Slow it down but keep line tension

[Matthew Brown]

I've been flying this plane I scratch built for a couple years and in its current configuration, it flies very well but it's fast. I have turned down the motor speed with the EFlite timer but it loses a lot of line tension to the point overhead maneuvers are impossible. I'm wanting to try to use it as a pattern trainer so I'd like to have lap times around 5-5.3 seconds. It's under 4 seconds as is. I know a lower kv motor and a larger diameter prop will get me to the speed I want but I need more line tension at those speeds.
Any ideas?

Matt

[Jim Oliver]

Difficult to be sure from the pic but could you have a little left thrust in the motor?

[Matthew Brown]

It has 2-3 degrees right thrust built in. Hate to go much more than that.

Matt

[john e. holliday]

From what I see. with out the speed you need fuselage side area.  Elongated rudder top and bottom.

[Matthew Brown]

I was wondering how much fuse side area played into line tension.


Matt

[Tim Wescott]

Line length?

Wing Span?

Weight?

Are the wings really as asymmetrical as they look in the picture, or is the picture distorted?

Does it do OK in loops and squares?

Does it fly OK at 45 degrees, or can you feel it getting mushy?

On 60 foot lines and 5.2 second laps you should be pulling around 3g in level flight (if I haven't messed up my math).  Straight overhead should see the plane pulling with twice its weight if it doesn't slow down[/i] and if the lines are that long.  Centripetal acceleration goes down as the square of the lap time, so it's worse at 5.4 seconds than 5.2 -- but with 60' lines 5.2 vs. 5.4 should be a matter of tuning, not the plane falling out of the sky.  The first step of trimming a plane is getting the thing pointed straight in yaw so it won't slow down in the overheads, and pointed straight in roll so it won't fly in on maneuvers.

I'm not going to go on, because until we hear more details we can only bloviate.

[Matthew Brown]

I've been flying on 58' .018 lines. Need to try some .015"s.
Wingspan is 40-42" maybe 44". I going off of memory and best guess here. Wings are symmetrical.
I don't think I have ever weighed it but I'd guess 24-26oz with battery installed.
At current speed I can't do squares as it's just too fast for me. Loops are clean as long as I don't tighten them too tight. Regular pattern sized loops are good.
At current speed, overheads  are very comfortable, no issues with tension.


Thanks, Matt

[Dan McEntee]

  Prop pitch has alot to do with line tension also. You may need to compromise between speed setting and prop pitch, and how your battery tolerates it.  It's a nice, light model, so I think you can tolerate some more pitch, and as weird as it may sound, maybe even some ballast on the CG. Line tension is a product of speed and centrifugal force. All the little adjustments have to work together. Tip weight may help, even where you put it. But I thi9nk the areas you need to work on are power and prop.
   Type at you later,
   Dan McEntee

[Doug Moisuk]

Sure looks like in trust to me. If the leading edge was all there you would measure from the prop tip to the leading edge on both sides using the same blade.

[Steve Helmick]

At that weight, I am pretty sure you can legally use two .012" braided steel lines, but you may want to be sure of the weight (and rulebook) first. Note that leadout location and tipweight will need to be changed to suit the lines and airspeed. Increasing the prop pitch at the tips really helps overhead line tension, but APC's generally do a pretty stout job from my experience.  Steve

[Jim Svitko]

I will go along with the post about using smaller diameter lines.  For a plane of that size/weight, you are dragging around quite a bit of unnecessary line weight which will be apparent when overhead.

[Matthew Brown]

Sure looks like in trust to me. If the leading edge was all there you would measure from the prop tip to the leading edge on both sides using the same blade.

This is a bit better pic of the thrust line. The initial picture skewed it's appearance quite a bit.

I weighed the plane with battery pack. 26.3oz. I bit heavier than I thought.
Span is 44.5" area is 400squares.

Matt

[Peter Nevai]

018 lines are way too much for that model. I flying a ST51 powered Sig Magnum on .018 70ft. lines. You should be need no more than .015

[Tim Wescott]

Steve's right about line size -- the rulz say 0.012" up to 40 ounces of model weight, although some folks advise going to 0.015" lines at 32 ounces or so because they're less springy.  At your weight you want the lighter lines.

You should probably consider getting a KR timer or a governing ESC and one of the Hubin constant-speed timers.  If your motor is slowing down in the overheads to to greater load, that'll show up as a slowdown, which you do not want.

[Ted Fancher]

When you balance the airplane on your left and right index finger tips at the wing tips where are the leadouts (fore and/or aft) of the point at which the ship balances?  Especially given the length and diameter of the lines if they are too far forward the line drag will yaw the airplane into the circle and potentially have a significant affect on line tension...most especially the higher the ship gets.

Ted

[Matthew Brown]

I was using .018 lines because that is what I used back when I was flying combat. They were leftover from those days. I have bulk spools of .018, .015 and .012.  I'll make up an extra set or two.
Any disadvantage to running longer lines? I thought maybe make up a set 65' or so.
I'll check leadout location relative to CG when I get home this afternoon.
I have a KR timer not in use. I can install it when I change out to a lower kv motor.

Matt

[Jim Svitko]

It is difficult to diagnose such problems via an on-line conversation.  There could be many factors involved in this.  Maybe there is an alignment problem somewhere.  You have been given some ideas to try so let us know what happens after you make a change.  If you can, make only one change at a time.  That way you will know if it made any difference.

For a plane of the size/weight you have, I think 65 foot lines are a bit long, even if you use the smallest diameter lines allowed by the rules.  Others might disagree but only you can determine what works for you.

[Jason Greer]

I didn't see it mentioned, but I may have overlooked it.  What ESC are you using?  Is it a non governing esc?  If so, then the model is going to slow down any time you go through a maneuver.  When the model slows, then the line tension is going to be reduced. At your 4 second lap speed, this is probably a non issue, but when you slow it down into the 5 second range, then this could be a problem.

[Matthew Brown]

I didn't see it mentioned, but I may have overlooked it.  What ESC are you using?  Is it a non governing esc?  If so, then the model is going to slow down any time you go through a maneuver.  When the model slows, then the line tension is going to be reduced. At your 4 second lap speed, this is probably a non issue, but when you slow it down into the 5 second range, then this could be a problem.

It may have a governor but I am not using it. Currently just running it wide open. Installing the KR timer will fix that I think though. If not, I have several other ESCs to swap to that I know have governors.
I'm not so sure it is a loss of speed through the maneuvers. Slowed down, it was really light on the lines even in level flight.
Hopefully I can get some time this weekend to swap motor and timer and get in a flight or two.
I have been running both 8-4 and 8-6 APC props. I have a couple APC 9-4.5s to try which seems to be the popular choice for the Ringmaster both glow and electric. Any other prop suggestions, with line tension in mind?

Thanks, Matt

[Brett Buck]

I'm sure that not using the governor is an issue, , but check the alignment and basic CG/leadout positions. The picture appears to show a rather extreme skew in the tail.

       Brett

[Matthew Brown]

I'm sure that not using the governor is an issue, , but check the alignment and basic CG/leadout positions. The picture appears to show a rather extreme skew in the tail.

       Brett

The airplane is straight. It's just an odd angle that make things look askew. In the pic the outboard wing looks huge compared to the inboard but the plane is completely symmetrical with the exception of the setback of the outboard wing for the battery.

[john e. holliday]

Am I correct in that this plane is flying clock wise?  Yes go to smaller lines.   I use mainly .015 lines on most of my planes.  Did play with .012 on 25 size planes and went back to .015's.  .012 is good for .51 size planes.

[Matthew Brown]

Am I correct in that this plane is flying clock wise?  Yes go to smaller lines.   I use mainly .015 lines on most of my planes.  Did play with .012 on 25 size planes and went back to .015's.  .012 is good for .51 size planes.

No, normal CCW from top looking down.

Matt

[Tim Wescott]

It may have a governor but I am not using it. Currently just running it wide open. Installing the KR timer will fix that I think though. If not, I have several other ESCs to swap to that I know have governors.
I'm not so sure it is a loss of speed through the maneuvers. Slowed down, it was really light on the lines even in level flight.

You need to have a governor somewhere in the system.  It can either be in the ESC with a constant speed command from the timer, or it can be in the timer, ala KR.

If you're used to combat, a plane that small may feel light on the lines even when control is solid, so you want to pay attention to (or say, if you already know) if it's just not pulling on your hand or if you're actually having control issues.

Even though I tend to fly small airplanes on long lines, I think you're at the limit of where you want to go with that plane.  I have an overweight Ringmaster that flew pretty well on 60' lines (eyelet to eyelet -- 62' by the rulz) -- but that was a slightly bigger, and much heftier plane.

Like a lot of other people here, I'm suspecting leadout position -- particularly now after your comment about it being light on the lines even in level flight.  Like Jim said, this could be due to a whole lot of things.  Trying to do it over the web will take longer than if you could just go fly with someone in the know -- but we'll help you out as much as we can.  You don't need to really worry about the plane until we start throwing out suggestions for more conventional stunt trainers.

[Steve Thomas]

Am I right in thinking that compared to .012s (which I'd happily use with that model), the .018s have roughly 150% of the line drag and 225% of the weight? Because if so, that's the first thing I'd be changing.

[Matthew Brown]

Don't recall who asked, but the leadouts exit centered 2" aft of the CG and are spaced 1" apart.


I'm going to make up a set of .012"s but after so many years flying 1/2A on them, they just seems so light!

[Steve Helmick]

I'd bet that LineII or LineIII will tell you to move the LO's to about 1/2"-3/4" behind the CG. Note that the line size, length, type and speed are important info for the program, and we don't know any of that stuff at this point. Not sure if there's a link to either program here on SH, but Tulsa Glue Dobbers or NCLR sites should have it. Time for some Googling.

I'd suggest running the program for a couple of speeds and line lengths to give some guidelines. Something like 55', 58' & 60' radius, 55, 60 & 65 mph might be good approximations. Steve

[Tim Wescott]

Don't recall who asked, but the leadouts exit centered 2" aft of the CG and are spaced 1" apart.

That's way too far back.  It's probably a good thing that you don't have a fuselage to scrub off much speed from flying sideways, but it's still going to induce too much yaw -- it'll make Odd Things happen in the corners.

Do what Line III says, and if you're ripping the thing up anyway, make the leadouts adjustable.  Leadout position isn't nearly as critical to performance on a flapless plane as flapped, but it still does make a difference, and until you get it settled you'll want the ability to make fine adjustments.

[Ted Fancher]

At the risk of displaying my dinosaur degree of modern powertrains wisdom what would be a ballpark IC equivalent of the motor in question and what prop is in use and at what RPM.  (Sorry if that was covered previously).

[Matthew Brown]

At the risk of displaying my dinosaur degree of modern powertrains wisdom what would be a ballpark IC equivalent of the motor in question and what prop is in use and at what RPM.  (Sorry if that was covered previously).

I can only guess based on calculated numbers. Prop is currently an 8-6 turning around 11-12K on the ground. No idea how much it unloads in the air. Maybe a .25 ball bearing engine?
Power wise, about 400 watts. If I remember correctly, 1 horsepower is about 746 watts.

Matt

[Tim Wescott]

I can only guess based on calculated numbers. Prop is currently an 8-6 turning around 11-12K on the ground. No idea how much it unloads in the air. Maybe a .25 ball bearing engine?
Power wise, about 400 watts. If I remember correctly, 1 horsepower is about 746 watts.

Matt

Dennis Adaminson pushes going by prop diameter alone, which if you were flying more normally would point to a .15 flying a "stunt run".  Given the size and weight of the plane, that may actually be reasonable.  26 ounces implies that you need around 300-330W peak (the rule of thumb is 11W/ounce peak for "full size" planes, but smaller ones seem to want more).  Ditto somewhere around 220W average.  Get it slowed down, and you may actually achieve that.

[Matthew Brown]

Dennis Adaminson pushes going by prop diameter alone, which if you were flying more normally would point to a .15 flying a "stunt run".  Given the size and weight of the plane, that may actually be reasonable.  26 ounces implies that you need around 300-330W peak (the rule of thumb is 11W/ounce peak for "full size" planes, but smaller ones seem to want more).  Ditto somewhere around 220W average.  Get it slowed down, and you may actually achieve that.

I've been looking at the electric Ringmaster setups here and many are running the APC 9-4.5. My motor has too high kv to run that much prop. I do have the Brodak recommended motor for the Ringmaster and am planning to swap it on to the plane.

I found Line III or II on NCLRA site. For .012" lines it said 1.05" at 5.1 seconds/lap. .018"s at 4 seconds/lap it said about 1.4".  I can add adjustable leadout mechanism to inboard tip but not sure if foam has been hollowed all the way to the tip. Could make it a little tougher to get done.

Matt