|
Salutti tutti,
The next time when flying your LIV during a quiet
moment take a moment and spare a thought for that wing out there that keeps you
aloft. It's an amazing piece of design and construction but it works soooh
well manipulating air pressures and flows that it keeps the increasingly obese
LIV aloft almost effortlessly. (For comparasion here in Italy is a
company building a new Frati design four seat aeroplane with a max gross
weight of around 2,900 -3,000lbs. The chord of their wing is 50% greater than
the LIV wing, the wing span longer by about 3 feet and their design studies
indicate they will have trouble meeting the required 61 knots stall speed for a
certified aeroplane) So getting back to our moment of TM in
the cockpit of the LIV contemplating the LIV wing just how much wing is actually
out there in the breeze? ....and the answer is not as much as you think.
Between BL 25.5 and BL171 is 38.87 square feet of wing. Add a square foot or so
for the wingtip and we'll call it a nice round 40 sq ft per wing. (If you have
winglets add at a guess 5 square feet to total a nice round 44 square
feet)
But you say I purchased 98 square feet of wing from
Lancair! So what or where is the difference and the answer is "you
are sitting on it". By design convention the wing planform that 'passes' through
the fuselage is included in the total wing area and if we include this area we
come upto the 98 square you purchased from Lancair. It seems to me as
the fuselage is nicely placed between BL25.5 port and stbd we are
effectively loosing wing area and consequently lift, but some of this
lift is undoubtedly replaced by fuselage lift but by how much I don't know.
Maybe designers deliberately use only calculated wing area to keep
everything simple. If you know more do let me know.
Back now to our moment of cockpit TM, we turn our
focus to how the fuselage weight and g loads are carried by the wing. Under our
seats are two 3/4" bolts which bolt the wing spars to the shear box...plenty
strong there. Look now at the couple of bits of prepreg and 6 bid layups that
attach the shear box to the fuselage sides and how strong are these?? Ever been
tested to the load limit of 9,250 lbs each side? which is
the ultimate load that the wing can exert on these parts before the wing
fails. My eyeball engineering suggests not but in the designer I must put my
faith, I hope he's correct...but being the sceptic that I am I'd still love to
see it tested.
Incidentally fellow amateur aeroplane
engineers, regarding wing g loads, stall speeds and fuselage
loads there may be a factor we've not considered yet Put the
brain into gear and see if you can work out what it is. It's a factor that in
straight and level flight is small and is usually disregarded but with
a high pitch rate it can become quite large, surprisingly large...I
think.
Ciao,
Roberto d'Italia.
psst.....tired of humdrum Lancair speeds?? Wanna go
fast...really fast?? Yesterday travelling around Rome came across a place
selling second hand machinery with 8 F-104 Starfighters out the front presumably
for sale. Will go there to have a proper look one day when the place is
open to find out more.
|