Raw Tournament Times

[bernard]

Brian, congrats to you and your team on an amazing time, even in such a low ceiling!

Did your team have the state wing chord bonus for their flights at the tournament?

[bjt4888]

Bernard,
The 3:41 time i quoted above for the Michigan state champion, Holt High School, was my unofficial time from the watch on my smart phone. I must have been focusing so much on watching their procedures that I didn't start my watch properly. I talked to them a couple of days ago and their official flight time was 3:46 in the 21 ft 4 in ceiling height, w/ 5-6 light touches on a (sort of) scrubbable ceiling. This is a raw flight time and they were using the regional wing.

They did test their state wing airplane quit a bit, but never got it above 3:25 in their home gym (28' ceiling) and 3:25 would be the "break time" that would make the state wing better (205 seconds plus 20.5 = 3:45.5) than the regional wing flying a 3:45. At states, they were planning on flying the state wing plane on their second official flight with a very aggressive ceiling scrubbing strategy if they needed to do this to win. Their half motor tests at 0.8 in oz launch torque with the state wing were about 2:00 flying to a height of 20 ft. (this would produce a 40 ft climb with a full motor, or a very aggressive, long ceiling scrub) This would have given them a theoretical time with bonus of 4:24. Of course, they knew that aggressive ceiling scrubbing works about one time out of five. As their excellent teacher was able to sign-up for the last flight time of the day, the Holt HS team already knew that they didn't need to take the risky, aggressive, state wing with .8 in oz of torque flying approach. They executed their alternate strategy perfectly with a crowd of about 50 people watching.

Hopefully any teams that are going to nationals are doing 1/2 or 1/3 motor testing in their gyms to determine launch torque to fully use the 65 ft ceiling that the University of Nebraska is generously making available. You will note from the pictures of this site that it has a peaked ceiling, so the usable ceiling height may be more like 50 or 55 ft. If our team was going to nationals, they would not be launching at full torque, but at a slight backoff (maybe wind to 1.1 or 1.2 and backoff to .9). Remember, a 65 ft. ceiling is still considered a "low ceiling" site. Unrestricted, full torque flights would probably require a 90 ft. ceiling (or more). Test to confirm as every airplane is a little different.

Brian T.

[someusername]

Regarding Brian T's latest post, I have a few more questions.

My first question is how do you increase your maximum height exactly? The gym at my school is roughly 30' tall, but even at full torque we could maybe get a maximum altitude of 40' (more or less). What variables could we change to increase the height without hurting our time?

Also, would the torque of a motor change much the more it is used? For example, if i test a motor's torque before it's ever been wound up and then test the same motor after its been tested say 10 times, would there be any difference?

And congratulations on your great times at the Michigan State Tournament!

[jander14indoor]

Absolutely, the turns to a given torque change as you use a motor. Generally getting lower for same turns.

But you need to put that in energy terms to understand how to take advantage of that properly. For rubber motors you can calculate energy stored in a motor by plotting the turns on horizontal axis, torque on horizontal axis. The area under that curve is directly proportional to energy. Winding curve is your input energy, unwinding curve is energy available to keep the plane in the air. More energy = longer times.

Others have mentioned they get best results from a motor after it has been used once or twice. That matches with years of experience of AMA flyers.

What's happening is the motor is storing more energy because the torque is falling off slower than the increase in turns. This is particularly true for the first couple of winds where you get a lot more turns and only a little torque drop off.

However, as you continue to use a motor, torque continues to drop, but turns don't continue to increase. You start storing less energy.

PS, I encourage you to challenge all this by collecting some data, it will make MUCH more sense if you do.
Make up 3-5 motors as identical as you can.
Wind one taking torque data vs winds until it breaks. Plot it. This establishes the max torque for those motors
Take a second motor and wind to 90% of breaking torque and unwind taking data both ways. The area under the unwind curve is the energy available to fly.
Wind that motor a second time, same max torque. Plot again. Torque should be lower on unwind, but turns much higher. Figure the area again, see if it is more than first wind.
Repeat that sequence until the motor breaks. Compare results
Do that with a third and fourth and fifth motor (until you patience wins out, but hey, repeatability is a critical issue in science and engineering).

From all that data you should be able to see if you want to fly contests on new, once used, twice used, whatever motors! With NO guessing.

Regards,
Jeff Anderson
Livonia, MI

[bernard]

For those who don't have torque meters or the time/rubber to wind and break some motors for graphs, I've posted some of mine, but I've moved it to the Winding topic since I think it is more relevant to that topic.

[bjt4888]

someusername wrote:

My first question is how do you increase your maximum height exactly? The gym at my school is roughly 30' tall, but even at full torque we could maybe get a maximum altitude of 40' (more or less). What variables could we change to increase the height without hurting our time?

Jeff Anderson and Bernard addressed you other question, so I'll give you some ideas for this one. The first step is to try to determine why your airplane is only climbing 40' under full torque. To help you with this, I need much more data. What do you mean by "full torque"? If you mean that you are winding to 90% of breaking torque (and my students tests of breaking torque indicates a range from 1.4 in oz to 2.1 in oz for typical motors in the .054 g/in to .06 g/in range (full weight motors of 15.75" to 17.5"). If you are launching at 90% of 1.4, or 1.26 in oz. and the airplane is only achieving 40 ' I'm assuming that you are using half (or other fractional) motors and you are actually climbing 20' and are predicting the full motor altitude of 40'. Is this what you are doing? Please describe.

Tell me exactly what you are doing and exactly what the airplane looks like throughout its flight. Also, when you load the motor on your plane at 1.26 in oz, can you see the motor stick bend (use a straight edge to check). Also, all the other data on the airplane would be helpful in this analysis: CG location, nose moment arm, wing incidence, stab incidence, tail moment arm, amount of left wing washin (all other surfaces are flat?).

A standard method to used to fly in a higher ceiling site is to use a propeller that flares less, or doesn't flare at all. If your current propeller is the Ikara wide bladed flaring with the back portion of the blade cut off at the spar and some additional pitch twisted in and the blade thinned progressively from the edge to the spar per the Chris Goins Double Trouble plan, you may want to try the same propeller without thinning the blade. Or, you could use the stock Freedom Flight kit propeller. The stock propeller is a typical "high-ceiling" symmetrical shape. Using a symmetrical propeller like this (also usually lesser blade area than a flaring prop) at a moderate pitch of between 12" and 13" (maybe even 10" or 11") will give you increased rpm over a flaring prop (if the same rubber is used) and should increase the rate of climb (if you don't have motor stick bending or twisting issues). You would think that higher rpm would be a disadvantage as it will use up turns quicker, but if this gets you to the ceiling and your let-down phase is reasonable, your duration may be maximized. Here's a hypothetical example based roughly on my student's data for a 8 5/8" 1.0 gram half motor (with 1.0 gram spacer half the length of the hook to hook distance, including rubber o-rings): 65x15 or 975 max winds and torque of 1.3 in oz, backoff 2x15 to 0.8 in oz, flight altitude 28 ft (hit the ceiling lightly), duration 2:20 and turns remaining of 60 for an rpm of 366. Prop pitch was about 32 degrees measured at the 3" radius or about 11.77". So, the full motor wound to 130x15 and backed off to about .8 in oz should fly about 56 ft altitude and 4:40 duration. This data is representative of a partially trimmed airplane. A better trimmed example should exceed 5:00 easily at 56 ft. climb altitude. FYI a typical rpm for the students flaring prop is about 320 and this is pretty ideal for a typical gym ceiling.

Brian T.

[someusername]

someusername wrote:

My first question is how do you increase your maximum height exactly? The gym at my school is roughly 30' tall, but even at full torque we could maybe get a maximum altitude of 40' (more or less). What variables could we change to increase the height without hurting our time?

Jeff Anderson and Bernard addressed you other question, so I'll give you some ideas for this one. The first step is to try to determine why your airplane is only climbing 40' under full torque. To help you with this, I need much more data. What do you mean by "full torque"? If you mean that you are winding to 90% of breaking torque (and my students tests of breaking torque indicates a range from 1.4 in oz to 2.1 in oz for typical motors in the .054 g/in to .06 g/in range (full weight motors of 15.75" to 17.5"). If you are launching at 90% of 1.4, or 1.26 in oz. and the airplane is only achieving 40 ' I'm assuming that you are using half (or other fractional) motors and you are actually climbing 20' and are predicting the full motor altitude of 40'. Is this what you are doing? Please describe.

Tell me exactly what you are doing and exactly what the airplane looks like throughout its flight. Also, when you load the motor on your plane at 1.26 in oz, can you see the motor stick bend (use a straight edge to check). Also, all the other data on the airplane would be helpful in this analysis: CG location, nose moment arm, wing incidence, stab incidence, tail moment arm, amount of left wing washin (all other surfaces are flat?).

A standard method to used to fly in a higher ceiling site is to use a propeller that flares less, or doesn't flare at all. If your current propeller is the Ikara wide bladed flaring with the back portion of the blade cut off at the spar and some additional pitch twisted in and the blade thinned progressively from the edge to the spar per the Chris Goins Double Trouble plan, you may want to try the same propeller without thinning the blade. Or, you could use the stock Freedom Flight kit propeller. The stock propeller is a typical "high-ceiling" symmetrical shape. Using a symmetrical propeller like this (also usually lesser blade area than a flaring prop) at a moderate pitch of between 12" and 13" (maybe even 10" or 11") will give you increased rpm over a flaring prop (if the same rubber is used) and should increase the rate of climb (if you don't have motor stick bending or twisting issues). You would think that higher rpm would be a disadvantage as it will use up turns quicker, but if this gets you to the ceiling and your let-down phase is reasonable, your duration may be maximized. Here's a hypothetical example based roughly on my student's data for a 8 5/8" 1.0 gram half motor (with 1.0 gram spacer half the length of the hook to hook distance, including rubber o-rings): 65x15 or 975 max winds and torque of 1.3 in oz, backoff 2x15 to 0.8 in oz, flight altitude 28 ft (hit the ceiling lightly), duration 2:20 and turns remaining of 60 for an rpm of 366. Prop pitch was about 32 degrees measured at the 3" radius or about 11.77". So, the full motor wound to 130x15 and backed off to about .8 in oz should fly about 56 ft altitude and 4:40 duration. This data is representative of a partially trimmed airplane. A better trimmed example should exceed 5:00 easily at 56 ft. climb altitude. FYI a typical rpm for the students flaring prop is about 320 and this is pretty ideal for a typical gym ceiling.

Brian T.

Unfortunately, I do not currently have a functional torque meter, so I do not have exact information on the amount of torque I am using. What I do know is that I use 2 setups. The main one is a 0.094 motor wound up to 1500 and backed off to 1400, which usually will get us to about the 40' or higher point. the pitch on the blade is set at 40.

The second setup, which is newer, is a 0.081 motor wound up to 2000 and backed off to 1900 using a propeller with a pitch of 30. Since this design is fairly new, I do not have exacts on the maximum heights or the times due to having bad luck with air currents in our gym, but it does show a lot of promise.

For both setups, I am using the freedom flight model with no wind chord bonus (but I do have the colored panel). I do not have any current information regarding the washin, but I would assume it is about 3/8" and it has worked well in the past. as far as the angles of incidence go, I also don't have measurements on those. The way I set my angle of incidence is by drawing a line on the wing posts and measuring the distance of the line from the motor stick, and this has also worked well for us. The incidence of the horizontal stabilizer is 0 or at the very least very close to it (maybe slightly above 0 if anything) and it is tilted so that the left side of it is also about 3/8" higher than the left.

I have had no issues with motor stick bending, or at least no noticeable issues. I glued some carbon fiber string to the top of the motor stick, which seems to have eliminated all or most of the motor stick bending problems. The center of gravity is set about 2" behind the TE of the wing on the top of the motor stick.

As far as the characteristics of the flight go, It seems to fly fairly well, though there are several issues I notice during the flight. The most prominent is that the circle tends to "drift" through the room I am testing in, so the path would look like a loopty-loop pattern if viewed from above, but it only drifts maybe 7 feet at most from start to finish. The circle radius is not very big, about 20' more or less, due to the size of our gym. I do not want to mess with this before nationals because I do not know if it would affect the launch or any other aspects of the flight in a negative way. But other than that (when not being affected by the air conditioning) It seems to fly with no problems. Our average time is about 2:30, but I have gotten several 3:30 from using the 0.094 setup, and I believe that I could easily get close to that with the 0.081 setup.

Thank you for all the help, and I apologize for not being able to provide exact numbers that would help with analysis.

[bernard]

Unfortunately, I do not currently have a functional torque meter, so I do not have exact information on the amount of torque I am using. What I do know is that I use 2 setups. The main one is a 0.094 motor wound up to 1500 and backed off to 1400, which usually will get us to about the 40' or higher point. the pitch on the blade is set at 40.

I highly recommend buying or making a torque meter. I've attached instructions for making a torque meter. Tim Goldstein's website also has a torque meter wire calculator that can get you length values for the wire widths you have; I recommend using 0.020" or 0.015" diameter wire.

[bjt4888]

someusername wrote, "

Unfortunately, I do not currently have a functional torque meter, so I do not have exact information on the amount of torque I am using. What I do know is that I use 2 setups. The main one is a 0.094 motor wound up to 1500 and backed off to 1400, which usually will get us to about the 40' or higher point. the pitch on the blade is set at 40.

The second setup, which is newer, is a 0.081 motor wound up to 2000 and backed off to 1900 using a propeller with a pitch of 30. Since this design is fairly new, I do not have exacts on the maximum heights or the times due to having bad luck with air currents in our gym, but it does show a lot of promise.

For both setups, I am using the freedom flight model with no wind chord bonus (but I do have the colored panel). I do not have any current information regarding the washin, but I would assume it is about 3/8" and it has worked well in the past. as far as the angles of incidence go, I also don't have measurements on those. The way I set my angle of incidence is by drawing a line on the wing posts and measuring the distance of the line from the motor stick, and this has also worked well for us. The incidence of the horizontal stabilizer is 0 or at the very least very close to it (maybe slightly above 0 if anything) and it is tilted so that the left side of it is also about 3/8" higher than the left.

I have had no issues with motor stick bending, or at least no noticeable issues. I glued some carbon fiber string to the top of the motor stick, which seems to have eliminated all or most of the motor stick bending problems. The center of gravity is set about 2" behind the TE of the wing on the top of the motor stick.

As far as the characteristics of the flight go, It seems to fly fairly well, though there are several issues I notice during the flight. The most prominent is that the circle tends to "drift" through the room I am testing in, so the path would look like a loopty-loop pattern if viewed from above, but it only drifts maybe 7 feet at most from start to finish. The circle radius is not very big, about 20' more or less, due to the size of our gym. I do not want to mess with this before nationals because I do not know if it would affect the launch or any other aspects of the flight in a negative way. But other than that (when not being affected by the air conditioning) It seems to fly with no problems. Our average time is about 2:30, but I have gotten several 3:30 from using the 0.094 setup, and I believe that I could easily get close to that with the 0.081 setup.

Thank you for all the help, and I apologize for not being able to provide exact numbers that would help with analysis.

See Bernard's previous post. A torque meter is the most important tool in the box after the winder.

Your objective for Nationals is to determine the winding (and torque value) and rubber and prop pitch/style that will give the best duration under a 65' ceiling. The only way to determine flight specs for a higher ceiling site when you only have a lower ceiling site to practice in is to use the partial motor testing methodology. This methodology is very simple to perform and it is very well described in an article on Ray Harlan's indoor specialties website. If you read this and do it, you will increase your potential for a high placing at Nationals dramatically.

Here's some data points from my student's testing for motors similar to the two motors that I believe you are testing. A .094" thickness motor will be about 15" long (before winding, not including the knot and with two black rubber o-rings) and its theoretical maximum turns is about 1,960. At 1,500 winds you are at about 76% of maximum. This wind will get you a maximum torque of about 1.0 in oz and with 100 turns of backoff you will be at a launch torque of about 0.44 in oz. The 40 degree pitch of you propeller (if measured using the Freedom Flight gauge that measures at the 2.25" radius) is equal to a local pitch of 11.8". Knowing that the Freedom Flight stock propellers increase in pitch about 1.8" from the 2.25" radius station to the widest part of the blade (at the 3" radius station), I would call this a 13.6" pitch propeller. 13.6" is pretty low pitch for rubber as thick as .094". If I were you, and if you have enough time to test this, I would increase the pitch to about 42 degrees, which corresponds to about 14.5" pitch at the 3" radius station. This change should slow the rate of climb and allow you to put more turns and torque into the .094 rubber. I would then try this rubber using a 1/2 motor and wind to about 80% of maximum turns, or about 1,575/2=787 turns (or maybe only 750ish would be ok), which will be a torque value of about 1.2 in oz and backoff about 100 turns for the first test flight. If this test flight climbs about 20 ft, then you are in pretty good shape to test less backoff. For the second test flight (still with a 1/2 motor) try backing off about 75 turns (which should correspond to about 0.6 in oz torque). If this test flight reaches about 25-28 ft., then you are almost there (hopefully, your duration is increasing nicely with each test flight). A 28 ft. altitude 1/2 motor test flight translates into 56 ft. of climb with a full motor. If you are still short of the 25-28 ft. range with a 1/2 motor, the next test flight would be a wind again to 750-785 turns and backoff 60 turns, etc.etc. till you get to 2:30 with a 1/2 motor and about 28 ft. altitude. This should translate to a 56 ft. climb and 5:00 flight at Nationals.

Another thought should you continue testing the .081" motor; 2,000 turns is only about 70% of the predicted breaking turns of 2,890 for a 20.5" motor of this thickness. With a 2,000 winding and 100 backoff, you are probably launching with only .35 in oz torque.

You actually do have incidence angles. Think about the triangle formed by the wing chord and the difference in height between the two wing posts (same concept for the stab incidence). Also, hopefully your wing washin isn't 3/8" as the kit recommended setting is 3/32" (and this works pretty good). Was this a typo?

Good luck and good testing,

Brian T.

[bjt4888]

someusername,
Sorry, I was typing too fast earlier today. Backoff winds when 1/2 motor testing should be approximately halved just like maximum turns are halved. I made a mistake in the post above indicating backoff turns for a full wind. For a first 1/2 motor test flight wound to 750 - 780 turns, a backoff of about 45 turns should give you a launch torque of .5 in oz. If this flight is safe, then you could increment torque up by backing off less on the 2nd and subsequent flights (ex. same max turns and backoff 30 and, if still safe flying character and under 28 ft. total altitude, try backoff of 15 or 20). I addition to determining the torque and winding strategy that will carry you to 1/2 the height of the 65 ft. Nationals site (probably want to shoot for 50 or 55 ft to be safe), 1/2 motor testing will demonstrate if your airframe can handle high torque. As torque is increased, your airplane will probably bank a fair amount in the first circle or two. This is ok as long as the bank doesn't cause the airplane to roll to the floor. It's not even a problem if the airplane descends in the first 1/2 circle or so and then starts climbing, although this is not ideal for a 65 ft site for this type of airplane.

Another article you could read about partial motor testing is in Indoor News & Views issue #120 (F1L Issue). It's easy to find on the web.

Good luck,

Brian T.