High Ceiling Strategy

[klastyioer]

im gonna sound stupid but i dont rly trust this method it sounds low key sketchy and something not necessarily meant for this class of planes, anyone wanna show me proof that it actually works? (words r deceiving)

[coachchuckaahs]

We used this method in 2016 (Wisconsin Nationals), for round valley this year, and for state this year. The method works very well, and is accurate in both altitude and time. It is how we are preparing for nationals this year too.

See me at nationals and I can show you our log book, and you can compare the half flights to the full flights.

Coach Chuck

[klastyioer]

We used this method in 2016 (Wisconsin Nationals), for round valley this year, and for state this year. The method works very well, and is accurate in both altitude and time. It is how we are preparing for nationals this year too.

See me at nationals and I can show you our log book, and you can compare the half flights to the full flights.

Coach Chuck

will do, ill l be in that room for practically that whole day

[izzanom]

I've been looking through the forums for strategies for nationals since there's a 40' ceiling there and ive only flown at 24' max. I keep seeing stuff about the partial motor technique and I was wondering if anyone could explain it to me.

[coachchuckaahs]

I've been looking through the forums for strategies for nationals since there's a 40' ceiling there and ive only flown at 24' max. I keep seeing stuff about the partial motor technique and I was wondering if anyone could explain it to me.

That technique has been covered extensively this year, but I'll repeat the key points, as there has been some confusion.

Partial motor testing is a method that allows you to test for a higher ceiling in a smaller gym. In the example we will consider a typical school gym at 24', whereas Nationals is 38-40 feet. Let's use 38 feet to avoid conflict with the lights!

Lets say you plan to use 2.5g of rubber at Nationals. You want to get your plane trimmed for that mass, and figure out the correct rubber linear density (width, or cross sectional area) as well as launch torque. Rather than finding a larger gym for extensive testing, you use a partial motor, half in this case. This method accurately trims the plane and optimizes the rubber.

In this example, us a piece of rubber of the SAME WIDTH, but only 1.25g. Thus, the loop length will be 1/2 of the Nationals loop length as well. REPLACE THE REAR HALF of the rubber with a stick, hook on each end, that also weighs 1.25g (and is balanced so its CG is exactly between hooks). (Note: if you want to be more precise, the wound portion RUBBER alone should be half the mass of the full rubber. Thus, the "half rubber" will weigh slightly more than half the full rubber, as you cannot have half a knot, and you still have two O-rings. So it should be heavier by the mass of one O-ring plus half a knot. But for the heavy rubber we are using this year, this will be a small factor).

Now wind to the SAME TORQUE (peak and unwind to launch) as you will at Nationals.

Launch the plane and watch the RISE of the plane, the difference between launch height and peak height. Double this to know what full rubber will do. Then add this full climb height to your launch height to see full rubber altitude. Adjust your launch torque, rubber width, prop pitch, trim, rubber mass (remember, if you change rubber mass, also change the stick mass to represent the other half of the rubber), and any other parameters to get the correct half rise height to give 38 feet on full rubber. Optimize for time, your time will be approximately half that of full rubber. Amazingly close, assuming your launch point is close to the floor.

Then at Nationals, simply get rid of the stick and make a full loop of rubber, twice the length of your optimized half loop. Now you are carrying the same mass, so trim does not change. You are launching with the same torque, so climb characteristics do not change. But you are winding twice as many turns to get this torque, as you have twice as much rubber. The key is that the mass of the plane stays the same, but the energy stored within that mass is now doubled, so the rise, cruise, and letdown are also doubled.

If you have optimized with a lighter piece of rubber without a stick, then adding additional rubber for ceiling height changes the flying mass, flying speed, trim, climb rate, etc. There is no good correlation to do this.

Coach Chuck

[calgoddard]

As usual, coach Chuck has given an excellent description of the theory and best practice for a particular technique that can be used to maximize flight times of an indoor duration rubber powered stick model, like a Wright Stuff airplane.

I would like to add two subtle points regarding practice with partial rubber motors.

First, the length of the partial motor stick should be approximately half the hook-to-hook distance in his example. This way the rubber motor knots will unwind in the same fashion as they do when the model is flown with a full rubber motor and no partial motor stick.

Second, when flying with a partial motor stick any bad tendencies of the model during the initial climb out (immediately after launch) will only take place for a portion of the time that they would if the model were flown with a full rubber motor and no partial motor stick. For example, if the model is flown with a half motor, it will exhibit any bad tendencies after launch for only half the time that would be the case if it were flown with a full rubber motor. This may mask, or appear to minimize, bad tendencies due to dynamic trim changes. Let me explain further. You will be launching your model at a higher torque for a higher ceiling than the launch torque you used in a lower ceiling. Motor stick bending may cause the model to initially fly flat or even downward for a few seconds before the torque "bleeds off" and the model begins to climb. When launching from a standing position, the model may not hit the ground when launched at a high torque using a half rubber motor. But with the same launch torque and a full rubber motor, it may hit the ground. There are other instances where brief undesirable dynamic trim changes due to high launch torque may be tolerable for 5 seconds, but not 10 seconds, e.g. relatively short duration changes in wing wash-in.

I hope this helps.

Good luck to all you students that are flying at the 2019 SO Nationals.

[coachchuckaahs]

Thanks Cal, both good points. Having a team that relies on half motor testing, I missed the obvious-to-me point of the dummy stick length. On our LPP testing for Round Valley, we used 1/5 Motors. The stick then was 4/5 of the rubber mass, and 4/5 of the hook to hook length. Despite the substantial extrapolation, the full rubber results were quite accurate!

I agree with the comment on bad tendencies on launch. You must have a critical eye on all phases of flight, as the duration of issues is multiplied.

Coach Chuck