Hi Alex (AVI);

Oops, I hope that wasn’t top secret. There goes my clearance.

So, as always, thanks for sharing your thoughts. Choosing an engine and especially scale that I wish to build are key decisions. The engine can sometimes be altered, but the scale is a pretty firm decision. I’m not quite there yet. Ross Ferguson built a 67% scale Spit at 1200 pounds gross, but widened the cockpit a bit for human usage. I could end up doing the same.

I have seen the Oz Spitfire, a Mk 26. I commend anyone who goes through this, but you’re right, a few things are off. Cowling, air intakes, tail wheel, that sort of thing. I think it’s a two-seater as well. I think the kit is $263,000, which will keep me from buying it.

Now, to answer your question about wood or metal, I should mention that I have made no final decision yet. Wood is faster and almost certainly cheaper. Lots of people do their homebuilts this way. However, I just simply like metal. It simply feels more “technical” than wood (I’m going to get bashed, aren’t I?) and closer to the real thing. Do I wish to build or fly? Well, both are quite important to me. But I really do like sinking my teeth into a good, challenging project, and love to shape metal. At age 46, I have to ask myself if this will ever happen, regardless of build method, but if I don’t like the item I’m working on, then I’ll stop. Again, I may convince myself that wood is it for me, we’ll see.

I want to show you something from another favourite forum of mine. It’s a motorized movie screen that doesn’t simply roll down, but rather deploy, like landing gear, and is kept stretched on a solid frame, although the actual screen has not been installed on these early pictures. I also enjoy home theater stuff, MOVIES, and recently bought a nice projector. I made this screen because I don’t like roll-up screens, they’re ugly, wrinkly and move whenever somebody exhales in the room. The link is here:

http://www.avsforum.com/avs-vb/showthread.php?t=802896&highlight=tom+kay+screen

Just copy, paste in the address line and hit enter. Scroll down and you’ll see a few pictures to open up. I made this at work over 1.5 years on our mill and lathe. Before you say “One and a half years??? How long will a whole airplane take?” please understand that I only worked on this at lunch time, plus a few stolen moments here and there. It works as it should, stops automatically, and will eventually be remote controlled from my sofa as soon as I buy the infrared input. I enjoyed the journey as much as the finished product. I often tend to do things the hard way, but for me it works. I like unconventional. This screen also allows us to use the 36″ TV behind it for garbage viewing and the expensive projector (consumable bulb) for movie watching. The screen misses the TV by an inch as it moves up or down. Sometimes people go OOH, AH when they see it.

Importantly, I also like to create. While Spitfires aren’t new, this project would force me to create new ways of doing things, like the spar.

The Falco and Corsair projects are terrific. The Falco reminds me a bit of the Lancair, which is one of my faves.

I hope this clears up some of the why’s.

Well, gotta go eat. I’d just die without food, I know it.

Cheers, Tom.

Hi Guys;

Here’s a first shot at a wing spar for the replica Spitfire. I hope it’s clear enough to see. Lots of bolts holding all the layers together, thick plates for all three types, center plates, second plates, and heavy machined plates. I can’t tell you what thickness at the moment, however this whole assembly is intended to slide between the stub spars on frame 5 just as the original did.

The spar caps are a little tough to see at this scale, but they are T-sections. They slide in between the two center plates. To bend the T-sections at the points where the spar is bent, I have just notched the web with a V, and bent the flange. If this is 7075, I’m not sure if that’s even going to be possible. 7075 might not be bendable????

Lightening or access holes might be possible through the web at some points. Hard to say how many or how big at this point. They might be needed for rivetting access. Not sure how that was done on the real machine.

There are lots of things that concern me, such as grain flow lines in the area that’s bent 6 degrees or so. There’s no heat treating and bending intended with this set up, just straight plate stock machined to final shape. The grain flow lines would generally be spanwise.

So, if you’re into the exercise, please pick out any obvious weaknesses, and I suppose to be a little optimistic, anything that seems good about the design too.

Cheers, Tom.

Hello Gentlemen;

QldSpitty; Ah, it is you ! And it only took me 17 iterations to figure it out. Yes, Dave’s Spitfire cockpit is truly incredible. Imagine having that in your rec room. I’d like to see all that he has, drawings, metal, the whole shmoo. I tried to write his friend Craig and see if I could get Dave’s email address, but no reply yet. I’d like to pick his brain about alloys and thicknesses of various frame pieces. Speaking of alloys, .080″ is indeed thick stuff for the leading edge. I wonder how much you could scale that down for a replica at half the original weight. I haven’t wheeled yet, but that seems thick to shove through the wheel. I’m hoping to use one at work (that has never been used !) if the powers will let me try it. Seems pointless to buy a 5000 dollar English wheel and never use it once over the years.

The golden rule with me is that I’ll take all the pics you can stand sending. Until your send button finger burns out. I am a visual creature, and I learn a lot by simply looking at the pics. Which brings me neatly to Chumpy:

Chumpy, thanks for that pic of the original spar. I have been banging my head against the wall for the last week or two, because I lost an article that I was given 20+ years ago, and I swear I’ve seen it lately. Don Campbell of Kapuskasing Ontario gave it to me when I flew up to visit him and his MkV restoration. Don had a stroke a couple years later and I don’t know who bought the project. The article is a write-up of how the Spit was generally put together, fuse and wings. It tells how the leading edge skins were stretched over the wood dies after a hot salt bath, and it has a terrific picture of the wing spar and separate tubes. I think THAT’S the picture, Chumpy, and I wonder if you have that entire article.

To show you how one can learn from a simple picture, I just learned that the main spar web is simply a U-channel bolted onto the back of the tubes, which are separated by stiff spacers. Add some angles on the front, and you have a spar. I say simple, but then the U-channel would be tapered, wouldn’t it. Suddenly not so simple anymore. I’m trying to work out in my mind if the stiffness of Mitchell’s wing comes from the two square tubes merely separated by a thin web, or if the web has a much greater role in maintaining stiffness than it would appear. Probably they both are sufficiently load-bearing.

If I were to design a wing spar, so far my mind tells me to place most of the strength in the web, and not the tubes, as they’d be hard to make and bend on a poor man’s budget. This is where the spar might differ a lot from Mitchell’s. Make the spar one main vertical thick layer of 7075-T7351 plate, with other partial-span layers bolted to it, progressively ending as you approach the tip, much like Mitchell’s leaf spring. On the top and bottom bolt angles of 7075 to attach the skins fore and aft. Or you could have two main vertical web plates, separated enough to slide a stiff T-section of 7075 between them on the top and bottom, so that you’d have attach points for the skins. That would be cleaner, I think.

At the root you could even do some machining of a thick plate to mimic the two tubes, but leave a little web with them to add stiffness top to bottom. Add one of those machined plates on the front and back of the spar web and have that whole sandwich slide between the stub spar booms as per original. That heavy machined part would travel 25 or 30 percent of the total span root to tip, then end. The next plate would travel closer to the tip, then also end. The only thing I haven’t worked out is how the angle or T-section on the top and bottom would seamlessly “meld” with the heavy machined plate at the root, so it would all act as one long flexible fishing rod with no kinks or weak points or stress risers. I really will have to draw this and post it, I know.

Have I lost everyone yet?

One thing that does surprise me is how many holes there are through the two tubes to hold on the web plate. I would have thought this would really weaken the spar tubes.

And Stuart, we need to talk to Mr. Mitchell again. We need his help, smaller scale. Can we leave that with you? Thanks Stuart. I know it might be a long distance call, but well worth it.

Thanks again all, Tom.

Hey MarkG;

No problem, and I see your example. Each time you locally whack the metal with the hammer, the total PSI would be immense, and therefore squish the soft aluminum outward away from the whack center. Therefore, expansion and if that expansion occurs on a flange, the web will curve whether it’s a straight section or a gently curved section.

One possible way to reduce this effect, I’m guessing, is to use a wood block to take the hammer blows and transmit the force to the metal flange. This would allow the wood to momentarily compress and spread the force out a bit, and you probably wouldn’t get that local squish effect as much. Also, unless your hammers are polished nicely, this will save you from getting scratches too.

Keep hammering ! Tom.

Hi AVI;

Well, I went to the website you linked me to, and it was an adult website. It appears that the metalcraftingmag is no longer using its domain on the net.

It could be that I have a virus or something on my computer that sends me to an unwanted site, but I love it when technology suggests entertaining alternatives. Not really!

It’s too bad if that site is gone. It would have been good to read the article.

Tom.

Hi QldSpitty;

Great reply. By the way, is this Ross?

Any-hoo, that’s the kind of detail that helps. That procedure is largely what I did for my second, more successful fuse frame sample. I’ll try one in full size soon, and pay close attention to working 30 degrees at a time, all the way along the folded flange. I used 3/4 plywood for my first two attempts, and it does get pretty “soggy” after a few million hits.

The shrinker is something I’d like to try, so I’ll have to go find one. If it works as I think it should, then I’ve largely got the frames figured out.

The spars are next. I did think of several plates of aluminum sandwiched and bolted together, sort of like a leaf spring with fewer plates as you approach the wing tip. Like a tapered section. I have to think of a way of adding flanges top and bottom, to attach wing skins, etc., but I think this is a reasonable approach. I do wonder about what someone else mentioned, and that is grain flow. I would machine the root end, and that means that the grain will be parallel to the spar except at the root where it’s bent 6 degrees or so. Cause for concern? Cracks likely at this point?

Thanks again, Tom.

Hey Chumpy;

That’s interesting. I’ve never seen that before.

I suppose that it would have to be cranked near the root, just like the original, and then attached to the spar web. Would they use bolts to go through the web and the solid “tube” or some kind of blind hole rivets?

Cheers, Tom.

Hi Bruce;

Thanks, and anything helps. But, how do you know this? Do you happen to have any drawings or material specs?

I’ve seen lots of drawings of the earlier wing spars, but wasn’t aware of the Mk 18. I’d like to have a view of that.

Cheers, Tom.