Sideslipping a Pitts?

[Edbear]

Who was bringing the yellow Pitts into Dairy Flat airfield last evening about 6:42pm, (and 13sec. approximately...)?

You wuz coming in quite fast and appeared from my angle to be sideslipping something fierce! I was heading South into Aucks and it looked like a deliberate sideslip. Pilot seemed to be having fun!

I know there are a couple of Pitts pilots on KB so wondered if it was anyone here?

[Bass]

The Pitts does not have flaps or trim tabs. Further, its wing section is fully symmetrical so that it flies the same inverted as upright. Consequently, as the speed comes down, the angle of attack rises and so does the nose, to the extent that you cannot see the strip with a straight in approach.
Side slipping on the approach is normal, and yes, it's fun.
I can't swear to it, but I suspect that it's more critical with the 2 seater than the S1 because of the bigger motor, longer nose and much heavier aeroplane.

[Edbear]

... it flies the same inverted as upright...

'Cept of course if inverted you push the stick forward for "up"...

Thanks for the info! It was a yellow and black and I didn't look to notice if the two-seater.

I suppose to make the abservation that the pilot appeared to be having fun is kinda like stating the bleeding obvious when referring to a Pitts...

[Swoop]

It belongs to a couple of guys who drive bigger things for a living.
You might see it in the air for a few more days...

[pete376403]

The Pitts does not have flaps or trim tabs. Further, its wing section is fully symmetrical so that it flies the same inverted as upright.

I'm not a flyer so anything I know about planes is from reading. Anyway, I understood that wings worked because of the non symmetry, The top of the wing is curved and the lower surface flat so there is a difference in airspeed over/under the wing, and therefore a difference in air pressure - less pressure on the top. (Bernoullis Principle.) Does the Pitts fly because of something else?

[Grub]

I'm not a flyer so anything I know about planes is from reading. Anyway, I understood that wings worked because of the non symmetry, The top of the wing is curved and the lower surface flat so there is a difference in airspeed over/under the wing, and therefore a difference in air pressure - less pressure on the top. (Bernoullis Principle.) Does the Pitts fly because of something else?

Not bad for a non-pilot Pete. Well we could get into a two-year debate here. The jury is out on Bernoullis at the moment.

For years it has been believed as you point out, that lift comes from the differing distance that air molucules have to travel over and under a wing. Because the air travells further over the top than the bottom, the air is thinner over the top and therefore has less pressure (simpliffied version). Less pressure means the aircraft is "sucked" up rather than pushed up because of the angle of attack.

Well ... the nay-sayers are now debating this long held (and cherished) version of things. Modern computer modelling has called the whole Bernoulli Theorem into question as they maintain that angle of attack (AoA) is the cause of lift. It not been proven either way so I'll just happily go with whatever it is that gets me into the air.

[pete376403]

Bernoullis also applies in your common or garden carburettor - the reduction in diameter of the venturi increases the air speed, so the theory says the air pressure reduces below atmospheric. However atmo pressure is being applied to the fuel in the float chamber, so this difference in pressure forces fuel up the jet where it mixes with the air. Even in a turbo (blow through) system, the boost pressure applied to the float chamber is higher than the boost pressure in the venturi as (in the venturi) the pressure has been reduced by the increase in airspeed and the fuel gets pushed (not 'sucked") up the jet.

So Bernoullis(or something like it) works here.

[Pixie]

Not bad for a non-pilot Pete. Well we could get into a two-year debate here. The jury is out on Bernoullis at the moment.

For years it has been believed as you point out, that lift comes from the differing distance that air molucules have to travel over and under a wing. Because the air travells further over the top than the bottom, the air is thinner over the top and therefore has less pressure (simpliffied version). Less pressure means the aircraft is "sucked" up rather than pushed up because of the angle of attack.

Well ... the nay-sayers are now debating this long held (and cherished) version of things. Modern computer modelling has called the whole Bernoulli Theorem into question as they maintain that angle of attack (AoA) is the cause of lift. It not been proven either way so I'll just happily go with whatever it is that gets me into the air.

It's actually magic.
The same way pixies fly

[Edbear]

Does the Pitts fly because of something else?

The Pitts is something else...! I reckon they are such a happy-go-lucky little sports plane that they just have to leap up into the air at every opportunity!

[Grub]

They can be nasty lil sods too. Because they're so short they ge seriously twitchyclose to the ground on approach. As you slow, the rudder looses authority and therefore its ability to stop any big swing that might develop.

Sideslipping is a dodgy manouvre in some aircraft, usually high-winged ones like Cessnas. The side-slip throws a wing wind shadow over the rear tailfin and elevator and completely takes away the very thing thwey need to function - airflow. Each aircraft is different and you gotta read the manual to see if side-slipping is banned.

[Jantar]

I'm not a flyer so anything I know about planes is from reading. Anyway, I understood that wings worked because of the non symmetry, The top of the wing is curved and the lower surface flat so there is a difference in airspeed over/under the wing, and therefore a difference in air pressure - less pressure on the top. (Bernoullis Principle.) Does the Pitts fly because of something else?

Pretty good alright, but as Grub points out, if Bernoullis theory was the only thing that causes lift then aircraft with symetrical airfoils would not be able to fly. On the other hand, if it was only AoA on a flat surface then in order to obtain sufficient lift for straight and level flight then a significant AoA would be required along with accompanying drag.

So, a combination is required. With a symetrical aerofoil, the Phillips point (the point at which air first contacts the wing) moves with the angle of incidence (AoI), and with an AoI of greater than zero the effective aerofoil is no longer symetrical. hence bernoullis theory still applies.

[Edbear]

They can be nasty lil sods too. Because they're so short they ge seriously twitchyclose to the ground on approach. As you slow, the rudder looses authority and therefore its ability to stop any big swing that might develop.

Sideslipping is a dodgy manouvre in some aircraft, usually high-winged ones like Cessnas. The side-slip throws a wing wind shadow over the rear tailfin and elevator and completely takes away the very thing thwey need to function - airflow. Each aircraft is different and you gotta read the manual to see if side-slipping is banned.

Don't know so much about the Bernoullis theory, but the Missus banned sideslipping on the Boulevard...

Pretty good alright, but as Grub points out, if Bernoullis theory was the only thing that causes lift then aircraft with symetrical airfoils would not be able to fly. On the other hand, if it was only AoA on a flat surface then in order to obtain sufficient lift for straight and level flight then a significant AoA would be required along with accompanying drag.

So, a combination is required. With a symetrical aerofoil, the Phillips point (the point at which air first contacts the wing) moves with the angle of incidence (AoI), and with an AoI of greater than zero the effective aerofoil is no longer symetrical. hence bernoullis theory still applies.

Whew!

[Bass]

I'm not a flyer so anything I know about planes is from reading. Anyway, I understood that wings worked because of the non symmetry, The top of the wing is curved and the lower surface flat so there is a difference in airspeed over/under the wing, and therefore a difference in air pressure - less pressure on the top. (Bernoullis Principle.) Does the Pitts fly because of something else?

If you are prepared to bolt enough power to it, you can pretty much make anything fly. I was told a story once about a relatively new graduate who wound up assisting with wing design on the A4 ? Skyhawk. He was trying really hard to come up with the most efficient design that he could and was running up a great deal of wind tunnel time. He was also behind schedule and holding things up.
Eventually the project leader took him aside to see what the problem was and then told him to run the numbers on a flat plate aerofoil.
It turned out that a flat plate was within 10% of the best design that he had come up with. The aeroplane had that much grunt that any reasonably thin wing section would work.
They have flaps and leading edge slats etc for the slow stuff (and that's when they really need the grunt cos the drag is huge).

I played around with RC models for nearly 20 years. I eventually graduated to racing them at international level and held the NZ record for a while. I don't know what speed a modern model racer is capable of but i suspect it will be in excess of 400 kph. Anyway, I got quite deeply involved in aerofoil design and performance. Modern racing aerofoils are asymmetric, but only just.

For general everyday model flying, I found that a fairly thick, fully symmetrical section is the most versatile, forgiving and easy to use. It doesn't lose as much as you would think in top speed either.

In summary, Mr Bernoulli plays a part, but in recent times it has been established that his theorem does not entirely explain a wing's behaviour. Standing vortex theory actually does rather better. In any case, the final shape of the wing used depends pretty much on what compromises the designer will live with and is not especially critical until the last few percent of performance is being chased.

If you want to put it all in perspective, consider how many modern aircraft with asymmetric aerofoils can sustain inverted flight - especially military stuff

[Grub]

I think this thread should be closed by the mods ... this is KB after all! My reasons for this request is that it doesn't meet Forum Criteria in a number of areas ...
- It is sensible
- It is informative
- Has stayed on topic
- No trolling has taken place
- It is not shallow, it has depth
- It explores intelligent and revealing discussion
- It enlightens us as to other facets of some of our members

[Swoop]

I was told a story once about a relatively knew graduate who wound up assisting with wing design on the A4 ? Skyhawk.

If it is the A4, then it might be relating to the rudder on that aircraft. Have a look at it and you see something similar to what you described with a flat plate.
Ed Heinemann (sp?) said that they would "go back and have another look at that later", but it worked fine... & "if it ain't broken" etc.