Pre-Preg

On Thursday, December 1, 2016 at 4:03:22 PM UTC-5, Jonathan St. Cloud wrote:
Just wondering why glider are not made with pre-preg. Seems like it would save weight.

Some factors:
1 Molds have to be able to stay stable at curing temperatures and maintain their dimensions over a life of many cycles.
2 In the life of the glider, it will get broken. If the structure can't be repaired in a shop that does not have an autoclave(all the shops that I know of), it likely has to go to the factory for repair.
3 Most of the external structures in our gliders are over built to some degree in order to make them durable enough to live in the real world.
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.
5 Prepreg materials obviously have storage requirements that add cost
6 They are generally more expensive and limited in choice of material properties.
7 Hybrid structures commonly used in modern gliders may well be limited by the availability of suitable materials. If you want your tail to stay on in a midair, you'd like to have some Kevlar in your tail boom. Or maybe you'd like some aramid in your cockpit to control where the catastrophically failing carbon goes. Tailoring the progressive failure of a nose is most commonly done with a mix of materials as well as laminating schemes.

FWIW

In Europe there is probability that it has much do with the cost of
certification of a new manufacturing process. Here where the weather is
often cr** people do go for light weight empty.

On Friday, December 2, 2016 at 4:15:15 AM UTC-5, Jim White wrote:
In Europe there is probability that it has much do with the cost of
certification of a new manufacturing process. Here where the weather is
often cr** people do go for light weight empty.

If it's good enough to fly, it's good enough to fly at 7 lbs / sq ft. Otherwise it's a better day for a bicycle, or hiking boots or maybe sitting indoors in the rain annoying the folks on r.a.s.

From the XC performance standpoint, there's little advantage to empty weight very much below 500# in a 15m sailplane. For self launching, well, weight is really important...

-Evan Ludeman / T8

On Friday, 2 December 2016 14:33:01 UTC+2, Tango Eight wrote:

From the XC performance standpoint, there's little advantage to empty weight very much below 500# in a 15m sailplane. For self launching, well, weight is really important...

-Evan Ludeman / T8

With lighter structure and materials you can build smaller wing and still have acceptable min. wing loading. Smaller wing - higher aspect ratio - higher performance (Diana-2 for example)?

On Friday, December 2, 2016 at 3:33:01 PM UTC+3, Tango Eight wrote:
On Friday, December 2, 2016 at 4:15:15 AM UTC-5, Jim White wrote:
In Europe there is probability that it has much do with the cost of
certification of a new manufacturing process. Here where the weather is
often cr** people do go for light weight empty.

If it's good enough to fly, it's good enough to fly at 7 lbs / sq ft. Otherwise it's a better day for a bicycle, or hiking boots or maybe sitting indoors in the rain annoying the folks on r.a.s.

From the XC performance standpoint, there's little advantage to empty weight very much below 500# in a 15m sailplane. For self launching, well, weight is really important...

-Evan Ludeman / T8

Most gliders work out at about 6 (30 kg/m^2) dry with a 240 lb pilot, don't they?

Most gliders work out at about 6 (30 kg/m^2) dry with a 240 lb pilot, don't they?


An ASW27 would be about 40kg/m^2 with a 240lb pilot weight

L

On Friday, December 2, 2016 at 6:28:43 AM UTC-8, Luke Szczepaniak wrote:

Most gliders work out at about 6 (30 kg/m^2) dry with a 240 lb pilot, don't they?


An ASW27 would be about 40kg/m^2 with a 240lb pilot weight

L

Cost and repairability are factors with pre-preg although power aircraft like the Lancair use prepreg extensively. Newer spread-tow pre-pregs are amazingly light and stiff.

From a performance standpoint, span loading is a significant factor. For an equal wing loading and span, the lighter sailplane with the lower span load has lower induced drag. Reynolds numbers also play a factor when the chords get so small, but the aero community seems to be getting better at developing profiles that aren't hurt too much by this.

Cheers,
Craig

On Friday, December 2, 2016 at 1:25:16 PM UTC-5, Craig Funston wrote:
On Friday, December 2, 2016 at 6:28:43 AM UTC-8, Luke Szczepaniak wrote:

Most gliders work out at about 6 (30 kg/m^2) dry with a 240 lb pilot, don't they?


An ASW27 would be about 40kg/m^2 with a 240lb pilot weight

L

Cost and repairability are factors with pre-preg although power aircraft like the Lancair use prepreg extensively. Newer spread-tow pre-pregs are amazingly light and stiff.

From a performance standpoint, span loading is a significant factor. For an equal wing loading and span, the lighter sailplane with the lower span load has lower induced drag. Reynolds numbers also play a factor when the chords get so small, but the aero community seems to be getting better at developing profiles that aren't hurt too much by this.

Cheers,
Craig

I've heard conflicting sides about pre-preg repairability. Greg said its a misconception and can be repaired fairly easily and I have seen a Sparrowhawk that has been repaired by him.

https://www.youtube.com/watch?v=JYcHDPzx1ao

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.