Light Weight Diving Vehicle

[Guest625101138]

Originally Posted by dtoshni

Dear Rick,

I am using this formula to calculate the Reynolds number. Is this correct?

Rey. Num. = density*velocity*chord length/abs. viscosity

Daniel

Yes.

I use 0.0013Pa-s for the viscosity. I think this is around 10C.

You might want to make the foils a little longer as the Re# is quite low if your speed is only 0.6m/s. The L/D will improve as the Re# goes up.

It would help if you provide some picture of what you have and drawings of the intended fins.

Rick W.

[dtoshni]

Ok..thanks Rick.

And one more thing Rick. I was just playing with the values in JavaFoil. I found one interesting thing with the airfoil cross section NACA 2410. When the angle of attack reaches 90 degrees, JavaFoil shows a Cl = .023 and Cd = 25 !!

Is this correct? Can the Cd reach such high values? I thought the maximum was that of a flat plate, with Cd = 2.

Daniel

[dtoshni]

Also Rick I wanted to ask you, What happenes to a NACA 2410 foil if the angle of attack is 180 degrees? I know the lift coefficient will be negative. But does that mean the lift will be upwards or downwards on the foil?

[Guest625101138]

I would be skeptical of results from extreme cases in JavaFoil. I expect the theory breaks down. I normally work inside the bounds of stall and not interested in data outside.

If you need to go backwards then the best solution may be a cambered plate foil. These have a narrow range of operation but will work as effectively in either direction. Maybe nothing more than a flat plate set at a slight angle. You just need to keep them thin relative to cord. Very simple solution.

[dtoshni]

Hmm.. Thanks Rick I'll think about it.