Flight B/C

[bjt4888]

Thanks!

For some reason, the horizontal stab was warped before the Mylar covering, and after I added the covering, it's fine now?- I'll keep your advice in mind for my next plane though! Thanks a lot

Another question(ahhh most of this forum is just me posting thank you so much for still answering my questions!!)
I had a sagging in my wings on one side because of a rib slanting, (it was straight at first but after gluing became crooked...) how important is it that the Mylar is perfectly applied? Also, why are some planes rounded at the edges?(For example, J&H's Hourglass planes, or the TSA flight endurance on Freedom Flight?) Thanks again

Cat,

Good that your stab flattened out. A flat stab is pretty important. Small unevenness in covering material is not important. The airplane that one of my teams won the Michigan States with in 2015 had the “most creative” looking covering of the group.

Things that matter:
1. Good propeller and rubber density properly matched (lots of testing here).
2. Good winding technique for maximum turns, good max torque and no knot chains.
3. Accurate measurement of rubber by density
4. Adequate testing to determine launch torque to achieve needed climb height. And very good quality logging of data.
5. Accurate alignment of the wing to fuselage, winglets to wing, and good trim settings for CG, wing washin, rudder offset and stab tilt.

There’s more, but this is a good start. Notice I didn’t mention airplane design. Any reasonable design will be successful with the above 5. Taken care of.

Brian T

[pumptato-cat]

Thanks!
What are your thoughts on using partial motors? Some people make multiple hooks and some people use a balsa stick as a placeholder. Opinions? (I have a low-ceiling gym and am scared of hitting the ceiling)

[bjt4888]

Thanks!
What are your thoughts on using partial motors? Some people make multiple hooks and some people use a balsa stick as a placeholder. Opinions? (I have a low-ceiling gym and am scared of hitting the ceiling)

Cat,

Partial motors are only a good idea if practicing in a gym that is much lower than the competition site. We use them when practicing in our 29 ft ceiling gym to get ready for the annual AMA contest that has a 65 ft ceiling.

To avoid hitting your ceiling just increment your launch torque progressively for each flight. For example, my students were flying yesterday and were winding to about 80% max turns and about 1.2 inch ounces for each flight. They then backed off turns for their first full power flight for a launch torque of 0.25 in oz. this produced a 1:30 flight that climbed only a couple feet from launch height. Their next flight was, again and always, wound full and backed off to 0.30 in oz. this flew to about 10 ft high. Next was 0.32, then 0.35, then 0.38, then 0.40 in oz launch torque for flights of 15 ft, 18-20 ft, 22-23 ft and about 26 ft.

Initial flights before these full wind flights are wound to about 50 winder turns and 0.3 in oz to produce level flights to “safety check” the airplane and make sure it’s not rolling or diving to the floor or turning too tight or too wide. One airplane required a slight change to wing incidence and washin before winding full. Use the formula to estimate breaking turns and wind to about 80%-90% using the method shown in my previously posted YouTube video.

Use this method every time you practice and you’ll most likely avoid any bad contact with the ceiling.

Brian T

[coachchuckaahs]

Cat:

I replied on Discord, but better to archive here, regarding partial motors.

Partial motors are needed to trim a plane in a low ceiling when a high ceiling is used to compete. If 2x height difference, test with 1/2 motor. If 4x, test with 1/4 motor. For example, my F1D kids are testing with 1/4 motor (0.1g) in a 50-foot hanger to prepare for the Salt mines (near 200 foot ceiling) in Romania.

You want to REPLACE the missing rubber with a stick that is the same length and mass as the missing rubber. The stick goes behind the rubber, so the rubber directly drives the prop. Putting additional hooks on the motorstick does not accomplish this, as the mass is missing.

The partial motor stick does not need new hooks on the plane. You simply make a bar, perhaps with 1/8" square balsa or any handy stick of balsa, with a hook on each end. If you do not have scraps of music wire (0.015 or 0.020"), you could fashion a hook from a staple, or maybe a SMALL paperclip. Glue the hooks at each and of the stick, binding on with sewing thread and a little thin CA. The stick for a 1/4 motor should be 3/4 the hook-to-hook length of your plane, 1/2 for a 1/2 motor. Then check the mass of the stick (1.5g for a 1/4 motor, 1g for a 1/2 motor), and ballast up if needed. Sand down or try again if too heavy. When winding, hook one end to your torque meter, the other to the rubber, and wind as normal (same torques, 1/4 or 1/2 the winds). Transfer the rubber o-ring from your winder to the prop shaft, and the stick hook from your torque meter to your tail hook on your plane.

This forum is best place to ask questions so they do not get lost in the noise of Discord.

PS: The less fraction of motor you use, the more the results may vary. Using a 1/4 motor is a substantial extrapolation. We get basic climb trim by doing that on the F1D's, but we will use 1/2 motors for initial flights in the salt mine to be sure things transfer accurately. In most cases for SO, a 1/2 motor can give you all the data you need. And yes, even when you have similar gym height, if your test gym has a "scary" ceiling, a 1/2 or even 3/4 motor can help you more safely test initially, but then change to full rubber once you are confident you have control of the climb.

Coach Chuck

[pumptato-cat]

Thank you so much!!! I really appreciate everyone's responses :)
I didn't get much time to practice because of reservation issues, but first flight with the Freedom Flight 2023 kit after adjusting wing posts got 1:32. I used .102 as suggested by the FF kit to start and used 40 winds on a 15:1 winder. (I forgot to log torque but I think it was around 0.41oz or so?) The gym was 30 ft high, but rafters+banners hanging down reduce it to around 18 ft. AC was on(They won't turn it off because the system used only allows AC to be shut off for the entire building, it's an old gym) and the plane hit the back wall. It had a bit of a rough start(wobbly), rose to around 14 feet after 3 circles(~10 sec), cruised for 20 seconds, and then started descending. I started in the middle of the gym, and the plane went to a corner, almost hitting a basketball hoop, and crashed into a trash can... any ideas on why this may happen? The plane's flight circle went from the center of the gym to around 15-20ft behind where I started launching. I'm thinking it might be due to AC but I'm not sure if it's the plane's issue. How can I slow the ascent of the plane? It's moving VERY fast, and never stays in one spot, always shifting the circle traveled to the left behind its original path)
The plane also wobbled a lot--the left wing would dip down, and the entire plane would roll to the left. It's way more than what I've seen other teams have... It seems to stall randomly too--I've adjusted the wing posts so it glides smoothly on 20 winds, but the plane behaves much differently in practice than in trim flights. It also lands with a decent amount of winds left, perhaps too much. I'd change to thicker rubber but .102 is already thick... Not sure what to do. I will try more rubber thicknesses and winds when I get a gym without AC(might be a while) but I'm too scared of the plane hitting anything to try more winds, because its flight path is so unpredictable... Any ideas on why it's behaving so oddly? (Thank you so much for helping me!!! I'm so glad to be flying :D)

[bjt4888]

Thank you so much!!! I really appreciate everyone's responses
I didn't get much time to practice because of reservation issues, but first flight with the Freedom Flight 2023 kit after adjusting wing posts got 1:32. I used .102 as suggested by the FF kit to start and used 40 winds on a 15:1 winder. (I forgot to log torque but I think it was around 0.41oz or so?) The gym was 30 ft high, but rafters+banners hanging down reduce it to around 18 ft. AC was on(They won't turn it off because the system used only allows AC to be shut off for the entire building, it's an old gym) and the plane hit the back wall. It had a bit of a rough start(wobbly), rose to around 14 feet after 3 circles(~10 sec), cruised for 20 seconds, and then started descending. I started in the middle of the gym, and the plane went to a corner, almost hitting a basketball hoop, and crashed into a trash can... any ideas on why this may happen? The plane's flight circle went from the center of the gym to around 15-20ft behind where I started launching. I'm thinking it might be due to AC but I'm not sure if it's the plane's issue. How can I slow the ascent of the plane? It's moving VERY fast, and never stays in one spot, always shifting the circle traveled to the left behind its original path)
The plane also wobbled a lot--the left wing would dip down, and the entire plane would roll to the left. It's way more than what I've seen other teams have... It seems to stall randomly too--I've adjusted the wing posts so it glides smoothly on 20 winds, but the plane behaves much differently in practice than in trim flights. It also lands with a decent amount of winds left, perhaps too much. I'd change to thicker rubber but .102 is already thick... Not sure what to do. I will try more rubber thicknesses and winds when I get a gym without AC(might be a while) but I'm too scared of the plane hitting anything to try more winds, because its flight path is so unpredictable... Any ideas on why it's behaving so oddly? (Thank you so much for helping me!!! I'm so glad to be flying )

Cat,

Unfortunately, it’s nearly impossible to determine necessary trim changes by flying when the blowers are on. Wobbling wings when under low power could mean you may need to move the CG forward a little. We’ve found in our testing that a small shift forward in the CG (like 1/8”) can change flight character quite a bit. Move the wing back maybe 1/4” at a time to see if this helps.

Are all your trim settings per the instructions? Since my teams are building our custom design from the FF kit, I know the details of the design, but if you list your trim settings (CG, washin amount, stab tilt and offset angle, wing incidence and airplane overall weight and location and weight of clay/putty ballast), I can give more specific help.

Yes, shift in the flight circle and drift across the gym is likely due to the blowers.

Good job getting started on flight practice.

Brian T

[bjt4888]

Cat,

And, yes, don’t try for more turns on the motor till you can test with the blowers off. See if one of the other schools in the district has calmer air. We’ve found that some gyms have blowers set very low on weekends when they are expected to be unoccupied.

Brian T

[bjt4888]

Cat,

I see that there is one question in your last post that wasn’t answered. How to slow the airplanes climb rate. Of course, you can’t really make any significant trim and flight character tests or observations with the blowers on in the gym. But once you are flying in calm air, there are several trim changes to consider. Which to work on first depends upon what the airplane is doing exactly. For example, if the airplane is circling tight and has a nose up attitude and climbs rapidly (rapid would be anything more than 3 ft climb per circle) and stalls repeatedly when descending, then moving the CG forward slightly (1/16” to 1/8” increments) would make sense. For this flight character, moving the CG forward would reduce the nose up attitude, increase the circle size and reduce the climb rate. CG and corresponding wing incidence is what my teams will usually try to get set first along with turn settings if circling too tight or too big.

Resetting the turn adjustments (stab tilt and stab tip fore and aft “angle”, which is this years FF kit method of adjusting the rudders) for more turn will also cause the airplane to nose down slightly; and conversely increase in turn settings will cause slight nose up change. Both of these conditions, in this situation, can be fixed by slight 1-2mm increase or decrease in wing incidence.

There are many other cases of “if it’s doing this, then adjust by doing that” and a good way to get help for fine trim is to post a video of a full flight in calm air (full meaning fully wound to 80-90% max turns, proper backoff and a good climb to within a few feet of the ceiling and a good descent).

This is the really fun part.

Brian T

[bjt4888]

Cat,

And, sorry, missed one critical trim to mention. Climb rate can be managed by altering propeller pitchonce an airplane is in pretty good trim. More pitch (with corresponding matched rubber motor density) will produce slower climb rate. This has to be balanced though as excessive pitch will reduce horsepower during cruise and let down and hurt your flight times. Final decisions on pitch will balance the need for slow climb with the effect on duration. We test all pitch diameter ratios from 1.4 to 2.0 typically.

Brian T

[pumptato-cat]

Thank you so much for the advice!!! :)
I've seen on past designs that the Horizontal stab is attached by two posts and tubes, similar to the wings on this year's FF design--except this year, you just glue the stab to the motor stick. How would I adjust this? I used duco cement, and have no idea how to slant the stab. In the instructions, it says, "offset the rudder to the left by angling the Tail Boom", but there isn't a tail boom?.. It's just a motor stick.. Am I misunderstanding something here? If not, how would you suggest adjusting angle of the stab? (it's glued to a piece of balsa that is glued to the motor stick) Thanks!
(also, we reserved a warehouse for flying with no AC! will update my previous post when we get some good flying in :D)