Typhoon 2+2

[Dean Pappas]

Hello Larry,
 
You want to preserve the location of the point that is 25% of the M.A.C.
(mean aerodynamic chord)
That preserves the moment arm lengths, balance point, yaw damping and
just about any other trimming behavior.
 
As an approximation, go half-way out on the wing panel (actually closer
to the root) find the point at 25% of that chord, and rotate things
around that point.
Your 35-inch panel is actually a 38 or so inch panel , from the cl of
the model. I am assuming about a 6" fuse width.
The error won't matter a bunch.
The MAC is 16.4" from the model centerline.
The 25% point is 10.5" forward of the trailing edge, that far out.
That's the spot that needs to stand still.
The tip has to move forward about 30% more than the amount the root
moves back, in order to preserve the 25% MAC position.
 
I presented the graphical method cor calculating the MAC somne time ago
in Flying Models, but maybe it's time for a repeat.
 
Wing sweep contributes a dihedral effect when the wing is lifting.
That's not the case in Knife Edge, so the
roll coupling in KE flight should not change.
Regards
    Dean Pappas
 

-----Original Message-----
From: Larry Diamond [mailto:ldiamon at kimball.com]
Sent: Thursday, January 30, 2003 11:49 AM
To: NSRCA
Subject: Typhoon 2+2



I'm planning on scratch building a Typhoon 2+2. Just received the
plans... 

In following a number of threads and talking to a few people I have some
design questions... 

I plan on reducing the wing to about 975sqin and tapering the trailing
edge forward about 1" (about 1 1/2 degrees). This is based on
conversations of what some have found to perform better for stall spins
and snaps.

Rough estimates. 

Root rib - about 18 
Tip Rib - about 8 
Panel span - about 35 to 35.5. 
Airfoil - same as plans for T2+2. 
Don't plan on changing the stab unless advised to. 

Accounting for CG appears to have three options. 

1) Move the wing tube hole in the fuse back. 
2) Move the wing tube hole in the wing panels forward. 
3) Combination of the two. 

Which is preferred and what effects does it have on other performance? 

I'm at a loss for how this might effect the dihedral. Still keep the top
of the wing flat and let the bottom fall where it may.

The intent of the plan will be to fly intermediate and take me into
advanced. I have some books on design on the way. However, I would like
to understand the relationships from practical experience.

The easy answer is to use a wing configuration that someone else has
that is tried and proven. I would be open to this. But would still be
interested in any thoughts for design.

Perhaps this could be a good tech article for the K-Factor or possibly a
running series. 

Larry 
NSRCA 3083 
AMA 5024 

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