Magician, Longer Inner Wing, Why? Good on Akromaster?

[Allen Eshleman]

The Magician has a longer inner wing. Why?  Would this be helpful on other designs?  For instance,  I am about ready to attach the wing of an Akromaster to the fuselage.  To get some space for the bellcrank assembly to be on the inside of the plane toward the ciricle and use a different bellcrank assembly than the one provided, I have considered making the inside wing a bit longer.  Would that cause any problems?

[Randy Ryan]

Allen,

Most stunt models do have a longer inner wing panel. The theory is that since the inner wing is traveling at some speed lower then the outer wing, lift is equalized. I don't know if the speed differential is really great enough to make such a thing necessary, and there are some stunters with equal span wings that seem to do just fine. No matter what, its is pretty much standard practice to make the inboard panel a bay or so longer then the outboard.

[Paul Smith]

Assuming the engine is the center of the airplane and it is flying at 60 MPH on 60' lines, the inboard wingtip is flying at 58 MPH and the outboard is flying at 62 MPH and making A LOT more lift.  This excess outboard lift will make the model roll in and you eat it.  The time-honored correction to this difference in airspeed is to offset the wing inboard so the slower wing is bigger.  

The other option is to have equal size wings and add enough tip weight to kill the excess outboard lift.  Most designers prefer the offset wing to one or two ounces of extra tip weight.

[Dick Pacini]

From what I have read here, many times, is that the time-honored traditions of longer inboard wings, engine offset and rudder offset have just about disappeared from modern stunt planes.  The issues that those practices addressed have since been solved by better design and trimming techniques.

[Dave_Trible]

Here is an area with very many ideas and most can be made or trimmed to work.  I've believed in equal span wings for many years-maybe it just seems right to me but I do like thinking I'm getting slightly greater drag on the outboard panel helping to keep the nose turned out and the lines tight.  Truth be known I usually built my Music airplanes with about 5/8" longer outboard panel for this reason which I think helped the old .46s hold the bird up there. A little more tip weight and maybe outboard flap area to keep from dropping on hard bottoms might be needed but I felt it a trade I was willing to make.  Today I still use equal span wings and feel I get a stable flat bottom as a result.  Again just one blokes way to do it.

Dave

Addendum;  although the tip weight will vary from airplane to airplane the most I ever had to carry was about 1 1/2 oz. so the difference isn't so much- maybe 1/2 oz more.  On one of my current airplanes I had to remove it all and grind away some of the weight box. 

[Randy Ryan]

Assuming the engine is the center of the airplane and it is flying at 60 MPH on 60' lines, the inboard wingtip is flying at 58 MPH and the outboard is flying at 62 MPH and making A LOT more lift.  This excess outboard lift will make the model roll in and you eat it.  The time-honored correction to this difference in airspeed is to offset the wing inboard so the slower wing is bigger.  

The other option is to have equal size wings and add enough tip weight to kill the excess outboard lift.  Most designers prefer the offset wing to one or two ounces of extra tip weight.

Paul, please quantify "A LOT" more lift. The speed differential is only about 6.6% tip to tip. Not being a wise guy, just trying to understand your reasoning.

[john e. holliday]

You are comparing two different airplanes by two different designers from different periods of model plane design.   If you are building an Akromaster, follow the instructions if it is your first one.   Both airplanes fly great if built and set up according to instructions.  Everybody has their way of flying and style.   This is where experience comes into play.   I built Dave Trible's "Shameless" and it was one terrific flying plane for me.   Have even thought of building another one, but hopefully build it much lighter.  Dave's Son-in-law now has the "Shameless" that I built and flew.   The "Shameless" had more wing outboard of the profile fuselage as well as a lot of fuselage side area behind the wing.   Made flying in wind a lot easier for me.

[proparc]

I built Dave Trible's "Shameless" and it was one terrific flying plane for me.   Have even thought of building another one, but hopefully build it much lighter.  Dave's Son-in-law now has the "Shameless" that I built and flew.   

I flew a Shameless down in Socal too. Terrific flying plane.

[Randy Ryan]

By all means, build the Acromaster per plan, its a great flying little airplane, I have a ball with mine.

[Paul Smith]

Paul, please quantify "A LOT" more lift. The speed differential is only about 6.6% tip to tip. Not being a wise guy, just trying to understand your reasoning.

With a 4-foot wing flying on 60-foot lines, the outboard tip has almost 7% more airspeed than the inboard tip.   That's A LOT more airspeed and a lot more lift.  Even comparing the center-of-lift on each wing (which is halfway between  the root and tip) the speed difference is substantial.

The idea is to start with the wing all by itself and find the true center of lift.  Then place the body on the center of lift.  The ancient designers were smart.

[Allen Eshleman]

This is a very interesting discussion. I understand the former thought about a longer inside wing.  I also see that most people today seemingly compensate by adding tip weight - something I never heard of as a teenager in the 60's.  I am now doing that, thanks to this forum and newer kits.  I also never knew anything about moving lines forward or backward. 

Actually I am building this Akromaster with several modification suggested on another thread in this forum where I asked questions. 

Mods include:

1.     I did not cut off the ends of the supplied leading and trialing edges.  Hence, I have 39 inches from wing tip to wing tip instead of the 34 inches stated on the box.  I don't know if the 34 inches was wing tip to wing tip or from one end rib to the other end rib - minus tips.

2.     The fuselage was lengthened in the back 1 inch to compensate for the McCoy 19 on the front.   (a suggestion I also got on the other thread, not the McCoy 19 - rather compensating for its weight)

3.     It will have working flaps.

4.     I used a metal 3 inch bell crank from a former plane (now in it's grave, I mean used for kindling), shortened to "2 1/2".  I would like to use the outer hole for the push rod to the flaps. 

I need a bit more room to fit the bell crank inside the ribs. 

My thought is to put the fuselage about "3/8" to the outside to make everything work smoothly and keep the push rods on the inside.

I haven't done it yet and could still change my mind.  However this is the motivation behind the idea to make the inside wing a bit longer.

Thanks again for all the info and discussion.  As you read idea here and the motivation behind it,  will the proposed off center placement of the fuselage cause any major negative problem with performance? 

It is more for convenience of building.

[Steve Helmick]

The more extreme the wing offset, the less tipweight used, the hairier the takeoffs. Close to equal spans and a significant amount of tip weight make takeoff much more consistent and safe, at the expense of a bit of weight. With side mounted engines (outboard cylinder), not a lot of tipweight is typically needed with equal span wing. More than 1" offset is always a bad idea. A half inch is plenty. 

IXNAY on that 2.5" bellcrank. Use the biggest bellcrank you can put in there, 3" minimum, 4" is better. Keep the controls slow in the plane. You want 3"+ line spacing at the handle, because less spacing yeilds less precision in your control input. If you make the controls slow enough to use 4" spacing, you're better off. This is not to suggest that you want touchy controls, but rather that if you put the right levers in the plane, you can use wider handle spacing. It's pretty simple ratios. If you use a 3" handle and 3" BC, you're at 1:1 ratio. Use about 5/8" to the pushrod hole on the BC and a 1" flap horn, then you're .625/1. That should be good. From there, on your Acromaster, you might hook the flap/elev. pushrod at 3/4" at both flap and elevator, and that would give 1:1 on the flap/elev. ratio...a good place to start, if not finish. If you can stretch the BC/Flap horn to .75" and 1.25" and the flap/elev. horns to 1", that would be even better. Make sure they're free to drop of their own weight, and seal the hingelines!  Steve

[Randy Ryan]

With a 4-foot wing flying on 60-foot lines, the outboard tip has almost 7% more airspeed than the inboard tip.   That's A LOT more airspeed and a lot more lift.  Even comparing the center-of-lift on each wing (which is halfway between  the root and tip) the speed difference is substantial.

The idea is to start with the wing all by itself and find the true center of lift.  Then place the body on the center of lift.  The ancient designers were smart.

Thanks but I'm not sold on "allot", at 55MPH the speed differential is only 3.85 MPH, and in reality the tip to tip comparison is not valid, mean cord per panel or center (true center of lift) of each panel would be more reflective since the tips basically are not really producing lift, the entire panel is. This the cuts the differential in half, or 3.5% or 1.92 MPH. I think about an aircraft flying straight and level and given a moderate rudder input. During the yaw movement the wings are flying at different speeds but generally the aircraft does not tend to roll because of this, it simply slips. Now a rapid and extreme rudder deflection will cause a roll effect, maybe even a tip stall, but not at such a relatively small differential speed.

[John Stiles]

I am building the wing on an older Ringmaster Imperial kit I got from Denny Adamisin. I noticed right away that the inner wing is one bay longer than the outer. I started to omit that extra bay, but decided against it. It remains to be seen whether the asymmetric look of the wing will outweigh the performance of the plane in flight. We shall see.

[Randy Ryan]

I am building the wing on an older Ringmaster Imperial kit I got from Denny Adamisin. I noticed right away that the inner wing is one bay longer than the outer. I started to omit that extra bay, but decided against it. It remains to be seen whether the asymmetric look of the wing will outweigh the performance of the plane in flight. We shall see.

Your Imperial will fly just fine and when it's finished the different lengths will be nearly un-noticable.

[Dave_Trible]

I am building the wing on an older Ringmaster Imperial kit I got from Denny Adamisin. I noticed right away that the inner wing is one bay longer than the outer. I started to omit that extra bay, but decided against it. It remains to be seen whether the asymmetric look of the wing will outweigh the performance of the plane in flight. We shall see.

John, I sure believe what I described on this topic above but would only apply it to new design.  If you are building some golden oldie then by all means build it as originally designed.  It will work as well as it always did and not change it to be illegal for classic or whatever.  These are more finite trim issues we discuss and shouldn't matter much to your Ringmaster. As a general principal I wouldn't change much of anything on an existing published or kitted design-it obviously worked.  Even that Acromaster.  I know that Mac .19 well.  It's not much more in weight than a muffled .15.  Shove it as far back in the mounts as you can then if you need to add that 1/2 oz of tail weight.  Other than that just build as designed.  Kit bashing and scrap box creation is how many of us learned but that's years, dollars and many junk airplanes to get your 'degree'.  Proceed at your own peril but keep grinning!!!!!

Dave

[Serge_Krauss]

A search on this or the SSW forum under my name will probably turn up at least one post addressing the unequal-wing thing, and Leonard, over there, has had a lot to say on it. My comments usually referred to a derivation Martin Hepperle formerly had on his site showing the spanwise lift bias (eccentricity) of a simple rectangular wing in circular flight. I have included a notebook scan of my scrawled summary. Essentially, I found my typical wing to have an eccentricity of about 5/8" - 3/4", but you can put in your own numbers. He used a freshman calculus method in his derivation that could be extended to tapered wings, probably with similar results, but smaller eccentricity with greater taper.

The idea here was to see where to place the fuselage on this simple wing to create equal inboard and outboard wing lifts. The problem though is that the further you place the thrust line outboard of the whole plane's lateral c.g. position, the more torque the thrust generates to yaw the nose inward along the circle. So you need tip weight to move the c.g. out to the thrust line, or you need a combination of out-thrust/rudder to rotate the thrust line back through the c.g. The tip weight though also creates inertia outboard that tends to tighten lines in maneuvers. So I think that much of the equalization of lift discussion over-simplifies the problems. Like it or not, these are engineering questions and require attention to the actual dynamics of models or some experimenting, the latter often leading the wrong way with adjustments that seem intuitively correct to the less experienced.

[Jim Thomerson]

I've flown several of the older designs, like the All American, which have excessively longer inside wings.  I like them, because I like free flight, and they permit me to fly free flight for the takeoff and getting up to speed.  I have added wing weight on the outside wing to balance the weight of the inside wing, and that helps.   

[Randy Ryan]

I've flown several of the older designs, like the All American, which have excessively longer inside wings.  I like them, because I like free flight, and they permit me to fly free flight for the takeoff and getting up to speed.  I have added wing weight on the outside wing to balance the weight of the inside wing, and that helps.   

HAHAHAH Jim, good one, I'm with you!!!

[jim gilmore]

Just a question here....
If a airplane has a truly symmetrical airfoil and zero wing and zero incidence at the stab.
How much lift does it produce in level flight ?
Or we could use a flat wing with no airfoil to speak of ?

[Jim Thomerson]

An airplane with a symmetrical or flat wing produces lift equal to its weight in level flight.  It does this by flying at a slight positive angle of attack.  I've seen figures on this and it is a half a degree or so for a stunt airplane.  For some reason this is easier to see when a stunt airplane is inverted vs upright.   

[jim gilmore]

SO we are assuming that to do a perfect wingover we must be appling a little down elevator to counter the excessive lift from the slight Paoa?

[Tim Wescott]

SO we are assuming that to do a perfect wingover we must be appling a little down elevator to counter the excessive lift from the slight Paoa?

You can assume anything you want.  I assume that in order to fly level I have to apply a slight bit of up elevator, in order to fly inverted I have to apply a slight bit of down, and in order to fly straight overhead I need to hold neutral elevator.

Of course, my assumption isn't defining what I mean by "apply".  And if by "apply" I mean "apply a bit of force" then the above statement ignores any trim force from the way I've dialed in the airframe.

You do have to hold less 'up' (or more 'down') on the vertical lines than the upright horizontals, and more yet when inverted -- this was a big focus of my practicing last fall as I worked to move from beginner to intermediate -- you could see the problem with bias in all my square loops.

[phil c]

It's a real pain to reinvent the wheel every few years.  "Wild Bill" Netzebands articles and columns in the Model Airplane News and American Modeler(in conjunction with Pete Soule and others) worked out all these problems at an engineering level in detail that is good enough for model airplane work.

For example, the effect of flight radius on inboard and outboard wings integrates out to a fairly simple equation that depends on the flight radus of the inboard wing MAC and the outboard wing MAC.  It turns out that is all you need and the effective MAC of the wing depends just on the length of the lines and the shape and span of the wing.  For a 48 in. wing the offset works out to about .45 in.  For a 60 in. span it is a bit more as Serge says, about .65 in. or so.  A practical effect of this is that if you build a full fuselage plane the thrustline is automatically set inboard of the center of lift and drag.  Just add enough tipweight to keep the wing level in maneuvers.  The Old Time Debolt All American had the inboard wing ~2.5in. longer than the outboard wing.  It is really tricky to take off because of all the inboard drag.

Another potential problem- if you build a profile version of the plane the thickness of the fuselage takes away most of the offset between the thrustline and the effective MAC.  Makes the plane harder to trim and harder to fly.  Adding outthrust can bring things back into balance, but you have to make sure the thrust line actually is directed more inboard.  Taking 1/8 in. aluminum and machining it into 1.5 in. long wedges for offset often doesn't do much.  The thick wedge moves the thrustline outboard and the angle move it back inboard with little change overall change.  Cutting a 3/32 in./1.5 in. wedge out of the outboard side of the motor mounts actually moves the thrustline back where it is on a full fuselage plane.

So go back and read Wild Bill's stuff.  He covers all the basics of producing a built from scratch plane complete with calculating forces on the pushrods so they don't collapse, control geometry, figuring static stability, getting the tip weight right for both takeoff and in flight, and so on.

Phil C

[Brett Buck]

Just a question here....
If a airplane has a truly symmetrical airfoil and zero wing and zero incidence at the stab.
How much lift does it produce in level flight ?

 The lift in level flight = the weight of the airplane. This requires some positive angle of attack, which you can figure out by using the wing loading and the lift equation, and assuming that the Cl is about 0.1 per degree. The elevator position is whatever it needs to be to hold that AoA.
 
   Brett

[Howard Rush]

For some reason this is easier to see when a stunt airplane is inverted vs upright.

That reason would be that the airplane isn't trimmed right.

[Howard Rush]

I once made some combat planes with longer outside wings, balanced with tip weight so they'd operate sorta normally in maneuvers.   They flew their free flight after the engine quit.  They'd just wander around inside the circle.

[john e. holliday]

Not enough wing tip weight.

[George]

...I have considered making the inside wing a bit longer.  Would that cause any problems?

It should not cause problems but is not necessary on such a small plane. My two have equal length wings.

George

[Allen Eshleman]

After reading all the above and having to work with the bellcrank as I have it installed,  I will definitely place the fuselage about the thickness of itself - 3/8 inch to the outside so that I can run the pushrod on the inside.  I have not yet put the wing in the fuselage but I'm several steps closer than when I started this thread.  I have since installed the bellcrank and the leadout lines.  However, I may have to redo the eyelets at the wing tip.  I also have to put the planking on the wing.  Because of a broken rib in that area,  I have to do some fixing there.  Thanks so much for all the advice and information.  I have though of doing a thread about all that I have learned on Stunthanger.  For now, I just need to put it to use.

[phil c]

I once made some combat planes with longer outside wings, balanced with tip weight so they'd operate sorta normally in maneuvers.   They flew their free flight after the engine quit.  They'd just wander around inside the circle.

Not sure what you did right there Howard.  Most of the top F2D planes have a larger outboard wing.  They usually do it with ~1/4 in. wider outboard tip.  Sounds like the leadouts were too far forward.