Project Intrepid aircraft

It's not my habit to write blog posts solely about stuff I do. In fact, It's not my really a habit to write blog posts full stop, which is not at all useful for somebody who has a blog... I am trying to make up for it by writing lengthy blog posts though.

One of the reasons why I haven't been blogging much lately and haven't been commenting much on other people's MOCs is that I've been very busy building myself. A few months ago I built a model of an FM-1 Wildcat, a WW-II carrier-based aircraft fighter used by the US Navy.

I'd been thinking about building a minifig-scale fighter aircraft for months when I finally built this. The reason why I didn't build one sooner was that I felt that it would be too difficult to add all the features I like, such as a working cockpit canopy and sufficient space to seat a pilot and a retractable undercarriage, on something this small. Part of the reason for building the Wildcat was that like many other US Navy WW-II aircraft, it was powered by a nice and big Radial engines. The main reason why US Navy aircraft had radial engines was because these engines were less prone to overheating when idling on an aircraft carrier deck than the water-cooled engines used in many land-based fighters, such as the Spitfire or P-51 Mustang, which require air to move through their radiators in order to stay cool. The advantage for building LEGO aircraft is that the size of the radial engine means that the aircraft's fuselages are fairly wide and since minifigs are fat this makes finding space for a pilot a lot easier.

Project Intrepid
With the Wildcat I finally had my own little fighter. What I didn't know at the time was that my regular collaborator Ed Diment (a.k.a. Lego Monster) had exciting plans of his own that involved naval aircraft. After having built his amazing model of HMS Hood he had set his sights for something a bit bigger: USS Intrepid, a minifig scale US Navy WW-II aircraft carrier. It's currently still very much a work in progress, but I'm sure I'll be blogging about it more in the future. Just to give you an idea, here's a (trick) picture showing the hulls of HMS Hood and USS Intrepid under construction side-by-side as well as Ed's wife ( Mrs. Monster, obviously).

You should also keep in mind that the flight deck is wider and longer than the hull and sits 45 plate widths above the water line. This is a big project! Ed obviously has his hands full building the ship and after having seen my Wildcat, he asked me whether I was willing to design and help build the aircraft for it. I was. I have built a few other things since, but WW-II aircraft building has taken up much of my time spent on LEGO-building ever since. Ed is modelling USS Intrepid as she appeared in early 1945. At that time she carried four types of aircraft: F6F Hellcat and F4U Corsair fighters, SB2C Helldiver dive-bombers and last but not least TBF Avenger torpedo-bombers.

During WW-2 USS Intrepid served in the Pacific fleet. Navy aircraft used over the Pacific used three basic colour schemes. Early in the war most aircraft were pale blue on top (probably best represented by LEGO sand blue) and light grey on the lower surfaces. In 1943 a tri-clour scheme was introduced, with white under-surfaces, dark blue on top and blueish grey on the sides and the tailfin. In late 1944 aircraft started to be painted in dark blue overall. It is very likely that many aircraft aboard Intrepid in 1945 were painted in the latter scheme. Unfortunately the LEGO parts selection in dark blue is very limiting (few invert slopes and hinges, for instance), which makes building an aircraft in dark blue overall a difficult proposition. Since aircraft in the older tri-colour scheme generally weren't repainted and hinges and other special parts are easy to get in white or blueish grey, I decided to build all of the aircraft in this scheme.

TBF Avenger
I decided to start with the Avenger. I've long had a soft spot for this type. It looks ungainly, but was immensely capable. As I wrote a few days ago, I tend to plan building my aircraft and one of the things I look at while planning are what parts I reckon will be difficult. On the Avenger I suspected that the canopy would be tricky as well as the unique wing-fold mechanism.

Building the canopy and gun turret involved some pretty serious compromises. The real aircraft can be crewed by as many as four people, a pilot in the forward cockpit, a radio operator in the aft cockpit, a turret gunner (guess where he sits) and a bombardier in the aft fuselage. In practice the roles of bombardier and radio operator were often done by a single person, but fact of the matter is, I only have space for the pilot on my model -and only with the cockpit canopy open.

Grumman devised a unique wing-folding mechanism called the 'sto-wing' for many of its shipboard aircraft. The outer wing panels swivel such that they end up flanking the aft fuselage. Allegedly the founder of the company, Leroy Grumman, worked out the geometry in his office one day using a paperclip and an eraser. I have built sto wings before, but on the Avenger the mechanism was complicated by the location of the undercarriage (in the wings) and by having to have the mechanism in the wing itself (rather than in an engine nacelle). The same is true of the Wildcat, but its wings are tiny and that means the construction doesn't have to be as sturdy as for the much larger wings of the Avenger. Fortunately, the Avenger's wings are also quite thick and after a few revisions things worked.


F4U Corsair
After I finished the Avenger, I turned my attention to the F4U, aka. the 'bent-wing wonder'. Powerful engines require a big propeller. The Corsair's designers came up with an interesting way of making sure that the propeller cleared the deck: rather than giving their plane long undercarriage legs, they had the inboard sections of the wings slope down at an angle and the outboards sections up, with the undercarriage legs attached at the lowest point.

Unsurprisingly, getting this shape right whilst still having enough space for the wheels to retract was the biggest challenge when building this model. Beyond that it was largely trouble-free. the cockpit canopy was a direct copy of the canopy I designed for the Wildcat. I also built a small flight deck tractor and some deck crew to go with it.

As you can see, the outer wing panels on the Corsair fold up for storage aboard carriers, which was easy to do on my model.

A6M3 Zero-Sen
Ed and I agreed a long time ago that Intrepid wouldn't be complete without at least one Japanese aircraft ready to dive down on it. My biggest question was: which one? After looking at a fair few pictures I decided to build the most famous of them all, a version of the Mitsubishi A6M Zero-Sen, also known simply as the 'Zero' or 'Zeke'.

Early and late model Zeros had rounded wing-tips. I chose to build a A6M3, with square wing-tips. The parts that are usually difficult on aircraft models are the undercarriage and the cockpit canopy. The undercarriage is simple; sits in the wings and retracts inwards. The opening cockpit canopy is once again simply a variation on the design I used on the Wildcat. Land-based Zeros were often painted dark green with light grey under-surfaces, but because the parts selection in dark green is even more limited than in dark blue, I chose to build the model in grey, similar to the colour scheme usually worn my Imperial Japanese Navy aircraft flown from aircraft carriers. The build went very smoothly, without any significant difficulties.

SB2C Helldiver
The same cannot be said about building the Helldiver. The real Helldiver had a lot of teething problems when it entered service: it was unstable, unreliable and suffered structural failures. the aircraft was so unpopular at first that it received a number of unflattering nicknames such as 'The Beast' and 'Son of a Bitch, 2nd Class'. I wasn't looking forward to building this model. I think the real-world aircraft looks ungainly and odd and I figured that building one out of LEGo would be problematic. When I started building it I knew there were several difficulties I needed to solve. The Helldiver has two sliding canopies, for instance, and an internal weapons bay smack in the middle of the fuselage where the wings are attached to it. Normally I try to build that area out of several overlapping plates, to give the aircraft sufficient structural strength. This was further complicated by the location of the landing gear in the leading edge of the wing, which meant that there wasn't much room there for structural bits.

The end result is reasonably sturdy although the fuselage can flex a bit and the space inside the weapons bay is a bit smaller than I would have liked. The canopies on my model are of a similar design to the canopy of the Avenger, which unfortunately means that there is no room for crew inside with the canopies shut. Fortunately the wing folding mechanism on the Helldiver is fairly simple, with the end panels simply folding up. However, I did spend a fair bit of time fiddling with the length of the outer wing panels and the location of the hinges to get them to fit properly.

F6F Hellcat
Before I give the erroneous impression that things always go to plan, it's time to introduce the F6F Hellcat, yet another Grumman product. Having built the other aircraft I figured that building the Hellcat would be smooth sailing. I figured that the biggest problem with the Hellcat would be the central section of the wings and fuselage. The Hellcat had a sto-wing, the undercarriage retracts into the wings and the wings sit at an awkward angle. As I was building the aircraft I realised that I was right about identifying the difficult bits. However, the solution that I came up with soon turned into a major pain.

The wings get their slight angle by mounting them to the fuselage using plate hinges. My LEGO version of the sto-wing also uses plate hinges and it seemed like a good idea to use the same set of plate hinges that were used to mount the wings for the sto-wing. A similar idea worked really well on my Fairey Swordfish. Unfortunately it was pretty much a disaster on the Hellcat because the position of the landing gear sits close to the hinge point of the wing. The wing didn't fit properly, leaving awkward gaps at the leading and trailing edges. It also sat at the wrong angle, when folded the aircraft was too wide and the landing gear itself also didn't work well. It frequently collapsed and the landing gear struts were too long. The rest of the aircraft was fine, but the whole thing was let down by the wing and undercarriage construction.

Ultimately I decided that the only thing I could do was to completely rebuild the wing centre section, with the actual wing connected to the fuselage with plate hinges and the outer section of the wings connected to the inner section with more plate hinges. It may sound like a wobbly construction, but it solved all the problems in one go, as it also gave me enough space to fix the landing gear.

All together now
After I completed the F6F, all four aircraft types for the air wing are done.

What is next is building them in larger quantities. Ed has already started building copies of the Avenger, which you can see here aboard a section of Intrepid that is still under construction. Together with my prototype, we have already got six of them.


We are thinking of the following numbers of aircraft

• 6 TBF Avengers (already completed)


• 6 F6F Hellcats


• 9 SB2C Helldivers


• 15+ F4U Corsairs

Obviously that still means a lot of work in the next months. It is likely that Ed and I will build copies of the Hellcats, much as we did with the Avengers. For the Corsair, however, I intend to make instructions. I will probably be sharing them with other users, which means that if any of you feel like having your own Corsair, in a few months time you will be able to build your own copy of my design.

Happy building!

Building scale models of aircraft in LEGO.

I get asked how I build my aircraft so often that I decided to make it the subject of a post. It seems like a far better idea than me waffling somewhere in the comments on my photostream or in some discussion group.

Making a plan
I know that a lot of builders start with a bunch of more-or-less random parts or a nice connection between a few of them and fiddle around with those until they find a shape they like, at which point they decide what it is that they'll build. I don't build like that. I know exactly what I'll build before I start and I often know how I'll build it in quite a lot of detail. I look at pictures of the real aircraft already thinking of how to build it and I make a plan. The plan can include a number of things, but usually involves the following things

• a drawing showing the dimensions of various parts of the aircraft


• a design of how to recreate the shape of the wings


• an idea of what the most difficult bits will be

How detailed the plan is and how much of it I work out on paper differs from aircraft to aircraft. The paper version can consist of a small sketch showing some of the dimensions- but sometimes is pretty elaborate. Here are some examples.

If you look closely you'll see quite a few aircraft and helicopters that I have already built, as well as a fire engine and a few planes I haven't built yet.
I'll now go over the three points on my list in a little more detail, to show a few tricks and the advantages of having them in a plan in the first place.

Working out the dimensions
For finding the dimensions, I tend to use a three-view drawing of the aircraft. I look up its length or wingspan, calculate to how many plate widths those lengths correspond and from that work out to how many studs a cm in the drawing corresponds. I might download and print the plans from the internet and scribble on the printout or use drawings in a book as the basis for my own little drawing. In any case, I like to have a piece of paper next to me when I build. Alexk-, whose F-22 I blogged little more than a week ago, does something similar, but takes a more high-tech approach. Here you see a drawing of the F-22 with a scale superimposed on top of it, showing to how many plate widths the aircraft corresponds.



The shape of the wings
I always spend a lot of time on getting the leading and trailing edges of a wings and the horizontal tail plane the proper angle. Because I tend to build wings using plates (as opposed to using bricks on their side) this usually means using wedge plates. In the last few years, LEGO have introduced a whole range of wedge plates with different angles and often these are enough.

For some aircraft. however, the angle of the leading edge doesn't correspond to anything LEGO make. In that case a bit more creativity is required. Sometimes it is possible to use plate-hinges in combination with different wedge plates to get the proper angle.

Mike Psiaki's F-22, which I also blogged last week also uses the technique, as do the models of the Eurofighter Typhoon built by several people, including my own.

A nice example of a plan, also for a Eurofighter, and with a similar wing design is John Lamarck's.

Sometimes using a little maths can come in handy. I promise not to go overboard on the equations this time, but the Pythagorean theorem can be very useful. It describes the relative lengths of the three sides of right-angled triangles. The sides of triangles with certain angles have integer lengths (phythagorean triples). These can be very useful, because using Pythagorean triples, you can make really sturdy triangles. One example is 3,4,5 (because 3²+4²=5², I did manage to sneak one equation in here after all).

In other words, the diagonal of a right-angled triangle with sides that are 3 and 4 studs long is exactly five studs long. I used this handy set of numbers to mount the complete wings of my A-7 Corsair at an angle.

Certainly in the latter case, the way I built the wing had a huge impact on how I built the entire plane. If I hadn't planned this, it would never have worked.

The difficult bits
My plan tends to include some ideas of which bits of the plane will be difficult to build and those are the parts I build first. For my Sea Harrier they were the cockpit section, nose landing gear and the jet intakes.


If you look at the completed model, you'll see that the bits that were already present in the work-in-progress picture are still there almost completely unchanged.

Similarly, for my Heinkel He-219 Uhu I started with the cockpit, radar antennae and the engine cowls.

Once the difficult bits are done, the rest of the build tends to be smooth and easy. Having a plan and knowing how big various parts have to be means I rarely rebuild parts of a MOC that I have already built. I also rarely start something that I don't finish.

I love it when a plan comes together!
The plans I drew before building my E-2C Hawkeye are among the more detailed I've done.

I worked out the dimensions, I designed the outline of the wings, I figured out how to build the nose section and the radome and how the aft fuselage would taper; all before putting any bricks together. If you look closely at the wings you'll see that I've also the technique of combining wedge plates to get the proper angle for the wings. When building it there were still a few things I needed to sort out, but I ended up sticking pretty close to the plan.

Even though it was built more than two years ago, the Hawkeye is still one of my most complicated models and I don't think I could have built it without a plan.

This is not me trying to tell any of you to do things my way. Everybody should build how they see fit. Obviously there are other approaches, but having built a few dozen aircraft models in the last few years alone, I find that this approach is what works best for me. Perhaps some of you can use some of my ideas to your advantage.

Happy building!

Dr. Spontaneous

I was just looking through the LEGO Military group pool on flickr to see if I had missed anything, and was pleasantly surprised to discover a talented builder that I haven't heard of who goes by Dr. Spontaneous, so I'll be blogging a couple of fantastic vehicles that he posted a few days ago.

First up is the VDS Medium Adaptable Artillery Truck (which is apparently based on an older creation of his), complete with stabilizing support struts:






















Of equal note is his VDS Advanced Infantry Fighting Vehicle, which sports an anti-RPG cage and room for three dismounts:























It's not often that builders are able to incorporate working features and an interior into creations while still keeping them compact enough to be able to pass for being minifig scale, and Dr. Spontaneous has done both with flying colors. Keep it up!

Victory Day

PigletCiamek, yet another excellent builder from Poland, has built a cemetery for Soviet soldiers who were killed while fighting occupying German troops in Poland near the end of WWII - complete with a rusty T-34 perched on a monument - to commemorate the 65th celebration of Victory Day, which was observed this past Sunday on May 9 to mark the unconditional surrender of the German military and the end of the Third Reich. Similar to Victory in Europe Day (VE Day for short) that's observed in the West on May 8, Victory Day is observed in the East (albeit a day later, as the German surrender took place May 9 Moscow time), and is celebrated each day with the Victory Day Parade in Moscow.

My favorite part of the diorama itself is the former Soviet soldier in a wheelchair paying tribute to his fallen comrades, and the tilted part of the monument that the T-34 rests on is also an exceptionally nice detail.

Stealth

The current flickr Lego Military build contest has a category dedicated to stealth technology. The category is intended for fictional designs, but I felt it might be a good idea to take a little look at some stealthy aircraft built in Lego by various people and to explain a bit more about stealth technology. I'll stick to aircraft for now, but the same technology can also be applied to helicopters and ships, for instance. There are a few things many people don't understand about stealth technology. It does not make an aircraft invisible to radar. What it does is reduce the distance over which a particular radar can detect the aircraft. Radar works by having a transmitter sending out radio waves. If an object is in the path of these radio waves, a small fraction of the waves is reflected and this can be picked up by a sufficiently sensitive receiver. Usually the transmitter and receiver use the same antenna.

A little mathematics
This is not your average blog post, because as a physicist and possibly a bit of a bore I now feel the need to introduce some mathematics -not because I want to scare the readers away, but because I do this sort of thing for fun and feel the mathematics are useful to illustrate the effect of stealth technology. The radar energy I_iper surface area that strikes the aircraft is inversely proportional to the square of the distance d from the transmitter.


E_o is the energy transmitted by the radar.

Similarly, the radar energy per surface area I_r that gets reflected back to the receiver is inversely proportional to the distance from the aircraft to the receiver squared multiplied by to the aircraft's Radar Cross-Section R and proportional to the aircraft's Radar Cross-Section R (typically given in m²). Combining this with the first equation gives:



The radar cross-section is what stealth is all about. It is a complicated function that depends on the shape of the aircraft and the direction from which it is seen, the material it is made of and the frequency of the radar and probably a few other things. Major contributors to the cross-section are the engine compressors and engine inlets, perpendicular surfaces on the airframe, edges such as the leading edges of the wings, externally carried weapons, and not surprisingly the aircraft's own radar antenna.

The last equation tells you the following: if the target aircraft is twice as far away, the energy that gets back to the radar is 2⁴=16 times as small. In the real world the receiver will be picking up all kinds of radio waves, for instance background noise and reflections from birds or radar reflections from the ground. Signals processors and fancy computer algorithms can help to isolate the reflected waves from an aircraft from all this clutter, but there is a limit to I_r below which a reflection from an aircraft will not be detected. This limit obviously sets the maximum distance at which the radar can detect a target of a given radar cross-section. The last equation also shows that if a radar can only just detect an aircraft with a given value for R at, say, 100 km, reducing the value of R by a factor 10,000 (=10⁴) will mean that the maximum detection range drops to only 10 km. While radar stations with a 200km spacing between them would be enough to detect an aircraft in the former case, an aircraft with a radar-cross-section that is 10,000 times lower can easily slip through the gaps.

Of course, a factor of 10,000 is a pretty big deal. The cross-section can be lowered using a combination of two different approaches. An aircraft (or ship) can be coated with purpose-designed materials or structures that absorb rather than reflect much of the radio waves that strike it. The aircraft can also be shaped such that radio waves that strike it are reflected away from the direction of the transmitter/receiver. Obviously, for building a LEGO stealth aircraft, this is the factor that matters.


The first stealthy aircraft
One of the first aircraft specifically designed with features to reduce the radar cross-section was the Lockheed SR-71 Blackbird, a high-flying reconnaissance aircraft used by the US Air Force from the 'sixties to the 'nineties. The leading edges of the wings incorporated structures designed to absorb radar. The wide 'chines' along the forward fuselage were there for aerodynamic reasons, but also decreased R.

Lockheed Blackbird by Lego Monster

The vertical tail fins were canted inward to prevent them from being perpendicular to the wing. The cones in the intakes were fitted for aerodynamic reasons as well, but also served to cover the engine compressors. Unfortunately all the efforts ultimately had little effect, however, because chemicals sprayed into the exhausts to prevent contrails from forming caused the massive wake of the aircraft to be visible to radar!


Full-blown stealth
Unlike the Blackbird, reducing the radar cross-section was of paramount importance in another aircraft designed by Lockheed, the F-117A Nighthawk. This was designed with one mission in mind: slipping undetected through enemy defences and bombing high-value targets with pin-point accuracy. The engines are buried deep inside the fuselage and the intakes are covered by grids (which appear as solid surfaces to radars). Because a radar antenna is a fantastic radar reflector, it didn't have one! The aircraft's shape was chosen such that most of the radar energy that strikes it is reflected in fairly narrow beams (spikes in the radar cross-section) away from the radar. Because computer programs at the time could not yet accurately predict how radio waves are reflected by curved surfaces, the shape was made up of a combination of flat areas, leading to a weird faceted look.

F-117A Nighthawk by Mad Physicist

The aircraft was covered in special radar-absorbing coatings and its laser-guided weapons were carried internally. F-117As served with great success in the Gulf War of 1991, but by the end of the century the aircraft was showing its age and a single F-117 was shot down over Serbia in 1999, possibly because the aircraft flew more-or-less the same route for several days in a row and was actually spotted visually. All F-117s have now been retired.

Stealth, the next generation
At the time of the shoot-down, new and weird shapes were already flying. The USAF had taken delivery of 21 B-2 Spirit bombers (of which I have yet to see a decent LEGO version) and was developing its new air-combat fighter: the F-22 Raptor. The F-117s odd-ball shape seriously affected the aircraft's aerodynamic performance, but by the early 'nineties computer technology had finally caught up with the physics, and it was possible to build stealthy aircraft with smoother shapes and much higher performance.

F-22 Raptor by Alexk

The F-22 still has a number of features in common with the F-117. Large parts of the fuselage still consist of flat panels, but they now blend together more smoothly. Its intakes are not square (but trapezoidal), reducing reflections from perpendicular surfaces. The intake ducts are very long and curved, minimising returns from the engine compressors. While it can carry weapons externally, most of its weapons are carried in internal weapons bays. A final concession to stealthiness is something called 'planform alignment'. Since edges are large contributors to the radar cross-section, designers of stealth aircraft often align the leading and trailing edges of the wings with those of the tail planes and inlet lips. There will only be a spike in the radar cross-section in a direction perpendicular to the edge and since most of the edges line up there will only be a few spikes.

F-22 Raptor by Mike Psiaki

Reducing the cross-section by a factor of 10,000 comes at a price. The B-2 and the F-22 are the most expensive combat aircraft ever built, at roughly $2 billion and $200 million per aircraft, respectively.

Most nations cannot afford to design and operate aircraft that are this expensive and most modern European fighter aircraft (Eurofighter and Rafale), the American Super Hornet and also the PAK-FA currently under development in Russia are designed to have a reduced radar cross-section where it matters most: from the front.

There is much more to say about stealth technology. I've only talked about reducing visibility to radar for aircraft. Many modern ships have superstructures that avoid perpendicular surfaces to reduce their visibility to radar. An other important aspect for aircraft is their jet exhaust. It is much hotter than the surrounding air, which means it can be visible to Infra-Red detectors. The F-117 and the F-22 have rectangular engine exhausts instead of more normal round ones to allow the hot exhaust gasses to cool down more quickly.

If you were to chose to build a Stealth aircraft for the competition, there are a couple of things you might want to keep in mind:

• the engines ought to be buried deep inside the fuselage to hide their compressors


• planform alignment: leading and trailing edges are often parellel


• weapons are carried internally


• the shape often uses large flat surfaces


• you should avoid perpendicular surfaces, so tailfins, for instance, should be at an angle

Check out Magnus Lauglo's 'Black Arrow' to see an awesome example of a fictional stealth aircraft.

Black Arrow by Magnus Lauglo

Happy building!