Re: Resin volume placed on foam
To give Rutan much credit..he erred by being a bit too heavy in resin but the result is safe homebuilt structures. Keep in mind, he had full access to all that Raytheon Beechcraft R&D had available, therefore he knew all the latest techniques and materials we had, and still his method at RAF was what is taught in our Q2 and other tool-less composite aircraft plans sets. I chatted many times with the folks at Scaled Composits and they never used any other method on any of the concept aircraft at the time.
In Production this porosity condition is why now the pressure and temps are "ramped" both up and down. Porosity in the finished product is caused by error in regulation. Over decades and with much R&D at Beech and Boeing, later Airbus; the correct programs were discovered. Mostly the early issues were with too high pressure and simply throwing the coals to the fire so to speak. Todays methods with honeycomb core the situation of improving bond to the curing pre-preg at lower peak pressures is addressed using adhesive film.
Rob has a valid point that too much vacuum can and will dry the wetout. Insufficient resin. The bleeder wicks the uncured resin by design. What thickness were you using Rob?
Using Infusion the resin is drawn through the dry layup at a rate that is timed..so the over vacuum condition is controlled. At the size of this airframe I have doubts that a great deal of weight is built in by using the plans methods. Non structural parts, for myself, I have no qualms about using the vacuum process and tooling (caul and contoured).
I accept the Frankenbird is a bit heavy but I'm not concerned about a compressive failure in heavy chop either. I could stand to loose a few pounds off my 64 year old tired ass to make up the difference. That is why the Canard and Wing are per plans Dragonfly.. wet out..stipple..squeegee....dry micro..sand sand sand...primer..more sanding..primer again..more sanding. Not much fun but part of the process.
From: main@Q-List.groups.io <main@Q-List.groups.io> on behalf of Rob de Bie <robdebie@...>
Sent: Wednesday, March 24, 2021 8:26 AM
To: main@Q-List.groups.io <main@Q-List.groups.io>
Subject: Re: [Q-List] Resin volume placed on foam
Eugen, that looks like an excellent setup, especially with the vacuum (buffer) tanks. That saves a
lot of running hours on your pump.
One additional comment, triggered by your photo: I experienced that vacuum bagging resulted in a
very dry layup, too dry actually. Maybe the bleeder layer was too thick? I never completely
understood what happened there. Thinking about it now, just maybe the vacuum was too deep, and the
resin started foaming, and ended up in the bleeder? I don't know, but it shows again that vacuum
bagging can have unwanted effects, and vacuum level control is important. Watch out for this effect.
On 24 Mar 2021 14:02, Eugen Pilarski wrote:
> For the vacuum bagging I build up a pump station with a digital pressure switch (SMV ZSE30A), so
> I’m able to set up any pressure level which the process requested. Please find below the link with
> some drawings and pictures. https://aerobase.weebly.com/vaccum-pump-station.html
> For the vacuum pump unit I use Brand Thomas , please find below a link from eBay to show a example,
> In my last vacuum bag projects there was not any issue about temperature but to find leaks in my bag
> was the biggest challenge at all :-)
> Please find below a picture from bulkhead FS83 after 16h fixed in vaccum bag.
> Best regards
>> Am 24.03.2021 um 13:35 schrieb Rob de Bie <robdebie@... <mailto:robdebie@...>>:
>> From memory, the Cri-Cri build manual suggest the use of a regular household vacuum cleaner, for
>> the build step where you glue the aluminum skin on the Klegecell ribs.
>> I would guess you can pull just a light vacuum with a vacuum cleaner, maybe 0.2 or 0.3 bar, which
>> would be perfect. But I would take a look at the cooling of the motor - if there is no air flow,
>> there is no cooling I guess.
>> On 24 Mar 2021 08:22, Christoph Steiner via groups.io <http://groups.io> wrote:
>>> Here is the description of the Cozygirrls LoVac method:
>>> Christoph Steiner
>>>> Am 23.03.2021 um 21:21 schrieb Jay Scheevel <jay@...>:
>>>> I looked there too, Bruce, but I could not find their videos on vacuum bagging. Maybe they took
>>>> them down. I remember them using a fish tank pump for vacuum.
>>>> Hey Sammy Hoskins had the Cozy Girls show us some light vacuum bagging at one of our Field Of
>>>> Dreams events in Illinois. It was very interesting and may be what you’re looking for.
>>>> Bruce Crain