While the EXP series' performance is what sets them apart from the rest, not everyone sees the engineering that went into making them such superior airframes. A lot of it is hidden under the cowling, canopy, and covering. Certainly sound aerodynamics come into play, but there is much more. EXPs feature revolutionary composite reinforcing of critical areas, and even employ some old principles to gain strength while saving weight.
When designing the EXP series, nothing was discounted as a way of improving the finished planes. One example is the extensive use of reasonably priced (compared to carbon) G10 composite material. There are times you need low weight and strength, but expensive carbon is not necessary. For these applications, Extreme Flight saved weight and money while sacrificing nothing to make the planes stronger and more rigid.
I've been flying the EXP series planes for about a year, and exclusively since about March. It has taken almost all of that time to go completely through the planes to discover all of the little things we are going to talk about, and I am not sure I have yet found everything!
Motor box Re-enforcing
This had to be the strongest part of the airplane for a lot of reasons. First, it gets torqued constantly, and takes a lot of abuse in prop strikes, out of balance props, etc. You also want the entire assembly to be as rigid as you can get it so the power is transferred to the propeller instead of being wasted flexing the motor box.
As you can see, the front of the motor box is reinforced with strong lightweight G10 composite material. This is the area where a a lot of motor box failures occur..... right behind the firewall. The face of the firewall itself is also covered in G10. This keeps the X mount from denting in the firewall if you over tighten it, like happens with bare wood, and avoids unwanted thrust angle changes
Extreme Flight solved a few big problems with it's carbon rod reinforcement of their motor box. As you can seem it is braced top and bottom. This makes the whole unit extremely rigid, which is what you need to get the maximum energy going from the motor.
Notice the carbon rods are mounted to thick plates that are extensions of the firewall and landing gear plate. The top rods anchor at the rear right into the first former. These are the most solid and rigid attachment points on the plane. They are also backed by strong G10 composite material. This is one stout assembly!
To achieve rigidity, most motor boxes extend way back into the battery compartment, and this can interfere with changing out the battery. On EXPs the motor box sides stop right at about the rear of the front former. This allows a very generous space for the battery, and there are no motor box sides to interfere with strapping the pack in. You don't have to struggle to change out the pack....just drop it in where you want it! Notice how the battery, strap, and deans plug are all right out in the open where you can easily get to them.
Extreme Flight has Incorporated several ingenious solutions to motor and ESCs cooling. Since everything is air cooled, the obvious answer is more air, though these are a few novel solutions for how to move it about where it is needed. First are the cooling baffles that come with the kit. Since we are flying scale aerobatic planes that have air openings on each side of the spinner, it makes sense to channel that air to the motor, which is exactly what the baffles do. They assemble with very little effort and do the job as simply as possible, which is always the best solution.
Notice the holes in the firewall. The one in the middle is for the collar on the motor shaft to stick through, but the other four line up perfectly with the exit holes on the back of the Torque 2814 motor. The baffles channel the air into the motor, it flows unrestricted out the back and through the holes in the firewall. My Torque motors have consistently run 10-15 degrees cooler in the EXP series planes than any other plane I have flown them in.
The next photo is a rear view of the firewall. Here you can plainly see through the firewall and into the back of the motor and it's windings. This is where the air exits the motor completely unrestricted, and this is why Torque motors run so cool in these planes.
The power system for EXP series planes are part of a totally integrated package. The EXPs were designed around these motors, which is why that is all I will run in them.
More Composite Goodies
We've all ruined at least one 3D plane by pulling a weak landing gear mount out. This seems to be the Achilles' heel of a lot of otherwise nice airplanes. Extreme Flight addressed this by putting in a huge G10 composite landing gear block. You can see it in the photo just under the battery tray. The plate keys into the three formers, making the entire structure extremely durable.
Notice the G10 composite plate extends past the front LG support former all the way to the first former, and keys into that former. This not only gives the landing gear mounts more support, but it stiffens the entire front of the airplane.
In most big impacts, the carbon landing gear will take the impact and flex enough to ward off any damage. If you really pile it in, the gear will again take the abuse and fail, usually saving the airframe from any damage. Of course, you can break anything if you hit hard enough and the right way, but it is hard to imagine any other plane on the market could take this...........
When you look a little deeper, you will see that even with extensive use of G10 composite, there is still a lot of carbon fiber in these planes. Carbon rods run from the first former all the way back to just ahead of the stabilizer. The next photo is the Extra, and you can see the turtle deck also has a rod running along each side. This is presumably because Daniel Holman uses this location to catch and release his planes!
There are also carbon rods running the length of the fuse along the bottom corner, and another just above that. since they are so hard to see against the black covering, I have drawn in some red arrows to highlight their location.
Also reinforced are the wing tube mounts, another critical area. Notice too the dual carbon anti-rotation pins on the wings. Also, at at the last former visible in this picture, the fuselage is braced by yet another carbon rod. The more you look through these planes, the more expensive carbon and G10 lightweight material you will find. You will see lots of bragging about the use of composites in other manufacturer's advertisements, but Extreme Flight just puts them in the plane and acts like that's how an elite airframe should be built..... because it is.
With the kind of throw we demand from our 3D planes, the standard servo arms are generally not long enough. Extreme flight again turns to G10 composite for the answer. The solution is a simple extension that slides over the back of the standard servo arm, and secures with a single screw and a little cyanoacrylate glue. Being a bit obsessive, I used two screws, but you can certainly see what a neat and tidy looking item it is. It is simple, and elegant, like the rest of the airplane.
On problem we have had with 3D style planes from the beginning has been getting enough movement in the control surfaces without having a huge gap in the hinge line. A big gap gives you poor control response (especially at low speed), and can contribute to serious, plane destroying high speed control surface flutter. A big gap is bad, but until now there has not been a good solution to avoid it and still have enough movement.
Extreme Flight addresses this with deep bevels in the leading edge of the control surfaces, and in the trailing edges of the flying surfaces. You will see this on some larger planes, but this is the first time this technique has been applied to a plane in this smaller size.
Because I build my EXPs as soon as I get them, I don't have a picture of an unassembled elevator and stabilizer, but here you can plainly see the deep bevels. Also visible is how tight of a hinge gap you can get with these planes.
I generally seal all my control surface gaps with clear Monokote, but on one of my EXPs I forgot and only discovered my mistake 100 or so flights down the road. You don't need to seal the gaps on these planes, but I will still do it because I always have, and this way as far as the air is concerned, there is zero gap.
With the EXP's beveled surfaces, I can get nearly a full 90 degrees of throw out of the elevator. The Extra EXP below measured out at 88 degrees, but only because that is all the servo had. There was still enough movement left in the surface to get the full 90 if I wanted to use a longer arm. Still, I think 88 degrees is probably enough.
Another innovation in this size plane is a very old technique that dates back to the flying wires on WWI biplanes, geodetic construction. This is an extremely lightweight method, yet incredibly strong and rigid. Because this construction is so rigid, you are much less likely to have a control surface warp on you.
The EXP's stabilizer, elevators, and rudder are all made this way to save weight in the tail without giving up any stiffness or durability. This is a very labor intensive and expensive method of building a plane, but nothing has been compromised on the EXP series.
Below is the elevator of my beloved original MXS EXP.....
One little departure from conventional geodetic construction is the little brace that bridges the leading edge of the elevator and the counterbalance. This is an area that is very vulnerable to snagging on high grass, runway edges, etc. You can really tear an elevator up if you catch it on the ground the wrong way, but Extreme Flight has beefed the structure up considerably here.
I caught my elevator in the grass when I blew a harrier turn and broke the counterbalance. With the geodetic construction, it amazingly popped right back into place, and I was able to glue the break simply by injecting some CA in there, through the covering, with a diabetic hypodermic syringe. A little heat with the trim iron, and the hole made by the needle closed up. You could not even tell the elevator was ever broken. It is these kind of things that used to make me crazy, but the repair came out so good that I actually forgot about it.
On another MXS, while transporting, my flight box fell over on the elevator and smashed it up really good. I fixed this by removing the covering on the bottom (where repairs show the least) , pressed everything back were it belonged, CAed it, covered it up. Good as new.
Form my experience so far. I have been able to make these repairs simply because they sustained so little damage in incidents that you have probably ruined elevators and stabs on other planes.
One of the things I have found infuriating is how easily you can damage a canopy simply if you are a little careless putting it on the airplane. The rear edge takes the beating almost every time, and on most planes it's thin plastic anyway. Especially vulnerable is the bottom rear corner of the canopy because that's where it touches down. If you get it a little crooked you can fold that corner right under, and most times that's all it takes to fatigue enough that it later frays or breaks off all together. I've seen a few canopies where the whole back edge was all chipped up and jagged.
Now, granted, I am a bit persnickety about little details like this, but it is little details that set the EXP series so far apart from other planes. The EXP canopies are thicker and tougher than most other canopies anyway, but there is more.
Working on a new Edge EXP yesterday I made a little discovery. The inside of the canopy on the bottom rear corner is reinforced with strong, lightweight G10 composite material! As long as the Edge has been out, no one has ever brought this up because it is such a small little detail. I might just be the first person who has ever noticed it, but clearly this is the kind of attention to detail that Extreme flight puts into every one of it's products. Little things like this give you a quality product that will hold up to daily use, and maybe even some unintended abuse.
There is nothing really innovative here except wood working principles that have been proven over the centuries. This is an SFG that I recovered. You will notice how all the joints are notched and keyed. This gives you the largest amount of wood to wood glued surface, and an incredibly strong bond, all while making a surprisingly light structure.
You can tell from the direction the wood grain runs that Extreme Flight was going for maximum rigidity. Any rigid flying surface is going to flex less, and be more effective.
SFGs are mostly an after thought for some airframe manufacturers, but for Extreme Flight it is another place where solid engineering and superior build quality makes a difference in the flying.
The big details set the EXPs apart from the rest of what's available, but the little things like this make just as big of a difference. Thing is, the EXPs are full of little things like this. I am sure I missed a detail or two, or maybe even haven't discovered them all yet, so I fully expect to be adding to this report in the future. You just have to look at how well things are thought out on these planes and these things will start jumping out at you.
Finally, no blog report would be complete without some sort of video. Below is a compilation of some previous footage that showcases how all this attention to little details adds up to so much performance.