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Biplanes, wings to fuse calcs?

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Mcmark

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Sep 24, 2013
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401
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Owings, MD
Guys,
I'm trying to blend airplanes. Mount a set of wings from one airplane to another.
How do I calculate this? The top wing that I want to install is swept 6* and the spars are 2" farther aft in the wing. I've used the calculators on the net but from my searches they aren't to be trusted.
Based on using what I've been able to find, it looks very close.
Regards,
Mark
 

Birdman100

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Jun 12, 2013
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807
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Novi Sad, Vojvodina
Which two airplanes you want to blend (and why if I may ask)? What do you want to calculate, aerodynamics or structure (or perhaps both)?
 

Mcmark

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Sep 24, 2013
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401
Location
Owings, MD
Short story, bought the Smith in my avatar and raced at Reno. 4412 airfoil is lousy for racing and acro. I live on east coast, racing is looking marginal in the coming years. Want a better acro wing. Acroduster 1 wing has the correct configuration, spar centers and layout all fit the smith. Just going to use the structural layout and and make the wings straight instead of elliptical. The airfoils will be same as Pitts, why fix what isn't broken.
 

TFF

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Memphis, TN
Make sure the tail volume will match the wings. My Starduster 1 is a bigger plane than a Smith. The plane could be pitch sensitive.
 

Mcmark

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Sep 24, 2013
Messages
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Owings, MD
Wing area is the same, having flown it, tail could probably be reduced. Not going to, just based on feel. Even with the current wing, the airplane was flown with a rearward CG.
 

Mcmark

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Sep 24, 2013
Messages
401
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Owings, MD
That's my thought as well, but the wings are moving forward by 2" based on the internal structure. Both wing are 36", the original wing nose rib is 5" and the new wing will be 7.25".
Using the web calculators, its within an inch of where it was. I just don't know the math to be certain.
 

ultralajt

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May 9, 2009
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1,574
Location
Slovenia
Another solution!
I would strip Smith wings of original ribs, and make another set of ribs with different airfoil, install them on the spars and recover the wings.
Complete wing structure will remain the same except ribs...of course with new leading edge covering ply)
But finding out proper airfoil that allows ribs to be attached to the existing spars could be difficult.
Probably constructions angle of attack of new wings should be checked and properly set. (diffrent airfoil with different zero lift angle of attack.)
 

Mcmark

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Sep 24, 2013
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401
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Owings, MD
Having been in the const industry for 25+yrs, much easier to build new than to remodel. I've got the original drawings and considered it.
 

4trade

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Nov 1, 2010
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527
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Lahti/Finland
Make sure the tail volume will match the wings.
Tail volume should be enough. 4412 is non symmetrical airfoil and changing symmetrical one with same wing area reduce moment.
 

Autodidact

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Oct 21, 2009
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Location
Oklahoma
Can you explain a bit further? Reduces the moment to what effect?
When a wing has positive camber (as in non-symmetrical), it generates a nose-down pitching moment. A symmetrical wing generates little or no pitching moment and therefore the tail has less of a pitching moment generated by the wing section (aside from that related to CG placement) to deal with. Look at the horizontal lines in the chart below; On the left page it looks like an elongated "S" leaned over on it's side, and is the pitching moment coefficient about the 25% chord point - it only changes very slightly with AoA. On the right page it is almost just a horizontal line coinciding with the zero axis, and this is the pitching moment coefficient about the aerodynamic center which implies that the aerodynamic center travels just a little bit compared to the 25% chord point.

Basically, symmetrical airfoils don't need as much tail area (all other things being equal).

untitled.jpg

To change your aircraft to a symmetrical airfoil, you will need to increase the angle of incidence to make up for the lack of camber - or for aerobatics, I assume you leave the chord line parallel with the thrust line and trim for the correct AoA and just put up with the trim drag in the interest of flying upside-down as well as rightside-up? Can an aero engineer elaborate on that?
 

TFF

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Interesting that a Starduster 1 claims 110 sqft, Acroduster 1 105 sqft, and Smith at 100 sqft. If the numbers drop in line, they drop in line. I have never sat in the Smith at my field for fear of not being able to get out. Never sat in my Starduster either but have in my friend's. Mine is still in pieces.
 

Mcmark

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Sep 24, 2013
Messages
401
Location
Owings, MD
TFF,
Square the wings off at the end of the aileron and round the leading edge like the Wolf, Raven wing and the sq ft is about 100.
My Smith is not anywhere near stock, which makes it an orphan. The original seat is gone and the new is down on the lower longerons, the seat back is moved back like most of the S1 Pitts have been done to allow more comfort, more G, more room, etc. The fuse structure is not big but the way it is I can fly it comfortably, the guy I got it from was 6'3" and 275. I'm only 6' and working my way back to 200. Because the basic layout of the Acroduster 1 wing worked, I intended to use the wing in its entirety. But then I was convinced to use the structure but improve the ailerons.
If I can figure the formula to check my country boy engineering and satisfy myself that they will bolt up, I'll be on my way back to competitive acro with something a bit different to antagonize my friends with. Why be normal?
Regards
Mark
 
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