I don't want to go with you at 3000lbs and especially still be along for the
landing. Them alum gear legs ain't going to take 3000lbs for very long...
with even smooth landings, let alone some that I've made and managed to roll
away from ....or others that some (and myself) have walked away from (with
the airplane sitting a little closer to the ground!). Let alone the airframe
strength when you consider the substantial wing structure differences to get
the first SR to 3000lb gross safely. (ie double stringer thickness, 60%
thicker leading edge skin, approx 6 times the thickness for front pickup
fittings, lift strut reinforced with internal square 1/8" wall tube x 2 per
side, etc, etc)
Your quick calculations do make sence though and I concure, to a
point,..although I'm pretty sure MAM's 6G's is failure (might be wrong) and
if so then really only a safe 4G airplane at 1650lbs.
The other thing that Ontario Region is catching people for here now,
especially when they go to floats/larger engines and ask for a higher gross
weight is the requirement to meet Minimum HP (which of course translates
into your statement of being able to pass a climb test!). To try that one
out at 3000lbs on a Rebel and we get:
Pmin=0.016W + C x square root of (W cubed) / b
Pmin=0.016 (3000) + 0.018 x square root of (3000 cubed) / 30'
Pmin= 48 + 98.59
Pmin= 146.59 BHP
W=Gross weight in lbs, C= constant of 0.018, b=wings span feet
According to this 150HP O-320 would be sufficent in theory, but I don't want
to be in there when the trees are coming up quick as I know damn well it
won't climb at that weight behind 150HP! You are going to need at least 210
to 250HP I would think to pass a climb test. With that many ponys pulling
you might just have the engine "part ship" and leave with your firewall as a
unit!
Fun to play with numbers....nobody gets hurt sitting in a chair typing on
the keyboard ..ouch wife slapped me in the head 'cause suppers cold!!
Wayne
----- Original Message -----
From: "Dave King" <
kingdws@shaw.ca>
To: <
murphy-rebel@dcsol.com>
Sent: Monday, February 23, 2004 12:45 AM
Subject: Re: REBEL MTOW
Jerry
I think it might be possible to be legal at a hair over 3000lbs in a Rebel
if it would pass the rate of climb test. To start with you have two
limitations
one is allowable wing loading tempered with the G loading.
First thing is if the airframe is actually strong enough. This is a gross
calculation
but would be close enough to see if it might work. And yes I can do a
proper
analysis of the wing and hand it to TC to watch their eyes roll back in
their heads
(and then not even look at it.)
You have a 6.6G airframe at 1650 so at 4.4G (Utility) you have 2450 lbs at
3075
you are good for 3.5g... All of which provide adequate margins.
At the higher rate you will have more wear , more loose rivets and
accelerated aging all of which
you can inspect for. Ie the smokers around the airplane. Some are normal
pull rivet
probs and other are just going to be hard landings at higher weight. If
you
were truly
playing in dangerous grounds you would be seeing a lot more or that and
all
the time.
And it would start and continue around any high stress point such as
attachments and fittings.
Performing inspections would alert you to where any problems start. That
is
half of it.
The other half is the wing loading. With flaps you could have up to 20.5
lbs per sqr foot
as per CH549. It's actually a formula that takes into account the flaps
but
put it this way
without flaps you are limited to about 13.3 lbs per square foot.
Except for high performance amateur-built aeroplanes, the wing loading M/S
(W/S) shall not be greater than:
(i) For wings without flaps, M/S = 65 Kg/m2 (W/S=13.3 lb/ft2); or
(ii) For wings with flaps, the value calculated using the method of
Appendix A of this Chapter, but not exceeding 100 Kg/m2 (20.4 lb/ft2).
So without flaps and 150 square feet of wing on a rebel you can LEGALLY
fly
away at 1995 lbs or 905kgs
Since it has flaps you can fly away LEGALLY at 3075lbs or 1395kgs
As long as you can pass the minimum rate of climb test at that weight you
are legal.
The above is right off of the page of Transport Canada and Chapter 549. So
it is Good info.
So even the 3000lb guy in Alberta is PERFECTLY legal if he passed the
climb
test.
Dave
I agree with you there has to be a limit,the 3000 lber has to be typo
error,but in regards to inspectors in B.C. they used the formula for load
and square ft. of wing,and climb test,and from what I've been told their
within limits,and far as insurance goes totally legal with Certificate of
Registration. The inspectors here checked with MOT came up with the same
results you are getting,since it is up to builder,problem being their has
to
be a limit. And to repeat myself I was not trying to step on anybody just
stating facts from B.C. end.
THANKS
jerry
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