D-LZ129 POH
Mark
Fisher
mf70@hotmail.com
1-6-01
This model is Freeware. Any and all adaptations are
permitted, as long as 1) it is not resold, and 2) credit is given to Mark
Fisher.
This is a model for X-Plane 7.63 and 8.15.
Behavior of the two versions is significantly different. Points where the two
flight models diverge will be noted.
Hi! I'm not a real Zeppelin pilot - the
following are just some elements that I've found useful in operating the
Hindenburg in X-Plane.
Side view at: http://www.wolfsshipyard.mystarship.com/Misc/Airships/Airships.htm
Getting started.
1)
Start X-Plane
2)
Check current weather - if wind is under
10 KT, proceed.
3)
Load the Zeppelin into X-Plane.
4)
Go to “Settings /
Data Input & Output...” and put “landing gear
vert force” on screen.
5)
Go to "Settings/
Weights and fuel." Note that the default settings represent
a test flight loading rather than a transatlantic loading. The
“book” value of the real Hindenburg’s maximum buoyancy was
525,000 lbs. I have set buoyancy values in PlaneMaker to get correct values in
8.15. However, buoyancy behavior has changed between 7.63 and 8.15. In 7.63,
your maximum buoyancy will be 326,000 lbs., far below “book.”
Sorry. If you like, you can open the model in PlaneMaker and reset buoyancy to
600,000 lbs. or so. Don’t worry about “excess” capacity;
that will be dealt with in the “weigh off” step below.
6)
Set "payload",
"fuel,”
and "jettisonable"
loads until total weight is around 540,000 lb. This should leave you still
heavy. This includes 40,000 lbs. of “ground crew,” equivalent to
200 men on ropes.
In the real aircraft, buoyancy was affected by
several variables:
|
Variable |
Location |
Use |
X-Plane
analog (see discussion) |
|
Hydrogen |
(14)
separately releasable chambers |
Emergency
lift dump (you can't get hydrogen back) Also used at end of voyage to ease
ground handling. |
Maximum
buoyancy is determined in PlaneMaker. “Displacement
control” on control panel can be thought of (in
this model) as the gas volume. No fair adding lift in flight! |
|
Water 88,000 Lb |
Held
in a number of tanks, and collected from rain. |
Trimmed
CG and balanced fuel loss. |
Ballast is trimmed through "Weight & fuel"
entry at two points: “jettisonable
ballast” and under the “weapons” tab
as ten “1 ton ballast”
objects. |
|
Fuel 146,000
Lb (fuel and oil) |
Some
fuel tanks were fitted for emergency dump. |
Emergency
lift source. |
Can
be trimmed through "Weight &
fuel" entry. No fair refueling in flight! |
|
Crew |
Crew
could be ordered forward or aft. |
Affected
cg, to help adjust attitude of the ship. |
CG
is set in PlaneMaker, but, in all versions up to X-Plane 8.15, does not
affect trim of ship. |
7)
Set props to 0 pitch. That's mid-range.
Start engines. While you're on the ground, get a feel for your engine control.
THESE ARE MANUAL PITCH PROPS. IT IS POSSIBLE TO OVERSPEED THE ENGINES - WATCH
THE TACHOMETERS. Redline IS 1400 rpm forward, and 1120 in reverse thrust. The
original was rated for a maximum 1300 HP @ 1400 RPM for no more than 4 minutes.
Cruise power is 850 Hp, or 26 in. Manifold pressure.
8)
“Weigh Off.” This is a vital
part of lighter than air operation. Once you have left the ground, you will
have only indirect ways to know your state of buoyancy. To weigh off:
·
Dismiss
your ground crew: Move “Ballast” control to “Ground Crew”
and press the “space” bar four times. This releases the four
“ground crew” units, and sheds 40,000 lbs.
·
Turn on “Settings / On screen data
output / landing gear vert force.” Wait for the
readouts to stabilize. S-l-o-w-l-y move displacement control up (simulating
“gassing up”) to trim weight until you see ~2000 lbs.
total loading on the gear. You are now at neutral buoyancy.
·
To ascend, set "Ballast"
control to "Water Ballast" and press the
<Space> bar. Each press releases one 2000 lb. tank of water. If your
weigh-off was precise enough, you should take off on the first release. (In
actual practice, the Hindenburg would release as little as 300 lb. to lift
off.)
In Flight.
Engine
arrangement is (This is not the Hindenburg’s numbering system, but it is
more logical in XP)→
It is possible to set port engines forward and
starboard engines reverse to exaggerate turn rate. Use prop pitch control to
set reverse pitch, not the "." key for reverse thrust. Keep rotation
rates low – XP does not see any drag when forward speed is zero, and does
not “realize” that the nose and tail would present TREMENDOUS
resistance to turning, even aside from their polar moment.
In this version, directional control is through
aileron and elevator trim. Using the
joystick will move the control surfaces MUCH faster than would have been
possible. In reality, the captain gave control commands to the rudder and
elevator operator, who cranked large wheels to set control position.
As fuel is burned, you will reduce buoyancy by
lowering the “buoyancy control,” equivalent to dumping lift gas.
(Obviously, adding lift gas by
raising the buoyancy control while in flight is cheating.)
In flight, buoyancy status can be deduced from
pitch trim while holding a constant altitude. If you’re forced to keep
the nose up to maintain altitude, you are flying heavy – release some
ballast. If you are ploughing nose down to maintain altitude, you’re
light – valve off lift gas. Both of these operations should be one pixel
at a time! Paradoxically, in reality, a heavy ship had to be trimmed nose down
to maintain level flight.
In THIS VERSION of the Hindenburg, set and use autopilot as normal, once buoyancy is
correct. Unlike most X-Plane aircraft, it WILL hold altitude (=/- 500 ft) on
its own. The autopilot is NOT an
anachronism - the original had a rudder autopilot. (Yes, the radar altimeter IS
anachronistic, but there would have been other means of precise altitude
information at low elevations AGL – such as a lead line.)
(In the
"X-Plane stock" Hindenburg, an autopilot WILL work for altitude, if
buoyancy is fairly close, but it CANNOT hold a heading - the autopilot is
connected to the ailerons for heading control, and the Hindenburg has none!)
We can simulate the reversing diesel engines by
setting the prop pitch to full advance (16 degrees) or full negative (-16
degrees) via the on-screen pitch handles, or F5 and F6 keys if that is restored
in 807. Reduce throttle FIRST and wait (~30 seconds or better!) for engines to
spool down, set new prop pitch, then re-set throttle to desired RPM. It is
possible to set props for full forward and advance throttle to max, but FULL
throttle in reverse will stall the props and overspeed the engines!
In landing.
Make sure your remaining ballast is in one ton
increments. You may “transfer” ballast from the general
“jettisonable” supply to the more precise one-ton units by going to
the “Ordnance”
pane of the “Settings / Weights and fuel" menu and using
the Clear
(click – load) buttons to “refill” the
ballast drums. You must then go back to the “Fuel/Payload”
pane and REDUCE the jettisonable load by an equivalent amount.
Use reverse thrust to bring the ship to a stop
at about 1000 feet AGL. Check your VVI. Valve gas in 1000 lb increments (that's
ONE PIXEL on the slider) or release ballast (using "space") to VERY
SLIGHTLY heavy (1000 lbs or so).
Extend handling ropes (G key). As the ground approaches, you may release
some trim ballast to reduce decent rate.
You may call it a good landing if speed is under
5 kt. at touchdown (that way, the little guys have a chance to grab your
mooring ropes...). Once you touch down, go back to the “Ordnance
pane” of the “Settings / Weights and fuel"
menu and using the Clear (click – load) buttons to
restore the four “Ground crew” units to add 40,000 lb. or so for
"stick." This simulates releasing an equivalent amount of gas for the
same purpose, and the weight of the 200 plus (!) ground crew.
Construction notes:
This Hindenburg model diverges from reality in several
areas, due to my lack of knowledge of the original or limitations of the
software.
1.
Buoyancy model: Thanks to an analysis by
Chuck Bodeen, I have developed an improved understanding of X-Plane’s
buoyancy model. X-Plane goes through two steps: a) It determines the volume of
air that would have to be totally displaced to achieve the maximum buoyant lift
as set in PlaneMaker, assuming a “standard atmosphere.” b) It then
calculates the current available lift by multiplying that volume by the current
ambient pressure and the position of the “displacement
control.” If lift exceeds the weight of the
structure and load, the ship rises. In X-Plane, buoyancy steadily decreases
with altitude; when the atmosphere is not dense enough to provide support for
the vehicle, it stops rising.
The catch is that this
is most closely analogous to a hot air balloon, where the volume of the balloon
is constant. This is not how an
envelope containing lift gas works. A lift gas envelope is allowed to expand as
it rises. When its gas has expanded to fill the available space, it is at
pressure height. Any excursion above this point results in venting of gas,
either through controlled release or rupture of the envelope.
For lift gas
aerostats, the vehicle is not stable in altitude; if there were enough lift gas
molecules to lift 100 lbs. at sea level, those same molecules would be
providing the same 100 lbs. of lift at 20,000 feet, though they would have to
expand to double the volume to do so. Toy balloons and radiosondes regularly ascend
until the envelope ruptures; the dirigibles must closely monitor the expanding
volume of lift gas.
2.
Weights (from (http://www.dwv-info.de/e/publications/2000/hbe.pdf)
are set at:
|
Category |
Documented value |
US value |
X-Plane Default setting |
|
Empty weight |
118 T |
236000 Lb |
236000 |
|
Service weight |
220 T |
440000 Lb |
359426 |
|
Load |
72 Passengers + 11 T cargo. |
89760 (Service weight minus theoretical
buoyancy) |
0 |
|
Fuel |
88 M3 Fuel 4500 L Oil |
139500 Lb Fuel 7134 Lb Oil |
73,325 (Max 146650, representing total
consumables) |
|
Ballast |
40 M3 Water |
88,000 Lb |
20,000 (Max 40,000) + 20,000 in “1 ton
ballast” units |
|
Bouyancy |
200,000 M3 Hydrogen, or 18 T |
472,940
Lb (see below) |
326000 (in 7.63) 529,000 (in 8.15), with 100%
“displacement control” |
3.
The
biggest problem in long flights is compensating for fuel burn. The real Hindenburg would have vented hydrogen
as well as collected rainwater for ballast. After burning, say 100,000 lb fuel,
you’ll have to decrease lift by 100,000 lb or collect rainwater to
balance out
4.
Internal foils to simulate fuselage lift.
They have a special low-drag .AFL to avoid affecting the overall lift-drag
picture too much.
5.
Re-arranged airfoils. As mentioned above,
the autopilot controls the elevator and ailerons. The "stock"
Hindenburg has no ailerons!
6.
Trailing lines. Deployable via the
"gear" control, the "crew" can get them out in about 20
seconds. Hatches on nose are for crew access to nose trailing lines.
7.
Prop specs. Hindy turned 19 FOOT
wheels!!! The originals would have been fixed, with reversing diesel engines,
but X-Plane can't do THAT trick. Instead, we can use the “manual
prop” pitch control, and set it at either + or – 16 degrees.
8.
Fuel consumption rates. Diesels are far
more efficient than gasoline engines, so consumption is far lower, at 170
gm/hp/hr.
|
RPM |
Fuel Consumption; lb/hr |
Speed. |
||
|
Engine |
Prop |
Total |
Per Engine |
|
|
1450 |
715 |
1430 |
357.5 |
82.7 |
|
1350 |
675 |
1166 |
291.5 |
78.3 |
|
1250 |
625 |
880 |
220 |
69.3 |
|
1150 |
575 |
660 |
165 |
66 |
Unknowns and future issues:
1.
At the moment (7.63 and 8.06) The F5/F6
keys do NOT control prop pitch.
2.
As of 8.15, longitudinal trim does NOT
change when the GC is moved fore or aft. This is not a show-stopper, as the
ship was generally flown in pitch trim, using the elevators for pitch control.
Mark
mf70@hotmail.com
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