One thing I found is that leaving the straight 90 degree LE has the benefit, that when positive, the top edge acts as a turbulator and more lift is generated.

The one thing I don't know is how the thickness of the flat plate airfoil effects this effect.

I find this especially true of my 3D machines.

I have found the same thing.

The LE on the octagonal one has been left straight 90 degrees for that reason. I too think that the squared-off LE seems to act as a turbulator.

I have experimented with this and found that when rounded, the LE the performance is slightly degraded. So square/blunt LE is definitely better on Nutballs.



I've experimented with the Nutball LE of the vert stab and TE of the rudder and found that performance is improved if the (stab) LE is rounded and the (rudder) TE is tapered to a thin edge.


The biggest effect was thinning (tapering) the elevator down to a thin edge.


What is interesting about these findings is that "thick and blunt at the front" and "tapered to thin at the rear" seems to work best on the Nutball. This is, of course, a very rudimentary description of something akin to an airfoil.


Thinning the dihedral panels at the tips also seems to improve performance.




As for thickness of a flat plate, I don't know how this affects things either. It seems to be an area that hasn't been previously considered.


With 3-D machines, as with the Nutball, some degree of drag is desirable as it slows the machine down. Both 3-D machines and Nutballs spend a lot of time in post-stalled condition in which the last thing you want is laminar flow over the wing. You need plenty of turbulent prop wash over the wing to keep the air moving energetically over the control surfaces.


This rather suggests that you might expect an improvement in a 3-D machine of you cut the first 2 inches of the LE off and replaced it with a straight 90 degree, square-section LE to disrupt the airflow to the max before it gets onto the wing surface.

If your LE is thicker at the tips and thinner near the cord it acts as an 'anti tip stall device'.

I had a rip roaring Mini Master back in the early 70s' designed for the ST 23 and had a 46 on mine. (no mufflers back then ) Over weight and over powered it had a nasty tip stall. I maidened it at a fun fly a full day drive from my home and it's the only model I had. Couldn't figure it at the time. Panic set in. I FB took a square of balsa, split it into two triangles and glue it out at the tips. CURED! A great weekend was had and the model survived for about 350 flight after I warped in some washout.

The AMCO MM …………..

Dave

Thats interesting, i must have ago myself.

Yes, Terry, it is an interesting topic.


After much thought, it seems to me that - if we are discussing LE shape - perhaps there is another factor that should be considered? This other factor is the distance between the prop and the LE. Call this distance 'X'.

On Nutballs, this distance 'X' is small. But on conventional 3-D planes it is much larger (because the motor is on the end of the fuselage).

I suspect that a blunt/square-cut, sharp edged LE might work better than a rounded LE on planes the smaller 'X' becomes. So perhaps it works best on a Nutball because the motor is effectively mounted on the wing itself - rarely done with conventional 3-D planes with fuselages.

Of course it is hard to verify this, but it has given me an idea.

The idea is that, rather than trying to introduce additional thickness to "streamline" a Nutball and bury the battery within the wing's "airfoil" to reduce drag, it might be more effective to keep the design to a thin flat plate and install the motor such that the propeller is close to the squared-off LE and has an uninterrupted turbulent airflow aft of the LE (i.e. the battery isn't directly in the prop wash behind the prop). Twin motors could be better in this respect, with the battery located between them and forward of the props (on a boom or proboscis) in clean air. Contra-rotating props to match the dihedrals might be of benefit.

Just a thought.

The 'Y' factor...............….

I've built loads of deltas, some pointy and some, like the Simple Delta, with the blunt nose.

The SD is by far the best.

Why? Don't really know.

Gold , with our brief experiment with the Martian Spaceship and Martian Dart , the idea of the “terraced LE” wing presented not only a rounded LE , plus a Delta wing which offered some unique and wonderful flight characteristics … crumbs for thought ...

Dave

Two contra rotating props, that sounds like the full size one way back in the 40s, no dihedral if I recall correctly

Terry,

Yes - exactly right.

The full sized one (the Chance Vought V-173) was designed by Charles Zimmerman of NACA (later re-named NASA).

He ended up as NASA Division Chief for the first human spaceflight program (Project Mercury). One smart cookie.

Anyway, he also designed, built and wind-tunnel tested model Nutball-like disc wings with dihedral outer panels...... a man way ahead of his time.


To quote directly from NASA's own historical account of Charles Zimmerman's work, his research efforts focussed on aircraft capable of extremely low-speed take off and landing operations. I like that......

Glen:

My Crack Yak and Crack Wing both have the terraced LE, but not as pronounced.

Probably copied from your idea.

Originally Posted by pardshaw

I have always left all the edges on my Nutballs as squared-off, never rounded or tapered.


So.... first step.......round the LE of the vertical stabiliser, taper out the top, bottom and TE of the rudder. Does it make a difference?


Yes it does. The handling (already good) is better and slightly less power seems to be required.



Second step....... taper the dihedral outer panels to give a thin edge. This too adds a noticeable improvement to the handling - it seems to improve the responsiveness a touch.



Third step........ taper the TE of the elevator on the underside. Wow! Big result..... the balance is completely altered and a lot of down trim is needed to force the nose back down. Clearly by tapering the underside, the wing has been given a reflexed section and this is generating a big force at the tail end, pushing the nose up. That was a big surprise - and it shows the aerodynamic response of the Nutball to thinning out the airframe extremities is actually pretty large. It surprised me, anyway.



Can these findings be made use of in any way? I think so..........

Neat idea! About how far from the edges does your taper start?

I've only done the tapering thing on 3 Nutballs so far, but the results have been very consistent.

There are probably several ways of making the taper, but I've used only one.

First, I need to say that the Nutballs I've tapered have all been 28" dia.

Second, they've all been 10mm thick, laminated from two sheets of 5 mm 'depron' (actually under-floor extruded polystyrene insulation which is cheap and readily available in the UK).


So.... on the 2 dihedral panels and the elevator, the tapering runs from a thickness of about 1mm at the outermost edge to 10 mm across a zone about 2" wide. I'll post a photo to show.

On the rudder, the tapering is to 1mm also, extending to a full forward thickness of 10mm after about 2 inches. The top and bottom of the rudder are similarly tapered, and this makes the rudder quite thin around its immediate periphery, yet it seems to need no re-inforcing to compensate.

The front of the rudder is rounded to streamline it.

The only bit of the periphery not tapered is the entire LE of the main centre panel and this is left square-cut and sharp edged. I have experimented with rounding it off and it degrades performance - definitely better sharp and square cut (90 degrees to wing surface).

The tapering down has all been done on the underside of the wing.

I have drawn a line with a felt-tip pen to show where the tapering starts from.


I use a coarse (80 grit) flat sanding block to sand the depron. It is an unpleasant job because the particles are statically charged and will 'stick' to everything, including you.

YOU MUST WEAR A DUST MASK... you do not want plastic fragments in your lungs as the body can't deal with them.

The effect on the handling of this tapering and rounding (keeping main panel LE squared off) has surprised me in two respects:-


Firstly, it improves the handling considerably - but you do need to be skilled at trimming out. It may seem skittish at first if it isn't properly balanced. It is sensitive to side-thrust which must not exceed two degrees right. Even slightly too much side thrust will cause the airframe to vere off, requiring constant small corrections resulting in PIO "twitching". It is that sensitive.

Similarly, the down thrust is also important and it must be set to the usual 5 or 6 degrees. I suspect that Zero degrees down thrust just wouldn't fly.

It is interesting that the tapering out has sweetened the handling but made the Nutball a more demanding plane to fly.

I suspect that is because the Standard Nutball is built with squared off edges all around the periphery. I also suspect these squared-off edges induce more drag than the tapered off edges, and that this drag is "a good thing" for beginners as it acts like trainer wheels on a kid's bicycle. Take this away and you need to know how to ride.....

Somehow, tapering the outer panels seems to "set the inner Nutball free" from its draggy trainer wheel periphery, and it now responds much more precisely to it's owner's commands.

Secondly, I did think initially that sanding the wings down to 1mm would make them weak and vulnerable to flexing and damage in the air. It hasn't.

Perhaps the thinly tapered wings act in a similar way to primary feathers on a bird's wing. Theses taper down to next to nothing from the central shaft, yet remain effective despite being very thin at their outer margins.



That changing the periphery shape (tapering it) brings about significant changes maybe shouldn't be that much of a surprise - the circumference (periphery length) of the 28" Nutball is 87". This modification changes 71 of those 87" across a width of 2". So we have affected an area of 142 square inches, or - if you prefer - about square foot. Since a 28" Nutball has a wing area of 4.3 square feet, we have modified almost 25% of the airfoil.

You can get the idea of the airfoil from the photographs, but here is an additional sketch that might help.


The sketch is of the underside of the Nutaball.

The sketch illustrates a 10 mm thick Nutball disc of 28" diameter.

The sketch shows (as the shaded peripheral area) the extent of the area that is sanded down to form a taper, from the full thickness of 10 mm to the outermost, peripheral thickness of 1 mm.

The sketch shows that the width of the tapered zone is about 2", but that there are maximum and minimum width. The maximum width on the dihedral panels occurs along the lateral mid-line of the wing. The maximum width on the elevator panel occurs on the longitudinal mid-line.

Since 28" is 711 mm, the central bulk of the airfoil is 1.4% thick for the most part. Since the periphery is tapered down to 1mm, the airfoil is 0.14% thick at the periphery.



The sketch is just to illustrate what I've done so far on two of my round (regular) Nutballs. The same idea is also used on my irregular-octagonal Nutball.