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rtfm

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Serious question, and advice/opinions sought:
I'm beginning to have second thoughts about using a tapered wing on the Fleabike.

"Standard" Fleas have rectangular wings. This makes positioning the pivot points easy (at say, 24% chord). But what about tapered wings? Where do I position the pivot points? At the 24% position of the inner rib, and the 24% position of the outer rib also (green circles)? Or do I work from the Aerodynamic centre of the wing as a whole (red circles)?
1630210844685.png
Unless I can get this sorted quickly, I might have to use my existing wing half (ribs and spars, no spar webs yet) for firewood, and start again with a rather ugly rectangular wing. That would be a pity, but not a disaster.

Anyone?

Duncan
 

Topaz

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Serious question, and advice/opinions sought:
I'm beginning to have second thoughts about using a tapered wing on the Fleabike.

"Standard" Fleas have rectangular wings. This makes positioning the pivot points easy (at say, 24% chord). But what about tapered wings? Where do I position the pivot points? At the 24% position of the inner rib, and the 24% position of the outer rib also (green circles)? Or do I work from the Aerodynamic centre of the wing as a whole (red circles)?
View attachment 114885
Unless I can get this sorted quickly, I might have to use my existing wing half (ribs and spars, no spar webs yet) for firewood, and start again with a rather ugly rectangular wing. That would be a pity, but not a disaster.

Anyone?

Duncan
You work in relation to the Mean Aerodynamic Chord (MAC), if the wing is tapered and straight. If, like your wing, there is sweep, you have to be sure to note the spanwise position of the so that it's properly positioned fore-and-aft. Straight, un-swept wings will be easier, but it can be done with tapered/swept wings, too.
 

rotax618

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As I noted when you proposed that planform - you open a can of structural and aerodynamic worms for no benefit other than to be “different”
I wish you luck.
 

rtfm

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As I noted when you proposed that planform - you open a can of structural and aerodynamic worms for no benefit other than to be “different”
I wish you luck.
Point taken, rotax618.
I've spent the afternoon creating a straight rectangular wing, which is both free of aerodynamic gotchas, as well as probably easier to build. But I still don't like the full-size final rib - looks kinda ugly to me. Oh, well...
 

rotax618

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It’s a bike not a fighter, a rectangular wing or at most a rectangular centre section with a tapered tips, simpler/lighter is what is required.
 

rtfm

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I reluctantly agree. You know how it is - one gets an idea, and it becomes an all-consuming passion. It takes both time and counter advice to finally percolate through and allow one to see things differently.
 

rtfm

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OK, here is my (proposed) paint scheme. The wing is a bit cheeky, because although it is a rectangular planform, it will *look* like a sexy curved wing. Ha ha. And what do you think about the basic colours and shape of the fuselage?

I like it (although it is probably going to change slightly as the days wear on) but HOW does one actually paint this? I think I can cut a pattern on the CNC so that I get both sides identical, but my issue is - how do I paint it. I presume an initial coat of white paint all over. Then I have two colours. I can see multiple applications of masking tape with all its attendant opportunities for inaccuracies in my future.

Is there an easier/more accurate/efficient method?

Duncan
1631653993785.png
 

Tiger Tim

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Looks to me like taping is the answer. If the edge is sloppy you just divide the two colours with a complementary or contrasting pinstripe. It’s called a ‘cheat line’ for a reason…
 

rtfm

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Well, it's official. I am crap at spray painting. I tried three times to spray on the spray putty undercoat with varying degrees of success, and ended up sanding almost all of it off. I *was* left with a very smooth surface on which to apply the paint, so I guess it wasn't a complete failure - just three times the work.

Then I tried to spray on the polyurethane paint. Most of it just ran off. So I tried a second coat. This time, runs all over the place. Sanded all the runs down, and then decided, buggerit - out came the paint brush and I have to say - a very nice job in the end. Paint brush for me from now on...

Duncan
 

Bill-Higdon

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Well, it's official. I am crap at spray painting. I tried three times to spray on the spray putty undercoat with varying degrees of success, and ended up sanding almost all of it off. I *was* left with a very smooth surface on which to apply the paint, so I guess it wasn't a complete failure - just three times the work.

Then I tried to spray on the polyurethane paint. Most of it just ran off. So I tried a second coat. This time, runs all over the place. Sanded all the runs down, and then decided, buggerit - out came the paint brush and I have to say - a very nice job in the end. Paint brush for me from now on...

Duncan
A number of sailboats are brush painted P.U. paint, a master can do a beautiful spray job, a lot of the rest of us forget about it.
 

Jaredjhale

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Seeing as how you already have the shape and basic bend lines, why not make this out of aluminum? Use 6061-T6, maybe .063, and then weld the seams. I don't think it would be heavier that plywood.
Could he braze the seams instead of weld them?
I'm asking because I for my own tank I would prefer that as I have some of the Harbor Freight aluminum brazing rods and brazing is fairly easy, though time consuming since aluminum is a heat sink, and also welding aluminum is fairly challenging (on a MIG) from what I've heard.
 

Angusnofangus

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Could he braze the seams instead of weld them?
I'm asking because I for my own tank I would prefer that as I have some of the Harbor Freight aluminum brazing rods and brazing is fairly easy, though time consuming since aluminum is a heat sink, and also welding aluminum is fairly challenging (on a MIG) from what I've heard.
I am the first to admit that I am not a welder. That said, My daughter's ex was a welder and he let my daughter try her hand at welding aluminum with MIG. She did a very good job. Someone who is knowledgeable can weigh in any time.
 

TFF

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It might seem extreme but if you want to see if harbor freight aluminum brazing rods are up to the task, make a test panel and beat it with a hammer. That is how tough you want the joint. The joint can’t break any easier than the main metal.
 

rtfm

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There seems to be a very large difference in performance in aluminum welding rods. This is a very illuminating video test of the major brands. Some of the rods are quite impressive. I'm considering making an aluminum gas tank using this method...

Duncan
 
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