phil alvirez's blog View Details
Archive for October, 2014
Posted by phil alvirez | Oct 28, 2014 @ 11:16 AM | 7,821 Views
as in the song 'the gambler', you need to know when to hold it, when to fold it, when to walk away, when to run,
so i am back into my other hobby: oil painting on canvas.
when it freezes and gets windy, i better watch for a rare chinook (you know, the warm weather from the north that sometimes blows in winter) to fly sometime during the day so it is warm enough for my bones, and not early in the morning.
in the meantime, i have something else to keep me busy.
i may bring some comments at the forums now and then, but otherwise you will not hear from me very much.
until next spring....
Posted by phil alvirez | Oct 27, 2014 @ 08:53 PM | 8,461 Views
i started a thread on the subject, trying to learn which 1 is better. at another forum i got data that allowed me to fully understand the differences. see: http://www.rcsoaringdigest.com/pdfs/...SD-1992-03.pdf (page 20). the point is that i wanted to know which is better and why, and now i got that. the most important thing is that, besides being more sensitive than stab/elevator, when giving 'down' commands it falls into negative decalage, that is, negative incidence respect to the wing, and that means unstable conditions, that may place the plane in critical situations.
i have been testing it, and have learned that the plane behaves erratic, i think due to this situation. there are also other factors that contribute to making this less convenient, and that is regarding to structure, as it is either fragile or heavier, tends to flex too much and vibrate, more difficult to build and repair, so i think i will stick with the conventional stab/elevator,
again, my view is that perhaps for full size airplanes that fly in transonic regime it is not only better but necessary due to the shock wave near speed of the sound, but not for models.
Posted by phil alvirez | Oct 26, 2014 @ 12:17 AM | 7,586 Views
conclusions on trimming and decalage
the data that i have found the most precise on the issue was mentioned by mikeruth in his post 3919 of the forum of the radian: https://www.rcgroups.com/forums/show....php?t=2089760
he said: Page 20 of this article is a very good explanation of Setting decalage and CG.
I have been using this for years. http://www.rcsoaringdigest.com/pdfs/...SD-1992-03.pdf

the article was re-issued on 1992, and the copyright by Frank Deis is from 1990. it is the oldest i have ever seen on the subject, so the credit goes to him, and the flight test goes as far as 1973.
(by the way, the drawing has a mistake: in the rectangle at the left it says that cg is too far "forward" but should be "aft").
it shows how to do it and also shows tests on fixed stab and moving stabilator.
i will make a condensation of all that matters in that article. the goal is to have a decalage of about 1 to 3 degrees.
(decalage is the angular difference between the wing airfoil and the stabilizer).
this is the way i interpret it:
1.-start with a 33% balance point (called center of gravity);
test fly the plane:
2.-for a fixed stab (with moving elevator), trim the elevator until the plane glides well:
if the elevator is not parallel to the fixed stab, move the cg accordingly:
a.-if the elevator is up, move the cg back a little and try again until the elevator is parallel to the stab.
b.-if the elevator is down, move...Continue Reading
Posted by phil alvirez | Oct 25, 2014 @ 09:08 AM | 7,168 Views
Akin 45: a stretched super kinetic-see: https://www.hobbyking.com/hobbyking/s...dProduct=39853
the concept: i had the idea of using a hotliner, that is sort of a sailplane with clipped wings, to enhance its performance for soaring by enlarging its wing, as it has all that it takes to make a sailplane, including folding prop. got the super kinetic because has a good size and there is a spare wing available. the original wingspan is 32 inches (815 mm) and enlarged it to 45-1/2, and added some dihedral at the tips. 2 1.5mm cf rods at the sides near the nose to reinforce it, and also some carbon fiber veil to the nose and a piece of 2mm steel wire to the stab spar at the center. added area to the rudder. made an exhaust opening at the top of the canopy near the back to improve air flow to cool the motor and esc. i named it Akin 45 because it is a plane akin to the kinect, just longer wing. weight gain from extra wing is 34 grams, and wing area jumps from 130 to 194 sq in. weight without pack is 333 gr and with the 3x850 (72 gr) is 405. originally balanced at 34 mm with the pack at the back of the canopy compartment. no ailerons to start, although i left the servos at the tips for a future use if needed, but i don't expect so. (then i will remove them and cover the slots). tested it and is erratic, as if the cg is too far forward, so i moved the pack to the under compartment an now balances at 39 mm. now is more predictable, but still more tests are needed. it is...Continue Reading
Posted by phil alvirez | Oct 25, 2014 @ 09:01 AM | 6,932 Views
swift gull 35": a compact sailplane. the idea is to use parts already available and stretch the wing to make a sailplane-for soaring.
starting with parts for a mini-swift 24" http://hobbyking.com/hobbyking/store...dProduct=11306
plane: http://hobbyking.com/hobbyking/store...ider_PNF_.html
motor: http://hobbyking.com/hobbyking/store...or_1800kv.html
servos: https://www.hobbyking.com/hobbyking/s...cro_Servo.html
parts: https://www.hobbyking.com/hobbyking/s...0mm_Parts.html
esc: https://www.hobbyking.com/hobbyking/s...ontroller.html
pack: https://www.hobbyking.com/hobbyking/s...poly_Pack.html
prop: http://www.freakware.de/p/luftschrau...105-a66152.htm
i ordered 2 wings and used 1 for the center panels with constant chord and the other 1 for the tips. the reason for a gull wing dihedral is that, as the swift has the stab and the wing on the same line, the stab is in the wing's wake, and this means turbulence and consequently erratic response and unstability, so raising the center panels not only keeps the stab clear, but lowers the center of gravity and makes the plane more stable. and it worked as expected.
well, i had the chance to fly it and needed a lot of up elevator trim, so i checked the decalage and it was 0-0. meaning that there is no angular difference between wing and stab. no good. and it balances at 33%. so i decreased the stab incidence and tested it. this time it came with a lot...Continue Reading
Posted by phil alvirez | Oct 24, 2014 @ 11:19 AM | 5,647 Views
an old sage once told me:
the key to happiness and success is learning to like what is good for you and what you have to do.
this way you also will be enjoying all of that and it will be easier and fun.

think about it.