Today's Message Index:
----------------------
1. 09:12 AM - Re: weight & balance (Jim Boyer)
2. 09:14 AM - Re: weight & balance (Jim Boyer)
3. 09:57 AM - Re: weight & balance (Ray Krause)
4. 10:04 AM - W&B S/S -- remarks re Oscar's post (Timothy Willis)
5. 10:30 AM - Re: W&B S/S -- remarks re Oscar's post (Ray Krause)
6. 08:08 PM - Re: weight & balance (taildrags)
7. 08:14 PM - Re: weight & balance (taildrags)
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Subject: | Re: weight & balance |
Sounds like you are getting very close though Ray. Have you had your final inspection
by a DAR yet?
Cheers,
Jim
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Subject: | Re: weight & balance |
Hi Oscar,
Will you send me a copy of your Piet weigh and balance sheet?
Thanks,
Jim B.
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Subject: | Re: weight & balance |
Jim,
No inspection, yet. Have to put the wings on, do final rigging W/B and a lot
of other little stuff.
Ray
Sent from my iPad
> On Feb 18, 2016, at 9:12 AM, Jim Boyer <boyerjrb@comcast.net> wrote:
>
> Sounds like you are getting very close though Ray. Have you had your final
inspection by a DAR yet?
> Cheers,
> Jim
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Subject: | W&B S/S -- remarks re Oscar's post |
=8B
Oscar is certainly right to recommend a pre-build spreadsheet for W&B, in
order to plan well and to save iterations-- Plan B,C,D.... Years ago I
wrote a fab pre-build W&B spreadsheet. Unfortunately that was a PC crash
and several PCs ago, and I no longer have it. However I will share a
feature and some findings.
I had a "what if" feature in the Excel model so that I could move a battery
fore or aft to improve balance. Of course moving it away from the firewall
also adds longer heavy wiring. Thus IMO this partial solution falls among
the category of "desperate corrective measures."
Slanting the wings aft obviously is a very effective way to alter CG to
within bounds. My major concern as a fat boy has been my nearly 100 lbs.
over the 170-pound "FAA pilot." I discovered that every *25 pounds *of
added pilot weight required a movement of the wing back* one inch*. My
setup features an A-65, and while I did also test for a Corvair instead, I
do not recall those comparative data. I did not run versions with a Model
A engine, radiator, etc.
My setup also features an 18 gallon fuselage tank, which accentuates W&B
considerations... about 100 lbs. (16 gals) difference between full and
empty-useable. In this regard a *wing *tank empty/full and a passenger
yes/no made almost no difference. I added a "thousand pound passenger" as
a test, and it moved the resultant CG nearly nil, under an inch, since both
are right at the CG.
I have concluded that I will slant my cabanes aft 6 inches. If in actual
practice that is not enough, I will develop a close relationship with Jenny
Craig, a virtuous step in its own right.
Tim in Central TX
=================
>> Okay, so really, builders don't need to be waiting till their aircraft
are almost finished before thinking about W&B. In fact, the earlier you
start to think about it and start getting numbers in your head, the more
confident you'll be about it when it comes time to do the final, actual W&B
and fill in the forms that you'll show at the end. Once you have the bare
fuselage -covered or not- on the gear, you're ready to start measuring and
weighing. At that point you can start plugging some numbers into a W&B
spreadsheet and it will be even easier if you don't have the wings or
engine on the bare fuselage because you can move it around the shop or
hangar very easily. Not only that but if you don't have the cabanes and
centersection mounted yet, it will be even easier to get your helper to
climb into that front cockpit to do the weighing to get the passenger
moment arm calculated.
>>
>> With the fuselage on the gear (as long as the geometry is locked in and
the gear mounting brackets are actually bolted to the fuselage or at least
pinned in place in final locations), you can determine the various moment
arms for the main gear and tailwheel, as well as the moment arms for pilot
and passenger. If you're using a nose tank you can also determine the
moment arm for it if you have the tank fabricated and can set it
temporarily in place in the forward fuselage. All of this can be done with
nothing more than masking tape, markers, a string and plumb bob or fishing
weight, and a couple of simple bathroom scales since the accuracy of the
scales doesn't matter too much at that point. They just need to be
reasonably accurate and the readings repeatable, and the actual weights
won't matter much in order to determine moment arms.
>>
>> As a starting point I can offer the Excel spreadsheet that I've used for
the W&B on 41CC, and I can probably also cook up a simple spreadsheet for
com ing up with the passenger and pilot moment arms after you've taken some
simple readings on a rainy workshop day when you and a helper are able to
make some measurements slowly, carefully, and thoughtfully. If you do it
right the first time, you'll never have to do it again. The upside to all
of this is that if you start the process early, you can make adjustments as
you go along and not get surprised at the very end when you find out your
airplane has a heavy tail and you have to find a way to offset or move it.
>> --------
>> Oscar Zuniga
>> Medford, OR
>> Air Camper NX41CC "Scout"
>> A75 power
Message 5
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Subject: | Re: W&B S/S -- remarks re Oscar's post |
Tim,
Very interesting comments and well written, thanks.
Ray Krause
Sent from my iPad
> On Feb 18, 2016, at 10:03 AM, Timothy Willis <timwillis01@gmail.com> wrote
:
>
> =8B
> Oscar is certainly right to recommend a pre-build spreadsheet for W&B, in o
rder to plan well and to save iterations-- Plan B,C,D.... Years ago I wrot
e a fab pre-build W&B spreadsheet. Unfortunately that was a PC crash and se
veral PCs ago, and I no longer have it. However I will share a feature and s
ome findings.
>
> I had a "what if" feature in the Excel model so that I could move a batter
y fore or aft to improve balance. Of course moving it away from the firewal
l also adds longer heavy wiring. Thus IMO this partial solution falls among
the category of "desperate corrective measures."
>
> Slanting the wings aft obviously is a very effective way to alter CG to wi
thin bounds. My major concern as a fat boy has been my nearly 100 lbs. over
the 170-pound "FAA pilot." I discovered that every 25 pounds of added pilo
t weight required a movement of the wing back one inch. My setup features a
n A-65, and while I did also test for a Corvair instead, I do not recall tho
se comparative data. I did not run versions with a Model A engine, radiator
, etc.
>
> My setup also features an 18 gallon fuselage tank, which accentuates W&B c
onsiderations... about 100 lbs. (16 gals) difference between full and empty-
useable. In this regard a wing tank empty/full and a passenger yes/no made a
lmost no difference. I added a "thousand pound passenger" as a test, and it
moved the resultant CG nearly nil, under an inch, since both are right at t
he CG.
>
> I have concluded that I will slant my cabanes aft 6 inches. If in actual p
ractice that is not enough, I will develop a close relationship with Jenny C
raig, a virtuous step in its own right.
>
> Tim in Central TX
> =================
>
> >> Okay, so really, builders don't need to be waiting till their aircraft a
re almost finished before thinking about W&B. In fact, the earlier you star
t to think about it and start getting numbers in your head, the more confide
nt you'll be about it when it comes time to do the final, actual W&B and fil
l in the forms that you'll show at the end. Once you have the bare fuselage
-covered or not- on the gear, you're ready to start measuring and weighing.
At that point you can start plugging some numbers into a W&B spreadsheet a
nd it will be even easier if you don't have the wings or engine on the bare f
uselage because you can move it around the shop or hangar very easily. Not o
nly that but if you don't have the cabanes and centersection mounted yet, it
will be even easier to get your helper to climb into that front cockpit to d
o the weighing to get the passenger moment arm calculated.
> >>
> >> With the fuselage on the gear (as long as the geometry is locked in and
the gear mounting brackets are actually bolted to the fuselage or at least p
inned in place in final locations), you can determine the various moment arm
s for the main gear and tailwheel, as well as the moment arms for pilot and p
assenger. If you're using a nose tank you can also determine the moment arm
for it if you have the tank fabricated and can set it temporarily in place i
n the forward fuselage. All of this can be done with nothing more than mask
ing tape, markers, a string and plumb bob or fishing weight, and a couple of
simple bathroom scales since the accuracy of the scales doesn't matter too m
uch at that point. They just need to be reasonably accurate and the reading
s repeatable, and the actual weights won't matter much in order to determine
moment arms.
> >>
> >> As a starting point I can offer the Excel spreadsheet that I've used fo
r the W&B on 41CC, and I can probably also cook up a simple spreadsheet for c
om ing up with the passenger and pilot moment arms after you've taken some s
imple readings on a rainy workshop day when you and a helper are able to mak
e some measurements slowly, carefully, and thoughtfully. If you do it right
the first time, you'll never have to do it again. The upside to all of thi
s is that if you start the process early, you can make adjustments as you go
along and not get surprised at the very end when you find out your airplane
has a heavy tail and you have to find a way to offset or move it.
> >> --------
> >> Oscar Zuniga
> >> Medford, OR
> >> Air Camper NX41CC "Scout"
> >> A75 power
Message 6
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Subject: | Re: weight & balance |
For all those who asked, I've uploaded my W&B spreadsheet to the forum but if you're
unable to get it that way, email me privately and I'll send it to you.
The usual caveats apply, especially "the numbers in this spreadsheet are for NX41CC
ONLY!" Do not use them for your airplane except as a starting point so
you can check to see if your numbers are reasonable. The other thing I'd like
to mention is that I did not author this spreadsheet. It was generously shared
with me and it is in that spirit that I share it with others. Like Tim, I
also added another tab so that I would have a "what-if sandbox" to play in without
messing up the REAL sheet with the real numbers. In fact, I would suggest
that once you enter your final numbers into the real sheet, that you lock those
cells so you can't inadvertently change the numbers that shouldn't change.
Ray: the spreadsheet doesn't care if you have a one-holer, two-holer, or twelve-holer...
you can either leave the numbers for passenger weight and moment arm
as "zero", or else eliminate those cells to streamline the spreadsheet. And
if you're building a 3-cockpit Air Camper, just add rows for another cockpit and
passenger ;o)
As I mentioned, you don't need to have a complete airplane to start entering values
into the sheet. For sure you can add the basic information at the top, but
then as you measure the moment arms relative to the datum that you choose,
you can start entering those values into the sheet and begin playing what-ifs.
If the datum that you choose is going to be the wing leading edge and you don't
have the centersection mounted yet, you'll have to enter values relative to
the firewall and then later adjust those numbers when the distance from leading
edge to firewall is determined. I have set the precision of weights and moment
arms to one decimal place (roughly to the nearest 2 oz and 1/8"). I've
played with it by increasing the precision of them one at a time and then both
together, but I decided that I do not have eyes or tools that can measure closer
than that. I've tried decreasing the precision to whole pounds and inches
only, but that is unsatisfactory. If I were going to simplify one of the two,
I would use whole pounds but keep tenths of an inch of length.
You may argue about the acceptable range of 15 to 20" aft of wing leading edge
for the CG and you may argue about the allowable maximum gross weight of 1,088
lbs. You just won't be arguing them with me ;o)
Anyway, here is the spreadsheet.
--------
Oscar Zuniga
Medford, OR
Air Camper NX41CC "Scout"
A75 power
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=452991#452991
Attachments:
http://forums.matronics.com//files/nx41ccw_b_2014_117.xls
Message 7
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Subject: | Re: weight & balance |
...oh, and also- my empty weight includes 3 quarts of oil in the engine, which
is the minimum amount recommended by Continental. You can argue about whether
minimum oil should be included in the aircraft's empty weight, but I won't fly
the airplane without it. You can make it whatever you want it to be when you
weigh your airplane and edit the notes in those cells appropriately.
--------
Oscar Zuniga
Medford, OR
Air Camper NX41CC "Scout"
A75 power
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=452992#452992
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