control movement weight. Pretty sure they weren't to concerned, probably more interested in the increase up front: horse power.

And to put the P26A in it's place: Three years later the ME 109 took to the skies.

Did read where the P26 is credited with the first single "mono-wing", all metal against another single wing all metal dog fight victory.

Already know my RV-6 has an incredibly fast roll rate, it'll be interesting to check and compare. Know the P26 is faster by 30kts on 550hp vs., 160hp, but climb rate and roll might be interesting to compare.

Not sure on the rubber question. Found lots of interesting stuff, a site that has everything about free flight as PDFs. It is in one of those that I found the numbers. Here is a link to a resource-webpage says plans, but it has all kinds of stuff, including a section on how to make canopies: George White's collection - 850+ useful articles

I did create a word document table that has strands listed from 1 thru 34. The chart is for 1/4" Super Tan. It does not go by weight, but is a 75% safety Torque chart.

For instance a single strand can be wound to 2.3 inch-lbs, or .01197917 Ft-lbs or .01624157 newton-meters. Length is not a factor to be concerned with.

The 34-strands are rated for 620.4 Inch-lbs, 3.23125 ft-lbs, 4.380987 newton meters.

Plan is to test up to 12-strands or 6-loops. 317.4 inch-lbs/2.241337 newton-meters worth.

Curious, do you know that rubber bands will last longer if you keep them in a refrigerator? My 10-lb box of 1/4" Super Tan has priority over everything else in the frig, except it better not block the 12-pack of Molson Ice.

Once the testing starts, going to have some fun. How many wraps do I need on the paper tube? Right now I choose a width of paper and roll it up. Now will investigate a way to loose some weight in this area.

The test most looking forward to is the rubber band on the Peavey Rotating Motor Mount, hoping by being able to move it forward in the fuselage, hoping I'm saying, hoping to save balance weight-ideally once the engine model is complete, it will balance the model without adding anything else.....

Although it is designed to accept lead fishing weights as part of the design-the intake tubes from the rotary blower to the cylinder heads.

Incase not much balance weight is needed, the lead can be replaced with superlight weight and bendable aluminum tubing 3/16" O.D.. Mix/match as needed once plane is at weight & balance stage.

Tonight I'm looking rest of parts over. Will reprint the electrical harness, looking to see if anything else is needed. Only one re-print at this stage, already tossed too much of this impossible to get photo paper because of mistakes in the drawing.

The pushrods are 1/8" dia. tubing, they were in a coil, had to straighten. That was done by using a heavy walled 3/16"T x 3"w x 3ft Long aluminum angle as a backing plate. Using my wood mallet and rotating the aluminum tubing was able to straighten really fast! Light taps with the mallet did it.

A few photos of dry fit test, no glue yet:


Still dry fit, but look at the shine!


Look how the cylinder on the right is catching some light, yep, whole length is shiny!


How about some gold fuselage and yellow wing shine?







Mike

[mbauer]

Today glued some parts to the engine model.

Zip Dry released a couple of parts after two days of drying, now using Gorilla Clear Adhesive. Stringy, hard to control how much out of the tube, but, it seems to be working.

Here the cylinders have been glued into place:


The most difficult part to make so far has been the Spark Plug electrical harness. Some engines have it in front, some have it in the back. Went with the front version.

It almost didn't make it. Small hard to bend glue tabs, very difficult to work with. This is the 14th version. Lots of wasted paper to get it to this look. Decided after about 10-hours into it, if this one didn't work, was going to drill holes in the engine case for the spark plug leads. It could look better, but thinking it will work as shown.

Here is the engine, electrical harness, and oil sump:


While the sump and harness are curing, decided to start cutting the wood parts out. Using 1/32" plywood for support inside the tail horizontal stabilizer and vertical fin. Yes, they only go half way, the Elevator and rudder will be able to be bent for control/trim purposes.

Here are some photos of the plywood and ribs. Note how easy 1/32" plywood is to cut. Standard scissors:




Now for a fit test after sanding of the edges on the plywood:


Still using the Gorilla glue, working Okay, however it does have excess glue showing in spots. Here the Front spark plug leads are installed. Used black paint and white paint to simulate the connectors and spark plugs:

You can see the copper colored wire I found in the bead section of the local big box store (WM). Copper colored wire bends easy and is the correct size for this scale.

Copper wire for front spark plugs glued, will add back wires next:


You can see the simple finger drill in use for drilling all the different holes needed. Purchased a t a local welding supply store, it is a tip cleaner drill for Oxygen/Acetylene cutting torch tip cleaner. Very small drill bits come with it.

Back spark plugs glued, now time to bend and shape for final gluing:


Pushrods are from a 1/8" coil of aluminum tubing. To straighten used a piece of aluminum angle and the wood mallet I made. Light taps as a rolled the tubes around, didn't want to flatten them, just make them straight. Worked great.

First set of pushrods installed, notice all the back spark plug wires have not been completed yet:


Past the halfway point now for pushrods, and the wires:


More to see soon....

Mike

[mbauer]

Here are some photos of the front of the engine.

This engine has been sized from a photo. I did not have the actual specifications for the engine. As such the photo used was from a museum, another photo was used to do the cylinder fins.

I know that the original probably had a different style of fins and the electrical harness was probably in the back, but not sure. All I could find were photos, no actual working numbers to use for the actual scale.

The photos were not the best, angles were bad, didn't show all the details, however here is the model with the front side almost done:






At this stage, the engine models weighs 2.4oz. Have some lead weights to use on the back side for the intake ports on the engine. Looks like might need to use some for the exhaust pipes as well.

Time to start gluing the fuselage. Install the rubber band tube, will be some testing of the power system to ensure the paper tube can handle the multiple rubber band loops I plan to use.

The rubber band tube is different this time, it won't be glued to the engine, going to be a real happy moment if my plan for this works!

Mike