Wright Stuff C

[lechassin]

I just understood "half motor". It's half the length, I thought you meant half the winds Great idea, I'll verify that there isn't undue tension on the motor stick and I'll add a gram to compensate for the loss of rubber.

[giraffesarecool]

Where could I find rubber that is thinner than the ones included in the freedom flight kit? I’m thinking anywhere between .05” and .07”.

[CrayolaCrayon]

Where could I find rubber that is thinner than the ones included in the freedom flight kit? I’m thinking anywhere between .05” and .07”.

On the Freedom Flight website, you can order custom cut rubber.

[calgoddard]

lechassin -

Don't add clay ballast to your airplane when you fly it with a half rubber motor to make up for the removal of rubber motor weight. You need to make a half motor stick and use that instead of clay ballast.

Say you want to test how your airplane will fly with a 2 gram rubber motor and make sure it doesn't hit the ceiling in your gym when launched at high torque.

Make up a 1 gram rubber motor that should be about half the length of the 2 gram rubber motor.

Make a partial motor stick that is also half the length of the 2 gram motor. SEE CORRECTION OF LAST STATEMENT BELOW. It can be made from a length of 3/32-inch square balsa wood stick with 0.020-inch music wire hooks secured to each end. The distance between the outer ends of the hooks on the partial motor stick should be half the length of the 2 gram rubber motor. I like to bend the inner ends of these hooks at 90 degrees, press them into the side of the balsa wood stick, wrap the ends with thread, and coat with CA. This ensures that the hooks will not pull free under the pulling force of a highly wound rubber motor. This partially completed half motor stick should weigh less than 1 gram. Then wrap a suitable length of thin Copper wire (without plastic insulation) around the middle of the half motor stick to bring it up to exactly 1 gram in weight.

The rear hook of the half motor stick will be connected to the rear hook on the motor stick (fuselage) of your airplane. The wound half rubber motor will be connected between the prop shaft hook and the front hook of the half motor stick.

You need to understand several things about the dynamics of the use of a half rubber motor.

First, the torque readings will be the same as if you were using a full rubber motor instead of a half rubber motor, they will just occur at half the number of winds.

Second, with a half rubber motor your airplane will fly to X feet of max altitude at launch torque Y, but will fly to 2X feet of max altitude at launch torque Y with a full rubber motor, i.e. a rubber motor of twice the weight and twice the length (but the same nominal width).

Third, here is a subtle point not appreciated by many indoor fliers, even those with experience. Any unusual flight pattern traits during the bleed off of high torque observed when flying with a half rubber motor will last twice as long with a full rubber motor when both flights are launched with the same launch torque. Here is an example. With a half rubber motor, the airplane launched at shoulder height at 0.3 inch-ounces of torque momentarily descends but recovers and starts climbing before it hits the floor. With a full rubber motor launched at shoulder height at 0.3 inch-ounces of torque the airplane descends and hits the floor. Motor stick bending for twice as long on the full rubber motor flight likely caused this scenario.

[coachchuckaahs]

A minor (or not so minor) clarification to the excellent summary by Cal: The stick that substitutes for the rear half of the rubber is 1/2 of the "hook-to-hook" length of your plane, not 1/2 of the rubber loop length.

We have always used this method. Last year in a test gym with an 18' ceiling we dialed our planes on half rubber and got 2:30-2:45 no-touch at 18.5" obstruction. We went through many pieces of rubber, as we came down from mile-high altitude, and we found the same prop optimized with substantially different rubber. Once we achieved the flight we wanted, we made up full rubber and competed, attaining 5:08 with about 38' obstructions in the contest. We did touch, but this was because the early part of the flight went over a rather large crowd providing more lift (and drift) than anticipated.

We are using primarily 1/4 rubber (and a 3/4 stick) for F1D testing, since we do not have a Hindenburg hanger at home for testing.

With very light rubber (F1D 1/4 rubber is 0.1g), you also need to account for your O-rings and knots, as these are mass and do not contribute to the energy for flight. Therefore, we weigh several knots form broken rubber, and of course know the tare weight of our o-rings. We wind with the stick in place on our torque meter, so we only need an o-ring at the prop end with half rubber, whereas 2 o-rings for full rubber. But, for example, if full rubber is 2g, and knot is 0.015g of that, then we calculate half of 1.985g (0.9925g), then add on the knot, to get 1.0075g. This is our cut and tied rubber. As you can see, it made a very small difference, but when down at 0.1g for 1/4 F1D, it is more important.

We then fly and log altitude (actually we log altitude on every lap until cruise is established). Lets say the event will be in a 25' gym, then we want 12' rise on half rubber. If rubber is too strong, maybe it climbs to 16', which would be 32' (climb) on full rubber. In our 20' test gym, we are still clear of the rafters, and can recover the plane and try thinner rubber (or more pitch) to get 12' rise.

Remember also it is the vertical rise, not height above the floor. So if your plane starts at 1' and goes to 13', that is 12' rise. At competition on full rubber, you also start at 1', and the plane rises 2X12, or 24', for a very close pass at the rafters.

And Cal makes a very important point, that duration of poor behavior at the start of a half rubber flight is also doubled.

Coach Chuck

[lechassin]

I'm glad you clarified that, I never would have thought of it, thanks much.

*runs to remove ballast and make 1/2 motor stick*

[calgoddard]

Coach Chuck is right - the half motor stick should have a length that is half the hook-to-hook distance of your airplane.

I got caught up in the half motor thing when I was writing and made a mistake.

Thanks Chuck for proof reading my post about use of a half motor stick.

[lechassin]

Alright, stick is made and working, installs and removes easily from both planes (press fit at the CG end) and the planes behave as you said (in the house). Faster winding process, less rubber usage, and no more lost planes

Will the remaining knots be proportional also? If we have half a row of knots on landing with the short motor, will we also have half a row on the full motor? I mean twice the actual number, but half the row?

In other news, we made a support with two small ball bearings for the hook end of the torque meter, it's much smoother and centers perfectly every time.

[coachchuckaahs]

Yes, the knots remaining (or turns remaining) are proportional as well. We express turns remaining as fractions of routes of knots.

To clarify, the half stick hooks to the rear book on the plane, and the front of the stick hooks to the rubber. Put the stick on the torque meter, then you up rubber as usual after winding. Robert to prop, the back end of stick to tail hook.

Coach Chuck

[lechassin]

We had a good trimming session today; the 1/2 motor with stick is very convenient and very close to proportional. On a 1/2 motor the times were 42" to 53" but with no single setup performing identically both ways (something had to give in one direction or the other). A setup that accommodates only a rudder change and nothing else results in reduced times. I don't think Luke will be able to do reliably do anything more than a rudder change and two winds/launches within the 8 minute allotment, so we have some work to do...

Our best two-way setup with identical airframe/motor/winds/torque and only a rudder change, yielded 1'19" to the left and 1'03" to the right.

Our best no compromise flights were 1'37" to the left and 1'25" to the right:
https://www.youtube.com/watch?v=sKxZvII ... e=youtu.be
https://www.youtube.com/watch?v=9cX91g3 ... e=youtu.be
To get these times, the initial climb is too violent both ways and the flight path going right is too erratic. The CG was at 31% with 2mm decalage. We moved the CG to 23% with 3mm decalage to get the more conservative flights but then we can't get to the rafters even at maximum launch torque (too much drag from excessive decalage?). If we hit something it doesn't dive straight down to the floor anymore but it still loses a lot of altitude, which is not acceptable. 23% already seems too forward to me, unless you all think otherwise.

We want those max times with only a rudder change. Trimming for that is a frustratingly circular protocol where any one change demands other changes. For example: a small rudder change makes the plane bank a little more, so a bit more more decalage and slightly higher launch torque are needed, both to make up for the slightly reduced lift during banking, but the increased drag might ruin everything.