Grob II/Acro

[Kenneth Kilbourne]

What causes the buckling/oil canning on the bottom of the ailerons and the
elevator on Grobs? I have looked at 6 ships and they all have the same
problem.
What's the fix?
KK

[Bob Kuykendall]

On Sep 15, 8:09*am, Kenneth Kilbourne >
wrote:
> What causes the buckling/oil canning on the bottom of the ailerons and the
> elevator on Grobs? I have looked at 6 ships and they all have the same
> problem.

That's just the way lightly-built non-sandwich composite skins age.

> What's the fix?

I don't think it has shown itself to be a real problem in most cases.
JJ will probably correct me if I'm wrong, but in the absence of other
damage, they are probably structurally sound. And on these two-
seaters, the performance hit is negligible. So the best fix is
probably just to not look at them.

Thanks, Bob K.

[Brad[_2_]]

On Sep 15, 8:09*am, Kenneth Kilbourne >
wrote:
> What causes the buckling/oil canning on the bottom of the ailerons and the
> elevator on Grobs? I have looked at 6 ships and they all have the same
> problem.
> What's the fix?
> KK

not sure about the fix, but am guessing the cause is no foam core on
the lower skin, and several ribs that are now giving the "starved
horse" look.

I've seen the same thing on the Grob Astir's on our field.

Brad

[Grider Pirate]

On Sep 15, 8:50*am, Brad > wrote:
> On Sep 15, 8:09*am, Kenneth Kilbourne >
> wrote:
>
> > What causes the buckling/oil canning on the bottom of the ailerons and the
> > elevator on Grobs? I have looked at 6 ships and they all have the same
> > problem.
> > What's the fix?
> > KK
>
> not sure about the fix, but am guessing the cause is no foam core on
> the lower skin, and several ribs that are now giving the "starved
> horse" look.
>
> I've seen the same thing on the Grob Astir's on our field.
>
> Brad

"They all do that" is the common refrain. I'm pretty sure it's caused
by the shrinkage of the fiberglass/resin matrix over the decades. Back
in the days when I built 'Old Time' free flight planes with very
pronounced undercamber, the same thing would happen to the silk
covering between the ribs.
I don't think there is a fix worth doing.

[jb92563]

On Sep 15, 8:09*am, Kenneth Kilbourne >
wrote:
> What causes the buckling/oil canning on the bottom of the ailerons and the
> elevator on Grobs? I have looked at 6 ships and they all have the same
> problem.
> What's the fix?
> KK

Grob 109 Motorgliders have that on the undercambered ailerons as well.
Not on the elevator though.

Poor design caused it.

The solution is to redesign it yourself since Grob will not do it.

It would be quite a process to build, test and get approval for a
change to the certified aircraft.

Bottom line, it is not worth the trouble to change so you just
tolerate the flaw.

Ray

[[email protected]]

Just got an email from the Mfg. It confirms the lower skins of the
ailerons and portions of the elevator of the G-103 Twin II are two
plys of solid laminate, as the repair manual says. The lower skins
are not sandwich construction, therefore, what you are seeing is not
delamination.

"The waves are normal and no Problem, it look not nice. You can not
repair this"

aerodyne...