Grob Twin Astir

Group,
My club is looking to convert a Twin Astir brake system to a Hydraulic Disk from a Mechanical Drum. Our serial number does not fall within the serial number range of the Kit that is offered by Lindner. We have the Lindner kit and will be going with a 337. My question is does anyone know of a 337 on an Astir brake mod? Also, I have been trying to find info on any different versions of the Astir and can't find much. Is there any reference online that points to different models or versions? Ive read that water ballast was an option and some models came with a disk brake from the factory (These have a different wheel carrier structure). Does anyone know if gross weights remained the same on the Astir through the production run? This info may hel when submitting paperwork to the FAA.
Thanks!

On Thursday, January 28, 2016 at 8:56:01 PM UTC-7, K m wrote:
Group,
My club is looking to convert a Twin Astir brake system to a Hydraulic Disk from a Mechanical Drum. Our serial number does not fall within the serial number range of the Kit that is offered by Lindner. We have the Lindner kit and will be going with a 337. My question is does anyone know of a 337 on an Astir brake mod? Also, I have been trying to find info on any different versions of the Astir and can't find much. Is there any reference online that points to different models or versions? Ive read that water ballast was an option and some models came with a disk brake from the factory (These have a different wheel carrier structure). Does anyone know if gross weights remained the same on the Astir through the production run? This info may hel when submitting paperwork to the FAA.
Thanks!

It was brought to my attention in a PM that my first post may have been too vague for a legitimate answer. Utah Soaring Association (USA)is retrofitting a disk brake onto a G103 Twin Astir. It was also pointed out to me that there were 7 different variants of the Astir (?!). The USA club owns two Twin II's (One an Acro) and two Astir's. I know of some factory options for the Astir (Including a trainer version) but never anything close to 7 variants. Is there reference for this somewhere?
Our Astirs have the welded steel tube wheel carriers which rotate sideways under the rear seat when they retract.
Thanks for any info.

Originally Posted by K m

On Thursday, January 28, 2016 at 8:56:01 PM UTC-7, K m wrote:
Group,
My club is looking to convert a Twin Astir brake system to a Hydraulic Disk from a Mechanical Drum. Our serial number does not fall within the serial number range of the Kit that is offered by Lindner. We have the Lindner kit and will be going with a 337. My question is does anyone know of a 337 on an Astir brake mod? Also, I have been trying to find info on any different versions of the Astir and can't find much. Is there any reference online that points to different models or versions? Ive read that water ballast was an option and some models came with a disk brake from the factory (These have a different wheel carrier structure). Does anyone know if gross weights remained the same on the Astir through the production run? This info may hel when submitting paperwork to the FAA.
Thanks!

It was brought to my attention in a PM that my first post may have been too vague for a legitimate answer. Utah Soaring Association (USA)is retrofitting a disk brake onto a G103 Twin Astir. It was also pointed out to me that there were 7 different variants of the Astir (?!). The USA club owns two Twin II's (One an Acro) and two Astir's. I know of some factory options for the Astir (Including a trainer version) but never anything close to 7 variants. Is there reference for this somewhere?
Our Astirs have the welded steel tube wheel carriers which rotate sideways under the rear seat when they retract.
Thanks for any info.

Try this link to EASA TCDS for Grob sailplanes

https://easa.europa.eu/documents/typ...s-lsa/easaa250

:-) Colin

On Saturday, January 30, 2016 at 2:49:27 PM UTC-7, K m wrote:
On Thursday, January 28, 2016 at 8:56:01 PM UTC-7, K m wrote:
Group,
My club is looking to convert a Twin Astir brake system to a Hydraulic Disk from a Mechanical Drum. Our serial number does not fall within the serial number range of the Kit that is offered by Lindner. We have the Lindner kit and will be going with a 337. My question is does anyone know of a 337 on an Astir brake mod? Also, I have been trying to find info on any different versions of the Astir and can't find much. Is there any reference online that points to different models or versions? Ive read that water ballast was an option and some models came with a disk brake from the factory (These have a different wheel carrier structure). Does anyone know if gross weights remained the same on the Astir through the production run? This info may hel when submitting paperwork to the FAA.
Thanks!

It was brought to my attention in a PM that my first post may have been too vague for a legitimate answer. Utah Soaring Association (USA)is retrofitting a disk brake onto a G103 Twin Astir. It was also pointed out to me that there were 7 different variants of the Astir (?!). The USA club owns two Twin II's (One an Acro) and two Astir's. I know of some factory options for the Astir (Including a trainer version) but never anything close to 7 variants. Is there reference for this somewhere?
Our Astirs have the welded steel tube wheel carriers which rotate sideways under the rear seat when they retract.
Thanks for any info.

Had a phone chat with the original poster this morning. USA owns two Twin Astir 1's with the retract. The serial numbers are 5 apart, 3285 and 3290. The G-103 production underwent some serial production changes. For example, some have a single retract handle in the front seat, others in both seats. It's not clear what changes may have been options or serial production changes. ltb-Lindner.com hopefully has serial production data and would know whether the G-103 in question was produced with a drum or disc brake. The service bulletin allows retro-fitting of a disc brake on serial numbers 3000-3139, except for the T models (fixed gear). Presumably, higher serial numbers weren't included because they were built with disc brakes installed. At least one of the above has a disc brake. If that's the case, then it would seem the disc brake installation could be made as restorative without a 337. Maybe someone qualified could chime in about that. There were some further improvements made to the original disc brake system, which would be an approved installation.

Frank Whiteley-

At 18:24 31 January 2016, Frank Whiteley wrote:
On Saturday, January 30, 2016 at 2:49:27 PM UTC-7, K m wrote:
On Thursday, January 28, 2016 at 8:56:01 PM UTC-7, K m
wrote:
Group,
My club is looking to convert a Twin Astir brake system to a
Hydraulic
=
Disk from a Mechanical Drum. Our serial number does not fall
within the
ser=
ial number range of the Kit that is offered by Lindner. We have the
Lindner=
kit and will be going with a 337. My question is does anyone
know of a
337=
on an Astir brake mod? Also, I have been trying to find info on
any
differ=
ent versions of the Astir and can't find much. Is there any
reference
onlin=
e that points to different models or versions? Ive read that water
ballast
=
was an option and some models came with a disk brake from the
factory
(Thes=
e have a different wheel carrier structure). Does anyone know if
gross
weig=
hts remained the same on the Astir through the production run?
This info
ma=
y hel when submitting paperwork to the FAA.
Thanks!
=20
It was brought to my attention in a PM that my first post may
have been
t=
oo vague for a legitimate answer. Utah Soaring Association (USA)is
retrofit=
ting a disk brake onto a G103 Twin Astir. It was also pointed out
to me
tha=
t there were 7 different variants of the Astir (?!). The USA club
owns two
=
Twin II's (One an Acro) and two Astir's. I know of some factory
options
for=
the Astir (Including a trainer version) but never anything close to
7
vari=
ants. Is there reference for this somewhere?
Our Astirs have the welded steel tube wheel carriers which
rotate
sideway=
s under the rear seat when they retract.=20
Thanks for any info.

Had a phone chat with the original poster this morning. USA owns
two Twin
A=
stir 1's with the retract. The serial numbers are 5 apart, 3285
and 3290.
=
The G-103 production underwent some serial production
changes. For
exampl=
e, some have a single retract handle in the front seat, others in
both
seat=
s. It's not clear what changes may have been options or serial
production
=
changes. ltb-Lindner.com hopefully has serial production data
and would
kn=
ow whether the G-103 in question was produced with a drum or
disc brake.
T=
he service bulletin allows retro-fitting of a disc brake on serial
numbers
=
3000-3139, except for the T models (fixed gear). Presumably,
higher
serial=
numbers weren't included because they were built with disc
brakes
installe=
d. At least one of the above has a disc brake. If that's the case,
then it
=
would seem the disc brake installation could be made as
restorative
without=
a 337. Maybe someone qualified could chime in about that. There
were
some=
further improvements made to the original disc brake system,
which would
b=
e an approved installation.

Frank Whiteley-

The Nutmeg Soaring Association of Freehold, NY has 3 Twin 1's,
and has sold another one, for a total of 4 which we have owned.
We retrofitted one with a disc brake IAW TM 315-50 last spring.
That one still has the old cast aluminum parts in the gear cage.
After a few months of operation with the new disc brake, a side load
managed to bend the disc plate, and render it inoperable. Our
mechanics deemed the part to be either substandard or under-
designed and filed a complaint with TOST through Wings and
Wheels. It took a few months, but TOST responded by replacing
the bent disc with a new stronger one, and also said they would
replace other older defective discs in the field. We have
corresponded with at least one other Twin 1 club operator in
Germany who told us that they previously had a disc brake, had
problems with it, and went back to the drum brake to avoid the
previously noted problems. So, it seems entirely possible that the
Utah late serial number Twin 1 was originally produced with a disc
brake, but later changed to the drum brake configuration due to an
under-designed disc brake plate. If you get a new disc brake from
TOST, it should now come standard with the thicker reinforced
plate. Ours has been fine since we installed the beefed up plate.

Mike Opitz

The Nutmeg Soaring Association of Freehold, NY has 3 Twin 1's,
and has sold another one, for a total of 4 which we have owned.
We retrofitted one with a disc brake IAW TM 315-50 last spring.
That one still has the old cast aluminum parts in the gear cage.
After a few months of operation with the new disc brake, a side
load
managed to bend the disc plate, and render it inoperable. Our
mechanics deemed the part to be either substandard or under-
designed and filed a complaint with TOST through Wings and
Wheels. It took a few months, but TOST responded by replacing
the bent disc with a new stronger one, and also said they would
replace other older defective discs in the field. We have
corresponded with at least one other Twin 1 club operator in
Germany who told us that they previously had a disc brake, had
problems with it, and went back to the drum brake to avoid the
previously noted problems. So, it seems entirely possible that the
Utah late serial number Twin 1 was originally produced with a
disc
brake, but later changed to the drum brake configuration due to
an
under-designed disc brake plate. If you get a new disc brake
from
TOST, it should now come standard with the thicker reinforced
plate. Ours has been fine since we installed the beefed up plate.

Mike Opitz

On thinking this issue through a little further, we have come to the
conclusion that it would be pretty easy to tell if the Twin had a
previous disc brake installation. The disc brake uses a hydraulic
reservoir located underneath the rear seat pan. If there was a
previous disc brake in the glider, the reservoir, or at least evidence
of the FRP mounts will be there to see. If one finds this evidence,
then a disc brake installation would be a restoration to the OEM
condition, and not need a 337 form. Also, if the logbook history is
complete, there would be an annotation of a change from the
original disc to a drum brake configuration. Hope this helps..

Mike Opitz

The Nutmeg Soaring Association of Freehold, NY has 3 Twin 1's,
and has sold another one, for a total of 4 which we have owned.
We retrofitted one with a disc brake IAW TM 315-50 last spring.
That one still has the old cast aluminum parts in the gear cage.
After a few months of operation with the new disc brake, a side
load
managed to bend the disc plate, and render it inoperable. Our
mechanics deemed the part to be either substandard or under-
designed and filed a complaint with TOST through Wings and
Wheels. It took a few months, but TOST responded by replacing
the bent disc with a new stronger one, and also said they would
replace other older defective discs in the field. We have
corresponded with at least one other Twin 1 club operator in
Germany who told us that they previously had a disc brake, had
problems with it, and went back to the drum brake to avoid the
previously noted problems. So, it seems entirely possible that the
Utah late serial number Twin 1 was originally produced with a
disc
brake, but later changed to the drum brake configuration due to
an
under-designed disc brake plate. If you get a new disc brake
from
TOST, it should now come standard with the thicker reinforced
plate. Ours has been fine since we installed the beefed up plate.

Mike Opitz

On thinking this issue through a little further, we have come to the
conclusion that it would be pretty easy to tell if the Twin had a
previous disc brake installation. The disc brake uses a hydraulic
reservoir located underneath the rear seat pan. If there was a
previous disc brake in the glider, the reservoir, or at least evidence
of the FRP mounts will be there to see. If one finds this evidence,
then a disc brake installation would be a restoration to the OEM
condition, and not need a 337 form. Also, if the logbook history is
complete, there would be an annotation of a change from the
original disc to a drum brake configuration. Hope this helps..

Mike Opitz

On Thursday, January 28, 2016 at 7:56:01 PM UTC-8, K m wrote:
Group,
My club is looking to convert a Twin Astir brake system to a Hydraulic Disk from a Mechanical Drum. Our serial number does not fall within the serial number range of the Kit that is offered by Lindner. We have the Lindner kit and will be going with a 337. My question is does anyone know of a 337 on an Astir brake mod?


We did a conversion on a Twin Astir at Cal City, ~1996. It was a side folding gear.... I think. The glider had earlier been owned by Bob Harris, and he used it for wave learning before taking the single Grob to the record climb. The Astir was operated by Douglas Soaring Club, when it had the conversion. We used a Cleveland wheel and disc. With a standard (4 or 6-ply) main wheel and heavy payload, anything other than a greaser landing resulted in too much sidewall flexion, which broke out the disc, and amazingly didn't grab on the calipers and create havoc.
The solution was to use a ten-ply sidewall tire, for very little flexion and higher psi in the tire. This then made for kangaroo results, if you plopped on with any vertical energy. The glider was sold to an operator in SE Colorado, and he was warned very directly about it's landing handling.

N173SS was then totalled within about six months time, by a commercial pilot who failed to latch the canopy, ballooned, released and crashed adjacent to the runway, NTSB Identification: DEN99LA028.

I don't know if you can get the FAA file on N173SS for a glider that is deregistered. We had a local DAR create the data for the 337 that was issued. I just thought you should know some of the drawbacks we experienced in the process. The drum brake was always a poor decelerator, but the disc offered a whole different potential for problems (nose overs and belly rubs, PIOs, wrong fluid installation, etc.).
No difference in payload other than the reduction by the added gear weight. Every pound counts in the older multi-repaired airframes. Good luck with yours and hope this info helps.

Cindy B

On Friday, February 12, 2016 at 12:06:32 PM UTC-7, CindyB wrote:
On Thursday, January 28, 2016 at 7:56:01 PM UTC-8, K m wrote:
Group,
My club is looking to convert a Twin Astir brake system to a Hydraulic Disk from a Mechanical Drum. Our serial number does not fall within the serial number range of the Kit that is offered by Lindner. We have the Lindner kit and will be going with a 337. My question is does anyone know of a 337 on an Astir brake mod?


We did a conversion on a Twin Astir at Cal City, ~1996. It was a side folding gear.... I think. The glider had earlier been owned by Bob Harris, and he used it for wave learning before taking the single Grob to the record climb. The Astir was operated by Douglas Soaring Club, when it had the conversion. We used a Cleveland wheel and disc. With a standard (4 or 6-ply) main wheel and heavy payload, anything other than a greaser landing resulted in too much sidewall flexion, which broke out the disc, and amazingly didn't grab on the calipers and create havoc.
The solution was to use a ten-ply sidewall tire, for very little flexion and higher psi in the tire. This then made for kangaroo results, if you plopped on with any vertical energy. The glider was sold to an operator in SE Colorado, and he was warned very directly about it's landing handling.

N173SS was then totalled within about six months time, by a commercial pilot who failed to latch the canopy, ballooned, released and crashed adjacent to the runway, NTSB Identification: DEN99LA028.

I don't know if you can get the FAA file on N173SS for a glider that is deregistered. We had a local DAR create the data for the 337 that was issued. I just thought you should know some of the drawbacks we experienced in the process. The drum brake was always a poor decelerator, but the disc offered a whole different potential for problems (nose overs and belly rubs, PIOs, wrong fluid installation, etc.).
No difference in payload other than the reduction by the added gear weight. Every pound counts in the older multi-repaired airframes. Good luck with yours and hope this info helps.

Cindy B

Thanks! Working through the 337 process as we speak. We have a Tost brake assembly and we have strengthened the gear structure at the attach point.

Have you tried rebuilding the drum brake? My club used to have a Twin Astir retractable and the drum - tiny though it looked - always did a fair job of stopping the ship. It was strong enough to make rubbing the underside of the nose on the runway a concern.