Warbirds Replicas Focke-Wulf 190 Build Log

[Lipo Man]

4 minutes ago, Gordon McConnell said:

Slow progress over the last few weeks. I have completed the wing root fairings and filled and sanded them to shape. Also, I have attached the wing servos on their mounting plates with hardwood blocks and small wood screws. The servo wiring has been run in the slot cut in the lower wing surface. I have filled in the slot with some balsa strip as I think that is structurally more sound than leaving it open. The downside is that I would need to cut into it again if I ever have to replace the wiring. Servo replacement is possible as I have made a plug joint in the servo bay cavity.

I don't know if it will work, but when I installed the servos in mine I also routed a piece of nylon string through the servo wire channels.  If I ever need to replace a servo I'm hoping the string will allow me to pull the wires of a new servo through the channel.  Seemed worth a try - although I'm hoping I never have to use it!

[Gordon McConnell]

The wing dowel is embedded in a block which was epoxied into a slot cut in the leading edge and then reinforced with the wing bandage and epoxy laminating resin. I think that has worked out well and should be stronger than sinking the dowel into the foam behind the leading edge balsa section.

 

As others have done, the rudder and elevator servos have been mounted on bearers made from scrap ply which are glued to square section balsa supports on the fuselage inside walls. The control rods are made up to length and holes cut in the aft fuselage sides to exit to the elevator and rudder control horns.

[Gordon McConnell]

Getting a bit impatient to get on with the covering, I started on the fin and tailplane. I have not used brown paper before so I was at the bottom of the learning curve. I watched Ron Gray's video a couple of times before starting. The brown paper is from Amazon and is used as masking for car spraying. I also tried some from Hobbycraft but this seemed to soak up the PVA an wet the other face. The fin and tailplane came our well and gave me confidence to complete the ailerons, elevator and rudder. The PVA I used was Gorilla Wood Glue.

 

[Gordon McConnell]

Having gained confidence, I then started on the wings. I cut out the paper to do a lower and upper semi-span separately, there was no chordwise joints. I am uncertain whether this was a good idea. I slightly thinned the PVA with water and brushed it onto the brown paper. It seemed to start drying on the paper quite quickly so I hurriedly positioned it on the wing and used my finishing iron to smooth flat. All seemed well at first but after drying overnight, a lot of bubbles appeared. I applied the iron again and they went away but only to return later.

I am contemplating try to strip the paper off and start again but I might try to cut the bubbles and stick the paper down again. Any repair tips will be gratefully received!!

 

[Ron Gray]

14 minutes ago, Gordon McConnell said:

but this seemed to soak up the PVA an wet the other face

My suggestion is that the PVA was thinned too much. I use the Hobbycraft brown paper and don't have that problem.

 

Regarding the bubbles, no need to peel it all of, just run a scalpel gently right the way down the length of the area then 2 more cuts at the ends of the line to form an H. Gently peel back the brown paper, it has bubbles so it won't have stuck down, apply some more PVA to it then smooth down. I suspect that the reason for the air bubbles is that there was either insufficient PVA on the brown paper or it had dried out before you laid it down, you said in your post above 'It seemed to start drying on the paper quite quickly'.

 

There is a bit of a knack to this brown papering lark but you'll soon get the hang of it. 

[Gordon McConnell]

Thanks Ron. I think you are quite correct on the thinning of the PVA. I tried another panel with hardly any water in the PVA and that worked much better. No bubbles visible. Maybe trying to cover the whole semi span was ambitions. Perhaps I would have found it easier to try to do it in two parts to avoid the adhesive drying out.  I will try the repair as you suggest. Lots of bubbles to work on!! 
Thanks again for your good advice. 

[Lipo Man]

41 minutes ago, Gordon McConnell said:

Thanks Ron. I think you are quite correct on the thinning of the PVA. I tried another panel with hardly any water in the PVA and that worked much better. No bubbles visible. Maybe trying to cover the whole semi span was ambitions. Perhaps I would have found it easier to try to do it in two parts to avoid the adhesive drying out.  I will try the repair as you suggest. Lots of bubbles to work on!! 
Thanks again for your good advice. 

I had this exact issue on mine. I repaired a lot of the bigger bubbles as Ron describes, but I left quite a few smaller ones. Now that everything is painted they really aren’t noticeable, so I’d say don’t lose sleep trying to make it perfect. Once you’ve got your scheme on it they’ll disappear into the background. 

[Ron Gray]

Another little trick to get rid of bubbles, pick a little hole in one of the bubbles then use Superphatic glue with the thin nozzle and ‘inject’ it into the bubble. Remove the nozzle then massage the glue into the bubbles. It’s amazing how it wicks through the bubble ‘field’ and sticks them down.

Edited March 15 by Ron Gray

[Gordon McConnell]

LiPo Man and Ron. Thanks. Will try the aliphatic glue solution as well. Some of the bubbles are very small and good   to know they may not be noticeable.  

[stu knowles]

Gorilla PVA as I recall is very thick consistency compared to many PVAs. I use PVA from a 5 litre bottle from the Builders Merchant which is really used to size walls and plaster.  I imagine that cheap 'Pound Shop' PVA will be better for this purpose than best quality wood glue.

 

Chris Golds was  probably the pioneer of BP/PVA covering.  If you read up on his methods he pastes the brown paper and the wood surface.  Lays on the BP and does all the trimming (make sure that both sides of the wing/control surface or whatever are done together or shinkage will cause a warp) and then he pastes both sides again and hangs it up so that both sides can dry evenly.  Since Ron did his video I have tried his method and its good too, a lot less prone to mess.

 

I think that the bottom line is that BP and PVA covering can be applied using slightly differing methods to get the same result.  From my experience the key points are to lets the BP 'ease' for  few minutes after pasting but before applying to the model and always do both sides together.  The PVA can be used quite liberally and doesn't cause significant weight gain.   

 

If you are getting bubbles use more paste and let it stand a couple of minute to relax before applying to the wood.  If you don't believe that the paper shrinks as it dries just apply it to a single side of a 1/4 balsa tailplane and see how much of a bananna has arrived in the morning.  If the PVA has been applied liberally a hot iron will stick down bubbles and loose ends.  The paper is likely to bubble soon after being applied but before it has dried.  If this happens give it a little longer to ease before applying to the model but in any event, DON'T PANIC.  Leave it to dry.  Most bubbles will shrink away as it dries and a light iron will deal with any remaining.

 

Chris Golds also applies two or three coats of the PVA paste all over after the first application with sanding in between to prep the model for paint.  If you have a persistent bubble, tear, not cut it open, apply paste and brush it back down.  Torn edges disappear more easily than cut edges.

 

I have covered several models with BP.  Its cheap, light and non critical in its application.  With practice I don't exit the covering session quite so tarred and feathered with off cuts of brown paper as I did in the beginning.  Its  a perfect method for any all sheet airframe like the 190 or Tempest subject of this thread.

[Gordon McConnell]

I have experimented a bit further with the Gorilla PVA. I thinned it very sparingly with only a couple of drops of water and applied it very liberally to the BP. I did not leave it long before applying to the veneer. This has worked much better with no bubbles. I also have done one wing with applying a thin coat of Balsaloc to the veneer and letting that dry before applying the BP/PVA. That has worked well too. 

I think as Stu has said there are several variations of the method which can be used. In my case, with no previous experience, I am getting used to the process and the finer details which guarantee success.

Having expert advice from those on the Forum is a great help to progress quickly up the learning curve.

Thanks. 

[RICHARD WILLS]

All useful tips chaps . Looking at the bubbled wing it may be worth removing that patch rather than laboriously dealing with each bubble ( I agree that too thin glue or not enough glue was definitely the issue . 

If you just lift the paper at the trailing edge and then reactivate the glue with your covering iron , you can peel that bit off . 

Dont leave the iron in one place too much though as it may melt the white foam . 

Ive used a sort of "mine sweeper " back and forth action in front of where its lifting . 

[Gordon McConnell]

Thanks Richard. I am going to do that as I had a look at it again this morning and it is really a bit of a mess on one wing only. 😀 Away for a couple of weeks so it will have to wait a bit. 

 

 

[Gordon McConnell]

I eventually removed the bubbled covering on one wing and replaced it. What seems to work is using Balsaloc on the wing skin veneer prior to applying the PVA coated, brown paper. I am also convinced that the Gorilla PVA is not the best for this job and next time I will buy some cheaper PVA from the builders merchants. 

 

I have got to the painting stage now and will final fit the flying control surfaces prior to the finishing paint coat. I have used Halfords white primer on the lower surfaces and grey primer on the upper surfaces.