Flight B/C

[bjt4888]

I've read every post in the Flight B/C thread for this year and am excited to put some dedication into my plane in the next few months. Thank you to all the coaches and students that have contributed so far; I have learned so much just from reading your posts.

A little background on who I am:

I'm currently a sophomore, and this is my second year competing in Science Olympiad. My school has had a lock on the state competition for the past couple of years: I think we're on a 4 or 5-year Nationals streak. Last year was my first year in Science Olympiad, and I did it pretty much just for the Astronomy event (hence my name). Although Division B was available for me in middle school, I never tried to join it. In tryouts, I did pretty abysmally in everything I tried out for except Astronomy (I placed first in the school), so I was placed onto the B team (the worse of the two teams) and filled into 2 events that I did not try out for: Wright Stuff and Bridge. Build events aren't very strong in my school (and also our general area of the country), and I myself wasn't very keen to fill in the gap as a freshman. Our school is mostly a test-event school. Luckily, my partner and close friend had already bought a kit from FFM and was excited to build it (I think he did Gliders in Division B). We met often and had the plane built in winter. However, to say that we were beginners was an understatement: We broke our plane multiple times testing it outside in the wind and had zero idea on how to trim it (we had to look over the flight tips in the FFM manual for a couple of minutes each time we wanted to adjust). We had better success after testing the plane in the school gym with the kids in Wright Stuff on the A team. They had built and perfected their plane over many years, climbing a steep learning curve without ever using a kit (they've told me that their first plane wasn't made of balsa and weighed a whopping 24 grams). With times of 90-100 seconds, they easily dominated local invitationals, Regionals, and States by a comfortable margin. They gave us an old 5:1 winder and we used a lot of their tools. As for us, we never flew in competition until Regionals because our plane kept breaking (thank god Wright Stuff was an exhibition event for the longest time). At regionals, my partner and I managed to snag 1st place with a time of ~35 seconds, 400 winds on the rubber, and a huge stall after climbing. Our A team would have doubled our time if their plane didn't break after hitting the rafters (hence the 400 winds, we were extremely cautious about the 30 ft + ceiling). A and B teams placed 1st and 2nd in regionals respectively (by a long shot), but you're only allowed to send one team to states so the A team moved on. They scored 1st in states with 1:33 and 29th at Nationals. If it weren't for my partner and my mentor, I probably wouldn't be writing this post right now.

Fast forward to this year. Like last year, I'm on the B team for the school, and I am once again competing in Flight (formerly Wright Stuff). I'm mildly infuriated with my placement and want to prove that I am worthy of the A team, as there is a chance that I might be moved up if I do well. I had my plane constructed (from FFM) in time for the first invitational but did not test it beforehand. Our first flight was the trim flight within our 10-minute timespan. After launching, the propeller hook immediately came off, and since we left our toolbox on the sidelines, we had to vacate the floor (and our official flight) to repair the plane. Oh well, at least Flight was exhibitioned.

We started a flight log shortly afterward and started practicing in the gym every morning for two weeks to prepare for the next invitational (except for one particularly tough day during midterms week). Parameters consisted of the required ones plus Flight Notes and Changelog. We had a rough start and wouldn't get the plane to climb because it was always rolling in too much, but I fixed that when I found out that the wing was tilted ~5 degrees on the left side and the stabilizer even more on the right side. I had them reglued and the plane started climbing. I added 2 CF wing posts on the right side (like last year's design) to control the right wing. The finished weight of the plane was ~7.75 g (you can probably get it down to 7.5 with better gluing technique), so we could afford to make addons. The next big hurdle was that the plane kept stalling and losing a majority of its height after the climb stage, which limited flight times to around 50 seconds. We could never get the plane to cruise and climb on the same flight, and that was probably because we thought that moving the CG forward meant moving the wing forward. At one point the front wing post was only an inch behind the front of the motor stick. We realized this around 2 days before the Carnegie Mellon Invitational. That was also when we learned that we had to trim for a 4-meter ceiling, due to miscommunications with the club board. We had one day of testing left, so I made a 1/3 motor because I thought that you needed smaller motors to simulate a lower ceiling (I was wrong). In anticipation of my wrongness, I didn't attach the hook too tightly so I ended up removing it and using the regular rubber. The session ended with the plane crashing into the basketball hoop and the winglets breaking.

At the tournament (2 days ago from the time of writing) I tested the plane during my 3 spare blocks. The entire tournament I was basically either in my events or testing the plane; I had only 1 hour of free time between arriving and the last block when I was able to eat. The night before, I found this forum and began to read the posts. That was when I learned to trim properly, the importance of getting your rubber and propeller right, etc. The Flight supervisor was very nice and gave us from check-in until the end of the 7th block to get our official flights in (basically the whole day instead of the 10 minutes in the rulebook). I didn't know this and checked in at the beginning of my registered block. The plane weighed 8.04 grams with ballast included, and the rubber 1.89 (could be optimized). We didn't have any tools besides our 15:1 winder and other stuff I had from my house, and we looked on in envy at the other teams who had funding from the high school, armed with torque meters, glue accelerators, and the such. In previous testing blocks, our plane was flying around 40-50 seconds (on par with the top teams) but still had the stalling problem mentioned before. I read a forum post about moving the CG back 1/8 of an inch each time after testing, and that probably saved the event. In combination with that, I also experimented with adjusting the front wing post, propeller pitch (eyeballed, did not have a pitch gauge), and clay ballast on the wings to modify the circle size. I also watched the A team fly their J&H kit plane to 51 seconds. They also had another self-designed plane, but they had difficulty trimming that one to fly in low ceilings. With around 10 minutes left in my last free block, I hit a golden trim and my plane flew 1:23, hitting a trash can at the end. Interestingly, the plane never climbed more than a foot or two from its launch height but had a great cruise and descent with barely any stalling or imperfection. It probably would've neared 1:30 if it did not crash, with a peak altitude of maybe 6-7 feet. This was my first official flight and the one that would clinch first place by 25-30 seconds. I still had a second official flight left, so I trimmed the plane to have a wider circle and to climb more. It climbed to the ceiling and lost around 3 feet after a hit (I think that's pretty good stability), but the descent was way faster than my 1:23 because it was porpoising and losing a lot of energy to stall. I have a video of this flight and the configuration of the plane is in my flight log, which I will attach below this post (Making it public for now but might hide it once I get better). I did not record in the flight log for any of my test flights or the first official flight because of time constraints (also forgot my computer), but I was able to record stuff on the plane in configuration for the second official flight after arriving back home. My goal is to do extremely well in all of my events so that I can be moved up to A team and attend states/nats this year (and even if I'm not, the B team is really rocking it, we could beat A team if we work hard enough).

tl;dr Basically how I got to this point and how I got 1st place at my last invitational

Here are some questions I have:

1. After many rips and vert. stab/winglet breaks, the quality of the mylar covering has decreased dramatically. the right cell of the wing and the entire horizontal stabilizer have sagging mylar. For rips, I have resorted to using scotch tape to fix them, which increases mass but I don't think my plane is overweight. I might redo the entire wing and HS if needed from the parts of the second plane in the kit.

2. How much is overweight? How close to 8 grams should you be, and if you're already over, would it be ok to add a little more ballast or glue?

3. If I do the HS again, I might make it adjustable using the same balsa-straw fitting used on the wing. Thoughts? I've heard that there's a specific coupling of angles between the HS and wing that works the best. Is this true?

4. Is there a preferred distance between the wing and the HS? Should I set that and move CG only with clay?

5. I'm making a new flight log below my old flight log with added parameters and neatness. Am I missing anything?

6. I'm already looking into rubber/propeller optimization because I think that we'll hit 2 minutes and above soon. What advantages does a broad flare propeller offer compared to a symmetrical Ikara? Why do people sand that and not the symmetrical one?

7. For dud flights (flights that immediately dive or stall) I tend not to record them in the flight log, because I usually make adjustments and finger-wind the propeller a bit before launching again. Is this okay? There are 31 flights recorded, but probably 20 more in duds and another 20 unrecorded from the tournament.

8. Any comments on my flights?

Thanks to all of you for providing wonderful information in a public forum so that areas without any special coaching (like mine) have the ability to do well in flight. I hope that my flight log, post, and video can help others wishing to get better at flight like I am. And sorry for the wall of text!

Flight 1 (1:23): https://drive.google.com/file/d/1LA0HER ... share_link
Flight 2: (1:12): https://drive.google.com/file/d/18EtYh8 ... share_link
Plane Image: https://imgur.com/a/Jtvu6Va
Flight Log: https://docs.google.com/spreadsheets/d/ ... sp=sharing

Astronomy,

Good job detailing your experience to date and good job building and getting a start on trimming.

2. We build to 8.05 grams after ballast.
3. I assume that you are referring to an incidence adjustable stabilizer. This is not necessary or desirable for SO if you are using a tailboom.
4. Yes, more distance between wing and stabilizer allows more rearward CG placement and lower overall decalage angle (look this up; it's the difference between the wing and stabilizer incidence angles). The limit for overall length, of course, is the box dimensions
5. I'll look at your log later this morning.
6. The Ikara flaring propeller, if modified per my pictures in the 2015 Scioly.org forum (which is linked earlier in this thread) and instructions you've no doubt already read in my earlier posts gives additional flight duration if carefully matched to rubber density and if various blade pitch angles are tested. It does this as the "flaring" or flexing of the blades outward during the high power early portion of the flight slows propeller rotation and reduces climb rate and the reduced pitch (flexing back to original shape) during later, low power, portion of the flight increases power so that a greater portion of the rubber band unwinding time provides adequate power to continue flight.
7. If you have all airplane parameters at reasonable settings (starting with kit recommendations), there should be no "dud" flights unless "dud" means slightly less duration possibly due to starting a new motor or not getting a good winding on the motor. Follow my instructions for test execution and winding in the document in my first post and in the video I attached in my first posts.
8. I can look at your flights later in the day.

Here are the parameters that it would be good to supply inorder for us to give more specific and accurate assistance:

Please supply the following:
1. center of gravity location (measure with motor attached and measure as a distance from the wing trailing edge).
2. wing incidence measure and tailboom incidence measurement
3. left wing washin measure (eyeball this; is it about 1/4", 3/8" or 1/2"). or measure by supporting wing (with blocks) LE level on the workbench and measuring.
4. stabilzer tilt measurement (same method as above 3.)
5. rudder offset measurement (for "C" FF kit this is the stabilizer offset angle; for "B" FF kit this is the tailboom angle; measure by laying some graph paper on your building board, using pin blocks or just blocks to keep fuselage straight along one line of the graph paper and measuring the sideways displacement of the tip of the tailboom).
6. climb height for a particular flight (I'm sure this is in your log)
7. length and weight of the rubber motor (always know the density of your rubber motor)
8. maximum torque that the rubber motor was wound to
9. maximum turns rubber motor is wound to
10. exact number of backoff turns
11. launch torque value for the flight
12. turns remaining at the end of the flight (don't let the prop unwind after it lands at end of flight; pick up and remove motor and put back on torque meter and wind backwards to count remaining turns).

You may have a lot of this in your log; just including the full list so that you (and others) have it.

Brian T

[pumptato-cat]

we looked on in envy at the other teams who had funding from the high school, armed with torque meters, glue accelerators, and the such

As a beginner in Flight, this is not a cheap event. If you want to succeed, either get your school to fund you or fund yourself. I've personally bought everything using my own funds for this event. I hate to say it, but you're gonna have to spend some money to win, as with most build events.

When I am flying my plane, I notice that it does not climb very well, and goes into a constant stall

I'd wait on more details from bjt4888(and provide more info about the plane) but for now I think you should lower wing incidence.

[bjt4888]

Cat,

Good job offering assistance!

Astronomy,

I looked at your videos and log and have the following thoughts. First of all, good job winning at Carnegie! Flights looked pretty good for a difficult room (low ceiling and air currents). In the 1:23 flight it looks like you have quite a bit of roll during the initial circles. As your CG and other specs from the log look within range except for washin amount, you could increase washin to reduce roll and improve climb rate (increase this parameter incrementally maybe 2 mm at a time). Washin, CG placement, launch torque and propeller type and pitch are the methods usually used to work on climb rate and climb height. We never adjust wing incidence (hence decalage) to affect climb rate or climb height. There is generally a "most efficient" decalage angle for each CG location range ("range" as you need to decide how much or little pitch stability you can live with; as you correctly noted, a little more decalage (1-2mm) and a little more forward CG (again maybe 2 mm) from the optimal location can increase pitch stability and help with "upset recovery" in bad air). As a side note, having the plane roll, thereby reducing climb rate and overall climb is actually an effective strategy for the very low ceiling at Carnegie (unfortunate that a notable university could not provide a better room).

As you see from my previous comment, you could add the following to the flight log: max torque at full turns, backoff turns and launch torque and turns remaining (also a good idea to show the weight of the o-rings in the log as they vary from .081g - .097g per pair). I see that you have a note to start "backoff winding" for future flights. Also, it's a little curious that all of your test flights show exactly the same rubber density of .067 (grams/inch?; you need units here and on all parameters). As you didn't indicate rubber motor loop length, I can't see your calculation for rubber density. Are you calculating for each motor? The teams that I coach have tested rubber densities between .060 g/in and .067 g/in. The difference between .0645 g/in and .0655 g/in (for example) is significant.

The single most important factor you could address to increase flight time is to wind the motor fully. A .067 g/in density motor that weighs 1.98 grams (per your log; many in this range) will be about 13.92" long. This length of this density motor will easily take 1,500 turns after it has been used a couple of times and students that are winding aggressively will get 1,575 (this is 90% of breaking turns using the equation I shared in my early posts). Once you have done a few basic "safety flights" with low turns always, always, always wind to 80-90% of breaking turns and backoff to the desired launch torque (initial flights maybe 0.25 in oz and later flights maybe .035 - .045 in oz, depending upon trim). Watch my winding video (link in my early posts). Note in the comments for my video that this is a helicopter motor I'm winding and it is about 20" of .052 g/in, so I'm putting in about 2,400 turns. Use the equation to calculate max turns for the slightly shorter (15.5" - 14"), thicker (.060 g/in - .067 g/in) motors commonly used this year. Also, you'll see this with further "full winding" practice, but best flights are generally with the 3rd through 6th use of a motor (with each use capable of a few more winder turns usually). We've gotten really good flights with 8th and 9th uses, but we wouldn't want to compete with a motor with this many uses as risk of breakage would be too high.

I also see your note about using the lighter plastic o-rings in the future. These o-rings will require a different type of propeller hook (reverse-s is best). These o-rings are lighter and will allow more of the rubber motor mass to be put into the rubber itself. That being said, my teams don't use them as they are a little more challenging to attach to the hooks. We would use them however if we were going to Nationals as, by my estimate, they would be good for another 5 seconds.

Keep up the good work.

Brian T

[coachchuckaahs]

Hi, I have a few questions about my plane that I recently built and flew, (div B)

When I am flying my plane, I notice that it does not climb very well, and goes into a constant stall where the nose is pointed very upwards when it is flying. How can I fix this? Right now times are around 40 seconds and I would assume that a better gliding flight will yield better times.

Second, when winding rubber, I find that I am only able to get to 1100-1200, instead of the 1400 I was able to achieve before. I follow the exact same steps, as suggested in this forum, and rubber weight is still the same. How can I get the extra 200 turns?

Any help would be greatly appreciated, thanks in advance!

If the nose stays up, or drops through repeatedly, you are stalling. You will either need to reduce your decalage (wing incidence vs stab incidence) or move your CG forward. It would help to have a LOT more information about your trim setup, particularly the CG location relative to the rear wing post, the wing incidence measurements, and the stab incidence (if adjustable). A video of the flight would also help.

As far as the rubber is concerned, what is the LOOP LENGTH, straightened but not stretched, BEFORE any winding (i.e., right after loop is made)? The rubber varies in thickness, and so while the "width" may be the same (as supplied by the kit maker), the density or thickness may vary, and you may have a much shorter loop length than you had prior even though the mass is the same. If the loop length and mass are the same (or the density measured as g/in), then it is in your winding technique. But I suspect you have a shorter loop of rubber.

Coach Chuck

[Astronomyguy]

Thank you guys so much for the quick responses! I've followed all of the advice and my plane definitely seems more stable roll-wise after increasing the washin by 3 mm.

1. After many rips and vert. stab/winglet breaks, the quality of the mylar covering has decreased dramatically. the right cell of the wing and the entire horizontal stabilizer have sagging mylar. For rips, I have resorted to using scotch tape to fix them, which increases mass but I don't think my plane is overweight. I might redo the entire wing and HS if needed from the parts of the second plane in the kit.

Sorry for not making this a question - I was going to ask whether it would be a good idea to redo the entire wing and horizontal stabilizer because of the loose mylar (it probably is, and I'm planning to do that before I test again on Monday).

1. How much does loose mylar (a little sagging in a couple of the blocks between the ribs, some rips where it is no longer attached to the carbon fiber, and not being attached to the winglet) affect flight times?

2. Are there any preferred mylar gluing techniques? I just spray the top of the frame, lay the mylar on a flat surface, turn the frame over and roll it on the mylar. I cut the excess with an x-acto knife.

I tested the plane again today, this time with the rubber lubed. Unfortunately, the knot slipped once we got to ~110 winds. This is probably because I tied a square knot instead of the knot shown in the NFFS video on rubber tying. I also added a rubber log and anything missing from my flight log per instructions of Coach Brian. I also calculated my rubber density again, and it seems to be 0.055 instead of 0.067. I know the ideal range is 0.06 - 0.065, but I don't have much rubber left and don't know what thickness my remaining strands are (I took them out of their bag to use them for another project). I'm thinking of ordering another batch of rubber. What thickness is recommended to get to the 0.06 - 0.065 g/in range? I'm thinking of ordering a custom cut batch from Freedom Flight.

Here's my flight log again, updated for today: https://docs.google.com/spreadsheets/d/ ... sp=sharing

[danxmemes]

Hi, I have a few questions about my plane that I recently built and flew, (div B)

When I am flying my plane, I notice that it does not climb very well, and goes into a constant stall where the nose is pointed very upwards when it is flying. How can I fix this? Right now times are around 40 seconds and I would assume that a better gliding flight will yield better times.

Second, when winding rubber, I find that I am only able to get to 1100-1200, instead of the 1400 I was able to achieve before. I follow the exact same steps, as suggested in this forum, and rubber weight is still the same. How can I get the extra 200 turns?

Any help would be greatly appreciated, thanks in advance!

If the nose stays up, or drops through repeatedly, you are stalling. You will either need to reduce your decalage (wing incidence vs stab incidence) or move your CG forward. It would help to have a LOT more information about your trim setup, particularly the CG location relative to the rear wing post, the wing incidence measurements, and the stab incidence (if adjustable). A video of the flight would also help.

As far as the rubber is concerned, what is the LOOP LENGTH, straightened but not stretched, BEFORE any winding (i.e., right after loop is made)? The rubber varies in thickness, and so while the "width" may be the same (as supplied by the kit maker), the density or thickness may vary, and you may have a much shorter loop length than you had prior even though the mass is the same. If the loop length and mass are the same (or the density measured as g/in), then it is in your winding technique. But I suspect you have a shorter loop of rubber.

Coach Chuck

Thank you!
CG is at slightly in front of the rear wing post, about 1 cm. I have my wing incidence up because without incidence the plane does not climb at all. Loop length of rubber is around 15 inches, is this rubber too short? Something else I noticed is that within one box of 1/4 pound FAI rubber is that some places the rubber is much more dense than others. How can I get the best rubber possible for competitions?

Again, thank you for all your help, I'll get back to you when we fly next tuesday!

[bjt4888]

Thank you guys so much for the quick responses! I've followed all of the advice and my plane definitely seems more stable roll-wise after increasing the washin by 3 mm.

1. After many rips and vert. stab/winglet breaks, the quality of the mylar covering has decreased dramatically. the right cell of the wing and the entire horizontal stabilizer have sagging mylar. For rips, I have resorted to using scotch tape to fix them, which increases mass but I don't think my plane is overweight. I might redo the entire wing and HS if needed from the parts of the second plane in the kit.

Sorry for not making this a question - I was going to ask whether it would be a good idea to redo the entire wing and horizontal stabilizer because of the loose mylar (it probably is, and I'm planning to do that before I test again on Monday).

1. How much does loose mylar (a little sagging in a couple of the blocks between the ribs, some rips where it is no longer attached to the carbon fiber, and not being attached to the winglet) affect flight times?

2. Are there any preferred mylar gluing techniques? I just spray the top of the frame, lay the mylar on a flat surface, turn the frame over and roll it on the mylar. I cut the excess with an x-acto knife.

I tested the plane again today, this time with the rubber lubed. Unfortunately, the knot slipped once we got to ~110 winds. This is probably because I tied a square knot instead of the knot shown in the NFFS video on rubber tying. I also added a rubber log and anything missing from my flight log per instructions of Coach Brian. I also calculated my rubber density again, and it seems to be 0.055 instead of 0.067. I know the ideal range is 0.06 - 0.065, but I don't have much rubber left and don't know what thickness my remaining strands are (I took them out of their bag to use them for another project). I'm thinking of ordering another batch of rubber. What thickness is recommended to get to the 0.06 - 0.065 g/in range? I'm thinking of ordering a custom cut batch from Freedom Flight.

Here's my flight log again, updated for today: https://docs.google.com/spreadsheets/d/ ... sp=sharing

Astronomy,

See here for some pictures of our construction process and parameter measuring. Pictures are not all of airplanes for this year's rules: https://drive.google.com/drive/folders/ ... share_link

1. Very loose mylar as I see in you pictures will increase drag and potentially reduce flight times.
2. See the directory above for pictures of the covering frame with flying surfaces adhered and ready to cut out. The Freedom Flight kit comes with wood to make a frame and instructions as to how to do this. We glue to flying surfaces with the typical 3M77 spray glue and attach mylar to covering frames with plain chapstick and then smooth (till just smooth, it isn't helpful to make "tight"; especially with this year's wide wing designs).

.06 - .067 g/in is roughly .090" - .100" wide rubber strip. This is not an exact thing as rubber varies in density about 5-6%. So, I've purchased rubber 1/8" rubber strip for motor "stripping" that varies from .079 g/in - .085 g/in. This variance is in the same box and consecutively cut motor "blanks". Ideal range depends upon your propeller type, pitch and overall airplane trim.

I've received rubber from Freedom Flight (in kits) that is labeled .087" that is about .060 g/in (some years) and rubber labeled .094" that ranges from .062 - .065 g/in (usually).

Yes, a good knot is necessary in order to wind to 80+% of max turns. We only get to 85-90% on the third use and thereafter.

Keep up the good work. Reach for three minute flights (in a reasonable 24 ft ceiling gym).

Brian T

[bjt4888]

Astronomy,

As Coach Chuck noted above, be sure to measure density of rubber motors before winding the motor. Once you wind a motor, it permanently stretches almost 0.5” in loop length.

Density calculations on used rubber motors will not be correct.

Brian T

[randomdogonapc]

Is anyone else having trouble making the broad flaring Ikara? The props that I have don’t see to have enough surface area to cut them into the correct shape on the plans from 2015.

[bjt4888]

Is anyone else having trouble making the broad flaring Ikara? The props that I have don’t see to have enough surface area to cut them into the correct shape on the plans from 2015.

Random,

Not sure what you mean. A few pictures of what you’re doing would be good.

Brian T