aro

That's OK. Since it's the difference in pressure that produces lift it just means the flow underneath needs to slow down more.

It may be a damn fool argment, but every attempt to explain seems to raise a few questions. In your article you say: Isn't this the equal transit time theory? But videos showing pulsed smoke e.g. in the other thread, clearly show that the flow doesn't get to the trailing edge at the same time. How does this work and why doesn't the air underneath "pile up" ahead of the wing? I don't know - but I guess some of it ends up flowing over the wing in the faster stream, as well as around the wing in the wider circulation patterns. In fact it seems like there must be less air flowing under the wing, to allow for the downward flow off the trailing edge.

Actually I take that back - it doesn't require it at all, since the venturi is only one surface. It just demonstrates that static pressure reduces as air speed increases - which is OK. It is the step comparing half a venturi to a wing that is incorrect - which is commonly taught.

There are certainly instructors who teach the equal transit time theory, and CASA appears to require it. From the part 61 MOS: "Apply Bernoulli’s theorem of constant energy flow to describe how an aerofoil produces lift, limited to the variation of kinetic energy (dynamic pressure) and potential energy (static pressure) as air flows through a venturi or over a aerofoil" Explaining how an aerofoil produces lisft using the variation of pressure as air flows through a venturi seems to require an incorrect application of Bernoulli, presumably equal transit time. In fact, a venturi doesn't explain lift at all, because the air comes out the other end travelling in the same direction at the same speed, so it cannot possibly produce lift.

Settle down, I agree with you. All I was trying to say is that I don't understand the point that was being made in the original reference to sprintcar wings.

Flat on the top is an approximation. So is flat on the bottom for a conventional airfoil. There is more curvature on the bottom of the SC airfoil. If you measure the distance along the surface from LE to TE it is further on the bottom - which is a problem for the equal transit time theory. But I thought we had agreed that the equal transit time theory doesn't hold water?

I said sprintcar wings have nothing to do with an airliner. Probably what I should have said is that sprint car wings are curved on the bottom for a totally different reason than the wings on an airliner.

I basically understand what you are saying about the SC wing. I found the stuff about avoiding accelerating air over the top near the speed of sound quite interesting. I just wasn't getting the point of comparing it to a sprint car wing.

I still don't understand your point here. He says that from what they are taught, people expect that a wing curved on the bottom and flat on the top would produce a down force not lift. And yet that is not the case for SC wings. I'm not sure whether you are agreeing or disagreeing?

If you understood Aerodynamics for Naval Aviators better you probably wouldn't be arguing with completeaerogeek. They did mean all the lift, not just the top part of the aerofoil. Bernoulli's equation explains the pressure above and below the wing (as long as the assumptions in the theory are valid) - it also tells us that as the flow slows down, the pressure increases. And lift is the difference in pressure between the top and bottom of the wing. It doesn't even matter if the pressure above increases, as long as the pressure below increases more. Sprint car wings are just a high camber wing at a high angle of attack, upside down so they produce downforce rather than lift. Totally different and unrelated to the wing on an airliner.

Fundamentally, I am agreeing with you. A practical understanding of what is happening is not difficult, and helped immensely by videos like the one at the start of the thread. Also videos of tuft testing wings as they stall - widely available now on Youtube - help immensely in visualizing flow and what happens when the wing stalls. However I wouldn't say Bernoulli, Newton etc. are practical aerodynamics - they are theory. And anytime you have to include assumptions you are acknowledging complexity, because the assumption basically says "this bit is too complex to include, but it doesn't make a significant difference in this situation so we can ignore it." It introduces complexity because you have to understand exactly when the assumption holds, and when it does make a difference and you can no longer ignore it e.g. assumptions that ignore compressibility. Newton and Bernoulli and all these theories of lift tell us nothing useful about the cause of a stall. Fluid dynamics can probably predict a stall based on viscosity and pressure gradient or something (I don't know) but we learn nothing about that as a pilot. What we need to know is that at some AOA the flow can no longer follow the shape of the wing, and there ia a large reduction in the amount of lift. This is based on AOA, which in turn is based on speed and load factor. It can also be influenced by contaminants on the surface, depending on the airfoil. This is what I meant when I said "why the wing stalls and what happens". This is practical aerodynamics, and I agree that it is not complex.

A lot of this thread is like one person arguing that red traffic lights mean stop, others arguing that green means go. Newton, pressure, bernoulli etc all exist and all play a part. What is wrong is many of the oversimplified explanations generated by people who didn't properly understand it in the first place. People tend to seize the first one they think they understand and promote that as the right answer. Newton: is a law of the universe. It is not optional. Lift force is generated by accelerating a mass of air downwards. There is nothing else it can come from. Whatever other explanation is used, Newton is involved. Pressure: lift comes from a difference in pressure between the top and bottom surfaces of the wing. There is nothing else acting on the wing that can cause lift. It doesn't really matter whether the pressure below increases or the pressure above decreases, it is the difference that matters. The difference in pressure caused by the wing causes air above and below to accelerate downwards, which is required for the lift force. Likewise the acceleration produces the pressure difference. This sounds paradoxical, but the law is "every action has an equal and opposite reaction" - since they are equal and opposite, you can call either the action, and the other the reaction. Bernoulli: The air over the top of the wing is travelling faster and has lower pressure than the air below, so this is consistent with Bernoulli. However Bernoulli is based on conservation of energy. I suspect energy is transferred from the higher pressure areas to the lower pressure areas in the act of accelerating the air, which would tend to invalidate the assumptions. Bernoulli applies as far as the bernoulli conditions are satisfied, but we don't have equal transit time, and the air doesn't always (usually doesn't?) split exactly at the leading edge. The classic explanation of the bernoulli effect is a venturi, but this is not the only situation where it applies. It's just an example that has been used and abused. Air deflected by the lower surface: Air pressure is a result of the number and energy of molecules bouncing off the surface. A higher pressure has more molecules or more energetic molecules bouncing off the surface. So this explanation is really just a different way of saying that the bottom surface has a higher pressure than the top surface. Some other observations: Lift from a flat plate: Have a look at the streamlines around a flat plate producing lift. The pressure field starts to deflect the air ahead of the plate, causing the airflow above and below to be similar to a basic airfoil. Symmetrical airfoil: similar to flat plate i.e. the airflow above and below is NOT symmetrical Airfoil shape: The purpose is to precisely control the flow of air around the wing to reduce drag, to prevent it from detaching (stalling) over a wider range of angles of attack, and to control where along the chord the acceleration occurs, which influences the pressure distribution (centre of pressure) and how it changes at different angles of attack. Supersonic? Way beyond my knowledge, but I think one of the keys is to shape the top surface to avoid the airflow detaching, without the influence of the changing pressure ahead of the wing modifying the airflow. You really need to know very little of this to fly an aircraft. You need to know the effect of speed on lift and drag, why the wing stalls and what happens, the effect of surface contamination etc. Newton, Bernoulli etc are really irrelevant to the task of flying an aircraft. They are taught badly, without real understanding, and I think most pilots are confused. * Aerodynamics is complex. I have been interested and learning about it as a hobby for 30+ years. Year 12 physics and chemistry is very helpful but the more I learn, the more I discover that I don't know. These explanations probably also have errors and inaccuracies. I have concluded I have no hope of understanding it properly, unless one day I go back to uni and study it at a tertiary level. Luckily, that level of knowledge isn't required to fly an aircraft.

That isn't 177 serious accidents. There is a difference between an accident and an incident and, I would argue, between an accident and a serious accident. RAA list about 5200 registrations - does 88500 flights sound right? About 17 flights per aircraft per year? Not out of the question if you have a lot of aircraft hat are not flown much, but it sounds low. 1 in 500 aircraft would be about 10-11 serious accidents per year (i.e. around 1 a month) - which again sounds plausible.

Sounds wrong to me. If it was one in 500 aircraft had a serious accident it would be more in the range I would expect. You really need to see the raw figures, number of flights, number of accidents and how they are defined.

An outboard pickup should siphon if it is run through the wing, as long as the join is well below both pickups and fuel can flow freely both directions?

The battery also tends to stabilize the output from the alternator. Disconnecting it might be OK if you have the big capacitor (and it's in good condition), it's possible it might be OK without it, or it might cause a voltage spike that fries all your avionics... It's a gamble.

The master contactor performs the function of the battery isolator being discussed, with the advantage that it can be located at the battery with the switch on the panel. I don't understand the failure mode where a high current fuse or second solenoid with multiple switches etc. would help, but a starter warning light (and perhaps overvoltage warning light) and master contactor wouldn't do the job.

PA28s I have flown had a Starter Warning light that is supposed to warn that the starter is still engaged. As others have noted, a master contactor wired to the master switch is common practice. (But not necessarily in RAA aircraft) It should disconnect all power at the battery including the starter circuit so it can be used if the starter switch sticks. I think it is standard in Cessna and Piper aircraft. A starter warning and master contactor has most of the bases covered I think. I second the recommendation of the Aeroelectric connection for those interested in aircraft electrics. http://www.aeroelectric.com No sense in reinventing the wheel.

Good question. It appears to me that the mandatory inspection is required immediately, with further duplicate inspections required after maintenance on the control system. If it was only required after maintenance, why would you specify only 19 reg aircraft but not all other RAA aircraft? The duplicate inspection after maintenance would apply equally to all. The only logic I can see is that the inspection is to detect cases where control system problems have existed since initial assembly, and this is only considered a likely problem for 19 reg aircraft.

Kaz was explaining the meaning of "shall" not "should". The question was is "should" the same as "shall" and the answer still seems to be no.

The AN requires a mandatory inspection before next flight. This grounds all 19 reg aircraft, where ever they are, until the inspection can be carried out. A quick look at the RAA registration list suggests that is about 1500 aircraft grounded without warning. You might think that is no big deal - some might see that as a little extreme. Maybe that is not what the RAA intended, but that is how I read the "Action required: Mandatory inspection requirement before next flight"

The difference between should and must/shall is fairly well accepted. Should is a strong recommendation. Ignoring it may be unwise, but is not prohibited. Must/shall does not give an option. e.g. You must obey the speed limit. You should slow down when it is raining. In one case you can be charged if you ignore it. In the other you cannot, although it could be used as evidence to support other charges e.g. negligence.

The requirement for a duplicate inspection is not new or controversial. However, I'm not sure whether people are reading the notice carefully? It lists: "Duplicate Inspection" and "Mandatory Inspection" and "Action Required: Mandatory Inspection requirement before next flight" The mandatory inspection appears to ground all 19 reg aircraft immediately, until they are inspected. If the requirement was only for a duplicate inspection after maintenance, why would you single out 19 reg over other aircraft? And it appears that every inspection needs to be reported to the tech manager ("On completion of the inspection, and if any issues are identified..." is different to "On completion of the inspection if any issues are identified...") so it wouldn't surprise me if this will be checked, at least on registration renewal if not earlier. Could it even be a test to see which owners read and take notice of airworthiness notices? Most should be carried out and reported fairly quickly, if they are done. Alternatively it could be an error and they are not ready for a deluge of reports with one for every aircraft...

The earlier you start braking, the bigger difference it makes in your stopping distance. The problem in a taildragger is that you have a high AOA in a 3 point attitude, so by the time you get the tail down, let alone get enough weight on the wheels for significant braking you are too late to make a big difference to your stopping distance. I have seen suggestions to touch down almost at approach speed and brake immediately with the tail up for the shortest landings, eliminating the time spent in the flare, because at flying speed the tail is powerful enough to stop the nose over and the early braking has most effect on the total distance. This is obviously a potentially risky technique requiring a large amount of skill to reduce braking as the tail loses effectiveness. I suspect it was more appropriate to larger, faster taildraggers requiring long runways. I wouldn't try it myself. In the tailwheel aircraft we fly, we are better to accept that the brakes make minimal difference to landing distance. (Incidentally, I have noticed that wheel vs. 3 point landings give a good demonstration of how much drag the wing can produce. The aircraft slows noticeably faster without braking in a 3 point attitude than tail up.)

1) is all down to the programming - it can do whatever you like. As I understand it, primitive ABS just senses the rate of change in the rotation of the wheel. If it exceeds what is possible from normal braking (i.e. a locked wheel goes from rotating to stopped almost instantly), it releases the brake. However systems now could be much smarter, and take more parameters into account. However, the anti-groundloop stability suggestion obviously would be a problem if you felt the need to deliberately groundloop. 2) If you tied it into a system like a Dynon (or any similar system) you could have a pressure sensor to detect when the brakes were applied, and release them if the tail lifts (say) 10 degrees from the attitude where the brakes were first applied. This would stop a nose over even when tail up braking after landing. The more I think about it, the more I think a mechanical switch in the tail is the hard way to do it... we have the technology to make it a much smarter (and simpler and more easily tunable) system.