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Re: Bugatti Racer....wow!

Posted by Christer on Thu Dec 06, 2001 08:41:01 AM

In reply top Re: Bugatti Racer....wow! posted by MGM on Wed Dec 05, 2001 06:10:51 PM

Mick,
it works like this, I think:

If we start with a normal tail, the horisontal stabilizer doesn?t produce lift upwards, it produces down force.
On the wing, the centre of gravity is always ahead of the centre of lift and without the control of the stabilizer it would nose over forwards, sort of flipping through the air.
The horisontal stabilizer provide longitudinal control and the fin provides directional control.
The V-tail layout is not very common, it has been used on a few aircraft and a few gliders as far as I know.
The angle between the two halves is approximately 90 degrees and the funktion of elevator and rudder are overlayed on the two control surfaces. The 90 degrees layout gives horisontal and vertical vectors adequate for both longitudinal and directional control but, there are flaws as well, if there wasn?t this design would be more common. The main advantage is reduced drag.

If you take a look at the Bugatti the angle between the two halves is approximately 130 degrees and it wouldn?t give an adequate horisontal vector for directional control. As you can see there is a small fin oriented downwards so it isn?t a V-tail as such, more like a normal arrangement however inverted. With contra rotating propellers, producing no slip stream effect, this small fin would take care of the matter.

No to the wing, if you look at a wing head on it is approximately straight. There is, however a slight V-shape of a few degrees, called positive dihedral. This is to provide lateral stability. If the aircraft, in steady horisontal flight, is subjected to turbulence or a gust of air equilibrium is disturbed. If it rolls the downwards going wing will increase its span thus increase its lift and counteract the roll. If you take two pencils, hold them together as wings exaggerating the angle, then roll the pencils and you?ll see what I mean. The air flow "sees" the horisontal projection of span. Positive dihedral should not be exaggerated since it reduces aileron response.
If you have negative dihedral, wings sloping downwards, the aircraft would be very itchy with an impresive aileron response.
(The swedish jet trainer, the SAAB 105, had a straight wing in its prototype form but was deemed too stable. Therefore subsequent models had negative dihedral to make it more of a handful.)

If I understand Your last question, You mean two wings at 30 degrees negative dihedral and a normal fin of the same size but no stabilizer.
Well mate, You?ve just built yourself a dart and to my knowledge those suckers never stop rolling! :-)

I hope I?ve made it as clear as mud?!

Christer

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