Gary's BT 69" Spitfire Mk1

[Gary Clark 1]

So, here goes....

 

Approx 6 years ago I started a BT spitfire (my first Spitfire) but after approx 6 months of interrupted building, I decided to bench it as I wasn't too please with how it was going. There were issues with the wing which had been built up to the top surface being skinned and the retracts fitted but it just didn't fit the fuselage correctly which I blamed on the way the kit had been cut. The fuselage was pretty untidy around the fairings, probably due to the wing not fitting correctly.

 

Overall not a build I was happy with hence why it went into the loft. All that being said, I have decided to correct and finish this build. The wing is in the bin, fairing removed and re-made and progress so far below. I rebuilt the centre section but you can see what I mean about it not fitting the fuselage correctly

 

 

As per the photo, the reason the wing didn't fit properly was due to the position of the front "box" being too far forward and also too long. This meant all this plus the fairings needed removed. Not a fun job. I got it done, built a new one and you can see the difference below

 

And fairing started. Stll need a fair amount of sanding but the shape looks alright

 

The whole model needs a real tidy up and plenty of bits may find themselves being removed before being replaced. I feel like it would be quicker to restart but I hate the idea of it beating me.

 

Hopefully the thread will be of interest and fingers crossed she'll look tidy and presentable soon

 

Gary

 

 

 

Edited November 8, 2022 by Gary Clark 1

[Paul De Tourtoulon]

Go for it Gary, I will be following,,,,

[Nigel R]

Following, the BT mk1a is high up on my list of "when I'm feeling brave" projects.

[Ace]

Please, mojo and perseverance usually = swan.

[Nick Somerville]

Great to see you back on the BT building, Garry. I echo Ace’s comment.

[Gary Clark 1]

Thanks chaps. 

 

I know Nick, the P-47 isn't finished either but I've got all my other projects complete so that I can focus on this. It was a toss up of the two and to know this was mocking me from the loft was too much so had to get it out again. It's probably more work than I thought it would be so feels like I'm starting from scratch a little so hopefully it starts to look like a model I'd be happy with again. 

 

Gary

[Gary Binnie]

Good stuff, I'm a little bit further along but I did start it about 15 years ago!!

 

My kit was cut by Bob Holman in the US, pretty good apart from some upper fuselage formers being cut to the outer skin line. I can measure parts for comparison.

 

Had a lot of trouble with the retracts which resulted in a rebuild of that area once I had obtained the original retract units.

 

It needs the lower wing skin adding (saving up for the balsa!) and I will probably rebuild the tailplane/elevator.

 

Have to decide how to power it, I do have a Laser 75 but I'm thinking about electric now.

 

      Cheers

 

           Gary

 

 

[Jon H]

The laser 75 or 80 was often put forward as a powerplant for these but the performance is poor. 

 

The the model is built out of thin air then they fly, but if its built to a more realistic weight (12lbs or so) then the 75 will not have the power. We have always recommended the 120 but as demand for BT models and the 120 have mostly dried up we discontinued the engine. I will be finishing a handful more 120's at some point to clear the last of the parts but we will not be making more after that. 

[Gary Clark 1]

A 75 or 80 does seem small for this Jon so agree with the need for something bigger. My plan is electric for this one as I bought the motor when I started building it years ago. I also have the 83" Mk IX kit here and that will definitely be glow powered and probably by a Laser.

 

Gary it looks great, hopefully seeingine will spur you on to finish. Retracts are probably my least favourite part of a warbird. My intention for this will be to throw money at the problem and buy Electron retracts as they have a great reputation 

 

Gary

[Gary Binnie]

Thanks, I'm really more into gliders at the moment, my flying field is too rough for anything with wheels so there are other models in the loft not being flown and no drive to finish this one anytime soon.

 

I was sold 'correct' Unitracts (direct from the company) that looked different to the originals, I could not get the geometry to work at all, I moved the bearers but that was only partly successful. Years later I managed to obtain the retracts shown on the plan (probably also Unitracts) and the problem became obvious, the mounting rails were in a different position. The original retracts could have worked if I had made spacers to the exact dimensions needed.

 

I promise not to hijack this thread but I have loads of photos of the build should you want to see them.

 

Retract on the right is correct for the plan, it's easy to see that the mounts are in a different vertical location.

 

2.

 

 

 

 

[Gary Clark 1]

That's interesting Gary, strange to see the mounts in different places from the same company. I would have went for unitracts but no joy when emailing them even though I was asking for 3 different sets of retracts.

 

Don't feel like your hijacking, this is the main reason for these forums so we can all see and learn from each other. Get as much on as you like!!

 

Gary

 

[Gary Binnie]

Some people get possessive in threads, there is a great one on RC Groups concerning a Middle Phase build.

I have largely abandoned that platform due to excessive advice (in the style of Harry Enfield's 'only me' character if you remember it).

I had the same on a motorcycle forum recently, even after stating my engineering and motorcycling background quite clearly it carried on.

 

I strongly agree that these threads are great places to collect information and techniques, particularly useful with Brian Taylor builds because of the lack of instructions and complexity.

 

A marvel is that he designed about 15 models, drawing plans and cutting the parts himself (no lasers), produced fibreglass parts, built them then flew, winning the Nationals with this model.

I can't even finish one of his designs that the parts had been cut for me in 15 years!

[Jon H]

4 hours ago, Gary Clark 1 said:

Retracts are probably my least favourite part of a warbird. My intention for this will be to throw money at the problem and buy Electron retracts as they have a great reputation 

 

Warbirds and retracts get a bit of a bad rep and its quite unfair in my experience. 

 

Without being too rude about it, the issue is most often than not down to the pilot not getting the landing right and expecting their retracts and mounts to tolerate the same abuse as a fixed gear model with a nice carbon or fibreglass undercarriage. This is simply not the case and i follow a very rigid and set procedure for landing my warbirds to minimise the guess work and prevent damage. 

 

To be clear, i do not exclude myself and have bashed a retract or two over the years. But i know it was my shocking landing and not the model that was at fault so i just fix the damage and move on. 

 

There can be more at work than just pilot skill as the setup, balance, trim etc of a warbird can make it a delight to land or a complete pig. A friend's Hangar 9 Spitfire was impossible for him to land due to massively high rates with loads of expo. Taking 80% off the rates and wiping out the 75% expo made it a doddle to land. 

 

When it comes to reliability i like air, but decent electric will be fine. The only electric retracts i have known have been pretty cheap and they arent super reliable. Again there is a lot of hysteria about air retracts loosing pressure and it does happen. My 12 year old La7 has suffered 4 retract fails over the years with 3 of them down to air loss caused by dirt in the fill valve. I now check this before starting to make sure its all good. Even if not, just land on the belly. Done right it rare any real damage is done and its not something to worry about. 

 

One final thing to remember about retracts is to get them retracted immediately once you leave the ground on your first flight. Dont fly about for 10 minutes with the gear down. Get them up, clean up the aircraft and loose that drag. Also should the engine go or some other emergency forces an off field landing damage will be reduced if you leave the gear up so its very important to get them out of the way as soon as you can. The same is true of a deadstick in flight. Leave the gear up until you know for sure you can make the runway. 

[Gary Clark 1]

I agree Jon, I just don't like the faff fitting them but once they're in, they're fine. I agree with the reliability of air and my experience with the cheaper electrics has been poor but due to the depth of this wing I don't have much room for an air bottle. Obviously it could go in the fuselage somewhere but good quality electric ones save be having air hose going between the two.

 

I got some work done this afternoon. I got the cowl on and fitted but the front former at the top of the fuselage sat too high. I can't remember where I got this cowl and may not be a BT one so decided to make it work. Having a look from inside the cockpit, the top skin at the front was poorly fitted and wasn't the correct shape so only one solution....it all got cut off

 

I remade the formers and adapted them to slope down slightly to fit the cowl. This isn't a competition model so nobody will notice 

it 

 

I think it looks OK so will leave that there. I've got some balsa drying after curving it for the top skin so hopefully get that done tonight a d some work on the fairings.

 

The tail is mainly done and looks OK. It has rivet detail but not panel lines for some reason. Not sure why I decided that but it needs a few more then its done. Still a bit more scale additions on there but a part I don't have to re-do.

 

Gary

 

Gary

[Gary Clark 1]

I got the top skin on and checked the fit of the cowl 

 looks much better now and time to move onto the fillets tomorrow. I need to cut the top skin to open the cockpit again but ill get the fillets sorted first. Feels like progress so hopefully I can keep the momentum 

 

Gary

[Jon H]

looks good to me. I have 3 Spitfires waiting in the build queue at the moment and ideas for another 2. Dose any man really need 5 1/5 scale Spitfires of differing marks and power plants? Probably not but it sounds fun. If only i had the room 😞 

[Paul De Tourtoulon]

37 minutes ago, Jon - Laser Engines said:

looks good to me. I have 3 Spitfires waiting in the build queue at the moment and ideas for another 2. Dose any man really need 5 1/5 scale Spitfires of differing marks and power plants? Probably not but it sounds fun. If only i had the room 😞 

Another one up for grabs in france, top flight at 160€,,,

[Peter G Simpson]

I love the BT 69" Spitfire 1a, I have built three of them. The first used an old Laser 100 which had plenty of power for pulling it round the sky and never stopped. It was tall so the cylinder head rubbed in the inside of the cowl. The most recent example I built 2 years ago uses a laser 120 which is shorter and doesn't rub on the cowl. I firmly believe that a Laser 80 would power the spit, but agree with Jon that it would be underpowered so conditions would need to be right! A good argument for the 120 is that, regardless of me building the tailfeathers extremely light, I still needed nose weight... so if the 120 fits why not use it and take advantage of its extra mass.

 

The first two used Unitract Retracts, which worked very well. For my recent build I just couldn't get hold of any Unitracts. I did managed to get John Hope on the phone once, he promised to make a set for me, but nothing came of it. So I set about building my own set. I'm no mechanical engineer, but I fancied the challenge and the result turned out well. I bought a set of 130mm oleos from hobbyking (SKU:344000018) and 100mm radioactive airwheels. the correct wheel for 1/6.4 would be 3.82" x 1.2" but such a wheel is not available. On the first Spit I used 3.5" wheel but it looked too small so this time I used 4" x 1.5" instead. The wider wheel does make fitting it in the wing a bit tight, but it works. 

 

After studying the plan it looks like BT intended the leg to lies parallel to the U/C bearers when up, so I ended up with a drawing which I shall publish here in case anyone else wants to build one.

[Peter G Simpson]

One final suggestion.... not wanting to hijack your thread Gary...

 

I always struggled with balancing aircraft, particularly low wingers. It's easy to identify CofG on the plan, but once the model is complete not so easy. Secondly supporting the aircraft during the process of balancing. So for my latest builds I incorporate a brass tube into the wing at the correct CofG. The tube passes through the wing so that I can easily string up the model and check the CofG whenever I make any changes to the installation.

 

In the below picture, note the component tray on the top of the cowl at the same position where ballast will be placed. I can then load up the tray until the aircraft hangs level and cycle the gear to check shift in CofG.

[Graham Davies 3]

That's a great idea Peter. Nicking that!

 

Graham

[richard dalgleish]

2 hours ago, Peter G Simpson said:

One final suggestion.... not wanting to hijack your thread Gary...

 

I always struggled with balancing aircraft, particularly low wingers. It's easy to identify CofG on the plan, but once the model is complete not so easy. Secondly supporting the aircraft during the process of balancing. So for my latest builds I incorporate a brass tube into the wing at the correct CofG. The tube passes through the wing so that I can easily string up the model and check the CofG whenever I make any changes to the installation.

 

In the below picture, note the component tray on the top of the cowl at the same position where ballast will be placed. I can then load up the tray until the aircraft hangs level and cycle the gear to check shift in CofG.

Thats a great idea. I might incorporate that on my next build.

I have the same model just recently completed awaiting a test flight. How do you find the landings with the BT Mk1A, does it have a tendandcy to nose over.

[Jon H]

I tend to balance my warbirds a bit 'tail heavy' to help keep them on their wheels. This can make them a little more sensitive in flight, but i counter this just by lowering the rates. It works nicely and means i can taxi round without worry and that always looks cool. 

 

 

[Peter G Simpson]

35 minutes ago, richard dalgleish said:

Thats a great idea. I might incorporate that on my next build.

I have the same model just recently completed awaiting a test flight. How do you find the landings with the BT Mk1A, does it have a tendandcy to nose over.

Hi Richard, it does not seem to have a tendency to nose over. I have seen spits with this problem, but I think it was down to lack of undercarriage forward rake. The CofG is quite near to the centerline of the wheel, and if retract angle is only 90 degrees, which are more common retracts, then it can lead to not enough forward rake. I have it balanced as per plan and characteristics are just right. 

I found a video of one of the early flights of my Spitfire at Smeatharpe Aerodrome. This was before I got the engine running quite right, it was running a little rich which is why there are a couple of coughs, but after I got it tuned right the engine runs very sweetly. 

 

 

 

[Paul De Tourtoulon]

I put a bit of tape marked with a pen to start, when I have got it 'just right' after a few flights generally as Jon tail heavy a drop of vinyle glue is easy to find

with your fingers, I used to use a pin.

[Gary Clark 1]

Thanks for the input gents, keep it coming!

 

Peter, she looks fantastic, well done. I really like that idea for CG too.

 

I git some work done on the fillets but it's been really frustrating. I've found the 1/32 ply base for the fillets starts to change shape and pull up and away from the wing at the front due to nothing to keep it's shape. Maybe I'm missing something so will have to have another long look at the plan but had to come in before I got too frustrated! 

 

I got the cockpit cut out and that looks good with a check of fit of the canopy. 

 

Question for the guys who have built this before. I have skinned the top of the centre section with 2 thicknesses of balsa. 1/16 outside of the fairings base and 1/32 underneath the fairings with the intent of them slipping in to prevent a ridge bigger than the panel line would be. Hopefully that makes sense but is that what you have done or just skin it all in 1/16? 

 

Gary