Well, I'm sure these are probably old, recurring questions, but perhaps those of you who have been on longer can point me to the relevant threads.

I'm getting back to flying enough that I can start to notice the trim of the plane and there are a couple of problems (of course).

Upright and level flight, the outer tip is a bit low and inverted it is a bit high. I can just see the bottom of the wing inverted and almost can see it upright. I've checked for warps and flap/elevator misalignment and that looks pretty straight, but obviously something is off, so where's the most likely source of the trouble? Or what should I specifically try to measure/observe to get better clues?

This seems to be making the line pull decrease in outsides, though the plane will fly at the top of the circle pretty well, line pull is about what I calculated. This is my E-Panther, outer wing is 1 inch shorter than inner, as is the flap. No rudder offset and about 1/2 degree of motor offset.

Whatcha think?

John Witt

well its either a twist warp, could be subtle, or if this is the one you converted to electric? its very possible the vertical CG is off. If the leadouts are lower than the vertical CG it will cause the symptoms you are having. the way to check this is to hang it in a door jamb from the leadouts. The wing should be vertical to the ground ( or plumb if your a framer) My guess is that you will find it hanging with the bottom tip of the wing towards the direction of the wheels, just like it is in flight. Now look at where your battery is in the fuse. If you can move it down lower in the fuse it will help this.
If this is not what I recall, that is electric, ignore the battery comments,,
If the wings are perpendicular to the ground,, then you have a warp issue and tweaking the flaps, or adding a trim tab is the solution. But my guess would be towards the vertical cg being off

Thanks everyone,

I suspended the plane by the leadouts and it does hang slightly outer tip low compared to the door jamb. Plumb silly of me not to think of that. By pressing very lightly on a gear leg, I could cause it to even out, so I think I'll try it with a little weight attached to the outer gear leg and see what happens. The battery sits just aft of the CG right on top of the center wing skin, and the motor centerline is also about even with the top of the wing. The leadouts feed out on the underside of the tip as well.

I sat the plane up very carefully on a table and measured to the TE and then the flap TEs and they are pretty good. Less than 1/32 difference and then inboard one is the high one, which should counteract the effect I'm seeing. However, it's still possible to have an imperceptable warp or assymetry, of course.

BTW, Dennis, is the Mythbuster symmetrical, or does it have a shorter outboard wing?  That is an elegant bird, nice work. These electric planes can sure have clean noses. Next thing you know, someone will be wanting to convert it to glow.

John

Hi John.

Thank you for kind words about the Mythbuster.  It is equal span.  If it was converted to glow I would change the airfoil and probably lower the wing a smidgen - for better vertical CG.  in the end it could LOOK the same but it would not be the same airplane as the electric version.

Re the Panther:  While vertical CG might be off a little, remember that your E-power version is MUCH better balanced than a glow version would be.  The Panther with an upright engine - especially one with a heavy muffler - would be seriously top-heavy compared to yours.

If it was me I would try flap tweaking. OR since it looks like you used a moneycote finish, you might do better trying to twist and shrink JUST A LITTLE twist in the wing.

Being naturally lazy, I thought I'd try adding a little weight down low on the landing gear leg first and see if vertical CG is the issue. I'd have to cut into the covering and structure of the tip to move the leadouts. I have the battery as low as it would go and far aft to get the longitudinal CG in the right place. Can't imagine how nose heavy one of these would be with a Fox 35 and fuel tank in the nose.

Also, I moved the motor down about 3/8 inch to get the thrust line closer to the wing CL (see picture). I was reluctant to cut the wing sheeting to build a battery box in the wing, but I think next time I'll do a hybrid structure that's got a battery cutout and come up with a way to carry the wing bending and torsional moments around the battery. The structure will be a little heavier that way, but save other trimming problems, perhaps.

Thanks for the suggestions.

John

That's a good idea.  I have some sheet lead and I'm just going to wrap some around a gear leg. Weather permitting I can test it Tuesday PM after work and see if there's improvement. I'm also thinking I could take along a bit of thin aluminum and tape a tab to one of the flaps as a second thing to test. I only get two flights, so have to make each one count. Ship has eighteen flights now.

Once I get an answer -- I'm inclined to think it's the vertical CG -- I can do something like the heavier wheels. I could machine up some with solid aluminum hubs. Does anyone still make the old Kraft wheels?. They were relatively heavy, but low drag.

John

Thanks for the comments, Dean.  The Panther is a somewhat dated design and the sheet on the belly is close to the bottom of the wing, so the batteries really can't go there. It was meant to have a Fox 35, upright like nature intended.

I built the Panther because it is an icon from my misspent youth and I had the plans. I figured I'd learn a lot from it and thought of it as a sort of test-bed expendable plane. It's actually flying well enough to remove the thought of it being expendable, and it's a good exercise in learning to trim. Keep in mind, I never was much of a PA flyer many years ago (45), so I'm really still on the steep part of the learning curve.  What I didn't want was something that flew so poorly that it would be an obstacle to learning aerobatics, and, while it certainly isn't a world class design, it was fairly easy to build and so far is not limiting me. One of these days it will, then it will be time for a new plane.

I'm learning so much from the forum and watching PW, HR and DR that my ideas about another plane are changing pretty fast. I do know it will be electric. I would never have restarted in CL if I had to deal with glow engines again.  I love the sound of that thing spooling up.

John

After some consideration about how to do it, I ripped out a couple of bulkheads and part of the center sheeting and moved the battery forward and buried it into the leading edge. This lowers the battery by abut 1 inch. I moved the timer and ESC so they are now aft of the CG. Overall, the plane seems to be very slightly nose heavier than it was, so I may need to add some tail weight. We'll see.

This move doesn't completely put the battery on the wing center, but should help a lot, and should reduce the amount of added weight req'd to get the CG down as required. Some more testing this weekend, I think.

John

Dean,
I have plans drawn up for a Gee Bee stunter with the battery vertical ni front of the wing leading edge. seems like a logical way to keep the weight close to the CG

As a comment, I don't seem to have a balance problem by putting the battery in the tank area. I assume this is a result of the motor being relatively light motor.

Got in two flights this morning in dead air. Lateral balance looks pretty good from the center of the circle, so moving the battery looks like a good thing. Vertical eights pretty smooth at the top with nice line tension. It will fly right up at the top of the circle with good tension, can only make about three laps up there before I get dizzy. The ship is going to take a small amount of tail weight, I think. It's not turning as tight as before unless I really yank on it, but of course the flip side of that is that level flight is flat as a pool table. I'm about ready to move the lines out one notch on the handle as well. May get a chance to try that stuff this evening.

My wife is out of town, so I couldn't get down to the Stunt-a-Thon. Guess I'll use the time for building.

One of the things I didn't think about when building the Panther was being able to adjust the leadouts, so I may bite the bullet and rip into the wingtip and alter that as well. I have 3 degrees of sweepback on the leadouts, but they are about 2 inches apart. I'd like to move the front one aft about an inch. I can see the plane yawing some when I push or pull hard.  We didn't do that stuff back in the 50s.

I'm beginning to get to the end of the big trim changes. Getting hard to see the differences. I need to fly some more, for sure.

I also turned the power setting in the timer down a bit, from 90/95 to 88/90, since the laps were a bit fast last time.

Regards to all, and thanks for the comments. The contributions from the forum have made progress with this bird much faster--lots of things I would not have thought of.

John

On recommendation of wiser heads ( hard to find any older ones), I replace the E-Flite Power 46 with a Rimfire 35-48-1000kV. The Rimfire is 4 oz lighter than the E-flite and I was also able to remove about 1 oz of lead strips wrapped around the tailwheel strut. I had to make a spacer/adapter to fit the Rimfire mount to the mounting rails that were installed for the E-flite. I was also able to lower the motor slightly to get the thrust line nearer to the wing CL and get the vert CG down just a bit more.

All in all, the balance point came out to be nearly perfect -- it was still nose heavy with the E-Flite and the battery moved forward.

The performance is --dare I say--"sparkling".  The plane is really beginning to feel pretty good. The ESC is set to RPM mode at 9600 RPM with an APC 11-5.5, laps are 5.05 sec on 65 ft lines. Overhead performance is good, it will loop around the top of the circle with full up, turning about 15 ft diameter loops.  32 flights now, 110 minutes total time.

John

Good stuff John,
keep plugging away at it,,

JW:
From the start of your E-Panther adventure to where you are now - you HAVE really gone a long way!  Thanks for sharing all you are learning too.

Alan H is successfully flying both his Nobler and his new Vector (slightly larger than the Panther) on 2100 packs.  Comparing your set-ups the biggest difference I see is the line length and the prop.  He is using 60' eye to eye and you are using 65'; he is using a 12x6 and you a 11x5.5.  I wonder if you could reduce your power draw and get the get the full pattern in if you shortened your lines, powered down to a roughly 5.0 lap time, then set your timer to about 5:30?

Hmmm, never occurred to me after reading your last note.  This applies to ALL of us:

THE TRIMMING CYCLE (or ANOTHER 12 Step Plan  )
1. Fly the bird, wish it flew better
2. Adjust the power
3. Adjust the CG
4. Tweak the flaps
5. Adjust the tip weight
6. Adjust the line length
7. Adjust the prop size
8. Shim the tank, change the plug.  For electrics change the governor gain, timing or PWM rate.
9. Adjust control throws, neutral settings and anything else that can be made straight or crooked
10. Thrust line tweaks - always good for a laugh
11. Re-examine and potentially re-adjust any/all of items 2-10 based on a change to any one of them that might affect another (huh?)
12. Fly the bird, wish it flew better  

(all offered in jest!)     >   >

OK, I'll give those things a try. I have some 60 ft lines and I also have a 12-6 and a pusher 13x6.5. I could cut the pusher down to 12 inches and repitch it -- that's about the largest diameter I can run with the current LG length.

So what your suggesting is: Get the line length down--reduces drag and weight a little. Reduce the RPM some and slow the plane down a little more--reduces power requirement.

When you run the motor backwards with a pusher prop, does the ESC (Castle Phoenix 45) automatically re-jigger the timing for the opposite rotation, or is that a separate adjustment?

In each one of these flights, I have been practicing PA as well, so the demands on the plane's performance are gradually increasing. Slowing the plane down is probably a good idea, because I feel rushed trying to do a square loop for instance, even with the bottoms at around 10 feet or more. I always shorten the down leg and screw up the second loop.

I've been thinking seriously of giving up on trimming the Panther and building a Nobler, just because it is such a known quantity and I always like the way mine flew back in the good 'ol days. Or perhaps some other ship like a Vector or maybe an 80% Impact (or even a Mythbuster!!). I could lift the whole power train out of the Panther and that would keep the cost down.

Thanks for the suggestions and the encouragement. This is being a lot of fun, in no small part because of the support from the U/C community. You guys are great.

John

Actually, the CC software states that it adjusts the timing automatically, but I think you are right, if you swap two of the leads it's a "don't care"; the phase angle leading the magnets just switches.

So I cut down the pusher 13-6.5 and it makes a rather fat bladed 12 incher. At 8800 RPM on a test run in my garage, it really pulls, noticeably stronger than the 11-5.5. So I set it back to 8600--still pulls pretty strong.

We'll see as soon as the wind dies down a little. Sure is funny watching it spin the wrong way, but the breeze is going the right way. 

John

Do as Dennis advised.
Not only the higher pitch asks for lower revs, the larger diameter increases the efficiency.
So you can do with a slower setting. 
My thoughts:
Set your timer at 1 min 15sec. Make 4 hops and vary the rpm setting one notch at a time.
Make notes of lap times and fly a single wingover, feel how it's overhead, do one or two loops and check for roundness.
Most likely you'll find that the larger the prop diameter, the easier it becomes to fly round loops.
Take the setting that seems to yield the best results, put in a full battery and go for the full schedule.
As the level laps are by far the larger part of the schedule, the increased efficiency will bring the current down there.
While the manoeuvres will draw more current, they won't outweigh the gain on the rest.

After thinking it over and doing a couple of test runs in the shop, I decided the same thing. So I got in two flights this morning with the cut-down 13(now 12)-6.5 pusher and 60 ft lines. ESC set at 7800 RPM and it turned out to lap at 5.0 sec. A little bit of mist and substantial wind. Where I fly there is 70-80 ft high row of trees on one side, so in this wind there is a substantial amount of turbulence--I get to see the top and bottom of the wing. I got blown out of overhead 8s, so it was hard to say about the line pull and pusher prop. In level flight it pulls pretty hard, so I can probably slow down some more. If the weather doesn't get worse today, I can go back and try it a little slower yet.

The battery used 1450 mAh for 4 minutes which is just about the same energy rate as before, even though the plane is going faster. That's probably just the difference in line drag.

Not sure these flights show much of anything to draw a conclusion from because of the weather. The plane certainly is not worse!!

Good suggestion about the small hops. I'll go back when I have a little more time and take the computer so I can program the ESC.

Alan, I hope your jet lag doesn't last and you can enjoy Geneva.

John

The Panther at my first stunt contest. Was a lot of fun, and the only electric there. A lot of interest shown, however.

http://flyinglines.org/OBSSC.09.html

John

Based on what I heard there, if I had to make a guess, I'd say Jack Pitcher.

Another interesting point: Flying in the 10mph +/- winds I was using about 100 mAh less battery capacity than the usual near calm winds I fly in. About 1650 instead of 1760. I think this has been reported by Alan Hahn and others, but this is the first time I've seen it. Was true for all 6 flights I made.

John

Couple of good outcomes there John.  On the motor rubing: you think anything happened to make it touch - did the cowling move, or is the motor getting "loose" - as in the bearings wearing out?

Thanks for the kind words, guys.  The bird has turned out to be a big return on the building investment.

The motor appears to be just fine. I think the noise has been there right from the time the motor was changed from the E-Flite 46 that was in there. I had done some trimming on the bottom cowl that was where I thought  the noise was coming from. The top cowl flexes a little as the hold-down screw is tightened, so the sound was there more or less depending on that screw.

It was only interfering a few thousandths of an inch, but apparently was making the cowl act like a sounding board which was amplifying the sound.

I did some experimenting again this weekend (8/30/09) with the pusher prop set up. I have a prop which started life as an APC 13-6.5 E Pusher. The motor I have is a 1000kv, not ideal for this prop. I set the rpm to 8400, and on the first flight was getting 4.6 sec laps. Way too fast!

Since I did not want to run the motor any slower (getting the "Too slow to govern properly warning"), I started cutting the prop down to see how that worked. I've ended up with the prop cut to 9.3 inches dia, which makes this funny looking paddle-bladed thing that looks like it belongs on a crop duster. The laps are now at 5.4, a little too slow, so I'm going to bump the RPM back up to 8450 or 8500. Battery power was down about 150 mAh (1640 mAh--5 minutes). Line length is 64 ft eye to eye, about 68 ft turning radius to A/C centerline. Dead calm air. I'm amazed that the prop is delivering this level of efficiency cut down like it is.

The plane flew pretty well at this setting and I was able to do my first ragged outside squares, still at this speed a little light on the overhead 8.

I think I need to see about a 11-4 pusher if there is such a thing, or repitch a prop to get that. Also, maybe change the motor to one that's about 650kV for my 4 cell battery.

John

I have decided to make some more changes to the Panther. I ordered some new 2650 mAh batteries to replace the 2250s now being used. The new batteries will fit in the front bay, but will require relocating the cooling air exhaust duct forward. New batteries are 30mm longer than the old ones and about 1 oz heavier.

The front ducting will get rebuilt with 1/16 inch thick 5 ply instead of the 1/8 inch lite ply now in that spot. I will rebuild the motor mounts and spacers to move the motor back a little with the goal of having the overall weight and CG location stay the same.

The current power usage is 360 mAh/minute. If I allow 5:45 to do the whole pattern, that will mean I need 2070 mAh. That is 78% of the charge for the 2650 batteries, so should work OK with a little margin.

Also planned is a motor change to 850 kV from the current 1000 kV, in order to let the governing work more effectively with large props at lower revs. The CC Phoenix wants to be at 70% throttle minimum to govern properly. 13.8V * 850 rpm/V= 11730 rpm x .70 = 8211 rpm, a much better place to be for using a 12-4/5/6/prop size.

I'll post some more pictures as this progresses, probably in about 1 1/2 weeks. 

John

Report on Sunday flights. I keep learning something every time around. First things first: this was the day of the 100Th flight! A real milestone for me and the Panther! 

This is the new setup:

Turnigy C3548 800 kV motor
APC 12-6 prop
Zetron controller with the following settings: Start speed and end speed set to 50% (25 on the dipswitch binary sum)

CC Phx 45 ESC set to SET RPM mode at 8500 RPM for all three bands.

64 foot lines, 5.2 sec laps.

I had been running the same set mode RPM set to 9500 with an 11-5.5. The timer had been set to 100% throttle and with these settings, the plane was slowing too much in the corners and other places where the power demand was high. Paul Walker suggested I adjust the timer's power settings.

Apparently the timer's power setting acts in a fashion other than I had understood in its interaction with the ESC. It seems that the power setting acts more like the throttle pedal in your car (Perhaps Alan or Igor can elaborate on this). If you have the setting at 100%, there is no room left for the ESC to govern the prop RPM as the load increases. With the timer power set at 50%, the ESC can now go up or down from the midrange to maintain the set RPM. The action seems to be involved with the input pulse width the ESC is getting from the timer, but the set RPM number in the ESC applies and the prop still turns 8500 or whatever it's set to.

It's a major difference, as the Panther pretty much quit wallowing its way through the squares and maintains good overhead tension. I started the day with the 11-5.5, and ended up with the 12-6, 1000 RPM lower. My thanks to Paul.

The Zippy batteries seem to be pretty heavy. I will have to take one to work to weigh it. They did however get me to the 6 minute flight mark. Now I have to learn to do the rest of the tricks. 

John

John,
I am not positive what you are saying. But that never stopped me from "bloviating"!

With your kV, it may be that 9500 rpm was just unattainable for your battery in the overheads. The only constraint on an electric motor--( at least until the windings begin to melt!) is the rpm curve it can make. If the motor kV is too low, it just won't be able to make that rpm---even if there is very little load.

So all you can do --well, for the least expensive option---is to go to a propeller that can make the thrust you need, but at a lower rpm. And that's what I think you did with the 12-6 prop. So now the ESC has enough reserve battery voltage to juice up its output when you pull the nose up.

I think as we buy new ESC's, the ICE controller will open a lot of eyes--when you can see the output power % curve, you will know exactly what your combination (motor and  battery) are capable of.

But getting back to one thing you said, the timer output has almost no effect in "Set RPM mode", other than choosing one of the 3 set rpm values (four if you include "off").

If you are running in high or low governor mode, there is another constraint that the ESC is limited to certain rpm bands (which depend on the # magnets). I don't recall if you were running in that mode with the 11-5.5 prop. In that case 9500 might have been too high if you were in low mode (or was that high mode--I have forgotten how that actually worked!).