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phil alvirez's blog
Posted by phil alvirez | May 07, 2013 @ 04:32 PM | 7,814 Views
akropolitan (from greek=inhabitant of the heights) is a hybrid that uses the fuse/tail/avionics of a fox 2.35 meters ws: http://www.bananahobby.com/4-ch-fms-fox-arf.html and a wing that i designed for thermaling, so it has the looks that i like, and flies more to my liking.
i enlarged the wing to 100" with undercambered, thin airfoil, 10" chord, 960 sqin; 2 pieces wing with gull dihedral to lower the center of gravity, and raised tips. 1/8x1/4 over/under spruce main spars with 1/64 webs, and 2 sets of 1/8 sq over/under spruce spars. 1/16 v trailing edge, 1/8 cf tubing leading edge. 1/4" dural join bar plugged in cf tubings. covering is hangar9 HANU950 transparent red, and solarfilm SLF125 tr yellow tips. auw is 1100 gr (about 39 oz) with a 3x1300 pack. i also enlarged the tail by adding 1" to the chord of the elevator and rudder. balance is at 33%, and the pack sits at the back of the canopy. after further tests i added 1" more to the rudder, as it was sluggish. i added quanum telemetry (16 gr). elevator is very sensitive anyway. although not intended for it, recently i flew it in extremely windy and gusty weather. it handles it well but there is wing flutter when climbing on full power. but on calm to moderate wind it is ok.
Posted by phil alvirez | Apr 22, 2013 @ 05:29 AM | 9,844 Views
i have been flying my planes for many years, but it has been in warm weather...until now.
in those years, i got into thermals regularly, and grew under the impression that it had to be warm weather in order to climb with the help of hot air (the so called 'thermals'). but recently i have been flying near freezing, and have witnessed my planes climbing and staying up there for a long time. some say that is the differential temperature that makes air go up. that is, if there is air at, let's say, -20c, and surrounding air is -10c, that mass of air will go up. so if in freezing air, and then we encounter not-so-freezing air, that makes planes go (or stay-up) there, why call them 'thermals'? shouldn't be more correct to call them something like 'rising air'? or 'risers'?
the original word comes from greek: therme=heat. see:
i found this in etymologies:
from Greek therme "heat," from PIE *ghwerm-/*ghworm- "warm" (cf. Latin fornax "an oven, kiln," formus "warm," Old English wearm; see warm). Sense of "having to do with heat" is first recorded 1837. The noun meaning "rising current of relatively warm air" is recorded from 1933.

and the last 1 brings the key word (relative), as i mentioned when i said that it is the differential temperature. 'relatively warm air' means that what matters is that some mass of air is warmer than the surroundings.
there is some interesting data about their shape here: http://www....Continue Reading
Posted by phil alvirez | Apr 12, 2013 @ 02:50 PM | 4,429 Views
at the beginning, sailplanes flew from slopes, like at elmira, new york, where an upward draft kept them airborne. no need to go anywhere, just stay into the upward wind. like the planes at slopes do, so a shorter wing was better for smaller diameter turns.
then they began to get into thermals, and as they gained altitude could go somewhere else and get into another thermal. so distance was the goal, and then wings began to get longer and thinner-the trend that we see today. but models that copy the shape of full size narrow wings find themselves into trouble, as they tip stall easily. the problem is due to the air density, that makes the smaller wings less efficient the smaller they get (that Reynolds number thing).
and if we look at birds, sure those that stay around, like buzzards, haws, and eagles, have short wings, and those who go places, like albatross, have long, narrow wings. and the chord of all is almost the same all through the wing. no taper nothing. just the tips. so they may know better, after millions of years of evolution. and they use turbulators too. just think about it.
Posted by phil alvirez | Mar 30, 2013 @ 05:49 PM | 4,994 Views
radios with nicads or similar.
i came back in 2006, just at the time when 2.4 was released. i got a DX6 and soon realized that the battery in the tx (8 nicad cells) didn't last long. then some1 released a 3 cells lipo for txs and have used it for 6 years, and since i have had no problems-with that radio.
last year i got 1 DX6i, that comes with 4 nicads, and used it with them. last season began to experience power failures. i had several planes crashing. i began exchanging rxs, then escs, replaced connectors for larger, also larger packs. nothing helped. then began to suspect the towers nearby were the cause. or the windmills that were installed not far away (they operate with microwaves). then 1 day when i landed, walked to my plane and at the moment i was going to switch the tx off i noticed that the screen was blank-and the switch still was on. i thought that my tx was history.
but at home i decided to check, starting with the easiest thing. and when pressing the cells i noticed that the screen came back to life: it was a false contact! i decided to install a 2 cells lipo (the largest that fits is the 2x610-and i had it), so i did the mod similar to the way of the orange tx http://www.hobbyking.com/hobbyking/s...y_Mode_2_.html . (see last picture on the right). melted a rectangular hole and fitted a male connector, and adapted the pack to match. as i have a lipo charger that charges and balances at the same time, and am familiar with lipos, i didn't have to get anything else. now the radio operates flawlessly. i strongly recommend to do this to all radios that use batteries of single cells, as are prone to have false contacts unexpectedly, as happened to me.
Posted by phil alvirez | Mar 30, 2013 @ 12:20 PM | 6,855 Views
Lynx was developed to find out if a sailplane with 1.5 meters wingspan and same weight and wing area than a 2 meters (like the Rex) can get into smaller diameter thermals.
the 460 sq in wing that sits on top of the fuselage and is held in place with 1 nylon bolt, has an undercambered airfoil with 8" constant chord and tips tapered to 5", 4 polyhedral panels. over/under 1/8x1/4 spruce spars with 1/64 ply webs, 1/16 'v' shaped trailing edge, 1/8 carbon fiber tubing leading edge and 3-1/16x1/8 spruce turbulators. covering is ultracote transparent orange; the auw is 510 grams with a 2x1000 pack.
the fuselage is made from the foam remainders of the 1st fuselage from the Thermal Rex, that was replaced with a spare that i was lucky to get when i got the asw28.
the nose section was badly damaged, but from the wing trailing edge aft was in good shape, so i adapted a balsa and ply front section that runs from the trailing edge of the wing to the nose, using a foam insert between the trailing edge and leading edge so that section is solid foam. the sides and bottom are 1/8 balsa with 1/64 plywood, and i added a plastic canopy from sig mfg. motor/prop/spinner/esc/pack are the same as the Rex. when checking the elevator pushrod i learned that there was too much drag, due to the 's' shape trajectory, so i replaced it with a servo near the top of the fin. now i get a smooth, precise response.
i still have to have good weather to compare both, but from the preliminary short tests they are stable and perform well. it is going to be an interesting evaluation in thermals.
Posted by phil alvirez | Mar 27, 2013 @ 06:23 PM | 4,270 Views
when i was doing indoor free flight i met some of the greatest folks ever. and got advice from the best. besides the technical, some gave me a point of view that is worth considering. Steve Brown, world champ, once asked me: are you having fun? i said 'yes', and he said 'good'. that was all.
another of the greats, Walt Van Gorder, when advising me about a plane said : 'it ain't easy. if it were, it wouldn't be fun'.
so there you have it. all about this hobby is making it fun, having fun doing whatever. nothing is easy or difficult: it's fun.
enjoy.
Posted by phil alvirez | Mar 27, 2013 @ 12:21 AM | 4,463 Views
the idea started when i was considering getting a fuselage of a sailplane similar to the ask 21 that i like very much, and design a wing/tail for thermaling, even if this means not looking scale-like. i just like the shape of modern sailplanes fuselages. so this means engineering the whole thing to match the fuselage, and it is not an easy task. after shopping for a suitable fuselage, i ended up buying first a 2 mt ask 21 from hobby king, and later an asw 28 from same source. then i decided to give them a try as they are, before discarding the wings and tayloring new sets for thermaling, with larger area and higher lift airfoils. the result was that both planes crashed several times due to strong tendency to tip stall. i tried improving them by adding dihedral to the '28, and then enlarging their wing area, but even if showed some improvement, still they were not pleasurable to fly, to say it mildly.
i have been able to work on the '28 wing. the new wing, that has more area, also uses a naca 6409 high lift airfoil that i have used extensively through the years, and polyhedral, and the results were a great improvement, and no more tip stall tendency. with this i even managed to get rid of the ailerons, so now i am able to do all that i need with only rudder and elevator.
see my blog. i will add more as i finish-and fly test-them.
Posted by phil alvirez | Mar 09, 2013 @ 10:08 AM | 4,396 Views
Maverick started with the availability at the time, of the fuselage/canopy/prop/spinner of the Dynamic-s, a hotliner with v-tail: http://www.hobbyking.com/hobbyking/s..._EPO_PNF_.html

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.
the wing is 8" chord and 5" tips, undercambered airfoil, and uses 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 600 sq in and 690 grams auw, the wing loading...Continue Reading
Posted by phil alvirez | Feb 18, 2013 @ 09:03 PM | 5,157 Views
those were the days, my friend...
chapter 1.-in 1 of my many lives (my son calls me 'the cat', as i have lived-and survived-many adventures), i had a hobby shop at a mall, where i gave free building and flying lessons to my customers, most of them children from 8 years up. i had a building board and benches where they sat, and customers passing by were amazed at the sight-and some became members of the free club. when they finished their planes they took them to the field and i taught them to fly, be control line or radio. at the time i had my 1st Elf, a high wing trainer with a single channel radio, that was so stable that could fly free flight, and everybody wanted to fly it.
you can see pics of it somewhere here (i think is page 5-this is getting out of hand!)
2.- soon i learned that i had to arrive at dawn to be able to fly it, and even then they learned that and i had to do something else to have a chance to fly it. so i decided to sell kits, and later ready to fly planes, with free flying lessons included. this way at least i had the chance to fly mine now and then.
3.- there were visitors that became fascinated with the plane once they had the chance to fly it. 1 of them was a lady that walking by the mall became interested in giving her husband a plane so he could get into the hobby. she even went to the field and wanted to try it, so i handled her the transmitter and gave her some instructions and there she was, having a ball. once the engine stopped, the plane...Continue Reading
Posted by phil alvirez | Jan 24, 2013 @ 12:49 AM | 5,409 Views
when you get into 3d, 1st you want to learn to fly without crashing too often. of course, using epp will cut your training time considerably. once you don't crash too often, and your crashes are not catastrophic anymore, then you can think of improving your plane's performance. you read or hear from other guys talking about lighter planes performing better. sometimes you even watch them flying and speculating about it. then you know that you would like to build light so your plane helps you to do things easier. but how far can you go? when are you passing the boundaries of building light and getting into building fragile? and if you fly at a place where other guys fly at the same time and some are sort of kamikaze hunting for targets, you don't want to build fragile, even if you don't hit hard anymore. so, 1st you decide if you are going to fly only when there is no danger of midairs and build light, or to fly whenever and build strong. then, you begin building planes each 1 lighter than the 1 before. but you have to decide when to stop. that is, if you still have ideas on how to save a few grams without the plane disintegrating in mid air. but it is lots of fun. for instance: when i began building 'compact' 3d (24" ws, 100 gr auw), and using 6mm epp, my 1st plane ended up at 100 gr auw with a 2x300 pack (lipo). with the motor developing 140 grams of thrust on 2 cells, its power-to-weight ratio was enough to do 3d comfortably. then i went further and built a 2nd 1 that weighed 85 grams. what a difference! it flies slower, that gives me more time to think what am doing, so it's easier to do anything. when this happens, you don't want to go back to the heavier 1, that you can fly when the place is crowded and you don't care much if something happens, and also because it can take more punishment. but that creates 2 separate categories. so maybe it's good to keep both to fly depending of circumstances.
Posted by phil alvirez | Jan 19, 2013 @ 02:43 PM | 4,510 Views
i have shown before some plastic models from my son. now he has released a post here http://www.track-link.com/forums/new...ral/43435/flat. where you can see them. they are around the middle of the post, and he will be showing 1 by 1, with historic details and the camouflage he used on each 1.
i hope this will be of some use (or entertainment) to you all. some drawings (the 1s framed) are by me. he started doing plastic models in the 80's, when i owned a hobby shop in vancouver, and he had free access to materials and models. now you see how that evolved.
Posted by phil alvirez | Jan 12, 2013 @ 02:12 PM | 5,304 Views
Phil's Thermal Rex, or Phil's Rex for short, is a hybrid from a fuselage of the scale ASW 28 sold by hobby king. see
http://www.hobbyking.com/hobbyking/s...ider_PNF_.html
and the full size: http://www.easternsailplane.com/east...hleicher/ASW28
the reason why i choose this fuselage is because the looks are like science-fiction but it is very much like the full size. although i did not use the wing shape (especially the wing tips).
(i will be adding data at the bottom of this thread)
the new balsa wing it is a 2mt wingspan, 460 sqin, 543 gr auw w/2x1300 lipos; naca 6409 airfoil.
i used the foam fuselage and tail, and avionics, and designed a woody wing with larger area and an undercamberer airfoil for slower flights.
i got the whole plane and decided to try it as is, before discarding the wing. and boy, was i for a surprise! it falls into a stall and a spin unexpectedly, and i crashed it several times, breaking the nose and reinforcing it, until i throwed away the wing and started my own. fortunately with it the plane is now stable and predictable. originally it comes without dihedral, contrary to the full size, that has some. as the stock was too unstable and prone to snap roll, i added dihedral as per the full size and this helped a little bit; then increased the chord, adding area to the trailing edge, which helped more-but still was a handful. then it was when went into the balsa wing. it has a planked leading edge, polyhedral, and is covered with...Continue Reading
Posted by phil alvirez | Dec 16, 2012 @ 06:57 AM | 5,125 Views
t tail
conclusions
aerodynamically keeps the horizontal tail clear of the wing wake, and this means no turbulence (and only 2 corners), so it is the cleanest of all, and there is a better reaction and sensibility. based on my experience, as i have 3 planes with it, i can confirm this. full size planes, especially sailplanes, use it extensively, and passenger planes like de havilland dash 7 and 8 too, so must be a strong reason for that. another thing is that it can be placed with the leading edge slightly ahead of the fin's leading edge, getting a cleaner entry-and improving even more its efficiency. an example is the ask 21. see http://www.alexander-schleicher.de/p...k21_main_e.htm
installing it, the cleanest way is placing the servo at the fin. or you can use a cable, but this means some drag to the servo. to eliminate drag you can install a linkage with 2 belcranks, but it is more complicated.
also, it is heavier than conventional, as the fin has to be built stronger. but that could be very little if you do a good job engineering it.
and is more prone to damage if you fly competition and do those landings (crashes) to get to the spot-or if your landings are not smooth.
i have a 2 mt sailplane radian that has conventional tail (really it is a low 'x' tail) and it also behaves great, so at the end of the day it depends of what you like best.
i like better t tail for the aerodynamics reasons, and now i do smooth landings, but i must admit that you can live with any way that provides you good results, as long as you do a good installation with as little drag as possible and land smooth.
Posted by phil alvirez | Dec 01, 2012 @ 06:39 AM | 5,171 Views
from the beginning of time, man has dreamed of flying. the wildest of all dreams. and for those who are into this, flying is an adventure. the final frontier. just being able to fly an airplane is all that it is. and for models there are several ways to do it: starting from the easiest, to get an rtf (ready to fly) plane, to an arf (almost ready to fly), to build it from a kit, to build it from plans, or to design your own, the goal is the same: to be able to fly. to experience that thrill of controlling it if it is radio or control-line, or to watch it flying, if it is free flight. of course, having total control in 3 axis that radio control gives us is the ultimate experience of fully controlling it (that is, if-or-when you are able to do so). but even if you are not having total control of it due to being learning, is still a wonderful feeling. i know, sometimes things may go wrong, but that is another thing that adds to the fun. if you could count that everything is going to go right for sure, it wouldn't be the same. the unexpected is the key factor that adds to the feeling of adventure.

but, oh what a glorious feeling, don't you think?
Posted by phil alvirez | Nov 20, 2012 @ 03:04 PM | 5,532 Views
Thermalis is an idea of an electric sailplane for soaring in calm to moderate wind. it has 80" wingspan and 10" chord almost to the tip, and 764 sq in; weighs 926 grams (32.5 oz) with a 3x1400 mah pack. i just started evaluating it and will provide comments whenever i get enough flights, but so far am flying in cold weather with no thermals. am also playing with cg and trim.
nov 21-the concept: a simple sailplane for rudder and elevator-no ailerons, for relaxed flying and getting into thermals (hence the name), in moderate wind conditions. the wing is 1 piece polyhedral and the fuselage is box type, 1/8" solid balsa, like the horizontal tail and rudder. still, as i wanted to try spoilers and flaps for the 1st time, i decided to add them. the flaps are of the split type (similar to the 1s used on the full size douglas dc-3). another feature that i added was the t tail, that is not as simple as conventional tail, i must admit (i will comment on this later).
>>>will be adding details. check at the bottom.
testing the Thermalis‏
21/11/2012
i started with the cg a little bit forward from the point for which i designed it. the launching went fine, with a strong climb at half throttle. the motor is very powerful and with the 10/6 folder it has lots of power. the climb is at about 70-80 degrees without tendency to tip stall, that was haunting me with the other sailplanes before. the glide is the best i have got compared with the other...Continue Reading
Posted by phil alvirez | Nov 14, 2012 @ 11:19 PM | 5,373 Views
at the beginning i posted a link to an article where it stated that thermals are like horizontal donuts that climb, with the wind going up at the center and down at the edges.
we all believed that article (it was back in the 60's), but recently i found another approach. http://www.xcmag.com/2007/07/thermal...rt-1-thermals/ where he brings an explanation that comes very close to how cumulus nimbus grow, including the same shape, so am beginning to lean towards this idea.
so this way thermals don't turn left or right, just wind goes up inside and down outside-and this matches with the other theory in that sense, so you turn any way you find is better to stay put.
and the idea of trimming the planes to glide to the left from those days could be to balance the torque of the motor, be rubber bands or engine-and somehow it became customary and we did gliders that way too. just a guess.
Posted by phil alvirez | Nov 02, 2012 @ 05:02 AM | 5,422 Views
on shape of thermals



i found this, providing data regarding the shape of thermals:

http://www.xcmag.com/2007/07/thermal...rt-1-thermals/

which looks very much the way cumulus nimbus behave.

by the way, i just started a thread in the forum "thermal":
http://www.rcgroups.com/thermal-36/
and still another view:
http://www.soartech-aero.com/Thermals.htm
and 1 more: http://www.rcgroups.com/forums/showt...64#post4966743
Posted by phil alvirez | Oct 31, 2012 @ 09:46 AM | 5,671 Views
have you wondered what shape a thermal has? a bubble? a cylinder?

i found an article in a model airplane's magazine (american modeler-august 1961-page 42), where the author (Bill Winter) provides a link on the thermals shape and behaviour, from an article from Soaring magazine, by Clarence Cone, issues april/may/june 1961.
this is the link: http://soaringweb.org/Soaring_Index/...61_Apr_08.html page 8

the link was lost, but managed to retrieve it.
Posted by phil alvirez | Oct 08, 2012 @ 09:21 AM | 5,997 Views
october 8, dawn, near freezing, some frost; no wind on the ground, some up there. plane: stock radian 2 mt sailplane; 1400x3 pack; dx6i tx. i didn't notice any change in trim with the extra 16 grams of the quanum tx. ran motor for 5 min total for 6 flights (some 50 sec each). programmed for 11.5v alarm, which is about 3.8 per cell. watching the screen now and then, i could predict when it was going to hit. i didn't hear the 1st 2 beeps, as my hearing is not so good, but when i heard the 4 beeps repeating, landed at once. it was showing 11.48v, which is about 30%. at home the charger showed 50% at 11.54 when started charging, and took .575 ah to charge to 92%. i guess the pack recovers after a rest-the time it took to get home. my experience is that it is not difficult to glance at it occasionally, and the readings are helpful, once you know what figures to target. in my case i was aimimg at 3.8 per cell, so i was ready when the figures were getting close to that.

to me, it is a practical approach, so the quanum works fine with these basic readings, even without the amps device installed. as i said, once you know what figures to program to stop flying. i hope to test the amps meter when i get it, and the weather brings a chinook (indian summer), otherwise i will have to wait until spring. am getting too old to handle cold. today i had to wear my mask (balaclava they call it) that covers my nose to prevent me to catch a cold again (am just recovering from the worst flu...Continue Reading
Posted by phil alvirez | Oct 04, 2012 @ 09:40 AM | 5,333 Views
turbulators:
1.-stability increases;
2.-speed increases;
3.-drag is reduced;
4.-glide is more flat;
5.-duration increases;
6.-the most effective location is at leading edge;
7.-if using only 1, place it at the leading edge;
8.-when using more (besides the 1 at leading edge), placed at certain % similar to birds, all of the above increases even more than when using only 1;
9.-thickness has to be small (like thread).

steps:
1.-stability increases a lot (more than with turbulators);
2.-drag increases a lot;
3.-speed is reduced;
4.-glide is not as flat;
5.-duration is reduced;
6.-location (% of chord), thickness, and adding more steps does not change performance noticeably;
8.-thickness has to be large. i mean, about 1/4" and up.

conclusions:
1.-turbulators: increase stability and efficiency; drag is reduced; speed increases; reynolds increases;
2.-steps: increase stability enormously and efficiency is reduced. drag is very large; reynolds is reduced.

june 17, 2013: i have been using turbulators for a long time. most of them with spars at the surface, as part of the structure, an also threads glued along several positions of the wing, running parallel to the span, over the covering. in recent times i built 2 identical wings, 1 with turbulators, and another without them (on the surface) and compared the plane's performance, even measuring its speed. now am working with sailplanes around the 2 meters (80") wingspan.
what i do with all...Continue Reading