If the question is to use forced induction on a uav...

The answer is probably, "Hell Yeah!". I have been learning everything there is to know about practical, turbocharged-systems. So over the next few posts, I will hopefully generate a reasonable technical approach to safely turbocharge a 4-stroke Briggs and Stratton Animal engine or a Raptor. It depends on which one I can find and afford here in Central Europe.

We have found a few 1.5# turbos good for 3-4psi of boost. The mad scientist in me says that I think we can find some light super chargers and run them on a small electric motor for less weight. I know that the whole point of a turbocharger is more about recovering wasted energy in the exhaust system. However, I wonder if the weight/power generated ratio would be better served with a high efficiency electric motor. Since they are pretty amazing these days.

As I come up with some numbers for weights, and possible concepts, I will keep everyone in the loop.

Smoking Ace Update

We are still alive. Just working on some other projects at the moment.

The Smoking Aces are still under construction. After flying the planes for hours on simulators and finally the real thing, we realized that you can't cheat physics. It makes for some interesting behaviors in short-coupled tail designs. What is kind of cool is that deeply-swept wings actually set the maximum angle of attack for the aircraft. We surmise that it is due to over-wing airflow. As the aircraft pitches, the airflow over the wing obscures the clean flow over the tail and finally completely blocks the flow.

Not so much block, but the distance between the tail and the wing is shorter than the mean turbulence. So the dirty air is not laminar enough to make a well-circulating flow around the tail. As the tail loses laminar flow and finally gets only turbulent flow it loses lift and finally stalls. This reduces the effectiveness of the tail and the plane rotates back to balance the tail input. This seems reasonable enough an explanation to the pitch wobbles, that are only partially-tamed by gyro input.

The first time we saw this behavior, it was exciting. Our pilot certainly thought so.

There is even a slight regression in our projects. Not so much as a negative thing, but more an artistic reawakening. I have to finish working up some drawings so we can discuss some design requirement changes. Building the Smoking Aces, we discovered that what we thought was a lot of space, was not. We also found out that 1000 in*lbs is a tough thing to take out in such a small space. Considering each wing applies this, we found some strange deflections in the air frame when the wings support large flight loads. These were certainly not unexpected, but we did not realize that our load paths were not as well controlled as we though.

Looking back through some old documentation, I found some of our original "Fat Man" designs. What we learned with the "Fat Man" was that fuselage depth or in its case root thickness was our friend. If you have healthy wing roots, there is a lot more space to manage payloads. More so, there is a trade off with larger thickness designs. The trade-off that is important is that often their curvatures do not change much.

When you build metallic structures, you see the need for structural caps. Without them, it is hard to fix skin to the structure without some heroic measures for the most part. Next time I will talk about some of the things that did not work for us.

Smoking Ace Pt.1

Ok, this is not the most verbose of howto's .I will start explaining the most important parts of the pics belo.w.
These are the basic structural elements of the Smoking Ace fuselage.

One thing that I have to say is that it is going together quickly. There are some unforeseen technical bits trying to assemble the fuselage. Mainly around the stiffness of the joints between the sections. The fuselage is 42" long at the moment. A tail and nose cone have not been added, I hope to have them and the lid done soon.

Special thanks to Bill Sheffer at Unique Cutting & Metalworks for his help and support on this project!

Coming Soon: How to Build a Smoking Ace

Hey everyone,

Next month I will start a simple construction project, demonstrating how to build a "Smoking Ace". It is not always pretty but the goal is to be straight. Please check back in the next few days or weeks to see our progress.

Adventures in Aircraft Model Validation

After several months of working on the Smoking Ace, I have learned one thing. Balsa is not your friend.
Aluminum is not so bad, but it is what it is and you need to make sure you bolt it up.

We have been working on conreol systems for the plane. It works like a normal pusher. The simulator models that we use suggest that it is pretty predictable to fly. I hope that is the design and not the simulator dumbing things down, so that my feelings are not hurt. Our primary model is X-Plane 9.3. It was pretty easy to build a model in the system, for what it is worth. I could plot out a simple airfoil and plot out the weights and measures of the plane as we are predicting them. I had to use a custom airfoil, our low moment  airfoil is well understood, but is not super common in general libraries. We use the e204 with a 16" chord.

We chose 16" because it allows us to get 2000 square inches of wing area in a reasonable span. No, there is
nothing reasonable about wings that are longer than I am tall by a ways. That would be fine, but there are two of them. Which means we have to take it outside to assemble the plane. As a reference, this is gives us a do not exceed gross vehicle take off wing loading of 50.2 oz/square foot.This is a little high, but for a 14' wingspan it is not out of bed.This is all in the batteries. This is an electric plane, with a 65cc equivalent motor driving a 22" fan.

This configuration should give us around 30 pounds of thrust. Hopefully, this will be more than enough to keep it flying. The plane's primary mission is to fly straight and level and take pictures and instrument readings. I think that the configuration will be successful at this. The Smoking Ace turns like a school bus, so it would be unexpected for us to try and snap roll it.The sim says behaves like a normal pusher configuration.

I mean that unlike a puller plane, when you put on the power you have to put on elevator or the nose dives. To compensate for this a bit our elevator is set at 4 degrees nose down. This us effective at counteracting the
offset of the line of thrust to the center of gravity. There is no vertical tail in this configration. So we have a soft feeling rear end. Combined with our shortish, blended fuselage, means that we have to use the inner  ailerons sometimes in flight as poor man's elevator. Long wings and an aggressive sweep makes this an effective technique. Double, mid-span control surfaces help to give us an effective rudder. Differential roll inputs counter-act the other roll inputs and change the drag profiles of the wings and developing a yaw moment with little roll.

In the next generation of the aircraft, there will be duckerons on the wing tips. Yeah, I know this is not an
approved, aerospace term. Which was discussed in an earlier posting. Properly termed, they are drag rudders.

Using X-Plane sizing them was pretty easy. Sure I can estimate that a drag force at the tip of the wing will
 result in a given yaw moment. However, it is hard to estimate the tip effects on approach when the drag rudders are too close to the wing tips. We found that they should be one chord or so from the wing tip. Farther out made them more effective, but it also made them impractical during low altitude maneuvers. They were so effective that they burned off airspeed and slammed the plane into the ground. Watching your model cartwheel wing tip over tip is exciting, but depressing.

NOTE: You have to release the brake when you are in X-Plane. Otherwise it has some crazy effects... I would have  thought that if you kept making the same mistake, they could figure that out and say... release the brake... or if you throttled up and the plane was not moving... some other visual cue may help.

On the other hand, I kind of thought that most of the planes were kind of lackluster to fly. The differences
between a Piper Cub and a 747 were not as striking as I would have hoped. A Cub should have felt a bit under powered and then feel kind of flippy. When it got into its acrobatic range. Where the tail and rudder became effective nearstall conditions.

If you want the latest revision of our model, you can get it here. If you find something interesting, or if we made a mistake please feel free to comment at info@fatmanflying.com .

The Smoking Ace is in the jig

I got the parts for the Smoking Ace this weekend from Bill at "Unique Cutting and Metal Works". Bill is great to work with and help us on this project.

The parts are coming together well. They were bracketed this weekend and got a coat of enamel. The issue that I see at the moment, is that small variations in a straight line make a big difference now that the spars are weight reduced. Lots more small radii to worry about. I do not think it is a big deal, but I lost a bunch of holes because they were too close to other penetrations.

The best thing, that has come out so far, is that the battery carriers really look like they fit as designed. That is cool, I hope that I can get the heat pipe design to work too. One of my coups of engineering will be to steer some of the motor, esc and battery heat to the same spot across a Peltier device and out to the free stream. I am not sure it will be worth more than a few volts, but something is better than nothing. Peltier recovery is one of several technologies that we hope will get our electronics power-management efficiency up.

I will get some pictures up as soon as the fuselage gets a bit further along. One of the most interesting things about this design, is that it is based on triangles. Any third year structures student will remind you that triangles are the only self supporting shape. Self-supporting makes the air-frame easier to construct because it tends to stiffen up as you assemble it. This means that you can break the assembly up a bit more than normal and things self-support and then support when assembled. Anything that makes this easier to do is good.

More to come.

UGV Autopilot Revisited

We have been working on lots of projects lately, mostly about the UAVs again. Only two hands and all, the last parking lot test that we ran were successful in clear areas. If you just wanted a clear circuit, our simple guidance system was good about being repeatable around 20mph. However, we want to get more in the low end in this, so that we can handle cornering better. The avoidance model is where we are looking for some help.

We are trying to get a working optical flow system to work at these speeds. You can get a working system at low frame rates, but we will need to increase our computing capacity to get it to work successfully at these speeds. Our issue we think, is in the matrix inversions. The determinant terms are making too many things blow up by divisions of small numbers. 

We are looking for anyone with experience getting an effective Kalman filter to work on Android. We have a few older phones, bhat we think would be a good platform for doing 2d control. Yes, I am mixing discussions a bit. If we can better estimate the net acceleration, it would help debug our optical flow system. We are having to bracket our responses so that the AI does not jerk the wheel. This seems to be an  issue. If optical flow can be used to manage the jerk, I think that we can even have moving obstacles in the scene and still reacquire the path with no issue.

It seems to be that the vectors estimated with Kalman divides by zero and runs a huge acceleration and that ruins the math for several iterations. Then the ringing dies out and the system cam go on, by that time we are either running for the hills because a dog liked the truck or because something blew across the scene. I have to find the math error. 

Contour 1080p HD helmet cam

So far so good with the helmet cam. We have been playing with its high frequency stabilization technology. This is pretty effective at taking the jelly and jam out of the motor shakes. Which is a good sign, it is effective at taking out suspension bob when riding a bike, but low frequency motion it can only do so much with. If you move the camera 3" it can't take the shake out of that. You would not really expect it to.

At night, or in low-light conditions it gives a pretty good picture until it is hard to see. Once you break that threshold it is too dim as well. It does have a pretty good sensor, it can pick up even small changes in brightness well and does well with edges.

At the moment, I have yet to get virtual dub to open a quicktime movie. None of the plugins that have been found work. Although I am loathe to say it, it may be better to just go the Quicktime Pro route. Legendary fail of customer support is always a reason why Mr. Jobs' overpriced fanboi kit rarely graces my workspace. It may be a necessary evil this time. Especially, if it can automatically export all of the movie's frames in one drop.

I am not done testing the camera, but so far I recommend it. For the money, it is very usable, rugged and has a functional output that is good for tv viewing. Reliving past exploits are always a great way to kill  time while you lie to yourself about  how good you were.

Countour HD Helmet Cam

We are looking into using the Contour HD helmet cam as the data source for some GIS experiments. After a detailed review of available products, we found the Contour. It is a well-received  and rugged helmet cam aimed at mountain biking and snowboarding. Out of the box, it is a well built camera with an interesting rubberized back cover that gives access to the battery and the memory card in one flip of the thumb.

I will see about posting the movies that were shot with the camera. The output is a QuickTime movie, that we will feed to virtual dub. Virtualdub will strip the frames out of the movie so that we can analyze frames to look for patterns in the vegetation. The goal is to make a semi-automated habitat estimator and/or plant specie histogram.

As my batteries run low at dinner, I promise more interesting things to come.

Can't Get It Up?

Hey it happens to everyone...

No little blue pills, but a rainy afternoon is keeping us from seeing how the wings sit in the mount. There is a bit of concern that the lovely tolerance that made the spars so easy to insert, is making life hard for other reasons. It will not be an issue. As long as the system is stiff once it is bolted together. There is some concern that the foam may crush under side-load. That could be fixed but I do not see a good solution that will work.

The fix if necessary is a wing root cap. That is probably a good idea under most circumstances. However, what could it hold to? The thing that was great about the design was that it had little in the way of internal structure, it is foam after all. That may be limiting the usable weight in the end because you cannot make strong mounts between primary parts.

We will see. At the moment I cam going to see if 0.060" piece of Aluminum sheet will tip the system in the right direction. It may need more like 0.090"  to correct the wing tip height. I can't see that until it stops raining enough to take it outside and measure it. Ten foot wingspan makes it problematic to measure in the house. Oh yeah, it is being built in a 900ft^2 apartment that I live in at the same time. It is a good drill for the initial facilities that I will have in CZ. I will dream of the day of such a large place.

More to come...

Lifting Bodies Are More Than Just Another Pretty Shape - Opinions on Aircraft Design

Lifting Bodies Are More Than Just Another Pretty  Shape - Opinions on Aircraft Design

There are many ways to look at aircraft design. Most of which are field dependent, why design for supersonic flight if your device will never climb above 500'? It would be cool thought, right? I digress, if you are designing for normal flight regimes you will be operating at an altitude with an engine power curve which will vary by altitude and temperature. Now, if you are designing in other regimes, you need to know where you can get small performance boosts where they are available.

Managing wing thicknesses is and use the concept of "wing tip thrust". By making tip vortices more manageable there is a significant reduction in overall wing drag. This "free" reduction in drag is called "wing tip thrust". Like this, there is another simple idea to take into account. If you can design a fuselage that is not pressurized with an essentially flat belly, you can play some shape games. These shape games can effectively make a Clark-Y airfoil. Now it is more complicated than this, but if you begin your mental experiments from this perspective, you can eek out some under-represented performance.

But how do he do it? It is all in the magic. If lift is generated by circulation of a lift envelope, that is created by the difference in pressure created by fluid moving around a shape. Why not generate lift around your fuselage? It will not get you 25% of your lift... but if your fuselage planform area is 15% of your wing area and you can get 40% efficient lift out of minding your p's and q's you could be looking at 6% more total lift. Yeah, you are right, this is all pie in the sky stuff. However, if you could generate 2-3% more lift for the length of your flight, you could reduce the angle of attack on your wings and trim out your drag. Reducing your drag means that you use less energy in the case of electric or less fuel in the engine.

Less fuel means that you can carry more, or fly farther. Nice. 1-2% may not be a lot if you weigh 4oz. . However, if you are looking at varying wind conditions or being able to react to changing conditions and you can play some games about fuselage profiles. Why not, it is not really so hard to get as much as 5-6% out of playing your profiles against each other. That makes for a good amount more flight time in rc. Not the 7min guys, but as you go for 20min... you get 21min. Yeah, it does not sound like much, but if it makes your fun go for 22min... It will be worth it.

Why do I pick Clark-Y? They have flat bottoms, reasonable thickness and a fast taper to the trailing edge. Construction-wise they are easy to construct, because you can lay them on a table. Their CL/alpha is pretty steep, so 1-2deg can get you something and if you can play with what level is, you can get a fuselage angle of attack to a point where you can make some dividends. Most importantly is that they do not separate their boundary layer fast. Most designs will never get to a critical angle of attack, drag will eat you alive if you fly your fuselage at such a high angle of attack.

We make lots of 60" fuselages these days with a mean 12" beam. That gets us an additional 4-5lbs of lift at take off and 1-2 lbs at cruise. Nothing to write home about, NASA will never give me a Ph.D. for it, but it does get me lots of "clever"s and "I would not have thought of that"s. Pretty high praise in engineering circles.

Fuselage Design Schemes - Vertical Tails do not Make Your Ass End Look Better

Lots of things cross my mind when I start putting pen to paper on a new fuselage. Mostly, it is about needs to go inside, and then how to build it. Over the last few generations of this design, it has become clear that slow-speed, heavy lift (payload/fuselage <0.7) We start to see several key principles begin to precipitate. Today we will focus on the differences in aircraft balance schemes.

Aesthetically, I am not a vertical tail man. They are functional and in many designs they are necessary. My career began in the low-observability sphere. So a large perpendicular plate nailed to the end of your vehicle who is trying to hide invites bigger radar returns. In most of my training and experience, we get away from this with large sweep angle wings and oblique surfaces. Sometimes, these choices do impact performance. If you are working against sines of the angle, you will always have more surface area to get the same net effect.

Balancing the vertical surface weight and the total surface area is always a game. If you look through Jane's for modern high performance, low-observable aircraft, you will see a common theme of split tails. Two tails, let a designer get a net effect and still not have a large single vertical surface. Ok, yeah it weighs more sometimes this is necessary and even suggested.

These principles are not necessarily limited to high-performance  aircraft. Just trying to keep the sail-area down on the aircraft is important. Otherwise it is blown all over the sky like a potato chip in a hurricane. If you are trying to make a vehicle that can stay on station it is easy to fly a slow  constant angular speed turn with a bit of roll angle, rather than balancing a lot of rudder input and trying to fight the wind the whole time and flying search patterns. Sweep angle also lets designers move the center of pressure around for the wing alowing for different internal position management of work payloads.

Many designs on which I have worked use low angle wing tips instead of a vertical tail. Highy-swept low speed wings get most of their roll control from the wing sweep and large ailerons or spoilerons are goos at helping with pitch contro. One interesting solution is coined a "duckeron". I cannot vouch for the scientific nature of the name. A "duckeron" or even a "quackeron" is a surface that consists of a pair of  tip-mounted surfaces at the far end of each aieron. These surfaces open and increase the drag on the wing tip. This is a bit counter intuitive, unike spoilers which run along the span of the wing these are actuay on the trailing edge of the wing and allow for effective yaw control. Sweep helps increase the distance between the wing tip and the aircraft center of gravity. This is the moment arm distance used to calculate the force applied to yaw the aircraft.

It is a pretty clever idea and allows for reduced cross-section yaw control. On rc models and small UAVs the duckeron is a simple single-servo-per-side solution. Rather than only connecting a single surface to the servo arm, you use a pair of rods. As the arm swings pushing the rods away from the hing line opening the surfaces equally. However if there is a clearance issue, the ratio of the opening rates can be changed via a cam or simply varying the lengths of the rods. A shorter rod needs more arm sweep to move the surface through a given range. The air disruption over the wing would make the use of a spoiler less effective. There could be several reasons to use spoilers and ducks at the same time for different flight control cases.

You do have to take into account that the drag at the tip may be an unplanned load on your wing spar. One other kind of side-benefit of using ducks is that they act as airbrakes during landing, even as a counter-balancing yaw force during approach. As a counter-balance on approach you would pay a much steeper drag penalty than a rudder, but they woud be able to apply a much larger yaw force.

Touching Pee-pees in the Dark and Adventures in Airplane Bonding

Our first really big pane is about to come off of the line. I guess it is easy to see that I was slacking. Not really, just got side-lined by a bunch of stuff.

Today, I wanted to talk about the bonding experiences. We are pretty good with the cheap and cheerful 60min and 90min epoxies available from Loctite. In general, they are worthy of their cost. For the most part:

•  they get it done
•  are easy to clean
• decent finish that is sandable, but micro-balloons help immensely
• and wet chemistry does not rip the skin off of your hands

 The other side of the coin is that :

• they are not super hard
•  sometimes leave a sticky surface which needs hand washing a bunch of times to get the surface clean
• cheap means heavy
• in the warm, humid air of Florida sometimes the pot runs really fast.

It is exciting to see it melt through two cups and run epoxy all over your surface and drip down your leg. The steam is cute on a  100% humidity afternoon. Around here, it is not uncommon to see rising off of your sneakers, but it is exciting to see rising off of your freshly-laid skin. It still burns your skin ... boiling water is hot... If the cup gets to be hot to the touch, or the epoxy runs really fast then you only have a few more minutes before the epoxy fixes.

We have some other adhesives and layup chemistries used by the "pros". Ok, yikes. There are enough flames, warning symbols and ventilation requirements that we honesty did not have the facilities to use them. However, some basic tests show that the stuff from Aircraft Spruce is really hard and easy to sand. It stuck to everything , was hard to get off of skin, and 10:4 is not an easy ratio to eyeball. So it needs a scale and  a fan to pull air away. I can only say it must be best with vacuum-bagged molds and infusion systems.

I would suggest using either, just know what you are getting into. With any bonding system, rough your bond area with steel wool, clean your area with a clean cloth and alcohol. Cleaning with alcohol is to pick up any grease, dust, grime and hair. Test your bond between scrap pieces of material.

Cool New Stuff At Our Zazzle Shop

Every drop helps the cause.

Thank you for your support.

Adam

make custom gifts at Zazzle

Hairspray Trick Addendum

If you are reading more about using hairspray to pre-wet rc models before they are glasses...

This works great with balsa models. It seems to be a pretty reproducible effect on wood because the wood absorbs some of the hairspray. The wood keeps the spray wetter so it does not dry out as fast. Fast forward to a foam model. Foam does not absorb any liquid, relatively speaking. Raw hairspray dries really quickly. This is a problem, we have found in many wrecked sets of cloth that if the hairspray polymerizes past a certain (not discussed in this article) point, the epoxy will not wet the surface.

What it does do is bunch up the glass when you spread the resin. Pretty quickly you can see that something is wrong because it just does not behave. You cannot straighten out the new wrinkles fast enough to get in front of it. The weight of the resin does not hold down the old wrinkles,and you make a mess. If this starts happening, we just yank off the damaged glass and toss it. Yeah, it seems wrong at the time, but we have no idea how to clean it. Always looking for hints on that one.

After the glass is tossed, we roller the wet surface of the model to spread the remnant epoxy. That is just to help fill in a pockets or spread any runs. It just air-dries after that, just leave it. When it is dry, remeasure your glass and do it again.

All in all, the hairspray trick rocks, on wooden models. Not so good on foamies.

Remember try to do your epoxy work in warm or hot conditions at the lowest allowable humidities. Yesterday, a thunderstorm snuck up on us and we had a very energetic pot of Loctite 60min epoxy. It fumed and melted several  plastic cups and unbound the wax on a paper coffee cup in the span of 1min. Finally, it melted several plastic shopping bags while we ran cold water over it.

Basic chemistry class says, take the heat away from exothermic (heat generating) reactions to slow or reduce them. Live with a chemist and you know these things.

Practical Composites: Fiberglass Over Wood

We are putting together some good pieces for everyone see how we are doing it. The big tip that we can tell everyone is hair spray. It is too funny to think of either of us ever sing hairspray. One has been bald for half of his life, and I have never been a big coiffure kind of guy.

The pictures that I am including are of a model that is 57" (143cm) x 6" (15cm)  wide and 4" (10cm) tall.

                       

The glass sued is standard s-glass, 2oz per yd glass from Aircraft Spruce . Our experience shows for fuselages, two plies is more than enough for fuselages. Make sure that your plies are pig enough to cover all of the piece and hang over about an inch (2-3cm). More than that makes it hard to support the piece, the fabric keeps pulling away from the edge  or it gets tangled.

Apply the hairspray liberally to wet the surface of the cloth, then use a foam roller to spread the spray and wet all of the glass. It takes a few minutes to work the whole surface. When it dries, it will feel more like paper than silk.

Having learned the hard way. You can let these dry for 15min or so, until they are not tacky to touch. However, do NOT let them dry for lunch and a trip to the hobby shop. The hair spray dries too much and coats the glass so that the resin does not stick. That is bad, it will just wreck your finish and everything will look all orange peel or like bubble city.

I hope this helps with your projects.

Czech Book

Hey everyone,

I have been getting a lot of requests recently about my book that I wrote in Czech about life in Central and Eastern Europe. I have been posting it piecewise on my other blog "So Little Time" here.It has received many positive reviews and some libel, you can't win them all. If you want it in a more complete book-like form, let me know.

Thanks,
Adam

The Big Babies

We are about to go flying! I hope within the month we are airborne with ten pounds of dead weight. It is a big day. After several years, we are turning the corner. It was not easy, and I would like to thank my folks and friends for sticking with me. Inventorship is far from an easy process. Now it is time to give birth to revenue ;)

In order to continue a beloved American tradition, each of our factory Big Babies will have unique nose art. I have been drawing for months to get this many pictures together. I am sure if you know me and the project, you probably know each of them. So I will not spend much time explaining them, I hope that everyone likes them. I have shirts available on the cafe press site. I think that they really bring out the smile in me when I talk about the planes, or the women who inspired them.

More building on a budget tips

I have been speaking with many people recently about how they build their uav's and larger-scale working aircraft. We were going down the balsa road, which is not so bad. It makes a pretty stiff structure with relatively inexpensive materials. However balsa is graded and strong, light wood is not easy to find nor is it cheap. You can easily run up $300-500/board foot. That is a lot of balsa, I know especially in 3" strips. However, you get the idea that this is not a cheap way to go.

We have been using kiln stabilized wood and it is making a decent product. There have been some issues balancing the stresses in the airframe. Traditional methods more or less work to relax them. My consultations with other people in the community leads me to believe that there may be better construction techniques. The system that we have uses balsa and then fiber glass on top. Our main issue is that balsa takes so long to lay up. To do a good job, it could take upwards of 3-4 weeks of concerted effort to get everything pinned and glued, sanded and filled, sealed and prepped. It is a big job, especially on bigger models with large spans.

OMG the twist, you will make lots of little weights and hooks to untwist your larger pieces as well. In some ways it is a terrifying process for the beginner. It is not hard to do, it can be terrible to do well.Blah blah, no whining. The others use mostly styrofoam cores covered in composites. I have been experimenting this weekend with it too. I have found that you can have a pretty good product with almost no invested time. My realization is that the cheap epoxies available from the hardware store, are easy to handle, water washable, but are way to soft-cured. For these applications, an epoxy chemistry that cures with a hard surface is better than a softer one.

I assume that epoxy chemistries with harder fixing strengths are less easy to handle. We have made several layups and this really is the case. In Florida, it is hard to get away from the humidity and large swings in it. So we lay up outside and bring the layups inside the air-conditioned house. That seems to help even out the handling properties.

The following pictures are using LocTite 60min cure epoxy, 80 oz./yd glass cloth and 3mm depron foam. There are many relief cuts in the foam to help conform to the shape of the fuselage. The pieces are masking taped together, a foam-safe CA glue would work too, but I was trying to limit the number of seams that needed to be joined. Most of the tape is to enforce the shape of the fuselage, not to hold the piece together. Both halves of the fuselage took about 2h to sheet and the glassing took about 20min for one person. It is not perfect, but it is an experiment. My illustrious helpers would assist on the final version for sure.

This model is about 5' (150cm) long and averages 6" (15cm) in diameter.

Building on a Budget

So we are working out our system to build giant-scale planes on a budget. We build mostly our own designs. It is far more challenging to wing it. I have to say that building from forms is pretty challenging, and worth it for those of you who like to do it their way.

One suggestion that I have for you guys is, lattice. Maybe that is not an obvious description. We have the most luck building complicated curvatures, when we lay out a regularly spaced net of 1/16th inch (1.5mm) balsa strips x 1/4" (6mm) . The spacing is what ever makes sense for the model. I mean, you will need to work out some of this for yourself. We find that wings are good with 6"(15cm) pieces cord-wise and 20- 25% spacings span-wise. That way there is a reasonable pitch and still a good amount of coverage. Onto this, you glue your actual skin down.  This helps reduce the actual curvatures involved, but also allows for the skin to be supported without the need of a foam internal block. Use wood glue if you are working on a Styrofoam base or CA if you are working on a compatible base. CA will eat Styrofoam, even the vapors will destroy it.

We get all of our balsa from local suppliers. Our favorite supplier is www.solarbo.com .