Mclarenhpi

Hi, I have a stock superstar ep and it comes with the stock 2100mah battery 7 cells) with deans connector. Now my question is which battery should I use as a "backup" or second battery. I have been looking at these two choices; the 1900mah battery from tower hobbies http://www2.towerhobbies.com/cgi-bin...2874&P=1#mults or the 2000 mah nimh battery by great planes from tower hobbies http://www2.towerhobbies.com/cgi-bin...?&I=LE2764&P=1 . Now the reason I ask for your help is because I have heard from previous posts that the nimh batteries are not good on discharge rates and nicads are. To give a perspective on the amperage draw on this plane, I use the stock 2100 mah battery for around 7 minutes max which is good. Now i went out and previously purchased the 1100 mah 8 cell battery by great planes as a "second battery" http://www2.towerhobbies.com/cgi-bin...?&I=LXCFD9&P=7 , I cycled it and all and it even flew great on my easy star! However the problem that lies is that when I used this battery in the superstar, after 2-3 minutes the battery just couldn't turn the motor over anymore and I had to land (in a bush . My question is which is the best battery for me in my case, the tower hobbies 1900mah nicd, or the great planes 2000mah nimh?
Thanks, Sam

Matt Kirsch

My Feedback: (21)

You have to compare NiCd and NiMH of the same physical size, not capacity. Physical size is a good indication of how much current a battery can handle in general. You found out first hand when you tried the smaller 1100mAh pack. It was way more than the little 1100mAh pack could handle.

The 1900 NiCds are full Sub C, while the 2000 NiMH are 4/5 Sub C. Physically smaller pack means less current capacity. In this case it's okay, because you're not using the full capability of the 2100 mAh stock pack, and the 4/5 Sub C comes pretty close.

Either pack will work well.

There are other possibilities, though, and you don't necessarily have to shop at Tower. Personally, I would go with a 3300mAh NiMH pack for maximum duration.

TGDF

My Feedback: (3)

Boy do I need some help. I'm kind of boiling as I write this.

I've crashed a few planes and decided to get a gentle trainer because I felt I'd crashed the others because they were too fast for me. Even after I got the Superstar EP I realized that another problem I had was all my simulator experience was with a joystick. I was lost in Mode2. So I got a Realflight Simulator with a Mode2 Box just like my JR Tx. I've been practicing for 3 weeks waiting for the wind to die down so I could finally fly. I've gotten where I can fly just fine in Mode2 Even when I set the system for 10 Mph winds, gusts to 15Mph with 30 degree variability and I can land just fine.

The problem is, I can't get the plane off the ground. As soon as sthe plane gets close to takeoff speed, it ground loops. Into the wind, with the wind, cross wind, no wind, before I can take off, the plane spins around.

I put the plane together exactly as per the instructions. The Center of Gravity is at or a 1/8 inch forward of maximum but, while in the extreme, that could make the plane more stable, less responsive and a bit reluctant to rise off ground it should have nothing to do with the plane ground looping.

I've tried to stop the loop with rudder but it just loops faster in the other direction. I have no trouble on takeoffs in the simulator that require a bit or rudder.

I've tried a quick glance at my aircraft design books regarding lateral stability and the solution seems like it might be a larger vertical stabilizer. But that was a really quick look.Have you ever heard of this? Any suggestions? Unless I'm really mistaken, there's something seriously wrong with this plane. But I think it should be easily fixed.

Thanks.

BTW, did you ever settle on a battery?

Mclarenhpi

Hi Terry,
I had the same problem when I take-off and still sometimes do. Since the plane is a tail dragger, it sometimes may hit the ground right before the correct take-off speed and cause it to veer off course. When I first started flying the plane this was my main problem, I always put rudder input to correct it, but now (after 10 flights), it seems to just take off with gas. It could be due to my modification to the wheels. What I did was put a rubberband or two across the main wheel metals to cause tension and hold the two wheels from seperating during take-off because there is a-lot more downforce on the plane. Well anyway I just gave this a try and it worked very well, even with the landings because whenever I landed the landing gear bent and seperate but now it is a smooth landing and takeoff. It might be difficult to keep the rubber bands on the landing gear, but as long as there is tension it should work fine, give it a try and see if it works. I also thought of the balnce in the airplane so what I did to make balance very precise was put the esc on top of my reciever and used the velcro to hold it all together. I have one more thing to add to this, I have heard that people give the plane a little down elevator to get the tail in the air, I have personally not tried this becasue I am afraid thatif I do this, I will hit the propeller into the ground and cause problems.
As for my battery selection, I decided to buy both packs (2 2000mah nimhs; 1 1900mah). It turns out that the towerhobbies battery did not provide the performance at all, and that the nimhs, even though 4/5sub-c worked better! I could do better loops, and flight times were improved a little. I have included pictures of the rubber band set-up and my battery packs and also my fueslage copmartment to show the way I balanced the esc and reciever on one-another.
Hope this helps, Sam

TGDF

My Feedback: (3)

Mclarenhpi:

Thanks for the info re the battery and balance. I've been looking for the answer to the ground loop in at least 4-5 different threads. What I found is below.

I'm not sure exactly about Matt's answer. And Matt, I don't mean to dis you. Larger physical size batteries may actually discharge at higher rates than smaller physical sized batteries. That is the larger batteries may be able to deliver a higher instant amperage over time. But the rated size is what you get for total amps over time. As you discovered. The 1100AmpHour battery lasted just about 1/2 as long as the 2100AmpHour battery. That's just as it should be electrically no matter what the physical size of the package. The quantity of power that a 2100AH battery will put out (excuse me. All those figures are in Mili Amp Hours) 2.1 Amps in an hour, or 2100 one thousandths (milli) of an amp in an hour. Amp Hours means Amperes per Hour.

Now that's the total power in Amp Hours. if you discharge the battery at 1/4 amp per minute, the 2.1 Amp Hour (2100MAH) battery will last just over 8 minutes. 8 is just about 1/4 of 2.1. If you discharge it at 4 amps per minute the battery will only last about 30 sec. 2.1 divided by 4 is just about 1/2 minute.

If you found that the 1100MAH turned the prop OK but just for a shorter time AND it was NiMh (I don't think you say what kind of battery it was) then you know that a NiMh battery can deliver enough continuous instant amps to drive the prop, you just need one with more MAH. Like Matt said, just find the highest AmpHour rating you can for the same sized battery. That will give you the longest flight time.

I would think that the rebalancing problems of a different sized battery would far outweigh any increase in the flight time. Remember, landings are part of the fun too. And landing practice is probably the most important practice you'll get. That's how you save your plane for the next flight.

I did move my ESC back as far as the wires would allow and I relocated my receiver to the inside rear of the battery hatch, just below the blocks that buttress the rear of the battery. But the ESC and Rx are nothing compared to the motor and battery. I still had to put a huge coin, at least the size of an old US silver dollar on top of the fuse just ahead of the vert tail to get the CG back into the center of the recommended range. Thanks for the tip re the rubberband on the wheels, but as I note below, I found I could just gun it and take off. I'll be laminating a fiberglass wheel mount in a week or so. I've got to make one for another plane I built and they should be easy to make after I come up with a design that's both strong and light. Actually, I might fly it with the wire gear for a while. For as often as I'm bending the wires, I'll also have to design the fiberglass so it doesn't transmit that bending force to the fuse!!

I just looked over TowerHobbies. They have the GreatPlanes 2100MAH battery and the TowerHobbies generic 1900MAH battery. Now there is a 25% difference in price between these 2 batteries. And a newbie might go for the higher capacity battery, but I'd be willing to bet that these are the exact same batteries in different colored wrappers. They are the same sized cells in the same stack configuration. But department stores like to make the name brands feel that they aren't cutting into their business by making it seem like the brand name is better than the generic. So Tower rates them at some nomimal figure and Great Planes uses a different test. They even list the size as different but its only by fractions of a mm. How can standard battery cells be different sizes. The price difference is 25%, the capacity difference is only 10%. Even if that's true and they're not exactly the same, I'll save the 15% and benefit from the landing practice. But if you do find a 2500 or 3000MAH battery, let me know. Probably not. Again, same sized batteries (of the same type, NiCd/NiMh) are usually exactly the same. Like the guts of a VHS VCR or CD or DVD player, they're all made by only one or two manufacturers.



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WINNER!! WINNER!! WINNER!! Ladies and Gentlemen, we have a WINNER!!

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The prize goes to Piper Chuck who correctly suggested the width of stance as being a cause of the problem. I've posted another excerpt from a design book which I just missed by one page at http://www.terrencefoley.com/images/Ground%20Loop.jpg . I ran across it yesterday while on the Throne.

What it basically says it that on less than glider sized aspect ratio wings, the wheel stance should be at least 25% of the span! The SuperStar EP is well short of that. The two reference pages together suggest that first, all tail draggers are a bit laterally unstable at takeoff, and that, if the wheels are close together, the condition is aggravated.

Way to go Chuck!!!! (This was in All Forums >> RC Airplanes >> Beginners >> Hobbico SuperStar EP Select RTF w/Ailerons Newby . I've been looking for the answer to this in 4 different threads.)


My first modification to my EP will be a wide track, streamlined, fiberglass landing gear mount. In fact that may be the first thing of my own production that I may offer on my website.

(Note to mikeflyzz . For being the first to verify that he also had the same problem, PM me with your email address. When I make up the fiberglass landing gear, if they work, I'll send you a set on the house. Put away your discouragement and read on for what a good time I had once I got the plane off the ground!)


I'll try to keep this from becoming a war story so as not to bore those more experienced. I just hate to leave out detail because I find the experiences of others so helpful for myself.

The short version seems to be "Faint Heart n'eer Won Fair Lady." The old timer from Monday (who suspiciously was nosing in multiple foamies when he told me) was right. I just had to open the throttle wide open and go for it. It flew right through the instability and took off. If you're looking for something to float around the pattern and just plane enjoy, this plane is it. That's the short version.

I did re-balance the CG to pert near the exact center of the recommended range. (Naturally, when I got out on the field, there was another old timer who, when he saw the JA$5 coin, about the size of a 25pound olympic weight lifting plate that I'd taped to the top of the fuse to balance it, spent 10 minutes telling me that it was going to be too tail heavy, tail heavy is death, nose heavy don't matter....nya nya, nya nya, nya nya). He was a nice guy though and we fiddled with the plane for a while and discussed the situation. When he offered to test it out for me, I readily accepted. As this was going to be my first real flight, I knew that part of my problem was probably nerves. I figured if he got the thing off the ground it would put me at ease and I'd be less likely to be just plain all thumbs.

I tried a taxi first and showed him the ground loop. He tried it and sure enough, I wasn't nuts, it did it for him too. But we talked over this and that and he tweaked the wheels a hair and we finally decided to try and go for it. In all the times it spun around, it was always perfectly flat and never even started to flip so we decided we had nothing to lose.

He took off, flew around for 3-4 minutes (I've got a timer) and pronounced it a fine flying machine even if it did look like it had Judas' 50 pounds of silver on the tail.

I charged up the battery, took off and flew around another 5 minutes and change, proving that you really CAN learn to fly reading books and practicing on simulators (as long as you're well practiced on a simulator with Mode2 controls, not a joystick. That's why I cracked up my other stuff. The joystick doesn't develop the proper reactions).

We never got around to hand launching it.

The plane is a beauty. I think the estimates of 8 minute flights right out of the box will prove correct. After he flew, I was getting late for an appointment so I didn't fully charge the battery. Last time it took over 20 min to fully charge. I only charged it 17 min. After a 5 min flight I still had plenty of power on the throttle. I do have to admit one thing. It was a perfect day for flying. Humid but felt cool, just above 70F. Wind was 0-5 and declining. Overcast so no matter which direction you faced, there was no blinding sun. I just flew the pattern. Nice straight legs between and standard turns to the east and west on the ends.

The SuperStar EP flys EXACTLY like the PT40 trainer in the G2 simulator. EXACTLY. I can build properly and no adjustment or trim was necessary. (Now that means no coarse trim to make it fly properly. I don't bother to trim short flight legs if all I have to do is bump it 4-5 times in a leg.) I took off at full throttle. I cut it to 75% climbing and I was able to keep it about 30% once I got as high as I wanted. I'm pretty much blind in one eye (literally) and don't always see 100% out the other so just above the trees is fine with me. Without trim the plane tends to stay nose high. You've got to keep it from climbing even at 30% power. Turns are very steady with little rudder to keep the nose up. The guy who wrung it out for me looped it and said it did so easily but that it would not roll. I didn't see it when he tried to roll it so I can't comment on the roll. The loop was pretty. Mike even commented that it was a good glider. He shut off the throttle and it really floats. Landings again are just like the simulator. Bring it in under a tiny bit of power like you're going to be short of the runway, then chop power and it will land wherever you want. It will float almost all the way down the runway.

Its my kind of plane. If you want to do inverse hovers, forget it. But if you want to see what flying a real light plane is like: everything slow and steady, by the book, and with just enough power to do what its supposed to, you can't go wrong. $109 for the plane from Tower, $85 eBay delivered for a JR 6 ch with Rx all batteries, charger and full size servos I didn't use. Another 3 mini servos at $6 ea from eBay and Bob's your uncle. That's $212 total to get in the air.

When I first started going to this field, there were some old timers who just flew high wing trainers. But they had them so tweaked and trimmed I thought they must have gyros or electronic stabilizers of some kind. Their planes were rock solid on the straight legs and smooth as silk in the turns. This plane gave me a real taste of that.

Thanks again to all who responded.

boomix

Hello, I'had same kind of problem with my bird, I use this equipment and works very well, also flies 9 to 12 minutes depending wheater :

Battery : Radio Shack 7.2v 3000 mah nimh
Propeller : apc 10x10e ( also 11x10e works well )
Power system : S-600GD ( Part number GPMG0770 TOWER HOBBIES ), but you do not use the propeller included it is not good for this plane

I fly my superstar an altitude of 1,500 meters ( Mexico ) and flies very well and with less weight because a 6 cell battery pack

Hope it can help you