Has anyone got a Sea Otter that fly's okay ?

[TheFlyingBrit]

In my attempt to finally get my up/down thrust angle right on the Sea Otter, I decided there are two options available:
1) Trial and error using experimentation.
2) Find someone who has built one that fly's okay and get some physical dimensions.

I have decided initially to go with the latter option first, if anyone has built one of these planes and they have had success flying it. I would be grateful if you could measure the distance, between the motor shaft and the top surface of the rear fuselage.
This should give me a rough approximation of the motor angle, the fuselage top rear surface will be the datum point. I then have a starting point and can adjust the angle further by 1 or 2 degrees afterwards, if necessary.

 

[Ligbaer]

In my attempt to finally get my up/down thrust angle right on the Sea Otter, I decided there are two options available:
1) Trial and error using experimentation.
2) Find someone who has built one that fly's okay and get some physical dimensions.

I have decided initially to go with the latter option first, if anyone has built one of these planes and they have had success flying it. I would be grateful if you could measure the distance, between the motor shaft and the top surface of the rear fuselage.
This should give me a rough approximation of the motor angle, the fuselage top rear surface will be the datum point. I then have a starting point and can adjust the angle further by 1 or 2 degrees afterwards, if necessary.

build another? maybe it got out of whack during a crash.

 

[Scary]

In my attempt to finally get my up/down thrust angle right on the Sea Otter, I decided there are two options available:
1) Trial and error using experimentation.
2) Find someone who has built one that fly's okay and get some physical dimensions.

I have decided initially to go with the latter option first, if anyone has built one of these planes and they have had success flying it. I would be grateful if you could measure the distance, between the motor shaft and the top surface of the rear fuselage.
This should give me a rough approximation of the motor angle, the fuselage top rear surface will be the datum point. I then have a starting point and can adjust the angle further by 1 or 2 degrees afterwards, if necessary.

In my attempt to finally get my up/down thrust angle right on the Sea Otter, I decided there are two options available:
1) Trial and error using experimentation.
2) Find someone who has built one that fly's okay and get some physical dimensions.

I have decided initially to go with the latter option first, if anyone has built one of these planes and they have had success flying it. I would be grateful if you could measure the distance, between the motor shaft and the top surface of the rear fuselage.
This should give me a rough approximation of the motor angle, the fuselage top rear surface will be the datum point. I then have a starting point and can adjust the angle further by 1 or 2 degrees afterwards, if necessary.

 

[Scary]

the 2nd picture 1 3/4 the motor pod is parallel with top deck of plane, hope this helps it is a good flying plane.

 

[TheFlyingBrit]

View attachment 221427 View attachment 221426

Thank you, your a gentleman.
I am in work at present but as soon as I get up tomorrow, I will measure and see what what comparable measurements I get
It wouldn't take much variation in the position of the upright support and nacelle to throw the motor angle out. They would have been better to provide these dimensions on the plan so everyone could get consistency with there builds and motor angle.
The two positions on the fuselage you used will make excellent datum points for reference, thanks again much appreciated

 

[TheFlyingBrit]

build another? maybe it got out of whack during a crash.

Only the nose suffered during the crash the rest remained in tact, so I am fairly certain the issue isn't crash related.

The only difference between the last flight and crash, where it did at least get off the ground. Was the last attempt had a landing gear modification. I have omitted it this time and wondering if the landing gear inadvertently altered the motor angle and wing incidence in the previous flight ?
As I don't want to re-visit the landing gear option and just keep it a Sea/water plane I need to get the motor angle sorted once and for all.

 

[skymaster]

so is this a kit or scratch build, and what are you trying to do. if this is a scratch build chop the nose off and make it again just the nose and glue it to the plane adding a piece of tape for reinforment. and then try again this time ditch the wheels. good luck.

 

[TheFlyingBrit]

The nose has already been rebuilt the wheels are scrapped on this version, the issue is motor angle. I had 2 attempts but it wouldn't take off from a grass runway, even with a fair amount of power (using a 4S 1500mAh battery with a 8x4.5 prop well over powered for this model), it just wanted to tip up and bury the nose into the ground.
I was tempted to do a hand launch but realised that was pointless, as I increased throttle it just wanted pull down to the ground excessively while in my hand.
So now you have the background.
The previous flight with the wheels had a successful take off, but I didn't realise at the time the rudder was sticking on one side. With the prop wash passing over the rudder and the deflection of the rudder it went into a spiral dive, before I could react it hit the ground nose first.
During the nose rebuild process the wheels where ditched and I reverted back to the original Sea Plane design. However, it doesn't seem to want to fly this time around so revisiting the motor thrust angle.

 

[TheFlyingBrit]

so is this a kit or scratch build, and what are you trying to do. if this is a scratch build chop the nose off and make it again just the nose and glue it to the plane adding a piece of tape for reinforment. and then try again this time ditch the wheels. good luck.

I don't build FT kits. I only scratch build, the price of FT kits in the UK is ridiculas. I can buy an ARTF foam plane for the same price as a FT foamboard kit.

 

[TheFlyingBrit]

The previous version before the crash incorporating wheels.

The repaired version that is reluctant to fly.

 

[Monte.C]

I sure don't know about this particular design, but let's simplify this a little if we can. First of all there's no way there can be a great mystery here. Unless I'm missing something, the problem is in the up/down motor angle.

The prop sits behind the CG, so if it wants to pitch down with throttle, your thrust angle is too high - pushing in an upward direction - acting to raise the tail. You know it's that simple, right?

 

[Scary]

I fly mine off grass ,you have to give down elevator to get it on step then lift off

 

[TheFlyingBrit]

The front underside surface of nacelle to fuselage measurement, is identical to yours 45mm (1.75") if my conversion is correct.
However, I calculated that your prop center to top of the rear fuselage is approximately 105mm. My measurement is closer to 114mm which highlights an immediate discrepancy, which is most likely the cause of my problem.
I am pleased to confirm where the problem most likely is and it would explain the strong downward thrust of the nose. However, what I don't know now is how much of the 9mm is down to the rear of the nacelle being raised and how much of that difference is due to the motor position on the nacelle.
Thanks @Scary its given me something to work with.

I sure don't know about this particular design, but let's simplify this a little if we can. First of all there's no way there can be a great mystery here. Unless I'm missing something, the problem is in the up/down motor angle.

The prop sits behind the CG, so if it wants to pitch down with throttle, your thrust angle is too high - pushing in an upward direction - acting to raise the tail. You know it's that simple, right?

I understood the principle of why it was doing what it was doing. However, before I can resolve the problem I needed to understand where the problem originates.
The nacelle position at the front appears to be spot on in relation to the fuselage, its the rear of the nacelle where the motor is mounted where I suspect the alignment appears to be out.
Now I know where to start and what the error is, I have a factor to work with. I just need to determine firstly if any of the 9mm is due to motor position on the firewall. Basically is my motor mounted in exactly the same position on the firewall as @Scary or is there a small height variation. This variable needs to be subtracted from the 9mm error first.
Alternatively I can just measure the rear nacelle height versus the fuselage compared with the front, which is now a datum point (as its identical to @Scary). This measurement is more crucial, as its the measurement I will use to adjust the motor angle.

 

[Scary]

With the square sitting on top of the nacelle flush with motor mount bottom face there is 1/16 difference blade off square behind face of motor mount on top

 

[Scary]

Hope that made any sense

 

[Scary]

Have to take all that back I checked with a better square the face of the motor mount is square with top of nacelle ,sorry

 

[TheFlyingBrit]

Its suppose to be straight so you got it right . Assuming the nacelle is mounted perfectly horizontal, the motor would then also be perfectly horizontal with no up or down thrust angle. I believe that is how its supposed to be set up, the only thrust angle for this model is to the side.
As I scratch build there is always small variation in parts due to manual cutting etc and there are two areas where the error could have occured on my part:
1) Where the upright fits into the nacelle.
2) Where the upright slots through the fuselage and mounts onto the top wing surface.
Based on these two areas where variation can occur, I am not surprised I got an alignment issue. A far better option would have been a jig made from foamboard which confirms the correct motor alignment angle.
Usually my fire walls are constructed fairly accurately, so I will assume the motor height is central, I need to repeat the nacelle, fuselage measurement at the rear and compare with the front measurement.
I am off work from tomorrow morning, its my 3 rest days. So plenty of time to play about with the motor angle and get it sorted. I just got 3 new HRB 4s 1500 mAh 65C lipo's, which I will be trying out in the Otter once I get this angle sorted.

 

[Tench745]

Thank you, your a gentleman.
I am in work at present but as soon as I get up tomorrow, I will measure and see what what comparable measurements I get
It wouldn't take much variation in the position of the upright support and nacelle to throw the motor angle out. They would have been better to provide these dimensions on the plan so everyone could get consistency with there builds and motor angle.
The two positions on the fuselage you used will make excellent datum points for reference, thanks again much appreciated

The dimensions are on the plan, sort of. They're not called out as a measurement, instead the "motor nacelle support" has a pair of green reference lines included on the part. The upper line matches the lower surface of the motor pod. The lower line follows the upper surface of the fuselage.
The speed build kit has reference holes in the same place which Peter references at the 53:30 mark of the build video when he is assembling the motor pylon.

If you want to verify the angle of your own motor pod, it should be simple enough to print off just that section of the plan and cut it out as a template.

 

[Monte.C]

The dimensions are on the plan, sort of. They're not called out as a measurement, instead the "motor nacelle support" has a pair of green reference lines included on the part. The upper line matches the lower surface of the motor pod. The lower line follows the upper surface of the fuselage.
The speed build kit has reference holes in the same place which Peter references at the 53:30 mark of the build video when he is assembling the motor pylon.

If you want to verify the angle of your own motor pod, it should be simple enough to print off just that section of the plan and cut it out as a template.
View attachment 221510

Best answer ever in the history of answers.

 

[TheFlyingBrit]

During the assembly I did follow the green reference lines on the upright/pylon, although with scratch building its easy to lose or gain the odd 1 or 2mm here and there. The position of the upright/pylon is dependant on the wing slot position being accurate, ensuring wings in the exact location. Plus slight variation in the wing dihedral/angle again more possible variations there, extra glue or tape on the wing joint it all ads up.

(The jig suggestion would have allowed for variations during the building process, to be compensated for. The correct motor angle could then be achieved by alignment with the jig, which can be mounted on a datum point like the fuselage.)

When I first started building these foam planes I was a bit OCD very meticulous: particularly when transferring from plan to foamboard and the cutting out stage, even the final assembly. These days I take less care in the assembly process, the enjoyment is more getting them finished and in the air rather than building.

I suspect the problem with this plane is its just a bad assembly on my part and I am wasting my time. Tomorrows priority is remove all the reusable parts and have a ceremonial burning of the carcass. I am probably better using the parts to build something really basic like a bloody baron instead.