Lighter-than-air support for airship and balloon simulation in JSBSim and FlightGear

Anders Gidenstam

This page is about the development of basic support for lighter-than-air aircraft, such as airships and balloons, to the open source flight simulator FlightGear and the open source flight dynamics model JSBSim and aircraft using this support. The lighter-than-air support is now available in JSBSim/CVS and FlightGear 1.9.0 and later.

News

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Introduction

This effort consists of two parts: (i) designing and implementing the necessary changes to JSBSim to support lighter-than-air aircraft such as airships and balloons; and (ii) create some example aircraft models for FlightGear that use these new extensions. Both parts have made progress: the JSBSim extension has been accepted into JSBSim/CVS and FlightGear and I have three airship and two balloon aircraft models that flies well in FlightGear. The aircraft are presented in the hangar section below.

In JSBSim buoyant gas cells are specified in the new buoyant_forces section of the JSBSim flight model specification. Ballast is modelled using standard pointmass elements in the mass_balance section.

Work in progress documentation for buoyant_forces. This is part of the JSBSim Reference Manual available at the main JSBSim site.

Buoyant forces in JSBSim Todo list

Things I know are still missing in no particular order:

Feel free to drop me an e-mail (see bottom of page for the address) if you find some of this software useful or have other comments, suggestions or questions.

Aircraft hangar

The tar.gz archive for each aircraft should be extracted in $FG_ROOT/Aircraft/. You can find most of the aircraft below in my hangar (Enter Source Tree and click on Download master as .tar.gz). Some are also available from the FlightGear aircraft download page (for the latest FlightGear release) and in the FlightGear/git git repository.

NOTE: I have not extended the JSBSim trim code to tune the static condition on startup, therefore it is possible that the current weather conditions (when using --enable-real-weather-fetch leads to a for trimming infeasible static condition, either too light or too heavy, that can crash FlightGear. If you suspect that is happening try --disable-real-weather-fetch. Another pitfall is that the airships strongly object to being moved late during the initialization - this can happen if you have not specified a runway and FlightGear deems the default runway unsuitable under the fetched weather conditions. I strongly recommend explicitly choosing a runway with --runway=... if you experience problems.

Submarine Scout class airship (Submarine_Scout)

Note: This aircraft is available in FlightGear 1.9.0 or later. Please get it from the FlightGear web site (for the latest release) or the FlightGear git repository (the most recent Submarine Scout updates in FlightGear/git).

This class of small blimps were built in fairly large numbers for the Royal Navy in 1915 - 1919 to patrol costal waters and escort convoys. The early versions had cars made from slightly modified aeroplane fuselages while the last version, which is the one represented here, had a purpose built car. This model was called Submarine Scout Zero (SSZ). (Or possibly Sea Scout Zero - I have seen both names but I'll use Submarine Scout since that is used in the Admirality's "Handbook on S.S. Type Airships", 1917 and in the book "Airship Saga", which includes a contribution from one of the original designers of the SS class airships, as well as in George Whale, "British Airships, Past/Present/Future", 1919. The latter is a real treasure with quite a bit of interesting technical data.)

Some more information can be found at The Airship Heritage Trust.

Status: Beta, flies quite well (but a bit unfinished still).

Pilot's Notes at the FlightGear wiki.

The flight model currently has:

FlightGear Submarine Scout Airship FlightGear Submarine Scout Airship FlightGear Submarine Scout Airship

Zeppelin NT (ZLT-NT)

Note: This aircraft is available in FlightGear 1.9.0 or later. Please get it from the FlightGear web site (for the latest release) or the FlightGear git repository (the most recent Zeppelin NT updates in FlightGear/git).

Zeppelin NT is a modern semirigid airship made by Zeppelin Luftschifftechnik GmbH.

Status: Beta, but perfectly flyable.

Pilot's Notes at the FlightGear wiki.

The flight model currently has:

FlightGear Zeppelin NT at Princess Juliana International Airport, Saint Martin. FlightGear Zeppelin NT cockpit.

ZF Navy free balloon (ZF_Navy_free_balloon)

Note: This aircraft is available in FlightGear 1.9.0 or later. Please get it from the FlightGear web site (for the latest release) or the FlightGear git repository (the most recent ZF Navy free balloon updates in FlightGear/git).

This is a 35_000 cu.ft. hydrogen filled free flying balloon modelled on the US Navy 1930's standard training balloon.

Status: Alpha, but perfectly flyable.

Pilot's Notes at the FlightGear wiki.

The flight model currently has:

ZF Navy free balloon ZF Navy free balloon

LZ 121 Nordstern (Nordstern)

NOTE: This aircraft is now available in FlightGear/git (the most recent Nordstern updates in FlightGear/git). Further updates will be there and not here.

Nordstern was the second of two small passenger airships built by Luftschiffsbau Zeppelin in 1919 and 1920. Nordstern was designed to carry about 25 passengers on a Friedrichshafen - Berlin - Stockholm route but this route was never opened. The older sister ship Bodensee did run a regular passenger sevice between Friedrichshafen and Berlin during Autumn 1919. In compliance with the terms of the peace treaty after WWI both airships were grounded early in 1920. Nordstern was handed over to France in 1921 where she remained in (sparse) service with the french military until 1926 under the name Mediterrannee. Bodensee was handed over to Italy and remained in service there until 1928 under the name Esperia.

Status: Alpha, but flyable.

Pilot's Notes at the FlightGear wiki.

The model currently has:

FlightGear Zeppelin Nordstern. FlightGear Zeppelin Nordstern control car. FlightGear Zeppelin Nordstern control car.

LZ 129 Hindenburg (LZ-129 Note: The archive is out of date w.r.t. FG/git)

This airship hardly needs any presentation. It is really too complex to be added at this stage, but it is the airship I have the most information about - and it is really fun to work on the 3d model.

Status: Alpha, flyable but quite unfinished.
It is quite easy to fly and quite stable. Probably too stable in yaw, even.

The flight model currently has:

FlightGear LZ-129 Hindenburg moored at Friedrichshafen. FlightGear LZ-129 Hindenburg moored at NAS Sunnyvale, CA.

Excelsior high altitude balloon (Excelsior Note: the archive is severly out of date)

This is (or rather aims to become) a model of Excelsior III, a high altitude balloon used for the worlds so far highest parachute jump from 102,890ft on 16 August 1960.

Status: pre-Alpha, but perfectly flyable.

The flight model currently has:

Excelsior III balloon


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Copyright (C) 2006 - 2010 Anders Gidenstam
Email: anders-www [at] gidenstam.org
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