Flight B/C

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bjt4888
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Re: Flight B/C

Post by bjt4888 »

poonda wrote: February 4th, 2023, 10:43 am (division b, scratch build)
kind of a weird "issue" with trimming:

i'm flying with a slightly aft cg (1cm behind TE) and the plane is behaving pretty well except it starts climbing at literally 50 winds.
incidence and shimming are super conservative, glide looks good, 24cm ikara with 3/32 motor, 8.1g, and for some reason it climbs like 10 feet off a quick hand wind.

i was just wondering if this was happening to anyone else/if it wasn't optimal behavior?
Poonda,

Based upon the flying surface and fuselage measurements you sent to me via PM, your Static Stability Margin with the CG at 1 cm behind the wing TE would be 11.4%. So, this is a pretty reasonable CG location. Probably you have already tested this, but we are finding the wide wing chord design can take a negative SSM. We are flying at negative 1.9%. There is other data to support this unusual setup; Bill Gowen flies his F1M at negative 0.8% SSM (his F1M is another short wing span wide chord design). We were able to calm down the climb rate with "medium" flex flaring propellers. Really soft flaring propellers did reduce climb rate further, but reduced it too much for our airplane design.

Keep up the good work.

Brian T
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Re: Flight B/C

Post by bjt4888 »

bjt4888 wrote: February 6th, 2023, 4:10 pm
poonda wrote: February 4th, 2023, 10:43 am (division b, scratch build)
kind of a weird "issue" with trimming:

i'm flying with a slightly aft cg (1cm behind TE) and the plane is behaving pretty well except it starts climbing at literally 50 winds.
incidence and shimming are super conservative, glide looks good, 24cm ikara with 3/32 motor, 8.1g, and for some reason it climbs like 10 feet off a quick hand wind.

i was just wondering if this was happening to anyone else/if it wasn't optimal behavior?
Poonda,

Based upon the flying surface and fuselage measurements you sent to me via PM, your Static Stability Margin with the CG at 1 cm behind the wing TE would be 11.4%. So, this is a pretty reasonable CG location. Probably you have already tested this, but we are finding the wide wing chord design can take a negative SSM. We are flying at negative 1.9% on the Middle School airplanes and negative 3.3% on the High School airplanes. There is other data to support this unusual setup; Bill Gowen flies his F1M at negative 0.8% SSM (his F1M is another short wing span wide chord design). This negative SSM does sometimes result in diving to the floor when hitting obstructions. Our airplanes can handle light touches to the girders and they recover fine. A heavier touch that stops the airplane will often result in losing 6-8 ft, or worst case, diving to the floor.

We were able to calm down the climb rate with "medium" flex flaring propellers (test pitch/diameter ratios of 1.2 to 1.8). Really soft flaring propellers did reduce climb rate further, but reduced it too much for our airplane design.

Keep up the good work.

Brian T
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Re: Flight B/C

Post by WetUnicorn »

Hi, I'm in division C and I have some questions about CG and other things.

I’ve got a FF kit, and I had a question about my CG/ballast placement. Here are my current plane settings first: got 1.26g of total ballast and instructions say all at the nose but i got 0.55g at nose and 0.71 g 4 1/8" (~10.5cm) from the back of the plane. Is this optimal? Cg is at 2 1/8" back from TE, and wing position is 1/4" behind the kit recommendations. Front wing post/le is raised 3mm up for incidence. Prop pitch hasn't been changed (idk how to change anyways). Left wing washin I want to say is about 1/8" but I don't know if I'm doing it right…It flew at the birds invitational for about 1;30 mins, so I want to say it is reasonably trimmed. My question though, is that is it ok to have clay at the nose and clay towards the back of the plane? How will it affect my plane performance? Also what is the reason for putting all the clay at the nose? I haven’t tried moving the clay yet because I just got done with the invitational and I didn't want to change any settings in case it messed up my plane. I also don’t get a lot of gym practice (like 30mins a week) and I don't want to waste time experimenting with ballast/CG because what I have works (I mean at least right now that's what I want to know). I think my next step in trimming should be putting more winds in, I haven’t been winding to max and backing off as I should (discovery requires experimentation :) and I think also trying different rubber and stuff but I just wanted to confirm the trim settings I have now aren’t going to haunt me later :) I do have a video if it helps…

For CG I got a little confused while reading some posts. Just to clarify, moving the wings backward will move the CG forward in relation to the TE but move more mass towards the back of the plane, while moving the wings forward will move the CG backwards in relation to the TE while moving more mass to the front of the plane? So moving the CG forward and the wings backward will get you a more stable plane?

Also another question (sorry) but what are anyone’s opinions on flying outside? Like I said, I don't get a lot of gym time and there is literally no where else for me to fly (even a classroom) except my own house. So I’ve resorted to flying outside and that's where I get a lot of my data for my flight logs. Just wanted to ask how reliable is this/is it a good idea? I know lots of external factors (like wind arghh) and really influence how the plane flies and stuff, but just wondering. Thank you so much anyone willing to help me out here!!
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Re: Flight B/C

Post by CypherKat »

Astronomyguy wrote: February 4th, 2023, 8:50 pm I don't have any specific questions for this post but I feel like posting a progress update/venting about our performance at the Princeton Invitational today (I was at the same competition as CypherKat). Any general advice regarding my flights would be welcomed, though.

1. I've been practicing pretty much every day since my last update, and they have more or less been in the 40-80 second range. I polished up the imperfections on my plane one day (fixed rips with scotch tape, made a new HS with less loose mylar, etc. and found that it no longer flew well with my previous washin setting, combined with the fact that I did not precalibrate the decalage and CG from before the fix. The next day, I was able to hit an amazing time of 2:26 with the improved plane (CG, decalage, washin fixed) despite the plane being harassed by the HVAC system. I think it could have gone over 3 with a better venue in those settings. On the very next flight, the HVAC blew our plane into the basketball hoop, where it remained for a couple of hours until someone was able to get it down at the end of the school day, but then someone stepped on it and broke the plane in a couple of areas.

2. I fixed it up later that day (our last day before the invitational) but did not get to test the plane until the invitational itself. Using the plane's behavior from a couple of dud flights, I was able to get it up and running, but I did not have much time to practice as the 10-minute official time blocks took up the entire block back to back, with no space in between. In a large ceiling (30 ft) and necessitating a tight turn, I tried to trim my plane so that it would climb well. For my first official flight, the circle ended up shifting and the plane crashed and broke. Using CA I repaired it within 2 minutes and got a second official flight in. I moved the CG back and it had a better climb, but the circle shifted and it crashed again. Both times were around 1:10/1:20, but the second one definitely could have neared 2 minutes if not over it had it not crashed.

Here are a couple of things I noticed:

1. One of our rubber bands (Apparently, our only near-max mass one with a proper knot, bad decision to use and mix up my rubber previously) broke after I tied and winded it. I don't think this was a lube problem, it was one strand that repeatedly broke free from the knot or snapped (not sure which). I had to borrow rubber from our A team and constructed a good rubber band from .094 weighing 1.95. I wound and unwound it twice to break into it (is this the right thing to do?) and that was how our official flight was saved.

2. Our plane couldn't climb more than a couple of feet above where it was thrown. I think this is just a CG/decalage not being optimized issue, as well as torque not being optimized (we finally got our torque meter assembled but couldn't get it to work)

3. Circle shifting. Really is a sucker; the plane usually settles after a circle from launch and it remains stable until it suddenly shifts by 2 ft + in one circle, then crashes into something the next few. The plane seems unaffected during these shifts. I think I could start with a smaller circle, but the circle always gets wider as the torque decreases. How can I keep the circle constant during the cruise/descent? HS tilt is the obvious solution but it cannot be readily adjusted in competition. Would adding some clay on the inside edge work to lessen the circle by inducing roll? Plane stability could also be increased but because it would involve moving the CG more backward than optimal and lessening the decalage, the plane would fail to make use of the monster 30 ft it has. Preferably the plane should be able to climb to the ceiling and start a slow descent in a tight, unmoving circle. How would I trim for this?

I'm pretty angry because I knew that our plane was better, and we were just one place away from placing. Adding a minute (or maybe even 90 seconds) to our flight time wouldn't have been impossible if our luck had been better (plane wasn't broken the day before, more time to test, and rubber bands cooperating). But this happens, and it wasn't the worst of all outcomes so I'm satisfied. Just a bummer that this was the last invitational and we didn't get the gold.

Flight Log is now privated and sent to the coaches (times nearing 2:30 are too valuable to share the trimming for!!)
Flight Videos: https://drive.google.com/drive/folders/ ... share_link
(Best flight at the invitational was not recorded but it was basically the first one except it climbed higher and crashed higher, in a different spot)
Note that the 2:26 in the school gym also had a significant circle shift. We got extremely lucky that it did not crash into anything, most flights of that caliber in that venue aren't as lucky.

We also had another flight that was probably even better than the 2:26 - it was a 1:27 that clipped the ceiling of the gym before losing all of its altitude, somehow avoiding all obstacles along the way. This was unrecorded, and yet again circle shift was the culprit of the altitude loss.

Hello! My partner and I had crazy climb when we were first testing and our plane could have def done over 2 min during practices if it also hadn’t clipped the ceiling. Totally understand the disappointed. Walked out of flight knowing we had a decent time but just not the one I wanted. Next invitational is in 2 weeks so I’m hoping by then the plane will fly good, wanna get first at states in march too.
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Re: Flight B/C

Post by pumptato-cat »

WetUnicorn wrote: February 6th, 2023, 5:21 pm Also another question (sorry) but what are anyone’s opinions on flying outside? Like I said, I don't get a lot of gym time and there is literally no where else for me to fly (even a classroom) except my own house. So I’ve resorted to flying outside and that's where I get a lot of my data for my flight logs. Just wanted to ask how reliable is this/is it a good idea? I know lots of external factors (like wind arghh) and really influence how the plane flies and stuff, but just wondering. Thank you so much anyone willing to help me out here!!
Okay as a fellow sufferer with no classrooms or gyms to fly in, DO. NOT. FLY. OUTSIDE. I've heard so many horror stories and my Varsity team crashed their plane into a tree that way last year. My school does not have a gym so I have to reserve an auditorium at a nearby college. Email everywhere you can think of. You will find a place if you're desperate--I tried around 5 places before I found a good site to fly in. And I think jander14indoor said this a while back, but you can fly in anywhere that's large enough for the plane to turn circles. You don't need 20ft to at least trim the plane.

About the climb--My plane likes to climb anywhere from 5-10ft in one circle, too. If I try to fix it by changing washin/decalage it'll refuse to climb more than like 10 feet so I'll take bad climb over no climb, I guess..
Last edited by pumptato-cat on February 6th, 2023, 8:27 pm, edited 1 time in total.
anything'll fly if you throw it hard enough
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Re: Flight B/C

Post by WetUnicorn »

pumptato-cat wrote: February 6th, 2023, 8:24 pm
WetUnicorn wrote: February 6th, 2023, 5:21 pm Also another question (sorry) but what are anyone’s opinions on flying outside? Like I said, I don't get a lot of gym time and there is literally no where else for me to fly (even a classroom) except my own house. So I’ve resorted to flying outside and that's where I get a lot of my data for my flight logs. Just wanted to ask how reliable is this/is it a good idea? I know lots of external factors (like wind arghh) and really influence how the plane flies and stuff, but just wondering. Thank you so much anyone willing to help me out here!!
Okay as a fellow sufferer with no classrooms or gyms to fly in, DO. NOT. FLY. OUTSIDE. I've heard so many horror stories and my Varsity team crashed their plane into a tree that way last year. My school does not have a gym so I have to reserve an auditorium at a nearby college. Email everywhere you can think of. You will find a place if you're desperate--I tried around 5 places before I found a good site to fly in. And I think jander14indoor said this a while back, but you can fly in anywhere that's large enough for the plane to turn circles. You don't need 20ft to at least trim the plane.

About the climb--My plane likes to climb anywhere from 5-10ft in one circle, too. If I try to fix it by changing washin/decalage it'll refuse to climb more than like 10 feet so I'll take bad climb over no climb, I guess..
Yeah I feel for your varsity team...funny story but had a kit from last year and decided to build pre season to practice weight optimization, but since it wasn't a kit for this year I just practiced flying outside. I wasn't watching my torque meter and a thermal took it to the top of the apartment building (cause I was flying in my subdivision literally) and I was sad but not a big loss as it wasn't competition plane. 3 days later I walk to my neighbor's bushes in the back and I see the plane sitting atop the bushes like nothing ever happened. I was 1. super thrilled cause the mylar wasn't even ripped and 2. decided to name it 'rooftop survivor' :lol: Thanks for the advice though. I got the same climb problem but de-winding helps even if it is ridiculously a lot. Only thing with small places is circle drifting (it's mild, not worried about it), but even a little bit and it will crash into walls and stuff.
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Re: Flight B/C

Post by pumptato-cat »

Wow, that's amazing-no mylar tears??
I flew somewhere with no air conditioning last week and the circle drift was completely gone. Not sure if outdoor flying will be an accurate representation of indoor flying.
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Re: Flight B/C

Post by coachchuckaahs »

WetUnicorn wrote: February 6th, 2023, 5:21 pm Hi, I'm in division C and I have some questions about CG and other things.

I’ve got a FF kit, and I had a question about my CG/ballast placement. Here are my current plane settings first: got 1.26g of total ballast and instructions say all at the nose but i got 0.55g at nose and 0.71 g 4 1/8" (~10.5cm) from the back of the plane. Is this optimal? Cg is at 2 1/8" back from TE, and wing position is 1/4" behind the kit recommendations. Front wing post/le is raised 3mm up for incidence. Prop pitch hasn't been changed (idk how to change anyways). Left wing washin I want to say is about 1/8" but I don't know if I'm doing it right…It flew at the birds invitational for about 1;30 mins, so I want to say it is reasonably trimmed. My question though, is that is it ok to have clay at the nose and clay towards the back of the plane? How will it affect my plane performance? Also what is the reason for putting all the clay at the nose? I haven’t tried moving the clay yet because I just got done with the invitational and I didn't want to change any settings in case it messed up my plane. I also don’t get a lot of gym practice (like 30mins a week) and I don't want to waste time experimenting with ballast/CG because what I have works (I mean at least right now that's what I want to know). I think my next step in trimming should be putting more winds in, I haven’t been winding to max and backing off as I should (discovery requires experimentation :) and I think also trying different rubber and stuff but I just wanted to confirm the trim settings I have now aren’t going to haunt me later :) I do have a video if it helps…

For CG I got a little confused while reading some posts. Just to clarify, moving the wings backward will move the CG forward in relation to the TE but move more mass towards the back of the plane, while moving the wings forward will move the CG backwards in relation to the TE while moving more mass to the front of the plane? So moving the CG forward and the wings backward will get you a more stable plane?

Also another question (sorry) but what are anyone’s opinions on flying outside? Like I said, I don't get a lot of gym time and there is literally no where else for me to fly (even a classroom) except my own house. So I’ve resorted to flying outside and that's where I get a lot of my data for my flight logs. Just wanted to ask how reliable is this/is it a good idea? I know lots of external factors (like wind arghh) and really influence how the plane flies and stuff, but just wondering. Thank you so much anyone willing to help me out here!!
The stability is where the CG is relative to the center of lift, essentially. For our purposes we can say it is where the CG is relative to the primary lifting surface, or the wing. Since these planes have the CG for stability close to the rear of the wing, we often use that for reference.

So, moving clay toward the front of the plane increased stability by moving the CG forward. Moving the wing back moved the CL back a bit, but also moves the CG FORWARD relative to the primary lifting surface (wing), since the wing is only about 1/3 of your mass.

Why put the clay all at the front? These planes, particularly C division, are very short-coupled (tail distance from wing is short), which makes it VERY sensitive to trim changes. Therefore, you want the wing as far forward as possible to maximize your tail moment. Moving the wing forward decreases stability (because the CG moves back relative to the wing). Therefore, if you put all, or most of the clay at the nose, you can put the wing as far forward as possible to maximize the tail moment and still have the needed stability. If you have a moveable wing, then put ALL of the clay at the nose and adjust the wing for CG location. If your wing is fixed, you may need to move a small amount of clay back for balance purposes.

You indicate that your CG is 2.125" BACK from the wing trailing edge? That sounds way back for this year's C div planes. Be sure you are balancing with rubber motor installed, and measuring from the rear wing post. Generally we have seen 1-2" in front of the rear of the wing

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Re: Flight B/C

Post by vjshe »

I was trying to use the rubber max turns calculator that was provided to me by coach Brian, the calculator gave me very bad results(I was getting 200 max winder turns when the tested max was 108).Later I was browsing the NFFS library of resources and I found another rubber calculator by Roger Willis when I used it I got almost perfect results (Predicted max winds 108 actual tested max was 110) https://docs.google.com/spreadsheets/d/ ... sp=sharing This sheet contains all the calculations I did, what did I do wrong?
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Re: Flight B/C

Post by bjt4888 »

vjshe wrote: February 7th, 2023, 6:07 pm I was trying to use the rubber max turns calculator that was provided to me by coach Brian, the calculator gave me very bad results(I was getting 200 max winder turns when the tested max was 108).Later I was browsing the NFFS library of resources and I found another rubber calculator by Roger Willis when I used it I got almost perfect results (Predicted max winds 108 actual tested max was 110) https://docs.google.com/spreadsheets/d/ ... sp=sharing This sheet contains all the calculations I did, what did I do wrong?
Vjse,

Send me the rubber motor loop length and rubber motor weight. Don’t include the knot when measuring length and just pull the motor straight when measuring. Don’t stretch it when measuring. Also, what type of o-rings (ex. Two black rubber o-rings from the FF kit package). I’ll use the formula and explain it to you.

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