Air Foils

[Whorges]

I'm building a Sagitta 600, and I'm wondering what type of airfoil it has and what it's characteristics are. I've decided to go for the aileron build with the spoilers. Any point in usuing 2 aileron servos for flaperons/reflex? Was (the kit is pretty old these days) it a decent plane?

Are there any links that directly discuss airfoils, there modification for different scale planes/Re and which kits have which foils and why?

What about Flaps? Until recently I've never had a plane with flaps. Is the point to be able to control glide ratio on final, or to be able to dive out of cloud suck without building up too much speed? Or simply to add reflex/camber for cruise/thermal modes? I think I'm destined for the smart ass answer: Yes. on this one but I just wanted to know if I missed anything.

[djnibler]

Hello. Pretty sure the Sag600 uses an E205 airfoil. It's a floater foil by todays standards but has more speed than the Clark-Y which was popular back in those days. Back then the E205 was considered fast. The Sagitta is a good plane... I think someone won the Nostalgia nats with a Sagitta 900 a year or two ago.

If you are going to go to the trouble of building it with ailerons, I'd definitely use 1 servo in each wing.

I don't know of any link that discusses the history of airfoils in the soaring scene, sorry.

The point of flaps is all that you mention above. But generally if you are going to use them for camber/reflex, it is helpful to have them on an airfoil that is meant for it, otherwise you don't get much in return. I don't know how well the E205 responds to camber/reflex but I'm sure some of the guys on this board will. And no, you didn't miss anything (for standard Thermal contest soaring anyway).... except for maybe adding camber during launch.

[BMatthews]

If you're building from a kit then there's a mod that is really easy to do and should help a lot. The Saggita uses the Eppler 205 which was very popular at the time. I had a Top Flite Metric that used the same airfoil. The problem with the way it was used in both these kits was that the leading edge sheeting ended at the high point of the wing. As you probably know this causes the covering to produce a sharp line at the area between the ribs right where the sheeting ends. This tends to produce a very draggy separation bubble that shows up as very poor slow speed flight charactaristics.

Michel Selig examined this in his original wind tunnel project that was reported in Soartech 8 some years back now. His findings and recomendation was that the top sheeting should extend over the spar and back to about the 50 to 60% chord point. By that time the "worst" of the work expected of the airflow is over and the flow can deal with a little discontinuity easier than at the high point of the airfoil.

I got around my issues by adding turbulators and that helped the low speed end of things a lot. But the 205 is not a floater airfoil. Your Saggita will work best if you let it fly a bit faster than a typical floater. And this is its strong point anyway. It's a fast cruiser that can test a lot of air in a hurry. You'll be able to range out further than with a floater and find lift that would have been out of the question with a slower and steeper descent model like a Gentle Lady or similar. It's an adjustment but once you get the hang of it it's a far better way to soar. You'll also find you can let the model go downwind further and still come back with lots of altitude.

Beyond that I would encourage you to produce a very nice and accurate little leading edge template that is used to check your shaping of the leading edge. It should go up onto the upper sheeting far enough that any mis-shaping of the leading edge is quite apparent. I'd make it from a thin metal card about 3 x 4 inches with the leading edge shape cut out in one end. Use a strong light from behind it and carefully work sections of the leading edge down so the light passing around the cutout template is very little. If you do both these things I think you'll find that the Eppler 205 is a superb airfoil and that your Sagitta will be able to hold it's own with many of the modern 2 meter models.

Flaps provide lift and drag. For contest landing it allows you to steepen the glide slope and hit the spot with a low enough speed that the model isn't destroyed. For even more braking effect consider programing in crow if you can. That's where the flaps go down and the ailerons reflex up. This induces a form of extreme aerodynamic twist in the wing and generates a HEAP of drag.... next best thing to a parachute.

For general sportflying I'd suggest flaps to play with and forget the crow. It's just not really needed outside of the contest circuit.... unless you like playing with stuff like that then go for it. It's really a sight to see a glider coming down in a vertical dive without any extreme speed buildup.

In any event ensure that your flaps have at least 80 degrees of throw. A full 90 is even better. If there's less than 60 you won't get the full speed control that they can give.

If you go for the full program wing then you also have the option of adding some camber changing. This would be where you droop or reflex both the flaps and ailerons over about a total of a 5 to 6 degree range. 3 to 4 degrees of droop can add some nice extra camber for slow flying and about 2 degrees of reflex will really put some ZIP into a fast cruise return from downwind. If you have the all singing, all dancing TX you can program the whole works in if you have separate aileron channels and one channel or separate channels for the flaps. Don't get carried away with the camber changing though, a little goes a long way. More than 3 or 4 degrees of droop produces more drag than lift. But when your power is coming from a winch you may find it is helpful to use a touch more flap throw. Also more than 2 to 3 degrees of droop in the ailerons will start to generate some stronger adverse yaw effects that require a lot more coordinated rudder to counter.

One last tidbit. Even with strong differential throw in the ailerons (and you should be using this) it is still possible to easily tip stall if you're flying very slow and try to turn sharply. Any turns at low airspeed near the stall point MUST be done with just a hair of stick and then have patience to wait for the model to gently roll into the desired turn. This is especially important when trying to ghost your way in during a landing. Start yanking on the stick and you will cartwheel that thing in a blink. This is typical of most, if not all aileron sailplanes.

[OVSS Boss]

The above guys are correct, Eppler 205. CG needs to be 37% of root cord, this is dead nuts from a number of sources. i have had two 600's and one 900 and they all flew very well.

[Whorges]

Thanks guys I really appreciate the info. I'm excited about your answer b/c I've been flying gentle ladies for years and this will be a switch, yes?
So is it sufficient to put turbulators or should I extend the top sheeting? Luckily I'm just getting to the part of the build where I have to put the sheeting on the top and it will still be easy to do if that's what you'd recommend.
Any suggestions on a target weight?
I was planning on building in the spoilers, would you reccommend flaps over spoilers? My understanding is that if you want to do camber/reflex then the flaps should be at least 1/3 of the cord? It's a little late to plan on adding flaps for where I am in the build, but maybe I'll build a 2nd wing later on.
Do larger planes fly more efficiently b/c of larger Re numbers? Whats a good 3m wood build for TD flying? Something not "floaty" but capable of flat land flying and full house flap/ailerons/spoils/tails?
So many questions sorry :O), just excited about something more than R/E.

[BMatthews]

A switch from a GL? OH YEAH! Your'e in for a heap of new learnin'. At first you'll wonder how in hell to keep it in the air but as you get the hang of it you'll soon be able to match the Lady and from there you'll keep on improving and there'll be no looking back from there. The ability to be able to speed up without the glide slope steepening in a noticable way is heady stuff indeed. And winds that would have you heading for home will take on a whole new fun aspect. Some of my most fondly remembered flying days are with a fast aileron model in cold blustery conditions that had most of the rest of the club grounded. Me and one or two other brave souls flew anyway and found out that it's possible to dynamic soar in the rapidly changing wind gusts. Not dynamic like now where the model moves from calm to windy and flys an orbit through the transition but crabbing across the wind and turning hard and pulling up into any gust that tries to pick up the windward wing. Try THAT with a GL.

I'd say definetly go for the sheeting. It's easy at this point. Just get some new wood for the sheeting so it's one nice smooth curve over the spar and back to the 50% point and shorten the cap strips. Don't bother with any support spar under the rear edge unless you are industrious.

Then later on if you need any slow speed help then try the turbulators.

It's only on the upper surface you need to extend the sheeting On the lower side that area is already flat.

[djnibler]

If you are going to build in flaperons, don't add the spoilers... they really aren't needed. But if you aren't going to add the flaperons, then definitely add the spoilers. Spoilers just kill lift to allow you to lose altitude for landing.... they don't really slow the ship down, just make it fall. Of the two, flaps are much, much better.

Larger ships fly better because of the "scale effect". There may be a really good scientific explanation for it but if there is, I sure don't know it ;) There are more things to consider than that when choosing a plane though. Evidence of this is in the fact that for each kind of contest, a popular span has been reached.... people aren't just going bigger by the day (anymore). Take a standard Thermal Duration contest for example: a giant ship might fly longer in dead air than a smaller ship when starting from the same height, but it won't launch as high as a slightly smaller ship and it will be harder to land.

And by the way, when I called the E205 a floater, I said "by today's standards" (MH32/RG15/etc). It definitely isn't a 70's gas bag foil and it will range out better than those. As BMatthews said, your biggest problem initially will probably be flying it too slow since you will be used to the Gentle Lady.

[Christian Baron]

The E205 has some disadvantages, see here a description:

http://www.aerodesign.de/profile/e205_sd7037.htm

I would use the very similar SD3021 with some improvements against the E205, if you don't want to change very much and want to have the similar optic like the original Sagitta, otherwise take the Bubble Dancer airfoils from Mark Drela instead.
I'm wondering that discussions like this are very rare in this forum. In the german forum these discussions are the main topic for each glider.
Christian

[Wylie Shaw]

The E205 has some disadvantages, see here a description:

http://www.aerodesign.de/profile/e205_sd7037.htm




Huh?

[Leif]

I dont read German either..... :(

[Christian Baron]

Translate it with the Google translater or a similar program, sorry!
By the way the diagrams are saying it all.
Christian

[markdrela]

The E205 has some disadvantages, see here a description:
http://www.aerodesign.de/profile/e205_sd7037.htm


To summarize that web page, the E205 has severe separation bubble problems. It's really better suited for 10-20 lb gliders. Extending the D-tube sheeting can help somewhat, but that's a band-aid. The S3021 or S3014 are very much better for something like the Sagitta -- almost ideal I think. The AG3x series are geared for even smaller and lighter gliders.

Note that all this is relative. When the E205 appeared on the Sagitta it was a major improvement over the flat-bottom stuff, but still not as good as what could be achieved.

[Whorges]

Sounds like a turbulator would help. Suggestions on size, cord location?

Normally I try to do coordinated thermal turns as slow as I can without stalling. But in this case it sounds like the E205 becomes very inneficient at low speeds. Should I keep the speed up even though I'm trying to thermal?
In other words how does all of this translate for sink rate and L/D?

Does the separation bubble only form at really low speeds? Or the entire useful speed range?

So it becomes important (read critical) to consider changing air foil design when a model is scaled down b/c it will be flying at smaller cord and slower speeds thus lower Re numbers.

[BMatthews]

When I saw the word "kit" in the original post along with some other wording that hinted that the project was already underway I geared my response to getting the best you could out of what you have.

If you're willing to make new ribs and a new wing then I would recomend Mark's AG34 as used on his Bubble Dancer and Allegro Lite.

Mark, the Saggita 600 is a two meter so I'm assuming that it fits in with the operating range that your Allegro Lite operates within.

If you stick with the 205 you WILL need to let it fly a little faster in the thermal turns. But when it's operated at the proper speed it should not have any worse a sink rate than the Gentle Lady at the near stall sort of typical thermalling turn speed.

The separation bubble forms when the air is being worked hard at lower speeds and correspondingly higher lift coefficients. At these air speeds the reynolds number is also low and the airfoil starts working in the 100 and down range of speeds where you'll see that the lift curves often start to fall apart with various oddities in the typically computed results.

For turbulators on my Metric I used two stripes of 3/32 automotive trim stripe tape. One at about the 10% chord point and the other at about 20%. Yes that was a belt and suspenders solution but the results were immediate and highly noticable and all positive for the range of speeds I operated the model. You can probably get away with one at the 15 to 20% point with some experimenting. The turbulator strip should be made from two layers to get close to the same thickness as a business card.

[oakman7004]

Sounds like a turbulator would help. Suggestions on size, cord location?

.
Accorting to the Aerodesign homepage..(if I understood correct with my school german. :) )

30-40% of cord from LE located on the top. So try 35%!

Cheers Jonas Ekman

[schrederman]

I would'nt recommend the Bubble Dancer/Alegro Lite airfoils for your project. They are intended for lighter wing loadings in ideal conditions. Sure, when needed you can balast them up, but why fly ballasted all the time. I'd use the 3021 for calmer conditins, or the 3014 if you're going to encounter much wind. Maybe a 7037 would be good for this model, in that wing-loading range. Remember that ballasting increases the forward speed but also increases the sink rate.

Just my take on it

Jack Womack

[histarter]

Schrederman and Bmatthews have it right on, and are excellant gurus.
I tend to use 1/32 thick turbs for expressive corrections, and then tune them by limiting their length from the inboard side... snip!
It works quite well for me.

[schrederman]

By the way, if you look at the Yardbird or the Houston Hawk, they both have the sheeting extended beyond the crest of the airfoil. It does seem to help the performance of these airfoils. I also extended the sheeting on a Grand Esprit, now owned by John Hill. That modifiaction made a difference in that model, as well, even with it's older, flat-bottomed airfoil.

See ya...

Jack Womack

[Ray Hayes]

Jack,

Sounds like you Texas guys have been watching my Big Birds fly. I designed the Big Bird about 8 years ago with the sheeting past the high point on a 3014 airfoil. I learned this trick in the seventies flying the F3B contests when everything was wood construction. I was always was competitive in the F3B speed runs partly because of the sheeting. But let's face it, the composits and molded wings took it one step farther with the ultimate in true airfoil shape. My 2m Lil Bird has the same application. Another benefit of the curve in the top sheeting extending past the airfoil's high point is a big improvement to wing strength.

Ray Hayes
http://www.skybench.com
Home of Wood Crafters 06

[Hawksnest]

Jack,

Sounds like you Texas guys have been watching my Big Birds fly. I designed the Big Bird about 8 years ago with the sheeting past the high point on a 3014 airfoil. I learned this trick in the seventies flying the F3B contests when everything was wood construction. snip Another benefit of the curve in the top sheeting extending past the airfoil's high point is a big improvement to wing strength.

Ray Hayes
http://www.skybench.com
Home of Wood Crafters 06

Dang it Ray, I thought you told me this stuff in confidence, now you go and blab to these guys in Texas. They will tell everybody, now you will have to tell me something new. :D Bill G.

[Ray Hayes]

Bill,

I promise you will be the first to hear about the specs on my new design that I have mentioned in the past. It is getting very close to test flying.

Happy New Year Bill.

Ray Hayes
http://www.skybench.com
Home of Wood Crafters 06

[Hawksnest]

Bill,

I promise you will be the first to hear about the specs on my new design that I have mentioned in the past. It is getting very close to test flying.

Happy New Year Bill.

Ray Hayes
http://www.skybench.com
Home of Wood Crafters 06

Thanks Ray, then I'll have something on that Womack guy again. :cool:
Happy New Year to you Ray, & Jack, and all you guys. Bill G.

[schrederman]

Happy New Year from Texas... soon to be New Mexico...

Jack Womack

[BMatthews]

....Does the separation bubble only form at really low speeds? Or the entire useful speed range?.....

Missed this part on the first time through....

On wings with discontinuities there's almost always separation bubbles in the wake of the hard transitions like the end of sheeted areas and around exposed ribs. My understanding is that these bubbles are very small or may be non existent when the pressure variations are low as happens during higher speed flight where the lift coefficient is lower. As you slow down you ask the airflow over the wing to work harder with higher lift coefficients and the pressure variation between the upper and lower surfaces change and the extra work causes the separation bubbles to grow until they bump up well above the boundry layer and into the more laminar flow region. At that point they are changing the way the air flows so that it does not follow the airfoil shape any longer and higher drag is the result. Turbulators add some energy to the boundry layer turbulence and that encourages the separation bubbles to remain smaller for longer and thus delay their effect.

At least that's my story and I'm sticking to it.... :D

[BrentD]

near the top of this thread I saw a mention to you flying a GL now, and a mention of a Sagitta winning the nats in NOS.

Sagittas are specifically prohibited from Nostalgia events, and the basic reason is they were a quantum leap ahead of the other ships flying at the time. If you're going from a tame, slow flying GL (which most of us flew at one time or the other), to a Sagitta, that alone is going to be a pleasant surprise for you.

My 900 is sorely missed; if one would show up for less than the 200 they usually get on Ebay, it would be on my board (or in my car) right now.

Much luck,
Brent

[Ray Hayes]

Now we are headed for memory lane, nothing wrong with that.

my 2 cents:

The Bird of Time is NOS legal and the Sagitta is not, but if the builder knows how to make the BOT wing strong, I'll take a BOT over a Sagitta any day. I have tons of flight hours on both models and my prefernce for the BOT starts with the airfoil, far superior to the fat E205 and of course bigger flys better.

What is good about the Sagitta is it looks good in the air and the airfoil is thick enough to easily convert it to a strong wing.

Way back in 1979, I went head to head with Lee's army of Sagittas and about six top pilots in a F3B warm up contest I put on. My hodge podge BOT won the two day event. The secret to an outstanding BOT is 41 oz flying weight with ballast capabilities. The Sagitta is an excellent flyer, but to small to compete with a BOT.

Ray Hayes
http://www.skybench.com
Home of Wood Crafters 06

[BMatthews]

Ray, methinks the pilot may be just a LEEETLE modest as well :D To take on a band like that and come out on top it not only takes a good model with perhaps a bit of an unfair advantage but a good pilot to capitalize on it as well. I doff my cap to you...

[Ercoupe Ed]

Hey there Ray!
I REMEMBER that old RED BOT of yours!
Watched it fly many times, how many times did I time for you????
I learned a lot!
I recently purchased two sets of pristine original BOT plans on Ebay.
Been giving some thought to scatch building another one.
What's your opinion on using carbon fiber tubing for spars, and lightening the thing up a bit, perhaps put in a ballast tube if needed?
Hmmm, thinking a 3014 airfiol like you suggested earlier in another post, staying with original 118 inch span, and adding flaps with servos in wings.
Also considering a wooden pod and carbon fiber tailboom,,,, and it would look something like a Frank Zaic "Thermic" glider.
What do you think?
Simply isn't anything like a good BOT!!!
Hey did you ever put flaps in any of your Big Birds or Skybirds?
Just curious????
Only really good Sagitta I ever saw was Scotty's Big Red.
Susie Lipp and Nick used to have good luck with Sagittas.

Ed DeBolt

[Ray Hayes]

Here is the whole story, AMA Model Aviation mag coverage and photos from the past.

http://www.skybench.com/nostalgia/articles/rayf3b.html

Hope you all enjoy this as much as I enjoy bring it to you.

Ray Hayes
http://www.skybench.com
Home of Wood Crafters 06

[Ercoupe Ed]

How many times can I remember LOFT members cringing when Ray Hayes set up his speed pylons at local contests???
LOL!
I had to put TWO POUNDS of ballast in my airplane just to make it go faster!
Hey did I tell you I spent some time with Eric at Oshkosh, all we did all day was trash you! LOL!!!
Pod said I don't know if Ray would like it here, there aren't any sailplanes!
When's the LOFT annual meeting next month?
Hey I bought a Cherokee Two from Tom Martin, am going to get started on it soon. Nice kit and ALL WOODY!!!
Always wanted to build a nice scale sailplane, and his deal was hard to beat!

Se you later!
Ed

[Ray Hayes]

I'll pack a towel in my van for you, your going to need it when you see my 164.5 inch ASK 18 fly.

Eric and his boy will be flying in my Wood Crafters 06, they have made everyone of them, what is your excuse Mr Woody?

Eric and I have flown contests all over the country, from CA to VA to Canada to FL
and many points in-between dating back to the seventies. It's a great hobby.


Best regards,

Ray Hayes
http://www.skybench.com
Home of Wood Crafters 06

[Ercoupe Ed]

I'll make plans to make your 06 Wood Crafters!
There's this thing called WORK that has got in the way, and also been involved very heavily in the battle to save Smith Field, but just brought aboard some VERY HEAVY ARTILLERY from out of town to help put the COUP DE GRAS on the local airport authority!!!
Watch the local RAVE THEATER MARQUEE in the near future.
I am bringing an entire Hollywood production to Ft Wayne for a PREMIERE SHOWING , with the help of a friend of mine who has been bringing her California based business to Ft Wayne and opening a new division here. I am Midwest Operations Director now.

Check out this link!

www.onesixright.com

I have the movie on DVD but will be bringing the BIG SCREEN version along with the director-producer of the movie and one of the major pilot-actors in the film itself to Ft Wayne for a PREMIERE showing here, it's going to be a BIG DEAL!

Right now, lining up sponsors.
After that, we start filming a very similar historical documentary on Smith Field Airport, that's what's kept me very busy!

I need to get in touch with Eric and invite him up for this premiere,
Tell him there are ERCOUPES in the movie!
And they used to rent out in the late 1940's early 1950's for $3.50 an hour with fuel at Los Angeles metropolitan ( Van Nuys Calif).

If you talk to him, tell him I want to talk to him. I didn't have his phone number. If you want, look me up in the book and give me a ring!
I'm the one on Bayview.

Blue skies!

Ed DeBolt
Midwest Operations Director
Blackburn-DeBolt productions

Slim City USA assistant director

[Whorges]

So I've been doing a lot of reading. Different airfoils perform differently at different Re numbers. Since we all fly in air, density and viscocity don't change. That leaves scale and velocity.

In thermal soaring we'd like to have the following:
1. L/D wicked good
2. Minimum sink rate: mmm, zero!
3. Speed range: W---I---D---E

We tend to fly in 2-3 modes:
1. Cruise/Search: fast and hopefully flat. V is up, C(L) is down, L/D still high
2. Thermal: slow for tight turns (and minimum sink???). V is down, C(L) is high, sink rate is important, but L/d is not critical here (with in reason)?
3. Landing: V is down, L/d is down
4. Launch: Powered (winch): L/D who cares, C(L) HIGH,
4a. Launch: Hand throw/Zoom: V is high, C(d) LOW, L/D high

For sake of discusion let's limit it to 1 and 2.
1. V is up, Re is up, C(l)/C(d) = L/D needs to be high. But the exact numbers very with scale and wing loading (cubic loading a better perameter? neither is dimensionless and both are independant of Re?). So let's say you pick a scale (span)for building reasons. This leaves the following design perameters: Aspect ratio, weight, airfoil. I think if you specify those three, then the Re is set if you're flying at minimum sink or max L/D. Of course you can play with camber/reflex but essentially this is still choosing airfoil.

Now to the crux of the matter. What are the trade-offs for the given design parameters?

As wing loading goes up, we gain in velocity, Re, L/D--"stays the same" but I doubt it's really linear outside some range, handling improves?, control authority improves? but we increase sink rate, and the plane may not read the air as well, and we need more structure to handle the loads.

Aspect ratio appears to always be high for gliders. What are the trade offs for this?
In other words why aren't we flying at higher weights and bigger cords for a given span? This would increase move us to high and more efficient Re numbers???

Once you've decided on wieght and aspect ratio it's time to fit an airfoil. A given foil will produce lift equal to weight at alpha and speed, thus we have our Re number--if the airfoil is efficient at these parameters great, otherwise pick a different foil yes?

Personal Conclusion: Planes at different scales and equal cubic loadings will fly at different Re numbers and therefore are not equivalent. Different scale planes should have different airfoils.

I'm too tired to know if any of this is right--Good night.

[BMatthews]

Whorges, you're getting the idea now. It's pretty much as you say but a bit more clear cut than you think. Let's deal with flying as in your points 1 and 2 for now.

There's truly only two speeds to fly at during soaring. One is the minimum sink speed and the other is the speed that delivers the best L/D for the model. You should be at the best L/D when searching and shift to minimum sink for thermalling to get the most out of the rising air.

That's the ideal situation and of course there's exceptions like with most things. But the exceptions are typically forced on you by odd circumstances. Like a thermal that's very turbulent may force you to fly a touch faster than the min. sink speed just to maintain good control. Alternately if you are lucky enough to find a good sink hole during your best L/D searching it's best to give up a bit more by slighty nosing down to increase speed quite a bit and leave the area as soon as practical.

For me I do this all with the trim lever. A glider pilot really should be using the elevator trim as a primary flight control. That and a LOT of flying to really learn where the model works is what it takes. I went so far as to instal a 3/4 inch long 2-56 screw in my trim lever so I could find the darn thing easily on the fancy molded and very cluttered modern transmitters I use these days. It was well worth it. Last year I got an Airtronics radio that has digital trim levers where the levers just move a little and then pop back to center. Now I have no way to feel where the trim is and I KNOW I'm going to hate that once I start flying this TX seriously in a soaring machine.

[Ray Hayes]

Digital trims is why I haven't purchased the latest and greatest Tx. Too old to learn new tricks and besides, I always know where my elevator trim is set with my trusty Futaba. I get a big kick listing to guys crumbling about elevator trim setting on their new stuff. KISS

Ray Hayes
http://www.skybench.com
Home of Wood Crafters 06

[Joe Minton]

Bruce & Ray -- LOL

I have two JR TXs, one with digital trims (its heavy too) and the other without. I much prefer the "without" for the reasons you both refer too. I fly with the trims. When I use the digital TX, I get accused of trying to play music with my Xmtr by fellow flyers ;o)

Take a look at the HiTec "Neon" Tx. It is light, cheap, has four channels & there are no digital trims. Imagine: a simple featherweight Tx with enough channels for RES (+ electric motor).

Okay, back to the topic ---- :o

Joe Minton

[schrederman]

Whorges...

Everything in design is a tradeoff. Limiting drag is the best way to get #s 1 & 2 in your post. There are many ways of doing that, and some are very subtle. There are two kinds of drag.

Induced drag is produced by the wing as it produces lift. The higher the coefficient of lift, the higher the induced drag will be. That's why gliders use lots of wing. They can fly at low coefficient of lift and still support the weight. The higher the angle of attack of the wing, the higher the CL and the higher the induced drag. The faster the model flies, the more lift it produces, so the angle of attack goes down, and so does the induced drag.

Parasitic drag is the drag produced by everything else passing through the air. It's the true friction drag, and it increases with the square of the airspeed. It's caused by open hinge lines, rough surfaces, separation bubbles, intersections between the wing and tail to the fuselage, surface area, etc.

That's why the molded stuff flies so good compared to most woodies. The smoothness of the surfaces and the tightness of the hingelines all add up to limit drag. That's also why my wings on my full-scale ship will be painted soon. Gotta be ready for those 1000 feet-per-minute, West Texas thermals!

Other than limiting drag, pick your airfoil for it's primary purpose, duplicate it as truly as possible, and go have fun...

Jack Womack