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Old 12-03-2006, 04:21 AM   #1
flyingbear
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Question easy star porpoising

I have trouble with our easy stars trying to pitch up,stall,recover, and repeat.CG is OK to spec..Since I cannot change the angle of incidence of the wing or horozontal tail, the only thing I can see to do is to move the cg forward with weights.I can partially correct the problem in flight with nose down elevator.Any suggestion?

George
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Old 12-03-2006, 05:14 AM   #2
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Nah, sounds like you just need to trim it. Since you are correcting with down elevator, try adding some down elevator trim. With a little trial and error you should be able to get it flying smooth and straight (no porpoising) with your hands completely off the controls.

As it happens you can tweak the CG slightly based on taste. I tend to like my Easy Star's CG just a tad forward (nose heavy), trading a little agility for stability. The Easy Star is fairly forgiving on CG; most planes are pickier...

But, don't mess with CG to correct a plane's trim. With a little practice, trimming will become second nature. You might think that once you get a plane trimmed, you'd be done, but it doesn't always work that way. Things get out of adjustment (control surfaces bumped), different battery packs move the CG slightly, different wind conditions, etc. I often find I have to tweak the trim a little on almost every flight...

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Old 12-03-2006, 05:21 PM   #3
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My ES with a stock motor but a 3S LiPo tends to porpoise if I'm climbing full throttle and then I cut the throttle quickly. I've learned to back it off a little slower and that avoids the porpoising. I don't know why this occurs, but it does for me.

On a related but also unrelated subject, once my battery came loose inside the fuselage and could move forward and backwards in flight. Now That was an Interesting short terrifying flight of multiple stalls, to say the least.
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Old 12-06-2006, 10:04 PM   #4
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Originally Posted by rocket_jim View Post
My ES with a stock motor but a 3S LiPo tends to porpoise if I'm climbing full throttle and then I cut the throttle quickly. I've learned to back it off a little slower and that avoids the porpoising. I don't know why this occurs, but it does for me.
Yeah, I've noticed that tendency, too. Pretty subtle with non-LiPos; I imagine your battery gives you pretty healthy thrust, and so the tendency would be more obvious. I don't know if the thrust angle on the motor is wrong, or if you just can't trim some planes correctly for all power levels. I tend to just trim my Easy Star for glides, and accept some nose-up tendency while it powers up... I usually don't bother to roll off the power; I just expect that porpoise at the top...

Originally Posted by rocket_jim View Post
On a related but also unrelated subject, once my battery came loose inside the fuselage and could move forward and backwards in flight. Now That was an Interesting short terrifying flight of multiple stalls, to say the least.
Yeah, I've had this happen, too! Sort of a vicious cycle: if a loose battery shifts the CG back, the plane tends to nose up, which causes the battery to slide further back, which shifts the CG further back, which makes the plane nose up more, etc. If a plane has space all the way back to the tail, and a battery slid back there, I guess you could just hang it up, you're doomed!

And if your ES canopy is like mine (pops off if you even glance at it), you can't count on it to hold the battery in... I've ever had a battery eject in flight... been lucky... so far...

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Old 12-06-2006, 11:31 PM   #5
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Thanks for the responses! Full nose down trim did not quite resolve the problem with one ES.I moved the CG forward a little with a fishing wieght in the nose and both fly fine now. I wonder if it is the variation in the angle of attack of the horizontal tail resulting when it is glued in?

George
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Old 12-07-2006, 07:07 PM   #6
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Originally Posted by flyingbear View Post
Full nose down trim did not quite resolve the problem with one ES.I moved the CG forward a little with a fishing wieght in the nose and both fly fine now. I wonder if it is the variation in the angle of attack of the horizontal tail resulting when it is glued in?
Hmmm... What does your elevator look like with full nose down trim?

If it doesn't really angle down very much, you may just need to adjust your servo linkage. Turn on your radio, hook up a battery, make sure your sticks and trims are centered. This should move your servos to their "center" position. At this point the elevator and rudder should both be neutral (not deflecting either way). If either of them isn't neutral, use a small Allen wrench to loosen the nut holding the control horn to the control wire, and let the control surface move to neutral (again, making sure your servo is centered, too.) Then tighten that nut back up. Now you should be able to dial in enough trim to make the Easy Star fly nicely.

If your elevator is angled way down (say, 20 or more degrees), then you have a bigger problem, like (as you say) the tail feathers being misaligned. This should be fairly obvious; look at your ES from the rear, and see if the horizontal stabilizer is "flat", parallel with the body. If you still have the two-sided sticky tape holding the tail on, you might consider taking that off and gluing the tail on. First make sure it is fitting correctly, so that the tail features are straight with the rest of the plane. I used CA glue, but you could use others...

Good luck!

~~~~~~~~~~ let's go carve some air ~~~~~~~~~~
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Old 12-17-2006, 09:42 PM   #7
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Thanks,ADHOC
It's taken a little time to get good flying weather here. The Easy Star that I have been working with checked out OK as far as the control neutrals and horizontal stabilizer position goes.I previously used CA to attach the horizontal since the tape did not hold in our cold Montana conditions.We fly in rough fields by our home at 5100 ft.I have experimented with and without lead in the nose and it just does not fly well at the suggested CG.With the CG moved forward , it does fine.Good climb,loops,turns with bank,etc.
The stock rudder seems OK to me ,but I read a lot about increasing the size of the rudder.Is this worthwhile? How about increasing rudder throw by moving the pushrod attach point?

George
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Old 12-18-2006, 12:27 AM   #8
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Originally Posted by flyingbear View Post
The stock rudder seems OK to me ,but I read a lot about increasing the size of the rudder.Is this worthwhile? How about increasing rudder throw by moving the pushrod attach point?
Either or both of these work fine. I've done both, and that way you've got extra control to work with. I usually fly with low rates (50% or less), because with the bigger rudder and increased throws you don't need much. But sometimes it is fun to switch to high rates and crank it around in semi-tight turns (as tight as you can get with a high-dihedral, stable flier)...

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Old 12-18-2006, 04:51 PM   #9
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flyingbear,
I bought an EasyStar last summer and experienced the porpoising you refer to also. Many do as I found out in searching for answers. I think mine was due to a slight curved fuselage not allowing the wing and horiz stab to be at proper angles to each other, moving the CG never did eliminate it completely. I shortly after moved on to aileron planes and never experimented much in seeing if I could improve it, but here are some of the posts I had saved.




Several links from others talking about this:
http://www.rcgroups.com/forums/showp...postcount=5745
http://www.rcgroups.com/forums/showp...postcount=1852.
http://www.rcgroups.com/forums/showp...&postcount=115
http://www.rcgroups.com/forums/showp...&postcount=472


other sites:
EasyStar build log by sargentw: loaded with info
http://www.rcgroups.com/forums/showthread.php?t=350408

EasyStar Fan Page with modifications:
http://www.mpx-easystar.de/

good flying, almsy
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Old 12-19-2006, 07:25 PM   #10
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I would try moving CG forward just a little. If it is not simple to move things around, just stick a quarter in teh nose somewhere where it won't move. Try it.

Most likely the H-Stab is up slightly in the back from incorrect installation. If you can't move it, then a little down trim will work. It adds drag but if you are flying under power most of the time it won't matter much. If you like to thermal the plane then you may want to try and move the h-stab.

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Old 12-22-2006, 08:58 PM   #11
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Default Porpoising

I took my father&his Easystar out yesterday, and I saw him experiencing the same problem.

I had less of a problem with it (almost nothing), presumably because of the following:

1. I anticipate more than he does, so I give a bit of nose down (or perhaps less nose-up) when the nose stops sinking/starts raising, instead of giving nose down inputs when the EZ* is about to stall

2. I fly faster. I prefer to fly it in large swooping curves, using the natural finesse of the wing, instead of slow and angular patterns. If I fly it slowly and haltingly, then the porpoising happens here and there as well.


FWIW,

Chris.
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Old 08-18-2007, 04:18 AM   #12
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Default easy star

Since I have changed to 8 cell NiMh batteries,both my Easy Stars fly very well without ballast and with a very small tendency to porpoise at times.I think this depends on flying conditions and how I am handling them.Thanks for the help.

George
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Old 09-11-2007, 03:17 AM   #13
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Originally Posted by adhoc View Post
Yeah, I've noticed that tendency, too. Pretty subtle with non-LiPos; I imagine your battery gives you pretty healthy thrust, and so the tendency would be more obvious. I don't know if the thrust angle on the motor is wrong, or if you just can't trim some planes correctly for all power levels. I tend to just trim my Easy Star for glides, and accept some nose-up tendency while it powers up... I usually don't bother to roll off the power; I just expect that porpoise at the top...

Yeah, I've had this happen, too! Sort of a vicious cycle: if a loose battery shifts the CG back, the plane tends to nose up, which causes the battery to slide further back, which shifts the CG further back, which makes the plane nose up more, etc. If a plane has space all the way back to the tail, and a battery slid back there, I guess you could just hang it up, you're doomed!

And if your ES canopy is like mine (pops off if you even glance at it), you can't count on it to hold the battery in... I've ever had a battery eject in flight... been lucky... so far...
My AeroBird had the same problem. A rubberband around the canopy and fuse. No more problem.

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Old 09-11-2007, 10:45 AM   #14
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Porpoising is usually caused by too much up trim in the elevator. If you want the plane to fly well you have to fix the h-stab alignment or you have to put in down elevator, and down causes lots of drag.

Using a lot of nose weight to this is control this is a very bad approach. Plane will be a real dog.

HOW TO FIX THE WING/STAB ALIGNMENT PROBLEM

Set the CG to the factory position and then don't move anything, or mark it so you can get it exactly back to this position.

Do several hand glides to see how the plane behaves. You can mark how far it glides. Not a precise measure but it is at least a reference point.

Disconnect the elevator and rudder control lines and tape over the ends so you can't get glue or debonder into the tube.

You can unglue the h-stab and reset it if it is glued. It will take some work. Use CA Debonder to break the glue joint.
http://www2.towerhobbies.com/cgi-bin...?&I=LXK299&P=7

First, make a mark so you can tell the current alignmnet. Just a swipe across the joint is all you need. I suggest one on each side. Use a pen, or something that will give you a very fine line. Pencil may work.

Now, work the debonder in to release the glue. This will take a while as you have to work it deep into the joint. Don't rush it. A little at a time. I don't think you need to unglue the fin, but I could be wrong.

Once you get it loose, you can reset the stab.

Move the front of the stab up a little. Rotate the top mark forward, perhaps 1/16 of an inch. See if you can reset it with double sided tape temporarily.

Now, do a hand glide and see if you get a longer glide. You should. Remember all glides are done from a LEVEL throw and with the motor off. Into the wind but for this to be a good reference it is best if there is no wind at all.

Once you feel you have a good glide, secure the h-stab. Again I would suggest double sided tape, whic his what the RTF package uses. Heavy duty carpet tape should work.

Now reconnect the controls, retrim and go test fly it on a CALM day. If you have succeeded in removing the porpoise, you can remove the tape and reglue, although if you use strong carpet tape you may not need to reglue.

Give it a try.

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Old 09-11-2007, 12:17 PM   #15
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Im a believer of "battery placement can make or break your plane" the batt is the greatest influence (most cases) on the CG of the plane. I dont know much about your fuselage.. but why weight down the plane further for balance when your moving your batt can do it for you...

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Old 09-11-2007, 12:58 PM   #16
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I have yet to fly an Easystar but was into sailplanes years back and frequented the same problems, simply shifting weight slightly forward usually did the trick, only time adding weight was during windy conditions, note winds can change alot during flights, often more wind at higher elevation, gusty can give you fits...remember my first roller coaster, over controled and things became worse, give max down trim and stick if necessary, bring it down and adjust prior to next flight...BEST
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Old 02-02-2014, 08:00 PM   #17
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Originally Posted by AEAJR View Post
HOW TO FIX THE WING/STAB ALIGNMENT PROBLEM
resurrecting a long-dead thread to give props for some great advice. i spent some time hand-gliding and tweaking then did a powered flight. it was a hands-off launch and with a gentle climb. minimal trimming for full/no throttle. i like my ez*again and i can remove the weights hanging off it. thanks!
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Old 03-10-2014, 01:39 PM   #18
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A lot of models porpoise behaviour is due to holding a touch of elevator to do level flight ... as you move stick to maintain it - you don't return to the offset neutral ... the trick is to recognise that you are unknowingly holding offset and alter trims to get rid of it.

If you want to see porpoise action ... try my SE5 on full throttle ! Makes a Rodeo horse look like a paddock pony !

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