Originally Posted by tdearth

It would also be nice to have reference bumps or dimples at the CG on the top of the wing. Because of the mass of the motor above the plane it is easier to balance the plane upside down.

I agree that upside down is the way to balance. Here's how to to it properly, as demonstrated by Lockey with one of his Depron creations:
http://www.rcgroups.com/forums/showp...ostcount=20017

Or you can use your thumb and finger!

As for locating the CG, it's easy if you note that the rear of the vent is directly over the step.

Originally Posted by bluebird

I maidened mine yesterday and love it. Took off from the grass, no problem using a HK 3530-1000 on 4 cells. I did a static test which showed about 22 amps and 330 watts. The motor was cool after flights.

The 4 cell 2200 made the CG a little forward which tended to drop the nose in turns. I did some cutting and moved the battery back to put the CG over the step. No more nose drop. I still want to move the CG back a little because of all the up trim needed.
There is a noticable lack of response to up elevator when nose heavy.

I have a 2810-9 motor and some new batteries on the way.

Here is the motor data.

Joe

Thanks for the data Joe.

I'm surprised you had to move the battery that far aft to get her to balance. I've found with the 2810-9 motor and 4S 2200 she balances right on the step with the pack at the back end of the existing battery compartment.

Scott

Difference in a 4S 2200 pack, depending on C rating and manufacturer, could be as much as 70g. More than enough to cause a need to move farther back...Pete M

Originally Posted by pmisuinas

Difference in a 4S 2200 pack, depending on C rating and manufacturer, could be as much as 70g. More than enough to cause a need to move farther back...Pete M

Here are my weights (including wires and connectors:
2200 20C 3s 170g
2200 30C 3s 195g
2800 25C 3s 240g
2200 30C 4s 255g

To balance on the step, the 4s has to protrude about 1/2" into the compartment behind the battery channel. (I removed the bulkhead at the back end of the channel.) This is not an issue as far as I'm concerned, as there's lots of room for everything.

Hoping to get out and try 4s this afternoon. I did a brief flight on 3s this morning but the wind picked up and it was too bumpy for safe and enjoyable flying.

The wind dropped and I was able to get in a flight before dark to try out 4s. Earlier in the day I had got some readings on 3s, so I had a baseline to compare with.

Using a 4s 2200 30C battery and 8x4 APC prop, the model accelerated faster than it did on 3s and was able to climb vertically from takeoff. It was obviously faster in level flight. So the simple answer to the basic question is: Yes, 4s does give it quite a performance boost.

Does it do this at the expense of excessive current draw? No, the momentary peak current on opening the throttle was 26A (380 watts) and the average power at WOT, including during vertical climbs was about 20-22A (300-320 watts). These are quite conservative figures and in line with Scott's comment that an 8x4 would work nicely on 4s.

When I slowed down to what I considered a comfortable cruise, as I did several times during the flight, the power required turned out to be 10-12A (140-170 watts). Minimum cruise power just staying in the air was about 8A (120 watts).

My earlier brief test flight on 3s with 8x6x3 prop also gave a peak static reading on opening the throttle of 26A (260 watts), while average power at WOT was around 18-20A (200-220 watts).

I didn't get a very precise reading of cruise power on 3s but would estimate it to be around 12-14A (130-155 watts) from previous information. (You would expect the power required to be similar, regardless of 3s or 4s, and that's roughly what we see.)

Bottom line? Polaris Ultra flies very nicely on either 3s or 4s. If you feel the need for vertical climb and extra top speed, go for 4s. If you're satisfied with 45-60 degree climbs and a little less top speed, 3s is ample for normal flying, including aerobatics. I will use both 3s and 4s at different times, but mostly, I think, 3s.

Don't forget, you need to change the prop for the different voltages. Running on 4s with the 8x6x3 would draw a lot of current!

My 4 cell was 70 C, so it is heavy. I did the same as Daedelas (sp?) and cut out the back wall of the battery slot. The battery was about 3/8" into the large opening behind the slot.

I wouldnt pay too much attention to my previous data as that motor was something I pieced togrther from three motors. It was running a little loud and rough.

When I get my other motor, I will log some data to get an idea of peak and crusing amps of some different combinations.

Really bad weather today, but I did take advantage of a little "quite" before the storm to sneek in an Ultra maiden flight. 50 degrees with a little drizzle and the water was like glass - who could resist! I charged up a pack and charged down to the water.

The flight was WONDERFUL!!!! Ultra needed up trim (nose heavy), but trimmed out easily and flew very well. Ultra rolls much more axially than the kit version. Tracks well through loops both large and small. Still lands like a Polaris - smooth as silk. After 5 minutes, the drizzle was turning to rain, so I only got in one flight, but I'm still grinning from ear to ear!

Remember, I'm not using the stock motor, and I was slightly nose heavy on my 4S battery even though I set it back into the ESC compartment by 3/4" after cutting out the rear brace from the battery slot. I may eventually put in a larger motor (heavier) with a higher kV so I can use a 3-cell battery.

McD

Originally Posted by kingsflyer

The flight was WONDERFUL!!!! Ultra needed up trim (nose heavy), but trimmed out easily and flew very well. Ultra rolls much more axially than the kit version. Tracks well through loops both large and small. Still lands like a Polaris - smooth as silk.

McD

I envy you for the chance to fly the Ultra off water. About three months to go here.

I was just thinking the same about the axial rolls and smooth loops while I was testing 4s today.

I love water touch and goes and the Ultra is a true Polaris in that you can hear the hull as it gently touches the top of each wavelet as it settles in on the water. I now have ULTRA POLARISITIS!!!

Originally Posted by kingsflyer

I love water touch and goes and the Ultra is a true Polaris in that you can hear the hull as it gently touches the top of each wavelet as it settles in on the water. I now have ULTRA POLARISITIS!!!

Congratulations on your successful maiden flight kingsflyer! It must be nice to have water outside your back door.

D66, thanks for providing more in-flight data. I must get one of those data loggers.

Scott

www.ModelAero.com

The typical 4s 2200 30C battery weighs about a 1/3 more than a 3s battery and needs to be moved back to get the model to balance correctly on the step. The existing battery "channel," however, has a "wall" across the back preventing the battery from going back far enough. All you have to do is to cut out the wall, allowing the battery to protrude slightly into the space behind. This also gives you a place to tuck the connectors out of the way. It's a distinct improvement all round. You might want to add a small block of foam to extend the floor of the channel back by 1/2" or so, but it really isn't necessary.

I installed industrial strength Velcro (hook side) in the bottom of the channel and add a couple of patches of the fuzzy side of the Velcro to each battery. By the way, you'll find that the Velcro straps built into the fuselage get in the way. You may want to cut them off completely, but at the very least you need to shorten them, as otherwise they bunch up and prevent the cockpit unit from fitting properly.

As noted above, I'm very happy with the 4s setup for more performance but also consider 3s ample for normal flying.

If you do go 4s, be sure to:

• Use an ESC that is designed for 4s (many with linear BEC are only good for 3s and may shut down the power to the radio if overloaded)
• Change the prop to reduce the load (8x4 works well with stock motor)
• Get the balance right

SS pushrods, servos, ESC came in today for Salty Ultra! Guess what I'm doing tonight!

Weather fcst is 80 degrees this weekend!

I was able to squeeze in another flight this evening after the rain and before sunset. What fun! I pushed the envelope a little harder this evening and got some nice high alpha flying. The Ultra has less wing wobble than the kit and steers easily with the rudder even at full elevator and very nose high, high alpha. I was able to get a pretty decent knife edge, but it needed a lot of opposite aileron to keep the wings vertical. My ESC must have a little brake programmed in because the prop stops turning at throttle idle on landing approaches. It looks kind of cool and the Ultra doesn't mind at all, it just keeps on line and lands like a lady. Two great flights now, and not a single DROP of water inside the Ultra. Way to go Scott!

McD

nice to hear high alpha is better than expected!
What was your AUW with Lipo during that flight?

mine is coming along....
got some SS/CF pushrods made, servos installed, I went with the external elevator servo

gatorb8

What kind of connection is that from the CF to SS?