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Fournier rf-4 electric conversion?

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Colin Maxfield09/06/2011 12:07:01
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i am thinking of building the fournier rf-4 from the free plan in the july magazine. i would prefer to modify to electric power, could you perhaps advise me on a suitable size electric motor ( brushless ).
thank you, colin
Pete B - Moderator09/06/2011 13:18:44
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The AUW is shown as about 3lb 10oz in IC form, Colin, so aim for a motor and prop combo which will give you 300-350 W/lb for a spirited performance. Something like this should be entirely adequate, coupled with a 40A ESC and a 3S 2200 Li-Po. The 970kv motor will allow a bigger prop to turn at lower rpm, which will extend the battery time.
 
Edit: It's just a thought but the RF-4 has been designed for IC so will be beefed-up beyond electric flight requirements. I have the VMAR RF-4 which is 80" span and weighs just 3lb all-up. It may be worth seeing where you can safely lighten the structure during the build, such as building up the tail and rudder rather than solid sheet, etc.
 
Pete

 

Edited By Pete B on 09/06/2011 13:25:35

Colin Maxfield10/06/2011 08:17:52
13 forum posts
hi pete, thank you for your very helpfull advice. regard, colin
Peter Miller10/06/2011 08:25:48
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A built up tail would save on nose weight too. The 1/4 ply F-1 could be 1/8" however there is not much more weight saving to be done on the fuselage.
Simon B10/06/2011 13:25:48
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Maybe a few lightening holes?
Tim Hooper12/06/2011 00:02:06
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Posted by Simon B on 10/06/2011 13:25:48:
Maybe a few lightening holes?
 
 
Probably not worth the effort. Balsa is light by nature!
 
Try cutting back on ply and adhesive instead.
 
tim
Widgey Woo16/06/2011 17:54:32
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Hi, Did anyone else get a free plan with 2 sides printed the same? Both sides of my Fournier sheet had fuselage detail? No wings?
 
Widge.
Pete B - Moderator16/06/2011 18:05:43
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Posted by Widgey Woo on 16/06/2011 17:54:32:
Hi, Did anyone else get a free plan with 2 sides printed the same? Both sides of my Fournier sheet had fuselage detail? No wings?
 
Widge.
 
It's been noticed by a few, Widge - solution is here.
 
Pete
Peter Miller17/06/2011 08:10:05
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You can save most weight by wood selection. Take some scales to the model shop.
 
However using very soft wood to save weight will weaken the model.
Grasshopper20/06/2011 16:18:28
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Pete B, in your post you said to go for 300-350 W/lb for a spirited performance: I think you meant 300-350 Watts perhaps? On the other hand it would be interesting to see a motor glider with infinite vertical performance!

Totally agree on the possible motor choice. I have used many of these EMAX type motors from GC and they are excellent performers and great value for money.
 
Peter (Birnie) - no relation!
Pete B - Moderator20/06/2011 16:35:34
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My dumb thumbs extend to the keyboard, too, Peter If I had a motor glider with that
sort of performance, I'd be well-impressed - and I'd have to call it Saturn V........
 
You are right, I was thinking in terms of 100W/lb, thus 300-350W.
 
I agree with your thoughts on the EMAX motors. The one's I've had seem a bit smoother-running than the Turnigy-type range and I'm, as I type, fitting a brutish BL4030 into a Super Decathlon
 
Pete
 
Peter Miller20/06/2011 18:08:04
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I know nothing about electric power but one of our club members is building it from my plans.
 
When he collected the plans from me he mentioned 300 Watts so I guess that is right.
Grasshopper22/06/2011 11:50:54
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Getting to grips with my electric conversion for the Fournier RF4.
 
The motor Pete B suggested was a Emax BL2720/07 . I had one 'in stock' from another project so I will be using that and having done the sums I find that the weight of the original glow + tank +servo is about 20 grams more than that motor+ESC+3S LiPO so the CofG will be in about the same place. The difference will be taken up in a folding propeller - one of the advantages of going electric.
I will no doubt lighten the front end to take account of the smoother running of an electric over a glow but will make the judgements as I build. So - next job is to get in some wood and start the fuselage.
I have a mate who can laser cut the wing parts once I have the wing plan so roll on the end of the month and my subscriber copy!
 
Peter
 
.

Peter Miller22/06/2011 18:26:07
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I had to add 3 ounces of lead in the nose. Use it usefully to keep the front end strong'
Grasshopper24/06/2011 16:04:17
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Thanks Peter for the 'lead' update.
 
I will be moving F1 forward by about 4cm so that the prop position remains the same.
 
The BL2820/07 motor weighs 144g against the glows 225g so if the 158g LiPO is in about the same position as the tank is currently I should be able to jiggle its position to get the correct CofG: hopefully without adding any lead - but we will see!
 
Peter
David Thorpe 212/08/2011 19:18:49
8 forum posts
re electrification of this lovely model, I can't find reference (I may be blind) to the prop size to use with the brushless motor.
Grasshopper mentions a folding prop, I'd want to stay more scale like with a fixed prop
 
Any ideas folks
 
David
Grasshopper13/08/2011 10:27:06
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In my experience with several model motor gliders, a fixed prop creates huge drag so if you want anything like acceptable soaring performance I suggest a folder.
 
Peter
David Thorpe 213/08/2011 17:50:37
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Thanks for reply ~ I'm still unsure about prop size, folder or fixed.
 
I do fly several e soarers so appreciate the drag implication of a fixed prop and am prepared to accept this as a "scale" sacrifice as, with the wing loading as it is, one is unlikely to exploit much thermal advantage anyway I would guess.
 
David
 
ps the Giant Cod motor suggestion for this motor is 11 or 12" dia which seems far too big and a certain grass cutter! From the plan with C/L horizontal 10" or less looks right ~ what do you reckon?
Peter Miller13/08/2011 19:24:54
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You are right. It isn't intended to thermal and would probably need a killer thermal to really take advantage of it.
 
My SC 30 FS is turning a 9 X 6 if it is an help to you

Edited By Peter Miller on 13/08/2011 19:25:14

David Thorpe 215/08/2011 08:45:19
8 forum posts
Thanks, 9x6 was what I'd hoped/thought was about right.
 
Talking about killer thermals, just about a week ago I got in one and with spoilerons deployed still found it hard to lose height to the point I began to think I might lose the model! I reckon a brick would have flown.

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