I promised to post something about the DoubleEnder prototype, so here it is:
This idea started to go on paper about 3 years ago. To come up with the actual concept took several years of imagination and research prior to that. The concept originated from several ideas. I've been flying cubs for a long time and like what you can do with them, but what can be improved upon? Performance, handling, visibility and safety were some of the driving factors.
The visibility idea came from another airplane, the Partenavia P68 Observer. It's a twin engine six seater and has a bubble canopy up front. Flying in it is a lot of fun due to the extreme visibility. Visibility in a cub is such an important factor for landing off airport. Then add the performance you can get with slats at high angles of attack, but that you cannot use practically in a cub since you can't see where you're going ... and all of a sudden the bubble canopy starts to make a lot of sense. Other than the usefulness in landing and taxiing off airport, it is also a thrill to be able to see so much, right down to between your feet. It's a whole different perspective.
The need for safety is quite obvious. One of the biggest contributing factors to accidents in a cub is a low to the ground stall/spin. The slats increase that safety margin by a lot, and give it the low speed maneouverability that is just not available without it. There's also many places I like to fly over (low), where no matter how quickly you may react, if that engine quits it's going to be an ugly day. Sometimes on long cross country's I end up taking detours just to be able to keep a safe landing spot below (highways, avoiding long stretches of water etc.) Wouldn't it be nice not to have to worry about such things? Wouldn't it be nice to be able to lose an engine, and have it be a non event where you just add some power and keep going to your destination. Wouldn't it be nice to be able to just push the direct button on the gps and fly straight to where you're going without concern of the terrain below. Hence the need for twin engine. The other safety requirement is to have a good "crash cell" around you in case of a mishap. The fuselage and engine mounts were designed to withstand some pretty strong impacts. We also incorporated a front crush cell in case of frontal impact, in order to have some buffer before getting into the main structure.
I was hoping to have something that could fly with a cub and perform somewhat like it. It wasn't designed to be a hot-rod airplane in the first place, but somewhere along the line it ended up in that category. I like the way a cub "feels", and I was hoping to somewhat retain that. The wings and tail surfaces were left identical to a cub, and even the relative positions remained the same. The gear and wing struts are also off a cub, and in the same relative position. You could swap wings, tail-feathers, gear, and struts with a cub and it would fit right on. This was also done for ease of parts availability. I incorporated a cg that was further aft than a cub, since a cub flies better with some weight in the back, and you're able to get on the brakes a lot harder. The neat part is when you have a passenger there is almost no effect on cg since the seat is located very close to the center of cg.
The performance comes from a combination of wing mods, cg, lots of power, and the fact that you are able to use high angles of attack and still see where you're going.
The push-pull setup came from the requirement of control at very slow speeds with a single engine failure. This airplane can fly in the 20's when hanging on the slat, and an engine failure with a standard configuration twin would just make the airplane yaw and lose control at those low speeds. Add to that the places where this airplane is meant to fly and land, and a slight deviation off course could end up real bad in certain scenarios.
The project came to completion with basically a three man team. I initially came up with the design and concept. I then linked up with Doug Keller (ksecub on this site), who did all the structural engineering and analysis, as well as the canopy, in 3D CAD. Doug has a lot of experience building experimental cubs and was the man behind the Husky Cub, the Carbon Cub prototype, and his current hot-rod cub (which is a hell of a performer). He's also done engineering work in the past for Sherpa and Cubcrafters. The blueprints were then handed over to Eric Lewis who built it. Eric used to work for Sherpa and was Byron Root's right hand man. He built some of the Sherpa prototypes.
A few years later, the DoubleEnder was finally ready to fly (that was in March 2010). I got to be the test pilot, and I'll spare you all the details, but there's been some very exciting times at first! Since then, we've been constantly tweaking and modifying certain things on it.
It flies really well. It actually exceeded my expectations as far as performance and feel. The performance is right up there with some of the lightweight or hot-rod cubs. And it still "feels" similar to a cub. If you're used to a cub, you'd feel right at home in this thing. Also all the control placements in the cockpit were kept identical to a cub in order to maintain that familiar feel we all like. It was a pleasant finding to have relatively no negative aerodynamic issues. Most of the problems we encountered came from the powerplants (such as engine cooling issues, fuel system, proper exhaust configuration etc). Even though we are still fighting some of those issues, it's easier to tackle than aerodynamic problems.
This airplane is far from being close to its final form. It was meant to be a proof of concept, and now that we know it works well, we are refining it, and going the extra length to make the design even better. We still have a lot of things in the works.
Here's some of the features of this airplane as it is today:
- 2 Rotax 914 (turbocharged 115hp each) (no mixture or carb heat controls needed) (premium or avgas)
- Custom built exhaust and relocated turbo on the front engine
- Independant fuel system for each engine
- Warpdrive 72 inch 3 blade propellers (ground adjustable)
- 12 inch heavy duty extended gear
- soon to have a set of extra long and reinforced AOSS's
- 35 inch Bushwheels + tailwheel
- Dakota cub squared off wings
- Cubcrafters 2300 lb wing reinforcements
- 25 gallon fuel tanks
- Heavy Duty Wing Struts
- Equal length flaps and ailerons, both with 2 inch extended chord
- Wayne Mackey's slat and selectable drooping aileron system
- VG's located behind the slat
- Roll control spoilers linked to the aileron, located behind the slat, similar to a Helio Courrier
- 3 inch extended elevator and rudder
Of course, none of this would of been possible without our used car salesman Mike Olson. He gave us the redneck influence and support that was required throughout. Mike has been nominated our exclusive dealer and is in charge of providing information and sales. Please contact him directly for further information, he'll be glad to be of assistance.
Here's a few pictures, there's some more in my gallery ...