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 M^3Fuel 4500 L Oil	139500 Lb Fuel 7134 Lb Oil	73,325 (Max 146650, representing total consumables)
Ballast	40 M^3Water	88,000 Lb	20,000 (Max 40,000) + 20,000 in “1 ton ballast” units
Bouyancy	200,000 M^3Hydrogen, 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. Austin says he’ll look at it, perhaps for 807.

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

Resources:

http://www.altfrankfurt.com/Spezial/Zeppelin/Hindenburg/

Data from: http://www.hindenburg.net/crossing.htm

MONDAY, MAY 3

· 8:15 p.m. -- The Hindenburg lifts off and heads northwest, as searchlights follow the tail emblazoned with the ominous swastikas.

· Chief Steward Kubis accompanies passenger Joseph Spah to feed his dog at the ship's rear.

· 9:30 p.m. -- A mailbag is dropped over the city of Cologne.

· 10:00 p.m. -- The ship crosses over The Netherlands at a height of 1000 feet.

· A light dinner of salad and cold meats is served; Commander Pruss greets some of the passengers.

· 12:00 a.m. -- The Hindenburg enters a storm over the North Sea.

TUESDAY, MAY 4

· Dodging the gales, the Hindenburg flies back over Belgium at a height of 600 feet.

· Commander Pruss follows the English Channel westward, rising above the storms to 2100 feet.

· 5:12 a.m. GMT -- Sunrise.

· The ship descends to her standard cruising altitude of 800-1000 feet.

· Breakfast.

· Colonel Erdmann and Captain Lehmann discuss the possibility of sabotage.

· 10:00 a.m. -- 200 miles south of Ireland.

· Due to illness, passenger Philip Mangone stays in his cabin.

· Chief Steward Kubis sells writing paper and Hindenburg stamps; he offers the passengers playing cards and Chinese Checkers.

· The passengers conduct business, read, smoke or drink. Matilde Doehner knits, while Stewardess Imhof plays with Walter and Werner in the saloon.

· 11:00 a.m. -- Kubis serves bouillon.

· Kubis again escorts Joseph Spah to the kennel.

· Lunch is served. The ship's clocks are set back two hours.

· 270 miles southwest of Ireland, altitude 900 feet. Due to headwinds, the Hindenburg can only muster 51 knots; it heads out over the Atlantic.

· Chief Engineer Sauter replaces a faulty pump on the auxiliary diesel

· 4:00 p.m. -- Dr. Ruediger leads a tour of the ship; the passengers are made to wear sneakers offered by Steward Nunnenmacher. Group 1 (consisting of Leonhard and Gertrud Adelt, Peter Belin, Berger Brinck, Irene Doehner, George Hirschfeld, and Joseph Spah) is shown the kitchen, fuel and water tanks, emergency steering controls, engines, control gondola, radio room, officers' mess and crews' mess. Much to Ruediger's consternation, Spah leaves the group to visit his dog.

· 5:00 p.m. -- Ruediger leads Group 2 on the tour.

· Making 53 knots at a height of 600 feet, the Hindenburg has covered 310 miles since noon.

· The 6:00 news is broadcast into the lounge.

· Margaret Mather acts as unofficial chaperon to Irene Doehner.

· Dinner.

· Lehmann heads high into the bow to play his accordion in solitude.

· 11:00 p.m. GMT -- The Hindenburg is 400 miles north of the Azores.

WEDNESDAY, MAY 5

· 6:00 a.m. -- 1300 km east of St. John's, Newfoundland, Canada.

· 7:18 a.m. GMT -- Sunrise.

· Breakfast.

· Commander Pruss orders a full inspection of the ship.

· 9:30 a.m. (to 5:30 p.m.) -- The ship suffers a radio blackout due to severe electrical disturbances along North America's eastern seaboard.

· Lunch. Clocks are set back 3 hours.

· Joseph Spah ventures into the ship unaccompanied.

· Dr. Ruediger attends to Cook Groezinger after the latter spills hot soup on his foot.

· Off the coast of Newfoundland, passengers spot lighthouses on Cape Race and icebergs below.

· The 6:00 news is broadcast into the lounge.

· Erdmann, Hinkelbein, Witt and Lehmann discuss suspicious passengers.

· Dinner.

· 10:00 p.m. -- Captain Lehmann entertains the passengers with his accordion in the lounge.

THURSDAY, MAY 6

· The Hindenburg follows the south coast of Nova Scotia, at a speed of 63 knots and a height of 700 feet.

· 4:10 a.m. -- 450 miles east of Lakehurst.

· 5:49 a.m. -- Sunrise.

· Breakfast.

· Passengers begin to pack.

· 11:40 a.m. -- The Hindenburg flies over a foggy Boston.

· Lunch.

· The ship passes over Providence, Rhode Island.

· Stewards gather baggage and bedding.

· 3:07 p.m. -- The Hindenburg flies back and forth over New York City, giving passengers views of the Empire State Building, the Bronx, Harlem, Central Park, the Battery, Times Square, a game at Ebbets Field (between the Dodgers and the Pittsburgh Pirates), and the Statue of Liberty.

· 4:00 p.m. -- The ship arrives at the Lakehurst Naval Air Station, but Commander Pruss decides to ride out the storm. He heads southeast and, upon reaching the ocean, goes north along the New Jersey shore as far as Asbury Park. He then turns inland again.

· The passengers are served sandwiches.

· 6:12 p.m. -- Charles E. Rosendahl, Commanding Officer of the Lakehurst N.A.S., notifies the Hindenburg: "

· 6:23 p.m. -- Rosendahl sends message: "

· Steward Nunnenmacher prepares a table in the dining room for Customs purposes.

· Captain Lehmann bids farewell to some of the passengers.

Data from http://www.pr.erau.edu/~case/library/reports1

/21.html :

During its nine months of operation in 1936, this airship had made more than 55 flights; flown 2,764 hours, cruised l9l,583 miles, crossed the ocean 34 times, carried 2,798 passengers and more then 377,000 pounds of mall and freight, all without mishap.

Its length was about 803.8 feet; height, 147 feet; maximum diameter, 135 feet; fineness ratio (length over diameter), about 6; total gas volume, 7,063,000 cubic feet; normal volume, 6,710,000 cubic feet. Weight of ship with necessary equipment and fuel was 430,950 pounds; maximum fuel capacity, 143,650 pounds; total payload 41,990 pounds, and total lift (under standard conditions) was 472,940 pounds. Its rated cruising speed was about 75 statute m.p,h.; its maximum speed was slightly over 84 m.p.h. Passenger space was entirely within the hull.

The control system was the conventional Zeppelin type control, with two rudders acting as a unit for horizontal control, and two elevators acting likewise for vertical control. Emergency elevator and rudder control wheels were installed in the stern of the ship. An electrical gyroscopic device attached to the forward rudder wheel provided automatic steering.

The outer cover consisted of cotton fabric on certain parts of the frame; on others, linen, depending upon stresses to which it was exposed. All exterior surface of such fabric was treated with several coats of cellon and a mixture containing aluminum powder. As protection against ultra violet rays, the inner surface of the fabric on the upper part of the ship was coated with red paint.

In each of the sixteen compartments of the ship was a gas cell containing the lifting gas, hydrogen. The middle cells were separate, whereas the two bow and the two stern cells were inter-communicating. The gas cell material consisted of a film placed between two layers of fabric. Nettings were provided to prevent all sharp edges from damaging the gas cells. It was stated that the amount of gas leakage through this fabric approximated a maximum diffusion rate of about 1 liter per square meter per 24 hours.

Fourteen automatic and an equal number of manually operated or maneuvering valves were affixed to the cells. A single maneuvering valve was affixed to cells numbered 1 and 2 and cells 15 and 16, Gas could be released from the cells by manual operation of the valve controls located in the control car, and hooked up with the valves by a series of wires and pulleys. This was done under the supervision of the captain or the watch officer in charge. The automatic or emergency valves were provided to reduce the pressure of the gas in the cells under certain circumstances. The cells were numbered from stern to bow, from 1 to 16. The maneuvering valves of cells No. 3, 4, 5, 6, 7, 8, 9, 10, 11, 13 and 14 were connected to a master wheel in the control car which operated all of them as a unit, and there also were independent control for the separate maneuvering valves so that the gas in them could be released as desired.

Electrically actuated gas fullness or pressure units were connected to the gas cells to indicate visually by sensitive meters in the control car the pressure and hence the relative fullness of the gas in the cells. These units were located in the ships axial corridor, or walkway. The accuracy or sensitivity of this system was not definitely established. An appreciable amount of gas might have been able to escape before such escape would show on the visual indicator unless that indicator was kept under close observation. According to Witness Eckener, a cell could lose at least 200 to 300 cubic meters of gas before the indicator would show such a loss. Such an amount is only a very small proportion of a cell's content.

Between every two cells a gas shaft was provided into which gas could be valved directly from the cells. The shafts extended vertically from the lower walkway through the axial walkway to the top of the ship for ventilation purposes. On the top they came in contact with the outside air under the protection of specially designed gas hoods or ventilators.

Four Daimler Benz diesel engines, type LOF-6, each having a maximum rating of 1100 hp. were used to propel the air ship. They were contained in four outside engine cars, or gondolas, and were suspended laterally on the ship's hull by struts, Engine-room telegraphs provided communication between the control room end the individual engine cars. The fuel used by the engines was a diesel-oil.

The four-bladed propellers attached to each engine were of wood and 19 feet, 9 inches in diameter. The blades were armored with brass sheathing about 1 1/2 inches in width, on the leading edge, from about the 43-inch radius to the tip of the blade. The sheathing was bonded to the ship's structure through the engine. Tests were made with the prototype of the propellers used on the ship. They were tested to loads 50% in excess of the thrust to which the propellers would be subjected at take-off, which was three times greater than the thrust which would be imposed at cruising speed. They also successfully withstood the block tests. They were limited to 1400 r.p.m. in forward rotation and 1120 r.p.m. in reverse rotation. These revolutions were below the fluttering speeds of the blades.

The electrical power plant of the ship consisted of two 50 hp. diesel-driven generators with switchboards and distribution system. These generators were independent of the outside propelling engines. The electric generators and principal members of the system were located amidships on the port side of the keel. Current was generated for purposes of lighting, cooking, radio and steering. There were two circuits one of 220 volts, the other of 24 volts. The ship's electric wiring was of copper and was installed in accordance with the rigid regulations governing the German Lining Societies. The lead to the stern light, which was on a 220-volt circuit, using a very heavy cable protected by a special fuse, extended from the electrical power plant along the lower walkway and thence to the light. No electric wiring extended above the equator except in the extreme nose of the ship.

The main mooring steel cable was fixed to the tip or nose end of the ship. The port and starboard bow trail ropes were attached to the ship at frame 244.5. These trail ropes were about 413 feet in length. It is understood that in landing the ship, it was the practice to approach the ground mast from leeward and drop the wire cable and the two trail ropes. The main cable was then coupled to a mooring mast cable leading through the top of the mast. By moans of a winch, the cable was then reeled in, pulling the mooring cone on the ships nose into the corresponding cup on top of the mast.

The trail ropes were coupled to ground ropes and led out to the sides to keep the ship headed into the wind and towards the mast and to prevent it from over-riding the mast structure, In the stern, at ring 47, an after mooring cable was in practice let through a metal fair lead. At ring 62 a port and starboard spider was let out at landing. Besides those enumerated, the ship was provided with other mooring or landing tackle, for such use as circumstances warranted.

Water was generally used for ballast. The emergency ballast was contained in fabric containers, four of which, of 500 kilograms of water, Were suspended in the bow and an equal number in the stern. To the right and left of the lower walkway were suspended a number of other ballast tanks, some of 2500 liters each and others of 2000 liters each. The ballast tanks could be emptied partially or totally by the elevator men by means of control wires connected the ballast stand in the control room. Several of the fuel tanks could also be used for ballast purposes.

The radio-room was located above the after end of the control car. Its equipment provided for two-way radio telephone and telegraph communications. It included a short wave and a long wave transmitter, each with 200-watt antenna capacity; two all-wave receivers and two direction finders. The frequency of the short wave transmitter was 4160 to 17,500 kcs. The frequency of the long wave transmitter was 120 to 500 kcs. The frequency range of the receivers was 12 to 20,000 kcs. Power for the transmitters was obtained from a 220-volt direct current supply generated by the ship's electric power plant. The receivers obtained their high voltage from batteries, and power for their filaments was obtained through a series resistor from the 24-volt ships generator. For the short wave transmitter, there was a trailing antenna of 26 meters length. For the long wave transmitter, a trailing antenna of about 90 meters length was used. These trailing antennas were located directly below the transmitters and ran through an aperture in the keel of the ship. There was a fixed antenna extending from the control car about 15 meters toward the stern. The fixed antenna was used only for receiving purposes. In addition to this equipment, there was located in the bow an emergency transmitter and receiver, current for which was obtained from a generator driven by pedal power. This emergency set employed a trailing antenna about 20 meters in length.

The ship was inflated with hydrogen. According to the evidence adduced, this gas has the following characteristics: It is colorless, odorless and tends to diffuse in all directions. The only way that hydrogen could be detected by smell would be due to the presence of impurities as a result of the process by which it was produced, or contamination from some source such as rubberized fabric. Hydrogen, for lifting purposes, has a density of approximately 5 pounds per 1000 cubic feet, depending on the temperature and pressure. Its lifting power is the difference between the density of air and its own density. The density of air is about 75 pounds per 1000 cubic feet. Assuming pure hydrogen, its lifting power would therefore be about 70 pounds per 1000 cubic feet. An opinion was advanced that the general order of pressure of the gas within the cells of the ship was somewhere between half an inch and one inch of water pressure. It was stated that the density of hydrogen corresponds to air at a temperature of 5000° F. and that the chimney effect of its escape through the gas shafts of the ship was so very great that there was no possibility of its moving down the shafts into the lower parts of the ship.

The flammable limits of a mixture of hydrogen and air are probably between 4.5% and 62% of hydrogen. Other experiments have shown variances from 8 - 9.8% to 66%. The temperature at which chemical activity between hydrogen and oxygen takes places is between 507° to 557° Centrigrade. This temperature range is dependent upon the amount of hydrogen present. The range of activity of combustion will be from the lower limit of 4.5%, at which there will probably be an invisible union without evidence of flame. A combustible mixture would be more hazardous in an atmospheric condition of 98% relative humidity, and temperature 60° Fahrenheit, than in dry air with relatively low humidity, since dry hydro-oxygen is more difficult to ignite and its ignition temperature is higher. In an explosion the flame propagates in all directions in the combustible range between 15 to 45% of hydrogen. These figures were arrived at experimentally with glass or metallic apparatus which did not have effect upon the combustion temperatures. Catalytic metals having adsorption properties would be likely to affect the combustion at lower temperatures. Finished duralumin would not be expected to have material catalytic effect upon hydrogen.

The whole metallic structure of the craft was bonded.