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So I was teaching ground school...

minitour

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First question.
...when I had a few questions pop up that I have no clue as to the answer. Figured I'd ask.

Biplanes...Low (relatively) pressure above the low wing and above the high wing. But relatively higher pressure below the wings (still low, but...higher than the low above the wing). Does the higher pressure below the top wing cancel out the low pressure above the bottom wing?

If I confused you, I'll apologize in advance.

Second question.
In the carubretor, the air goes through the venturi and is accellerated, the pressure drops and so does the temp. Cold air can't hold as much moisture as warm air, so the moisture comes out and can freeze and voila...carb ice.

Same thing. Wing. Air over the wing is accellerated and the pressure drops. I would imagine the temperature does too. Their question. What temperature range are you going to pick up ice. The best I could give them was a figure I was told in CSEL ground school a few months ago which was 2 to -20 degrees C. Any opinions/thoughts on that one?

Third question.
This one is from me...not from them.
I'm going to be teaching an instrument student. He wants to learn in a 172 with dual nav/com, two VORs one with GS, an ADF and DME. Obviously, I'll be teaching the VOR, VOR/DME, NDB, ILS, LOC, etc. approaches...

We have a diamond with G530/430 available too. Any harm in taking one or two flights and having him go in the diamond to shoot the GPS approaches? I'd like to at least teach my students the approaches unlike how I was taught (by a CFII friend of mine a month after my instrument checkride).

Also, the other way. I have a student that will be doing his instrument shortly in the Diamond. So it's VOR, GPS, ILS/LOC, etc. Any harm in taking him up in the 172 for 1-2 flights for the NDB approaches/holds?

I just want to make sure I don't miss anything.

Thanks for any help!

-mini
 

rcsimpson

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I'll try the biplane question. I don't think the pressure extends too far away from the wing surface. The wings are several FEET apart so there is no interference/interaction/affect etc. of one wing on the other wing.

I'll add one more comment that's really more of a question too about the temperature dropping over the wing itself. Wouldn't the friction of going through the air conteract this cooling and somewhat cancel it out?
 

DC8 Flyer

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minitour said:
First question.
...when I had a few questions pop up that I have no clue as to the answer. Figured I'd ask.

Biplanes...Low (relatively) pressure above the low wing and above the high wing. But relatively higher pressure below the wings (still low, but...higher than the low above the wing). Does the higher pressure below the top wing cancel out the low pressure above the bottom wing?

Never flown a Bi-Plane so not 100% sure, but the pressure change with airflow over the wing is very local and doesnt extend multiple feet above the wing.

If I confused you, I'll apologize in advance.

Second question.
In the carubretor, the air goes through the venturi and is accellerated, the pressure drops and so does the temp. Cold air can't hold as much moisture as warm air, so the moisture comes out and can freeze and voila...carb ice.

Same thing. Wing. Air over the wing is accellerated and the pressure drops. I would imagine the temperature does too. Their question. What temperature range are you going to pick up ice. The best I could give them was a figure I was told in CSEL ground school a few months ago which was 2 to -20 degrees
C. Any opinions/thoughts on that one?
The pressure change, thus temp change, of the air over a wing is less than the pressure. velocity, and temp change you get through a venturi. Plus the air going through the venturi is "alone" in a way, it doesnt have "warmer" air surrounding it to prevent icing. If you watch airliners lift off on humid days you can see the condensation form on the wings, large pressure drop, large temp drop but high angle of attack. You don't typically see those same "clouds" on the wings in cruise.
Third question.
This one is from me...not from them.
I'm going to be teaching an instrument student. He wants to learn in a 172 with dual nav/com, two VORs one with GS, an ADF and DME. Obviously, I'll be teaching the VOR, VOR/DME, NDB, ILS, LOC, etc. approaches...

We have a diamond with G530/430 available too. Any harm in taking one or two flights and having him go in the diamond to shoot the GPS approaches? I'd like to at least teach my students the approaches unlike how I was taught (by a CFII friend of mine a month after my instrument checkride).

Also, the other way. I have a student that will be doing his instrument shortly in the Diamond. So it's VOR, GPS, ILS/LOC, etc. Any harm in taking him up in the 172 for 1-2 flights for the NDB approaches/holds?

I just want to make sure I don't miss anything.

Thanks for any help!

-mini

hope those help a little
 

StrykerFL

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I would definately reccommend taking up your student in a newer technology airplane. He will thank you for it later. It is a damn shame that some people out there pay tens of thousands of dollars only to learn in an antiquated piece of 1960's/70's technology. If the technology is available and the student is willing to pay for it, do some lessons in the Diamond. I teach primarily in the Cirrus SR20/22 and currently have a few instrument students; I make it a point to take them up in the 172 or put them in the sim to show them how much different it is to not have the large format display glass PFD/MFD. Besides, they might not always be flying an all glass panel airplane.

GPS approaches unfortunately are only read about by most pilots. You need to take the time to show your students and customers how to do them especially if your school has the equipment available.

Good Luck.
 

MKaprocki

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minitour said:
Second question.
In the carubretor, the air goes through the venturi and is accellerated, the pressure drops and so does the temp. Cold air can't hold as much moisture as warm air, so the moisture comes out and can freeze and voila...carb ice.

Same thing. Wing. Air over the wing is accellerated and the pressure drops. I would imagine the temperature does too. Their question. What temperature range are you going to pick up ice. The best I could give them was a figure I was told in CSEL ground school a few months ago which was 2 to -20 degrees C. Any opinions/thoughts on that one?

I believe a big factor in carb icing is the vaporization of the fuel. The air going through the venturi is part of it, but when the fuel vaporizes it really drops the temperature even more.

Obviously fuel isn't being vaporized around the wing, so the temp drop isn't as severe.
 
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NYCPilot

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First Question.
The pressure differentials are localized around each respective wing and do not affect each other. Although you may have high pressure adjacent to the low pressure below and between the wings, the spacing between the two wings disallows any interference caused by the dissimilar air pressure areas being formed around the respective wings. Intuitively, why create a second wing on the bottom (or top -arbitrarily, just the same) if the second wing will cancel out any of its lifting properties. In other words, what good would that bottom wing do if it weren’t able to provide and lifting action due to the lack of low pressure above. It wouldn’t make sense for the bottom part of the lower wing to only generate the equal and opposite reaction for lift. Not efficient. Although it varies, the majority of lift is produced by the low pressure above, not below the wing. This of course fluctuates as AOA increases.


Second Question.
The same principle (Bernoulli’s) applies with the airflow over the wing. A decrease in pressure induces a decrease in temperature. With visible moisture present, your wing can accrue ice within the temperature range of +5 degrees to -20 degrees.


Third Question.
It would be beneficial to expose both students to each of these aircraft and approach types. Depending on which aircraft he uses for the checkride, the student will be responsible for knowing how to perform approaches with any installed navigational equipment. If he’s going to be using the GPS equipped airplane, he better know how to perform them. There is a lot to be gained from learning to use the old VOR and NDB approaches. Although NDB’s are pretty much on their way out, GPS is far from universal and is still being debugged. Eventually, we will se a more widespread GPS landscape, but for now, a solid understanding for the present systems is essential. In a post somewhere on the regional interview board, I came across some mention of NDB approaches and holds being asked of applicants flying in the sim. NDB’s have always been an Achilles heal for many pilots and the ability to fly one well, in different wind conditions will do wonders in developing a students instrument skills. If you want to beat your student up, have him do lots of partial panel NDB holds into approaches. That’ll hone his skills well, as it did mine.

Another issue may be that the student is on a tight budget and flying a more expensive aircraft to experience a GPS approach may be financially preclusive. Otherwise, by all means show him how to shoot a few of these.
 

minitour

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Thanks for the help everyone!

-mini

*edit*
I have a followup to the icing question.

We already know that warm air holds (can hold) more water vapor than cooler air. So...if we reduced the temperature of the air over the wing, could we then theoretically force the water vapor out of the air, onto the wing, then freeze it producing structural icing with no visible moisture? Or am I reading way too into icing?

-mini
 
Last edited:

CurlyD777

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minitour said:
Thanks for the help everyone!

-mini

*edit*
I have a followup to the icing question.

We already know that warm air holds (can hold) more water vapor than cooler air. So...if we reduced the temperature of the air over the wing, could we then theoretically force the water vapor out of the air, onto the wing, then freeze it producing structural icing with no visible moisture? Or am I reading way too into icing?

-mini

Basically the NASA studies and FAA approved studies have always stated that icing occurs when visible moisture is present with subzero temperatures on the airframe.



Visible moisture, ie clouds, is simply when the air temp is the same as the dew point. It is possible for the air to be exactly at the right temperature so when air is accelerated over the wing, it can cool and produce visible moisture. (This is very evident if you ever watch large airlines land with flaps extended...look for the wing tip vortices on the wing tips of the flaps.)



As for icing to occur from this phenomenon, it would have to not only be at the exact temperature and moisture level to allow visible moisture to be formed from the slight temperature change, but also have the moisture that is forced out to be large enough particles to accrue on the wing itself. (On a side note, the temperature drop for the air accelerating over the wing is not very significant, so there is very little change in the temp / dew point spread)



I have personally experienced a very small trace amount of icing on the upper leading edges of my 172 on a 30-32 degree evening in a very hazy atmosphere. (a high moisture content air) This could be from the slight change in temperature over the leading edge, or it may have been from the high moisture level in a sub zero environment.



Now I’m no NASA expert on this field, I’m just a pilot who lives in Minnesota that has do deal with icing 9 months out the year (with thunderstorms the other 3 months)


Hope this gives some insight...
C.
 

ClassdAviator

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What about when, for example, a high performance fighter jet pulls a high G manuever and you see a vapor cloud over the wing? My thought is that there is an "extreme area" of low pressure which causes the moisture in the air to condensate. I have pondered this since watching a recent airshow.
 
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