Scioly.org

lechassin wrote: ↑February 12th, 2020, 5:50 am Xiangyu,

I forgot to mention that a good strategy to test in HVAC is to wind the motor using only as much torque as is needed to cruise (in our case 0.015 in.oz). The plane will stay at head level and descend, and the longer you get it to do that, the longer the plane will fly from higher up. As you're doing that, make sure you also test the plane's behavior right after launch, everything else you do affects that. Ultimate height will be random under HVAC, but if it launches well, it will climb well too, then you just need to test best torque when you arrive at any given venue.

(Edit, we need 0.15 in.oz to cruise, not 0.015)

Thanks for the advice! I will let you know how testing goes this weekend.

We have been having some problems with our plane. I'll list the specs and the situation. 8.1g monoplane, Freedom flight model. Center of Gravity is 22.8cm from the nose. We used the props provided by the kit, which are 2-bladed and fit the 8cm gap. We strengthened them with clear tape rather than carbon fiber and they spin smoothly and quietly. Our wing is slightly warped (unintentionally) so that the back edge of the left side of the wing is slightly lower than the front edge. On the right side, the front edge is very slightly lower than the back edge. We have not used the shim block yet this season. The angle of attack is about 4 mm and the stab is neutral. We haven't been calculating torque for 2 reasons; one, our plane isn't going higher than 25 feet, and 2, we don't know how to work ours, as it's wildly inconsistent. (We have the one shown on the Freedom Flight Website.)
Here are the problems we have been facing; We have two rubber bands that we have been using right now, .072' and .087'. Lets start with the .072'. This rubber band is about 2.47 grams and we have been able to fit about 1700 winds before it starts to tense up. The biggest problem is that this rubber band works smoothly and the plane rises slowly for the beginning of the flight but quickly loses power and the plane stalls at about 15 feet usually at 35 seconds. (Turning Left). Within 5 seconds, the plane has touched the ground so we have been capped at 40 seconds. Usually, about 1/3 to 1/2 of the winds remain. We moved the rudder in every way possible, moved clay back and forth, changed the angle of attack, but can't get more than 40 seconds. No matter what, the rubber band runs out of power too quickly with many winds left.
The next logical step is to increase the thickness of the rubber band to generate more power. However, this has been creating problems for us as well. We moved up to .087', which is about 2.5g as well. We have been able to fit about 1300 winds at most before it starts to feel like its about to break. It rises pretty well and reaches about 25 feet. It was actually rising too fast but we made the rudder extreme and now it flies quite a tight circle with the inner circle part of the wing quite lower than the outer part of the wing. This is a terrible solution and I hate it but makes it rise slower actually and has helped us a little on time. (Also turning Left). However, as would be expected, it quickly runs out of winds COMPLETELY and falls down like a helicopter literally. This is because the propeller stops spinning because the rubber band is entirely spent. We have been capped at about 45 seconds for this rubber band as well. The logical solution would be to get a longer rubber band of .087'. The problem is that we have ran out and won't receive it by our next invitational. For this reason, we have desperately been putting everything we have into the .072', but it simply isn't powerful enough. Don't even talk about the bonus. We are able to get the bonus but it only makes one circle and is about 8 seconds. Right now we are trying to break 60 seconds on the left turn. Any advice on what to do? We have a lot of rubber like .072, .0625, .065, .058, .098 and above .1, but we just dont have any more .087.

It's easier to interpret CG as a percentage of the wing chord or as distance from the wing's leading edge, but yours sounds OK.

Assuming the "slight" wing warp is actually easy to see, the biggest thing would be to remount and/or tweak your wing straight, or even build a new one (you can use balsa from a local hobby store and a grocery bag for covering). Whatever you chose to do, use this video to guide you: https://www.youtube.com/watch?v=fqAXTjMOl8U&t=359s. Wing warping can be used to advantage but IMO that's only after the plane is otherwise optimized. The way your wings are warped will cause excess banking to the right, and excess side slipping to the left. When you solve that, you won't need as much power and you can use your thinner motor, which will unwind your prop slower. Your thicker motor has enough power but it's spinning down the prop too fast, as you've noted.

Even after that, the reality is that your setup has inherent limitations that will hold you back even when optimized. 40 seconds is actually pretty good this year i.e.: one of the kit manufacturers is getting just a little over 1 minute with a well-trimmed bipe (lower wing loading) and he's a pro. All the available kits and props are ill-suited to this year's specs, so they require modification.

Even better, if you look at these planes overall, you'll see that it's not hard to just copy our 8.0 gram biplane with your own supplies. The longer motor stick carries more knots, the longer tail is easier to trim, and the prop flares during launch and unwinds slower, yet still produces good thrust that will get you above 50 feet if you want. I'll post this again not because it's the only good option, but *cough* because it's the only option that is being disseminated *cough*: https://www.youtube.com/watch?v=vmB4-4IBuXU

Finally, 1300-1700 knots isn't enough this year, we fly with 5000. Think of how long your flights would be with four times as many knots. A longer thinner motor is part of that, but I recommend you get your torque meter working to get a good sense of maximum winding ("feel" isn't good enough). Not to harp too much on what's available for purchase, but the torque meters we saw didn't appeal to us any more than the kits. We made a very long (ergo precise) torque meter out of a 3 foot section of PVC pipe (Home Depot), balsa scraps for the ends, and a 36" piece of 0.020 music wire (Ebay). The hook is a piece of bent coat hanger glued through a tiny loop in the music wire, and after some use we even added two ball bearings (Ebay) to the hook assembly to reduce friction. The readings are exquisitely precise.

lechassin wrote: ↑February 13th, 2020, 7:12 am It's easier to interpret CG as a percentage of the wing chord or as distance from the wing's leading edge, but yours sounds OK.

Assuming the "slight" wing warp is actually easy to see, the biggest thing would be to remount and/or tweak your wing straight, or even build a new one (you can use balsa from a local hobby store and a grocery bag for covering). Whatever you chose to do, use this video to guide you: https://www.youtube.com/watch?v=fqAXTjMOl8U&t=359s. Wing warping can be used to advantage but IMO that's only after the plane is otherwise optimized. The way your wings are warped will cause excess banking to the right, and excess side slipping to the left. When you solve that, you won't need as much power and you can use your thinner motor, which will unwind your prop slower. Your thicker motor has enough power but it's spinning down the prop too fast, as you've noted.

Even after that, the reality is that your setup has inherent limitations that will hold you back even when optimized. 40 seconds is actually pretty good this year i.e.: one of the kit manufacturers is getting just a little over 1 minute with a well-trimmed bipe (lower wing loading) and he's a pro. All the available kits and props are ill-suited to this year's specs, so they require modification.

Even better, if you look at these planes overall, you'll see that it's not hard to just copy our 8.0 gram biplane with your own supplies. The longer motor stick carries more knots, the longer tail is easier to trim, and the prop flares during launch and unwinds slower, yet still produces good thrust that will get you above 50 feet if you want. I'll post this again not because it's the only good option, but *cough* because it's the only option that is being disseminated *cough*: https://www.youtube.com/watch?v=vmB4-4IBuXU

Finally, 1300-1700 knots isn't enough this year, we fly with 5000. Think of how long your flights would be with four times as many knots. A longer thinner motor is part of that, but I recommend you get your torque meter working to get a good sense of maximum winding ("feel" isn't good enough). Not to harp too much on what's available for purchase, but the torque meters we saw didn't appeal to us any more than the kits. We made a very long (ergo precise) torque meter out of a 3 foot section of PVC pipe (Home Depot), balsa scraps for the ends, and a 36" piece of 0.020 music wire (Ebay). The hook is a piece of bent coat hanger glued through a tiny loop in the music wire, and after some use we even added two ball bearings (Ebay) to the hook assembly to reduce friction. The readings are exquisitely precise.

Thank you so much! On an aside, do you think we should be using the shim block in any way and is it possibly hindering our performance by not using one.

I think you are referring to warping the wings with a shim? We keep things as simple as possible and avoid warping but others disagree.

Before you try making the prop from scratch, please try adjust the pitch of the prop come with the kit. Besides changing the rubber width to match prop, you can adjust prop pitch to match rubber.

Reduce the prop pitch by 5, 10, 15, 20 degrees by twisting the spars with 1 or 2 pliers (it will break after 1-2 twist). If it works better with your rubber, you can try page 2 of
viewtopic.php?f=299&t=13264#p373061 to make it better.

For our plane, 20 degree reduced, match 0.058 rubber (the thinnest from the kit).

Best,

Tiger

Chameleon02 wrote: ↑February 13th, 2020, 8:50 am
Thank you so much! On an aside, do you think we should be using the shim block in any way and is it possibly hindering our performance by not using one.

The shims should be used late in the trimming process. First get the plane flying well in a circle at lower power, no stalls, nose level, good circle, vary power somewhat. This has to be successful both directions. You need to get the wing straight to begin with, as others have mentioned. A crooked wing only creates drag, as you need other adjustments to counter it.

Once you have good circles, start trying higher power. If the plane rolls into the circle at higher power, then you need to use the shims to present a little (very little) wash in on the inboard wing. And so this adjustment will be different for each direction turn. As others have noted, this can also be done with wing offset, but I don't believe the kit has that option. We use a little of both.

But if you don't have perfect trim to begin with (and a straight plane), you are only adding drag by making countering adjustments to other surfaces.

Coach Chuck

I just finished typing a PM answer just as you were typing your algorithm! I'll post the PM for all to see, slightly different from your approach but mostly the same, I'll leave in the opinions that are maybe best reserved for PMs...

"The bottle in the prop video is something else, here's what we're using now: https://www.kmart.com/propel-zero-water ... 293120001P

Cut the blades from the cylindrical section with the length of the blade 45 degrees from the long axis of the bottle to get the helix (make sure there's more pitch at the root). I don't think the shape of the blade is that critical (within reason). We drew something pleasing. Your 1.6 grams should be fine but if your plane is over 8 grams, try to get the prop down to 1.1 grams, that's what the one one in the video weighs and there's nothing special about it.

When you first fly a plane, set decalage and CG to first get a perfect cruise with a good radius using partial winds. Once you have that, increase the torque in small increments and assess the climb. In your case you're power-stalling. Reduce decalage and be aware you may need to move your CG aft (tail weight or wing forward) to keep the flat cruise. The flaring prop will also reduce launch power stalling. We repeat these steps several times, and we accept that a compromise between launch and cruise is inevitable.

Once you nail that, increase the launch torque and repeat the same steps as needed. Going left, at some point you will get that descending launch, which is indeed from the additional prop counter-torque, increased banking, and decreased lift. First make sure the additional rubber tension isn't bending the motor stick, that reduces stab incidence. If the motor stick is OK and the turn radius is large, add decalage and move the CG forward (nose weight or wing aft) as needed to keep a flat cruise. If the radius is too small, just reduce the rudder, in my experience that won't affect cruise.

Our planes all have a max launch torque that is unmanageable and it can be a variety of things like shaking prop, bending motor stick, too much height, etc...

As an aside: You can see on Yotube that some of the experts are really unhappy about this year's rules. They claim they're worried about our well-being but I think they're just having trouble adapting their knowledge and offering good products. Our plane is not unique except that it methodically address each troubling rule with a specific design feature: the small stab mandates a long tail moment and a forward CG/higher decalage. The small prop mandates an extra blade. The high rpm mandates very long/thin rubber, and that mandates a very long motor stick. Limited power mandates maximum lift at minimum decalage and that mandates two wings. The 8 gram target with the long motor stick and long tail mandates a frail structure, so reliable bracing is needed to avoid breakage and warps, ergo braced wing tip fences. The frail stab cannot rest on the floor after a landing or it will warp, ergo inverted rudder.

Everything follows. If you look at all of the kits this year, not one of them addresses every issue and the results are what they are: planes that are difficult to trim and don't fly very long. We are total beginners and with the help of the lay-people on this forum we were already matching the manufacturer's times back in September: https://www.youtube.com/watch?v=u77yWYz5yow

So frankly, I would discard any kit and build your own. You're welcome to copy ours and I can give you the exact specs of each part, and if needed we can do a complete build video. It'll take 3 hours to build a plane and an hour to make the prop. Everything is dirt cheap, we use superglue and balsa off Ebay and the covering is bags held with 3M77 spray from Home Depot."

Chameleon02 wrote: ↑February 12th, 2020, 8:53 pm We have been having some problems with our plane. I'll list the specs and the situation. 8.1g monoplane, Freedom flight model. Center of Gravity is 22.8cm from the nose. We used the props provided by the kit, which are 2-bladed and fit the 8cm gap. We strengthened them with clear tape rather than carbon fiber and they spin smoothly and quietly. Our wing is slightly warped (unintentionally) so that the back edge of the left side of the wing is slightly lower than the front edge. On the right side, the front edge is very slightly lower than the back edge. We have not used the shim block yet this season. The angle of attack is about 4 mm and the stab is neutral. We haven't been calculating torque for 2 reasons; one, our plane isn't going higher than 25 feet, and 2, we don't know how to work ours, as it's wildly inconsistent. (We have the one shown on the Freedom Flight Website.)
Here are the problems we have been facing; We have two rubber bands that we have been using right now, .072' and .087'. Lets start with the .072'. This rubber band is about 2.47 grams and we have been able to fit about 1700 winds before it starts to tense up. The biggest problem is that this rubber band works smoothly and the plane rises slowly for the beginning of the flight but quickly loses power and the plane stalls at about 15 feet usually at 35 seconds. (Turning Left). Within 5 seconds, the plane has touched the ground so we have been capped at 40 seconds. Usually, about 1/3 to 1/2 of the winds remain. We moved the rudder in every way possible, moved clay back and forth, changed the angle of attack, but can't get more than 40 seconds. No matter what, the rubber band runs out of power too quickly with many winds left.
The next logical step is to increase the thickness of the rubber band to generate more power. However, this has been creating problems for us as well. We moved up to .087', which is about 2.5g as well. We have been able to fit about 1300 winds at most before it starts to feel like its about to break. It rises pretty well and reaches about 25 feet. It was actually rising too fast but we made the rudder extreme and now it flies quite a tight circle with the inner circle part of the wing quite lower than the outer part of the wing. This is a terrible solution and I hate it but makes it rise slower actually and has helped us a little on time. (Also turning Left). However, as would be expected, it quickly runs out of winds COMPLETELY and falls down like a helicopter literally. This is because the propeller stops spinning because the rubber band is entirely spent. We have been capped at about 45 seconds for this rubber band as well. The logical solution would be to get a longer rubber band of .087'. The problem is that we have ran out and won't receive it by our next invitational. For this reason, we have desperately been putting everything we have into the .072', but it simply isn't powerful enough. Don't even talk about the bonus. We are able to get the bonus but it only makes one circle and is about 8 seconds. Right now we are trying to break 60 seconds on the left turn. Any advice on what to do? We have a lot of rubber like .072, .0625, .065, .058, .098 and above .1, but we just dont have any more .087.

Cham,

A 2.5 g .072" motor will take 3,000 turns. One of your biggest issues is that you're not winding fully. Once you do, you will need the torque meter and you will need to backoff wind.

See previous posts in the forum for details.

Brian T

jinhusong wrote: ↑February 13th, 2020, 10:40 am Before you try making the prop from scratch, please try adjust the pitch of the prop come with the kit. Besides changing the rubber width to match prop, you can adjust prop pitch to match rubber.

Reduce the prop pitch by 5, 10, 15, 20 degrees by twisting the spars with 1 or 2 pliers (it will break after 1-2 twist). If it works better with your rubber, you can try page 2 of
viewtopic.php?f=299&t=13264#p373061 to make it better.

For our plane, 20 degree reduced, match 0.058 rubber (the thinnest from the kit).

Best,

Tiger

I know folks are worried about competition, but would you mind listing some of your plane/motor/prop specs and flight times? Curious to see what your setup yielded.

A lot of people are having trouble getting to one minute or going both ways, so it may not pay to get too fancy, but some folks are stuck at 1'30" and IMO they're gonna need to pull out all the stops to get much more