What are your guys times right now?

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Re: What are your guys times right now?

Post by torqueburner » January 30th, 2015, 6:50 am

InfiniCuber wrote:
Well, my plane seems to be climbing all right, but it doesn't climb very high. I've snapped several rubber bands like a .081 30 cm loop broke many times after about 80 or so winds on a 15:1 winder. So getting more turns is becoming difficult. Also, the knots that show up once wound hit my motor stick and when they hit it mid-flight, it shakes the plane a bit (you can hear the plastic covering shake).
First, to expand on Jeff Anderson's comment above, the first thing that I notice here are the dimensions of the motor. Assuming that a "30 cm loop" is made from about 60 cm of rubber, knotted at the ends, and knowing the density of Tan Super Sport rubber, I'm guessing that your loop is nowhere close to the maximum of 2 grams allowed by the rules. (around 1.2 g maybe?) So the first thing you can do is to use a longer loop so that your motor is as close to 2 g as possible. If the 80 winder turns you mentioned were put into a 1.2 g motor, you could expect about 120 turns or more on a 2 g motor.

You also talk about knots. Are you stretching the rubber out to around 4-5 times its rest length when you start to wind, and gradually shortening this distance as the wind progresses? If not, you should try this, as it can reduce the tendency to form the knots you are observing, and allows you to pack more turns, and therefore more energy into the same piece of rubber.

Finally, you indicate that your plane doesn't climb as well as you'd like. Without knowing more details, I'm guessing that maybe the rubber is too narrow for the prop you are using, as speculated by others in this thread. The rubber delivers the greatest torque at the beginning of the flight, but the torque quickly decreases, especially if you are using a loop that is shorter than than the maximum allowed. So the duration of the climb may be shorter than you need for these reasons. What is the torque when you are at maximum winds, and what is the torque after you back off to launch?

Back to the rubber size, as hinted at by others, there is an optimum size for a given plane/prop combination. Thinner rubber will give you more winds for a given mass motor, but more winds isn't a guarantee of longer flights. One of our planes is currently flying best on a 2 gram loop of rubber cut to 0.105", which results in a loop about 14" long (includes 2 o-rings). This gives us way fewer turns than you could put onto a narrower loop, but the prop has a fairly high pitch, and the results are pretty good. Our best flight in a 19 ft. ceiling is currently 3:28.

So I hope that this helps.

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Re: What are your guys times right now?

Post by InfiniCuber » January 30th, 2015, 12:09 pm

jander14indoor wrote:Rubber is your fuel and your engine. Thickness is power/climb. Mass is fuel. NEVER fly with less than 2.0 gm of rubber, its like flying with a half full tank of fuel.

Jeff Anderson
Livonia, MI
I remember hearing this, i didn't think too much about it. But I guess I'll have to give it a try, so thanks!
torqueburner wrote:First, to expand on Jeff Anderson's comment above, the first thing that I notice here are the dimensions of the motor. Assuming that a "30 cm loop" is made from about 60 cm of rubber, knotted at the ends, and knowing the density of Tan Super Sport rubber, I'm guessing that your loop is nowhere close to the maximum of 2 grams allowed by the rules. (around 1.2 g maybe?) So the first thing you can do is to use a longer loop so that your motor is as close to 2 g as possible. If the 80 winder turns you mentioned were put into a 1.2 g motor, you could expect about 120 turns or more on a 2 g motor.

You also talk about knots. Are you stretching the rubber out to around 4-5 times its rest length when you start to wind, and gradually shortening this distance as the wind progresses? If not, you should try this, as it can reduce the tendency to form the knots you are observing, and allows you to pack more turns, and therefore more energy into the same piece of rubber.

Finally, you indicate that your plane doesn't climb as well as you'd like. Without knowing more details, I'm guessing that maybe the rubber is too narrow for the prop you are using, as speculated by others in this thread. The rubber delivers the greatest torque at the beginning of the flight, but the torque quickly decreases, especially if you are using a loop that is shorter than than the maximum allowed. So the duration of the climb may be shorter than you need for these reasons. What is the torque when you are at maximum winds, and what is the torque after you back off to launch?

Back to the rubber size, as hinted at by others, there is an optimum size for a given plane/prop combination. Thinner rubber will give you more winds for a given mass motor, but more winds isn't a guarantee of longer flights. One of our planes is currently flying best on a 2 gram loop of rubber cut to 0.105", which results in a loop about 14" long (includes 2 o-rings). This gives us way fewer turns than you could put onto a narrower loop, but the prop has a fairly high pitch, and the results are pretty good. Our best flight in a 19 ft. ceiling is currently 3:28.

So I hope that this helps.
Thank you, this was very helpful!! I do stretch my rubber about 3 times its length when winding, but my motor is only about 1.4 g one of them was 1.6. So I will definitely try using a full 2 grams of rubber! About the rubber size, my best time was actually the with my thickest rubber, .091". I got 1:40 with it. Not what I want, but it is my best. I am using the ikara propeller that comes with the freedom flight kit (not using that plane tho haha), I don't quite remember the pitch, though.
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Re: What are your guys times right now?

Post by Toms_42 » January 31st, 2015, 8:21 am

InfiniCuber wrote:
jander14indoor wrote:Rubber is your fuel and your engine. Thickness is power/climb. Mass is fuel. NEVER fly with less than 2.0 gm of rubber, its like flying with a half full tank of fuel.

Jeff Anderson
Livonia, MI
I remember hearing this, i didn't think too much about it. But I guess I'll have to give it a try, so thanks!
torqueburner wrote:First, to expand on Jeff Anderson's comment above, the first thing that I notice here are the dimensions of the motor. Assuming that a "30 cm loop" is made from about 60 cm of rubber, knotted at the ends, and knowing the density of Tan Super Sport rubber, I'm guessing that your loop is nowhere close to the maximum of 2 grams allowed by the rules. (around 1.2 g maybe?) So the first thing you can do is to use a longer loop so that your motor is as close to 2 g as possible. If the 80 winder turns you mentioned were put into a 1.2 g motor, you could expect about 120 turns or more on a 2 g motor.

You also talk about knots. Are you stretching the rubber out to around 4-5 times its rest length when you start to wind, and gradually shortening this distance as the wind progresses? If not, you should try this, as it can reduce the tendency to form the knots you are observing, and allows you to pack more turns, and therefore more energy into the same piece of rubber.

Finally, you indicate that your plane doesn't climb as well as you'd like. Without knowing more details, I'm guessing that maybe the rubber is too narrow for the prop you are using, as speculated by others in this thread. The rubber delivers the greatest torque at the beginning of the flight, but the torque quickly decreases, especially if you are using a loop that is shorter than than the maximum allowed. So the duration of the climb may be shorter than you need for these reasons. What is the torque when you are at maximum winds, and what is the torque after you back off to launch?

Back to the rubber size, as hinted at by others, there is an optimum size for a given plane/prop combination. Thinner rubber will give you more winds for a given mass motor, but more winds isn't a guarantee of longer flights. One of our planes is currently flying best on a 2 gram loop of rubber cut to 0.105", which results in a loop about 14" long (includes 2 o-rings). This gives us way fewer turns than you could put onto a narrower loop, but the prop has a fairly high pitch, and the results are pretty good. Our best flight in a 19 ft. ceiling is currently 3:28.

So I hope that this helps.
Thank you, this was very helpful!! I do stretch my rubber about 3 times its length when winding, but my motor is only about 1.4 g one of them was 1.6. So I will definitely try using a full 2 grams of rubber! About the rubber size, my best time was actually the with my thickest rubber, .091". I got 1:40 with it. Not what I want, but it is my best. I am using the ikara propeller that comes with the freedom flight kit (not using that plane tho haha), I don't quite remember the pitch, though.
If your best time is with your thickest rubber, your prop is probably too big. We were getting around 2:00 with 94 rubber and the really huge ikara props (the flaring ones) and after switching to the smallest props we broke 3 minutes with 0.87 rubber. We are trying to trim the props smaller for use with 81 rubber.
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Re: What are your guys times right now?

Post by someusername » January 31st, 2015, 2:35 pm

I have several questions regarding the trimming of the plane:

1. If we do get our rubber to weigh 2g, that would cause the rubber to be very loosely hanging when it it all out of winds . Should I still make the motor 2g or place my rear hook farther back?

2.I am also having an issue of my plane rolling hard to the left when in high torque. I have increased the angle of attack on the left side of my wing to try and counter it, but that doesn't seem to be having very much effect. any ideas?

3. We have been using a thicker rubber band to achieve our best times ( 2:50 with a 0.091 thickness ). Every time we try and switch to a thinner rubber band of about 0.081, we can barely break 1:30. Would increasing the prop's pitch help with using the thinner rubber band or only make it worse?

Any feedback would be greatly appreciated.
Last edited by someusername on February 2nd, 2015, 9:41 pm, edited 1 time in total.
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Re: What are your guys times right now?

Post by bjt4888 » January 31st, 2015, 7:00 pm

Someusername,
See some suggestions below.

Brian T.

++++++++++++++++++++++++++++++++++++++++++++++++
by someusername » Sat Jan 31, 2015 6:35 pm

I have several questions regarding the trimming of the plane:

1. If we do get our rubber to weigh 2g, that would cause the rubber to be very loosely hanging when it it all out of winds . Should I still make the motor 2g or place my rear hook farther back?

The rubber motor will not be loose. It is likely that the airplane will land with as many as 300 - 600 turns still remaining. You do not need to move the rear hook farther back. A typical hook to hook distance for this type of model is between 10" and 13".

2.I am also having an issue of my plane rolling hard to the left when in high torque. I have increased the angle of attack on the left side of my wing to try and counter it, but that doesn't seem to be having very much effect. any ideas?

Rolling to the left during the initial power burst can be a desirable flight character for low ceiling flying (anything below 50 ft. or so). Banking about 10 degrees in the first power circle is what we are looking for in some cases (depending upon the propeller and rubber). This banking effectively reduces the rate of climb and might allow a higher launch torque and greater duration. If your banking is excessive to the point that the airplane may crash under power, or if the banking continues too long and you are not getting to the ceiling with a reasonable amount of torque, a typical solution would be to first test more combinations of propeller blade area, propeller pitch and rubber thickness. Another solution can be to increase the wing offset. It is typical to have the wing offset about 0.5 inches (left wing or left wing main panel longer than the right). I could be of better assistance if you would provide much more data. What is your typical launch torque and describe your typical flight.

3. We have been using a thicker rubber band to achieve our best times ( 2:50 with a 0.91 thickness ). Every time we try and switch to a thinner rubber band of about 0.81, we can barely break 1:30. Would increasing the prop's pitch help with using the thinner rubber band or only make it worse?

Increased pitch and/or increased propeller blade area will usually require thicker rubber unless the pitch is already too low. What propeller, propeller pitch and airplane are you using? Remember, as Jeff Anderson and others have already stated in this wiki, thinner rubber will not necessarily result in more duration. The correct rubber thickness will depend upon the particular propeller blade area, blade shape and blade pitch and blade performance (ex. does the blade flare or not). In past years, maximum performance (without using a torqueburner arrangement) is has been achieved by thinning a "flaring shaped" propeller by sanding the blades. This strategy would probably be worth trying for this year too. Google search "Chris Goins Double Trouble" plan and construction narrative.

Any feedback would be greatly appreciated.

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Re: What are your guys times right now?

Post by InfiniCuber » February 1st, 2015, 7:48 am

Toms_42 wrote:If your best time is with your thickest rubber, your prop is probably too big. We were getting around 2:00 with 94 rubber and the really huge ikara props (the flaring ones) and after switching to the smallest props we broke 3 minutes with 0.87 rubber. We are trying to trim the props smaller for use with 81 rubber.
I am using the 24 cm prop from ikara that congress with the freedom flight kits. What other prop should I be using?
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Re: What are your guys times right now?

Post by retired1 » February 1st, 2015, 12:35 pm

A 30 cm loop very probably will be less 2.0 g unless you are using very heavy/large O-rings. If so, you are giving away power/duration.
Also, what is the pitch of both blades. The props are too high a pitch to start out and there is about 5 degrees difference between the blades.

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Re: What are your guys times right now?

Post by bjt4888 » February 1st, 2015, 4:51 pm

InfiniCuber,
You have indicated that you are using the Ikara propeller that comes with the Freedom Flight kit (but you are not using the Freedom Flight kit airplane) and your best time so far is 1:40 with .091" rubber and I believe that your last question is about what other propeller you should try.

I would like to try to help you, but would only be able to give general suggestions unless you can supply more information. Supply this information with your question and you will get very good, very specific ideas: airplane design specs, motor thickness, weight and length and indicate if black rubber o-rings or sliced plastic tube o-rings, for the particular best flight: maximum turns wound into the motor, backoff turns, maximum torque, launch torque, turns remaining when the airplane lands (measure by de-winding on your torque meter), propeller pitch at a particular radius (measure it at the 3" radius), flight description (here is an example of a flight description: climbed quickly about 6' in the first circle then five more circles to the ceiling (21 ft.) at about 1:00, cruise about four circles then descending for about 40 seconds, calm air, smooth flight no stalling and flat wings with little or no banking, approximate 25 ft. circle size).

Knowing data like this and more about your airplane and airplane flight characteristics would direct you to the propeller, motor, winding, trimming variable that you could work with to try to gain longer flight times.

Here is a general suggestion though. The students I am coaching are having pretty good success by increasing the pitch of the Ikara prop that comes with the Freedom Flight kit to about 12" (32.5 degrees at 3" radius) if it is not already 12". They have measured pitch on about eleven of these propellers and they have found most to be like this: 8.5" pitch at 1.5" radius, 10" pitch at 2" radius, 11" pitch at 2.5" radius, 12" pitch at 3" radius, 12.7" pitch at 3.5" radius and 13" pitch at 4" radius. This is not ideal pitch distribution, but they are getting flights of between 3 minutes and 3:15 in a 28' ceiling site pretty consistently. They are having greater success with a propeller that was modified from the "wide blade flaring" Ikara propeller. The modifications are similar to those shown on the Cezar Banks Leading Edge plan and the Chris Goins Double Trouble plans (attached). The Leading Edge plan shows a wide bladed Ikara "flaring" propeller with the trailing edge of the blade from the propeller spar rearward removed to reduce blade area and improve flaring. The Double Trouble pland shows a blade thickness diagram for sanding the Ikara "flaring" propeller to make it flare better. Obviously, I am not recommending using the exact Double Trouble or Leading Edge propellers as they are much smaller in diameter to fit the SO rules from that year. I am recommending the blade area reduction (reducing the wide bladed Ikara, not reducing the already small bladed Ikara that comes with the Freedom Flight kit) and the blade thinning (but maybe not quite as thin as shown on the Double Trouble). Generally, wider bladed propellers that are truly flaring will require thicker rubber motors to get the very best duration. The amount or trimming, thinning and initial pitch setting will require experimentation and testing. Another route to higher performance propellers, of course, is to build a balsa wood bladed "bucket prop".

Bye-the-way, based upon your current duration results (not knowing your ceiling height), it sounds like you are not winding your rubber motor hard enough. See previous posts in this forum about winding technique and winding close to maximum turns (and about finding the best launch torque, etc.).

Brian T.
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Re: What are your guys times right now?

Post by someusername » February 2nd, 2015, 8:18 am

based on bjt4888's post, how do you guys measure the radius and pitch of the prop? I am using the 24cm Ikara proeller, the one that comes with the Freedom Flight model, and I am also using the Freedom Flight plane.
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Re: What are your guys times right now?

Post by retired1 » February 2nd, 2015, 8:39 am

Freedom Flight sells a small pitch gauge. It comes disassembled, so it has a bit of a lower shipping cost.
I have seen instructions for building a pitch gauge that is similar. The nice part off FF's is that it has the receiver for the nose button built in.
Ray Harlan has instructions for building a very simplistic one.

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