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FT Sea Otter troubles

#1
Hey everyone! After reading at this forum for years here is my first post!

I just build a Sea Otter but I'm having an hard time making it fly. It just wants to dive nose down, despite of the full back on the elevator, so right after launching it, it dives in the grass. The CG is 70mm after the leading edge, as "prescribed" in the plans. Now I'm playing around with the motor angle, tilting it up like a bixler, but it still has the same attitude.
I'm missing something here, with that motor mounted high up, it just makes the airplane tilt. Honestly I'm completely lost here:)

any tips will be greatly appreceated, I really want to fly this plane!
 

Ketchup

4s mini mustang
#2
First off, welcome to the forums! I have never flown a sea otter, but I know some ways in which you could find out what the problem is. You should try a glide test with the plane, just throw it without throttle. If the plane glides straight then your problem is because of thrust, and if it doesn’t then your problem is because of something else like cg. Also, check to see if your elevator is moving in the right direction (when the elevator goes up the plane should go up).
 

Hondo76251

Well-known member
#3
Are you hand throwing it?

This can be tricky due to the low airspeed of a hand launch, especially in a bird with a high mounted engine (ie: if your wings aren't making lift, and your motor is producing thrust it can be a fast ride to the ground and there isn't much the elevator can do about it)
 

Sero

Well-known member
#4
Peter says in the video on this plane that thrust angle isn't needed as the tail is directly in the prop wash which help keeps it straight.
As Hondo points out the wings don't have any prop wash and therefor no artificial lift when launching. I would make sure I have enough elevator throw and all the controls are going in the right direction. Then when launching give it a bit more throttle and a harder toss. Also most water planes you can use grass as a runway and just take off as if you had wheels.
 
#5
Hej everyone! Sorry if I haven't replyed but I've been away from the hobby for a while... I manage to solve the problem! First, I increased the elevator throw as suggested by Sero, and then I researched a bit about the CG... The thing is that in the build page of the Otter they reccomend the CG to be 70mm from the leading edge, wich it makes it incredibly tail heavy! In another video though (don't remeber wich one) they recommend for the CG to be between 1,75 and 2 inches if I'm not wrong. Now she flies sooo good! And glides greatly even if the whole build is quite heavy.
Thanks every one for the help!
 
#7
Hej everyone! Sorry if I haven't replyed but I've been away from the hobby for a while... I manage to solve the problem! First, I increased the elevator throw as suggested by Sero, and then I researched a bit about the CG... The thing is that in the build page of the Otter they reccomend the CG to be 70mm from the leading edge, wich it makes it incredibly tail heavy! In another video though (don't remeber wich one) they recommend for the CG to be between 1,75 and 2 inches if I'm not wrong. Now she flies sooo good! And glides greatly even if the whole build is quite heavy.
Thanks every one for the help!
I'm glad I saw this thread before trying to maiden my freshly built Otter. The plans have the CG at 2.5" from the leading edge on both the templates and the the cover sheet. Peter mentions in the build video that it should be 1.75" - 2.00", and then even mentions as close as 1.50" for new pilots. That's a BIG difference! Glad to hear you got it sorted out, hopefully it will go smoothly for me also. I've never flown off water before, this should be interesting. Attached is a pic of mine. IMG_1827.jpg