? ? Sent:?Tuesday, April 05, 2016 at 8:07 PM From:?"Mark Langford via KRnet" <krnet at list.krnet.org> To:?krnet at list.krnet.org Cc:?"Mark Langford" <ml at n56ml.com> Subject:?Re: KR> Adverse Yaw Owen wrote:
> However, I also read an article about how important gap seals are for > increasing climb performance. See http://www.n56ml.com/troy/ for more on gap seals. Just looking at that big honkin' gap that you get when you build the wings per the plans, you can guess that there's an improvement in performance with gap seals. I built my wings with a Frise aileron, and with gap seals on that, I saw no benefit at all to the seals, mainly because the gap seals itself if you do it right. See http://www.n56ml.com/owings.html[http://www.n56ml.com/owings.html][http://www.n56ml.com/owings.html[http://www.n56ml.com/owings.html]] for more on that (near the bottom). Some folks would think that life is too short to spend this kind of effort on the ailerons, but I thought it was pretty simple and made a lot of sense. I will do my next one the same way, but will likely use a piano hinge at the top for simplicity and drag reductions (eliminating those external hinges from the airstream). Mark Langford ML at N56ML.com http://www.n56ml.com[http://www.n56ml.com][http://www.n56ml.com[http://www.n56ml.com]] ----------------------- I'll offer a completely different view of gap seals based on my experience testing them on my KR with the Diehl Wing/RAF-48. First off, if you built per plans, you should have a piano hinge that goes across the complete span of the aileron. While it's not even close to a "seal" it's also not an open flow of air up through the aileron hinge, so it isn't really disturbing the air flow on the top side of the wing. However, the gap seal will help streamline across teh gap from the bottom of the wing to the bottom of the aileron. Now for the real world testing... I used the mylar gap seals stuck to the trailing edge of the wing with 3M double stick tape. I tested both with and without the gap seals. With several climbs to altitude and several speed runs. I found no discernible difference in the performance numbers of my aircraft between flying with and without the gap seals. However, I did find that the mylar film really sucked up tight against the bottom of the aileron and caused the ailerons to bind to where it took a significant amount of muscle to move the ailerons at higher speeds. I was not at all comfortable with flying the plane with the ailerons in such a heavy condition, so once I had completed the testing, the gap seals were removed. My testing with the gap seals was an attempt to differentiate between real numbers vs anecdotal pilot induced fantasies; although since I'm pretty big on making speed improvements, I was really expecting big gains. That turned out to be not the case. I made it a point to fly the plane under conditions as identical as possible with the same load conditions between testing with and without gap seals. Just because I saw no performance advantage with the gap seals, and on my plane, a significant disadvantage, doesn't mean you won't find them to be advantageous on your plane. Also, I'll emphasize again, my testing was with RAF 48 Diehl Wings. Those that have tested with the "new" AS series airfoil have reported significant performance improvements. I thought my original test data was lost to time, but thanks to the archives, I readily located my original post with the testing data from Sept 2, 2000. See the post and test data below. Jeff Scott Los Alamos, NM ------------- KR Pilots and Testers. Over the course of the summer, with some supplies from Mark Langford and Oscar Zuniga, we tested my KR-2S with the ?per plans? installation of the RAF 48 Airfoil and Diehl Wing skins with the use of Aileron gap seals. The seals were a thin mylar film that was stuck to the bottom of the wing with 3M 444 industrial double sided tape, then the leading edge of the gap seals were taped over with electrical tape. The mylar film bridged the gap between the trailing edge of the wing and the leading edge of the aileron on the bottom of the wing. The first order of business was to fly some performance numbers with the airplane. I started every session with the plane grossing 1075# and the temperature at 65 deg F at a pressure altitude of 6500 feet ASL. I did my time to climb testing by establishing a climb at a given airspeed at 6200 feet, then maintaining that climb speed through 6500 feet and timing it up through 7500feet. I tested at the speeds around my best rate, so I could establish times for climbing at 85, 90, 95, and 100 mph IAS. The results of the time to climb testing are posted below. The first row was my time to climb speeds with the plane in the same configuration it has flown in since the first flight 3 years ago and was intended to be a baseline to use for comparison. It didn?t necessarily work out that way. The second set of numbers were flown after the aileron gap seals were installed. While installing the gap seals, I noted that the Starboard Aileron was mounted with a misalignment of roughly 1/8 ? 3/16 of an inch with the aileron mounted low in relationship to the wing. I remember this problem from construction, but the plane had flown so well that I had forgotten about it over time. My expectation was that this would probably cause a left roll in the plane. As expected, the plane wanted to roll left. If I released the stick, the roll was slow, but was definitely there. The surprising thing was how much pressure it took on the stick to maintain level flight. The ailerons were now very heavy which made the controls somewhat unharmonious with the light elevator. Flying the plane cross country was fatiguing while fighting the slight roll. The ailerons were so heavy, that it was difficult to feel the elevator in a turn while horsing on the ailerons and for the first time since my second flight in this plane, I overshot a landing while trying to feel out the plane on approach. I suspect that the lower performance numbers after installing the gap seals was due to the amount of right aileron I was holding. It was much like flying with both ailerons hanging down like flaps. The obvious solution was to order a new piano hinge and remount the aileron properly. After remounting the starboard aileron, I flew another set of test numbers (row #3) with the aileron gap seals still installed. Now the climb performance is picking up. The only problem is that the plane now has a very, very slight right rolling tendency and the ailerons still seem to be very heavy. Time for another cross country breakfast trip. Again, in smooth air the plane was somewhat fatiguing to fly as it took constant pressure on the stick even though the rolling tendency was very slight. Just a little bit of light chop on the way home rolled the plane around enough that it was uncomfortable to fly. However, the ailerons still seemed extremely heavy and the controls unharmonious. I also strongly suspected that the gain in climb performance was probably due to me remounting the aileron that was hanging down in the wind more than the addition of the aileron gap seals. The only way to find out for sure was to remove the seals. The final row of numbers is after I had removed the aileron gap seals. I can't account for the fact that the climb performance made another slight improvement. However, the major change was that now the ailerons are back to a light touch and the plane is very comfortable to fly cross country again. The elevator and ailerons also feel to be a little closer in harmony to each other which makes for an easier plane to fly. Time to climb pressure altitude of 6500? to 7500?. 65 deg F. 1075# gross weight. Configuration IAS 85 90 95 100 As built 2:34 2:20 2:50 2:45 Gap seals installed 2:34 2:33 2:43 3:00 Starboard aileron remounted 2:10 2:20 2:22 2:35 Gap seals removed 2:05 2:08 2:16 2:25
