1QwkSport2.5r

I use 2-line fuel tanks. I fill the tank through the carb line using my field box and fuel pump. The field box is a standard model airplane field box - holds my jug of fuel, fuel pump, starter, etc. If you don't have a field box or fuel pump, use an 8-10oz fuel bulb. The latter is more cumbersome, but works fine for smaller fuel tanks.

I tried 3-line fuel tanks - "uniflow" - but didn't like how it worked, so I converted it back to 2-line and have had better luck.

trapper7

I ordered a bulb.

1QwkSport2.5r

If you get into it more and build more boats, you will probably want to get a field box. It does come in handy if running multiple boats and refueling a lot.

trapper7

Just had to add some racing stripes!

trapper7

Well, shes about finished! We tried things out on some dry grass. At first we had trouble starting. Pretty sure it was due to having the carb set for 20% Nitro, while we now have 5%. Once at a richer setting it ran pretty nice. And the back-flip worked like a charm.

The servos seem to sit and hum at times, not sure why? (If you 'bump' say the steering or throttle the hum usually goes). The overall weight is just under 6 lbs with fuel.

1QwkSport2.5r

She looks mighty nice! Good job! The humming is due to the cables having just a little friction/resistance and the servo not being able to center itself. I run into it too. Adjust your trims to get it to stop. Usually a couple clicks of steering or throttle trim takes care of it. You could also try to get a little silicone oil down the control cable tubes to lube them up.

trapper7

OH my...she went pretty good. Our CG is perhaps not ideal. And i think the flaps are too low to the water surface. So they were dragging. Long story short, she flipped on a turn. Any wisdom how to dry her out? Radio seems fine. Just the engine.

1QwkSport2.5r

Dump the water out, turn the engine over quickly upside down to clear as much water as possible, dry out the glow plug and ensure it still lights, and get the engine running. I run at least 4oz of fuel through the engine running wide open and plenty rich. You still want it to get warm and run long enough to blow all the water out. If you don't get it dry enough inside, your piston ring may rust slightly causing it to be lightly seized in the cylinder. Try to avoid this.

trapper7

When the boat sits in the water should it sit level?

1QwkSport2.5r

Mine sit a little transom heavy when sitting idle without the engine running. It's not as important with how it sits in the water at idle as much as it is how it balances out of the water. Held up by the prop tips should have the bow hang at roughly a 20-30 degree angle downward as a starting point. If your weight distribution in the hull is reasonable, it should sit level or slightly transom heavy (deeper act) when idle.

trapper7

Trying to understand the science here: Why does the boat operate best with the bow hanging at roughly a 20-30 degree angle downward (hung from the prop tips)?

trapper7

Trying to understand the physics here: Why does the boat operate best with the bow hanging at roughly a 20-30 degree angle downward (hung from the prop tips)?

1QwkSport2.5r

Just to be clear - the "balancing act" is such that having the bow essentially being heavier is to give it enough pressure to not blow over at speed and not too much to cause it to plow/submarine. If the bow is too light, the bow will want to lift at speed and flip over. Too much bow pressure will want it dig in up front when powered up. The prop is your thrust line - think of this thrust as a fulcrum. The thrust will add pressure to the bow the more throttle you give it, but only to a point. The best happy medium I've found was if the bow hung a bit lower than the transom when held upright by the prop. Of course fine tuning it to be perfect takes a little more time to do.

trapper7

Its just weird, do I move the engine (blade fulcum forward) or backward (due to engine weight)!

1QwkSport2.5r

I would shift the engine fore/aft to get the balance right. I avoid changing the thrust angle of the engine unless I am on a last ditch mission to make something work. If the bow hangs level or higher than transom when holding it up by the prop, move the engine back a little bit and test again. If the bow hangs too low, move the engine forward.

trapper7

K moved engine so it hangs from prop ok. Waiting for next op

trapper7

One thing I am considering is slicing an angle on the bottom trailing edge of the flaps. At lower speeds they drag in the water. Any thoughts?

1QwkSport2.5r

Do it. You don't want your rudders dragging in the water.

trapper7

[attach=config]2209517[/attach]fixed!

1QwkSport2.5r

Looks good! Hopefully you can post a video of that bad boy running! The boat looks great! Good work!

trapper7

had real problems getting her to run...fed her through carb with dropper. Finally ran lroperly. Must have been water someplace. Ran her on wood chips, my son at the controls!

trapper7

Couldn't figure out how to post video. May get her out on the water tomorrow. BTW, have you ever seen a glow plug leaking by the center pin? Looks like it was bubling so i replaced it. I wonder if with all the water that got in if it can get super high compression and somehow blow the seal in the plug? It may have also just been a little oil setting there "boiling" off?

1QwkSport2.5r

Sometimes the center post of the glow plug can leak. I would replace it as a safety measure. If you can wiggle the center post, replace it. If it's solid but leaks a little bit, it's probably fine to use. I have had a couple leaky seals on glow plugs - I replaced them so they didn't make a big mess and in a worst case scenario having the plug drop the center post into the engine OR blowing it out.

trapper7

Burned another tank on our wet lawn last night, seems fast. Gonna be interesting on water.

1QwkSport2.5r

Most of the time, the running characteristics are fairly different from dry ground to water. Have a retrieval method handy..