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View Full Version : Discussion Do crucifix flat foamies have "chines" like the SR-71?


Iso Octane
Oct 03, 2007, 10:37 AM
Going way way way out on a limb here, but do the crucible fuselage of profile planes benefit from a "chines" like effect?

From wiki:

Chine is also an aerodynamic term referring to the intersection of the upper and lower fuselage surfaces of the Lockheed SR-71 Blackbird which form a 'lip' around the forward fuselage of the aircraft.

The aerodynamicists discovered that the chines generated powerful vortices around themselves, generating much additional lift near the front of the aircraft, leading to surprising improvements in aerodynamic performance.[22] The angle of incidence of the delta wings could then be reduced... Landing speeds were also reduced, since the chines' vortices created turbulent flow over the wings at high angles of attack, making it harder for the wings to stall.

MarkusN
Oct 03, 2007, 11:03 AM
I'd say so. However full development of the vortices mentioned would be disturbed by the prop blowing along the fuse.

So, the horizontal surface will definitely contribute to the behavior of the plane, but the effect will greatly be affected by the propeller slipstream.

BMatthews
Oct 03, 2007, 04:12 PM
Crucifix, not crucible... Crucible is the container you commonly melt metal in. You had me puzzled for a moment though.... :D

Iso Octane
Oct 04, 2007, 03:30 PM
Oops, "crucifix", got it!

The reason I ask is because I'm building myself a foamy right now and have decided to use a simple thin box fuselage instead of crucifix. It looks better and nicely fixes the tail-twist issue.

It seems "aero devices" are all the rage these days with the foamies. Wing fences, air brakes, serrated LEs, perforated control surfaces, and it goes on. Seems like these things really do enhance performance. It had me wondering about the crucifix fuselage.

BMatthews
Oct 05, 2007, 04:01 PM
While I agree that there may well be some LEX effect from the flats to either side I've seen many other flat box style fuselages like you're planning on that fly, hover and generally 3D just fine. Go for it.

Brandano
Oct 07, 2007, 08:04 AM
Why not "cruciform" instead? Anyway, if you feel that you need better vortex control at high AOA you can just add a couple of strakes on the side of the nose or some LERXes. I am not sure how well these perform in the turbulent flow coming from the prop, I think they are most beneficial on pusher designs