Fuselage cross section

[Luis Strufaldi]

My question today is about the influence of the fuselage cross section regarding wind. Let me explain

There's basically two types of fuselage cross section: Square (like many tradition planes - a nobler, for instance) and Round (like the molded shell type planes, say a Yatsenko Shark).

Does the round cross section improve wind penetration or cross wind handling any better then a squarish fuse?

Considering that putting a round fuse together requires use of a special jig (Al Rabe's videos comes to mind), is it worth the hassle form the engineering/handling standpoint or is it just a cosmetic feature?

[Tim Wescott]

Hey Luis:

I suspect that a fuselage with rounded top & bottom and straight sides is going to be very similar aerodynamically than an elliptical fuselage.  So I don't think there's a great advantage to a fully round fuselage in that regard.

[Lauri Malila]

I'd say that aerodynamical  difference is too small to be noticed.
But structurewise, round cross section, and especially molded structures with double curvature, manage with less material for same stiffness. And less material equals less weight, low weight of components far from cg is allways good.
I have seen this many times when people have duplicated Yatsenko designs but with classsical construction methods, they just don't perform as well.

L

[Chris Wilson]

Would have thought that a more square cross section would knife edge better in the overheads since the air can't slip around the section as easily

[Tim Wescott]

Would have thought that a more square cross section would knife edge better in the overheads since the air can't slip around the section as easily

If you do the math on the centripetal acceleration you'll find that it provides all the lift you need.

[Igor Burger]

round cross section, and especially molded structures with double curvature, manage with less material for same stiffness.

sure? depends how you define "stiffness" ... speaking about bending stiffness, I would say that square is much better ... speaking about torsion, round will be better, but I saw broken fuselage in flight because of bending forces, never torsional.

[Igor Burger]

If you do the math on the centripetal acceleration you'll find that it provides all the lift you need.

sure? :- )))))

[Luis Strufaldi]

Basically what I can take is that the shape of the fuse does not influence (or minimally influences) how a plane handle wind, either headwind or crosswind. The major gain would be in torsional "inertia", or simply put, it would handle torsional stress better.

But only if the fuse is moulded, right? I mean, to have this gain, we are talking about a fuse made from a single piece of wood "bent" to a near "tubular" (or an elliptical) shape.

Would a "planked" fuse have the same torsional rigidity?

[Tim Wescott]

Basically what I can take is that the shape of the fuse does not influence (or minimally influences) how a plane handle wind, either headwind or crosswind. The major gain would be in torsional "inertia", or simply put, it would handle torsional stress better.

Yes, except for the indoor stunt class that Igor refers to, where you fly 5 second or longer laps on really short lines, and use side force generators to make up the difference.  I assume that these planes would not handle wind very well.  I'm pretty sure that Igor was just tossing that out for the humor of it.

But only if the fuse is moulded, right? I mean, to have this gain, we are talking about a fuse made from a single piece of wood "bent" to a near "tubular" (or an elliptical) shape.

Would a "planked" fuse have the same torsional rigidity?

A molded fuselage is going to have the greatest rigidity/weight, a "planked" fuselage or even a rectangular "box" fuselage will come in second, and a profile fuselage would come in last.  That's kind of a sweeping statement that's subject to all sorts of modification depending on what materials people are using, but given the same materials it holds.

[M Spencer]

Its important on a box / flat sided fuse , not to have it to narrow at the tailplane .
A good 3/4 at the leading edge , maybe an inch . Aft of the hinge ( at ) it can taper in more .

The ' box ' type fuse can still form a cone. A Square one ! .

its a pity it isnt the underside .


Probly the most important thingo is the vertical stabaliser , for consistant line tension.
Mr Compostellas ' Airfoiled ' set up is pretty hot , Almost symetrical Finwith outside of rudder flat .
Though he uses a curve on the inside face .

You can see on this Spitfire underside view the aft fuse. taper set up . This gives a broad Stabilizer Mount and better ?? torsional ridgidity ,
Wing to stab . Or keeps the Flying Surfaces true !



You need to glue the things togeter fairly well if your flying in good sailing weather , an Silk is good on an I beam type , as
you can put the fuse over your knee and pull the tips up and down a few inchs without breaking it . A D tube might snap
if you test the beam strength that way .

Heres a PLANK Spit Fuse , the formers and plank edges are beveled .


I started one of these SQUARE  ( split at shoulder hight , built inverted ) then cut the lower rear edge and Beveled formers under
to a std. angle through . so its pretty simple . After youve figured it out on paper . And That ones Not Fat aft , a straight side
to sternpost . Was good in the wind , to twang .018 laystrate in square bottoms , and pulled like Eck in 20 Knots, downwind/ manouvreing.

[EddyR]

Having built two Bearcats with round fuselages I have seen no difference how they fly compared to the more conventional body design. Things that do effect them are low wings and dihedral. Once these are trimmed  they fly the same.
Ed

[Chuck_Smith]

To he original question, YMMV but I think the pilot's flying skill and ability to trim the ship trumps the fuse shape.

Aerodynamically? Unless the wing is mounted significantly above or below the fuselage centerline I (again, YMMV) doubt it would make a difference, and it might not in any case.

I believe one could, theoretically, make a case that a square cross section might ever so slightly increase pitch response ( at the cost of drag ) but it's an esoteric argument at best.

All of the above is IHMO and opposing viewpoints will be welcomed, lol!

[M Spencer]

If We explore outside parameters to establish principles , we have a better understanding of the subject .   .

Did a scale profile Meteor NF11 , with the Oriental Wing , back 1999 . Stupid enough to part with it as it weighed 60Oz.
Now find they fly fine at 60 Oz. on 70 ft. of .018. HOWEVER on 60 ft. of .015 stainless . a 58 In long 7 in deep profile fuselage
has a ' slight ' tendancy to stretch the lines , and in the gusts. In fact a vertical eight has a 90 degree ' hesitation ' in responce on the
reversal of movement . Which is disconcerting .



Looking at the Fuselage , 58 in overall length , 1/2 in width , we can deduce it has a 116 to 1 aspect ratio . Longitudeinally .
Nother pitcher to rub the point in .



Itchin to replace the sucker for ' some time ' now . Line tesion , at least the lack of it , isnt really an issue . . . . .  .

VERTICALLY , the Width / Breadth must be around 1/14th !

NOW an OPPOSITE evaluation Might Be Thus .



Aint No Fuselage !

[M Spencer]

If we look at a UNRESTRAINED object in WIND , traveling , either it moves with the wind, restrained by INERTIA & Gravity and suchlike .
Cross Wind ( lateral ) being present only twice per lap , in level flight. Manouvres get trickier !

The Dreaded Airship maybe gravity isn't the issue , with its anti gravity !.  But Figured Helium / hydrogen filled wheels ( tyres ) still have say 3 Oz. inertia even if filled with Neg. 3 Oz. of Gas .

[img][/https://c2.staticflickr.com/2/1295/4675196173_3939939f34_b.jpgimg]

A FLAT ( vertically) ARROW can be more efficient . or theyed be MADE like that !

[img][/https://s-media-cache-ak0.pinimg.com/736x/30/1c/f5/301cf5bd0eb8b663392b4428b032b3ed.jpgimg]

Bullets apparently , the rifleings a bit awkward if theyre SQUARE . 





Thus we can deduce a flat plate will have significant cross wind resistance , and a ROUND fuselage the Minimum , for the cross sectional area ,
If we are utilisinf Fixed Dimensions due to structural / strength considerations . Preumeably a Flater Round fuselage would be better still at ingnoring X Winds.

[M Spencer]

Hyrumph