If you have two flapless wings that both produce the same maximum lift (I assume that would be in a square corner), one has an 18% airfoil and less wing area, the other a 14% airfoil (same approximate shape, just thinner) and more wing area, would they both generate the same total drag (including all categories of drag that apply to a wing), or would one produce more drag than the other?

Thanks.

That's a good question, and Bob Hunt has a Stunt News article written by Igor explaining it.  Either you or I could use XFoil to figure out the aero part.  I'll see if I can do it tomorrow.  Then there's the wing weight, but all that is calculable.  If it's for a stunt plane, there are a couple other considerations, both of which favor the thicker wing for stunt:

The thinner wing will be slapped around by turbulence more than the thicker wing because of its lighter wing loading.

The thinner wing will have a higher ratio of drag in maneuvers to drag in level flight than the thicker wing.

For combat planes, which have different design requirements than stunt planes, the optimal thickness seems to be about halfway between those.  `

This is from Ted Fancher and does at least address some of the questions here:

As I mentioned in the Doctor article in Stunt News, flaps pretty much only do a few things. First and most importantly, by changing the airfoil from an uncambered section to a cambered one they inherently increase the lift per unit of total area (assuming the gap between the main plane and the flap isn't so excessive as to allow the value of the flaps to be largely defeated); second, they increase the induced drag and, therefore, the total drag (induced plus all others ); third, they produce a negative pitching moment (the cambered wing which results from deflected flaps has a natural desire to rotate about itself in the direction opposite to the camber).

With the above understanding and the realization that turning high g maneuvers in the pitch axis requires abundant lift, it becomes obvious that if we eliminate the flaps we need to achieve the necessary lift in another manner. Lift produced is the result of air density (we've no control over that), surface area (we can make a wing any size we wish), the effectiveness of the airfoil (co-efficient of lift), angle of attack and the wing planform (aspect ratio), and, importantly, the square of the airspeed.


Thus, if we eliminate the use of an airfoil which can be variously cambered (via flap deflection) we must re-manage the other aspects to regain the necessary lift. We can; A. increase the area thus reducing the wing loading; B. devise a more efficient airfoil for the unflapped configuration; C. utilize a more efficient planform (a higher aspect ratio develops more lift at a lower angle of attack and less drag than does a lower aspect ratio of the same area. Both can produce the same approximate maximum lift but the lower aspect ratio will require a higher angle of attack and produce more drag in doing so.); D. fly faster.

Thus, as has been suggested, it is factually obvious that a very lightly loaded, high aspect ratio flapless airplane flown at very high speeds and with sufficient tail authority can indeed turn in the pitch axis at very high rates…certainly higher than a slower, higher loaded, low aspect ratio ship encumbered by an airfoil which fights the very thought of a tight pitching maneuver in opposition to its natural desire. So, “Yup” a well-designed combat ship can turn on a dime…and does every day.

Despite the suggestion in the rule book that we are supposed to be flying five foot radius corners, the fact are that we both don’t and (before the nay-sayers jump on the apparent dichotomy) can’t do so in a competitive fashion in a stunt pattern. The reason is simple. We simply don’t have the reflexes to do so in a precise fashion. Thus, the event has evolved into the development of aircraft which can turn reasonably “tightly” but can do so with precision and consistency. Heck, even nose heavy toads have won the Nats by flying “reasonably” tightly and very consistently.

Now, where does the foregoing leave us in terms of designing a flapless ship competitive enough to compete at the highest levels?

At first blush it would seem that we need only make the wing big enough to produce the lift we need and forget about the flaps. This isn’t far wrong, actually. Put a decent airfoil on a large enough wing (keep the leading edge reasonably blunt and the high point fairly well forward), provide decent tail authority and an outstanding engine run (<80% percent of ANY otherwise competitive package>) and you can fly pretty dang good patterns. The basic DOCTOR can fly 500 points plus flight after flight in the hands of a good pilot when the engine runs right (sometimes a problem).

However, conditions are seldom perfect and it is under less than perfect conditions that the shortcoming of the flapless ship begin to manifest themselves. Once again, we have to look at what exactly flaps do which we will regret not having under those conditions. In addition, what negative things happen when we pursue high lift through simply enlarging the area of the wing?

Two of the answers go hand in hand. One of the predictable bad conditions we encounter is high winds. High winds make the airplane accelerate in consecutive maneuvers. The greater the area (lighter the wing loading) the greater the acceleration. Thus our flapped ship with its greater drag for a given amount of lift will resist acceleration better. The unflapped ship will, conversely, make matters worse because of its larger “sail” area. It will accelerate at a much greater rate. In addition, pitch rate for a given control deflection will vary more since the lift produced by the tail increases as the square of speed also, ergo, the tail gets more effective as the ship accelerates.

There is, however, a flip side to this coin. In calm air (another dreaded competition condition) the unflapped ship has it all over the flapped one in that wake turbulence is significantly less without flaps (especially flaps deflected large amounts for unnecessary reasons) thus reducing the hazard of turbulence encounters and simplifying the flyer’s task by minimizing the need to maneuver in and out to try to avoid the wake. This advantage comes very near worth putting up with the high wind disadvantage above.

It should be noted that other means are now available to help control the wind-up in the wind more effectively than just a few short years ago. High RPM low pitch systems are natural speed controllers and go a long way toward harnessing the wind up and making it controllable. Tuned pipes are one way to go but are handicapped by the high weight involved. I think the current development of four strokes for our purposes should be high on the “must check out” list for anyone seriously contemplating a flapless competition ship. FYI, the DOCTOR is now flying with an OS Surpass .40 and as the system is refined is producing the best combination yet utilized…including a very good Aero Tiger .36. So far this combination includes a 10 X 4 Tornado three blade, conventional 10 percent Sig fuel, and a slightly choked down venturi. Delightful to fly.

Some have postulated that flapless ships by definition have to turn body angle “beyond” the desired pitch track because the symmetrical airfoil must have a positive angle of attack to produce lift. This is technically correct but my experience has been that given adequately low wing loading and enough speed the phenomenon is unobservable.

The center of Gravity is pretty much cast in concrete. Flapless ships pretty much end up at 15% of the average chord. (15% MAC for the technically oriented). With the Aerodynamic Center of a symmetrical wing pretty much fixed at 25% MAC this provides a modest “tension” between the lift and the CG which provides the feedback necessary to the controls for precision changes of direction. The CG can be moved further aft but begins to feel sensitive and tracking in maneuvers may suffer. Further forward and the the arm between lift and weight makes for excessive differences in required control input uphill versus downhill.

Tails needn’t be as large as for flapped ships since they don’t need to overcome the negative pitching moment of the cambered wing (deflected flaps) in maneuvers. Fifteen percent of the wing’s area is probably a minimum and anything over 20% probably more than necessary. Either will provide adequate stability margin for an easy handling ship. I think the current practice of low aspect ratio tails for stability in turns is probably still valid. I’d start with about 4.5 to one.

Modestly higher aspect ratios (for the wing) are probably desirable, say 5.2 to 5.5 to one. The greater the aspect ratio (span/average chord) the less the angle of attack necessary for a given lift requirement. This would mean; 1. a smaller wing area is necessary for a given weight, and; 2. the reduced necessary angle of attack required in hard corners would result in less of the theoretical need for body angles in excess of the track change desired, i.e. it wouldn’t seem to have turned “inside” the desired track.

The wing should be tapered so as to approximate the “ideal” elliptical lift distribution. A simple taper should suffice with probably a minimum of a 75% tip/root ratio and a minimum of 65-70%. Chords at the tip of less than nine inches or so are likely to be less effective than they should be. I’m guessing that the taper should be distributed between the leading and trailing edges so as to result in a quarter chord line perpendicular to the fuse. I’m really open on this and would be interested in divergent points of view. I doubt very much that a swept forward quarter chord is desirable but a slightly swept one could be stabilizing in roll.

The resulting airplane should be flown slightly faster than an equivalent flapped ship, using a power train which produces airspeeds as consistent as possible in all attitudes. The compromise of a slightly higher speed and the therefore slightly smaller useable wing area should produce a very flyable airplane even under adverse conditions.

Anything else….hmmm? I’ll have to think about it.

Ted

A lot of that is wrong.  Ted knows a lot about stunt, but he has a habit of making up theory to explain it. 

Expand?

The only data points I have is that the Sig Skyray has a 5:1 aspect ratio and a 18% wing, while the Fright Streak has a somewhat thinner wing (15%?) and a 4:1 aspect ratio -- and the Skyray, in particular, seems to be well-regarded as a practice plane for beginners.

So, do you think that these planes could be -- size for size -- significantly improved?

A lot of that is wrong.  Well, Howard,  I guess if you say it's wrong it must be since, as you frequently point out, you're smarter than the rest of us all put together.

Ted knows a lot about stunt, Thanks, I guess, for the back handed compliment.
but he has a habit of making up theory to explain it.  This--if I may quote a much smarter man-"is [just plain] wrong."

 

Howard,

If you had been sitting over my shoulder for the last fifty odd years or so (you weren't...I checked)  you would have seen that everything I've done in terms of stunt model design since I was a teenager was specifically intended to address things I'd learned about flying machines of every conceivable size from hand launched gliders and indoor stuff to full size Boeing 747s and most everything in between.  Every such design was intended to utilize what I had learned to make it better than the one that preceded it.

No I can't punch a calculator, point at the results and "declare" to you or anyone else that it means anything.  I have, however, experienced things in aviation, read about the principles involved, witnessed how they affected the vehicles I fly (whether in the cockpit and/or standing on the ground with a handle in my hand).  I realize that engineers feel that such "experiential" knowledge is worthless but, believe it or not, those who have experienced such things don't always agree with you.

What I've experienced--combined with a modest amount of intelligent understanding of aerodynamics and consideration of what I thought could have a positive effect on the performance of those aircraft--I've utilized to design and fly aircraft that are more than competent and, in the case of stunt models, competitive with pretty much anything else that people have designed, built and flown regardless of their pedigree or learned degrees.   I may be "wrong" but all that wrongness has accumulated a lot of plastic hardware over the last five or six decades flying those poorly conceived craft about one flight for every hundred you fly and every several hundred that Paul, David, Orestes and others who "pound 'em in" fly.  I guess I must have fallen into a string of dumb luck.

I'm not for a minute saying any "tweaks on George's Nobler" I may have come up with were magic breakthroughs; but neither were any of them dismal failures.  Every stunt ship I've taken from pencil, paper and eraser to the competition circle was not only built to fly competitively but also to experiment with things that I believed (due to my real world exposure to things that fly) might have a positive effect on the performance of the stunt pattern. Not once in my stunt flying life did I simply build an airplane, find it somehow "magic" and "make up a theory" to support the magic.  First of all, there never was "magic".  Most of the airplanes I designed and competed with were competent but none were magic.  That is why I continued to design more airplanes trying out different things I felt might make them better.  (It is also why I bemoan the likely takeover of our event by buy and fly adherents who will declare a "Shark" or something similar to be as good as it gets and, therefore, stop trying to make something a tiny bit better since doing so would take some thought and effort.) 

You might also want to read some of my articles and note that I regularly make it clear that the sources of many of the things I espouse came not from me but from the mind of or are the fruit of the labor of others...not the least recipient of which has been your very successful flying buddy.  I have willingly over the years (and with no small amount of effort) shared what I believe to be valuable information for use by others who share my fascination with stunt but have "never" pretended to be the "oracle" from which those thoughts were borne anew.  Nobody--wherever or from whomever those thoughts came from--is/was forced to either read it or utilize it.  As a result I'm not inclined to apologize for having taken the time for sharing.  I think most of it was of more value to budding stunt fliers than "...most of (what Ted said) is wrong."


IOW, theory (right or wrong from my point of view, yours or anyone else's) has always preceded everything I've done with with respect to stunt model design.  I make no apology for developing some of those theories on my own.  The evidence of their pragmatic value is reasonably substantial even if not substantiated to multiple decimal places.


Bottom line, Howard, if it makes you feel good to think of Ted as a backwoods lout who throws balsa wood and hot stuff up against the wall to see what sticks, go right ahead.  But if you think no thought, or study, or hands on experience, or experimentation or intelligence with regard to what makes a stunt ship work well went into their development you're just flat "wrong"...once again, to quote.

If you think your note pissed me off, I expect you're right.

Ted

For stunt.  I'm interested in reading the article by Igor the Brilliant.  Do you recall the date of the SN issue?

I don't think it's been published yet.  I got a peek at it. 

This question came up when I flew a Teosawki for the first time.  (I know you object to planes of this type, and your objections were addressed in the Sakitumi: scratch or kit built with stunt wing construction replacing the combat-style wing, a very attractive fuselage shape and conventional finish---all weighing in at about the same weight as a Teosawki, due to the use of 4 lb wood.  There is a full-fuselage version in the queue with the same weight goal, thus eliminating the objection to profiles).

The first time I flew the Teo, I was amazed that such a thin wing could fly so well.  All the thin wings I had flown before had much higher wing loadings, and I believed that thinner wings can't fly stunt at all.  The feel of the Teo was different from Flight Streaks and Skyrays (I had trouble getting several Skyrays to track in level flight*): graceful and effortless are the best words I can think of to describe it.  The very large TVC probably had a lot to do with it, as well as the larger overall size of the Teo and its engine (LA46).  And of course these are subjective impressions, so do not constitute evidence. 

*Possibly a neurological limitation on my part since inverted level was even less stable than upright level.

I became curious whether the thin, double-tapered Teo wing was part of the successful formula, or whether a scaled-to-match total lift 18% airfoil would perform as well (or maybe better).  Also constant chord or tapered.  I had no idea how to calculate the area required for an 18 percenter to generate equivalent lift.  Perhaps XFoil can answer that question.

I guess this is the final rock v. hard place for flapless planes.  The light loading is needed for cornering performance, but leaves the plane vulnerable to wind and turbulence.  Not that this is anything like news!  I'm just attracted to flapless planes for some unknown reason (nostalgia?) and ways to optimitize their performance interest me.
 

My guess is that an 18% airfoil on that airplane would handle the same, but could turn tighter or be built heavier.  I regret that I haven't done any figuring yet.  I've been trying to finish a stunt plane.  I'll also guess that the main reason the Teosawki flies well is because it has a long tail (disregard this guess if it doesn't).  I slapped together an airplane to test fuel systems by putting a couple of half-inch plywood disks on the front of an F2D model and a long aluminum tube for a fuselage, and it flew pretty good stunt.

Howard,
I appreciate your taking time to respond to each of the points in my posts on this topic, especially in the middle of a refinishing project.  That level of thorough com is fairly rare.  Ted is thorough too. 

Your comments about refinishing remind me of the old joke about a guy who is banging his head against the side of a building.  A woman walks up to him and says, "Sir, why are you banging your head against the side of a building?"  The guy replies, "Because it feels so good when I stop."  Think of how good it will feel to have your newly refinished beauty ready to show off.  Will you grace us with pictures?  How about taking bets on base color.  $10 on orange for me.

This morning James Aron of my airplane painters' support group recommended Isocyanate Death Paint clear coat as a way out of one problem I'm having with the finish.  If I survive spraying that, I'll eventually post a picture.  Orange is involved, although I keep sanding through the orange.

I still haven't answered your original question.

Perhaps that is Mr. Aron's ever-so-cunning method for eliminating some of his Nats competition.  Did he perchance offer to sell you a special respirator designed for Death Paint at an incredible bargain price? 

The original question can wait. 

.....More importantly, two other factors play at least as big a role.  One thing I've found over the years that the quickest, lightest, easiest way to improve performance is to add 10-15% to the span.  Putting 3 in wide tips on a 48 in. plane will make a dramatic difference in performance.  With a fairly highly tapered wing the motor doesn't even notice the extra area, but the plane does everything better.....

Phil,
Is this improvement simply a function of increased wing area?

BTW, I notice that you're flying Expert.  Just out of curiosity, what is your weapon of choice?  I/C or electric?

Phil,
How would the performance of the G-VI change if you switched to an 11" prop?

If you have two flapless wings that both produce the same maximum lift (I assume that would be in a square corner), one has an 18% airfoil and less wing area, the other a 14% airfoil (same approximate shape, just thinner) and more wing area, would they both generate the same total drag (including all categories of drag that apply to a wing), or would one produce more drag than the other?

Thanks.

Well, given a symmetrical section on a flapless wing, the wing area would be the same. You'll find the slope of the Cl vs AoA for the 0014 and 0018 airfoils are essentially the same. So for a given angle of attack the thickness won't affect the lift coefficient, and thus the required area would be unchanged.


Now, if the airfoil was cambered, that's a whole 'nuther deal. The camber line IS important. Look at an indoor microfilm model. The thickness is effectively zero. But the camber line is what's important when calculating required wing area since it ( camber ) shifts the lift curve to the left on a plot of Cl cs AoA.

Next, compare the curve of drag coefficient vs AoA for the two airfoils and you'll see there is no discernible drag penalty for the thicker wing. But it's easier to build, so go for it. You will only pay a small weight penalty.

Well, given a symmetrical section on a flapless wing, the wing area would be the same. You'll find the slope of the Cl vs AoA for the 0014 and 0018 airfoils are essentially the same. So for a given angle of attack the thickness won't affect the lift coefficient, and thus the required area would be unchanged.

I can't be sure exactly what Kim meant, but I think he meant to start out with two wings, of different thickness, with area adjusted so that the lift right at the onset of stall is the same.  Not (I hope) that he thinks that the CL vs. pitch slope is different from one to the other.

If that's the case then the thicker wing could have less area.  And then his question kind of makes sense, except for the part where he's ignoring everything else that's going on.

It increases the incidence of the tail. It also creates a pitching moment contribution from the fuselage as show by Munk and later work by Multhropp. Further, it reduces the apparent mass effects of the displaced air as the aircraft rotates. This change in downwash angle can be remarkably high. So given the tail volume coefficient and horizontal tail efficiency ( which can be greater than unity on a stunt ship due to the propeller slipstream) the flap deflection's effect on the tail's  positive contribution to the aircrafts overall pitching moment combined with the introduction of a positive pitching moment from the fuselage - can be higher than the wing's increase in negative moment due to the increase in camber.

For a stunt plane, the sign of pitching moment from flaps (for the whole airplane) depends on the configuration.  A local guy told me that his elevator linkage disconnected during a wingover.  He attempted to recover by giving full control, first one way and then the other.  The airplane went straight into the ground.  A change in CG or tail geometry could have caused it to turn either the same direction the elevator would have turned or the other direction. 

Nice theory Chuck, but beside that theory I have some real experience ... and that tells me that flapped models go to corner signifficantly harder than flapeless. Also CG for flapped model must be much back 

But I am open mind, you can easily convince us if you can show us well flying stunter with fixed elevator :- ))))))

Ahhh, but now we are in "stick free response" which differs from ""stick fixed response". Different things. 


With the elevator free to seek it's happy place the aircraft response is changed and the aircraft is free to find its neutral point. Think about it...free elevator- you defelct the flaps down, the downwash will tend to push the free-floating elevator down! In a very loose sense, it acts like a trim tab for the stab in that condition. When a trim tab goes down , the hinged control surface moves in the opposite direction. Same with an airplane where  the CG is the "hinge".

Yep, bad example.  It would be interesting to determine the net pitching moment of a stunter with fixed elevator.  I suspect we are both too lazy to calculate it.  An experiment could be conducted over tall grass if anybody wants to donate an airplane for it. 

Canards work.  They have essentially that configuration.  I wonder what happened to Bob Hunt's canard?

Some of the early CL models used flaps instead of elevator to try to dodge Jim Walker's patents.  They weren't very popular.  From that I'm going to presume that they worked, but not terribly well.

    My Dad had one. He said it would fly, but had minimal control and you would never dream of looping it.

     Brett

Wake turbulence is a function of induced drag.

it is the prop that causes a huge amount of wake turbulence

It is easy to extend (beside the fact that induced drag is function of lift and prop makes part of the lift and therefore directly makes wake turbulence) ... the induced drag is function of speed ^2 ... and therefore of available power ... so if the large prop can recharge energy lost in that maneuver, it is directly source of that turbulence :- ))) ... not to mention that if model slows down in that maneuver, it will come back later, when the turbulence is little slower

and if someone does not believe that statement with flaps, I recommend to try flapeless indoors with props = 1/3 of span flying in dead calm gym ... I never had problems with wake turbulence :- )))) 

Howard said "Wake turbulence is a function of induced drag.  For a given speed and loop radius, a plane with a lighter span loading will have less wake turbulence, with or without flaps."

I forgot about the prop when I said that.  I reckon the prop wake could be calculated-- at least how much energy it puts into the air in a corner. 

HI Howard

Paul Walker told me it is the prop that causes a huge amount of wake turbulence, do you have any info to share about  this?

He has said that he has less problem with an 11.3"-diameter prop in still air than with a bigger prop.  My guess as to the mechanism was that the higher speed of the small prop's wake blows its wake toward the outside of the maneuver.  This wouldn't affect me, but may be of benefit to you guys who put your consecutive maneuvers in the same place.  Igor probably has a better explanation.  I wonder if prop size has the same effect with electric power.

It is interesting, We had a talk about this once ,and Paul said that he flew his ship with a very tiny prop one time, maybe a 9 or 10 inch diameter in dead calm, he said that he could just stand flat footed and do consecutive maneuvers, over and over without any problems from turbulence, this is one thing that convinced him to go to the smaller props, of course that is seemingly out the window now, he is using much larger diameter ones.

Randy

  I think that was a 9-4 on a 45FSR at around 15000 rpm, at Reno.

   Brett

Chck, 2 notes:

1/ what means 17% reduction? I think Paul says that smaller prop makes less turbulence, so looks like your calculations show something just opposite :- )))

2/ you say larger prop is more efficient, but if efficiency means the same what I learned in my courses of physics, mens outpup power / input power, then if the plane flies the same speed and therefore it needs the same power, and you say larger prop is more efficient, then it must need less input power right? so you mean if I replace my 11" prop by larger 12" I will need smaller battery in my model? ... great I must try it :- ))))

First, the effect of tip losses are less on a larger prop ( at the same thrust as a smaller one)  because either the pitch is less or the angular velocity is reduced or a combination of both. (For example, we could go from a 10" to an 11" and reduce the pitch, or we can use an 11" at the same pitch but a lower angular velocity.) In other words, the percentage of tip loss to to total losses decreases with diameter up to a point.

Every prop has some optimum, so expression that larger prop is more efficient is someow "not so accurate" :- ))) it could be better ans also worse, depending on conditions.

My example shows you fact that since we fly our models with relatively large props prepared to make lot of thrust when necessary (when slowed), so somewhere at very high advance ratio, means on descending part in attached picture, larger prop simply works with worse efficiency becuase it will push it to even higher advance ratio.

Every prop has some optimum, so expression that larger prop is more efficient is someow "not so accurate" :- ))) it could be better ans also worse, depending on conditions.

My example shows you fact that since we fly our models with relatively large props prepared to make lot of thrust when necessary (when slowed), so somewhere at very high advance ratio, means on descending part in attached picture, larger prop simply works with worse efficiency becuase it will push it to even higher advance ratio.

    The failing that we often have with this discussion is that people are used to assuming that "efficient" = "better" when in stunt it's arguably the opposite.

    I gave up trying to have sensible discussions about power, thrust, and props on SSW in about 2003! It's impossible because there are so many ingrained notions about it, and nobody likes the actual definition of power.

    Brett

He he, I hear ya.

a propeller's Power Coefficient, Thrust Coefficient, Speed-Power Coefficient and Activity Factor are sometimes hard things to grasp, but essential to understanding and predicting propeller performance. When you get into dimensionless numbers with the 5th root...takes a few beers to absorb it all. That, and the formulas fall apart at low velocities, because they predict infinite thrust when the velocity is zero. We know that ain't true.
 
Actually, the Speed-Power Coefficient is the one that can predict how diameter affects performance, but the math is probably beyond the nerd-o-meter quotient for a forum such as this so I've stayed away from it and tried to simplify it and talk in terms of force, which Newton showed us is the time rate change of momentum.

If anyone is really interested though, a great resource is the Hamilton Standard Rept. PDB 6101A, Generalized Method of Propeller Performance Estimation

  There's a famous chart within it of Power Coefficient as a function of Advance Ratio that ties it all together. Genius.  

It's from the 60's and my well-worn original copy was handed down to me by a mentor. One thing to note: when using it you need to take a step back and reduce efficiency for a model's prop by about 20 percent because of the thickness of our props compared to full-size aircraft. That, and we use fixed-pitch props which makes it a little more complicated. Not overly so, but easy to forget sometimes as you bash the equations.

Thankfully, we design jets and fans these day, making thrust calcs a lot easier!

    The problem we always seem to run into is that even if we knew the performance and could predict it perfectly in every regard in an engineering sense, no one has ever defined why one prop is bette" than another in terms of getting better stunt scores. Plenty of obvious potential measures of goodness are demonstrably not the correct ones, but that doesn't seem to change anybody's mind. Static thrust and diameter being the two most obvious candidates.


  BTW, Chuck I was not particularly referring to you above!  Just a general comment on this sort of thread.

   Brett
 

I built a model in spring without having read this discussion which I think relates directly to this discussion. The model flew extremely well(calm and windy weather) when the motor behaved so I figured I'd post my findings here.
You can see the picture of the model in this post: http://stunthanger.com/smf/index.php?topic=29019.0

Wing

Wing root chord	11.00
Wing tip chord	6.00
Wingspan (in.)	39.50
MAC (in.)	8.50
Area (sq. in.)	335.75
A/R	4.65

Stab & Elevator

Stab root chord	2 7/8
Stab tip chord	1 1/2
Elevator root chord	2 1/4
Elevator tip chord	1 1/4
Span	15.2500
Area	60.0469
Elevator/Stab %	44%
Stab/Wing %	18%

      
Other dimensions

Spinner backplate to LE	7  3/16
Cylinder centerline to LE	5 5/8
Wing TE to Stab LE	9 5/8
Motor weight (oz.)	6.7

            

In addition, I think it is also worth noting that the leading and trailing edge have the same sweep angle.


The model started with a smaller stab(12.5" span) which gave it an area 16% of the wing area. The model flew just like a any other flapless design: soft corners and if pushed, it would slow down in corners and stall. After increasing the span of the tail to give me 18% ratio, the model became very easy to steer and it stopped stalling.This proves the point Ted made earlier:

Tails needn’t be as large as for flapped ships since they don’t need to overcome the negative pitching moment of the cambered wing (deflected flaps) in maneuvers. Fifteen percent of the wing’s area is probably a minimum and anything over 20% probably more than necessary. Either will provide adequate stability margin for an easy handling ship. I think the current practice of low aspect ratio tails for stability in turns is probably still valid. I’d start with about 4.5 to one.

Unfortunately I was not able to confirm or deny the aspect ratio statement:

Modestly higher aspect ratios (for the wing) are probably desirable, say 5.2 to 5.5 to one. The greater the aspect ratio (span/average chord) the less the angle of attack necessary for a given lift requirement. This would mean; 1. a smaller wing area is necessary for a given weight, and; 2. the reduced necessary angle of attack required in hard corners would result in less of the theoretical need for body angles in excess of the track change desired, i.e. it wouldn’t seem to have turned “inside” the desired track.

The model has a 4.65 aspect ratio and did not exhibit any unusual behavior that you describe.

The wing should be tapered so as to approximate the “ideal” elliptical lift distribution. A simple taper should suffice with probably a minimum of a 75% tip/root ratio and a minimum of 65-70%. Chords at the tip of less than nine inches or so are likely to be less effective than they should be. I’m guessing that the taper should be distributed between the leading and trailing edges so as to result in a quarter chord line perpendicular to the fuse. I’m really open on this and would be interested in divergent points of view. I doubt very much that a swept forward quarter chord is desirable but a slightly swept one could be stabilizing in roll.

My model had 55% ratio which seemed to work well in all but extreme situations such as panic yanking on controls. For my next experiment I'll shoot for 70% but am concerned that increased wing span will cause the model to wind up in high winds.

Steven,
Very sharp looking design.  Reminds me of the Super Whipsaw, which was a favor of mine back in the days of youth.