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Old Sep 15, 2011, 06:32 PM
Registered User
Deutschland, HE, Marburg
Joined Aug 2011
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Guillows Bf-109 Kit 505 Conversion

Hi there.

I would like to show you my first Guillows build and also my first self-build plane ever.

It's equipped with a Nine Eagles P-47 brick (similar to the AR6400), an extra servo for ailerons and the NE P-47 motor (which has some more power then the Parkzone P-51 motor).
Before the maiden flight, i would like to ask you some questions since i'm not really sure if it will fly at all, due to the following reasons:

-The weight got relatively high with 72 grams including battery
-I think the center of gravity is too far back. It's somewhere under the
instrumental panel of the cockpit. I marked it in one of the pictures.

Will it fly (controllable) with this CG ? Is it too heavy for the motor?

What do you think about the plane?
Are there any suggestions before i'll try to get this thing in the air?

Thank you
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Last edited by admiral_adonis; Sep 15, 2011 at 06:44 PM. Reason: spelling
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Old Sep 15, 2011, 06:53 PM
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UNGN's Avatar
Southlake, TX
Joined Jan 2008
7,327 Posts
The furthest you want the cg back is 1/3 the chord from the LE.

It sound like yours is behind this. I would not fly it like this.

72g is very heavy for this motor/gearbox but it should be able to fly. Combined with the rearward cg, however, it will likely stall and not be able to recover.
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Old Sep 15, 2011, 07:09 PM
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Magickid's Avatar
Australia, QLD, Brisbane
Joined Jul 2011
136 Posts
to fix it maybe use a bigger motor? then the CG will come forward too
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Old Sep 15, 2011, 08:14 PM
What????
SoCal "The High Desert"
Joined Nov 2003
126 Posts
UNGN has the right idea and that sounds about right with that tapered wing planform. It would be really good if you could find somewhere with that elusive "tall grass" to try some test glides and make CG adjustments. Your 109 looks really good, btw.
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Old Sep 15, 2011, 08:59 PM
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NEK of VT, U.S.A.
Joined Nov 2010
79 Posts
That look very good for a first build. Actually it would look good if it was your tenth build. Nice job. My first 5 plane or so looked horrible.
Yes, the CG looks way too far back.
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Old Sep 16, 2011, 12:29 AM
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nemoskull's Avatar
United States, AZ, Yuma
Joined Sep 2009
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the plane looks great! try a bigger battery. as for tall grass, i got a patch i dont mow just for that. the wife does not seem to care, mostly cuz she dont know! its close to 24 inches!
the joys of living in the county.
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Old Sep 16, 2011, 04:49 AM
Registered User
Deutschland, HE, Marburg
Joined Aug 2011
19 Posts
Thank you for your replies.

For a bigger motor i would need a different receiver as this one can only supply 1-1.5 amps.

Battery is already a Hyperion 240mAh with about 8 grams.
I calculated that i would have to remove about 5 grams of weight from the tail (or add 35 grams to the front ). Sounds like nearly impossible for this tiny aircraft.

So the build was a fail? That would be really annoying^^.
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Old Sep 16, 2011, 05:30 AM
Wizard
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Australia, QLD, Brisbane
Joined Jul 2011
136 Posts
no way! its not a fail it looks great!. just try adding some weight/taking some weight
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Old Sep 16, 2011, 07:52 AM
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UNGN's Avatar
Southlake, TX
Joined Jan 2008
7,327 Posts
If you can't take 5g out of the tail, I'd gut it and have it as a nice static display model.

Don't even try to fly it if the CG is behind the center of the wing. It would need an onboard gyro to fly stable and it's too nice a plane to crash after flying only 10 feet.

On any of these guillow builds, its a good idea to take out all of the excess balsa in the formers and build light behind the CG, because many called for a big lump of clay in the nose to balance.
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Old Sep 16, 2011, 08:24 AM
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Centreville,VA,USA
Joined Apr 2001
3,977 Posts
Great looking build.

Whenever I do a build, I'm never really sure where the best CG is. When I get close to adding the e-gear I temporarily place all the gear where I think it should go including the flight battery/s and I test toss it holding where I think the CG should be onto a soft surface. I adjust the battery/s or e-gear untill I get the best glide. I usually place Velcro inside the plane so I can also have a little adjustment dependin on the different batteries I may be using.

For me this has worked every time then under power usually only slight trims may be needed.

Good luck

Pete
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Old Sep 16, 2011, 10:03 AM
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Deutschland, HE, Marburg
Joined Aug 2011
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I also tried to move the equipment as close to the front as possible. But there is very little room inside the fuselage. The receiver cannot go further than that.
Also the battery is as close to the front as it is possible.

The only thing i could do is change the pushrods for rudder and elevator.
I used 0,8mm steel wire. I think i could save 2-3 grams by changing them to 0,8mm carbon. Just ordered it and will try when it arrives here.

I also thought of changing the balsa rudders to depron, but the original rudders are so light that my scale doesn't display anything, which means they are below or close to 1 gram. So i think it's not worth it.
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Old Sep 16, 2011, 12:14 PM
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United States, AZ, Yuma
Joined Sep 2009
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one of the tricks i use is to make everyting from 25% back from the L.E. to the nose sheet balsa. i make everything everything back as light as possible. this helps to ballence the plane, as well as make the front stronger, more crash resistance.
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Old Sep 16, 2011, 01:47 PM
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Plymouth, Devon
Joined May 2007
2,475 Posts
As others have said, very nice, very clean build. I reckon you could get the board a bit further forward by mounting it on the diagonal. If you fit over-long control rods (and carbon will be a lot lighter) first you won't have to worry about getting in there to attach them to the board and can trim them to fit afterwards. You can get some weight off the formers behind the wings by wrapping some sandpaper around a dowl and feeding it down the fuse, but remove the elecs first as you don't want them clogging up with balsa dust.
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Old Sep 16, 2011, 05:30 PM
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glewis's Avatar
USA, FL, Tampa
Joined Jul 2002
4,917 Posts
Nice job! your model looks very good.
I built a 24" span Comet Stuka. I used the same electronics you did. My model weighs 70grams. It does fly well but it's no speed demon either.

My opinion is your model will fly fine at your current weight but it will not fly with the cg way back there. The carbon rods will help but you are really going to have to move the receiver up into the nose.
If you can't move the receiver you could add weight to he nose.
You need the cg at about 25% of the root chord.
If you can't get the cg close to that then you could go to a heavier motor like a 10 gram outrunner and a 2 cell pack.

Please don't try to fly it until the cg is corrected.
We would hate to see it destroyed in about 2 seconds, you did too nice a job building it.

Glenn
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Old Sep 16, 2011, 05:37 PM
Registered User
Deutschland, HE, Marburg
Joined Aug 2011
19 Posts
Thank you.

I just mounted a 500mAh battery with rubber band under the nose. With that weight it comes relatively close to the cg i calculated by software.

The plan says "free flight point of balance" is about 25mm from le. I calculated a cg for 8% stability at ca. 31,5mm from le. With the large battery and maybe a bit of additional weight i could possibly manage that cg.

But then the plane gets a real "lead zeppelin" of 80 grams

Don't believe it will fly with this ballast...(?)
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