Ground School Exam Questions & Question Banks
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Ground School Exam Questions
Hi all,
got a couple of questions for a atpl theory course entrance test which I am stumped on. Probably just being thick but:
1. Given that in general, the top surface of the wing is responsible for the creation of most of the lift, what type of aerofoil would give the greatest lift characteristics?
a low wing
b mid wing
c high wing
d low or mid wing.
2. increased fuel densities will increase or decrease the performance of the aircraft engine. Allowing for the same fuel type and volume, what would be the effect of using a fuel of specific gravity 0.75, as opposed to the published sg of 0.8?
a increased performance
b decreased performance
c no effect on performance
d insufficient information.
ta to anybody who helps, unless ur wrong of course!
got a couple of questions for a atpl theory course entrance test which I am stumped on. Probably just being thick but:
1. Given that in general, the top surface of the wing is responsible for the creation of most of the lift, what type of aerofoil would give the greatest lift characteristics?
a low wing
b mid wing
c high wing
d low or mid wing.
2. increased fuel densities will increase or decrease the performance of the aircraft engine. Allowing for the same fuel type and volume, what would be the effect of using a fuel of specific gravity 0.75, as opposed to the published sg of 0.8?
a increased performance
b decreased performance
c no effect on performance
d insufficient information.
ta to anybody who helps, unless ur wrong of course!
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OK, I'm only a lowly PPL, but my guesses would be
1c and 2d
Reasons:
1c) In a high-wing a/c the upper surface runs across the entire span, so should, logically, create slightly more lift than an interrupted (by the fuselage) mid or low wing. Indeed if you look at some of the Russian high-wing a/c, the aerofoil appears uninterrupted over the fuselage (in other words the profile is, or at least appears to be, carried through the entire span). Same goes for the stuff I usually fly....
2d) As the first sentence states "will increase OR decrease" there must be some other info required to determine the outcome.
My 2 cents
1c and 2d
Reasons:
1c) In a high-wing a/c the upper surface runs across the entire span, so should, logically, create slightly more lift than an interrupted (by the fuselage) mid or low wing. Indeed if you look at some of the Russian high-wing a/c, the aerofoil appears uninterrupted over the fuselage (in other words the profile is, or at least appears to be, carried through the entire span). Same goes for the stuff I usually fly....
2d) As the first sentence states "will increase OR decrease" there must be some other info required to determine the outcome.
My 2 cents
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hedges,
you might find some clues here:
http://www.aerospaceweb.org/question...cs/q0184.shtml
note that (quote) The efficiency factor, e, varies for different aircraft, but it doesn't change very much. As a general rule, high-wing planes tend to have an efficiency factor around 0.8 while that of low-wing planes is closer to 0.6 (unquote)
How did we ever live without Google
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you might find some clues here:
http://www.aerospaceweb.org/question...cs/q0184.shtml
note that (quote) The efficiency factor, e, varies for different aircraft, but it doesn't change very much. As a general rule, high-wing planes tend to have an efficiency factor around 0.8 while that of low-wing planes is closer to 0.6 (unquote)
How did we ever live without Google
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As an aeronautical engineer the answer for 1 i think is low wing. Why else is this day and age of engineering and advanced aerodynamics testing would large aircraft manufacturers continue to use a low wing configuration on the newest aircraft such as the A380 and 350 when much of the emphasis is on reduced fuel consumption due to low cost movement in avaition. This is acheived by reducing drag and increasing lift to increase the specific fuel consumption sfc. Could be talking balls through!
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The total drag is the sum of parasite and induced drag.
Total Drag = Parasite Drag + Induced Drag
But the net (or total) drag of an aircraft is not simply the sum of the drag of its components. When the components are combined into a complete aircraft, one component can affect the air flowing around and over the airplane, and hence, the drag of one component can affect the drag associated with another component. These effects are called interference effects, and the change in the sum of the component drags is called interference drag.
Total Drag = Parasite Drag + Induced Drag
But the net (or total) drag of an aircraft is not simply the sum of the drag of its components. When the components are combined into a complete aircraft, one component can affect the air flowing around and over the airplane, and hence, the drag of one component can affect the drag associated with another component. These effects are called interference effects, and the change in the sum of the component drags is called interference drag.
OC619
P.S. Of course that could be complete B******S.
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I suspect this is one of those 'learn the answer they want' questions. The notion that the top surface of the wing (assuming an allusion to equal transit time effects) creates most of the lift has never really managed to convince me.
Thin delta wings and symetrical aerofoils suggest otherwise (for example).
Thin delta wings and symetrical aerofoils suggest otherwise (for example).
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hedges I guess you get more laminar airflow over the uninterrupted wing surface in a high wing config.
Smoothflier you are right of course, but there are other considerations as well. A high wing on a big transport takes up A LOT of space inside the fuselage where the spars go through. Had the pleasure of being on both the AN-124 and AN-225 and this eats up a lot of - to a passenger airline - valuable real estate. Doesn't matter much on these transports, as the wing effectively devides the upper deck which carries crew only anyway. Typically flight crew in the front compartment and cargo/service crew in the back. Plus, these things were originally designed for military use, where comfort is a second thought - at best. Add to the above access for servicing (the engines are a long way up on the ANs), and you may find that the cumulative benefit from having a low wing outweighs the aerodynamic advantages of a high wing. But, like seemingly everyone on this thread, groping in the dark here...
Smoothflier you are right of course, but there are other considerations as well. A high wing on a big transport takes up A LOT of space inside the fuselage where the spars go through. Had the pleasure of being on both the AN-124 and AN-225 and this eats up a lot of - to a passenger airline - valuable real estate. Doesn't matter much on these transports, as the wing effectively devides the upper deck which carries crew only anyway. Typically flight crew in the front compartment and cargo/service crew in the back. Plus, these things were originally designed for military use, where comfort is a second thought - at best. Add to the above access for servicing (the engines are a long way up on the ANs), and you may find that the cumulative benefit from having a low wing outweighs the aerodynamic advantages of a high wing. But, like seemingly everyone on this thread, groping in the dark here...
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High Wing - I too have my suspicions! Here's a paraphrase of what I found on the Coanda effect:
"The reason why air flows faster over the top of a wing, especially since the molecules don’t meet up with the ones they started with, is that it speeds up because the pressure is lower, and not the other way around - Bernoulli’s process may start things off, but something else must take over.
For example, the length of the path taken by air flowing over the top of the wing of a Cessna 172 is only about 1.5% greater than it is under the wing, so only about 2% of the needed lift at would be developed at 65 mph (indeed, 2% is the figure calculated by aircraft modellers as to the complete contribution to lift from Bernoulli). On those figures, it would appear that the minimum speed for this wing to develop enough lift to keep the 172 in the air is over 400 mph, or, looked at another way, the path length over the wing would have to increase by 50%. The thickness of the wing in that case would be almost the same as the chord length!
Assuming the Cessna weighs about 2300 lbs, and is moving at 140 mph with an angle of attack of 5 degrees, the vertical velocity of the air its wing deflects is about 11.5 mph. Taking half of that (from the lift formula), Newton's second law shows that the 172 in the cruise must shift about 5 tons of air (about five times its own weight), of air per second to keep flying. That means it must accelerate all the air within 18 feet of the top of the wing.
That’s a lot of air! What’s happening is that the air bending around the top of the wing is accelerating the air above it downwards, leaving a gap, or a lower pressure until the air pressure is equalised. This lower pressure will suck air from the front of the wing and shoot it down and back toward the trailing edge. It is therefore the top surface of the wing that is the critical part, and the magical force called “lift” is really the opposite of the downward trend of the air."
Phil
"The reason why air flows faster over the top of a wing, especially since the molecules don’t meet up with the ones they started with, is that it speeds up because the pressure is lower, and not the other way around - Bernoulli’s process may start things off, but something else must take over.
For example, the length of the path taken by air flowing over the top of the wing of a Cessna 172 is only about 1.5% greater than it is under the wing, so only about 2% of the needed lift at would be developed at 65 mph (indeed, 2% is the figure calculated by aircraft modellers as to the complete contribution to lift from Bernoulli). On those figures, it would appear that the minimum speed for this wing to develop enough lift to keep the 172 in the air is over 400 mph, or, looked at another way, the path length over the wing would have to increase by 50%. The thickness of the wing in that case would be almost the same as the chord length!
Assuming the Cessna weighs about 2300 lbs, and is moving at 140 mph with an angle of attack of 5 degrees, the vertical velocity of the air its wing deflects is about 11.5 mph. Taking half of that (from the lift formula), Newton's second law shows that the 172 in the cruise must shift about 5 tons of air (about five times its own weight), of air per second to keep flying. That means it must accelerate all the air within 18 feet of the top of the wing.
That’s a lot of air! What’s happening is that the air bending around the top of the wing is accelerating the air above it downwards, leaving a gap, or a lower pressure until the air pressure is equalised. This lower pressure will suck air from the front of the wing and shoot it down and back toward the trailing edge. It is therefore the top surface of the wing that is the critical part, and the magical force called “lift” is really the opposite of the downward trend of the air."
Phil
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Higher density fuel = greater calorific value per cube = more power until density causes flowrate problems.
High wing v. low wing is interesting. You get greater gound effect from low wing. Does this affect unsticking?
High wing v. low wing is interesting. You get greater gound effect from low wing. Does this affect unsticking?
Think effortless has got the second one sorted.
Remember that calorific value is a measure of energy per unit of mass (usually in either kJ/g or kwh/kg if a recall correctly). You have the same volume of fuel (say 1000 litres) so in this example in decreasing the s.g. you would have 50 kgs less fuel (750 versus 800kg). This would have a similar effect with regards to fuel flow (less little burny things going to engine per minute) but obviously with much smaller figures = answer b, decreased performance (of the aircraft engine at least).
For the first question I would go with answer c.
As already pointed out the top wing produces more lift than the bottom. An aircraft with a high wing normally has an airfoil shape along the complete length of the upper wing so the ratio of lift producing top wing to bottom would be higher on a high wing aircraft than one with a low wing configuration.
I think the reasons for low wing airliners is partly to do with safety and evacuating large wide-bodied aircraft passengers out over the wings when ditching and the like.
Of course I am willing to be proved wrong!
Remember that calorific value is a measure of energy per unit of mass (usually in either kJ/g or kwh/kg if a recall correctly). You have the same volume of fuel (say 1000 litres) so in this example in decreasing the s.g. you would have 50 kgs less fuel (750 versus 800kg). This would have a similar effect with regards to fuel flow (less little burny things going to engine per minute) but obviously with much smaller figures = answer b, decreased performance (of the aircraft engine at least).
For the first question I would go with answer c.
As already pointed out the top wing produces more lift than the bottom. An aircraft with a high wing normally has an airfoil shape along the complete length of the upper wing so the ratio of lift producing top wing to bottom would be higher on a high wing aircraft than one with a low wing configuration.
I think the reasons for low wing airliners is partly to do with safety and evacuating large wide-bodied aircraft passengers out over the wings when ditching and the like.
Of course I am willing to be proved wrong!
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smoothflier
The decision to use a high wing/ low wing from PoF is due to dynamic and static stability as far as I can remember, I suppose lift does come into it too.
The notion that a high wing has an uninterupted upper surface I don't agree with because you need a pressure differential between upper and lower surface and there is no lower surface and as such no lift created in this area.
CMIIW
The notion that a high wing has an uninterupted upper surface I don't agree with because you need a pressure differential between upper and lower surface and there is no lower surface and as such no lift created in this area.
CMIIW
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Smith,
Personally I don't get the lift reasons and I fired off a question in Tech Log asking about the general notion of lift the way it is taught.
The reason the Cessna may have slightly more efficiency could be related to stability in the sense that because it uses less dihedral (wing angle up a bit pointing lift vector toward centre) than a low wing, because high wings are generally more laterally stable as the weight is slung beneath the centre of lift...I guess.
Personally I don't get the lift reasons and I fired off a question in Tech Log asking about the general notion of lift the way it is taught.
The reason the Cessna may have slightly more efficiency could be related to stability in the sense that because it uses less dihedral (wing angle up a bit pointing lift vector toward centre) than a low wing, because high wings are generally more laterally stable as the weight is slung beneath the centre of lift...I guess.
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As always, the questions are simplified to the point of banality! There are so many considerations involved that a discussion of the real-life implications of the various options is pretty much a waste of time. These questons can really only be answered by reference to the source material that produced them, rather than by genuine knowledge of the subjects at hand.
I suspect that 172driver has probably got the 'right' answers, or at least those the examiner is looking for, but I'm not an expert or current in CAA-type examination technique.
Scroggs
I suspect that 172driver has probably got the 'right' answers, or at least those the examiner is looking for, but I'm not an expert or current in CAA-type examination technique.
Scroggs
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I did what sounds like the same entrance exam a year ago. I was stumped on this high/low/mid wing Q for ages and in the end plumped for the high wing option.
If its the LMU exam you are doing then it is the right answer!!
If its the LMU exam you are doing then it is the right answer!!
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airlaw question
Hi,
ICAO states that VFR minima in class B airspace are 1000 ft vertical and 1500m horizontally from clouds and 5 km vis below 10000 ft or 8 km above 10000 ft
In some jar question banks they state, when asked aboud vfr minima in class B airspace, the correct answer as 5km vis below 10000 ft or 8km above 10000ft and clear of clouds ..
This clear of clouds part worries me, as i thought clear of clouds was only a factor in class F and G airspace, below 3000 ft amsl or 1000 ft agl whichever is higher ..
Anyone knows what the correct answer should be?? My guess is the JAR-ATPL exams follow ICAO regulations but i wouldn't be surprised if this is one of those differences between JAR and ICAO ..
thanx,
Jan
ICAO states that VFR minima in class B airspace are 1000 ft vertical and 1500m horizontally from clouds and 5 km vis below 10000 ft or 8 km above 10000 ft
In some jar question banks they state, when asked aboud vfr minima in class B airspace, the correct answer as 5km vis below 10000 ft or 8km above 10000ft and clear of clouds ..
This clear of clouds part worries me, as i thought clear of clouds was only a factor in class F and G airspace, below 3000 ft amsl or 1000 ft agl whichever is higher ..
Anyone knows what the correct answer should be?? My guess is the JAR-ATPL exams follow ICAO regulations but i wouldn't be surprised if this is one of those differences between JAR and ICAO ..
thanx,
Jan
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Hello, hope this helps.
ICAO state, in chapter 4 of annex 2 (visual flight rules), that in class B airspace aircraft must remain clear of cloud at all times, regardless of altitude. As regards to the vis, it is correct that 8km above 10,000 feet is required and 5km below.
The only other time you are required to be 'clear of cloud' is in class F and G below 3000 feet amsl.
The answer for the 'feedback' is CLEAR OF CLOUD and 5 or 8km depending on altitude.
Regards.
ICAO state, in chapter 4 of annex 2 (visual flight rules), that in class B airspace aircraft must remain clear of cloud at all times, regardless of altitude. As regards to the vis, it is correct that 8km above 10,000 feet is required and 5km below.
The only other time you are required to be 'clear of cloud' is in class F and G below 3000 feet amsl.
The answer for the 'feedback' is CLEAR OF CLOUD and 5 or 8km depending on altitude.
Regards.
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thanx for the reply ..
where did you find the icao statement?? in my copy of annex 2 chapter 4 is only one page and i don't see it mentioned.
And according to feedback questions clear of clouds should be correct instead of 5 or 8 kms and 1500 m, 1000 ft .., so i should just go for that answer when asked on the exam?
thanks again,
Jan
where did you find the icao statement?? in my copy of annex 2 chapter 4 is only one page and i don't see it mentioned.
And according to feedback questions clear of clouds should be correct instead of 5 or 8 kms and 1500 m, 1000 ft .., so i should just go for that answer when asked on the exam?
thanks again,
Jan