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Air Plane Wing

09/23/2010 6:01 AM

Hi friends,

I am trying to make one small motor powered airplane. But the problem is that when I am making its wing straight it stalls & goes upward. But making it in v shape its starts fly. like

so can any buddy help me?

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Guru

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#1

Re: air plane wing

09/23/2010 6:58 AM

Is the picture posted what your building. If so, bi-planes lend themselves to another set of issues when rigging the wings. In most cases the upper wing incident is set so it will stall 1st, the lower wing will stall 2nd. The "V" installation as you called it is the dihedral set in degrees off 0 plane. Dihedral improves the suitability of the aircraft. A truly flat wing is normally a unstable platform and is used in most aerobatic type air craft to improve performance. There are several books on aircraft wing design out on the market. If you Goggle this, you can choose one the fits your needs. Good luck on your endeavors, it is fun to experiment.

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#3
In reply to #1

Re: air plane wing

09/23/2010 7:13 AM

thanks dud u improved my knowledge

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Guru
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#2

Re: air plane wing

09/23/2010 7:12 AM

Think about it. The AOA (Angle of Attack) of the wing is too high.

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#4
In reply to #2

Re: air plane wing

09/23/2010 7:18 AM

this is not my plane but in my plane i have kept it hardly 10-11 deg.

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Guru
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#5
In reply to #4

Re: air plane wing

09/23/2010 8:09 AM

Intrinsically, 10° to 11° seems too much. You should google angle of attack and learn how that impacts the performance of the plane and read about stalls.

Both subjects will help you understand what is happening and why.

You could compensate with the elevator, but high AOA on wings, even when compensated for, will create a lot of drag. You need to strike a balance between lift and drag to get the best efficiency for flight.

This is a good learning opportunity on the principles of flight that you can enjoy.

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Guru

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#6

Re: Air Plane Wing

09/23/2010 4:12 PM

Many things going on here and I am not an expert at any of them. But, here are a few comments that might be useful. Hopefully other CR4 members that know more than me will add to this.

First, if you don't know about ROLL, PITCH and YAW then look up the terms. You can't properly think about this or properly communicate about your model airplane without knowing these terms.

Straight and level flight requires the balance of forces. This requires that the MANY things which cause a force on the airplane must be balanced. Most of what you care about for this posted question relate to PITCH and LIFT.

1) If the wing is any good at all then the faster it moves forward through the air the more lift it will produce.

2) If the wing's Center Of Lift (COL) is near the planes center of gravity (CG) then the lift should just be an upward force (assuming the plane is right side up). If the wing's COL is forward of the planes CG the the lift will also cause a pitch up. If the wing's COL is rear of the planes CG then the lift will also cause a pitch down.

3) The tail's horizontal stabilizer (flat part) is a small wing. It might seem odd, but everything stated in #2 is true here too. The horizontal stabilizer has a part that moves (elevator) that allow the shape of the small wing to be changed and typically the lift force will increase or decrease.

4) The tail's vertical stabilizer (up and down part) is a small wing. Everything from #2 is basically true but we are talking about YAW here. Everything from #3 is basically true but we call the part that moves the rudder.

5) The dihedral that fixitorelse brought up in comment #1 does many things, most of which I never understood. But, the high wing of airplanes like a small Cessna and the dihedral of a model plane like yours will move the effective COL higher. This is most useful when you consider that if the COL is above the CG the plane will seem like it wants to stay right side up (airplane is hanging under wing). If the COL of the wing is below the plane's CG then the plane will seem like it wants to flip over (airplane is balanced on top of wing). High wings and dihedral are nice for inexperienced pilots and pilots that want a plane that will seem like it wants to fly itself. Having the COL near the planes CG makes the plane seem less stable, but it also helps the plane make rapid turns as required for crop dusters and high performance aircraft.

6) Dihedral often is part of an intentional design goal of having one part of the wing stall before another part. This is probably not something you want to think about until you better understand the basics.

7) As the wing's angle of attack (AOA) increases several things happen, but for basic discussions you can assume that the lift will increase.

With an understanding of the above items you will start to be able to understand the flaps, ailerons, trim tabs, slats and other things related to the stability and control of the airplane.

Let us know how you are doing. We are not really here to answer other people's questions. We are here to talk about fun stuff. Post your success, your failure or just your comments. That is what we are here for.

Good luck

Bruce

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#7
In reply to #6

Re: Air Plane Wing

09/23/2010 10:56 PM

Bruce your reply was fully correct, also check your point of balance, it might not be totally the wing

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#9
In reply to #6

Re: Air Plane Wing

09/24/2010 6:08 AM

definitely i will rpl thanks for info

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#8

Re: Air Plane Wing

09/24/2010 12:01 AM

BruceFlorida gave you the answer - but to focus on the bit of immediate interest to you.....

Think of the mass of the body of the aeroplane hanging under the "middle" of the wing and imagine that the upward air pressure on the wing is effectively applied at that "hanging point". Now assume for the moment that the distance between the aeroplane mass and the hanging point is near enough to zero. If this is the situation for the aeroplane with the straight wing and it pitches up because the tail is a little heavy, or whatever the reason, the no new force or moment developed to correct and increase of pitch and the pitch keeps increasing until the aircraft stalls (i.e. angle of attack of wing exceeds about 12 degrees to direction of air flow).

Now, if the wing is bent upward at the tips as you said, this has the effect of lifting the average height of the upward air pressure and so effectively lifts the hanging point above the aeroplane mass - the distance between the two points is now greater than zero.

This time when the aircraft pitches up as before, the fact of there being a distance between the two points means that the rotation will cause the aircraft mass to move forward of the hanging point. This in turn will cause a new moment (turning force) to develop that it will operate to try and rotate the aircraft back the other way - and if the effect is big enough it will bring things into equilibrium and further aircraft rotation will stop before the aircraft wing stalls.

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#10
In reply to #8

Re: Air Plane Wing

09/24/2010 6:23 AM

"ow, if the wing is bent upward at the tips as you said, this has the effect of lifting the average height of the upward air pressure and so effectively lifts the hanging point above the aeroplane mass - the distance between the two points is now greater than zero."

I understand center of gravity, as far as center of lift (COL) relative to aft/stern, but the idea of vertical COL has no bearing on the problem.

Aircraft have placed wings in the center of the fuselage, below the fuselage, and above the fuselage successfully.

The original picture is also a bi-wing.

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#11
In reply to #10

Re: Air Plane Wing

09/24/2010 8:10 AM

The real life story is a little more complex and can bury he force model I explained. You need to think in term of two dimensions and not one as you have. Imagine a pendulum that is bolted solid to an aircraft flying level, with th pendulum vertical - equivalent to CofM below CofL. Now rotate the aircraft so it is nose up. Then the CofM is forward of the CofL and just as the bolted pendulum is now tilted "back" and tries to fall to "vertical" so too does the aeroplane tend to nose back down again.

The above is a static analysis. The real world is dynamic and another effect will be that the increased drag of the now tilted wing will try and slow the aircraft as its mass tries to continue forward and make things worse. All these forces interact at the same time - but on this occasion that effect is presumably not important. Of course he increased lift, with angle and the "leaning back pendulum" effect will also tend to decrease the pitch up effect.

I was/am just trying to engender an understanding of why the phenomena that the original post occurred.

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#12
In reply to #11

Re: Air Plane Wing

09/24/2010 10:23 AM

Just because I can, let's throw in another complication.

Most non-high performance wings also have a feature called aerodynamic twist. This means that the angle of the wing chord to neutral pitch continuously varies from the root to the tip, with the tip twisted downward relative to the root. The affect of this is so that the tips (where the ailerons are) will continue to fly where the root may be stalled at high angles of attack, such as when in a landing configuration where the ability to maneuver is at a premium. Of course too much twist may degrade performance (ie, higher drag) at cruise speeds, so, as said earlier, everything is a trade off.

Sadly, this kind of wing feature is rarely built into model aircraft. The only time I've used it was in R/C sailplanes.

Hooker

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#13

Re: Air Plane Wing

09/25/2010 1:40 AM

thanks to all above.u all spent time to ans. my problem.i am trying all the suitable solutions u have given & definitely rply after success. thanks buddies!

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#14

Re: Air Plane Wing

09/27/2010 4:50 AM

Good Day, From your picture I can quickly see what's the problem. In short it is the size and/or the speed of your propeller in front. Let me explain. From your picture you have quite a small propeller in relation to where your wings are placed. Remember there must be an airflow sufficient enough OVER your wings and your wings' shape must be such that it obeys Bernoulli's or Newton III's Law. (Actually more than that!). Many people think that it is only the shape of the wings, but it is the overall design.

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#15
In reply to #14

Re: Air Plane Wing

09/27/2010 6:19 AM

Actually, it is CG (center of gravity), and AOA, angle of attack that determine the pitch up problem.

The prop only needs to generate enough power to get the minimum airspeed. In this case the aircraft pitches up and stalls; it never achieves level flight. This tells me it is an issue of CG and/or AOA, not the prop.

Some aircraft have no prop at all (i.e., jets and sail planes) and successfully fly. So, the concept that the prop must push air over the wing is a little misleading.

If it was an underpowered prop the aircraft would never take off in the first place.

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#16

Re: Air Plane Wing

09/28/2010 8:45 AM

hey buddys i made that plane it flys up to 2-3metre.but want to fly more thus i am going for extra light weight electric motor. so if any buddy know about lightweight battery of 6-9 volt.plz tell me.or any info about it. i am searching its info on internet.but not got yet.if u have any info plz tell me.u can see all my work in link below. http://picasaweb.google.com/111035852810569847708/RubberBandPoweredhomemadeAirplaneJpg?authkey=Gv1sRgCJ39pcC8wu2vYw#

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