Thread Tools
Jun 27, 2012, 11:04 PM
Registered User
dk31's Avatar
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?
Sign up now
to remove ads between posts
Jun 27, 2012, 11:23 PM
RC Airplane (Recently Crashed)
mutha's Avatar
Quote:
Originally Posted by Razors edge 29
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
Jun 27, 2012, 11:25 PM
QuAd FaNaTiC
Razors edge 29's Avatar
well Its official

I am building a ply firewall; this is ridiculous
Jun 28, 2012, 12:58 AM
Registered User
baui2000's Avatar
Quote:
Originally Posted by dk31
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
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.
Last edited by baui2000; Jun 28, 2012 at 01:04 AM.
Jun 28, 2012, 06:04 AM
Registered User
Del-Dredd's Avatar
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.
Jun 28, 2012, 07:13 AM
Registered User

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: 151
Size: 39.5 KB
Description:

Name: side view a.jpg
Views: 110
Size: 41.0 KB
Description:

Name: Top View.jpg
Views: 114
Size: 40.2 KB
Description:
Thank you all for the great reading in this thread!

Regards,
Wayne
Jun 28, 2012, 07:23 AM
RC Airplane (Recently Crashed)
mutha's Avatar
Quote:
Originally Posted by mutha
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
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)
Last edited by mutha; Jun 28, 2012 at 07:28 AM.
Jun 28, 2012, 07:33 AM
Registered User
baui2000's Avatar
Quote:
Originally Posted by mutha
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
Jun 28, 2012, 08:04 AM
Registered User
Prof100's Avatar
Quote:
Originally Posted by Bluey_65
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
Jun 28, 2012, 09:39 AM
When pigs fly rc
rcrich's Avatar
Besides for steering on the water does the water rudder help on take off and landing with floats?
Jun 28, 2012, 11:24 AM
QuAd FaNaTiC
Razors edge 29's Avatar
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!!!!
Jun 28, 2012, 02:54 PM
Registered User
dk31's Avatar
Quote:
Originally Posted by baui2000
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
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.
Jun 28, 2012, 03:20 PM
Registered User
baui2000's Avatar
Quote:
Originally Posted by dk31
@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.
Jun 28, 2012, 03:34 PM
Aus
Aus
ʎןɟ inverted ɹǝpunuʍop
Aus's Avatar
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
Jun 28, 2012, 04:22 PM
Registered User
dk31's Avatar
Quote:
Originally Posted by baui2000
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?


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