HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Jun 27, 2012, 11:04 PM
Registered User
dk31's Avatar
Athens
Joined Oct 2009
727 Posts
What's the deal with the COG? Instructions say 8mm, but at this distance it feels tail heavy. Some experianced guys at the field suggested that COG should be at the front spar. I moved forward the battery, changed the COG to 5.5mm and it flys far far better. Is there any chance that Multiplex got it wrong?
dk31 is offline Find More Posts by dk31
Reply With Quote
Sign up now
to remove ads between posts
Old Jun 27, 2012, 11:23 PM
RC Airplane (Recently Crashed)
mutha's Avatar
Australia, VIC, Melbourne
Joined Jan 2011
2,839 Posts
Quote:
Originally Posted by Razors edge 29 View Post
just finished installing the G15 950 kv motor into funcub with alum motor mount.

It will spool up to about 85% throttle before the vibs start. I'm using s 12x4 APC. but, maybe I should try a higher pitch prop, perhaps a 12x6.

I am going to test fly as is tonight weather permitting.!
I would advise you get the vibs out first ... bent motor shaft or worse ...

You never know what might happen in flight
mutha is online now Find More Posts by mutha
Reply With Quote
Old Jun 27, 2012, 11:25 PM
R.C. Aviation Fanatic
Razors edge 29's Avatar
Canada
Joined Aug 2009
20,468 Posts
well Its official

I am building a ply firewall; this is ridiculous
Razors edge 29 is online now Find More Posts by Razors edge 29
Reply With Quote
Old Jun 28, 2012, 12:58 AM
Registered User
baui2000's Avatar
Česká republika, Jihomoravský, Brno
Joined May 2011
32 Posts
Quote:
Originally Posted by dk31 View Post
What's the deal with the COG? Instructions say 8mm, but at this distance it feels tail heavy. Some experianced guys at the field suggested that COG should be at the front spar. I moved forward the battery, changed the COG to 5.5mm and it flys far far better. Is there any chance that Multiplex got it wrong?
Sure it's 8mm and not 8cm?
My CG is about 10mm behind the front spar, so around the recommended 8cm from LE. Any further back and I it starts dolphining. I wouldn't be too surprised if more forward CG worked as well and made FC more stable, but I like it as far back as possible for better aerobatic performance.


Quote:
Originally Posted by mutha View Post
I would advise you get the vibs out first ... bent motor shaft or worse ...

You never know what might happen in flight
I would swap the prop first, it doesn't necessarily have to be bad to have vibes with a low pitched prop. Prop itself probably starts to vibrate because of too high RPM, I wouldn't be too surprised with G15.
baui2000 is offline Find More Posts by baui2000
Last edited by baui2000; Jun 28, 2012 at 01:04 AM.
Reply With Quote
Old Jun 28, 2012, 06:04 AM
Registered User
Del-Dredd's Avatar
Near Aberystwyth - Wales
Joined Aug 2004
2,116 Posts
CoG on the Servo wire channel is the norm, 80mm is to far back for most.
Light motor, or tail weight is how to achieve 80mm if you want it, most dont bother as if flies very well at 65mm.
Del-Dredd is offline Find More Posts by Del-Dredd
Reply With Quote
Old Jun 28, 2012, 07:13 AM
Registered User
Australia, VIC, Lara
Joined Jun 2011
6 Posts
Another Fun Cub

I finally finished my Fun Cub this week.
I 'd like to thank the following contributors to this thread for their time and valuable assistance while I put this together:-
Prof100, Sammy70, Mavlo77 & Cloaked
The Fun Cub ended up with the following after much deliberation:-
Tail Servos: HS-81
Wing Servos: HS-55
Motor: Emax GT2812/10
ESC: Hobbywing Platinum -40A
Battery: Zippy 2200 25C Series
Prop: APC Style 11 x 5.5E from HK
Paint: Tamiya Color For Plastics
Servo Reverser: Turnigy 3 ch Servo Reverser
Name: Side View.jpg
Views: 120
Size: 39.5 KB
Description:

Name: side view a.jpg
Views: 85
Size: 41.0 KB
Description:

Name: Top View.jpg
Views: 87
Size: 40.2 KB
Description:
Thank you all for the great reading in this thread!

Regards,
Wayne
Bluey_65 is offline Find More Posts by Bluey_65
Reply With Quote
Old Jun 28, 2012, 07:23 AM
RC Airplane (Recently Crashed)
mutha's Avatar
Australia, VIC, Melbourne
Joined Jan 2011
2,839 Posts
Quote:
Originally Posted by mutha View Post
I would advise you get the vibs out first ... bent motor shaft or worse ...

You never know what might happen in flight
Quote:
Originally Posted by baui2000 View Post
I would swap the prop first, it doesn't necessarily have to be bad to have vibes with a low pitched prop. Prop itself probably starts to vibrate because of too high RPM, I wouldn't be too surprised with G15.
yeah what ever gets rid of the vibrations ... you will be thankful of a complete rev range as soon as you get used to the FC you will want to throw it around ... it is big fun.

EDIT: I have a 10x6 on mine with a 1000kv motor (prior to crashing it I had no vibe issues and now have ply bracing and metal mount)
mutha is online now Find More Posts by mutha
Last edited by mutha; Jun 28, 2012 at 07:28 AM.
Reply With Quote
Old Jun 28, 2012, 07:33 AM
Registered User
baui2000's Avatar
Česká republika, Jihomoravský, Brno
Joined May 2011
32 Posts
Quote:
Originally Posted by mutha View Post
yeah what ever gets rid of the vibrations ... you will be thankful of a complete rev range as soon as you get used to the FC you will want to throw it around ... it is big fun.
True, it's a Fun plane I fly 13x6.5, no vibe issues at all even when I punch the throttle full open. You don't usually see Cubs in unlimited vertical climbs
baui2000 is offline Find More Posts by baui2000
Reply With Quote
Old Jun 28, 2012, 08:04 AM
Registered User
Prof100's Avatar
Canton, Michigan USA
Joined Jul 2007
16,355 Posts
Quote:
Originally Posted by Bluey_65 View Post
I finally finished my Fun Cub this week.
I 'd like to thank the following contributors to this thread for their time and valuable assistance while I put this together:-
Prof100, Sammy70, Mavlo77 & Cloaked
The Fun Cub ended up with the following after much deliberation:-
Tail Servos: HS-81
Wing Servos: HS-55
Motor: Emax GT2812/10
ESC: Hobbywing Platinum -40A
Battery: Zippy 2200 25C Series
Prop: APC Style 11 x 5.5E from HK
Paint: Tamiya Color For Plastics
Servo Reverser: Turnigy 3 ch Servo Reverser
Attachment 4971261

Attachment 4971262

Attachment 4971263
Thank you all for the great reading in this thread!

Regards,
Wayne
Wayne,

It looks good in the photos. Make sure you video the first flights.

Bill
Prof100 is online now Find More Posts by Prof100
RCG Plus Member
Old Jun 28, 2012, 09:39 AM
When pigs fly rc
rcrich's Avatar
USA, NY, Chester
Joined Apr 2008
2,445 Posts
Besides for steering on the water does the water rudder help on take off and landing with floats?
rcrich is offline Find More Posts by rcrich
Reply With Quote
Old Jun 28, 2012, 11:24 AM
R.C. Aviation Fanatic
Razors edge 29's Avatar
Canada
Joined Aug 2009
20,468 Posts
At least with a decent firewall i wont be afraid to punch the throttle and put her through the paces.

The plastic pieces were in there damn good; hard enough to get out.

The whole front end of mine was flexing - enough to disconnect a few esc to motor connectors. Motor is brand new and shaft not bent.
It would vibrate at 50% throttle at air field.

I tried a 9x7.5 prop ane same thing

No more screwing around, the stress marks from front end flexing are visible on my funcub now ane i am not happy. I put a lot of effort into painting and detailing her.

Bad, bad, bad design!!!!
Razors edge 29 is online now Find More Posts by Razors edge 29
Reply With Quote
Old Jun 28, 2012, 02:54 PM
Registered User
dk31's Avatar
Athens
Joined Oct 2009
727 Posts
Quote:
Originally Posted by baui2000 View Post
Sure it's 8mm and not 8cm?
My CG is about 10mm behind the front spar, so around the recommended 8cm from LE. Any further back and I it starts dolphining. I wouldn't be too surprised if more forward CG worked as well and made FC more stable, but I like it as far back as possible for better aerobatic performance.

Quote:
Originally Posted by Del-Dredd View Post
CoG on the Servo wire channel is the norm, 80mm is to far back for most.
Light motor, or tail weight is how to achieve 80mm if you want it, most dont bother as if flies very well at 65mm.
...Yes I meant COG 5.5cm from the Leading edge (right at the front spar) .It flies very nice - I will also try 6.5cm to see if it gets even better.

@baui: I measured 6cm LE to the back end of the front spar. So I guess youre at 7cm. Anyway, at 8cm the plane flies really ackward - I think it's a mistake of the manual.
dk31 is offline Find More Posts by dk31
Reply With Quote
Old Jun 28, 2012, 03:20 PM
Registered User
baui2000's Avatar
Česká republika, Jihomoravský, Brno
Joined May 2011
32 Posts
Quote:
Originally Posted by dk31 View Post
@baui: I measured 6cm LE to the back end of the front spar. So I guess youre at 7cm. Anyway, at 8cm the plane flies really ackward - I think it's a mistake of the manual.
I just measured it exactly and yes, you are almost correct. But so am I 75mm from the LE, she flies great.
It doesn't have to be awkward, CG isn't the only thing influencing the way aircraft flies. My setup is a bit on the heavy side (4S 2200mAh packs and 600W motor) and the vertical CG / weight distribution plays major role too.
baui2000 is offline Find More Posts by baui2000
Reply With Quote
Old Jun 28, 2012, 03:34 PM
Aus
ʎןɟ inverted ɹǝpunuʍop
Aus's Avatar
Australia, ACT, Amaroo
Joined Jul 2011
1,154 Posts
I just received the Hobby People 4th of July sale advertisement (I previously lived/worked in the US) and they have the FunCub kit on sale for US$99.99 .

http://www.hobbypeople.net/index.php...uncub-kit.html
Aus is online now Find More Posts by Aus
RCG Plus Member
Old Jun 28, 2012, 04:22 PM
Registered User
dk31's Avatar
Athens
Joined Oct 2009
727 Posts
Quote:
Originally Posted by baui2000 View Post
I just measured it exactly and yes, you are almost correct. But so am I 75mm from the LE, she flies great.
It doesn't have to be awkward, CG isn't the only thing influencing the way aircraft flies. My setup is a bit on the heavy side (4S 2200mAh packs and 600W motor) and the vertical CG / weight distribution plays major role too.
I guess it depends on what one is looking for. So far I didn't know CoG has anything to do with weight or acrobaticability. But again do you think that when they wrote the manual, they had in mind 4S /1.5 kilo acrobatic setups and they came up with the 8cm?
dk31 is offline Find More Posts by dk31
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Discussion Fun Cub sinowace Hitec/Multiplex USA 14 Oct 09, 2011 04:43 PM
Discussion Multiplex Fun Jet at the lake bah7566 FPV Talk 31 Jan 03, 2010 09:19 AM
For Sale Multiplex Fun Jet -- PRICE DROP Toby W Aircraft - Electric - Airplanes (FS/W) 2 Dec 28, 2009 09:51 AM
Video Multiplex Fun Jet FPV set up test bah7566 Electric Plane Talk 0 Dec 25, 2009 10:05 PM
Wanted multiplex fun-jet or trade! heli123 Aircraft - Electric - Jets (FS/W) 0 Nov 14, 2009 11:02 AM