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This thread is privately moderated by phil alvirez, who may elect to delete unwanted replies.
May 27, 2016, 08:41 AM
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lifting stab on r/c

am in the process of evaluating lifting stab on 2 meters sailplanes. my goal is to use them for thermaling. not competition; to be able to stay up longer with less effort.
but above all, if it is easier to detect thermals and if a plane can be trimmed so if it senses a thermal stays there, like the free flight planes do.
also, i am trying to stablish a comparison: how a lifting stab influences the flight? stability? under power? does it help make the airplane more thermal efficient? easier to detect thermals? does it increase drag too much?
all of this will be tested in a future.
if you are interested, keep looking into this post. will be updating it at the end.
r/c models of all kinds use flat or symmetrical stabs that do not generate lift at zero degrees of angle of attack.
in ancient times, guys that flew free flight duration began using flat stabs. until some1 'discovered' lifting stabs, and from then on, all the planes use it. even to this day the indoor free flight power (rubber) use them. all of them.
there was a guy who collected plans from all over the world, together with comments of their designers, and published them. even wrote a detailed study and showed it on his books of 1951/52 (pages 5 to 20), and 1953 (pages 3 to 18). his name is Frank Zaic, and all of this was widely discussed and used by everybody-including all the experts and those who won all the competition for many years.
these books still can be reached by google.
recently i got intrigued and began trying it. i used 1 of my gliders that had a flat stab and replaced it with a lifting stab of same size.
the test was brief due to the weather but as it improves i will collect data and show in here. but so far, i was able to move the cg beyond the limits that can be used with flat stab.
i hope some of you that are interested will keep posted and see how this experiment develops. am not sure how it will; i think it could let me detect thermals easier, but it is just a hunch. time will tell.
so, keep in touch.

>>>may 29, 2016: but 1st i will bring the post where i provide details on the maverick, that is the precursor of the planes that am flying now and with which am performing the evaluation of lifting stab. am using the same wing for these planes. here it is:
Posted by phil alvirez | Mar 09, 2013 @ 11:08 AM | 4,918 Views
Maverick started with the availability at the time, of the fuselage/canopy/prop/spinner of the Dynamic-s, a hotliner with v-tail
i used the prop/spinner that come with it, and found a motor that looks close enough to the stock.
but the main difference is that i designed it for thermaling, with a larger wing, and t-tail instead of the v-tail.
as the v-tail comes with a wide base that works well for a t-tail, and the wiring for the servos, it made my life easier. mounting the wing on top, too.
the tail instal is similar to the Thermalis, except that there are no belcranks, and the elevator servo sits up near the stabilizer, with a direct-and short-pushrod that provides precise commands. the rudder servo sits at the bottom. stab is 10% of wing area, flat, 1/8" balsa, 14" long. the wing is 8" constant chord, tapered at the tips, (that are 9" long) to 5"; undercambered airfoil, polyhedral, and has an over/under spar of 1/8x1/4 spruce with 1/64 ply webs, and 3 turbulators; the leading edge is 1/8 cf tubing with 1/8x1/4 balsa, and the trailing edge is 3/16x3/4 balsa. ribs are 1/16 hard balsa, has 1 center section flat, and is held in place with 2 nylon screws that fit into the stock mounts in the fuselage. the covering on top is transparent orange solarfilm and transparent red ultracote lite tips, the bottom is clear microlite.
i found the motor 35-36/910 kv, that weighs 117 grams, the closest to the stock, and it works fine. it delivers an enormous amount of power. with 613 sq in and 830 grams auw, the wing loading is similar to the Thermalis, and the glide is good for thermaling. the climb is spectacular at 1/2 throttle and specs in no time, so the 3x1400 pack lasts a long time. i fly it for about 1 hour (several flights) with that pack, even without thermals. later learned that at climb high power the wing flutters, so added diagonal ribs to the 3 main panels and replaced the covering with ultracote regular and the flutter is gone.
>>>also:found a fiberglass fuselage that is very light and strong-and even more streamlined. saved even more weight. with it the plane weighs 650 gr auw instead of 830 of the maverick. this places it in a different class. maverick does fine in windy weather, but this 1 is for calm to moderate wind.<<<
i must say that after searching for input on the issue, the thing that impresses me most is the huge amount of comments with different ideas of why it does not work but have not tested it themselves.
>>>on the other hand, found this link to F1A free flight sailplanes, where all use lifting stab:
i must admit that these have a rule that counts wing and stab area as a total, but still, their performance is great, and i would be happy with that, as my purpose is not to win a contest. and still, all those that flew under rules that didnt have a requirement for area still used lifting stab, and were high performance machines and are very good at thermaling. like these:
>>>june 13, 2016: today i was able to do some tests of the lightweight version that uses the same wing of the maverick. almost no wind, ideal for it. stab 10% of the wing area (same as the flat stab version), but with lifting airfoil with 10% thickness. it flew fine, climbing to about 80 meters, where i went turning around and getting the feeling. then when it was at about 60 meters i decided to land it. but to my surprise, it did not come down. it was into a thermal, and remained there for several minutes. it didnt have the vario, i just kept turning and noticing how it did not descend. it was an exhilarating experience. still too soon to say that it is more sensitive to thermals than with a flat stabilizer, but sure it did very well at relatively low level. maverick, with same wing (but heavier) does not catch thermals so well, so it could be due to its lighter weight. need to perform many more flights to be sure.
Last edited by phil alvirez; Jun 16, 2016 at 11:31 AM.
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