Re: Blanik L-13 polar

[BTIZ]

I have not seen any polar for the L-13 other than the one in the factory
manual POH. It does not reference the flap positions.

I have flown the L-13 and the L-23 (no flap)
For the L-13, the flaps do lower landing speed and the angle of the fuselage
on approach which affects the AOA of the wing. I always found it was easier
to keep the tail wheel off the ground with full flap landings.. those
landing the L-13 without flaps tended to strike the tail wheel on the
ground, not good for the last fuselage former, and prone to cause cracks in
the mount.

I have not had a tail wheel problem with the L-23 and no flaps.

at 1/2 flaps, there is not detent so it must be held there, does allow
better performance in weak ridge/wave or thermals, full flaps does tend to
add to the drag factor. And there is a speed limit with full flaps.

BT
"A.Wolfert" > wrote in message
...
> Does anyone have a polar curve for the Blanik L-13 with the Fowler flaps
> out? I found several "normal" polars on the web, but none for the flaps
out.
> Background for this question is whether there is any benefit in using the
> Fowler flaps in weak thermals.
>
>
> Ton Wolfert
>
>
> All e-mails are scanned for viruses
>
>

[BTIZ]

I'm wondering of your trouble with the L-23 tail wheel is ground handling..

there is now a factory service bulletin to not push the aircraft backwards
across terrain, only paved surfaces.. the spring attach for the tail wheel
is not meant to flex when moved backwards.. only forwards..

BT

"nowhere" > wrote in message
m...
> > I have not had a tail wheel problem with the L-23 and no flaps.
>
> Conversely, my club has had quite a bit of trouble with our L-23's
> tailwheel (and the bulkhead which it is attached to) but no trouble
> with our much older L-13s. This is despite the fact that probably 75%
> or more of the L-13's landings are done with flaps retracted. This
> surprised me as the 23's tailwheel LOOKS much more sturdy!

[F.L. Whiteley]

We replaced our initial L-23 tail wheel suspension donuts at one year due to
failure. We've just encountered the second failure at the second year
point. We do not allow pushing backward of the glider. We do lift the tail
most times to rotate the glider when not on a paved surface. Most landings
are on the main, rather than two-point. As we are at 5500msl, our actual
touch down speeds are likely higher than most operations.

The rubber donuts are weak, likely by design, to prevent damage to the
frames. Since both sets failed about the same time of year, I suspect wear
plus heat may be the culprits. Air temps have been in the upper 90F to over
100F daily since 7/1. Surface heat is much higher and the support donuts
are both close to the surface and in an enclosed area that may act something
of a collector. I don't know what effect 120-140F temperatures may have on
the rubber and don't know if it's vulcanized or not. I doubt if they are
custom made, but probably from some other application and adapted to the
tail wheel design. As they are relatively cheap, it would appear a 6 month
replacement cycle would be appropriate for our operation.

YMMV

Frank Whiteley
Colorado


"BTIZ" > wrote in message
news:ZPVZa.9576$2g.7946@fed1read05...
> I'm wondering of your trouble with the L-23 tail wheel is ground
handling..
>
> there is now a factory service bulletin to not push the aircraft backwards
> across terrain, only paved surfaces.. the spring attach for the tail wheel
> is not meant to flex when moved backwards.. only forwards..
>
> BT
>
> "nowhere" > wrote in message
> m...
> > > I have not had a tail wheel problem with the L-23 and no flaps.
> >
> > Conversely, my club has had quite a bit of trouble with our L-23's
> > tailwheel (and the bulkhead which it is attached to) but no trouble
> > with our much older L-13s. This is despite the fact that probably 75%
> > or more of the L-13's landings are done with flaps retracted. This
> > surprised me as the 23's tailwheel LOOKS much more sturdy!
>
>

[Bruce Greeff]

Don't rely on the L13 bulkhead. There is a SB out for material strength
on the bulkhead. Apparently some were manufactured using too soft a
material. If yours is affected then lateral loads are going to cause the
bulkhead to collapse.

We have had three failures in one year with bulkhead 14 deforming on the
L13. One was a ground loop, the others appear to be overstress from
landing on rough grass. Might be an idea to start using flaps on landing
(current procedure is to land with no flaps) - or maybe the summary is
to get our runway graded again...

[nowhere]

> I'm wondering of your trouble with the L-23 tail wheel is ground handling..
>
> there is now a factory service bulletin to not push the aircraft backwards
> across terrain, only paved surfaces.. the spring attach for the tail wheel
> is not meant to flex when moved backwards.. only forwards..
>
> BT

We try to move the Blaniks forward only for just this reason.
Unfortunately they do sometimes get moved backwards (either because of
ignorance or laziness) and this in addition to the many potholes on
our grass strip certainly puts some strain on them. Pushing backwards
was quite common before we bought a golf cart for towing the gliders
around the field so the ships probably did suffer a lot from this.

One thing I have noticed is that the tails take a lot of abuse when
the ship is braked too hard after landing, putting the nose on the
ground and letting the tail come down with an almighty bang when the
glider comes to a halt. This is likely excacerbated on the 23 as there
is a perception in the club that it is roomier than the 13 with the
result that it is frequently flown by the larger pilots. If you get a
couple of big people on board both wearing chutes the nose grounds out
quite easily. I just ignore the wheel brake altogether normally. The
landing roll of a Blanik on a grass strip into our usual headwind is
virtually nil even without the brakes!