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1. 08:51 PM - deck angle (taildrags)
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I thought I'd change the subject line to reflect the actual topic of discussion
here ;o)
I just reviewed the plans (Orrin Hoopman's 1-19-33 plans, Drawing No. 1) and it
calls for 2 degrees of incidence on the wing, achieved by making the rear cabane
struts 1" shorter than the front ones. The cabanes on my airplane are not
built per plans, but after studying their actual geometry in AutoCAD, when my
cabanes are canted back by 3-1/2" from the vertical as they are, my wing incidence
is within 1/2 of a degree of what it's supposed to be, or about 1.5 degrees.
I can probably get that half-degree back after changing out my main gear
tires to the 8.00x6s as I'm planning to do.
Now to the broader topic of the deck angle. It has been said by several Piet pilots
that they feel like a deck angle of 12.5 degrees is about right. With another
2 degrees of incidence built into the wing, that puts the AOA of the wing
in the 3-point landing configuration at about 14.5 degrees. I took the liberty
of snipping a small section from Michael Shuck's very interesting paper called
"Commentary On The Pietenpol Airfoil", copyright 2004 by Michael, full credit
and admiration is here given to Mike for both being a Piet lover and for
having tremendous skill in the analysis of airfoils. That snip is attached.
Highlighted in yellow is the region of interest, which is the region where the
coefficient of lift Cl reaches its maximum... the critical AOA. The first column
on the left is alpha, the angle of attack. The second column is the coefficient
of lift. Notice that Cl is at its maximum at an alpha of around 14 degrees,
and it drops off at higher angles of attack.
Hmmm... sounds like the seat-of-the-pants Piet pilots know just as much as the
aerodynamicists! My conclusion here is that if a Pietenpol airfoil is operated
at a deck angle of 12.5 degrees in the landing configuration, it is just about
at the critical AOA and if the airspeed is dropping, the wing will be stalling.
Perfect. I don't consciously try to land my airplane tailwheel-first because
I generally find that that will cause porpoising to start, but theoretically
it would land nearer to full-stall if I held the nose a bit higher than I
normally do at touchdown.
I'm very interested to do some flight testing in calm morning air with the bigger
tires. They are on their way here from Colorado Springs as we speak...
--------
Oscar Zuniga
Medford, OR
Air Camper NX41CC "Scout"
A75 power, 72x36 Culver prop
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=473188#473188
Attachments:
http://forums.matronics.com//files/pietcl_508.jpg
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