Sagitta XC stab

[sekollera]

Hello,

I picked up a Saggitta XC recently and am in the process of setting it up. Recently I was told that I should build a new stab for it since the stock one does not have proper elevator authority at higher speed and can cause it to lose control.

Does anyone have a plan for such a stab? I have one that I can reverse engineer but I am too lazy to design it and just want to build off some plans.

Also, is it worth taking away the rudder balance and fixing it to the vertical for the same reasons?

Thanks in advance,
Adam

[Ollie]

The tail moment arm is too short. Also, the tails areas are to small. Check it out:

This comes from Dr. Mark Drela:

"Ch = (A_hori/A_wing) * (tail_arm/avg_wing_chord)
Cv = (A_vert/A_wing) * (tail_arm/avg_wing_span )

A well-sized tail will be in the range...
Ch = 0.35 - 0.50
Cv = 0.02 - 0.035
If the Ch and/or Cv are below the minimum values, the handling will suffer."

[rdwoebke]

Check out this thread:

http://www.rcgroups.com/forums/showthread.php?t=474768&highlight=sagitta+xc

I have had an in progress Sagitta XC for about 3 years now myself. I think it is suggested if you just upsize the Sagitta XC stab you should be OK.

Ryan

[rogerflies]

I built my XC horizontal stabilator and rudder/fin sized per the plans, but the tail boom was extended six inches. I didn't use the rudder balance.

[sekollera]

Thanks for the info. My question was a bit vague.

My collegue has Saggi XC built by a very respected builder - he found the elevator problem many years ago. He solved it by building a NACA-profiled symmetrical elevator of the same area but about four times thicker than stock. Now it handles "like a pussycat". Two newer owners also declare the same.

So I'd like to build this elavator and not lengthen the fuse.

Does anyone have such a plan? FWIW, I have my collegue's elevator and can reverse engineer it in case no one has it.

/Adam

[OVSS Boss]

Just strap on top and bottom "spars" that add atleast about 1/4-3/8" in thincness (and cut lightening holes in the big sheet in the stock stabs) and give it a try first, I thinken all the Sag stabs I have ever had except the first I built. Another point, just do not go too fast, the whole thing is not made to keep up with a SBXC.

Marc

[looweegee]

i built a sagita xc back in the early 80's. huge plane. i didn't have a problem with the stock elevater. i would suppose more is better here in this case. mine came to an end doing loops and the wing root failed at the joiner to the fuselage. i suggest using lots of carbon fiber on the center wing section spars. where can i find a kit XC these days?

[cosmicpossum]

"where can i find a kit XC these days?"

Short of lucking on one on EBay or something, this place will be releasing one sometime in the near future: http://www.aerosphereonline.com/mm5/merchant.mvc?Screen=PROD&Store_Code=A&Product_Code=214&Category_Code=Unlimited

[Phoebusflyer]

Here is a pic of my almost finished XC. I built it according to the instructions. That was before I found all the really good build info and threads on this website!!

[rdwoebke]

Pheobus,

You might consider adding Marc's suggestion above of putting a bottom "spar" on the horizontal stab.

Myself I have had my Sagitta wings in this state since about early 2004. I need to get motivated on it again so I can fly it in 2008 Nats XC.

Ryan

[erich]

Pheobus,

Great looking plane. Just the thing for a Texas boomer. Looking forward to seeing your cover job.

erich

[rdwoebke]

Erich,

How is your Sagitta XC flying these days? Have not seen many posts from you since you finished that build thread, so thought I'd check to see how you are enjoying it? Have you had it "out on the road" yet?

Ryan

[Phoebusflyer]

Will go ahead and add the extra thickness to the stab. Will cover soon, I hope. Depends on Overtime from work!! Gotta save money for the Real one!
And thanks for the kind words!! I had a great time building her.

[hasselblad7]

I just bought the short kit from the classifieds. From the above discussion, has anyone considered making the elevator a traditional hinge type? I thought full pivot elevators tend to stall before giving any significant control force from the low thickness. It seems to line up with the post about making the elevator much thicker.

I know the Bird of all time ARF has a full flying elevator, How's the authority on that?

[Phoebusflyer]

I don't think full flying elevators stall any quicker, but you thicken the elevator to increase the control force applied. Like turning a flat plate into a thicker, fully symmetrical airfoil, more force applied!

[hasselblad7]

The tail moment arm is too short. Also, the tails areas are to small. Check it out:

This comes from Dr. Mark Drela:

"Ch = (A_hori/A_wing) * (tail_arm/avg_wing_chord)
Cv = (A_vert/A_wing) * (tail_arm/avg_wing_span )

A well-sized tail will be in the range...
Ch = 0.35 - 0.50
Cv = 0.02 - 0.035
If the Ch and/or Cv are below the minimum values, the handling will suffer."

Here are some numbers for the above equation according to my plans:

Elevator Area = 247.5"
Elevator Arm = 37.5"
Fin Area = 123"
Fin Arm = 37.5"
Ave wing cord = 12.06"
Wing Area = 2100"
Span = 174"

Plug it in:

Ch= 247.5/2100 * 37.5/12.06 = .0366

Cv= 126/2100 * 37.5/174 = .0137

So according to Dr Drela it looks like the the fin is the problem not the elevator. I wonder if he owns an XC :)