It is very possible perhaps even likely that some positive is needed in the wing but perhaps not as much as exist. A 3/8 incidence change is huge and the plane is flying fairly well right now with only a slight problem of requiring down elevator for power off during landing. Change should come in the form of small increments.

Yep, forgot to multiply the 12 inches to the sin of 2 degrees. Thats what I get for not writing it down and just punching the numbers into the calculator. I'll shim 1/16" to 1/8" and maybe just leave it alone at that time. I will let you know what happens.

Just remember too, that with the water drag at takeoff pulling the nose down, and the sudden reduction in this nose down couple when the model leaves the water, will also feel like a sudden nose up pitch, even though the models basic aerodynamic trim is fine. It might just be a bit of slow reaction by the remote pilot.
Evan, WB #12.

G'day John,

Here's how I trim out a new model, and it's about the same as BMatthews and the others are telling you here.

First get the balance right;

Fly straight and level at 3/4 throttle or so and use the radio elevator trim so it will fly hands off. Leave the trim where it is for the next three tests.

Get some height and dive at 45 degrees and let go. If the model rapidly pitches up it's nose heavy, if it slowly pitches up it's about right, if it stays nose down or dives further it's tail heavy.

Fly level with the power as above and roll inverted. If you need a lot of down elevator to fly level inverted it's nose heavy. Not much down elevator, it's about right. No down elevator required, could be tail heavy.

Power as before, pull up to 45 degrees and roll inverted then hands off. If it pitches rapidly toward the horizon it's nose heavy. Slowly toward the horizon, about right. Continues up at 45, tail heavy.

Change the balance, fly and retrim the elevator with radio, then repeat as required.

Next get the elevator response right;

If after adjusting the balance the model flies heavy with insufficient elevator authority to stall and spin, loop, bunt, flare for landing or rotate for takeoff, increase the elevator throw.

If the model is twitchy and there is more than enough authority ie it stalls with small elevator inputs, stalls out of loops and bunts, is easy to over rotate on takeoff and landing. Reduce elevator throw.

If the elevator authority is good but the model is still a bit twitchy, add exponential to the elevator.

Now set down thrust;

Fly straight and level power as before, trim elevator with radio for hands off. Open throttle to full and observe the model response.

Nose rapidly rises, model speed may reduce. Adjust thrust line down.

Nose gently rises, speed reasonably constant. Thrust line about right.

Nose stays level or drops, speed increases. Adjust thrustline up.

Repeat the test but this time close the throttle.

Nose stays level or climbs, speed drops adjust thrust up.

Nose drops gently into a glide, speed drops a bit. Thrust about right.

Nose drops badly and speed increases. Adjust thrust down.

Once you are happy with all these adjustments fly the model and set the elevator trim with radio, land and check the elevator position.

If the elevator is faired with the tail plane or close. Great, adjust your linkage so that you can return the radio trim to neutral.

If the elevator is deflectd a fair amount. Also leave it alone unless you could use a bit more authority in the direction it is deflected or if you are pylon racing (the drag is almost insignificant, you would be better of spending your time reducing drag elsewhere).

If the elevator is deflected a large amount or if you really have to have it faired adjust the incidence either tail plane or wing. Be aware that in your case if you adjust the wing you will be adjusting the thrust at the same time because the engines are mounted on the wing.

Don't adjust incidence until you have everything else to your liking.

There's more to it if you are seriously into aerobatics but this will get you close for sport and scale flying. It's a bit of individual feel thing to, set the model up to where you like it.

How did you get on with water spray and prop clearance? Was I right about it being OK?

Lovely looking model and looks like a great site for flying.

Dave H

Dave H, I will print these instructions and take it to the lake with me tomorrow. I think I am going to end up living with the slight down deflection of the elevator after I get done with your testing and trimming instructions. I didn't do all these tests yet, however when I did set the elevator down a bit, the plane felt really good to me in the air. Upsidedown only took a slight down elev. to keep level. Rolls were good and pitch sensitivity was just to my liking. I do like expo though and always program it in before I fly the first time. I figure that when you are testing out an airplane the first time, you might just need maximum throws to keep it off the ground and with expo, you can have max throws and still dial the sticks down to be not so sensitive.

You were dead on with the water spray issue. I don't even think a drop was picked up by the props at any time during taxiing, slow and low or fast and high. The plane picks up on step at about 4 mph / about 10-15 ft. The video does not show any spray what so ever.

I don't know if you have looked at the other thread but here are the video links to the first 2 flights. My kids took them so they may get you a little dizzy.

http://www.youtube.com/watch?v=8bTo5qyQfV0
http://www.youtube.com/watch?v=C0iUIjfFuIA

Hadn't seen the videos, so thanks for that they are great. Loved the 'hey dad you are too far away' and ' I'm running out of battery'.

The only spray I could see was fairly well aft and under the wing, you won't know for sure till you fly in a bit of rougher water, but it looks pretty good to me. If you do have to go with spray rails keep them as far aft as you can get away with, if they extend too far forward they may reduce directional stability in the water.

I think from memory that you kept the incidence angles and balance as per the original? In that case the small amount of down elevator that I saw as you taxied in on the first video would be due to the original pylon mounted engine design. The high thrust line coupled with the low drag line would have required a small amount of up trim to trim out. Lowering the thrust line as you have means the required elevator trim is now further down.

I have just realised that my comments about trimming the up and down thrust won't apply to your model very well. They are more applicable to a conventional model with the engine well in front of the wing. With your engines only just in front of the balance point you would need large amounts of thrust angle change to see any result. I don't think you need it any way.

Also be aware that if you move the balance point around you will affect the relationship between the hull step and the balance point, you will potentially affect the water handling.

You might want to do the first series of tests to see where you think the balance is out of interest, but if you have kept the original incidence and balance you will be very close. The model certainly looks like it flies nicely and you seem fairly happy with it. Looks like a very successful experiment to me, but then again I'm a sucker for twins and water planes.

Well done

Dave H