99GrandTouring

I posted this in training with no response so I thought maybe it was the wrong forum to ask, so here it is again.

Hello all, let me start off by saying I've read the basics and understand most of it.
I've been wanting a small glider I can take anywhere and fly, I've also been wanting an electric plane so why not combine them.
I purchased this glider because well I really like it however it is a small glider with limited space.
Heres what I'm looking for and have come up with.
I want about 5 minutes runtime (approx) just enough to get some altitude, and I want to use a reciever batt (no bec, because its a glider)

Heres what I'm not for sure about.
Which motor / battery combo
if I should go with a speed controller or just on off switch
and what will fit
now I really don't want to overpower this glider at all, in glow fuel an .049 would be more than sufficient (I use them on 2m)
so what do you all think / reccomend? the plans show full size equip I'll use mini servos and such.
thanks guys and hopefully it will work out well!
Heres some pics showing the glider/specs and size restraints


oh, as far as batteries and such I have no batteries or chargers so I'll have to get them as well, suggestions? (I don't know if I want to use lipo or not though)
Thanks guys!

GeeW

Hi 99GT
Ok looking at the box top specs. I would suggest a direct drive Speed 400 motor driving a 6 x 3 folding (Graupner?) propeller. Motor could be either 6volt or 7.2 volt.
As for batteries 7 or 8 cell 500AR nicads, or 8 cell 1050 Nimh. If using a 7.2 volt motor then 3 cell Lipo of about 1600mAh will work, but motor life will not be very good.
If you look at the Graham Mcalister Design website under his 'Thistledown' design you will see that you specs are not so different. Hope this helps rather than confuses!
regards

GeeW

99GrandTouring

Thanks GeeW
Do you have to have a speed controller or can you have just a switch that you turn it on and fly until the batteries are dead?
Also how big / how much does a battery pack of that configuration weigh? Do you have a link by chance with those size batteries shown?
Lastly will it all fit? Do you have the address to the website you mentioned?
Thanks again!

DrZiplok

G'day 99GT.

I think GeeW is on the right track with the DD 400 from a simplicity perspective, but looking at your plan there I'm wondering how much space you have in the nose.

You need about an inch and a quarter inside the nose to fit a Speed 400 motor, and the top view of the fuse makes it look much narrower than that. If so, you can either widen the nose or look at a smaller motor.

One of the downsides of the 400 size motor is that you're looking at adding two-plus ounces for the motor, plus another four or five for even a small battery. Your 11oz glider is now an 18oz monstrosity.

Another approach to consider - slightly more expensive - would be a small brushless motor. A CDROM-style motor from someone like gobrushless.com can be easily bulkhead mounted; you'd just drop the sanded noseblock, double up the front former and attach the motor and spinner there. Using a 10A brushless speed control and a small 3S, 10C lipo (TP730, etc) will let you deliver ~70W (about the equivalent of the DD speed 400 setup) for about three ounces. Some judicious shopping will get this setup under $100 (plus $30 for a charger). These motors can deliver a lot of torque, so you can use a larger folding propellor which will give you better climb performance (since speed is probably not interesting to you with this model).

One benefit from the either setup is that you'll have a BEC in the speed control and so you can drop the RX battery. The brushless setup should come out very close to the glider's design weight; especially if you use some micro (9g) servos. The HS-56HB would do just fine.

With a Lipo-aware ESC, you have *lots* of servo headroom at ESC cutout, so don't worry about the BEC side of things (one good reason to go 3S rather than 2S).

HTH

= Mike

99GrandTouring

ok after viewing that site its pretty obvious to me I have no clue, i guess becaus I've never been around electrics or have any friends that fly them so i have no idea what motors do what.
does anyone out there sell a "package" deal that would work for me?
I mean, motor, controller, speed controer and batteryl all together? and if so could someone point me in thier direction?
This would be most helpfull.
As far as the fuselage it has options in the plans for widening it, which I can do, my biggest concern is weight with an electric setup in this small glider.
Thanks!

99GrandTouring

I took another picture with a ruler for reference to size to give you all a better idea.
as you can see size is limited, I think I could move the servos as far rearward as possible, and the plans has for drilling optional "lightening" holes into the vertical and horizontal stabs but I could leave the material in it to help offset the weight up front.
Is there any sites with more info on using BEC with lipos and the runtime you get after bec cutoff?
Thanks again guys

DrZiplok

OK, this makes it pretty clear that you're not going to get any of the common can motors into the front of this plane and get decent climb performance; you would have to go down to something like an IPS-size motor (20 or 30W max) and then you're looking at a gearbox as well.

Ideally you don't want to be offsetting much; as I noted above using lightweight servos will save you a lot - I would avoid committing to locations for the servos until you have all the parts balanced.

There are a couple of different issues here; first is that with a lipo pack, you will tend not to fly to cutoff - if you're just using the motor to climb to altitude, the 10 or so minutes of runtime you'll get should equate to hours of soaring. 8)

Second - it depends a lot on the particular pack you're using, the servos, how much you're using them, etc. Typically with a glider you're not loading your servos hard, or moving them very often, so idle current draw is very low and your run time even if you do hit cutoff will be pretty long.

Remember that once you hit cutoff, you're not going to be climbing any more, so you only really need run time to get you back down, and you'll easily see that.

Sadly, this is an area in which there are just too many options to give you a hard and fast answer, but here's a start.

This motor:

http://www.gobrushless.com/ccp51/cgi...ME:motors:CCDR

This speed control:

http://www.balsapr.com/catalog/speed...ductId=V753750

and this battery:

http://parkflyermotors.com/secure/sh...=369&catid=106

for example will spin a cheap GWS 7x3.5 prop for about 10 minutes non-stop, and give you over 10oz of thrust while doing it. Total weight of this power system is about 3.3 ounces, cost right on the $100 estimate I gave you above. You will need a Lipo charger for this battery (figure $25-30 for a simple one like http://www2.towerhobbies.com/cgi-bin...&I=LXHNW5&P=ML).

Note that the GWS prop I mention is not a folding prop; it's fairly small and should not present a lot of drag, but if you find that it's problematic there are small folding props that can be adapted to the 3mm shaft of the brushless motor.

I hope this helps a little.

= Mike

99GrandTouring

Thank you!! That points me in a pretty good direction.
One last question, when it comes to batterys and speed controllers does it matter what mah I use as long as the cells stay the same?
meaning if I go with a 3C 1000mah I'd get longer run time, but if I went with a 4C you would get more power / current flow?
Basically is it safe to increase mah as long as I keep the same number of cells or would I have to upgrade the speed controller?
Thanks again!

GeeW

99GT
You've got the idea. More mah= more flight time (and more weight). You do not need to upgrade the speed controller if you increase the mah.
Increasing the cell count will increase the current and power but may well fry the motor, also you can run into problems on the number of servos you can hang off the speed controller.
Other than that I agree with DrZiplock on his advice and apologise for my absence over the last few days.........my wife finally had me cornered on some liitle jobs that needed doing!
Regards

GeeW

99GrandTouring

guys I'm getting ready to start on this one and was wondering, the motor will be firewall mounted, but should I make any modifications for the battery for cooling etc?
If so, suggestions, or ideas that won't add alot of drag?
Thanks!