Wright Stuff C

[CrayolaCrayon]

Confession: lechassin is my son Luke, I'm Eric the Dad. He hasn't built yet this year, he's winding, launching, observing performance, and trimming. I rationalize this because we aren't using a kit designed by an F1D champ and delivered to our door pre-developed. I think what we're doing is better, because while the rules do allow kits, they also say we should be designing the plane. To me that precludes kits entirely, but if other kids can buy a design, then I think it's fair that I give my boy a design *dons flame suit*.

The rubber inconsistency and rapid deterioration: one break-in run and three flights for an all-day trim/practice session means a LOT of rubber but I don't see how one could get good trim information with a motor that loses power each subsequent flight.

Just be aware that he'll have to build his own planes for competition. It is illegal to fly a device built by an adult or coach at competition (I'm sure you know this). Remember he'll have to execute the whole thing by himself with a partner.

Your rubber should be doing the exact opposite after each flight. Max torque should be increasing as the rubber stretches, so should the winds you're putting in. Check for burrs in the rubber, especially near the knot. Don't be afraid to push the motors to their max.

[lechassin]

As the number of winds a lightly used motor will hold increases, does this come at some cost to the total energy that the motor can deliver? I ask because we really would prefer to get more than two flights out of a motor for trim sessions, but we don't know how to ensure that the data we derive from observing a flight is consistent. Can we run the motors more than two flights and get reasonable trimming data by using some established protocol that has been published? We would love to read about that, hint, hint . For example,a rule of thumb like "wind x number of turns past the previous flight then wind back down to desired torque".

Luke will build the plane if only because I'm more interested in what kind of young man he becomes than in what he achieves at WS, but I will never believe that's the spirit all over...

Last year, I finalized the design and set up jigs made of machinist's blocks so that a monkey could crank out identical planes one after another in 3 hours that required little or no trimming. We started doing it that way when we realized how easy it was to get these things stuck in the gym's rafters. We quickly learned not to become attached to the planes like we do in other kinds of aeromodelling. We already have one of this year's planes stuck in a tree

[jander14indoor]

One of the great things about Wright Stuff is how many aspects of science/technology (and as a result how to be a successful human) it can teach you.
In my by coaching lectures/presentations I try to stress how important jigs, fixtures & gages are to building what you intend to build. Consider having your students design and build those too. Much room for creativity and improved understanding there.

Energy and winding. This is an annual topic, and if you search you can find the following discussion repeated several times.
Others are better at winding than I am, you already have that advice. But how do you evaluate the results?
First, you MUST have a torque meter. Eric, I think you've already mentioned you have one.
Now, make up a couple of motors as identical as you can. Length isn't really important, short is fine to save rubber as the results scale nicely with length. I typically pick 4 inch motors to keep total winds down but not too low.
Now, using the torque meter and a winding recipe, wind your first motor to breaking. Every X winds, as convenient record the torque. Plot it torque vs turns.
Next, take a second motor and using the same winding recipe, wind a second motor to 90 or 95% of the previous breaking torque. Now UNwind it, again taking data. Plot all that.
Take a third motor, again wind using same recipe, but to say 80%.
Of course, variability has a say here, you might want to repeat those test points a couple of times for completeness, but one set will demonstrate the basic principle.
You should notice a couple of things.
- The wind up is an s curve, steep at first, then flattening out, then climbing steeply again.
- The unwind curve is LOWER than the wind curve, AND THAT IS WHAT YOU FLY ON. And the 80% unwind curve follows the same as the higher one, by dropping quickly to that unwind curve.
So, what can you learn from this? lots if you take it further.
It shows why always winding to near max and back off to launch torque is good. You always end up with more turns (more energy, more fuel in the tank) than winding up to launch torque only, and the harder you wind, the more turns you will have when backing off. If that is all you do, you will have learned some very useful lessons, but there is more.
The area under the curve IS the total stored energy (might need some units conversion, but its there). That lets you answer your question about energy, and experiment meaningfully with many questions.
- You can compare different rubber widths/linear densities.
- You can compare different rubber batches.
- You can compare the effect of multiple winds, resting times, etc.
- You can compare different winding recipes.
And so on.
Note, these are quantitative comparisons, not qualitative, not opinion.
AND, none of this requires a gym! Not that you won't need to take it to the gym to find out what times you get from different energy storage and release curves, but you can at least make that a pre-known quantity to vary in conscious ways.
Science and engineering at its best.

Jeff Anderson
Livonia, MI

[calgoddard]

The quality of the rubber can make a significant difference in the flight times that can be achieved. Rubber used for flying indoor models should be stored in a dark, cool environment. Keep it away from sunshine as UV radiation can adversely affect its ability to store and yield energy. Tan Super Sport (TSS) rubber is normally used by most indoor and outdoor free flight modelers. I understand that TSS rubber is a hybrid of natural rubber and synthetic rubber. It is commercially available from FAI Model Supply, Freedom Flight Models, and other sources.

TSS rubber replaced TAN II rubber, which is no longer manufactured and can be very expensive, depending on the batch, assuming you can find any for sale. The May 1999 batch of TAN II rubber is legendary for its quality. Many (if not most) indoor flying records have been set using May 99 TAN II rubber. Recently 90 grams of TAN II rubber was allegedly sold for $1500!

According to experts, including Don DeLoach, since 2009 all batches of TSS rubber are “good.”

Flying with TAN II rubber is not necessary to win any WS competition. In WS competition the following factors are each more important than the quality of the rubber, provided the rubber is decent: 1) air frame design: 2) prop design; 3) trim; and 4) winding. The single most important factors that determine success in the WS event are extensive practice and good record keeping, i.e. the creation and use of detailed flight logs.

Not infrequently rubber used in WS competitions is of poor quality. As a general rule of thumb, the rubber used in free flight should be capable of stretching at least 6 - 8 times its relaxed length without breaking. Some rubber can be stretched up to 10 times its relaxed length. Make up a single loop of the rubber that you want to test that is one foot long. Secure one end of the loop to a stooge, e.g. a cup hook screwed into a board clamped to a table. Lay an extended tape measure out in front of the stooge. If the loop won’t stretch to at least 6 - 8 feet in length without breaking, the quality of the rubber is suspect.

[CrayolaCrayon]

Recently 90 grams of TAN II rubber was allegedly sold for $1500!

I can attest to this. I've seen lots of auctions on ebay. Especially one where around 40 grams went for +400$

[coachchuckaahs]

Confession: lechassin is my son Luke, I'm Eric the Dad. He hasn't built yet this year, he's winding, launching, observing performance, and trimming. I rationalize this because we aren't using a kit designed by an F1D champ and delivered to our door pre-developed. I think what we're doing is better, because while the rules do allow kits, they also say we should be designing the plane. To me that precludes kits entirely, but if other kids can buy a design, then I think it's fair that I give my boy a design *dons flame suit*.

The rubber inconsistency and rapid deterioration: one break-in run and three flights for an all-day trim/practice session means a LOT of rubber but I don't see how one could get good trim information with a motor that loses power each subsequent flight.

While getting to the gym is important early on, as you have done, I would STRONGLY urge you to have the kids build ALL prototypes. That is how they learn and get proficient in building. These planes are rather simple, can be built with minimal investment.

Others have answered on the rubber. Winding properly, and understanding YOUR rubber, is important to success. Much has been written on winding in the past, review the forums. Generally the rubber energy storage goes up, at least for the first 4-6 full winds. This thin rubber is easy to break, it does not take too much over-torque during winding. But a pound goes a long ways, and is not very expensive.

I think I saw one batch of 5/99 Tan II rubber at 60g unused 1/8" go for almost $2000. It came out to almost $10,000/pound. Not needed for SO.

Teach the kids to weigh every part, before and after gluing, and to log every conceivable aspect of every flight.

Coach Chuck

[coachchuckaahs]

As the number of winds a lightly used motor will hold increases, does this come at some cost to the total energy that the motor can deliver? I ask because we really would prefer to get more than two flights out of a motor for trim sessions, but we don't know how to ensure that the data we derive from observing a flight is consistent. Can we run the motors more than two flights and get reasonable trimming data by using some established protocol that has been published? We would love to read about that, hint, hint . For example,a rule of thumb like "wind x number of turns past the previous flight then wind back down to desired torque".

Luke will build the plane if only because I'm more interested in what kind of young man he becomes than in what he achieves at WS, but I will never believe that's the spirit all over...

Last year, I finalized the design and set up jigs made of machinist's blocks so that a monkey could crank out identical planes one after another in 3 hours that required little or no trimming. We started doing it that way when we realized how easy it was to get these things stuck in the gym's rafters. We quickly learned not to become attached to the planes like we do in other kinds of aeromodelling. We already have one of this year's planes stuck in a tree

You are implying what I have seen in other posts, that the kids don't do the building. Do you have concrete evidence or observations? I have seen high school kids do amazing build jobs on much more complicated planes (F1D), and their workmanship is impeccable. We continue to hear accusations that some teams have adult-built planes, but never any solid reasoning for these claims. I would be interested if you have anything concrete. You can PM if you prefer.

As far as losing planes, there is no need. My kids only built two planes last year. If you test with half rubber, you can work on height (launch torque, rubber width) at half altitude and never risk the plane. Last year we never ran with full rubber until the actual contest (Region, State, Nationals). Even when the contest gym was same height as our test gym, we tested with half rubber. Things scale very nicely. See last year posts on this topic.

If you are winding hard in practice, you may only get 2-3 flights out of the rubber, though a more conservative wind should get you 5-6. But, you want to be sure to wind the same in practice as the contest. If you never went to full launch torque in practice, strange things may occur in the contest. However, for a given launch torque, the plane trim should not change for different wind aggressiveness. The altitude may change.

Coach Chuck

[calgoddard]

You can wind a rubber motor to a given “max” torque, and then back off to a predetermined launch torque that will get your airplane just below the highest obstruction when it has reached its peak altitude. In the indoor free flight community this is called a “no touch” flight which is often preferred in WS competition due to its safety given that you only have two official flights. However, a week later a rubber motor of the same size (length and weight), made from the same batch of rubber, and wound the same way may cause the same airplane to climb too high in the same gym, hit a beam or a light fixture, and plunge toward the floor. What happened? Well differences in ambient temperature on the different flight days affect both the density of the air and the hysteresis of the rubber. In the past the preferred strategy in WS competition has been to perform a conservative first official flight and to adjust the launch torque higher on the second official flight (based on data in your flight logs) to get closer to the ceiling obstructions without hitting the same. The high time of the two official flights used to be your base score for every other set of WS rules that I can recall. However, this strategy is somewhat compromised by the WS 2020 rules due to the bonus for orbiting in opposite directions on the two official fights which gains you the total of both flight times as your base score.

[lechassin]

There's a lot of good information posted and I appreciate it. There's more than we can absorb now but we will come back to it.

Our planes and props are early designs. They behave well at partial thrust (like in the videos I posted), but as we increase the torque and number of knots, the flight path becomes more erratic, I think because of excessive thrust or turbulent propwash. We are flying at high torque to discern the next design changes, but it does sometimes cost us a plane.

We aren't logging yet, but we hope to soon. We're still changing the airframe itself or tweaking the up trim, moving the CG, or adjusting the rudder throw. We just tweak and fly again right away; it's more time efficient.

As for who is building the planes: I am certain "built by the kids" means different things to different people, and it is a simple reality that some people have more "moral flexibility" than others. Supervision likely ranges from "none" to "micro-managing". Since the degree of independence that is required isn't specified, there's no way to enforce anything anyways.

Luke's plane last year was the first plane from his school to fly at all ever, let alone over a minute. He has no interested coaches, no school support (dedicated gym time, dedicated funds, etc...), no team mates, and started from zero knowledge. The fact that I'm heavily [excessively?] involved is IMO perfectly ethical and is the necessary kick-start that was sorely lacking. I hope by the time my younger boy comes of age that he will be on a team that has some of the characteristics I discern in other teams, but I also hope The System will be lenient for now.

[coachchuckaahs]

The half motor approach allows high torque flights with much lower risk, as climb is cut in half.

Logging is important even (especially) at early stages, as you make changes. Otherwise you forget what changed and worked vs did not work. I would encourage you to start logging now! Or log book is our most valuable tool

Coach Chuck