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Un-flyable FT Cruiser

Toownky

Junior Member
#1
Hi everyone,
I already built an FT Explorer and everything went fine, the plane flies great.
I tried the FT Cruiser for my second build. A nice looking twin engine, how should I not be tempted :p

So, I balanced the plane before maiden flight, using a 2200mAh (260g). Everything seems OK, but the plane instantly flip over (nose up) as soon as I increase a little bit the throttle. It behave as it was very very very tail heavy.

Second try with a 5000mAh battery (470g. maybe a bit excessive :D). The plane is - obviously - unbalanced, crazy nose heavy when using the CG marks. It does not really solve the problem, but at least I can more or less fly it...

I checked everything I can. Wings profile seems OK, tail is straight, control surfaces are properly aligned. The only modifications I did : added BBQ Skewer to the tail (same as FT explorer), and gave the plane a nice colored look using 45mic wing tape.

I desperately need some help here ! Any idea of what I could have done wrong ?

IMG_20160204_210216130.jpg
 

ofiesens2

Professional noob
#3
I think they added some angle of incidence/thrust angle to the nacelles on the wings. Are you sure that it has been implemented properly? Bixler mentioned in the review episode that the plane wanted to pitch up before they added the down thrust angle.
 

makattack

Winter is coming
Moderator
Mentor
#4
Agreed, it sounds like if the engine nacelle doesn't have that little rectangle of foam that tilts the power pod down a bit, that might explain it. It's only one foamboard thickness, so it's not hard to add in. It goes the width of the nacelle and is maybe an inch long.

With my build, a 2200mAh battery has to be pretty much all the way up in the nose for it to balance out.
 

Toownky

Junior Member
#5
I forgot to mention the "spacers" but yeah, they are installed and I double checked they in the correct position :)
Also tried to hand launch the plane and it does not glide very well (the thing is quite heavy), the nose does pitch up if I throw too hard.
 

ofiesens2

Professional noob
#6
It really just sounds like a CG issue. Maybe for now, disregard the FT CG marks and experiment with your own. In general, the CG will be in front of the center of lift, which in this case is the point of the airfoil with the highest camber width.

Note*** I am not to be held criminally responsible for and accidents that come out of playing with the CG :p
 

Toownky

Junior Member
#7
Best results so far are with a 5000mAh battery, all the way up to the front, and another 2200mAh battery stripped to the first one, just used as a ballast :( The CG point is now in forward the wing leading edge, there's definitely a problem somewhere ;)

I can "fly" the plane, but it requires all my (not so great) skills to just keep it in the air. Not very fun.

Maybe I'll build another one, veeeerrrrryy carefully just to make sure. Too bad, the Halloween livery is really nice to see in the sky !
 

Bayboos

Active member
#8
Don't give up so fast, just give us more to work with. Some pictures from the front and from the side (so we can check the surfaces), control surfaces neutral positions, etc. would be very nice. And of course, if you are capable of flying the plane, a video of the flight may help as well. You may also want to check if there isn't any mix added "by accident" (e.g. by using the same program for the Explorer and the Cruiser) to your Tx/Rx of choice, adding up elevator when you increase the throttle. Also, check if the fuselage/wings are stiff enough (too much thrust with too little stiffness may cause the motors to "pitch up" when adding power). I personally did have a similar problem when the firewall partially detached from the pod - it was still held in place by the tape, but it was moving a tiny bit - enough to mess up the trim.
 

Toownky

Junior Member
#9
I don't have the plane right now, but I'll definitely take pictures if it can help.

The radio profile has been carefully checked too, configured from scratch. I configured a switch to change between differential thrust mix settings (no differential, 30%, and 100% for crazy mode), but no "strange" mixing.

Wings seems stiff enough, no significant bending "by hand", nor visible one in flight. After a little "accident" with my explorer, I added a carbon tube in both the explorer and the cruiser, glued to the spars.

I'll check the power pods for any play, thanks for the advise !
 
#10
It does sound very much like an offset thrust angle problem. And, as mentioned, it could be a matter of flex rather than misalignment; I've had similar issues when I was flying with a post-crash partially-detached firewall (that shifted position as thrust increased).

Moving and/or reinforcing the engine nacelles would be the best way to fix such a problem, but in the short term you could potentially deal with it by mixing a bit of down elevator into the throttle.

I'd also be inclined to shift the CG back to the FT default once you've got it fixed. If we're right about the thrust angle thing, the CG was not to blame.