On 10/9/2021 9:45 AM, Ryan wrote:
Larry how many KR's are overweight after the original spars were designed?
Does a solid spar have more or less flex than a boxed type?
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
I could probably say without question that 100% of the KR's built weight
more than Ken Rand's KR at 480 pounds. Many pass the 700 pound mark and
several pass the 800 pound mark. The original spar design listed in the
plans states a "design limit" of 7G at 800 pounds. That's 5600 pounds.
A flying weight of 1200 pounds would give you a "design limit" of
4.66G's. I don't know of anyone doing unlimited aerobatics in a KR so
that is probably sufficient for 100% of the KR builders. That was
flight tested by Marty Roberts, rest his soul, when he pulled 6 G's
pulling out of a failed aerobatic maneuver in his 760 pound empty KR
with him at 200 pounds and some amount of fuel on board. That was
recorded on a G meter, not an estimate.
Keep in mind that the original wing plan called for "spar shear web" on
one side only on the outer wing panels. Later plans suggest shear web
on both sides of the outer wing panels similar to the wing center
section. In addition, if you use the new wing that uses the larger spar
caps you've added additional strength. As to the flex I have no idea but
I'd want to see a solid spar flex 2X the standard spar I saw tested at
one of the Gatherings at Mt.Vernon to pass on that one. The following
photos are on the 2008 Gathering at Mt.Vernon site at www.krnet.org.
http://www.krnet.org/mvn2008/080921256.jpg
http://www.krnet.org/mvn2008/080921265.jpg
http://www.krnet.org/mvn2008/080921282.jpg
For 50 years, well 49 maybe, the belief has been that the wing attach
fittings are the weak point in the wing. I've seen at least three
crashed KR's ( one a fatality) and not a single failure of the WAF's.
I've seen spar caps literally pulled in two pieces horizontally and wing
structure in pieces that would fit nicely in to a fireplace and the
WAF's were still intact.
The KR's are experimental so you are free to build to any design you
wish but to add unnecessary strength and weight to an already adequate
structure gains you nothing and can affect performance. Unless someone
can point me to an in-flight structural failure of a KR at any weight
I'll continue to believe the above statements.
Larry Flesner
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