Aerofoils

[Former Member]

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[Erfolg]

These days, as i am still using old wings, after 15 year lay off. Eppler 205.

In the case of E205, it is/was easy to build, seemed to penetrate well in windy conditions, would move out smartly with a little down, with very little hight loss. Yet it could hang around with the best of them. Well not quite as well as a undercambered section. But undercamber only works in still air with no thermals.

I have tried MH32 on a small model, recently built, I was after the low camber, so as to be able to fly fast (for me). It is hopelessly inaccurate as it is a built up, open wing. It seems to work well, but is no floater, you need to seek out good air, but allows you to move about efficiently.

I am now considering the wing section for a new sports plane, I will probably use NACA008 (you know the symetrical one, with the well rounded leading edge), just like the control liner stunt models of yor. To get a acrobatic performance, the high drag being something to live with. Al;though I may thin the section a little.

Now I have about 3 months of building work left, i hoipe to have more time for me.

Erfolg

[Former Member]

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[Simon Chaddock]

Well I do know what the airfoil section is on my plastic RTF - NACA2412  - because I looked it up!

To my mind it is too fat (12%) which means its ok for lifting capability & strength with a gentle stall but the drag rises very rapidy with speed. As soon as I get some 3mm depron I am going to build my own wing to see if I can do better & also to try out using this new fangled material!

Erflog - If I read my NACA numbers correctly 008 has a 8% thickness ratio which is not that thick! Even the Spitfire which was considered to have a "thin" wing used NACA2213 (13%) at the root and 2209.4 (9.4%) at the tip.

[Erfolg]

Simon

You are right about the thickness, i was going from memory. Could it be that the KK Spectre  etc. used Naca 018? If so Naca 008 would probably be about right. Given that the objective back then was to get a constant speed, through the manoevres. I am not that concerned about constant speed, requiring good stall properties at high alpha (as they like to call it these buzz word infested days), living with a  delta v (see how I can get into it), whilst the plane is in any plain (ohh! this is really heaven). 

As for the Spitfire, given the need to get weapons and undecarriage in there, it could be that this was a significant driver in the thickness ratio as well as the obvious strengthand aerodynamic qualities?

Regards

Erfolg 

[Bob Cotsford]

aerfoils section - generic size 44 trainer.  Sorry, but I've no idea what I use as I often crib them from models that fly well, such as the Wot family, or just draw a nice looking curve with the fat bit  somewhere nearer to the front than the back, and enough depth to fit in some woodwork .

[Martin McIntosh]

I stick with the RAF 30 on most of my aerobatic designs (i/c-F3A) because I have not found a better one!

[001]

I wonder if the designers of the cheaper range of ARTF sports/trainer models, or even scale, actually use a known aerofoil or just draw something that looks about right?

There was a discussion on these forums about a CAP that apparently has the wing upside down. 

I would expect that the planes designed by the larger European or American manufacturers for far Eastern assembly specify the aerofoil to be used.

Chris Foss seems to get his sections right, power and glider, obviously due to his hands on experience.

[Simon Chaddock]

Only partly to do with aerofoils but

I never did like the bottom hinged aileron on the RTF Wing Dragon, up travel was limited, particularly as the aileron horn was also at the bottom. In fact I had to limit the travel to prevent the servo stalling on up.

So yesterday I changed it to a top hinge but it was necessary to reverse the ailerons R to L and when I did I found they were a completely different thickness! They fitted flush in their correct positions so the whole L & R wings are actually of different thickness, by about 3mm & that's nearly 10%! It does not seem to effect the flight characteristics so maybe this rather confirms that the exact wing section is not that critical on such a model.

With a judicious bit of foam crushing they now fit flush and by moving the servo arms round they are also strongly differential (the rudder will become even less needed!). At the same time I "buried" the servos fully in the wing to reduce drag a touch. I doubt any of it will make that much difference but I enjoy the challenge!

I have just finished the rib template for a Clark Y set of depron wings for comparison. Any bets on whether they will any better or worse?

[Former Member]

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[Erfolg]

There is a question of how you define better!

For gliders it is about distance travelled relevant to height lost, but at what airspeed?

For racing slope soarers it may be about drag, at high speed?

For aerobatic models it could be about, stall characteristic, performance inverted, about maintaining air speed in the dive or climb etc.

What are you after? how will you know if you have achieved your objectives?

Erfolg 

[Simon Chaddock]

My intention is the depron wings (built up with ribs & a fully stressed skin) will be the same span, area, thickness ratio & no heavier than the original solid foam.  Will be with everything else the same the test will be does it stay up as long and be capable of the same aerobatics.

Not very scientific but it may help confirm my belief that a wings thickness ratio and leading edge profile have more influence on a models performance than the detail of the section. I will also get some useful experience using depron. 

[Former Member]

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[Erfolg]

• Simon

I tend to agree with Eric with regard to the LE radius. The one thing to be avoided at all costs is a sharp leading edge, it will stall unpredictably and the drag will be high. The point made about the loading of the wing is also very important.

There are some excellent books on aerofoils. Virtually any will tell you the broad features

Of

• section type, undercambered, symetrical and flatish bottomed sections.
• Section percentage thickness
• Camber
• chord to speed issues, Reynold numbers

All the features have an effect on the performance of a model.

Sections do matter, but it depends what you are doing, to what extent they matter. Gliders can be very demanding on the correct selection of wing section. An example would be an F3b, with a heavily undercamberd, thin depth, narrow chord, wing. It probably would not survive the launch, if that were to managed, the speed run would probably be slow, never mind if it could pull the high speed turns.

On the other hand a trainer with a clakish y'ish section, drawn with a French Curve, would probably work as good, as far as the modeller were concerned as would Clark Y, or similar section.

It also does matter how the wing is made in some instances, mouldies are a must of high performance gliders of all disciplines (well most).

Erfolg

    

[Ernie]

Hi Guys, surely the aerofoil depends on the function..A nice deep symmetrical job for a fun fly...lots of strength, fine upside down, and slow if required...This if course would look plain daft in my WW1 scale job...Here we have a shallow undercambered section, with all its structural and covering problems...A trainer, might have the eternal Mr Clark's Y, or a derivative, drawn round the legendary shoe

ernie

[Martin McIntosh]

A bit puzzled by fun fly sections. A symmetrical would seem the obvious choice for this type of model but on each occasion I have tried it the model just screws out of outside loops. The almost flat bottomed section a la Limbo Dancer seems to work best. Why? 

[Former Member]

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[Martin McIntosh]

Phil, I am talking about the Limbo Dancer in each case, this of course being a high wing model. With the supplied wing you can outside loop as tight as you like all day and it does not snap out, but fit a symmetrical wing which is otherwise identical and it will immediately snap out of a tight bunt. Just wondered what the theory may be behind this.

[Erfolg]

Martin

I do not know the Limbo Dancer, but there are a number of characteristics that aerobatic models  seem to have

• Symetrical wing, can be quite thick,  as speed is generally not required, drag can be good, as it can reduce acceleration in down hill type moves.
• They are often mid winged, to help keep tha principle drag inducing elements, along a common line on the longitudinal axis.
• Side area is often generous to help in knive edged moves.
• The principle masses are kept as near the same point as possible, to reduce inertia effects.
• High power to weight ratio, with weight minimisation a desirable feature.
• Above all the aircraft is true both dimensionally and weight distribution.

Why yours does not fly true I do not know. But it could be trueness issue, or maybe  CG related. A aerobatic model flyer will probably know. But i do not think it is because the wing section is symetrical, but others may know better!

Erfolg 

[Former Member]

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[Former Member]

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[Martin McIntosh]

Hi, I am not really talking about an individual model but the type in general, because fitting a semi symmetrical wing to say a F3A or Cap type simply causes the model to zoom when the speed is increased and means that you need a fistfull of down for inverted figures, whereas the normal symmetrical wing does not cause inadvertent snap rolls unless the model is unduly heavy.

Right thrust is still right thrust inverted because it is countermanding the roll effect caused by the torque and gyroscopic effect of the motor, which of course is still rotating in the same direction.

Being former F3A British champion and twice team member, I know most of what is worth knowing about aerobatics, but it is this fun fly section thing which is bugging me!

[Former Member]

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[001]

I would have thought that in relation to the air, right thrust is always right thrust. (The wind doesn't know or care!)

[Former Member]

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