Help! Help needed regards the optimum thrust angles for the Sea Otter

[TheFlyingBrit]

I have had 3 un-successful flights with my Sea Otter, the first two where due to lack of power and vertical thrust angle. I replaced the original motor and gave the motor slightly more up thrust, which appeared to do the trick. However the third flight resulted in a spiral dive which has resulted in a full front end re-build. I have since found a damaged aileron hinge, which could have been a contributing factor, or just a consequence of the crash.
I have finally got around to the repair and realised the side thrust angle appears quite excessive, compared to another Sea Otter I was watching on You Tube.

I was wondering if anyone on the forum who has built and flew one of these planes, could provide an optimal side thrust angle. Ideally based on the angle of deflection from the center line of the nacelle ?
I would also be interested to find out if I have my up thrust is correct too. However, that might be a bit harder to measure as there may be some slight variation in nacelle angle from model to model (depending how it was built). One option would be to use the rear fuselage top face as a datum point.
Any help would be appreciated.

 

[Monte.C]

I have had 3 un-successful flights with my Sea Otter, the first two where due to lack of power and vertical thrust angle. I replaced the original motor and gave the motor slightly more up thrust, which appeared to do the trick. However the third flight resulted in a spiral dive which has resulted in a full front end re-build. I have since found a damaged aileron hinge, which could have been a contributing factor, or just a consequence of the crash.
I have finally got around to the repair and realised the side thrust angle appears quite excessive, compared to another Sea Otter I was watching on You Tube.

I was wondering if anyone on the forum who has built and flew one of these planes, could provide an optimal side thrust angle. Ideally based on the angle of deflection from the center line of the nacelle ?
I would also be interested to find out if I have my up thrust is correct too. However, that might be a bit harder to measure as there may be some slight variation in nacelle angle from model to model (depending how it was built). One option would be to use the rear fuselage top face as a datum point.
Any help would be appreciated.

Which Otter are you running? DHC-3 with the motor in the nose, DHC-6 twin, Supermarine Sea Otter?

 

[TheFlyingBrit]

The Flite Test Sea Otter with the nacelle mounted above the wing and pusher style prop arrangement.

Neither of the images are of my plane and its not me in the picture either .

 

[TheFlyingBrit]

Picture before the tragic incident.

After the crash

Actually the crash picture is interesting, the aileron hinges look okay , so maybe it wasn't crash related damage to the aileron hinge it might be post crash damage.
No closer to solving the spiral dive

 

[Scary]

Hope this helps

 

[Monte.C]

Hope this helps

Wow.
Vertical makes perfect sense to me. That sideways angle is pretty darn severe. No dispute, I'm just surprised.

Vert makes sense because my widgeon took a bit of up thrust. My twin motors are definitely in front of the CG, and pretty high off the CG too. For this Otter the prop is just behind the CG. I get that.

Really good looking plane too, from what I can see.

 

[Tench745]

No closer to solving the spiral dive

What did the "spiral dive" look like? What did you do just before it started? What did you do to try and recover?

 

[TheFlyingBrit]

Hope this helps

The side thrust looks identical thanks, I need to inspect the up/down thrust angle more closely

 

[TheFlyingBrit]

Hope this helps

The horizontal view suggests the motor is perfectly in line with your nacelle, whether or not there is any incidence in the nacelle angle its hard to say from the photo.
I am continuing with my repair work tonight so will take some close up pictures to post later. I am pretty happy the side thrust is correct now, as its identical to yours.

 

[Pieliker96]

The side thrust looks identical thanks, I need to inspect the up/down thrust angle more

Mine flies well without any up/down, just parallel to the upper fuselage surface.

 

[TheFlyingBrit]

What did the "spiral dive" look like? What did you do just before it started? What did you do to try and recover?

Climbed steadily from take off nice and straight I decreased throttle slightly going into a right hand turn, the plane then started to level out. Roughly 2 to 3 seconds after that it suddenly turned right and dived going into a tight spiral dive. Immediate instinct was kill the throttle and hands off the sticks. Then about 12ft off the ground tried opposite aileron deflection and some up elevator but no response. It hit the ground nose first, The rest of the plane seemed intact. No flashing light on the receiver, so no lost signal.
However, I recently discovered a damaged aileron hinge on the RHS and today the same on the RHS elevator hinge ?

 

[TheFlyingBrit]

Mine flies well without any up/down, just parallel to the upper fuselage surface.

I will bear that in mind before my next flight. First I need to measure the motor height front and back versus fuselage top.

 

[Monte.C]

Mine flies well without any up/down, just parallel to the upper fuselage surface.

That's what I think I see in @Scary's photo and I fully agree, judging in relation to my flying boat setup.

 

[TheFlyingBrit]

Couple of photos
First picture with nose removed ready for repair.

Next 2 photos show the motor angles, although the side view isn't the best of angles.

 

[TheFlyingBrit]

Mine flies well without any up/down, just parallel to the upper fuselage surface.

It appears the nacelle isn't level compared with the fuselage top, which means now that my up thrust adjustment has inadvertently corrected the angle to bring the motor level.
What a guess that was sorted.

 

[Tench745]

Climbed steadily from take off nice and straight I decreased throttle slightly going into a right hand turn, the plane then started to level out. Roughly 2 to 3 seconds after that it suddenly turned right and dived going into a tight spiral dive. Immediate instinct was kill the throttle and hands off the sticks. Then about 12ft off the ground tried opposite aileron deflection and some up elevator but no response. It hit the ground nose first, The rest of the plane seemed intact. No flashing light on the receiver, so no lost signal.
However, I recently discovered a damaged aileron hinge on the RHS and today the same on the RHS elevator hinge ?

That sounds like a classic stall-spin entry. Spins happen when you have excess yaw when flying near stall speed. The inboard wing will stall before the outboard wing which initiates the dive and the excess yaw starts the rotation.
Basic recovery for a spin is to set the throttle to idle, neutralize ailerons, apply opposite rudder to stop the spin, and get the nose down to regain flying speed. Your instincts were good, you were half way to a successful recovery. If you have a tail-heavy condition it will make recovery more difficult. Many RC planes will self-recover from a spin as long as the CG isn't too far aft.
Here's a video of a real life Cessna entering a spin and recovering. I suspect it will look familiar.

 

[TheFlyingBrit]

That sounds like a classic stall-spin entry. Spins happen when you have excess yaw when flying near stall speed. The inboard wing will stall before the outboard wing which initiates the dive and the excess yaw starts the rotation.
Basic recovery for a spin is to set the throttle to idle, neutralize ailerons, apply opposite rudder to stop the spin, and get the nose down to regain flying speed. Your instincts were good, you were half way to a successful recovery. If you have a tail-heavy condition it will make recovery more difficult. Many RC planes will self-recover from a spin as long as the CG isn't too far aft.
Here's a video of a real life Cessna entering a spin and recovering. I suspect it will look familiar.

Thanks that basically sums up what happened, it was probably a little tail heavy too so that would have compounded it.

 

[HighFlyer88]

I have had 3 un-successful flights with my Sea Otter, the first two where due to lack of power and vertical thrust angle. I replaced the original motor and gave the motor slightly more up thrust, which appeared to do the trick. However the third flight resulted in a spiral dive which has resulted in a full front end re-build. I have since found a damaged aileron hinge, which could have been a contributing factor, or just a consequence of the crash.
I have finally got around to the repair and realised the side thrust angle appears quite excessive, compared to another Sea Otter I was watching on You Tube.

I was wondering if anyone on the forum who has built and flew one of these planes, could provide an optimal side thrust angle. Ideally based on the angle of deflection from the center line of the nacelle ?
I would also be interested to find out if I have my up thrust is correct too. However, that might be a bit harder to measure as there may be some slight variation in nacelle angle from model to model (depending how it was built). One option would be to use the rear fuselage top face as a datum point.
Any help would be in

I'm late to thisparty but this is my absolute favorite airplane, and I also dealt with this issue. First things first, make sure your elevator is as parallel to the main wing as possible, mine was always forcing the nose down. As for thrust angle, I don't use any bit of that sideways angle, I based mine off my Bixler 3, I pointed the motor perfectly straight back, and just slightly upwards of the elevator position. I can glide very well, along with absolutely insane snap rolls, flat spins, and outside loops without even trying. Hope my late message helps. New to this forum.