G 103 Twin II weight troubles...

The Twin II of our club has an empty weight of 415 kg wich, with a max.
permitable total mass of 580kg leaves a max. payload of only 165kg.........

Now we are trying to solve this problem because we want to ad an extra
20 kg of payload. so the payload can be increased to 185 kg

the options are to:
replace the big heavy mainwheel and tyre by new TOST or Beringer
lightweight aloy wheels
Grind down the very thick (GROB style) gelcoat to a minimum
Replace the battery for a LiPO type
Remove radio and electro sink-clim indicator incl all electrica wiring.
Remove all pollstry.

And then?????????

Someone recognises this problem and who encouterd a solution??

Eric

On Apr 5, 4:31*am, Eric van Geetsum wrote:

replace the big heavy mainwheel and tyre by new TOST or Beringer
lightweight aloy wheels

Lighter weight wheels are often less durable, and more prone to
breakage. And I don't know about the ones you mention, but I rather
doubt that they are much lighter than the original.

Grind down the very thick (GROB style) gelcoat to a minimum

That's an interesting candidate. Gelcoat generally runs .012" to .020"
thick, and weighs about 10 lbs/gallon. A Grob twin is going to have
about 520 ft^2 of painted area, so there'll be around 1200 cubic
inches of gelcoat on it; that's around 5.2 gallons and about 52 lbs.
However, the gelcoat is rarely very evenly applied, so some spots will
be thicker than others. If you try to sand some of it off, you won't
get very deep before you get to green in some spots. You might get
maybe 1/4 of it off before that happens Then you either leave those
areas and sand others, resulting in an uneven surface, or you stop
there. After the sanding, you'd probably end up applying a gallon or
so of finish to clean it up some. That sounds to me like a rather
dubious enterprise.

Replace the battery for a LiPO type
Remove radio and electro sink-clim indicator incl all electrica wiring.
Remove all pollstry.

And then?????????

Someone recognises this problem and who encouterd a solution??

All aircraft gain weight as they age, and they generally gain more
than anybody expects. I think maybe it is proof that dark matter
exists.

I think that the thing to do is, at next annual inspection, first
clean out all the dust and dirt and grime from everywhere that you can
reach. Then, as you suggest, strip the instrumentation and wiring down
to the bare minimum. I think you need the radio and antenna, but maybe
use a newer, lighter one. Remove any extra plumbing. Recruit lighter
instructors.

Thanks, Bob K.

Put bags of helium into the fuselage?

On Apr 5, 4:31*am, Eric van Geetsum wrote:
The Twin II of our club has an empty weight of 415 kg wich, with a *max..
permitable total mass of 580kg leaves a max. payload of only 165kg..........

Now we are trying to solve this problem because we want to ad an extra
20 kg of payload. so the payload can be increased to 185 kg

the options are to:
replace the big heavy mainwheel and tyre by new TOST or Beringer
lightweight aloy wheels
Grind down the very thick (GROB style) gelcoat to a minimum
Replace the battery for a LiPO type
Remove radio and electro sink-clim indicator incl all electrica wiring.
Remove all pollstry.


The Beringer wheel/brake/tubeless tire (forget TOST for weight
savings...), LiFePo4 battery (not LiPo) like this:
http://www.batteryspace.com/lifepo42...rweight-1.aspx
(damn shame they are out of stock on these), less/different
instruments and wiring, skimping out on the upholstery will probably
buy you ~10kg, but it'll cost a few thousand Euros to make the glider
less safe/comfortable to fly, not to mention the EASA implications...
but grinding gelcoat to shave weight?? I suppose you can have it all
(mostly all) ground off and then refinished in PU for a scant 15,000
more Euros or so... but at that point you could just sell your current
ship and as is and upgrade to one with more useful load or different
type altogether.

Besides that you have Bob's skinny instructors and jsbrakes's
helium!

-Paul

On Apr 5, 7:49*am, Bob Kuykendall wrote:
On Apr 5, 4:31*am, Eric van Geetsum wrote:

replace the big heavy mainwheel and tyre by new TOST or Beringer
lightweight aloy wheels

Lighter weight wheels are often less durable, and more prone to
breakage. And I don't know about the ones you mention, but I rather
doubt that they are much lighter than the original.

Grind down the very thick (GROB style) gelcoat to a minimum

That's an interesting candidate. Gelcoat generally runs .012" to .020"
thick, and weighs about 10 lbs/gallon. A Grob twin is going to have
about 520 ft^2 of painted area, so there'll be around 1200 cubic
inches of gelcoat on it; that's around 5.2 gallons and about 52 lbs.
However, the gelcoat is rarely very evenly applied, so some spots will
be thicker than others. If you try to sand some of it off, you won't
get very deep before you get to green in some spots. You might get
maybe 1/4 of it off before that happens Then you either leave those
areas and sand others, resulting in an uneven surface, or you stop
there. After the sanding, you'd probably end up applying a gallon or
so of finish to clean it up some. That sounds to me like a rather
dubious enterprise.

Replace the battery for a LiPO type
Remove radio and electro sink-clim indicator incl all electrica wiring.
Remove all pollstry.

And then?????????

Someone recognises this problem and who encouterd a solution??

All aircraft gain weight as they age, and they generally gain more
than anybody expects. I think maybe it is proof that dark matter
exists.

I think that the thing to do is, at next annual inspection, first
clean out all the dust and dirt and grime from everywhere that you can
reach. Then, as you suggest, strip the instrumentation and wiring down
to the bare minimum. I think you need the radio and antenna, but maybe
use a newer, lighter one. Remove any extra plumbing. Recruit lighter
instructors.

Thanks, Bob K.

The problem with being a light instructor is you get assigned all the
overweight pilots to fly with. It gets old after a while. Pedal
powered self launch may be the answer. Just keep working at it until
the power to weight ratio becomes favorable.

Andy

At 11:31 05 April 2011, Eric van Geetsum wrote:
The Twin II of our club has an empty weight of 415 kg wich, with a max.

permitable total mass of 580kg leaves a max. payload of only
165kg.........

Now we are trying to solve this problem because we want to ad an extra
20 kg of payload. so the payload can be increased to 185 kg

the options are to:
replace the big heavy mainwheel and tyre by new TOST or Beringer
lightweight aloy wheels
Grind down the very thick (GROB style) gelcoat to a minimum
Replace the battery for a LiPO type
Remove radio and electro sink-clim indicator incl all electrica wiring.
Remove all pollstry.

And then?????????

Someone recognises this problem and who encouterd a solution??

Eric

Is this a Grob Acro II. The RAF operate those for the Air Cadets. We never
had a problem with weight with them, in fact the opposite. We were able to
put 242lbs on both seats, making a total of 484lbs (220Kg) payload. From
memory 415Kg seem rather a lot for an Acro II

On Apr 5, 7:31*am, Eric van Geetsum wrote:
The Twin II of our club has an empty weight of 415 kg wich, with a *max..
permitable total mass of 580kg leaves a max. payload of only 165kg..........

Now we are trying to solve this problem because we want to ad an extra
20 kg of payload. so the payload can be increased to 185 kg

the options are to:
replace the big heavy mainwheel and tyre by new TOST or Beringer
lightweight aloy wheels
Grind down the very thick (GROB style) gelcoat to a minimum
Replace the battery for a LiPO type
Remove radio and electro sink-clim indicator incl all electrica wiring.
Remove all pollstry.

And then?????????

Someone recognises this problem and who encouterd a solution??

Eric

Eric,

That seems on the heavier end for a Grob 103 Twin II. I have the
weight and balance sheets form 3 different G103s in my folder here
(including one I'm a part owner of) and the average empty weight is
about 882 pounds (which is just about exactly 400kg). The lightest
one is about 870 pounds (around 395kg). This is with standard
instruments and a single battery under the rear seat.

Two obvious questions:

- Has the ship had major repairs?
- Is there some heavy ballast installed?

Finding 20KG of extra payload sounds pretty unlikely unless there is
something strange going on...

Erik