I’m coming to the conclusion that the most important law in my aeroplane is Ohm’s Law! 😀

This has been a really fascinating thread from the perspective that it highlights the fact that after more than 100 years since the Wright brothers events at Kittyhawk we still cannot define lift generation! I had always assumed that there was someone way more clever than me who had this whole shooting match put to bed with the definitive answer but it looks like I’m wrong.

…Ian you fly the 340 for Virgin so maybe you can clarify, generally aircraft have their CP aft of the CofG, which creates stability, and this stability causes a nose down pitching moment, this is why the tailplane has a downward force & negative angle of incidence which forces the nose up and level again, but the Airbus has it the opposite way? i.e. the CP is forward of the CofG, which means that the tailplane must cause an upward force to cause a nose down pitching moment to counteract the nose up tendancy (our ATPL instructor told us Airbus manufacture in this way), but one thing I have noticed with the Bus is that the tailplane appears to have the same angle of incidence as Boeings etc, if this is the case what causes the pitch up moment? surely the downwash theory must hold true for the tailplane as well? because if the first link I gave is to be believed, Bernoulli’s theory would suggest that there would not be enough lift provided by the tailplane airfoil?
(of course if my instructor was talking out of his proverbial disregard the above)

If the cg to cp layout is different in the bus compared to normal aircraft well that’s news to me! Below approx FL250 our tailplane works conventionally but above that a whole new set of ball games kick in. At higher levels a pair of FCMCs (fuel control and monitoring computers) pump 6.5 tonnes of fuel from the center and 4 inner fuel tanks into a tank in the tailplane called the trim tank. What it is trying to do is to stick the c of p right over the c of g. This will unload the tailplane so that it creates no upforce or downforce. If the tailplane is not producing any lift then it also producung minimum drag. The stability issue is resolved for us by the fly by wire. The FCMCs then shift fuel forwards and backwards throughout the flight to maintain the c of g to within 0.5% MAC of its optimum position. Within certain parameters before landing the fuel comes forwards again so the trim tank is empty on arrival. To give you an idea of how important this is I recently did a return flight from Hong Kong to Heathrow with an unserviceable transfer pump so we could not use the system. The recalculated plan upped the fuel burn by 4 tonnes to 114 tonnes compared to a serviceable system (approx 3.5% increase)! The A330, 340 and 380 are the only airliners utilising this capability today.
When you multiply those savings by the number of sectors our aircraft fly every year the savings run into millions (and fwiw we spend roughly a million sterling a day on fuel!).

So it started on my 10th birthday then!

Would you care to elaborate your theory then Ian? 🙂

Let me guess, Newton’s 1st, 2nd & 3rd law of motion & vertical velocities?

Now I don’t know who ‘owns’ the theory that I understand but here goes:

I have seen wind tunnel tests where smoke pulses have been introduced into windtunnel airflow around a wing section which totally disproves the often quoted misunderstanding that ‘if 2 air particles meet the leading edge at the same time and one goes over while the other goes under they have(!) to meet at the trailing edge at the same time’. The reality that I have observed is that the particle above arrives at the trailing edge after the particle below. Therefore the ‘has to travel further in the same period of time’ theory does not stand up.

Now what I was taught (and seems to be perfectly plausible to me) to explain the increase in speed of the air over the wing was Vortex Generation Theory. A plate (or wing section) presented at an angle to an oncoming airflow will generate an area of dead air (low pressure) behind it. This is usually with a swirl (the vortex) and it is this lower pressure behind the upper surface that is the inducer to accelerate the top surface flow.

I’m sure there are flaws in my understanding but we have to get away from the dreadful mis-instruction going on in the first paragraph.

In a spin, one wing is moving leading edge forward, the other is moving trailing edge forward. Why is this a stable state?

I think herein lies your problem. The stalled wing does not have a reversed airflow as you seem to imply. The airflow is still flowing from front to rear but the angle of attack has exceeded the stalling angle.

A very good choice IMO. I personally am happier with Key Pub choosing their own moderators (based on what they see on the board) as it stops the bickering that seems to go on after elections. After all it is their train set.

lets just say its Blue-Purple 😉 😀

James

errrrr no… it’s as purple as an extremely purple thing can be! I know, I get to see it closer than anybody.