Fine adjustments for maximum duration

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bjt4888
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Fine adjustments for maximum duration

Post by bjt4888 »

All,

So, Pumptato-Cat has been sharing her flight log data and videos with me via the forum secure methodology and is doing pretty well. Her current flight times would have placed her in 5th place behind four of my teams that just competed in the Boyceville Satellite (virtual) Invitational. Boyceville had 154 teams competing (59 entered the Flight Event) from 17 states and my four teams (two varsity teams and two JV teams from two schools) had flights that were between 23 and 41 seconds longer than the other best teams (this is after taking a significant deduction for our relatively high ceiling heights of 28-29ft). I'd like to help every team that can see this info on the Forum get to this next higher level. I'm telling you all this in order to encourage teams to go for more and keep working hard on their testing, test planning and data analysis.

As Cat is flying pretty well now and is tracking the following data points: motor weight, max turns, max torque, backoff turns, launch torque, climb height and flight time, and she had worked quite hard to get her center of gravity (balance point) location pretty close to optimal and has worked on her airplane turn settings to get a reasonable circle size and reasonable climb, she (and you) will likely gain some flight duration by following the recommendations below.

Cat,

So, one more question and strong recommendation for data other than starting to measure and log motor density data for every motor. You will definitely want to start logging "turns remaining". After all flights land, you can pickup the airplane and hold the propeller so that the motor doesn't unwind anymore. Then carry the airplane to the torque meter and hook the motor on the meter and the winder and wind backwards to count the remaining turns. This is one of the primary data points used to determine if you need thicker (denser) or thinner (less dense) rubber.

Do you have a feel for how many turns were remaining after your last few flights? Be specific in answering this question. For instance, "When I picked up the airplane, the motor was hanging from the hooks and had almost zero knots remaining. The propeller turned for about two seconds and then it stopped and there were no knots left." An answer like, "There were very few knots remaining" will not help me analyze the flight much. Lots of turns remaining (if trim is reasonable) indicates a too thin motor and very few turns remaining (again, if trim is reasonable) indicates a too thick motor.

Looking at your flights and noticing the relatively high launch torque that it took to get only 24 ft high, I believe that you probably went a little too far in adding clay to the nose to move the CG forward and eliminate stall (you did this by using the glide test method I recommended, which is similar to the method that Josh recommended too) Don't feel bad about this, this year's airplanes are very, very difficult to find the perfect CG location on. So, to test this, try removing 0.050 grams of clay from the nose (yes, this is 50 milligrams, a very tiny amount) and fly it with a lower launch torque (like 0.4 in oz) and observe. If it doesn't change much, keep removing 0.050 grams and flying again and again till the airplane nose "comes up" a little during the flight and the circle gets a little smaller and it climbs a little higher and the duration increases. Then find the launch torque that gets you to the 24 ft height and see what the flight time is.

When our airplanes were flying a tiny bit nose heavy, they looked fine, but were actually flying a little "flat". I knew that moving the CG back in very tiny increments might make them better. We removed a total of 0.10 grams of clay from the nose in two .050g increments (our clay is not on the airplane nose) and added 10 seconds at 24 ft.

Once you have performed this very gradual incremental CG shift test and once you have density data (measure the length of every motor loop) and once you are recording turns remaining, it will be possible to hone in on the perfect density and propeller pitch. Also, you should be able to get 95-110 winder turns on .094" rubber (with at 15:1 ratio winder) and this will give a nice boost in flying time vs. winding to only approx 1,000 turns before backing off (yes, this is true even though you will probably backoff to the same, or lower, launch torque).

You really can't make these final fine adjustments for maximum duration without taking all of the data. Without this data (density and turns remaining along with all the other data you have), you'd just be guessing and it would take forever to find more duration.

Once trim is very close to optimal (CG and washin especially) and motor density appears to be pretty good (turns remaining similar to backoff turn count; if winding to 80-95% of max and clean flight; no ceiling hits, etc.) then it's time to start trying different propeller pitches by maybe increasing or decreasing in 2 degree increments, and then it's time to try different custom made propellers (flaring, larger diameter, etc.).

If you are flying 3/32" rubber (called .094" in the Freedom Flight Kit) and you buy a 1/4 pound box from FAI Model Supply (which will make about 55 motors) you will find that the motors you make will range from .061 g/in to .065 g/in and this is a very good range to test for the Freedom flight kit with the kit propeller and with other possible custom propellers.


Brian T
Last edited by bjt4888 on December 22nd, 2022, 3:37 pm, edited 2 times in total.
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Re: Fine adjustments for maximum duration

Post by pumptato-cat »

Thank you!!! In my flight log there is a parameter called "# remaining"---should have been more specific with that. That's the parameter that logs turns left.
I'll do some glide tests at my next flight session and try to remove weight, thanks! Currently, it's gliding to the ground and the nose is definitely not pointing up. I'm hesitant about this decreasing circle size, though-my plane's around 18ft or so in circle size currently. Is that too small? I don't know how else I can increase the circle size.
I'm waiting on a new rubber shipment soon but for now I'll do the best with the rubber I have.
Thank you so much!!!
there are so many types of birds and i enjoy looking at all of them
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Re: Fine adjustments for maximum duration

Post by bjt4888 »

pumptato-cat wrote: December 22nd, 2022, 7:18 pm Thank you!!! In my flight log there is a parameter called "# remaining"---should have been more specific with that. That's the parameter that logs turns left.
I'll do some glide tests at my next flight session and try to remove weight, thanks! Currently, it's gliding to the ground and the nose is definitely not pointing up. I'm hesitant about this decreasing circle size, though-my plane's around 18ft or so in circle size currently. Is that too small? I don't know how else I can increase the circle size.
I'm waiting on a new rubber shipment soon but for now I'll do the best with the rubber I have.
Thank you so much!!!
Cat,

Sorry, I didn't catch that "# remaining" was the turns remaining. What threw me off was that the number recorded for some of the rows was so small. Very small turns remaining usually is an indicator of rubber that is too thick. The one student that I am coaching that is using the stock Freedom Flight Kit has found that .065 g/in is definitely too thick and also had very few turns remaining when using this density. However, .062 or even .060 g/in might be about right. As you will see when measuring the "3/32" or ".094" rubber that comes from the kit manufacturers, the range in density of this rubber is about .060 g/in (occasionally this low) to .065 g/in, with a typical density of .062 to .063 g/in. You will probably want to test motors of .060 to .062 g/in next. And, definitely, watch my rubber winding video and practice winding to 95 - 110 winder turns before backing off.

You're doing a great job with the event!

Brian T
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Re: Fine adjustments for maximum duration

Post by bjt4888 »

So, an addendum to the recommendations above. As you remove 0.50 g clay from the nose (of course, keep total weight at or above 8 gram requirement) you might not actually see the airplane “nose up” slightly. You may just see that the airplane flying speed slows down and the duration improves. Also, you’ll probably see the climb rate increase slightly so that a full climb to a 24 ft ceiling might take .02 to .04 in oz less launch torque than before.

If your airplane is very close to the 8 gram minimum, the .050 gram balls of clay removed from the nose (it’s the Freedom Flight kit that i am most familiar with and this kit is setup so that all of the clay ballast is attached to the nose so that the wing can be as far forward as possible) can be attached to the motor stick at the CG location in order to keep the airplane at the required 8 gram weight.

Brian T
Last edited by bjt4888 on December 23rd, 2022, 9:29 am, edited 1 time in total.
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Re: Fine adjustments for maximum duration

Post by pumptato-cat »

Yeah, I think the small numbers are due to the low winds I've been putting in. I'll try winding to 100 next time-hopefully I'll start breaking some motors! ;) I'll definitely do some more glide tests.
Thank you so much!!! :)
there are so many types of birds and i enjoy looking at all of them
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Re: Fine adjustments for maximum duration

Post by bjt4888 »

pumptato-cat wrote: December 23rd, 2022, 2:58 pm Yeah, I think the small numbers are due to the low winds I've been putting in. I'll try winding to 100 next time-hopefully I'll start breaking some motors! ;) I'll definitely do some more glide tests.
Thank you so much!!! :)
Cat,

Sounds good on the more aggressive winding. For the testing of removal of small .05 gram amounts of clay from the nose, this is not glide testing. This testing is done by removing the clay, winding the motor and launching at moderate torque. See my notes above. You already did enough glide testing to get the CG close.

Brian T
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Re: Fine adjustments for maximum duration

Post by pumptato-cat »

Whoops, misread your message. Thank you! I might have to build a new plane-the current one is a bit too overweight.
there are so many types of birds and i enjoy looking at all of them
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Re: Fine adjustments for maximum duration

Post by bjt4888 »

Cat,

Be sure to read my first post in this thread carefully to get these next steps. Also use thinner rubber like .062 g/in or .060 g/in.

Brian T
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