I am scratch building a small .15 size plane just because I have an engine sitting around. I like the look of the sig lil something extra and or the herr little extra (I think they are the same plane, both no longer available) however I though about making the wing with a wing tube more like the sig something extra 40 size plane. I looked at the building plans to the something extra and it looks like the wing has a straight leading edge and has a tapered trailing edge. The way the instruction read, it sounds like it has a constant wing depth (from top spar to bottom spar) for building ease. Perhaps I am wrong but the sheer web in the kit are 1.75 inches tall and the instruction only say to cut to width not hight so I am assuming that the spars are a constant 1.75 inches apart.

Questions:
1. Is this commonly done this way? 2. How will this affect aerodynamics (tip stalls, slow speed flying, ect.) to have a constant depth, tapered wing?

Yes, this is quite common. Generally a favourable result as it works a bit like washout does, the wing section being a thicker percentage of thickness at the tip slightly lowers the stall speed of the tip section thus tends to allow lower speed without tip stall.

Thanks. That is what I was thinking. The undesirable properties would be more drag at the tips, is that correct?

WHAT?

NO!

It is the opposite. This is wash IN, not wash out!

Thicker camber sections will stall SOONER as the airflow will have to move farther compared to the root of your wing, therefore its separation bubble will be larger and when it bursts will dump more lift than if it is a same camber wing section because the thicker cambered airfoil section will have a higher coefficient of lift generally. Therefore its stall will be even sharper than a normal tapered constant cambered wing. HIGH wing tip loading is NOT a good thing. Add in change in reynolds numbers and the problem increases unless you know the CL/AoA curves for different Reynolds numbers at different camber(thickness values).

If you can guarantee that your plane will never go over the stall angle at low speed landing, then tip loading and therefore aileron authority, can be thought of as a good thing except it loads your wing spar up unnecessarily.

Washout definition is that the wing ROOT will stall BEFORE the wing tip. Therefore giving you aileron authority in all conditions. This can be done through several methods. Change the airfoil that has a higher stall angle than the root. Rotate the wingtips downward with the same airfoil. Add dihedral giving effective washout. If you know the landing speed and therefore its Reynolds number you can pick an airfoil that has a higher AoA at a lower Reynolds number than the Root of the wing. Usually this requires fairly extensive wing taper.

Sorry, no free lunch.

Your described method is opposite of what you think you are getting. It does provide more lift at the wing tips and aileron authority, but regarding stalling is bad.

It can also go against you.
When a wing section has more percentage thickness, or more percentage camber (or both) then its critical Reynolds Number increases. By that I mean the Reynolds Number (Re)below which the section has a big jump in drag coefficient and sometimes an early stall.
Check out various sections in Selig's books of wind tunnel tests and you will see what I mean. He tests at a range of Re, and you will clearly see the effect of reducing Re.
I have tried to attach a scan of Selig's test of the Eppler 374 section, from which you can see that changing Re from 300k to 200k makes little difference, but consider what happens if the root section re is 200k and the tip is 100k or 60k. Buy Selig's books (Soartech Publications), well worth while.

It is often best on models to reduce the section's thickness and camber when Reynolds Number is reduced.

On a tapered wing, the tip is obviously operating at a lower Re than the root, so this idea of keeping the top to bottom measurement the same while reducing chord will work SOME of the time, but at other times is asking for trouble. You need to check the performance of the section at the reduced Re (and who among you bothers?) or you could have problems.

Designing a (chord) tapered wing with the same family of symmetrical airfoils having a thicker profile percentage wise as you progress toward the tip is a trick that has been practiced in Control Line stunt since CL stunt began. It works.

CL stunt patterns include square corners of insanely small radius. The goal is 5' radius. The average stunter flew at around 50mph. The corner was often turned as the plane was headed straight into the ground and started at 10'. Some corners resulted in the stunter making it's 90* turn to inverted. Some had the plane coming out right side up parallel to the ground. You really didn't want your model tip stalling as it made those corners. When we designed those planes, we made sure the flaps tapered at least as fast as the chord tapered. We also kept an eye on the absolute chord of the flap as it approached the tips. Too narrow a chord and those flaps would give you tip stall.

Yes, your idea works, but there are a number of other things that have to be considered. Nothing works in aerodynamics all by itself.

Building a wing as you suggest, with a constant depth, is actually easier to build as well. It's easier to build and it tip stalls less. It's a great idea.

I couldn't agree more. I often see guys trying to apply full scale theory/logic to our models and most times it just dosen't work out in practice. If it did, most of my airplanes would fly like poop LOL. For the guys that want to preach airfoils, washout, reynolds numbers and all this other stuff. Please run the numbers at models wing loadings and power to weight ratios. I'm willing to bet it will change the ballgame drastically.

Interesting thoughts and views here. Definately appreciate educated imputs.

Exactly. Depends on the airfoil in question.

Got the books.

Can download said profiles for free to anyone who is interested. Do a search for Selig and Illinois Urbana champagne university and you will find his site with the ability to download the data files. In zip form by the way.

As to a5BY why on stunt you can get away with it. Even in a stall you are generating lift. It does not matter in a control line if one wing tip stalls as centrifugal force from the line holds the model in the air and therefore you can tip stall all you want. Likewise said models are so overpowered it does not matter if you are flying in a 100% stall all the time. In fact for stunt you want the tip to stall quite often as it will make a snappier performer.

Last time I was at control line combat, no one was using a wing such as you guys describe. Everyone was using constant taper, constant airfoil properties.

Thanks for the informative post Speedy. It really helps further the discussion. PS. wing loading has nothing to do with a stall, just means you can get out of said stall very quickly and easily.

Wing loading has everything to do with a stall. This is why heavier airplanes land faster. It does not have anything to do with AOA induced bubble seperation and I beleive that to be what you are refering to. A said airfoil will have seperation at the same AOA regardless of the wing loading however that is but one way to stall an airfoil. Another would be to stall your tip airfoil by cranking in alot of aileron while slow. I have flown everything from high performance sailpanes, pylon racing, pattern, IMAC and Helicopters and the only real experience is that in most cases airfoils don't matter much at our wing loadings. Granted with an aerobatic airplane you would want a symmetrical airfoil and for sailplanes a semi with a touch of camber. Eample, the flight difference between a S2048 and RG 15 was un-noticable to me. IMAC type airplanes have a wide difference in airfoil shape but none are a standout to being better than the other. Now if we had the same wing loading and same speed it would be a different story.

Not trying to be offensive but my question is: Are these little facts you state derived from R/C Model experience or are you quoting what you have read/learned on full scale theory/practice?


Oh and CL stunt airplanes do fly just as any other airplane and to get the " turn Radius " that Da Rock is refering to takes some tweaking of the airplane. I work with a CL guy that is one of the best, in fact he just showed me his Nats 2012 airplane yesterday. We have had discussions at length and have found that some of the things that adversly affect my airplanes do in fact affect his as well. We had quite a lengthy disscusion about tip stall and stalling the wings in the corners of a manuever. We both agreed that moving the CG aft and reducing the amount of elevator and flap throw would cure the issue. It worked like a charm. Now take an R/C model and try to do that optimum 5' corner radius and what would happen? The airplane would surely stall but the CL airplane does not. reason, the CL airplane has half the wing loading. Hmmmmm wing loading does influence stall.

RC or CL with same wing loading/planform will both have a 5' turn. CL plans do not have half the wing loading. Why you believe this is a head scratcher unless you are equating the tensile force from the wire as a rule of thumb that it eliminates about half the loading on the plane. This is roughly true. Lift = force after all Force x time = power. Same power is required to turn and change the momentum of the aircraft in question. Difference is that the CL airplane has a wire that it can turn around due to centrifugal force allowing tighter turns as it does not have to do as much work to change its momentum and remain in the air compared to a regular plane. You will note that said CL plane slows WAY down(DRAG due to stall) when one does these radical turns whereas the regular RC plane does not as much.

As for your top paragraph, different airfoils etc don't matter nearly as much as the pilot in question. A good pilot can compensate for atrocious design. An excellent pilot can make an atrocious design look like gold. Especially in things like sailplanes. I have to laugh at the guys agonizing over the perfect airfoil. Maybe for a NATS plane, but otherwise, ha. Same with pylon racing. Its 90% pilot 10% plane.

Actually, there are a number of details that don't work out here. Combat wings usually aren't trying to turn 5' radius turns at 55mph. Those babies really are overpowered for sure, whereas the stunt models back in the day were close to 60" wingspan models behind Fox .35s that were tuned to run rich, not at peak power. Nothing close to overpowered. The 4cycle-2cycle run only kicked into 2cycle after the g-load went up.

As for wanting the tips to stall, that would blow the quality of the corner and your score would be trashed. You really did not want your control line stunter tip stalling at every corner, not if you wanted to win. Since the inboard tip saw a slower airspeed it was often the first to go as well. It also had the disruption the leadouts and lines provided, although the lines did damp the inside wing, something the outside didn't get. The outside wing was the trouble maker and it going would roll your plane at you, also not what you wanted. You didn't get away with anything and for sure you didn't want tip stalls. They ruined your score and your day. A stunter staggering around the sky didn't win. You didn't get snappier performance, you got a model that lost direction, control and speed when it tried to snap.

During my years of competitive stunt flying, the ST.46 showed up but you really didn't see it on Nobler sized models.[/qupte]

As for combat wings, they went through a number of fads when I was messing with them, but trying to get them to tip stall was never one of the tricks. Slowing down in combat really doesn't do a lot for you. Most of the planforms were pure hershey bar. There were a number of 'high aspect ratio' wings that would pop up every so often, but I can't remember anyone touting his design for it's ability to try and snap roll. Combat wings are really locked into a tighter design envelope than stunters are. You seldom saw planform taper that amounted to much. They need wing area and are limited with what they can get away with in span, so the taper percentage seldom was much. They need the lighter wing loading for the same reason stunters wanted it.

The lower the weight of the model and the lower the wing loading, the less lift needed to turn the sucker when the g-load hits like a ton of bricks.

This is funny because in post # 9 you stated this " Exactly. Depends on the airfoil in question". Not to mention your whole second paragraph here is nonsense. I have competed for a spot on the US soaring team, have been a factory pilot for a helicopter manufacturer and worked up to the IMAC unlimited class. I am a fairly decent pilot but if my aircraft is not flying at 100% capability it shows in my flying. There is nothing worse then trying to fly a perfect manuever or a tight race course when you have to put in as many correction inputs as you do control inputs. It makes for a much higher pilot workload that even the best pilots can't hide.

You seemed to avoid/ignore my previous question. What model experience do you have?

DaRock knows what he is talking about, you will be best off if you listen to him.

Not sure if you just hit reply or if you intended to reply directly to me but I have been agreeing with Rock from post 1

Maybe I don’t understand when you say wing tube.
But it seems to me this was done this way because the wing tube is of a constant diameter from tip to root and all of the wing rib cords need to slide onto the tube. No other reason.

I built a .60 size plane of my own design in the mid 1980's with a symmetrical tapered foam wing. The wing transitioned to a thicker percentage airfoil at the tip. I still have it and it flys great. Hundreds of flights on it with no damage except a broken prop. See attached pic. I did add invasion stripes so it was easier to see in the air.

What works really well on controlline stunter has no bearing on what works well on a RC bird -
(also I have NEVER seen a 5 ft radius turn on a stunter - on a combat maybe )
on good areobatic rc we use the thinnest sections weight and strength will allow
as for the lift curves etc.. phooey
Each case has to be tried on it's own actual in use merits .
Build n fly more - the actual needs will gradually show up.

The rule book calls for a 5 foot radius corner but some years back Bob Hunt (I think it was) did some testing and measuring and found that the more typical corner was more like an 18 to 20 foot radius. He then went out of his way to develop a truly silly looking control line stunt model which was light enough and had enough wing area to actually do something really close to a 5 foot radius corner. Guess what.... The judges all hated it. It was too abrupt. Mind you those same judges had been conditioned by many years of looking at more traditional models.

Anyhow, back to the topic at hand.....

As I recall the Somthin' Extra has a constant chord and constant thickness wing with tapered full span ailerons. And the amount of taper isn't all that much. So really while techincally it's not a constant chord I suspect you'd really have to be fussy to find it truly behaving like a tapered wing. Which is very likely why it is so successful a design. The reason that the webbing isn't tapered in width is because the main portion of the wing is simply a constant chord and thickness.

Yeah, the 5' radius was "advertising talk", but if you've ever watched someone fly a good control line pattern you'll question the 20' radius as well.

As for "What works really well on controlline stunter has no bearing on what works well on a RC bird" that's not really any more truthful than the 5' radius claim. The discussion was whether or not the OP was a workable idea, to have the thickness remain constant while the chord tapered. Using the CL stunters turning ability as an example most certainly wasn't a claim that everything from CL stunt would cure everything wrong with any RC bird.

If you've ever watched a good flyer (Bob Hunt would be a good choice for sure.) do a pattern then you can ask yourself what radius was required for that square loop you most certainly saw him fly. The top line is 45* from the pilot's shoulders. He's usually flying 60' lines. Figure the top line of that square loop is going to be roughly 33' from the pavement. The bottom line better be around 5' from the pavement (or the judges are going to score you badly). That means the top to the bottom of the square is about 35', and the top line will be a little less than 30' long while the bottom line will probably be a bit more 35' too. (the plane is tracking along a semi-sphere, btw)

If you've ever seen that square loop flown, you'll admit that it looked like the plane flew farther in those 4 sides than it flew in the "square corners". It really does fly a square looking "square loop". And the square figure eight looks just as impossible. So now think about what you saw. There isn't even a hope those maneuvers have room for a plane to get two 20' radius turns bracketing the straight lines you saw flow, is there. Think about what you're seeing.

You're watching a 5.5' guy standing out there. The plane comes straight down at 90* toward the pavement and suddenly is going parallel to the pavement about level with that 5.5' guy's shoulders. You're amazed while you watching, and danged if you didn't see a maneuver that looked square. If he had a plane that couldn't do better than 20' radius turns, his square sides would not have existed. The turn out of the top of the square would not have been finished before the turn to make bottom of the square had better be started. The sides of the square aren't long enough for a 20' radius stunter to get two turns stuffed into the maneuver with room for some vertical.

The 20' radius is bull****. You can't fly square loops or square eights on 60' lines that have square sides with a plane that turns that badly. You probably can't even get round loops squeezed in between your 45* top and a 5' bottom. BTW, if you think I forgot about the plane's room being more than the 39' of AGL the 45* top actually has, I haven't. The distance from the stunter at 45* to where it will be flying 5' AGL is around the semi-sphere and is a bit more than 40'. You can't get two 20' radius turns into that distance with anything approaching 'straight sides to your loop'.

If you build a .15 powered RC plane with a RTF weight of 28 ozs or less and 300-400 square inches of wing area the only concerns about the airfoil are about how fast you want the plane to fly.
Most old designs I've seen that made their way to publication have wings that are unnecessarily thick.
A 8-12% airfoil will produce carefree handling at all speeds if you hold the plane to the 28 oz RTF limit. You'll end up with a .15 powered plane that has excellent vertical, top speed and will land at walking speed.
A pair of 1/4"x 1/4" hard balsa spars in a 36 inch span wing that is 1" thick is all the strength a plane like this needs. I've tested .15 powered planes in this size range to the point of wing failure and 1/4" balsa spars are all you need.
1/8" balsa sheet for the fuselage's box with 1/32" or 1/64" ply doublers that extend back to the wing saddle is all that is needed, with a 1/8" ply firewall.
Keeping the weight of the model down will make all your aerodynamic concerns about the wing pretty "moot". Once you see your plane in action, it will become obvious.

Sorry guys, I did that post above off the top of my head. In fact, a CL stunter on 60' lines would have about 49' of straight line to fly from the 45* location to the 5' AGL location. (they follow that path when doing wingovers and the vertical sides of square loops) So from the top of a square loop is actually a trip of about 49' to the bottom of that same square loop.

If the stunter only turned 20' radius turns, then it would be able to fly about 9' sides for it's square loops. Unfortunately, there wouldn't be room for any straight line along the top. There is a fair amount less than 49' of distance up there.

If you've ever seen a decent pattern flown, you know it's quite possible for even average CL stunt flyers to do square looking maneuvers.

So back to the original issue...........

Square looking is deceiving
as are many " proven aerodynamic facts"
Once you start measuring things - surprises are the rule- not the exception.
How fast are really slow flying models actually traveling.?
When we were doing design work on slow indoor aerobatic stuff- we found that getting a cruise speed of under 4 yards (meters) per second, was far more difficult than it seemed.
Many indoor models will not even get close to this
The ONLY one we found which did it reliably?
The VAPOR.
None of the superlight Bind n Fly acrobatic models even came close
When we duplicated the wing loading of the VAPOR on a 30 gram model- (The Vapor weighs 17 grams) we came close
The Vapor had more chord and an extremely low aspect ratio.

Thanks for all the responses. What I am trying to make is a miniture Sig Somethin Extra. PTERODACTYL, the wing tube is just a aluminum tube that goes through the center of the fuse and holds the two wing halves perpendicular to the plane ( it allows the wing to be center mounted and be able to be removed, it will also give me more roome inside of the center of the fuse to put my electronics) , the tube only extends into the first two ribs of the wing. BMatthews, I have been looking at a lot of the pictures on the internet and have seen a few from the top view and although the alerons are tapered, the wing is also slightly tapered. I was thinking of thinning down the wing some and building up the tail surfaces with sticks instead of solid material to make it lighter.

Heck, I know I am the one who asked the original question, and I thank all of you for your responses and I got quite a lesson, but probably more than I can understand. Thanks again for all the info. I will do as combatpigg suggests and get the plane under 28 oz and fly it.

It will be interesting to see how well you are able to stay under the 28 oz goal with plug in wing panels.
I usually build the fin and rudder out of sticks...but choose light 1/8" balsa sheet for the stab / elevator. I'll use 1/8" aluminum brazing rod bent into a U shape for the elevator half joiner, and just sew it to the stab to support it in the middle. Balsa saw dust soaked with thin CA works in inlay the joiner to the elevator halves.