Brodak SV-11 CG

[Keith Miller]

Hi all!
Just finished assembling the SV-11. It's a nice ARF, fits together really well and seems light (61 oz finished).

Brodak says to balance it at 3 1/4" aft of the LE at the root, (and they say it should be "nose heavy" when held there...)
That's about 19% of the MAC.
For a stunt ship, that seems very far forward to me.

My model actually came out at 3.75", which is 23%. I'm good with that as a starting point. I'm accustomed to 30% for my RC aerobats.

An online calculator (https://rcplanes.online/cg_calc.htm) gives me:
- 25% works out to about 4" from the LE at the root (15% stability margin)
- 30% is at 4.5" (about 11% stability margin).

I'm quite familiar with trimming for CG, but I thought I'd ask because I know that some airframes vary from the norm. For instance, I have an RC Dirty Birdy pattern ship that, no kidding, balances at 50% and flies AWESOME!  And a little Baby Flight Streak flies OK when balanced at the leading edge.

Might any of you have actuals for your SV-11s?

Thanks in advance!
Keith in San Diego

[George Truett]

The SV-11 plans I got years ago from Randy (drawn by Carl Raichle) show the CG at 3-3/16" back from the leading edge at the root.  On the plans, wing sweep measures slightly less than 1.5".

[Peter in Fairfax, VA]

Though I can not comment specific to the SV 11, your 23% MAC sounds good.  My Pathfinder calls for 20%, but 25% is working for me. 

The trimming guide Paul Walker published handles this in the same basic way many of us have used forever:  Adjust CG to influence pitch sensitivity.  One method to add nose weight is to use a "heavy hub," if your power plant will accommodate.  Starting out a little nose heavy, then moving the CG back as you get comfortable.

What is the power plant?  With IC, the CG varies as the fuel load changes.

A fellow club member:

"Nose heavy planes fly poorly.  Tail heavy planes fly once."

Peter   

[RandySmith]

Hi all!
Just finished assembling the SV-11. It's a nice ARF, fits together really well and seems light (61 oz finished).

Brodak says to balance it at 3 1/4" aft of the LE at the root, (and they say it should be "nose heavy" when held there...)
That's about 19% of the MAC.
For a stunt ship, that seems very far forward to me.

My model actually came out at 3.75", which is 23%. I'm good with that as a starting point. I'm accustomed to 30% for my RC aerobats.

An online calculator (https://rcplanes.online/cg_calc.htm) gives me:
- 25% works out to about 4" from the LE at the root (15% stability margin)
- 30% is at 4.5" (about 11% stability margin).

I'm quite familiar with trimming for CG, but I thought I'd ask because I know that some airframes vary from the norm. For instance, I have an RC Dirty Birdy pattern ship that, no kidding, balances at 50% and flies AWESOME!  And a little Baby Flight Streak flies OK when balanced at the leading edge.

Might any of you have actuals for your SV-11s?

Thanks in advance!
Keith in San Diego

Keith  I set mine  at  3  3/8 to  3  1/2  inch, at the  center  of the  wings, that is  from the  leading edge, some have  ran them  forward  or  more rearward, The  plane is  very stable in calm and  winds at  3.5 inches, and  still has  a very hard  flat turn,  BUT  as  always  the  handle  size, overhang, pilot sensitivity  will  affect this,  BUT  the  3.5 inches, with a  4 inch  handle  setting  will  be a  great place to start

Randy

[RandySmith]

PLEASE  do NOT  set it at  4.5  inches, it will  be  extremely  tail heavy

Randy

[Keith Miller]

The SV-11 plans I got years ago from Randy (drawn by Carl Raichle) show the CG at 3-3/16" back from the leading edge at the root.  On the plans, wing sweep measures slightly less than 1.5".

Thanks George!

[Keith Miller]

....One method to add nose weight is to use a "heavy hub," if your power plant will accommodate.  Starting out a little nose heavy, then moving the CG back as you get comfortable.

What is the power plant?  With IC, the CG varies as the fuel load changes.

Peter

Hi Peter -
Super Tigre 51 with alum spinner; not suited for a weighted hub, but there's room in the nose to plop a couple weights if needed.

[Keith Miller]

Keith  I set mine  at  3  3/8 to  3  1/2  inch, at the  center  of the  wings, that is  from the  leading edge, some have  ran them  forward  or  more rearward, The  plane is  very stable in calm and  winds at  3.5 inches, and  still has  a very hard  flat turn,  BUT  as  always  the  handle  size, overhang, pilot sensitivity  will  affect this,  BUT  the  3.5 inches, with a  4 inch  handle  setting  will  be a  great place to start

Randy

Hi Randy
3 1/2 inches from the LE at the center of the wing - isn't that 4" or more at the root, given the LE sweep?

[George Truett]

Maybe this snip from the plans will help.  You've confused me a bit, I consider the center of the wing and the root the same thing?  Another view added.

[RandySmith]

Hi Randy
3 1/2 inches from the LE at the center of the wing - isn't that 4" or more at the root, given the LE sweep?

NO it is  3 1/2 inches   measured  at the  center of the  wing from the  LE  , the  sweep  has nothing  to do with the  measurement,  or  you can  set it at the  thick point of the  airfoil at the  root  ( center of wing)

Regards
Randy

[Keith Miller]

Maybe this snip from the plans will help.  You've confused me a bit, I consider the center of the wing and the root the same thing?  Another view added.

This is great - thanks!
I consider the "center of the wing" to be halfway from the root to the tip. That's where the MAC is generally located.
But I can see the confusion.


The ARF has a 13 1/4" wing root (at the edge of the fuselage). The inboard wing is 28.5" from fuselage to the tip, at the middle of the chord. The maximum inboard span, when measured from the fuselage side to the aft edge of the swept tip plate, is 29 1/4".
Are the plans you're referencing the same?

That would validate your plans are about the same as the Brodak ARF, and that your CG would work for my ARF

Thanks again sir!

[Keith Miller]

NO it is  3 1/2 inches   measured  at the  center of the  wing from the  LE  , the  sweep  has nothing  to do with the  measurement,  or  you can  set it at the  thick point of the  airfoil at the  root  ( center of wing)

Thanks, Randy; I read "center of the panel", but you really mean center of the whole wing, which makes perfect sense.
Sweet!
Thanks

[RandySmith]

Thanks, Randy; I read "center of the panel", but you really mean center of the whole wing, which makes perfect sense.
Sweet!
Thanks

Hi Keith
I use  the  center of the  wing, in the  middle  of the fuse  because  it is the  easiest way to  measure, It is  sometime  impossible, to set the  points  of a  balancer, on the  middle  of  1/2 of a wing panel  on one side, and  on the other side,  You can very easy, run into an area that is  just  paper !,  Many people  use things  like  eraser  tips ay=t the fillets  to measure the CG balance,  so  At THe   fuse  is  the  most logical place,  Yes you can do it  differently, but  I ,and many others  do it this  way,  You can also  set  it  from   LE  measure, or  Flap hinge linge measure, or  TE of  wing.  IE...   a  10 inch root, at the  center,  you can set  3.5 inches from  LE,  or  6.5  from  TE, it is both the  same.
I designed  both the   SV-11  KIT   and  SV-11  ARF  ARC,  so  Yes  they  use the  same  size wing.  Some  foam wings out there  are  NOT  correct, and some  Plans  are  NOT correct,  They were made by  other  people, and  the plans have  been  copied, by   others,  The  Wing is  60.5  inch  span, The  spinner  is  2 inch exactly,    You can  look on the  plans ,  check with ruler  if there is any doubt

Regards
Randy

[RandySmith]

in addition  , pay  attention  to the  4 inch span on the handle   to start  with

[Keith Miller]

Randy, thanks! I'm set.