No, it's not done to speed up the curing. However, most resin employed
nowadays - especially for carbon fiber lay-up - do need a (post-) curing
treatment. The exact temperature is given by the resin manufacturer.

--
Bert Willing

ASW20 "TW"


"smjmitchell" a écrit dans le message de
news: ...
Yes a post cure is normal for any composite structure. A glider or any
composite aircraft should be aiming for a Tg of at least 54 + 27 = 81 deg
C.

54 deg C comes from NASA CP 2036 / CR 3290 per the JAR VLA ACJ's (white
surface on a hot day).

27 deg C (50 deg F) is the standard margin between Tg and the service
temperature that is recommended in MIL-HDBK-17 and accepted by
certificatioon authorities around the world.

Generally I would post cure at a higher temperature than 55-60 deg C but
one
needs to be careful of the core material and this varies depending on the
resin. Often you can get the resin manufacturers to run Tg tests for you
to
provide advice on the exact temperature and cycle to use for a particular
application.


I guess what I was really getting at though was whether manufacturers are
using heat to speed up the initial cure so they don't have to stand around
waiting for the room temperature cure. I wasn't really refering to post
cure.







"Bert Willing" wrote in
message ...
Depends on the resin which is used - the L20 resin for example must be
cured
at high temperature (around 55-60 deg C) for some hours (typically
overnight) in order to obtain the final strength of the resin and to push
the glass transition temperature to above 54 deg C.
Easy to do, though: Make a shelter of thick foam plates where the mould
just
fits in, put a temperature-controlled hot air fan in it and switch it on.

--
Bert Willing

ASW20 "TW"


"smjmitchell" a écrit dans le message de
news: ...
Is hot curing common in glider factories ? Are these using ovens,
heater
blankets or perhaps heated moulds ?



"Bert Willing" wrote in
message ...
You have two moulds for each wing, and two moulds for the fuselage
(plus
two
for the stabilizers). All can be layed up in parallel (you need three
men
less than 8 hours on one mould), that takes one day. Spraying of the
gel
coat is done the night before. Glueing them together and hot-curing
them
takes another day.

However, cost is counted in manhours, not in days. The time needed for
layup
is about the same for carbon and for glass (some experience needed,
though)
and the planiform of the wing has no influence whatsoever.

Improvements for this? The capital expenditure for any of it never
pays
off,
so just forget about it.

The main amount of manpower is needed AFTER the thing is demoulded -
finishing is quite a job, even for professionals. And that has been
the
reason why Grob gliders were very reasonably priced at their time -
they
just had less finish.

--
Bert Willing

ASW20 "TW"


"smjmitchell" a écrit dans le message
de
news: ...
As far as building a Junior in two days, maybe, but I'd still think
in
terms of 680 man hours as the substantial difference is fixed gear
vs
retract. Two days is a meaningless concept without knowing whether
30-40
people were involved for 8 or 12 hour shifts.


I suspect that one Junior emerged from the factory every 2 days but
surely
they must have spent longer on the line than 2 days. If for instance
you
have 5 stations on the line and each airframe spent 2 days at each
station
that is a total of 10 days on the line. Now if 3 guys worked in each
station
with two shifts that is a total of 5 (stations) x 2 (days) x 3 (#
guys)
x
8
(shift hours) x 2 (# shifts) = 480 hours. This seems achievable for
a
simple
glider. I just cannot see how a sailplane of conventional
construction
could
be made in an elapsed time of only 2 days when cure time etc is
allowed
for.

If indead it is true that the Junior was made in 2 days with two
shifts
then
this deserves careful study. Does anyone have a PDF copy of the
Junior
maintenance manual ????

Janusz ... do you have any more info on this ????


Frank,

Filament winding is one method that's been shown to work, at least
by
Rutan.

There is a lot of conflicting information around on exactly how
Rutan
builds
his airframes. Some people say thay he uses a tape layer and others
filament
winding. How confident are you in your information that he filament
winds
?
If filament winding is used (and I believe this is probably the
case)
then
I
am assuming he uses prepreg tow ???? Or is he using a wet layup
with
one
of
the resins that has an extraordinarly long pot life (1-2 days)
(there
are
some excellent wet layup resins available now that are meant for
this
sort
of application).


However, there are limitations to the process that might make it
impractical
for most glider production.

Such as ????


Even then, the pod took something like 7 hours
to wind and the fuselage was 24 hours of continuous processing.

Are you refering to the Boomerang ????

It sounds like you have some knowledge of the Rutan processes ...
can
you
outline the process. What does he use for the plug to wind around
???
What
sort of winding machine - a simple two axis thing or something more
complex
?? What sort of tow (12k ... 24k etc) ??? Does he wind a grid
arrangement
of stiffeners on the inside of the fuselage ??? (it appears so from
some
photo's you see) And the really big question .... how does he get
the
outside smooth (perhaps this is one of the limitations you mention
??? -
perhaps this involved a lot of hand filling and sanding ?). What is
the
cure
... oven ??? room temperature ??? What are the thickesses of the
skins
?
What is the typical winding angle ?