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General control line discussion => Open Forum => Topic started by: Keith Miller on August 07, 2020, 12:06:04 PM
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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
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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".
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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
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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
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PLEASE do NOT set it at 4.5 inches, it will be extremely tail heavy
Randy
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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!
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....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.
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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?
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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.
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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
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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!
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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 y1
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Thanks, Randy; I read "center of the panel", but you really mean center of the whole wing, which makes perfect sense.
Sweet!
Thanks y1
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
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in addition , pay attention to the 4 inch span on the handle to start with
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Randy, thanks! I'm set.