MarkD

I have been working on an enlarged version of the old Hot Kanary biplane , similar as to what was published in M.A.N. back in the mid 80's. ( 1500 sq. in)

Here is a pic of a 1/3 scale mock-up made from cardboard and CAD plans.

Some people have been telling me that the plane is too " short coupled"

My question is how do you determine this? What is the technical definition of a plane's "moments"

The distance from the cg ( Leading edge of top wing ) all the way to the front tip of the spinner is 22.3 in. ( about 18" to the prop )

The distance from the CG to the approximate center of the horizontal stab is 37.4 inches.

Any thoughts appreciated.

Mark D

jneesy

a good example of a short coupled plane is a pitts special dont know the technicalities but it has to do with the length of the fuselage behind the wing but your design doesnt look too short to me

Johng

My Feedback: (4)

Think in terms of wingspan - or more conveniently, half-span. Generally, at least in my mind, if the tail is about as far from the CG as the wingtip is, that's a "normal" tail length. Much shorter than that, and you would call it short-coupled. It's pitch response will be quick. Longer than that makes for a very "groovy" plane that tracks well.

Scar

My Feedback: (3)

As Johng indicated, the "short coupled" plane will be very responsive in pitch. Some would call that "very agile". Some might call it "unstable", which is probably what your friends meant when they called the Hot Canary "too short coupled."

If you're accustomed to building and flying agile, aerobatic planes, you'll love this one. If you are not, you will find it "too short coupled" too.

Good luck!
Dave Olson

MarkD

Thanks to all for your input.!!

JohnG: If we go by your method it actualy works out to be a bit "long" coupled. The WS is 55" , so the ratio would work out as 37.4/(55/2) or 1.36 to 1.

There seems to be something about the reverse stagger that at first glance seems to tell the eye something doesn't look right.

I kept most of the outlines used in the magazine plan, but I did give it much more conventionaly shaped tail feathers. The rudder/fin is also larger in area, as I want to put in a 50 or 60 cc ZDZ instead of the original Zenoah G38. I did have to move the firewall forward a bit to account for the lighter modern engines and the aft mounted elevator servos. The original fuselage design used a rather complex combinations of longerons, sheet fuselage sides and a lot of balsa infill. I redrew mine to use sheet balsa sides with a skeletonized ply doubler, as is so common today.

If I can keep the weight down to 15-15.5 lbs, the wingloading will be about 24 oz/ft. The airfoil is a NACA 0016, so it should be fairly tame at slow speed.


Thanks,

MarkD

Johng

My Feedback: (4)

Yeah, I didn't think it looked like a "too short" tail. I think it looks pretty good. The little dorsal fin has a way of masking how long the fuse is too. And chopping the wings in half and stacking them probably modifies my little rule of thumb a bit. I would guess you are at a good length.

CrazyHerb

My Feedback: (1)

Cool design...I like the modern tail on it....

Build it!!!

I might do something like that outta foam for a Ryobi!!

CrazyHerb