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What is the effect of flap on attitude?

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What is the effect of flap on attitude?

Old 09-18-2008, 09:07 PM
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lejongleur
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Default What is the effect of flap on attitude?

I have been meddling, I mean programming a DX6i transmitter for my few remaining intact planes recently, and I would like to understand the effect of using flaps in level flight.

I realize that they tend to add lift and drag, and hence the plane may fly slower, (and possibly be more likely to stall at low speeds?)

But my real question is - does adding flaps pitch the nose up or down? As they are behind the CG, I would think that they might tend to lift the tail rather than the nose.

Maybe an irrelevant question, but anyone got any thoughts? I appreciate all your comments...Chris
Old 09-18-2008, 09:11 PM
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TedMo
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Default RE: What is the effect of flap on attitude?

You have the right answers. Generally it will require some down elev. compensation. However, not always, Get up high and see what it does. On occassion it requires up elev.
Old 09-18-2008, 09:22 PM
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Flying freak
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Default RE: What is the effect of flap on attitude?


ORIGINAL: lejongleur

I have been meddling, I mean programming a DX6i transmitter for my few remaining intact planes recently, and I would like to understand the effect of using flaps in level flight.

I realize that they tend to add lift and drag, and hence the plane may fly slower, (and possibly be more likely to stall at low speeds?)

But my real question is - does adding flaps pitch the nose up or down? As they are behind the CG, I would think that they might tend to lift the tail rather than the nose.

Maybe an irrelevant question, but anyone got any thoughts? I appreciate all your comments...Chris

Flaps are there to increase lift this means you will stall at a LOWER speed but dont forget that to maintain the same speed you will need to increase power
Old 09-18-2008, 09:25 PM
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lejongleur
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Default RE: What is the effect of flap on attitude?

Thanks for your answers, but will the nose tend to go up or down when flaps are applied? Or is it specific to the airframe?
Old 09-18-2008, 09:25 PM
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Default RE: What is the effect of flap on attitude?

the use of flaps will cause a pitch up on attitude, so you will need to counter with slight down elevator. The flaps will lower the stall speed and when descending, it gives a quicker rate of descent.
Old 09-18-2008, 09:29 PM
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lejongleur
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Default RE: What is the effect of flap on attitude?

Thanks - that gives me a starting point for my programming. I guess I will try flying around at a decent height and try different amounts of flap to see what happens.

I appreciate all your comments...Chris
Old 09-18-2008, 09:35 PM
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Default RE: What is the effect of flap on attitude?


ORIGINAL: lejongleur
But my real question is - does adding flaps pitch the nose up or down? As they are behind the CG, I would think that they might tend to lift the tail rather than the nose.

There is no one correct answer on this as It can be either way depending on many factors including the pitching moment of the airfoil used and many other varibles.

One can generalize however that the more common reaction with our typical airplanes is a pitchup.

If you are asking this in anticipation of programing in a flap to elevator preset mix then I would suggest holding off on doing so untill you actually flew the aircraft and tried it to give you an idea of which direction and percentage of preset you wanted.

John
Old 09-18-2008, 09:37 PM
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lejongleur
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Default RE: What is the effect of flap on attitude?

John, your suggestion makes 10,000% sense - that's what I will do...Chris
Old 09-19-2008, 10:55 AM
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Default RE: What is the effect of flap on attitude?

I am by no means an expert on this, but having had a few planes with flaps now, I have an observation regarding the pitch up effect. I initially programmed some down elevator into my flap mix, but I noticed that the faster I was going, the more the plane pitched up, even with the down elev. (btw, it should be noted that I have my flap setup on a knob, rather than a switch, so I can bring them down a bit at a time.)

I started experimenting with using less flap until the plane had really started to slow down. As the nose starts to drop, I add in more flap, eventually I reach the point where even with full flap the nose will drop. Now I don't have the down elev programming anymore, and still have no problems with pitch up. I just wait longer to deploy the flaps.

I think its kind of the difference between expecting the flaps to slow you down and give you more lift, and expecting that the flaps will give you more lift once you've slowed down.
Old 09-19-2008, 01:17 PM
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Default RE: What is the effect of flap on attitude?

Here's the key: Every plane is different as is every pilot. Start with none and do some experementing to find out what works for you and your plane.
Old 09-19-2008, 01:37 PM
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Default RE: What is the effect of flap on attitude?

Ditto... Unless you have knowledge as to what mixes are needed, the only solution is to fly the plane. There is no pitch up effect per se, the pitch from adding flaps can be up, down, or nothing. Unwanted pitch can be offset with elevator and sometimes even crow. The key is to flight test. I'd also suggest slowing down flap deployment and any related mixes to occur over several seconds, many radios can easily be probrammed to do that. The slow deployment softens transition from clean to flapped flight. I generally go for about 5 seconds or so.
Old 09-19-2008, 03:55 PM
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Tall Paul
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Default RE: What is the effect of flap on attitude?

On my Senior Kadets with normal flaps, the nose will rise with flap. At full power, the pitch up is uncontrollable with elevator! I have to pull off power to keep the plane from looping.
On my Low Wing Kadet and PT-19, with split flaps, the nose drops with flap.

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