pdilley

Hi all, I am new to this exciting hobby, I bought a Green Sleeves electric sailplane (2m) with Speed 600 motor and an E-Flite NiMH pack. (probably not as good as Nicad?).. What I am wanting to learn is what is the next step in improving the performance of this kit? I believe this means reducing the weight so that the thermal soaring performance increases which means a new (brushless?) motor, maybe a reduction gear setup and a new folding prop with different dimensions and a different flight battery pack. I understand that much so far, but that is where it ends, now I am clueless when it comes down to the nitty gritty of determining all the numbers and calculations to be able to put together my own flight system replacement. Thats where I need help.

Here are some specs on the kit to help:




Specifications

• Wing Span - 2000mm / 78.7"
• Weight - 1430g / 3.15lb
• Length - 1024mm / 40.3"
• Wing Area - 38.4dm2 / 595.2 sq.in.
• Airfoil - Modified RG15
• Ready fitted speed 600 class electric motor with spinner & folding prop.
• Requires 3 cell lipo or 8-10 cell 1700mAh battery

Below is the space/cavity I have to work with:

Sky Sharkster

Hello pdilley, Welcome to Wattflyer!
There are quite a few threads on 2 meter upgrades, here's one;
http://www.wattflyer.com/forums/showthread.php?t=18214
If the listed weight for the Greensleeves is correct, you'll be looking at the higher end of the power range, about 200-250 watts. An AXI 2820-10 with a 3s (3 cell) 2000-25000mAH LiPoly and a 10 x 6 folding prop should be about right. This would require a 40 amp ESC.
Here's a free "Motor Calc", if you find a motor you like, run the numbers through it to get an estimate on amp draw, efficiency and watts out.
http://brantuas.com/ezcalc/dma1.asp
Good Luck!
Ron

pdilley

Thank you Ron,

I'll read those links. Another question, is there some simple explained page that will introduce the not-math smart reader to start learning how to determine something like that. That calculation link seems like it might help a lot! If weight is the primary deciding thing, then it might be simple to concentrate on any calculations on that alone? Or is it not exact and more of guess and miss. I'm still clueless at how to pick the prop with the different number for length and the other one.

Cheers,
Peter

Sky Sharkster

Hello Peter,
The most common way to figure out how much power you'll need is "Watts per Pound". Here's a thread asking a similar question;
http://www.wattflyer.com/forums/showthread.php?t=30541
If you scroll to post # 7, Mike (rcers) lists the generally-accepted formula for weight, performance and airplane type.
As you can see, I gave you a figure slightly higher than # 1, about the middle of # 2, based on a 3-1/4 lb aircraft. For aircraft that are more highly loaded (wing loading, the amount of weight each square foot of wing area must support) than a Sailplane, I like to use 100 watts per pound.
Another general rule regarding propellers is that a smaller diameter, high-revving prop is good for maximum speed and a larger-diameter, slower-turning prop is good for thrust. This disregards (for the time being) the second figure listed on prop specs, the pitch or "twist" of the blades.
Now a sailplane is a large, slow-moving aircraft. We would like it to climb in a safe, stable manner and then shut off the motor to glide. So a large diameter, medium pitch prop would be a logical choice.
For this application and type of aircraft, an outrunner or geared inrunner are usually chosen. They will turn a large diameter prop at decent RPMs, generating a lot of thrust and torque without too much forward speed (prop speed) which is exactly what we need.
As you begin plugging numbers into the calc, notice the "prop speed" and how it changes with the prop size. If you reduce the first number (prop diameter) and increase the 2nd number (pitch), the airpeed goes up. Not what we want! This is for faster aircraft like pylon racers and Hotliners. We want good thrust and medium-low speed.
So, my guess is you will end up with a 9" (diameter) x 5" (pitch) prop rather than an 8" x 6", as an example.
Again, look at the amp draw, thrust and motor efficiency. Try to stick to one motor + voltage, but change only the prop diameter and/or pitch.
Soon you will get a feel for how these factors interact, it's just a new subject or skill and like anything new, the more you do it, the easier it becomes. I find it helps to print out a couple of pages (of the more promising choices) as I go, so I can see them side-by-side. Once they're off the screen it's hard to remember all the specs!
I know it can appear baffling, but the light will go on. When that happens, you will be on your way!
Hope this helps!
Ron

pdilley

Ron,

What a great golden nugget of information. I am printing it out as I type. I am going to study this in depth and do a few runs through the calculator and see how it works. I have to say the weakest point for myself and probably a few other beginners as well is how these reduction drives work in the mix. They seem to a beginner to just skew all the numbers up for us when we are trying hard to get a grasp on the basic numbers themselves. The plain English explanations help a whole lot and I am sure others will find this post a great help as they get their grips on the whole electric side of this hobby.

Thank you.

Cheers,
Peter

Sky Sharkster

Hi Peter, glad to hear my explanation makes sense, sometimes I forget that everyone hasn't been at this for 20 years!
I agree that the gear drives and ratios make it more confusing; Perhaps a little backround will help. One of the main differences between electric motors and internal combustion motors is the torque generated. Because of the number and mass of moving parts, I/C motors have lots of torque and limited RPM. Electrics are the opposite. In the beginning, there were only "Inrunners" and these are capable of very high revs, 30,000-40,000 RPM, believe it or not. But they aren't capable of turning any decent-sized props at these speeds, very little torque since they have low moving mass. So, with an excess of available RPM and a need to generate torque, the simple solution is reduction gearing. If the little motor is happy at 40,000 RPM, gear it DOWN by 4:1 or so. Put a fair-sized prop on it. The motor is happy, spinning away, and we get our torque, since the PROP is only turning 1 RPM for every 4 motor revs. Sort of like low gear in your car.
Enter the outrunner; The outer case (or "can") revolves, generating torque on its own. Able to turn a large prop without gearing.
So, with the many types of airplanes and flying styles, we have direct-drive inrunners (usually high-speed planes, small, high-pitch props) Geared inrunners (larger, slow-flying planes like 3D models or sport planes) and outrunners. Here's a couple of links with a general description of each;
http://adamone.rchomepage.com/guide5.htm (scroll to near-bottom)
http://www.flyingsites.co.uk/howto/electric2.htm
Hope this helps!
Ron

cbatters

Great info.

xuzme720

Ummm... just wondering how slingshots relate to a discussion on sailplanes? I understand getting off topic but that is way off, even for me!

AEAJR

pdilley,

What did you finally do and how did it work for you? Help others learn from your experience.

robertybob

I also have a Greensleeves and need to replace the motor and s/c. I am stuck with a 3200mw 2 cell battery and I want to mount the new brushless motor in the stock location. Im very happy with the way my Greensleeves flies and I am not after a large performance improvement in the glider just a reliability improvement. What I need is the brand, size, and anything else that will get me a direct replacement brushless motor, s/c and a suitable prop. Contact details of a triader who has a good track record and can supply me with what I need would be good I am totally illiterate when it comes to smoke powered devices (when the smoke escapes they dont work any more) Thanks

AEAJR

This should work:
http://www.maxxprod.com/mpi/mpi-264_...ombo%2019A.pdf

The included prop is not a folder.

I assume the stock Greensleves prop is an 8X4 which is typical for a speed 600. You can try the 8X4 it with this motor set-up but a 9X6 folding prop would be better.

If you want to stand it on its tail, get this one:
http://www.maxxprod.com/mpi/mpi-264_...ombo%2025A.pdf

robertybob

Thanks for the info, Its given me a great start in my search. As I said, I am a total Illiterate about these sparky things. having been a confirmed nitro sniffer since I was about 8yo (over 55 now)

AEAJR

How about an update on these Green Sleves gliders? How are you doing with the upgrades?

Weight?

How are they flying?

robertybob

Sorry about the delay with the results of my Greensleeves Mods. I finally settled on an eWatts 2217-2000 brushless motor and an eWatts ew25a ESC. together with a Graupner 9x5 folding prop. I am running with a 3300mw 2 cell lipo. The difference it has made to the Greensleeves is fantastic. It now flies out of my hand with only the gentlest of throws and does loops without falling out at the top, a big improvement. I look forward to looking at the new Greensleeves 2000 when they arrive at my local hobby shop

cbatters

Can you provide spec/link to 2217-2000. Trying to find a similar motor at www.hobbycity.com

Would also be great to se a pic of how you mounted the motor.



Clint

robertybob

Google eWatts and you will find all the information you need. I used the mount that came with the motor and just screwed it to the front of the fuse. That allowed me to drill the holes to mount the motor. The original motor was mounted with some down and right thrust but I mounted the brushless straight This only causes a slight right turn in the climb under power and its easily fixed with a little left rudder and its only there when the power is on.

AEAJR

Do you fly this strictly as a power plane or do you thermal or slope soar the Greensleves?

robertybob

I fly my greensleves as a power plane from the local school oval and as a slope/thermal soarer from a local site used by hang gliders and parragliders. It is about 500m above the valley floor in the hills behind the Gold Coast.