Hi everybody
Having visited HomebuiltAirplanes for quite a long time and having learned a lot from all the contributors, here some insights in my own way of work. Eventually this give back can give some inputs in favor of your projects.
Having designed the foot-launchable xxtherm1 together with some friends, I started a project of some bigger scale eight years ago. The xxtherm2 was planned as a serial version of the former, but the project evolved on an other direction. Today I walk this road together with my son, he doing the hardware, and I myself crunching the numbers.
Having observed quite a lot of projects starting with a lot of good will, hard work and money, but mostly aborted due to different reasons, it become clear that it is not sufficient to design just an aircraft. You have to put as much effort in developing a way to build that thing. That's common-place in this forum. Even for a one off part.
To build an xxtherm2 in under 300 hours and with a reasonable amount of hardware costs, some processes had to be changed. We intended to avoid sanding and polishing surfaces, puting release agents on, laminating by hand in expensive cnc-cut solid molds and finally finishing the surface with more sanding and polishing and some glossy painting. Instead we learned resin infusion with aircraft-certified epoxy resins (it took my son 2 years to develop a fully reliable process even for sheets 0.1 mm thick. Imagine a recumbent beer and the difference in speed between the resin and the air bubbles reaching the vacuum front ;-). We developed a method to build accurate parts in so-called Wet-Hardshells layed on templates. We also developed a method to build seamless ing panels without glueing to half's together and a methode to build seamless fuselage tubes. The only mold we use is for the cockpit, because this can not be wraped with a flat sheet. But also here we dont use a polished pattern.
Here a short view of the processes, and they are really as easy as they seem. It is all in carbon for the xxtherm2, but works also in glass or kevlar.
We spray a gel-coat on a flat glass plate covered with a release film (FlexPlas from Infiana), infuse a first thin layer of carbon fibre (spread carbon 160 g/m2) with a Compoflex bleeder and let cure for 24 hours. This forms the hard part of the wet-hardshell. Then we infuse the further needed layers of carbon on this first sheet. This wet-hardsell is layed on cnc-cut rib templates or rolled to a round tube and cured. Due to the internal stiffness of the hard layer and an appropriate distance between the templates, the results are perfectly straight surfaces. And the ends of the parts are glued wet in wet at the closing seams and the whole comes out with a brillant white (or colored) finish.
Due to the immediate second infusion after curing of the first one, we have enpough bonding-energy between the layers. Some small details help holding the wet layers in place even when rolling a fuselage tube. More about this in future postings.
The really important point is: we only have two (2) simple infusions on a flat surface, nothing more. We are not doing any work in a mold. And we are not doing any work in preparing a pattern or a mold. Exept for the cockpit as mentioned.
After the second infusion the hardshell with the wet additional layers is layed on the templates for curing.
If this is of interest I will post more on this site.
Have a good time
Helmut
Here some impressions.
A seamless nose.
Templates and a glass-kevlar hardshell for a stab.
Different hardshell samples for wings, stabs, flaps and ailerons.
A flap hardshell with first layer in 105 g/m2 glass and two parts 160 g/m2 carbon.
The infusion run from trailing edge to trailing edge for a seamless construction.
The next step will be the addition of a corrugated core in the inside.
The only not wet but hard part. It's a massive cnc-milled mdf pattern.
Having visited HomebuiltAirplanes for quite a long time and having learned a lot from all the contributors, here some insights in my own way of work. Eventually this give back can give some inputs in favor of your projects.
Having designed the foot-launchable xxtherm1 together with some friends, I started a project of some bigger scale eight years ago. The xxtherm2 was planned as a serial version of the former, but the project evolved on an other direction. Today I walk this road together with my son, he doing the hardware, and I myself crunching the numbers.
Having observed quite a lot of projects starting with a lot of good will, hard work and money, but mostly aborted due to different reasons, it become clear that it is not sufficient to design just an aircraft. You have to put as much effort in developing a way to build that thing. That's common-place in this forum. Even for a one off part.
To build an xxtherm2 in under 300 hours and with a reasonable amount of hardware costs, some processes had to be changed. We intended to avoid sanding and polishing surfaces, puting release agents on, laminating by hand in expensive cnc-cut solid molds and finally finishing the surface with more sanding and polishing and some glossy painting. Instead we learned resin infusion with aircraft-certified epoxy resins (it took my son 2 years to develop a fully reliable process even for sheets 0.1 mm thick. Imagine a recumbent beer and the difference in speed between the resin and the air bubbles reaching the vacuum front ;-). We developed a method to build accurate parts in so-called Wet-Hardshells layed on templates. We also developed a method to build seamless ing panels without glueing to half's together and a methode to build seamless fuselage tubes. The only mold we use is for the cockpit, because this can not be wraped with a flat sheet. But also here we dont use a polished pattern.
Here a short view of the processes, and they are really as easy as they seem. It is all in carbon for the xxtherm2, but works also in glass or kevlar.
We spray a gel-coat on a flat glass plate covered with a release film (FlexPlas from Infiana), infuse a first thin layer of carbon fibre (spread carbon 160 g/m2) with a Compoflex bleeder and let cure for 24 hours. This forms the hard part of the wet-hardshell. Then we infuse the further needed layers of carbon on this first sheet. This wet-hardsell is layed on cnc-cut rib templates or rolled to a round tube and cured. Due to the internal stiffness of the hard layer and an appropriate distance between the templates, the results are perfectly straight surfaces. And the ends of the parts are glued wet in wet at the closing seams and the whole comes out with a brillant white (or colored) finish.
Due to the immediate second infusion after curing of the first one, we have enpough bonding-energy between the layers. Some small details help holding the wet layers in place even when rolling a fuselage tube. More about this in future postings.
The really important point is: we only have two (2) simple infusions on a flat surface, nothing more. We are not doing any work in a mold. And we are not doing any work in preparing a pattern or a mold. Exept for the cockpit as mentioned.
After the second infusion the hardshell with the wet additional layers is layed on the templates for curing.
If this is of interest I will post more on this site.
Have a good time
Helmut
Here some impressions.
A seamless nose.
Templates and a glass-kevlar hardshell for a stab.
Different hardshell samples for wings, stabs, flaps and ailerons.
A flap hardshell with first layer in 105 g/m2 glass and two parts 160 g/m2 carbon.
The infusion run from trailing edge to trailing edge for a seamless construction.
The next step will be the addition of a corrugated core in the inside.
The only not wet but hard part. It's a massive cnc-milled mdf pattern.
