Goodyear K-Type Airship
|Type||Airship, Aerostat, Military airship|
|Manufacturer||Goodyear Aircraft Corporation|
The Goodyear K-Type airship, designated ZNP-K in the US Navy, was the main maritime patrol airship for the US Navy during World War 2. The non-rigid airships (a.k.a. blimps) were 75 to 79 meters long, had a volume of about 404000 to 425000 ft^3 (11500 to 12000 m^3) and were powered by two Pratt & Whitney R-1340 or Curtis-Wright R-975 engines fitted on outriggers on the control car. The prototype was the K-2 which first flew in December 1938. A total of 133 K-Type airships were built during the war, the last, K-135, was delivered in April 1944.
Important controls / keys
Aerodynamic flight controls
- Rudder (Aileron input is also transferred to the rudder for convenience.)
- Elevator (The elevator trim is seldom used see below for pitch trim.)
The US Navy ZNP-K airship (from K-9 and later) has two Pratt and Whitney R-1340-AN2 radial engines with fixed pitch propellers.
- Throttle (PgUp/PgDn) - Increase/decrease engine RPM and power.
- Mixture levers (M/m) - Leaner/richer mixture.
Gas and Envelope
- Q/q - Open/close the damper (air intake) for the fore ballonet.
- Ctrl+Q - Open forward ballonet air valve (air outlet). Closes on key release.
- A/a - Open/close the damper (air intake) for the aft ballonet.
- Ctrl+A - Open aft ballonet air valve (air outlet). Closes on key release.
- F/f - Open/close the gas valve.
- R - Pull the rip cord to quickly deflate the envelope. Do NOT use in midair.
The fore and aft ballonets (air-filled bags inside the envelope) serve two purposes: (i) by inflating/deflating they maintain the pressure differential and volume of the envelope when the gas changes volume; and (ii) the trim of the airship can be changed by the relative inflation of the ballonets. While the required envelope pressure dictate the total volume of the ballonets the airship can be trimmed by having one ballonet more or less inflated than the other.
Envelop pressure management
When the airship rises the gas in the envelope expands and consequently the total volume of the ballonets has to decrease or the envelope pressure will increase. There are pressure relief valves that automatically open when the pressure in the ballonet exceeds a set limit (which is lower than that of the gas relief valve to prevent gas being valved before both ballonets are empty) but the prudent airship pilot would rather use the manual ballonet valves than rely on the relief valves.
When the airship descends the increasing ambient pressure causes the gas in the envelope to contract and to maintain the envelope pressure above the ambient pressure the total volume of the ballonets has to increase. The pilot has to set the ballonet controls for inflation. Monitor the gas pressure gauge!
On the US Navy ZNP-K airship pitch trimming is done via the relative inflation of the fore/aft ballonets rather than with the elevator trim. Shifting air between the ballonets moves the center of gravity.
- To trim towards nose heavy - set the fore ballonet valve for inflation and/or the aft for deflation.
- To trim towards tail heavy - set the aft ballonet valve for inflation and/or the fore for deflation.
If the airship is above pressure height, i.e. the altitude where the lifting gas occupies the entire volume of the envelope, the ballonets are empty and cannot be used for pitch trimming (and the simulated airship is likely to go badly out of trim). Ascending above pressure height also result in loss of lifting gas, beware of losing too much or you will be unable to maintain the envelope pressure when descending to the ground again.
Center of gravity range FIXME.
The US Navy ZNP-K airship normally carries no ballast for inflight adjustment. Use on ground only.
- w - Show current on-ground weight. Only works when on the ground.
- W - Weigh off to 1000lbs heavy by adding/removing ballast. Takes about 10 seconds and is only applicable when on the ground.
Ground crew / Mooring mast
The US Navy ZNP-K airship currently uses the non-period mast truck from the Zeppelin NT. In actual service either mobile tripod masts towed by tractors or fixed stick masts where used.
- Y - Release mooring mast connection or wire.
- U - Attach mooring wire. Only possible when close to a mooring mast.
- y/u - Play out/winch in mooring wire.
- Alt + click on terrain - Place the mooring mast.
When landing to a stationary mast (which is the usual case in FlightGear), approach straight into the wind and land short of the mast and taxi up to it under as precise control as possible. The US Navy ZNP-K is not very manoeuvrable at low speed so special care is required. In real life it would land into the hands of a ground handling party and once stationary a mobile mast would be moved up to the nose of the ship and connected to the mooring attachment there.
The mooring mast is visible over the multiplayer network. It is also possible for other pilots using ZNP-K, Zeppelin NT or Nordstern airships to dock with your mast.
Cockpit and instruments
Disclaimer: These instructions are derived only from common sense together with certain available documentation and have no connection whatsoever to any instructions for the real ZNP-K airships.
Installation and Dependencies
- US Navy ZNP-K (Development version for FG/git, click "Download ZIP".)
This aircraft depends on instruments from some other aircraft. Install a matching version of these too.
- If the airship is in a sufficiently heavy state when FlightGear starts it might crash at the mast. In particular this may happen at high altitude airports. Initializing with a significantly reduced amount of fuel and payload may help.
- Download page with other lighter-than-air aircraft for FlightGear. Requires the LTA support available in FlightGear 1.9.0 or later. Note: The most up to date version of the US Navy ZNP-K airship is available here for FlightGear/git.