Ken …. I remember now the history of this picture. The plane had been hanging in the garage in a slightly damaged condition, when I quickly put masking tape on the canard and dropped an arbitrary ST60 into the mounts just so I could take a picture of it. As flown the plane had a reverse ST60, fitted with a regular tractor prop,…. Put on backwards. That gave me a pusher.
This airplane design, which I’ve been meaning to start a thread about, is based on the desire to have high rotation rate with maximum damping. The swept wing, like we said above, had the benefit of higher damping than a straight wing and I could mount the power in the crotch of the trailing edge and have weight concentrated near the cg. Lower pitch moment of inertial. Lower pitch inertial potentially yields faster rotation rate, and better damping.
The canard configuration also is something that modelers keep trying to make work in a stunt ship. In theory the canard could be a two pronged benefit for stunt design. The canard essentially doubles the Cmq or damping due to pitch rate. It also reduces Cm.alpha. A low Cm.alpha promotes a quicker response to control inputs. Quick response and robust damping as the controls are fixed.
The history of the test flights (2) of this plane is worthy of discussion on this thread, and is germane to the topics of swept wings, stability, and locating a/c aerodynamic center (neutral point).
As I said, the plane had two flights total. As you can see, mounted on the canard surface is a SuperTigre muffler. This was for the first flighs. It was stuffed with lead. Like, a bunch of lead. I had no idea where the c.g. of the airplane should be. I tried calculating where the NP was, but like Serge is finding out, I didn’t really trust the numbers I was getting. So … I added a bunch of nose weight to be safe for the first flight.
It flew ….. not too bad for a first flight …. It had a blinding corner and wasn’t really twitchy in level flight, It came out of the blinding corners flat and stable, and It did glide relatively well to a landing.
Second flight ….. lets take out some nose weight ….. how much? I dono … maybe half of what’s in there? …… OK. Takeoff … good enough. Maneuvers in flight still outstanding. Blinding, after having removed nose weight. Motors getting ready to quit ….. gain a little height so I can see the glide tendencies.
The motor quits …… the plane cones to a dead stop instantly, 24 feet up in the air. It immediately, I mean immediately, flips over inverted and spirals gently down to the ground like a leaf. If it was unstable why did it fly? When the motor quit it became severely unstable. What happened?
The conclusion is that with the motor running, increased velocity over the tailplane due to the prop wash, was enough to provide stability. As soon as the motor stopped, the velocity on the tail fell, the “effectiveness” of the tail was reduced and the plane was no longer stable. The application of this to “normal” designs is that the tail area close to the propwash is more effective than that out at the tips of the stab/elevator. Low aspect ratio tails may be good (as we’ve found to be true).
I will close by saying what Brett always recommends .... you can measure and calculate all you want, but it really comes down to flight test and how it feels and performs.