We need a technical and logical discussion.

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exhaustgases
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We need a technical and logical discussion.

Postby exhaustgases » Mon Aug 14, 2017 1:42 am

And yes as time goes on this will be in the correct place, as it is political.
This is to look into the brain trust on this site, lets see who the thinkers are.

I want to start this out with something everyone has been taught about a certain scientific topic, but I have to lead up to it first.
Its so nice this is an automotive site and has a nice concentration of engine related topics. So let me start out with the good old carburetor.
I can't just spew what I think about this topic I need input and some logic, it may even change what I think about it.
So I ask has anyone ever measured the velocity of the air entering the air horn of a carburetor at full song and at the same time the pressure with in the venturi. And yes this is going to be interesting, and when done with this first discussion I hope we can come up with a few more.

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Re: We need a technical and logical discussion.

Postby joe 90 » Mon Aug 14, 2017 2:42 am

You really need to define what sort of engine and what sort of carburettor and how many cylinders per choke.

That's a good start.

Otherwise some will mention apples, others, potatoes.

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Re: We need a technical and logical discussion.

Postby exhaustgases » Mon Aug 14, 2017 1:20 pm

Pick any old 60's street chev a 6 or an 8 cylinder its not going to matter a whole lot for what I'm getting to.
Maybe stick with a single barrel carb on the 6 cylinder. And actually anything that anyone has ever measured would be nice. And when I bring up the reason for this, I know this carb example is not going to be a real accurate representation, but it helps show the science. I would like to see the negative pressure at various volumes and air speed. And yes of course the shape of the venture would be a factor but how much?

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Re: We need a technical and logical discussion.

Postby exhaustgases » Mon Aug 14, 2017 7:26 pm

I guess not many here know much about aerodynamics ?

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Re: We need a technical and logical discussion.

Postby David Redszus » Tue Aug 15, 2017 11:23 am

exhaustgases wrote:I guess not many here know much about aerodynamics ?

I think you might mean "fluid dynamics" which includes both air and fuel flows.

The air flow through any induction system can be measured by use of an air mass flow sensor. If the signals are logged we can see mass flow rate for any operating condition of speed, throttle, or air density.

Years ago I built an air mass flow bench for testing carbs. Seemingly identical carbs did not flow the same.
But, flow rate was limited by a low pressure ratio and did not reflect true mass flow in a running engine; neither does any flow bench.

We then ran a fuel signal suction sensor to measure the fuel pressure draw under various conditions. Again, identical carbs did not deliver the same fuel signal.

We did learn that fuel flow was much more tricky than air flow. Some of the variables evaluated were:
Fuel Jet diameter
Jet Discharge coefficient
Fuel specific gravity
Barometric pressure
Venturi pressure
Fuel lift height
Gravity effects

We did not examine fuel viscosity or fuel evaporation cooling effects.
At that point we decided that our time was much better spent on fuel injection systems and
mapping than on old carbs.

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Re: We need a technical and logical discussion.

Postby exhaustgases » Tue Aug 15, 2017 3:22 pm

Well I guess I need to jump into it. The main thing I'm looking for is airfoil shape and negative pressure. I'm out to kill the lift theory of the airplane wing, which my brother and I see eye to eye on. As private pilots we laugh at what we and everyone is taught in public school that a plane will only fly with the camber or curvature on the top of the wing, that increases air flow and causes vacuum or negative pressure. They all seem to think that is the major force sucking the wing up. NO. Its the high positive pressure from angle of attack that does I would say 95% or more of the lifting.
And I do thank you for your carb test info David, it would be interesting to see that fuel suction sensor.

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Re: We need a technical and logical discussion.

Postby exhaustgases » Tue Aug 15, 2017 7:32 pm

Wow, not many here can handle it,huh?

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Re: We need a technical and logical discussion.

Postby David Redszus » Tue Aug 15, 2017 7:33 pm

They all seem to think that is the major force sucking the wing up. NO. Its the high positive pressure from angle of attack that does I would say 95% or more of the lifting.


Well that certainly is easy to prove. Or not.
I have an airfoil dynamics program that allows almost any foil shape and attack angle to be entered.
It will calculate the lift and drag, surface velocity, stagnation pressure, streamlines and stall angles.
We could easily fly the wing upside down at various attack angles and predict the lift and drag forces.

This is really old stuff and is found in almost every textbook on the subject.

For those interested, Google Dr. Hanley at Hanley innovations to get this program for yourself.
It also works on automotive wings and spoilers.

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Re: We need a technical and logical discussion.

Postby exhaustgases » Wed Aug 16, 2017 1:20 am

And right on again. That is the first argument flying upside down. I say a plane with a flat wing could fly as well. Its all about the positive pressure.

It drives me nuts when I see a post on an airplane site that says its the lift on the airplane propeller that sucks the plane through the sky, makes you wonder what makes the huge wind storm behind the plane.

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Re: We need a technical and logical discussion.

Postby joe 90 » Wed Aug 16, 2017 4:28 am

It's more likely a bit of both .


But as you say, even as a kid in school I always thought we were being lied to.

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Re: We need a technical and logical discussion.

Postby David Redszus » Wed Aug 16, 2017 10:11 am

And right on again. That is the first argument flying upside down. I say a plane with a flat wing could fly as well. Its all about the positive pressure.

Wrong. It is ONLY about the negative pressure. But airfoil camber does increase the pressure differential between the upper and lower surface. Attack angle increases or decreases the pressure differential. A flat wing can and does fly, but only with sufficient attack angle. If the attack angle is increased, at some point the wing will stall, EVEN WITH MASSIVE underwing pressure. A further example is the ground effect of a front automotive wing. As the wing is lowered, the downforce increases without a change in wing camber or attack angle. Up to a point. When the wing is too low, air can no longer flow under the wing, and downforce is lost. Even though air is flowing above the upside down wing.

The end plates on wings is further proof of air flow. The end plate winglets point upward toward the lift surface and not downward toward the pressure surface of the wing.

It drives me nuts when I see a post on an airplane site that says its the lift on the airplane propeller that sucks the plane through the sky, makes you wonder what makes the huge wind storm behind the plane.

A propeller has the same shape as an airfoil and works the same way. The air entering the propeller swept zone splits air flow above the foil and below the foil. The negative pressure, or lift, moves the propeller forward.
But every action must have an equal and opposite reaction. However much force is moving the propeller forward is matched by the force of the air behind the prop. At some point behind the wing, the velocity of the upper and lower airstreams become equal and are rejoined.

Go to the Hanley Innovations web site and buy Dr. Hanley's program. It's better than a textbook, or at least quicker and easier to understand.

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Re: We need a technical and logical discussion.

Postby exhaustgases » Wed Aug 16, 2017 12:40 pm

I see a propeller more of a screw than a vacuum cleaner. Similar to a boat propeller.
So what we need to see is for say a 737 at normal cruise what is the negative pressure per square foot on the top of the wing in and area of most camber and in the same area on the underside of the wing. I say the pressure on top is next to nothing in the minus direction, just like a carburetor venturi that is measured in inches of water. If there was anysort of great suction on that surface all the sheet metal would be pulled off the wing.
And small aircraft especially the fabric covered wing ones would be ripped apart on the first flight.

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Re: We need a technical and logical discussion.

Postby David Redszus » Wed Aug 16, 2017 1:52 pm

So what we need to see is for say a 737 at normal cruise what is the negative pressure per square foot on the top of the wing in and area of most camber and in the same area on the underside of the wing

What you are asking to see is the surface pressure profiles along the wing surfaces. It does not matter what wing we use, even the venturi shape of a carburetor.

I say the pressure on top is next to nothing in the minus direction, just like a carburetor venturi that is measured in inches of water. If there was anysort of great suction on that surface all the sheet metal would be pulled off the wing.

The pressure on the upper surface must be lower than the bottom surface or else the plane won't fly.
How much pressure differential exists will be determined by air foil camber, attack angle and air speed.

As far as pulling all the sheet metal off, why do you think they went from lightweight fabric coverings to much heavier sheet metal held in place with thousands of rivets.

Please take a peek at Prof Hanley's airfoil programs.

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Re: We need a technical and logical discussion.

Postby exhaustgases » Thu Aug 17, 2017 12:43 am

I agree the pressure is less at the top of the wing, because of the excess of pressure at the bottom even with the venturi effect at the top there still has to be an angle of incidence to make the higher positive pressure than the top, as well as an added angle of attack. And we both agree that wing will fly upside down, again its always the higher positive pressure of the wing forcing down the air, just like a fan blade or helicopter is doing.
Fabric covered wings are still flying this day and age and they don't rip off from suction. With the advent of high speeds the fabric didn't last very well and then of course the ageing effect from weather deteriorates it in time.
What I want to see is what is the pressure at the top of the wing vs the bottom of the wing so we can see what pressure is the load bearing pressure for lack of a better term.

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Re: We need a technical and logical discussion.

Postby joe 90 » Thu Aug 17, 2017 1:18 am

My first plane was a paper one.

It flew OK for a short distance.


It's the differential in pressure between the top and bottom of the wing.
You can't have one without the other.
But the largest part of it will be the vacuum at the top of the wing.


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