The Hercules is the most stable plane I have flown but there are three things you need to do so your plane will be stable too!!!!
1. A delta wing will not fly tail heavy.
The CG on the stock Hercules kit is back 9.5". If it is tail heavy it will be almost uncontrollable. Mark the CG before you start building and build light behind the CG. If you are having any stability issues move your CG forward.
2. The Hercules is tolerant of unequal thrust
but you should try to have the same thrust from the twin motors. Listen to the motors as you throttle up and you will be able to hear different pitches if they are not running at the same speed. Use only the same brand and rating of motors and ESCs. Try new props if you are having any trouble. Connect both ESCs to a common battery connection so the motors have the same input voltage.
3. Servo and flight surface linkages need to be tight
and secure and not flex under stress. What appears good on the ground may be flexing in the air, especially on a big plane line the Hercules. Stress test everything before taking off.
4. The Hercules delta design can fly so slow
that it you may not have enough air flowing over the elevons to control the plane. Watch the videos and see how easy it lands. It doesn't stall like you are used to. You can have the elevons full up and the plane will still fly and can do a very steep decent with the nose up.
One fin or four?
The delta shape likes central vertical fins for stability. The tip fins help to control yaw and help keep the elevons off the ground but the plane flies better with a vertical stabilizer in the center. We also need a rudder since the plane needs to be able to be steered on the ground and there are no wheels. Ground control and slow flight performance is improved if there is a rudder behind each propeller. The Hercules in the videos only has one vertical fin so you can choose which way you want to build your plane. Two rudders are included in the kit. The Hercules takes off grass in 15 feet even without wheels so the rudders are only in use for a couple of seconds every flight.
As you decide where to put your servos for the elevator make sure you leave room for the vertical stabilizers and rudders. Use one servo on each of the rudders for simplicity and strength. Put the rudders behind the props if you use the wing extensions.
The skid makes the plane easy to get in the air.
I have used skids on planes for landing gear since I saw how well seaplanes could take off the grass and snow in the 80s. The skid needs to be well attached. The skid needs to be strong. The skid needs to be slick. The skid can be used to easily hand launch the plane.
The EPP foam makes a good skid if properly reinforced. It has the ability to be a shock absorber. It is very strong for it's weight. It is not slick so a surface has to be applied to the bottom of the EPP skid to make it slick. We like to glue a piece of common 2 liter pop bottle to the bottom of the skid with Goop adhesive. This not only makes the skid slick but adds strength as it wraps around the curve at the front.
The skid has to hold the nose of the Hercules up at an angle that allows the plane to take off without rotation.
The back of the skid makes the perfect grip for hand launching. When the Hercules is in your hand the plane balances on CG and you have a solid flat surface on the back to wrap your fingers around.
The skid has to be in front of the CG (center of gravity) or the plane will flip on landing. The sweep of the wing would put the twin skids too far back for stability unless they poke out the front of the plane.
I used 2" wide Velcro to attach the skid to my plane because I wanted to be able to easily change the skids during beta testing. It was also nice to be able to take it off for the water bottle weight demonstration. The Velcro adds weight and sticks so well it pulls the laminate off of the foam rather than releasing but I like it. I used small strips of Velcro on the front and back of the skid that I wrapped up to the top of the wing for strength. I have also attached a skid by melting dozens of small holes through the laminate and Extreme tape with my soldering iron and hot gluing the skid in place. The skid is under the battery compartment adding strength to the bottom of the plane in a potentially weak area.
We only used 6 spars in the plane that flew at 9 lbs / 4+ kg / 18 oz/foot in the videos to show the spar strength. We include 8 spars in the kit so you can modify the spar system how ever you need to to fit your camera equipment motors and batteries. Our Hercules with the extension kit has 10 spars to reinforce the plane.
The spars, Extreme Tape and laminate work together to stiffen the wing and make it one of the lightest and toughest planes available.
Fiberglass spars are flexible and have to be positioned directly over each other to get maximum tension and compression strength. Before you decide where you want the spars glue the wing together and lay out the rudders, your cameras, batteries, motors and radio to help you decide where you should install your spars. Make sure you are looking at both the top and bottom of the plane as you make your choices.
I copied this to this thread and I think it describes our building philosophy.
Why do we suggest you install the radio and batteries after covering the plane?
Many flyers build our planes using more traditional method of putting all of their radio in one compartment.
They install the radio before they cover the plane and cover over the top.
They lay the servos down and hide them in the wing.
I have to admit it is prettier and seems logical.
All parts of the wing structure should contribute to the strength and durability of the plane.
The wing is made from EPP foam that resists crushing
Top and bottom spars create an "I-beam" that is many times stronger than a single spar alone.
Spars add compression strength
Reinforced tape adds tension strength to prevent tearing
The shock cord helps prevent the most common tear in a wing that happens with a frontal impact.
Our strong laminate makes the plane into a uni-body structure so all parts work together.
Our EPP elevons don't break and can bend with the wing protecting the hinge line.
Our years of combat have taught us to make the parts easy to get to and change.
Having quick access to the radio makes it so repairs take minutes not hours.
The plane is stronger and more crash resistant if there is no empty space in the wing.
I build and laminate the wing then go back and cut holes for the servos radio and batteries.
This helps me to judge the CG and get the parts in the right place.
It lets me cut the bare minimum amount of foam out of the wing making the wing stronger.
The radio and batteries become part of the structure of the wing.
I route wires though razor blade slits that cut through the tape and laminate and press in the wires.
I'm careful not to cut through reinforced tape and spars that are needed for strength.
I cover the slits with a clear piece of clear tape over the top.
I tape the receiver in place so I can see the power light and have easy access to bind to the transmitter.
If I have to replace a part, I pull off the tape, replace the part then replace the tape.
I glue the servo in the wing with a hot glue gun rather than gluing mounting brackets in the wing.
I stand the servo up with the servo arm barely exposed on the top of the wing.
I only put glue on the top edges and ends on the servo so I can get it out without cutting the foam.
The servo becomes part of the wing and is very solid without much work.
If I need to replace a servo I use my heat gun to soften the glue and replace the servo.
The pushrods are on the outside of the wing so they don't bind and are easier to install, inspect and service.
I put the pushrod under the servo arm to keep it close to the wing.
I put a staple over the middle of the push rod to keep it from bending and glue it in the wing.
Batteries are protected if the flat side of the battery faces forward rather than an end or edge.
The battery can withstand an extreme hit in this position without wire damage or mushrooming.
This does tend to leave the battery wire to ESC wire plugs on the top of the wing.
Having the battery wires exposed makes changing the batteries simple without weakening the plane.
Our years of combat have taught us to try to make repairs and battery changes as painless as possible.
We are still adding pictures and refining the details but the instructions are fairly complete and can be seen here.
It takes a lot to break one of our planes but it doesn't take a lot to fix one of our planes. Here are some tricks!!!!
If you wreck a combat plane
...... calm down, eat a sandwich, go to a movie. Do not start ripping off the tape a laminate! Secondary damage of a frantic repair can be worse than the primary damage. The EPP foam will return to it's original cut shape. Rarely is there wide spread damage. A surgeon doesn't rip off all of a patient's skin to fix a broken bone, he makes the smallest hole possible.
If there is a tear or several tears
..... gently pull the tear(s) open farther and use a glue gun at low temperature or gorilla glue or Goop to fill the tear and push it back together and let it set. Make only the smallest cut possible to get access and glue into the tear. decide if the tear needs structural reinforcement so it doesn't happen again. Put 6" strips of reinforced tape across the tear and put laminate over the top. Try to blend it in with the original build.
If the shock cord gets cut
..... It rarely will break but it is possible to get a prop cut that cuts the cord too. Apply a 6" strip of reinforced tape top and bottom over the cut and laminate over the reinforced tape to keep it from breaking down in the sun. Try to blend it in with the surrounding tape and appearance. This usually isn't hard if you are using the same tape and laminate as the original build.
If a spar is broken
..... do not rip out the old spar or start pulling off the tape and laminate. Take a soldering iron and melt a 12" slot through the old laminate and tape along the old spar with 6" on each side of the break and insert a new 12" spar and glue it in place. Place a piece of clear tape or laminate over the repair and no one will notice you even had to fix it. Total repair time, 15 minutes and very little secondary damage from tearing into the plane.
If the Formica is broken
..... and needs to be replaced (sometime you can just add a little glue and forget about it if the crack does not affect the flying or appearance of the plane) or you need access to a broken spar under the Formica cut the laminate and tape on 3 sides barely enough to uncover the Formica hold a hot iron on the Formica and wait until the hot glue releases and lift off the Formica and then do as little secondary damage as possible as you make the repair. This only works if you used a glue gun in the first place to glue the Formica. When the repair is done replace the Formica, iron the flap back down, a little spray adhesive may help and then put a patch of reinforced tape and laminate that blends in with the old surface. If you do this right it is almost invisible and only takes a half hour to make a major repair without ripping into the whole plane.