Weight & Balance
Moderators: GAHorn, Karl Towle, Bruce Fenstermacher
- ghostflyer
- Posts: 1395
- Joined: Mon Apr 21, 2008 3:06 am
Re: Weight & Balanced
The problem could be the weight and balance is being done from a incorrect datum point . It was stated the firewall was used ,I am under the impression the center of the axles should be used as the measurement datum point .
- Bruce Fenstermacher
- Posts: 10320
- Joined: Tue Apr 23, 2002 11:24 am
Re: Weight & Balance
The datum for all models according to the TCDS is the front face of the firewall.
CAUTION - My forum posts may be worth what you paid for them!
Bruce Fenstermacher, Past President, TIC170A
Email: brucefenster at gmail.com
Bruce Fenstermacher, Past President, TIC170A
Email: brucefenster at gmail.com
Re: Weight & Balance
Cessna has you measure the distance between wheel weigh points, then convert to datum later in the calculation. as long as you keep all the numbers straight during the weigh, get a total, then convert the distances, you are OK. the original weight & balance form that has the weighing procedure takes it step by step, but assumes no fuel and no oil.... weigh the aircraft, then after you calculate the basic w&b, you convert to datum. then you add unuseable fuel and full oil for the "licensed empty weight" using arms from datum.
if you weigh with full fuel.... remove all fuel mathematically after the weigh point numbers are converted.... use the TCDS/Spec for the arm of the fuel. then the unuseable fuel is added back in. it's only unuseable in flight, in some attitude (it is the fuel left in any tank when the engine sputters during any maneuver the aircraft is allowed to do in the category it's certified in). it's not as accurate to do it this way... only more convenient
I usually weigh with full oil and make note in the weighing record. realistically, it's no different than any piece of fixed equipment, and all the adverse load calculations, etc. require full oil anyway
you can also use the weigh points as measured from datum and skip the formula.... same results and is easier to follow. btw, the metal Pipers are the same, the rag ones are worse, uses the same formula, but have 2 datums
if you weigh with full fuel.... remove all fuel mathematically after the weigh point numbers are converted.... use the TCDS/Spec for the arm of the fuel. then the unuseable fuel is added back in. it's only unuseable in flight, in some attitude (it is the fuel left in any tank when the engine sputters during any maneuver the aircraft is allowed to do in the category it's certified in). it's not as accurate to do it this way... only more convenient
I usually weigh with full oil and make note in the weighing record. realistically, it's no different than any piece of fixed equipment, and all the adverse load calculations, etc. require full oil anyway
you can also use the weigh points as measured from datum and skip the formula.... same results and is easier to follow. btw, the metal Pipers are the same, the rag ones are worse, uses the same formula, but have 2 datums
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- Posts: 3481
- Joined: Sat May 06, 2006 6:05 pm
Re: Weight & Balance
Just thinking here and sometimes that can be dangerous but wouldn't you want the CG as far forward as possible when it's empty? Since the datum is the firewall, everything you load in the plane will move the CG aft. The plane is never going to go flying by itself so why worry that it is not in range when empty?
That just gives more latitude in loading and the pilot still makes the decision what to carry and where to load it based on whatever the final LOADED CG is going to be. I have a fairly stock plane (weight-wise anyway) and its empty CG is right at the front at 49.9 Index Units, right where I want it to get full usage of the CG range when loaded.
Am I missing something here?
That just gives more latitude in loading and the pilot still makes the decision what to carry and where to load it based on whatever the final LOADED CG is going to be. I have a fairly stock plane (weight-wise anyway) and its empty CG is right at the front at 49.9 Index Units, right where I want it to get full usage of the CG range when loaded.
Am I missing something here?
Richard Pulley
2014-2016 TIC170A Past President
1951 170A, N1715D, s/n 20158, O-300D
Owned from 1973 to 1984.
Bought again in 2006 after 22 years.
It's not for sale!
2014-2016 TIC170A Past President
1951 170A, N1715D, s/n 20158, O-300D
Owned from 1973 to 1984.
Bought again in 2006 after 22 years.
It's not for sale!
-
- Posts: 3481
- Joined: Sat May 06, 2006 6:05 pm
Re: Weight & Balance
Thanks Arash!!! That is what I was missing!
Richard Pulley
2014-2016 TIC170A Past President
1951 170A, N1715D, s/n 20158, O-300D
Owned from 1973 to 1984.
Bought again in 2006 after 22 years.
It's not for sale!
2014-2016 TIC170A Past President
1951 170A, N1715D, s/n 20158, O-300D
Owned from 1973 to 1984.
Bought again in 2006 after 22 years.
It's not for sale!
Re: Weight & Balance
Likely that was a senior moment and highly unlikely the reason that you were unable to mount a C/S .....but mounting a C/S was not an issue for me and I believe has not been a unsolvable issue for a few others.I am under the impression the center of the axles should be used as the measurement datum point .
Jim McIntosh..
1953 C170B S/N 25656
02 K1200RS
1953 C170B S/N 25656
02 K1200RS
Re: Weight & Balance
And the reason (in an effort to remove confusion) that modern aircraft have their datum situated in " space" forward of the nose so that all figures are positive.I think only items loaded aft of the CG point will move the CG aft, right? The datum is an arbitrary point that just gives you a reference.
Jim McIntosh..
1953 C170B S/N 25656
02 K1200RS
1953 C170B S/N 25656
02 K1200RS
Re: Weight & Balance
I plan to reweigh my own some day as it was calculated too far aft. In any event, ....if you need to shift operational C.G. aft.... I've always preferrred to use a case of bottled WATER for ballast. It can be adjusted by removing individual bottles...and it can be VERY USEFUL in the event of survival needs.
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
Re: Weight & Balance
A case of Vodka would be better it won't freeze until -16.51 degrees F.
John E. Barrett
aka. Johneb
Sent from my "Cray Super Computer"
aka. Johneb
Sent from my "Cray Super Computer"
Re: Weight & Balance
Wait.... Will that affect my balance...???
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
- Green Bean
- Posts: 163
- Joined: Tue May 06, 2003 2:13 am
Re: Weight & Balance
In some parts of the world, Vodka, has been used as a Deicing Fluid.
- Green Bean
- Posts: 163
- Joined: Tue May 06, 2003 2:13 am
Re: Weight & Balance
In the case I am familiar with, the airplane was a 727. Vodka was used as a replacement for the empty tanks of deicing fluid. Since is was over 90 proof and 40 percent alcohol, it worked very well, and it was cheaper than the usual glycol..
Everyone was happy, almost.
Everyone was happy, almost.
Re: Weight & Balance
One of the reported problems experienced by the defunct Soviet Air Force during the Cold War period was the impossibility of keeping the aircraft de-icing systems serviced with alcohol due to theft. The fluid was denatured by the addition of formaldehyde to no avail, and resulted in numerous hospitalizations and injuries.
(BTW, 80 proof vodka will freeze at approx. 16 degrees F so it might not be the best anti-icing fluid in Siberia)
(BTW, 80 proof vodka will freeze at approx. 16 degrees F so it might not be the best anti-icing fluid in Siberia)
'53 B-model N146YS SN:25713
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.
50th Anniversary of Flight Model. Winner-Best Original 170B, 100th Anniversary of Flight Convention.
An originality nut (mostly) for the right reasons.