Lysander wing shape design - wing taper towards fuselage?

[warhawk]

One thing I always found interesting with the Westland Lysander is the way wings taper towards fuselage (they narrow instead of usual widening)

 

img source: Wikiwand

 

Is there any reason for this design decision apart better visibility - e.g. some aerodynamic or structural advantage?

Thanks

Edited April 15, 2021 by warhawk

[Scimitar F1]

Good question. Looking at the picture alone could it be done for pilot visibility reasons? It is not done to minimise drag.

[Graham Boak]

I see no reason for it other than to combine crew (not just pilot) visibility with the required wing area.  This approach was fairly common on high wings, even on biplanes.

[Dave Fleming]

Another example of a similar design approach was the Vickers Type 253, where the inner porting of the wing swept forward to give the pilot a clear view downwards

 

[Jamie @ Sovereign Hobbies]

I know Graham Boak knows this, but to address any possible thoughts of "why not just move the wing backwards" the answer is "to place the centroid of lift where it wants to be on the fuselage" or else you'd end up with a longer tail and a heavier aircraft (thus needing a bigger wing to get the STOL characteristics wanted and perhaps needing a bigger, heavier engine ahead of the wing)...

 

Engineering is always a compromise.

[Graham Boak]

Thanks Jamie, but if you moved the wing backward you wouldn't want a heavier engine but a lighter one?  As you imply, it is the relationship between the centre of lift (effectively  the quarter-chord line) and the c.g., the latter being slightly forward of the former for stability.  You'd certainly need to rebalance the whole design.

 

The benefit of the Lysander's approach is that it increases the field of view for both the pilot and the observer, whereas moving the wing backwards would limit the observer's f.o.v.

[Dave Swindell]

The Lysander wing also tapers in thickness towards the fuselage. 

The maximum bending moment on the spar will be at the wing strut attachment point, and for this reason this will be the point of maximum thickness. 

As you move away from this point both inboard and outboard the bending moments will reduce, therefore the thickness can be reduced whilst still maintaining the same strength. This is desirable to reduce structural weight.

To maintain the same aerofoil section as you reduce its thickness you also have to reduce it's chord to keep the same thickness to chord ratio, this will also have the benefit of reducing structural weight.

As Graham suggests, the inboard taper angles could indeed have been influenced by giving the pilot and observer/gunner the best possible fields of view.

The outer wing taper angles could also have been influenced by where the desired centre of lift was required.

If the wing had had a straight trailing edge perpendicular to the centreline with a swept leading edge the centre of lift would have been further aft than the design with the leading edge perpendicular to the centreline.

As Jamie said, it's all about achieving the best compromise for the design parameters.

This wing planform wasn't unknown at the time, off the top of my head, the GAL Monospar for example.

 

 

[Agent K]

Visibility, given that the aircraft was originally conceived and designed as an Army Co-operation aircraft (= Artillery spotter etc.), before it was adapted for and used in SOE and other operations. Some of the above detail takes me back to my Aeronautical Engineering Degree and I won't add to it, other than to concur and acknowledge some very solid aeronautical knowledge there!

[Jamie @ Sovereign Hobbies]

4 hours ago, Graham Boak said:

Thanks Jamie, but if you moved the wing backward you wouldn't want a heavier engine but a lighter one?  As you imply, it is the relationship between the centre of lift (effectively  the quarter-chord line) and the c.g., the latter being slightly forward of the former for stability.  You'd certainly need to rebalance the whole design.

 

The benefit of the Lysander's approach is that it increases the field of view for both the pilot and the observer, whereas moving the wing backwards would limit the observer's f.o.v.

 

You're right and I didn't articulate myself very well! I meant that the net result of making the tail longer to balance an engine relatively further in front of the wing is a heavier fuselage, needing bigger wings, and thus heavier still and perhaps needing more power which lumps you with a larger engine which probably weighs more too and thus you're back to square one!