Some thoughts on Rubber Motors...

[Mitch]

Hello to all you FF Rubber Powered Nuts out there... that's me and who else?

I was thinking this morning(this can be a bad thing... only 1st cup of coffee). I noticed the torque meter on my winder has a chart for 'Breaking Torque for 1/8" Rubber'. I have been using 3/16" in my models, but I am planning on going to 1/8" and I can increase the strands to get the same amount of rubber.

The benefit to this is that I will be able to get more winds with the same weight of rubber. I have noticed in other kits (non Guillow's) the rubber is 1/8. I have not been using this as I thought is was too small.

For my flight of my 100 series SE5, I used 1/8 as the model is very small (18 inch ws) I only had 500 winds on the motor which was 1.2 inch ounces of torque. I see the breaking point for that rubber is about 6 in oz. Next time I will wind to 3, then 4 in oz. She had a 7 inch Peck prop.

For my 200 series DH4 I plan to use 6 strands of 1/8" rubber. She will have an 8 inch Peck prop.

I plan to start using 1/8 rubber on most of my models and use the 3/16 for the models that have a ws over 30 inches. (1000 and 2000 series)

It seems to me the biggest factor in getting these models to fly is understanding our power supply and proper propeller!

so... any questions, comments, or thoughts are welcome... now for that 2nd cup of coffee!

Mitch

[WIDDOG]

Hi Mitch very interesting topic.

Sorry I can't remember which book I read about choosing the proper prop and rubber combination. However, I remember it mentioned as a good indicator is if the model lands with a lot of extra winds left in the motor. This could indicate that the prop is too large or the motor is too weak.

[Mitch]

Hi All,
I got some tests on 3 types of rubber. No surprises but here is what I did and came up with.
I used non lubed rubber in all tests. I figured that would be worst case senario. I used 2 feet of rubber for the tests.
I used Gulliow grey, 3/16. Sport Tan 3/16, and Sport Tan 1/8.

1. Guillow Grey: Broke at 16 inch ounces
2. Sport Tan 3/16 : Broke at 7.8 inch ounces
3. Sport Tan 1/8: Broke at 5.4 inch ounces.

Each test was with 4 stands of rubber.

So then if did more test flighs with my FW 190. I did not turn on the counter... Just wound the motor to 5.0 in oz. I am still making adjustments to add weight aft on the FW. On my second flight I got things right and the plane flew for 28 seconds. I could safely wind her up to 6.0 in oz, but she landed 2 feet from the parking lot and I will wait until I get to a bigger field.

Mitch

[David Lewis]

If the airplane is nose heavy, that means you could move the motor peg back (if you want a longer motor run), or lighten the nose (if you want lower wing loading).

[Mitch]

Thanks Dave... that makes sense. But I am going to keep this as they are with the FW190. The fuselage gets very narrow and I drilled a lot of lightening holes in the next frame back so I can not remove any more from the inside to make more room for my motor.

NOTE: For future builds on the 400 series I will move the rear peg forward just 1 bay, not 2.

I will add the tail wheel and other details to the FW190 now and fly her for timed flights for the Guillow Challenge and that will be that...

...lesson learned.

Mitch

[NcGunny]

Mitch have you built any of the Living Room flyers? I watched a guy with one this weekend. Not sure of the make but it had long wings that went up to a 45° angle before the tips. It just kind of circled around....but somehow it mysteriously gained power and rose from the ground to get more height and kept circling. It was quiet a amazing thing to watch. Was wondering how you would wind ur motor that it could do this?

[Mitch]

Well, that's 2 things you are talking about and... no, to both. I do not fly indoors. And I have not build an ROG (Rise off Ground) plane. At least not yet. There is a category called "embryo" for FAC. They have the category at WESTFAC V, I plan to build an EasyBuiltKit called the Debut. It is a small model with short wings and is ROG. We use a small table and without a push just let it go it must ROG to the air. I have seen (on YouTube) indoor flying and the planes will always circle to the left. That is from the turning prop. I am sure they test there planes before videos are taken, and make sure with adjustments to fly in a tight circle.

Observers ask me how I "fly" my plane, and I explain it is 'free flight' that is why I need to walk into the field, but I tell them how I expect my plane to fly and it comes close to that... Of course there is wind and updrafts that effect the plane, but they are amazed that the plane behaves the way I predict.

I started this Thread, so we can all understand our power source better. I think it is simple, but misunderstood, and needs to be respected. The more knowledge we have the better we will be able to use the power of the rubber motor!

Mitch

[NcGunny]

Kk.. This guy launched his plane by hand and it just circled until it was like a foot off the ground. Then suddenly it sped up and rose to maybe 8 ft and went back to circling. I was wondering how you could make a motor almost seem like it is a 2 stage...hope that explains it..lol. I was kinda like "the plane is cool..ohh look it circles,ohh its running out of power..What the h.ll!! It just took off again!"

[Mitch]

I do not know... was this on YouTube? Maybe you can post the link and share. There are other people here with more knowledge than myself...

Mitch

[NcGunny]

It was at a hobby shop we went to. I even stood there with my phone in hand and never thought to record it.

[Mitch]

Okay... next time ask when you are there... you were probably in shock and were speechless at that moment... life goes on.

So next interesting item for power systems. I plan to fly two 400 series planes on Sunday. They both have the same hook to peg length (11 inches) and will swing the same 9 inch prop. The Bf-109 and the Zero... I need to glide and trim the Zero, but she will be heavier than the 109. (She is already heavier) I plan to use the same batch of rubber and make up the same motor for each. The wing area is a bit more on the Zero so I should calculate the wing loading for each plane. The 109 has the extended wing as per the Guillow plans for a flying model. The Zero also developed an extra ordinary washout after I removed the top paper, replaced, re-shrunk and doped. It will be interesting to see how she flies! I could try to fix it, but I like the way it looks and will see how it works!

I need to start taking notes and document what I am doing so I can make decisions based on records and tests with documentation. Both of these planes were built specifically for competition flying! They are at the Zenith of my current building know how. Now I need to learn and understand my power system...

The RUBBER BAND!

If you never saw it... here is 1 pound of Sport Tan Rubber! That's 475 feet! 1/8 inch weighs 1 gram per foot. I am thinking about 2 foot length and 3 loops or 6 stands. That would be a 12 gram motor, modest for the planes in my weight category... we'll see how that works for a start!



Mitch, Always Building, Always Flying, Always Having Fun!