Sportstar - split flaps

[pitfield]

I'm now training in a Sportstar (which I very much enjoy). The aircraft has split flaps, and I am not convinced that split flaps provide much lift enhancement. There's no question that they're effective drag enhancers, but because they don't affect the chord or shape of the top surface of the wing, I don't understand how they can have a significant impact upon wing lift. My tentative conclusion is that using flaps on takeoff is of negligible benefit.

 

Would somebody kindly explain why I'm right or wrong?

 

Thanks & best wishes.

 

Chip

 

 

[jcamp]

Without exact knowledge of the a/c etc

 

Deflection of split flaps increases the camber and hence the lift. The top surface bit is important to a point as in 'what over simplified half truth do you believe in'. On takeoff at low deflection the (bigger) increase in lift presumably outweighs the (smaller) increase in drag.

 

Do it by the flight manual.

 

 

[motzartmerv]

The split flaps do increase lift, to a degree. IF you look in the manuel it tells you that the stall speed is reduced by 4 kts (from memory) with full flap. So some extra lift is being produced. With one stage of flap down for takeoff it gets you airbourne quicker.

 

The reaction of the air being forced downwards still applies with split flaps, its just not as marked as normal flaps. But drag is increased quite a bit..

 

enjoy, she's a lovely acft..

 

cheers

 

 

[Deskpilot]

Hmmm, have to think about this one myself. How about: take a molecule of air and split it two at the leading edge. One half going over the wing the other below it. Now measure the distance traveled to the trailing edge of the lowered flap and I think you'll find that the upper half of the molecule has had to travel further than the lower half. Now, as they need to get to that point on the trailing edge, at the same time, the top one will have to have traveled faster and the lower and in doing so, produced a lower pressure across the top of the wing. That make sense?

 

This of coarse, leads to another question. With the flap down, there's a big, open caven left twix wing and flap top surface. How much drag, vortecies or other disturbing phonemea does this induce?

 

 

[motzartmerv]

Well, thats the whole idea isn't it, to increase drag, aswell as lift..

 

I realise that we are all taught the dividing of the air and the molecules coming back together thing, but its been well proven that this simply isn't the case.. It just doesn't happen, but, for educational purposes its still taught because its nice and simple.. so perhaps i should stop now hey??

 

With respect to split flaps i think you will find its mostly the reaction (newton) thats causing the extra lift..ie, airlfow being deflected downwards.. equall and opposite force applied to the wing, equal in strength, opposite in direction..aswell as increase in mean camber

 

cheers

 

 

[Barefootpilot]

Remeber if flaps only increased lift we would have them down all the time becaues they would be making the wing more efficiant. There will always be an increase in drag with any flap setting (excluding reflex flap of course!) but at small flap settings the increase in lift outweighs the increase in drag.

 

Adam

 

 

[Al B]

Hmmm, have to think about this one myself. How about: take a molecule of air and split it two at the leading edge. One half going over the wing the other below it. Now measure the distance traveled to the trailing edge of the lowered flap and I think you'll find that the upper half of the molecule has had to travel further than the lower half. Now, as they need to get to that point on the trailing edge, at the same time, the top one will have to have traveled faster and the lower and in doing so, produced a lower pressure across the top of the wing.

This is simply untrue - there is no reason why they would have to meet. I wish I knew where this myth came from. Please see What is Lift?

 

Specifically, please see Incorrect Lift Theory to explain why that theory is incorrect.

 

Cheers,

 

Al

 

 

[Yenn]

motza. I think you have hit the nail on the head. What is taught is sheer theory and not necessarily true, my opinion is that lift comes from deflecting air downwards, and the split flap does just the same as any other flap.

 

 

[lazerin]

Pitfield, the sportstar's flaps are as follows:

 

15 degrees - a bit more lift

 

30 degrees - a lot more drag

 

50 degrees - full blown speed brake

 

The split flaps, when deployed, will increase the angle of attack, because the chord line now has the trailing edge further back and down. However, as these are split flaps, you correctly guess that this only works so far. If you go past 15 (probably even at 15), the fact that the bottom trailing edge and top trailing edge is split means a lot of drag will be created.

 

As motzartmerv mentioned, using the first stage of flaps (15) will get you off the ground sooner, which will be handy if you have a short field and want to clear an obstacle. Your climb performance does suffer a bit though, due to the increased drag. With full flaps at climb power, it might not even climb at all if the conditions aren't just right.

 

For the record, I'm in the camp that lift is not purely due to one or the other theory (bernoulli vs equal/opposite reaction from air impacting bottom surface of wing) and that either theory will dominate over the other based on various circumstances.

 

e.g. a slow flier with a high camber wing will rely a lot more on bernoulli's principle, while a low camber, symmetrical wing of an aerobatic aircraft will rely more on the angle of attack.

 

 

[Deskpilot]

Well that certainly got you guys out of bed, didn't. Did you read how I started my post, like having to think about it and 'how about'. What ever 'theory' you believe and follow, stick with it. Flaps increase lift to a point, then become air breaks. Them's my opinions anyway.

 

 

[pitfield]

Thanks to all of you for your assistance. It's a great thing to have a resource like this and I'm very grateful to those who make it possible.

 

 

[Guest basscheffers]

At Parafield, we don't use flaps on take off at all on the Sporty; it is all smooth tarmac and lots of it. Except of course once or twice for short field practice.

 

I can imagine on a runway not as smooth, you may want to use take off flap to get off the ground a little sooner.

 

 

[Guest redleader]

Like all flap devices they increase the Apparent curvature of the wing/chord. Remember the line drawn along the mean of the upper and lower surfaces. Split flaps work by moving that mean. This gives to a greater increase in circulation. Which components fulfill newtown and bernouilli gives rise to the resultant lift / drag relationship for the individual shape.

 

Think about How do you make a cylinder provide lift? Think of the relative velocitys of the air around the cylinder and due to air having a viscosity (stickyness) you vector add. So you rotate it hence the term circulation. So if you shrink the cylinder down really small and place them in the shape of your wing. You can computationally CFD(computional fluid dynamics) solve thoose vectors to establish the performance of the shape.

 

Might sound a bit dumb but it is a bit like an ocean wave that the particles don't really move transitionally across the oceans. I.e a particle of water directly moves from los angles to sydney it actually just rotates. air is a bit similar as you move an object through it as air is a fluid.

 

Anyway i am on night shift at the moment while i write this so it may not be that clear.

 

 

[Guest drizzt1978]

I suggest doing a take off without flaps.....and make up youre own mind!!!!!;)

 

Did that accidentaly in a Jab and the bast!@# wouldnt lift up at take off speed.thumb_down

 

Gave me a real fright!! (early lesson) be kind!!!

 

re MIchael