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OK, Stupid Swordfish Question.....


europapete

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Hi Gang, just been looking at Reini78's really nice model over on RFI. A thought popped up (HEY! Quiet at the back!) that on the vast majority of Swordfish models one see's, it looks like the lower wings have anhedral. I don't have many ref's for this. Should they have anhedral or be neutral? 

Btw, to my eyes the Hanriot fighter from WW1 always seems to have the same look also.

Edited by europapete
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4 hours ago, europapete said:

it looks like the lower wings have anhedral. I don't have many ref's for this. Should they have anhedral or be neutral? 

 

If you check out this video, it has some excellent frontal shots showing the lower

wings. Have to agree with Chris above, 0 Anhedral.

 

Fairey Swordfish "why Pilots loved this Mistake of an aircraft"

 

Regards

 

Alan

 

 

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Put a ruler across it. The visual impression of lower wing anhedral is seductive, but is an illusion brought about by multiple factors.

The lower wing had slight dihedral, but the false impression of anhedral is given by:

a) the lower wing dihedral being less than the upper wing dihedral, which is contrary to the more usual pattern, and therefore goes against cultural expectation so "looks weird". (On the Hanriot, the bottom wing is dead flat and the upper wing has dihedral. Again, put a ruler across it)

b) the considerable tapering in thickness of the lower wing root sections, all of which is done on the underside, so that when the eye is drawn to the fuselage / wing root interface, a real focal point, the apparent anhedral there is what captures the attention. Look at the top surface though, and put a ruler across the lower wingtips, and you will see that the lower wing does have slight dihedral

Edited by Work In Progress
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Although I haven't done a rigorous test, my impression has been that Tamiya's 48th kit tends to look that way.  I don't know whether there's something about it that leads a builder to end up with a wrong angle; it seems too consistent or common to just be carelessness.  I also don't think that it is an optical illusion, but I suppose it is possible.

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Just had a look at the official rigging instructions for the Swordfish which gives the dihedral of the lower main wing as 1 degree +/- 15 minutes with the upper main wing dihedral

at 3 degrees +/- 15 minutes.

 

HTH

 

Cheers

Dave

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If the dihedral is in the rigging instructions, but not in the drawing, then the drawing is wrong, however you put your ruler.  I think that we can ignore variation in wing thickness over most of the span.  The rigging is checked with dihedral boards placed on top of the wing.

 

PS  This is ignoring any changes between static and flying - because it is measured static.  However in-flight loads will only increase the dihedral.

 

PPS  This is ignoring bunts or inverted flying.

 

PPPS  Real aircraft are complicated.

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From a design/aerodynamics point of view it would make absolutely no sense to have anhedral on the lower wing (as this would counter the positive stability effect from the upper wing).

 

Generally, biplanes have either;

  • dihedral on both wings

or,

  • dihedral on one wing

I would guess the Swordfish lower wing has either no dihedral, or 1 or 2 degrees of dihedral.

 

It may be in the leading particulars of the pilots notes.

 

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On 2/27/2023 at 11:29 PM, Ed Russell said:

PPPPS - Many drawings are incorrect in some aspect or another

PPPPPS - Unless a photograph is at exactly the right angle, what you are measuring is not quite right.

Even if at the right angle, you cannot accurately measure lengths and angles because of the parallax effect.  For example, in a photo taken centrally head on, the wingtips are further away from the camera than the wingroots, and this will cause distortion.

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On 2/28/2023 at 3:16 PM, Ed Russell said:

No need to guess - the rigging instructions are quoted above.

Unfortunately, the rigging instructions quoted don't include how the dihedral is measured, although my guess is that it's the upper surface of the wing, probably along a spar. Aerodynamicists prefer it to be defined with respect to the chord line, which is somewhere in between the upper and lower surface of the wing: that's what it generally is when given in specifications. For those who might want to know more about that (you need to scroll down to the A4D dihedral example) or see some deceptive appearance of non-existent dihedral/anhedral in photos and drawings, see https://tailspintopics.blogspot.com/2014/03/anhedraldihedral-and-wing-sweep.html

Edited by Tailspin Turtle
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