Ribblet airfoil alternative to Naca 4415?

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Paoloz

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Hy, I've the plans of an airplane that use a Naca 4415 airfoil. I've read Ribblet book and I find he's a geneius!
I'd like to build this airplane with a Riblett airfoil what do you suggest?
Regards
Paolo
 

Paoloz

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is a kind of Storm 280.low wing. 475 kg Mtow, 40mph stall with flaps, 135 mph cruise. Wing span 7,8 mt, wing cord 1,34 mt. I'm looking for a very safe stall behavior and low speed approach. (what about using flaperons instead of flaps and aileron? even if I've seen very few low wing aircraft with flaperons)
Paolo
 

Max Torque

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Paolo,

I would be looking at Riblett's GA35A413.5 and GA35A415 airfoils for this application. Take a look at page 106/Figure 8 in Riblett's book GA Airfoils. Either one will work, and both are superior to the NACA4415 IMO, but I'd lean towards the GA35A415. Changing from the NACA4415 to either of these shouldn't require any re-engineering other than changing the airfoil shape.

Ailerons and flaps would be my choice, but best to stick to the plans for this unless you have a lot of building experience and design knowledge.

In the attachment, I've overlayed the NACA 4415 (yellow lines) with the Riblett GA35A415 (top picture - white lines) and GA35A413.5 (bottom picture - white lines) to give you an idea of the differences.

Tom
 

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wsimpso1

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If I were applying a new foil to an existing design, I would absolutely match the wing thickness at the spar. It looks from Max Torque's plot that just using the base foils will end up thin, and you would be designing new structure at higher weight. Better to maintain known structure and scale the foil to fit over the structure. Write back if you need help on the correct method for scaling foils.

Billski
 

Paoloz

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If I were applying a new foil to an existing design, I would absolutely match the wing thickness at the spar. It looks from Max Torque's plot that just using the base foils will end up thin, and you would be designing new structure at higher weight. Better to maintain known structure and scale the foil to fit over the structure. Write back if you need help on the correct method for scaling foils.

Billski[/QUOTE
I agree yes please help me to scale
 

pwood66889

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Generally, Paolo, the first 2 digits (37 above) is the point of most camber/thickest part of the wing. Riblett uses 37% MAC for more laminar flow but sharper stall. Do you have his second opus? On "spin resistant" airfoils?
Percy in SE Bama, USA
 

Autodidact

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Paolo, the GA30-415 is the Ribblet airfoil that is most like the 4415. They both have their max thickness at 30% of the chord datum, max camber is at the same place, and the rest of the vertical dimensions are practically the same. They both have virtually the same moment coefficient curves as well. The main difference is that the Ribblet airfoil has the "corrected" nose contour, i.e., the nose is drooped a little and so it may have a slightly greater stalling angle and you would need to investigate whether the tail has the capacity to raise the nose up that much.
 
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Paoloz

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Generally, Paolo, the first 2 digits (37 above) is the point of most camber/thickest part of the wing. Riblett uses 37% MAC for more laminar flow but sharper stall. Do you have his second opus? On "spin resistant" airfoils?Percy in SE Bama, USA
No i haven't, could you send to me?
 
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