Stoney the Clark Y and the Gottingen 398 were early efficient airfoils. When the two were compared it was found that when camber was removed both airfoils exhibited the same characteristics were observed for similar maximum thicckness. IIRCthe four digit NACA series sprang from these two airfoils
Perhaps. I'd have to dig through my copy of Abbot and Doenhoff to check this, but good enough for me. Like I said, I don't know much about the Clark Y...
The Trim Drag increase occurs becaue the chord line angle between the leading edge of the horizontal stabilizer to the trailing edge of the elevator changes with the deflection of the elevator to assist in change of pitching moment of the aircraft - simialr ro deplpoying flaps. With 'increase in relative AoA comes an associated increase in drag - both Induced and parasite, of the horizontal stabilizer/elevator system'
Yes. I sort of skimmed the wave tops on the trim drag issue to keep from getting bogged down in the theory.
Stoney I am confused on this one. by definition the 23000 series has a .02 radius (of chord), perfectly round at LE - why 'flat on bottom, particularly on a symmetrical aircfoils
I was probably a little too vague with this. I didn't have my copy of Ribblet's book at hand--its packed up--so I sort of swagged the description of this. In the interest of full disclosure, Lednicer disagrees with some of Ribblet's conclusions in a response he wrote criticizing Ribblet's work, but given the well documented stall behavior of the 23000 series airfoil, they did something to it. I don't understand it all myself, but what Ribblet postulated was the method with which they minimized the pitching moment of the airfoil modified the forward part of the bottom airfoil surface. Not necessarily changing the leading edge radius, but the leading edge profile beyond the radius portion. Something about how they flattened the area directly behind the radius on the bottom of the airfoil interferes with normal flow at very high AoA. I'll see if I can't find the book and post an excerpt straight from the book.
In the meantime, looking at the top image on this page of a 23015, you can see the "flattened" portion of the airfoil lower surface, directly behind the leading edge out to about 25% chord. http://www.laboratoridenvol.com/info/tech/perfils.en.html
This is the portion of the airfoil that Ribblet argues "decambers" the forward portion of the airfoil, thus causing the very sharp stall characteristics that are exacerbated in the thinner 23000 series airfoils. The 23015 doesn't have a very sharp stall, but if you look at the 23009 (which was the thickness used on the wing tips of most 23000 airfoil aircraft, it gets very severe. I can't imagine a worse place to have a portion of the wing stall with very little warning.
Stoney - one reason for both leading edge twist and a planform taper was to drive the lift distribution inboard to more closely approximate an elliptical lift distribution. With twist however, you also increased drag due to lift as one of the penalties. Both the 51 and the Spit had twist all the way out to the tip - the 190 only to about 80% span - why? who knows?
Again, I kind of skimmed the wave tops to avoid some of the complexities of planform taper, its advantages and disadvantages, etc. For the most part now, designers use twist to combat tip stall tendencies, as they've determined that elliptical lift distribution can be most easily achieved through planform taper only. Obviously some still disagree today. On my Formula 1 design, I was using zero twist, and a 45% taper ratio to get close. I planned to use a 15% thickness airfoil through the whole wing to avoid thickness taper. I even considered using a 17% thickness at the wingtip before I decided to just keep the same thickness for construction simplicity. Further, I was using a lower aspect ratio wing (for a lot of reasons), which made the chord at the wingtip long enough to have a decent Reynold's Number at landing speeds. Another part of this I didn't touch on was that several WWII fighter planforms, especially the Russians', introduced sweep into the wing as well, which reduces Clmax, but again, I didn't want to get into that.