Fokker D.Vlll - GeoffS

[Peter Miller]

8 hours ago, PatMc said:

I believe Fokker & Platz were influenced by Junkers in using thick wing sections in order to produce a fully cantilever wing. The D. VII wings were designed to be fully cantilever & flown without interplane struts but pilots were unnerved by the wings not always remaining parallel under even normal flight loads so struts were fitted to the production aircraft.

 

Re aileron differential/adverse yaw ; the Wright Bros were aware of it before their first powered flight, they used coupled rudder to compensate from the first fight on.

OTOH some fighter pilots deliberately flew into combat zones with some rudder (& opposite aileron) to induce a yaw in order to disguise the true direction they were flying in by a few degrees. The idea was to cause the opposition to misjudge their aim. It was successful to the extent that some pilots were said to have used the tactic during dogfights in the early days of WW2.  

My father used to describe how, when the anti aircraft guns started firing at them the pilot would put the aircraft into a steep bank but not actually turn.  All the guns would then start firing off in the direction of the expected turn

[Geoff S]

Quote

 

Did a trial fit of the port wing to the already built centre section which is attached to the fuselage.  There seem to 2 things to take into consideration.

 

1: The root rib needs to be square to the top wing spar.  This isn't immediately obvious if you build the wing to Peter's method as it's built on top of the bottom sheeting and the ribs are square to the tapered bottom.  There is no dihedral at the top (it's totally flat) any dihedral effect is due to the tapered underside of the outer wing panels.

 

2: Because the bottom of the wing tapers the bottom dihedral brace should be at the same angle.  The braces supplied by Sarik in the CNC parts are all straight.  On my trial fit I couldn't get the top flat until I realised the bottom brace was pushing against the bottom sheeting and preventing the wing to adopt its proper angle.  To correct this I sanded the bottom brace until it allowed the wing angle to adopt its designed position.  Of course this weakens the brace. I think I glued them in with Titebond, which means a little water may allow me to remove the bottom dihedral braces and replace them with ones at the correct angle.

 

 

Here's the wing sections dry-fitted.  The main spars are exactly in line (or should be!) which means the l/e sheeting can cover the join (I have some long 1.5mm x 100mm wide sheets which should do the job.

 

This view shows the quite significant taper/dihedral on the wing's lower surface and the flat top surface.

 

 

[Geoff S]

I managed to remove the lower dihedral braces after an hour or two of regular dabbing with water (one of the advantages of using a non-waterproof glue like original Titebond).  I've made a rough angled brace to try and it gets the wing exactly where it should be.  So anyone building this model using the CNC parts be aware that the lower dihedral braces need to be changed.  The drawing also shows both braces as completely straight.

[Geoff S]

Here's the replacement dihedral braces compared with the original (this one is sanded to accept the dihedral angle).

 

 

The wing fits as it should now.