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DB Spitfire Build


Tim Flyer
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c7c7110e-2209-4324-bf9e-39f32f19df2f.jpeg2651cf15-61ae-4050-ac9f-f3916af25dac.jpegFinished extending the retract well today and mounted the retracts . There needed to be extra space at the front of the well to allow forward sweep on extension . It’s now all done . I dread stuck retracts on models so am happy to slightly oversize the wells to prevent this. They will be glassed with fine sheet and epoxy later . To make it easy to see the sweep and pintle angle I took three photos. I also needed to cut a hole in rib 212 to allow the aileron servo wire to pass . Using the retract bay would have added risk of the wire fouling or being cut by the gear.

464d95a4-9cad-45a0-a289-e82f9e9e36b9.jpeg

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I also excavated the wheel well floor a bit further so no mounting fillets will be required and the wheel bay cover should be fairly flush with the bottom of the wing. I will add the bumps on top of the wing a bit later . Although I haven’t needed to excavate into them they should help add extra rigidity to to bay floor sheeting.

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Posted by Tim Flyer on 21/01/2021 15:12:12:

. I dread stuck retracts on models

Why? There is not much you can do once it is stuck, so why worry?

I dont ask that to be difficult, more as an example of how to make your warbird flying life easier.

If you watch videos on youtube of models with retract failures you will often see unstable landing approaches, a flare at 10ft leading to a stall, excessive or really slow speed, no flare at all.. In simple terms, a landing that would end badly even with wheels is now guaranteed to end badly as they have no wheels. The one time they needed a smooth landing, they loose the plot.

Why does this happen? Distraction. The pilot is in such a flap about their wheels not coming down that they panic (fearing damage to the model) and then make an utter mess of the landing, causing damage and so the cycle repeats. If they would just do a normal approach and land, its unlikely anything will be broken.

I have had retract failures on all of my current fleet of warbirds at one time or another (la7 4, P39 3, Seafury 1, Hurricane 1) over their collective 25 years ish in the air. All were belly landed without major incident and only things like the retract doors were damaged in a few cases and the odd bent needle. Even my wooden props made it through!

The key is to plan ahead and not worry. Gear wont come down? never mind i will belly land. Do a normal approach with a tiny bit of excess speed, get down to about a few foot off the ground, kill the engine, wait until its just about to touch down (like, 1 inch up) and then put the flaps up to prevent damage. The model will plop onto the ground and that will be the end of it.

The same is true of a deadstick. Firstly, leave the gear up! warbirds glide like stones, you dont need extra drag. Next, can you make the runway? Decide now, dont try and decide you cant make it 4 feet off the ground as it stalls because you tried to stretch out your glide. If you cant be 100% sure you can make it, accept it, im landing in the field...where can i go? Pick a spot, flaps down, gear up (unless you want to put them back in the wing again later?) float it down and repeat the last part of the retract failure plan you have already made. Again this is something i have experienced twice on my La7, once on my Hurricane and once on a P47 i was test flying for a friend. I got the La7 back to the runway on its wheels after its prop exploded, the other two ended up in the field with minor bruises.

I guess my point here is not to spend time worrying about what you dont have (engine, wheels, an aileron..whatever) and concentrate on what you do have. You see it in full size aviation all the time, just fly the aeroplane. Fly it as far into the crash as you can and have a plan in your mind ahead of time so you know what to do when something happens, make sure you know the exact location of all your switches so you can find them instinctively. If you do all that, you can just shrug your shoulders when the gear gives up and dazzle everyone with your calm and perfect belly landing.

I appreciate that it is not always easy to remain relaxed in the heat of the moment. When the prop on the la7 exploded i hit the engine kill switch instinctively. It was only 10-15 seconds later when i needed that finger for the retracts that i realised i was still hanging on to the switch and had bent it with my slightly panic induced iron grip. Exploding props was not something i had anticipated, but i now have that plan in my head as well just in case i need it.

One final thing. If the gear wont retract and get stuck halfway up, dont roll upside down and try and get them to go. Just land and fix it as you can almost guarantee that if they wont go up, they wont come down.

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Thank You Rich smiley

And thank you Jon for your very useful brief on stuck retract procedure.

All I was trying to say in my build log really is explained by a maxim that I attempt to follow in most of my hobbies /work.

PPP = PPP (* Poor preparation = * Poor Performance).

So in my view spending an extra hour refitting the wheel wells for optimum clearance was time well spent...despite my frustration with my error embarrassed

Obviously knowing what to do when something goes wrong is very very important indeed, but in my view no compromises should be taken in building a model which might reduce its reliability.

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Posted by Tim Flyer on 22/01/2021 09:46:22:

Thank You Rich smiley

And thank you Jon for your very useful brief on stuck retract procedure.

All I was trying to say in my build log really is explained by a maxim that I attempt to follow in most of my hobbies /work.

PPP = PPP (* Poor preparation = * Poor Performance).

So in my view spending an extra hour refitting the wheel wells for optimum clearance was time well spent...despite my frustration with my error embarrassed

Obviously knowing what to do when something goes wrong is very very important indeed, but in my view no compromises should be taken in building a model which might reduce its reliability.

Yea absolutely. All steps should be taken to prevent a problem forming in the first place yes

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Thanks chaps. I sheeted the bottom of the inner wing section today but left out putting the plywood top skin on until I’m ready with all the gear for the retract plumbing. I would rather test the two wings together. Unitract recommend using a half litre fizzy drink PET type bottle which they say will take the required pressure of about 60 psi . Having never inflated a plastic bottle I will be rather careful..my shock pump is very accurate too. I know what it’s like when a high pressure tyre pops so I won’t be overdoing it !

I have now started on a “dry run” assembly of the starboard wing . This part of the build should faster having now already completed most of the port wing.

I have not yet sanded leading edges or wing tips in order to avoid hangar rash while the second half is constructed. and didn’t fancy making dust before I need to. One good thing on this model is that they don’t waste much wood  .  It’s nice not having to sculpture from massive square blocks of balsa. Better to laminate a roughly profiled piece with sheet and then sand to shape as in this DB kit. 

Edited By Tim Flyer on 22/01/2021 18:02:13

Edited By Tim Flyer on 22/01/2021 18:05:55

Edited By Tim Flyer on 22/01/2021 18:07:11

Edited By Tim Flyer on 22/01/2021 18:08:17

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Hi Tim

Although not the DB Spitfire build I thought this build blog of a MKIX Spit very interesting with lots of ideas. The guy (Scalebuilder) has his own website and sells 3d prints of many parts and in different scales , wheel hubs etc.

https://www.rcscalebuilder.com/forum/forum_posts.asp?TID=29346&PN=0&TPN=15

Dave

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Thanks Dave that looks a useful site .

On my DB Spitfire the starboard wing is well underway now. I’m at the stage of fitting the retract in. This time I am being careful and used my pump to unlock the retract and made sure there was plenty of clearance from the retract bay wheel well front side as the wheel moves forward in the well on extension of the gear.

One thing I have needed to do is recycle the odd bit of spare wood in the kit when I have run short of strip .
Its certainly fortunate I have spare supplies of balsa too. I have added the odd balsa gusset here and there to from triangular strip I had spare . I also glued the wing tip on . Once the wheel well is complete its back to flap construction and then sheeting .

I’m going to leave out the central ply top wing sheeting until the fuselage is constructed as I want to see how and where the retract air bottle will best fit plus I will be making a flat indented shelf in the front topside of the wing to accommodate a lower fuel thank for my Laser 180. Leaving the sheeting off for the moment simplifies modifications and fitting out.

The stabiliser and fin need to be built before I can start the fuselage.

Edited By Tim Flyer on 29/01/2021 17:24:02

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Hi Jon Its actually a beastie...it’s a hi tech 5685 with metal gears and 11kg torque rating so plenty powerful. It’s not small just standard size but looks small as tucked away. The ailerons are getting Futaba 3004s at 4kg as they don’t need much but I’m using the heavy duty ones for flaps and elevator.

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  • 2 weeks later...

Thanks chaps yes I posted yesterday that I saved the text. I will next have to add photos. Some of my albums on this site seem to have been corrupted last week too so it may take  a few moments.  
 

I have been getting on with building the tailplane.
 

Construction is quite simple and it slots together fairly easily after minor filing.

I initially glued the ribs in horizontally as per instructions but later pinned the tail plane to the board with spacers while applying the leading edge to take out some mild warping, with application of a bit of diluted pva.

I sheeted the whole tail plane in “one hit” using pre cut sheets and used a bit of diluted pva to get the tighter curve in the front sheeting.

I’m pleased to say that the tail plane has come out straight?.

I found it necessary to deepen the channel in the grooved spacer blocks between elevator and tail plane so the hinge wire can pass freely on assembly. I “case hardened” the wood hinges with cyano to reduce wear. if you need a very long drill to ease the hinge holes putting wire with sharpened end works very well in the dremmel. I didn’t bother drilling Ruth’s hinges out and adding nylon bushes as I had done on the ailerons, as the wood hinges are already thick and strong looking and I didn’t want to make the lining up of the 4 hinges on assembly any harder.

I’m now fettling the joint between tail plane and elevator so I get a nice fit and will than get on with sanding the edge profiles.

I glued in the elevator joining wire yesterday. I prefer to do that after sanding as there is less damage risk. The kit wire elevator joiner was made too wide to fit . When I checked it on the plan it also too wide and would interfere with the rib. I didn’t fancy getting my torch out and soldering up a narrower one (didn’t want an open door to the cold in the workshop plus I have lots of balsa dust), so I re bent the existing joiner. As the steel was fairly mild it took the new bend well with no signs is weakening or cracking. Like the rest of the kit the joiner is a nicely made bit of quality hardware and DB have sensibly used a nylon bush in it too to stop sloppiness and vibration.  
If DB are reading this log it might be worth them noting that the joiner needs to be a bit narrower (by around 2-3 mm) . I photographed it on the plan to show ( will add photo later) . 

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Thanks chaps yes I posted yesterday that I saved the text. I will next have to add photos. Some of my albums on this site seem to have been corrupted last week too so it may take  a few moments.  
 

I have been getting on with building the tailplane.
 

Construction is quite simple and it slots together fairly easily after minor filing.

I initially glued the ribs in horizontally as per instructions but later pinned the tail plane to the board with spacers while applying the leading edge to take out some mild warping, with application of a bit of diluted pva.

I sheeted the whole tail plane in “one hit” using pre cut sheets and used a bit of diluted pva to get the tighter curve in the front sheeting.

I’m pleased to say that the tail plane has come out straight?.

I found it necessary to deepen the channel in the grooved spacer blocks between elevator and tail plane so the hinge wire can pass freely on assembly. I “case hardened” the wood hinges with cyano to reduce wear. if you need a very long drill to ease the hinge holes putting wire with sharpened end works very well in the dremmel. I didn’t bother drilling the hinges out and adding nylon bushes as I had done on the ailerons, as the wood hinges are already thick and strong looking and I didn’t want to make the lining up of the 4 hinges on assembly any harder.

I spent some time fettling the joint between tail plane and elevator so I get a nice fit and then sanded the edge profiles. Again the Perma-Grit tools were invaluable. 

I glued in the elevator joining wire yesterday. I prefer to do that after sanding as there is less damage risk. The kit wire elevator joiner was made too wide to fit . When I checked it on the plan it also too wide and would interfere with the rib. I didn’t fancy getting my torch out and soldering up a narrower one (didn’t want an open door to the cold in the workshop plus I have lots of balsa dust), so I re bent the existing joiner. As the steel was fairly mild it took the new bend well with no signs is weakening or cracking. Like the rest of the kit the joiner is a nicely made bit of quality hardware and DB have sensibly used a nylon bush in it too to stop sloppiness and vibration.  
If DB are reading this log it might be worth them noting that the joiner needs to be a bit narrower (by around 2-3 mm) . I photographed it on the plan to show ( will add photo later) . 


Im going to cover the elevator with Solartex and probably glass the tail plane after applying dilute pva as sanding sealer so it won’t get deeply soaked with epoxy and too heavy. 

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Cheers Dave . It’s only a minor thing and re -bending it was easy in a vice...but obviously a good job I didn’t glue it in first! So definitely care needed. My joiner may just have been a one off sizing error as it was obviously hand made.

As the wood hinges are in set positions in this design it’s best to put the joiner in last.
 

I do really like the hinge design as it looks much more scale like with no visible gaps on the control surfaces.  It’s also going to be great being easily able to remove the control surfaces for painting.

 

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Thanks John that’s great. Unfortunately I always write from my mobile and the spell check comes out with some shocks which I often miss 

Regarding todays build log the Tailplane is complete apart from covering. I decided to go back to the wings and finish off a few bits like flap reinforcement on wing no 2 and also started sanding the wing tips .

I must say sanding wing tips is quite satisfying ?. A simple job turning a chaotic shape into a sleek profile ... plus it isn’t fiddly! 

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Just a short update 

I’m still working on the wings doing “small bits”. I just reinforced the outer sheeting retract cutout on wing 2  which will eventually see an access cover made from thin aluminium plate. 

I’m also doing the odd bit of filling and tidying. I’m only roughly profiling the wing tips and will not finish the leading edge at this stage. that’s partly due to damage risk and I also want to see exactly how the wing fits into the fuselage.

I also added the wheel well “bumps” to the top of the wing. I used tracing paper from the plan to help me properly locate them . I haven’t needed to gouge through the wing top surface to accommodate the wheels, so their location wasn’t critical but I didn’t want to be told they look wrong when I eventually take it to the field ?
 

The fin and rudder are next on the list. 

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I sheeted the Fin this afternoon  . I wetted the inside of the sheet with diluted pva to help it bend on the inner acute angles . I also used slightly narrower strips rather than wider sheets, as that makes the multiple curve easier to form and did both sides together to try to retain shape and symmetry. 
The rudder will require more finishing on the edges before Solartex covering . I will add photos of the finished fin after I have trimmed the sheeting and added the leading edge...it looks like a pin cushion at the moment ?

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