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included in the post below is reference to Dave
Morss's LA to Lakeland 6 hour record.
I assume he didn't land with empty tanks?
Anyone know how much gas he had?
(this is pertinent to the thread).
I don't know what the tailwind was that day but
workiing backwards it looks like he had to have more than 140 gals
----- Original Message -----
Sent: Friday, January 14, 2005 5:14
PM
Subject: Re: Approved Weights for Lancair
IVP/IVPTs
My thanks to Roberto d'Enginero for providing
the calculations that substantiate the points that I was trying to make in my
previous post, those being:
1) You can load an aircraft well past
its listed gross weight and it will still fly.
2) The more weight you add
the less safe the situation.
3) You cannot fly an airplane with a stall
speed greater than its maneuvering speed Va.
Whether the ultimate gross
weight is 18,000 or 28,500 pounds is irrelevant to the point. In the spirit of
Bob's post I should point out that Bob is using the wing lift and the gross
weight interchangeably. This is not correct (I'll take those quarters back).
Using the 18,000 pound number as the ultimate gross weight is, by design,
calculated to be conservative. As Bob pointed out, the load carried IN the
wings (including the wing structure) is not factored . Also not considered is
the lift generated by the fuselage, the vertical component of the propeller
thrust at high alpha and the effect of temperature on the composite
structure. Bob's assertion that the wings will clap at 18,000 pounds
gross is very probably inaccurate and would require empirical determination.
Perhaps Roberto d'Testpilot would volunteer.
Bob writes "
Brent continues with the mythical
200% (8.8G) ultimate load factor, which doesn't exist and never
has!"
Ouch, this one is gonna hurt. I would direct you to the Lancair
published flyer circa 1992 attached. Next to G Loading (ultimate) you
will see the "mythical" +8.8. Also note the 2,900 pound gross weight and 82
gallons of fuel.
Bob also writes "My apologies to the persons named, it's not the purpose of my
posting to embarrass anyone." Not to worry, I am offended by people with
malicious intent , not by ones who are well meaning but misinformed. I suspect
the only one you have embarrassed is yourself.
People who live in false
premiss(es) shouldn't throw conclusions.
My theory is this. The
original IV was designed with a 2,900 lb gross and a 2.0 to 1 safety
factor. A IV wing weighs about 180 Lbs all up or 360 Lbs the pair and
both will carry 492 Lbs of fuel (original 82 gallons) for a total of 852
pounds of wing and fuel and the balance of 2048 pounds in the fuselage. It is
the fuselage that is trying snap off the wings so if you reduce the factor of
safety to ultimate failure from 2.0 to 1.5 (Part 23.303 spam can margins) you
get a new fuselage weight of 2731 lbs. Add back the wing weight and you
get 3583 Lbs gross weight. Interesting close to the 3550 now published.
The increase in gross weight from 2,900 lbs to 3,550 lbs has come at
the cost of a reduction in the factor of safety from ~2.0 to ~1.5. and
an increase in stall speeds.
Lancair DID do an empirical wing strength
test, back when the earth was still cooling, and as I recall (and I am
probably wrong) the wing failed at ~11 Gs. This would correspond to a
fuselage weight of 22,528 and a gross weight of 23,380 lbs. Factor in
fuselage lift and vertical thrust component and 28,500 isn't so far off the
mark. However, a test IS the best way to know for sure so, Roberto, if you
want your quarter, do the test and send me the results. If the wings come off
at 23,250 Lbs (half way between our numbers) take off weight, you win.
Is a gross weight of 3,550 Lbs safe? Safety is relative and if you
load your plane more than the situation will allow your relatives will find
out.
Regards
Brent Regan
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