Videos to accompany the Jan 2011 issue article - 20/12/10
In my January 2011 issue article I've been looking at 'lift' and the factors that can influence this important trait. Like last month I've selected some videos to accompany the article and which will, I hope, help to improve understanding. Right, let's get started!
One more visit to the classroom! This is the classic experiment for any of you who doubt the power of atmospheric pressure alone to lift a 747.
This little video is for fun. It shows that wings do not have to be the conventional ‘continuous curve’ shape. As long as the air is forced on a longer journey one side of the wing compared to that on the other, you will create lift. This wing just has some “ridges” around the periphery, but it’s enough to do the job. It might not fly well, but it does fly!
Two other factors which we saw effected lift were airspeed and the CL value. This video shows the crew of an A380 trying to correct a shortage of the former with a bit more of the latter than is usual!
The A380 is very heavily loaded – too heavily. There is some evidence this may have been a maximum load take-off test. Despite the use of full power the pilot has failed to secure sufficient airspeed before rotation. On rotating he still can’t get the required extra airspeed because his aircraft is now in a very high drag configuration (nose up) and the engine thrust is no longer aligned with the desired direction of acceleration along the runway – i.e. they are angled partially downwards.
The only course open to the pilot now is to put all his hope in the wing designers and ask for more lift via a greater angle of attack (AoA). Luckily for him, his wish is granted – albeit not without some damage to the aircraft’s rear! Notice that as soon as he has the aircraft off the ground he abruptly decreases the angle of attack by releasing some of the up elevator – by doing so he avoids the almost inevitable stall. This crew were very lucky indeed that the airstall didn’t eith stall or pancake back down on them. They owe the engineers that designed those wings a very large “thank you”!
A treat to finish with – what you can achieve if you really know what you doing and someone else is paying the bill!
To design a wing that can fly well at low speed is not so difficult. To design one that can fly at Mach 2.3 is do-able. To design one that can do both these things exceptionally well - is remarkable. The Su-47 was a technology concept aircraft designed in Russia. It was intended to evaluate new technologies such as; composite construction, new aerodynamics, zero stability, fly by wire etc. Only one example was ever completed. Here it is “doing what it does best”.
I hesitate to show this video to modellers. We get so used to seeing 3D flying, but remember this is not a model, it’s a full size, jet powered fighter aeroplane weighting several tonnes. The thing that most impresses me however, is not the slow speed ultra-high AoA stuff, it’s just how tight a Derry turn this thing can do. Every bit of aerodynamics I know tells me that plane should experience a high speed stall at that rate of turn! It almost makes the Euro-Typhoon look “ordinary”. If this doesn’t make your heart beat faster I can only conclude that you have water in your veins – not blood! Enjoy.
Don't forget to check the link below to Part.1 and look out for our further explorations in the February issue.
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Discussion on the Articles and Feedback etc. By David Burton 2
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