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Jan 23, 2018, 09:33 PM
Displaced Alaskan
Boondawg's Avatar
Thread OP
Discussion

Greetings From An Old/New Member Of The Sport!


Hello!
I have been away from the sport since the early 80's, and have recently decided to get back in & up. I was never really a great flyer, but I always enjoyed building those early kits. As a child, I cut my teeth on most of the rubber-powered tissue & dope planes Guillows had to offer, including the Giant Scale P38 Lightning & B-17 Flying Fortress. I then moved on to Cox Control Line for awhile before getting into Radio Control with mostly small, too fast .049 powered "darts".

I then moved into gliders.
My favorite balsa kits were the Carl Goldberg line of products.
I enjoyed the floaters, but I thought the old-time Valkyrie & Comet Zipper was a little bit above my building skill level at the time.
That is when I found The Gentle Lady & The Sophisticated Lady.
I was in love
Then I discovered you could attach a .049 powerpod to top of those wings and do away with hand & Hi-Start launch.
Ohhhh boy!

Then came electric power.
I immediately moved into the Carl Goldberg Electra Deluxe & The Mirage 550.
Not quite floaters at 3 pounds each, but none-the-less, I was in love with these 2 electrics.
In the 80's I built, flew, & crashed, 2 of each these, before leaving the sport.

And here I am, some 35 years later, to begin again.
I could have just went with a PNF, RTF or an ARF and got back in the air for a really great price nowadays.
But I really wanted to build, too, like in the old days.
There just didn't seem to be a lot of balsa kits out there in the style I liked.
What to do?

Ebay!
I have just acquired, new-in-box, 1-Carl Goldberg Electra Deluxe & 1-The Mirage 550.
My favorite of old!
Kind of expensive at $100 each, considering the old heavy wood (heavy tail section), beer-can sized obsolete motor (that i'll never use anywhere), light-wingloading (free-flight style) airfoil, bulky aerodynamics, etc.
But what cost, nostalgia?!

I am going to start with The Electra.
With all the updated technology nowadays, I'm hoping to bring the weight in at around 30 - 32 ounces.
As is usually the case when starting something new, I have jumped in with both feet, without doing much research.
Here's what I have purchased*:

Brushless Motor: KV930 Motor
Prop: 10x8 Folding Prop (may be too big...)
ESC: 30A Brushless Speed Control
Servos: SG90 Mini Gear Micro 9g Servo
Battery: 1800mAh 3S 11.1V Battery
Charger: Kinexsis KX80 80W AC/DC Battery Charger
Radio - Flysky FS - I6 2.4GHz 6 Channel Transmitter & Reciever

What mistakes have I made?
Motor not big enough?
Battery not big enough, or too big (weight-wise)?
Servos too small?
Prop too big?
Any foreseeable problems you can think of?

I realize I probably should have asked these things BEFORE I bought in, hook line & sinker, but you know old dawgs & new tricks!
Total Cost For Everything* (minus the Mirage 550, which was another $100) : $300.00

*Including:
Hot Stuff Super T Thin & Medium CA Glue
X-acto Knife & Extra Blades
Sandpaper & Sanding Block
Glue Tips
30 Minute Epoxy
Fine Fiberglass Cloth
Gold-N-Rods Control Rods


I think all that's left to buy is:
2 Rolls Ultracote
Application Iron
Pin Striping

P.S. I bought the Fine Fiberglass Cloth & 30 Minute Epoxy for strengthening the nose cowling on the Electra (it can use the extra forward weight), and the nose cowling and wheel pants on the Mirage 550.
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Jan 23, 2018, 10:38 PM
B for Bruce
BMatthews's Avatar
We need more information on the motor to suggest anything. But other than the possible prop mis-match it all seems pretty normal.

In particular we'd need specs on the motor wattage or maximum current ability to evaluate the motor. The Kv value is sort of like the "built in gearing" for a brushless motor. You want the right way with the low Kv value but we still need the current or wattage info.

With today's light motors and light battery packs and if the kit does not have balsa that barely floats then it should be possible to build your Electra up to a much lighter weight than you expect. I've seen a couple of scratch built GL's that are electric powered here in build threads recently that came in at the high 'teens or low 20's for weight. So it can be done. But only if the wood is light enough.

In particular look at the wood for the tail surfaces. If you can use the firmer stock for the spanwise parts of the fin and stabilizer and replace the rest with light stock you can avoid needing a bit of nose weight.

You may also want to consider installing the motor so it is in front of the front mounting bulkhead instead of behind it. that'll mean making up a bit of a cowl but it'll let you move the motor ahead and also slide the flight battery up closer to the nose. And that'll save you needing to add too much nose weight.


The servos are fine. It doesn't take much power to move the surfaces on a glider due to the low flying speeds. But do pay attention to good free moving hinges and clean pushrod installations that don't bind.

And Welcome Back ! ! ! !
Jan 23, 2018, 11:24 PM
Displaced Alaskan
Boondawg's Avatar
Thread OP
Thanx!

The Brushless Motor:
KV:930
Max Efficiency: 80%
Max Efficiency Current: 20A (>75%)
Current Capacity: 15A/60s
No Load Current @ 10V: 0.5A
No. Of Cells: 2-3S Li-Po (6-10S NIMH) battery
Motor Dimensions: φ28 x 28mm
Shaft Diameter: φ3.17mm

I have a standard "X" type motor mount, as well as a 45 degree squarepost mount, incase I want to run the motor out there a-ways.
I also have plenty of extra balsa, bass wood, & pine, as well as light plywood for any kind of firewall modifications I may desire.
I even hear it don't hurt none to lengthen the nose of the fuselage a few inches on the Electra.
Supposedly produces a much more flyable vessel!

I am also going to lighten the rear as much as possible.

Any advice on folding prop size?
8x6?
9x5?
Do I have too much prop at 10x8?
Last edited by Boondawg; Jan 23, 2018 at 11:38 PM. Reason: Spelling
Jan 24, 2018, 02:12 AM
B for Bruce
BMatthews's Avatar
Did you cut and paste the info or copy it and type it in? I ask this because it says max current 20A but then lists a current capacity of 15A for 60Sec max. That seems odd. Sort of like something got missed.

Anyway.... if you can put 15A through the motor on a 3S Lipo pack running at roughly 12v through the middle of the discharge curve than that's 15A x 12v = 180 watts. Now if you can keep the weight down to, let's say, 25oz that is 25/16= 1.56 lbs. And that means you'll have 180/1.56 = 115 watts/lb of model weight. And that figure translates to a vertical climb or near enough that there's no difference.

Now if you run it at some reduced throttle it's clearly still going to climb at a pretty good clip. And likely as not it'll maintain altitude at just into an "idle" power setting.

And in case you're wondering the shaft size at 3.17mm is 1/8".

The only real way to say for sure if the prop is too much is to buy a wattmeter and run the setup through the meter and see if it pulls too much power.

Now the way these motors are you can set the power delivery with the prop size. Smaller prop pulls less total power. And clearly you've got LOTS of power if you load the motor down with a larger size. The trick is to use a size which won't let the smoke out. These motors will happily spin whatever you put on them. They don't know they have a limit. But they do and they'll run hot in the windings and burn themselves out.

If you don't mind buying another prop or smaller blades for the hub if that's the sort you have I think 9x5 blades would be just fine. You'll pull a little less current, the motor will be happier and if you still pull enough current to reach somewhere around 70 to 80 watts/lb the model will climb at a roughly 60į angle with a fair speed to boot. So clearly still well powered. And FAR better performance then the old can motor with the heavy 7x C size nicad packs of Ye Olden Days....

If you know you're back for good this time I would really suggest buying a wattmeter. They are so cheap now and such a great tool for picking props for motors that it's almost foolish to NOT have one.

Sounds like you've got the old skill for picking your wood density and knowing where to use it. Keep the tail light and by all means extend the nose if you like. I wouldn't go more than around 1 to 1.5" or it'll start to look like Pinocchio telling a fib. But a little will sure aid with getting a balance with less nose weight.
Jan 24, 2018, 09:41 AM
Displaced Alaskan
Boondawg's Avatar
Thread OP
Thanx for all the math!
I am so horrible at it.
I did copy-&-paste, but the descrepancy in the motor specs Is probably a translation error from Chinese to English. Not knowing much about the new power systems, I went with the big prop thinking that I could just run at low speed = slow flying, while overpowering the plane would give me that emergency pull I may need if I ever get into trouble. Although, I will admit that that kind of thinking has worked well for me in the past with snow machines & motocross, it didnít work so good with the V8 I put in the Chevy Vega...
I think I will buy a smaller prop.
I do have a voltage meter, but Iím not sure that translates to a watt meter. Math. Who needs it!
Thanx for all the help!
Jan 24, 2018, 12:19 PM
Displaced Alaskan
Boondawg's Avatar
Thread OP
Question: What would be the result of removing some of the dihedral & polyhedral from the wing?
Reduced recovery from banking in turns and loss of a lot of the docile properties of the wing? Keeping the weight slung in a low-hanging cradle under the wing guarantees that gravity will always want to return that weight to that position?
Jan 24, 2018, 03:28 PM
B for Bruce
BMatthews's Avatar
Quote:
Originally Posted by Boondawg
Question: What would be the result of removing some of the dihedral & polyhedral from the wing?
Reduced recovery from banking in turns and loss of a lot of the docile properties of the wing? Keeping the weight slung in a low-hanging cradle under the wing guarantees that gravity will always want to return that weight to that position?
That's a bad idea. On rudder steered models the design relies on coupling between the yaw from the rudder and how it works with the dihedral to roll the model. Take away some of the dihedral and you rapidly reduce the roll response of the model and it's ability to make easy and positive turns. And not in a good way.

The "pendulum" aspect of the weight well below the wing does have some effect. But it's far from the only feature at work that pushes the model back to level flight. Again the dihedral works in a way that the change from side to side from either yawing or side slipping causes the wings to see a change in angle of attack from each side. This produces a STRONG rolling action to return the wing to level flying. Or to roll the model if the source of the side slip is the rudder being pushed to one side or the other. And that effect is stronger than the effect of the weight hanging below the wing.

Besides, in a balanced turn the weight THINKS it is hanging directly below the wing. So no help there.

So bottom line is "leave it alone". Carl knew what he was doing when he designed the original Gentle Lady that was the basis for the later Electra. If you reduce the dihedral nothing good will come of it..... unless you go whole hog on such an "upgrade" and move directly to ailerons in the wings.
Jan 24, 2018, 03:39 PM
Displaced Alaskan
Boondawg's Avatar
Thread OP
Looking around the site here, I get the feeling I may be in the wrong place. Either that, or I have gotten really old, and left behind. A lot of the conversation here seems to be next level kind of stuff. I see people talking about lots of math, to the point of almost being an alien language. I feel like Peewee Herman at a rocket surgery convention! All my cheesy questions seem incredibly dumb by comparison.

Is building & flying still fun these days? Because, it kind of sounds like an intellectually competitive chore. I don’t remember it being like that 40 years ago. What used to be about splitting wood now seems to be about splitting hairs! How did any of that old stuff we built even fly?!

I remember being amazed that the stuff we built flew! It was uncalculated, daring, exciting! Maybe it’s just that all of the tricks have been discovered, and now it’s all formulaic. Maybe it was just that I was in it at the very beginning of electrics, with a lot of the unknowns yet to be discovered.

Re-entering the sport, I just hope it hasn’t traded in it’s fun of putting something you created into the air, for the pursuit of the quest for perfection.

Of course, it very well could be that I have become one of those stereotypical old timers, shaking a clenched fist at the sky, angrily cursing a future he does not understand.
Jan 24, 2018, 04:14 PM
B for Bruce
BMatthews's Avatar
Quote:
Of course, it very well could be that I have become one of those stereotypical old timers, shaking a clenched fist at the sky, angrily cursing a future he does not understand.
Look over here on your left... I'm the third one in line shaking my own fist along with you...

I've always been good at doing simpler math like the stuff I did above. But the higher level stuff rapidly turns into some otherworldly language that I don't even try to tackle.

For myself I don't like working in foam and plastics. But on the other hand when I look at some of the VERY creative models done in foams in the Foamie section by folks that design and build their own creations I have to smile and accept that creativity is far from dead.

The hobby of FLYING has grown in leaps and bounds. But then it was always held back by the massive number of folks that wanted to fly but had every excuse under the sun not to build even a basic kit. It's THAT group that has swelled the ranks in recent years and resulted in the equipment we need being such a mass market thing and so much cheaper than ever before.

You're likely also bamboozelled by the computer based transmitters with all their programmable features. But once you master them and can set up the basic operations you'll love the ability to make minor and simple changes. But it IS a big uphill learning curve.

If you like building check out the Vintage and Old Timer forum here as well as the Balsa Builder forum. And there's often some really nice balsa work being done in the Electric are Scale Kit/Scratch Built forum. Balsa building is far from dead. In fact I'd say that it's just as popular as ever. The thing is that way back when we had more builders because if folks wanted to fly they HAD to build. A lot of the folks that built only because they HAD to have gone ARF. But those of us that enjoy our bench time are still out here and still building. And we still draw in new recruits to this side of creating what we fly.

But I do agree that with ARF's quad copter drones, FPV, auto stabilization, self guided UAV's and all the rest it's a highly confusing landscape. But just zero in on what you like and enjoy what you enjoy.

EDIT- You asked about your voltmeter in comparison to a wattmeter. Two totally different tools. With the voltmeter you can measure current through the motor if it has a high enough current range. And with that and knowing the battery voltage you can calculate the watts. It's volts x amps = watts. But a cheap wattmeter that plugs in and tells you the battery voltage while under load and the current draw and also calculates the watts all at the same time and gives you all that data right on the little screen is only $20 from a place like Hobbyking. So it makes little sense in a hobby that costs what this costs to not order up such a meter when ordering other things.
Jan 24, 2018, 04:59 PM
Displaced Alaskan
Boondawg's Avatar
Thread OP
Well explained.
Thank you!

I however do reserve the right to go off on another tangent at a later date, titled “I like to keep my money in my nehborhood doing business with my local hobby shop, but they really don’t seem to care enough to make that possible, as opposed to just buying my gear on line”.

It really wouldn’t be all that much effort.
1. Have stock in store. If I need you to order it, I’ll just order it myself.
2. Know something about what you sell. I don’t need you to read the back of the box for me.
3. Know the local clubs and events. I can look it up on the internet, too.

People used to hang out and shoot the shiz at hobby shops. Exchanging information and ideas. Now when you ask a question, they look at you like you just threw up on their cat.

Wait, I was gonna do this later.....

Post Script: I am going to order a watt meter. And a Valium.
Last edited by Boondawg; Jan 24, 2018 at 05:08 PM. Reason: Fragmented sentence
Jan 24, 2018, 06:23 PM
Greediest Suer
Ron H's Avatar
You could make a rib pattern for a flat wing prior to assembly. 3-5 degrees of dihedral makes a good aileron trainer since they will help to level the wings but not do the job for you. 0-3 degrees, you should have ailerons.

Here is a link with links inside that may be worth a look. https://www.rcgroups.com/forums/show...lectra-Project
Jan 25, 2018, 02:06 PM
Displaced Alaskan
Boondawg's Avatar
Thread OP
Quote:
Originally Posted by Ron H

Here is a link with links inside that may be worth a look. https://www.rcgroups.com/forums/show...lectra-Project
Thanx!
Jan 27, 2018, 12:56 PM
Registered User
E-Challenged's Avatar
I am a big fan of Pat Tritle's designs. Pat designs for Dare kits which are sold by Brodak as "full"kits. His designs are also sold as "short kits" by Manzano Laser Works. Short kits consist of plans and laser cut parts sheets plus vacuum formed parts. You can peruse Pat's catalog at his website "Pat's Custom Models" His designs are mostly smallish and lightly wing loaded using inexpensive power systems, suitable for flying in small venues with smooth takeoff and landing strips and relatively calm air. Some of the designs have wingspans of up to 60 inches. I'm starting on his DC-3 model sold by Brodak.
Jan 28, 2018, 12:03 PM
Displaced Alaskan
Boondawg's Avatar
Thread OP
Quote:
Originally Posted by E-Challenged
I am a big fan of Pat Tritle's designs. Pat designs for Dare kits which are sold by Brodak as "full"kits. His designs are also sold as "short kits" by Manzano Laser Works. Short kits consist of plans and laser cut parts sheets plus vacuum formed parts. You can peruse Pat's catalog at his website "Pat's Custom Models" His designs are mostly smallish and lightly wing loaded using inexpensive power systems, suitable for flying in small venues with smooth takeoff and landing strips and relatively calm air. Some of the designs have wingspans of up to 60 inches. I'm starting on his DC-3 model sold by Brodak.
Very cool!
Thanx for the information!
Jan 28, 2018, 09:17 PM
Closed Account
Quote:
Originally Posted by Boondawg
I see people talking about lots of math, to the point of almost being an alien language. I feel like Peewee Herman at a rocket surgery convention! All my cheesy questions seem incredibly dumb by comparison.
Here's the thing: If you put too much prop on a glow engine, you wouldn't hurt it. It just wouldn't have the "oompf" to spin the prop very fast. It might even quit. You'd get the idea, and put on a smaller prop. Or go down in pitch.

Electric motors are "too dumb" not to hurt themselves. The "kV" of a motor is thousands of RPM per volt. Give the motor full throttle and it will try to pull enough current out of the battery to spin the prop at that RPM. Little prop - no problem. Big prop - problem!

It's kind of like the difference between gas and electric chainsaws. Get the gas one stuck in the kerf and the engine quits. Get the electric stuck, and it just chews harder until it blows the circuit breaker....

....except there is no circuit breaker on your electric powered model! So the weakest link will fail first; either the motor or speed controller (ESC) will cook itself.

That's why you have to do a little more math than we did in the old days. Don't worry; experienced electric fliers will be glad to help you. If you don't want to do all the math, online calculators (like e-calc) are great helpers too.


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