Fuselage design for better knife edge flight.
 

Hey guys, I've been having one of my characteristic mental meanders into aircraft design, brought about by an article on the subject.

One thing that it alluded to was fuselage shapes to get better knife edge performance. THere was a comment about having slab sided fuselages work better than rounded ones for a more efficient lfting body, this stands to reason at least in my mind as there would be less spillage of air around the fuselage.

Now this got me thinking about a change to the centre of pressure of the fuselage. I admire Nat Penton's way of getting the CP forward by using more wings to create lift closer to the CG. Now by my way of thinking, would be a reasonable assumption that fuselage depth has grown to the size it has because the fuselage is not efficient in producing lift unless it's of a very large size. Now, if we were to change the shapes of the noses of our aircraft to be more efficient lifters, this would negate the need for a deeper fuselage, which would in turn reduce the shift aft of the CP due to a deep turtledeck?

I guess what I'm saying is, would a more efficient fuselage negate the need for a deep one?

RE: Fuselage design for better knife edge flight.
 

Sure would! When we say deeper fuse we mean taller fuse around the canopy, yes?

If you were to lay a Xigris fuse side by side to an Integral, you would notice difference...Xigris is taller, narrower and I hear a bit draggier (stands to reason). Xigris fuse side is more flat slab type compared to many maybe even all earlier fuses. It is also taller/deeper which should improve it capability to lift in knife edge flight. Indeed that is the early report from the few who are flying the model.

BTW, Xigris fuse side area is approximately 750 sq inches per my measured estimate.

One way to make the fuse a bit "more efficient" would be to corrugate the sides along the length....to trap air if you will. Would look quite ugly but totally functional. Pattern is a functional sport afterall and in the air it wouldn't amount to a hill of beans difference in the looks department. I doubt the judges would even give it a second thought.

If the fuse sides were dimpled like a golf ball that would also be a positive in the lift department but a negative in the drag department possibly robbing too much power from the powerplant.

RE: Fuselage design for better knife edge flight.
 

I was out flying knife-edge with my Balsa Nova 1.20 today. This airplane was specifically designed to excel in knife-edge flight...and it does. I agree with you that working on fuselage design forward of the CG should be productive. Increasing the lateral area from the nose to the CG should allow a model to maintain knife-edge flight at a lower (fuselage) angle of attack...and improve rudder authority. I hope you will keep us posted on your solutions.
Best Regards
JC

RE: Fuselage design for better knife edge flight.
 

I sense a flying test bed coming on.

RE: Fuselage design for better knife edge flight.
 

no need to test... go to www.insightrc.com

check out voodoo express and pentathlon.

Although not pleasing to many, form equals function.

Chuck

RE: Fuselage design for better knife edge flight.
 

Yeah, you're right there, the voodoo express is a polariser. It's been mulling over in my head that a lot of the modern designs are caught in the "looks cool" category, and the voodoo express is in the "build only what is required" category.

I'm looking to be somewhere in the middle. Something that looks cool but "has what is required". Getting these two things to gel will be fun!

RE: Fuselage design for better knife edge flight.
 

But what is the goal? Standard F3A designs have been able to do knife-edge loops for years now with half-rudder. Do you want more lift in your fuselage so that you can loop with 1/4 rudder? Do you fly knife-edge all day long or do you want what we all to, to pull a minute-long fourpointer with just aileron and no rudder/elevator input? The problem isn't fuselages not lifting sideways, it's roll coupling. There's no such thing as a non-coupling aeroplane unless we're talking counter-rotating props but the coupling can be reduced with wing and stab position, thrustline and of course the mighty CG-issue.

I'll take a plane that barely does knife-edge with full rudder any day if it does so without rolling towards the wheels or canopy.

RE: Fuselage design for better knife edge flight.
 

Been there, flown that

http://www.carf-models.com/public_ca...=Valiant%20F3A

Except it still doesn't take that much rudder to fly on knife-edge :]

RE: Fuselage design for better knife edge flight.
 

I can second what Brett said about the Valiant. When I flew Bryan's I did knife-edge from one end of the box to the other without touching the ailerons or elevator except when the wind bumped it. Took some time to get used to how little rudder it actually took, but once I got used to that, everything else was gravy.

RE: Fuselage design for better knife edge flight.
 

I don't see a problem with oval fuse, I do amazing knife edges with my two pass ports without touching ailerons or elevator..

RE: Fuselage design for better knife edge flight.
 

I've always wanted to try something with the fuse sides set up like a traditional 3-chine boat hull, but like many ideas I've never gotten around to it.

It might be an improvement (over what?) or it might be a complete disaster introducing a whole new range of problems. Small wings sticking out the top and bottom will probably achieve a better result but would just be too ugly to put on a pattern ship (there's a picture of this floating around somewhere from a US site)

Far better for the schedule makers to get back to designing smooth, graceful patterns instead of the aerodynamically hard patterns they have today. It takes no more pilot skill to fly an integrated half roll around the bottom of a loop than over the top of it but the pilot needs a better plane to do it right. Same with snaps in uplines, no reason to have them there when they can be put in downlines.

RE: Fuselage design for better knife edge flight.
 

But when you see a well-excecuted upline snap, it's truly a thing of beauty! (You should see the Valiant do one :D)