Date: Thu, 27 Jul 1995 23:32:22 -0400
From: KSPREUER@aol.com
Subject: C.G. ENVELOPE
Phil Johnson wrote about the weight and balance envelope of the Mark IV. The
way he plotted the info is interesting. I think though that there was a
mistake in the labeling of the graphs. The first set of coordinates appear to
be the empty fuel case and the second the full fuel case instead of vice
versa. His analysis uses the sample data from the POH. I don't have that yet,
but did some backward calculations to investigate. According to Phil the max
front seat loading is 395 lb and at that you have to keep 280 lb in the back
seat. That is a bit low if you are a big couple.
I think the best way to approach the weight an balance is to arrange the
airplane equipment so that when the most usual pilot flys he must carry about
50 lbs of balast at sta 35 or the equivalent. ( I choose sta 35 because that
is the floor in front of the instr. panel and makes a convenient place to
fasten a couple of shot bags.) This is what I did with the 3 place and it
worked very well. What you do is arrange equipment you are going to put in
the airplane anyway so that the empty moment is such that you must carry the
balast when flying alone (at full fuel, since this will be the most aft C.G.
condidtion). The C.G. for this case is 102.5. For the sample case in the POH
and a pilot that weighs 200 Lbs the empty moment changes from 119545 to
121023. This equates aproximately to re-locating a 35 lb battery 42" or
perhaps a 400 lb engine 3.7" I ran some figures using my back calculations.
(watch out for errors since some of the stations may be different than the 3
place). I increased the empty moment by 1478 in-lbs and used the same empty
weight of 1080 lbs.
empy wt 1080 1080 1080 1080 1080 1080
empty mom 122200 122200 122200 122200 122200 122200
fuel 46 0 46 0 0
0
pilot 200 200 400 400 400
460
balast @35 50 50 0 0 0
0
rear 0 0 0 0 570
510
total moment 163631 135750 173681 145800 204510 201870
total wt 1597 1330 1747 1480 2050 2050
c.g. 102.5 102.1 99.4 98.5 99.8
98.5
This gives 400 lbs front seat load and full use of the 46 gal fuel load. Or
if you carry 510 lbs in the rear seat you can get full use of the fuel with
460 lb in the front. Of course a lighter pilot must carry more balast when
alone! The point is there is some flexibility to center the C.G. envelope
around your particular situation.
Phil,
Given that you are a big guy and you have a little heavier engine you should
take advantage of moving the engine back as far as you can to get a little
more clearance between the firewall and engine as you can.