Flight B/C

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pumptato-cat
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Re: Flight B/C

Post by pumptato-cat »

I have another question:
1) Someone told me to laminate my FF blueprint so I don't get glue on it-but it's way too big to laminate :[ I'm afraid i'll ruin it even if I use wax squares, any ideas? Does Dave have PDFs of his blueprints available? I don't want to email him about something so trivial... (he seems to be busy ;-;)
I'm going to just cover the entire thing with transparent wax paper for now.. (gotta get building soon)
2) My dining table isn't flat... I used a level and there are three indicators. The center says that it's flat, but the other two say otherwise. (the left one is especially wonky) When I flip it over(the level), the center indicator goes crazy and says that it's crooked?? Does it really matter if it's a flat surface? I think I'm overthinking things again but would appreciate any advice :)
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Re: Flight B/C

Post by coachchuckaahs »

Cat:

A level indicates if the surface is LEVEL, not if it is flat. It does not have to be level. Should be flat. If you lay a large (3-4 foot) level on the table, does the middle and both ends touch at the same time?

We use wax paper. We tape the plan to a 1/2" foam board (Hobby Lobby), then tape wax paper over it. Cut the wax paper to be slightly larger than the part you are working on, rather than wrapping it around the edges of the foam board.

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Re: Flight B/C

Post by pumptato-cat »

Thanks! I got it to work-- table seems to be flat. Hopefully it's not warped :)
Another question (sorry they're endless 😅)
Should the FF 2023 kit's ribs be on top(lap joint) of the leading and trailing edges, or is it sandwiched between them(end joint)? They aren't long enough to form a lap joint with the edges. I'm not sure how it's supposed to look...
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Re: Flight B/C

Post by pumptato-cat »

Sorry for the separate posts, I thought of this after posting and it's giving me an error message when I try to edit my previous post:

Also, for CF rod cutting-- has anyone ever had any issues with carbon fiber rods used in wings? I was very careful while cutting(Went outside, used gloves+N-95, washed pieces after finishing, sealed with CA glue on ends(used a capillary applicator so it didn't add too much weight)) but I'm still a bit concerned... (lung cancer, filaments in bloodstream, etc. are some horror stories I've heard D:)
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Re: Flight B/C

Post by jander14indoor »

As already noted, for building on you need FLAT, not level. Though relatively level is nice.
I'd think twice about building on any surface your parents might shoot you for when (not if) you get super glue on it!
Instead, I use foamboard insulation (either the pink or blue stuff) available at most home centers. I like it 1 1/2" thick or more because it is stiff, and you can stick pins in it without poking through into your hands. But 1" thick can work. That stuff is more than flat enough for our purposes. Since I mentor many teams, I'll typically buy a 4X8 ft sheet and cut it down to useful sizes depending on the size of the plane I'm building. Real cheap then. If you don't need that many building boards, see if they have any scrap they'll sell cheap or even give you. Or if you can buy smaller sheets. Make sure you explain what you are going to use it for.
Another material commonly used are acoustic ceiling tiles. Also sufficiently flat, not so big, but also not so thick. But modelers have been using them successfully for YEARS.
One advantage on building on boards like this, you can assemble your wing/tail/whatever, apply glue, and then move it out of the way while it is drying.

Carbon Fiber. Note, I'm not a doctor, but this stuff is relatively neutral, especially in finished products like these rods vs loose fibers. No you don't want to breath any dust from cutting, but that's true about almost any dust. The precautions you took should be more than adequate.

Frankly, the main chemical risks come from the glues we use, NOT the carbon fiber.
- Some people become sensitive to CA fumes, especially after repeated use. Happened to me. Not deadly, but my sinuses shut down for a week after I use normal CA. I have to use the odorless stuff, and then I don't have a problem. And DON'T splash CA in your eyes, or get the fumes near your eyes, you won't be happy. Not to mention gluing body parts together.
- Balsa cement, the solvents are definitely not friendly.
Now, don't panic over this. Simply take precautions. Use in a well ventilated space, avoid excess exposure, consider the use of an activated carbon face mask. These are not high risk issues, but certainly something to be aware of and take action accordingly.

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Re: Flight B/C

Post by bjt4888 »

pumptato-cat wrote: October 28th, 2022, 4:36 pm Thanks! I got it to work-- table seems to be flat. Hopefully it's not warped :)
Another question (sorry they're endless 😅)
Should the FF 2023 kit's ribs be on top(lap joint) of the leading and trailing edges, or is it sandwiched between them(end joint)? They aren't long enough to form a lap joint with the edges. I'm not sure how it's supposed to look...
Cat

Rib tips should be butted to the carbon spars. Note that there is a slight “fish mouth” laser cut into the rib tips to accept the carbon rods.

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Re: Flight B/C

Post by pumptato-cat »

Thank you so much!!! I should've noticed that... Yeah I must've been overthinking things again.
Another question(Sorry ;-;)

My wings came out nice and straight, but the horizontal stab is horribly warped(actually it's not that bad. i'm not sure if it'll affect flight though and I can't afford to strip the mylar off and redo it if it does affect flight) and I don't know how it got that way(I was extremely careful) Any suggestions? Should I weigh it down with wooden blocks or something?(that fixed the warp on my vertical stabilizers, but I don't know if it's going to work on CF rod joints)
Last edited by pumptato-cat on October 29th, 2022, 8:44 pm, edited 1 time in total.
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Re: Flight B/C

Post by bjt4888 »

pumptato-cat wrote: October 29th, 2022, 7:30 pm Thank you so much!!! I should've noticed that... Yeah I must've been overthinking things again.
Another question(Sorry ;-;)

My wings came out nice and straight, but the horizontal stab is horribly warped(actually it's not that bad. i'm not sure if it'll affect flight though and I can't afford to strip the mylar off and redo it if it does affect flight) and I don't know how it got that way(I was extremely careful) Any suggestions? Should I weigh it down with wooden blocks or something?(that fixed the warp on my vertical stabilizers, but I don't know if it's going to work on CF rod joints)
Cat,

Good job getting this far in the project so early in the year. Stab twist during the covering process for this type of construction is common and easily fixed. You can correct as you attach the stabilizer to the fuselage. When attaching the stabilizer to the fuselage, set the stab tilt to the desired angle (ours is left stab tip 3/8" higher than right stab tip, or 1.94 degrees) and then glue the leading edge of the stab only to the fuselage with CA (of course since only leading edge is being glued, measure tilt using leading edge only). Let, this leading edge glue joint get strong (2-3 minutes, or use accelerator). Then, sight with your eye at table level from the nose of the airplane towards the stabilizer to view the twist and slightly squeezed the trailing edge carbon rod against the fuselage with your finger (protected with a small piece of wax paper) while shifting your finger pressure slightly to the left and to the right. When doing this finger pressure shifting, you'll see the twist get worse in one direction and disappear when squeezing in the other direction. When the twist is gone. have a partner glue the trailing edge rod to the fuselage with one drop of CA.

After this TE joint is strong, you can pick up the airplane and do some more of this adjustment (as the joint will usually be able to be squeezed and shifted still with finger pressure still as it is bonded with just one drop of CA) until the stab is flat ( I usually will have students twist maybe one degree more as the stab usually tries to twist back again), then add another drop or two of CA to fix the flat stab more securely to the fuselage.

We will sand a slight 2 degree angle across the fuselage (or tailboom depending upon design) so that the stab to fuselage joint is as gap free as possible after setting the tilt.

See the picture of me demoing this process in this Google folder: https://drive.google.com/drive/folders/ ... share_link

About half of the stabilizers that my students build have slight twist. The stabs are flat after construction and take on this twist as the covering is attached. I'm thinking that the students that have flat stabilizers after covering are attaching the covering at the stab LE and TE midpoint first and then attach towards tips after the mid point.

Keep up the good work and good questions.

Brian T
Last edited by bjt4888 on October 30th, 2022, 8:25 am, edited 1 time in total.
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Re: Flight B/C

Post by pumptato-cat »

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 :)
Last edited by pumptato-cat on October 31st, 2022, 10:16 am, edited 2 times in total.
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Re: Flight B/C

Post by jander14indoor »

It has to do with how lift is distributed across a wing.
For an infinite length wing (yes, only theoretical, but why high performance manned gliders, passenger liners, etc have long, thin wings, also called high aspect ratio), the lift is distributed evenly front to back and side to side.
For 'real' wings that have an end, the lift falls off towards the tip, and even more severely towards the front and back at the tip. So, depending on what the tradeoffs are, some plane designers (to save weight & drag) simply eliminate the surface area where there is low lift. One classic example is the WWII Spitfire fighter from England with those beautiful eliptical wings. Alternatively, you can eliminate the loss in lift by adding tip fences or winglets to prevent that lift fall off. Its one reason (but only one, its hard to design these right) you see many indoor designs with tip fences. They also provide the needed dihedral for stability.
So, why don't we round off SO wings? Several reasons. One, we typically are limited by the rules for wing area, but weight isn't so hard to hit. So we go for the most wing area possible. For another reason, they are trickier to build.

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