Tuesday, March 9, 2010

Time to Stuff Your Nose, And How to Make a Safety Officer Crazy

He Ain't Heavy; He's My Ballast

It seems to me that there are two kinds of people who build plastic model airplanes; those who have built something with tricycle landing gear and those who will build something with tricycle landing gear. You might skate on that one if you only build stuff from The Great War, but everybody else is going to have to contend with the problem sooner or later, whether it be in the form of an A-20 or P-39, or in something a little bit more contemporary like an F-86 or a MiG. It's like riding a motorcycle. If you ride, sooner or later you'll fall off. If you build, sooner or later you'll have to contend with a small amount of space and an aft CG. That's how things work.

There are a couple of ways you can handle the problem. Some are good, and some aren't. My personal preference is to put ballast in the model to make it sit like it's supposed to, but there are some options available, so let's consider them first.

First, you can try to buy a kit that has ballast, and a predetermined place to put it, already provided. Tamiya does that with a few of their kits, but only a few. Life's good if you can limit yourself to building just those subjects but things might not be so hot if you ever intend to expand your horizons and build something The Big T doesn't kit.

Or, you can build the thing gear up, or maybe even down, and put it on a stand that keeps everything in the air so sitting level on a surface doesn't matter. (You could also tie thread around it and hang it from your ceiling like we used to do when we were kids, but most folks don't care for that approach anymore...) This technique is what you might call avoiding the issue but it works, although it does somewhat limit your display options and, in the hang-it-from-the-ceiling option, will introduce you to Mr. Dust Bunny as well.

If you don't want to stick it on a pole or hang it from the ceiling, you can put some sort of prop under the tail and, in point of fact, there are more than a few kits out there that provide you with a clear rod for just that purpose. It looks really silly, though, and screams to the world: "Hey everybody; I can't figure out how to make this thing sit on it's landing gear so I stuck this clear thingy back there!" 'Nuff said about that one, ok?

You can drill holes in the tires and permanently affix the thing to a base or diorama. This seems absurd at first glance but it works well, definitely plants the model where you want it to be, and has the substantial additional benefit of ensuring that your completed work of art doesn't slide off the base when your non-modeling friends decide they just have to pick the thing up to look at it. This concept works really well if you're the guy who opens up every single panel on your model so you can add lots and lots of otherwise-unseen detail, because a nose full of avionics, guns, and so forth just doesn't leave a whole lot of room for things like ballast. Just be sure to pin down that nose wheel too. Trust me on this one.

You can stick something that might actually be around the real airplane up under the fuselage, someplace behind those tricky main mounts. Candidates here include maintenance stands, jacks, and sawhorses. They all work and can look ok in a diorama of almost any flavor but aren't really convincing if the model is a stand-alone, once again proclaiming to the world that you couldn't figure out how to keep the thing from sitting on its keester any other way. Your friends probably won't say anything about it to your face, but they might talk about you when you aren't around to defend why you did what you did. If you're possessed of a fragile nature you might want to shine that approach right on by as well.

Finally there's ballast, which is what most folks depend on to avoid Tail Sitter Syndrome with their models. Before we go adding it, though, let's determine whether or not we even need the stuff because, strange though it may seem, not everything with a nosewheel needs weight in the front. For example, an F-100 does, because of where the main landing gear legs (those "main mounts" I keep talking about) attach and because so much mass (including a big chunk of the wings) is found aft of the them. None of the other Century Series fighters need ballast, and neither does an F-4, F-15, or F-16. Sometimes a model of an F-111 does, mostly in the bigger scales and depending on how you configure the wing sweep. A Crusader doesn't need weight either, but a Skyhawk does, and on it goes.

So how do we figure out if we need ballast up front? That's really easy; just hold or tape all the big pieces together so you've got a basic airframe, and put two of the fingers on one hand at the locating point for those main mounts, then use that as a pivot while you lift the nose with the other hand. Hold the nose gently, to the point where you've almost let go of the model, and see what the airplane does. If it wants to drop into a nose-down attitude it's highly doubtful you'll need any sort of ballast at all. If it rocks like it can't make up it's mind where it wants to be or if it swings towards the tail, you're going to need weight up front. The only real wild card is the stuff that goes on last, such as ordnance or tanks, and if you've got a lot of that sort of thing hanging off the airplane and you just aren't sure about things, go ahead and use a little ballast. It can't hurt anything. Just keep in mind that it isn't necessary a fair amount of the time if your passion is contemporary jet airplanes.

But what if we need weight in the nose of our project? What are we going to use? Let's think about the requirements of our particular kit for a moment; where can we put our ballast, and how much space is there to put it in? Are we going to need a little weight or a lot? Figure that stuff out now, gang, 'cause it's really important to your project and a little head-work now will avoid a whole bunch of self-inflicted profanity down the road. As for the ballast itself, I personally use lead. (If you do too, be sure to observe all the safety caveats that go with the material; wash your hands when you're through using it, don't eat it, and keep it away from your kids, food, pets, etc.) It's heavy, and it's soft. Melting it is a bad idea because of the fumes it gives off when it's molten (and so is using fusible metals like we used to do back in The Good Old Days, because they're a lot more toxic than we ever thought they were, being right up there with lead in their ability to kill you by degrees), but you can cut it or whack it into shape with a hammer (but not while it's actually in the airplane---reserve your whacking for places that won't destroy your project!). My ballast of choice is the lead balls used by the folks who shoot black powder, because there are a lot of sizes to choose from and they're easy to find if there's any sort of large gun shop near your house. You can also use fishing weights or lead wool; the main thing is to use something that offers a lot of density for its size. Wheel weights are heavy, for example, but they aren't as heavy as an identically-sized hunk of lead because they're alloyed with other, lighter metals.

Once you get past what you're going to use for weight, you get to use your creativity to figure out where to put it so it'll actually serve its purpose on the model. I'm probably sounding like a broken record by now, but you're looking for space a little bit forward of the main mounts, the farther forward the better so you can have leverage as well as simple weight working in your favor. Sometimes there's not much room at the very tip of the nose (Huns and Sabres offer excellent examples of this phenomena) but you can generally find room somewhere. In a notorious tail-squatter like the P-39 the gun bay is your first and best choice for ballast. The Scooter we're working on at the moment has a .451 diameter pistol ball in the extreme nose and three of the same immediately behind the cockpit bulkhead, while the MiG-17 you see illustrating this piece has its weight in the nose abouve the intakes and nose gear well. In that case the ballast is stuffed pretty much everywhere it can be made to fit. A model with tricycle gear will make you think a bit, that much is certain!

After you put the weight where you've determined it belongs you'll need to attach it as permanently as you can to the model, and for that purpose I'd like to suggest 5-minute epoxy or similar. You can use cyanoacrylate, but it's generally not a good idea because it's great in tension but lousy in shear. That means that you can pull straight up or straight down on something you've glued with it and it'll stay put, but a whack from the side will knock it loose every time. White glue, wood glue, contact cement and similar just won't work. Use epoxy. Bulkheads help too, if you feel like making them, but a lot of times they aren't really necessary. You be the judge on that one.

In theory you now have a better idea of how to make your trike-geared airplane models sit like they're supposed to. Like a lot of things in our hobby, putting ballast in a model is really easy to do once you start thinking about how you should do it. Just use a little sense and plan ahead.

Here are a couple of quick-and-dirty sketches to prove beyond any doubt that I wasn't Replica's artist back in The Old Days. They do serve, however, to provide a quick tutorial in the sorts of places you can stick ballast in a model airplane.

Here's a classic tail-sitter basking in the South Texas sunshine. The P-39 in any scale is often the modeler's first introduction to the notion of ballast. The Airacobra in the photo is a little tougher to keep on its gear than some other P-39 kits because of its size, mass, and relatively heavy plastic; it's the Special Hobby P-39D kit in 1/32nd scale. All the weight in this model is in the nose, as far forward as it can go. This kit would've been a real challenge if it had been built with the nose panels removed; there's lots of stuff up there but absolutely no room for weight if those panels are off. (I've been told I may have achieved scale weight with this project. That may be true, but it sits on its gear and the nose strut hasn't collapsed yet. Yet...

The recent HobbyBoss MiG-17 in 1/48th scale offers a challenge because of the placement and relationship of its cockpit, nose gear well, and bifurcated intake, but there's still enough room in front of the cockpit and above the intake trunk to make things work. This time I used .375 diameter round balls, although I ended up smacking a couple of them with a mallet to get them to fit where I needed them to be.

The MiG-17 compounds the problem  because of its wing sweep; a fair amount of wing lies behind the main mounts. This is the part where planning becomes our Friend. Look at that massive tail and those wings; things could be worse but it's a lot tougher to put ballast in a Fresco than it would be in a Hun.

Making Do With What You've Got

I'm thinking we need at least one picture of a real airplane each time we publish something new, so here's one for today:
Here's a 22nd BG B-26MA getting ready for a mission at Port Moresby in late 1942. The aircraft is unidentified but the photo has lots to offer in spite of that. The aircraft is being fueled (note the fuel hoses running to the wings on either side of the fuselage) and the crew ladder is extended from the nose gear well, just in case you were wondering how to get in and out of a Marauder on the ground. The thing that really grabs your eye, though, is the way the 500-pound GP bombs (apparently painted yellow, not uncommon early in the war but more often found on Navy bombs than those of the AAF) are being unloaded from that deuce-and-a-half; they're being unceremoniously rolled out the back to land on the ground. No bomb handlers, no special equipment and, in all probability, no safety officer either. Fact is, those bombs are about as safe as they can be because they haven't been fuzed yet; at this point they're just so much olive drab dead weight. The fin assemblies are on the ground near the starboard prop, and the fuzes will be installed once the bombs have been winched into the aircraft and secured to the bomb shackles. Note the uniforms too; one guy is wearing a boonie hat, the fellow with his back to us at the left has on a Kelly helmet of WWI vintage while a third man sports a baseball cap. The uniforms are pretty much all over the ballpark.
They fought with what they had.                                                                          AF Museum via Worman

So here we are at the end of our time; just one lonely little minute left for today. Be good to your neighbor and we'll see you again soon.


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