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Newbie help With Sea Otter

#1
I just finished the FT Sea Otter build. This is my second build, my 1st was the FT Flyer. I used Hobby Lobby foam board instead of Adams and I used Minwax on it trying to be sure it was water resistant. It ended up quite tail heavy so I added some weight to the nose.
Now without the battery the total weight is 900 grams and I don't think the "b" size motor setup that I used is going to be adaquit. I tried it on grass and it barely budged. I'm too chicken to try to hand launch it or to launch it from water.
How much should I be worried about the weight of this Otter? Should I just use a bigger motor and prop?
 

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Gazoo

Active member
#2
I know this will not help much but mine was pretty lethargic on the B-pack and 8" prop when it was the recommended weight. It could barely keep itself in the air.

I'm guessing that the C motor and a really aggressive pitch prop may make it flyable but think that it will probably be a poor flyer.

I wonder if making a longer motor nacelle with a motor mount on the front and back with two motors would do the trick?
 

Gazoo

Active member
#5
My brain can't stop thinking about this.
Nacelle.JPG


And, by the way, your build looks really nice. Love the detail in the canopy.
 
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#6
Thanks, I held the canopy on with magnets. BTW is EVRYONE using a conventional prop with the Otter or is anyone use a reverse prop?
 
#7
Thanks, I held the canopy on with magnets. BTW is EVRYONE using a conventional prop with the Otter or is anyone use a reverse prop?
No need for a reverse prop. Just have the writing on the prop facing forward and the motor spinning ccw looking at it from the front.

Ray
 

Gazoo

Active member
#9
If you use a reverse spinning prop, I believe that you should reverse the angle on the firewall. otherwise yo will have severe torque issues. You may have already known this but someone else reading this may not, so I just wanted to point that out.
 
#10
The thrust angle is one of the reasons that I asked the question. It seemed like the thrust angle is set for a conventional (CCW) prop but I wanted to be sure. I'm very new at this.
I'm thinking about trying this motor.
 

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#11
That is a decent motor, but because the Otter is limited to an 8" prop, the kv is too low.

For 3S parkflyer size motors, an 1100kv generally makes max power with a 9 or 10" prop. It's underpropped at 8" and you would be missing the max power mark. It would be great on a Spitfire, Mustang, or most other FT models that can use 9 and 10" props.

For the Otter, you want something more in the 1400-1500KV range. Most motors in this range will make max power with an 8" prop.

Heads Up has a couple that would be well suited. The Power Up 450 'Speed' 1500kv makes 31 oz. thrust on an APC 8x4, drawing about 20 amps. I'd wager that this would let you take off from the grass. :)

Oh, and reverse props are mostly used for quads and multi-motor planes. Single engine pusher planes generally use a standard prop mounted with the numbers facing the front of the plane.
 
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#12
Thanks Strix, that sounds right. I should have figured in my limited prop size, but I ordered that motor last night. I'll try it with an 8x6 prop and go from there. I might end up building this over and trying to lighten it up.
 
#15
Well it flew with the larger motor and a 8 x 6 Prop, but it flew poorly as predicted.
I still had to remove some of my balancing weight from the nose to get it to launch from the grass, so it flew tail heavy.
Tried to attach the video but apparently it is too big to upload.