Blanik L23 repair

Recently, our club's Blanik L23 was damaged during a take off incident
in which a wing struck the ground with sufficient force to crease the
wing slightly at the aileron juncture. I understand that the wing is
designed to fail at this point so that the major portion of the
structure will survive such an incident.

I have been tasked with finding someone who can engineer and execute a
repair on this otherwise solid ship.

Any suggestions appreciated.

We are in Colorado, USA.

--- Jens Peter Aarnaes

Earlier, aarnaes wrote:

...I understand that the wing is
designed to fail at this point so that the major portion of the
structure will survive such an incident.

**** Disclaimer: I am not an A&P nor an aeronautical engineer. I'm just
a guy who's been around a lot of broken gliders, and who develops
gliders in his spare time for fun and, well... fun. *****

**** Warning: Long reply: This spun out much farther than I intended
when I started. ****

I've seen many, many L13 and L23 wings with that damage pattern,
However, I personally believe that the story that this damage is the
result of an engineered weakness to be one of soaring's urban legends.
I think that if that were true, there'd be a commonly-available kit of
repair parts that addresses it. And yet, it seems that every gliderport
I visit has at least one Blanik wing on a trailer, creased at the
flap/aileron junction, no repair kit in sight.

I have been tasked with finding someone who can engineer and execute a
repair on this otherwise solid ship.

First off, situations like this are why you often see "Left wing
wanted" ads at r.a.s and w&w. It's almost always least expensive and
most effective to replace rather than to repair. But let's take it as
read that there are currently no L23 wings available.

My bet is that it will not be possible to engineer a repair until the
exact extent of the damage can be ascertained. And that can't really
happen until the wing is opened up at the damage site.

So I think the first step is to find a competent party to unrivet and
remove the obviously creased external skins while observing the medical
rule of doing no harm. That means someone who can really and truly
drill and snap the head off of a countersunk rivet, as per AC43.13,
without the drill touching anything but the rivet, and do it right 95
times out of 100.

I think that the chances are good that, once you get the crinkled skins
off, the wing spar springs back to its original position, and all
you'll need to do is straighten and reinforce a few ribs and
stiffeners, match-drill new skins from the old ones, replace the skins,
and you're done. If the repair can be done with straight replacement of
skins and AC43.13 type repairs on the internals, no engineering is
really required. But you can probably shortcut the repair a bit by only
replacing portions of the damaged skins, and splicing them in using
repair strips and rivet patterns calibrated to restore the original
strength - that's where your engineering comes in.

If the wing spar doesn't spring back, or if it is cracked or badly
kinked or it cracks or kinks as you force it back into line, your wing
is probably screwed. Inboard of about .7 of the semispan, you probably
cannot economically splice the main spar.

BTW, you can get copies of AC43.13 off of the Web; search for it with
Google or (my personal favorite) Dogpile. Download and study Chapter 4
(especially 4-58e) so you know what you're getting into.

I'd caution you to take care about the wing twist as the repair is
performed. With the skins removed, or even substantially unriveted, the
remaining structure is extremely limber in torsion, and even a few
thousandths of an inch displacement per hole in a line of rivets can
stack up into a substantial unintended washout or washin. BT and DT,
got the T-shirt and the sunburn. My advice: make twist templates on the
opposite wing before starting the repair.

Here's the key thing: What I've described is a lot of slow, careful,
and fiddly work. It can be done with basic handheld power tools (though
I wouldn't start it without a compressor and high-speed airdrill), but
it still requires a skilled and dedicated repairperson. And when that
repairperson works at an established shop, they're getting paid and the
shop is getting paid and the rent is getting paid, and before you know
it it's costing $75/hr for 200 hours of work. That's $15000, never mind
the parts, for a glider that might not bring much more on the used
market.

But that's not to say that your repair won't happen; just that it
probably won't happen economically at an established shop.

I recommend that you resist the temptation to turn to a local community
college or Industrial Arts program and have them make a project of the
repair. I've never seen that work right. An instructor with the best of
intentions making promises that their inexperienced or unmotivated
students can't keep can cause things to go to worms in a hurry. The
best I've seen such an arrangement work out is that nothing bad (in
fact, nothing at all) happened for two semesters.

Here's your dream scenario: Somewhere in your area is someone who has a
tiny lathe and a tiny drill press in a tiny basement workshop. This
person makes things just for the fun of making them. They worked in
Sunnyvale or Burbank before retiring, or somewhere in San Diego or
Renton. They know somebody who still holds AI. They do everything with
a deliberate care and slowness that drives onlookers mad with the
desire to just pick up a power tool and say "Here, lemme do that for
you." But they do things as right as they can be done, and certainly
right enough. They do not have a drill bit with a bunch of rivet heads
stacked up on it like tiny shrunken heads anywhere in the shop; they
snap the heads off one by one with a pin punch like it shows in the
book, like they were shown by the foreman who rescued them from the
production line and put them on the Specials that the other production
line guys had messed up.

All you have to do is find that person and turn them into a glider
pilot, or at least a glider enthusiast...

Or maybe I'm just telling another fairy tale...

Good luck, and best regards

Bob K.
http://www.hpaircraft.com/hp-24
http://www.hpaircraft.com/glidair

aarnaes wrote:
Recently, our club's Blanik L23 was damaged during a take off incident
in which a wing struck the ground with sufficient force to crease the
wing slightly at the aileron juncture. I understand that the wing is
designed to fail at this point so that the major portion of the
structure will survive such an incident.

I have been tasked with finding someone who can engineer and execute a
repair on this otherwise solid ship.

Any suggestions appreciated.

I'd start with a call to the USA dealer.

--
Change "netto" to "net" to email me directly

Eric Greenwell - Washington State, USA

www.motorglider.org - Download "A Guide to Self-launching Sailplane
Operation"

Eric Greenwell wrote:
I'd start with a call to the USA dealer.

Been done... BA and Blanik want a repair plan to review. They can't
provide one for us, but will gladly let us pay $$ to develop one that
may or may not satisfy them. We are trying to decide whether to total
the ship for full insurance value, or accept a payment from the
insurance that we don't yet know will cover the repair costs. The
repair plan is on our dime, so once we find out the insurance would not
cover the repair, we are already out the $1500 or so for generating the
proposal.

Our A&P has peeled back the skin around the bent spar and it is indeed
creased significantly, so Bob K's intial suggestions have been
followed.

At the moment it seems the last suggestion of Bob's is the only cost
effective way to repait the ship. Find someone willing to work for
pennies per hour to do what looks like a very fiddly repair. Agree
with Bob about apparent excess inventory of bent L-23 wings.

-Tom

I have four Blanik L-23 wings (and one fuselage) available in various
states of condition - from airworthy to needing repair.

Roy B.

Earlier, Roy Bourgeois wrote:
I have four Blanik L-23 wings (and one fuselage) available in various
states of condition - from airworthy to needing repair.

Thanks, I knew I remembered your earlier post, I just couldn't remember
who posted it. Here's the link to photos you included:

http://web.mit.edu/dsimmons/www/gbsc/

Looks promising to me.

Thanks again, Bob K.