Diamant 18m

I had a Diamant 18 from 1974 - 1983. I had about 750 and some odd hours
in it. The info from Art on the Glider Forum is good. The 18 had an
AD on the spar stubs that limited your VNE until it was accomplished.
Most of the ones around had already had the earlier ADs on the flap
counterweights and the rudder damper done already by the factory which
had a representative travel around and fix them (Fred Jiran). I flew it
for a long time and sold it without ever complying with the spar stub
AD, because in normal flying, it was rarely necessary to go that fast
anyhow. The factory, FFA from Switzerland was still supporting it and
provided a kit to accomplish the spar stub AD.

It's a real floater for a glass ship. It has a very good L/D, but it
comes at a relatively slow speed. It looks a lot like an ASW-12 and has
a similar max L/D, but the whole performance curve is shifted over to
the left, so everything happens about 10mph or more slower than the
ASW-12. But compared to the 12, it's a much easier and safer ship for
ordinary mortals to fly. It has a lot of washout in the wing, which
I think is one of the reasons the stall/spin behavior is very good, but
this hurts it's high speed performance. This is both good and bad. I
think it could still stay up on weak days better than any ship I can
think of, even today, except maybe the LightHawk. It would make an
excellent contender in the "micro-lift" arena, even today. It has a
very slow stall speed and landing speed. You can get it down below 30
knots when thermalling. The real expert on Diamants is Dan Pierson.
He used to fly his with as much or more than 70 gallons of water.
This would put him even or even better than the ASW-12 and
tantalizingly close to some of the big open ships like the Nimbus 2 at
the time. Dan still has his 18 and has extended the wing to 19 meters.
He had taken up "open cockpit" Diamant flying with the aft part of the
canopy removed the last time I talked to him. I don't think you would
want to land it gear up, as the fuselage is actually a foam sandwich
construction and the amount of glass over the foam is pretty thin and
would not take much abrasion. Once you got into the foam, your hind end
would be scraping the surface in very short order, I think.

The rather small size, of the landing gear definitely comes into play
when you fly it with that much water. It was a real big risk to take
off on that gear with that kind of weight. You could only do it at
carefully checked runways with no chance of any holes or bumps, and
even then, it was a big risk. With no water ballast, the gear is
adequate, although on the small side - I think it used the same size
hub and tire as a Libelle which was a much smaller ship. I never flew
mine with more than 45 gallons. I considered the 25 gallon difference
between me and Dan Pierson as my safety factor, since no formal
structural analysis of flying with that much water had been done :-)
The wings are big and one piece, but not really all THAT heavy, I mean,
esp. compared to a Nimbus 2 or ASW-17 inner panel. The main pin on
the spar stub had to be lined up just right with the bearing on the
root rib of the other wing, or it just would not go together, and it
was a rather bluntly rounded pin, so it was very difficult to visually
tell if it was lined up right. I found that it was easier to do it by
feel out on the wingtip. There was a certain "sweet spot" and you
could with practice find that pretty easily. When it was lined up in
the sweet spot, it would just fall together very easily. But if you
were not in the sweet spot, no amount of force would help. It had a
rigging lever similar to a Libelle, but that was totally useless.

As far as flying qualities, the flaps are very nice and very effective
for decreasing landing speed and help give you a better view over the
nose (your feet) when landing. The dive brakes are also very effective
and combined with the landing flap position and the excellent view, and
the very low stall speed, make it a very nice ship to land. The
reclining position is very comfortable once you get used to it. It is
very narrow in the cockpit, but pretty long, that's pretty obvious just
from looking at a picture of the ship. The rudder is very heavy on
the 18. That is really because it has a very large area, and is driven
by a pushrod system and the lever arm that drives the pushrod in the
nose is only a few inches long, so the amount of force required from
your feet can be quite high just due to the mechanics of the short
lever arm. The all flying tail is quite sensitive, but not any more so
than a Nimbus 2 or a Std. Cirrus. The ailerons can have a lot of
friction, and the forces are high compared to some other designs. The
ailerons use these drivers that have ball bearings with races at 45 deg
angles to translate the lateral motion of the pushrods to an up and
down motion. These can get dry and were usually not accessable because
the fittings they attach to the wing by had been filled over with
filler. But you can remove the filler and take them appart to clean
and grease them. I used to try to spray a light weight lubricant on
the bearings but then you get more dirt in there and you can't get in
there and clean it out without taking them apart.

Alex Caldwell
Tulare,CA

phil collin wrote:
I'm looking into buying an 18m Diamant. There doesn't appear to be much
info about this particular model on the net other than the BGA's tech
sheet and a few odd references. I have no issue with it being flapped
etc. I wondered if anyone had experience with the 18 metre Diamant or
new of a url for more info. I'm told Jane's World Sailplanes has some
good info but other than that nada.

here's hoping

Phil