outboard wing vs inboard wing

What was the purpose of having a longer inboard wing panel than the outboard wing panel on older control line models. I am doing all kinds of mods to this airplane and one more is not going to be a problem. I want to know why some planes were designed like this? I am wondering if I should make the wing panels the same length?.

The earlier planes like ringmasters, voodoo were built with longer inboard wing to compensate for control line weight. Instead of adding more weight on out board wing builder felt a longer inboard wing will give more lift. With inprovement of engine power, longer inboard wing were slowly done away with. balsa4me.

>The earlier planes like ringmasters, voodoo were built with
>longer inboard wing to compensate for control line weight.

Ringmasters have equal panels. Currell

>What was the purpose of having a longer inboard wing panel
>than the outboard wing panel on older control line models. I
>am doing all kinds of mods to this airplane and one more is
>not going to be a problem. I want to know why some planes
>were designed like this?

Because the inboard wing flies more slowly, since it's closer to the center of the circle. It's only a little, but it's detectable. An asymmetry of about 1/2-3/4" is about what's needed to compensate for this. It's not really critical, but you can save yourself some tipweight if you use it.

Earlier airplanes had more asymmetry than this, sometimes up to 3". This is way too much and can cause problems unless you make some accomodations for it.

Most airplanes today have somewhere in the 3/4" range, some more, some less. Some none at all, too, which is generally OK, but expect to have a disproportionate amount of tipweight, like 3 or more oz on a 60-sized plane.

> I am wondering if I should make
>the wing panels the same length?.

Probably doesn't matter too much. 3/4" won't hurt anything on a 35-40 sized airplane. . What airplane is it?

It geometrically and mathamatically flies a different sized arch to the outboard wing.

You can work it out using an equation, i dont know it off the top of my head but if anyone wants it I can get it ( or someone would know )

And the times ive worked it out.. it equates to exactly what brett is saying.. 1/2 - 3/4 NO MORE!

Quote PJ - "Outside Triangles? "

Ask the Barry's (Dale and Derek) They unwind their lines after a flight with this maneuver . . . looks good too!

Points down, I hope!

[photo not recovered: 3e69bb3870f12ad5.jpg]

"If the facts do not conform to the theory, they must be disposed of." - Maier's Law

The points are down. That is the only way.

This is a Nobler ARF

Hi

I think asymetry is more to do with where the thrust line is.

If you consider the lift component alone, then what has been
written above is correct. The faster outer wing produces more
lift than the slower inner wing. The effect of this is simply
to move the centre of lift outboard by a small amount.
For a 98 cm (38.5 in)span on 15.9m (52 foot) lines I calculate
the centre of lift to be about 8 mm (5/16 in) outboard of the wings
geometric centre. In practice, the lift center will be close to
this position. The model should be trimmed so the CG is on the
lift centre in the spanwise direction. This can be done initially
by adding 1/2 the line weight to the inner wing and balast to the
outer wing but must be fine tuned in flight by watching the roll
tendency of the plane and adjusting tip weight appropriatly.

But so far, this does not address the question of asyemetry. We can
have a symetric plane or an asymetric plane, both require the same
ouboard CG offset to fly without rolling. Fuselage position is
relatively unimportant (within reason) to this aspect of flight.

There are different arguments then can be made in relation to thrust
line. If the thrust line is through the CG, the plane will pull away straight on release. If it is outboard of CG, the plane will tend to curve into the circle, if it is inboad of CG, the plane will tend to pull out as it acceletates. The drag of the aircraft (without lines) will tend to be close to the centre of lift. Having the thrust, CG
and drag aligned ought to keep our forces ballanced through varying
conditions of speed and power. But we have been forgetting line
drag. Line drag being compensated by LO position is not a consistant
ballance through all speeds because the drag coefficient (Cd) on
the lines increases at lower speeds so the ratio of line drag : centrafugal force is somewhat greater at lower speeds which tends to yaw the plane in. An argument can be made for bringing the thrust
line inboard of the CG because at lower air speeds, the engine puts more of it's power into thrust while at high air speed, most power
goes into prop drag. This means that with an inboard thrust line,
there is a greater moment between the drag and thrust force couple
that can maintain or increase yaw. This inboard thrust line can be
cahieved through side thrust or fuselage placement. Therefore
there an asymetrical plane would require more sid thrust than a symetrical plane to achieve the same yawing flight characteristics.

Ken, you can effectively "trim" that thrust line by angular engine offset (I would better call it effective engine moment or effective engine offset).

>Ken, you can effectively "trim" that thrust line by angular
>engine offset (I would better call it effective engine
>moment or effective engine offset).

I thought that is what I said with more words.

I just wanted to point out: if you miss the proper thrust line at design or building, you can still solve it by engine offset AFTER building - at trimming.

Ken,

>Line drag being compensated by LO position is not a
>consistant ballance through all speeds because the drag coefficient
>(Cd) on the lines increases at lower speeds so the ratio of line
>drag : centrafugal force is somewhat greater at lower speeds
>which tends to yaw the plane in.

We started to discuss this a while back. Based on some very nice studies by Pete Soule' (links somewhere in SSW here), line Cd doesn't vary significantly enough to consider, across our speed change range. CF and line drag CAN be considered to vary as square of velocity.

Using one of Pete's equations (Aeromodeller Annual 1971-72?) I usually do not make leadouts adjustable: they go where the tension load aims through them to the CG. As "limp tension elements," lines can only pull along their length, and can't "push" across their length. They affect yaw attitude by how the leadouts "re-aim" the pull axis. When unloaded, pull's line of action aims to the CG.

So, theoretically, the lines don't touch the leadout guides in unloaded flight, and line drag applies to the model AT the CG.

On insides, prop gyro precession tends to yaw the model nose out, which aims the momentary mean line of pull force AHEAD of the CG -- result: a couple tending to yaw the nose in. And vice versa. Dimensions can be estimated to reduce precession yaw very usefully.

Other maneuver loads arise from the lift and drag required.

Aerodynamic loads on a CL model's wing balance around what I've always called the "dynamic flight radius." I center the fuselage, engine and tail masses on that radius to avoid roll (from lift) and yaw (from drag) under load. (The 'centerline masses' are lifted AND retarded through their centerline by, respectively, maneuver lift and the associated induced drag.)

Unequal panel spans achieve this. Where a momentary imbalance DOES occur, the leadouts again serve to "re-aim" pull force to oppose the tendency with a countering moment...

As Brett notes, the asymmetry required is not great. Keep in mind that the difference in panel spans is TWICE the asymmetry dimension, which is how far you move the "center" spanwise.

>So, theoretically, the lines don't touch the leadout guides
>in unloaded flight, and line drag applies to the model AT
>the CG.
>

Hi Lou

Yes I see what you mean, we can take line drag as through the CG.

>>>So, theoretically, the lines don't touch the leadout guides in unloaded flight, and line drag applies to the model AT the CG.<<<

>>>Yes I see what you mean, we can take line drag as through the CG.<<<

... guys this looks like IQ test ...

just as a practical matter, if you look down the line when the plane is flying slow, it seems the lines have much more "bow" in them than they do when the plane is flying fast. A 1 sec. difference in lap time makes a noticeable change in the bow of the lines. I think there is a lot more going on with the lines hanging off the tip than just the drag.

I have heard it said may times that the outboard wing is traveling faster than the inboard wing and it produces more lift. Combat airplanes have no fuselage but and they fly level anyway. It is true the faster a wing goes the more lift it produces. I have built the same identical stunt airplane one with the fuselage on center and one with the fuselage offset and they both fly perfect. The only difference that I have noticed is with the fuselage offset the fuselage itself adds weight to the outboard wing therefor wing tip weight is sometimes not needed. If you balance an airplane exactly on the center of the wing, if the fuselage is offset the outboard wing will be heavy. If you balance an identical airplane exactly on the center of the wing, if the fuselage is NOT offset the outboard wing will not be heavy unless you add wing tip weight. From what I have personally observed you can build a lighter weight airplane without with tip weight. Wouldn't it be nice to have a fuselage that could be adjusted by sliding it back and forth across the wing to get the exact balance needed so no wing tip weight is ever needed. A combat wing flies good because of the wing tip weight.

>I have heard it said may times that the outboard wing is
>traveling faster than the inboard wing and it produces more
>lift. Combat airplanes have no fuselage but and they fly
>level anyway. It is true the faster a wing goes the more
>lift it produces.

Yes it is true if the wing is in lift. As lift is proportional to velocity squared, the lift diferential is much greater than the
speed diferential.

L = 1/2 p V^2 S Cl

If it were not true, the plan would fly fine ballanced on it's exact geometric centre.

>I have built the same identical stunt
>airplane one with the fuselage on center and one with the
>fuselage offset and they both fly perfect. The only
>difference that I have noticed is with the fuselage offset
>the fuselage itself adds weight to the outboard wing
>therefor wing tip weight is sometimes not needed. If you
>balance an airplane exactly on the center of the wing, if
>the fuselage is offset the outboard wing will be heavy. If
>you balance an identical airplane exactly on the center of
>the wing, if the fuselage is NOT offset the outboard wing
>will not be heavy unless you add wing tip weight. From what
>I have personally observed you can build a lighter weight
>airplane without with tip weight.

The fuselage position is not really the relevant issue for roll,
CG is position is. If the CG is outboard of lift centre, the plane rolls outboard tip down. If CG is inboard of lift centre then it rolls inner tip down. CG position is primarily a function of span and flight radius. Centre of lift is not too greatly effected by fuselage position so for symetric and asymetric planes of the same
span, the CG must be near the same position. So I would agree the asymetric plane is generally lighter and may well need no tip weight to fly properly.

The fuselage has weight and serves the same purpose as wing tip weight. Move the fuselage to the correct location and NO wing tip weight is required.

The fuselage, unfortunately, also has the engine mounted in it. Move it too far outboard, and you put the engine thrustline outboard of the center of drag. This causes the plane to yaw inward. You also need the CG outboard of the thrustline if you want good hand launches. So there is a limit to how long you can make the inboard wing, and you'll need some tipweight if you're going to do combat-type hand launches. For some underpowered designs (e.g. 1/2-A) it might even be advantageous to have a longer outboard wing, with a corresponding large amount of tipweight. I built some 1/2-A combat planes like this once (back when we all ran Tee Dees) and line tension was excellent in the wind.

>The fuselage has weight and serves the same purpose as wing
>tip weight. Move the fuselage to the correct location and
>NO wing tip weight is required.
>

Sort of true, but consider that:

1) - The thrust line moves with the fuselage, and unless you also cant the engine to get the thrust line through the CG, you are changing *more* than just how much tip weight

2) - Usually, you also move the *tail* with the fuselage. The net effect being that the CP of the whole airplane moves laterally with the cotnrol deflection. Of course, you can leave the wing and tail in the same relationship, and move the fuselage over (meaning the tail is not centered on the fuse any more. Aerodynmaically, that's sort of OK, but now you get a differential *structural* deformation since one side it cantaleivered further out than the other.

3) - 2) is not *really* true. The fuselage affects the flow of air over the wing, so moving it side-to-side is not aerodynamically "invisible"

Short answer is that this road was travelled in the 40's, and air hasn't changed much since then. The Right Answer(tm) is to use from 0 to 1" of asymmetry in the wing, a very slightly larger outboard flap (to compensate, I assert, for the fact that the tail should be asymmetrical too, but isn't), and whatever tipweight is required to make it fly wing level.

>>>Usually, you also move the *tail* with the fuselage<<<
Not only that, it also changes flaps to wing chord distribution and thus AC in corner position over the span. It has similar effect.

BTW Brett, are you already building model with adjustable stab position? ... it should be as usual as adjustable leadouts are