Bonding in progress !
Bonding process continue…
Only the central beam is bonding, while leading and trailing edges will be bonded later.
The weight is very close to 130g ! Hope the strength will be also there !
Part of the aluminum trailing edge will be removed and a hard wood leading edge will be probably added.
According to my records, the epoxy resin weight used up to now is 17g.
Actual weight 126g before leading and trailing edges bonding, therefore the total epoxy resin used so far is 20g.
Keeping my fingers crossed while carbon-carbon Fin is under bonding process, I drawn a possible back up using a classic construction method similar to the one I used before.
This is what I have found …
of course the tissue will be crossed 0° -45°.
Revisiting the Balsa Fin Design some width dimensional data are changed because of the Carbon Skin thickness that modify the end product dimensions.
Generally I use to make the Appendage’s Areas equivalent to 6/6.5% of Sail Area.
Taking an average Sail Area of 7300cm², the Appendages areas may vary from 438cm² and 474cm. The Fin will use 3/4 of that area = 328cm² to 355cm²
Taking into account final dimension, I reduced the balsa width dimensions. See Profiles.
Since I do have introduced a 4x4mm square tube as well the 4mm brass rod the fin thickness will be constant from top to bottom and by consequence the profile thickness will change from 6.2 at the Top to 7.0% at the Bottom.
Meanwhile the Trailing Edge on the Full Carbon Fin is bonded and Leading edge under way.
I think the Final Carbon Fin will be some few grams above the expected weight. Off course the trimming of aluminum trailing edge will partially compensate.
Balsa Fin preparation …
A Bad News that become a Good News !!! While I was cutting the Aluminum stripe excess a strange noise pop up indicating local dis-bonding. Decision taken : Remove the aluminum stripe all together, [i]removing at the same time the risk of cutting my fingers when manipulating around the trailing edge and at the same time reducing the Fin Weight !!!..
[/i]I’m getting old and forgetting some tricks, in the past the “123” Fin was made by using an Aluminum stripe plenty of holes to ensure better bonding !!!
After discussion with my friend Mechanical Engineer, I decided to let thinks as they are, further a sharp truncated trailing edge of 1mm of thickness appears to be more efficient hydro dynamically.
The Aluminum stripe is replaced by epoxy resin as in the picture.
Actually the Fin appears very stiff, but test with 3.0kg bulb will be made at the end of next week and not before.
For the Balsa-Carbon Fin I changed my mind, instead of one carbon square tube I introduced two carbon carbon tubes. Don’t ask me why, just a guess for strength. Full Carbon Fin is “resting” waiting for total polymerization (one week).
Basic Fin components are bonded except the leading edge.
Only one face sanded.
Actual weight 70g, this include the addition of Leading Edge carbon Rod and epoxy resin used for bonding.
Standby for a while due to annual shops holiday.
Missing carbon tissue
Wood plates for clamp
Soft foam
Carbon Fin bending test with 3kg bulb will be carried out this week according to that setting :
As planned, today after 9 days from assembly, I have performed the ‘bending test’ of the carbon Fin with the 3Kg Bulb.
The results are not the ones I would have hoped, but still inside for a future use.
With a 5.5mm thick Fin is probably the max I could achieve.
5.5mm / 80mm chord = 6.8% thus better than 7% if all that has some meaning for our models.
Of course under water the 3.0kg Bulb will become 2.72kg and the Fin will bent less…!
These are all excuses to justify the Fin use !!!
No shape hysteresis noted.
The test will be repeated next WE when the polymerization will be more mature.
I know it’s a little late to bring this up, but may I suggest an alternative design? If you make a center spine of carbon fiber sheet, and laminate two square carbon fiber tubes on either side at the point of maximum camber and pad with structural foam to fill the shape, you get multiple shear planes which greatly improve the stiffness. I make my RG65 foils this way and they are very rigid both in bending and torsion. FWIW.
Cheers,
Earl
Hi Earl, not sure to understand, You means replacing the ‘air’ with foam ?
Could be possible a small section drawing ?
Thank You Cheers Claudio
Just drawing up my understanding, please correct me if wrong, see below
Here’s what I meant. Dimensions are for RG65.
Cheers,
Earl
Thank You Earl. It may be good for a RG65 with about 750g Bulb and 5cm x 30cm long Fin. Thickness percentage may be between 8% and 9% and this is too high. I tried to inject some polyurethane foam, bit dirty job ! I will see tomorrow if it help !
Cheers
Claudio
PS: A friend of mine use for the RG65 the Helicopter rotor symmetric blades are very good !
This arrangement is stiffer than the helicopter blades. Thicker sections on an RG65 (with relatively sharp entries) may be an advantage as they inhibit stalling of the foil during tacks. Things get strange at the low Reynolds numbers that the lightweight RG65 operate at.
If you’re worried about thickness I’d suggest shaving the square CF tube down after attaching to the backbone. The important things are the shear planes between the CF assembly and the foam/wood “cheeks.” (For readers not familiar with the concept: when two parallel, touching plates are subject to bending, one wants to slide relative to the other. If they are glued together, the glue resists the sliding and thus the bending.)
Cheers,
Earl
Agree with shear strength provided by the opposite bonded surfaces, so far I was using the inner strength provided by the bending strength and shape’s inertia, apparently air does not provide enough shear strength !!! LOL !.
Cheers
Claudio
Almost all what I need is delivered, missing only the Polyethylene film that I will get today.
The Fin was sanded to the final shape after some mastic use to correct the surface.
Before sanding and after, the weight is the same.
Typical tool to clamp the Fin and Carbon Tissues
Ready !
All materials needed are available.
160g/m² Carbon tissue cut at 0° and 45° + 48g/m² glass as top surface finish.
Epoxy lamination today