Converting Wattage Crazy 8 to Nitro.

[jlnajarro]

I’m looking to convert a Wattage Crazy 8 to Nitro using a AP .15 and 9x4 APC , 250 MAH Batt, 555 Hitech receiver , Cirrus servos CS-10/alierons , CS-10/throttle, CS-26/elevator, CS-26/rudder.

Total weight with 2 oz of fuel = 23 oz.

The spec says it should be 26 to 30 oz when going electric.

The problem is the plane keep ballooning to a vertical position, when I cut the throttle. I have tried adding a bit down thrust to the inverted installed engine but still seems to have the same problem.

Any Suggestions ?

[Steve McBride]

The ballooning problem is probably from too much down thrust. With a shoulder wing model where the thrustline is along the wing and tail centerline, I would start with 0 downthrust and work from there.

Steve

[jlnajarro]

Thanks , I will give it a try. Although have read on the web that some have suggested that adding down thrust helps reduce ballooning.

[vintage1]

Originally posted by jlnajarro
Thanks , I will give it a try. Although have read on the web that some have suggested that adding down thrust helps reduce ballooning.

It does reduce ballooning UNDER POWER. But you report ballooning when you gut the throttle, so what steve says is probly accurate.

You probably have to use up trim to compensate for the downthrust under power. Cut the throttle and the speed + up trim makes it balloon.

The 'callsic' way of trimming free flighters was first of all to set the trims for a flat even glide, and then use downthrust to compensate for excessive staling under power.

With radio models that don't need so much stability, you can mess with teh CG as well.

First of all check the CG. Get that right FIRST.

Then check the glide and if thats OK adjust engine thruts to make it nice and clean under power - some people trim for a climnb under power, some like it level.

If the wing section is asymmetric, then I'd use a bit of downthrust so it flies inverted with less 'down' on it, but if it is an aerobat, Steves advice is 100% sound. You want the plane to be zero-zero setup, and with the CG quite far back, so it doesn't need much up trim to fly level, and speed increases don't tend to make it 'zoom' .

So I'd get the CG right and rip out the downthrust and have another go.

Then play with the trims and CG until it flies the way you want it.

If there is a tendency to climb too fast under power but NOT when you cut the throttle you can add downthrust.

The other way to get things trimmed is to compare the way the plane behaves in a dive and or inverted. If when you dive it it tries to pull out hard on neutral sticks, you have the CG pretty far forward - so the uptrim you need to keep the nose up in level flight is making it want to pull out.

If the dive stays put or steepens, your CG is way far back.

Likewise if it takes a a LOT of down to hold it in inverted, the CG is too far forward.

Since its now a slimer, I guess you will have to add weight or move the battery pack...

[jlnajarro]

Thanks for the info. I reduced the down thrust to almost zero , and made sure the CG was set to the recommended starting point , and Bingo the Ballooning vanished. I think it still may be a bit nose heavy for my liking but that is easily corrected.

Thanks.


Now my only problem is getting my AP .15 to give some decent vertical preformance.

I started out with a APC 8 x 4 @ 13000 RPM , decent climb out , weak vertical , engine sags when vertical.

Then I moved to a APC 9 x 4 @ 11500 RPM , nice climb out , fair vertical however engine sags when vertical

The thing that bothers me is when I use a 9 x 4 and set the high speed needle valve using the a standard pinch test the engine preforms beautifully , it even trys to pull out of my hand in vertical position.
In the air when it starts to lean out its a different story. It flys fine for sport flying but and any thing vertical the engine start to sag.

I was thinking of using more nitro such as 30% instead of 15% . I really like the weight of a .15 size engine so I would rather find the correct engine prop combo instead of just adding a larger engine.

My goal is to have a light 3D .15 size hovering machine.

[Viper Pilot]

Sounds like you need to experiment with props some more. There must be a combo that would work out!! At 23 oz AUW the power HAS TO BE sufficient.

VP

[vintage1]

Looks like you need to sort out tank location and engine tuning.

It should be rich to slightly burble and misfire when held static - it will lean out in the air anyway, and even more when going straight up.

One of the reasons for electri power. Works the same in every direction :)

[Viper Pilot]

You could also try putting a one-way valve between the muffler and the tank. This builds up some extra pressure in the tank, and might eliminate your problem.

VP

[jlnajarro]

Thanks all for your suggestions. I think I found the the problem , I had a slit on tubing lead from the muffler. I now get awesome vertical , rolling taking off right into a vertical climb. :D I still need to adjust the throws abit for 3D and get the CG moved back.


Ps. I'm curious , I would like to know more about the this one way valve thing.