Pre-Preg

On Friday, December 2, 2016 at 6:48:16 AM UTC-6, Bruce Hoult wrote:
Most gliders work out at about 6 (30 kg/m^2) dry with a 240 lb pilot, don't they?

My LS6 runs around 8psf (39 kg/m2) dry with me in it (240 on a good day). I would think you would have to get into open class or older std gliders to get as low as 6 psf...

Works great for no-ballast (Beer ballast?) contests...

Kirk
66

For the guys with an engine weight does make a difference. Imagine if the 100 pounds of engine and fuel were offset by construction methods that lowered the empty weight of the glider by even 50-70 pounds. YOu would functionally have the same wing loading range as a pure glider.

Just saying.
On Thursday, December 1, 2016 at 4:09:14 PM UTC-8, wrote:
4 Pretty much nobody cares much about weight, except the little gliders. For all the rest we just want to know how much water can we get in it.

On Monday, December 5, 2016 at 2:23:59 PM UTC-5, Jonathan St. Cloud wrote:
For the guys with an engine weight does make a difference. Imagine if the 100 pounds of engine and fuel were offset by construction methods that lowered the empty weight of the glider by even 50-70 pounds. YOu would functionally have the same wing loading range as a pure glider.

Just saying.
On Thursday, December 1, 2016 at 4:09:14 PM UTC-8, wrote:
4 Pretty much nobody cares much about weight, except the little gliders.. For all the rest we just want to know how much water can we get in it.

Different building methods in same factory brings several issues I could think of.
Cost of buying and storing different materials, cost of process, possible mistakes in manufacturing, return on investment, different flying characteristics. Just throwing this out there.

On Monday, December 5, 2016 at 4:58:14 PM UTC-5, Casey wrote:
On Monday, December 5, 2016 at 2:23:59 PM UTC-5, Jonathan St. Cloud wrote:
For the guys with an engine weight does make a difference. Imagine if the 100 pounds of engine and fuel were offset by construction methods that lowered the empty weight of the glider by even 50-70 pounds. YOu would functionally have the same wing loading range as a pure glider.

Just saying.
On Thursday, December 1, 2016 at 4:09:14 PM UTC-8, wrote:
4 Pretty much nobody cares much about weight, except the little gliders. For all the rest we just want to know how much water can we get in it.

Different building methods in same factory brings several issues I could think of.
Cost of buying and storing different materials, cost of process, possible mistakes in manufacturing, return on investment, different flying characteristics. Just throwing this out there.

Maybe this is why GP decided to put the batteries in the wings. Removal for light days without changing CG. All other FES gliders have batteries behind cockpit and have to fly with batteries.

On Monday, December 5, 2016 at 7:59:28 PM UTC-5, Casey wrote:
On Monday, December 5, 2016 at 4:58:14 PM UTC-5, Casey wrote:
On Monday, December 5, 2016 at 2:23:59 PM UTC-5, Jonathan St. Cloud wrote:
For the guys with an engine weight does make a difference. Imagine if the 100 pounds of engine and fuel were offset by construction methods that lowered the empty weight of the glider by even 50-70 pounds. YOu would functionally have the same wing loading range as a pure glider.

Just saying.
On Thursday, December 1, 2016 at 4:09:14 PM UTC-8, wrote:
4 Pretty much nobody cares much about weight, except the little gliders. For all the rest we just want to know how much water can we get in it..

Different building methods in same factory brings several issues I could think of.
Cost of buying and storing different materials, cost of process, possible mistakes in manufacturing, return on investment, different flying characteristics. Just throwing this out there.

Maybe this is why GP decided to put the batteries in the wings. Removal for light days without changing CG. All other FES gliders have batteries behind cockpit and have to fly with batteries.

Aren't the light days the ones where you most need the batteries?

Three further points with pre preg;-
1-Uni directional (UD) pre-preg, which is extensively used in wings, is
difficult
to form into compound curves;- it wrinkles
2-stray fibres, with pre-preg stray fibres can puncture the vac bag. The
wing
skins don't come out of the moulds until after the wings have been fully
glued
together. It's a bad day to discover a single stray fibre has killed the
vacuum
during the cure of a skin and you've just glued it to a good
spar/skin/installed
controls etc
3 - wet lay up wings post cure at 60C, normally out of mould. Pre-Preg
cures
at least 80C maybe hotter but this must be done in the mould. This means
the part and mould thermal expansion must be closely matched and the
longer the part , the more compound curves, the more difficult this
becomes.

Dry fibre resin infusion probably offers the best way forward as it can
provide
similar fibre fractions to pre preg but without the above and earlier
mention
drawbacks.

Fraser

At 21:58 05 December 2016, Casey wrote:
On Monday, December 5, 2016 at 2:23:59 PM UTC-5, Jonathan St. Cloud
wrote:
For the guys with an engine weight does make a difference. Imagine if
th=
e 100 pounds of engine and fuel were offset by construction methods that
lo=
wered the empty weight of the glider by even 50-70 pounds. YOu would
funct=
ionally have the same wing loading range as a pure glider.
=20
Just saying.
On Thursday, December 1, 2016 at 4:09:14 PM UTC-8,

=
wrote:
4 Pretty much nobody cares much about weight, except the little
gliders=
.. For all the rest we just want to know how much water can we get in it.

Different building methods in same factory brings several issues I could
th=
ink of.
Cost of buying and storing different materials, cost of process, possible
m=
istakes in manufacturing, return on investment, different flying
characteri=
stics. Just throwing this out there.

On Tuesday, 6 December 2016 08:45:13 UTC+1, Fraser Wilson wrote:
Three further points with pre preg;-
1-Uni directional (UD) pre-preg, which is extensively used in wings, is
difficult
to form into compound curves;- it wrinkles
2-stray fibres, with pre-preg stray fibres can puncture the vac bag. The
wing
skins don't come out of the moulds until after the wings have been fully
glued
together. It's a bad day to discover a single stray fibre has killed the
vacuum
during the cure of a skin and you've just glued it to a good
spar/skin/installed
controls etc
3 - wet lay up wings post cure at 60C, normally out of mould. Pre-Preg
cures
at least 80C maybe hotter but this must be done in the mould. This means
the part and mould thermal expansion must be closely matched and the
longer the part , the more compound curves, the more difficult this
becomes.

Dry fibre resin infusion probably offers the best way forward as it can
provide
similar fibre fractions to pre preg but without the above and earlier
mention
drawbacks.

Fraser


I tend to disagree with most of that.
UD is difficult on complex shapes yes, but what is complex about a wing? It is basically straight. If you can laminate it with wet laminate, you can do it with prepreg.

You would cure the skins then glue the rest in. Well, this would be my approach. The spar can be co-cured in there if you like. Makes for easy small steps in manufacturing.
Similar way to the concept behind a F1 car. Outersking, honeycomb and inserts, innerskin.

Don't see the issue with postcure. No need for it to be done in the mold with Prepreg. We were postcuring suspension to 180-220 deg C out of the mold and had no issues. They were cured at 130 to start with.
As far as thermal expansion goes, why not make your molds out of tooling prepreg? Works like a charm, and if you have a decent glider you will make plenty of gliders out of the mold and you will always have the same shape. Beats having to rework your molds every couple of years

Aren't the light days the ones where you most need the batteries?

I was thinking of a comp. Motor only used to prevent land out and longer day. But I suppose on a rec flying day one could take out on a light day as well. I would think that flying a light day and booming day are no different other than more turns and less aggressive speed, but a lighter craft would benefit. I'm not even sure what the GP batteries weigh.

On 12/5/2016 7:59 PM, Casey wrote:
On Monday, December 5, 2016 at 4:58:14 PM UTC-5, Casey wrote:
On Monday, December 5, 2016 at 2:23:59 PM UTC-5, Jonathan St. Cloud wrote:
For the guys with an engine weight does make a difference. Imagine if the 100 pounds of engine and fuel were offset by construction methods that lowered the empty weight of the glider by even 50-70 pounds. YOu would functionally have the same wing loading range as a pure glider.

Just saying.
On Thursday, December 1, 2016 at 4:09:14 PM UTC-8, wrote:
4 Pretty much nobody cares much about weight, except the little gliders. For all the rest we just want to know how much water can we get in it.

Different building methods in same factory brings several issues I could think of.
Cost of buying and storing different materials, cost of process, possible mistakes in manufacturing, return on investment, different flying characteristics. Just throwing this out there.

Maybe this is why GP decided to put the batteries in the wings. Removal for light days without changing CG. All other FES gliders have batteries behind cockpit and have to fly with batteries.

Probably has more to do with allowable max weight of non-lifting parts...

Luke Szczepaniak

On Monday, December 5, 2016 at 7:59:28 PM UTC-5, Casey wrote:
On Monday, December 5, 2016 at 4:58:14 PM UTC-5, Casey wrote:
On Monday, December 5, 2016 at 2:23:59 PM UTC-5, Jonathan St. Cloud wrote:
For the guys with an engine weight does make a difference. Imagine if the 100 pounds of engine and fuel were offset by construction methods that lowered the empty weight of the glider by even 50-70 pounds. YOu would functionally have the same wing loading range as a pure glider.

Just saying.
On Thursday, December 1, 2016 at 4:09:14 PM UTC-8, wrote:
4 Pretty much nobody cares much about weight, except the little gliders. For all the rest we just want to know how much water can we get in it..

Different building methods in same factory brings several issues I could think of.
Cost of buying and storing different materials, cost of process, possible mistakes in manufacturing, return on investment, different flying characteristics. Just throwing this out there.

Maybe this is why GP decided to put the batteries in the wings. Removal for light days without changing CG. All other FES gliders have batteries behind cockpit and have to fly with batteries.

Putting the batteries in the wings reduces the weight of non lifting parts which means the wing spars and root area don't have to be made as heavy.
UH