ASK-21 Weight and Balance

[Carl Baxter]

I'm trying to make sense of the weight and balance section in the
ASK-21 manual but having no success. They give an equation for r sub
R, which I assume is the empty CG, but it's not specifically called
out. The units don't balance; there is length on one side of the
equation and length squared on the other. There is an example given
for calculating "inflight CG" and the results seem to be out of
limits but they don't comment so I'm not sure I've got that right.
There is a Load Envelop with Empty Weight on the abscissa and r sub R
on the ordinate. Where does the in flight CG come in? Or is r sub R
also the inflight CG

At 360kg (the nominal empty weight of the aircraft) there is only 8 mm
of CG range within the envelop. Is it really that small? I
understand the Schweizer weight and balance calculations but the
English translation of the Schleicher manual has me puzzled.

Any help would be appreciated. Thanks.

Carl

[[email protected]]

On May 31, 6:23*pm, Carl Baxter >
wrote:
> I'm trying to make sense of the weight and balance section in the
> ASK-21 manual but having no success. *They give an equation for r sub
> R, which I assume is the empty CG, but it's not specifically called
> out. *The units don't balance; there is length on one side of the
> equation and length squared on the other. *There is an example given
> for calculating "inflight CG" and the results seem to be out of
> limits *but they don't comment so I'm not sure I've got that right.
> There is a Load Envelop with Empty Weight on the abscissa and r sub R
> on the ordinate. *Where does the in flight CG come in? Or is r sub R
> also the inflight CG
>
> At 360kg (the nominal empty weight of the aircraft) there is only 8 mm
> of CG range within the envelop. *Is it really that small? *I
> understand the Schweizer weight and balance calculations but the
> English translation of the Schleicher manual has me puzzled.
>
> Any help would be appreciated. *Thanks.
>
> Carl

r sub R is the calculated empty weight CG location relative to the
leading edge of the wing at the root.
It is also shown in the vertical axis of the diagram below.
The manual assumes most pilots will use the diagram, however the
information to calculate flight Cg is avaialable on the following
pages. Note that the only place(that I saw) where rear pilot moment
is shown is in the example calculation. Note that moment values of
pilot masses are negative.
Good luck
UH

[[email protected]]

On May 31, 6:23*pm, Carl Baxter >
wrote:
> I'm trying to make sense of the weight and balance section in the
> ASK-21 manual but having no success. *They give an equation for r sub
> R, which I assume is the empty CG, but it's not specifically called
> out. *The units don't balance; there is length on one side of the
> equation and length squared on the other. *There is an example given
> for calculating "inflight CG" and the results seem to be out of
> limits *but they don't comment so I'm not sure I've got that right.
> There is a Load Envelop with Empty Weight on the abscissa and r sub R
> on the ordinate. *Where does the in flight CG come in? Or is r sub R
> also the inflight CG
>
> At 360kg (the nominal empty weight of the aircraft) there is only 8 mm
> of CG range within the envelop. *Is it really that small? *I
> understand the Schweizer weight and balance calculations but the
> English translation of the Schleicher manual has me puzzled.
>
> Any help would be appreciated. *Thanks.
>
> Carl

Carl,

Are you simply trying to determine acceptable pilots weights for
flight, or ar you trying to actually understand the German "math".


The way the German two seaters do the weight and balance is kind of
simple for the user, if you don't need to understand how the got to
their conclusions.

What they do is specify a CG range for each possible empty weight.
There is a chart in the manual for this.

As long as your empty CG falls in the acceptable limits of this chart,
then the given pilots weights apply and will fall within limits.

Front pilot: 154 ~ 242

Front pilots less than 154 , use ballast weights as specified, and /
or seat ballast

Rear pilot 0 ~ 242Baggage within posted limit




You must respect gross weight limit


BTW Grob uses a similar un-undertandable W&B in their manual. They
also have an additional section in the manual for USA which tries to
explain the german part....but also not understandable.......


Cookie

[AT]

On 1/06/2011 6:23 AM, Carl Baxter wrote:
> I'm trying to make sense of the weight and balance section in the
> ASK-21 manual but having no success. They give an equation for r sub
> R, which I assume is the empty CG, but it's not specifically called
> out. The units don't balance; there is length on one side of the
> equation and length squared on the other. There is an example given
> for calculating "inflight CG" and the results seem to be out of
> limits but they don't comment so I'm not sure I've got that right.
> There is a Load Envelop with Empty Weight on the abscissa and r sub R
> on the ordinate. Where does the in flight CG come in? Or is r sub R
> also the inflight CG
>
> At 360kg (the nominal empty weight of the aircraft) there is only 8 mm
> of CG range within the envelop. Is it really that small? I
> understand the Schweizer weight and balance calculations but the
> English translation of the Schleicher manual has me puzzled.
>
> Any help would be appreciated. Thanks.
>
> Carl

Carl

The BGA web site has Data sheets for many gliders that are very helpful.

They can be found at
http://www.gliding.co.uk/bgainfo/technical/datasheets.htm

John

[Max Kirschner[_2_]]

At 03:01 02 June 2011, at wrote:
>On 1/06/2011 6:23 AM, Carl Baxter wrote:
>> I'm trying to make sense of the weight and balance section in the
>> ASK-21 manual but having no success. They give an equation for r sub
>> R, which I assume is the empty CG, but it's not specifically called
>> out. The units don't balance; there is length on one side of the
>> equation and length squared on the other. There is an example given
>> for calculating "inflight CG" and the results seem to be out of
>> limits but they don't comment so I'm not sure I've got that right.
>> There is a Load Envelop with Empty Weight on the abscissa and r sub R
>> on the ordinate. Where does the in flight CG come in? Or is r sub R
>> also the inflight CG
>>
>> At 360kg (the nominal empty weight of the aircraft) there is only 8 mm
>> of CG range within the envelop. Is it really that small? I
>> understand the Schweizer weight and balance calculations but the
>> English translation of the Schleicher manual has me puzzled.
>>
>> Any help would be appreciated. Thanks.
>>
>> Carl
>
>Carl
>
>The BGA web site has Data sheets for many gliders that are very helpful.
>
>They can be found at
>http://www.gliding.co.uk/bgainfo/technical/datasheets.htm
>
>John
>
>
I have made up a spreadsheet to show where the C of G is for our K21,
especially useful when using spin wieghts.

The C of G range in mm is
Spinning
Forward limit 234
Forward of 315 Does not spin
320 to385 322 to 385 Incipient
aft 400 400 Sustained spins
Aft limit 469

Flying with the weights confirmed the manual, it was not possible to spin
with the C of G forward of 315 mm
It would incipient with the C of G between 322 and 385.

Being heavy I could not get the C of G aft of 400 to sustain a spin.

If you want a copy of the spread sheet drop me a mail

Regards
Max