Thust Line Question for pushers
 

Let's talk Zagi 400X.

Of course, most of us know it has a tray with a built-in thrust angle as well as a vertical offset for the motor. On my maiden voyage, I crashed hard and ripped the motor from the tray; it was toast. From there on out, I discarded the tray entirely and used the "5 minute motor mount" mentioned on www.yourzagi.com. (greetz!)

After trashing a Wingwarrior Raider panel set, I recently rebuilt the actual Zagi 400X airframe. Worn out from zip ties, I epoxied a plywood transom to the TE. The motor sits directly on it with no shims (lazy). The motor now has a thrust angle parallel to the TE of the airframe. The original Zagi400X thrust angle is negative (pitched nose down vs the chord line) and sat up a bit higher in the tray.

Nowadays, altitude gain is very difficult. Airspeed is always borderline stall. I've tried many variables. I truly suspect my problem to be thrust angle yet there is VERY LITTLE documentation about this critical metric.

My question is- where is the optimal thrust line? Does it have to do with the CG? Does it have to do with the chord line? Can this advice be applied to other airfoils?

Thanks in advance :)

RE: Thust Line Question for pushers
 

Thrust lines major influence is the cg. With a pusher mounted above the cg the plane wants to go nose down. The bigger the difference the higher the moment. The props pointed up to push the back of the wing down. It's more effective to lower the motor or raise the cg.

Mike

RE: Thrust Line Question for pushers
 

Mike-

Yes. When the motor/prop is not shooting directly thru the CG, then it has a torque effect about the CG.

Wouldn't it be more efficient to shoot the motor's rotational axis thru the CG of the plane? That way it never tends to pitch the craft...

[&:]

RE: Thrust Line Question for pushers
 

Mostly it's a balancing act and with most electrics getting the cg on the thrust line is difficult due to the weight of the batteries. A flying wing needs reflex to fly, that can be minimized with the proper thrust angles/cg location. My Elipstik has a modified cg and thrust line. Reflex is minimized and it flies inverted hands off.

Mike

RE: Thrust Line Question for pushers
 

ok now an easy answer. put your zagi on a flat surface, such as your table. squat down and eyeball your zagi from the side view. the motor should be parallel to the table. my home built zagi's fly perfect using this technique, of course you'll have to trim your controls for your virgin flight.