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Weight and Balance - RF4D printer friendly version
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jb92563
Second Lieutenant

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Location: Lake Elsinore, CA, USA
Registered: Mar 2007
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Posts: 583

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Posted Wednesday, September 8, 2010 @ 06:44 PM  

Seeing as how I plan on getting into aerobatics I think the CG position will be very important.

I have been looking for a suitable method of weighing and think that I might as well just buy a digital scale
as there does not seem to be any available near by.

The most economical, highest resolution I could find is the one below that does up to 750 lbs at 0.2lb resolution for $210 USD:

http://www.oldwillknottscales.com/my-weigh-pd-750-commercial.aspx

I will use it under the main wheel and a digital bathroom scale under the tail.

Where is the ideal CG point for aerobatics?

[Edit by jb92563 on Wednesday, September 8, 2010 @ 06:45 PM]

[Edit by jb92563 on Wednesday, September 8, 2010 @ 06:46 PM]

--------------------
Ray
RF4D #4057 N-1771 Rectimo 1400cc
http://picasaweb.google.com/jb92563/FournierRF4D
http://www.touringmotorgliders.org

Jorgen
Captain

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Location: Lund, Sweden
Registered: Apr 2007
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Posts: 833

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Posted Thursday, September 9, 2010 @ 03:08 PM  

Hi Ray,

We used a VERY analogous scale when XST was weighed for Swedish certification- an oak plank and a counter weight as I remember. In the square "What type/brand of scale was used?" on the weighing form we simply stated "OAK's". You might as well have some fun while completing these sometimes tedious tasks, we did check it with a digital scale later that confirmed the weight. Most flying communities seem to include someone working in a place were digital scales are available, but sometimes it takes some time to "ferret them out" and a simple method as this one is often adequate at least until you can get your hands on a digital scale. In the flight manual the CG-range is stated on page 14:

http://www.cfiamerica.com/images/RF4D_Flight_Manual-v2.3.pdf

I must confess I haven´t paid that much attention to weight and balance when loading up for trips, but when doing aeros you should off course not have a lot of unecessary stuff aboard such as loose items in the back, full tank of gas etc.

May the 4´s be with you/ Jörgen

[Edit by Jorgen on Saturday, September 11, 2010 @ 01:51 PM]

jb92563
Second Lieutenant

Gender: Male
Location: Lake Elsinore, CA, USA
Registered: Mar 2007
Status: Offline
Posts: 583

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Posted Thursday, September 9, 2010 @ 07:28 PM  

Haa...that simple and cheap method had not even occured to me.

A simple balance would work just as well with a few calculations.

I might just do that and with a good long lever arm I would not need too many sand bags.

Since mine has the 1400 cc cylinders conversion plus alternator, starter and a couple batteries I had been wondering about the balance for some time figuring its probably quite nose heavy.

I am about to replace the batteries and figure its the opportune time to position it to improve the balance.

I knew if I put this out there someone would have a good suggestion as always.

Quote:

2.6 Center of gravity (c.g.)

-reference: upper stringer of fuselage horizontally
-datum: wing lending edge root chord

foremost c.g. - 11.8 inch (30cm) aft datum
aft most c.g. - 19.3 inch (49cm) aft datum

in flight conditions:
empty weight lbs. - 572 (260 kg) - 595 (270 kg) - 615 (280 kg)
c.g. - 12.2...17.2 - 12.2...17.3 - 12.2...17.4
in. aft datum

I do not see where 19.3" is acceptable in flight?

Seems like 17.4" is the max aft depending on empty weight?

Am I missing something? or are they just stating 19.3" in case you have a very heavy empty weight?

[Edit by jb92563 on Thursday, September 9, 2010 @ 07:30 PM]

--------------------
Ray
RF4D #4057 N-1771 Rectimo 1400cc
http://picasaweb.google.com/jb92563/FournierRF4D
http://www.touringmotorgliders.org

Bob Grimstead
Captain

Gender: Male
Location: Perth, Western Australia or West Sussex, England
Registered: Dec 2006
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Posted Tuesday, September 14, 2010 @ 02:22 PM  

Hi Ray,

Don't forget that 'in flight' means with the main wheel retracted -- not sure how you'd measure that.

Mine both have their empty C of G in the middle of the stated 'empty weight' range, although one has its battery on the left floor just ahead of the main spar, and the other has it at the back of the luggage compartment. Make sure they're very secure. HDO's (the blue one) battery came out and punched a hole in the fuselage. My head was less than a foot in front of that. Don't like to think what would have happened if it had punched a hole in my head!

I fly aerobatics with a maximum of 17 litres at take-off (I figure it takes a couple of litres to taxi out and climb to height) and NOTHING ELSE at all aboard.

Don't forget to empty your pockets or put your keys etc in zippered pockets (zipped up of course).

To be sure there's nothing rolling around in your rear fuselage, find somewhere quiet and windless, turn your prop horizontal and lift up your tail as high as it will go, then waggle it side-to-side and up and down.

When I bought WGN (the red one) there were no fewer than EIGHT loose objects floating around in the rear fuselage, any one of which would have killed me if it got into the elevator linkage.

Good luck, take care, and have funnnnn!

Yours, Bob

Bob Grimstead
Captain

Gender: Male
Location: Perth, Western Australia or West Sussex, England
Registered: Dec 2006
Status: Offline
Posts: 2027

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Posted Sunday, June 14, 2015 @ 06:11 PM  

Hi Guys,

We've just re-weighed Wagon after its re-cover. The job was done by the professional Planeweighs company with high-tech digital scales.

Here's a reminder that there are other relevant threads at:

http://sbeaver.com/cgi-bin/fournier/cutecast.pl?session=B9X5FfTna7NySOB9t7prOoj1nu&forum=18&thread=876

and...

http://sbeaver.com/cgi-bin/fournier/cutecast.pl?session=B9X5FfTna7NySOB9t7prOoj1nu&forum=17&thread=1007

Standard, empty, with no extras, she weighed 258kg, with CoG dead centre at 39.57cm AOD.

With me aboard and no fuel (the most aft CoG case, of course, after a long flight) it was 332kg and 42.70cm AOD.

With me and a full main tank (take-off case): 357kg and 38.44cm AOD.

So the CofG is nicely in the midddle in all three cases.

With all the options, including smoke pods added, the empty weight comes to 274kg. Add me, full fuel and 10kg of baggage on the shelf and there's still 7kg spare!

Yours, Bob

[Edit by Bob Grimstead on Sunday, June 14, 2015 @ 06:13 PM]

--------------------
Flying and displaying Fournier RF4Ds VH-HDO and G-AWGN, building replica RF6B G-RFGB and custodian of RF6B prototype F-BPXV

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