Friday, November 21, 2008

New variant of the shape I have been thinking about

Here is my today's result from iRhino:

The idea is that the fuselage center section blends into wings like on blended wing body, but it only forms a minor portion of the shape, high aspect ratio wings continue from the blended part and there is a tail in the rear. I have not drawn this as I was thinking because I have been thinking either V-tail or T-tail. This picture doesn't yet have a rudder.

Now the difficulty is that I have hard time on getting the Rhino do what I think. The loft is challenging, because it follows airfoil shape, it follows the configuration and contour from the top I was thinking, but the problem is to vary the airfoil shape in the center section so that the transition from the right side to the left side is smooth and more circular than in this thing where it is pretty sharp (the sharpness there is completely unintentional and will go away as soon as I figure how to loft this thing properly).

The wing tips did not loft as I planned, and also the elevator has wrong airfoil shape in the tip, the scale2D produced results I was not planning to get. There is still something to learn in Rhino. I need to ask from maybe Jani tomorrow how to do this right.


Unknown said...

Have you looked into a Goldschmied fuselage. They claim that a Goldschmied fuselage generates negative drag.

Kestas said...

With the most CAD software you can use "blend" operation for joining fuselage body with the wing root. But the better way is to use "loft" operation covering a 3D wireframe model developed from controlled cross-sections and longitudinal splines.
But for the begining you need to develope an internal layout of fuselage - put in place pilot(s), equipment, structure elements (wing spar, for example), powerplant, etc. and only after that you may cover them with external shell.
In any case - good job, Karolina.
I like it!

Unknown said...

Thanks for your comments!

Well, I have a different approach:
This is a configuration layout and I am not in detailed design yet. In detailed design I need to pay attention how to fit everything inside, but at the moment I have no such requirement as I am lofting to get my initial configuration layout ideas illustrated and documented (instead of sketching them by hand).

The blend function in CAD software does not do aerodynamically accurate blend. In my picture, every cross section is an airfoil (it is not drawn to scale though yet and it is not yet based on any of my calculations, these can not be yet accurate because I haven't chosen the airfoils (there needs to be couple of different airfoils over the span)).

In detailed design later for sure, I will place virtual people and virtual engine on their places when doing the loft. Wing spar will fit very easily to the blended part and the rest of the wing is like a sailplane wing with at least 14...15% thickness.

I plan to loft the engine nacelles to the wings, similarly than they are blended in the SR71. However, there are remaining issues with this blended idea. For example a large propeller for each engine is needed for my design point and the blended idea works best as a low wing or mid wing configuration. This in turn requires long landing gear legs. Long landing gear legs add weight, and unnecessary weight hampers performance (and causes a requirement for a bigger engine). It is going to be lots of optimization to reach a synergestic design rather than just put a tube, cone, wings and somehow join them. The intended target requires a lot more than that.

Unknown said...

Allen - the Goldschmied fuselage would work with a tubular cross section. I need to compare it with the BWB, might be that the tubular cross section for the planned use case is:
- simpler (does not require separate pressure hull)
- more easily pressurized
- can benefit from pressure thrust

Unknown said...

On the other hand, the Goldschmied tubular fuselage has to be compared with lift producing BWB center section equipped with suction the comparison to be fair. It might turn out, that with suction, the BWB center section turns out more efficient. However, I do not know for sure without studying further.