Deltas are unique animals. Due to the long centerline chord and very low operational lift coefficient, I think you'll find that the Rn and shape affected effects might reduce the extent of the laminar flow however, the benefit of a good shape is still there. The only difference is that deltas, and their lifting capabilities, aren't as affected by airfoil shape as more conventional wings are. One good example of this is the story I relate in my airfoil article, which regards the wing development for the A-4 Skyhawk.Or is it that deltas are simply immune to the benefits of laminar airfoils?
Sufficient for what? The big points being made here are:if im understanding this correctly, the argument against the proposed airfoil is the fact that to get the desired low drag of the airfoil is to have the trialing edge to tilt up 5 degrees? but what about the Cl vaules, sufficent? stall carcteristics? just to denie the airfoil because of the trailing edge seems to be shallow at least? sorry for spelling, im on my phone.
The comment about extra complexity for negative flap deflection is strange, there's no difference between flaps than can go from 0 to 45 degrees deflection and those that go from -5 to 40 degrees deflection.The reason I personally don't like reflex flaps is that they require mixers and other additional weight/complexity in the control system that you could avoid just by choosing an airfoil better suited to the purpose.
I know a couple of serious competition pilots (European champion, 1st and 2nd at world championships) and serious competition pilots don't reprofile their wings. Ever.Composites creep over time, even the oven-cured pre-molded ones. Competition sailplane pilots have their wings reprofiled at the start of every season. It's still easier than building a whole new wing, and you'll get most of the improvement you might get from a new airfoil without having to build a new wing.
Some ballpark blending isn't going to help you. Even on optimized gliders it's extremely hard to achieve laminar flow over anything except the straight wing.well, it's not as optimal as a glider but I can't see where you're getting the word 'completely' from. For one thing I have no 90 degree intersections like even the glider has, it's a pusher so there is no disruption from the prop wake, and the nose end of my plane is inspired by a glider nose, as close as can be gotten using angular aluminum (I'm going to skip the strake/round blending in order to eliminate that intersection). In fact the profile of the front is pretty close to that of a sailplane. So aside from the center four feet of the fuselage the entire thing could be a laminar wing, and like I said, no intersections!
Given the type of aircraft the OP is talking about, simply reflexing the flaps isn't going to do much (if any) good. You'd want to do the ailerons, too. That means mixers, with all the attendant complexity and weight I mentioned above.The comment about extra complexity for negative flap deflection is strange, there's no difference between flaps than can go from 0 to 45 degrees deflection and those that go from -5 to 40 degrees deflection.
Well, then the technology has changed for top-end gliders in the last few years. I have several friends (with admittedly 7-10 year old designs) who do reprofile their wings. One of them has his glider in the shop up at Crystal right now. Either way, it still doesn't change the original point: The Lancair 235 kit the OP is talking about is 25 years old, minimum, and it doesn't have the latest sailplane refinements. Many of the early molded composite kits (Lancair included) were notorious for arriving at the customer with some built-in warpage and distortion. A quarter-century of sitting probably hasn't improved that situation. The airfoil very likely isn't an NLF-0215(f) anymore, but rather an N-sorta-LF-xx(whatever) now. It's still easier to reprofile the wing than build a whole new one, and unless the OP is ready, willing, and able to build his new wing to competition sailplane tolerances, changing out the wing is likely to make things worse, not better.I know a couple of serious competition pilots (European champion, 1st and 2nd at world championships) and serious competition pilots don't reprofile their wings. Ever.
That's only done on some of the older gliders (especially LS-3 and ASW-20 are notirous IIRC) where the spar is directly attached to the outer sandwich panel. Hence most new gliders are built with a sandwich core, even over the spar caps and only need a new skin if the gelcoat turns bad. That usually happens after 10-30 years.
The most optimized glider profiles do perform considerably better which isn't strange if you know that there's 95 and 75% laminar flow at high speeds (below 150 kts and around 3 ft of chord)Do others here have any reason to disagree with Billski's calculations?
That's not enough. To achieve laminar flow you need turbulators, specialized ailerons, flaps and especially seals of those two and the airplane has to be kept extremely clean. You also need very high quality of the gelcoat surface.Let's just assume, for a moment or two, that a whole new wing needed to be designed/built for a Lancair 200 kit. A totally clean sheet design, head to toe, and the resulting construction of this wing would be dead nuts perfect(competition sailplane standards accuracy/quality). Given the goals are to be a bit different than the original plane, that is, the plane would be geared much more heavily toward competition (with a 100-120hp engine), would anyone hazard a guess for an appropriate airfoil to replace the 0215(f)?
Wittman Tailwind has the same equivalent drag area as Lancair Legasy FG. Retractable gear legasy has less drag only thanks to the retracred gear.If you can lower the "cost" (drag) for the same lift by 50% that's profit right?
It is. What I recall about the AR-5 and Nemesis is that 30 to 35% of the drag at top speed is wing drag and almost all of that is skin friction.
The drag of a laminar flow is spectacularly lower than turbulent flow, not just a few percent. It's less or more proportional with the boundary layer thickness and by extending the boundary layer a further 10% you're reducing the drag a lot more than that 10%.
Yes, on motorplanes laminar flow is difficult in reality because of propwake, surface finish, ice, metal. But that AR-5 and Nemesis are a lot draggier when you use a normal airfoil, not just a tiny bit. Want proof? Mention any plane without a modern laminar airfoil than can keep those two within sight.
Mention any commercial, comparable plane that can less or more keep up with the Cirrus 22, Lancair 300/400, Glasair III or Lancairs without the use of a laminar airfoil.
Why do you think this has roughly the same drag as these two? Magic bullets or actual science that works in reality and not just in discussions?
Aerodynamics is only considered "magic" by those who don't sincerely understand it. Those who do, have proven (Klaus Savier, John Sharpe, Boermans?) that with a good understanding one can achieve huge gains, Klaus got more than 50% drag decrease...
Sure, they claim that. According to pilot reports it's more in the 180 region in reality. That's about 80% more drag compared to the Lancair...Wittman Tailwind has the same equivalent drag area as Lancair Legasy FG. Retractable gear legasy has less drag only thanks to the retracred gear.
Wittman uses basically a conventional 4-digit NACA airfoil on a wooden wing and a simple tube and fabric fuselage. Makes 220-230mph on O-320. Outraces Longeze with the same engine.
There are many sources confirming that Tailwind can fly faster than 200mph with O-320 engine/ For instance, CAFE report and Airventure Cup races results. Equivalent drag area of well-built W10 is 2.03 sq. ft. as determined at CAFE tests. One can find that this figure is very close to that od fixed gear Lancair and Glasair. The overall sporead is under 10%. Other high-performance planes with similar wing area differ mostly by their retracted gear. This proves that not much is dependent on the airfoil and the skin gloss.
According to the CAFE report they got 217 mph squized out of it, the Lancair Legacy 293.. Not to mention the Legacy has close to two times the range, space and useful load. If you make a fair comparison to planes that are actually comparable it's still considerably draggier, by dozens of percents as for example the Glasair IIFG (231 mph and still 40% more useful load)There are many sources confirming that Tailwind can fly faster than 200mph with O-320 engine/ For instance, CAFE report and Airventure Cup races results. Equivalent drag area of well-built W10 is 2.03 sq. ft. as determined at CAFE tests. One can find that this figure is very close to that od fixed gear Lancair and Glasair.
It proves? Except that your assumption and statements above are completely wrong, it doesn't prove anything.The overall sporead is under 10%. Other high-performance planes with similar wing area differ mostly by their retracted gear. This proves that not much is dependent on the airfoil and the skin gloss.
You're still comparing a high versus a low wing, a composite versus traditional, taildragger (fg) against trigear (fg).If we want to compare apples to apples, we have to look first at Lancair 320 against W10 as they have the same engine, O320.
You were the one to mention the Legacy that had similar drag to the Wittman. Though correct the Legacy is indeed twice a Wittman in size and weight and power..Lancair Legacy
Sure, but every engineer knows that's far from relevant since the prop flow completely alters the flow around your fuselage, a good 60% of the total drag..Note that the drag area of W10 was accurately determined in CAFE tests by glide at controlled zero thrust. The same value was obtained for Wittman's own W8 in 1950s by propless glide tests arranged by August Raspett. Certainly not bad.
You didn't do engineering did you? More range (payload), more room and more useful load do require more structures, volume and THUS also more wing and tail area. That all adds up in condiserably more drag.The higher useful load and corresponding longer range of Lancair and Glasair is accompanied by considerably heavier airframes and means nothing for drag area comparison.
Did anyone say that tailwind wasn't boosted too? No.It is easy to undrrstand that Vary-Eze cannot reach 258mph with stock O-200 engine and any ariframe mods. This requires even smaller drag area than that of Ar-5, which has about one square foot. The O-200 engine of Klaus Savier is highly modified and there is no disclosed information on its altitude performance, and it is known that O-200 performance can be highly boosted. Look at the Formual One racers.
Again, you're clearly no engineer.MCR-01ULC has exactly the same wing are as W10 per plans. Its wing is well-optimized for both low cruise drag, low stall and acceptable weight. It is an european microlight plane which must have the stall speed under 40mph and takeoff weight limit is 991lb. The use of laminar arfoil would result in larger area due to lower CL and heavier airframe weight.
Which is a significant number from my point of view.If we'll instead double the profile drag, for instance, use a four digit NACA airfoil with fabric cover in Ar-5, the speed will drop by 9%.
But you used the wrong assumptions. A 15-meter glider typically has more than 50% of its non-induced drag from its fuselage, tail and interference drag, only the open class ships get to the 2/3rd and they do just. According to Boermans, designer of 80% of the now top sailplanes and according to Schempp-Hirth..Indeed, the proportion of profile drag in total drag area of a high performance sailplane is exactly opposite ant it typically contributes to more than 2/3 of the total lift-independent drag. this means that profile drag Cd here is at least 0.005. May be it is 0.004, but certailnly not 0.0025. These numbers are consistent with other real world test data at similar conditions and represent a honest achievement for a designer. Sorry, I wore no pink glasses.