# No one can explain WHY planes fly...

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#### poormansairforce

##### Well-Known Member
Lower pressure because it is moving faster.
Faster air in and of itself does not have lower pressure than the atmosphere around it. I've experimented with it and it just ain't so. Try rolling up a piece of newspaper into a tube and blow through it. If faster air has less pressure it should collapse but it doesn't. Now roll it into a shallow funnel and blow through the smaller end. What happens and why?

Do you know why the slipstream from a propeller contracts in diameter after leaving the prop?

##### Well-Known Member
I think focussing on "low pressure" and "air being pulled / sucked" just confuses the issue.
Air isn't pulled to a low pressure region, it's pushed by the higher (local) pressure.
No magic forces involved.

#### henryk

##### Well-Known Member
Air isn't pulled to a low pressure region, it's pushed by the higher (local) pressure.
=thru !(phisic)

#### Aerowerx

##### Well-Known Member
Faster air in and of itself does not have lower pressure than the atmosphere around it. I've experimented with it and it just ain't so. Try rolling up a piece of newspaper into a tube and blow through it. If faster air has less pressure it should collapse but it doesn't. Now roll it into a shallow funnel and blow through the smaller end. What happens and why?

Do you know why the slipstream from a propeller contracts in diameter after leaving the prop?
Poor analogy.

What is the crushing strength of a tube made from newspaper? I would say if there is a pressure difference it may not enough to overcome the strength of the tube.

First you say that faster air doesn't have lower pressure. Then you say that blowing through a tube doesn't collapse. Then you say that a slip stream contracts. Two completely different situations. One is confined. The other isn't.

#### poormansairforce

##### Well-Known Member
What is the crushing strength of a tube made from newspaper? I would say if there is a pressure difference it may not enough to overcome the strength of the tube
Did you try it? A small section of newspaper rolled up so it has a single layer over the majority of the tube has very little strength.

First you say that faster air doesn't have lower pressure. Then you say that blowing through a tube doesn't collapse. Then you say that a slip stream contracts. Two completely different situations. One is confined. The other isn't.
Air has viscosity so you can't act on all the molecules instantly. One molecule at at time. Think that through and you'll see that we literally have to expand or compress the air anytime we propel it or turn it. Once it leaves the source that acted upon it the atmosphere around it will quickly equalize it to ambient pressure/density.

The tube has just enough back pressure from friction to keep this from happening but the shallow angle funnel will keep expanding the airflow so the atmosphere can collapse the tube. A propeller expands the air as it works on it and the slip stream contracts after leaving it. Thats why blowing between 2 sheets of paper works the way it does. But we shouldn't confuse this with producing lift. On a flat surface the atmosphere will quickly compress the airflow to ambient pressure/density because nature abhors an imbalance. Only by turning or expanding the airflow can we create pressure change over a continuous surface.

I had done a bunch of experiments years ago but I'm sure you won't want to hear about them. Anyone can do them and I certainly don't feel the need to keep talking to walls either. Peace.

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#### mcrae0104

##### Well-Known Member
HBA Supporter
Log Member
Faster air in and of itself does not have lower pressure than the atmosphere around it.
So Bernoulli was wrong?

I've experimented with it and it just ain't so. Try rolling up a piece of newspaper into a tube and blow through it. If faster air has less pressure it should collapse but it doesn't.
This experiment doesn't prove that there is no pressure difference. The difference in static pressure is extremely slight, and the tube--even one made of newspaper--can stand up to it.

#### poormansairforce

##### Well-Known Member
So Bernoulli was wrong?
On an open system, yes. Or, more correctly, doesn't apply. Since we are dealing with airflow the math can give a rough estimate of lift but doesn't explain the actual process.

The difference in static pressure is extremely slight, and the tube--even one made of newspaper--can stand up to it.
Then why does the funnel collapse?

#### Aerowerx

##### Well-Known Member
This experiment doesn't prove that there is no pressure difference. The difference in static pressure is extremely slight, and the tube--even one made of newspaper--can stand up to it.
Exactly my point.

#### poormansairforce

##### Well-Known Member
Again, just observations from experiments that were free or nearly so. Bought a garage sale leaf blower that I raided the motor and impeller from. But thats why I mentioned its a thread about nothing...just like religion or politics nobody wins because everyone is right. Its all good.

#### mcrae0104

##### Well-Known Member
HBA Supporter
Log Member
On an open system, yes.
Please describe what you mean by "open system." Your experiment of fluid moving through a pipe is exactly what Bernoulli worked with and does not what the definition of an "open system." Either he was right or you are. The evidence supports Bernoulli and not your claim.

Then why does the funnel collapse?
It doesn't collapse when I do as you describe. Perhaps you can provide more detail about your experiment so that it can be reproduced.

#### poormansairforce

##### Well-Known Member
Your experiment of fluid moving through a pipe is exactly what Bernoulli worked with
A pipe or system as Bernoulli worked with will not deform. It is contained.

It doesn't collapse when I do as you describe. Perhaps you can provide more detail about your experiment so that it can be reproduced.
It does for me. A 3/4" hole at one end and maybe 1 1/2"+/- at the other and 12"-16" long. Blow through the small end.

#### Aerowerx

##### Well-Known Member
A pipe or system as Bernoulli worked with will not deform. It is contained.
Was that an actual physical experiment done by Bernoulli, or a theoretical construct?

In a theoretical construct it would be assumed that the pipe would not deform.

In a real physical experiment it may deform but the deformation would be very very tiny.

You should be careful using absolute terms like "not", "never", "always". And yes, sometimes I find myself using them.

#### poormansairforce

##### Well-Known Member
Was that an actual physical experiment done by Bernoulli, or a theoretical construct?

In a theoretical construct it would be assumed that the pipe would not deform.

In a real physical experiment it may deform but the deformation would be very very tiny.

You should be careful using absolute terms like "not", "never", "always". And yes, sometimes I find myself using them.

#### jedi

##### Well-Known Member
Or you could say that everyone can explain how airplanes fly as it appears that everyone has a different method of making sense of the real world. Wing lift is not the only thing that has more than one explanation or is difficult to put into words.

God is the historical creator of things that are difficult to understand. Only in the last few centuries have we found explanations for many former acts of God. Explain gravity, light (and lightning), thunder, etc. You can see that we are making progress.

The various lift explanations are far from complete so rather than let this thread die I thought now might be a good time to give it new life.

That reminds me, life is another one of those things that is difficult to explain even though we all know what it is.

Does life come from God or mothers? Are mothers God? Happy Mothers Day to all of you out there who are mothers, have or have had mothers, were mothers or would like to be mothers or make mothers.

Have a Happy Mother's Day Ecard (Fun Song)

#### Jay Kempf

##### Curmudgeon in Training (CIT)
Ok. I will step in.

Even my boy was able to see and feel it

Yeah, but...?

The fan outlet only blows over the top of the wing. Any shape will do that and it would work if you inverted wing it would still work and if you just inverted the tube it would still work but gravity helps the ball anyway. So what is this actually showing. If you took the airfoil shape out of this and just blew air faster across one end of the tube in the same ambient zone it would still work. Which explains NOTHING!

This actually explains very well how an exhaust ejector works by inducing a flow...

#### BJC

##### Well-Known Member
HBA Supporter
so rather than let this thread die I thought now might be a good time to give it new life.
Do we get to vote on that ?

BJC

#### henryk

##### Well-Known Member
=plasma thruster...

=fluidic thrusters.

#### jedi

##### Well-Known Member
It's not that no one can explain how wings create lift. The fact is that very few people have the patience to listen to the full explanation and those that do dispute the facts. It is all simple physics clocked in the mysteries of fluid dynamics.

Now, does anyone want to understand lift or is it that it is like love, a wonderful mystery.

Want a real argument? Try to explain why there is love between spouses.