Project Ladybug

Aerofoam

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Also, with angled blade bolts, the lead/lag movement will cause elevation changes, being out of plane could induce odd vibrations and cause
bending forces on the hub/shaft assembly.
 

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The steel hub:
This one is meant to be easiest to make, if it does really work.
I will upgrade it to a better one when the whole thing works.
The sketch does not show but the steel plates are meant to be bent to 7.5° angle at the tips.
The blade roots will be made thicker to mate with the plates.
Can be a bit tricky but will be good if it gets me past the initial tests.
It is constrained both in vertical and horizontal axes.
The bumper thingy is not made yet.

steel.png
 
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btd1982

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having separate blade straps like that is better for an aluminium or steel material. It means you can keep the grain in-line with the direction of load. I don't think twisting the straps will work as the bolt goes out of alignment with the straps parallel, for the bolt holes to align you would have to offset the straps out of parallel. Could you use a spherical plain bearing instead of your rubber bushing and have pitch links ?
Splined drive would be my choice but it is harder to produce.
 

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having separate blade straps like that is better for an aluminium or steel material. It means you can keep the grain in-line with the direction of load. I don't think twisting the straps will work as the bolt goes out of alignment with the straps parallel, for the bolt holes to align you would have to offset the straps out of parallel. Could you use a spherical plain bearing instead of your rubber bushing and have pitch links ?
Splined drive would be my choice but it is harder to produce.
I dont see how the bolts will go out of alignment with the plates. I am thinking of not twisting the plates but putting a shim that has an angled cut for the blade. So the blade root will mate with the cut perfectly. I also need to cut the plate bolt holes at an angle to match the bolt angle. I want to use a PVC foam shim for a start and upgrade it to some tougher material later.
 

Aerofoam

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I would either vacuum bag them, or make a mold. As small as yours are, the mold would be relatively easy, only about 4ft. long.
 

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@btd1982 does the hocus pocus thing but I guess it won't work here.
I will try a mold-less way of doing it.
It may be primitive by industry standards but I am hoping it will be quality enough to go through the initial cycle of development.
I only need it to hold its form and stand the forces that will try to tear it apart.
 

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I would either vacuum bag them, or make a mold. As small as yours are, the mold would be relatively easy, only about 4ft. long.
Making the mold is more of a future thing for me as I will try a mold-less method first.
I want to do a wet layup with no vacuuming.
As I will make a thin skin I believe issues with wetting the cloth will be minimal.
Of course I do not want to use more resin than necessary either.
I will not make two sides of the blade and glue them either.
I will wrap the cloth around a cured rib and spar structure.
I expect minor failures like some collapse on the skin where there is no support from the inside between ribs.
I need to find a good way of sealing the blade tip and root.
The root section is also a bit of an issue, I will do what is best and less costly.

I will cure at room temperature but there is also the possibility of postcure heat treatment like a couple hours of baking in 90-120 degrees.
I will do it if I can do it with my electric heater, it will be like an open oven.
I tent to use available materials that I have at home.
I only have some small tools at home.
 
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After 40 minutes of wrestling in the mudpit I set the fiberglass resin composite blade rib specimen aside to cure.

I spent several days getting some stuff out of my way before I start getting may hands dirty with composites. The materials I had ordered had arrived already. The templates I had gotten made were already there and my mind was clear from the distractions that I swept away. But I still wanted to take it slow and days passed without action until today. Humidity was 44% which is under the 65% indicated on the resin specs. Temperature was 28°C which was more than ideal but was OK if I was to be quick.

Things get out of control: I calculated that I would make 15 grams of resin hardener mix for the two ribs that I had templates for. But the kitchen scale was not quick enough to change numbers and I poured more resin than enough. Then I had to put more hardener and again more hardener and I ended up with 48 grams of resin which was three times as much as I needed.

The walls of the template was a little porous and I though I should put some masking tape to cover the pores and make the walls smooth which would also act as a mold release agent. But his time the walls were too smooth and the cloth didn't stick as I though it would. I had a hard time putting the cloth back to where it should be every time it came off as it was too tacky.

At the and I could not execute the plan 100% and it turned into an experiment rather.
I will see the results tomorrow morning when they should have dried completely.
This was my first time dealing with composites, I need to come up with new tricks to end up with repeatable good results.
 
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I have already discovered two ways of how not to make a wing rib.
Main issues were; I started using the resin too early while it was still too thin, I need to wait until it becomes a little viscous before I start applying it otherwise the cloth does not stay in place. The more pressing issue is it is very hard to remove the piece from its "mold", or even impossible without damaging it. My first attempt was to line the inside of the PVC foam airfoil cutout which proved to be hard to do precisely. So I moved to the second method of lining the outside of the product that came out of the first attempt. Neither worked well. So I will need to move to a third way which has a better potential of working. The picture shows the mold which was the product of the first attempt and the work piece wrapped around it. I haven't yet been able to separate them although there is a layer of glossy paper tape between them.

Edit: Shortly after my post the piece came out very easily off the mold.

IMG_20220626_094017.jpg
 
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Aerofoam

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I have already discovered two ways of how not to make a wing rib.
Main issues were; I started using the resin too early while it was still too thin, I need to wait until it becomes a little viscous before I start applying it otherwise the cloth does not stay in place. The more pressing issue is it is very hard to remove the piece from its "mold", or even impossible without damaging it. My first attempt was to line the inside of the PVC foam airfoil cutout which proved to be hard to do precisely. So I moved to the second method of lining the outside of the product that came out of the first attempt. Neither worked well. So I will need to move to a third way which has a better potential of working. The picture shows the mold which was the product of the first attempt and the work piece wrapped around it. I haven't yet been able to separate them although there is a layer of glossy paper tape between them.

Edit: Shortly after my post the piece came out very easily off the mold.

View attachment 1155202

Tip:
After mixing the resin, pour it into a paper plate to keep it shallow with as much surface area as possible. This will delay the cure.
In a cup, the resin insulates itself and it will start heating itself from the center, then go off on you.
I have actually had resin get hot enough to start burning when allowed to stay in a cup...
 

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IMG_20220627_161431.jpg

The second specimen from the first attempt. The resin got thicker and and an unplanned natural pattern came about.
Imprecise and not repeatable.
 

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I have spent weeks ordering products to use in making the ribs and waiting on delivery of them. Turned out that most of the materials I have ordered were useless. I had ordered strips of aluminium to use as templates and tapes and all but there were no ways to shape them precisely. But I have come close to achieving precision and repeatability. The latest specimen is like below. I am confident I am only a couple of tries away.


IMG_20220726_133326.jpg
 

Aerofoam

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I saw this coming, it would be easier to either make a mold, carve solid wood blades, or vacuum bag over foam cores, you need to maximize the repeatability and the interior structure needs a lot more strength to stand up to the high RPM load you will need for a small rotor.
The hollow form with ribs is cool, but could only be made repeatable with expensive precision silicone inserts that are in the layup when you put the whole thing in a mold to hold shape, then autoclave it for 12 hours.....
Way too much $$$ work...
Foam core is the easiest, probably cheapest, but wood could be as simple as making a prop duplicator with a router and then a dummy blade to trace from foam....
Or as I originally suggested, have a set of shaper blades made for the top and bottom foil shape and find a cabinet shop to make endless amounts of blades from a light wood like beach, or bass.
 

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I am thinking of a whole new way of making the blades; a method which is more robust in every way and easier to implement too. I will need different tools for it though. If I have some luck in this new method the time I've spent fruitlessly can be compensated.
 

btd1982

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I am thinking of a whole new way of making the blades; a method which is more robust in every way and easier to implement too. I will need different tools for it though. If I have some luck in this new method the time I've spent fruitlessly can be compensated.
Machine leading edge from billet aluminium ? 😉
That's the way I'd go but that's mainly because I have no clue how to build in any other material.
 

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Machine leading edge from billet aluminium ? 😉
That's the way I'd go but that's mainly because I have no clue how to build in any other material.
I will still go with fiberglass composite but employ a different way of construction. There will probably be some need to protect the leading edge but I will not address this issue just yet, I wonder if it can be done by gluing some tough metal on. I may also have some trouble getting the cordwise CG right as I haven't found any literature about it for my selection of airfoil. I will put it at around 25-27% for now.
 

Aerofoam

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I will still go with fiberglass composite but employ a different way of construction. There will probably be some need to protect the leading edge but I will not address this issue just yet, I wonder if it can be done by gluing some tough metal on. I may also have some trouble getting the cordwise CG right as I haven't found any literature about it for my selection of airfoil. I will put it at around 25-27% for now.

That CG range should be fine, if you vacuum bag it, use a thick layup, you are making more of a propeller than a rotor, it needs to be strong.
The inserts for blade grips should be wood, or AL. and probably extend to 35% from the hub, or transition to a full length spar...
 

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That CG range should be fine, if you vacuum bag it, use a thick layup, you are making more of a propeller than a rotor, it needs to be strong.
The inserts for blade grips should be wood, or AL. and probably extend to 35% from the hub, or transition to a full length spar...
I have spent a long time trying to make ribs and put spars and skin on them but ironically my new method employs no ribs at all. Making ribs was like wrestling in a mudpit which many times I wanted to give up halfway through the hour long process. However the skin fabric that I had bought was barely enough for the design with ribs and will not be enough with the new construction which needs like twice the amount. I will need to wait for an additional order to arrive and use 1.5 times the fabric as I was planning to make it extra strong. I am not using a software to design composite structures and am going by instincts for now.
 
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