I should have mentioned that Ron Wanttaja wrote a Kitplanes article on
tail volume about 20 years ago while I was building my KR2S fuselage,
and got me thinking about that and the KR2's reputation for being pitch
sensitive in flight. He created a chart with about 20 airplanes on it,
along with their calculated horizontal tail volume coefficients. If the
KR2 was added to that list, it would have been dead last by a large
margin, with the KR2S somewhat better, thanks to the extra 14" bay that
was added. I have that chart saved somewhere, and will post it when I
come across it again.
Now I'm not saying that KRs are unflyable, not at all. I just thought
I'd stack the odds in my favor while I was building mine, and am quite
happy with the results. Any plane as small as these is going to be more
sensitive than a larger plane (all other things being equal), but the
small tail makes it worse. Widening the horizontal stab is enough
enough....you can do it with mere foam and carbon fiber like Troy did.
It's arguable that a stress riser is created that would increase stress
of the horizontal stab spars, but if you put enough vertical force on
that tailplane, you are already done for, I suspect.
Mark Langford
m...@n56ml.com
http://www.n56ml.com
Huntsville, AL
On 2/4/2021 8:50 AM, Mark Langford via KRnet wrote:
Larry Flesner wrote:
> Questiion. Was and by how much was the tail area enlarged in the 2S
> over the KR2? Mark, was your tail volume enlarged over the 2S? If
> anyone has the numbers I'd be curious how my standard KR2 tail area on a
> 24" stretch fuselage compares the the 2S.
Yes, my plane is more stable as a result of the longer horizontal stab,
plus the extra few inches added to the fuselage, and the more forward
sweep to my wings (due to adapting the new airfoil to the existing
spars). See the link below for details and how to figure it out.
I calculated all that stuff for the KR2 vs the KR2S twenty years ago
or so, but am too busy (and lazy) to do it again. I got this from
Pazmany's book, which the link below refers to. I can definitely say
that my KR2S (and most others, I'm sure) is a lot more stable than the
KR2 that I'm now flying, and the KR2 has a "forward of center" CG almost
all the time.
See link:
https://www.eaa62.org/technotes/tail.htm#:~:text=For%20the%20Vertical%20Tail%20Volume,area%20and%20b%20%3D%20wing%20span
Mark Langford
m...@n56ml.com
http://www.n56ml.com
Huntsville, AL
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