RK,
You didn’t pick an easy one, did you?
If I have the plane right, the deBolt Sportwing is a forward-swept flying wing. Flying wings are generally more critical on CG location. I don’t think the Sportwing uses wing twist to increase the pitch stability, so I suspect it will be more sensitive, as well. And I doubt it has reflex, which is the other way to get stability—but I wouldn’t use reflex on a plane I expected to fly inverted. Anyway, the fundamental rule of landing gear location regardless of type is that you put where the CG demands that it go.
There are some rules of thumb for tricycle gear that have been borne out by detailed calculations for full scale aircraft:
1. The fore and aft location of the main wheels is always behind the CG by a bit more than the maximum angle of attack during landing at the minimum airspeed. Just think of this as the stall AOA, plus an additional angle for stability. The stability angle varies, but assume something like 5 to 25 degrees for a model. More on this below.
2. The gear length matters. Not just that it has to be long enough for prop clearance, but also has to provide the right static inclination, or “stance.” If the stance is negative, ie. nose down, then the elevator has to work harder to “unstick” the nose gear for rotation. If the elevator effectiveness is low, or low at low speeds, it will be going pretty good before you can rotate. So shoot for level or slightly nose high. The issue with a flying wing would be that if the setup demands a lot of elevator to rotate, it could get real exciting the instant after the nosewheel unsticks.
3. If you use a larger stability angle on the mains, it will also take more elevator authority to rotate. So using a large angle, which sounds good at first, has consequences. For a wing, I would suggest going with a very small stability angle—say 5-10 degrees—and then incorporating a tail skid. Airliners all have tailskids so there’s no shame it putting one on a Tri-gear Sportwing.
4. Because it is a flying wing, and CG at takeoff will be critical, I would absolutely do your calculations using a full fuel tank. Takeoff will be the tough requirement, so tank is full.
5. As far as the lateral separation of the mains, something around 40 degrees relative to the fuselage centerline, with the apex at the contact point of the nosewheel should work fine.
6. Put the nose wheel as far forward as you can since this is a flying wing and pretty stubby. Normally, the nose wheel should take about 5-15% of the static load. Too much and the plane tends to “wheelbarrow” and lose directional stability. Wider mains helps this a lot. If this concept doesn’t make sense, think about tongue weight on a trailer. It is not really the same problem, but you can see that weight distribution on three point wheeled vehicles matters.
So just take the plan sideview, decide where you are going to put the CG, and draw in the angles to locate your gear.
I had an interesting time with a monowheel flying wing. If the wheel was not in exactly the right spot, it was virtually impossible to take off. This was a plank wing. I don’t recall if it had any washout or not. The plane flew great once airborne and was not squirrelly—implying that the CG was well located, and the elevators were sufficiently effective for flight. But if the wheel was moved back just a bit—say if the gear bent during landing—it was next to impossible to take off.
I hope this helps. You have a fun project going, and I would definitely give the tricycle gear a shot. You might make it adjustable if you can.
Good luck,
Dave
PS—The only trike gear model plans that I have laying around are for the old Jetco Sabre Stunt. It is pretty short-coupled for a stunt plane (going to be similar to your situation), and the gear is only 8-1/4” apart, fore and aft. The mains are 40 degrees behind the CG. This is the contact point for the wheel, not the axle.
PPS--I think your mains are going to be almost directly below the forward edge of the trailing edge spar. I'd beef it up with a full length strip of 1/8 aircraft ply. Probably sew a one-piece wire to it with Spectra fishing line. Give you a torsion gear. The side view layout with the angles will tell you if you need to cant the gear either forward or aft.