Flight B/C

[Astronomyguy]

Received my FF kit Friday and have been building it yesterday and today. I’m looking to fly tomorrow (exciting!) and I’m building more carefully and closer to the manual this year. Some questions:

1. I changed to a soldering iron this year to trim mylar and found that it wasn’t as neat as I expected it to be - the Mylar tends to curl up when heated so the edges always curl around the cf if they’re not burnt and I have to uncurl and cut them using an xacto. Does that make a difference (small pieces of mylar on the edge of cf rods) or is it too trivial of an improvement to spend time on?

2. I’ve had 2 or 3 holes in my mylar and I found that mylar tends to stick to itself through static electricity, so instead of fixing holes like I did last year (with scotch tape or gluing mylar scraps on holes) which got heavy real quick, Im just putting mylar scraps on the holes and rubbing them to make them stick. Is this the normal way to fix holes?

3. The duco cement I have on hand is from 2 years ago and has thickened to the point where it just doesn’t work anymore, so I haven’t used it. Should I be using duco? Is it easier to cut through than super glue?

4. So I accidentally installed my tail boom upside down which results in the HS being a couple mm lower than normal and maybe tilted up by a degree or two. Is HS incidence a thing, and is it beneficial/detrimental to my plane in this case?

5. How important is it to have the leading edge of the wings level? I had some problems with this last year but forgot what happened when they weren’t level. Right now, my inner (left) wing is a couple mm higher than my outer. I expect this to increase the turning radius slightly - is this true? How does this affect flying compared to wing wash?

Thanks,
Astro

[Hartman]

Received my FF kit Friday and have been building it yesterday and today. I’m looking to fly tomorrow (exciting!) and I’m building more carefully and closer to the manual this year. Some questions:

1. I changed to a soldering iron this year to trim mylar and found that it wasn’t as neat as I expected it to be - the Mylar tends to curl up when heated so the edges always curl around the cf if they’re not burnt and I have to uncurl and cut them using an xacto. Does that make a difference (small pieces of mylar on the edge of cf rods) or is it too trivial of an improvement to spend time on?

2. I’ve had 2 or 3 holes in my mylar and I found that mylar tends to stick to itself through static electricity, so instead of fixing holes like I did last year (with scotch tape or gluing mylar scraps on holes) which got heavy real quick, Im just putting mylar scraps on the holes and rubbing them to make them stick. Is this the normal way to fix holes?

3. The duco cement I have on hand is from 2 years ago and has thickened to the point where it just doesn’t work anymore, so I haven’t used it. Should I be using duco? Is it easier to cut through than super glue?

4. So I accidentally installed my tail boom upside down which results in the HS being a couple mm lower than normal and maybe tilted up by a degree or two. Is HS incidence a thing, and is it beneficial/detrimental to my plane in this case?

5. How important is it to have the leading edge of the wings level? I had some problems with this last year but forgot what happened when they weren’t level. Right now, my inner (left) wing is a couple mm higher than my outer. I expect this to increase the turning radius slightly - is this true? How does this affect flying compared to wing wash?

Thanks,
Astro

1. The small pieces of mylar are probably trivial but it's nicer to have a clean edge since they might cause a bit of drag when flying, making the plane less efficient.
In general to anyone reading this, building a clean plane allows for a much better flying experience since a lot of issues beginners might have can be directly bypassed. Read directions twice or three times and really understand them before building if you're new. And take your time measuring and adjusting before gluing.

2. Can't really speak to that. Only issue that might show up is that the pieces might blow away when flying. I believe some people have done this and used the spray glue to keep the patch in place.

3. Duco is easier to adjust than super glue and is slightly lighter when done correctly, but super glue has the major advantage of drying nearly instantly. It is possible to soften/dissolve super glue with acetone, same as duco. Just a bit messier.

4. HS incidence is a thing, but I'm not totally sure what your situation is. Is it the leading or trailing edge that's higher? If it's the leading edge, you might want to rectify that. I believe no incidence is the most 'normal' but there are some instances where you'd want the trailing edge to be a bit higher. Not totally sure which instances those are, though.

5. Yes, your circles will likely be slightly bigger. If the leading inner edge is tilted higher and the trailing edge is 'level' in comparison, this is basically wing wash and will add more lift to the inside of your wing and make the circles slightly larger as a byproduct. If the whole wing is tilted, then the plane will simply turn in a larger or smaller radius. I believe the latter situation is in essence the same as tilting your HS.

[pumptato-cat]

I'll wait on the coaches to provide better input for some of these but here's what I know.
1) I use a fresh X-acto blade. Never had any issues with this; just cut slow and carefully. I have heard of people using a cautery pen instead of a soldering iron. I bought one and I'll report back on how that goes when I build something with it.
2) If you use the search function in the forums and search phrases related to or similar to "mylar patches" or "torn mylar" there's some information. I used 3M77 to attach small patches. I sprayed it directly on the patch because SciOly planes are already heavy so weight doesn't matter too much to me. However, I've known some teams that dilute the glue with a lot of Naptha and paint the patch before gluing instead of directly spraying.
3) Dunno, depends on the purpose I guess? For things you want to adjust easier, use Duco. I've found CA to be very hard to dissolve with acetone(not sure if that's just a me problem, though--but once I spent half an hour brushing the same joint with acetone and it never dissolved).
4) What's HS? I feel like this is something I should know...
5) Hartman pretty much summed it up well but I'll try to explain the last part further. I'm assuming you mean that the entire wing is tilted, not wash-in--if so, I think I recall something about how the wing determines the angle at which the plane flies(the wing will always be flat instead of the motorstick IIRC). So, if the right side of the wing was lower than the left, the plane would have to fly with the wing flat--doing so would lift the right side up to be level and decrease stab tilt(assuming it was set for left circling) as the entire plane rotates counterclockwise, and vice versa if the wing was tilted the other direction.
Hope that makes sense, and please correct me if I'm wrong!

[zedsfh]

Pumptato- I believe that HS is short for Horizontal Stabilizer.

[coachchuckaahs]

Received my FF kit Friday and have been building it yesterday and today. I’m looking to fly tomorrow (exciting!) and I’m building more carefully and closer to the manual this year. Some questions:

1. I changed to a soldering iron this year to trim mylar and found that it wasn’t as neat as I expected it to be - the Mylar tends to curl up when heated so the edges always curl around the cf if they’re not burnt and I have to uncurl and cut them using an xacto. Does that make a difference (small pieces of mylar on the edge of cf rods) or is it too trivial of an improvement to spend time on?

2. I’ve had 2 or 3 holes in my mylar and I found that mylar tends to stick to itself through static electricity, so instead of fixing holes like I did last year (with scotch tape or gluing mylar scraps on holes) which got heavy real quick, Im just putting mylar scraps on the holes and rubbing them to make them stick. Is this the normal way to fix holes?

3. The duco cement I have on hand is from 2 years ago and has thickened to the point where it just doesn’t work anymore, so I haven’t used it. Should I be using duco? Is it easier to cut through than super glue?

4. So I accidentally installed my tail boom upside down which results in the HS being a couple mm lower than normal and maybe tilted up by a degree or two. Is HS incidence a thing, and is it beneficial/detrimental to my plane in this case?

5. How important is it to have the leading edge of the wings level? I had some problems with this last year but forgot what happened when they weren’t level. Right now, my inner (left) wing is a couple mm higher than my outer. I expect this to increase the turning radius slightly - is this true? How does this affect flying compared to wing wash?

Thanks,
Astro

1. Soldering iron should leave a clean edge. You may want to experiment with temperature of the iron and speed that you move along. You should be able to drag the iron along the carbon for a clean finish, but speed is critical. Too slow you can overheat the epoxy in the carbon layup. If you prefer not touching, leaving a little margin, you can tack this down with #m&& thinned with Naphtha or LectraClean (https://www.homedepot.com/p/CRC-19-oz-L ... 1001119370).. Be sure to use ventilation with these solvents. For SO, we typically thin the 3M77 about 60 or 90 to one by mass. Use a small brush. Drag the wet brush along the carbon where the covering is overhanging and surface tension will seal it down.

2. We use the same thinned 3M77 to apply patches. Apply the patch as you are (static electricity), and then touch a wet brush around the edges and the glue/solvent will wick under quickly. We have also on occasion used a small bit of covering, dusted it VERY LIGHTLY with 3M77, and place this over the wound. Trick is keeping it flat. We put it on the end of a tongue depressor or scrap balsa with a VERY THIN coat of Vaseline (wipe it off and its still too much), spritz the #M77 while protecting the exposed wood with a scrap of paper, then turn over and apply to the hole.

3. For most SO parts we simply use thin CA. It is simple and dries fast. However, Duco has the advantage of being repositionable with acetone. We use 50-50 thinned Duco (acetone) on joints that may need repositioning. I am not sure what you mean by "cut through".

4. The height error should not matter. The incidence will affect your trim. Trim at slow speed is determined by your decalage, the difference between incidence of the wing and the stab. Since you added a little positive incidence to the stab, you will have to add a bit positive to the wing as well. Given the same endpoint on decalage, there is no difference in terms of the wing/stab aerodynamics. However, think about what is happening here. Both the wing and stab end up a little more positive, relative to the motorstick. But the wing and stab determine the flight characteristics, so really the MS is slightly more NEGATIVE than in the design case. This results in a little additional down thrust, which can limit climb at higher torque. This may or may not be an advantage, and is one reason we make both our wing and out stab adjustable.

5. As others have pointed out, if you are talking about Just the leading edge (tilted relative to the trailing edge), this causes left wing wash in, which MAY be needed for some kit designs, especially those with tip plates. But excessive wash is drag. You will want to be able to adjust the wash amount. The second possibility is that you mean the WHOLE wing is tilted, relative to the wing posts. If this is the case, and the left wing is high, then as the wing is what is flying, it will move the motorstick to the right a bit. This is fine, as many designs actually have a slight offset of the wing (left wing longer than right wing) to help with counteracting the torque. Do recognize however that this also may counter some of your tail tilt (horizontal stabilizer tilt), and you may need to add some more tail tilt. The tail tilt is the HS tilted to the right (left side high) to enhance circling at lower speeds.

Coach Chuck

[bjt4888]

Received my FF kit Friday and have been building it yesterday and today. I’m looking to fly tomorrow (exciting!) and I’m building more carefully and closer to the manual this year. Some questions:

1. I changed to a soldering iron this year to trim mylar and found that it wasn’t as neat as I expected it to be - the Mylar tends to curl up when heated so the edges always curl around the cf if they’re not burnt and I have to uncurl and cut them using an xacto. Does that make a difference (small pieces of mylar on the edge of cf rods) or is it too trivial of an improvement to spend time on?

2. I’ve had 2 or 3 holes in my mylar and I found that mylar tends to stick to itself through static electricity, so instead of fixing holes like I did last year (with scotch tape or gluing mylar scraps on holes) which got heavy real quick, Im just putting mylar scraps on the holes and rubbing them to make them stick. Is this the normal way to fix holes?

3. The duco cement I have on hand is from 2 years ago and has thickened to the point where it just doesn’t work anymore, so I haven’t used it. Should I be using duco? Is it easier to cut through than super glue?

4. So I accidentally installed my tail boom upside down which results in the HS being a couple mm lower than normal and maybe tilted up by a degree or two. Is HS incidence a thing, and is it beneficial/detrimental to my plane in this case?

5. How important is it to have the leading edge of the wings level? I had some problems with this last year but forgot what happened when they weren’t level. Right now, my inner (left) wing is a couple mm higher than my outer. I expect this to increase the turning radius slightly - is this true? How does this affect flying compared to wing wash?

Thanks,
Astro

Astro,

Sorry to not reply quicker. You've gotten some good direction from PumptatoCat and the others though. Here are my comments as well as some questions for you.

1. I use a cautery pen, but I think it works the same as a soldering iron pretty much. I don't get any significant curled covering near the flying surface edges. I hold the pen close enough (maybe 1/4" away) so that the "melt area" goes all the way to the edge of the flying surface. This take practice. You definitely need to keep the pen/iron moving at the correct rate so as to avoid overheating and overtightening the covering of the actual flying surface. When trimming with heat, you will notice the covering of the surface on slightly changing (but not excessively tightening) just opposite the pen/iron.

2. Yes do as the others suggest. Tiny mist of 3M77 on a carefully cut bit of covering. Pick up with tweezers (if you have them) and carefully position and press into place. When I patch a lighter airplane (EZB, etc.) I use OS Film with very thin (almost all thinner; naptha not acetone) 3M77 painted around the hole. Then positions the OS film patch and activate the glue with straight thinner (go around the in place patch and don't touch it; thinner will wick under and activate glue). None of this is necessary for SO as the airplanes. See my "Wing Cutting/Span Correction" video on the newly updated NFFS SO website "Video Catalog" (link from Coach Chuck in the second post of this thread) to see this super thinned glue brushing method.

3. Others have given good recommendations on Duco. We use Duco for the few joints that require a little time to position (ex. attaching winglets to wing, attaching a fin to a tailboom, attaching very tiny gussets, etc.), otherwise we use very tiny drops of medium CA for all joints (see the glue tool we use in the first "Resources for Students" on the newly updated NFFS SO website here: https://www.freeflight.org/science-olym ... resources/

4. The tailboom for the Div B FF kit is symmetrically tapered, so I'm guessing that you are referring to the Div C kit tailboom. This tailboom bottom side is unusually shaped this year and is "curve contoured or scalloped" quite a bit and by installing upside down you have given the stabilizer 2.046 degrees of positive incidence (inverse sin of .0357 which is the TB height difference of .21875" minus .09375" over the 3.5" chord of the stab). A little positive stab incidence (like 0.5 degrees) would not be an issue, but over 2 degrees is a bit much and will lead to quite a bit of wing incidence to compensate. I would have you cut the TB off the fuselage and stab (clean all bits off the LE and TE by scraping with a blade) and fashion a new TB from the remaining scrap that the TB was laser cut from and redo this step (there is enough extra wood around where the TB was laser cut to easily fashion a new TB. This is the only item I'll disagree with Coach Chuck on as I have the benefit of having the kit in front of me and can see the unusual "Scalloped" shaping of the bottom of the TB.

5. Depends upon what you mean by the words "level" and "higher". Pictures with the airplane carefully aligned to the camera (in a google folder and link shared) would make this easy to diagnose. I am guessing that you are not referring to left wing washin (referred to as warp/twist in the kit instructions), which is desireable in a small amount (maybe 1/8" washin this year based upon the pictures in the kit). If the "left wing higher" causes inadequate stabilizer tilt (or wrong direction tilt) that would probably be the only issue.

Brian T

[Astronomyguy]

Thank you everyone for the responses! Here's some updates/responses to the answers I've had:

1. I probably won't be using the soldering iron anytime soon unless my plane breaks really bad and I have to make another one, but I'll definitely practice and check out the videos on it next time I use it. I used the sharpest point I had but the melted mylar would always make a residue on the point which had to be scraped off.

2. The mylar pieces I stuck on without any glue are actually still holding up after 2 days of flying so I'm sticking with that for now. Would thinned duco work as an adhesive? Thinking of using that in the future if I have more holes to patch.

3. I will be getting duco and acetone to thin it. I still have a bottle of thinned duco from two years ago but that might be past its shelf life.

4. I ended up attaching a piece of scrap balsa to prop up the end of the HS, lessening the height difference to about half a millimeter. Considered taking off the tailboom but the scrap balsa was a much quicker fix. Image in google drive link below.

5. I was referring to the entire wing being tilted and not the wing warp, but I fixed that and it's all good now.

One thing I noticed from my flights is that the plane tends to wobble straight or slightly to the right at launch for a couple seconds before turning into its counterclockwise loop. I assume that it's because the left side of the wing has more lift than the right, but my wing warp is minimal (1/8 in.) and the torque isn't that high (0.3-0.4 oz/in). The effect seems to be more prominent on higher torque, which is weird because the plane is supposed to bank inwards at high torque instead of out. I'll PM a video to the coaches.

https://drive.google.com/drive/folders/ ... sp=sharing (HS photo)

[coachchuckaahs]

AG:

Please post complete trim parameters, including CG, incidence, and all angles. Of particular importance for this issue is the left wing wash in and the net rudder offset angle, which includes the Tailboom-to-Motor Stick joint, the Horizontal Stabilizer (HS) to TB joint, and the vertical fin to stab joints. BUt all winding and trim parameters should be included in a request for trimming help.

The wedge you used on the HS to TB joint should be fine and is a typical means of adjusting HS incidence

I would guess that you are moving too slowly with the soldering iron, or it is too hot, to cause balling of melted covering.

Coach Chuck

[bjt4888]

Thank you everyone for the responses! Here's some updates/responses to the answers I've had:

1. I probably won't be using the soldering iron anytime soon unless my plane breaks really bad and I have to make another one, but I'll definitely practice and check out the videos on it next time I use it. I used the sharpest point I had but the melted mylar would always make a residue on the point which had to be scraped off.

2. The mylar pieces I stuck on without any glue are actually still holding up after 2 days of flying so I'm sticking with that for now. Would thinned duco work as an adhesive? Thinking of using that in the future if I have more holes to patch.

3. I will be getting duco and acetone to thin it. I still have a bottle of thinned duco from two years ago but that might be past its shelf life.

4. I ended up attaching a piece of scrap balsa to prop up the end of the HS, lessening the height difference to about half a millimeter. Considered taking off the tailboom but the scrap balsa was a much quicker fix. Image in google drive link below.

5. I was referring to the entire wing being tilted and not the wing warp, but I fixed that and it's all good now.

One thing I noticed from my flights is that the plane tends to wobble straight or slightly to the right at launch for a couple seconds before turning into its counterclockwise loop. I assume that it's because the left side of the wing has more lift than the right, but my wing warp is minimal (1/8 in.) and the torque isn't that high (0.3-0.4 oz/in). The effect seems to be more prominent on higher torque, which is weird because the plane is supposed to bank inwards at high torque instead of out. I'll PM a video to the coaches.

https://drive.google.com/drive/folders/ ... sp=sharing (HS photo)

Astro,

I am replying to your PM in the public forum as my reply will hopefully be helpful to other students and as my reply will not reveal any of your private data as we will be discussing the trim parameters that are public in the FF kit instructions. Good job recording data!

Per your logged data, your CG is at 2.7 cm - 2.9 cm forward of the rear wingpost. This is 1.0625"-1.14" fwd of rear post. The kit instructions recommend 1.1875" to 1.875" forward of rear post so your setting is likely oo far back for initial testing (I suspected this based upon the "wandering/nose light" character of your flight video). Your wing incidence is currently 4 mm or 0.157" and is within the kit recommended range of .14"-.19". However, I am wondering about your tailboom shim. It appears to be a stack of three pieces of 1/16" thick wood. As the tailboom taper is only 1/8", if your tailboom is basically in line with the motor stick, a 3/16" shim would give you negative incidence in the stabilizer which would add a little over one degree to the total decalage making the .157" of positive wing incidence too much. So, possibly, you have too much positive wing incidence if you also have some negative stab incidence. You'll have to measure this to verify as whether there is stabilizer (TB) negative incidence as this can't really be seen in the picture. Rudder offset at 0.6mm or 0.236" is per plan. Left wing twist/warp as the kit instructions calls it (this is more properly called "washin") is noted in your log as 0.6mm, which is 0.236". The kit recommendation is for .125" or 0.3 mm. The stabilizer tilt you indicate on your log is 0.7mm. The kit recommendation is 1.5cm tilt; right stab tip this much higher than the stab center (at the tailboom joint). This may seem like a lot of stab tilt, but a V-dihedral airplane with tip plates on the stabilizer will likely need a lot of turn setting.

So, your best bet is to increase stab tilt to the kit recommendation, double check decalage (esp. any negative inc. in stabilizer), cut left wing washin by 50%, and probably move the CG forward again and start with very low power flights. If you haven't had a chance to read the first document in each of the NFFS website "Building" and "Flying" tabs, please read these carefully too https://www.freeflight.org/science-olym ... resources/

Typically, it is not a good idea to make more than one trim change at a time, but in this case the three to four changes are all to basically to get the settings to match the kit manufacturers recommendations; which would be your best starting point. If you want to make one change at a time, I'd reduce the washin to 3 mm (or less; see if you can get it to roll left) first, then increase the stabilizer tilt to 1.5 cm (tip to stab center measure), then move the CG forward to at least 1.1875" fwd of rear post. And before all of this, verify the stabilizer negative incidence (if any) and possibly correct this to zero.

Have fun and great job starting so early.

Brian T

[Astronomyguy]

Astro,

I am replying to your PM in the public forum as my reply will hopefully be helpful to other students and as my reply will not reveal any of your private data as we will be discussing the trim parameters that are public in the FF kit instructions. Good job recording data!

Per your logged data, your CG is at 2.7 cm - 2.9 cm forward of the rear wingpost. This is 1.0625"-1.14" fwd of rear post. The kit instructions recommend 1.1875" to 1.875" forward of rear post so your setting is likely oo far back for initial testing (I suspected this based upon the "wandering/nose light" character of your flight video). Your wing incidence is currently 4 mm or 0.157" and is within the kit recommended range of .14"-.19". However, I am wondering about your tailboom shim. It appears to be a stack of three pieces of 1/16" thick wood. As the tailboom taper is only 1/8", if your tailboom is basically in line with the motor stick, a 3/16" shim would give you negative incidence in the stabilizer which would add a little over one degree to the total decalage making the .157" of positive wing incidence too much. So, possibly, you have too much positive wing incidence if you also have some negative stab incidence. You'll have to measure this to verify as whether there is stabilizer (TB) negative incidence as this can't really be seen in the picture. Rudder offset at 0.6mm or 0.236" is per plan. Left wing twist/warp as the kit instructions calls it (this is more properly called "washin") is noted in your log as 0.6mm, which is 0.236". The kit recommendation is for .125" or 0.3 mm. The stabilizer tilt you indicate on your log is 0.7mm. The kit recommendation is 1.5cm tilt; right stab tip this much higher than the stab center (at the tailboom joint). This may seem like a lot of stab tilt, but a V-dihedral airplane with tip plates on the stabilizer will likely need a lot of turn setting.

So, your best bet is to increase stab tilt to the kit recommendation, double check decalage (esp. any negative inc. in stabilizer), cut left wing washin by 50%, and probably move the CG forward again and start with very low power flights. If you haven't had a chance to read the first document in each of the NFFS website "Building" and "Flying" tabs, please read these carefully too https://www.freeflight.org/science-olym ... resources/

Typically, it is not a good idea to make more than one trim change at a time, but in this case the three to four changes are all to basically to get the settings to match the kit manufacturers recommendations; which would be your best starting point. If you want to make one change at a time, I'd reduce the washin to 3 mm (or less; see if you can get it to roll left) first, then increase the stabilizer tilt to 1.5 cm (tip to stab center measure), then move the CG forward to at least 1.1875" fwd of rear post. And before all of this, verify the stabilizer negative incidence (if any) and possibly correct this to zero.

Have fun and great job starting so early.

Brian T

Thanks for the reply! I tested today with the intention of moving to slightly higher torques in an attempt to induce roll and moving the CG forward. I remeasured the CG last night and it turned out to be 2.3 cm in front of the rear wingpost instead of 2.7 after I had moved some clay up, so I must've either measured it wrong earlier or moved the CG backward - probably the former. I gained at least 10 seconds from moving the CG forward, and I think I overdid it on the last flight as the angle of incidence was looking pretty sharp. Don't know for sure though because people had started entering the gym and the air currents were disrupting the plane significantly. I plan on increasing stab tilt for a tighter circle - does it help make the plane more resistant to circle drift? - it was a noticeable problem this morning. As for washin, the behavior seemed to improve at higher torques so I'll leave it where it is for now in anticipation that it'll help me when I go full power (Initial torque is still at 0.4 oz-in). Could launching the plane tilted inwards also help induce roll? I remember doing the opposite last year to counteract the inward roll. Flight log should still be accessible so you can see what I have, I'll upload the videos tomorrow.