Certify a straight tail 172 for IFR?

Clark1961 said:
Okay, we're done here if you can't admit that a fluid only flows from high pressure to low. I detest your intellectual dishonesty in this discussion.
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you don't need pressure high or low to make air flow. I don't set at the computer all day. So don't start with your hate BS.

The flow thru the venturi is caused by moving the venturi thru the air, the air pressure does not change outside the venturi. With the increase in velocity with in the venturi causes a low at the narrowest part of the air passage. Which causes a flow into that area, there is no flow caused by any out side pressure.

If you do believe you need a pressure differential to cause a flow, ask your self how much pressure is in a water fall.

Remember that pressure is a restriction to flow. there is no restriction in a venturi. no restriction = no pressure.
 
Tom-D said:
you don't need pressure high or low to make air flow. I don't set at the computer all day. So don't start with your hate BS.

The flow thru the venturi is caused by moving the venturi thru the air, the air pressure does not change outside the venturi. With the increase in velocity with in the venturi causes a low at the narrowest part of the air passage. Which causes a flow into that area, there is no flow caused by any out side pressure.

If you do believe you need a pressure differential to cause a flow, ask your self how much pressure is in a water fall.

Remember that pressure is a restriction to flow. there is no restriction in a venturi. no restriction = no pressure.
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No hate BS here Tom, never has been. We're done on this topic. I'll agree to disagree but that's about it.
 
Clark1961 said:
How is there flow from the low pressure outside the venturi to the higher pressure you claim is inside the venturi?
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It's not higher pressure inside and lower pressure outside, it's different pressures at different points inside the tube due to different velocities at different points inside the tube. IOW, there's no flow from outside to inside, there's just flow through it. Here's a picture:
Venturi-Meters-017_400_200_thumb.gif


See this page for details.
 
Ron Levy said:
It's not higher pressure inside and lower pressure outside, it's different pressures at different points inside the tube due to different velocities at different points inside the tube. IOW, there's no flow from outside to inside, there's just flow through it. Here's a picture:
Venturi-Meters-017_400_200_thumb.gif


See this page for details.
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Since you claim there is no flow from outside the venturi, the air somehow magically appears inside the venturi?

Ron, drop the sophomoric attempts to distract from the simple truth that flow is from high pressure to low and the controlling pressure is outside the venturi.
 
Clark1961 said:
Since you claim there is no flow from outside the venturi, the air somehow magically appears inside the venturi?
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It doesn't flow across the wall, it flows through from the opening in the front to the opening in the back, and the pressure is about the same at each end. The flow through the venturi tube is driven by the aircraft's motion through the air, powered by its propulsion system. However, the pressure taps at the various points along the length of the tube allow one to take advantage of the differences in pressure at each point to drive the gyros in the instruments.
Ron, drop the sophomoric attempts to distract from the simple truth that flow is from high pressure to low and the controlling pressure is outside the venturi.
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I would if it that were true, but it isn't. The pressure differential is controlled by the ratio of inlet area to throat area and the velocity of the air through the tube, not the ambient air pressure outside the tube.

And I'm sorry for attempting to explain this at a sophomore level -- perhaps I should try freshman, or maybe kindergarten? :dunno:
 
Ron Levy said:
It doesn't flow across the wall, it flows through from the opening in the front to the opening in the back, and the pressure is about the same at each end. The flow through the venturi tube is driven by the aircraft's motion through the air, powered by its propulsion system. However, the pressure taps at the various points along the length of the tube allow one to take advantage of the differences in pressure at each point to drive the gyros in the instruments.
I would if it that were true, but it isn't. The pressure differential is controlled by the ratio of inlet area to throat area and the velocity of the air through the tube, not the ambient air pressure outside the tube.

And I'm sorry for attempting to explain this at a sophomore level -- perhaps I should try freshman, or maybe kindergarten? :dunno:
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Thank you for finally admitting what we all know and that is the fact that air flows into the venturi from outside of the venturi. It's quite a simple concept and it is extremely unfortunate that it took you this long to admit it. Most of my students would have admitted it from the very beginning because it is a simple truth.

However, once again you try to distract from the truth about the pressure in venturi by jumping to pressure differential. I'm sorry that you chose this path instead of admitting the simple facts of the venturi which you previously attempted to argue.

Now pay attention and drop all your misguided pretense. In order for there to be flow in the venturi there has to be pressure drop along the length of venturi. That is a simple statement of fact. The pressure within the venturi relative to the atmospheric pressure is what provides the motive force which drives the instruments. The pressure drop within the venturi also results in a temperature drop.

Okay, that's the end of today's lesson. Come back tomorrow with a good attitude and we'll continue your education of fluid flow. Have a real nice day now, ya' hear?
 
Clark1961 said:
Thank you for finally admitting what we all know and that is the fact that air flows into the venturi from outside of the venturi. It's quite a simple concept and it is extremely unfortunate that it took you this long to admit it. Most of my students would have admitted it from the very beginning because it is a simple truth.

However, once again you try to distract from the truth about the pressure in venturi by jumping to pressure differential. I'm sorry that you chose this path instead of admitting the simple facts of the venturi which you previously attempted to argue.

Now pay attention and drop all your misguided pretense. In order for there to be flow in the venturi there has to be pressure drop along the length of venturi. That is a simple statement of fact. The pressure within the venturi relative to the atmospheric pressure is what provides the motive force which drives the instruments. The pressure drop within the venturi also results in a temperature drop.

Okay, that's the end of today's lesson. Come back tomorrow with a good attitude and we'll continue your education of fluid flow. Have a real nice day now, ya' hear?
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I'm with Clark on this one. How about we test it. Someone send me two temp probes and I'll stick them on the outside of the venturi and on the inside on my Flybaby.
 
Clark1961 said:
Thank you for finally admitting what we all know and that is the fact that air flows into the venturi from outside of the venturi. It's quite a simple concept and it is extremely unfortunate that it took you this long to admit it. Most of my students would have admitted it from the very beginning because it is a simple truth.

However, once again you try to distract from the truth about the pressure in venturi by jumping to pressure differential.
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Since pressure differential is what we're trying to achieve, I don't see that as a distraction. But I do see a real problem in your understanding of how a venturi is used to provide the motive force to operate an air-driven gyro in planes of the vintage under discussion. Again, read the discussion on the page I linked to understand how it all works, because the ambient air pressure outside the venturi really isn't relevant.
 
jesse said:
I'm with Clark on this one. How about we test it. Someone send me two temp probes and I'll stick them on the outside of the venturi and on the inside on my Flybaby.
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already done that, sort of. I used to work at a place with some turbine-converted C47's and they still had the venturis mounted. They had temperature probes in the venturis. Within the range of the measurement tolerance there was no change in venturi throat temperature with airspeed.

Yes, if I put on my physics hat we know from fluid mechanics 101 that if the venturi throat has a pressure lower than the ambient pressure then it must be at a lower temperature than ambient temperature. But if i put my engineer's hat back on, it's not enough to make any meaningful difference for something like icing.
 
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timwinters said:
Clark, dude, you must remember who you are debating with:



He's just decided to diversify:








:lol:
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You have created quotations out of thin air -- I never said all the things you attribute to me, and I most certainly am an engineer -- got the diploma from the University of Michigan's College of Engineering right here on the wall to prove. Please remove your false and insulting post at once.
 
JHW said:
Yes, if I put on my physics hat we know from fluid mechanics 101 that if the venturi throat has a pressure lower than the ambient pressure then it must be at a lower temperature than ambient temperature. But if i put my engineer's hat back on, it's not enough to make any meaningful difference for something like icing.
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Thank you, from a fellow engineer.
 
Tom-D said:
you don't need pressure high or low to make air flow. I don't set at the computer all day. So don't start with your hate BS.

The flow thru the venturi is caused by moving the venturi thru the air, the air pressure does not change outside the venturi. With the increase in velocity with in the venturi causes a low at the narrowest part of the air passage. Which causes a flow into that area, there is no flow caused by any out side pressure.

If you do believe you need a pressure differential to cause a flow, ask your self how much pressure is in a water fall.

Remember that pressure is a restriction to flow. there is no restriction in a venturi. no restriction = no pressure.
Click to expand...

:confused::confused::confused: You're kidding right?:rofl::rofl::rofl: Because that's the funniest thing I have read in days. It's the ONLY thing that makes it flow, it defines flow.
 
I'm looking into a way to test this on my Flybaby venturi.
 
JHW said:
already done that, sort of. I used to work at a place with some turbine-converted C47's and they still had the venturis mounted. They had temperature probes in the venturis. Within the range of the measurement tolerance there was no change in venturi throat temperature with airspeed.

Yes, if I put on my physics hat we know from fluid mechanics 101 that if the venturi throat has a pressure lower than the ambient pressure then it must be at a lower temperature than ambient temperature. But if i put my engineer's hat back on, it's not enough to make any meaningful difference for something like icing.
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How many degrees do you loose pulling 6" of vacuum? Please apply 100% humidity and a 35°F/2°C factor if relevant.
 
jesse said:
I'm looking into a way to test this on my Flybaby venturi.
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Suggestion, the radius of your flying wires is similar to the radius of the venturi leading edge. Go fly through some cold clouds and compare the amount of accumulated ice on the wires and the venturi. Then note whether or not there is any ice in the throat of the venturi or whether it's all on the venturi inlet. This last check will probably need to be done by an associate on the ground post-crash.
 
easy enough to calculate, let's use the simplest approximation that it's adiabatic, ideal gas, yada yada, and just look at the ideal gas law

(Pressure)*(specific volume) = (R gas constant) * (temperature)

for our purposes we can assume specific volume and R are constants, so we can say that P2/P1 = T2/T1

My old ercoupe's venturi would pull about 5.5 inches vacuum at 5000ft.

I personally won't fly a non-deiced aircraft in clouds colder than +5C.

Standard pressure at 5000ft is going to be around 24.9 in Hg

so:
T2=T1*(P2/P1)=(5c)*(24.9-5.5)/24.9
T2=3.9
T2 - T1=1.1C

So 1.1C is our theoretical maximum temperature drop, which is already pretty insignificant. In real life it will be less of a drop because there is heat transfer from the air through the body of the venturi.
 
JHW said:
Suggestion, the radius of your flying wires is similar to the radius of the venturi leading edge. Go fly through some cold clouds and compare the amount of accumulated ice on the wires and the venturi. Then note whether or not there is any ice in the throat of the venturi or whether it's all on the venturi inlet. This last check will probably need to be done by an associate on the ground post-crash.
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Your FlyBaby has the same problem that the early 170/2s do they simply do not have the panel space for equipment to do a proper layout.
 
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Tom-D said:
Your FlyBaby has the same problem that the early 170/2s do they simply do not have the panel space fir equipment to do a proper layout.
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you can get a lot of space for instruments with something like the skyview 7in version, but you still need to find a place for a nav radio.

I've been kicking around the idea of a Onex as a commuter but it's the same problem, not enough panel space to make it IFR
 
JHW said:
easy enough to calculate, let's use the simplest approximation that it's adiabatic, ideal gas, yada yada, and just look at the ideal gas law

(Pressure)*(specific volume) = (R gas constant) * (temperature)

for our purposes we can assume specific volume and R are constants, so we can say that P2/P1 = T2/T1

My old ercoupe's venturi would pull about 5.5 inches vacuum at 5000ft.

I personally won't fly a non-deiced aircraft in clouds colder than +5C.

Standard pressure at 5000ft is going to be around 24.9 in Hg

so:
T2=T1*(P2/P1)=(5c)*(24.9-5.5)/24.9
T2=3.9
T2 - T1=1.1C

So 1.1C is our theoretical maximum temperature drop, which is already pretty insignificant. In real life it will be less of a drop because there is heat transfer from the air through the body of the venturi.
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What if the airframe is cold soaked from being at a higher altitude?

Sorry, y'all can fly IFR with venturiis if you want. To me they make a plane useless for IFR. The best value for the money getting non venturi driven gyros in the plane is going to be an Aspen.
 
JHW said:
easy enough to calculate, let's use the simplest approximation that it's adiabatic, ideal gas, yada yada, and just look at the ideal gas law

(Pressure)*(specific volume) = (R gas constant) * (temperature)

for our purposes we can assume specific volume and R are constants, so we can say that P2/P1 = T2/T1

My old ercoupe's venturi would pull about 5.5 inches vacuum at 5000ft.

I personally won't fly a non-deiced aircraft in clouds colder than +5C.

Standard pressure at 5000ft is going to be around 24.9 in Hg

so:
T2=T1*(P2/P1)=(5c)*(24.9-5.5)/24.9
T2=3.9
T2 - T1=1.1C

So 1.1C is our theoretical maximum temperature drop, which is already pretty insignificant. In real life it will be less of a drop because there is heat transfer from the air through the body of the venturi.
Click to expand...

Ya gotta use absolute temperatures if ya wanna do the math
 
Ron Levy said:
Since pressure differential is what we're trying to achieve, I don't see that as a distraction. But I do see a real problem in your understanding of how a venturi is used to provide the motive force to operate an air-driven gyro in planes of the vintage under discussion. Again, read the discussion on the page I linked to understand how it all works, because the ambient air pressure outside the venturi really isn't relevant.
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You see what isn't there...which is typical for those attacking without basis.

Get your story straight, first you said there is pressure rise, now you say pressure doesn't matter. If you knew what you were typing about the story would be consistent...
 
Henning said:
Would you be so kind Dr?
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okay, very well

we were presented with the following incompetent calculation:
so:
T2=T1*(P2/P1)=(5c)*(24.9-5.5)/24.9
T2=3.9
T2 - T1=1.1C


it should be something like:

so:
T2=T1*(P2/P1)=(5c+273)*(24.9-5.5)/(24.9)
T2=-56c (if I did the arithmetic right which is doubtful)
T2 - T1= a bunch

so shut the f*** up you folks who don't understand computational fluid dynamics. Okay?
 
Clark1961 said:
okay, very well

we were presented with the following incompetent calculation:
so:
T2=T1*(P2/P1)=(5c)*(24.9-5.5)/24.9
T2=3.9
T2 - T1=1.1C


it should be something like:

so:
T2=T1*(P2/P1)=(5c+273)*(24.9-5.5)/(24.9)
T2=-56c (if I did the arithmetic right which is doubtful)
T2 - T1= a bunch

so shut the f*** up you folks who don't understand computational fluid dynamics. Okay?
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I'm not smart enough for the math, but I can certainly stick some probes on an airplane and fly.

Talked to my friend into embedded hardware. He just ordered the parts. Next week he'll have me two temperature probes, a small box, a self contained battery, and a SD card.

I'll stick one probe on the inside of the venturi and one outside of it. Zip tie the box somewhere and go flying.

It will record the temperature of both probes every second and save it to the SD card as a CSV. Should have results by end of next week.
 
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jesse said:
Talked to my embedded hardware guy. He just ordered the parts. Next week he'll have me two temperature probes, a small box, a self contained battery, and a SD card.

I'll stick one probe on the inside of the venturi and one outside of it. Zip tie the box somewhere and go flying.

Should have results by end of next week.
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keep in mind the reason that the venturi doesn't want to ice up is that the body is warmed by the air outside the tube...any roughness inside the venturi would be a bad thing but a smooth surface would probably prevent ice from adhering to the walls.

None of the comments change the physics...
 
JHW said:
yep you're right, i screwed that up in my haste. 7 years of college down the drain
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Jeff - You're way above Tom and Ron...that's all I can say.
 
Heck, I knew it was a lot from using venturi evacuators. I could make snow with those in Louisiana.
 
Henning said:
Heck, I knew it was a lot from using venturi evacuators. I could make snow with those in Louisiana.
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BS.. with out a decompressing gas there will be no cooling.

the hose you used to blow air thru the evac, was what was causing the cooling.

just like the air escaping the tire freezes up the valve stem.
 
Clark1961 said:
and what is the pressure ratio there Tom?

yer outa yer league...
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The same as it will be in a refer unit.

Compress the air, it will heat. allow it to reach room temp, then allow it to expand it will cool.

There is no college math require to figure this out.
 
Tom-D said:
The same as it will be in a refer unit.

Compress the air, it will heat. allow it to reach room temp, then allow it to expand it will cool.

There is no college math require to figure this out.
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so?

yer still outa yer league as long as you don't understand that a fluid flows from high pressure to low pressure (or high potential to low potential if you'd rather include gravity) I'm not gonna mess around with you on this and handle you with kidd gloves...
 
Clark1961 said:
so?

yer still outa yer league as long as you don't understand that a fluid flows from high pressure to low pressure (or high potential to low potential if you'd rather include gravity) I'm not gonna mess around with you on this and handle you with kidd gloves...
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What high pressure or what low pressure ?

In a venturi there is none, your reference even said that. the flow is in one end and out the other, no restriction = no pressure.

That velocity created in the narrow portion creates a flow into that portion. There will be no vacuum pressure created until there is a restriction to that flow.
there is actually more air exiting the venturi than entering the venturi.
Even any old Navy trained Hydraulic mechanic knows this, why does it escape a college brainyack.

Or are you applying the wrong principals, by over thinking the obvious.
 
Tom-D said:
What high pressure or what low pressure ?

In a venturi there is none, your reference even said that. the flow is in one end and out the other, no restriction = no pressure.

That velocity created in the narrow portion creates a flow into that portion. There will be no vacuum pressure created until there is a restriction to that flow.
there is actually more air exiting the venturi than entering the venturi.
Even any old Navy trained Hydraulic mechanic knows this, why does it escape a college brainyack.

Or are you applying the wrong principals, by over thinking the obvious.
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Tom - I didn't reference anything so you are obviously confused. Come back later after you've had a chance to think about the impossibility of flow from low pressure to high pressure.
 
Tom-D said:
What high pressure or what low pressure ?

In a venturi there is none, your reference even said that. the flow is in one end and out the other, no restriction = no pressure.

there is actually more air exiting the venturi than entering the venturi.
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Umm... What???

Since nobody has repealed Bernoulli's principle, under steady-state or near-steady-state conditions flow in = flow out.

Under the same principle, the restricted section causes an increased velocity => decreased pressure. This decreased pressure is in turn what enables pseudo-vacuum gyro operation.
 
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