Monty
Well-Known Member
In reading one of Orion's posts in another thread he mentioned using a thick (.035) skin with countersunk rivets (not dimpled) to achieve a smooth wing profile.
I thought this deserved more discussion, since aluminum and laminar profiles are usually considered to be mutually exclusive.
Lets say, you used thick skins and thinner internal structure, so that the internal structure would tend to conform to the skin rather than the other way around. Further, lets say you made a really good jig with form blocks to profile the wing skin properly. Something like CNC cut MDF.
Could you get a laminar section to perform? Is it worth the trouble? Is it worth the weight. On my little bird, the wing would weigh twice as much as it does now, to accomplish this. The drag reduction seems to be significant if one compares "standard roughness" to smooth finish laminar section.
However, when one compares smooth finish to smooth finish the results are different entirely. So the question is: Is "standard roughness" realistic for typical sheet metal construction?
I seem to recall reading that things aren't typically that bad. The rivets are in a row chord-wise, so the disturbance is not as bad as you would think.
The laminar sections have more pitching moment. Trim drag goes up. The laminar sections all perform better at high CL numbers, but my design has relatively low CL numbers in flight, because of the stall speed requirement.....Seems to me there is really not much to gain in this department. Is going off down this path chasing ghosts?
Cessna citation: various models use the 230XX and modified versions
Questair Venture: 230XX
So it seems speed and these old sections are compatible.
It would seem that the major gains for the more exotic sections happen at high CL ie. Sailplanes, or high altitude, not so much for sport planes.
Is this Heresy?
I thought this deserved more discussion, since aluminum and laminar profiles are usually considered to be mutually exclusive.
Lets say, you used thick skins and thinner internal structure, so that the internal structure would tend to conform to the skin rather than the other way around. Further, lets say you made a really good jig with form blocks to profile the wing skin properly. Something like CNC cut MDF.
Could you get a laminar section to perform? Is it worth the trouble? Is it worth the weight. On my little bird, the wing would weigh twice as much as it does now, to accomplish this. The drag reduction seems to be significant if one compares "standard roughness" to smooth finish laminar section.
However, when one compares smooth finish to smooth finish the results are different entirely. So the question is: Is "standard roughness" realistic for typical sheet metal construction?
I seem to recall reading that things aren't typically that bad. The rivets are in a row chord-wise, so the disturbance is not as bad as you would think.
The laminar sections have more pitching moment. Trim drag goes up. The laminar sections all perform better at high CL numbers, but my design has relatively low CL numbers in flight, because of the stall speed requirement.....Seems to me there is really not much to gain in this department. Is going off down this path chasing ghosts?
Cessna citation: various models use the 230XX and modified versions
Questair Venture: 230XX
So it seems speed and these old sections are compatible.
It would seem that the major gains for the more exotic sections happen at high CL ie. Sailplanes, or high altitude, not so much for sport planes.
Is this Heresy?
