NLF 0414(f) on a lancair

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by gschuld, Nov 7, 2009.

Help Support HomeBuiltAirplanes Forum by donating:

  1. Nov 7, 2009 #1

    gschuld

    gschuld

    gschuld

    Well-Known Member

    Joined:
    May 9, 2007
    Messages:
    422
    Likes Received:
    9
    Location:
    Toms River, New Jersey
    So lets say that someone aquired an early untouched Lancair 200/235 kit. And he wanted to gear the plane from the get go for competition but preferably without completely destroying it's real world capabilities. By competition I mean some sport air racing events, Airventure, possibly some attempts at some mid distance records in the C1-A weight class.
    [​IMG]

    Klaus Savier currently has arguably the fastest 0-200 powered two place around. He has flown his highly modified Vari EZE to an over 250mph average at the AirVenture race. His Vari EZE turns a (LSE composite) 64x68 two blade prop. That's a lot of prop for an 0-200. According to what I have read, his motor has not been substancially altered internally(he does not turn high rpms) but he certainly has done a lot ignition wise to help with efficiency.


    Anyway, lets assume that an 0-200 engine with roughly identical specs and power output was to be put into a to be built Lancair 200 kit. Reportedly, the Lancair 200 was capable of 193mph in cruise and believe around 215mph flat out with a dead stock 0-200 and stock 0-200 powered unmodified Vari EZE canards have been reported to be capable of 180mph cruise, 205 flat out.
    Note: These performance specs appear to vary quite a bit depending on who's plane is being discussed.

    The stock wings on the Lancair are of the NLF -0215(f) variety. This airfoil has found its way into a number of successful kit aircraft, including nearly all the other Lancairs. If searching for uncompromizing speed though, the NFL -0414(f) with it's 70% laminar flow would seem to present a good opportunity for improvement. Even though the airfoil has been around for quite a while, even the Nemesis NXT planes use only a (reportedly)sightly modified (decambered) 0414(f). Though Bruce Carmichael has written more than once that the 0414(f) could be viable airfoil for an everyday use type of fast glass plane, in practice it is almost never seen on a plane other that a pure racer. The Cirrus VK-30 used the airfoil, but it also used a complicated fowler flap/cruise flap combination along with it. According to the published articles on the Cirrus VK-30, with the cruise flaps reflexed about 5 degrees or so in cruise, the overall drag reduction was significant. Coincidently, the modification of the 0414(f) for the NXT planes included a slight decambering of the airfoil. Which sounds a whole lot like effectively building a slight "reflexed cruise flap" into it from the beginning.

    So I guess what I am getting at is what the likely performance difference would be if one switched from a 0215(f) to a 0414(f) on a 0-200 powered Lancair racer. I'm not talking about complexity of construction or issues related to such a drastically different airfoil building wise. Obviously not a stitch of the original wings could be used. Not talking about the engineering issues either, this is strictly for THOERY between the airfoil shapes.

    Could a 0414(f) winged Lancair be tamed to a reasonable degree in the stall, landing speed area? Bruce Carmichael's articles suggest that a 0414(f) equipped with a cruise flap can substancially improve the lift characteristics at low speed while their drooped, and really reduce drag at cruising speed with them reflexed up a bit as the setup on the VK-30 incorporated.

    Any thoughts?
     
  2. Nov 7, 2009 #2

    autoreply

    autoreply

    autoreply

    Moderator

    Joined:
    Jul 8, 2009
    Messages:
    10,732
    Likes Received:
    2,542
    Location:
    Rotterdam, Netherlands
    I don't now both airfoils, so I won't comment on that. Regarding the reflexed airfoil however, a bit of negative flap definitely helps (quite a bit) on reducing drag, mainly by improving the amount of laminar flow. At very high speed a 5 degree upward deflection of a laminar airfoil can result in 10 to 15% drag reduction in otherwise optimized laminar airfoils, not being the aforementioned ones.

    The gain is thus real, very real. From anecdotal stories it might be as high as 25%, but that of course depends on the airfoil. Testing this is extremely simple by the way, simply put a microphone in your boundary layer (outside the prop wake) and listen till you got to the point where the flow gets turbulent. Then change flaps and listen again.

    I wouldn't be surprised by the way if a modern airfoil can improve the optimal 414 performance by another 10 or 20%, there've been huge achievements in low speed aerodynamics.
     
  3. Nov 8, 2009 #3

    gschuld

    gschuld

    gschuld

    Well-Known Member

    Joined:
    May 9, 2007
    Messages:
    422
    Likes Received:
    9
    Location:
    Toms River, New Jersey
    [​IMG]
    Figure 4. NLF-0414F Wing Section

    [​IMG]



    This is the 0414(f). I am far from an expert here, but I have read that the benefits of cruise flaps vary greatly depending on the specific NLF airfoil. From not much at all to something to really write home about.
     
  4. Nov 8, 2009 #4

    Starman

    Starman

    Starman

    Well-Known Member

    Joined:
    May 17, 2009
    Messages:
    2,011
    Likes Received:
    61
    Location:
    High in the Andes Mountains
    I can't really comment on much of the rest, but the statement looks incorrect due to camber applying to all or at least most of the front end of the airfoil while reflex applies onlytot the back of the airfoil. You can reduce the camber of an airfoil and still not have a reflexed trailing edge.
     
  5. Nov 8, 2009 #5

    orion

    orion

    orion

    Well-Known Member

    Joined:
    Mar 3, 2003
    Messages:
    5,800
    Likes Received:
    135
    Location:
    Western Washington
    OK, a little dose of reality - first off, as has been said many times, here and elsewhere, if you have to reflex your flaps to get a decent high speed cruise then you've chosen the wrong section to start with. Also, choosing a section just because someone else has selected it for their plane is one of the worst reasons to use a particular shape there is and more often than not, the original choice was based on criteria just as poorly thought out.

    No, you don't have to do a custom shape - there are myriads of beautifully suitable shapes out there but proper selection requires at least a modicum of knowledgeable analysis that attempts to optimize the wing shape for the mission you're trying to fly.

    Furthermore, as was pointed out above, the reflexed flap approach works better for some than others and most often, it really depends on the performance envelope. In other words, different airplanes will most likely respond differently to said reflex, some better than others. But in most cases of actual application, the benefit tends to be barely measurable.

    Then the other aspect of this that is rarely mentioned is simply this: The drag improvement that you might see for the airplane is only partly a function of section characteristics. A large part of the improvement is simply from the decreased wing pitching moment and thus a decreased magnitude of trim drag. In other words, choose the right section in the first place, preferably one with a small section pitching moment, and you'll be much better off than trying to make something work that was never intended for this end of the size and performance spectrum.

    Another item to point out is simply that comparing performance of two significantly different configurations (Lancair and an Ez) is relatively meaningless since the design requirements for either and their basic characteristics will drive the performance figures in somewhat different directions. Just the difference in seating arrangements will generate different drag characteristics in of itself so comparing top ends based on available power really has no congruence.

    And finally, wen you look at the airplane as a whole, the drag contribution of the wing is only a small portion of the whole. You'll get more benefit by paying proper attention to your cooling drag than from building a new wing (unless the original is really screwed up of course).

    If you want all out performance then do this right - anything else is wasted effort and will most likely not deliver what you're after.
     
  6. Nov 8, 2009 #6

    PTAirco

    PTAirco

    PTAirco

    Well-Known Member

    Joined:
    Sep 21, 2003
    Messages:
    3,481
    Likes Received:
    1,005
    Location:
    Corona CA
    Beechcraft designed a wing with a laminar flow section for the Bonanza when it was in the prototype stage and tested it extensively, in every flight regime imaginable, against the standard section "old" NACA wing section - in the end the standard wing one out. The speed difference was negligible and the handling was vastly better with the old section. Like Orion says, wing sections will play only a fairly minor role in the overall drag of the aircraft, but can make a vast difference to the way it handles.
     
  7. Nov 8, 2009 #7

    Topaz

    Topaz

    Topaz

    Super Moderator Staff Member

    Joined:
    Jul 30, 2005
    Messages:
    13,862
    Likes Received:
    5,474
    Location:
    Orange County, California
    Yep. Reflexed flaps were a fad of the 1980's and early '90's, when there were a group of airfoils being released that weren't really suited to light general-aviation use, but were grabbed as the 'latest thing from NASA' by the homebuilders of the time. NLF-0215f, LS(1)-0417, NLF-0414f, etc. They turned into the 'fashionable' airfoils to use, since they showed low drag numbers in the wind tunnel and a couple of airplanes that flew fast and well (despite the choice of airfoil) used them. The NLF-0215f was even featured, I believe, in a Sport Aviation article, touting it as the 'next great airfoil for homebuilt use.'

    But as has been pointed out, all of them have simply huge pitching moment values at cruise, resulting in a lot of trim drag. It was a case of marketing/grant-writing gone awry. The NLF-0215f, for example, was really an airfoil more suited to sailplanes, but at the time all the NASA research grant money for airfoils was in general aviation. The researchers wrote up the airfoil for "general aviation" use to get the grant. It's got way too much camber and is too aft-loaded for sportplane use, but people latched on to the research paper title and saw the low minimum drag values it got. Then to muddy the waters further, the results published in the paper (I have it) are for Reynold's number values that aren't of use to anything but a business turboprop - which was what NASA thought a 'general aviation' airplane was. The authors did their research on NASA's dime, and tailored the report to their audience to get the funding. That's pretty common, but nobody told the homebuilders.

    When someone figured out how much trim drag was being created to keep the nose up with these airfoils on an already-built airplane, they figured they'd reflex the flaps and ailerons to de-camber the airfoil and reduce the Cm. The other thing was to fill in the bottom cusp on these airfoils (which was another airfoil fad at the time) to decamber the last 25% of the chord. The heavy aft camber tended to load up the aileron and flap bearings, and cause 'heavy', sticky controls. Both of those methods worked, but recognize them for the 'fix' that they are, not a design feature.

    Far better to choose the right airfoil from the beginning.

    The use of reflex flaps on sailplanes is a necessary evil, since current airfoil technology doesn't allow a fixed-geometry airfoil to have a drag 'bucket' wide enough to encompass the entire flight envelope needed for sailplanes. If an airfoil were designed that allowed for that, you'd see reflex flaps disappear from sailplanes in short order. Sportplanes don't have that need, since they're primarily only concerned with minimizing section drag at cruise, and don't need to also do so at climb speeds.

    One thing I'm finding in my own recent work is that I'm setting the wing loading and span to the performance requirements, and then that tells me a lot about the airfoil I'll want to use to match those parameters. In other words, I don't pick the airfoil first and design the wing to suit it, I'm doing it the other way 'round: Choosing an airfoil to match my wing characteristics and needs.
     
    Last edited: Nov 8, 2009
  8. Nov 8, 2009 #8

    autoreply

    autoreply

    autoreply

    Moderator

    Joined:
    Jul 8, 2009
    Messages:
    10,732
    Likes Received:
    2,542
    Location:
    Rotterdam, Netherlands


    I completely disagree with you guys on this matter.

    First of all, it's a matter of definition, is negative chamber the same as a reflexed airfoil? Yes, it's just a different phrase for the same.

    Having a less unfavorable pressure gradient definitely can help you in having more laminar flow and thus much lower drag and that might require some "negative" flap deflection if your airfoil is designed for this. In fact the last profiles of Boermans have Cd values (at very low Cl's and in our Reynolds range) that have never been achieved before by any airfoil, ever. He used negative flap deflection to get there...

    I agree with most of the other comments however, if you're trying to beat Mike Arnold or Rare Bear, you might gain a bit by moving to the most optimal NLF airfoils, but as long as you're not striving for the nec plus ultra, don't bother too much since it's a small contribution with a non-optimal design.
     
  9. Nov 8, 2009 #9

    Denis

    Denis

    Denis

    Well-Known Member

    Joined:
    Feb 24, 2009
    Messages:
    304
    Likes Received:
    4
    Location:
    Lviv, Ukraine
    I think much drag reduction can be achieved here without changing the airfoil. The wing profile drag of this plane most likely contributes to no more than 30% of the total drag area. If we'll take for instance, aWittman W-9 Tailwind with remover landing gear, we'll get almost the same drag, maybe slightly more. And both these palnes are generally more efficient than a canard pusher with similar areas.
    I don't beleive Klaus Savier don't overrev O-200. Most likely he do it at max speed. It should be evident from the external view of his prop. A 64" prop can efficiently operate at 3400RPM. The Savier's modified O-200 has custom higher compression pistons apart from adaptive ignition and fuel injection. All these measures allow one to either get considerably more HP at tthe sea level, or retain the same cruise power at higher altitude. I suggest the latter is at least 50% higher than that of a stock O-200. A Lancair with similarly prepared powerplant most likely will overtake that Varyeze effortlessly, just like a Lancair 320.
     
  10. Nov 8, 2009 #10

    Lucrum

    Lucrum

    Lucrum

    Well-Known Member

    Joined:
    Jun 10, 2008
    Messages:
    956
    Likes Received:
    189
    Location:
    Canton, GA
    Anyone have graphs (Lift, Drag and pitching moment) of the HSNLF213 airfoil they could share. I'd like to compare them with the graphs from "Airfoil Optimizer".
     
  11. Nov 9, 2009 #11

    Richard Schubert

    Richard Schubert

    Richard Schubert

    Well-Known Member

    Joined:
    Feb 5, 2009
    Messages:
    160
    Likes Received:
    47
    Location:
    Pittsburgh, PA
    This report
    Title page for ETD etd-05232002-014415
    explores how to achieve a wide drag bucket with this airfoil using an adaptive flap.

    Search for these report numbers on the NASA server to find more info on HSNLF213
    19880014355_1988014355, 19910020784_1991020784, 19900003224_1990003224
     
  12. Nov 9, 2009 #12

    orion

    orion

    orion

    Well-Known Member

    Joined:
    Mar 3, 2003
    Messages:
    5,800
    Likes Received:
    135
    Location:
    Western Washington
    Although the paper is well written and thought out, keep in mind that this is a theoretical study based on numerical analysis and while the student did support his analysis with model based wind tunnel verification of the code (for which I give him credit), there is a vast difference between that and the real world.

    Also notice that the drag of the section with the reflexed flap did not actually go down - all it did was extend the lower drag numbers over a wider range of lift coefficients. I'm not exactly sure how useful that would be in GA since most of the airplanes fly with very low cruise lift coefficients so would not be able to take full advantage of that range.

    But it is a well written thesis and worth reading.
     
  13. Nov 9, 2009 #13

    wsimpso1

    wsimpso1

    wsimpso1

    Super Moderator Staff Member

    Joined:
    Oct 19, 2003
    Messages:
    6,004
    Likes Received:
    3,260
    Location:
    Saline Michigan
    I find this whole discussion amusing. Thanks Orion and Topaz for detailing why the NLF 0414 and others are not good ideas...

    The foil the Lancair 320 starts with seems to be a poor choice also. Much ballyhooed for its low drag, but with big pitching moments so it ends up giving away the drag advantage through big trim drag, and the cusps give it ailerons that need more structure to make strength and heavy aileron feel too boot. Changing to another foil not well suited to the airplane would not make a huge difference...

    Next are the assertions of big drag improvements due to the better foils. Please. Route air over the wings, the wings divert the air downward and slow the air some in the process. Most foils behave pretty much like all other foils in this way. What makes anyone think that some magic profile is going to change this very much? Sure, laminar flow will help, but we already have a bunch of laminar flow wings - the low hanging fruit is gone, and the conservative laminar foils are now the starting point. Extending laminar flow a little will further reduce drag a tiny amount, but this is not going to be earth shaking in a power plane with an aspect ratio of 8. Maybe it will make for a competitive advantage in a sailplane... We still have to cool the engine, get the flow around the people and stuff, we still have the interferences and excrescences and control surface gaps, and so on.

    So, please put aside your magic bullets. There is no magic... If you want less drag to either go faster or go the same speed on less fuel, you are going to have to do the hard work elsewhere in airframe design...

    Billski
     
  14. Nov 9, 2009 #14

    bmcj

    bmcj

    bmcj

    Well-Known Member HBA Supporter

    Joined:
    Apr 10, 2007
    Messages:
    12,973
    Likes Received:
    4,917
    Location:
    Fresno, California
    Very good Billsky... you made me break out my dictionary! ;)
     
  15. Nov 9, 2009 #15

    shadow

    shadow

    shadow

    Member

    Joined:
    Sep 23, 2008
    Messages:
    17
    Likes Received:
    2
  16. Nov 9, 2009 #16

    Topaz

    Topaz

    Topaz

    Super Moderator Staff Member

    Joined:
    Jul 30, 2005
    Messages:
    13,862
    Likes Received:
    5,474
    Location:
    Orange County, California
    That's what sailplanes are doing - moving the drag bucket around. Matching the minimum drag to a given flight condition. For a sportplane I agree - I can't see the point.
     
  17. Nov 9, 2009 #17

    autoreply

    autoreply

    autoreply

    Moderator

    Joined:
    Jul 8, 2009
    Messages:
    10,732
    Likes Received:
    2,542
    Location:
    Rotterdam, Netherlands
    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...
     
  18. Nov 9, 2009 #18

    Starman

    Starman

    Starman

    Well-Known Member

    Joined:
    May 17, 2009
    Messages:
    2,011
    Likes Received:
    61
    Location:
    High in the Andes Mountains
    Seeing those two wheel pants - You just almost sold me on looking up a laminar section rather than designing my own airfoil.
     
  19. Nov 9, 2009 #19

    autoreply

    autoreply

    autoreply

    Moderator

    Joined:
    Jul 8, 2009
    Messages:
    10,732
    Likes Received:
    2,542
    Location:
    Rotterdam, Netherlands
    Which is exactly what most people here objected to. Simply choosing a laminar profile isn't going to help you. You will experience a very small decrease in drag since the rest of your design is also completely non-optimal and you're most likely not going to achieve any serious laminar flow.

    If you look at that glider; simply having the wing run straight through the fuselage instead of this minimal fairing will increase your total drag by maybe 20%. Everything has to be optimized, not just the profile ;)
     
  20. Nov 9, 2009 #20

    Starman

    Starman

    Starman

    Well-Known Member

    Joined:
    May 17, 2009
    Messages:
    2,011
    Likes Received:
    61
    Location:
    High in the Andes Mountains
    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!

    So, what's so completely non optimal about it? If you wish go to my thread if it would cause thread drift here.

    Are you thinking it's because it has a wide speed range and I may not be able to reflex the trailing edges correctly due to the tail authority issues? ...Or is it that deltas are simply immune to the benefits of laminar airfoils?
     
    Last edited: Nov 9, 2009

Share This Page



arrow_white