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Electric Graupner Cirrus

Old 01-19-2009, 07:19 PM
  #1  
sly1
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Default Electric Graupner Cirrus

I would like to electrify my ancient Graupner Cirrus since I do not have the space or the inclination to use a Hi-start. Has anybody converted a 3 meter sailplane to electric power? What brushless motor ond prop combination would give me fair launch performance?

Thanks in advance for any help.

Sly1
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Old 01-21-2009, 11:58 AM
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Sky Sharkster
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Default Electric Cirrus?

Hello Sly1, Welcome to Wattflyer!
I don't own the Cirrus, but will make a few general suggestions;
Sailplanes can fly well with less overall power than other electric planes. Most aerobatic models recommend 100 watts per lb,. but a powered-glider will do just fine on 75 w/lb, or even less.
So, for a 3 lb model, 225 watts would be OK. Depending on the overall strength + efficiency of the particular aircraft, a little less or more may be better.
Here's a thread with an article from Ed (Aeajr) describing how to size a motor to a sailplane, and other Member's suggestions;
http://www.wattflyer.com/forums/showthread.php?t=10287
And from threads I've seen for the Bird of Time 100" sailplane, flyers have used the Hyperion G2220-14 or AXI 2820-10, E-Flite 10 or 15.
For outrunners, a low Kv is needed, so it can swing a large-diameter prop, like 12" or 13" diameter, 7" or 8" pitch.
Inrunners will be geared, with a planetary gearbox, using about the same prop size.
Last, if you go here;
http://www.espritmodel.com/index.asp...S&Category=551 You will find models with a similar wingspan and weight, check which motors they suggest.
And here;
http://www.nesail.com/categories.php...42c573c4b1462a
Again, click on models with similar weight, size, wingloading and see what they recommend.
Hope this helps!
Ron
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Old 01-21-2009, 11:04 PM
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AEAJR
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Sky Sharkster is right, in fact if you are using a brushless motor and a large prop, you can get by with about 60 watts per pound, but I would recommend about 75 as a target.

I don't know the specs on the Cirrus, but if it is about 72 ounces, or 4.5 pounds, then something in the 260 to about 360 watt range would be good.

Target a motor that has a recommended prop with of at least 11 inches and 14 would be better. You will probably be looking at a motor with a KV between 800 and 1400 KV.

Assuming a 3 cell lipo ( 10V under load ) and 30 amps, that would give you 300 watts, for example.

I just put a Rimfire in my Dust Devil and am very happy with it.

Using the specs above and this calculator
http://www.electrifly.com/config/index.php

Rimfire 42-40-800 / GPMG4670,
http://www3.towerhobbies.com/cgi-bin...-800&search=Go

3 cell lipo, 13X8 prop, drawing 32.5 amps. I would recommnd at least a 2400 mah 20C pack, and larger is always better. Use a 40 amp ESC or larger.

If that is a 3 servo RES plane, the included BEC will be fine. IF it is a 6 servo plane you may wish to use a separate receiver pack or get a UBEC to power the receiver.

This would be about 80 watts/pound and would likely give you a 60 degree climb or better. Figure six 30 second climbs per pack on a 2400, maybe more.

That is only one example from one MFG, but it is a start. This would work very well
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Old 01-22-2009, 01:38 AM
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sly1
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Default Electric Graupner Cirrus

Hello Sky Sharkster and AEAJR,

Both of you have given me a lot of good information. Thanks to both of you.

I have dig out the 25+ year old plans from the attic and decide whether or not to butcher the fuselage to install a motor or to "pod" mount it on top of the wing. Back in 1987 I maidened it with a high start and the used a pod mounted OS 10, which did a fair job of getting it up. It may be a while befor I finish this project, but I will keep you posted.

Sly1

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Old 01-22-2009, 11:29 AM
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The OS10 will still work, if it still runs. And some would say if it ain't broke,dont fix it. So let's look at the pros and cons of going electric.


First the negatives:

You can easily move a pod between gliders. If you mount the electric in the nose it is fixed to that glider.

Electric will cost more, since you have to buy everything. If this is your first electric then you need a battery charger along with the motor, ESC, and battery.

If you decide to mount it internally, you will have to eliminate the pod and cut the nose off the glider, which is time and effort.

You may have to move servos to make room for the battery.

On the positive side:

Pod Mounted Electric

You could put an electric motor in the power pod and not have to modify the nose. This gives you some of the other positives I will list here, but not all of them. The pod based electric will come out heavier overall and you can't use a large prop. I don't think a folding prop would work on a pod.

Any electric option is quiet and clean. You won't disturb the neighbors and you won't be cleaning gunk off the plane and yourself. No fueling in cold weather either.

You can can fly in locations where they might kick out a glow powered plane. No glow support equipment and fuel to bring and no fuel related storage or maintance.

The Electric gives you the opportunity for controlled climb as you can decide when to stop the motor. You also get multiple climbs.

You can use the motor to help get you back from a bad down wind position. No more "missing the field" issues.


Nose mounted Electric

You have the electric advantages listed above plus the electric option eliminates the drag of the pod, the top weighting of the power pod and the drag due to the fixed propeller. You can use a larger folding prop for better climb.

Weight - Often the motor, esc and battery can be positioned so that they add minimal weight through the elimination of the nose weight you used to balance the plane. Today's light brushless motors and lipo batteries are amazing.

There are good and bad for each option. Personally I have never flown glow and don't intend to start now. The idea of a glow motor on one of my beautiful gliders makes my skin crawl, but that is me. Electric is how I started so this is what seems natural to me.

I have seen a LOT of new electric gliders. I have not seen a new glow glider since I started this hobby almost 6 years ago.

I think electric gliders look sleek. I think pods look... podish. I have a removeable electric pod for one of my gliders. I used it once, then neer again.

Just some food for thought.
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Old 01-23-2009, 02:03 AM
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sly1
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The OS10 sould stll run - I did carfully "pickle" it along with several other glow engines. I am gradually bringing my fleet back to life after a layoff since 1989.
I now fly helicopters as well, a glow Raptor 50 and Trex 450 (electric). I am stll a beginner with helis and progress is slow.
Gliders are more relaxing especially if you dont have to deal with glow engines and the associated hassle. Thats why I am considering electric power for the glider. But then I really hate to butcher the nose of the Cirrus. So, I will go POD electric for a few flights and if all goes well and the fuselage still holds together with cracking etc, I will install the motor in the nose.

Thanks for all your great input AEAJR.

Sly1
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Old 01-23-2009, 09:31 AM
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AEAJR
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Post some notes on your conversion from glow pod to electric pod. I am sure people will be interested.
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Old 02-03-2009, 01:48 AM
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maguro
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Arjan did a fantastic job upgrading a 30 year old Cirrus and converting it to electric power. Here is a link to a Google translation of his Dutch language build log: http://translate.google.com/translat...istory_state0=
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Old 02-06-2009, 03:19 AM
  #9  
sly1
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Default Cirrus

Thanks Maguro. Yes, Arjan has done a great job in restoring the Cirrus, and his build log is very helpful to me. I am in the process on converting my ancient Cirrus to electric power. One of these dys I may have a build log as well.
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Old 06-29-2015, 12:04 PM
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neilk
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Hi

I'm looking for this post in the Dutch forum but can't find it (page not found)... I'd really like to see Arjen's build log as I want to electrify mine too... Any idea how to find it ? I have tried searching the Dutch forum for what I think are the right keywords in dutch but can't find it

thanks
Neil

p.s. I can't seem to get the search of these forums to work. I enter cirrus, or graupner cirrus, and searched this specific forum or all forums but I get no results. I found this post only via google....
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Old 06-29-2015, 12:26 PM
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I think I've found it

http://www.modelbouwforum.nl/threads...pagina-3.47021
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Old 06-29-2015, 10:03 PM
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Originally Posted by neilk View Post
Yep, that's Arjans build log.
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