rubber bands

_deltaV
Member
Member
Posts: 48
Joined: February 25th, 2015, 5:36 pm
Division: C
State: FL

rubber bands

Postby _deltaV » January 19th, 2016, 12:04 pm

How many times can you guys wind up your rubber bands before they begin to not perform as well? Because of shipping issues I was down to one rubber band for testing yesterday and noted that the first 4 flights were consistent in terms of climb, height, circle radius etc., the next flight performed the best and went a good 20 seconds longer, then the subsequent 4 flights began to vary in terms of the above factors^. I kept the number of winds consistent on each flight in order to try and see a relationship because it makes sense that the band becomes more elastic/broken in and thus has less torque for the same winds, etc., but the data doesn't seem to indicate that. Do you guys stop using your rubber bands after a certain amount of flights?
Boca Raton High School
- Helicopters - Microbe Mission
- Chem Lab - Experimental Design

"Remember kids, the only difference between screwing around and science is writing it down." -Adam Savage

bernard
Administrator
Administrator
Posts: 2002
Joined: January 5th, 2014, 3:12 pm
Division: Grad
State: WA
Location: Seattle, WA
Contact:

Re: rubber bands

Postby bernard » January 19th, 2016, 1:19 pm

How many times can you guys wind up your rubber bands before they begin to not perform as well? Because of shipping issues I was down to one rubber band for testing yesterday and noted that the first 4 flights were consistent in terms of climb, height, circle radius etc., the next flight performed the best and went a good 20 seconds longer, then the subsequent 4 flights began to vary in terms of the above factors^. I kept the number of winds consistent on each flight in order to try and see a relationship because it makes sense that the band becomes more elastic/broken in and thus has less torque for the same winds, etc., but the data doesn't seem to indicate that. Do you guys stop using your rubber bands after a certain amount of flights?
I'll note that it depends on how hard you are winding (winding up to 90% of breakage vs. 40% of breakage). I haven't flown this season, but last season I think I got many flights out of each rubber band, when doing full test flights, I usually didn't notice much change over time, and usually my rubber bands were worn out after a couple of flights due to heavy winding. For your trim flights, your rubber band will last longer probably because you're straining it less.

The first one or two winds of a rubber band tend to be quite different from later winds, so you'll probably want to do your trimming and tournament flying on rubber bands that have been broken into (which can be done by some moderate winding and stretching). I've noticed that when winding close to breakage, I can sometimes do two winds and already see some tears--and if you do, I wouldn't recommend using them at tournaments, as they could snap in your hands, losing valuable time since you've got a short time to do all your flights.

Do you have a torque meter? If you have time and a lot of patience you can start with a fresh motor, wind it to breakage, to see max turns. Then take a new fresh motor, wind it close to breakage, and every couple of winds record the torque; then unwind the motor, recording torque for every couple of unwinds. Then do it again, winding close to breakage and unwinding, all along recording torques. Graph, and compare how the unwinds look. I'd expect the first two to look more different than later ones, and later one they'd get more consistent. I did some torque curves last season and though I did this but apparently I didn't...

Also forgot to mention that your rubber band does get longer as you wind it, in case you didn't notice. Maybe a 1-inch stretch after the first wind, then 0.5" and then smaller stretches that are less noticeable.
"One of the ways that I believe people express their appreciation to the rest of humanity is to make something wonderful and put it out there."

jander14indoor
Member
Member
Posts: 1560
Joined: April 30th, 2007, 7:54 am

Re: rubber bands

Postby jander14indoor » January 20th, 2016, 6:08 am

<SNIP>I kept the number of winds consistent on each flight<SNIP>
If you are only winding to turns, you cannot expect consistent output from the motor nor consistent flight results unless you are way under winding the motor.

If you are winding hard to turns, your results should be similar to bernard's description. First wind will give the greatest torque and highest flight, but probably not longest. That will break in the motor. Next wind will be under wound (if done to same turns) because the motor has stretched significantly. Torque will be down, altitude lower, possibly longer because of longer cruise. Next wind will be still lower torque and even more under wound. Motor should stabilize for a few flights until damage accumulates significantly degrading motor and increasing likelihood of breaking.

If you are NOT winding hard, your results after the first flight will be pretty consistent and the motor may last a long time. But your flights will be shorter than they could be.

For practice, trim and learning, that is OK. To start.

But in competition, you need to wind you motors to a turn or two short of breaking every time. That means you need to use broken in motors (not broken down) and can only expect a couple of good flights from a given motor.
And that means you should practice like that at least part of the time.

Remember, your motor is both your engine AND your fuel tank. Turns are fuel to keep you flying. TORQUE is the power to get you to the ceiling and keep you there. You need to maximize both.

Do that experiment on winding and recording torque Bernard suggests. It will be eye opening to plot the data.

Jeff Anderson
Livonia, MI

calgoddard
Member
Member
Posts: 239
Joined: February 25th, 2007, 9:54 pm

Re: rubber bands

Postby calgoddard » January 20th, 2016, 8:03 am

dfaris -

Your thought process shows that you have excellent insight. The fact that you are seeking advice on this blog shows that you are committed to
learning the theories and translating that knowledge into success. Bravo!

Bernard and Jeff have given you excellent advice about winding the rubber motor for a WS airplane.

Let me make a couple of further points that will help explain inconsistent indoor flights.

The torque versus turns curve for a given rubber motor will vary with changes in the ambient temperature.

The climb, cruise and descent of the model airplane will vary with changes in ambient temperature, both due to the performance of the rubber and changes in aerodynamic drag.

These phenomena are taken into account by experienced indoor fliers.

The more extreme the temperature variation the more significant the impact on flight performance.

It is a good idea to note the gym temperature for each flight session on your flight logs.

I had the privilege of flying with the late Cezar Banks, one of the greatest indoor fliers of all time. He taught me that if I was not breaking rubber motors I was not winding enough.


Return to “Wright Stuff C”

Who is online

Users browsing this forum: No registered users and 1 guest