Just enough basics, which will improve our Knowledge on Air's Interaction with the RC aircraft.

Aim:-
1. to Design foamies better with this knowledge
2. To fly better
3.To make modifications in your aeroplane/heli.
4. on the lighter side, to tell family, we are doing something worthwhile

PLEASE do not cut copy, even if you do value add  .

Learn through generating discussion, like Anwar Bhai says, it is always better.

pulled out from my other post. Pruned it a little. To make understanding of RC flying clear.

firstly in level flight weight= lift =CL ½ σ V² S. CL is coefficient of lift, which depends on your wing angle of attack (position of the nose in level flight) shape, camber etc, ½ σ V² is called the dynamic pressure, simply put, number of air molecules for a given time, ALSO CALLED THE INDICATED AIRSPEED, 'S' is your wing area.

Now, aeroplane has lift and weight acting as one couple (noseup or down will in RC language, will depend on the cg, because weight acts along it, and position of wings because centre of pressure through which the lift acts).

It also has thrust and drag couple acting on it. nose up or down will depend on position of your engine and wings, which if you are not designing, is pretty much taken care of,

Couple of Forces. For aeroplane to fly in level unaccelerated flight all these couple have to balance so that the residual is zero. If the aeroplane is say designed to get airborne at 30 kmph, it will get airborne at 30 kmph, if the wind that is blowing is 30 kmph, the ground speed at which will get airborne will be zero. But remember the thrust drag couple will have to be zero, which means, you have to open power normally as you do in nil wind condition. If the winds are 40 kmph the aeroplane after getting airborne into wind will travel rearward at 10 kmph. With respect to ground, however with respect to air it is still travelling at 30 kmph. Bottom line CL and S being same it is the ½ σ V² (the number of air molecules for a given time above and below the wings) which matter.

"Coanda Effect", Tendency of the fluid in motion to get attracted to the nearby surface, AN 72, C-17 Globemaster, are some of the aeroplanes successfully uses this effect (Blowing of engine air to increase lift and reduce forward speed).

Coanda effect... I was watching this interesting thread : http://diydrones.com/profiles/blogs/coanda-effect-saucer-ces-uav

There is a cool build document too : http://ardupilotdev.googlecode.com/files/How_to_build_a_Coanda_Effect_Saucer.pdf

Since I have the ArduIMU v2, might try this some day !

I didn't see this post, see my reply in your other post (Link below).

also read

http://www.rcindia.org/rc-general-topics/aerodynamics-is-this-possible/new/#new

Anwar Bhai, I need to get intro to ArduImu, Help. your info link in this thread will help this thread

VGs (Vortex Generators) used on wing root which makes root stall before tip, so that the aeroplane does not wing drop during stall. (Example:- Jet Provost) They are also used spanwise at about 20% chord, this makes the flow go turbulent and a turbulent air flow sticks to the wing more than a laminar (Non turbulent) flow. SO ? so the aeroplane stalls at lower speed and higher nose up, does aerobatics well. PRICE TO PAY? more Drag and fuel consumption. (Example:- B Ae Hawk). VGs on the root of the Pitot Tube energizes Fin and this keeps the aeroplane 'directionally Locked In' and does not roll left and right at low speed (Like what the RC Extra 300L does at low speed). Example MiG 29.

This can be tried on a C/Foamie to have a clean stall characteristics

I am planning to build a plane with 75 inch span, root chord 16 inch, tip chord 1 inch (elliptical wing). Now the problem is stabilizer dimensions. i want the horizontal and vertical stabs to be as small as possible. This will be a slow flier/glider with a polyhedral wing an no ailerons. how much horizontal and vertical stab do you think i can get away with?

Quote from: augustinev on December 10, 2010, 07:48:27 AM
Anwar Bhai, I need to get intro to ArduImu, Help. your info link in this thread will help this thread

It is just a sensor board with an arduino and 3axis gyros, accelerometers and option to add a magnetometer.  Basically, it has everything you need to get sensor information for full stabilization and enough processing power to run a control system using these sensors.

PM me more details, basically, if you want to knock off fin elevator weight, give it more moment arm, (Restricted by weight increment due fuselage length) if it is going to be on a stick you can knock off a lot.

If you sweep back slightly a polyhedral wont require fin, two small winglet will give you directional stabilty and reduce Lift dependent drag as well. Elliptical wont work with polyhedral and winglet. with a 15 deg sweep winglet. believe me you can knock off fin.

if you are interested, this is the data. if you plot, you will come across the C of P should be able to determine moment arm from there, problem is i have assumed symmetrical wing, introduce camber , the stall model and the C of P will change.

Quote from: augustinev on December 10, 2010, 06:15:30 PM
give it more moment arm, (Restricted by weight increment due fuselage length) if it is going to be on a stick you can knock off a lot.

this sounds good, the fuse is just a CF tube. sweeping the wing wont be possible. The wing is going to be slightly cambered one with, max height of the caber only 1.5 inch.
And thanks for posting the data, but unfortunately i am mathematically challenged person
is there a formula which gives stab surface area w.r.t to arm length and wing dimension?

Ok

Let me give you a practical solution. Theorically, if the point at which wing lift is said to act is on the CG, you wont require any tail down force. Thats not practical, So Have flexibity of shifting the entire wing forward and aft, now you are restricted by the amount of elevator force you want for any manoeuvrings you envisage the model will do. That's it you are sorted.

In a Nutshell. Keep your elevator restricted to the force you envisage you require for the manoeuvrings limits. Keep the point where you think the wing is lifting the ac (Determined by trial and error) very very slightly behind CG. if you can keep a all moving tail plane (Instead of elevator) which will reduce the size and weight of it.if you can have a small ventral fin as well. this will reduce the size of the dorsal  fin as well.

Any more query, feel free to PM

got it! thanks a lot augustinev!
There is one more question that is bothering me from some time. Check out the attached image. Notice the sharp angle on the upper surface. How will this airfoil perform w.rt. gliding performance? Which one will you recommend between this triangular airfoil and a flat plate for better glide ratio.

Interesting!!,

I guess it is easy to make that's why you chose this, if you are using coro, join at the ends and put a vertical piece at about 20 % chord, you will get a decent bi-convex. This wing is a single wedge design. I have flown a double wedge, great supersonic performance, poor low speed stall and subsonic performance. Your single wedge, At about 7 deg α this wing will stall. section CL will be at about 0.15-0.17 at 4 α.

The point of max thickness is good, before that point the air would have gone turbulent and will stick on until 7-10 α. Stall however will be abrupt. Glide ratio will not be too great to talk home about. landing will be at slightly high speed but will be good, rest assured on that.

Like us even air likes curves. keep it curvaceous for the air. These are just opinions based on scanty info you provided. Try it, if the results are contrary, give me a holler

Ah!! one other thing, FLAT plate Aerodynamics.

Is is an interesting, huge, ever debated, still enigmatic topic. Suffice to say, Advantages of Flat plate wings are at high RN, that's why you see them on missiles. low speed performance is poor, there is always a leading edge stall / bubble. BUT but, there is virtually no movement of C of P in the working ranges of α (angle of attack).

PS
Your single wedge, ?  if you invert it and give it a little reflex camber on the trailing edge, it looks more like Kline Fogleman's aerofoil. A sensational one during mid-late seventies.

you must be thinking why doesn't this guy just curve it a little. Thats why i am going to start my build and put it on a thread; that will clear the mist.
BTW i asked the airfoil question because of KF airfoil only. I thought it would behave just like KFm2.

yeah, we (My friend and I) tried some Spads with KFm2 and m3. flew well. it had a round LE (Coro Bends).

Waiting to see your model. All the best.

This is what I have experienced

Flat/pointed edged airfoils have higher stall speed and its unpredictable. So, you need to have enough airspeed to have control of the flying surface. If you need more adrenaline pumping flying then pointed flat air foil should give you that. Flying on prop is another story.

Rounded edges are always better as it gives predictable stall speed. More graceful and less nerve-wracking to fly.

Another thing, you would not see much difference with a triagular section airfoil and a smooth curved airfoil of similar dimension. All these airfoil doesn't matter much in RC flying as their effects are too small to notice. Either you need to have a proper wind tunnel with appropriate instruments to measure the parameters from your model or you need to have a larger aircraft to study the effects of airfoil shapes.

thanks for the tips Izmile.

Quote from: izmile on December 11, 2010, 07:12:25 PM
you would not see much difference with a triagular section airfoil and a smooth curved airfoil of similar dimension

this is good news for me, lets see how it turns out.

izmile
True to the bone. We do a lot of prop controlled flying for complex AD to matter.

For control forces and servo needed read my post

http://www.rcindia.org/beginners-zone/how-to-calculate-the-type-of-servo-needed/new/#new

Vortex Generators's on a RC plane, see this

as per them (http://www.precisionaerobatics.com/product_details.php?pid=648) it gives additional valuable extras which are used to enhance even further the low speed 3D capabilities of the plane and Knife Edge type maneuvers.

PS
Thanks Praveen and Santhosh for the correction

read 'Rep 34' of this post for Reynolds number and it importance on wing design (scratch build)

http://www.rcindia.org/self-designed-diy-and-college-projects/build-log-back-packable-2-meter-glider/new/#new