
Airship Tails - ColinWright
http://neil.fraser.name/news/2011/12/16/
======
leoedin
Airships aren't the only aircraft to use V tails. Early Beech Bonanzas[1] and
the Robin ATL[2] both have "ruddervators" - a V tail which combines the
function of elevator and rudder into two control surfaces.

[1]: <http://en.wikipedia.org/wiki/Beechcraft_Bonanza> [2]:
<http://en.wikipedia.org/wiki/Robin_ATL>

They also both use mechanical control mixers. This is a diagram of the Robin
mixer - <http://i.imgur.com/yVLQA.jpg>

The Bonanza was first flown in the late forties.

I'd imagine that the choice to use fly by wire on the Zeppelin NT was more to
do with the logistics of routing control cables to the fins, rather than
because of complexities in manual control. On that sort of scale, a fly by
wire system is going to save you a fair amount of weight in control wiring and
brackets, and makes the gondola system far more flexible.

------
jordanb
> However, unlike the four fin system, three fins cannot be controlled by a
> human. To turn left, the top fin needs to be deflected, while the two angled
> fins need to be deflected by an amount which can only be computed by the
> sine and cosine of 2π/3 radians times the deflection of the top fin. Turning
> while climbing becomes even more complicated.

This is like saying that no human could hope to catch a ball flying through
the air because it would require doing ballistic calculations in one's head.

I think the author should investigate the combination of control surface
manipulations needed to make a coordinated turn in an aircraft, or doing a
crosswind landing.

Or if he really wants to have is mind blown: how helicopters are flown.

~~~
kaib
While the brain is able to combine a lot of sources of perception and create
complicated control outputs there are limits to this process. Coordinated
turns and crosswind landings are mostly about matching the quite
straightforward controls with the external situation and are not comparable to
the three surface control problem.

The author spent some effort to build a joystick to demonstrate to us how the
problem could be solved. I would think it appropriate you spend some time
researching your point of view, maybe with a quick model in X-Plane. We will
all be richer for what you find.

~~~
jordanb
I think we'll have to disagree that maintaining coordinated flight is
"straightforward." Or especially performing a crosswind landing, which is the
controlled _de-coordination_ of an aircraft so that it can hit the ground at
exactly the right orientation.

<http://www.youtube.com/watch?v=mMvLuUJFHYk>

If someone insists that it is 'straightforward' I'm left to conclude that
either they're a very experienced pilot who has been doing it for so long that
it's difficult for them to remember what it was like to learn, or they don't
have an understanding of what's involved.

Consider this: You're flying an airplane. The elevators are trimmed to
maintain level flight. Now you turn the yolk to deflect the ailerons, and the
aircraft rolls. In this rolled state--say we're rolled 20 degrees from
vertical--the elevators are no longer horizontal. They're 20 degrees off the
horizontal meaning their force is no longer 100% pitch. It's now a combination
of pitch and yaw. Firstly this means that they're no longer trimmed properly
to maintain level flight and the aircraft will begin to pitch, secondly they
are now causing the plane to yaw into the turn. So now you have to bring the
rudder into the equation to compensate for the elevators, but it's also no
longer a 100% yaw control surface, it now affects both pitch and yaw and you
are left with a situation which should look very similar to that in the
Zeppelin NT.

Describing the problem of coordinated flight, you end up with calculations
which would be quite difficult to do by hand, and one might conclude that "no
human" could hope to pull it off while sitting in a cockpit. Yet it is
something humans can not only do, but with a bit of practice can do without
even having to try very hard, by learning to "feel" the aircraft.

I think the author's joystick is neat and I congratulate him for making it. My
only point is that the author errs in saying that "no human" could directly
handle the Zeppelin NT's control surfaces. I think is error is not in
overestimating the complexity of the problem but in underestimating the human
ability to handle such problems.

------
pepijndevos
I'd love some background on how this is the first airship in the US since the
Hindenburg, and what Google has to do with it.

~~~
epikur
I think the distinction was that it was a zeppelin, not a blimp. Google does
not seem to be involved in its development, you can just pay to take a ride in
it.

Relevant article: <http://www.airships.net/farmers-blimp>

edit: the currently mountain view based blimp's official site,
<http://www.airshipventures.com/>

~~~
tsotha
Zeppelin is just a brand (at this point, anyway). While the Zeppelin NT isn't
a blimp, it's not a rigid airship either, but rather a hybrid of the two with
an internal frame. Better than a blimp at high speeds and in bad weather, but
I doubt the design would scale to the size of the 1930s behemoths.

~~~
jordanb
Well the maker of the Zeppelin NT is the original Eckener entity that created
the Zeppelins, so to the extent that a "Zeppelin" is an airship built by
Luftschiffbau Zeppelin GmbH, the Zeppelin NT is a real Zeppelin.

But I think it's not accurate to think of the Zeppelin NT as a blimp with some
rigid parts. The original Zeppelins had non-rigid fabric gas chambers as well,
hung from a duralumin frame which also supported the airfoils and helped the
fuselage maintain shape.

The gas chambers of a Zeppelin NT support their own shape through positive
pressure, as in a blimp. But they don't have to also support the airfoils,
etc. For that, the vessel has a rigid composite structure.

So I think it's more accurate to describe the Zeppelin NT as "a rigid airship
with self-supporting gas chambers." And I see no reason why the design could
not be scaled up to Graf Zeppelin or Hindenburg size if economics permitted
it.

~~~
tsotha
>Well the maker of the Zeppelin NT is the original Eckener entity that created
the Zeppelins, so to the extent that a "Zeppelin" is an airship built by
Luftschiffbau Zeppelin GmbH, the Zeppelin NT is a real Zeppelin.

Well, yes. He said "this is a Zeppelin, not a blimp", which is a lot like
saying "this is a Chevy, not a butterfly". A blimp built by Zeppelin would
still be a Zeppelin, and Zeppelin builds all sorts of things that aren't
related to airships.

The reason I don't think it will scale well is, like a blimp, pressurization
of the gas bag is what keeps a hybrid in the proper shape. This means as the
size of the airship increases the envelop pressure must also increase to deal
with greater external forces, making the lifting gas heavier and therefor less
efficient.

The US navy fielded blimps larger than the Hindenburg until the early '60s,
but they were never able to get more than about half the Hindenburg's lift
capability for this reason.

With a hybrid you still get the benefit of placing engine pods more
efficiently and you don't have to worry about the nose collapsing if you go
too fast. However, if you were going to go through the trouble and expense of
building an 800 ft airship there's no reason to sacrifice that much lift.

------
learc83
Anyone know what he used to build that--Lego technic?

~~~
ColinWright
As well as being an uber-geek who was head-hunted by Google, Neil is a bit of
a Meccano guru. Here is his blog post about building a 3G centrifuge to see if
lava lamps would work on Jupiter:

<http://neil.fraser.name/news/2010/03/03/>

