FT-Cruiser Issue, please help!

[Exhodus]

Hi Everyone,

I'd like to ask for help with "debugging" my Cruiser, I've spent a good amount of time building it and it came up very nicely, but somehow it wants to lift its nose and Im out of ideas why...
Even if I hold it in my hand as I throttle up the nose starts to rise up to vertical and contines want to turn on its back all this with zero airspeed

Its not a CG I've double checked it, even moved it to be a bit noseheavy, second thought was the motor angle, so I changed it, now the motors are visibly pointing down, the issue still persists...

My last idea is the wings angle of attack, its around 3 degrees positive but it shouldn't matter when the plane is in my hand does it?

Any suggestions?

 

[FlyingMonkey]

Well, yeah it will matter to some degree. The propellers will cause a rise, and that's why many airframes have what you'll see referred to as "down and right" angle built into the firewall.

This is to counteract the tendency to pull up and to the left. There's a Flite Test episode where they show you how to mix some down thrust into the throttle to help with this pitching that occurs when you apply more throttle.

 

[FlyingMonkey]

 

[earthsciteach]

One way to know if it is the thrust angle is to take it up and cut throttle. If it comes down in a gentle glide, you need more down thrust.

The angle of incidence of the horizontal stabilizer can contribute to the pitching up of the plane, as well.

That is a great looking FT Cruiser, by the way!

 

[Exhodus]

Thanks Guys!

About the mixing, I really want to avoid that, this airframe should not need such underhanded tricks its designed better than that I believe! Also what I know about the theory of aviation, with a mid mounted wing, and the trust line so close to the cord line it "theoretically" would need very small downtrust, and I already gave it a lot! Granted I did not testfly with the added downtrust yet, because it still wants to turn for the ceiling in my hands so Im looking for possible causes.
On its first flight, (it had positive angle in the motors than, so uptrust) it pulled into vertical right after liftoff and had it fall from around 3 meters almost vertically.... luckily I managed to pull it to horizontal positon and cut the throttle so basically no damage

About the incidence of the horizontal stab, I measured the incidence of the wing to the h-stab, so the wing is +3deg with the h-stab being 0

Thanks for the compliment

 

[Liemavick]

What KV motors are you using? Are the props true counter rotating or is one flipped? Just curiosity more then a solution.

 

[aiidanwings]

This plane needs considerable down thrust. I don't know what the rule is, but I've always started by aiming the thrust to a point halfway between the far edge of the wing (from the motor) and a point above/below the wing equal to the vertical distance of the wing to the motor center line.

Edit- Thrust pitch/roll issues can also indicate the prop is too large for the airframe.

 

[Exhodus]

Thx aiidanwings! The oversized prop issue is new for me, it could be useful, as I plan to use a big prop on my new power pod for my other planes!

Sadly thats not the problem here, this plane has two identical 1650kv Turnigy outrunners with 7x4 3 bladed props on each, one of the props is counter rotating, and they are set up so they are rotating towards the fuse

 

[Exhodus]

Been through a new testflight, the nose up attitude lessend, a lot, but still there.. so I guess I'll add even more downtrust.
Sadly the plane had a bad tendency to pull to the left, so much actually that it took full aileron deflection to counter act it, but when the wind helped in to the left the plane pretty much went out of control and crashed, tried my best to lessen the crash and it happend in tall grass, so it will only need a nosejob.

 

[Jaxx]

Exhodus,

It may be a thrust angle issue. I think I remember Josh B. talking about the thrust angle issue he had to resolve when test flying the prototype for this swappable. Take a look at the following links:

http://flitetest.com/articles/Thrust_Angle

http://flitetest.com/articles/Motor_Thrust_Angles_Down_and_to_the_Right_Why_