DB Spitfire Build

[Tim Flyer]

I put the fin leading edge on this morning. The curve was quite easy to form on the balsa strip after wetting with diluted pva and leaving for a few minutes. I’m still using the Titebond aliphatic as my adhesive. It does have a faster “grab” than pva but still allows decent working time. My perma grit curved edge sanding blocks were useful again on pre sanding the fin curve before applying the strips . I also find them very good at getting nice smooth curves in the wing wheel well sheeting . 

[Dwain Dibley.]

Hi Tim, nice work Matey.

I'm interested to know why you used diluted pva and not just water.

D.D.

[Tim Flyer]

Cheers Dwain thank you for your comments.

 

Water works very well too and is suggested in the instructions .
I use diluted PVA partly as I have a few gallons of it and also because it adds strength with very little weight. If I get micro cracks in the wood by “over bending it is already there to sort them out. There is another slight issue with water use and that is that it might “delay the tack” of the aliphatic glue I use. The diluted pva starts drying faster and is tacky.  I have a small  jar of it on my building bench and its very useful. 
 

I also used pva as the medium when I added the fibreglass to reinforce the split flaps as it’s more convenient than epoxy. I will be covering with epoxy though . I’m using the dilute pva as a sanding sealer firstly too.

 

When making curves in balsa , to  soak the wood I only apply it on the part with the major curves so if I was worried about adding weight the amount added would be really minuscule. 

Edited February 20, 2021 by Tim Flyer

[Dwain Dibley.]

Thanks Tim, I appreciate you taking the time to explain. I have a jar of diluted pva, for Brown paper covering, I will use this for bending purposes too from now on.

D.D.

[Tim Flyer]

Cheers as in most things in modelling there are many ways to achieve the same thing . I haven’t done much paper covering. I’m using glass on this model as it goes so easily around the compound curves. As long as I seal the balsa well first I won’t be adding much weight. 

[Tim Flyer]

I started on the fuselage structure today. Yesterday I had glued the balsa outers to the ply fuselage sides and glued some of the two part fuselage formers together.  The second  step is slightly fiddly and requires gluing the two rear balsa side formers into the central formers while inserting a spreader which slots in to give the exact shape . I made sure the slots were free with a bit of filing and fitting before attempting assembly. It went together fine but did need encouragement from clamps to push the tabs in fully.  

 

 

 

As the instructions mentioned it’s best to use wood glue rather than cyano to increase working time.
Obviously cyano can be used very well for fast model assembly but it’s easier to make sure wood glue runs the complete length of a join rather the just ‘spot tacking ‘ for which cyano is better suited. (Similar to difference in spot welding an seam welding). That is important when we join fairly weak materials such as balsa. 

[Tim Flyer]

Today I set up my SLEC jig and joined up the main frame. A jig isn’t essential but it makes it much easier checking the fuselage is straight. I also used a few extra clamps . I also glued the firewall on whilst doing this as it helps to keep the structure straight and doing it all in one hit is convenient.

 

 

 

I didn’t glue in the front wing dowel locator former in at this time as I will wait until the inner balsa side spacers are fitted in the next stage. That will ensure it is centralised. I was surprised the instructions say that should be glued at the initial stage as it needs to be exactly central in order to locate the wing retaining dowels 

[Ron Gray]

Good progress Tim.

[Tim Flyer]

Cheers Ron. It’s definitely a model that had its “initial shock” value when I opened the box and saw all the bits, but the path ahead is now getting clearer. Can’t wait to get the wings on !
I’m also pleased I started using the bench bandsaw to help release the ply parts from their sheet as using hand tools gets laborious and fiddly for the small components.
The laser cutting is very accurate and it all seems to go together well with only light work needed to remove the carbon with a small file. 

[Ron Gray]

The carbon burns on laser cut pieces can be a nuisance and difficult to get out of sheet balsa! Apart from gentle sanding I'm not sure what else can be used, I built a 30" Sinbad a couple of weeks ago and because I wanted to cover it in transparent film I wanted to make sure that the carbon didn't show through, I spent ages gently sanding down all exposed edges - black fingers! I've now got a somewhat larger kit arriving next week with laser cut parts and as that too will be covered with transparent film I'm hoping there won't be too much of the black stuff to get rid of.

Edited February 25, 2021 by Ron Gray

[Tim Flyer]

That definitely sounds a task when using clear covering. Luckily the Spitfire will be painted .  It can be slightly tedious freeing and then sanding the ply parts. Once the carbon is removed they fit well though. 
 

Today I got a bit further and put the tail plane on. I didn’t fit the ply wing seating as it will interfere with the clamps. Next job is fitting the fin which will require a bit of fettling! 
 

 

Edited February 26, 2021 by Tim Flyer

[Tim Flyer]

Not a great deal to report today as I didn’t get much time given a number of spring garden tasks ! 
I spent some time getting a good fit for the fin with careful filing, but cannot attach it until the elevator is in . I will cover the elevator with Solartex before fitting to make it easier. 

I also added the rudder control horn which is some sort of clear “plexiglass” which is used to avoid spoiling the looks but enables lightweight pull-pull wire actuation. I added a couple of small balsa tabs on top of the control horn to aid adhesion when covering the rudder in Solartex. I will also do that next. The tail wheel wire is installed and it will be a free castor version as per instructions. 

 

Once the fin elevator and rudder are in I will sort out the elevator linkage which will probably be a snake. The focus is to keep the tail end light as being a mk1 Spitfire the nose is short. 

[Dwain Dibley.]

Nice work Tim, I notice you have managed to hang onto some solartex, you little Tinker.

I just had to stump up for some Oratex . LOL

I add the tabs (making a slot in the wood) as you say, prior to covering, and then add the horns though a slit in the covering.

Now following with Glee.

D.D.

[Tim Flyer]

?Hi Dwain ...yes still got a bit of Solartex. I have glued the horn in so will be cutting the slit as I cover ?

Edited February 27, 2021 by Tim Flyer

[Tim Flyer]

The fin and rudder are now Covered . I’m now trying to install a SLEC heavy duty snake for the elevator. The control horn on the elevator is metal and it is braised onto the joiner wire . So far be this part has been a bit of a pain. It was initially the wrong size to fit the elevator, and needed re bending )which wasn’t difficult).

However I just cut prepared the snake and found the plastic bushed hole in the control horn is sloppy when using an M2 clevis. The hole in it is 2mm rather than the usual 1.5 mm found in most control horns. Maybe they expect users to choose an M3 clevis and metal rod?

 I might have to use a ball link instead as I don’t want a sloppy elevator link and don’t want to add unnecessary rear weight with M3 control rod. 

[Ron Gray]

Can you drill it out and bush it with a bit of the 'handle' of an ear bud. Ive done that on ply horns before now, works very well. (Not my idea it's one from @RICHARD WILLS)

[Tim Flyer]

Hi Ron Thanks for that suggestion ?. I will try tomorrow... I recon I might be able to push their bushing out and add the ear bud custom bushing ..  great idea?

[LHR Dave]

Coming along nicely Tim.

Still watching and learning.

 

Dave

[Tim Flyer]

Cheers chaps. I pushed out the old bushing and added the new one as per the great suggestion. The M2 clevis now fits nicely with no slop . The SLEC one metre Heavy Duty snake is just the right length to reach the servo. Any shorter and it wouldn’t have worked . Once it was connected I glued the fin on . It’s really important to get it all sorted before the fin is fitted as access is limited and elevator cannot be fully removed afterwards. I also added a picture of the brace I used to hold the tail plane level whilst adding fuselage cross braces. Next job sheeting!

 

 

[Ron Gray]

Nice alignment jig @Tim Flyer

[Tim Flyer]

Thanks Ron . It’s quite important on this model to try to get it straight for the cross bracing as the tail is quite flexy when first fixed. Although they are quite spindly strips the cross braces do manage to increase the tail stiffness a lot.
I’m still going to need to be very careful when sheeting that I don’t ruin the symmetry.I will probably use a variation on this as support rather than the cardboard box recommended in the instructions. 

[Ron Gray]

25 minutes ago, Tim Flyer said:

 rather than the cardboard box recommended in the instructions. 

?

[Tim Flyer]

I have now started the sheeting putting in the top and bottom tail sheets. I asked my DIY jig as mentioned earlier as I was a bit concerned about using a cardboard box.

 

The sheeting went quite ok and I firstly wetted the sheets along the outside of the curve and later brushed on diluted pva. As long as enough time is taken the sheets easily bend with a bit of light hand pressure. The key is to take time and not to try to put the curve in all at once. I used my standard Titebond glue and pinned the sheets and also used some elastic bands. I removed the bands after a short while to avoid over curving the sheet which might give the “starved cow look”.

I need to add more sheets now I have put in the cockpit rails . There are also some balsa strips that need adding as I put sheeting in   also to avoid the “starved look”.
One slightly confusing point is where to stop sheeting near the middle section where the rear wing fairing runs to the back of the wing. I think I will need to sheet the whole lot and simply add the fairing over the top as the wing fairing won’t add much strength on its own . 
 

 

 

[Tim Flyer]

By the way when you do the bottom tail sheet remember to allow plenty of overlap for the rudder channel. You may notice my sheet is a bit short at the bottom but I can easily rectify that by cutting in a couple of small pieces. 

Edited March 8, 2021 by Tim Flyer

[Tim Flyer]

I’m steadily getting on with sheeting the fuselage. I added the ply front top sheeting after putting in the elevator and rudder servos and securing the elevator snake. The pull-pull rudder wire will go in later ... probably after covering. 
 

The ply front top sheet needs to make a rebate for the cowl . I actually centred it on both the formers to also allow a small rebate for the rear sheeting to join. I’m using as large as possible sheets to keep the weight down and try to minimise jointing . It’s going to be slightly fiddly butting the sheeting near the rear wing fairing former as there isn’t much support there so I may add a few fillets. I haven’t made the cockpit sheet cutout to size yet so that’s just a rough cutout to allow clamping. 

 

 

Edited March 15, 2021 by Tim Flyer