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Calling all Skimmerphiles!

Old 03-16-2015, 03:28 AM
  #51  
tobydogs
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lol..., i don't think the discussion of adding washout to the wing is in my thread. i think of wash out as adding a twist/shape ect...ect to the wing tips to help with stall issues or something like that....not really sure the skimmer has any twist in the plans of the wing. just a simple , straight forward build and join the to halves flat. one side stays weighted down on the table and the other is lifted up several inches..around 6 or something that looks really high.

i can see where a dihedral jig board would make it easier to be setting the angle and making sure both are aligned correctly before the glue dries just not sure you'll really need it for the skimmer.
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Old 03-16-2015, 04:24 AM
  #52  
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Most of the Skimmer threads I've read do mention a washout for that very reason: lessening the chance of tip stall, which I hear this (these actually, the 400 has the same recommendations) plane is prone to do without it.
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Old 03-16-2015, 10:55 PM
  #53  
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i can seriously say the skimmer is an awesome bird and will glide in smooth and long. if your not low enough as you approach the runway you get plenty of tries to go around. i'v stayed up 40minutes no problem using minimal power and my biggest complaint is a sore neck sitting in a chair looking straight up..

the last time i flew it was in the late fall last year and took videos with the keychain camera velcroed to the fuse side facing rearward. tried to speck it out and it was a little cloudy so distance views weren't spectacular.

i did 2 or three go arounds and glided in for a smooth landing. a guy at the tables said"you sure got your money out of that one" that flight lasted maybe 30minutes but seemed longer to everyone else around.

i may owe you a big thanks this year flywheel...,your motivating me to dig out the bird of time and get her in the air. she's sitting on a shelf without a rx waiting for one to free up which is pure laziness on my part.
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Old 03-17-2015, 01:21 AM
  #54  
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LOL, I too have a BOT "in the wings" But I'm putting off building her until I feel my skills are up to par for such a beautiful bird.

Please be sure to post your build thread!
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Old 03-17-2015, 01:28 AM
  #55  
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it's sort of boring and was drawn out do to flying season in the middle of start to finish.....but heres the bot build thread i started in 2012 here at wattflyer.


http://www.wattflyer.com/forums/showthread.php?t=65731
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Old 03-24-2015, 01:45 AM
  #56  
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Stopped at the hobby shop today, got most of what I needed. they don't carry AeroNaut anymore, and actually had very few folding props period, just small ones. So I ordered a air of 11x6 from Espirit. 12 x 6AeroNaut folders are like teeth in a chicken's beak, so I'll just see what the 11.6 does. Most of the threads I've seen of the Skimmer which use the heavier, less efficient brushed and nickel setup seem to do OK on even smaller props. We'll see.

Stuart, your thread is actually one of the ones that inspired me to do a 600, and I got many good ideas from it (I linked to it in post #1).
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Old 03-24-2015, 04:33 AM
  #57  
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Stuart, I noticed on your build you used the 1" TE stock that came with the kit for your full strip ailerons, How did this work out in practice? I'm thinking of doing something similar, not for ailerons but for camber control and was wondering if 13% of mean chord is enough.
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Old 03-24-2015, 11:38 PM
  #58  
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the te strips worked perfectly as ailerons and i used plenty of hings to keep it operating smoothly. a lot of the decision on doing full length was dialog with other builders and glider pilots. i could also program them to add camber or mix in rudder with turns. for the most part i power up to vertically climb to a really high altitude and shut down to search for thermals turning via ailerons a lot.

theres no issues with tip stalls when turning while flying slow and low.

a really great help was Ajear here at wattflyer. he is or was president of the long island silent flyers club. gliders are his choice of rc flying. perhaps pm him with your questions on camber mods.
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Old 03-25-2015, 01:12 AM
  #59  
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I think AJEAR invented RC sailplanes! Actually I did consult Ed, and his reply came with the disclaimer that he is not an aeronautical engineer. All the research I did came up with nothing for camber control, but for ailerons I found a few pages that recommend they be at least 12% of total wing area. Using this formula then 12% of 532 = 63.84 SqIn. That works out to about two 1" x 32" full strip ailerons (or in my case, camber strips). If I stretch them from the second root bay to the tip piece than I will have just about that. However, the ailerons on most planes span only half of a wing at best; I don't know if full span ailerons are figured the same way. At least I couldn't find anything.

I also grabbed a pair of 1.25" wide TE strip when I was at the HS yesterday, so if someone chimes in saying I need more I can increase the CS surface area to 80c.i. However, you say the 1" strips on your bird work great as ailerons, so for something as simple as camber and reflex I should be good.

As far as tip stalling is concerned, did you incorporate any washout (if so how much)? I hear this design tends to drop a wing at slow speeds without it. At least on the 57" 400 model it does. There aren't a lot of 600 build threads out there.
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Old 03-25-2015, 02:16 AM
  #60  
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Generally, for flaps/camber control especially, its best to have them relatively wide. On my Supra for example the flaps vary from 22-24% of the cord starting at the center and going to the first polyhedral break. Ailerons are wider yet varying from 24% at the polyhedral break to about 25% at the tips. (had to fix my sloppy math)

The wider control surface allows you to use smaller deflections to get the same results. That means less drag for any given amount of control authority.

Less drag is (one of) the main goals in sailplane design.

Last edited by Larry3215; 03-25-2015 at 02:20 AM. Reason: sloppy math!
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Old 03-25-2015, 03:20 AM
  #61  
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Originally Posted by Larry3215 View Post
Generally, for flaps/camber control especially, its best to have them relatively wide. On my Supra for example the flaps vary from 22-24% of the cord starting at the center and going to the first polyhedral break. Ailerons are wider yet varying from 24% at the polyhedral break to about 25% at the tips. (had to fix my sloppy math)

The wider control surface allows you to use smaller deflections to get the same results. That means less drag for any given amount of control authority.

Less drag is (one of) the main goals in sailplane design.
25%? Really? On these wings that would be an average width of almost 2 inches. I've never seen full span control surfaces that big on anything other than a 3D plane.


But I can see where it would require less deflection (almost none, probably ).

BTW, this plane has simple dihedral, not polyhedral wings. So full span means just that: Root to tip. And these are NOT landing flaps.

Last edited by FlyWheel; 03-25-2015 at 03:52 AM. Reason: added image
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Old 03-25-2015, 05:08 AM
  #62  
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On the Supra for example - 3.7 meter span - the camber change from full reflex to max camber for thermal turning is only 6mm of movement. Aileron deflection is 10mm max IIRC.

Flaps of course go "down" as far as possible - you want to get as close to 90 degrees of down as possible for landing control.
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Old 03-25-2015, 05:13 AM
  #63  
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Originally Posted by FlyWheel View Post
25%? Really? On these wings that would be an average width of almost 2 inches. I've never seen full span control surfaces that big on anything other than a 3D plane.


But I can see where it would require less deflection (almost none, probably ).

BTW, this plane has simple dihedral, not polyhedral wings. So full span means just that: Root to tip. And these are NOT landing flaps.
Many sailplanes use full span 'flaperons'. Virtually all DLG's and many 2 meter birds have full span ailerons that are also used as landing flaps.

If you dont have spoilers, then you need flaps with as much down as possible. Other wise, landings will be much more random

They are also used to get down out of big lift without over speeding - another very handy feature to prevent lost sailplanes.

Thats how I lost my first two sailplanes - Gentle Lady's. I had no glide path control and couldnt get one down out of strong lift before it disappeared to who knows where. The second one I couldnt slow down enough to land on a narrow slope and it flew off into the Los Angeles basin somewhere.....

I highly recommend flaps or spoilers of some kind.
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Old 03-25-2015, 05:55 AM
  #64  
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OK, I'll take your recommendation under advisement. If necessary I can change camber/reflex to camber/flaps or reflex/spoileron (without the "ron", obviously) simply by changing the control rod length and playing with the switch's end points. I was thinking of making additional rods so I could do this as needed for different conditions anyway.

Personally though, with a predicted 0.89:1 static thrust ratio I can't help but doubt that I'll ever encounter a thermal I can't escape from.
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Old 03-25-2015, 08:02 AM
  #65  
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Originally Posted by FlyWheel View Post
OK, I'll take your recommendation under advisement. If necessary I can change camber/reflex to camber/flaps or reflex/spoileron (without the "ron", obviously) simply by changing the control rod length and playing with the switch's end points. I was thinking of making additional rods so I could do this as needed for different conditions anyway.

Personally though, with a predicted 0.89:1 static thrust ratio I can't help but doubt that I'll ever encounter a thermal I can't escape from.
Says the man who has never been in a boomer thermal

Here is a log file from a 1 hr 52 minute flight of mine last year. The motor run was under 30 seconds for launch only. I spent those two hours moving from one thermal to the next as they blew through my field.

There are several places on that graph where the climb rate was over 500 ft/minute for sustained periods.

Keep in mind, your almost never flying directly over head when thermaling.

You find a thermal, then you have to drift down wind with it in order to climb. Thermals move with the prevailing wind. They never sit still in one place.

Each one of those peaks is me centering on the thermal at a relatively low altitude, then climbing while the thermal moved down wind at aprox 10 mph. The valleys are when I turn and start flying back UP wind, when the model gets too small to see, so I can find the next thermal to climb back up again. The really steep decents are me deploying the spoilers to get down faster before the model disappeared in the distance or the clouds.

The problems occur when you're down wind a ways and at altitude and then hook into a nice thermal. Winds at altitude can often times be much faster than at ground level. They also are often moving in a completely different direction from the ground winds. Thermals also often get stronger and bigger as you climb. Sometimes much stronger.

It takes surprisingly little time to go from a model that looks a little small to one that is gone when the wind is blowing the model away and its climbing like a homesick angel!

Its very easy to get to a point where the model is getting too small to see to control well. Its easy to loose orientation when the model is 1500 ft down wind and 1500 ft in the air. Its also very very easy to over speed when the model is at great distances. Powering out of a thermal is risky at best. You're as likely to blow the wings off as save the model unless you stay relatively close and low.

The safest way to de-thermal is to drop the flaps or deploy the spoilers, put the nose down as far as you can without over speeding (test this at low altitude ahead of time) and head UP wind. If you go far enough up wind you will always find sink. Hopefully before the model disappears

Just remember that "up wind" at altitude may be 90 degrees or more different from "up wind" on the ground.

With the spoilers on my Bubble dancer fully deployed I can dive at around 45 degrees without over speeding. With full crow on the Supra its about the same.

Then of course there is the landing. Sailplanes are generally much more efficient than regular power models when gliding. They dont want to slow down on their own. They are also much more subject to ground effect.

That means they can easily get down to less than one wing span and then absolutely refuse to slow down or go any lower. That can add up to a difficult time landing with any precision. Its really embarrassing (and sometimes damaging) to be landing and then have your model stop its decent 2 feet off the ground and sail on for hundreds of yards beyond the spot you were aiming for

Of course, if your landing area is big enough and you dont mind walking, its no big deal.

Im lazy and have bad knees and tend to take risks at hi altitudes when Im way down wind (plus the occasional ALES contest), so I ALL my sailplanes have spoilers or flaps that work very well
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Old 03-25-2015, 03:14 PM
  #66  
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http://www.rcgroups.com/forums/showt...ps#post4044841

Flaps increase lift, Reflex decreases it, does reflex have any affect on ground effect (the Skimmer is notorious for it)? I believe aeajr just uses down elevator and dives his 2 channel birds.

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Old 03-25-2015, 06:21 PM
  #67  
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Well, now you have two completely opposite recommendations from two "experts" - unknown drips under pressure

I keep expecting 5 or six others to jump in here and offer up additional conflicting opinions. This is after all, the internet!

In a sailplane, when you want to increase lift using flaps or full span flaperons, the amount of deflection you use is very small - as small as possible - to reduce drag while increasing lift.

Sailplanes are all about less drag. There is always a drag penalty when you increase lift, but small deflections reduce the amount of extra drag.

On the other hand, again in a sailplane, when you are trying to control your glide path (to get out of a thermal or to land precisely where you want) you will often deflect the flaps or flaperons as far possible. You WANT as much drag as possible without a bunch of extra lift.

Thats why the flaps are designed to drop as far as possible - 90 degrees is perfect - on the Supra and every other flapped sailplanes I know about.

Spoilers are a little different as they only add drag while Decreasing lift.

You can use reflex or spoilers or flaps or flaperons to get through ground effect. However, if you're only using reflex with small deflections it wont be nearly as effective. You really want that extra drag to slow the model down or you will find your reflexed model landing hot.

Crow for example is dropping the flaps while reflexing the ailerons - again to increase the drag while killing the lift - especially on the tips - at the same time.

Ideally on a sailplane, you would control landing flaps/crow/spoilers using the throttle stick or a slider so you can have precision control while landing or adjusting your glide path. Camber control is usually on a three way switch. One position for cruise, one for thermal and one for reflex/speed mode. Many TD pilots also will have a launch mode on another switch - usually spring loaded if launching from a winch or with DLG's. With an electric you dont really need a launch mode.
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Old 03-25-2015, 06:33 PM
  #68  
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Almost forgot - sometimes when landing, you DO want extra lift from the flaps but DONT want the drag.

I keep talking about landing long and over shooting the target, but there will also be plenty of times you will find yourself in just the opposite situation - landing short.

In that case, it can be a life saver to get down into ground effect and add just a hair of flaps or switch to thermal mode to extend that glide as far as possible.
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Old 03-30-2015, 04:51 AM
  #69  
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Build Review

The build thread starts here: http://www.wattflyer.com/forums/showthread.php?t=75580
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